Biomass, Biofuels, Biochemical 9780128218785

Table of contents :
Front-Matter_2021_Biomass--Biofuels--Biochemicals
Front Matter
Copyright_2021_Biomass--Biofuels--Biochemicals
Copyright
Contributors_2021_Biomass--Biofuels--Biochemicals
Contributors
Preface_2021_Biomass--Biofuels--Biochemicals
Preface
1---Circular-Bioeconomy--An-Introduction_2021_Biomass--Biofuels--Biochemical
Circular Bioeconomy: An Introduction
Introduction
Defining Circular Bioeconomy
Biologization of Economic Growth—The Emerging Concept of Bioeconomy
Sustainability and Resource Efficiency Boosted by Biomass-Based Resources—Circular Bioeconomy
Multifarious Choice in Feedstock Acquisition for Circular Bioeconomy—Renewable Biomass and Waste Valorization
Biorefineries—Pivotal in Circular Bioeconomy
Essential Factors Governing the Transition to a Circular Bioeconomy
Conclusions and Perspectives
Acknowledgments
References
2---Environment-and-Material-Science-Technology-for-An_2021_Biomass--Biofuel
Environment and Material Science Technology for Anaerobic Digestion-Based Circular Bioeconomy
Introduction to Waste to Product Biorefineries
Anaerobic Digestion as a Pretreatment for Waste Valorization
Feedstocks
The Process
Operational Parameters
Mesophilic or Thermophilic
Single Feedstock or Codigestion
Single Phase or Two Phase
Wet or Dry
Biogas
Digestate
Material Science for Biogas Upgrading to Biomethane
Mixed-Matrix Membranes
Polymers of Intrinsic Microporosity
Thermally Rearranged Membranes
Biogas as Building Block for Bioproduction of New Materials
Biogas Bioconversion into Polyhydroxyalkanoates
Biogas Bioconversion into Ectoine
Biogas Conversion Bioreactors
Digestate Valorization into New Bioproducts Using Photosynthetic Microorganisms
Macromolecular Components of Microalgae Biomass
Proteins
Carbohydrates
Lipids
Pigments
Processes for Biofuel Production from Microalgal Biomass
Thermochemical Conversion
Biochemical Conversion
Chemical Conversion
Photosynthetic Microbial Fuel Cell (MFC)
Conclusions and Perspectives
Acknowledgments
References
3---Biomass-to-Fuel-and-Chemicals--Enabling-Te_2021_Biomass--Biofuels--Bioch
Biomass to Fuel and Chemicals: Enabling Technologies
Introduction
Types of Biomass
Agricultural Residues
Forest Biomass
Energy Crops
Algal Biomass
Urban Waste
Conversion Technologies for Biofuels and Biochemicals
Thermochemical Technologies
Gasification
Pyrolysis
Hydrothermal Liquefaction
Transesterification
Biochemical Technologies
Fermentation
Anaerobic Digestion
Microbial Fuel Cell
Challenges Faced
Conclusions and Perspectives
References
4---Water-Recycling--Economic-and-Environmenta_2021_Biomass--Biofuels--Bioch
Water Recycling: Economic and Environmental Benefits
Introduction
Water Recycling Processes
Natural Recycling
Artificial Recycling
Water Reuse Applications
Domestic Wastewater
Potable Wastewater
Toilet and Urinal Flushing Wastewater
Gardening and Vehicle Washing Wastewater
Agricultural and Landscape Irrigation Wastewater
Industrial Wastewater
Construction Industry
Processing Industry
Environmental and Recreational Industry
Managed Aquifer Recharge/Groundwater Recharge
Water Body Construction or Restoration
Economic Benefits of Water Reuse
Economic Value of Recycled Water
Reducing Water Cost
Reducing the Cost of Drainage System
Treatment Cost
Operation and Maintenance (O&M) Cost
Energy Costs
Cost Benefits in Terms of Public Health Protection
Environmental Benefits of Water Reuse
Preventing Environmental Pollution
Reduce Diversion of Fresh Water Use
Meeting Water Demands During Drought Stress
Reduction in Wastewater Discharge
Improvement in Public Health
Energy Saving
Reduced Use of Fertilizers in Agriculture
Recycled Water Used to Create or Enhance Wetlands
Conclusions and Perspectives
References
5---Environmental-Impacts-of-Recovery-of-Resources_2021_Biomass--Biofuels--B
Environmental Impacts of Recovery of Resources From Industrial Wastewater
Introduction
Environmental and Natural Resources
Nutrient Resources
Nitrogen Resources
Phosphorous Resources
Carbon Resources
Biosolid Resources
Energy Resources
Water Resources
Recovery Technologies
Physicochemical Processes
Stripping Processes
Air Stripping Process
Steam Stripping Process
Membrane Processes
Membrane Contactor
Reverse Osmosis Process
Forward Osmosis Process
Electrochemical Processes
Biological Processes
Recovery Products
Fertilizers
Biogas
Thermal Energy
Bioproducts
Cellulose and Synthetic Materials
Cellulose Materials
Synthetic Materials
Environmental Impacts
Water Resource Impacts
Aquatic Life Protection Impacts
Greenhouse Gas Reduction Impacts
Sustainable Agriculture Impacts
Human Health Impacts
Environmental Economic Impacts
Contribution of Resource Recovery in Circular Bioeconomy
Conclusions and Perspectives
References
6---Role-of-Bioeconomy-in-Circular-Econom_2021_Biomass--Biofuels--Biochemica
Role of Bioeconomy in Circular Economy
Introduction
Biomass in the Hierarchy of Waste Management
Biomass Transformation Technologies
Thermochemical Pathways
Biochemical Pathways
Use of Biomass for Providing Energy
Potential and Availability of Lignocellulosic Biomass
Concepts for Sustainable Development
Bioeconomy
Circular Economy
Pillars of Circular Economy
Circular Economy and Cradle to Cradle Frameworks
Bioenergy in the Framework of Circular Economy
Synergies in Bio- and Circular Economy
Deviations in Bio- and Circular Economy
Contribution of Bioeconomy to the Circular Economy
Food Waste Valorization From a Circular Economy Perspective
Contribution of Anaerobic Digestion to the Circular Economy
Carbon Footprint Reduction Through Bioeconomy
Potential and Encounters to Harvest Best Possible Assistances
Missing Thespians for Sustainable Bioeconomy
Challenges and Solutions for Sustainable Bioeconomic Pathways
Conclusions and Perspectives
Acknowledgment
References
7---Waste-Biorefinery-Development-Toward-Circular-Bioe_2021_Biomass--Biofuel
Waste Biorefinery Development Toward Circular Bioeconomy With a Focus on Life-Cycle Assessment
Introduction
Global Scenario of Waste Generation and Refining System
Waste as a Resource for Sustainable Economic Development
Importance and Significance of Refining Waste Residue for Sustainable Energy and Bioproducts
Types of Waste Biorefinery
Forestry Biorefinery
Animal Biorefinery
Agricultural Biorefinery
Industrial Biorefinery
Food Waste Biorefinery
Wastewater Biorefinery
Algae-Based Biorefinery
Effective Utilization and Nutrient Recovery
Waste-Refining Technologies and Logistics for Handling, Transport, and Distribution
Anaerobic Digestion/Codigestion
The Principle of Anaerobic Digestion
Factors Affecting Anaerobic Digestion
Aerobic Composting/Co-Composting
The Role of Mineral Additives During Composting
Thermochemical and Hydrothermal Conversion of Biomass
Pyrolysis
Influencing Factors
Gasification
Hydrothermal
Use of Hydrothermal Treatment in Excess Sludge
Centralized and Decentralized Models for Sustainable Biorefining
Near-Neutral Preextraction
Acid Prehydrolysis/Pulp Mode
Alkali Pretreatment and Cellulose Saccharification Fermentation for Ethanol Production
Challenges and Perspectives of Waste Biorefineries in Developing Countries
Integrated Waste Biorefineries
Techno-Economic Assessments of Waste Biorefineries
Life-Cycle Assessment for Sustainable Waste Biorefineries
Biorefinery in Developed and Developing Countries
Conclusions and Perspectives
Acknowledgments
References
8---Valorization-of-Industrial-Wastes-for-Biofuel-Pro_2021_Biomass--Biofuels
Valorization of Industrial Wastes for Biofuel Production: Challenges and Opportunities
Introduction
Waste Valorization
Processing Technologies
Thermochemical Conversion
Pyrolysis
Combustion
Gasification
Biochemical Conversion
Fermentation
Anaerobic Digestion
Mechanical Extraction
Valorization of Food Industry Wastes
Valorization of Paper Industry Wastes
Valorization of Wood Processing Industrial Wastes
Valorization of Agro-Industry Wastes
Valorization of Biodiesel Industry Wastes
Challenges and Opportunities
Conclusions and Perspectives
Acknowledgments
References
9---Sustainability-of-Gaseous-Biofuels--Potential-Uses-_2021_Biomass--Biofue
Sustainability of Gaseous Biofuels: Potential Uses Technological Constraints and Environmental Concerns
Introduction
Classification of Biofuels
Biofuels of the First Generation
Biofuels of the Second Generation
Biofuels of the Third Generation
Gaseous Biofuels
Biogas
Applications and Uses of Biogas
Constraints in Biogas Production
Biohydrogen
Production of Biohydrogen Through the Dark Fermentation Process
Production of Hydrogen by Photobiological Process
Biophotolysis
Direct Biophotolysis
Indirect Photolysis
Photofermentation
Application and Uses of Biohydrogen
Syngas (Synthetic Gas)
Conclusions and Perspectives
References
10---Significance-of-Anaerobic-Digestion-in-Cir_2021_Biomass--Biofuels--Bioc
Significance of Anaerobic Digestion in Circular Bioeconomy
Introduction
The Role of Anaerobic Digestion in Organic Waste Treatment
State-of-Art
Future Developments
Anaerobic Digestion and Bioeconomy
Biogas as Renewable Energy
Biogas Upgrading
Digestate: Waste or Raw Material?
Coupling Anaerobic Digestion and Composting
The Role of Anaerobic Digestion in Biorefineries
Biorefineries and Circular Bioeconomy
Schemes of Biorefineries
Biorefineries, Including Anaerobic Digestion
Special Cases
Lignin- and Fiber-Based Biorefineries
Algae and Anaerobic Digestion Biorefineries
Bioplastics
Other Wastes
Economic, Environmental and Social Assessment
Conclusions and Perspectives
References
11---Lignocellulosic-Biorefinery-for-Value-Added-Pr_2021_Biomass--Biofuels--
Lignocellulosic Biorefinery for Value-Added Products: The Emerging Bioeconomy
Introduction
Lignocellulosic Biomass—Markets and Supply Chains
Processing and Conversion Technologies for Lignocellulosic Biomass: Techno-Economic Aspects
Thermomechanical Processing of Biomass
Pyrolysis
Thermochemical Treatments
Biochemical Treatments
Potential Uses of Lignocellulosic Biomass Fractions Within the Circular Bioeconomy
Cellulose
Cellulosic Textiles
Nanocellulose
Biofuels, Bioproducts, and Products Obtained by Chemical Reactions
Hemicellulose
Biofuels, Bioproducts, and Products Obtained by Chemical Reactions
Oligosaccharides
Lignin
Bio-oil
Benzene, Toluene, and Xylenes (BTX)
Carbon Fiber
Polyurethane
Lignin-Phenol Formaldehyde Resins
Vanillin
Nanoparticles
Utilization of Lignocellulosic Fractions in a Biorefinery
Value-Added Products from Lignocellulosic Biomass With Scalability Potential
Bioethanol
Bio-oil
Platform Chemicals
Synthetic Fuels
Conclusion and Perspectives
References
12---Microalgal-Biorefinery--A-Sustainable-Technology-To_2021_Biomass--Biofu
Microalgal Biorefinery: A Sustainable Technology Toward Circular Bioeconomy and Microalgal Biomass Valorization
Introduction
Microalgal Biorefinery: Promising Technological Platform for Circular Bioeconomy
Raw Materials for Microalgal Biorefinery: From Viewpoint of Circular Bioeconomy
Inorganic Carbon
Organic Carbon
Nitrogen (N)
Phosphorus (P)
Trace Metals
Products From Microalgal Biorefinery: Key to Achieving Sustainable Societies
Energy Carriers
Chemicals
Materials
Fertilizers
Foods
Feeds
Cosmetics
Technological Strategies for Enhancing the Contributions of Microalgal Biorefinery to Circular Bioeconomy
Increasing Microalgal Biomass Acquisition
Improving Energy Efficiency of Overall Microalgal Biorefinery Process
Conclusions and Perspectives
References
13---Microbial-Biosurfactants--Production-and-Appli_2021_Biomass--Biofuels--
Microbial Biosurfactants: Production and Applications in Circular Bioeconomy
Introduction
Classification of Biosurfactants
Glycolipids
Lipopeptides and Lipoproteins
Phospholipids and Fatty Acids
Polymeric Surfactants
Particulate Surfactants
Factors Affecting Production of Biosurfactants
Carbon Source
Nitrogen Source
Aeration and Agitation
Salt Concentration
Environmental Factors
Genes for Biosurfactants Biosynthesis
Rhamnolipids
Sophorolipids
Surfactin
Industrial-Scale Biosurfactants Producers
Commercial-Scale Production of Biosurfactants
Biosurfactants From Industrial Wastes: A Role in Circular Bioeconomy
Applications of Biosurfactants
Environmental Applications
Polyaromatic Hydrocarbons (PAHs)
Heavy Metals
Pesticides
Microbial Enhanced Oil Recovery (MEOR)
Medicines
Antimicrobial
Anticancer
Antiadhesives
Cosmetics
Food
Agriculture
Conclusions and Perspectives
Acknowledgment
References
14---Bioelectrochemical-Systems-for-Fuel-Production_2021_Biomass--Biofuels--
Bioelectrochemical Systems for Fuel Production: A Techno-Economic Analysis
Introduction
Concepts and Present Status of Circular Bioeconomy
Variants of Bioelectrochemical Systems Used for Fuel Production
Microbial Fuel Cell (MFC)
Microbial Electrolysis Cell (MEC)
Microbial Electrosynthesis
Fuel Generation From Bioelectrochemical Systems (BES)
Electricity Generation and Wastewater Treatment in Microbial Fuel Cells
Generation of Hydrogen and Methane in Microbial Electrolysis Cells
Synthesis of Higher Chain Organic Molecules in Microbial Electrosynthesis Cells
Bioelectrochemical System (BES) Technology: Identification of Key Areas for Improvement
Modifications for Reuse of Finite Resources
Scope of Waste-Based Resource Utilization
Process Optimization for Reduction of Greenhouse Gas Emissions and Energy Utilization
Constraints Toward Scaling-up of BES
Future Scope: Bystanders to Contributors in the Loop of Circular Bioeconomy
Future Research Scope With Respect to Identified Key Areas
Tailoring Bioelectrochemical Systems for Translation Toward Contributor
Conclusions and Perspectives
References
15---Microbial-Electrochemical-Technologies-for-_2021_Biomass--Biofuels--Bio
Microbial Electrochemical Technologies for CO 2 Sequestration
Introduction
Microbial Electrosynthesis of Organic Chemicals From CO 2
Background
Factors Affecting Yield of MES
Cathode Materials Used in MES
Biocatalysts Employed in MES
Separation of Products Formed in MES
Other METs for CO 2 Sequestration
Microbial Carbon-Capture Cell
Type of Photosynthetic Microorganism Used in MCC
Importance of Photosynthetic Microorganism to Achieve Circular Bioeconomy
Factors Governing the Performance of MCC
Applications of MCC
Bioelectricity Production
Wastewater Treatment
Biofuel Production
Recovery of Other Valuable Products
Bottlenecks of the MCC
Plant Microbial Fuel Cell
Role of Plants and Their Intercellular Mechanism in P-MFC
Factor Affecting the Performance of P-MFC
Applications of P-MFC
Prospects and Challenges in P-MFC Toward the Circular Bioeconomy
Potential and Bottlenecks in the Application of METs
Future Outlook in the Application of MET to Attain Circular Bioeconomy
Conclusions and Perspectives
References
16---Bioelectrochemical-Systems-for-Remediation-and-Re_2021_Biomass--Biofuel
Bioelectrochemical Systems for Remediation and Recovery of Nutrients From Industrial Wastewater
Introduction
Bioelectrochemical Systems (BESs)—An Overview
The Spontaneity of Reaction in a BES
Functions in BES
Mechanism in BES
Factors Influencing BES
pH
Conductivity
Ion Concentration
Soil Porosity
Soil Moisture
Temperature
Magnetic Field
Inoculum and Substrate
Design of Reactors
Types of BESs
Plant Microbial Fuel Cells (PMFCs)
Microbial Solar Cells (MSCs)
Microbial Electrosynthesis (MES)
Microbial Electrolysis Cells
Enzymatic Fuel Cells (EFCs)
Microbial Desalination Cells (MDCs)
BES in Remediation Technology
Nutrient Removal and Recovery From Wastewater
Influence of Nitrogen Over the BES Process
BESs: Nitrogen Transformation and Recovery
Removal and Recovery of Phosphorus
Background
Phosphorous Recovery in BES
Metals Removal in BES
Metals Removal in MFCs
Recovery of Metal in MECs
Recovery of Metal Using Biocathodes
Direct Metal Recovery Using Abiotic Cathodes
Conversion of Metals Using Biocathodes
Challenges and Limitations of BES
Concept of Circular Bioeconomy of BES
Components in Circular Bioeconomy as BES
Value-Added Products
Bioalcohols
Biomethane
Biohydrogen
Short-Chain Fatty Acids
Medium-Chain Fatty Acids
Conclusions and Perspectives
References
17---Polyhydroxyalkanoate-Production-From-Feedstocks--Tech_2021_Biomass--Bio
Polyhydroxyalkanoate Production From Feedstocks: Technological Advancements and Techno-Economic Analysis in Reference to Ci ...
Introduction
Polyhydroxyalkanoate Polymers
Parameters of PHA Production
Substrate
pH and Temperature Regimes
Oxygen Microenvironment
Organic Loading Rate and Acids
Different Feedstocks and Microbial Involvement
Prokaryotic PHA Production
Eukaryotic PHA Production
PHA Production Utilizing Transgenic Plants
Production of PHA Using Available Waste Streams
Lignocellulosic Waste
Waste From Dairy Industries
Case Study of WHEYPOL
Waste Streams From Biodiesel Industries
Waste Lipids
Case Study of ANIMPOL
Waste From Sugar Industries
Plant Oil
Bioconversion of Syngas
Waste (Water) Recycling After PHA Production
Techno-Economic Analysis of PHA Production
Life-Cycle Assessment (LCA)
Global PHA Producers and Market of PHA
Bioplastics in Relation With Circular Bioeconomy
Benefits of Bioplastics Over Conventional Plastic—Environment and Public Health
Benefits in Waste Utilization
Challenges and Prospects of PHA
Conclusions and Perspectives
Acknowledgement
References
18---Agro-Industrial-Waste-Valorization-for-Biopolymer-P_2021_Biomass--Biofu
Agro-Industrial Waste Valorization for Biopolymer Production and Life-Cycle Assessment Toward Circular Bioeconomy
Introduction
Agro-Industrial Wastes
Types and Origin
Global Generation of Agro-Industrial Wastes
Nutritional Value and Chemical Characteristics
Valorization Options for Agro-Industrial Wastes
Bioactive Compounds
Hydrolytic Enzymes
Biosurfactants
Animal Feed from Cheese Whey
Biofuels
Polyhydroxyalkanoate (PHA)
Biopolymers Production
Conventional Approaches and Their Drawbacks
Microbial Strains Involved in Biopolymers Production
Role of Genetic Engineering to Augment the Biopolymers Production
Agro-Industrial Waste Valorization for Biopolymers Production
Biopolymers Produced from Agro-Industrial Wastes
Extraction of Biopolymers from Agro-Industrial Wastes
Fermentation Processes to Produce Biopolymers
Applications of Biopolymers
Agricultural and Environmental Applications
Biomedical Applications
Food Industry Applications
Cosmetic and Personal Care Applications
A Roadmap Toward a Circular and Sustainable Bioeconomy from Waste Valorization
Impact Assessment
Case Studies on Agro-Industrial Waste Valorization to Attain Circular Economy
India
Thailand
Hong Kong
Conclusions and Perspectives
References
19---Process-Integration-for-Cost-Effective-Lignocellulos_2021_Biomass--Biof
Process Integration for Cost-Effective Lignocellulosic Bioethanol Production—An Avenue for Promoting Circular Bioeconomy
Introduction
Current Status of Bioethanol Production and Consumption
Feedstocks for Bioethanol Production
Sources of Lignocellulosic Biomass
Composition of Lignocellulosic Biomass
Overall Processing Routes of Bioethanol Production From Lignocellulosic Wastes
Pretreatment
Hydrolysis (saccharification)
Fermentation
Bioethanol Recovery
Challenges in Bioethanol Production From Lignocellulosic Wastes
Lignocellulosic Biomass: A Resource in the Circular Bioeconomy
Importance and Opportunities of Process Integration
Reaction-Reaction Integration
Separate Enzymatic Hydrolysis and Fermentation Process
Simultaneous Saccharification and Fermentation
Simultaneous Saccharification and Cofermentation
Consolidated Bioprocessing
Reaction-Separation Integration
Fermentation Coupled With Pervaporation
Fermentation Coupled With Gas Stripping
Fermentation Coupled With a Vacuum Chamber
Separation-Separation Integration
Energy Integration
Conclusions and Perspectives
References
20---Green-Chemistry-for-Green-Solvent-Production-an_2021_Biomass--Biofuels-
Green Chemistry for Green Solvent Production and Sustainability Toward Green Economy
Introduction
Solvent Selection Criteria
Contribution of Green Solvents in Green Chemistry
Environmental Factors and Impacts of Organic Solvents
Green Solvents in Green Chemistry
Production and Utilization of Green Solvents: Challenges and Opportunities
Solvent-Free Processes
The Solvent-Free Nanofluids
Supercritical Carbon Dioxide in Extraction and Purification
Extraction of Sunflower Oil
Alcohol Recovery Using Supercritical Fluid Extraction
Role of Supercritical Fluids in Biodiesel Production
The Economic Viability of Supercritical Fluid Extraction Technology
Organic Synthesis Under Microwaves in the Absence of Solvent
Other Approaches or Types of Solvent-Free Processes
Water as a Green Solvent
Deep Eutectic Solvents/Natural Deep Eutectic Solvents
Production of Deep Eutectic Solvents
Applications of Deep Eutectic Solvents
Ionic Liquids/Bio-Ionic Liquids
History of Ionic Liquids
Physicochemical Properties of Ionic Liquids
Melting and Degradation Temperatures of Ionic Liquids
Viscosity of Ionic Liquids
Density of Ionic Liquids
Organic Synthesis in the Ionic Liquid Medium
Applications in Industries
Eastman Chemical Company
Biphasic Acid Scavenging Utilizing Ionic Liquid Process
Difasol Process
The Economic and Environmental Aspect of Ionic Liquids
Supercritical/Subcritical Fluids
CO 2 as Supercritical Fluid
Water as Super-/Subcritical Fluid
Ethanol as Super-/Subcritical Fluid
Bio-based/Renewable Solvents
Production of Bio-based Solvents
Applications and Opportunities of Biosolvents
Green Solvents for Polymerization
Bioeconomy of Green Solvents and Sustainability Toward a Green Economy
Challenges and Recommendations
Conclusions and Perspectives
References
21---Sustainable-production-of-bioadsorbents-from-munici_2021_Biomass--Biofu
Sustainable production of bioadsorbents from Łmunicipal and Łindustrial wastes in a circular Łbioeconomy context
Introduction
Municipal Waste
Types and Origin of Municipal Solid Waste
Generation of Municipal Solid Waste
Waste Disposal Problems
Nutritional Value and Chemical Constituents of Municipal Waste
Valorization Options of Municipal Waste
Industrial Waste
Types and Origin of Industrial Waste
Generation and Disposal of Industrial Waste
Nutritional Value and Chemical Characteristics
Other Valorization Options of Industrial Waste
Bioadsorbents
Sources and Types of Bioadsorbents
Industrial By-Products
Agricultural Waste Materials
Microbial Bioadsorbents
Algae as a Bioadsorbent
Bacteria as a Bioadsorbent
Fungi as a Bioadsorbent
Mechanism of Adsorption Process
Physical Adsorption
Chemical Adsorption
Bioadsorption
Factors Affecting the Adsorption Process
Effect of Temperature
Effect of pH
Effect of Pressure
Effect of Adsorbent Activation
Surface Area of Adsorbent
Effect of Initial Metal Ion Concentration
Effect of Concentration of the Biosorbent
Conventional Bioadsorbent Preparation
Direct Preparation of Bioadsorbents From Waste
Applications of Bioadsorbents for Green Biotechnology
Circular Bioeconomy
Case Studies on Bioadsorbents Production From Municipal Waste
Case Studies on Bioadsorbents Production From Industrial Waste
Fly Ash
Steel Industry Wastes
Aluminum Industrial Waste
Fertilizer Industrial Waste
Other Industrial Waste (Leather Industry and Paper Industry)
Benefits of Circular Bioeconomy
Benefits of Waste Utilization
Environmental Benefits
Monetary Benefits
Benefits to Public Health
Limitations in Circular Economy Process
Conclusions and Perspectives
References
22---Life-Cycle-Assessment-of-Agricultural-Waste-Ba_2021_Biomass--Biofuels--
Life-Cycle Assessment of Agricultural Waste-Based and Biomass-Based Adsorbents
Introduction
Bioadsorbents
Chemical Activation
Thermal Activation
LCA Studies on Bioadsorbents Compared to Commercial Activated Carbon
Goal and Scope
Life-Cycle Inventory
Impact Assessment and Interpretation
Environmental Hot Spots for Sensitivity Analysis
Modification of LCA Studies With a Cascade Approach
Sequential Stages of Utilization
Valorization of Different Outputs Obtained Across the Stages
Environmental Benefits
Challenges and Barriers in Bioadsorbent Utilization
Conclusions and Perspectives
References
23---Technology-Transfer-From-Bench-to-Industry_2021_Biomass--Biofuels--Bioc
Technology Transfer From Bench to Industry: Closing Loop
Introduction
Important Factors for Technology Transfer With Respect to Circular Bioeconomy
Successful Scale-Up of Technology
Utilization of Process Waste Streams
Environmental Assessment
Social Factors
Location of Industry
Public Awareness
Market Demand and Economic Considerations
Case Studies for Technology Transfer With Circular Bioeconomy Approach
Starch Industry Wastewater (SIW) as Raw Material to Biopesticide
Process Description
Process Scale-Up
Bioreactor
Centrifuge Operation
Utilization of Supernatant Generated During Centrifugation Process (Waste Stream)
Characterization of Biopesticide
Environmental Assessment
Market Demand and Economic Considerations
Location of Industry
Biodiesel Production Using Municipal Sludge Fortified With Crude Glycerol
Process Description
Relation of the Technology With Respect to Circular Bioeconomy
Fermentation (Recycling of Waste Material as Carbon Source)
Biomass Settling
Cell Disruption and Lipid Recovery
Transesterification
Scale-Up Challenges
Fermentation
Biomass Harvesting
Environmental Assessment
Market Demand and Economic Considerations
Location of Industry
Wastewater Sludge to Biopesticides
Process Description
Scale-Up Challenges
Pyrolysis
Process Description
Challenges in Scale-Up
Conclusions and Perspectives
Acknowledgment
References
24---Circular-Bioeconomy--Countries--Case-S_2021_Biomass--Biofuels--Biochemi
Circular Bioeconomy: Countries’ Case Studies
Introduction
Definitions and Terminologies
Circular Economy
Bioeconomy
Circular Bioeconomy
Concept of Circular Bioeconomy
Sources of Information
Policies to Promote Circular Bioeconomy in Various Countries
India
National Biotechnology Development Strategy 2015–20 [18]
China
Biomass Role in China’s Circular Bioeconomy
13th FYP of China [25]
Project BB China [26]
European Union
Toward a Circular Economy: A Zero-Waste Program for Europe (2014) [28]
Enabling Framework
Modernizing Waste Policy and Target
Bio-based Industries Joint Undertaking [29]
EFFECTIVE [30]
EMBRACED [31]
BIOSKOH [32]
BIOWAYS [33]
The Circular Bio-society in 2050 [34]
Strategic Innovation and Research Agenda [35]
Sustainable and Circular Bioeconomy, the European Way [36]
Closing the Loop—An EU Action Plan for the Circular Economy [37]
InnovFin: EU Finance for Innovators [38]
InnovFin Circular Bioeconomy Investment Platform
United States of America
National Bioeconomy Blueprint, 2012 [41]
Strategic Plan for a Thriving and Sustainable Bioeconomy, 2016 [39]
Enhancing Bioenergy Value Proposition
Mobilizing Nation’s Biomass Resources
Cultivating End-Use Markets and Customers
Expanding Stakeholder’s Engagement and Collaboration
FY2021 Research and Development Priorities Memorandum [44]
American Leadership in Industries of the Future
American Health and Bioeconomic Innovations
Brazil
National Strategy for Science, Technology and Innovation, 2016 [46]
RenavoBio [47]
South Africa
The Bio-economy Strategy, 2013 [48]
Status of Circular Bioeconomy in Some Other Less Developed Countries
Case of Namibia: A Problem or an Opportunity?
Challenges and Opportunities
Conclusions and Perspectives
Acknowledgment
References
25---Challenges-for-Microbial-and-Thermochemical-Tran_2021_Biomass--Biofuels
Challenges for Microbial and Thermochemical Transformation Toward Circular Bioeconomy
Introduction
Social Aspects of Resource Recovery and Circular Bioeconomy
Processes to Attain Circular Bioeconomy
Resource Recovery Using Microorganisms
Composting
Residual Pollutants from Contaminated Feedstocks
Odors
Organic Waste to Biogas and Volatile Fatty Acids (VFAs)
Anaerobic Digestion to Biogas, H 2 and Volatile Fatty Acids (VFAs)
VFAs to Polymers and Other Value-Added Products
Bioplastics to Biogas and VFAs
Residuals to Feed and Food
Fermentation of Liquid Residues to Food and Feed
Fermentation of Solid Residues to Food and Feed
Advantages of Fermentation
Energy and Chemicals Recovery
Combustion
Ash
Gasification
Syngas to Value-Added Products
Pyrolysis
Other Technologies
Integration Strategies to Attain Circular Bioeconomy
Conclusions and Perspectives
Acknowledgments
References
26---Plastics--Toward-a-Circular-Bioecono_2021_Biomass--Biofuels--Biochemica
Plastics: Toward a Circular Bioeconomy
Introduction
Resources for Plastic Production and Their Classifications
End of Life (EoL) of Plastics and a Linear Economy
Circular Bioeconomy Indicators
End-of-Life Treatment Options
Key Parameters in Plastic Biodegradation
Hydrophobicity
Degree of Crystallinity
Surface Topography
Molecular Size
Plastic Degradation
Mechanical Degradation
Regrinding
Adhesive Pressing
Compression Molding
Injection Molding
Thermal Degradation
Photo-Oxidative Degradation
Microbial Degradation
Microbial Degradation of Plastics
Polyethylene Terephthalate (PET or PETE): SPI Resin ID Code #1
Polyethylene (PE)
High-Density Polyethylene (HDPE): SPI Resin ID Code #2
Low-Density Polyethylene (LDPE): SPI Resin ID Code #4
Polyvinyl Chloride (PVC): SPI Resin ID Code #3
Polypropylene (PP): SPI Resin ID Code #5
Polystyrene (PS): SPI Resin ID Code #6
Polyurethane (PUR): SPI Resin ID Code #7
Polylactic Acid (PLA): SPI Resin ID Code #7
Polyamide: SPI Resin ID Code #7
General Inferences of Microbial Biodegradation
Innovative Approaches: Companies, Start-Ups, and Institutes
Conclusions and Perspectives
References
27---Circular-Economy-and-Carbon-Capture--Utiliz_2021_Biomass--Biofuels--Bio
Circular Economy and Carbon Capture, Utilization, and Storage
Introduction
Carbon Capture and Storage
CO 2 Separation Processes
CO 2 Transport
CO 2 Storage
Issues Regarding Carbon Capture and Storage
Carbon Capture and Utilization
Direct CO 2 Reuse: Enhanced Oil Recovery
CO 2 to Chemicals
CO 2 to Liquid Fuels—Methanol
From the Hydrogen Economy to the Methanol Economy
Methanol Within the Methanol Economy
Methanol Production
Sustainability of the Circular Methanol Economy and Application
Mineral Carbonation
In Situ
Ex Situ
Industrial Wastes as Feedstock
Coal Fly Ash (CFA)
Steelmaking Slags
Red Mud
Cement Kiln Dust (CKD) and Waste Cement (WC)
Others Sources of Carbonation Materials
Serpentine, Olivine, and Wollastonite
Energy Consumption and Costs
Carbonates and Carbonated Products Fate
Conclusions and Perspectives
References
Index_2021_Biomass--Biofuels--Biochemicals
Index
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B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Citation preview

