Membrane Processes
Description
Separation processes are challenging steps in any process industry for isolation of products and recycling of reactants. Membrane technology has shown immense potential in separation of liquid and gaseous mixtures, effluent treatment, drinking water purification and solvent recovery. It has found endless popularity and wide acceptance for its small footprint, higher selectivity, scalability, energy saving capability and inherent ease of integration into other unit operations. There are many situations where the target component cannot be separated by distillation, liquid extraction, and evaporation. The different membrane processes such as pervaporation, vapor permeation and membrane distillation could be used for solving such industrial bottlenecks.
This book covers the entire array of fundamental aspects, membrane synthesis and applications in the chemical process industries (CPI). It also includes various applications of pervaporation, vapor permeation and membrane distillation in industrially and socially relevant problems including separation of azeotropic mixtures, close-boiling compounds, organic-organic mixtures, effluent treatment along with brackish and seawater desalination, and many others. These processes can also be applied for extraction of small quantities of value-added compounds such as flavors and fragrances and selective removal of hazardous impurities, viz., volatile organic compounds (VOCs) such as vinyl chloride, benzene, ethyl benzene and toluene from industrial effluents.
Including case studies, this is a must-have for any process or chemical engineer working in the industry today. Also valuable as a learning tool, students and professors in chemical engineering, chemistry, and process engineering will benefit greatly from the groundbreaking new processes and technologies described in the volume.
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Dr. Sundergopal Sridhar, PhD. is a chemical engineer from the University College of Technology, Osmania University, Hyderabad. He has been working as a scientist in the area of membrane separation processes at the Indian Institute of Chemical Technology in Hyderabad for the past 20 years and has published over 130 research papers and is the recipient of 30 prestigious scientific awards.
Siddhartha Moulik is a scientist at the Indian Institute of Chemical Technology in Hyderabad. He has published 16 research papers in various international journals, 2 book chapters, and 39 papers in conference proceedings. He is also the recipient of 8 prestigious awards in his field.
Content
Preface xvii
1 Tackling Challenging Industrial Separation Problems through Membrane Processes 1 Siddhartha Moulik, Sowmya Parakala and S. Sridhar
1.1 Water: The Source of Life 2
1.2 Significance of Water/Wastewater Treatment 5
1.3 Wastewater Treatment Techniques 8
1.4 Membrane Technologies for Water/Wastewater Treatment 11
1.5 Membranes: Materials, Classification and Configurations 12
1.5.1 Types of Membranes 12
1.5.1.1 Symmetric Membranes 12
1.5.1.2 Asymmetric Membranes 13
1.5.1.3 Electrically Charged Membranes 14
1.5.1.4 Inorganic Membranes 14
1.5.2 Membranes Modules and Their Characteristics 14
1.6 Introduction to Membrane Processes 17
1.6.1 Conventional Membrane Processes 17
1.7 CSIR-IICT's Contribution for Water/Wastewater Treatment 21
1.7.1 Nanofiltration Plant for Processing Coke Oven Wastewater in Steel Industry 22
