Environmental Science 9781783325405, 9781783325740, 1783325402

Table of contents :
Environmental science [p1-3]
Environmental science [p4-5]
Environmental science [p6-11]
Environmental science [p12-47]
Environmental science [p48-83]
Environmental science [p84-103]
Environmental science [p104-119]
Environmental science [p120-127]
Environmental science [p128-135]
Environmental science [p136-145]
Environmental science [p146-163]
Environmental science [p164-177]
Environmental science [p178-189]
Environmental science [p190-191]
Environmental science [p192-193]

Citation preview

ENVIRONMENTAL SCIENCE

Arti Malviya Dipika Jaspal

α Alpha Science International Ltd. Oxford, U.K.

Environmental Science 192 pgs. | 99 figs. | 12 tbls.

Arti Malviya Department of Engineering Chemistry Kajsgnu Baraub College of Technology Bhopal Dipika Jaspal Department of Applied Science Symbiosis Institute of Technology Pune Copyright © 2020 ALPHA SCIENCE INTERNATIONAL LTD. 7200 The Quorum, Oxford Business Park North Garsington Road, Oxford OX4 2JZ, U.K. www.alphasci.com ISBN 978-1-78332-540-5 E-ISBN 978-1-78332-574-0 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the publisher.

Preface The author’s feels immense delight to present this book on “Environmental Science” intended to meet the academic requirements of Environmental science for students in all universities. This book has a holistic approach to the subject for uncomplicated and reasonable conception. The contents of the book are designed, analyzed and discussed in such a manner that students are motivated to study subject with dedicated interest. We hope that the book serves its purpose and proves valuable to the readers from varied backgrounds. The authors are thankful for the patience and support of their family members and inspiration of their well wishers and friends. We want to express our appreciation to the entire team of Narosa Publishing House for whole hearted cooperation, sustained interest and well-timed publishing of the book. Suggestions for additional improvement and refinement of the text and presentation will be deeply appreciated and acknowledged. Arti Malviya Dipika Kaur Jaspal

Contents  v

Contents Preface 1. Ecosystem and Environment

iii 1–35

1.1 Ecosystem 1.1 1.1.1 Components of Ecosystem 1.2 1.1.2 Classification of Ecosystems 1.4 1.2 Trophic Levels 1.5 1.3 Energy Flow 1.5 1.4 Food Chain 1.6 1.5 Food Web 1.8 1.6 Ecological Pyramids 1.8 1.7 Abiotic Components 1.10 1.7.1 Hydrosphere 1.11 1.7.2 Lithosphere 1.11 1.7.3 Atmosphere 1.13 1.8 Biosphere 1.17 1.9 Biogeochemical Cycles 1.17 1.9.1 Carbon Cycle 1.18 1.9.2 Nitrogen Cycle 1.19 1.9.3 Hydrological Cycle or Water Cycle 1.20 1.9.4 Phosphorus Cycle 1.21 1.10 Biodiversity 1.22 1.10.1 Types of Biodiversity 1.22 1.10.2 Measurement of Biodiversity 1.24 1.10.3 Importance of Biodiversity 1.25 1.10.4 Threats to Biodiversity 1.28 1.10.5 Conservation of Biodiversity 1.31 Review Questions 1.35 2. Energy 2 .1 2.2 2.3 2.4

Types of Energy Classification of Energy Resources Fossil Fuels Biomass

2.1–2.36 2.1 2.2 2.3 2.5

vi Contents

2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13

Geothermal Energy Solar Energy 2.6.1 Solar Ponds 2.6.2 Solar Cookers 2.6.3 Solar Greenhouses 2.6.4 Solar Desalination 2.6.5 Solar Cells 2.6.6 Solar Furnaces 2.6.7 Solar Water Heaters Wind Energy Hydro Energy Ocean Energy Nuclear Energy 2.10.1 Nuclear Fission 2.10.2 Nuclear Fusion Hydrogen Energy 2.11.1 Hydrogen Fuel Cell Energy Scenario Case Study

3. Water Pollution

2.9 2.11 2.13 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.21 2.22 2.25 2.25 2.28 2.30 2.31 2.33 2.35 3.1–3.20

3.1 Water Pollution 3.1 3.2 Types of Water Pollution 3.1 3.3 Sources of Water Pollution 3.2 3.4 Water Pollutants and its Effects 3.3 3.5 Control Measures 3.7 3.6 Water management and Conservation 3.7 3.7 Waste water Treatment 3.8 3.7.1 Waste Water Analysis 3.8 3.7.1.1  Water Analysis Parameters 3.8 3.7.2 Treatment Process 3.11 3.7.2.1  Domestic Waste Water 3.11 3.7.1.2  Industrial Waste Water 3.19 3.8 Case Study 3.19 Review Questions 3.20 4. Air Pollution 4.1 4.2 4.3 4.4

Air Pollution Sources of Air Pollution Classification of Air Pollutants Adverse Effects of Air Pollutants 4.4.1 Global Warming

4.1–4.15 4.1 4.1 4.2 4.3 4.5

Contents  vii

4.4.2 Acid Rain 4.6 4.4.3 Ozone Depletion 4.7 4.4.4 Photochemical Smog 4.8 4.5 Control measures 4.9 4.5.1 Control Devices 4.9 4.5.1.1  Devices for Particulate Contaminants 4.10 4.5.1.2  Devices/methods for Gaseous Contaminants 4.11 4.6 Air Quality Index (AQI) 4.12 4.7 National Air Quality Standards 4.13 4.8 Case Study 4.14 Review Questions 4.15 5. Soil Pollution

5.1–5.8

5 .1 Importance of Soil 5.1 5.2 Soil Formation 5.1 5.3 Soil Profile 5.2 5.4 Soil Pollution 5.3 5.5 Sources of Soil Pollution 5.3 5.6 Effects of Soil Pollution 5.4 5.7 Methods to Control Soil Pollution 5.5 5.8 Soil Erosion 5.6 5.8.1 Agents of Soil Erosion 5.6 5.8.2 Effects of Soil Erosion 5.6 5.8.3 Control of Soil Erosion 5.7 5.9 Case Study 5.7 Review Questions 5.8 6. Sound Pollution

6.1–6.7

6.1 Noise Pollution 6.1 6.2 Classification of Noise Pollution 6.1 6.3 Sources of Noise 6.2 6.4 Impact of Noise Pollution 6.3 6.5 Noise Mitigation /control 6.5 6.6 Case Study 6.6 Review Questions 6.7 7. Waste Management 7.1 7.2 7.3 7.4 7.5

Types of Waste Effects of Poor Waste Disposal Solid Waste Types and Sources of Solid Waste Solid Waste Management 7.5.1 Waste Generation

7.1–7.10 7.1 7.2 7.2 7.2 7.3 7.4

viii Contents

7.5.2 Onsite Handling 7.4 7.5.3 Collection of Waste 7.4 7.5.4 Transport 7.4 7.5.5 Processing and Recovery 7.4 7.5.6 Disposal 7.4 7.5.6.1  Landfill 7.5 7.5.6.2 Incineration 7.5 7.5.6.3  Recycling and Reusing 7.5 7.5.6.4 Pulverization 7.6 7.5.6.5 Pyrolysis 7.6 7.5.6.6  Waste to Energy 7.6 7.5.6.7  Plasma Gasification 7.6 7.5.6.8 Composting 7.7 7.6 3R’s of Waste Management 7.8 7.7 Institutes Working on Waste Management 7.9 7.8 Case Study 7.9 Review Questions 7.10 8. Environmental Ethics and Society

8.1–8.17

8.1 Ethics 8.1 8.2 Morals 8.1 8.3 Objectives of Ethics 8.1 8.4 Principles of Ethics 8.2 8.5 Fields of Ethics 8.2 8.5.1 Personal Ethics 8.2 8.5.2 Professional Ethics 8.3 8.6 Ethical Theories 8.3 8.7 Ethical Situation 8.4 8.8 Code of Ethics 8.4 8.8.1 Codes of Ethics of Institution of Engineer 8.5 8.8.2 ACM 8.5 8.8.3 Ethics for IEEE 8.7 8.8.4 Advantages of Code of Ethics 8.7 8.9 Environmental Ethics 8.8 8.10 Some important Environmental Laws/acts in India 8.8 8.11 Environmental Impact Assessment (EIA) 8.11 8.11.1 Aspects of Environmental Assessment Impact (EIA) 8.12 8.11.2 Process of EIA 8.13 8.12 Environmental Education 8.15 8.13 Case Study 8.17 Review Questions 8.17

Contents  ix

9. Sustainable Development

9.1–9.13

9.1 Sustainable Development 9.1 9.1.1 Principles of Sustainable Development 9.2 9.1.2 Challenges for Sustainable Development 9.3 9.2 Sustainable Agriculture 9.6 9.2.1 Advantages of Sustainable Agriculture 9.6 9.2.2 Techniques of Sustainable Agriculture 9.7 9.2.3 Benefits of Sustainable Agriculture 9.8 9.2.4 Threats to Sustainable Agriculture 9.9 9.3 Organic Farming 9.10 9.3.1 Aims of Organic Farming 9.10 9.3.2 Practices of Organic Farming 9.11 9.3.3 Advantages of Organic Farming 9.11 9.3.4 Limitations of Organic Farming 9.12 9.4 Case Study 9.13 Review Questions 9.13 10. Green Technology 10.1 Goals of Green Technology 10.2 Fields of Green Technology 10.3 Advantages of Green Technology 10.4 Limitations of Green Technology 10.5 Green Building 10.5.1 Goals of Green Buildings 10.5.2 Advantages of Green Buildings 10.5.3 Green Building Programs 10.6 Green Business 10.6.1 Advantages of Green Business 10.6.2 Green Business Ideas 10.7 Green Computing 10.7.1 Goals of Green Computing 10.7.2 Pathways to Green Computing 10.7.3 Advantages 10.7.4 Steps to go Green (Computer Ethics) 10.8 Green Chemistry 10.9 Some Green Components 10.9 Case Study Review Questions Bibliography Index

10.1–10.11 10.1 10.2 10.3 10.3 10.3 10.4 10.5 10.5 10.6 10.7 10.7 10.8 10.8 10.9 10.9 10.9 10.10 10.11 10.11 10.11 B.1–B.2 I.1–I.2

1

Ecosystem and Environment

Environment includes everything around an organism i.e., living as well as non living things. It includes physical, chemical and other natural forces which constantly interact with the living organisms. Living elements are known as biotic elements (animals, plants), while abiotic factors include air, water, sunlight etc. Environmental study involves studying the interrelationships among these factors.

1.1 Ecosystem An ecosystem is a community of living organisms (flora, animals and microorganisms), in combination with the nonliving components of the environment ( air, water, mineral, soil) interacting with each other. The term Ecosystem was coined by Tansley. He defined ecosystem as “the whole system including not only the organism complex but also the whole complex of physical factors forming what we call the environment” An ecosystem can be as small as a glass of water or as large as an ocean. It consists of all the living and the nonliving things in an area. Ecosystems are the basic units of biosphere. These are governed by factors like climate, soil, topography, time, species distribution, decomposition potential etc. All the biotic (living) and abiotic (non-living) components of the ecosystem are considered to be linked together through energy-nutrient cycles.

Characteristics of Ecosystem:

1. 2. 3. 4.

Ecosystem is the smallest unit of biosphere. It is a self contained system. Ecosystems have structural diversity in terms of the variety of species. An ecosystem circulates the energy and regulates the flow of minerals and elements inside and outside the system. 5. Ecosystem comprises of both living and non living components. 6. Ecosystems have smaller units called communities. A community mainly considers the living organisms and excludes the abiotic factors. It is a collection of species populations.

1.2  Environmental Science



7. Ecosystem is dynamic in nature and continuously regulates the variable flow of energy and minerals. 8. All ecosystems existing on earth are distinct from each other. 9. All ecosystems have feeding hierarchy from producers to decomposers.

1.1.1 Components of Ecosystem Components of Ecosystem

Biotic Components

Abiotic Components

Producers (Autotrophs)

Organic Substances

Consumers

Inorganic Substances

Herbivores Carnivores Omnivores Decomposers (Micro-organisms)

Physical Factors Humidity Light Temperature

Fig. 1. Components of Ecosystem

The abiotic components are those which are nonliving and include inorganic components, organics and the climatic factors like light, temperatures, soil wind etc. The biotic components of an ecosystem include · Producers or autotrophs: These are those who produce complex organic substances from simple inorganic molecules using an external source of energy, mainly light or chemical reactions. All green plants and some microorganisms come under this category. Autotrophs are of two types. (i) Photoautotrophs which fix the solar energy and (ii) Chemoautotrophs which oxidize inorganics and produce complex organics. · Consumers: These organisms cannot produce their own food and are dependent on producers. These get food energy by consuming plants or animals. They can be further classified as follows: (i) Herbivores: Organisms that directly feed on the producers. Hence they are also called as plant eating animals or primary consumers. Examples include deer, cow, goat, rabbit and grasshopper. (ii) Carnivores: Organisms that feed on the herbivores. They are also called as flesh or meat eating animals or secondary consumers. Examples include tiger, lion, fox and sharks. (iii) Omnivores: Organisms that feed on both plants and flesh. Examples include bear, turtles, humans and owl. These are the top carnivores or tertiary consumers.

Ecosystem and Environment  1.3



· Decomposers: These are organisms that consume dead plants and animals. The primary decomposers include bacteria and fungi. They are also called saprotrophs. They convert the complex organic into simple inorganics like CO2, H2O, phosphates and sulphates etc. “Fallen leaves...”, dead trees and faecal waste of animals are called detritus, and consumers feeding on detritus are called detrivores. For example: ants, termites, earthworms etc. Abiotic components

Biotic components Primary consumer Herbivores

Sun

H2 O

Secondary Consumers Omnivores Carnivores Animal Parasite Scavengers

Producers Green plants bacteria

Climate

CO 2 ts

rien

Nut

Decomposers Microbes Autotrophs

Heterotrophs

Fig. 2. Interrelationship between Abiotic and Biotic Components Consumers Herbivore

Grass

Carnivores

Ants

Lizard

Fungus Decomposer

Fig. 3. Relationship between Biotic Components

Rattlesnake

1.4  Environmental Science

1.1.2 Classification of Ecosystems Ecosystem

Anthropogenic

Natural

Aquatic

Terrestrial

Crop field

Gardens

Fig. 4. Outlined Classification of Ecosystem



1. Natural ecosystem: These are the ecosystems which are self sustained and do not require any human interference. They can be (a) Terrestrial ecosystem: These include land, rain forests, deserts and grasslands. · The forest ecosystem: The ecosystem having abundance of producers or autotrophs and has high density of living organisms is called forest ecosystem. · Tropical evergreen forest: These forests receive a mean rainfall of 80-400 inches annually. These are characterized by dense vegetation with tall trees. The temperature and light remain constant throughout the year. · Tropical deciduous forests: These have an abundance of shrubs and bushes and have diverse flora and fauna. · Temperate evergreen forest: These have less number of trees with most of the plants having a feature of reduced transpiration. · Temperate deciduous forest: These forests are located in temperate regions and have sufficient amount of rainfall. · Taiga: It is mainly coniferous forest with sub zero temperatures. · The desert ecosystem: These ecosystems are those which receive annual rainfall less than 25 inches. The flora and fauna are not abundantly populated due to scarcity of vegetation, intense heat and temperature and low water availability. Shrubs, bushes, grasses, succulents, insects, camels, reptiles are the major biotic components of such ecosystems. · The grassland ecosystem: Grasslands are situated in both the tropical and temperate regions of the world. Grasslands mainly comprise of grasses with few trees and shrubs. The two main kinds of grasslands ecosystems are the savanna (tropical) and the prairies (temperate).

Ecosystem and Environment  1.5

· The mountain ecosystem: The ecosystem is mostly treeless with alpine vegetation and known for animals with fur on their body. (b) Aquatic Ecosystem: This includes oceans, rivers, and seas. This can be fresh water (river and lake water ecosystem) or marine water ecosystem (under the sea). · Such ecosystem exists in water. It encompasses aquatic flora, fauna. This can be marine ecosystem, which is one of biggest ecosystems covering around 75% of the earth’s surface with about 97% water available. This ecosystem is characterized by the presence of large number of dissolved salts and minerals in it. Another category of aquatic ecosystem is the fresh water ecosystem which includes lentic fresh water ecosystem, constituting still water bodies like lakes, ponds, dams etc., and lotic fresh water ecosystem, constituting fast flowing water bodies like rivers. As per the characteristics of landscapes, aquatic ecosystem can be Wetland (marine, estuarine, lake, riparian and marshy), Mangrove and Coral reef. 2. Artificial ecosystem: These are man created ecosystems which are maintained and controlled by human beings. There is flow of energy from and within the system. These include crop fields, aquarium, botanical gardens etc.

1.2 Trophic Levels The trophic level of an organism is the position it holds in a food chain. 1. Primary producers i.e., the organisms that make their own food from sunlight and/or chemical energy from deep sea vents are the basis of every food chain . These organisms are called autotrophs. 2. Primary consumers are animals that eat primary producers; they are also called herbivores (plant-eaters). 3. Secondary consumers eat primary consumers. They are carnivores (meateaters) and omnivores (animals that eat both animals and plants). 4. Tertiary consumers eat secondary consumers. 5. Quaternary consumers eat tertiary consumers. A typical food chain can be represented as: Autotrophs ® Herbivores ® Secondary consumers ® Tertiary consumers ® Quaternary consumers

1.3  Energy flow Energy is the ability to do work. Biological species derive their energy from the food they eat. The energy in biological systems is derived from the suns energy.

1.6  Environmental Science

Energy stored in food

Decomposers

Energy stored in food

Consumers

Chemical energy stored through photosynthesis

Herbivores

Solar Energy

Producers

It is possible by conversion of light energy into chemical energy by the process of photosynthesis. The producers carry out the process of photosynthesis in an ecosystem. The stored chemical energy in the producers is then transferred to other higher life forms through food chain. 6CO2 + 12 H2O ¾® C6H12O6 +6O2 +6H2O The flow of energy is governed by the laws of thermodynamics as under (i) Energy can neither be created nor be destroyed but can be transformed from one state to another and (ii) Transformations of energy always results in some loss of energy. The transfer of the energy is always unidirectional, that is the flow or movement of the energy is always from producers to the consumers. At every trophic level a depreciation in the energy content takes place. This occurs because the energy captured is utilized for various biological activities at each lavel.

Microbial activity

Biological Activities/Metabolism at each level

Heat loss at each level

Fig. 5. Energy Flow in an Ecosystem

1.4 Food Chain A food chain is the path by which energy passes from one living being to another. The transfer of food energy from the source in plants through a series of organisms by repeated eating and being eaten up is referred to as food chain. A food chain is a transfer of the energy that passes from producers to consumers. Energy

Sun

Producer

Grass

Primary consumer

Grasshopper

Secondary consumer

Shrew

Fig. 6. Representation of Food Chain

Tertiary consumer

Owl

Ecosystem and Environment  1.7

Types of Food Chains 1. Aquatic- Water-related food chains constituting sea plants and animals are called aquatic food chains. For example: Algae ® Larva ® Dragon fly Larva ® Fish Raccoon Phytoplankton ® Zooplankton ® Fish ® Seal ® Shark 2. Terrestrial: Land-related food chains with land plants and animals are called terrestrial food chains. Grass ® Rabbit ® Fox ® Tiger 3. Grazing food chain: The chain starts from plants and ends with carnivores, passing through herbivores. The energy is derived from the autotrophs. Ecosystems with such type of food chain are directly dependent on an influx of solar radiation. Autotrophs ® Herbivores ® Primary consumer ® Secondary consumer Plants ® Insects ® Sparrow ® Hawk Grass ® Rabbit ® Fox ® Tiger Plants ® Grasshopper ® Frog ® Snake 4. Detritus food chain: The organic wastes derived from the grazing food chain ( fallen leaves, plant parts or dead animal bodies) are termed as detritus. This chain starts from dead organic matter and ends in inorganic compounds. There are certain groups of organisms which feed on dead bodies of animals and plants are called detrivores. The energy contained in the dead organism is used in this food chain. Such ecosystems are thus less dependent on direct solar energy. These depend chiefly on the influx of organic matter produced in another system. For example, such type of food chain operates in the decomposing accumulated litter in a forest. Dead Plants ® Bacteria Dead Plants ® Wood Louse ® Black bird Dead Plants ® Mites ® Insects ® Lizard

Significance of food chain:



1. The studies of food chain help understand the feeding relationship and the interaction between organisms in any ecosystem. 2. They also help us to appreciate the energy flow mechanism and matter circulation in ecosystem and understand the movement of toxic substances in the ecosystem. 3. Food chains help to understand the affect of natural and anthropogenic disturbances on ecosystem. 4. The study of food chain helps us to understand the problems of biomagnifications (pollution).