Biomass, Biofuels, Biochemicals

Series Editor

Ashok Pandey

Circular Bioeconomy— Current Developments and Future Outlook Edited by

Ashok Pandey Centre for Innovation and Translational Research CSIR— Indian Institute of Toxicology Research Lucknow, India

Rajeshwar Dayal Tyagi BOSK-Bioproducts Quebec City, QC, Canada

Sunita Varjani Gujarat Pollution Control Board Gandhinagar, India

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-821878-5 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Susan Dennis Acquisitions Editor: Kostas Ki Marinakis Editorial Project Manager: Cole Newman Production Project Manager: Sujatha Thirugnana Sambandam Cover Designer: Greg Harris Typeset by SPi Global, India

Contributors Ndao Adama  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Kokou Adjallé  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Ruth Amanna  Biorefining Research Institute, Lakehead University, Thunder Bay, Ontario, Canada Roshan Appa  School of Environmental Science and Engineering, Indian Institute of Technology, Kharagpur, West Bengal, India Anusha Atmakuri  INRS Eau, Terre et Environnement, Québec, QC, Canada Mukesh Kumar Awasthi College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Sanjeev Kumar Awasthi College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Somdipta Bagchi School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Manaswini Behera School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India B. Bharathiraja  Department of Chemical Engineering, Vel Tech High Tech Dr. Rangarajan Dr. Sakunthala Engineering College, Chennai, India Puspendu Bhunia School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Silvia Bolado Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain Kellie Boyle Department of Civil and Environmental Engineering, Carleton University, Ottawa, ON, Canada Alessandro Carmona  Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain Júlio César de Carvalho  Department of Bioprocess Engineering Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil

and

xix

Contributors

Indrajit Chakraborty Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal, India Jo-Shu Chang Department of Chemical Engineering, National Cheng Kung University, Tainan; Department of Chemical Engineering and Materials Science, College of Engineering; Research Centre for Smart Sustainable Circular Economy, Tunghai University, Taichung, Taiwan Shraddha Chavan  INRS Eau, Terre et Environnement, Québec, QC, Canada Hongyu Chen  College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Hong Il Choi Department of Chemical and Biological Engineering, Korea University, Seoul, Republic of Korea Sanket Dey Chowdhury  School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Sovik Das Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal, India Swati Das PK Sinha Centre for Bioenergy & Renewables, Indian Institute of Technology, Kharagpur, West Bengal, India Rajesh Roshan Dash School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Israel Díaz  Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain Amadou Diop  Delmar Chemicals Inc, Montreal, QC, Canada Patrick Drogui Institut National de la Recherche Scientifique (INRS), CentreEau Terre Environnement (ETE), Université du Québec; INRS Eau, Terre et Environnement, Québec, QC, Canada Brajesh K. Dubey Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal, India Oumaima El Hachimi  INRS Eau, Terre et Environnement, Québec, QC, Canada M.R. Karimi Estahbanati Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada María Fernández-Polanco  Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain

xx

Contributors

Jorge A. Ferreira Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Xavier Font  Composting Research Group, Department of Chemical, Biological and Environmental Engineering, Escola d’Enginyeria, Universitat Autònoma de Barcelona, Barcelona, Spain Vimala Gandhi Department of Microbiology, Government Science College (Autonomous), Bangalore, Karnataka, India Vivek Kumar Gaur Environmental Biotechnology Division, Environmental Toxicology Group, CSIR-Indian Institute of Toxicology Research; Amity Institute of Biotechnology, Amity University Uttar Pradesh, Lucknow, Uttar Pradesh, India Makarand M. Ghangrekar Department of Civil Engineering; School of Environmental Science and Engineering; PK Sinha Centre for Bioenergy & Renewables, Indian Institute of Technology, Kharagpur, West Bengal, India Kirubanandam Grace Pavithra Department of Chemical Engineering, SSN College of Engineering, Chennai, Tamil Nadu, India Rishi Gurjar  School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India K. Hasim Suhaib School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Allen Hu  National Taipei University of Technology, Taipei, Taiwan, ROC Lan Tran Huong  Institut National de la Recherche Scientifique (Water, Earth and Environment Research Center), University of Quebec, Quebec, QC, Canada Sung-Won Hwang  Department of Chemical and Biological Engineering, Korea University, Seoul, Republic of Korea J. Jayamuthunagai  Centre for Biotechnology, Anna University, Chennai, India Mahmoodreza Karimiestahbanati  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Susan Grace Karp  Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Mahdieh Khajvand  Institut National de la Recherche Scientifique (INRS), CentreEau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Nouha Klai  Civil Engineering Department, Mcgill University, Montréal, QC, Canada Lalit R. Kumar  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada

xxi

Contributors

Sunil Kumar  CSIR-National Environmental Engineering Research Institute (CSIRNEERI), Nagpur, India Sushil Kumar  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Gabriel Sprotte Kumlehn Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Duu-Jong Lee  Department of Chemical Engineering, National Taiwan University; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan Patrik R. Lennartsson Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Luiz Alberto Junior Letti Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Tao Liu College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Zannat Mahal  Biorefining Research Institute, Lakehead University, Thunder Bay, Ontario, Canada Challa Mallikarjuna School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Natesan Manickam Environmental Biotechnology Division, Environmental Toxicology Group, CSIR-Indian Institute of Toxicology Research, Lucknow, Uttar Pradesh, India Julien Mocellin  Institut National de la Recherche Scientifique (Water, Earth and Environment Research Center), University of Quebec, Quebec, QC, Canada Ali Khosravanipour Mostafazadeh  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada P. Mullai  Department Chidambaram, India

of

Chemical

Engineering,

Annamalai

University,

Raúl Muñoz Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain Dillirani Nagarajan Department of Chemical Engineering, National Cheng Kung University, Tainan; Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan Suraj Negi  National Taipei University of Technology, Taipei, Taiwan, ROC

xxii

Contributors

Banu Ormeci Department of Civil and Environmental Engineering, Carleton University, Ottawa, ON, Canada Laura Palacio Institute of Sustainable Processes, University of Valladolid; Department of Applied Physics, Faculty of Sciences, University of Valladolid, Campus Miguel Delibes, Valladolid, Spain Aishwarya Pandey  INRS Eau, Terre et Environnement, Québec, QC, Canada Ashok Pandey Centre for Innovation and Translational Research, CSIR-Indian Institute of Toxicology Research, Lucknow, India Louis-César Pasquier  Institut National de la Recherche Scientifique (Water, Earth and Environment Research Center), University of Quebec, Quebec, QC, Canada Anil Kumar Patel Department of Chemical and Biological Engineering, Korea University, Seoul, Republic of Korea Anita Pettersson Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden S. Pilli  National Institute of Technology, Warangal, India Rajat C. Pundlik School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Sudip Kumar Rakshit Biorefining Research Institute, Lakehead University, Thunder Bay, Ontario, Canada Aryama Raychaudhuri  School of Infrastructure, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India Xiuna Ren College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Tobias Richards Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Elena Rojo  Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering; Institute of Sustainable Processes, University of Valladolid, Valladolid, Spain Kamran Rousta Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Mahdieh Samavi Biorefining Research Institute, Lakehead University, Thunder Bay, Ontario, Canada Antoni Sánchez Composting Research Group, Department of Chemical, Biological and Environmental Engineering, Escola d’Enginyeria, Universitat Autònoma de Barcelona, Barcelona, Spain

xxiii

Contributors

Balasubramanian Sellamuthu  Centre de Recherche du CHUM, Montréal, Québec, QC, Canada I. Abernaebenezer Selvakumari  Department of Chemical Engineering, Vel Tech High Tech Dr. Rangarajan Dr. Sakunthala Engineering College, Chennai, India P. Senthil Kumar Department of Chemical Engineering, SSN College of Engineering, Chennai, Tamil Nadu, India Sang Jun Sim Department of Chemical and Biological Engineering, Korea University, Seoul, Republic of Korea Carlos Ricardo Soccol  Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Cenit Soto  Institute of Sustainable Processes, University of Valladolid; Department of Applied Physics, Faculty of Sciences, University of Valladolid, Campus Miguel Delibes, Valladolid, Spain Parimala Gnana Soundari College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China Esteffany de Souza Candeo Department of Bioprocess Engineering and Biotechnology, Federal University of Technology, Ponta Grossa, Paraná, Brazil Eduardo Bittencourt Sydney Department of Bioprocess Engineering and Biotechnology, Federal University of Technology, Ponta Grossa, Paraná, Brazil Mohammad J. Taherzadeh  Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Anita Talan Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Ilies Tebbiche  Institut National de la Recherche Scientifique (Water, Earth and Environment Research Center), University of Quebec, Quebec, QC, Canada Bhagyashree Tiwari  INRS Eau, Terre et Environnement, Québec, QC, Canada Luis Alberto Zevallos Torres Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Rajeshwar Dayal Tyagi Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec; INRS Eau, Terre et Environnement, Québec, QC, Canada Sunita Varjani  Gujarat Pollution Control Board, Gandhinagar, Gujarat, India Ellen Caroline Silverio Vieira  Biorefining Research Institute, Lakehead University, Thunder Bay, Ontario, Canada

xxiv

Contributors

Steven Wainaina Swedish Centre for Resource Recovery, University of Borås, Borås, Sweden Adenise Lorenci Woiciechowski Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Paraná, Brazil Bhoomika Yadav  INRS Eau, Terre et Environnement, Québec, QC, Canada Song Yan  Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Sravan K. Yellapu  Institut National de la Recherche Scientifique (INRS), CentreEau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada Zengqiang Zhang  College of Natural Resources and Environment, Northwest A&F University, Yangling, PR China

xxv

Preface The book titled Circular Bioeconomy—Current Developments and Future Outlook is a part of the comprehensive series on Biomass, Biofuels, Biochemicals (Editorin-Chief: Ashok Pandey). This book intends to cover different aspects of waste biorefineries, resource recovery from waste generated, bioelectrochemical systems (BES), techno-economic analysis in technology transfer, and global scenario of circular bioeconomy. It also provides state-of-the-art information and perspectives for future developments. The global bioeconomy summit defined bioeconomy as the “knowledge-based production and utilization of biological resources, innovative biological processes and principles to sustainably provide goods and services across all economic sectors.” Increased population, industrialization, and changes in the living standard of humans lead to an unsustainable linear economy. With increased resource consumption and degradation of environment, there is necessity of transition toward a sustainable sociotechnical system. Environmental consequences (such as biodiversity loss, resource depletion, and pollution of soil water and air), economic problems (such as supply chain damages and market fluctuations), and societal matters (such as poverty, unemployment, vulnerability, and insufficient work orders) produce a tributary stream, wastes, and residues. Sustainability is the balance between environmental resource usage, economic growth, and ethical impartiality. There has been a constant search for new designs in consumerist and production approaches to move toward a sustainable development by environmental activists, law makers, scientists from different backgrounds, and industrialists. Due to the increased awareness, member states of the United Nations adopted sustainable development goals in 2015 to motivate and implement sustainability and circular bioeconomy. Proper establishment of global circular bioeconomy lies, at maximum extent, in establishing techniques to convert industrial and municipal waste, residues, and a tributary stream into bio-based chemicals, food and bioenergy, etc. A variety of raw materials are needed globally to develop an extensive collection of waste-to-wealth approaches to achieve necessities. Integration of biological and thermochemical processes for nutrient recovery and conversion of wastes into various products help in quicker implementation of the circular bioeconomy approach. Social aspects in resource recovery also play a vital role in circular bioeconomy. Circular bioeconomy aims to “close the loop” and allow sustainable use of biological resources. The zero liquid waste approach of circular bioeconomy leads to

xxvii

Preface

the development of lignin, microalgal, lignocellulosic, industrial waste, municipal waste biorefineries; waste to wealth, resource recovery concepts. Global inclusiveness is necessary in the development of an organization to ensure knowledge sharing, research support, and biotechnological tool development for commercialization of products as well as for demand and supply chain assessment, which has the potential to realize the successful transition of linear economy to circular bioeconomy. Increased plastic pollution necessitates the demand for the utilization of biodegradable plastics. The waste management principle allows the use of waste plastic as a resource for energy and other products. Waste plastics can be converted into bio-based products such as biopolymers, which in turn would reduce environmental and economic load, hence contributing to circular bioeconomy and sustainability. Life-cycle assessment, techno-economic analysis, and production process play important roles in any waste management process. Wastewater can be considered as a valuable resource that possesses compounds which can be converted to fuel, nutrients, and chemicals through chemical, physical, and biological processes. BES has attracted attention in the recovery of nutrients from industrial wastewater. In BES, electrical energy is produced from chemical energy (and vice versa) by employing microbes, algae, etc. Phosphorous and nitrogen are important toxicants and can be recovered as nutrients from wastewater. Precious metals can also be recovered from wastewater using BES. Topics covered in this book include environment and material science technology for anaerobic digestion–based circular bioeconomy; enabling technologies for the conversion of biomass to fuel and chemicals; economic and environmental benefits of water recycling; role of bioeconomy in circular economy; waste biorefinery development toward circular bioeconomy with a focus on life-cycle assessment; sustainability of gaseous biofuels outlining the state of the art on the assessment of the potential uses of gaseous biofuels, technological constraints, and environmental concerns; significance of anaerobic digestion in circular bioeconomy; lignocellulosic biorefinery for value-added products as the emerging bioeconomy; microalgal biorefinery as a sustainable technology toward circular bioeconomy and microalgal biomass valorization; a techno-­ economic analysis of BES for fuel production; BES for remediation and recovery of nutrients from industrial wastewater; technological advancements and ­techno-economic analysis in reference to circular bioeconomy in the production of poly-­hydroxyalkanoate from feedstocks; sustainable production of bioadsorbents from municipal and industrial waste in a circular bioeconomy context; closing the loop in the technology transfer from bench to industry; challenges for microbial and thermochemical transformation toward circular bioeconomy; use of plastics in a circular bioeconomy; and circular bioeconomy and carbon capture, utilization, and storage.

xxviii

Preface

The book summarizes the current knowledge about the techno-economic analysis to understand the ground reality of implementing resource recovery, waste biorefinery, and the BES concept for the remediation of pollutants of various industries and closing the loop of economy. The book provides latest developments in circular bioeconomy using biotechnological and bioengineering technologies, life-cycle assessment, techno-economic analysis, etc. The chapters included in the book provide state-of-the-art information on the subject matter, and potential advantages and limitations of technology transfer, i.e., linear economy to circular economy/bioeconomy. We highly appreciate the excellent work done by the authors in compiling the relevant information on different aspects of circular economy, which we believe will be very useful to the scientific community. We gratefully acknowledge the reviewers for their valuable comments, which helped in improving the scientific content of various chapters. We thank the Elsevier team comprising Dr. Kostas Marinakis, Senior Book Acquisition Editor, and Cole Newman, Editorial Project Manager, and the entire Elsevier production team for their consistent hard work in the publication of this book.

Ashok Pandey Rajeshwar Dayal Tyagi Sunita Varjani Editors

xxix

Circular Bioeconomy: An Introduction a

Dillirani Nagarajana,b, Duu-Jong Leeb,c, and Jo-Shu Changa,d,e

Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan cDepartment of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan d Department of Chemical Engineering and Materials Science, College of Engineering, Tunghai University, Taichung, Taiwan eResearch Centre for Smart Sustainable Circular Economy, Tunghai University, Taichung, Taiwan

b

1 Introduction The global economy is fast growing, with an ever-increasing population and increased necessity for resources. Industrialization, urbanization, and demands for the modern society are met by fossil fuel-based energy, chemicals, and consumables. Crude oil, coal, and natural gas are the major drivers of the current linear economy, and this model inadvertently increased the dependency on fossil fuels. Until a few years ago, fossil carbon held the monopoly for energy and fuel. The realization that fossil fuel reserves are finite and the emission of greenhouse gases (GHGs) is detrimental was a game-changer. Increased use of fossil fuels resulted in elevated GHG emissions, which ultimately led to global warming, climate change, severe geological effects such as ocean acidification, decrease in ice cover, melting of glaciers, sudden flooding, and decrease in general air quality [1]. The natural cycle relies on environmental sinks such as ocean and terrestrial plants for atmospheric CO2 reduction, but the balance was severely perturbed since industrialization. At present, global CO2 emissions are 33 Gt per year in 2019 as reported by the International Energy Agency. In addition to energy-related emissions, nonfossil fuel industries are an additional source for emissions. In China, nonfossil fuel industries alone contribute to about 5% of their total emissions, which is 466 mt in 2016 [2]. The adverse effects of increased fossil fuel consumption are apparent in recent years, but scientists believe that it will become intense in the coming years if business as usual happens. The Paris Climate Agreement asserted the participating countries to limit global warming to less than 2°C over the next 15 years,

Biomass, Biofuels, Biochemicals. https://doi.org/10.1016/B978-0-12-821878-5.00006-4 Copyright © 2021 Elsevier Inc. All rights reserved.