1.8 Potential of Pervaporation (PV), Vapor Permeation (VP), and Membrane Distillation (MD) in Wastewater Treatment 24
1.9 Conclusion 32
References 33
2 Pervaporation Membrane Separation: Fundamentals and Applications 37 Siddhartha Moulik, Bukke Vani, D. Vaishnavi and S. Sridhar
2.1 Introduction and Historical Perspective 38
2.2 Principle 40
2.2.1 Mass Transfer 42
2.2.2 Factors Affecting Membrane Performance 44
2.3 Membranes for Pervaporation 45
2.4 Applications of Pervaporation 46
2.4.1 Solvent Dehydration 46
2.4.2 Organophilic Separation 55
2.4.2.1 Removal of VOCs 57
2.4.2.2 Extraction of Aroma Compounds 58
2.4.3 Organic/Organic Separation 64
2.4.3.1 Separation of Polar/Non-Polar Mixture 64
2.4.3.2 Separation of Aromatic/Alicyclic Mixtures 70
2.4.3.3 Separation of Aromatic/Aliphatic/Aromatic Hydrocarbons 71
2.4.3.4 Separation of Isomers 72
2.5 Conclusions and Future Prospects 77
References 78
3 Pervaporation for Ethanol-Water Separation and Effect of Fermentation Inhibitors 89 Anjali Jain, Sushant Upadhyaya, Ajay K. Dalai and Satyendra P. Chaurasia
3.1 Introduction 90
3.2 Theory of Pervaporation 91
3.2.1 Applications of Pervaporation 92
3.2.2 Advantages of Pervaporation 93
3.2.3 Pervaporation Performance Evaluation Parameters 93
3.3 Various Membranes Used for the Recovery of Ethanol 94
3.3.1 Organic Membranes 94
3.3.2 Inorganic Membranes 102
3.3.3 Mixed Matrix Membranes 104
3.4 Effects of Process Variables on Ethanol Concentration in PV 106
3.4.1 Effect of Feed Flow Rate 106
3.4.2 Effect of Ethanol Concentration in Feed 107
3.4.3 Effect of Feed Temperature 108
3.4.4 Effect of Permeate Pressure 109
3.5 Effect of Fermentation Inhibitors on Pervaporation Performance 109
3.5.1 Effect of Furfural Concentration 112
3.5.2 Influence of Hydroxymethyl-Furfural 113
3.5.3 Effect of Vanillin 114
3.5.4 Effect of Acetic Acid 115
3.5.5 Effect of Catechol 116
3.6 Conclusions 116
References 117
4 Dehydration of Acetonitrile Solvent by Pervaporation through Graphene Oxide/Poly(Vinyl Alcohol) Mixed Matrix Membranes 123 Siddhartha Moulik, D.Vaishnavi and S.Sridhar
4.1 Introduction 124
4.2 Materials and Methods 126
4.2.1 Materials 126
4.2.2 Preparation of Graphene Oxide 126
4.2.3 Fabrication of GO Membrane 127
4.2.4 Structural Characterization of GO/PVA Mixed Matrix Membrane 127
4.2.5 Pervaporation Experiments 127
4.2.6 Determination of Diffusion Coefficients 129
4.2.7 Membrane Characterization 130
4.2.8 Hydrodynamic Simulation 130
4.2.8.1 Specification of Computational Domain and Governing Equations 130
4.3 Results and Discussions 132
4.3.1 Scanning Electron Microscope 132
4.3.2 Differential Scanning Calorimeter 132
4.3.3 Effect of GO concentration on PV Performance 134
4.3.4 Sorption Behavior 135
4.3.5 Concentration Distribution of Water within the Membrane 135
4.3.6 Effect of Feed Water Concentration 137
4.3.7 Effect of Permeate Pressure 137
4.4 Conclusions 139
References 139
5 Recovery of Acetic Acid from Vinegar Wastewater Using Pervaporation in a Pilot Plant 141 Haresh K Dave and Kaushik Nath
5.1 Introduction 142
5.2 Materials and Methods 144
5.2.1 Chemicals and Membranes 144
5.2.2 Preparation and Cross-Linking of Membrane 144
5.2.3 Equilibrium Sorption in PVA-PES Membrane 144
5.2.4 Permeation Experimental Study 145
5.2.5 Flux and Separation Factor 146
5.2.6 Permeability and Membrane Selectivity 147
5.2.7 Diffusion and Partition Coefficient 147
5.2.8 Thermogravimetric Analysis 148
5.2.9 FTIR Analysis 148
5.2.10 AFM and SEM Analysis 148
5.2.11 Mechanical Properties 149
5.3 Results and Discussion 149