1.8  Environmental Science

1.5 Food Web In different ecosystems there are several food chains which are existing and the food chains cannot exist independently. Any consumer cannot just feed on a single species. Therefore, the relationship of plants and animals in an environment, where several food chains are linked together with each other is called food web. The actual consumption of food and its pathway is studied through food web. A predator from one food chain may be linked to the prey of another food chain. The interlocking patterns formed by several food chains that are linked together are called food webs. For Example: Owl Kingfisher Small fish Tadpole

Shrew

Frog Water beetle

Snail

Beetle

Spider

Grasshopper

Wood mouse

Snail

Algae Green plant

Fig. 7. Examples of Food Web

1.6  Ecological Pyramids An ecological pyramid is a diagram that shows the relationship of amounts of energy or matter contained within each trophic level in a food web or food chain. These pyramids were devised by Charles Elton and are thus also called Eltonion pyramids. In a pyramid food chains are represented sequence wise with producers at the base, followed by herbivores and finally carnivores . Producers ® Herbivores ® Carnivores There are three types of ecological pyramids depending upon the number of individuals, amount of biomass and amount of energy. · Pyramid of Numbers · Pyramid of Biomass · Pyramid of Energy Pyramid of Number: The Pyramid of number shows the relationship between producers, herbivores and carnivores at successive trophic levels in terms of their numbers. It shows the number of organisms at each trophic level per unit area of an ecosystem. The diagrammatic representation of the relative decrease in the number of organisms at each trophic level in food chain is called Pyramid of number. It may be erect or inverted or spindle shaped. A spindle shaped pyramid is obtained when a large tree supports many herbivores birds which are in turn eaten up by eagle which are few in number. Other examples of pyramid of number are a pond ecosystem and grassland ecosystem.

Ecosystem and Environment  1.9

Tertiary consumers Secondary consumers Primary consumers Producers

Fig. 8. Pyramid of Number (Upright Pyramid - Grassland Ecosystem, Pond Ecosystem) Hyperparasites Parasites Herbivores Plants

Fig. 9. Pyramid of Number (Inverted Pyramid - Parasitic Ecosystem)

Carnivores Herbivores

Tree

Fig. 10. Pyramid of Number (Spindle Shaped Pyramid – Tree Ecosystem)

Pyramid of Biomass: The total amount of matter present in organisms of an ecosystem at each trophic level is is known as biomass. Pyramid of biomass records the total dry organic matter of organisms at each trophic level in a given area of an ecosystem. Pyramid of biomass may be erect or inverted or spindle shaped. As per Fig. 11 A, the total biomass of producers is more than the herbivores which is contrary to Fig. 11 B.

1.10  Environmental Science Tertiary consumers Secondary consumers

Tertiary consumers

Herbivores

Secondary Consumers

Plants

Primary consumers Producers A

B

Fig. 11. Pyramid of Biomass (A = Grassland ecosystem, B = Forest ecosystem)

Pyramid of Energy: The pyramid of energy shows the amount of energy input to each trophic level, in a given area of an ecosystem, over an extended period. This depicts the flow of energy from producers to the top consumers. It is a graphical representation of the amount of energy trapped per unit time and area in different trophic levels of food chain, with producers forming the base and top carnivores the tip. The flow of energy is always unidirectional and continuous. The energy content is expressed as Kcal/m2/yr. Of the three types of ecological pyramids, the energy pyramids give the best picture of overall nature of the ecosystem. Pyramid of energy is always ERECT.

Tertiary consumers Secondary consumers Primary consumers Producers

Fig. 12. Pyramid of Energy (Upright or Erect)

1.7 Abiotic Components The abiotic components of ecosystem include all the nonliving components of the environment. Inorganic substances like carbon, hydrogen, phosphorous, sulphur, organic compounds like carbohydrates, proteins, lipids, and climatic factors like water, soil, air and light, are the key elements. The important abiotic components are hydrosphere, lithosphere and atmosphere.

Ecosystem and Environment  1.11

1.7.1 Hydrosphere Hydrosphere is a system where water exists. We live on a planet that has more than 70% of the surface covered with water. Water containing region is termed as hydrosphere. Approximately 97% of all the water on Earth is in the oceans. The other 3% is held as freshwater in glaciers and icecaps, groundwater, lakes, soil, the atmosphere, and within life. Water is the major constituent of almost all life forms (more than 60% water by volume). The main reservoirs of water include atmospheric moisture (snow, rain and clouds), oceans, rivers, lakes, groundwater, subterranean aquifers, and polar icecaps. The importance of hydrosphere can be listed as: 1. Every biological cell is made up of water and it is required to perform all the basic metabolic activities. 2. Drinking water regulates the proper functioning of the cellular actions. 3. Water is called as universal solvent and dissolves in it various gases which are essential for the survival of living forms in water. Nutrients like nitrate, nitrite, ammonium ions and other ions are dissolved in water. 4. Water can act as a habitat for the organisms. 5. Water is used for other purposes like washing, cleaning and industrial processes. 6. Agricultural activities are dependent on the availability of water. 7. The oceans play a very important role in the climate change by absorbing the green house gases and for redistribution of the energy received from the sun. 8. Thus, hydrosphere / water helps in temperature maintenance of the earth. 9. Without hydrosphere, the other components of ecosystem cannot be maintained.

1.7.2 Lithosphere Lithosphere is the solid, rocky crust covering entire planet earth. It contains minerals, rocks and soils. It constitutes one thirds part of the Earth. The earth consists of three major zones or layers i.e., crust, mantle and core. · The Crust is composed of two types of rocks, granite and basalt. The continental crust is mostly granite (20 to 70 km thick) and the oceanic crust is basalt( ~ 8 km thick). The boundary between crust and upper mantle is called the Moho. · The Mantle is the largest layer of the Earth. The middle mantle is composed of very hot dense rock. · The Core of the Earth is like a ball of very hot molten metals. Temperature being high in this region, all the metals in this zone is in the liquid state. The outer core is composed of the molten metals like nickel and iron (3700oC)

1.12  Environmental Science

whereas the inner core of the Earth has temperature around 4300oC and pressures is huge. Due to the predominance of nickel and iron in the core, it is also called ‘nife’. Crust Moho

30 km

Upper mantle 700 km Sial layer Mantle Lower mantle

2900 km Liquid metals

Outer core

5150 km Rigid

Core Inner core

Fig. 13. Components of Lithosphere

Lithosphere can be studied under two types: 1. Oceanic lithosphere, which is related to oceanic crust and exists in

the ocean basins. It is slightly denser than the other type of lithospheres. (mean density of about 2.9 grams per cubic centimeter). 2. Continental lithosphere, which is associated with continental crust, and is much thicker than the oceanic lithosphere (mean density of about 2.7 grams per cubic centimeter). Continental crust

Sedimentary deposits

Oceanic crust 10 km

Lithosphere

100 km

Plastic asthenosphere Upper mantle (down to 670 km)

Fig. 14. Structure of Lithosphere

200 km

Ecosystem and Environment  1.13

The most distinguished aspect associated with Earth’s lithosphere is its tectonic activity. Tectonic activities are the interactions of the gigantic slabs of lithosphere called tectonic plates. These activities are responsible for Earth’s most dramatic geologic events like earthquakes, volcanoes, orogeny (mountain-building), and formation of deep ocean trenches. The importance of lithosphere can be listed as: 1. It is the area where we live. 2. It is reservoir of the earth’s resources. 3. Lithosphere serves as source for minerals and elements like iron, aluminium, calcium, copper and magnesium etc. which are required by human beings for various activities like tool making and machines. 4. Lithosphere acts a store house for fossil fuels. Fuels like coal, petroleum, natural gas are all obtained from the lithosphere. 5. It contains various nutrients required for the survival of living organisms mainly plants. 6. Lithosphere supports large oceans and rivers and lakes which are required for balanced ecosystem. 7. Geographic variations of the lithosphere affects climatic patterns.

1.7.3 Atmosphere Earth’s atmosphere is made of a mixture of gases called air. Nitrogen gas makes about 78% of Earth’s atmosphere. The second most abundant gas is oxygen, which makes 21% of Earth’s atmosphere. Atmosphere structure

On the basis of chemical and physical properties

On the basis of temperature

Troposphere

Stratosphere Mesosphere

Thermosphere

Chemosphere

Fig. 15. Structure of Atmosphere

Ionosphere

1.14  Environmental Science

Table 1.1 Principal components of Dry Air

Constituent Nitrogen Oxygen Argon Carbon dioxide Neon Helium Methane Krypton Hydrogen

Percentage by Volume 78.08 20.94 9.3 0.036 0.0018 0.00052 0.00013 0.0001 0.00005

Concentration (in ppm) 780900 209400 9300 360 18 5.2 1.3 1 0.5

The atmosphere of earth can be divided into various layers depending on the temperature. Various layers are as follows: · Troposphere: The first layer of the atmosphere is the Troposphere with tropopause as its outer limit. The troposphere goes from 0 km to 16 km. All the weather phenomena occurs in the troposphere. More than half of the air in the total atmosphere is in this layer. This layer contains the O2, N2, CO2, and H2O. The temperature of this sphere drops with altitude (positive lapse rate). · Stratosphere: The second layer is called the Stratosphere. The stratosphere extends from 16 km to 50 km. The temperature goes up with altitude (negative lapse rate). The protective ozone is present in this region which protects us from harmful UV radiations from the sun. The increase in the temperature in this region is due to absorption of the ultra-violet rays by ozone. The outer limit of stratosphere is called stratopause. · Mesosphere: The Mesosphere goes from 50 km to 90 km. In the mesosphere, the temperature drops with altitude. The temperature falls to -75oC in this sphere. The mesosphere is the coldest layer of the atmosphere. This layer contains O2+, NO+. The outer limit of mesosphere is called mesopause. · Thermosphere: The Thermosphere goes from 90 km to 300 km. In the thermosphere the temperature goes up with altitude. The thermosphere is the hottest layer of the atmosphere. Curtains of light called auroras occur in this layer. The Ionosphere is found in the thermosphere. · Exosphere: The Exosphere is the outermost layer of the atmosphere. The temperature in the exosphere goes up with altitude. Satellites orbit earth in the exosphere.

Ecosystem and Environment  1.15

10,000 km

Exosphere

690 km

Thermosphere

Mesosphere

85 km

Stratosphere Troposphere

50 km

20 km

Fig. 16. Layers of Atmosphere

Table 1.2 Major Regions of Atmosphere Layer

Altitude Temperature (km) (oC)

Chemical Species

N2, O2, CO2, H2O Life exists here

Troposphere

upto 11

15 to –56

Stratosphere

11 to 50

– 56 to –2

O3

Mesosphere

50 to 85

–2 to –75

O2+, NO+

Thermosphere 85 to 500 –75 to 1200

Feature

O2+, NO+, O+

Absorbs harmful UV radiations Meteor burns here High temperature layer

1.16  Environmental Science Earth's atmosphere

Temperature (°F) –140–120–100–80–60 –40 –20 0 20 40 60 80

120 110 100 Thermosphere 90 Mesopause

Ionosphere, magnetosphere begin

75 Percentages at selected 70 altitudes are percentages 65 of sea level pressure. 60 90 km, 0.0001% 55 50

Altitude (km)

80

45

70 Mesosphere

40

60 50

50 km, 0.1% Stratopause

30 25

40 30

Stratosphere

Ozone layer (main concentration)

20 10

35

20 Mount Everest 8.85 km, 28%

15 10

Tropopause Troposphere

5

0 0 –100–90–80 –70 –60–50 –40–30–20 –10 0 10 20 30 0 250 500 750 1,000 Temperature (°C) Pressure (millibars)

Fig. 17. Temperature Profile of Atmosphere

The importance of atmosphere can be listed as: 1. Atmosphere acts a reservoir for the water during the hydrological cycle. 2. The presence of ozone in the stratospheric region of the atmosphere makes life possible on earth. This protects living organisms from the harmful UV rays coming from the sun. 3. The availability of oxygen for the living organism is also ensured by the atmosphere. 4. The temperature is kept moderate by the atmospheric layers. Without atmosphere, nights would have been too cold and days would have been scorching. Atmospheric air molecules absorb the suns energy and maintain optimum temperature required for the survival of life on earth. 5. It provides us the medium through which the transmission of energy, heat and sound can take place.

Ecosystem and Environment  1.17

1.8 Biosphere The biosphere is a biological component of earth systems, which also includes the lithosphere, hydrosphere, and atmosphere. The term was developed by English geologist Edward Suess. It includes all living organisms on earth, together with the dead organic matter produced by them. The biosphere serves as the highest level of biological organizations, which begins with parts of cells and proceeds to populations, species, ecoregions, biomes and finally, the biosphere. It is unique as there is no other place where life exists in the universe. The biosphere supports about 3 to 30 million species of plants and animals, fungi, single celled prokaryotes like bacteria, and single celled eukaryotes like protozoan. No biosphere has been detected outside the earth.

Biosphere

Hydrosphere

Lithosphere

Atmosphere

Fig. 18. Relationships between Components of Ecosystem

1.9 Biogeochemical cycles A biogeochemical cycle is a pathway by which a chemical matter moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) components of  the Earth. The exchange of chemical nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc. taking place through the biological and physical world is known as biogeochemical cycle. Some of the major biogeochemical cycles known in nature are carbon cycle, nitrogen cycle, oxygen cycle, water cycle, phosphorus cycle and sulphur cycle. Biogeochemical cycles are basically of two types: · Gaseous cycles like carbon (as carbon dioxide), oxygen, nitrogen cycles etc. In gaseous cycles, the elements have a main reservoir in the gaseous phase, and the reservoir pool is the atmosphere or water. Gaseous cycles are well buffered cycles and do not get disturbed owing to their large capacity to adjust. · Sedimentary cycles like sulphur, phosphorus cycles etc. In sedimentary cycles, the elements main reservoir pool is lithosphere and the biogenetic materials involved in circulation are non-gaseous. Such cycles gets easily disrupted by environmental changes, since the bulk of the nutrients remains immobilized in the earth.

1.18  Environmental Science

1.9.1 Carbon Cycle

Fig. 19. Carbon Cycle Combustion

Fuel

Respiration & Metabolism

CO2 in atmosphere and dissolved in water

Photosynthesis

Decay Respiration & Metabolism

Green plants

Death

Animals

Fig. 20. Basic Carbon Cycle Flow Diagram

Carbon is a very important element, as it makes up organic matter in the ecosystem. Carbon constitutes about 49% of the dry weight of the organism. Thus, carbon cycle is an essential biogeochemical cycle. The carbon cycle naturally consists of two parts, 1. Terrestrial which involves the movement of carbon through terrestrial ecosystem, and 2. Aquatic including movement of carbon through marine ecosystems. The cycle consists of two basic processes 1. The non biological process which includes combustion, volcanic eruption, salt formation etc. 2. The biological process constituting photosynthesis and respiration.

Ecosystem and Environment  1.19

Carbon enters the atmosphere as carbon dioxide (0.03% in air) during the process of respiration and combustion. Carbon dioxide is absorbed by the autotrophs (producers) to make carbohydrates (photosynthesis). Animals (consumers) feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide, formed during respiration. The animals and plants eventually die. The dead organisms are eaten by decomposers and the carbon of the dead bodies is returned to the atmosphere as carbon dioxide. The fossilized plants and animals are available as fossil fuels for combustion thereby releasing carbon dioxide to the atmosphere. In the aquatic carbon cycle marine animals changes carbon in their diet to calcium carbonate for making shells. Over time the shells of dead organisms collect on the seabed and form limestone. Due to earth’s movements this limestone may eventually become exposed to the air where it’s weathered and the carbon is released back into the atmosphere as carbon dioxide. Erosion and dissolution also returns the carbon of the limestone to the living carbon cycle. Volcanic action also releases carbon dioxide.

1.9.2 Nitrogen Cycle Nitrogen is one of the primary nutrients significant for the continued existence of all living organisms. It is a necessary component of many biomolecules like proteins, DNA, and chlorophyll. Although nitrogen is abundant (79%) in the atmosphere as dinitrogen gas (N2), it is largely unapproachable in this form to most organisms. The availability of nitrogen is ensured to the producers (plants) only after its conversion from dinitrogen to ammonia (NH3) or oxides of nitrogen. The process of converting N2 into biologically available nitrogen is called nitrogen fixation. Nitrogen fixation is performed by microorganisms (biological fixation) which convert nitrogen into inorganic compounds. Some nitrogen-fixing organisms are free-living (Azobactor, Clostridium) while others are symbiotic nitrogen-fixers, which require a close association with a host to carry out the process. For example, certain species of  Rhizobium, are symbiotic nitrogen-fixing bacteria. Some blue green alga like Nostoc, Callotrix, Anabena are also capable of fixing nitrogen. Nitrification is the process that converts ammonia to nitrite and then to nitrate. There are two distinct steps of nitrification that are carried out by distinct types of microorganisms. The first step is the oxidation of ammonia to nitrite (NH4+ to NO2– ), which is carried out by microbes known as ammoniaoxidizers (Nitrosomonas, Nitrosospira, and Nitrosococcus). The second step in nitrification is the oxidation of nitrite (NO2–) to nitrate (NO3–), carried out by Nitrospira, Nitrobacter and Nitrococcus. Denitrification is the process that converts nitrate to nitrogen gas, thus returning it to the atmosphere. This is done by denitrifying bacteria like Pseudomonas and Micrococcus etc. When an organism excretes waste or dies, the nitrogen in its tissues is in the form of organic nitrogen (e.g. amino acids, DNA). Various fungi and prokaryotes then decompose the tissues and release inorganic nitrogen back into

1.20  Environmental Science

the ecosystem as ammonia in the process known as ammonification. This ammonia then becomes available for uptake by plants and other microorganisms for growth. The nonbiological fixation or physical fixation of nitrogen involves the reaction between nitrogen, hydrogen and oxygen, using high amount of energy. This enormous requirement of energy is catered by the cosmic radiation, lightening, thunderstorms etc. The resulting ammonia and nitrogen oxide then reaches the earth through rain water.

Fig. 21. Nitrogen Cycle

1.9.3 Hydrological Cycle or Water Cycle 5. Transportation 5. Transportation 4. Condensation

6. Precipitation

7. Deposition 4. Condensation 6. Precipitation

3. Sublimation

9. Showmelt runoff

1. Evaporation 9. Surface flow

1. Evaporation 9. Surface Flow

8. Infiltration 10. Plant uptake 9. Groundwater flow

Fig. 22. Hydrological Cycle

8. Percolation

Ecosystem and Environment  1.21

Hydrological cycle is one of the most important biogeochemical cycles in the biosphere. It is essential for maintaining the availability of earth’s water supply. The water cycle or hydrological cycle is a continuous cycle where water evaporates, travels into the air and becomes part of a cloud, falls down to earth as precipitation, and then evaporates again. This repeats again and again in a neverending cycle. Water keeps moving and changing from a solid to a liquid to a gas, over and over again. Following are the major processes involved in it: · Evaporation: This is the process of conversion of liquid water to a gaseous state. Most of the evaporation process occurs from the ocean. · Transpiration: This is the biological process that transfers of water from the plant to the atmosphere as water vapour through numerous individual leaf openings (stomata). · Condensation: This is the process by which water vapour changes its physical state from a vapour, most commonly, to a liquid. Water vapour condenses onto small airborne particles to form dew, fog, or clouds. · Precipitation: This is the process that occurs when water particles fall from the atmosphere and reach the ground in the form of rain, hail or snow. · Infiltration is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. When the rate of precipitation is more than the rate of infiltration, water moves as runoff water and collects in ponds, lakes, rivers, streams, oceans or ditches etc. · Percolation: This is the movement of water though the soil, and it’s layers, by gravity and capillary forces. The prime moving force of groundwater is gravity.

1.9.4 Phosphorus Cycle Phosphorus is present in living system as phosphates. It is required for the growth and development of organism. It is an important constituent of RNA and DNA. It also forms exoskeleton of insects. Rocks, minerals and natural phosphorus deposits are the reservoirs of phosphorus. Phosphorus cycle is a type of sedimentary biogeochemical cycle where phosphorus moves through the lithosphere, hydrosphere and biosphere. It reaches the soil through rain or any other natural process like weathering. From soil, plants absorb the inorganic nutrients and convert them to phosphates. The organic form of phosphates in the soil can be converted to inorganic form by the process of mineralization by the bacteria. Animals consume the plants and phosphates reach their biological system. Decomposers release the phosphorus into the soil through the process of decomposition.

1.22  Environmental Science

Rocks/ Minerals Decomposition

Run off/Weathering

ATP

Soil

Metabolism by plants and animals

Decomposition

Organic phosphate

Inorganic phosphate

Absorption by plants

Fig. 23. Phosphorus Cycle

1.10 Biodiversity Biodiversity is the variety of flora and fauna on earth. It includes all life forms- from the unicellular fungi, protozoa and bacteria to complex multicellular organisms such as plants, birds, fishes and mammals. The number of species of plants, animals, and microorganisms, the enormous diversity of genes in these species, the different ecosystems on the planet, such as deserts, rainforests and coral reefs, are all part of a biologically diverse Earth. According to the United Nations Earth Summit (1992) “Biological diversity is the variability among living organisms from all sources, including, ‘inter alia’, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part, this includes diversity within species, between species and of ecosystems”.