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Biomass, Biofuels, Biochemicals

peak CO2 emissions by 2020–30, achieve zero net emissions by 2050, and work toward negative emissions thereafter [3]. In order to achieve this, an increase in zero-/low-carbon fuels in the energy mix, a substantial decrease in emissions by carbon sequestration, and enhanced atmospheric sinks were proposed [4]. In spite of all the efforts, CO2 emissions are on the rise by 0%–2% every year and it has been estimated that energy demand is expected to increase by 20%–40% by 2040 due to population growth (World Energy Outlook, 2019). The present scenario suggests that the actions are not on par with the demands with respect to climate change mitigation and Paris Climate Agreement standards. Since fossil fuels are finite and nonrenewable, the search for sustainable resources of energy led to the use of sustainable bio-based feedstock for economic growth. Biomass is simply a source of renewable carbon obtained via photosynthesis of terrestrial plants, whereas fossil fuels are biomass-based carbon that has been subjected to geological pressures over centuries. Other than fossil fuels, many other resources such as phosphorus, certain metals, minerals, rare gases, and fertilizers are declining, and there are no feasible alternate resources for such commodities. The current economic model—linear economy—is defined as “the production and consumption of goods that (partially) ignore environmental externalities linked to virgin resource extraction and the generation of waste and pollution,” or most commonly known as the “extract-produce-consume-trash” model [5]. The voracious consumption of fossil fuels associated with complete disregard for environmental effects and sustainability has led to the adverse effects mentioned earlier. Waste is generated in enormous amounts and is dumped in landfills, further polluting the environment. Such effects have raised some major debates—Is the current lifestyle in many developed countries sustainable? Also, it casts heavy doubts on the efficacy and optimal performance of the linear economy model that promotes the disposal of valuable resources without any awareness regarding continuity in the supply chains. Even though we acknowledge that change is necessary, a paradigm shift is required to challenge the operating linear economy. New economic models are required that could understand and overcome the limitations of a linear economy. The new economic models have to be supported by technological innovations that could be made profitable, revolutionary business models that promote cascading use of raw materials and lengthening the value chain by reverse logistics, research and analysis of the market demand and supply capacities along with consumer awareness, and finally new organizations that support the economic model [6]. Circular bioeconomy is a relatively new economic growth model, which aims at decoupling environmental growth from fossil fuel dependence and providing biomass-based feedstock for consumption. Waste is also considered as a valuable source of energy/resources and is processed via extraction, recovery, followed by disposal. This chapter provides a comprehensive description of the basic concepts of circular bioeconomy and is structured as follows. Section  2 discusses

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Biomass, Biofuels, Biochemicals

in detail about the three underlying principles of circular bioeconomy, namely sustainability, circular economy, and bioeconomy. Section 3 presents the various alternative biomass-based feedstocks for driving circular bioeconomy. Section 4 describes biorefineries, the biological equivalent of petrochemical refineries. Section 5 discusses the various factors governing the successful implementation of circular bioeconomy. Finally, the conclusion and perspectives section presents important challenges and future research perspectives for the realization of circular bioeconomy.

2 Defining Circular Bioeconomy Circular bioeconomy is an inter- or transdisciplinary principle that integrates certain essential principles of sustainability, circular economy, and bioeconomy. More authors believe circular bioeconomy as an intersection of circular economy and bioeconomy [7–9], while some authors believe that both the terms can be used interchangeably [10, 11]. In this section, a clear view about sustainability, circular economy, and bioeconomy is presented. This is expected to provide a bigger picture, of which circular bioeconomy is a valuable and indispensable concept. The essential incertitude behind the fast-growing linear economy is the underlying sustainability options. Thus, the sustainability of the resources that drive global growth is pivotal. The earliest definitions of sustainability were based on the concepts put forward by forestry experts such as von Carlowitz and Evelyn. They defined sustainability principle based on wood harvesting as “the amount of wood harvested should not exceed the volume that grows again”—reassuring that nature will replenish itself, given the time [12]. Recently, sustainability was defined by Geissdoerfer et al. as “the balanced and systemic integration of intra- and intergenerational economic, social, and environmental performance.” Sustainability is assessed based on the three most essential “pillars”—environment, economy, and society. The link between sustainability and environment was exposed when the exponential growth of the global economy postindustrialization, powered by fossil fuels, resulted in severe environmental effects including ozone depletion, increased GHG emissions, global warming, and climate change. This in turn affected the society—the people. So, in other words, the three pillars can also be “people, planet, and profit” [13]. Sustainability is of major concern in the recent past, mainly because of our discovery that fossil fuel resource is a double-edged sword—it is finite/nonrenewable and its use is associated with adverse environmental effects. With the current consumption rates, the coal and crude oil reserves of the planet will be depleted in 110 and 50 years, respectively [14]. Until today, the primary source of energy for economic growth, approximately 80%, is fossil fuels: coal—27.2%, crude oil—32.8%, and natural gas—20.9% [15]. Thus, as explained in the Brundtland Report, “sustainable

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Biomass, Biofuels, Biochemicals

­ evelopment is one that meets the needs of the present without compromising d the ability of future generations to meet their own needs” [16]. Sustainability cannot be achieved in the linear economy, and renewable resources for fuels, electricity, and certain chemicals need to be scouted. To this end, several renewable resources like solar energy, wind power, geothermal energy, and biogas production have been encouraged. Sustainability issues in the industrial sector led to the development of a new economic model that can be applied in many industries—the circular economy. Linear economy and consumerism promote vacuous consumption of valuable and finite resources, mass manufacturing of low-quality products with reduced lifetime, and enormous waste generation. This is evident in a global industry such as the fashion industry, where the production, consumption, and disposal occur every season [17]. The alternative circular economy model focuses on the preservation of natural resources, resilient and diverse resource pool, employing reverse logistics for making use of end-of-life products and bringing in order and structure to the system as such so that it can be further developed or interpreted in a different context. In other words, the circular economy relies on strengthening the supply chain and reinforcing the value chain of the inputs [18]. In this context, the circular economy was defined as “a regenerative system in which resource input, waste emission, and energy leakage are minimized by slowing, closing, and narrowing material and energy loops. This can be achieved through long-lasting design, maintenance, repair, reuse, remanufacturing, refurbishing, and recycling” [12]. The Ellen MacArthur Foundation put forward the most recent definition of circular economy as “an industrial economy that is restorative and regenerative by intention and design,” thus emphasizing sustainability (https://www.ellenmacarthurfoundation.org/publications). The three R’s of the circular economy are reduce, reuse, and recycle. The “reduce” principle emphasizes cleaner production techniques (eco-friendly, nontoxic), including reduced energy inputs, raw materials input, waste generation, and GHG emissions, by technological innovations. Eco-efficiency of the process as described by the process performance based on carbon and energy footprint and resource efficiency of the process based on cautious use of resources are the two essential drivers of the reduction principle of circular economy. The “reuse” part also implies that the entire production process for a particular product can be avoided in case if the product can be reused for the same purpose. However, this is dependent on the product itself, and the longevity/efficiency of the product and consumer men­ tality about prolonged product use versus new product purchase heavily influence the “reuse” principle. “Recycle” has received great research attention in the past years, mainly considering waste as a secondary resource for finite resources such as heavy metals, phosphorus, and other organic components. A waste hierarchy was introduced, in which a preferential order for waste disposal was proposed by reducing environmental impacts and by selecting prevention, reuse, recycle,

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Biomass, Biofuels, Biochemicals

and recovery over landfilling, which is not eco-friendly [19]. Wastes and residues rich in organic carbon can be processed by thermochemical/biological methods for energy conversion, thus recovering the energy in the waste and closing the loop. The Ellen MacArthur Foundation also added further dimensions to circular economy: (i) appropriate design—which promotes optimal product life and also facilitates disassembly and reuse, (ii) reclassification of material inputs into “technical” and “nutrients”—of which the technical materials are slated for reuse while the biologic nutrient materials can be returned to the environment or further processed via cascading use, and (iii) renewability—emphasizing renewable energy as the driver for circular economy accompanied by a reduction in fossil fuel dependence. In a nutshell, a circular economy aims at value retention and enhancing the longevity of the raw materials inside of the closed loop by cascading/multistep-based usage. The major limitation is the technological innovation in the implementation of the principle as such. In certain cases, the very physical nature of the raw materials or the waste generated makes it impossible to be recycled or remanufactured [20]. Cascading use must be reasonable in terms of energy and carbon footprint compared to the production of a new product from raw materials [7] and is dependent on the degree of circularity of the materials used [21].

2.1  Biologization of Economic Growth—The Emerging Concept of Bioeconomy The concepts of sustainability and circular economy advocate balanced resource consumption with concomitant environmental protection. Still, the driver for economic growth is fossil fuel-based carbon. Bioeconomy replaces fossil fuel-based carbon with renewable carbon in the form of biomass. In essence, bioeconomy is the biologization of the fossil fuel-driven economy, ultimately powered by ­carbon-based fuels. Decarbonization is not an objective such as that in a hydrogen economy. Nevertheless, bioeconomy aims at lowering the overall carbon footprint of the fuel development process by using sustainable biomass-based feedstock. A number of researchers also agreed to the fact that there is a major shift in research toward biomass-based material products as well, and a 50-50 split of the biomass resources between fuel production and material use can be expected [22]. Bioeconomy also supports the utilization of waste and residual biomass into valuable products such as feed, biofertilizer, and other bio-based products. In essence, bioeconomy has to (i) satisfy the demands of the industrial sector for raw materials, without significant interference in agriculture, (ii) supply the society with energy, food, and water, and (iii) provide concomitant environmental protection by balancing the resources supplied and the sinks for waste disposal [23]. In such a scenario, the sustainable supply of a sufficient amount of biomass without negative land-use effects is a potential stumbling block. In the past, it has been seen that the development of first- and second-generation

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biofuels based on food crops and dedicated bioenergy crops negatively affected the society by increasing food prices and competition with agricultural resources such as land and water [24]. The development of marginal land for the cultivation of dedicated energy crops such as Miscanthus and switchgrass can help alleviate land-use effects [25]. Evaluation of crop varieties that could flourish in marginal land with low-input agricultural systems needs to be explored to reassure sustainable biomass production [26]. Another major hurdle in bioeconomy is the cost-competitive production of bio-based energy and other materials compared to the available petrochemical industry-based products. Thus, heavy reliance on the development of a technological toolkit for functional conversion of biomass, cost-competitive production, and availability of sufficient and quality biomass are the three key factors that could pave the way for the realization of a sustainable bioeconomy [27].

2.2  Sustainability and Resource Efficiency Boosted by Biomass-Based Resources—Circular Bioeconomy Having described all the important aspects of circular bioeconomy, the definition for circular bioeconomy could be arrived as thus “the sustainable and resource-efficient valorization of biomass in integrated multioutput production chains (biorefineries) while also making use of the residues and wastes and ­optimizing the value of biomass over time via cascading” [22]. Thus, circu­ lar bioeconomy (CBE from now on) is a transdisciplinary approach integrating concepts of sustainability and cascading use and waste hierarchy from social, environmental, and economic perspectives. At the heart of CBE is biorefinery, the biological equivalent of petrochemical refinery where biomass feedstock is processed for multiple product extraction. Since CBE is a closed-loop system, a biorefinery design should include sustainability and circularity concepts. Biorefineries could process feedstock for multiple product production via integrated biorefineries, encouraging complete energy recovery from the feedstock applied, promoting resource efficiency [28, 29]. Cascading use of biomass is also promoted in biorefineries to extract high-value bioproducts from the biomass in various steps before subjecting to the final end-of-life product genera­ tion [30, 31]. The major goal of circular bioeconomy is decoupling economic growth from environmental pressure and fossil fuel dependency. Societal demands dictate that CBE could eventually be coupled to the United Nations Sustainable Development Goals to provide energy security, food security, and clean water, developments in the healthcare sector, climate change mitigation, and development of sustainable cities. Fig. 1 illustrates the basic concepts of circular bioeconomy and the goals and expectations out of it. The feedstock for CBE, the concept of circularity in biorefineries, and the factors affecting CBE implementation are discussed in detail in the following sections.

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Biomass, Biofuels, Biochemicals

Fig. 1  Circular bioeconomy concept— Principles, expectations, and goals.

3 Multifarious Choice in Feedstock Acquisition for Circular Bioeconomy—Renewable Biomass and Waste Valorization The most possible alternative bio-based feedstock for CBE is listed in Table  1. The list is by no means exhaustive, but it provides a general overview of the vast possible resources that could be used. The most important and the most commonly used of them all is the plant-based lignocellulosic biomass. Lignocellulosic biomass has a complex structure composed of heterogeneous polymers such

9

Biomass, Biofuels, Biochemicals Table 1 Source of Sustainable Feedstock for a Biorefinery in Circular Bioeconomy. Feedstock Category

Feedstock

Animal-based feedstock

• Manure—swine, cattle

Plant-based/lignocellulosic biomass

• Virgin biomass • Forest-based biomass—woods • Cash crops—corn, sugar beets, soy, palm, sugarcane • Dedicated energy crops—Miscanthus, Jatropha • Residual/waste biomass • Agricultural waste—bagasse, straw • Wood processing waste

Aquatic biomass

• Microalgae • Macroalgae • Small aquatic plants—water hyacinth, duckweed, water lettuce

Food waste

• Inedible parts of food—husks, peels • Materials after use—cobs, coffee/tea grounds • Restaurant/domestic food waste • Waste cooking oil

Waste

• Solid municipal waste • Biodiesel-derived glycerol • Municipal wastewater • Food and dairy industry wastewater • Animal husbandry wastewater

Sources for waste CO2

• Anaerobic digesters • Ethanol fermentation plants • CO2-rich industrial exhaust gases • Syngas

as cellulose, hemicellulose, and lignin. The structure is impermeable to water and highly recalcitrant to processing/pretreatment and hydrolysis [32]. The advent of eco-friendly and effective treatment technologies that do not affect the downstream processing, whether chemical catalysis or biological conversion, is vital. Lignin valorization is the most researched topic in lignocellulosic biomass processing. Lignin streams could be a potential feedstock for certain aromatics production for the replacement of petrochemical-based products, but the processing of lignin prior to its conversion is a major hurdle [33]. A number of methods including physical, chemical, thermal, and biological methods have been applied for lignin separation and depolymerization. Yet, the method tends to vary depending on the downstream conversion process and a “one-size-fits-all” approach does not work [34]. Based on the demands of the lignocellulosic biorefinery, a sustainable supply of biomass is challenging. It has been estimated that the United States has the potential to produce one billion tons of biomass per year by 2040 [35]. It must be noted that biomass production by agriculture is irrevocably related to fossil

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Biomass, Biofuels, Biochemicals

fuel consumption for fertilizer production and general operational procedures. This increases the carbon footprint of the biomass procured. In such a case, sustainability, land footprint, water footprint, carbon footprint, and GHG emissions associated with biomass production to meet the industry demands make the entire process questionable. And, petrochemical feedstock seems like a much better option [36]. Thus, careful evaluation of the feedstock source is essential to maintain a low-carbon CBE. For any feedstock, the logistics of feedstock procurement such as collection and transport also plays an important role. Positioning of biorefineries close to feedstock availability could be a viable option to cut off the extra costs [37]. Consideration of waste as a valuable resource is an important cornerstone in ­circular bioeconomy. Food waste is particularly rich in organic carbon content and could be used in biological fermentation processes for the production of ­various bio-based chemicals. It has been estimated that over 90% of the food waste is generated before consumption and contributes significantly to increasing GHG emissions [38]. In the European Union alone, 143 billion euros worth of food is wasted annually, and the cost includes the consumption of resources and environmental impacts [39]. Thus, food waste is a valuable resource in CBE. Other than that, wastewaters are a rich source of finite resources such as phosphorus. Wastewaters serve as a secondary source for P extraction, since the primary geological source is finite and declining [40]. Wastewaters are also a secondary source of rare earth metals, which has widespread applications in the chemical industry [41].

4 Biorefineries—Pivotal in Circular Bioeconomy Biorefinery is defined by the International Energy Agency as “the sustainable processing of biomass into a spectrum of marketable products and energy.” It also highlighted the fact that strong sustainability could be achieved in a biorefinery only if the product spectrum includes both energy (fuels—bioethanol, biomethane) and material products (chemicals, food, feed). Processing of the biomass for high-value products before subjecting it to other cascading steps could prove to be beneficial in terms of multiple product generation. The success of a biorefinery depends on the biomass that is being processed and the supply chain logistics. The quality and quantity of biomass available, geographical location, seasonal variation, and the variant lignocellulosic composition based on the source are the guiding factors for processing biomass in a biorefinery [42]. The inherent characteristics of biomass such as heterogeneous composition, high moisture content, variable elemental composition, relatively low net calorific value, and variable ash content make it difficult to develop a standard processing method. The net energy levels of biomass are about a little over half of that of coal; hence, the amount of biomass that has to be processed in place of coal is enormous [43].

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Biomass, Biofuels, Biochemicals

The technological limitations of lignocellulosic biomass processing include the recalcitrant nature of the lignin carbohydrate complex to hydrolysis methods, corrosive nature of the pretreated biomass solution, lignin valorization, minimizing carbon loss while processing, and the higher oxygen content that limits downstream processing. In a petrochemical refinery, the feedstock is almost the same without significant difference in composition, and the refinery as an industry is deep rooted in technology and skillful execution of their objectives [35]. Thus, technological innovations in the processing and catalytic conversion of biomass are indispensable for biorefineries to bridge the gap between the expectations out of a biorefinery and the current state of the biorefinery industry in terms of performance and accomplishments. The feedstock for biorefineries has evolved over the years from the first-generation cash crops to the second-generation lignocellulosic biorefineries. Currently, aquatic biomass such as microalgae, macroalgae, and aquatic weed plants is considered as potential third-generation feedstock for biofuel production. Microalgae are microscopic aquatic and terrestrial photosynthetic organisms capable of carbon capture, thus serving a dual propose of carbon sequestration and beneficial biomass production. In addition, microalgae are rich in valuable compounds such as lipids, fatty acids, antioxidants, pigments, and other such functional products [44]. The advantages of microalgae over terrestrial biomass are summarized as follows: (i) Microalgal cultivation does not require arable land and thus will not result in land-use changes, (ii) microalgae possess outstanding carbon fixation and photosynthetic efficiency, leading to high biomass productivity per given land area compared to terrestrial plants, (iii) microalgal biomass is available year around, and the cultivation/harvesting is not subject to seasonal variation, and (iv) microalgae can be cultivated in brackish water or nutrient-laden wastewaters, further promoting resource recovery [45]. Lipid-rich microalgae are preferred over other oil crop-based feedstocks for biodiesel production, due to their high productivity and noninterference in agricultural activities [46]. Spent microalgal biomass after lipid or valuable product extraction contains protein and carbohydrates and can serve as a feedstock in a biorefinery [47]. Low biomass production in the open cultivation systems and the need for a low-carbon process limit the potential development of microalgal biorefineries [45]. Nevertheless, waste microalgal biomass collected from polluted water bodies can be directly converted to fuel via direct combustion [48]. Macroalgae or seaweeds are a major source of functional components and have served as a source of nutrition over the years. Consequently, diverse feedstock can be applied in a biorefinery such as lignocellulosic biomass [49–51], forest biomass [11, 52], wood [53], food waste [54, 55], animal manure [56, 57], microalgae [47, 58, 59], macroalgae/seaweed [60, 61], aquatic plants [62, 63], and wastewater [64]. Thus, ensuring the supply chain by fostering sustainable/waste feedstock, optimal and efficient processing in integrated biorefineries, with appropriate market generation, can pave the way for the economic success of biorefineries [65].

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Biomass, Biofuels, Biochemicals

5 Essential Factors Governing the Transition to a Circular Bioeconomy The successful implementation of a circular bioeconomy requires radical changes to the way the current linear economy is functioning. Table 2 summarizes the feedstock and products of a petrochemical refinery and a biorefinery. It can be seen that biorefinery presents with an alternative for most of the petrochemical-based products. Accomplishment of industry-scale, functional biorefineries with cost-competitive and diverse product range is necessary. With the grandeur triumph of corn ethanol in the United States and sugarcane ethanol in Brazil, the biofuel industry has already made a significant mark in the bioeconomy sector. The feasibility of converting these existing fuel plants into biorefineries with cascading use of biomass needs to be evaluated, since the development of such an integrated biorefinery from scratch needs huge capital in establishing the production line and delivering the products to markets [74]. Based on the source of biomass, the product range can be defined. Niche markets for bio-based alternatives are on the rise based on consumer awareness regarding natural products with minimal side effects. Thus, biofuels and bio-based health sector products such as supplements and cosmetics are particularly well established. The question that remains is to integrate the production technologies for resource efficiency. Computer-aided simulations to brainstorm designs with reduced cost and environmental impacts, which preferably operate with renewable energy, need to be developed. Computer-aided simulations combined with life cycle analysis of an integrated biorefinery allow researchers to investigate the feasibility chains on structural and operational stages, and its impacts on environmental, social, and economic aspects [75, 76]. Research focus on the design and development of such integrated biorefineries is much needed and is expected to be functional by the time society is at the brink of fossil fuel depletion [77]. In place of solid fuels such as coal, microalgal biomass is considered as a potential alternative [78]. Terrestrial biomass-fired power plants suffer low performance mainly due to the low heating value of woody biomass, while the higher carbon content of microalgae aids in enhancing the efficiency of the combustion process [79]. Cocombustion of coal and microalgal biomass alleviates the low efficiency of woody biomass-driven plants and the technology used for the process is much similar to coal combustion, with minor modifications in the infrastructure [48, 80]. The second most important, but often overlooked concept is the biologization of the massive petrochemical industry. Fossil fuel forms the basis for a variety of commodity chemicals and materials that are common in daily use. At present, biomass-based organic chemicals only contribute to about 10% of the chemicals market and it is expected that by 2020, 25% of organic feedstock chemicals and 10% of liquid fuels could be bio-based in the United States (Report of the Committee on Bio-based Industrial Products, Board on Biology, National Research council,

13

Biomass, Biofuels, Biochemicals Table 2 A Comparison of Feedstock and Probable Products From a Petrochemical Refinery and Biorefinery. Parameter

14

Petrochemical Refinery

Biorefinery

Feedstock

Crude oil, coal, natural gas

Virgin/waste biomass, wastewaters, waste CO2

Fuels

Petrol/gasoline Diesel Fuel oil Jet fuel Hydrogen Methane

Green crude/biocrude/pyrolysis oil Bioethanol Biodiesel Biohydrogen Biobutanol Biomethanol Syngas Biomethane Microbial hydrocarbons [66]

Agriculture

Nitrogen fertilizers—ammonia, urea

Nitrogen recovery from wastewater by nitrification/denitrification, promoting bacterial nitrogen fixation

Pesticides

Biopesticides—plant extracts, bacteria, fungi

Plastics

Thermoplastics—polyethylene, polypropylene, vinyl chloride, styrene, ethylene glycol, tetraphthalic acid, polyvinyl chloride, polystyrene, polyethylene tetraphthalate [67]

Bioplastics—polyethylene furanoate, polylactide, polyhydroxy alkanoates, polyhydroxy butyrate, polybutylene succinate, polycaprolactone, protein-, lipid-, cellulose-, and starch-based bioplastics [68]

Carbonaceous material

Carbon black

Biochar-derived carbon black [69]

Chemicals and solvents

BTX aromatics, olefins, ethanol, other solvents [67]

Organic acids—glycolic acid, 3-hydroxy propionic acid, succinic acid, lactic acid, 1,3-propanediol, 2,3-butanediol, γ-valerolactone, tetrahydrofurfural, pentanoic acid, 1-pentanol, 5-hydroxymethyl furfural, furfural, levulinic acid [70] 2,5-Furandicarboxylic acid, 3-hydroxypropionaldehyde, sorbitol, isoprene [71]

Surfactants

Glycols

Biosurfactants—rhamnolipids, sophorolipids [72]

Rubber

Synthetic rubber

Plant-based rubber

Pharmaceuticals

Aspirin, antihistamines, other disposable supplies such as latex gloves, plastic syringes [73]

Biocosmetics (chitin, chitosan, collagen), vitamins, pigments, antioxidants, antibiotics, bioactive enzymes [68]

Food additives

Xylitol—sweetener Vanillin—flavoring agent

Others

Biocomposites, innovative construction materials

Biomass, Biofuels, Biochemicals

2000, https://www.ncbi.nlm.nih.gov/books/NBK232955/). As it can be seen from Table 2, alternative bio-based products are available for most of the petrochemical products. However, support for the bio-based chemical industry is few and far between. Apart from some major chemicals produced in industrial scale, research and development schemes for the development of bio-based chemical industry to compete with the petrochemical industry have not been performed. This disparity mainly arises from the fact that currently fossil fuel prices are low, compared to the procurement/pretreatment costs of biomass feedstock. The technology is still very new and needs abundant attention [81]. Bio-based plastics and chemicals do not require huge biomass quantities like those of biofuel productions, and the value web is intricate assuring higher job opportunities. However, it could not flourish in the absence of subsidies and incentives, mainly because of the competition with the bioenergy sector for feedstock and the requirement to be produced in integrated biorefineries for cost competitiveness [81]. While petrochemical industries could operate at 60% of their productive capacity, it is expected to be reduced to almost 50% in biorefineries with limitations in the continuous supply of biomass. Another potential renewable source for chemical production is CO2 captured from industrial exhaust or fermentation plants or ambient air, as mentioned in Table 1. Carbon capture and utilization in the chemical industry have the potential to reduce the global CO2 emissions of up to 3.5 Gt CO2-eq by 2030 [82]. Thus, waste CO2 is a potential CO2 source for a low-carbon, fossil fuel-independent chemical industry, but the processes are energy intensive requiring an estimated 55% of the total energy produced in 2030 [82]. From the economic perspective, it is the responsibility of all the stakeholders to take functional steps toward the development of a CBE. The difficulty in raising investments for CBE is mainly due to the unprecedented delays in profit generation and return on investments, because of the premature stage of the industry and the uncertainty factor in its success rate. Nevertheless, there is no choice but to transition toward CBE, but it is still a long way. CBE is a relatively nascent field, with huge potential for development anywhere in the world despite the socioeconomic status, due to the very nature of the concept that encourages regional applications as per the motto “think global, act local.” CBE is also expected to oversee a controlled use of biomass resources, ensuring sustainability, and defend against the depletion of natural resources. Environmental protection, in terms of reduction in GHG emissions and effective waste management, is another cornerstone of CBE. In the past decade, there has been a stable increase in the inclusion of bio-based products in the energy and material products sector. Bio-based products are promoted for their sustainability and biodegradability, two important environmental aspects of any product. The many variables presented in Table 3 play a crucial role in the realization of CBE. At present, implementation of CBE is heavily influenced by ●

Identification and effective use of biomass-based resources without generating potential aftereffects such as land-use change and interference with agriculture,

15

Biomass, Biofuels, Biochemicals Table 3 Factors Affecting the Development and Realization of Circular Bioeconomy. Factors Affecting Implementation of CBE Technological factors

• Development of a groundbreaking biotechnological toolkit for effective valorization of biomass in biorefineries • Innovation and result-based research from the academic/industrial sector • Reduce the environmental impacts of the current biological processes by replacement with greener sustainable methods • Reuse and recycle/upcycle waste feedstock • Smooth and beneficial technology transfer for large-scale application • Effective digitization of the data generated from the innovative research including gene sequences and innovative catalysts design • Culture collections for industrially important microbial strains

Social factors

• Eventual coupling to the United Nations Sustainable Development Goals • Provision of green energy, food, and energy security, and developments in the healthcare sector • Increase in consumer awareness • Acceptance of the products of biotechnological innovation • Regional job supply

Environmental factors

• Preservation of the ecological balance of the environment • Ensure strong sustainability—reassure that what was taken can be regrown/replaced • Climate change mitigation and reduction in overall GHG emissions

Economic factors

• Uncouple economic growth from fossil fuel-based carbon • Attract investment in the CBE sector and monitor return on investments— financing mechanisms • Develop circular bioeconomy-based business models • Setting global standards such as metrics and indicators for assessing economic growth in CBE • Promote stakeholder cooperation among various sectors • Develop markets for new bio-based products from cascaded use of biomass—market analysis

● ●

● ● ● ● ●

16

Variables That Play an Important Role

Realization of biomass residues and waste as a potential feedstock, Setting up a steady source of biomass for continuous operation of the biorefinery, irrespective of seasonal/geographical interferences, which implies local sourcing of biomass or relies on exporters, Innovation-based research and development in the biotechnology field for cost-effective and eco-friendly processing of biomass resources, Technological advances that promote cascading use of biomass without any reduction in the value chain, Analysis of the pros and cons of a single resource-based biorefinery versus an integrated biorefinery with multiple feedstock and processes, Accomplishment of biorefineries in industrial scale, Successful and amicable cooperation between academia, industry, and policymakers, sharing valuable research outputs and probable implementation strategies,

Biomass, Biofuels, Biochemicals

● ● ● ● ● ●

Coordination of market demands and supply chain or generate new markets for bio-based products, Societal and consumer awareness and acceptance of bio-based/biotechnological alternatives for conventional products, Global inclusiveness in data generation, management, and setting up global metrics and indicators or assessing CBE-based growth, and Establishment of at least a few token CBE objectives, designs, and principles to follow on a global scale, Addressing the potential shortcomings and bargains involved in a bio-based economy, Adoption, endorsement, and support for successful/potential CBE concepts by respective State representatives.