5.3.1 Sorption in PVA-PES Membrane 149
5.3.2 Effect of Feed Composition on Flux and Separation Factor 151
5.3.3 Activation Energy and Heat of Sorption 152
5.3.4 Permeability, Permeance and Intrinsic Membrane Selectivity 153
5.3.5 Diffusion and Partition Coefficient 154
5.3.6 Thermogravimetric Analysis 156
5.3.7 Surface Chemistry by FTIR Analysis 156
5.3.8 Surface Topology by AFM Analysis 159
5.3.9 Surface Topology by SEM Analysis 161
5.3.10 Mechanical Properties of the Membrane 162
5.3.11 Reusability of the Membrane 163
5.4 Conclusion 164
Nomenclature 165
Acknowledgement 165
References 166
6 Thermodynamic Models for Prediction of Sorption Behavior in Pervaporation 169 Reddi Kamesh, Sumana Chenna and K. Yamuna Rani
6.1 Introduction 170
6.2 Thermodynamic Models for Sorption 172
6.2.1 Flory-Huggins Models 172
6.2.1.1 Models for Single Liquid Sorption in Polymer 172
6.2.1.2 Models for Binary Liquid Sorption in Polymer 175
6.2.2 UNIQUAC Model 180
6.2.2.1 Calculation of Binary Solvent-Solvent Interaction Parameters (tij & tji) 181
6.2.2.2 Calculation of Binary Polymer-Solvent Interaction Parameters (tim, tmi & tjm, tmj) 184
6.2.2.3 Prediction of Sorption Levels for a Ternary System Using UNIQUAC Model 185
6.2.3 UNIQUAC-HB Model 187
6.2.3.1 Calculation of Binary Solvent-Solvent Interaction Parameters (t¿ij and t¿ji ) 187
6.2.3.2 Calculation of Binary Solvent-Polymer Interaction Parameters 188
6.2.3.3 Prediction of Sorption Levels for a Ternary System 189
6.2.4 Modified NRTL Model 190
6.2.4.1 Calculation of Binary Solvent-Solvent Interaction Parameters (t12 & t21) 192
6.2.4.2 Calculation of Binary Polymer-Solvent Interaction Parameters (tiM & tMi) 192
6.2.4.3 Prediction of Sorption Behavior for a Ternary System - Method 1 193
6.2.4.4 Prediction of Sorption Behavior for a Ternary System - Method 2 194
6.3 Computational Procedure 196
6.4 Case Study 202
6.5 Summary and Conclusions 207
References 208
7 Molecular Dynamics Simulation for Prediction of Structure-Property Relationships of Pervaporation Membranes 211 Shaik Nazia, Siddhartha Moulik, Jega Jegatheesan, Suresh K. Bhargava and S. Sridhar
7.1 Introduction and Historical Perspective 212
7.2 Molecular Dynamics (MD) Simulations 213
7.3 Calculation of Interaction Parameters 214
7.4 Calculation of Permeation Properties 216
7.5 Free Volume Analysis 220
7.6 Conclusions 224
References 224
8 Vapor Permeation: Fundamentals, Principles and Applications 227 Siddhartha Moulik, Sowmya Parakala and S. Sridhar
8.1 Introduction and Historical Perspective 228
8.2 Principle 229
8.3 Mass Transfer Models in Vapor Permeation 231
8.4 Membranes for VP 233
8.4.1 Inorganic Membranes 233
8.4.2 Polymeric Membranes: 236
8.4.3 Mixed Matrix Membranes (MMMs) 239
8.5 Applications of Vapor Permeation 243
8.6 Conclusions and Future Trends 252
References 252
9 Vapor Permeation - A Thermodynamic Perspective 257 Sujay Chattopadhyay
9.1 Introduction 258
9.2 Parameters Influencing Vapor Permeation 259
9.3 Sorption in Polymeric Materials 262
9.3.1 Sorption of Pure Liquid or Vapors 263
9.3.2 Sorption of Binary Mixtures of Liquids and Vapors 264
9.4 Vapor Permeation in Polymeric Membranes 265
9.4.1 Vapor Permeation Through Rubbery Membranes 265
9.4.2 Vapor Permeation Through Glassy Membranes 265
9.4.3 Vapor Permeation Through Crystalline Polymers 267
9.5 Thermodynamics of Penetrant/Polymer Membrane 268
9.6 Non-Equilibrium Thermodynamics 271
9.7 Design of Vapor Permeation Membrane with High Selectivity 273
9.8 Membranes and Membrane Modules 276