1.10.1 Types of Biodiversity The concept of biodiversity is studied at three different hierarchical levels: 1. Genetic biodiversity 2. Species biodiversity and 3. Ecosystem biodiversity

Ecosystem and Environment  1.23

Ecosystem diversity Species diversity

Genetic diversity

Fig. 24. Concept of Biodiversity

Fig. 25. Concept of Biodiversity

Genetic biodiversity: Diversity among the species arising due to the variation in the genes is called as genetic diversity. At finer levels of organization, biodiversity

1.24  Environmental Science

includes the genetic variation within each species. Within any given species, there can be several varieties, strains or races which slightly differ from each other in one or more characteristics such as size, shape, resistance against diseases, pests, insects, etc. These differences may arise due to diversity of the genetic makeup possessed by the organism arising because of chromosomal alterations, gene linkages, and natural modification of the genetic sequence. It may also arise due to environmental influence on individual organisms or its generation due to genetic or chromosomal mutations. Genetically differing life forms correspond to the richness of biodiversity. Continuously evolutionary changes lead to formation and survival of new species on this earth. The diversity in the genetic make-up of a species is termed as the genetic biodiversity. Species biodiversity: The richness of the range of unicellular fungi, protozoa and bacteria to complex multicellular organism like plants and animals is called species diversity. In other words, the richness of species in an ecosystem is called as species biodiversity. Species diversity is measured by relative chance of seeing the species in an ecosystem. It means that species very much different from each other is more diverse than those similar to each other. Ecosystem biodiversity: It is the variation of ecosystems on the earth where continuous interaction between the biotic and abiotic components occurs. It is the part of natural continuum. Ecosystems represent parts of a highly variable natural range and perception of change within this continuum is highly scale dependent. Ecosystem diversity includes variations in ecosystem like terrestrial and aquatic ecosystems such as deserts, forests, grasslands, wetlands, oceans, ponds, mountains, aerial etc. Landscape biodiversity: It refers to the size and distribution of several ecosystems and their interactions across a given land surface.

1.10.2 Measurement of Biodiversity Diversity refers to the richness of species in a community. Measurement of biodiversity involves collecting information on the number of species (richness) and the evenness of the species, using various mathematical indices. Diverse communities are thought to have improved stability, increased output, resistance to invasion and resistance against natural and anthropogenic disturbances. 1. Alpha diversity: It mainly reflects the richness of the species. It is measured for a community and is compared with species richness in different ecosystems.

High beta diversity

Low beta diversity

Fig. 26. Alpha Diversity of Two Communities

Ecosystem and Environment  1.25



2. Beta diversity: It is the variation in the richness of the species with changes along an environmental location. In case the species composition changes with the change in the location then beta diversity is high, but if beta diversity is low it suggests that the variation in the richness of the species does not exist and a single species is occupies the complete geographical location under study or investigation.

High beta diversity

Low beta diversity

Fig. 27. Beta Diversity in Mountainous Habitat



3. Gamma diversity: It is the rate of occurrence of the number of species with distance between the sites of similar habitat. It is applicable on larger geographical scale and also includes the rate at which newer or additional species are encountered. Variation in species diversity with change in area

Fig. 28. Gamma Diversity in Large Geographical Area

Significance of measurement of biodiversity The data helps in understanding the influence of environmental change on species in an area or a larger area and possible tracing out of the factors responsible for the change. The measurement of biodiversity becomes highly essential due to increasing anthropogenic influence on the organism’s habitat and ecosystem.

1.10.3 Importance of Biodiversity The varieties of organism present on the earth are of great importance for an ecosystem. They are directly or indirectly related to the survival of human beings and living organism and also are responsible for the overall balance of the earth’s ecosystem. The contribution of biodiversity to the earth and human beings is immense and without it, existence of this world cannot be imagined. The importance of biodiversity can be summed as follows:

1.26  Environmental Science

1. Economic services: · Medicinal value: The wide variety of living organisms, both plants and animals provide us with many useful drugs and medicines. There are still many plants and organisms which are still unexplored for their medicinal value. Some of the important medicinal products are Willow bark used for Aspirin production, Bee venom used for arthritis treatment, Penicillin and Tetracycline used as antibiotic etc. The plant originated medicines are not only curative but are much safer without any side effects. Biodiverse plants are applicable not only for treatment of diseases but also as air purifiers and even in herbal cosmetics and beauty products. · Fuel: The use of plants as fuels is one of the direct consumptive values of plants. A wide variety of plants are important sources of traditional fuels. Fuels derived from plants are now days known as biofuels. The best examples are corn, sugar cane etc. · Timber: Wood is one of the most important substances used and is economically very crucial in terms of energy. It is used for making furniture, household articles and construction of houses. Wood is an ecofriendly alternative available to us, ranging from very feeble plants to strong and stout trees. · Food: Availability of food is one of the basic needs of all living organisms whether animals or human beings. Mother Nature has provided enormous variety of food items of plants and animal origin. The biodiversity in vegetarian and animal diet provides a wide range to the living organism for their survival in a variety of land forms, climatic conditions or geographical areas, agricultural flexibility, taste choices etc. Various species are hunted (e.g. antelopes, birds), fished (e.g. cod, tuna fish), and gathered (e.g. fruits, berries, mushrooms), as well as cultivated for agriculture (e.g. wheat, corn, rice, vegetables) and aquaculture (e.g. salmons, mussels), for the purpose of food. Thus, biodiversity plays a crucial role in human nutrition through its influence on world food production, as it ensures the sustainable productivity of soils and provides the genetic resources for all crops, livestock, and marine species harvested for food. 2. Ecological services: Plants are among the one of the most precious gifts nature has given us. Plants and their varied forms perform multiple tasks and are valued for the below: · Balance in nature: The complex but essential linking of the variety of available life forms leads to an establishment of a balanced ecosystem where circulation of the nutrients is continuously facilitated. These nutrients are required for a balanced ecosystem. · Biological productivity: The rate of biomass production is calculated in terms of biological productivity. Productivity can either be primary

Ecosystem and Environment  1.27

or secondary. Greater the biodiverse forms on earth greater will be the rate of biological productivity. · Regulation of climate: All the living organisms comprise of carbon which is continuously cycled form atmosphere to the organism through photosynthesis and from organisms to atmosphere through the decomposition process. The amount of carbon in the atmosphere available as carbon dioxide is globally beneficial for the regulation of climate. Thus, biodiversity contributes to carbon sequestration and global climate change. · Degradation of waste: Microorganisms are important members of the biodiversity family which function as cleaners of the environment, by performing the decomposition process. · Cleaning of air and water: Plants absorb carbon dioxide and liberateoxygen acting as the purifiers of air. The importance of plants can be understood by the fact that survival of living organisms is not possible in anoxic environment and oxygen is continuously made available to the organism through atmosphere by the plants during carbon cycle. Plants not only convert the harmful carbon dioxide to oxygen but also act as absorbers of dust and other pollutant gases. The extent of noise can be minimized in highly vegetated areas, as plants act as sound absorbers too. Thus, plants are natural air purifiers, conditioners and sound absorbers. The great variety of plant species enables these multifunctional features of the plants. · Cycling of nutrients: Biogeochemical cycles in the ecosystem help in continous recycling of the minerals which are essential for existence. Plants play a key role in such cycles. For example: transpiration of water through the stomata of the leaves of the plants acts as a contributor to the water vapour in the atmosphere, which later forms clouds and rain. Some varieties of plants transpire less and other transpire more. Thus, various geographical regions with varied vegetation contribute to the weather changes and climate regulation. · Control of potential pest and disease causing species: Various living forms have pest controlling ability and act as natural pesticides. One of the most common microbial biopesticide is Bacillus thuringiensis. Certain plant materials like corn protein, garlic oil, and black pepper can also control pests without killing them. · Detoxification of soil and sediments: Detoxification of soil and sediments, stabilization of land against erosion and maintenance of soil fertility, are some of the attributes of biodiversity which provide suitable conditions for living organisms. · Water holding capacity: Plants not only transpire water but have excellent capacity to hold water through their roots / stems / leaves.

1.28  Environmental Science

This ensures the existence of living organism in the soil ecosystem, characteristic of humus, availability of water in the underground regions, flourishing or productivity of the farm lands, degradation of the rocks for soil formation etc. Certain species of plants hold water more and make it available for the organisms surviving in the desert region or water scarce locations. 3. Other benefits: · Recreation: People appreciate the aesthetic importance of the biodiversity and often chose to spend their leisure time with nature and its biodiversity forms. · Education and Research: Plants and animals are always a great source of education to society. They provide a rich source of inspiration for folk, art, architecture and informal education. · Traditional value: Plants and animals are often used as symbols, for example in flags, paintings, sculptures, photographs, stamps, songs and legends. They are also important religiously. Biodiversity is culturally related to various civilizations. People value emotionally and spiritually various plants and animals. For eg: Tulsi (Ocimum sanctum) is valued for its purity, neem (Azadirachta indica) for its air purifying ability. Many festivals link up trees like banyan (Ficus benghalensis), pipal (Ficus religiosa), and animals like, tiger, cow and even birds like crow, and identify them as traditionally important and essential forms. People value biodiversity ethically, culturally, religiously and socially.

1.10.4 Threats to Biodiversity The elimination of species is a natural process but the rate of extinction is quite slow. In the modern era, due to human actions, species and ecosystems are threatened with destruction to an extent rarely seen in the earth history. In the last 150 years, the rate at which species are disappearing is about thousands per decade. The main causes of extinction of the species are: · Population risk: Variation in the population rates can cause species to become extinct. Too much or too little population of any species can alter the balance of food chain, food web and the ecosystem as a whole. · An environmental risk: It refers to the changes in the environmental conditions surrounding the organism. Any alteration may not be adapted by the species and can lead to extinction. A changing global climate threatens species and ecosystems. The distribution of species (biogeography) is largely determined by climate, as is the distribution of ecosystems and plant vegetation zones (biomes). · Natural calamity: It includes fires, storms, floods, earthquakes, volcanic eruptions which can cause local extinction of most life forms.

Ecosystem and Environment  1.29



· Genetic risk: Changes in the species genetic level, mutations, chromosomal aberration also contribute to the reduction in the genetic variability. · Human actions which are responsible for the extinction of biodiversity through various actions include agricultural expansion, industrialization, hunting, recreational use of animals etc.



· Habitat loss/degradation/fragmentation is an important cause of known extinctions. Habitat damage occurs especially due to the conversion of forested land to agriculture, development of human settlements, industry etc. Habitat fragmentation is the process where a large land is divided into two or more fragments. This leads to high infant mortality, environmental hardships leading to death of biodiversity forms.



· Invasion of non-native species or Introduction of exotic species is an important and often-overlooked cause of extinctions. Organisms introduced into habitats where they are not native are termed as exotic species. They act as biological pollutants and cause large scale destruction.  The major contributor to depletion and extinction is the unnatural introduction of species into new environments. For example, Kudzu is a plant from Japan. It was brought to the US to help stop soil erosion. Kudzu is now a huge problem in some southern states. The plant grows very fast and can completely take over an area and out-compete native plants for space and sunlight.



· Pollution from chemical contaminants certainly poses a further threat to species and ecosystems. While not commonly a cause of extinction, it likely can be for species whose range is extremely small, and threatened by contamination. The most common causes are pesticides, industrial effluents, and emissions from automobiles. · Commercial hunting both legal and illegal (poaching), is a principal threat. Snowy egret, passenger pigeon, heath hen in USA are examples of animals, which are under such a threat. Poaching is the illegal taking of wildlife. Activities that are considered under poaching include killing an animal out of season, without a license, with a prohibited weapon, or in a prohibited manner. Wild life is sold for live specimens, folk medicines, furs, hides, skins ivory, horns etc. Threatened species: Threatened species is any species whether animals, plants, birds or microbes which is vulnerable to extinction in the near future. These are studied under three main categories depending upon the extent of threats to the species: 1. Endangered species: Those species which are likely to get extinct if the factors responsible continue to operate, are called endangered species. These are species which are greatly affected by the environmental influence or degradation and their population has reduced to a critical level as they

1.30  Environmental Science



2.



3.

could not survive the extreme alteration in the environmental which was once suitable for their survival. It includes eastern gorilla, grey parrot, ornate ground snake, siberian white crane etc. Vulnerable species: There are certain species which are under threat by the ever-changing environmental conditions and if the conditions would continue to remain contaminated their number may also reduce to a considerable extent and may reach to a critical level. They may be in immediate danger of extinction. Examples, giraffe, giant panda, plains zebra, tibetan antelope etc. Rare species: Rare species are those whose number is quite less naturally in this world. Their existence is limited to a very restricted habitat or geographical area or isolated area. They are not easily seen species. They are valued for their uniqueness. Rare species are also under risk because of the global environmental change. They may not be vulnerable or endangered but are definitely affected by the changing environmental pattern and climate and temperature. Giant panda, cheetah, california condor, wild bactrian camel, black soft shell turtle etc. All the above species are said to be threatened species and are in need of conservation. The IUCN Red List (Red data list, 1964) of Threatened Species is the world’s most broad account of the global conservation status of biodiversity. It uses a set of worldwide relevant criteria to evaluate the extinction danger of various species and subspecies. The aim is to make the public and policy makers aware about the urgency of conservation issues.



60 50 40 Vulnerable 30

Endangered

20

Critically endangered

10

sh es In se ct M s ol lu se s Pl an ts

an s

Fi

s ile

bi ph i

s Bi rd

R

ep t

Am

M

am

m

al s

0

Fig. 29. Percentage of Threatened Species According to IUCN Red List 2006

Ecosystem and Environment  1.31

Table 1.3 List of Threatened Species Worldwide According to IUCN Red List



Threatened species Tortoise Pelican Tiger Capped Monkey Black buck Sarpgandha Sandal wood tree Pitcher plant Philippine eagle Alagoas curassow Sea turtle

Threatened category Endangered Endangered Endangered Endangered Endangered Endangered Endangered Endangered Endangered Extinct in wild Vulnerable

Black Rhino Savanna elephant Whale shark

Critically endangered Vulnerable Vulnerable

Scientific name Testudo graeca Pelecanus onocrotalus Panthera tigris Trachypithecus pileatus Antilope cervicapra Rauwolfia serpentina Santalum album Nepenthes khasiana Pithecophaga jefferyi Mitu mitu Cheloniidae and Dermochelyidae families Diceros bicornis Loxodonta africana africana Rhincodon typus

4. Endemic species are those which are specifically found in a locality and not in any other region in the world (endemism). They are known for their uniqueness and are usually found in isolated, restricted faraway places having least external or human influences. There are two subcategories of endemism: paleoendemism and neoendemism. Paleoendemism refers to species that were widespread in the past but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen. Endemic species includes orange-breasted sunbird (Nectarinia violacea), Nilgiri leaf monkey, Bicolored frog (Clinotarsus curtipes) etc.

1.10.5 Conservation of Biodiversity Conservation is the protection, preservation, management, or restoration of wildlife and natural resources such as forests and water. Conservation refers to the global management of the human use of the biosphere for greatest sustainable benefit to the present generation while maintaining its potential to meet the needs and aspirations of the future generations. It aims at maintenance of ecological balance and life supporting system and preservation of the genetic or species diversity. It also aims at sustainable utilization of the bio diverse forms and ecosystem. Through the conservation of biodiversity the survival of many species and habitats which are threatened due to human activities can be ensured. Other reasons for conserving biodiversity include securing valuable natural resources for future generations and protecting the well being of ecosystem functions.

1.32  Environmental Science

Out of the several aims of conservation of biodiversity some of them have been listed below: 1. To preserve biological diversity involving prevention of species extinction and preservation of characteristics ecosystems and landscape. 2. Avoid unplanned development which would lead to breakdown of ecological as well as human laws. 3. To carry on careful and scientific exploitation of natural resources. 4. To maintain essential ecological processes and life support system. 5. To ensure the preservation of aesthetic and recreational aspects of environment. Biodiversity can be conserved in two ways in-situ and ex-situ. Biodiversity conservation

In-situ conservation

National parks

Sanctuary

Ex-situ conservation

Biosphere reserve

Seed bank

Botanical garden

Zoological parks

Aquaria

Fig. 30. Biodiversity Conservation Strategies

In-situ conservation (on-site conservation): It is the conservation of

genetic resources in natural populations of  plant or animal species, such as forest genetic resources in natural populations of tree species. It is considered the most appropriate way and the best strategy for conserving biodiversity. · It is the process of protecting an endangered plant or animal species in its natural habitat, either by protecting or cleaning up the habitat itself, or by defending the species from predators. · It is applied to conservation of  agricultural biodiversity in agro ecosystems by farmers, especially those using unconventional farming practices. · One benefit of  in-situ conservation is that it maintains recovering populations in the surrounding where they have developed their distinctive properties. · In situ conservation is applicable to wild animals and limited human activity is allowed. · Another is that this strategy helps ensure the ongoing processes of evolution and adaptation within their environments. · The gene pool of the organism or biodiverse forms does not get stagnant. · In-situ conservation is cheaper method than ex-situ conservation as it involves the protection of the organism in the natural ecosystem.

Ecosystem and Environment  1.33

· It is dynamic in nature and carried out as in natural habitats. · It is a long term conservative method. · It includes national parks, sanctuaries and biosphere reserves. National park is a legislated and confined reserve area where wildlife is taken care of for its betterment, without any human or external interference except for the buffered zone. It aims at providing a habitat for animals which are threatened and have economical, aesthetic and cultural and social importance. The area is thus suitably selected and legislatively governed where wild animal biodiverse forms can be conserved. For example: Yellow stone in USA, Royal in Australia and Kanha national park in India. A sanctuary is a greater geographical area than the national park where human or biotic interference is the form of grazing agriculture forestry timber gathering etc is permitted. A biosphere reserve is an ecosystem oriented conservation method where multiple land use is possible including conservation of wild animals, tribal inhabitants, domestic animals etc.



Human settlement Buffer zone Protected area

Fig. 31. Biosphere Reserve Zones

Table 1.4 Protected Areas in India

Conservation type/ Protected areas National parks

Number

Examples

89

Kaziranga national Park, Corbett National park, Gir, Bandipur, Hazaribagh National park Annamalai sanctuary, Chilka lake bird sanctuary, Manas wildlife sanctuary, Periyar sanctuary Nanda devi, Pachmari, Nilgiri, Sunderbans

Sanctuaries

492

Biosphere reserves

13

The motive of in-situ conservation gets diluted when activities like tourism increase the extent of interference with natural system.

1.34  Environmental Science

Ex-situ conservation (off-site conservation): Certain species cannot survive well in their natural ecosystem, due to some changes in it due to various reasons like genetic drift, inbreeding, environmental degradation, decreasing habitat quality, competition, overexploitation etc. In such conditions the organisms find it difficult to cope up, their population declines and they come to verge of extinction. Such species can be then only be protected through ex-situ conservation where the conservation of species occurs away from the natural habitat under human supervision. Ex-situ conservation is usually used as a last resort, when a population has become so small or so endangered that extinction is considered inevitable. The conservation involves collection of the endangered species, breeding under controlled or captivating conditions and flourishing of the same in zoos, gene farms, aquaria, arboretum, botanical gardens, seed banks etc. The conservation method provides better assurance for the survival of the protected species, since it takes care the food, shelter, habitat, health etc. The same techniques provides an advantage of the improving the traits of the organism or plants through Genetic engineering. · It is the process of protecting an endangered species of plant or animal outside its natural habitat; for example, by removing part of the population from a threatened habitat and placing it in a new location, which may be a wild area or within the care of humans. · Conservation comprises some of the oldest and best known conservation methods. It also involves newer methods. · It is the conservation of the life forms under human supervision and care. · Ex-situ conservation is good for species having small remaining populations. · It deprives the organism the opportunity to adapt to ever changing natural environment. · The gene pool of the organism gets stagnant and new life forms cannot evolve. · It needs financial investment for maintaining proper living environment for the organisms. · It is static in nature. · It includes zoo, gene pools, botanical gardens, seed banks etc. Although the method is quite favoured for the protection of endangered species but it deprives the organism the opportunity to adapt to everchanging environment. Thus, the gene pool gets stagnant. Few species get benefitted through this but it is quite expensive as compared to in-situ strategy of conservation.

Ecosystem and Environment  1.35

Review Questions

1. 2. 3. 4. 5. 6. 7. 8. 9.

Discuss briefly about the elements of the environment. Explain various components of an ecosystem. How are they interrelated? What is the role of decomposers in ecosystem? Explain the concept of food chain and food web. Explain energy flow in an ecosystem. Discuss ecological pyramids. Why pyramid of energy is always erect? What is atmosphere? Explain the temperature profile of the atmosphere. Explain all the biogeochemical cycles with neat diagrams. Define biodiversity. Write the major factors responsible for loss of biodiversity. 10. Differentiate between in-situ and ex-situ conservation.

2

Energy

Energy is the most fundamental requirement of our universe. All the living organisms require energy for growth and movement. The word ‘Energy’ has its origin from the Greek word, “Energeia”, meaning activity or operation. The ability of a system to perform work is called energy. It is the property of an object which can be transferred to different objects or can be converted into some other form, but can neither be created nor be destroyed.