6 Conclusions and Perspectives CBE is a seemingly perfect ideology and a new economic concept based on the sustainable use of biological resources. It aims at closing the loop of the current linear take-make-dispose scenario by promoting a reduction in the creation of waste, reusing/recycling resources encouraging resource efficiency, and putting forward a waste hierarchy prior to waste disposal. However, the research focus is specifically needed in the following areas: 1. Development of highly functional biocatalysts for the effective conversion of biomass-based sugars into material products such as commodity chemicals other than biofuels: Fermentation strategies can be applied for this, but biotransformation with highly effective enzymes might be economic compared to fermentation. Nevertheless, the choice depends on the product in need. On the other hand, huge funding is required for these biotechnology-based knowledge development projects, which could be undertaken by industrial research and development sectors or academic researchers with State support. 2. Provision of a common platform for the beneficial interaction of all the actors in the CBE development policy in any given country—academy and industry that provide the essential technological input, industrial sector for application of the developed technology, policymakers who design and develop policies for support and approval by State, and finally the State authorities who provide support by incentives and policy approval. 3. Development of a holistic approach for CBE—define and demarcate CBE from the overlapping principles of circular economy and bioeconomy. While a circular economy concept can be applied to any industry by reducing waste and value retention of the input resources, bioeconomy aims at decoupling economic growth from fossil-fuel driven economy and promotes a ­biomass-driven economic growth. CBE applied certain principles of both, but it is essentially transdisciplinary. Researchers should address the term in a much deeper sense and develop principles and policies based on CBE.

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Biomass, Biofuels, Biochemicals

4. Responsible use of biomass and prevent overexploitation of natural resources—biomass availability or biocapacity of a country is restricted by its geographical position, much similar to crude oil. Hence, overseeing biomass use and export is pivotal in CBE. The depletion of natural resources is potentially harmful to human society, the perils of which are already evident. Also, reduction in potential environmental threats including GHG emissions and land-use changes are crucial, since CBE is not decarbonization of the economy as envisioned in the hydrogen economy, but simply biologization of the input carbon.

Acknowledgments The authors gratefully acknowledge financial support received from Taiwan’s Ministry of Science and Technology under grant number MOST 108-3116-F-006-007-CC1, 108-2218-E-029002-MY3, 107-2221-E-006-112-MY3, 108-2621-M-006-020, and 108-2218-E-006-00.

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Environment and Material Science Technology for Anaerobic Digestion-Based Circular Bioeconomy Elena Rojoa,b, Alessandro Carmonaa,b, Cenit Sotob,c, Israel Díaza,b, María Fernández-Polancoa,b, Laura Palaciob,c, Raúl Muñoza,b, and Silvia Boladoa,b

a Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering, University of Valladolid, Valladolid, Spain bInstitute of Sustainable Processes, University of Valladolid, Valladolid, Spain cDepartment of Applied Physics, Faculty of Sciences, University of Valladolid, Campus Miguel Delibes, Valladolid, Spain

1 Introduction to Waste to Product Biorefineries The current increase in the production of wastes and greenhouse gases (GHG), together with the shortage of raw resources related to the growth in population and consumption, raises the need to research sustainable processes for waste valorization. The most promising solution which addresses all of these concerns is the circular economy (CE) or circular bioeconomy (CB) which has the potential to overcome the environmental and economic challenges in the coming years [1]. The objective of the CB is to reduce waste disposal and the consumption of natural raw materials, enhancing the circularity of the raw materials used and prolonging their lifetime in order to complete the economic and ecological cycles [2]. Currently, researchers are looking for alternatives to reduce or take advantage of waste and pollution while achieving a more sustainable use of resources by applying a biorefinery concept. This biorefinery concept refers to sustainable processes of conversion of different biomass into valuable bioproducts or bioenergy. The development of these processes provides potential economic, environmental, and social benefits by replacing fossil resources with renewable materials [3]. It includes a varied range of technologies and processes capable of separating

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Biomass, Biofuels, Biochemicals

biomass resources into their building blocks (carbohydrates, proteins, and lipids) which can be transformed into value-added products, biofuels, and chemicals [4]. The concept of biorefinery is likened to traditional petroleum refinery which produces fuels and chemicals from petroleum. But in the case of biorefinery, different types of biomass are converted into bioproducts which could transform the current fossil fuel-based economy into a bioeconomy based on the use of renewable resources [5]. Biorefinery has been classified into several ways—based on their feedstock, their production technologies, and their conversion routes [6]. One of the most promising biorefineries is that using the organic wastes as feedstock for profiting the economic potential of wastes and also improving the environmental management. In 2016, 2.01 billion metric tonnes of municipal solid waste (MSW) was produced globally, amounting to a footprint of 0.74 kg per person per day. Annual waste generation is expected to rise by 70% from 2016 levels to 3.40 billion tonnes in 2050 as a result of rapid population growth and urbanization [7]. Also, around 5 million metric tonnes of waste is produced annually from agriculture [8], 125.4 million metric tonnes of waste with high N content was produced annually from agriculture in 2017 [9], and 1.3 billion metric tonnes of food waste is produced annually [10]. A varied range of resources and products can be obtained from organic wastes, reducing dependence on fossil raw materials, reducing GHG emissions, and opening new ways to use renewable raw resources. Therefore, organic wastes are an important resource for bioconversion into valuable compounds for different applications [11]. Nevertheless, organic wastes are complex and highly heterogeneous materials which are difficult to use as feed in a continuous biorefinery. For example, MSW contains 34%–53% of organic waste (such as carbohydrates, proteins, and lipids) and high moisture and salt content which leads to fast decomposition and unpleasant odors [12]. It contains also paper waste (25%), plastics (13%), metals (9%), food (15%), yard trimmings (13%), and small amounts of hazardous substances [13], which makes it a residue with a varied composition that is difficult to treat. Organic wastes are useful, abundant, and cheap raw materials for producing valuable products, but the key challenges of these biomass streams (low energy, high moisture content, diverse composition, and distributed availability) must be overcome to exploit their potential [14]. In order to obtain a homogeneous biorefinery feed, a preliminary anaerobic digestion (AD) step is a very interesting and promising alternative. AD is a mature and consolidated technology with a great potential for efficient conversion of a variety of low-value feedstocks (such as the organic fraction of MSW or agriculture and animal wastes) into a highvalue biogas and a digestate. Biogas can be biotransformed to obtain new products of high interest or cleaned to produce biomethane. Important amounts of nutrients like nitrogen, phosphorus, and potassium are accumulated in the digestate [15] (Fig. 1).

26

Biomass, Biofuels, Biochemicals

Fig. 1  Schematic of the overall process of organic waste biorefinery based on anaerobic digestion.

Table 1 Composition of biogas. Biogas component

Concentration

Reference

Methane (CH4)

% (v.)

50–70

Carbon dioxide (CO2)

% (v.)

30–40

Hydrogen sulfide (H2S)

% (v.)

0–0.3

[16]

Ammonia (NH3)

% (v.)

0–1

[16]

Moisture

% (v.)

0–10

[16]

Nitrogen (N2)

% (v.)

0–5

[16]

Oxygen (O2)

% (v.)

0–5

[16]

Siloxanes

mg Si m-3

0–50

[16]

Volatile organic contaminants

mg m-3

0–4500

[16]

20–200

[16]

Halogenated hydrocarbons

−

-

ppmv Cl /F

As shown in Table  1, the biogas obtained by AD of organic wastes produces a mixture that typically contains 50%–70% CH4, 30%–40% CO2, and smaller amounts of hydrogen sulfide, as well as traces (in the range of ppm) of hydrogen, nitrogen, oxygen, and other volatiles species [16]. The presence of these compounds reduces the quality and impedes some alternatives of biogas valorization that requires an upgrading step to obtain biomethane. Recent research in material science is providing new types of membranes that are able to remove CO2 and other pollutants from biogas. Biogas upgrading using these new types of membranes would result in lower investment and operating costs compared to the physicochemical and biological technologies currently used [17]. In order to

27

Biomass, Biofuels, Biochemicals

comply with the ideas of the CB, biomethane can be used as a renewable biofuel or as feedstock to produce building blocks for the chemical industry. The high concentration of nutrients present in the digestate from AD makes this type of product an ideal growth media for algal microorganisms in biological reactors called photobioreactors. Nutrients are assimilated and transformed into microalgae biomass with a high concentration of proteins, carbohydrates, and lipids. Then, this biomass can be further valorized, applying the previous concept of biorefinery, into medium and high value-added products or biofuels that would optimize the entire process [18] and reduce the consumption of fossil fuels [3]. Microalgal photobioreactors also contribute to the reduction of GHG emissions by using CO2 as a carbon source. According to the World Meteorological Organization (WMO), the total GHG emissions increased 1.5% per year in the last decade (2009 to 2018) to reach a record value of 51.8 GtCO2 in 2018 [19], with a CO2 concentration in the atmosphere of 407.8 ppm [20]. Both GHG emissions and CO2 concentrations are growing globally, despite progress in climate policy. It is possible to obtain a global process (Fig. 1) as a solution for organic waste management which would establish a CB and reduce the environmental ­impact of these wastes. The first step of AD homogenizes the wastes and obtains two streams of biogas and digestate. The biogas can be cleaned to obtain biomethane using a new material membrane system or biotransformed into high v­ alue-added materials, such as polyhydroxyalkanoates or ectoine. On the contrary, the digestate can be used as media for microalgae growth which are valorized into bioproducts by applying different processes.

2 Anaerobic Digestion as a Pretreatment for Waste Valorization Biogas production by anaerobic digestion of wastes has increased remarkably in recent years, especially in Europe. Europe is nowadays the region with the largest number of anaerobic digesters in the world (approx. 18,000 units in 2017), followed by China (7000 units by 2015) and the USA (2200 in 2015) [21, 22]. This increase in biogas production has been triggered by the urgent need to reduce the European dependence on imported natural gas and to valorize the organic waste from the domestic, livestock, and industrial sectors. In 2016, European biogas supported a primary energy production of almost 16.1 million tonnes of oil equivalent (Mtoe), corresponding to an electricity production of 62.5 Twh and sales to heat district systems of 643,000 t of oil equivalent [23]. The anaerobic digestion of energy crops, urban solid waste, and livestock waste accounted for almost 12 Mtoe, landfill gas for 3 Mtoe, and wastewater treatment for 1.5 Mtoe. The European exponential growth of biogas production was only slowed down by the recent regulatory limit of 60% in the use of energy crops in Germany (the largest producer of biogas).

28

Biomass, Biofuels, Biochemicals

s SW d ste M ste l dge an wa n a l a u ts o l p l l a ble s cti iow ici s tri cia ima duc ta ct us er un age fra r b n pro ge rodu d e c o A M m i n w V -p I m n by se ga by co Or

1

Storage

2

Feedstockpreparation

3

4

8

Digestate storage

r Fe

Fig. 2  Diagram of biogas production plant.

til

r ise

5

6

Biogas storage

Biogas cleaning

s

ct

du ew o N iopr b

ity

c

9

7

BIO

tri

ec

El

et

/c

at

He

e

n ha

old om

Bi

CH4

el

Fu

d- ts de uc ad rod gh p Hi lue va

e

Fig. 2 shows a schematic process of industrial-scale anaerobic digestion, including the main stages. Different feedstocks ① are used and stored ② in appropriate tanks or buildings; to operate in stable conditions, to reach the maximum biogas production, and to obtain high-quality digestate, it is essential to prepare an adequate feedstock ③; anaerobic digestion occurs in the digester ④; biogas obtained in the anaerobic process is stored ⑤; the biogas must be cleaned before use ⑥; and biogas can be used to produce electricity, heat/cold, biomethane, fuel, or high value-added products ⑦ [24]. The other by-product obtained in the AD is the digestate which is collected and stored ⑧ in order to be applied afterward. Nutrients contained in the digestate can be recovered ⑨ and used as fertilizers or as algal biomass that can be further valorized as new bioproducts.

2.1 Feedstocks Different organic wastes can be used as feedstock for anaerobic digestion as a preliminary step of waste biorefinery: ● ● ● ● ●

Municipal solid waste Municipal sewage sludge Industrial and commercial waste Animal by-products Vegetable by-products.

29

1000

200

800

150

600

100

400

50

200 0 dg e em ta a nd nu re gr ap em as Fo h od le f to Bi ve ow rs Po as ta te t o fro pe m el s ho us eh ol A ds ni Fa m al ts bl ep oo ar at d or co nt en t O ld br ea d

0

Fr ui

Ca ttl

ag e

Power yield (kWhel/t fresh feedstock)

1200

250

Se w

Fig. 3  Methane production and power yield from different feedstocks [25].

300

slu

CH4 (m3/t fresh feedstock)

Biomass, Biofuels, Biochemicals

The characteristics of the feedstock used have major impacts on the biogas process and biogas yield (Fig.  3). The methane yield of each feedstock depends on its composition and how much protein, fat, and carbohydrate it contains. Feedstock composition therefore significantly influences the viability of a biogas plant. Conversely, certain feedstock can have a negative impact on the microbiology in the digester. A constant feedstock supply has to be ensured; it determines the technology used and it has a huge influence on the economy of a biogas plant and their associated costs such as collection, transportation, handling, and gate fees. Therefore, the whole plant concept should be based around the feedstock [25].

2.2  The Process Anaerobic digestion takes place through four successive stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis; the anaerobic digestion process is dependent on the interactions between the diverse microorganisms that are able to carry out the four aforementioned stages [26]. Fig. 4 depicts a simplified flow of the four digestion stages. The digestion process begins with bacterial hydrolysis of the organic biomass that contains complex polymers which are inaccessible to microorganisms. Insoluble organic polymers, such as carbohydrates, are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. In acetogenesis, bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogens convert these products to methane and carbon dioxide. The methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments.

30

Biomass, Biofuels, Biochemicals

Fig. 4  Anaerobic digestion process.

The process parameters affecting anaerobic digestion are the anaerobic conditions, temperature, system pH, volatile fatty acid content and conversion, availability of micro- and trace nutrients, mixing, toxicity, solid retention time, volatile solids loading rate, and hydraulic retention time [27].

2.3  Operational Parameters The most important process parameters that can be used to distinguish between the different anaerobic digestion plants are the operating temperature, feedstock and codigestion, complexity, and moisture content. Later, some trends per process parameter are presented.

2.3.1  Mesophilic or Thermophilic Anaerobic digesters operate on mesophilic (35–40°C) or thermophilic (50– 55°C) conditions. Mesophilic digestion is predominant because of the lower need for heating and is considered more stable. It is used in the treatment of sewage sludge, wastewater, and manure. Thermophilic digestion has an important field of application in the digestion of the organic fraction of MSW (30%–40% of the market) and 30%–50% higher production of biogas is obtained compared to mesophilic digestion. Stable thermophilic performance has been proven [28].

2.3.2  Single Feedstock or Codigestion Codigestion (anaerobic digestion of multiple feedstocks) improves the biodegradability and methane yield obtained with respect to single feedstock digestion in some cases by equilibrating the available substrates and nutrients required for the microbiota. The number of codigestion plants has increased in recent years to 13% of installed capacity, especially in the agro-industrial sector. The amount of coproducts is low and some plants foresee this option but make no (or little) use of it [28].

31

Biomass, Biofuels, Biochemicals

2.3.3  Single Phase or Two Phase In two-phase digestion, hydrolysis and methanization are operated separately. The physical separation provides optimum environmental conditions for each group of microorganisms and higher stability and control. Nevertheless, twophase operation has decreased since the nineties due to the higher investment and operating costs for two independent processes [28].

2.3.4  Wet or Dry Wet systems operate at low total solids ( hemicellulose ≥ lignin and residue yield (solid) follow a sequence of lignin > cellulose > hemicellulose > protein > lipid [71]. The HTL involves different and complex degradation pathways of various components due to their interactions with each other during the process; therefore, it becomes difficult to point an exact pathway. Commonly, it follows three steps, viz. depolymerization, decomposition, and recombination. The biomass is depolymerized and decomposed into highly reactive small compounds that are polymerized to essentially form biocrude and gas and solid compounds. The temperature and pressure change causes depolymerization of long-chain polymers to short-chain hydrocarbons and overcomes the complications related to

73

Biomass, Biofuels, Biochemicals

simplifying lignocellulosic biomass [72]. Further, it breaks down the monomers into smaller fragments via dehydration, deamination, and decarboxylation into glucose, organic acids, phenolics, and nitrogen-containing compounds. Finally, intermediate products undergo cyclization, condensation, and polymerization to form biocrude, water-soluble, gaseous, and solid products [73, 74]. The correlation of influence parameters in HTL such as reaction temperature, pressure, time, biomass concentration, solvent type, and catalyst loading has been established through several research studies [75, 76]. Moreover, co-­liquefaction has been carried out to improve the biocrude yield. The co-liquefaction develops a synergistic effect and is defined as the difference of biocrude yield of mixed feedstock and individual feedstock. The literature suggests that the HTL process houses complex pathways for obtaining biocrude, but the specific reactions that take place are not fully understood. This limited information on pathways limits the use of several feedstocks that can be utilized for co-liquefaction. Additionally, the use of density functional theory, principal component analysis, factorial design methods, and response surface methodology to identify the mutuality of various parameters can be evaluated. As the use of mixed biomass is increasing in HTL, several components may lower the biocrude yield. Therefore, the use of solvents to remove the retarding component may be performed. At last, the biocrude obtained consists of some impurities that reduce its yield and require upgrading biocrude through improving its thermodynamic properties.

3.1.4 Transesterification The production of biodiesel through transesterification takes place between vegetable oil/ animal fat (triglycerides) and alcohol (methanol, ethanol, and butanol; fatty acid alkyl esters) with or without a catalyst. The process involves exchanging of alcohol from an ester and is also termed as alcoholysis. The process yields one methyl ester molecule from each glyceride at every step, i.e., conversion of triglycerides to diglycerides, followed by conversion of diglycerides to monoglycerides, and finally monoglycerides to glycerol. The glycerol obtained is one of the major by-products of transesterification. The variables that affect the transesterification process are reaction temperature, reaction time, reaction pressure, the ratio of alcohol to oil, concentration, and the type of catalyst, mixing intensity, and the type of feedstock. Several studies have been conducted in the presence of a catalyst as triglycerides are immiscible with alcohol, which hinders the rate of transesterification drastically. The presence of catalyst improves higher surface contact, yielding biodiesel at faster rates, but increases expenditure on chemicals. The catalyst employed in transesterification is classified as homogeneous, heterogeneous, and biocatalyst, whereas noncatalytic biodiesel production involves supercritical alcohol and BIOX co-solvent transesterification. In a catalytic method, if the catalyst remains in the liquid phase as reactants during transesterification, it is termed as homogeneous (sodium hydroxide, 74

Biomass, Biofuels, Biochemicals

­ otassium hydroxide, and sulfuric acid) or else is known as heterogeneous, i.e., p solid phase (lipases, CaO, and MgO). Further, the selection of the catalyst type is driven by the amount of free fatty acid and water content present in the oil, other than the use of purely raw materials. The higher amount of free fatty acid desires the use of acid catalysts while the base catalyst is used in lower amounts to prevent saponification. The saponification renders the mix viscous due to the formation of gels making separation of biodiesel and glycerol difficult with a simultaneous drop in ester yield [77]. The homogeneous catalytic transesterification at the end of the reaction requires the separation of product, catalyst, and by-product, thus raising the cost of biodiesel recovery. It is carried out commonly at low catalyst concentrations (0.5–2 wt%) with low pressures, temperatures, and reaction time (333–338 K, 1.4–4.2 bar, and 1 h) [78]. The process deploys alkaline metal alkoxides, hydroxides, and sodium/potassium carbonates. The popularity of homogeneous base catalysts is due to moderate operation conditions, high conversion in minimal time, high catalytic activity, wide availability, and economy. To overcome the limitation posed by a base catalyst, acid catalysts preferably such as sulfuric acid, hydrochloric acid, Brønsted acid, and sulfonic acid can be used in the transesterification process. The acidified alcohol act as a solvent and esterification agents when directly mixed with oil to perform separation and transesterification process in a single step. The reaction rate can be stepped up by using greater amounts of acidified alcohol and at higher temperatures. However, the use of acid catalysts results in equipment corrosion, more waste from neutralization, the formation of secondary products, higher reaction temperature, and long reaction times due to weak catalytic activity. On comparison of C1–C4 linear alcohols with waste frying oil for the acid catalytic (0.1% H2SO4), the reaction rates varied were BuOH > n-PrOH > EtOH > -MeOH, whereas the reverse was true for the base catalytic process [79]. In contrast, a different-phase catalyst, i.e., solid, immiscible liquid, or gaseous in a heterogeneous catalytic transesterification, provides ease in separation and reuse of catalyst. Therefore, reducing the energy consumption, costly separation, difficult recovery of products/by-products with no aid to saponification ensures a high yield of biodiesel and glycerin recovery. The process can accommodate an extreme operating range of temperature (70–200°C) and subsequent development of a continuous biodiesel yield system (fixed bed reactor) in retrospect to batch operation inhomogeneous system. The heterogeneous are also classified based on neutrality. In heterogeneous catalytic transesterification, the acid and base are coated on a solid surface over a large surface area. The most common solid-base catalysts are basic zeolites, alkaline earth metal oxides, and hydrotalcite. The metal oxides (CaO and MgO) are inexpensive, readily available, and highly reactive. However, the leaching of CaO into the reaction mixture happens and limits the process. Similarly, heterogeneous solid acid catalysts, such as Nafion-NR50, sulfated z­irconia, and 75

Biomass, Biofuels, Biochemicals

tungstate zirconia, due to their acidic nature are being used for transesterification. On the contrary, the heterogeneous acid catalysis reduces equipment corrosion in comparison with homogenous acid catalysis. The Nafion has demonstrated greater selectivity toward the production of methyl ester and glycerol. Nevertheless, it is expensive and shows slow reactivity relative to liquid acids. Another way to conduct transesterification is the use of biocatalyst (a naturally occurring lipase) that has more number of advantages than chemical catalysts because it involves the synthesis of ester bonds rather than hydrolysis. The biocatalytic transesterification operates under moderate conditions (temperature, 35–45°C) and promotes catalyst recycle and easy product recovery with no by-product generation. Further, the enzymatic reactions are insensitive to free fatty acid and water content. Nonetheless, its application at large scale together with the enzyme’s high cost and inhibition accompanied by sluggish reaction rate requires due research to be conducted. The enzymatic biocatalyst is extracellular and intracellular lipases in nature. The production of glycerol inhibits enzyme functioning, which can be prevented by the addition of an acyl acceptor. The acyl acceptor binds glycerol to triglycerides, thereby preventing active sites of biocatalyst with expedited reaction rates. The formation/presence of triacylglycerol compounds does not degrade the quality of biodiesel as fuel [80]. The biocatalysts are tipped to outperform chemical catalysts and are becoming pivotal for biodiesel production. The catalytic transesterification involves a cumbersome process of recovery and separation of products/catalysts accompanied by a high cost of catalysts employed. These complexities in processes can be avoided by carrying out the process in a non-catalytic environment. These include the supercritical alcohol process and the co-solvent transesterification process. The supercritical alcohol method carries out transesterification reaction at high pressure and temperature (250–400°C) in moderate time duration (10–30 min) because of improved phase solubility and reaction rates. The transesterification of triglycerides by supercritical methanol, ethanol, propanol, and butanol has proved to be the most promising process [81]. Unlike the homogenous base catalyst method, it is not affected by the presence of water and free fatty acids, therefore allowing a wide variety of feedstock to be implemented [82]. The use of a lower value feedstock can significantly reduce the cost of biodiesel production. Conversely, the presence of water boosts the formation of methyl esters and esterification of free fatty acids, simultaneously. However, the process demands high energy consumption and a higher stoichiometric ratio of alcohol to oil to execute the reactions. On the contrary, co-solvent transesterification works on the principle of improving the solubility of methanol in oil. This promotes faster reaction rates (5–10 min) with no residues in products/by-products at ambient operating conditions and uses co-solvents such as tetrahydrofuran, BIOX. On completion of the reaction, clear separated biodiesel-glycerol phases are obtained in addition to excess alcohol and co-solvents. These excess quantities should be completely removed and final products should be water-free.

