Biology of-wastewater-treatment-vol 4

BIOLOGY OFWASTEWATER TREATMENT

Imperial College PressICP

University of Dublin, Ireland

N. F. Gray

Second Edition

BIOLOGY OFWASTEWATER TREATMENT

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Copyright 2004 by Imperial College PressBIOLOGY OF WASTEWATER TREATMENT (2nd Edition)

January 19, 2004 14:33 World Scientific Biology of Wastewater Treatment (New Edition) bwt

Acknowledgements

Acknowledgement is gratefully made to the authors and publishers of ma-terial that has been redrawn, reset in tables, reproduced directly or repro-duced with minor modications. The exact sources can be derived from thereferences. For permission to reproduce copyright material thanks are dueto the following copyright holders:

Chapter 1International Water Supply Association: Table 1.4aOce of Water Services (Ofwat): Tables 1.10a, 1.10bWater Services Association of England and Wales: Table 1.4b

Chapter 2Anglian Water: Table 2.1Blackwell Science Publishers: Fig. 2.23Cambridge University Press: Table 2.6Chartered Institution of Water and Environmental Management:

Tables 2.4, 2.5; Figs. 2.15, 2.22, 2.26, 2.27Edward Arnold (Publishers) Ltd.: Figs. 2.14, 2.16Ellis Horwood Ltd.: Figs. 2.19, 2.20, 2.21IWA Publishing: Fig. 2.6John Wiley and Sons Ltd: Fig. 2.17Dr H.J. Kiuru: Fig. 2.6Mr J. Lynch, County Engineer, Kildare County Council: Fig. 2.10McGraw Hill Inc.: Figs. 2.3, 2.4WRc plc: Table 2.7; Fig. 2.28

v


vi Acknowledgements

Chapter 3Academic Press: Tables 3.9, 3.10, 3.12Applied Science Publishers: Tables 3.13, 3.14Blackwell Science Publishers: Figs. 3.21, 3.25Chartered Institution of Water and Environmental Management:

Table 3.5Controller of Her Britannic Majestys Stationary Oce: Fig. 3.14CRC Press: Table 3.18Elsevier: Table 3.11John Wiley and Sons Inc.: Table 3.6McGraw-Hill Inc.: Table 3.17; Figs. 3.2, 3.17, 3.19Prentice Hall Inc.: Figs. 3.3, 3.5, 3.16, 3.18, 3.20, 3.27Dr T. Stones: Table 3.4D. Reidal Publishers: Table 3.16Water Environment Federation: Table 3.2; Fig. 3.24

Chapter 4Academic Press: Table 4.18; Figs. 4.1, 4.21Blackwell Science Publishers: Fig. 4.13British Ecological Society: Table 4.17; Figs. 4.27, 4.28British Standard Institution: Tables 4.5, 4.7Chartered Institution of Water and Environmental Management:

Table 4.21; Figs. 4.22, 4.25, 4.26, 4.31, 4.34, 4.40, 4.43, 4.49Ellis Horwood Ltd.: Figs. 4.46, 4.47Elsevier: Tables 4.14, 4.15, 4.19; Fig. 4.36IWA Publishing: Figs. 4.41, 4.44, 4.48John Wiley and Sons Inc.: Fig. 4.42Dr M.A. Learner: Tables 4.3, 4.4Open University Press: Table 4.9Dr I.L. Williams: Fig. 4.15WRc plc: Figs. 4.37, 4.39

Chapter 5Academic Press: Tables 5.2, 5.26, 5.28, 5.29, 5.30; Figs. 5.1, 5.12, 5.18b,

5.60, 5.79, 5.80, 5.83, 5.90, 5.91, 5.96Biwater Treatment Ltd.: Fig. 5.18aBlackwell Science Publishers: Figs. 5.92, 5.93Carborundum Abrasives GB Ltd.: Fig. 5.23C.E.P. Consultants, Edinburgh: Figs. 5.30, 5.31, 5.48Chartered Institution of Water and Environmental Management:

Tables 5.11, 5.25, 5.31; Figs. 5.14, 5.24, 5.25, 5.28, 5.88, 5.98


Acknowledgements vii

Ellis-Horwood Ltd.: Figs. 5.16, 5.33, 5.51, 5.52, 5.62, 5.63, 5.73, 5.77Elsevier: Tables 5.17, 5.24; Figs. 5.89, 5.112IWA Publishing: Tables 5.12, 5.32; Figs. 5.15, 5.34, 5.53John Wiley and Sons Inc.: Fig. 5.11Mr G. OLeary: Figs. 5.21, 5.22Editor of Oikos: Fig. 5.90Rosewater Engineering Ltd.: Figs. 5.26, 5.27Dr J.P. Salanitro, Shell Development Co: Figs. 5.4, 5.81Simon Hartley Ltd.: Table 5.8; Figs. 5.17, 5.20TNO Research Institute for Environmental Hygiene, Delft: Fig. 5.60Water Environment Federation: Table 5.21; Figs. 5.2, 5.5, 5.66,