2.1  Types of Energy Energy primarily exists in two basic forms, Potential energy and Kinetic energy. Potential energy

Kinetic energy

Kinetic energy

Fig. 1. Types of Energy

Potential energy is the energy which is possessed by any object in its stationary state i.e., it is the stored energy. It can be chemical, nuclear, gravitational or mechanical in nature. Chemical energy refers to the energy stored in the chemical bonds between two atoms. This stored energy is released and absorbed when bonds are broken and new bonds are formed during chemical reactions. Nuclear energy is the energy present in the nucleus or core of an atom. When the nucleus splits nuclear energy is released in the form of heat energy and light energy (Nuclear fission). Nuclear energy is also released when nuclei collide at high speeds and join to form larger nucleus (Nuclear fusion). Energy associated with the gravitational field is gravitational energy and mechanical energy is the energy acquired whenever work is done on an object. Kinetic energy is the energy due to the motion of an object. We can feel the kinetic energy of moving atoms as temperature or heat energy. Heat and thermal energy are directly related to temperature. Heat energy can also be produced by

2.2  Environmental Science

friction. This can cause changes in the temperature and phase of any form of matter. Electric energy is the kinetic energy of moving electrons, the negativelycharged particles in atoms. Energy conversion is the process involving transformation of one form of energy into another. There are numerous examples portraying the conversion of one form of energy into another. In an automobile engine, fuel is burnt to convert chemical energy into heat energy. This heat energy then gets changed into mechanical energy. In a battery, chemical energy is converted into electromagnetic energy. The mechanical energy of a waterfall is converted to electrical energy in a generator. Even the natural processes taking place involve the conversion of one form of energy into another. For example, green plants convert the sun’s energy (electromagnetic) into starch and sugar (chemical energy).

2.2  Classification of Energy Resources Energy resources are the sources of energy which are vital for the economic development. These energy resources and be segregated into various categories as under: 1. Based on origin Primary energy resources: Primary energy is an energy form naturally found which has not been subjected to any conversion or transformation process. It is energy contained in raw fuels, and also includes other forms of energy received as initial input to any system. Secondary energy resources: These energy resources are obtained from primary sources. Secondary sources of energy are used to store, move, and deliver energy in an easily usable form, for example petrol or gasoline derived from crude oil, electrical energy from coal burning, hydrogen obtained by electrolysis of water etc. 2. Based on Use Commercial sources of energy: These are available in the market at definite price; example electricity and gas are termed as commercial fuels. Non-commercial source of energy: Firewood, cow dung, and vegetable wastes can be collected and used as energy sources which are non commercial and are traditionally gathered. 3. Based on the Extent of Exploration Conventional sources of energy: Energy that has been in use from ancient times is known as conventional energy. Crude oil and natural gas are termed as conventional sources of energy. Non-conventional source of energy: These are those energy sources that are natural, inexhaustible and restorable. These are resources whose potential still needs to be explored. For example: solar, wind, geothermal, ocean, and hydrogen energy.

Energy  2.3

4. Based on Renewability Renewable energy sources: Energy that comes from a source that’s constantly renewed, such as the sun and wind, and can be replenished naturally on human time scale is called renewable energy. Examples include: solar, wind, biomass and hydropower. Currently, less than 2% of the world’s electricity comes from renewable resources. Non-Renewable energy sources: Energy from the ground that has limited supplies, either in the form of gas, liquid or solid, are called nonrenewable resources. They cannot be replenished in a short period of time. Examples include: oil (petroleum), natural gas, coal and uranium (nuclear). Oil, natural gas and coal are called “fossil fuels” because they are formed from the organic remains of prehistoric plants and animals. Energy resources

Based on origin

Based on Use Based on exploration

Commercial

Primary Non-commercial Conventional

Secondary

Based on renewing ability

Non-conventional

Renewable

Non-renewable

Fig. 2. Classification of Energy Resources

2.3 Fossil Fuels Fossil fuel is a general term used for buried combustible geological deposits of organic materials, formed from decayed prehistoric plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth’s crust over hundreds of millions of years. Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. Different types of fossil fuels are formed depending on the combination of animal and plant debris present, how long the material has been buried, and what conditions of temperature and pressure existed during decomposition.

Formation of fossil fuels Coal was formed from the dead remains of trees, ferns and plants that lived 300 to 400 million years ago. As the trees and plants died, they sank to the bottom of

2.4  Environmental Science

the swamps of oceans. They formed layers of a spongy material called peat. Over many hundreds of years, peat was covered by sand, clay and other minerals, and more rocks piled on top of it which pressed down the peat and turned it into coal. Time, Temperature, Pressure Peat

Lignite

Bituminous

 High moisture content  Least carbon content  High ash content  Least calorific value

Anthracite  Least moisture content  Purest form  High carbon content  Less ash content  High calorific value

Fig. 3. Types of Coal

Oil and natural gas were created from organisms that lived in the water and were buried under ocean or river sediments due to some natural process. Extreme heat and pressure cooked the organic material under layers of silt. In most areas, thick liquid called oil formed first, but in deeper, hot regions underground, the decomposition and metamorphic process continued until natural gas was formed. COAL

FOSSIL FUEL FORMATION

It took at least millions of years for coal to form-from land plants-huge ancient fern forest that existed over 300 millions years ago.

OIL & GAS

It took at least a millions years for oil and gas to form from ocean plants, like phytoplankton and algae, hundreds of millions of years ago.

Huge forests grew 300 million years ago covering most of the land.

Marine plants and animals die and sink to the bottom of the seabed.

The vegetation dies and forms peat.

Peat is compressed to form lignite.

Further compression forms bituminous coal.

Eventually anthracite forms.

The plant and animal layer gets covered with mud.

Over time, more sediment creates pressure, compressing the dead plants and animals into oil.

Oil moves up through porous rocks and eventually forms a reservoir.

Fig. 4. Formation of Fossil Fuels

Advantages

1. Fossil fuels are easily combustible and have high Calorific value. Calorific value is the amount of energy/heat released when unit quantity of fuel

Energy  2.5



2.



3.



4. 5.

undergoes combustion. On burning coal, petroleum derivatives or gas produces large amount of energy is released in comparison to other non conventional energy resource. This makes them one of the highest used energy sources even today. Fossil fuels are portable and can be easily stored and transported from one place to another. The reservoirs of fossil fuels are uncomplicated to locate due to establishment of advanced equipment technology, refineries process and extraction procedures. About 90% of the world’s economy is reliant on the utilization of fuels. Fossil fuels generate employment for millions of people in mining, oil industries, transportation etc.

Disadvantages





1. Pollution is one of the greatest disadvantages associated with fossil fuels. 2. Burning of fuels releases carbon dioxide in the atmosphere which is responsible of Green house effect. 3. Pollutants produced from the fossil fuel burning act as precursors of acid rain and ozone layer depletion. 4. Most of the nations are dependent on Middle East countries for the availability of oil and natural gas for constant supply of these resources. About 40% share of the world oil production is in hold of organization of petroleum exporting countries (OPEC). This results in world wide price fluctuations, social inequality and economic instability. 5. These are non renewable in nature and will tend to get depleted. 6. They cannot be replenished as their formation takes millions of years. 7. As the economy of the world mainly depends on the fossil fuels, their over exploitation has made the extraction process expensive currently. 8. Fossil fuels are housed deep within the earth’s surface, making acquisition difficult and extremely dangerous for those who work in this industry. 9. Transportation and storage of fuels is risky, especially gas. Use of natural gas can cause unpleasant odors and other problems especially with transportation.  10. During the coal extraction process a wide area of productive land is destroyed. The process of mining of coal or extraction of oil and gas is very perilous, complex and dangerous.

2.4 Biomass Biomass is the living matter derived from living or its residues and includes waste from agriculture, forestry, municipal and industrial waste like paper and wood

2.6  Environmental Science

mills, landfill disposals and every other form of biodegradable trash, by employing chemical, biochemical and heat induced procedures. Biofuels are differentiated form fossil fuel on the basis of the time required for their formation. Fossil fuels take millions of years for their formation and are considered nonrenewable. On the other hand, fuels derived from biomass which can be produced in short period of time are called biofuels. Biofuels are thus the energy resources from living organism or organic materials (living or once living) which are renewable and can be regarded as sustainable source of energy. Bioenergy is the energy derived either by direct use of biomass or its conversion into some utilizable forms. Biofuels can be classified as 1. Primary or unprocessed fuels like wood 2. Secondary or processed fuels like biodiesel, ethanol etc.

Biofuels can also be divided into following types:

1. Solid fuels like firewood, charcoal, animal dung etc. 2. Liquid fuels like ethanol and biodiesel. Liquid fuels are further divided into first generation and second generation biofuels. (a) First generation fuels are derived from sugars and starches. (b) Second generation biofuels: Second generation fuels refer to type of fuels formed by the conversion of cellulose, hemicelluloses and lignin, derived from plant matter into liquid fuels.Potential cellulosic source includes municipal wastes, agricultural waste, forestry, processing industry as well as new energy crops like fast growing trees and grasses. 3. Gaseous biofuels like biogas.

Biofuel production technologies: Some important methods by which bioenergy can be harnessed include 1. Fermentation for ethanol production: Biological fermentation of sugars to ethanol is the method to convert biomass into liquid fuel (biofuel). Materials like corn, wheat and other cereals which contain starch can be converted into sugars finally leading to the formation of ethanol. This is called fermentation. Yeasts carries out the fermentation process in absence of oxygen hence the process is also called anaerobic fermentation. In industrial production of ethanol, starchy substances are degraded to glucose by using amylase and then fed to yeast which metabolizes glucose to ethanol through fermentation. Cellulose from the biomass is also converted to ethanol by treating it with cellulose or hemicellolose or even lignin. Such biofuels are second generation biofuels. This treatment forms sugars which are converted to ethanol using microbes.

Energy  2.7 Harvested biomass  Straw  Corn stove  Wood chips  Forestry brash

 Shredding  Heating  Chemical treatment

Cellulose Enzymatic action

Sugars Fermentation

Yeast

Ethanol

2. Pyrolysis of wood to form alcohol: The degradation of wood is carried out in a limited supply of air therby converting it into a biofuel. Gases such as methane, CO, H2 and CO2 are produced during the process of pyrolysis. The procducts of pyrolysis also contain ash, carbon and small amounts of liquids. Depending upon the time and the processing temperature, pyrolysis could be slow, flash, fast or microwave. Pyrolysis is considered to be a simple and an economical technology widely used to produce different substances from wood such as activated carbon, charcoal etc. 3. Trans-esterification: Biodiesel production is accomplished by the process of transesterification, which is the process of conversion of fats or triglycerides into biodiesel, along with glycerin (valuable product in soaps). 4. Biomass gasification: The process involves heating biomass to high temperature in a low oxygen environment releasing an energy rich producer gas. It is the process that converts organic based materials into CO, CO2, H2 at a temperature greater than 700oC in a controlled supply of oxygen. Various steps involved are: (a) Harvesting biomass (b) Chopping (c) Dehydration or drying at 100oC (d) Pyrolysis or de-volatilization (200-300oC) is carried out to give a carbon rich residue called char and volatile products. (e) Combustion: The process involves reaction of volatiles and char with oxygen to form carbon dioxide and carbon monoxide. (C+O2 ® CO2) (f) Gasification: The char produced in the previous steps reacts with steam to give hydrogen and carbon monoxide. C+ H2O ® H2 + CO 5. Anaerobic digestion to yield biogas: The most commonly used mode is the production of biogas. It is a gaseous mixture comprising of mainly methane (55%) having fuel value of about 5000Kcal/m3. Biogas production occurs by anaerobic decomposition of organic matter. The organic matter could be cow dung or organic waste like leaves, algae, water weeds, distillery sludge, tannery waste etc. The tank called biogas tank is employed for production of biogas. It consists of a well constructed digester, a gas holder and connecting pipelines. Slurry of organic waste is fed into the digester from

2.8  Environmental Science

the inlet and optimum temperature of about 35oC - 48oC is provided. The bacteria an-aerobically (anaerobic digesters) converts the organics into usable gas which is collected and can be drawn off as per need. Bio gas

Mixing tank Overflow tank

Gas tank Ground

Ground Scum

Outlet pipe

Inlet pipe

Partition

Fig. 5. Biogas Digester

Advantages

1. The production of biogas is beneficial for rural areas. 2. The bioenergy and biomass ensure continuous supply of energy to the population. 3. It is comparatively less polluting than conventional fossil fuels. 4. It is cost effective as biomass and is a renewable source of energy. 5. Biomass can be effectively converted into biogas and liquid biofuels like ethanol, methanol etc.

Disadvantages

1. Except biogas production other methods are yet to be explored and established. 2. It is not completely pollution free source of harnessing energy. 3. The amount of heat obtained is not huge. 4. Continuous supply of biomass is required for energy production. 5. Research is needed to develop the methods to reduce the cost of biomass energy extraction.

Energy  2.9

2.5 Geothermal Energy Geothermal means earth’s heat. Geothermal energy is the energy obtained from the hot rocks (hot spots) present inside the earth (Geo). About 20% of Earth’s geothermal energy originates from the original formation of the planet and about 80% from radioactive decay of minerals. The most active geothermal resources are usually found along major continental plate boundaries where earthquakes and volcanoes are concentrated. This region is known as Ring of Fire .

Sources of Geothermal Energy

1. Hydrothermal Fluid: A hydrothermal fluid includes hot water, steam and associated gases. Naturally occurring large areas of hydrothermal resources are called geothermal reservoirs. 2. Geo-pressured Brine: These are hot pressurized water sources having dissolved methane gas lieing at depth of 10,000 feet or more below the earth’s surface. The temperature of geo-pressurized brines can be 149 oC to 204 oC. Types of energies which can be derived from these brines are thermal energy, from high temperature fluids, hydraulic energy, from high pressure and chemical energy, from dissolved methane gas. 3. Hot and Dry Rocks: Hot dry rock resources occur at depths of 3 to 5 miles everywhere beneath the Earth’s surface. The energy from hot dry rocks can be accessed by injecting cold water down to hot fractured rock, and drawing off the heated water. 4. Magma: Existing technology also does not yet allow recovery of heat directly from magma which is a very deep and most powerful resource of geothermal energy.

Uses of Geothermal Energy

1. It can be use for direct water heating. 2. It can also be used for generating electricity for domestic and industrial purposes. 3. The energy can be employed for drying.The warm water facilitates the growth of animals ranging from alligators, shellfish to amphibians to catfish. 4. It can be employed for aquaculture, fish farms and horticulture. 5. Its current uses includes heating buildings, raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk.

Geothermal power plants Geothermal power plants are facilities used to to convert earth’s heat energy to electricity. The type of geothermal energy plant employed at a location depends on the features of the geothermal reservoirs.

2.10  Environmental Science

Transmission line

Steam

Turbine & Generator

Production well

Cooling tower

Injection well

Geothermal zone

Fig. 6. Geothermal Power Plant

There are three types of geothermal energy plants: 1. Dry Steam: Steam plants use hydrothermal fluids that are primarily steam (dry). The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. 2. Flash Steam: Hydrothermal fluids are sprayed into a low pressure tank causing some of the fluid to rapidly vaporize, or “flash”. The vapor then drives a turbine, which drives a generator. After its impact on turbine, leftover water and condensed steam are injected back into the reservoir, (sustainable energy resource). 3. Binary Cycle: Most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants. Hot geothermal fluid and a secondary fluid (hence, “binary”) pass through a heat exchanger. The secondary fluid has a lower boiling point than water. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines. Because this is a closed-loop system, nothing is emitted to the atmosphere.

Advantages

1. Geothermal energy does not produce any pollution and helps in creating a clean environment. 2. It is a renewable source of energy. Geothermal power plants are unaffected by weather and night/day cycle, unlike solar panels that use solar energy, which is currently dependent on the sun and light.

Energy  2.11



3. These power stations do not take up much room and hence have less impact on the sorrounding environment. 4. Once a geothermal power station is installed, the energy is almost free. 5. Other than the generation of the power, useful minerals, such as zinc and silica, can be extracted from underground water. 6. Geothermal energy is “homegrown.” This helps in creation of jobs for local people, a better global trading position and less reliance on oil producing countries.

Disadvantages:







1. The biggest disadvantage of geothermal energy is high upfront costs, most of which refer to exploitation and drilling, also unavailability of skilled manpower, infrastructure and technology. 2. There are not many places where geothermal power station can be constructed. Hot spots are sparsely distributed. Thus, unavailability of suitable buiding location pose problems in adopting geothermal energy globally. 3. The biggest disadvantage of using geothermal energy source is low density of energy production. 4. The life span of a single bore employed for power generation is only 10 years. 5. We need hot rocks of a suitable type, at a depth where we can drill down to them. Also, drilling operations causes noise pollution. 6. Hazardous gases and minerals may seep up from underground during the drilling operations performed by the constructors, and can be difficult to safely dispose off. 7. Most of the sites, where geothermal energy is produced, are far from markets or cities, where it needs to be consumed.

2.6 Solar Energy It is the energy which is derived from the sun and is the most readily accessible source of energy. Solar technologies are largely characterized as either passive or active depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting the device to the sun and designing spaces that naturally circulate air. Solar power involves conversion of solar energy to electrical energy by devices like photovoltaic cells and concentrating solar thermal (CST) or concentrating solar power (CSP) technologies. A solar thermal power generation system collects and concentrates light to produce high temperature heat needed to generate electricity.

2.12  Environmental Science

All solar thermal power systems have solar energy collectors with reflectors concentrating light into a receiver. The receiver receives heated fluid which produces steam. The steam then converts to mechanical energy.

Types:

1. Linear concentrating systems which includes parabolic troughs and fresnel reflectors. 2. Solar power towers 3. Solar dish or engine systems The system comprises of curved mirror collectors with north south alignment which directs the light to receiver heating the fluid. The fluid passes its heat to low boiling liquid through heat exchanger which turns the turbo generator producing electricity. Solar power towers use a large field of flat sun tracking mirrors called heliostats onto a receiver on top of tower. The concentrated heat is utilized for direct heating or indirectly for electricity production. Solar dish or engine systems use a mirrored dish composed of large number of smaller flat mirrors formed into a dish shape. The dish shaped surface directs and concentrates light into thermal receiver which utilizes heat mechanically or electrically. Absorber tube

Curved mirror

Absorber tube and reconcentrator

Curved mirror Pipe with thermal fluid

Parabolic Trough Receiver/Engine reflector

Linear Fresnel Solar receiver

Heliostats

Dish/Engine

Central Receiver

Fig. 7. Types of Solar Thermal Collectors

Energy  2.13

Photovoltaic (Pv) cells convert light into electricity by semiconducting materials. PV systems employ solar panels made of solar cells which generate electrical power. Solar cells works on the principle of photovoltaic effect. Photovoltaic effects generate voltage and current by exposure to light. Various applications of solar energy are discussed below.

2.6.1 Solar Ponds A solar pond is a water body that collects and stores solar energy. Water warmed by the sun expands and rises. Once water reaches the surface, it loses its heat to the air through convection, or evaporation. The colder water, which is heavier, moves down to replace the warm water, creating a natural convective circulation that mixes the water and dissipates the heat. A solar pond is an artificially constructed water pond in which significant temperature rises are caused in the lower regions by preventing the occurrence of convection currents. A solar pond mainly has three zones. The first zone is the upper convective zone of clear fresh water that acts as solar collector. An intermediate or gradient zone is which serves as the non-convective zone which is much thicker. The last region is the lower convective zone with the densest salt concentration, serving as the heat storage zone. When solar radiation strikes the pond, most of it is absorbed by the surface at the bottom of the pond. The temperature of the dense salt layer therefore increases. The denser salt water at the bottom prevents the heat being transferred to the top layer of fresh water by natural convection, due to which the temperature of the lower layer may rise to as much as 95°C.

Solar radiations

Surface zone Insulation zone Storage zone

Cold water Hot water

Fig. 8. Solar Pond

2.6.2 Solar Cookers Solar cooker is one of the simplest applications of solar energy where the heat of the radiations is captured and utilized to cook food. The principle involved includes:

2.14  Environmental Science



1. Concentration of Light radiations 2. Conversion of Light into heat 3. Trapping heat for use The box type solar cooker has an insulated box painted black inside. It is covered by a glass plate which allows heat to enter inside but does not allow heat to escape out. It has a mirror to reflect more sunlight into the box. The food to be cooked is kept in containers inside the box. The containers are also painted black for maximum heat retaining. It can produce a temperature of 100° to 140°. When the cooker is placed in the sun, the energy from the sun’s radiations is absorbed and temperature inside the box increases.

Solar panel cooker

Solar parabolic cooker

Solar box cooker

Fig. 9. Solar Cooker

2.6.3 Solar Greenhouses These are the enclosures where crops, vegetables or flowers are provided with proper environment under adverse climatic conditions for plant growth and production. All greenhouses receive necessary sunlight from the sun required for photosynthesis and also supplementary heat during cold months from sun. In tropical countries ambient temperature is quite high so summer greenhouses can be designed for reducing the inside temperature and the plants receive sufficient sunlight required for photosynthesis. Solar greenhouse technology is one way of the using solar energy. It provides an ideal environment for plants throughout the year and helps to obtain maximum efficiency from plants. Solar greenhouses can be successfully employed to obtain vegetables, fruits, and flowers which are out of season or from another climate condition.