76

Biomass, Biofuels, Biochemicals

3.2  Biochemical Technologies Biological conversion of biomass engages biocatalyst to transform organic matter into valuable products. The end products generated depend heavily on the type of microorganisms employed that are broadly classified based on the consumption of oxygen, i.e., aerobic and anaerobic. The end products of aerobic processes comprise CO2 and water while several products are obtained when organics are subjected to anaerobic conditions. This is possible due to the variety of microbes that follows different degradation pathways and produce different products. The anaerobic disintegration is of two types, fermentation and anaerobic digestion.

3.2.1 Fermentation Fermentation is defined as a metabolic process that converts organic compounds to organic products with the help of enzymes produced by bacteria, yeast, and fungi. The fermentation process is differentiated from anaerobic digestion on the grounds of electron acceptor. The fermentation process is carried out with an organic compound being a terminal electron acceptor rather than elemental oxygen. There are three types of fermentation: (1) lactic acid fermentation, (2) ethanol/alcohol fermentation, and (3) acetic acid fermentation. The production of ethanol from energy crops (corn, sugarcane, etc.) has led to an increase in food prices and food vs fuel controversy, given that ethanol fermentation from biomass (such as wheat straw, rice straw, and forest residues) was explored due to their availability, affordability, and relatively high sugar content. The biomass mainly comprises cellulose (30%–50%), hemicellulose (20%–35%), and lignin. The cellulose predominantly comprises of a long chain of sugar molecules, while hemicellulose consists of xylose (five carbons). The remaining portion, lignin, is an insoluble polymer that is majorly present in forest and agricultural waste. The cellulose and hemicellulose together form a formidable 65%–75% of ­composition that can be easily fermented to bioethanol [83]. The pretreatment first demands comminution of the material to facilitate subsequent handling and then subject it to various approaches such as irradiation, steaming, hydrothermolysis, and biological and chemical treatment, viz. acid, alkaline, solvent, ammonia, sulfur dioxide, carbon dioxide, or combination of pretreatments in multiple steps, depending on the biomass composition [84, 85]. Generally, acidor ­enzymatic-based approaches are being used to hydrolyze hemicellulose and cellulose to obtain sugars that can be converted to ethanol. The use of acid for pretreatment is either as dilute acid at high temperature or as concentrated acid at a moderate temperature with additional removal of concentrated acid present in the system. The temperature in the pretreatment varies between 100°C and 290°C [84]. However, the yield obtained from the former is lower as compared to the latter. The ethanol yield from Festuca arundinacea Schreb by dilute acid, hot water, dilute alkali, and steam explosion pretreatment techniques was obtained as 256.6, 255.3, 255.8, and 230.2 L/dry metric ton biomass, respectively

77

Biomass, Biofuels, Biochemicals

[84]. To render pretreatment less expensive, lignin-solubilizing microorganisms are generally employed [86]. This category of pretreatment reduces the cost of chemicals and energy consumption as well as being environmentally friendly in terms of by-product disposal. But it is relatively slow due to several factors affecting the enzymatic fermentability of lignocellulosic materials such as cellulose crystallinity, the accessible surface area of cellulose, and cellulose protection by lignin. Additionally, lignin-solubilizing microbes also consume cellulose and hemicellulose and therefore face a major techno-economic hurdle for a largescale application. During enzymatic saccharification, the microbes (yeast, bacteria, and fungi) produce enzymes known as cellulase to aid the degradation of cellulose into glucose that can be fermented into ethanol. Regulatory parameters for the production of cellulase encompass carbon/nitrogen (C/N) ratio, presence of trace elements, and pH. An optimum C/N ratio of 7 [87] has been identified most suitable, which can be obtained by the addition of corn steep liquor, urea, ammonium hydroxide, and ammonium sulfate. The addition of ammonium hydroxide not only assists in maintaining the required nitrogen but also helps in regulating the pH of the culture medium. Likewise, the presence of metal cations such as Ca+  2, Mg+  2, Fe+  2, and Co+  2 is necessary for enzyme production [88]. However, a high C/N ratio inhibits fungal growth and enzyme synthesis. The cellulase yield also depends on the ease of consumption of carbon source by the microbes and the chemical composition of the feedstock. The various operating conditions also play a decisive role in the production of higher ethanol concentration, including (1) high tolerance to ethanol concentration, (2) inhibitory hydrolyzed compounds, (3) disruption of anaerobic conditions, and (4) low pH development due to sugar hydrolysis. Also, the lignocellulose-derived microbial inhibitory compounds (LDMICs) inhibit fermentative microbial growth by incurring damage to nucleic acids and the disruption of intracellular redox balance [89]. Therefore, further research aiming toward minimizing these limitations is essential to efficiently obtain lignocellulose-derived sugars for ethanol production. [90–92]. The fermentation involves a complex set of processes that converts glucose from lignocellulosic and sugar-rich substrates to pyruvate by Embden-Meyerhof-Parnas and EntnerDoudoroff pathways. The pyruvate is then decarboxylated to acetaldehyde. During acetaldehyde reduction, the NAD+ is regenerated to obtain ethanol. The pathway for fermentation is presented in Fig. 4A. In this regard, development in biochemistry and molecular biology accompanied by known operating conditions and process integration can enable the production of engineered cellulase that can assist in a higher yield of ethanol production even at large-scale industrial/commercial plants. Moreover, this will allow the use of a variety of lower value feedstocks with reduced chemical cost and by-product credits. Hydrogen is another source of green energy that can replace the conventional source of energy, i.e., fossil fuels due to high heating values of 120 to 142 kJ/g [93]. These values are far greater than that of classical hydrocarbon fuels such

78

Biomass, Biofuels, Biochemicals

(A)

Fig. 4  (A) Ethanol and glycerol production pathways. (B) Hydrogen production pathways. Redrawn after M. Zein, R. Winter, Effect of temperature, pressure and lipid acyl chain length on the structure and phase behaviour of phospholipidgramicidin bilayers, Phys. Chem. Chem. Phys. 2 (20) (2000) 4545–4551.

(B)

79

Biomass, Biofuels, Biochemicals

as diesel (45 kJ/g), gasoline (47.5 kJ/g) [94], bioethanol (29.8 kJ/g) [95], and methane (49.9 kJ/g) [96]. Hydrogen can be recovered from various methods such as electrolysis, thermal decomposition, microbial electrolysis cell, reformation of natural gas, high-density fuels, etc., but are expensive. However, an economical way to obtain hydrogen is with the help of fermentation, which is considered to be a sustainable solution as it can produce hydrogen through biomass conversion. Fermentation is one of the most extensively studied biological processes that produce hydrogen. Hydrogen acts as an important substrate to carry out the metabolism of anaerobic microorganisms to generate energy, but in the absence of an external electron acceptor, the excess electrons reduce the protons to obtain hydrogen molecules catalyzed by enzymes as shown in Eq. 6. 2H   2e   H2

(6)

The hydrogen yields through fermentation depend upon the type of substrate and operating conditions including the type of reactor, hydraulic retention time, organic loading rate, pH, inoculum, and pretreatment provided to the substrates. It is desired that the type of substrate being used is inexpensive and easily available. The complex organics are disintegrated into simpler forms, viz. organic acids and alcohols, which results in the release of hydrogen [97]. To expedite the hydrogen yield, the substrate must be accompanied by nutrient sources, i.e., macro (N, P, and S)- and micro (K, Mg, Ca, Fe, Mn, Co, Cu, Mo, and Zn)-nutrients. The nutrition requirement of the fermentation process can be determined by studying the chemical composition of the cells that generate hydrogen gas. All the nutritional components must be present in a balance to obtain optimum hydrogen yield, as the slightest of changes may affect the hydrodynamic pattern and hindering the liquid-gas transfer mass of hydrogen, i.e., the concentration and rate of the by-product generated. The production of hydrogen follows glucose to pyruvate, i.e., glycolysis pathway. Further, acetyl CoA obtained from pyruvate in the reaction catalyzed by pyruvate ferredoxin oxidoreductase (PFOR) and the intermediate products formed in these reactions, i.e., reduced ferredoxin, involved in the reduction of [FeFe]‑hydrogenases that eventually reduce protons yielding hydrogen. Additionally, formate catalyzed by pyruvate formate lyase from pyruvate can easily be converted to hydrogen and carbon dioxide in the presence of [NiFe]‑hydrogenases of [FeFe]‑hydrogenases [98]. The pathways for obtaining hydrogen are represented in Fig. 4B. The yield of various by-products obtained under various processes is shown in Table  2. Moreover, acetyl CoA is formed from pyruvate from PFOR and PFL, and on further fermentation, it is converted into other valuable products other than hydrogen such as ethanol, acetate, and butanol. The final mix will then contain various precious components that show a decrease in hydrogen yields as shown in Eqs. (7)–(9) [110]. The particular type of substrate and enzymes used for the

80

Table 2 Yield of different by-products of conversion of biomass through various technologies. Sl. No 1

Byproduct Bio-oil

Yield (% wt)

Substrate

Hydrothermal liquefaction

Marine microalgae biomass

43.2a

32.9 ± 2.3f

[99]

Loktak lake biomass

13.34

–

[100]

Natural hay

–

13.2

[101]

Oak wood

–

21.4

Walnut shell

–

14.7

Cellulose

–

Residual microalgae biomass ~ 45 Pyrolysis

2

3

4

Biodiesel

Hydrogen

Bioethanol

Transester­ ification

Fermentation

Fermentation

Values obtained on dry basis. Glycerol. g/kg. d mL/gVS. e mol H2/mol glucose. f High heating value kJ/g. b c

References

17 a

38.8f

Empty fruit branches

55

13–18

[56]

Birch

50–55

16.5

[44]

Pine

17.2

Poplar

17.4

Safflower seed

54

40.9f

[40]

Raw food waste

60.3

7.55

[43

Digested food waste

52.2

7.78

Loktak lake biomass

38.8

–

[100]

Pongamia pinnata

94.9

–

[102]

Vegetable oils and fats

95

–

[103]

Soybean oil

80

–

[104]

Used frying oil and 1-propanol (acid catalyst)

92.2 (4.2b)

–

[79]

Used frying oil and methanol (base catalyst)

91.9 (13.5b)

–

Kitchen waste

–

72d

[105]

Raw cassava starch

–

1.44e

[106]

Organic municipal solid waste

–

71d

[107]

Food waste

358a,c

–

[108]

Wheat straw hydrolysates

44

–

[83]

Corn stover hydrolysates

50

Kitchen waste a

Energy (kJ/g)

Process

30.9

– c

–

[109]

Biomass, Biofuels, Biochemicals

­ roduction of hydrogen is only justified if 60–80% is recovered from the theop retical energy stored in the substrate. C6H12O6  6H2O  6CO2  12H2

(7)

C6H12O6  6H2O  2CO2  2CH3COOH  4H2

(8)

C6H12O6  6H2O  2CO2  2CH3CH2CH2COOH  2H2

(9)

3.2.2  Anaerobic Digestion Anaerobic digestion is a process in which organic matter present in the biomass is degraded anaerobically in a digester by the action of several different microbial consortia. The product gas is composed primarily of methane and carbon dioxide with traces of hydrogen sulfide and water vapor. In the conventional one-stage digester, the biomass feedstock for the digestion process is coarsely shredded, humified, and placed into a reactor (temperature 35°C) with an active inoculum of microorganisms for methane production. Almost 60% reduction in the organic biomass can be achieved corresponding to a methane yield of 0.24 m3 per kg of the organic matter. The product gas can be processed to remove CO2 and H2S, and the solid residue can be dewatered and used as compost [111]. The conventional one-stage digesters can be replaced by two-stage digesters, attached film reactors, etc., mainly to improve the process efficiency and increase the solid and microorganism retention while decreasing the reactor volume.

3.2.3  Microbial Fuel Cell Cellulosic biomass is a renewable and readily available source of organic substrate for the conversion to bioelectricity in microbial fuel cells (MFCs). MFCs are biologically facilitated systems that enable the decoupling of oxidation and reduction reactions through the use of an electrochemical cell. The utilization of cellulosic or other insoluble biopolymers as substrates may require pretreatment and dispersal in solution to overcome mass transfer limitations. While using lignocellulosic materials (such as agricultural crop residues) as a substrate, several pretreatment (mechanical, physicochemical, and chemical) techniques can be employed not only to eliminate lignin and hemicellulose but also to decrease the crystallinity of cellulose [112]. Gregoire and Becker [113] demonstrated the feasibility of degrading complex and minimally processed corncob pellets in an MFC that comprises a single reactor integrating the elements of an air-cathode MFC and a leach-bed bioreactor. However, due to higher methane production, relatively low power output was obtained. It was concluded that the improvisation of reactor design can enhance the efficacy of the utilization of solid substrates for MFC [113]. Recently, microalgal biomass has also been explored as an electron donor in MFC [114, 115]. C. regular (0.43 g BOD, 0.025 g TN, and 0.009 g TP in per g biomass)-fed MFC achieved Coulombic efficiency as much as 61.5%

82

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and maximum power density of 1.07 W/m2. These results were compared with an acetate-fed MFC [114]. The abundance and renewability of lignocellulosic materials and algal biomass render them a promising feedstock for cost-effective electricity generation in MFC [116].

4 Challenges Faced To identify and implement sustainable biofuel production alternatives, addressing the obstacles and challenges is crucial. The various environmental impacts related to the first-generation biofuel production are habitat loss of the native species and GHG emission because of the competition with the agricultural and biodiversity lands. The cultivation of biofuel feedstock leads to the replacement of the large areas of biodiversity and indirectly driving deforestation. GHGs, including CO2, CH4, N2O, and CO, and air pollutants, including NH3, VOCs, NOx, and SOx, are emitted due to the replacement of the original system, cultivation, and the processing of feedstocks, transportation, and finally the use of biofuels. The pollution caused can directly impact on the species, ecosystems, and humans by tropospheric ozone formation, acid rain, ozone depletion, and changes in the regional weather pattern. Although the second-generation biofuel overcomes the limitation of food crop competition, it is still a large proportion of arable land to grow the non-food crops, thus not addressing the issue of the land competition. However, unfertile land can still be used to cultivate the feedstock, as they are non-food crops. The lignocellulosic biomass is complex and hence requires a powerful pretreatment technique to hydrolyze the complicated bonds of compounds. Biomass feedstock is vulnerable to microbe-aided decomposition facilitated by the moisture present in it. Also, the biomass which is distributed over a large area would incur the collection and transportation costs. The seasonal variation of feedstock cannot guarantee continuous supply for biofuel production. Although the third-generation biofuel production addresses a lot of issues, the requirement of optimum growth conditions for the growth of microorganisms still provides a limitation. The production and the extraction of biofuel need advanced technologies, which also increases the economic requirement by the processes. The fourth-generation biofuel production is still at its native stage and requires economic support.

5 Conclusions and Perspectives Rapid depletion of fossil fuel and the increase in oil prices have accelerated research regarding sustainable feedstock-derived fuel. The production of the first-generation biofuel mainly from food crops has been commercialized, but due to concerns about food security and change in land use, the sustainability of this process is uncertain. The second-generation biofuel can be used as an alternative as its non-food feedstock can be generated more sustainably. The strategic

83

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utilization of agricultural and forest residue as well as the high-yielding energy crops for the production of biofuels can play an instrumental role in ­proliferating circular bioeconomy. Various thermochemical and biochemical technologies for the conversion of biomass to second-generation biofuels have been explored but their production cost has hindered the investment in this sector. Additionally, the conversion technologies operate on a complex set of degradation/conversion pathways, which is further complicated by the use of different feedstocks having varying compositions. Comparative evaluation of several large-scale projects is necessary to identify the best available technology for biofuel production. Furthermore, the existing sustainability issues of the biomass supply chain should be addressed to ensure all-year-round delivery of feedstock to the conversion facility. A robust business model would attract investors and accelerate the commercialization of biomass-derived biofuel. Also, government policy support which reduces investment risk through renewable fuel incentives should cut down the investment barrier. Currently, biofuels are not cost-competitive with petroleum-based fuels. Thus, to encourage the utilization of biomass as a renewable energy source, the imposition of carbon tax while utilizing fossil fuel for power generation might help in preventing the depletion of fossil fuels. Also, to prevent the environmental pollution caused as a result of the open burning of the agricultural residue, special attention should be paid and strict laws should be imposed. Promotional campaigns about the benefits of renewable energy programs can influence the decision of different agencies about participation and investment in the industry. The government can also exploit media and the Internet to deliver information that will reach a wider audience. The participation of public and private sectors in ensuring continued investment in research and demonstration coupled with the policy support is essential for the commercialization of the biomass-driven biofuel industry.

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Water Recycling: Economic and Environmental Benefits Sushil Kumara, Anita Talana, Kellie Boyleb, Banu Ormecib, Patrick Droguia, and Rajeshwar Dayal Tyagia

a Institut National de la Recherche Scientifique (INRS), Centre-Eau Terre Environnement (ETE), Université du Québec, Québec, QC, Canada bDepartment of Civil and Environmental Engineering, Carleton University, Ottawa, ON, Canada

1 Introduction Water is the necessity to survive with extreme importance in our daily lives; hence, the need to improve and preserve the quality of water is growing constantly across the world. The global population is continuously increasing and due to this increasing population, the people around the world may experience freshwater scarcity that will disturb the daily activities of humans to a great extent. The freshwater resources are present in limited quantity, and hence, water management, treatment, and recycling methods are the only alternatives to meet the demands of freshwater in the coming decades so that future generations can enjoy sustainable life in terms of water. Various point and nonpoint sources are responsible for the contamination of valuable water resources. The industrial, domestic, and agricultural activities are the main water sources of water pollution. In addition, various environmental and global changes such as erosion and deforestation are also responsible for water contamination. The main water pollution sources are from industrial, domestic, and agricultural activities and various other environmental and global changes. Moreover, the contamination due to industries and agricultural activities is the main reason that freshwater resources in many places around the globe are polluted and not suitable for consumption. The global population has reached up to 7.9 billion [1] due to which the entire living population of the world may experience a great shortage of freshwater for drinking [2]. Therefore, there is a great need for the development of appropriate, low-cost, and speedy wastewater treatment technologies to reuse the wastewater in present time to attain global sustainability in terms of freshwater resources. This also

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aims at water conservation methods globally so that the coming generations can meet the necessities of life without compromising their needs. In view of this, various efforts have been taken to compare various wastewater treatment and reusing technologies. The efforts have been also made to introduce an approach for wastewater treatment and recycling methods. The technologies used have varied efficiency based on their performance, sludge production, life period, and operational requirements. Prior to discussing any water treatment technology and reclamation, it is very important to understand the quantitative and qualitative nature of water contaminants. There are many contaminants present in wastewater, but their toxic effects are only observed beyond certain limits and these certain limits are known as permissible limits of that contaminant [3]. The type of contaminants present in wastewater depends upon the nature of the municipal, agricultural, and industrial wastewater releasing activities. Thus, the various types of water contaminants present can be categorized as organic, inorganic, and biological based on their nature. Out of which the most common inorganic water contaminants are heavy metals, which are highly toxic and carcinogenic in nature. Additionally, nitrates, phosphates, fluorides, sulfates, oxalates, and chlorides also have some serious hazardous effects on human beings with other flora and fauna. The other toxic organic pollutants are from pesticides which include herbicides, insecticides, fungicides; phenols, polychlorinated biphenyls, formaldehyde, halogenated aromatic hydrocarbons, detergents, oils, biphenyls, polynuclear hydrocarbons (PAHs), polybrominated biphenyls, greases, etc.; in addition to these, normal hydrocarbons, aldehydes, ketones, proteins, lignocellulosic materials, pharmaceuticals, alcohols, etc., are also found in various types of wastewaters. Different types of biological contaminants such as various microbes thriving in wastewaters may be responsible for different types of diseases and especially for all waterborne diseases such as typhoid. The harmful microbes include fungi, viruses, amoeba, planktons, algae, bacteria, and other types of water worms. These water contaminants remain either in colloidal, solvated, or suspended form in water [4–6]. So based on the knowledge of the contaminants present in wastewater, the different types of wastewater treatment and reusing techniques are used to treat wastewater of different origins. Before using any technique, proper knowledge of the principles, applications, costs, maintenance, and suitability of the technique to be used for wastewater treatment is required. Moreover, a systematic method should be followed for the wastewater treatment and reusing based on understanding, assessment, and selection parameters of the technique to be used. Therefore, water treatment and recycling is an important issue and researchers are looking for low-cost and appropriate technologies. Wastewater treatment technologies are basically used for the three main purposes: wastewater treatment, reusing, and water source reduction. Further, recycled wastewater can be used for different purposes like irrigation, wetland construction, landscaping, and gardening. The recycled wastewater can be also used in industrial activities

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like washing of aggregates, curing of concrete, cooling water in cooling tower, and supplying water for material washing. All these activities associated with the reuse of wastewater contribute to economic growth and environmental protection in different ways. This also helps in building a sustainable circular bioeconomy in the surround and helps to conserve our natural resources. This chapter focuses on the selection of the appropriate technologies for specific types of wastewater treatment methods, reusing that also adds to the global discussions on water scarcity solutions.

2 Water Recycling Processes The water cycle, otherwise known as the hydrologic cycle, is the circulation of water within the environment. With the population increase, the advancement of society, and the subsequent increase in water needs, engineered water transport is needed to supplement the natural water cycle. The natural water cycle, along with the subcycles implemented anthropogenically, will be discussed in the following section with respect to water recycling and decontamination.

2.1  Natural Recycling The most fundamental recycling process is the water cycle. Water is naturally decontaminated while being circulated above, below, and on the Earth’s surface. The natural transitions from liquid to gas and the percolation of liquid water through sediments continually act to purify water. Evaporation, condensation, transpiration, and infiltration are the four main processes that achieve the continuous circulation and decontamination of water in nature. Evaporation is the transition from liquid to gaseous water or water vapor. Evaporation can occur from any surface as long as the liquid water is exposed to the atmosphere, and the atmosphere is not water-saturated. Typically, the surface of the water will become heated by the sun or will be exposed to warmer air temperatures resulting in evaporation. During this process, all contaminants are left behind when the water vaporizes. Condensation is the transition from gaseous to liquid water. Condensation will occur when warm, saturated air comes into contact with cold air or a cold surface, resulting in the release of liquid water due to the decrease in air temperature. Condensation allows purified water to fall back to the surface of the Earth, so effective precipitation harvesting can occur. Transpiration is the movement of liquid water from the roots of plants to the pores of the stems, leaves, flowers, and its subsequent evaporation from those pores. A significant portion of the water that circulates through plant life is eventually released back to the atmosphere. Through this evaporative process, the contaminants are left in the soils and plants, rather than transitioned into the atmosphere. Infiltration is when liquid water transitions from the surface to below the surface of the Earth. Precipitation and surface waters will move through

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open channels and pores in sediments allowing for natural attenuation before the water infiltrates groundwater sources. All of the processes mentioned earlier are essential for the natural water cycle, and they also play an important role in achieving the reuse of reclaimed water such as the de facto or unintentional water reuse when treated wastewater effluents are discharged to surface waters and enter the water cycle, or indirect potable reuse when augmentation of surface or groundwater is achieved by intentionally reintroducing reclaimed water in the water cycle. Through the water cycle, reclaimed water is further purified, conserved, and made available for a wide range of new uses, including the potable use. Other natural water recycling processes include wetlands, riverbanks, and aquifers where soil and plants act as natural filters removing organic carbon, nitrogen, pathogens, and emerging contaminants of concern from water. Biofilm growth on the filtration surfaces can further achieve the biological removal of organic contaminants and nutrients. Wetlands are well documented for their ability to improve water quality, and constructed wetlands can be designed not only to achieve higher removal and storage of organic and inorganic contaminants and polishing of reclaimed water but also to maximize wildlife habitats. Similar to wetlands, soil aquifer systems achieve natural treatment where reclaimed water slowly percolates through the soil achieving physical, chemical, and biological treatments of contaminants before reaching the aquifer.