5.72, 5.76, 5.103Water Research Commission, South Africa: Tables 5.13, 5.15, 5.16, 5.19,

5.20; Figs. 5.9, 5.67, 5.71, 5.74

Chapter 6Academic Press: Figs. 6.9, 6.21, 6.22Editor, American Journal of Botany: Fig. 6.14British Standards Institution: Fig. 6.3Carl Bro Consultants, Leeds (Lagoon Technology International, Leeds):

Tables 6.15, 6.16, 6.17, 6.19Chartered Institution of Water and Environmental Management:

Table 6.21, 6.22; Figs. 6.23, 6.24, 6.25, 6.26CRC Press: Table 6.13; Figs. 6.8, 6.10, 6.12Elsevier: Table 6.6IWA Publishing, London: Table 6.20; Fig. 6.16McGraw-Hill Inc.: Fig. 6.2National Standards Agency of Ireland: Fig. 6.4Pergamon Press (Elsevier): Fig. 6.17Springer, Wien: Table 6.3University of Pennsylvania Press: Tables 6.5, 6.8; Figs. 6.11, 6.13US Department of Agriculture: Fig. 6.1US Environmental Protection Agency: Table 6.2Dr J. Vymazal: Table 6.10Water Environment Federation: Tables 6.4, 6.7World Health Organization, Geneva: Table 6.18WRc plc: Tables 6.12, 6.14; Fig. 6.15

Chapter 7Academic Press: Table 7.3


viii Acknowledgements

Chartered Institution of Water and Environmental Management:Figs. 7.1, 7.2, 7.12, 7.16; Table 7.2, 7.4, 7.5, 7.10

Editor of Food Technology: Tables 7.11, 7.14Ellis Horwood Ltd.: Table 7.9Elsevier: Table 7.13Institution of Engineers in Ireland: Tables 7.6, 7.8IWA Publishing: Figs. 7.3, 7.17; Table 7.12Oklahoma State University, Stillwater: Fig. 7.7Texas State department of Health, Austin: Fig 7.8WRc plc: Fig. 7.6

Chapter 8Cambridge University Press: Tables 8.23, 8.25Chartered Institution of Water and Environmental Management:

Figs. 8.1, 8.2, 8.5, 8.6, 8.7, 8.12, 8.13, 8.13, 8.16;Tables 8.16, 8.24, 8.28

Ellis Horwood Ltd.: Tables 8.6, 8.7European Commission: Table 8.15IWA Publishing: Figs. 8.14, 8.15; Tables 8.3, 8.10, 8.11, 8.12, 8.26; 8.27,

8.29, 8.30John Wiley and Sons Inc.: Fig. 8.4McGraw-Hill Inc.: Table 8.5National Board for Science and Technology, Dublin:

Figs. 8.9, 8.10, 8.11; Table 8.2, 8.21National water Council: Tables 8.13, 8.32, 8.33Open University Press: Table 8.1Oslo and Paris Commissions: Fig. 8.17; Table 8.35, 8.36Water Research Commission, South Africa: Table 8.31WRc plc: Fig. 8.3; Tables 8.17, 8.18, 8.19, 8.20, 8.22, 8.34, 8.40, 8.43

Chapter 9Academic Press: Fig. 9.17American Public Health Association: Fig. 9.3American Society of Civil Engineers: Fig. 9.22American Society for Microbiology: Table 9.43; Figs. 9.4, 9.5, 9.12Americam Water Works Association: Figs. 9.1, 9.11Blackie & Co.: Figs. 9.24, 9.27Blackwell Science Publishers: Tables 9.6, 9.23Carl Bro Consultants, Leeds (Lagoon Technology International, Leeds):

Fig. 9.18


Acknowledgements ix

Chartered Institution of Water and Environmental Management:Tables 9.4, 9.5, 9.57

Controller of Her Britannic Majestys Stationary Oce: Table 9.20.DEFRA, London: Table 9.49Ellis Horwood Ltd.: Table 9.52Elsevier: Tables 9.3, 9.29; Figs. 9.15, 9.21Editor, Environmental Health Perspectives: Table 9.54Environmental Sanitation Information Centre, Bangkok: Table 9.33European Commission: Tables 9.16, 9.17, 9.30, 9.31, 9.32, 9.34IWA Publishing: Tables 9.11, 9.26, 9.46, 9.47, 9.50, 9.51, 9.53; Fig. 9.6John Wiley and Sons Inc.: Tables 9.9, 9.10, 9.27, 9.58;