Energy  2.15

Solar radiation Long wavelength radiated Short waves

Glass house

Fig. 10. Solar Green House

2.6.4 Solar Desalination A solar powered desalination unit produces potable water from saline water through direct or indirect methods of  desalination powered by sunlight. Countries such as Australia, Italy and Egypt have adopted this system as an alternative source of water for the population. Important elements required in solar desalination or solar stills are the solar radiations, production of water vapor from brine or salt solution, formation of condensate and its collection. The basic elements of solar desalination or solar stills include: · Solar radiations · Brine solution · Production of water vapors from brine · Condensation · Collection of water The systematic scheme is as follows (Fig. 11)

2.16  Environmental Science

Solar radiations

Cover of glass or plastic

Con

den

sati

on

Brine

Collection of condensate

Fig. 11. Solar Desalination System

2.6.5 Solar Cells A solar cell, or photovoltaic cell, is an electrical device that converts the energy of  light directly into electricity by the photovoltaic effect. When light falls on metals electrons gets excited and escape, which are collected and passed through wires, the electron flow thus, constitutes electric current. The operation of a photovoltaic cell requires 3 basic attributes: 1. The absorption of light, generating either electron-hole pairs or excitons. 2. The separation of charge carriers of opposite types. 3. The separate extraction of those carriers to an external circuit. A typical solar cell is a multi-layered material consisting of 1. Cover Glass - It is a clear glass layer that provides outer protection from the elements. 2. Transparent Adhesive - It holds the glass to the rest of the solar cell. 3. Anti-reflective Coating - This coating is designed to prevent the light that strikes the cell from bouncing off so that the maximum energy is absorbed into the cell. Titanium oxide, indium tin oxide, silicon oxide, silicon nitride can be used as antireflective coatings. 4. N-type and P-type Semiconductor Layer – The thin layer of silicon which has been doped with phosphorous and boron respectively. 5. Front and Back Contact or electrodes – These electrodes transmits the electric current. Silicon photovoltaic cell consists of a single crystal of p-type silicon with a surface layer of n-type silicon. When light falls onto p-n junction, electron and holes moves in opposite direction and if an external circuit is connected an electrical current is set up.

Energy  2.17

Solar radiations Electron flow Antireflective coating

Front contact N type Depletion zone

Load

P type Back contact

Fig. 12. Solar Cell

2.6.6 Solar Furnaces A solar furnace is an arrangement which is used to harness the sun’s energy with an aim to obtain extremely high temperatures for various industrial applications. This is achieved using a curved mirror (or an array of mirrors) or reflectors which concentrate light onto a point or target. It has the following major components: 1. Heliostats: These are remote-controlled movable mirrors which follow the sun’s trajectory and concentrate solar radiation. These arrays of mirrors increase the intensity of the sunlight manifolds. Heliostats are placed on slopes to prevent energy loss due to shade or the interception of reflected rays by neighboring mirrors. These are polished metalized glass that receives solar radiation and direct it to the parabolic mirror. 2. Tower: It is the structure atop of which the furnace is positioned to gather radiant energy from the sun. 3. Furnace: Furnace is the container onto which the radiations are concentrated. It can reach temperatures of over 3000°C, and is mainly used to develop different materials, melting, to process nano-materials and to produce hydrogen by cracking process etc. 4. Parabolic mirror: This is the curved mirror that concentrates the sun’s rays towards one point in the furnace (the target area).

2.18  Environmental Science

Sun

Solar radiations

Parabolic mirror Focus point Furnace Tower

Heliostats placed on sloppy region

Fig. 13. Solar Furnace

2.6.7 Solar Water Heaters Solar water heating (SWH) is another simple application of solar energy. It involves conversion of solar energy into heat energy which is trapped in water and makes water warm. This conversion involves application of solar thermal collector. The solar collector is the device which captures the solar radiations. Solar water heating system consists mainly of solar radiations collector and a storage tank. The water heating system can be either active or passive. The collector consists of an absorber, usually a sheet of high-thermal conductivity metal such as copper or aluminum. Its surface is coated to maximize radiant energy absorption and to minimize radiant emission. As water in the collector is heated, it becomes lighter and naturally rises into storage tank above. The solar water heaters require a well insulated storage tank with outlet and inlets connected to and from collector. The water circulates throughout the closed system due to convection currents. Sun Solar radiations Water tank Hot water out Cold water in Vacuum tubes Support stand

Heat absorbers

Fig. 14. Solar Water Heater

Energy  2.19

Several advantages and disadvantages of solar energy are as below:

Advantages

1. 2. 3. 4.

Solar energy is free and is available everywhere without any cost. Solar energy does not cause pollution unlike fossil fuels. Solar energy can be used in remote areas. Due to overexploitation of fossil fuels and its cost intensiveness solar energy is one of the promising energy resources.

Disadvantages





1. The biggest disadvantage of solar energy is that it can be harnessed only in day time. The unreliable climate means that solar energy is also variable as a source of energy. Cloudy skies reduce its effectiveness. 2. Solar collectors, panels and cells are relatively expensive to manufacture although prices are falling rapidly. 3. Solar power stations can be built but they do not match the power output of similar sized conventional power stations and are also very expensive. 4. Large areas of land are required to capture the sun’s energy. Collectors are usually arranged together especially when electricity is to be produced and used in the same location. 5. Solar power is used to charge batteries so that solar powered devices can be used at night. However, the batteries are large, heavy and need storage space.

2.7  Wind Energy Wind is a form of  solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth’s surface, and rotation of the earth. This wind flow, or motion energy, can be used to generate electricity. Wind turbines convert the kinetic energy of wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity. The electricity is then sent through transmission lines and distribution lines to power homes, businesses, schools, etc. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Wind turbines can be categorized into two classes based on the orientation of the rotor, vertical axis or horizontal axis. The following are the main components of wind turbine: 1. Blades: Most wind turbines have three blades, though there are some with two blades. Blades are generally 30 to 50 meters (100 to 165 feet) long,

2.20  Environmental Science

with the most common sizes around 40 meters (130 feet). It converts the energy in the wind to rotational shaft energy. 2. Drive train: This component usually includes a gearbox and a generator. 3. Gearbox: It is employed to increases the rotational speed of the shaft. 4. Generator: Wind turbines typically have a single AC generator that converts the mechanical energy from the wind turbines rotation into electrical energy. 5. Controller: The controller monitors the condition of the turbine and controls the turbine movement. 6. Tower that supports the rotor and drive train. Blade

Low speed shaft

High speed shaft Rotor hub

Bl

ad

e

Generator Nacelle

Gear box

Tower

Fig. 15. Wind Turbine

Advantages

1. Wind energy is a free, renewable resource. It can be renewed. 2. The wind blows day and night, which allows windmills to produce electricity throughout the day. 3. The power generation is cheaper than conventional methods. Its non polluting and does not require whole surface area. 4. Wind turbines can be installed without interfering with the agricultural activities. Up to 95% of land used for wind farms can also be used for other profitable activities. These can be installed on the buildings, hills, deserts etc. The installation also creates job opportunities for the local people.

Disadvantages

1. It causes sound pollution. 2. It offers low energy density.

Energy  2.21



3. The blades of wind turbine may kill the migratory birds. Wind turbines cause noise pollution and destroy the aesthetics. 4. The wind flow is variable and not regular. When the wind speed is low it is unable to generate electricity. Also it relies on weather for power generation. 5. The technology requires a higher initial investment than fossil-fueled generators. 6. Good wind sites are usually located in remote locations far-off from areas of electric power demand (such as cities). This requires establishment of infrastructure for the transmission lines to the demand regions.

2.8 Hydro Energy The energy derived from the flowing water is called hydro or hydel energy. Hydro energy can be used by conversion of kinetic energy of water into electrical energy by use of the gravitational force of falling or flowing water turning hydraulic turbines and generators. Thus electricity produced is called hydroelectricity or hydropower. It is the most widely used form of renewable energy. The fundamental parts of hydropower plants include, dam, reservoir, control gates, penstock, turbines and generators. A dam is a barrier that impounds water and serves the function of retaining water and stops its flow. The height of the dam decides about the hydraulic head. The head is the difference in the height of the water between the upstream water level and the water outflow. The long pipe which carries water from the higher water level to the lower elevation is called the penstock. The penstock carries high speed flowing water to the turbine connected to a generator which generates electricity.

Fig. 16. Hydropower Plant (Courtesy: NHA)

2.22  Environmental Science

Advantages





1. Water for harnessing energy/electricity is available in abundance and is free of cost worldwide. 2. It’s a pollution free source of energy. When water is used for production of electricity, it does not involve the production of green house gases unlike fossil fuels. 3. It is much more reliable than wind, solar power and other conventional sources of energy because of ready availability in the reservoirs. 4. By a hydropower plant electricity can be generated constantly. The working of power stations can be monitored and electricity production can be shut by closing the sluice gates whenever demanded. 5. Hydropower plants are versatile and multipurpose in nature. The reservoirs that are created by dams are used for water sports, irrigation, aquaculture, navigation, and leisure / pleasure activities. Dams are often one of the attractive tourist spots.

Disadvantages







1. The construction of dams should be of high standards so that they can be functional for longer time duration. It makes it cost intensive and requires proper and timely maintenance. 2. Hydroelectric power stations that use dams would submerge large areas of land due to the requirement of a reservoir. 3. People living in villages and towns need to move out from their dwelling place. This means that they lose their agricultural lands, property and businesses. Sometimes people are forcibly displaced so that hydro-power schemes can go ahead. 4. Variation in the volume of water in the reservoir and changes in the head height alters the production of electricity. 5. Dams are constructed on the natural pathways of the rivers. It changes the downstream river environment by inhibiting seasonal migration of fishes and inundating the grounds of aquatic creatures. It destroys the biologically rich and productive land, forests and grasslands and ruins natures balance. 6. The building of large dams can cause serious geological damage. Many cases have been reported where the building of dams has caused adverse effects, for example the Hoover Dam has triggered a number of earth quakes in the USA and Aswan dam in Egypt has led to alteration in the ground water level.

2.9 Ocean Energy Ocean covers 70% of the earth’s surface. Ocean energy is the energy obtained by ocean waves (using wave energy conversion into electricity), tides (using tides

Energy  2.23

barrages, fences and turbines to generate electricity), and salinity (salinity gradient power or blue energy) and ocean temperature differences. Ocean wave energy is the form of kinetic energy that exists in the moving waves of the ocean, since waves are caused by blowing winds over the surface of the ocean. Wave power has gigantic energy potential as wind blows with sufficient consistency forming continuous waves. The waves rise into a chamber and then rising water forces the air out of the chamber and moving air spins a turbine, which then turns a generator for electricity production. Tidal power is a form of hydropower that explores the movement of water, caused by tidal currents and rise and fall in the sea level and relate to the gravitational pull. Tidal power generation needs large increases in the tides at least 16 feet between low tide and high tide. Tidal energy is produced by tidal energy generators especially designed to capture kinetic motion of ebbing and surging of ocean tides for electricity production. Ocean thermal energy conversion (OTEC) is a method that uses temperature difference that exists between deep and shallow waters since the water gets colder with depth. This concept was first developed by Jacques in 1881. Greater the temperature difference greater is the efficiency (minimum temperature difference is 38oF). Different types of OTEC systems are: Closed cycle: It uses a low boiling fluid like ammonia to rotate a turbine which then generates electricity. In this, the surface warm water is pumped through a heat exchanger where low boiling fluid is vaporized which turns the turbo-generator. The vapours are condensed back into a liquid by another heat exchanger circulating cold deeper sea water. Working Fluid

Generator

Exchanger

Heat Exchanger (Condenser)

Discharge

Warm Water Cold Water

Fig. 17. Closed Cycle System

Open cycle: It involves keeping the warm surface sea water in a low pressure container where it boils. The increasing steam drives a low pressure turbine attached

2.24  Environmental Science

to a generator. The used steam is condensed back into a liquid by exposure to cold temperature from deep ocean water. Hybrid cycle: These systems are designed to combine the features of both closed cycle and open cycle systems. Another method of harnessing ocean energy is through osmotic power also known as salinity gradient power or blue energy. It is a method of harnessing the energy released when fresh water is mixed with the salt water. In such power plant fresh and salt water are directed into separate containers separated by a semipermeable membrane. The water molecules move to the salt water container by creating osmotic pressure. The pressure is then used to power turbine which generates electricity. The world’s first osmotic power plant was installed in 2009, Oslo, Norway.

Advantages







1. It is a renewable energy resource as waves will always keep on crashing along the shores unlike fossil fuels which are running out. Dependence on foreign nations and companies for fossil fuels can be reduced if ocean energies are utilized to their fullest. 2. It has large potential and versatility in terms of the ways by which ocean energy can be harnessed. 3. It is used for air-conditioning and aquaculture (cold water fishes like salmon and lobster thrive in nutrient rich deep sea water from OTEC process). 4. Ocean energy involves no damage of the land area as the power plants are to be installed in water. Thus, land is protected from the extraction process and drilling operations which affects ecological balance adversely. 5. No use of external fuel source for running of the machines for electricity production. In fact, wave power can have high efficiency of about 80% in ideal conditions. 6. The occurrence of tides is predictable and hence planning related to the running of power plants can be controlled to generate electricity. 7. It is environmentally friendly as no harmful products are created during the electricity production. It minimizes pollution and could provide employment opportunity.

Disadvantages

1. Its biggest flaw is the cost intensiveness and large initial investments of the large size projects or machines or technologies. 2. The ecological system gets affected due to setting up of the machinery. A large area is required for power plants which affects the environment and birds relying on tides. The machines disturb the habitat of creatures like crabs and starfishes and noise disturbs the sea life around them.

Energy  2.25









3. A minimum difference of temperature (38oF) is required for OTEC cycles to run. 4. There are not many areas where tides often occur with sufficient tidal level. This makes energy production process difficult. Only the towns that are nearby ocean get benefitted as it highly localized energy source. 5. Waves change their directions due to change in the flow of air and thus continuous energy production requires continuous monitoring. 6. Tidal power stations can only be used to a maximum of 10 hours a day as tides do not occur throughout the day. 7. Development of power plants disturbs the movements of large ships, cruise ships, recreational vehicles and beach goers. It is thus desired that these activities must be taken into account by the project developers and government officials before installation. 8. This also destroys the aesthetic look of the ocean. 9. An oceanic disturbance like storms, hurricanes damages the power plant equipments. The rough conditions of the salty water of the oceans destroys the equipments. 10. Technological development related to utilization of ocean energy is quite slow and the complete potential of ocean energy still needs to be explored.

2.10 Nuclear Energy The energy trapped inside the nucleus of an atom is called nuclear energy. Such energy is produced when nuclear reactions occur (a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce different products than the initial particles). Nuclear energy can be harnessed for mankind in two ways, nuclear fusion and nuclear fission. In the process of nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This process is the principle process of solar energy. In nuclear fission, atoms split apart to form smaller atoms, releasing energy. Nuclear power plants use nuclear fission for the production of electricity.

2.10.1 Nuclear Fission Nuclear fission is a reaction in which a large nucleus is bombarded with a small particle, in which the nucleus splits into smaller nuclei and several neutrons and large amounts of energy is released. All nuclear plants use nuclear fission for energy production and Uranium (235U) is the most common fuel used for the purpose. When a neutron bombards 235U, an unstable nucleus of 236U undergoes fission (splits) producing smaller nuclei such as Kr-91 and Ba-142 along with neutrons to bombard more 235U. Nuclear fission can either be controlled (as in power plants) or uncontrolled (as in armaments). The nuclear reactors are designed to maintain

2.26  Environmental Science

a controlled chain nuclear reaction where produced energy is used for generation of electricity. Controlled nuclear reactions can be carried out in nuclear reactors.

2.10.2 Nuclear Reactor The major parts of a nuclear reactor are: Reactor Vessel: Nuclear reactors use nuclear fission, which breaks the nucleus of a uranium atom into smaller atoms along with neutrons. The liberated neutrons break other nuclei into smaller pieces, which further release neutrons. The movement of these neutrons generates heat. This generated heat is utilized for electricity production. The commonly used fuels are Uranium, Plutonium or Thorium (U235, U-238, Pu-236 or Th-232).  Control Rods: For a controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this is not maintained and less number of neutrons are released then the reaction will die out and if the neutron number is greater than the reaction will be uncontrolled (an atomic explosion). Thus, it is required to have a neutron absorbing element in order to control the amount of free neutrons in the reaction space. Most reactors are controlled by means of control rods that are made of a strong neutron-absorbent material such as boron, graphite or cadmium. Since the movement of the neutrons causes the reaction, absorbing the extra neutrons slows down the reaction. Moderators: Moderators slow down the neutrons so that they have a higher chance of splitting the next nucleus. Materials used for moderators include graphite and heavy water, containing the isotope deuterium. Coolant: The coolant is the material that passes through the reactor core and transfers the heat from the fuel to a turbine. This is the place where heat-exchange process takes place. The materials employed for coolant can be water, heavy-water, liquid sodium or helium. Steam Generator: The heat from the nuclear reaction is used to heat massive amounts of water in the steam generator. The steam generator consists of bundles of tubes that superheat water. The superheated water from the steam generator turns turbines. The turbines then operate the generator, which creates electricity. Cooling Tower: In the cooling tower or condenser, water is cooled down to be used again in the cycle. Containment Structure: The concrete and steel structure around the reactor and associated steam generators is called containment. It is designed to protect the reactor from outside interference and to protect those outside from the effects of radiation in case of any serious malfunction inside. Pressurized water reactor is the most common type of reactor. It uses water as the coolant. The primary cooling water is kept at very high pressure so that it does not boil. It goes through a heat exchanger, transferring heat to a secondary coolant loop, which then spins the turbine. The boiling water reactor uses only

Energy  2.27

one loop and involves the hot nuclear fuel to boil the water as it goes out the top of the reactor, where the steam heads over to the turbine to rotate it. The other type of reactors are Molten Salt Reactor, High Temperature Gas Cooled Reactor, and Canada Deuterium-Uranium Reactor (CANDU). Containment structure

Turbine Control rods Generator Reactor

Steam Generator

Condenser

Fig. 18. Nuclear Reactor (Pressurized Water Reactor)

Containment Structure

Turbine Control rods Generator Reactor

Condenser

Fig. 19. Nuclear Reactor (Boiling Water Reactor)

Advantages

1. Nuclear reactions release a million times more energy, as compared to hydro or wind energy.

2.28  Environmental Science









2. As the energy liberated is huge, large amount of electricity can be generated. Nuclear power plants are able to meet the needs of industrial cities as well as suburban towns.  3. It is an alternative to the fossil fuels helping in reducing the consumption of fuels such as the coal or oil. This reduction of coal and oil consumption benefits the situation of  the global warming and decreases air pollution that affects the quality of life. 4. The biggest advantage of this energy is that there is no release of greenhouse gases (carbon dioxide, methane, ozone, and chlorofluorocarbon) during nuclear reaction. 5. As there is no emission of these gases during nuclear reaction, there is very little effect on the environment. 6. Presently, 12-18% of the world’s electricity is generated through nuclear energy.

Disadvantages







1. The biggest drawback of nuclear fission is that this energy source can be used for production and proliferation of nuclear weapons which are a major threat to the world, as they can cause a large-scale devastation. 2. A nuclear power plant requires large capital cost. This is because of the complex technologies required and the extreme safety measures that must be developed so as to ensure the safety of the surrounding areas. 3. The waste produced after fission reactions contains unstable elements and is highly radioactive. It is very dangerous to the environment as well as human health. Nuclear fission produces radiation, which is deadly for humans and animals if absorbed in large doses. 4. The people that work in nuclear power plants are at a great risk of developing serious health conditions and radiation poisoning. 5. The nuclear reactors need professional handling and should be kept isolated from the living environment. 6. The storage of radioactive elements for a long period is a challenge. 7. The power plants are associated with high risks and hence high level of security is required. 8. Although nuclear fission creates a clean-type of energy, like fossil fuels, it is not a renewable energy resource with our current technologies.

2.10.3 Nuclear Fusion Nuclear fusion is the energy-producing process taking place in the core of the sun and the stars. The core temperature of the sun is about 15 million °C. At such extreme temperatures hydrogen nuclei fuse to give helium and large energy. The

Energy  2.29

energy sustains life on earth via sunlight. In the fusion process lighter elements are “fused” together, making heavier elements and producing enormous amounts of energy. Humans have successfully carried out uncontrolled fusion reactions to make the hydrogen bomb, in which tremendous energy of the reaction is released at once, in a highly destructive manner. If the same amount of energy could be released gradually, in a controlled fusion reaction, similar to the reaction taking place in the sun, this could become the ultimate form of energy on earth. The experimental reactors that are in used today use deuterium and tritium as the main elements. Deuterium can be extracted from sea water. Tritium can be made from deuterium in contact with lithium. Fusion research began in the 1950’s, in England. In 1968, the Russians carried out the first reaction in their Tokomak reactor, which utilized magnetic confinement. In 1991, the Joint European Torus (JET) reactor produced 1.7 MW of energy through fusion reaction. Two years later, the US-based Tokomak fusion test reactors (TFTR) produced 10 MW.  Today there are some 25 experimental reactors in existence. The most important of them all is the International Thermonuclear Experimental Reactor (ITER) currently under construction in France, which hopes to achieve 500 MW of output for approximately 1000 seconds and is expected to be functional by 2050. Another way is magnetic confinement fusion which is an approach to generate thermonuclear fusion power using magnetic fields to confine hot fusion fuel in the form of plasma. Magnetic confinement fusion, attempts to create high temperature conditions by using electrical conductivity of the plasma to confine it in the magnetic fields. It involves balancing of magnetic and plasma pressure. Magnetic field energy is nowa days dominated by Tokamak approach and presently ITER France proposes the power generation through this technique to start by 2025. Tokamak device (invented in 1950) uses powerful magnetic field for torus shaped confinement of plasma. International thermonuclear experimental reactor is an international nuclear fusion research and engineering mega project based on Tokamak approach, built in France.