2.2  Artificial Recycling Due to water overuse, uneven distribution, surface and groundwater contamination, population increases, and climate change, many places in the world are experiencing water scarcity. Artificial water recycling is therefore very important to maintain water availability. Creating hydrologic sub-cycles that work simultaneously with the natural water cycle helps to mitigate water scarcity. Wastewater treatment plants are fundamental to modern society as they allow for sewage and other wastewaters to be decontaminated and released back into the natural water cycle or reused for anthropogenic activities. There are different standards for wastewater treatment around the world, but at the very minimum secondary (biological) treatment is desired for water reuse and recycling as preliminary and primary treatment processes mostly consist of physical separation processes and do not achieve significant organic carbon, nutrient, and pathogen removal. Furthermore, tertiary or advanced treatment may be necessary for some water reuse applications to protect the environment and the health of the public. For water reuse applications, it is important to first identify the end-use of reclaimed water and choose a treatment level to meet the needs and requirements of the selected water reuse. It is neither necessary nor desired to treat wastewater to the highest level, as this would increase the technical complexity of the system, energy demands, and the financial burden unnecessarily. Quality of reclaimed

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water required for irrigation would be much lower than the quality of reclaimed water required for direct potable use, and selecting the right level of treatment would help to achieve economic efficiency and long-term sustainability. In order to identify the right level of treatment or the right water reuse application, it is necessary to have a good understanding of how wastewater treatment works and the types of contaminants that can be removed with each of the treatment processes. Preliminary treatment of wastewater is designed to remove or reduce the size of entrained, suspended, or floating coarse solids (e.g., plastics, rocks, rags), as well as remove grease and scum and heavy inorganic materials (e.g., sand, gravel, glass). The objective of preliminary treatment is to protect the downstream operations and prevent clogging or damage to pumps and other equipment. Typically, preliminary treatment will involve a combination of flow regulators, coarse and fine screens, comminutors, macerators and/or grinders, flow equalization, grit chambers, and pre-aeration. The primary treatment of wastewater is the removal of readily settleable suspended solids and floating solids. The wastewater flow is minimized to allow suspended solids to settle to the bottom of sedimentation basins, and mechanical scrapers remove the settled sludge to be processed in sludge treatment units. Any particulate matter or grease that remains floating on the surface is skimmed off and removed from the sedimentation basin. In some circumstances, the addition of chemicals may be used to enhance the settling and removal of the suspended solids. The secondary treatment of wastewater removes the remaining organic suspended solids, as well as the colloidal and dissolved organics using biological processes. There are many different types of biological processes (i.e., aerobic versus anaerobic, attached versus suspended growth); however, they all employ the same methodology: large quantities of microorganisms are used in a controlled process to consume the remaining soluble and organic matter. Following the secondary treatment, if there is no tertiary treatment, the wastewater will be disinfected using by either chemical disinfectants (i.e., chlorine and ozone) or ultraviolet light. After the secondary treatment, there are still many constituents remaining in the wastewater, most importantly nutrients but also pathogens, heavy metals, nonbiodegradable organic matter, and emerging contaminants. If wastewater facilities are required to meet stricter discharge regulations or water reuse objectives, then the tertiary treatment may need to be used. Some of the commonly used tertiary treatment processes include biological or chemical removal of phosphorus, nitrification and denitrification for nitrogen removal, precipitation of heavy metals, ultra- and nanofiltration, and other membrane-based processes. Phosphorus and nitrogen removal is the most common application of advanced treatment to prevent eutrophication of surface waters after the discharge of wastewater effluents. Disinfection is still needed before the effluent is discharged.

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Some of the more advanced tertiary treatment processes include advanced oxidation to remove emerging contaminants, humic compounds, and taste and odor compounds; reverse osmosis to remove dissolved contaminants, salts, and natural organic matter (NOM); membrane filtration to remove turbidity, viruses, bacteria, and protozoa; and ion exchange to remove hardness, nitrate, NOM, and bromide compounds. Advanced treatment generates a high-quality effluent that is typically safe for the environment and agricultural, recreational, and industrial uses. Among the treatment processes summarized earlier, filtration, disinfection, and advanced oxidation are the most important processes for water reuse. Filtration can remove suspended solids, pathogens, and some of the dissolved constituents depending on the filter type and the pore size of the media. The ability of filtration to remove pathogens without the use of chemical disinfectants that may form disinfection by-products is advantageous in reuse applications. Larger microorganisms (i.e., protozoa) are easier to remove compared to smaller microorganisms (i.e., viruses), but microorganisms tend to aggregate and associate with particles in wastewater, and through physical adsorption and entrapment even viruses can be removed to some extent with filtration processes. Another benefit of the filtration processes is that they improve the clarity of wastewater effluents and the efficiency of physical (UV) and chemical disinfection processes that follow up. Depth filtration, surface filtration, membrane filtration, and biofiltration are widely used, and they offer a variety of capabilities and configurations. Depth filtration is the earliest filtration technology and typically uses a bed of several feet of mono-, dual-, or mixed-media consisting of sand, anthracite, garnet, or synthetic compressible media with backwashing. Surface filtration employs up to several millimeters thick stainless-steel screens or polyester fabric, and they are gravity-fed and backwashed. Membrane filtration uses the membranes of different pore sizes (0.05 μm for microfiltration, 0.002–0.005 μm for ultrafiltration, and  K+ > Ca2 + > Mg2 + and carbonate > chloride > sulfate > phosphate, respectively. Zeolites have also a great potential in the simultaneous recovery of N and P from wastewater [35]. Huggins et al. [36] showed that the granular wood-derived biochar had a great ability for the adsorption of PO43 − and NH4+ at high concentrations. Other adsorbents such as carbon nanotubes [37], Romanian volcanic tuff [38], and wheat straw [39] were also used for ammonium recovery. Flotation is a method of recovering solid particles or dispersed liquids from wastewater by inserting small gas bubbles. In this method, particles with lower

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density than the liquid phase can be easily separated. The surface properties of materials are the most important factors for the flotation process, even more significant than their size or density [32]. Flotation is usually used along with other recovery processes like coagulation to separate solid products from these recovery processes. Brosseau et al. [40] studied the potential of an innovative enhanced flotation separation process combined with natural-based green chemicals. They found that by using the green and unbiodegradable chemicals in this process, the recovery of total suspended solids can reach 58%–85% and 90%–97%, respectively. Sanchez et al. [41] studied the recovery of biodegradable particulate matter from a high-rate moving bed biofilm reactor by high-rate dissolved air flotation. They found that the solid capture efficiency of this system could enhance up to 96%. Moreover, they suggested this configuration as a high-rate wastewater recovery process that can be an alternative for carbon and energy recovery.

3.2  Stripping Processes Stripping is a physical process based on mass transfer, in which a vapor stream removes one or more components from a liquid stream. It is commonly used to remove harmful contaminates or recover nutrients. In resource recovery, the stripping process is mostly used for the recovery of nitrogen-based compounds. Common processes to recover these compounds from wastewater and other wastes often require the conversion of dissolved ionized ammonia as NH4+ to ammonia gas NH3. Accordingly, most ammonia recovery methods, including electrochemical and biological technologies, use stripping and absorption into an acid as a final step in the recovery [42]. The stripping process can be performed using air or steam, as explained in this section.

3.2.1  Air Stripping Process The basis of the air stripping process is to remove the dissolved gas in the liquid phase by contacting the liquid with air. The gas separation from liquid takes place based on diffusion to air. The mass transfer driving force for this separation is the difference between partial pressures of the dissolved gas in the liquid and air. For ammonia stripping, it must be in the gas phase to be separated from the liquid. Therefore, one approach to increase the efficiency of this process is using a packed tower to increase the contact between the liquid phase and air. Temperature, pH, and airflow rate are the factors that have the most impact on the air stripping process [34, 43, 44], while the effect of pH is usually dominant among these parameters [34]. The conversion of ammonium to ammonia takes place based on Eq. (1): NH4  OH  NH3  H2O

(1)

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Accordingly, by shifting pH to higher values, the equilibrium shifts toward the right side and leads to a higher recovery of ammonia. Lime or caustic soda can be used for the adjustment of wastewater pH and accomplish a high separation efficiency [45, 46]. Consequently, the main challenge in the stripping process is the need to add chemicals to increase pH prior to the stripping and acids to decrease pH after the separation [47]. The alkali and acid consumption for pH adjustment and neutralization of waste streams (to avoid undesirable environmental impacts) not only increases the cost of process but also can raise the salinity of the water. Wu and Modin [48] demonstrated that ammonia removal by air stripping can have a high efficiency of about 94%. Lei et  al. [49] optimized the ammonia air stripping process for pretreating anaerobic digestion. They reported that ­adding an optimal amount of calcium hydroxide and aerating for 12 h, NH4+-N and PO43 −-P were effectively recovered from wastewater. It is shown that a high initial pH of 11.5 is required for ammonia recovery from fresh pig slurry; however, the digestion permits an almost complete ammonia removal even without pH adjustment [50]. Gustin and Logar [45] studied continuous air stripping of anaerobic digestion effluent and showed that pH increase has the greatest effect on the ammonia removal; however, it occurs only until pH 10. They also showed that higher temperature and airflow rate can improve the nitrogen removal. As a simple technology, air stripping is widely used in the industry because of being cost-effective, simplicity of establishment and operation, and a high rate of recovery [34]. However, this process has some issues such as (i) scaling and fouling, (ii) precipitation of calcium sulfate or calcium carbonate, (iii) need for periodical maintenance, (iv) being nonappropriate at low ambient temperature, (v) need for pH adjustment, (vi) high energy consumption, and (vii) bigger footprint than membrane processes [51]. Table  1 summarizes the advantages and disadvantages of the air stripping process.

3.2.2  Steam Stripping Process The steam stripping process is very similar to the air stripping process with the main difference of working at high temperatures above 95°C. On the contrary, this process does not require any chemical to adjust the pH, which results in lower operational costs and environmental impacts. Toth and Mizsey [52] compared the economic aspects and environmental impacts of air stripping and steam stripping to remove halogenated compounds from wastewater of a real industrial plant. It was found that steam stripping was easier to operate than air stripping. Although it was expensive to supply steam than air, steam stripping was cheaper than air stripping because of the additional costs of air stripping. Moreover, due to the reusability of steam stripper top products, they found that steam stripping is more sustainable than air stripping and more environmentally friendly.

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Table 1 Advantages and Disadvantages of Different Processes for Resource Recovery. Air stripping Advantages

• Cost-effective • Easy to operate • High recovery efficiency

Disadvantages

• Needs to add chemicals and acids to control pH • Tendency to scaling and fouling • Needs for periodic maintenance • Being nonappropriate at low ambient temperature • High energy consumption • Bigger footprint than membrane processes

Steam stripping Advantages

• Lower operating cost in comparison with air stripping • No off-gas treatment is required

Disadvantages

• Requires high N-loaded concentration stream

Membrane contactor Advantages

• Low energy demand • Selective to ammonia removal • Proven technology and easy to operate • Very compact technology • No air pollution • Suitable for ammoniacal nitrogen removal to very low level

Disadvantages

• Needs periodic membrane replacement (fouling) • Requires skilled workers and control system • Being sensitive to fouling, concentration polarization, and chemical interaction with water constituents • No approval of the long-term reliability • Low mechanical robustness of membrane

RO Advantages

• No chemical is added to water • Ability to produce highly pure water

Disadvantages

• Very low rate of permeate flux • Low efficiency at high concentrations • Necessity of careful monitoring • Demands for pretreatment

FO Advantages

• Usable with minimum external input energy • Needs for lower chemicals for phosphorus recovery • Ability in simultaneous wastewater treatment and nutrient recovery • Applicable to complex and high fouling solution and being able to keep a wide range of contaminants • Possibility of combining with other treatment or recovery processes for higher efficiency • Low fouling propensity and high fouling reversibility in comparison with RO

Disadvantages

• Low water flux • Contaminant accumulation in draw solution in hybrid systems • Membrane fouling

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In this process, the ammonia is stripped from the liquid phase by steam, and then, the ammonia-rich steam enters the condenser to obtain a concentrated aqueous solution of ammonia. Mackowiak and Górak [53] developed an ammonia recovery steam stripping process that was capable of producing 25% of ammonia solution. Xiong et al. [54] studied nitrogen removal from mature landfill leachate that contains a large amount of nutrients, especially NH3-N. Their results showed that the removal efficiency of NH3-N could reach up to around 90%. Minhalma and De Pinho [55] coupled nanofiltration with steam stripping to treat ammoniacal wastewater. They optimized the operating parameters of this process to maximize the amounts of ammonia, cyanide, and phenol recovery. Ammonia steam stripping has several advantages such as having a lower operating cost in comparison with air stripping. The current research on this technology is focused on industrial case studies. Additionally, this method does not need off-gas treatment, since the produced vapors are condensed into a concentrated liquid stream. On the contrary, a difficulty of the steam stripping process is its requirement to a high N-loaded concentration stream (> 2 g NH4-N L− 1) to be economically competitive. This method may not be cost-effective for urban wastewater because of low ammonia content. Table  1 summarizes the advantages and disadvantages of the steam stripping process.

3.3  Membrane Processes 3.3.1  Membrane Contactor Membrane contactor technology usually uses permeable hydrophobic membranes, which are mainly hollow fibers, to separate gases like ammonia [56]. The most important factor in the membrane recovery processes is the mass transfer due to vapor pressure or the concentration difference between the membrane sides [57]. Previous works showed that up to 95% of free ammonia can be recovered using this technology [58]. The use of membrane contactors for ammonia recovery from wastewater is expected to increase in the near future because this process is simple and environmentally friendly, requires low input energy, and can produce a saleable fertilizer like ammonium sulfate [59]. The ammonia recovery from wastewater by membrane contactor technology requires the conversion of ammonium to ammonia, as presented in Eq. (1). This conversion is accomplished by increasing pH to a suitable high level [60]. In a membrane contactor ammonia recovery process from wastewater, ammonia is first transferred from the liquid bulk to membrane pore. After ammonia equilibrium with the air inside the membrane pores, it diffuses into air-filled pores. The ammonia then reacts with receiving component that is usually acid (i.e., sulfuric acid) and converts to ammonium salt. Finally, the ammonium salt is transferred from the membrane to the bulk strip solution. A summary of these steps is schematically illustrated in Fig. 2 [57].

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Fig. 2  A schematic of the fundamentals of membrane contactor process.

Ammonia recovery using membrane contactor technology has several advantages including (i) low energy demand and very compact technology; (ii) being selective to ammonia removal; (iii) proven technology and easy to operate; (vi) no air pollution; (v) sustainable to ammoniacal nitrogen removal to a very low level; and (vi) very compact technology. On the contrary, this technology has disadvantages such as the need for skilled worker and control systems and no approval of long-term reliability. Moreover, the membrane is sensitive to fouling, concentration polarization, and chemical interaction with water constituents, which imposes excessive pretreatment of wastewater. In addition, the membrane does not have enough mechanical robustness to avoid damages and needs periodic replacement. Table 1 shows the summary of the advantages and disadvantages of membrane contactor technology.

3.3.2  Reverse Osmosis Process In reverse osmosis (RO) process, two solutions with different concentrations are separated by a semipermeable membrane and a high operating pressure (2000– 10,000 kPa) is required to be applied to the concentrated solution to reverse the normal osmosis phenomenon [32]. This pressure provides the required chemical potential to pass water through the RO membranes and keep other solutes like ions. Typically, RO is used to produce pure water as an essential resource for different industries such as electronics, pharmaceutical, and medicine that need ultrapure water. However, this process can also be applied to the recovery of nutrients. RO membranes are capable to separate the contaminants and nutrients if they are not in the gaseous phase [32]. Most of the works on the recovery of resources using RO focused on nitrogen recovery. In this process, the recovery of nitrogen is affected by the pH of wastewater due to its effect on the conversion of ammonium to ammonia [61]. The previous works showed that RO is an effective process for ammonium recovery from wastewater. Kurama et al. [62] successfully recovered 96.9% of NH4 in the influent water. RO is also capable to recover phosphate and fluoride from wastewater [63]. The RO process can also be used along with other recovery technologies to enhance the efficiency of recovery. RO was incorporated in a hybrid osmotic membrane bioreactor to simultaneously recover phosphate and produce high-quality clean water from raw sewage [64]. Mondor et al. [65] coupled RO with electrodialysis for ammonia recovery from swine manure and found that this combination can be a proper way to not only recover ammonia but also

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trap the volatilized ammonia. Using an integrated process that includes ultrafiltration, RO, and cold ammonia stripping, 71% of the nitrogen in an animal slurry was converted to (NH4)2SO4 [66]. RO process is a promising approach for the recovery of resources as can simultaneously recover nutrients and water. As through this process no chemical is added to water, not only no auxiliary treatment is required to remove the excess chemical after the recovery process but also the quality of the output water will not be affected. On the contrary, RO suffers from some limitations such as (i) very low rate of permeate flux because of very high pressure losses, (ii) low operation efficiently at high concentration, (iii) demands for careful monitoring to prevent from supersaturation, (iv) fouling and scaling, and (v) necessity of pretreatment for high performance of the process. The advantages and disadvantages of the RO process are presented in Table 1.

3.3.3  Forward Osmosis Process Forward osmosis (FO) is a physical process that is based on the osmotic pressure difference between two solutions. In this process, water transfers across a semipermeable membrane from feed solution, with higher water chemical potential, to the concentrated draw solution, with lower water chemical potential. This osmotic pressure difference is the basis of mass transfer through the membrane [67, 68]. The draw solution in the FO process is usually composed of pure water and draw solute. The draw solute is selected based on its ability in the production of high osmotic pressure and restricts the solute to return to the feed solution and the low tendency to membrane fouling and scaling [69]. FO is usually used to concentrate nutrients in the solution, and then, the process is followed with other methods to recover the nutrients from the concentrated solution [67]. The FO process facilitates energy and nutrient recovery by simultaneously producing high-quality effluent and preconcentrated wastewater for anaerobic treatment [67]. The FO technology permits the separation of nitrogen, phosphorus, organic matter, and trace organic contaminants. In FO process, phosphorus can be almost completely recovered because of two reasons: (i) the electrostatic repulsion between the phosphate ions and the negatively charged membrane surface and (ii) the prevention of phosphate transport through the membrane. Another phenomenon that can prevent phosphorus from passing through the membrane is its size when phosphate has a large hydrated radius and cannot pass through the membrane [70]. Nitrogen recovery by FO is variable and depends on the nitrogen-containing compounds in the solution and the biological treatment process [71]. FO membranes reject neutral ammonia incompletely in comparison with ammonium ions [72, 73]. It is essential to develop new membranes and select the appropriate draw solution as key operational parameters to improve the efficiency of FO [74]. Holloway et al. [75] provided information to compare osmotic membrane bioreactor with

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other technologies and suggested an appropriate configuration. Xie et al. [76] reviewed the challenges and advantages of using three conventional membrane processes used in nutrient recovery from wastewater, i.e., FO, membrane distillation, and electrodialysis [67]. The integration of FO with other processes not only reconcentrates the diluted draw solution but also completes the process of nutrient recovery from wastewater by producing freshwater [76]. Due to the high fouling reversibility in FO, this process can be used for complex solutions without pretreatment. The integration of FO with anaerobic treatment is important for the recovery of energy and nutrient from wastewater [69]. This combination has been extensively discussed in the literature due to the high separation efficiency and high resistance against fouling. Achilli et al. [77] introduced coupled FO and membrane bioreactor as an alternative to membrane bioreactor processes because of its low fouling. Xie et al. [78] introduced a suitable hybrid FO and membrane distillation system for phosphorus recovery in the form of struvite (MgNH4PO4 ∙ 6H2O). Jafarinejad et al. [68] utilized a surface-modified nanofiltration membrane in FO process in order to enhance ammonium recovery. The separation efficiency of ammonium in the pilot scale was much lower than that of phosphorus and organic matter. It can be attributed to the low molecular weight of ammonium ions, like water molecules, that are allowed to diffuse through the membrane. Modification of membrane properties can help in solving this issue. One of the major advantages of FO is its capability in operation with minimum external input energy. Moreover, it benefits from other advantages including (i) need for lower chemicals for phosphorus recovery, (ii) ability in the simultaneous treatment of wastewater and recover nutrients, (iii) being applicable to complex and high fouling solution and being able to keep a wide range of contaminants, (vi) possibility of its combination with other recovery or treatment processes to recover efficiently, and (v) its low fouling propensity and high fouling reversibility in comparison with RO. Despite these advantages, FO has some disadvantages such as (i) low water flux, (ii) contaminant accumulation in draw solution in hybrid systems, and (iii) membrane fouling. The advantages and disadvantages of the FO process are presented in Table 1.

3.4  Electrochemical Processes Nutrient recovery by electrochemical methods can be divided into two general categories: (i) processes with sacrificial electrodes and (ii) processes using dimensionally stable anodes (DSAs). Generally, in processes using sacrificial anodes, the use of ions like Mg2 +, Al3 +, Fe2 +, or Fe3 + helps in chemical precipitation [34, 79– 82]. Processes using DSA anodes precipitate phosphate ions by changing the ­water matrix [34]. Among the sacrificial anodes, magnesium anode is known as a cost-effective alternative to chemically induced struvite (NH4MgPO4 ∙ 6H2O) precipitation [81]. Continuous electrochemical dosing of Mg2 + not only improves

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struvite recovery compared to one-time addition of chemicals but also would reduce or eliminate the cost of adding chemicals such as caustic. It is worth emphasizing that this process only works with streams that have an excess amount of ammonia for struvite precipitation [34]. Kappel et al. [83] showed that DSA could be used to change the pH of a water matrix instead of adding chemicals. With this method, phosphate can precipitate with the countercations in the solution. In addition, they showed that phosphate recovery is strongly dependent on the final pH and if the pH is greater than 9, more than 90% of the phosphate can be recovered. The recovered precipitates contain amorphous calcium phosphate and amorphous calcium carbonate. Therefore, this process does not require the addition of chemicals, which reduces the cost and complexity of the process. Wang et  al. [84] investigated the effect of adding plant ash to adjust pH for increasing phosphate recovery from livestock wastewater as an alternative to aeration and sodium hydroxide addition. In optimum experimental conditions, including an appropriate amount of plant ash, the adjustment of reaction time and initial dose of magnesium, the phosphate recovery efficiency reached around 97%. Kruk et al. [82] used electrolytic magnesium dissolution as an effective method for high-purity struvite precipitation. Moreover, this method was shown to be effective in removing phosphorus from fermented waste activated sludge supernatant. In addition, unlike traditional chemical coagulation or the use of aluminum sacrificial anodes, it can remove actual phosphorus and directly recover it as struvite. Hug and Udert [81] investigated the removal of phosphorus from stored urine using an electrochemical magnesium dissolution process as a technically and economically feasible process. The results of their research showed that the efficiency of current in electrochemical struvite precipitation was very high (about 100%) and energy consumption was low (1.7 W h g P− 1 at a potential of 0.6 V vs. NHE). Electrochemical methods such as electrodialysis can be used to recover ammonia in which the ammonia is concentrated in the cathode chamber of an electrochemical cell. Then, the recovered ammonia by acids such as H2SO4 can be used to produce ammonium salts [42]. Due to the OH− generation at the cathode during the electrodialysis of water, no PH adjustment is required. The disadvantages of this process include the need for additional electrolyzer to compensate for H2 losses, high cost due to the use of expensive Pt electrodes, and the possibility of deactivation of the Pt catalyst by Cl− [34]. Muster and Jermakka [85] used electrochemical processes combined with ammonium recovery processes, such as electro-oxidation or electrochemically assisted surface transfer mechanisms, to recover and remove ammonium. This novel process made it possible to recover

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ammonia from ammonia-rich streams (560–900 mg/L) only with theoretical energy (29.3 kJ/g-N), comparable to what Kuntke et al. [86] did for the recycle of H2 in an electrochemical system. Desloover et al. [87] investigated the effect of operating parameters such as current density, pH, ionic strength, and nitrogen concentration on the ammonium flux from anode to cathode in an electrochemical cell. In optimum experimental conditions, they were able to achieve a 96% NH4+ charge transfer efficiency and NH4+ flux equal to 120 g N m− 2 d− 1 for ammonium using synthetic wastewater. Using electrochemical cell (EC), Luther et al. [42] carried out the studies on the feasibility and efficiency of recovery and extraction of ammonia from synthetic and diluted human urine. Their results showed that the electrochemical process is suitable for ammonia recovery from complex wastewater with high ammonia concentration and can have high removal capacity (14.5 g N L− 1 d− 1) in comparison with direct stripping (1.6 g N L− 1 d− 1).

3.5  Biological Processes One of the methods of nutrient recovery from wastewater is biological methods that are performed using natural low-cost bacteria. The use of these bacteria is one of the major advantages of this process over other recovery processes [88]. Methods such as membranes can recover ammonia in either pure or high concentrations and are also cost-effective when the initial concentration of ammonia is high. However, when the ammonia concentration is low, these methods are not economically feasible. Biological processes can be more efficiently used for resource recovery in these cases. Phosphorus is one of the nutrients that can be recovered by biological processes, as a solution to excessive phosphorus consumption and the lack of natural phosphorus resources. The high potential of sewage for phosphorus recovery as well as its inappropriate disposal methods, which are usually harmful to the environment, has given special attention to phosphorus recovery from wastewater. However, if phosphorus is recovered from municipal wastewater, it can theoretically meet about 15%–20% of global phosphorus demand. Therefore, due to the irreversibility of phosphorus mineral resources, phosphorus recovery is a priority over wastewater treatment [89, 90]. Biological phosphorus recovery processes or Enhanced biological phosphorus removal (EBPR) is now considered more important than chemical processes (e.g., chemical precipitation) for phosphorus recovery. Microbial processes are flexible and can enrich dilute phosphorus as well as be used as part of an integrated approach to phosphorus recovery along with other recovery processes [90–92]. The ability of the EBPR process to concentrate phosphate in both liquid (e.g., anaerobic digester supernatant) and solid phases (e.g., sewage sludge/ash) has made it useful for phosphorus recovery. EBPR can be used to remove more than 90% of phosphorus in wastewater that contains 20–100 mg/L of phosphorus [89, 93].