9.9 Applications of Vapor Permeation 277
9.10 Conclusion 279
References 280
10 Vapor Permeation: Theory and Modelling Perspectives 283 Harsha Nagar, P. Anand and S. Sridhar
10.1 Introduction 284
10.2 Advantages of Vapor Permeation Process 287
10.3 Mass Transfer Mechanism in VP Process 287
10.4 Fundamentals of Vapor Permeation Modelling 288
10.4.1 Solution-Diffusion Mechanisms 289
10.4.2 Diffusion Modelling 290
10.4.2.1 Multi-Component Diffusion 292
10.4.3 Solubility Modelling 293
10.4.3.1 Equation of State Approach 293
10.4.3.2 Lattice Fluid-Based Models 294
10.5 Case Studies of VP Modelling 296
10.5.1 Modelling of a Multi-Component System for Vapor Permeation Process 296
10.5.2 Cost Effective Vapor Permeation Process for Isopropanol Dehydration 298
10.5.3 Vapor Permeation Modeling for Inorganic Shell and Tube Membranes. 299
10.6 Conclusion 301
References 302
11 Membrane Distillation: Historical Perspective and a Solution to Existing Issues of Membrane Technology 305 Siddhartha Moulik, Sowmya Parakala and S. Sridhar
11.1 Introduction and Historical Perspective of Membrane Distillation 306
11.2 Principle of Membrane Distillation 308
11.3 Mass Transfer in MD 312
11.4 Parameters Affecting Performance of MD 314
11.5 Heat Transfer in MD 317
11.6 Membranes for MD 318
11.7 Applications of Membrane Distillation 328
11.7.1 Seawater Desalination 328
11.7.2 Drinking Water Purification 333
11.7.3 Oily Wastewater Treatment 338
11.7.4 Solvent Dehydration 340
11.7.5 Treatment of Textile Industrial Effluent 343
11.7.6 Food Industrial Applications 345
11.7.7 Treatment of Radioactive Waste Water 346
11.7.8 Dairy Effluent Treatment 347
11.8 Conclusions and Future Trends 350
References 351
12 Dewatering of Diethylene Glycol and Lactic Acid Solvents by Membrane Distillation Technique 357 M. Madhumala, I. Ravi Kiran, Shakarachar M. Sutar and S. Sridhar
12.1 Introduction 358
12.2 Materials and Methods 360
12.2.1 Materials 360
12.2.2 Membrane Synthesis 360
12.2.2.1 Synthesis of Microporous Hydrophobic ZSM-5/PVC Mixed Matrix Membrane 360
12.2.2.2 Synthesis of Ultraporous Hydrophobic Polyvinylchloride Membrane 361
12.2.3 Experimental 361
12.2.3.1 Description of Membrane Distillation Set-up 361
12.2.3.2 Experimental Procedure 362
12.2.4 Membrane Characterization Techniques 363
12.2.4.1 Fourier Transform Infrared Spectroscopy (FT-IR) 363
12.2.4.2 X-Ray Diffraction Studies (XRD) 363
12.2.4.3 Thermo Gravimetric Analysis (TGA) 364
12.2.4.4 Scanning Electron Microscopy (SEM) 364
12.2.4.5 Contact Angle Measurement 364
12.3 Results and Discussion 364
12.3.1 Membrane Characterization 364
12.3.1.1 FTIR 364
12.3.1.2 XRD 366
12.3.1.3 TGA 367
12.3.1.4 SEM 368
12.3.1.5 Contact Angle Measurement 369
12.3.2 Case Study 1: Dehydration of Lactic Acid Using ZSM-5 Loaded Polyvinyl Chloride Membrane 369
12.3.2.1 Effect of Feed Lactic Acid Concentration on Membrane Performance 369
12.3.3 Case Study 2: Dehydration of Diethylene Glycol Using Ultraporous PVC Membrane 371
12.3.3.1 Effect of Feed Diethylene Glycol Concentration on Membrane Performance 371
12.4 Conclusions 372
References 373
13 Graphene Oxide/Polystyrene Mixed Matrix Membranes for Desalination of Seawater through Vacuum Membrane Distillation 375 Siddhartha Moulik, Sowmya Parakala and S. Sridhar
13.1 Introduction 376
13.1.1 Graphene and its Derivatives 378
13.2 Materials and Methods 380
13.2.1 Materials 380
13.2.2 Preparation of Graphene Oxide 380
13.2.3 Membrane Synthesis 381