Advantages



1. Nuclear fusion provides sustainable energy. 2. The raw materials like deuterium can be obtained from water using distillation process, while tritium can be produced during the fusion reaction as fusion neutrons interact with plentiful of lithium available on earth. It is estimated that terrestrial reserves of lithium would permit the operation of fusion power plants for more than 1,000 years, while sea-based reserves of lithium would fulfill needs for millions of years. 3. Nuclear fusion involves no emission of greenhouse or other polluting gases. Its major by-product is helium which an inert and non-toxic gas.

2.30  Environmental Science





4. The reaction is not associated with any risk of a severe accident, unlike fission process. This is because the fusion involves fusing, rather than splitting, there is a much lower chance of a chain reaction occurring. This makes nuclear fusion very simple to control and much safer than other forms of nuclear energy. 5. It has no long-lived radioactive waste. 6. Fusion energy can be used to produce electricity. Fusing atoms together in a controlled way release nearly four million times more energy than a chemical reaction such as the burning of coal, oil or gas and four times as much as nuclear fission reactions (at equal mass). Fusion has the potential to provide the kind of baseload energy needed to provide electricity to our cities and industries.

Disadvantages





1. Fusion reaction is difficult to start, as high temperatures (millions of degrees) and a pure high vacuum environment are required. 2. Technically complex and high capital cost reactors are necessary. The facilities, experts, and scientists that are needed to successfully run a nuclear fusion plant pose an economic challenge. Along with these high costs, harnessing the created energy is also expensive. 3. More research and development is still needed to bring the concept of controlled fusion to fruition. The full scope of dangers and effects of nuclear fusion energy are still to be understood in depth and need to be explored. 4. This science is well advanced but requires sustained development on a long time scale (20 to 40 years). 5. Higher heat levels produced are a concern.

2.11 Hydrogen Energy Hydrogen energy is regarded as future energy source. It is a colorless, odorless and combustible gas. Although it is present in very low amount in earth’s atmosphere (0.1 ppm), it is one of the most important and widely used industrial materials. In recent years, possibility of using hydrogen as fuel has increased due to the efficiency, renewability and non polluting nature of the gas. It is observed that combustion of hydrogen produces much more energy in comparison to other conventional fuels. The greatest advantage offered by hydrogen fuel is that the by product formed during the combustion of hydrogen is harmless and non toxic water. Thus, hydrogen can act as an efficient future energy source. Hydrogen does not exist freely in nature and it is locked up in enormous quantities in water hydrocarbons and other organic matter. It is produced from other energy sources and is often called as energy career where it can store and transport energy. Hydrogen can be prepared in following ways:

Energy  2.31

1. Industrial process: Breaking down of hydrocarbons can lead to production of energy rich fuels like methane along with hydrogen. The process of breaking of higher hydrocarbon into lower ones is called cracking. But, environmentally it is not regarded as efficient process as the decomposition process requires too much energy input which dilutes the objective of using hydrogen as efficient fuel. 2. Electrolysis: The process of splitting of water into hydrogen and oxygen by using electricity is called electrolysis. The process utilizes water as renewable energy raw material for production of hydrogen but again energy input is more than the output. It is calculated that about 1.4 J of electricity is consumed for production of 1 J of hydrogen. This method is thus uneconomical. 3. Reaction between water and metals: Reaction of metals with water produces hydrogen along with metal oxides. Hydrogen is employed as fuel and these oxides can be recycled back to their metal forms and can be reused again. The disadvantage associated with this method is the involvement of cost intensive technologies. 4. Gasification: Gasification is the process in which organic material like crops and livestock wastes are converted to hydrogen under high temperature conditions. 5. Steam reforming involves the production of hydrogen from methane but results in green house gas production which pollutes the environment. 6. Biophotolysis: The production of hydrogen from water with the help of sunlight is called biophotolysis. Hydrogen production from algal systems like chlorella, scenedesmus, corralina etc. occurs by the action of enzyme hydrogenase. In cyanobacterial system hydrogen gas is the resultant of nitrogenase enzyme. Another source of hydrogen energy production is halophilic bacterium (halobacterium halolobium). The production of hydrogen through biological method is much advantageous than electrochemical methods. Researchers are constantly focusing on genetic engineering studies for altering the characteristics of these microbes (photosynthetic bacteria and cyanobacteria) for hydrogen production. It is gaining attention as an environmentally acceptable technology. The national aeronautics and space admiration (NASA) is the largest user of hydrogen as fuel. NASA began to use liquid hydrogen in the 1950’s as rocket fuel, and was the first to use fuel cell to power electrical systems on space craft.



2.11.1 Hydrogen Fuel Cell Hydrogen fuel cell involves combustion of hydrogen and oxygen to produce water and electrical current which supplies power. Each fuel cell comprises of an anode, a cathode and a proton exchange membrane sandwitched in between anode and

2.32  Environmental Science

cathode. Hydrogen from the storage tank enters the anodic side of the tank, while oxygen from air enters from cathode side. In the membrane hydrogen gas splits into hydrogen atom and electron by catalyst. Electron moves through an external circuit delivering current to vehicle components or is used to illuminate a bulb or city or emergency response systems, hospitals etc. e

e–

Load H2 Hydrogen inlet

H+

H2

Electrolyte

H2

H2

H+

H2

H+

H+

H++

O2 O2

O2

Oxygen inlet

H2O Water outlet

Anode

Cathode

Fig. 20. Hydrogen Fuel Cell

H2 + O2 ® Electricity + water vapour ...(1) The cell involves the conversion of chemical energy stored in the molecular bonds into electrical energy. The catalyst present is made up of platinum nanoparticles. The surface of the catalyst is rough and porous so that maximum surface area can be exposed to the fuel gases. H2 ® 2H+ + 2e- ...(2) -2 O2 ® 2O ...(3) Fuel cells are divided into various types depending upon the electrolyte employed. This includes the following types: Fuel cell Proton exchange membrane Alkaline fuel cell Phosphoric acid fuel cell Molten carbonate fuel cell Metal hydride fuel cell

Electrolyte material Ion exchange membrane Aqueous alkaline solution Molten phosphoric acid Molten carbonate Aqueous alkaline solution

Temperature 60- 100 oC 60- 140 oC 160-220 oC 650 oC Greater than -20 oC

Advantages

1. Hydrogen gas employed for energy production is colourless and odourless. 2. It is non-polluting as pure water vapour is formed as by product. 3. It is non contributor to green house effect.

Energy  2.33





4. Being the lightest element it has the best energy weight ratio of any fuel. 5. A wide range of hydrogen production methodologies are available. The production of hydrogen can be facilitated through water which is an inexhaustible energy resource. 6. Hydrogen fuel cell is used to produce pure water for the shuttle crew. 7. It supplies power quickly, powerfully and clearly. 8. It involves hydrogen fuel cell which directly converts chemical into electrical energy.

Disadvantages





1. Hydrogen is not available in its pure form because of its high reactivity. It reacts strongly with oxygen and other elements. 2. If hydrogen is to be used it should be available in usable form which is not possible without the expense of energy. For example: decomposition of hydrocarbon or water for hydrogen production requires increased energy input. 3. Hydrogen is difficult to handle, store and transport. It is highly reactive and leaks effortlessly from containers, therefore requires specialised tanks. It is difficult to trace its leakage as it is odourless. 4. One of the biggest pitfalls of hydrogen fuel is that it is very expensive at present and this newer cost effective production technology is still to be explored and tested.

2.12 Energy Scenario Coal dominates the energy mix in India, contributing to 56% of the total primary energy production. Over the years, there has been a marked increase in the share of natural gas in primary energy production from 30.85 to 31.73 BCM (2.86% increase as on march 2018). India has huge coal reserves, at least 319.04 billion tonnes of proven recoverable reserves. This amount to almost 10.2% of the world reserves and it may last for about 230 years. Oil accounts for about 29.55 % of India’s total energy consumption. The majority of India’s oil reserves out of 594.49 Million tones are located in the Western Offshore (40%) Bombay High, Cambay, and Krishna-Godavari, followed by Assam (27%). Natural gas accounts for about 8.9 per cent of energy consumption in the country. The current demand for natural gas is about 96 million cubic metres per day as against availability of 67 million cubic metres per day. The all India capacity of installed electric power generating stations under utilities was 3,60,456.37 MW as on 31st July 2019, consisting of 45,399.22 MW- hydro, and other renewable sources as 80,632.80 MW. Nuclear Power contributes to about 2.4 per cent of electricity generated in India. India is endowed with a vast and viable hydro potential for power

2.34  Environmental Science

generation of which only 15% has been harnessed so far. India has a potential of around 48,500 MW from wind energy. With a capacity addition of 12,800 MW, it contributes to around 75% of the grid-connected non-conventional energy power installed capacity. India with an installed capacity of 19564MW ranks fifth in the world after Germany, USA, Spain and Denmark in wind power generation. The current potential for power generation from surplus agro and agroindustrial residues is estimated to be 17000 MW. The total estimated biomass power potential is about 22,000 MW. All India Power Installed Capacity (MW) 180000

Renewable Power Installed Capacity (MW) 30000

160000 25000

140000 120000

20000

MW

MW

100000 80000 60000

15000 10000

37415

40000

42623 4177

4678

4879

Small Hydro Power

Bio Power

Solar Power

5000

24473 20000 0

5780 993 le as sel ro ar G le wab Hyd ie c D u N ene R

l

oa

C

0 Wind Power

Fig. 21. Power Installed Capacity Renewable Energy Installed Capacity Growth (MW) 45000 38822

40000 35000

31702 24914

25000 20000

16817

15000

12403

10000

8088 3518

5311

28067

14792

10257

6161

001 01 20 -02 02 20 03 03 20 -04 04 20 -05 05 20 06 06 20 -07 07 20 -08 08 20 09 09 20 -10 10 20 -11 11 20 12 12 20 -13 13 20 14 14 20 15 15 -1 6

4880

33791

19974

20

20 0

99 ...

5000 2906 3179 0

19

MW

30000

Year

Fig. 22. Renewable Power Installed Capacity

Energy  2.35

2.13  Case Study





· In 2007, IAEA (Integrated architect-engineer association) released a publication outlining the major milestones to be achieved in establishing the required infrastructure for nuclear facilities. This consists of 19 elements which are central to the development of a nuclear program. The electricity demand is expected to exceed 40GW by 2020, the United Arab Emirates (UAE) has identified nuclear as an important source of future electricity supply. · The central salt and marine chemicals research institute is working on production of alcohol from seaweed. It is the joint project of Council of Scientific & Industrial Research (CSIR) and Ministry of New Renewable Energy (MNRE). It is an achievement in the field of green technology and eco-friendly approach towards development. · Established in 2008, Husk pioneered an off-grid power generation and distribution solution to serve rural customers in Bihar, India. Husk was the first company to use 100% biomass gasification from rice husk to generate 6-7 hours of electricity for households and small businesses. In 2014, a hybrid system generating 24/7 power using solar and biomass gasification technique was used.

Interesting Facts

· Half a kilo of the dry biomass produces about 1890 Kcal of heat which is equivalent to the heat available from a quarter of the Kg of coal. · The sun is 90 million miles from the earth, it takes less than 10 minutes for light to travel from that much of distance. · The largest solar power plant in the world is located in the Mojave Desert in California, covering 1000 acres. · The first geothermal power plant was built in 1904 in Tuscany, Italy · The first modern wind turbine was built in 1940’s in Vermont. · A wind turbine blade can be up to 260 feet long, and a turbine tower can be over 328 feet tall – taller than the Statue of Liberty · The world’s first nuclear power plant to create electricity for a power grid was USSR’s Obninsk Nuclear Power Plant (27 June 1954). · The largest hydroelectric power station in the world is the Three Gorges Dam in China. · World-wide, about 20% of all electricity is generated by hydropower. · In 1970, biggest solar furnace was built in France. A prototype is built in India, to be used as a solar crematorium. Reflective surface of 50 square meters will generate temperatures of 700 degrees Celsius, to replace the amount of 200-300 pounds of wood required for cremation.

2.36  Environmental Science

Review Questions

1. 2. 3. 4. 5. 6.

7. 8. 9. 10.

Classify and discuss the various energy resources. Discuss bioenergy as a non conventional energy source. Briefly explain the fossil fuel and related disadvantages. What is geothermal energy? Discuss its merits and limitations. Explain the use of solar energy for the purpose of water heating. What is photovoltaic cell? How electricity is generated by solar photovoltaic systems? How is wind energy used for generation of electric power? Discuss the principle of OTEC along with its merits and demerits. What is nuclear energy? Explain nuclear fusion and fission as energy source. Explain the working of hydrogen fuel cell.

3

Water Pollution

Water is most vital for supporting life on the earth. Almost 75% of the human body is composed of water. Water is essential for all the essential activities including photosynthesis. About two thirds of the surface of the earth is covered with water. It is considered to be a universal solvent as it has the ability to dissolve a variety of substances. Unfortunately human beings are exploiting the water resources and polluting them, thereby leading to a decrease in the availability of clean water. Also, environmental pollution is resulting in an unpredictable rainfall pattern which further dwindles the amount of water on the earth. This eventually poses a threat to the survival of the life.

3.1  Water pollution It is a term that describes the deterioration or degradation or contamination of the water bodies including lakes, ponds, rivers etc. It is defined as the inclusion of foreign substances which degrade the physical, chemical and biological characteristics of water, and make it unfit for use. A 1969 United Nations report defined water pollution as: “The introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities, including fishing, impairment of quality for use of sea water and reduction of amenities.”  Water gets polluted due to a natural process of decomposition of organic matter or due to anthropogenic activities. The main reason of water pollution is the discharge of the contaminants like chemicals, garbage, microbe’s etc.

3.2 Types of water pollution

1. Surface water pollution: The reduction in the quality of rivers, streams, lakes etc., is termed as surface water pollution. The pollution is the outcome of the discharge of sewage and industrial waste into these sources. 2. Marine water pollution: Ocean pollution occurs due to harmful substances from sources like industries, cities, farms, atmospheric deposition, accidental spillage, deliberate dumping etc.

3.2  Environmental Science



3. Underground water pollution: Such pollution occurs whenever pollutants make their way down to ground water either by diffusion, precipitation, and adsorption or by decay. It leads to contamination of underground water. On the basis of nature of substance polluting the water, water pollution can also be classified as; 1. Physical water pollution: This type of pollution is due to change in the physical characteristics of water like colour, taste odour, transparency, turbidity etc. 2. Chemical water pollution: The change in acidity, alkalinity, pH due to presence of organic and inorganic dissolved or suspended substances in water causes chemical water pollution. 3. Biological water pollution: Such type of pollution is due to presence of pathogenic bacteria, virus, fungi, protozoa, worms etc. which are infectious making water unfit for human consumption.

3.3 Sources of water Pollution 1. Point sources are identifiable points or places, such as a pipe or channel, which discharge directly into a body of water. This includes wastewater treatment plants, factories and industrial plants, septic tanks etc. Such sources are measurable discharge points. 2. Non-point sources or diffused sources are those where pollution arises over a wider area and it is often difficult to locate the exact place of origin. For example, fertiliser or pesticide washed from a field by rain may seep into a river or stream at many places both on the surface and through the soil. Such sources are called diffused or plume sources of water pollution.

Fig. 1. Sources of Water Pollution

Water Pollution  3.3

3.4  Water Pollutants and its effects Any agent contributing to water pollution is termed as a pollutant. On the basis of degradation water pollutants are divided two types: 1. Degradable pollutants: These pollutants can be broken down by biological means such as decomposers or micro-organisms. Such pollutants are also known as organic pollutants, e.g., leaf litters, sewage, garbage, plants and animals. 2. Non-degradable pollutants: These pollutants cannot be degraded by biological means. These are also known as inorganic pollutants, e.g., chemical pollutants and solid toxic substances. Several categories of pollutants are: 1. Chemicals and heavy metals: The effluents from the industries are let into the water bodies resulting in a change in the chemical characteristics of the water bodies, mainly pH. This further leads to many health hazards. The presence of fluoride, arsenic, chloride, lead and other heavy metals also are very harmful in excessive concentrations. The harmful effects of the presence of these contaminants range from damage to teeth, spinal cord, kidney, nervous system to cancer. 2. Garbage: Improper waste management practices can lead to land, air and water pollution. Municipal wastes are created by household consisting of paper, plastics solid wastes, hazardous waste etc. Solid waste generally obstructs the flow of water and leads to its stagnation. This stagnant water behaves as a dwelling place for insects like mosquitoes which are responsible for diseases like malaria and dengue. Sometimes the infectious waste along with disposable syringes etc. is also let into the water bodies which could be injurious and hazardous. Disposal of substances like plastics also becomes a matter of concern as their pigment contains highly toxic heavy metals. 3. Organic: This kind of waste consists of the waste from gardening, food and drink preparation and processing, animal housing and horticulture. Such waste components result in Leachate i.e., the liquid produced from organic waste, which is extremely polluting. Organic waste components are decomposed by the bacteria present in water utilising oxygen present in water. This leads to a considerable decline in the oxygen content of the water bodies which helps support aquatic life and therefore poses a threat. 4. Biological: Biological contamination of water can lead to several water born diseases. Water could be a direct or an indirect medium for the spread of such diseases. Faecal waste let into the water bodies is responsible for enteric (intestinal) diseases. This waste includes pathogens, which are disease causing microbes such as virus, bacteria, protozoa, and parasitic worms. All these pathogenic organisms travel through water and infect the person coming in contact with contaminated water. Some of the pathogenic

3.4  Environmental Science

microorganism present in water include B. Pseudomallei, Cryptosporidium, Giardia lamblia, Salmonella. Norovirus and other viruses. Some of the common water borne diseases are typhoid, hepatitis, dysentery, cholera, and typhoid. 5. Suspended solids and sediments: Sand, soil, mud, and other solids disposed off into the water bodies are also major pollutants affecting the physical quality of water bodies. Heavy rains carry dirt and silt and deposit them into the water. Dirt and silt setteling in the water body, prevent sunlight from reaching aquatic plants which affects photosynthesis and suffocates organisms that live at the bottom of the body of the water. 6. Radioactive wastes: Activities like mining and processing ores, use of radioactive isotopes for research, materials from radioactive power plants etc., result in the inlet of harmful radioactive substances in the water bodies. These are harmful and can accumulate in the human body leading to serious effects Eg. Sr90 Other harmful effects of water pollution are: 1. Spilled oil on water, due to accidents, affects the ecosystem, and the components are detrimental. Many animals can get destroyed when they swallow oil or consume oil contaminated prey. Oil and antifreeze present in water develops a sticky film on the surface of water with a bad odour, killing the animals. This makes oil the most damaging pollutant in water. 2. Biological magnification: One of the major effects of water pollution is the damage to the food chain. When harmful toxins are present in water they are transferred to higher level organisms through the food chain. Dangerous pollutants such as lead and cadmium are eaten by tiny animals which are then consumed by fishes and larger sea animals. Heavy metals like lead, mercury, iron, cadmium, aluminium, and magnesium are present in water sources. If these metals are present in the sediment, these reach the food chain through plants and aquatic animals. This causes heavy metal poisoning in the water. Biological Magnification is the phenomenon of increase in concentration of pollutant per unit weight of organism with the rise in tropic terms. This increase can occur as a result of: (a) Persistence, where the substance can’t be broken down by environmental processes. (b) Food chain, where the substance concentration increases progressively as it moves up a trophic level resulting into biomagnifications. (c) Low or non-existent rate of internal degradation or excretion of the substance. An example of biological magnification is the accumulation of mercury in the higher level of organisms through fishes that eat plankton tainted with mercury (Minamata disease, Japan).

Water Pollution  3.5

Another example is the persistent use of pesticides which leds to biomagnifications of DDT and reduction in the population of birds. Regular use of pesticides in agricultural fields causes a gradual increase in their concentration. This high concentration proves to be toxic for animals. Fish-Eating Birds

Magnification of DDT Concentration 10,000,000 Large Fish

1,000,000

Small Fish

100,000

Zooplankton

10,000

Producers

1000

Water

Fig. 2. Biological Magnification





3. Rain water and irrigation water collected on cultivated land that has been fertilized and treated with pesticides: This contains a large amount of nitrogen and toxic chemicals that get mixed with the water supply thereby polluting water. Fertilizers increase the growth of bacteria in water and raise the concentration of bacteria to hazardous levels. 4. Eutrophication: The word is derived from two Greek words, Eu means ‘good/well’ and trophs means ‘food’. Thus eutrophic means well fed or nutrient rich. Eutrophication is the enrichment of a water body by nutrients which results in excessive plant growth either by natural process or due to anthropogenic activities. Nutrients which are main propellers of eutrophication are nitrogen and phosphorus. These nutrients are required for the growth of aquatic flora. It is a natural process of aging of a water body, which is quite slow and takes geological time to complete. But, when the nutrients are contributed by the anthropogenic sources like sewage discharge, detergents, runoff of manure, fertilizers, livestock wastes, poultry waste, food processing waste etc., the process is comparatively faster due to which the eutrophication cycle shortens and leads to extinction of the water body early than due to natural causes.