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The main challenge for recovering phosphorus from potential sources is to separate it from heavy metals and toxins. However, if the biological process is integrated with other new recovery processes, it can be effective in phosphorus recovery [89]. As an example, Mulkerrins et al. [93] carried out experimental-scale studies on the recovery of nitrogen and phosphorus from food ingredients using biological methods. The results of their experiments showed that 96%, 97%, and 76% of COD (1697 mg/L), NH4-N (61 mg/L), and P (49 mg/L), respectively, can be recovered at the pilot scale using biological methods. Nitrogen in biosolids is usually not recovered, while fertilizers used in the fields can be replaced directly with nitrogen captured in biosolids [94]. In this regard, Winkler et al. [94] developed sludge biodrying plants that would recover 9.3 MW heat and 7.3 kton of a 40% (v/v) ammonium sulfate solution per year. They found that the final product had a high caloric value, hence offering a good replacement for brown coal, and met the European microbial and heavy metal quality standards needed for an application as organic fertilizer.

4 Recovery Products The most significant processes for the recovery of resources from industrial wastewaters were discussed earlier. In this section, different products that can be generated in the recovery of resources are presented. Different products such as fertilizer, biogas, thermal energy, bioproducts, cellulose, and microplastic/nanoplastic can be generated.

4.1 Fertilizers Three main nutrients in fertilizers are nitrogen (N), phosphorus (P), and potassium (K). They can provide a single nutrient, which is called straight fertilizers, or multiple ones. Multi-nutrient fertilizers consist of two or more components. The most common multi-nutrient fertilizer is NPK, a mixture of nitrogen, phosphorus, and potassium, which is called conventionally based on the weight percentage of N, P2O5, and K2O [95]. The recovery can be done in sewage, sludge, and sludge ash phases. The liquid phase has generally the lowest energy demand, greenhouse gas emissions, and recovery rate. The recovery of phosphorus from sludge ash has the highest energy cost and simultaneously the highest recovery rate along with the possibility of decontamination concerning heavy metals [96]. It should be noted that the quality of the fertilizers that are produced by the recovered nutrients must correspond with mineral fertilizers. They must have constant nutrients and steady distribution. Moreover, it should contain low salinity and sodicity, have no pathogen matter and odor, and have pH close to nature. In addition, their physical characteristics should be proper, and finally, they should be produced and used based on regulatory standards [95].

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The production of ammonia from mineral fertilizer is based on the Haber-Bosch process. The limiting factor of sustainable production is natural gas, as a nonrenewable source [97]. However, the utilization of biogas (that can also be produced from industrial wastewater) in this process is a promising approach from a circular bioeconomy point of view. On the contrary, phosphorus resources are scarce and are expected to deplete by the end of the current century. As a result, mineral fertilizer production requires the consumption of fossil fuels and, the price of mineral fertilizers is increasing due to the depletion of nutrients. In this situation, the recovery of phosphorus and nitrogen from industrial wastewater to produce fertilizers could be a promising alternative [5]. Struvite, NH4MgPO4·6H2O, is one of the most famous chemical compounds recovered from wastewater. It is produced from the simultaneous recovery of phosphorus and nitrogen. Struvite is a white-to-yellowish crystal which is known as one of the best biofertilizers because of the following characteristics: containing essential nutrients for plant growth, adding directly to the soil, minimum loss of nutrients low water solubility, low risk of contamination by pathogens, and ease of transportation [5, 95]. Struvite is produced by the crystallization process, during which it precipitates after contacting magnesium and ammonium ions with a solution containing phosphate ions, after alkalization (7  ethanol > ethyl acetate. LCA of SpC-CO2 permits the measurement of its environmental impacts. De Marco et al. [176] studied the LCA of the coffee extraction process from coffee beans using supercritical CO2. The LCA indicated that agricultural, transportation, and caffeine extraction steps have the highest environmental impacts. Different solutions were suggested to reduce the environmental impacts of supercritical CO2 including reducing fertilizer use at agricultural stages, improving electricity sources, and using renewable sources.

8.2  Water as Super-/Subcritical Fluid Water is another widely used substrate in SpC and even SbC forms that have a Tc and Pc of around 374°C and 22 MPa, respectively [177]. The processes that use SpC or SbC water are also referred to as hydrothermal processes. These processes are widely used in different industries, such as extraction, hydrolysis, and gasification processes [178]. Although the critical point of water is significantly higher than that of CO2, hydrothermal processes are practically interesting because of

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the unique specifications of water. At SpC or SbC condition, the water dissociates more readily and therefore the concentration of H+ and OH− increases. This phenomenon gives water a unique ability to simultaneously play the roles of a strong acid and strong base. Therefore, in the case that a reaction is required to take place at strongly acidic or basic conditions, SpC water and SbC water are promising alternatives that can substantially decrease the amount of generated waste [68]. SbC fluids are used for the fractionation of low molecular weight hydrocarbons to separate bioactive ketoses from aldoses [179, 180]. The main challenge of hydrothermal processes in the practice is technical difficulties related to the operation at severe temperature and pressure. The continuous-mode operation can be a solution to reduce this challenge; however, it increases the difficulties related to the training of specialists to work with such instruments [181]. Subcritical water: SbC water (T = 100°C at 1 bar and 374°C at 221 bar) has gained lots of attention during recent years because it can solubilize hydrophobic compounds [97, 182]. Many works investigated its potential in different applications because of its advantages such as being green, environmentally friendly, cost-­ effective, faster than other traditional solvent extraction methods, and producing high-quality extraction products [183]. The properties of organic solvents are closer to those of SbC water than ambient water that comes from a lower dielectric constant of water in SbC state [5]. SbC water is an excellent choice for dissolving organic molecules. Organic molecules are suitably soluble in SbC water thanks to low water polarity. SbC water can play the role of a catalyst in chemical reactions by generating H+ and OH− ions. Other than extraction and chemical reaction, SbC water has also a great potential in the analysis, like chromatographic separation of analytes. Lachos-Perez et al. [184] analyzed operating conditions of the extraction of nonpolar flavonoids (hesperidin and narirutin) from defatted orange peel using SbC water. They reported that the highest investigated temperature (150°C) and flow rate (10 mL/min) are optimum during which approximately 21% of the obtained extract was composed of these flavonoids. Pourali et al. [185] used SbC water to valorize rice bran to rice bran oil. They showed that using SbC water processing, cellulose and protein can be successfully converted into water-soluble di- and monosaccharides as well as essential and nonessential amino acids, respectively. They also found that rice bran liquefaction by SbC water had a residence time as low as 5 min. Ponnusamy et al. [186] studied the LCA of biodiesel production from algal biooils using SbC water. They found that the cultivation of algae is a stage that extensively consumes electricity. They also pointed out that with improved algae planting, energy consumption and greenhouse gas emissions are drastically reduced. This study showed that using SbC water as a solvent for the extraction of bio-oil from algae is energy-efficient and reduces energy consumption by five times compared to the traditional method.

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Supercritical water: SpC water is a promising green solvent as it imposes almost no pollution. It may only cause heat pollution in the case that is discharged directly into the environment. It is nonflammable and has no polluting effect when released to the atmosphere [177]. SpC water is, therefore, a promising alternative solvent for reaction and extraction purposes [187]. Working with SpC water is generally more difficult than SbC water because of extreme operating conditions. Therefore, technical difficulties can reduce by using SbC conditions [188]. Wang et al. [189] successfully used SbC and SpC water, to recover acetic acid from the polarizing film of waste liquid crystal display panels. They showed that this technology has the capability to remove 99.77% of the organic matter and recover 78.23% of acetic acid from the waste. The application of SpC in the synthesis of chemicals was investigated, and it was found that fructose and glucose can be valorized into C-3 (like pyruvaldehyde) and C-2 (like glycolaldehyde) molecules, respectively [190]. Glucose was hydrolyzed to glycolaldehyde with a selectivity of 75% at 400°C and 23 MPa with a residence time of 3 s in SpC water.

8.3  Ethanol as Super-/Subcritical Fluid SpC ethanol is another promising solvent from a circular bioeconomy point of view as it can be produced by the fermentation of renewable resources. Tc and Pc of ethanol are 240.9°C and 6.14 MPa, respectively [191]. Ethanol is commonly used as a co-solvent with SpC/SbC water, but in a few cases, it is applied alone as SpC/SbC solvent in some processes. One advantage of SpC ethanol in comparison with SpC water is its less corrosivity. It is a favorable solvent to deconstruct lignocellulosic biomass because it has a great solubility in ethanol [192]. Sun et  al. [192] investigated the liquefaction of cellulose in SpC ethanol and showed that by optimizing the temperature and adding 2,2,6, 6-­tetramethylpiperidinooxy as a catalyst, the yield of bio-oil enhanced up to 31.87% and reached around 58%. In addition, they reported that using this catalyst can enhance the yield of ketones formation more than two times. Hao et  al. [193] transformed grape seeds to bio-oil under both hydrothermal and SpC ethanol media and reported 49.2% yield of bio-oil can be obtained. Regarding LCA, a few works focused on ethanol and no work was found specifically on SpC ethanol. Vauchel et  al. [194] assessed the LCA of polyphenol extraction process from chicory using ethanol under different operational conditions. They concluded that although ethanol, as a green solvent for extraction process, increases the extraction efficiency of polyphenols compared to aqueous solvents, it has adverse effects on the environment. They also noted that environmental issues are important in optimizing the process and converting it to a sustainable process in addition to economic and production efficiency issues. Sawangkeaw et al. [195] conducted a comprehensive study on LCA of biofuel and biodiesel production process from crude palm oil by SpC alcohols like ethanol and methanol. SpC ethanol produces less waste and generates pure glycerol

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as a by-product. The LCA showed that the use of SpC ethanol for biodiesel production has detrimental environmental effects such as the influences on climate change, solar radiation, and ozone layer. The environmental effects of ethanol are less than methanol, and ethanol has more carcinogenic effects than methanol. In overall, LCA results showed that for biofuel production, SpC ethanol had more environmental impacts than SpC methanol.

9 Bio-based/Renewable Solvents Biomass is the main source of renewable solvent production. Bioethanol is the first generation biosolvent produced by fermentation of sugar or starch. However, the second generation of biosolvents can be produced by using agricultural residues, lawns, and arboriculture products or lignocellulosic materials, which are the renewable raw materials without affecting directly on the food chain. Several solvents can be produced from cellulose and starch, such as 2-methyl tetrahydrofuran (2-MeTHF), γ-valerolactone (GVL), and dihydrolevoglucosenone (cyrene) [3]. Apart from bioethanol, the other alcohols (glycols and other polyols) can also be produced from biomass, like biobutanol, octan-2-ol, propane-1,3-diol (PDO), butane-1,3-diol, glycerol, and solketal. Moreover, bio-based esters, ethers, and related chemicals may be produced from bioresources, such as ethyl acetate, lactic acid and lactates, GVL, and 2-MeTHF. Cyrene is another important bio-based solvent that can be derived from residual cellulosic biomass, which is commercially available [196]. Table 7 presents the recent works on biosolvents and their applications. As the processing of lignocellulosic biomass is more challenging than the sugars or starches, and the economic sustainability of bio-derived solvents depends on competitive prices and commercial-scale capacities; economic concerns should be considered for every (bio)solvent design [3]. Moreover, as the physicochemical property points of view, the biosolvents have good green characteristics, though toxicity investigation revealed that there is not a clear upgrading compared to conventional solvents, which may restrict their classification as green solvents. Therefore, in such a case, studying their genotoxicity in depth is required [100].

9.1  Production of Bio-based Solvents Overall, there are three main techniques to prepare biosolvents: fermentation, chemical conversion of biomass derivatives, and using the waste generated from other processes [196, 203]. Some alcohols can be produced by just fermentation (ethanol, butanol); however, the others (such as octan-2-ol) can be produced by a cracking process (of ricinoleic acid). Although conventional fermentation can be applied for producing biosolvents, some novel techniques are also being explored such as microbial electrosynthesis to enhance efficiency [204]. Furthermore, glycerol is the major by-product of the biodiesel industry that

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Biomass, Biofuels, Biochemicals Table 7 Recent Advances in Bio-Based Solvent Invention and Application. Solvent

Application

Results

References

Soybean- and moringa-based green biosolvents

Capturing lowconcentration carbon dioxide (CO2) from flue gas (via a superhydrophobic PVDF/Si-R hollow fiber membrane)

CO2 absorption efficiency reached up to 0.52 mol m− 2 h− 1 and 97% of efficiency. Comparable CO2 absorption flux to the conventional solvent of monoethanolamine (MEA)

[197]

γ-Valerolactone (GVL) and a set of glycerol derivatives

Membrane preparation

The membranes could be used for MF, UF, and NF.

[198]

Nonpolar renewable solvents; ethyl acetate and n-propanol

lipid extraction from spent coffee grounds

As an alternative for n-hexane. Extraction about 93% and 87% of the available tocopherol

[199]

2-Ethyltetrahydrofuran (2‐MeTHF)

Iron‐catalyzed cross‐ coupling reactions

The coupling occurs with excellent functional group tolerance under mild conditions

[200]

Ethyl acetate, ethyl lactate, cyclopentyl methyl ether (CPME), and (2-MeTHF)

Microalgal lipid extraction

2-MeTHF and ethyl lactate leading two and three times lipid extraction yields, respectively, compared to common solvents like hexane

[201]

(2‐MeTHF), obtained from crop’s by-products

Taking out of fat and oils for food (edible oil) and nonfood (biofuel) applications

For the substitution of petroleum solvents, such as hexane

[202]

could be utilized as a solvent after purification [196]. Some solvents like solketal are also manufactured from glycerol by a catalytic process. Some of them are produced by the reduction in carbohydrates, such as 1,2 pentanediol, cyrene, GVL, and 2-MeTHF [205]. Glycerol itself can also be converted catalytically or electro-catalytically (by oxidation, reduction, and dehydration), to different solvents such as acetol, dihydroxyacetone, glycidol, 1,3-propanediol, allyl alcohol, etc. [206, 207].

9.2  Applications and Opportunities of Biosolvents Bio-based solvents can be utilized instead of fossil-derived chemicals in different ways (as solvents or intermediates). For instance, in a range of C2 solvents, ethylene can be replaced by ethanol and bio-ethylene; for C3 range, glycerol, acetone, and lactic acid are used instead of propylene; in C4 range, butene and butadiene may be replaced by bio-butanol, isobutanol, and succinic acid; for C5 range, there are not any specific solvents from petrochemicals, but bio-based levulinic acid and furfural can be used; for C6 solvents, benzene is used as a

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fossil-derived chemical, but levoglucosenone and 5-(hydroxymethyl)furfural are able to be used as renewable solvents [205]. One of the applications of bio-based organic solvents is in analytical procedures, mainly by focusing on alcohols, esters, and terpenes. The solvent features in analytical chemistry can be fulfilled by polar biosolvents (as extraction solvents or mobile-phase part in liquid chromatography), but it is not easy to obtain nonpolar biosolvents, for instance, in the extractions of lipophilic constituents from a polar mixture [203]. Though bio-based solvents are not commonly harmless and nontoxic, by virtue of being renewable, they diminish worries regarding using petroleum and natural gas resources [208]. Glycerol is a green solvent and can be used as an originator of valuable chemicals, such as glycerol esters, alkyl glycerol alcohols, and ethers, which show much lower viscosity than glycerol. GVL as a biodegradable compound is used as a food additive. Biodegradable substances, like glucose, levulinic acid, 5-­hydroxymethylfurfural, and formic acid are produced by the producing GVL from the cellulose origin source. GVL has some outstanding properties, such as complete solubility in water, high boiling point, and low vapor pressure [93]. Ethyl lactate, a green solvent achieved from corn, has several applications. It is the ester of lactic acid; lactate ester is usually used in the paint and coatings industry, which is totally biodegradable, recyclable, noncorrosive, noncarcinogenic, and nonozone depleting. As ethyl lactate has high solvency power, high boiling point, low vapor pressure, and low surface tension, it is used frequently in the coatings industry, paint and graffiti cleaner. Consequently, it can replace the nongreen solvents such as toluene, acetone, and xylene for more safety reasons [2]. Table 7 shows the recent research and application of biosolvents which demonstrates that these solvents can also be used for carbon dioxide capture, extraction of lipids, fats and oils, reaction media, and membrane preparation. LCA is a method that is used to help the solvent selection and to evaluate which is the utmost suitable method for the management and handling of solvents as an environmental point of view. According to a LCA study, when chemicals such as methanol, ethanol, heptane, xylene, acetic acid, n-hexane, methyl-­ethylketone, mono-chloro-benzene, iso-propanol, di-methoxy-ethane, iso-hexane, xylene, pentane, formaldehyde, methyl acetate, diethyl ether are in the mixture, they had better be incinerated as the recapture of them has no environmental advantages. Conversely, for the chemicals which have a high effect in the process of production, like acetonitrile, benzaldehyde, butyl acetate, benzyl alcohol, iso-amyl acetate, and iso-butyl acetate, distillation technique is the finest way to optimize the production of these solvents [209]. From a statistics point of view, North America is the leading manufacturer and user of biosolvents, the production involves 33.78% of global solvent making in 2015, and Europe is in the second place by 26.62%. The Asia Pacific is estimated

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to have the highest evolution rate over the prediction time interval. The universal marketplace for green and biosolvents anticipated to rise at a compound annual growth rate (CAGR) of approximately 7.8%, and by the next few years it will get to 8610 million US$ in 2023, from 5480 M US$ in 2017 [210].

10 Green Solvents for Polymerization The production of polymers usually involves a polymerization reaction step that takes place in organic solvents. The critical importance of using green solvents in the polymer industry can be confirmed by taking into account that most of the polymerization reactions occur in organic solvents [211]. In the previous sections, different green technologies that can limit the dependency of industries to nongreen solvents were discussed. In this section, the potential of these technologies in the polymerization industry is discussed as an example. A solvent-free polymerization is an option for polymerization reactions; however, it is not possible in most of the cases [212]. Water, SpCs, ILs, and DESs are the most commonly used technologies for polymerization. Water in polymerization: Water can be used as a green solvent for a series of homopolymers and copolymers [213]. The first report regarding the utilization of water as the polymerization solvent is lipase-catalyzed ROP of five lactone monomers [214]. Commercial water-based polymerization is limited to radical systems because water damages active species in anionic, cationic, and catalytic polymerizations. Daigle et al. [215] studied catalytic polymerization of ethylene in water pressurized with CO2 and found that the attendance of CO2 reduces the negative effect of water on polymerization and significantly enhances the rate of reaction. Chaduc et  al. [213] analyzed reversible chain transfer polymerization of methacrylic acid in water using trithiocarbonate as a chain transfer agent and 4-cyanopentanoic acid in the role of initiator. They first dissolved methacrylic acid in the transfer agent and then added it to water. This method was found to be an excellent tool for producing high molecular mass polymers with very low dispersity. Deep eutectic solvents in polymerization: DESs are another category of green solvents that have emerged for polymerization reactions. The first works on the application of DESs for polymerization reactions concentrated on the incorporation of monomers into DES structure; however, the later reports dealt with using DESs as an inert green solvent [216]. Natural deep eutectic solvent (NADES) is a promising alternative for green polymer industries as a bio-based and environmentally friendly solvent. The high electric conductivity of NADESs which comes from being a combination of cationic and anionic species introduced it as a favorable solvent for electrochemical synthesis of conducting polymers. In addition, they can play the role of catalyst for polymerization reactions. Providing antimicrobial

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properties for polymers by some incorporated quaternary ammonium salts in NADESs is another advantage of this method. Despite these advantages, more research is required to find about the solubility of monomers and polymers in different NADESs to shed a light on the challenges in the polymerization industry. The high viscosity of NADESs and difficulty in its recovery because of low volatility are other challenges for its application in polymerization reactions [211]. Wang et al. [217] analyzed the potential of amide compounds, inorganic salts, and quaternary ammonium salts in polymer industries and reported it is possible to control the molecular weight of generated polymers by DESs. They also confirmed the living feature of the polymer produced by DES by examining the chain extension. Mukesh et al. [218] showed that hydroxyethylmethacrylate is self-polymerized in a DES that made by endothermic complexation between choline chloride and orcinol. This process produces stretchable ion gel that is proper to be used in supercapacitors as a solid polyelectrolyte. It is possible to increase the yield of poly(3-octylthiophene) production up to 100% using DES [219]. Therefore, DESs are promising alternatives to replace ILs and other solvents to develop a green industrial process for the synthesis of polymers. Ionic liquids in polymerization: IL technology is another alternative for the production of polymers using organic cationic or inorganic anionic species. This technology can help in enhancing the polymerization rate and molar mass of the polymer [178]. Nonflammability and recyclability are two significant advantages of ILs for polymerization industries [220]. ILs are used in different free-radical polymerization reactions such as radical polymerization, ring-opening polymerization, anionic/ cationic polymerization, and electrochemical polymerization [221]. The environmental effects of IL utilization as a “green” solvent for the polymerization industry are not yet completely investigated. The energy demand of this technology and recovery of IL are other issues that should be addressed for the polymerization reactions, because of the need for another solvent to recover polymer [212]. ILs can be used in the polymer industry not only as polymerization solution, but also as components of polymeric matrixes, the template of porous polymers, and electrolyte of electrochemical polymers [222]. Biedroń and Kubisa [223] investigated chain transfer to imidazolium ionic liquid in the polymerization of methyl methacrylate and showed that imidazolium ionic liquid is not a neutral solvent and contributes to the polymerization reactions. Xie et al. [224] studied the application of ILs in atom transfer radical polymerization and ring-opening metathesis polymerization and showed that this technology provides the tools to control the molecular weight and molecular weight distribution, increase the solubility of polymer, and enhance the stability of catalyst and possibility of catalyst recycling. Supercritical fluids in polymerization: SpC fluid technology is the most common approach for solvent-based polymer production, and SpC-CO2 is the most promising fluid for polymerization industries [225]. Ease of separating the formed

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polymeric powder from depressurized gaseous CO2 is a significant advantage for the polymerization process because it does not impose the energy-­intensive drying steps. The SpC process can also enhance the quality of polymer and safety of working with explosive monomers in the production of fluoropolymers [225]. This technology is used in the production of different polymers such as fluoropolymers, polysiloxanes, hydrocarbon polymers, polybutylacrylate, and polystyrene [226]. It also opened a window on the polymerization reactions that are impossible or difficult to take place [227]. SpC technology permits the generation of a vast range of polymers through free-radical, cationic, transition metal catalysis, ring-opening, and enzymatic polymerization reactions [175]. It is shown that low-cost poly(ether carbonate) copolymers can be dissolved in SpC-CO2 at mild conditions and can be used to make inexpensive surfactants [227]. Cooper et  al. [228] successfully prepared well-defined, highly porous cross-linked monoliths using SpC-CO2. They suggested this approach for the production of molded microporous polymers with narrow-bore capillaries due to ease of solvent separation. It is shown that controlling the average pore size and pore size distribution is possible either by changing SpC-CO2 density or by reverse micellar imprinting. DeSimone et al. [229] applied SpC-CO2 to synthesize fluoropolymers and proposed it as an excellent alternative for chlorofluorocarbons since fluoropolymers are rarely soluble in other solvents.

11 Bioeconomy of Green Solvents and Sustainability Toward a Green Economy The circular bioeconomy is getting more and more attention to global sustainability from different sectors. This concept can be defined as: “a system of industries that is recuperative or regenerative by purpose and design, which substitutes the end-of-life concept with restoration, going toward utilizing the renewable energy, removing toxic compounds from processes, and targets to the waste removal via the novel design of chemicals, systems, and commercial models” [230]. The selection of a suitable green solvent regarding bioeconomy is the main aspect to be considered in chemical processes (reactions). In this regard, three facets must be considered: chemical compatibility with the other chemicals in the solutions, solving of reagents, and operating temperatures. There are out of 12 green chemistry principles, among them, 2 should be considered mainly to choose the solvents in a chemical reaction or separation processes, as follows (quoted) [196]: – “Wherever practicable, synthetic methods should be designed to use and generate substances with little or no toxicity to human health and environment.” – “The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible, and also innocuous when being used.”

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Concerning analytical chemistry, the substitution of conventional solvents by ecofriendly solvents leads us to green analytical chemistry [93]. Moreover, regarding the green chemistry, analytical approaches should diminish or remove hazardous chemicals used in or generated by a technique. In this domain, utilizing DES/ NADES as solvents in the sample preparation step is in accordance with green chemistry, thanks to their low toxicity and high biodegradability. A shortcoming for the green analytical method is energy consumption, for example, concerning the existing green analytical evaluation tools, some techniques, such as nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and X-ray diffractometry are energy-consuming, while immunoassay, spectroscopy, and electrochemical methods are further energy-saving techniques. Hence, more research is required to develop sustainable analytical methods [86]. Despite the effective application of biosolvents in some industries, like cosmetics, solvents, inks, and other standard chemicals, these solvents still facing the narrow market and stockholder attention. The main obstacle to the bio-based marketplace is the costs, which are higher than conventional ones. Policy interferences can inspire the relative markets by investment motivations such as grants, loans, guarantees, etc., or by ratificating the production of conventional equivalents solvents more costly, or by making the use of biosolvents compulsory in some sectors [231]. To sum up, in order to evaluate the overall sustainability of a process, the financial and social aspects, that is, the socioeconomic signs must be taken into account. In fact, green chemistry is a fundamental portion of sustainable procedures for chemicals production. A general alarm for climate change is the main driving force in the shift from a conventional production line in a “take-makeuse-­dispose” system to a greener, circular economy. Waste removal via the development of chemicals and methods with reclaiming are important aspects of the circular economy. The transition from the planned unsustainable linear economy to a greener circular one is seriously vulnerable by considering the economic evaluations are not accompanied on a level playing field. The real costs of recognized “take-make-use-dispose” production rows need to be comprised of the expenses of supply exhaustion, waste control, and environmental contamination [232]. Different aspects of the evaluation of green solvents need to be considered, such as environmental effects of the manufacturing production, reclamation and dumping processes, and EHS (environmental, health, and safety) features. This multicriteria assessment can be attained by merging the EHS technique with the life-cycle assessment (LCA) technique. The EHS method emphasizes the essence of hazards of solvents, while the LCA method measures a generic energy usage comprising attributable resource use and discharges which is correlated to the solvent making and waste handling [233]. Economic aspects can also be estimated in terms of the raw materials and operating costs in the production

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process. The feed should be renewable, simply accessible, reasonably priced, and should not be utilized in the food industry in order to have no effects on food price sectors [234].