13.2.4 Performance of the Crosslinked GO Loaded PS Membrane 382
13.2.5 Membrane Distillation Experiment 383
13.2.6 Membrane Characterization 384
13.2.7 Computational Fluid Dynamics Study 384
13.2.7.1 Model Development 384
13.3 Results and Discussions 388
13.3.1 Membrane Characterization 388
13.3.1.1 SEM 388
13.3.1.2 Contact Angle Measurement 389
13.3.1.3 FTIR 390
13.3.1.4 Raman Spectra 391
13.3.2 Effect of GO Concentration on MD Performance 391
13.3.3 Concentration Profile of Water Vapor within the Membrane 392
13.3.4 Effect of Feed Salt Concentration 393
13.3.5 Effect of Degree of Vacuum on MD Performance 395
13.3.6 Effect of Membrane Thickness 395
13.4 Conclusion 396
References 397
14 Vacuum Membrane Distillation for Water Desalination 399 Sushant Upadhyaya, Kailash Singh, S.P. Chaurasia, Rakesh Baghel and Sarita Kalla
14.1 Introduction 400
14.2 Membrane Distillation 400
14.2.1 Direct Contact Membrane Distillation (DCMD) 400
14.2.2 Air Gap Membrane Distillation (AGMD) 401
14.2.3 Sweeping Gas Membrane Distillation (SGMD) 401
14.2.4 Vacuum Membrane Distillation (VMD) 401
14.3 Selection Criteria for MD Membrane 402
14.4 Characterization of Membranes in MD 403
14.5 Applications 403
14.6 Modelling in MD 404
14.7 Mass and Heat Transport in VMD 407
14.8 Recovery Modelling in VMD 410
14.9 Operating Variables Influence on VMD Process 411
14.9.1 Variation in Permeate Flux with Feed Rate 411
14.9.2 Variation in Permeate Flux with Feed Inlet Temperature 412
14.9.3 Variation in Permeate Flux with Permeate Pressure 415
14.9.4 Variation in Permeate Flux with Feed Salt Concentration 416
14.9.5 Effect of Runtime 417
14.10 Water Recovery 418
14.11 Fouling on Membrane 420
14.12 Conclusions 424
Nomenclature 425
Greek Symbols 426
References 426
15 Glycerol Purification Using Membrane Technology 431 Priya Pal, S.P.Chaurasia, Sushant Upadhyaya, Madhu Agarwal and S. Sridhar
15.1 Introduction 432
15.2 Glycerol 433
15.2.1 Impurities Present in Crude Glycerol 433
15.3 Sources of Glycerol 434
15.3.1 Transesterification Reaction 435
15.3.2 Saponification of Oils and Fats 436
15.3.3 Hydrolysis of Oils and Fats 436
15.4 Purification Processes 440
15.4.1 Conventional Method (Physicochemical Method) 440
15.4.1.1 Pre-Treatment (Acidification and Neutralization) 440
15.4.1.2 Solvent Removal 441
15.4.1.3 Activated Charcoal Treatment for Color Removal 442
15.4.1.4 Ion-Exchange Adsorption 442
15.4.2 Membrane Technology 443
15.4.2.1 Membrane Distillation (MD) 443
15.4.2.2 Operating Variables Affecting VMD Process 447
15.5 Material and Methods 453
15.5.1 Materials 453
15.5.2 Synthesis of Hydrophobic Polyvinylidene Fluoride (PVDF) Membrane 453
15.5.3 Methods 453
15.5.4 Membrane Characterization 455
15.5.4.1 Scanning Electron Microscopy (SEM) 455
15.5.4.2 Membrane Porosity Measurement 455
15.5.4.3 Membrane Thickness 456
15.5.4.4 Contact Angle 456
15.5.4.5 FTIR 457
15.6 Results and Discussion 457
15.6.1 Characterization of Membrane 457
15.6.2 Effect of Glycerol Concentration on Flux and Percentage Rejection 459
15.7 Conclusions 459
Nomenclature 460
References 461
16 Reclamation of Water and Toluene from Bulk Drug Industrial Effluent by Vacuum Membrane Distillation 467 Pavani Vadthya, Y.V.L. Ravikumar and S. Sridhar
16.1 Introduction 468
16.2 Materials and Methods 469
16.2.1 Materials 469
16.2.2 Membrane Synthesis 469
16.2.3 Membrane Characterization 470
16.2.3.1 Fourier-Transform Infrared Spectroscopy (FTIR) 470
16.2.3.2 Scanning Electron Microscopy (SEM) 470
16.2.3.3 X-Ray Diffraction Studies (XRD) 470