3.6  Environmental Science

The process starts with the oligotrophic lakes. Such lakes usually have clear water with no availability of life supporting nutrients. But slowly with the introduction of nutrients the lake becomes mesotrophic which has sufficient amount of nutrients to support biological activity and a self nourishing water ecosystem is created. Further increase in the nutritive content makes lake eutrophic. Excessive growth of plants (algal bloom) occurs due to continuous availability of the nutrients. The green blanket of the alga on the surface of water blocks the sunlight penetration thereby affecting the photosynthetic activity of the aquatic plants, which decreases the floral growth inside the water body, resulting in their destruction. The dead matter settles at the bottom of the lake resulting in its biodegradation. The process consumes oxygen dissolved in water and the dissolved oxygen (DO) level decreases in water. This suffocates the aquatic organisms surviving in the water body, which die gradually, and also add to the total organic load for degradation. This can also in extreme cases result in the extinction of many plant and animal species. The biological oxygen demand increases and an imbalance occurs between the rate of the decomposition and the rate of putrefying settlement of dead matter. The lake starts decomposition anaerobically producing gases like NH3, CH4, H2S, and liberating foul odour. The decomposition leads to creation of swampy or marshy land which gradually leads to the complete elimination of clear water body. Other consequences of the process is the clogging of the filters employed in water treatment plants, and death of birds and livestock feeding on such water, having toxic byproducts due to presence of bacteria like Clostridium botulinum. The flow of the water is slowed down due to long plants or filamentous weeds. It also traps the soild particles flowing along with the streams. Thus this water cannot be used for drinking and other purposes. Eutrophication can be controlled by adopting following measures: · Sewage water treatment to be ensured before discharging into water body. · Effective disposal of organic matter as sludge should be encouraged. This includes regular maintenance of lakes and removal of algal bloom mechanically or chemically. · Plantation of vegetation along the stream beads can be done so that absorption of nutrients can take place before water finally enters the streams. · Controlling the runoffs from the farms, and also regulating the amount and the timing of the addition of fertilisers to the fields, can serve to control eutrophication. The promotion of biofertilizers or manures can help reduce the problem. · Elimination of phosphates from detergents to reduce the contribution of phosphorus. · Mechanical aeration of the lakes can be encouraged to maintain the oxygen level in water body.

Water Pollution  3.7



· Several biological methods can also be adopted and experimented where certain micro-organisms can convert the excess of nutrients into harmless components.

3.5  Control Measures







1. Locating the point sources of water pollution and eliminating them. 2. Reduction of the quantity of waste or pollutants generated by an activity is the most desirable approach for pollution control. 3. Preventing air pollution can help reducing the acid rain which affects and increases the acidity of the water bodies. 4. Farmers must be provided guidance on good agricultural practices that will help reduce water pollution from agriculture. Minimising soil erosion by improved agricultural practices (e.g. by minimising surface runoff and leaving crop residues in the ground), more efficient use of nutrients (e.g., though the use of slow release fertilisers) and the development and use of biological pest control techniques in preference to the use of nonbiodegradable toxic chemicals are some of the measures for minimising water pollution from agriculture. 5. Biological (water hyacinth) and chemical methods can be adopted to reduce the water pollution load. Scientific techniques should be adopted for environmental control of catchment areas of rivers, ponds or streams. 6. The pollutants must be treated chemically and must be converted into the non toxic substances before discharging into the water body. 7. Administration of water pollution control should be in the hands of state or central government. Laws and practices should be recognized to prevent water pollution. Firm legislation should be enacted to make it obligatory for the industries to treat the waste water before being discharged into water bodies. 8. Public awareness must be initiated regarding adverse effects of water pollution. 9. Conservation is an important way to help preserve water as a global resource. (Treating water to make it clean enough to drink and use around the house requires a lot of energy, so it’s important to conserve as much water as possible, especially in areas where droughts are occurring).

3.6  WATER MANAGEMENT AND CONVATION Water management is the monitoring and control of the water resources to minimize ecological losses under set policies and regulations. Water conservation refers to the judicious utilization of the water resource for sustainability. Water

3.8  Environmental Science

conservation mainly aims at, ensuring water availability for present as well as future generations including conservation of energy and habitat. This also involves educating the common people, policy makers, farmers and land holders regarding the necessity of water conservation. Rain water harvesting is one such water conservation techniques. Trapping and storing of rain water for its future use is called rain water harvesting. It includes installation of rain water catching ducts, terracing slopes, expansion of water reservoirs, digging of ponds and lakes, construction of barrage, slopes and trenches etc. Another strategy is the protection of ground water resources from contamination. Also, sustainable utilization of ground water helps natural replenishment of water table. The protection of watersheds through maintenance of naturally vegetated strips along river banks and lakes also improves water storage and its quality. Watershed is a land area on which water flows across, or through it, on its way to rivers or lake. Watershed management framework supports sound and well planned scientific approach for natural water systems. It includes recognition phase followed by restoration, protection and improvement of the natural system. Efficient water management is an absolute priority for each and every human being for ensuring the availability of fresh and clean water for future.

3.7  Waste water Treatment Wastewater treatment is a process used to convert wastewater into a usable form that can be returned to the water cycle with minimal impact on the environment.

3.7.1 Waste Water Analysis The main objectives of the analysis are: 1. To evaluate the quality of waste water 2. To determine the extent of pollution 3. To decide the type of treatment method and technology 4. To check operational efficiency of treatment units 5. To prevent water pollution 6. To reuse water by effective and economical water management

3.7.1.1 Water Analysis Parameters 1. Physical: Physical analysis is the first step towards judging the purity of the water sample. Below are some of the important components in physical analyses (a) pH: It measures the potency of hydrogen ion concentration. pH is measured in a scale of 0 to 14 where the lower value of pH indicates acidity of the water sample whereas higher value of pH indicates alkalinity. pH 7 is considered to be neutral. A pH meter is generally used to detect the pH of the water sample.

Water Pollution  3.9

Fig. 3. pH meter

(b) Colour: There are many reasons for the occurrence of colour in water. The occurrence of colour primarily indicates the presence of impurity in water. The presence of colour in the water bodies need not necessarily be harmful until it is associated with the toxic chemicals. The presence of colour affects the amount of sunlight penetrating the water body and adversely affects the aquatic life. Some of the examples are the occurrence of a dark brown colour due to tannin in water, also a greenish colour due to the presence of algae. (c) Suspended solids: The term refers to the free floating solids present in water. Total suspended solids (TSS) determination is carried out by pouring the water sample through a filter with a definite pore size, which is pre weighed. After filtration the mass on the filter is dried and weighed and the weight expressed in mg/L. (d) Dissolved solids: Total dissolved solids (TDS) are those present in water and are not visible through the naked eyes. The components included in TDS are the salts of calcium, magnesium, sulphates etc. And even minor quantities of the organic matter dissolved in water. An increase in the TDS concentration may result in water becoming more corrosive, brackish and leading to scale formation. It could also affect the efficiency of the water sample for cooking or heating purposes.TDS is determined by taking a measured volume (100mL approx.) of sample and passing it through standard glass fibre filter. This filtered liquid is then poured into a ceramic dish which is pre weighed and kept in an oven maintained at 103-105OC. Dry the mass obtained till a constant weight is obtained. The weight of the residue, is noted. (e) Turbidity: Turbidity refers to the muddiness or cloudiness in the water samples. Turbidity in water arises mainly due to the presence of tiny suspended particles which are invisible by the naked eyes. The particles suspended could be sand, silt, mud, chemical precipitates and even

3.10  Environmental Science

germs and bacteria. Turbidity may block the pores of the zeolite and ion exchangers when water is subjected to purification. Also it can cause damage to the water pipes and valves which are in water passage. Turbidity in water samples can be determined by using turbidity meter. Nephelometric turbidity units (NTU) or Jackson turbidity units (JTLJ) are usually used for the measurement of turbidity.

Fig. 4. Turbidity Meter

2. Chemical: It becomes very necessary to carry out the chemical analysis of the samples of water in order to use the water samples for different purposes. (a) Alkalinity: It is defined as the tendency of water to neutralise an acid. The ions primarily responsible for alkalinity are OH-, HCO3- and CO3-2. OH-, HCO3- ions cannot exist together as these combine as below OH + HCO3– ® CO3–2 + H2O Alkalinity also helps to determine the amount of acid which could be added to water without changing the pH significantly. (b) Dissolved oxygen (DO): It is the amount of oxygen present in lakes, rivers ponds etc. Dissolved oxygen is very important for supporting the aquatic life. Fishes, plants, invertebrates etc. require oxygen for respiration. Oxygen is also required by organisms such as fungi and bacteria for the decomposition of the organic matter present in the water bodies. The concentration of DO present in the water bodies can vary from 1mg/L to 20mg/L depending on the factors like organism population, aeration and decomposition of the organic matter present. (c) Biological oxygen demand (BOD): It is the measure of the amount of oxygen needed by the organisms present in water to breakdown the organic matter present at a particular temperature and over a specified period of time. The determination is helpful in knowing about the pollution of water streams, lakes etc. The extent of BOD is of used to the water treatment plants. BOD of less than 1mg/L is usually present in drinking water. (d) Chemical oxygen demand (COD): It is a measure of the amount of oxygen which is required for the oxidation of the organic content present in water. It is also indicative of the amount of organic matter present in water.

Water Pollution  3.11

(e) Free Chlorine: Chlorine is considered to be the most ideal disinfectant. Chlorine can be added to water in the form of bleaching powder, chlorine gas or chlorine dissolved in water. Whenever chlorine is added to water some amount of the chlorine added reacts with the organic matter present in water and some of it remains available, known as free chlorine which possesses disinfecting action against disease producing bacteria. The sterilising action of chlorine is due to the production of hypochlorous acid and nascent oxygen on reaction with water. (f) Hardness: The inability to form lather with soap is termed as hardness. It is due to the presence of salts of calcium at magnesium. Hardness of water could be temporary (CO32- and HCO3-) or it could be permanent (Cl- and SO42-). Ethylene diamine tetra acetic acid is generally used to determine the hardness of the water sample using EBT indicator. (g) Bacterial: Besides the above mentioned parameters the determination of the presence of bacteria in the water sample also becomes essential, especially when it comes to portable water. More commonly the presence of coliforms, are indicative of the sanitary conditions of water. Coliforms are the bacteria which are found in the digestive tract of human beings and animals and are present in their faecal matter.

3.7.2 Treatment Process 3.7.2.1 Domestic Waste Water It is a liquid waste originating from the sanitary conveniences of domestic, residential, institutional, commercial and other public places. It consists of 99.9% water and 0.1% organic and inorganic solids. The organic matter includes carbohydrates, fats, proteins, urea, while inorganic includes ash clinkers sand mud grits etc. Sewage water also contains living organisms like algae, bacteria, virus, rodents etc. The sewage treatment is generally divided as: (a) Primary treatment (b) Secondary or biological treatment (c) Tertiary or final treatment.

Primary Treatment Primary treatment is carried out for the removal of the floating and the suspended materials including oily impurities. The major process involved in it includes: (a) Screening: A screen is a device with openings of uniform size for removing bigger suspended floating matter present in raw sewage. The process of removal of floating /suspended materials like leaves, papers, wood, twigs,

3.12  Environmental Science

dead animals etc. present in sewage water, with the help of screens is called screening. Direction of flow Effluent

Section Bars for screen

Perforated metal platform for screenings

Effluent

Fig. 5. Screens

(b) Grit chamber: These are the channels devised to remove the heavier materials like sand ash clinkers, egg shells, bone chips, from sewage water using the principle of sedimentation due to gravity. grit chamber raw sewage sewage with grit removed

grit removed periodically from collection trap

Fig. 6. Grit Chamber

(c) Skimming tanks: Materials like grease, oil, fatty acids, mineral oil, waxes, soaps etc from kitchens, restaurants and garages are allowed to pass through a tank where the compressed air is introduced from the bottom of the tank. The rising air bubbles coagulate the oily material which can be removed from the tank manually or by some mechanical device.

Water Pollution  3.13

Stilling compartment Slotted battles

Air pushed up-wards

Fig. 7. Skimming Tank

(c) Sedimentation: The process of keeping the sewage water undisturbed for some time in settling tanks where the suspended organic matter settles down is called sedimentation. The storage tank in which the flow of water is retarded is called sedimentation tank. The process of sedimentation is performed to remove gross settleable organic matter in order to avoid formation of sludge banks, clogging of treatment units and to reduce load on secondary units.

Decanting trough (outflow)

Sludge scraper arm

Sludge collecting trough Sludge Inlet

Fig. 8. Sedimentation Tank

Secondary Treatment This treatment method is carried out for the removal of finely suspended and dissolved organic matter present in the effluent from primary treatment unit.

3.14  Environmental Science

The processes involved are biological flocculation and precipitation followed by secondary sedimentation. The treatment process is also called biological process as it involves the conversion of unstable organics into inorganics with the help of microorganisms. The biological process is of two types viz. attached growth or suspended growth system. The attached growth system involves decomposition where microorganism perform their work by remaining attached to an inert support medium, while in case of suspended system the microbes remain suspended in the waste water and are aerobically free to perform decomposition anywhere in the bulk of the waste water.

Attached Growth System Trickling filters are the most commonly used biological treatment methods, involving the attached growth system. They are also called sprinkling or percolating filters. These consist of a bed of coarse, hard, rough filter media (silica sand, anthracite coal, activated carbon, metal fabric etc) over which sewage is sprayed. As sewage trickles down, biomass grows attached to the media surface. The organic matter present in the sewage is metabolised by the biomass. The attached biomass is called biological film or slime layer. The aerobic bacteria present in the biological film oxidize organic matter of the sewage. When the size of the microbial population increases it builds up starvation like condition for the microorganisms in the lower portion of slime layer. Here, microbes undergo endogenous phase of growth and loose their ability to cling to the media surface (sloughing of filter). The wasted biomass appears as suspended matter in the effluent. Rotating head/sprinkler

Ground level

Sewage inlet

Inert support Under drains

Fig. 9. Trickling Filter

Suspended Growth System Activated sludge process is the biological treatment process involving aerobic suspended growth systems. In this, sewage containing waste organic matter is aerated in a tank in which active biomass metabolizes the soluble and suspended organic matter. The resulting biological floc from the secondary sedimentation tank

Water Pollution  3.15

is recycled continuously to the aeration tank. This accelerates biological oxygen demand (BOD) removal. The main components of an activated sludge treatment process are aeration tank, sludge recirculation system, aeration system, excess sludge disposal system, primary and secondary sedimentation tank. The important features of activated sludge process are: · The biomass remains suspended in water · The biological films move in the bulk of the sewage · The treatment process (decomposition) is more efficient than trickling filter · It is more cost intensive than attached system Air

Preliminary treatment

Primary clarifier

Aeration Tank

Decondary clarifier

Wastewater influent Recycle Activated sludge Waste activated sludge

Primary sludge To sludge treatment and disposal

Fig. 10. Activated Sludge Process Flow sheet

Tertiary Treatment Tertiary treatment or advance water treatment is carried out for removal of contaminants from sewage water. It aims at removal of residual organic and inorganic substances in waste water. It is also used when · The quality of the effluent provided by secondary treatment is not upto the standard · For removal of nitrogen and phosphorus like substances · For removal of pathogens · When water need to be reused for drinking purpose or other domestic activities The various treatment processes are: 1. Ion exchange: The ion exchange process involves passing of water through a bed of ion exchange resin. During this, the undesirable ions are exchanged with similarly charged useful ions of the resins and are thus removed.

3.16  Environmental Science

2. Adsorption: This method is adopted to remove non-biodegradable organics, colour and odour producing substances from industrial effluent. This process involves use of adsorbents like activated carbon, alumina, bone charcoal etc. for the removal of impurities. 3. Disinfection: This method is usually the final process in domestic waste water treatment which involves the destruction of pathogenic microbes in water. The substances employed for their removal of pathogens are called disinfectants. These include the use of chlorine in the form of a liquid or gas, bleaching powder, ozone etc. These disinfectants deactivate the metabolic activities of the microbe’s thereby leading to the death of the microbes.

Other Treatment Processes Sludge treatment: Sewage sludge is a semi liquid mass formed out of solids of sewage mixed with varying amounts of water. It is the by product of sewage treatment plants. Its treatment is an important task in waste management. The treatment process is carried out using Sludge digestion tank. The sludge digestion tank consists of large cylindrical RCC tank with narrow bottom and is covered by fixed or floating roof. The principal purpose of sludge digestion includes: · Reduction of its putrefying ability · Removal of pathogens · Removal of usable water The above tasks are achieved by decomposing the organic matter under controlled anaerobic conditions. This is called sludge digestion. During this organic matter is converted to methane, carbon dioxide and water. This treatment can be carried out in a variety of tanks/ditches as below:

Roller

Gas dome ventilator Manhole Minium sludge level Gas

Supernatant removal Sludge inlet piping Stabilized sludge outlet

Fig: 11. Sludge Digestion Tank

Water Pollution  3.17

Septic tank: A septic tank is a combined sedimentation and digestion tank useful for small populations. The principle process involved is sedimentation and anaerobic decomposition. The organic matter results into formation of gases like methane, hydrogen sulphide, ammonia etc. Septic tank is generally rectangular in shape with or without narrow bottom and has two chambers. Access covers Vent Inlet

Inlet-T Outlet Scum

Sedimentation zone

Sludge

Fig. 12. Septic Tank

Imhoff Tank It is a two storied tank which has sedimentation tank on the upper chamber and a digestion tank on the lower region. As the sewage enters the imhoff tank the solids of the sewage settle in the sedimentation chamber through a narrow slot. The slot of the upper chamber is so adjusted that the gases produced during the process do not escape out through it. The tank is provided with a gas vent at the top. The collected sludge is withdrawn periodically through the sludge pipe. Biogas

Biogas

3. Gas vent and scum section Influent raw wastewater

Effluent pre-treated wastewater

Outlet partial treated sludge

1. Sedimentation

2. Sludge digestion

Fig. 13. Imhoff Tank

3.18  Environmental Science

Oxidation Ditch This treatment is operated for the small quantity of waste water produced by small communities. It is simple and a cheap method. The raw sewage is directly introduced into the aeration units which are 150-1000m long 1-5m wide and 1-5 m deep. Each ditch is equipped with rotor for agitation and oxygenation. The channels are followed by sedimentation tank and activated sludge is directed to ditch channels. Aerobic decomposition

Oxidation ditch Channels

Anaerobic tank

2° Clarifier

Raw sewage

Effluent

Fig. 14. Oxidation Ditch

Oxidation Pond These are the basins designed to treat sewage water. In this the putresible organic matter gets stabilized through symbiotic relationship between bacteria and algae. The sewage flow provides the organic matter to the aerobic bacteria which oxidize to carbon dioxide and nutrients. This carbon dioxide is used by algae which in turn gives oxygen to the bacteria. Sunlight

Wind (wind action promotes mixing and reaeration)

If oxygen is not present in upper layers of pond, odorous gases can be relased

O2 (during daylight hours)

O2 Reaeration

New cells

Algae

Wastewater

Dead cells

O7 Settleable solids Bottom sludge Organic wastes

NH3, PO–34, etc.

CO2

CO2

H 2S

NH3, PO–34, etc.

Aerobic zone

H2S +2O2  H2SO4 Bacteria

New cells

Facultative zone

Dead cells Organic acids, alcohols

CO2 + NH2 + H2S + CH4

Fig. 15. Oxidation Pond

Anaerobic zone

Water Pollution  3.19 Preliminary treatment Raw sewage

Screen

Primary treatment Grit chamber

Primary sedimentation tank

Secondary treatment Aeration tank

Secondary sedimentation tank

Tertiary final effluent

Recycle sludge Gas (CH2, CO2) Secondary sludge Sludge digestion tank Supernatant

Secondary sludge

Sludge disposal

Fig. 16. Flow Chart of Conventional Sewage Water Treatment

3.7.1.2 Industrial Waste Water Industrial wastewater is the water that has been produced during the making of any commercial product. It is a by-product of industrial or commercial activities. This water constitutes organic matter, inorganic (sodium, potassium, calcium, magnesium, copper, lead, nickel, and zinc), pathogens, and nutrients (most notably nitrogen and phosphorus). Also referred to as “waste water,” industrial wastewater differs from domestic wastewater or municipal wastewater (also called sewage). Industrial waste water differs in is composition depending upon the industry where it has originated from, while the composition of domestic water is more or less the same. The toxicity level of industrial waste water is high. The method used for treatment of industrial water depends upon the composition of the wastewater.