12 Challenges and Recommendations Figure  9 presents a brief overview of green solvent types, applications, and characteristics. However, there are some challenges in the application of these chemicals as a green chemistry point of view. The recent progress on solvent production from natural/renewable resources offers novel solutions that can improve sustainable analytical techniques, though there are various issues regarding these alternative solvents, such as lacking sensitivity, insufficient accuracy and precision, and augmented expenses [93].

Green solvents

Types

622

Applications

Biosolvent

Low vapor pressure

Polymerization

Ionic liquid

High recovery percentage

Chemical reaction

Biodegradability

Analytical chemistry

Deep uetectic solvent

Fig. 9  Green solvents; Classifications, properties, and applications.

Features

(not all of them)

Supercritical fluid

Low toxicity

Water

Sustanability

Environmentally freindly

Extraction and seperation

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According to the current knowledge about green solvents, we can see somehow the future outlook of these solvents. Regarding DESs, they are nontoxic for humans (e.g., choline and sugars) and have high potentials in drug delivery methods, bone therapy, other biomedical applications, and analytical chemistry [235]. The researchers believe that the DES and NADES in nutrition and environmental analysis application will develop, and the studies will emphasis on the following zones [86]: - synthesis of novel (NA)DES solvents by concentrating on polarity changes - improvement of the efficiency and selectivity of microextraction methods - utilizing these novel solvents as extracting sorbents or selective binding agents in analytical chemistry. Glycerol and 2-methyltetrahydrofuran are known as the two most important biobased solvents. Though application and adaption in the industry are normally slow, the oil refinery and the biorefinery systems can be in agreement with the chemical intermediate sequence. In this way, the products of bio-based solvent division can be used as primary, intermediates, and by-products as indicated in Fig. 10. Moreover, some of the solvents (such as propanediols) can be produced from bio-based materials (like glycerol) instead of oily-based chemicals (propylene in this case). Besides, the fermentation products (like butanol and acetone) can be used as the primary products of the petrochemical industry [205]. The main advantages of SpC fluids over conventional solvents are their insignificant environmental impact, low energy consumption, nontoxicity, nonflammability, and low cost. They are characterized by having low viscosity as well as high diffusivity, density, and dielectric constant, all of which are the characteristics that may be easily changed by fluctuating operating temperature or pressure. The high pressure of supercritical fluids can avoid the limitations of conventional solvents for chemical processes which is useful in the extraction of valuable compounds from plant materials. While interesting results have been observed, using the novel green solvents is still faced with some restrictions, including a high cost for supercritical extraction method, high expenses and data shortage on toxicity, and biocompatibility for ionic liquids. Considering the minimization of the number of solvent changes in chemical operations, purification, extraction, separation, and reaction technologies. Moreover, it would be necessary to consider the environmental and ­techno-economic assessment by considering the pros and cons of the novel green solvents [235]. As economical perspectives, based on the global “Green and Bio-Based Solvents Market” report, the marketplace is anticipated to reach US$ 10,680.5 million by 2024, with a compound annual growth rate (CAGR) of 7.5% growing from US$ 6,495.5 million in 2017 [236]. As future perspectives, there is still an abundant requirement for metrics for the assessment of processes in a beginning phase of

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Fig. 10  The route of biosolvent production. Reproduced from James H. Clark, Thomas J. Farmer, Andrew J. Hunt, James Sherwood Opportunities for bio-based solvents created as petrochemical and fuel products transition towards renewable resources, Int. J. Mol. Sci. 16 (2015) 17101–17159 with permission from the author.

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progress in green solvent areas. Moreover, there is a persistent necessity for economic pointers that integrate the presently expressed charges of refurbishing the environmental destruction triggered by industrial undertakings [232].

13 Conclusions and Perspectives Based on bioeconomy concept in green chemistry, recovery and reuse of designed solvents and producing renewable and nontoxic ones are considerably significant. The seventh principle of green chemistry—“renewable rather than depleting raw materials”—is an important aspect in the evolution from a traditional economy founded on raw materials to a bioeconomy with sustainable feedstock. Solvents derived from biomass are a noteworthy class of green solvents. Although they are comparable with petroleum-based solvents and can be utilized in various applications, the toxicity of these chemicals requires more studies. Various eutectic mixtures (solvents) can be synthesized in economical and sustainable processes. The properties of DESs are comparable to ILs, and they can be viewed as (non- or) low-toxic, and biodegradable (in some cases) green solvents, though high viscosity is challenging and more research needs to be performed to overcome this issue. Moreover, SpC fluids can be used as a suitable substitute to former solvents in the separation and other chemical processes due to their unique characteristics. Although water is known as a green solvent, the high polarity of water confines its application as a reaction solvent because of its low solubility in many organic reactants. Concerning the solvent-free approach, it is an easy and economical method that has advantages, such as cut contamination, lower cost, and environmentally friendly. In order to facilitate the development of green solvent applications, it is essential to consider a comparison between greenness and sustainability. Considering the green chemistry principles, the E-factor and the atom economy, which focus on the removal of waste and maximizing of resource efficiency, on the one hand, and process intensity and reaction efficiency, amount and essence of raw materials, on the other hand, lead to designing efficient green solvents. All in all, green solvents can be used in the future in different chemical processes, such as pharmaceuticals; phenolic compounds; oil, lipid and protein extraction; analytical chemistry like high-performance liquid chromatography and capillary electrophoresis; biomass processing; enzymatic synthesis; biopolymers; drug delivery; and catalysis and reaction media. In this regard, much attention has been on the environmental aspects of the solvents, while a substance deployment has an important role in sustainability as what it is made from. As an outlook, by considering the range of reactions in green solvents, and the properties, and behavior of these solvents to outfit the specific application, they can be labeled as designer solvents. By selecting the appropriate solvent, high reaction/separation yields, and a reduced amount of waste can be achieved. Often they are recyclable, which results in a decrease in the raw solvent costs.

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Sustainable production of bioadsorbents from ­municipal and ­industrial wastes in a circular ­bioeconomy context Balasubramanian Sellamuthua, Vimala Gandhib, Bhoomika Yadavc, and Rajeshwar Dayal Tyagic

a Centre de Recherche du CHUM, Montréal, Québec, QC, Canada bDepartment of Microbiology, Government Science College (Autonomous), Bangalore, Karnataka, India cINRS Eau, Terre et Environnement, Québec, QC, Canada

1 Introduction The concomitant increase in population and industrial development to meet the current consumption rate of human lifestyle lead to simultaneous reduction in natural resources and increased waste generation rate. From the start of civilization to until date, the quantity of waste generated by human and industrial origin was sufficient enough to pollute the entire planet including ocean, air, and both aquatic and terrestrial environment. The total quantity of municipal solid waste (MSW) produced in the US alone in 1960 was estimated as 88 million tons (MTs), which steadily increased to 262 MTs in 2015 [1]. Among the waste produced in 1960 6% was recycled and remaining 94% was landfilled, whereas, among the waste produced in 2015, due to science and technology development, 26% was recycled, 9% used for composting, and 13% used for energy recovery through combustion. However, 52% of waste disposal was done through land filling and other activities. The municipal and industrial sectors’ waste generations and disposal options slightly vary around the world. In the recent decades, a steady raise in reuse and composting was reported [1]; interestingly landfilling rate was decreased, which is a healthy sign for environmental protection and waste management options.

Biomass, Biofuels, Biochemicals. https://doi.org/10.1016/B978-0-12-821878-5.00019-2 Copyright © 2021 Elsevier Inc. All rights reserved.

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To protect the environmental health from pollution caused by these excess waste generations, industrial and human activities must be managed. Thus, environmental scientists and engineers have been developing various novel, eco-friendly, and sustainable treatment technologies to reduce waste generation and increase the recycling options through green biotechnology [2]. Sustainability refers the capacity to preserve the available natural resources and also to meet the environmental equilibrium. Furthermore, the developed technology should meet the present needs without affecting the future generations in terms of social, environmental, and economical aspects. Thus, the sustainable approaches are focusing on the environmental policies through waste reduction and recycling options without closing the loop of material end use through linear economy [3] in which we manufacture, utilize, and trash in the environment. So, we need to adopt a circular economy approach to meet our future needs through use of waste as a source (raw material) for various value-added product productions. A true bioeconomy can be achieved through sustainable production and product recovery such as food, feed, biobased products (biofuels, biopesticides, enzymes, and biofertilizers), and even energy generation using renewable biological resources. The circular economy and bioeconomy are the two main sustainability-oriented concepts, which are targeted to transform the current linear (fossil-based) economy into an efficient waste recycling process. The novel circular bioeconomy approach promotes the sustainable production of products from diverse types of wastes, such processes are designed and operated for (i) the reduction, elimination, or on-site recycling of waste and nonbiodegradable by-products, (ii) the removal of chemical substances that possess hazards to human and environmental health, (iii) the conservation and appropriate use of energy and resources for the desired purpose, and (iv) the elimination of chemical, ergonomic, and physical hazards from the work spaces. Wastes generated from both the municipal and industrial sectors cause immediate nuisance to the environment at their disposal site. Recently, researchers attempted to prepare bioadsorbents from these wastes as an alternative to the expensive commercial-grade activated carbon [4]. Bioadsorbents are biological materials involved in the biosorption or adsorption process and are capable of pulling together the toxic metals and dyes from wastewater. Biosorption process has been proven as the best water/wastewater treatment option currently available. Various types of novel low-cost bioadsorbents have been prepared from the following sources: (i) farming and domestic by-products, (ii) manufacturing by-products, (iii) wastewater sludge, (iv) marine materials, (v) soil and ore components, and (vi) microorganisms [5]. Wastewater treatment plant (WWTP) employs various operational methods such as chemical coagulation, photodegradation, precipitation, flocculation, activated sludge, adsorption, absorption, membrane separation, and ion exchange

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processes for pollutants removal and to meet the effluent discharge standards. Among the several treatment methods used in WWTP, the adsorption method is easy to implement, efficient, and cost-effective and requires less energy, and it is also possible to implement it in large-scale operations. Biosorption process has numerous advantages compared to traditional process, such as minimal production of chemical and biological sludge; external supplementation of additional nutrients is not required for the metal accumulation and bioadsorbent regeneration. In this chapter, the sustainable production of bioadsorbents from waste (municipal and industrial) and its application to reduce waste generation are presented with a life cycle assessment of bioadsorbents in the circular economy context. Furthermore, different types of bioadsorbents produced and their adsorption mechanisms are highlighted in the following sections.

2 Municipal Waste Municipal waste mainly originates from households (consisting bulky waste, yard and garden waste, and street sweepings) and commerce and trade (office buildings, institutions, and small businesses). This can be divided into two main categories: (i) municipal solid waste (MSW) and (ii) municipal liquid waste (MLW). The municipal solid waste (MSW) also called trash or garbage, which mainly consists of materials used on a daily basis such as packaging (newspapers, bottles, and cans), appliances (furniture, electronics, and batteries), and yard trimmings. However, the industrial, hazardous, or construction and demolition wastes are not part of the MSW as per Environmental Protection Agency (EPA). To protect the environment and surroundings, the produced waste must be collected and disposed. The regular waste management options are recycling, composting, combustion (possible energy recovery), and landfilling. In early 1970s, MSWs are frequently dumped or burned in open places to mitigate the volume of waste generated [6]. Most of the time industrial hazardous wastes were codisposed with MSW in the landfill, which creates huge environmental problems such as ground water contamination, emissions of greenhouse gases, and noxious fumes. Such old landfill pollutes the land and augments the disease-causing vector populations (rodents, pest, flies, and mosquitoes). The MLW or wastewater (WW) or sewage is generated from residences (toilet, bath, laundry, lavatory, and kitchen sink wastes) and surface runoffs. The WW is classified into four types: (i) sanitary sewage, (ii) industrial sewage, (iii) storm sewage, and (iv) mixed sewage (a mixture of all). Due to fast industrial revolution, economic growth and population increase led to parallel increase in wastewater production in both municipal and industrial sectors. Municipal and industrial wastewater treatment plants (WWTPs) treat MTs of wastewater ­worldwide by

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physical, chemical, and biological treatment processes [6]. These treatments generate enormous quantity of sludge (around 100–300 tons of sludge/WWTPday), which is considered recyclable waste [7]. Sludge primarily contains water (95%), organic and inorganic matter, and complex microbiome. The sludge generated from WWTP is classified into primary, secondary, or digested sludge depending on the treatment process used [8].

2.1  Types and Origin of Municipal Solid Waste The MSW can be broadly classified into two groups: (i) wet and (ii) dry wastes. The wet waste mainly includes food waste such as vegetables, meat, kitchen waste, eggshells, and leftover food, whereas the dry waste consists of plastics, cans, newspapers, metals, glass bottles, and wood materials. It is important to mention here that the composition of MSW differs in time and from municipality to municipality [9, 10]. Waste has been classified in numerous ways based on its characteristics and materials present in it [11, 12]. The general classification of MSW is as follows: (i) biodegradable waste, (ii) recyclable materials, (iii) inert waste, (iv) waste electrical and electronic equipment (WEEE), (v) composite waste, (vi) hazardous waste, (vii) toxic waste, and (viii) biomedical waste. Based on the MSW characteristics, it has been further classified as organic (easily biodegradable) and inorganic (nondecay in nature) solid waste [13]. The three main sources of MSW are mainly from urban, industrial, and rural sectors [14]; each one is containing different materials (Fig. 1).

Fig. 1  A flow chart representing the three groups of municipal solid waste.

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2.2  Generation of Municipal Solid Waste The current rate of MSW generation is around 2 billion metric tons/year. The World Bank estimated that the MSW production rate is likely to raise 3.40 billion MTs by 2050. At present, 13.5% of the generated MSW is reused and 5.5% is used for compost preparation. A report stated that nearly 40% of the MSW collected globally was not disposed in a proper way, which is either dumped or burned in an open land [15]. Developed countries such as USA, Canada, and members of the European Union possess only 16% of global population, but these countries alone produce nearly double the quantity of MSW (34% of MSW from the worldwide). In 2013, USA alone generated 254 MTs of MSW [15], and their composition is presented in Fig. 2. In addition, more than 93% of MSW produced in developing countries was not managed and disposed in a proper way. The 55%–80% of MSW produced in developing countries is from households, 10%–30% of MSW from commercial activities, and the remaining originates from industries, streets, institutions, and many others [16]. It was calculated that in North America roughly 4.9 pounds of MSW, whereas 1 pound of MSW in sub-Saharan Africa is produced (daily/capita). Based on this fact, the World Bank predicted that the waste generation is expected to triple in sub-Saharan Africa and to double in South Asian region alone, which will be equal to 35% of global waste generation by 2050. The consumption behavior and lifestyle of the people along with fast science and technology advancement in manufacturing sectors hugely contribute toward the

Composition of MSW Other, 3% Food, 15% Paper, 27% Yard trimmings, 14%

Metals, 9%

Wood, 6%

Plastics, 13%

Fig. 2  The segregation and composition of municipal solid waste (MSW).

Glass, 4%

Rubber, leather, and textiles, 9%

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MSW composition and production rate around the world [17, 18]. Interestingly, China and India contain >  36% of the world’s population but only produce 27% in the total quantity of waste generated around the world. This warrants a necessary action required to create awareness, regulations, and responsibilities of individuals, politicians, and policy makers to control the waste production and subsequent mitigation of environmental pollution and associated threat.

2.3  Waste Disposal Problems The solid waste management (SWG) and waste disposal is a challenging issue, which creates environmental problems and concerns around the globe. Particularly, in developing countries, SWG is poorly followed and, thus, environmental pollution and emerging microbial infections caused by potential pathogens such as Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumoniae, and Streptococcus pneumoniae rise day by day [19, 20]. Furthermore, large quantities of produced solid waste in metropolitan cities greatly affect public health by causing limitation in sanitation facilities, waste management, transport, and poor quality of water supply [21, 22]. Additionally, poor economy and inadequate infrastructure for waste collection, storage, transportation, and final disposal in a few developing countries (e.g., cities in East and North Africa) raise concern to the residents and environmental health. Human exposure to such wastes released at the facilities of waste management can be acute due to an accident causing a short-time exposure of ionizing radiation or hazardous substances, bioaerosols, dust, or chronic involving long-term exposure of the radiations or substances. In the UK, around 160,000 workers get employed in the management sector, and it is reported that 3800–4300 accidents happen every year, including the fatal injury rate of about 10 per 100,000 workers [23]. Many studies have been done to investigate the health effects of waste management activities on human population and environment [23]. Industrial and municipal waste (both organic and inorganic) disposal into the river, canals, and lakes in the developing countries is a common practice still happening without any concern about the environmental pollution and associated health problems to be faced by the future generations to come. The main reason for this practice by common people, industrialists, and government authorities was the lack of environmental education to the public, deficient in regular garbage collection and poor landfill management, and large quantity of population and associated waste generation rate. Most of the water streams in developing countries (e.g., India, China, Thailand, and other Asian countries) is polluted and filled with plastics and papers, indeed the toxic materials are also found. The presence of toxic substances in the environment and water sources further affects the natural biodegradation process and augments the BOD load. The irresponsible actions of residents by direct dumping of waste into water sources and burning toxic materials in the streets nearby residential area affect the public health. Such actions of inappropriate waste disposal in small quantities create large problems to the environment and public health. To mitigate and avoid

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such direct disposal practices, effective laws and education about environmental health are advised for people where proper waste and wastewater treatment/ management facilities are lacking [24].

2.4  Nutritional Value and Chemical Constituents of Municipal Waste The chemical analysis of municipal waste provides essential information about the composition and characteristics of waste, which leads to the designing of an effective waste management, disposal, and reuse options. Though large quantities of waste are generated every day, knowing its composition and nutritional value helps in creating novel materials and value-added products such as bioadsorbents, bioplastics, enzymes, biofuels, and bioflocculants production from waste. This is the beginning of any waste conversion to useful materials through circular economy. The waste possessing nutritional values can be explored to attain circular bioeconomy by using them as raw material in fermentation. It is also important to note that the solid waste composition varies from place to place and time to time, which mainly depends on the geographical location (including climate and weather condition), population, residential activities, and local public events. The actual chemical characteristics of solid waste is indispensable to select an appropriate treatment and reuse options, especially when waste is used as a raw material. Commonly, physicochemical properties (such as total carbon, total nitrogen, total phosphorus and potassium, C/N ratio, pH, and calorific value to name a few) of the municipal waste is conducted before the recycling step [25], and the typical MSW characteristics were provided in Fig. 3. A few compounds (ash, carbon, volatile compounds, and water content) of the MSW found to vary from one waste to another, which is provided in Table 1. The seasonal variations

Fig. 3  The common characteristics of municipal solid waste.

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Biomass, Biofuels, Biochemicals Table 1 Analysis of Characteristics of Different Wastes. Types of Waste

Moisture (%)

Volatiles (%)

Carbon (%)

Ash (%)

Mixed food

70.0

21.4

3.6

5.0

Mixed paper

10.2

75.9

8.4

5.4

0.2

95.8

2.0

2.0

60.0

42.3

7.3

0.4

–

–

96–99

52.0

7.0

20.0

Mixed plastics Yard wastes Glass Residential MSW

2.0 21.0

found to play a major role in moisture content change in MSW, and also different waste possesses different elemental compositions (Table 2). As per the study conducted by NEERI, India, the MSW generated in India possesses roughly 40%–60% of the compostable material, 30%–50% of inert compounds, and 10%–30% of recyclable materials. The chemical analysis revealed that the MSW collected in India contains nutritional value compounds such as nitrogen (0.64 ± 0.8%), phosphorus (0.67 ± 0.15%), potassium (0.68 ± 0.15%), and C/N ratio (26 ± 5%) [26], whereas the chemical constituents of the MSW collected in Nigeria revealed nitrogen (11 g kg−  1), phosphorus (3.2 g kg−  1), and potassium (10.7 g kg−  1). And, the elemental contents were found as follows: calcium (87.7 g kg−  1), sodium (18.4 g kg−  1), and sulfur (S) (2.3 g kg−  1). Interestingly, the organic content of MSW was 223.7 g kg−  1 [27]. In another study conducted in Bangladesh, the chemical characteristics of MSW revealed high in moisture, ash, and inorganic contents, but low level of nitrogen, phosphorus, and potassium were observed [27]. These studies conclude that the MSW generated in different places has different chemical characteristics, thus these analyses must be undertaken before planning suitable recycling options to achieve/develop a sustainable circular bioeconomy process. The waste originated from household activities (e.g., kitchen waste, plant residues, and sewage sludge) found to contain high concentration of organic nutriTable 2 Representation of Different Elements Present in Various Wastes. Types of Waste

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C (%)

H (%)

O (%)

N (%)

S (%)

Ash (%)

Mixed food

73.0

11.5

14.8

0.4

0.1

0.2

Mixed paper

43.3

5.8

44.3

0.3

0.2

6.0

Mixed plastics

60.0

7.2

22.8

–

–

Yard wastes

46.0

6.0

38.0

3.4

0.3

6.3

Refuse-derived fuel (RDF)

44.7

6.2

38.4

0.7

Bagasse treated with H2SO4

[3]

H2SO4

Heated in MF at T = 150°C for 24 h, soaking in 1% NaHCO3 solution overnight

Ethylenediamine (EDA)

1 g rice hull and 0.02 mol EDA heated at 80°C for 2 h

14.68

[4]

Mixture of dioxane, NaOH, epichorohydrin

Sawdust treated with dioxane(240 mL), 20% NaOH (24 mL), epichlorohydrin (40 mL) at 65°C for 5 h

188.8

0.1 N NaOH

Sawdust treated with 0.1 N NaOH and immobilized on alginate biopolymer

38.46

6.28 [5]

Acid Yellow 17

Spent brewery grains

0.13 M H2SO4

Suspended in 0.13 M H2SO4 for 1 h

Initial dye conc. 50 mg/L, adsorbent dosage 0.5 g, Contact time 40 mins at pH = 2

[6]

Rhodamine B

Coconut shell char

H2SO4

Coconut shell treated with H2SO4 at 1:1 (w/v) followed by heating in MF at 550°C for 7 h

41.67

[7]

Dark green PLS dye

Cashew nutshell carbon

Concentrated H2SO4

4 parts of each material with 2 parts of concentrated H2SO4 heated at140°C–170°C for 24 h

1

[8]

Palm nutshell carbon

0.84

Broomstick carbon

0.63

Methylene Blue

Barley straw

Water

Wheat straw

Straw pieces of 1 cm size were dried overnight at 65°C and soaked in water for 20 days at room temperature followed by drying overnight at 60°C

Oat straw

22.22

[9]

11.11 50

Esterified natural papaya seed

CH3OH and HCl

Papaya seed treated with CH3OH and HCl followed by washing and drying

250

[10]

Rice husk

0.5 N NaOH

Treated with 0.5 N NaOH at room temperature for 4 h

20.24

[11]

Coconut chopra meal

0.02 mol/dm3 HCl

Coconut chopra meal pieces of size less than 250 μm were soaked in 0.02 mol/dm3 HCl overnight and washed with distilled water until pH becomes neutral

4.99

[12]

Ni II)

Protonated rice bran

HCl, H2SO4, and H3PO4

Rice bran treated with HCl, H2SO4, and H3PO4 followed by washing with distilled water until pH comes to neutral range and then dried at 60°C for 24 h

102

[13]

Cr(VI)

Banana peel

Methanol and HCl

9 g of washed and dried banana peel suspended in 633 mL of 99.9% methanol to which 5.4 mL of 0.1 M concentrated HCl was added and then the solution was heated at 60°C and stirred continuously for 48 h.

131.56

[14]

2.22 mmol/g at 40°C

[15]

Heavy metals Cd(II)

Cr(III)

Continued

Table 1  Different Bioadsorbents Activated With Chemical Processes—cont’d

Adsorbate Type Pb(II)

Bioadsorbent Coffee residue

Activating Agent ZnCl2

Enteromorpha prolifera activated carbon (EPAC)

Activation Condition

Adsorption Capacity and/or Condition (mg/g)

References

Coffee residue washed with DW and dried at 60°C followed by impregnation with ZnCl2 solution at 85°C for 7 h. Then, the sample was carbonized at 600°C for 1 h

63

[16]

40 g EP impregnated with ZnCl2 solution containing 40 g of zinc chloride. After 12 h impregnation period, the mixtures were dehydrated at 100°C for 24 h and then pyrolyzed in a quartz tube under N2 atmosphere at 500°C for 1 h

(142.93–147.06)

[17]

Zn(II)

Tea factory waste (TFW)

Hot water and NaOH

Crushed TFW was washed with hot water (80°C) for four times and also with NaOH solution until TFW solution becomes colorless at room temperature

8.9

[18]

Hg(II)

Walnut shell

98% ZnCl2

Walnut shell was dried at 120°C for 24 h and then powdered, sieved (below mesh no. 170) and impregnated with 98% ZnCl2 in a weight ratio of 1:0.5(walnut shell:ZnCl2) followed by drying at 120°C for at least 5 h

151.5

[19]

Cork activated carbon

K2CO3 and KOH

Pretreated cork (0.5 mm–1 mm) was activated by K2CO3 and KOH at room temperature for 24 h and 2 h, respectively, followed by activation at 700°C–800°C for 1 h

removal efficiency = 98%

[20]

Peach stone activated carbon

K2CO3

Peach stone residue (