16.2.3.4 Sorption Studies 470
16.2.4 Experimental Set Up 471
16.2.5 Experimental Procedure 471
16.2.6 Flux 471
16.2.7 Refractive Index 472
16.3 Results and Discussion 472
16.3.1 Membrane Characterization 472
16.3.1.1 FTIR 472
16.3.1.2 SEM 473
16.3.1.3 XRD 473
16.3.1.4 Sorption Studies 474
16.3.2 Effect of Membrane Thickness 476
16.3.3 Effect of Polymer Loading 476
16.3.4 Effect of Permeate Pressure 477
16.4 Conclusions 479
References 480
Index 481
Chapter 1
Tackling Challenging Industrial Separation Problems through Membrane Technology
Siddhartha Moulik1,2, Sowmya Parakala1 and S. Sridhar1,2,*
1Membrane Separations Group, Chemical Engineering Division
2Academy of Scientific and Innovative Research (AcSIR), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad, India - 500007
*Corresponding author: sridhar11in@yahoo.com
Abstract
Membrane processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) for water and wastewater treatment have been developed, and widely used over the past few decades with proven efficiency. Currently emerging membrane techniques such as i.e., pervaporation (PV), vapor permeation (VP) and membrane distillation (MD) are being developed since they portray high potential with additional advantages and minor limitations over the conventional processes, and are thus regarded as next generation technologies. These processes can easily be retrofitted with existing conventional treatment methods for drinking water purifications, domestic, municipal and industrial wastewater treatment. The fundamentals of water resources available and their contamination, water and wastewater and their conventional treatment techniques, and the limitations of first-generation membrane technologies will be discussed in this chapter. The main focus is on technologies which are low cost and energy efficient, and provide high yield and desired purity with minimal sludge. The potential of second-generation membrane processes, i.e., PV, VP and MD has been explored and showed promising results by fulfilling all the ideal characteristics of next-generation membrane separation processes.
Keywords: Membrane technology, water/wastewater treatment pervaporation, vapor permeation, membrane distillation
1.1 Water: The Source of Life
Water has become the 'mother' and 'matrix' of life, essentially interlinked with the existence of biological lifecycles. Water is certainly the most precious natural resource that exists in the universe for human consumption. Water on the earth is available mostly as salt water (97.5%) with the remaining 2.5% being fresh water [1], which can be further distributed into 0.3% in lakes and rivers, 30.8% groundwater including soil water, swamp water and permafrost, and 68.9% as glaciers and permanent snow covers. Only 30% of the total fresh water resources are easily accessible to humans (as lakes and streams), which is shown in Figure 1.1. This raises a question on whether there will be enough fresh water available for future generations. Hence, there arises the need to make the fresh water resources sustainable; through recycle and treatment of wastewater, desalination of sea and brackish water, purification of contaminated groundwater and surface water for making them safe for drinking or utilization as process water. This chapter discusses the technologies required for drinking water purification and effluent treatment using first and second generation membrane separations.
Figure 1.1 Distribution of water on the earth.