3.8 Case Study

1. Santa Barbara Oil Slick (1969): On 28th January, 1969 when union oil company was performing oil drilling operation about 13 km from Santa Barbara channel, unexpected pressure change blew out all the drilling mud leading to vigorous spurting of crude oil for about 10 days. This oil slick resulted into death of many aquatic life and sea birds. 2. One of the dangerous effects ground water pollution came into light when bottled water was found to contain pesticide residues. Pollution Monitoring Laboratory, New Delhi found presence of pesticides in about 17 brands of bottled water above the permissible limits. Repeated exposure to even low concentration of pesticide residue can cause severe effects on living systems.

Interesting Facts

· Fresh water in the world is only 2.5% of the total water available on this planet.

3.20  Environmental Science



· The percentage of discharged untreated sewage, polluting rivers, lakes and coastal areas is more than 80%. · In China more than 70 percent of rivers and lakes are polluted. · In European and North American lakes and reservoirs, Eutrophication was recognized as a pollution problem in the mid-20th century. · According to the World Health Organization, 3.2 million children under the age of five in developing nations die each year as a result of unsafe drinking water and poor sanitation.

Review Questions

1. Define water pollution. What are its sources? 2. Write in short on Eutrophication. 3. Why is the analysis of water carried out? Explain various physical and chemical characteristics of water. 4. What are the objectives of waste water treatment? 5. Draw a typical layout of sewage water treatment plants. 6. Explain the theory of activated sludge process. 7. Write short note on digestion of sludge. 8. Differentiate between primary and secondary treatment process. 9. What is tertiary treatment of waste water? Why it is done? 10. Suggest various control and remedial measures to curb water pollution.

4

Air Pollution

Atmosphere is one the major components of earth’s ecosystem. It is essential for the survival of living organism. It consists of a thin layer of gases hovering over our planet and provides us air to breathe, and protection from harmful ultraviolet rays. By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases and water vapours.

4.1  Air Pollution Air pollution refers to the introduction of harmful substances in air. Whenever gases, dust, fume and odour is present in harmful amounts, air is said to be polluted. A contaminant that affects living organisms and property, and interferes with the pleasure of life is termed as an air pollutant. The problem of air pollution is alarming due to an increase in population, industrialization, increase in the number of automobiles and urbanisation. The presence of contaminants in air can be injurious to human health, plant life or even property. Pollutants such as smoke, dust, and several gases are continuously being released into the atmosphere due to several human activities, volcanic eruptions, forest fires, storms etc. These pollutants remain in the atmosphere until these are absorbed by the natural sinks (Humans or ocean). Problem arises when these contaminants are produces at a faster rate than their absorption. In such cases these accumulate, thereby affecting the environment. Some of the major components are the harmful gases like Carbon monoxide (CO), Carbon dioxide (CO2), Chlorofluorocarbons (CFC), Nitrogen oxide (NOx), Sulphur dioxide (SO2), and Ozone (O3).

4.2  Sources of Air Pollution Natural sources of air pollution include volcanic eruptions, forest fires, cosmic dust, decomposition process, pollen grains, sand storms etc. Man made or anthropogenic sources are the burning of fossil fuels, vehicular emissions, industrial exhausts, agricultural practices, wars etc.

4.2  Environmental Science

Point sources Stationary sources Nonpoint sources Air pollution sources Mobile sources

Line sources Area sources

Fig. 1. Sources of Air Pollution

4.3 Classification of air pollutants 1. According to origin (a) Primary pollutants enter directly from the sources into the atmosphere. Some of the examples of primary pollutants are CO, NO2, SO2 and hydrocarbons. (b) Secondary pollutants are the ones which are derived from the primary pollutants. For e.g., Ozone, photochemical smog etc. 2. According to chemical composition (a) Organic pollutants: Organic pollutants are of organic origin e.g., Hydrocarbons, amines, alcohols etc. (b) Inorganic pollutants: Inorganic pollutants are compounds of nitrogen, sulphur, halogens etc. 3. According to state of matter (a) Gaseous pollutants: CO, NOx etc. which are gaseous in nature come under this category. These also include organic gases like benzene, methane, butane, etc. (b) Particulates: These include smoke, fumes, sprays, dust etc. consisting of finely divided solids or liquids in colloidal state. 4. According to mobility: (a) Stationary sources: Sources could be classified as stationary and mobile depending upon their mobility. Sources which are stationary are also point sources. Industries, dry lake beds and landfills are point sources. (b) Non stationary are known as non-point sources. Vehicles, farming and construction equipments, planes and trains are non-point sources. Some important air pollutants and their sources have been summarised in Table 1.

Air Pollution  4.3

Table 1: Important Pollutants

Pollutant Carbon monoxide Sulphur dioxide Nitrogen oxides Hydrogen sulphide Chlorine Particulate matter Ozone Lead

Sources Incomplete combustion of carbon based fuels like petrol and diesel, and combustion of natural and synthetic products. Burning of coal in thermal power plants and industrial processes. Petroleum industry, sulphuric acid plants and domestic burning of fuels. Vehicles, power plants, coal fired and gas fired furnaces, explosive industry and fertiliser industry. Petroleum industry, dye and tanning industry, sewage plants, fertiliser industry and glass manufacture industries. Electrolysis of brine, industrial processes and breakage of chlorine cylinders. Combustion and burning of fuel, industrial processes, road construction. Volatile organic compounds and nitrogen dioxide form ozone as a result of photochemical reaction Metal refineries and other metal industries, automobile emissions, burning of coal, pesticides containing lead and arsenic, mining practices, waste incineration and manufacturing of lead batteries.

4.4  Adverse effects of air pollutants The different pollutants present in air pose threat to animals and human beings. Air pollutants such as carbon monoxide, oxides of sulphur and nitrogen, hydrocarbons and particulates are the important contributors. The effects are as under: A. Effects on human health and animals: The pollutants present in air are absorbed during inhalation. The impurities in the inhaled air can affect living beings in a number of ways. The impact depends upon the type and concentration of the air pollutants. Various effects are: (a) Major respiratory disorders caused due to the presence of pollutants in air. (b) Gases such as carbon monoxide combines with haemoglobin forming carboxy haemoglobin thereby reducing its oxygen carrying capacity of the blood leading to loss of judgment of the person. Also, it may lead to asphyxiation (chocking leading to death). (c) Oxides of sulphur lead to breathlessness, reddening of the eye and spasm of larynx. The oxides of sulphur are absorbed quickly and

4.4  Environmental Science









B.



C.

irritate the upper respiratory tract. These lead to the formation of H2SO4 interrupting the enzymatic activity. (d) Nitrogen oxides also interrupt with the oxygen carrying capacity of the blood leading to death. (e) Pulmonary effects, oedema and haemorrhage have been observed in dogs, cats, and rabbits on exposure to air contaminated with ozone. O3 also inhibits the activity of enzymes involved in the synthesis of cellulose and lipids. (f) Hydrocarbons if present in the environment react with the living cells. Certain hydrocarbons eg. benzopyrene show carcinogenic and mutagenic activity. (g) A number of particulates like pollens can initiate asthmatic attacks; dust particles can cause silicosis and asbestosis. (h) Hydrogen fluoride can cause fluorosis and mottling of teeth. (i) Accumulation of lead in animals causes paralysis and breathing troubles. There is complete loss of appetite. A prolonged exposure to lead can cause digestive system problems, damage the nervous system and even cancer. Effects on plants: Pollutants present in the atmosphere affect the plants adversely. (a) Acid rain formed as a result of the pollutants destroys the leaves reducing the levels of nutrients available to them thereby hindering their growth. Also, the nutrients present in the soil dissolved in acid rain and get washed away with a reduction in the nutrient content available to the plants. (b) Chlorosis (yellowing of the leaves), mottling, bronzing, reddening and stunted growth are affects of excessive sulphur dioxides. (c) Ozone as a pollutant directly affects the stomata and interrupts in the photosynthetic activity of the plant leading to stunned growth. (d) Excessive ultraviolet radiations enter the earth as a result of the ozone holes causing damage to plants and trees. (e) Oxides of nitrogen are responsible for suppressed growth of the plant and bleaching of the leaves. (f) Ethylene gas can lead to leaf abscission and leaf epinasty (folding of leaf). Economic effects: (a) Air pollution leads to corrosion of metals. (b) The acid deposition leads to damage of buildings, arts and architecture. (c) Pollutants like oxides of sulphur, ozone; hydrogen sulphide lead to destruction of paints and protective coatings and enhance the chances of corrosion.

Air Pollution  4.5

(d) Materials like rubber, textile fibers, paper, glasses, ceramics etc. are destroyed by the air pollutants like SOx, NOx, PAN, O3 (e) Due to destruction of arts and monuments, and degraded air quality, tourism industries are affected. (f) Expenditure is incurred due to adoption of technical measures for reducing the air pollutants. D. Effects on environment: The impact of air pollution on the environment has been broadly categorized as:

4.4.1 Global Warming The increase in the environmental pollution is leading to an increase in the amount of carbon dioxide in the atmosphere. This gas is released into the atmosphere as a result of burning of fossil fuels, forest fires, smoke from the vehicles etc. The solar radiation entering the earth is reradiated to the atmosphere. Carbon dioxide layer present prevents the reradiated heat to get dissipated into the space leading to an increase in the temperature of the atmosphere. This phenomenon is known as Green house effect. Solar radiations passing through atmosphere

Reflection by earth

Reflection by atmosphere

Infrared rays by earth

Fig. 2. Green House Effect

Some other gases also contribute to green house effect such as methane, nitrous oxide, water vapour and chlorofluorocarbons. The former arises from livestock manure and termite digestion whereas the latter comes into the atmosphere from their use as refrigerant and spray can propellants. Due to continuously increasing amount of such green house gases the average temperature of earth is raising worldwide. This elevation in temperature occurring globally is called global warming. The anthropogenic sources contributing to the problem are industries, transportation, deforestation, overpopulation etc.

4.6  Environmental Science

Changes in the global temperature alter the precipitation patterns, climate, and weather events. Other effects of global warming include increased sea level, submerged low lying areas, floods or drought like conditions, disturbed aquatic ecosystem, species extinction, reduced plant growth, massive crop destruction, destruction of habitats etc.

4.4.2 Acid Rain Acid rain is a kind of precipitation containing elevated levels of hydrogen ions. Normal rain water is slightly acidic with a pH range of 5.3-6.0. When the pH level of  rain water falls below this range, it becomes acid rain. This usually results from the oxides of nitrogen and sulphur.

Fig. 3. Acid Rain

The oxides of nitrogen and sulphur get converted into mild nitric acid and sulphuric acid and fall as acid rain. The acidic compounds formed in the troposphere region can descend down to the ground as rain, hail, fog or snow and is referred as wet deposition. Also, acidic particles and gases may deposit over water bodies, vegetation, buildings from the atmosphere in the absence of moisture as dry deposition. CO2 + H2O ¾® H2CO3 ...(1) SO2 + H2O ¾® H2SO4 ...(2) NO2 + H2O ¾® HNO3 ...(3) A small portion of the SOx and NOx that cause acid rain is from natural sources such as volcanoes, and lightning but the major contributor is the combustion of fossil fuels employed for generation of electricity, to run vehicles and industries.

Air Pollution  4.7

Acid rain is harmful for human beings, aquatic animals, plants and infrastructure. The flora and fauna of the aquatic environment of rivers, ponds, streams and lakes, gets directly affected as a result of acid rain. It harms the plants leaving brown and dead leaves. The soil ecosystem is also adversely affected. Trees become weak as the sunlight absorbing capacity decreases. Acid rain generally causes corrosion of metal structures, weathering of buildings and leads to peeling of the painted surfaces. It leads to leaching of minerals from the soil. The bacterial and fungal microorganisms of the soil also get affected due to acid rains.

4.4.3 Ozone Depletion The ozone layer is a blanket of naturally occurring colourless ozone gas lying 15 to 30 km above the earth in the stratosphere. It acts as a protective shield from the harmful ultraviolet radiation emitted by the sun. Ozone is continuously produced and destroyed in the stratosphere in the presence of UV radiations. The formation of ozone in the stratosphere takes place as under O3 + light ¾ ® O2+ O ...(4) O + O3 ¾® 2O2 ...(5) Net: 2O3+ light ¾® 3O2 ...(6) This ozone layer has becomes thinner towards the south pole. The ozone concentration has fallen by 40% within the past forty years. The reduction in the concentration of ozone in the stratosphere is termed as ozone hole. Carbon dioxide from combustion, CFCs, halons, HCFs from refrigeration units, air conditioners, cleaning agents and aerosol sprays and methane from anaerobic digestion are the main causal factors of ozone depletion. Ozone depleting substances (ODS) have a long lifetime in our atmosphere. Depletion of ozone starts when a pollutant like CFC which gets broken down and releases chlorine atoms. Chlorine atom reacts with ozone and destroys it. Solar and ultraviolet radiation

(Chain reaction)

CFC-11(CFCl3) Chlorine monoxide (ClO) Chlorine atom (Cl)

+ Ozone molecule Chlorine atom (O3) (Cl) CFCl2

Fig. 4. Depletion of Ozone

Oxygen molecule (O2)

4.8  Environmental Science

Due to the creation of such a depleted zone of low ozone concentration the harmful UV radiations reach the earth’s surface causing harm to the crops, skin cancers, sunburns, decreased immunity and cataracts (clouding of eye lens) in human beings. It affects the physiological and developmental process of the plants. UV radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians, and other marine animals and also severely decreases reproductive capacity.

4.4.4 Photochemical Smog Smog means smoky fog. Smog is an air pollutant that is formed in the atmosphere when gases and chemicals interact with sunlight. Two types of smogs are recognized. One is coal induced and other is photochemical smog. Coal induced smog is formed by the interaction of sulphur dioxide and water to form mist of sulphuric acid. This is also referred as London smog as it was first observed in London (1952). The burning of coal is the major reason why sulfur oxides are released into the air, the other causes stem from the production of crude oil and metallic ore. Photochemical smog is oxidizing smog formed due to interaction of nitrogen oxide, hydrocarbons and sunlight. Photochemical smog is composed of primary and secondary pollutants. It is visible as a brown haze, and is most prominent during morning and afternoon, especially in densely populated, warm cities. The first noticed incident of this smog was in Los Angeles, USA and thus it is sometimes referred as Los Angeles Smog. Its main contributors are the coal fired power plants, volatile organic compounds, and vehicular combustion. The NO2 when released form these sources to the atmosphere due to the influence of ultraviolet rays, undergoes a series of reactions along with other pollutants like hydrocarbons to form mixture of ozone, nitric acid, peroxyacyl nitrates (PAN). Even small traces of these substances can affect the respiratory tract of humans and animals, and damage crops and trees. Breathing problems can become aggravated due to prolonged exposure to smog. Some of the toxins produced during the formation of photochemical smog are carcinogenic. NO

VOC

NO2

VOC

UV NO + O

O2 O3

Fig. 5. Photochemical Pollutants

PAN

Air Pollution  4.9

4.5 Control measures

1. Industrial solutions: Industries should be located away from the city and the power plants should be equipped with smoke precipitators, filter devices, carbon capture systems etc. to reduce the percentage of pollutants present in the effluent air. 2. Improved vehicle design: The use of catalytic converters and efficient air filtration unit in vehicle systems should be encouraged as these help to control pollution. 3. Use of public transportation: People should be encouraged to use public transport as the increase in the number of private vehicles increases pollution. Vehicle pooling can reduce energy consumption as well as saves money. 4. Use of eco-friendly fuel: Selection of the fuel should be done considering low levels of impurities like sulphur, nitrogen, absorbed gases and ash. The use of fuel derived from non conventional energy sources should be developed and used. 5. Conservation of energy: It is required that the presently available energy resources should be efficiently and judiciously used so that their availability can be sustained. For example, turning off of light when not in use, buying green electricity, using natural gas, using rechargeable battery etc. 6. Afforestation: Tree plantation should be done along the road side as trees absorb the particulate matter, carbon dioxide and sound. Trees clean the air by absorbing carbon dioxide and introducing oxygen. 7. Enforcement of laws: The emission rates of the industries should be restricted. Governmental agencies must enforce strict rules and regulations for controlling air pollution. Air pollution monitoring should be carried out at definite intervals so as to maintain a safe environment. 8. Following 3 R’s: Reduction, reuse and recycling of materials helps to combat the problem of solid waste disposal and decreases load on industrial production. Reduction in the use of substances like lead in paints, cleaning agents and petrol, reduced use of vehicles, smart driving practices, recycling of paper etc. can contribute to the reduction of pollution. 9. Awareness: Technological advancement and laws enforcement cannot be successful unless people do not contribute to fulfilling the aim of air pollution reduction. People should be educated regarding the causes and harmful effects of air pollution.

4.5.1 Control Devices Air pollution control devices are a series of devices that work to prevent a variety of different pollutants, both gaseous and solid, from entering the atmosphere. These control devices can be separated into two broad categories – devices that control

4.10  Environmental Science

the amount of  particulate matter escaping into the environment and devices that control gaseous emissions.

4.5.1.1 Devices for Particulate Contaminants

1. Settling Chamber: It is one of the simplest devices used for collection of particulate materials present in the air. It basically consists of a chamber in which the dust laden gas velocity is reduced so as to allow the particulates to settle down due to gravity. Dust laden gas inlet Settling chamber

Hopper

Clean gas

Hopper

Fig. 6. Settling Chamber

2. Cyclone: It is equipment where the velocity of the inlet air is transformed into vortex from which the centrifugal forces tend to drive the suspended particles to the wall of the cyclone. Because of the difference in inertia of gas particles and larger particulate matter, the gas particles move up the cylinder while larger particles hit the inside wall and drop down. The dust drops downwards by gravity to the hopper bottom of the cyclone. Cyclones are widely used to control pollutants from cotton gins, rock crushers, and many other industrial processes that contain relatively large size particulate in the air. Clean gas

Dust laden gas

Hopper

Dust outlet

Fig. 7. Cyclone

Air Pollution  4.11



3. Fabric Filters: The use of fabric filters is one of the fairly simple methods that can be used to remove dust from flue gases. In such device the dust laden gas enters a bag house and passes through a bag filter made up of felt cotton, glass fiber, teflon, wool etc. Bag houses are used to control air pollutants from coal-fired power plants, steel mills, foundries, and other industrial processes. Butterfly valve Clean backwash air Bag support Bag supported by rings

Clean gas

Tube sheet

Dirty gas Left side cleaning cycle

Right side filter cycle

Collected solids

Fig. 8. Bag House

4.5.1.2 Devices/methods for Gaseous Contaminants 1. Adsorption: It involves passing of the gas stream through a porous solid material like activated carbon, activated alumina, fuller’s earth, silica gel etc., contained in an adsorption bed. The surface of the porous material attracts the adsorbate ( gas) either by physical or by chemical forces. The devices working on this principle are called adsorbers. 2. Absorption: It involves the contact between the contaminated gas and absorbing material in presence of a solvent (absorbent) in a unit called absorber. Various types of absorbers available include, spray towers, tray towers, packed towers, venturi scrubber etc.

4.12  Environmental Science Clean gas out

Mist eliminator

Water spray

Clean scrubber liquid

Dirty gas

Dirty scrubber liquid out

Fig. 9. Spray Tower

4.6  Air quality Index (AQI) The AQI gives the overall picture of the air quality. The AQI was developed by the Environment Protection Agency (EPA) U.S. The impact of air pollution on the public could be easily interpreted using AQI. The index is determined w.r.t six major pollutants viz. carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, and particulate matter. The daily air pollution levels could be translated into a number scale between 0 – 500. The impacts based on the scale are as under: AQI 0 - 50 51 -100 101-150 151-200

Pollution level

Effects Air quality is considered satisfactory with Good no risk. Air quality is acceptable with little concern Moderate for sensitive humans. Unhealthy for sensitive No harmful effects for general public but groups may affect sensitive people. Prolonged outdoor exertion must be avoided. This is specifically harmful for Unhealthy children and people with respiratory disorders.

Air Pollution  4.13

201-300 300+

Health warnings especially for children and people with respiratory disorders. Poses a health alert for all.

Very unhealthy Hazardous

The index is calculated as: I =

I high − I low C high − C low

(C − C low ) + I low

Where I = Air quality index, C = measured pollutant concentration, Clow= the concentration breakpoint ≤ C, Chigh= the concentration breakpoint ≥ C, Ilow=the index breakpoint corresponding to Clow, Ihigh= the index breakpoint corresponding to Chigh.

4.7 National Air Quality standards These standards give the amount of the pollutants which cannot be acceded for a particular geographical area at a give time with reference to the method of measurement, units, concentration and the time of exposure. National ambient air quality standards have been set by EPA for six main pollutants known as “criteria pollutants”. The current standards are as below: Table 2. Air Quality Standards (NAAQS Notification dated 18 th November, 2009) S. No. 1.

2.

Pollutant

Sulphur Dioxide (SO2), μg/m3 Nitrogen Dioxide (NO2), μg/m3

Time weighted average

Concentration in ambient air

Annual*

50

20

24 Hours**

80

80

Annual*

40

30

24 Hours**

80

80

3.

Particulate Matter (Size