The total mass of water on the earth is constant in its different phases such as ice, atmospheric water, clean water and ground water. The overall hydrologic cycle is a conceptual model that undergoes storage and movement of water between the biosphere, atmosphere, lithosphere and the hydrosphere. There is no starting point for the water cycle. Since three-fourth of the earth's surface is occupied by water, it will be wise to initiate its cycle from the oceans. Water gets warmed up in daylight and evaporates. Some water gets directly sublimated from the glaciers and icebergs and rises upward. At higher altitude, the gradual decrease in ambient temperature and pressure make the vapors supersaturated and they get condensed, forming clouds. The clouds roam miles across the earth and finally at a supersaturated state, fall in the form of rain, snow, hail, dew, frost or sleet over the Earth. Water is distributed in nature in different forms such as rain, river, spring, mineral water and seepage water, which get stored in different natural reservoirs such as atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields and ground water table [2]. Water is not only vital for sustenance of life, but also essential for socio-economic developments such as agriculture, industry, energy production, transportation, etc. The rapid industrialization and urbanization would have been scarcely possible without adequate supply of water. Renewable surface and ground water are the natural resources recognized to meet the increasing demands of society. With increasing population and exploitation of natural resources for one's own benefit, mankind has behaved in a wild manner by creating problems of pollution which are hazardous to life as well as aquatic flora and fauna. To combat water pollution, we must understand the sources and problems from the grassroot stages to be a part of the solution.
Water is the major requirement for a healthy life. Keeping water sources free from pollution is of utmost importance in the drive towards water conservation. Polluted water is the major source of diseases, and the land also becomes unfit to sustain life. At present, the potable water consumed by 80 to 90% of the population is of poorer quality by international standards and 2.1 billion people lack access to safely managed drinking water services [3]. Thus, the source of water available to humans is much lower than the 1% present in lakes, streams and underground. Misuse, pollution of water bodies and uncontrolled growth of human population further strain this limited resources. Surface water can be found on the land in the form of streams, ponds, marshes, lakes or other fresh (not salty) sources. Rivers are the main source of surface water and as many as 13 rivers in India are categorized as major sources of surface water with a catchment area around 252.8 million hectares. Surface water as reported by CPCB [4] from 120 rivers contains toxic metals. Toxic metals like arsenic, copper, chromium, nickel, mercury and lead were found to be present in rivers mostly in permissible limits except for few. CPCB has identified 1145 industries in the country that pollute river bodies. Ground water is found underground in the sweeps and spaces, soil, sand and rocks. A global scenario of ground water usage is represented in Figure 1.2. Current status of ground water in India is shown in Table 1.1 [5]. It is stored from rain and slowly moves through the geological formations of the soil. Ground water is the biggest source of drinking water in India as more than three-quarters of the Indian population depends on it but in more than 10 states, it is contaminated by arsenic.
Figure 1.2 Global scenario of ground water utilization.
Table 1.1 Status of ground water in India (5).
Level of ground water development Explanation % districts in 2011 0-70% (Safe) Areas which have ground water potential for development 71 70-90% (Semi-critical) Areas where cautious ground water development is recommended 10 90-100% (Critical) Areas which need intensive monitoring and evaluation for groundwater development 4 >100% (Over exploited) Areas where future ground water development is linked with water conservation measures. 15Unfortunately, water that is available as ground water resource is also being contaminated with naturally occurring chemicals besides fluoride, arsenic, lead, salt, aluminum, chromium, copper, pathogens, ammonia, nitrates or nitrites. Permissible and desirable limits of a few essential characteristics that determine the quality of water can be obtained from Table 1.2 [6]. Metal poisoning and bacterial contamination has also affected the ground water apart from contamination by fluoride, arsenic and nitrates. Arsenic levels beyond permissible limits in drinking water is the main cause of arsenic toxicity and skin cancer in Taiwan, China, Chile, Argentina, Mexico, India, Hungary Bangladesh, the United States and Thailand. Eleven countries in the world have more than 50% of their population drinking fluoridated water: Australia (80% population), Brunei (95%), Chile (70%), Guyana (62%), Hong Kong (100%), the Irish Republic (73%), Israel (70%), Malaysia (75%), New Zealand (62%), Singapore (100%), and the United States (64%). The graphical representation of fluoride and arsenic affected areas in India can be observed in Figure 1.3 (a) and (b) respectively (7, 8).
Figure 1.3 Range of (a) fluoride in ground water (mg/L)
Figure 1.3 (b) Range of Arsenic in ground water (µg/L) as reported.
Table 1.2 Drinking water specifications by Ministry of Water Resources, (Amended) (6).
Essential characteristics Desirable limit Permissible limit Color...