Figs. 9.7, 9.13, 9.23John Wiley and Sons Ltd.: Tables 9.22, 9.44; Figs. 9.26Editor, Journal of Hygiene, Cambridge: Tables 9.35, 9.48Kluwer Academic Publishers: Table 9.45McGraw-Hill Inc.: Fig. 9.10Pergamon Press (Elsevier): Fig. 9.20Van Nostrand Reinhold, New York: Tables 9.55, 9.56Water Environment Federation: Tables 9.15, 9.24; Fig. 9.19World Health Organization, Geneva: Table 9.18WRc plc: Tables 9.2, 9.19,9.36, 9.37, 9.38, 9.39, 9.42 ; Fig. 9.16US Environmental Protection Agency: Table 9.7, 9.8

Chapter 10Academic Press: Tables 10.4, 10.13, 10.15; Figs. 10.2, 10.19American Society for Microbiology: Tables 10.23, 10.25Applied Science Publishers: Table 10.7British Sugar Corporation Ltd.: Fig. 10.1Editor of Biotechnology Bulletin: Table 10.1Blackwell Science Publishers: Table 10.3; Fig. 10.13Cambridge University Press: Fig. 10.3Centre Europen dEtudes des Polyphosphates: Table 10.5Chartered Institution of Water and Environmental Management:

Tables 10.19, 10.26; Figs. 10.8, 10.9, 10.10, 10.11, 10.29, 10.38Dr A.D. Wheatley: Table 10.6Ellis Horwood Ltd.: Table 10.8; Figs. 10.27, 10.28Elsevier: Tables 10.20, 10.24, 10.29; Figs. 10.6, 10.22, 10.23, 10.24, 10.25,

10.26, 10.30, 10.35, 10.36Professor Isumi Hirasawa: Fig. 10.5IWA Publishing: Figs. 10.32, 10.37


x Acknowledgements

John Wiley and Sons Ltd: Table 10.12; Fig. 10.15Marcel Dekker Inc: Tables 10.21, 10.22Nature Press: Tables 10.9, 10.10; Fig. 10.4National Institute of Agricultural Engineering, Silso: Tables 10.17, 10.18Pergamon Press (Elsevier): Tables 10.12, 10.14; Fig. 10.14Purdue University: Fig. 10.33Surveyor Magazine: Fig. 10.12

Chapter 11Dr Annelies Balkema: Table 11.1Chartered Institution of Water and Environmental Management:

Fig. 11.1Elsevier: Tables 11.2, 11.4, 11.5; Fig. 11.5IWA Publishing: Tables 11.4, 11.6, 11.7, 11.8, 11.9, 11.10, 11.11, 11.12,

11.13; Figs. 11.2, 11.3, 11.4, 11.6

I would also like to thank Dr Anne Kilroy for permission to reproducejointly published material in chapter 3.


Contents

Acknowledgements v

Preface to the Second Edition xvii

1 How Nature Deals with Waste 11.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1. The wastewater problem . . . . . . . . . . . . . . . . 11.1.2. Legislation . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2. Nature of Wastewater . . . . . . . . . . . . . . . . . . . . . . . 141.2.1. Sources and variation in sewage ow . . . . . . . . . 151.2.2. Composition of sewage . . . . . . . . . . . . . . . . . 261.2.3. Other wastewaters . . . . . . . . . . . . . . . . . . . . 47

1.3. Micro-organisms and Pollution Control . . . . . . . . . . . . . 551.3.1. Nutritional classication . . . . . . . . . . . . . . . . 56

1.4. Microbial Oxygen Demand . . . . . . . . . . . . . . . . . . . . 631.4.1. Self purication . . . . . . . . . . . . . . . . . . . . . 631.4.2. Biochemical oxygen demand . . . . . . . . . . . . . . 93

1.4.2.1. The test . . . . . . . . . . . . . . . . . . . . 931.4.2.2. Methodology . . . . . . . . . . . . . . . . . 1011.4.2.3. Factors aecting the test . . . . . . . . . . 1121.4.2.4. Sources of error . . . . . . . . . . . . . . . 124

2 How Man Deals with Waste 1332.1. Basic Treatment Processes . . . . . . . . . . . . . . . . . . . . 133

2.1.1. Preliminary treatment . . . . . . . . . . . . . . . . . 1382.1.2. Primary treatment . . . . . . . . . . . . . . . . . . . 146

xi


xii Contents

2.1.3. Secondary treatment . . . . . . . . . . . . . . . . . . 1472.1.4. Tertiary treatment . . . . . . . . . . . . . . . . . . . 1482.1.5. Examples of treatment plants . . . . . . . . . . . . . 148

2.2. Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1512.2.1. The settlement process . . . . . . . . . . . . . . . . . 1512.2.2. Design of sedimentation tanks . . . . . . . . . . . . . 1572.2.3. Performance evaluation . . . . . . . . . . . . . . . . . 163

2.3. Secondary (Biological) Treatment . . . . . . . . . . . . . . . . 1732.4. Tertiary and Advanced Treatment . . . . . . . . . . . . . . . . 178

2.4.1. Tertiary treatment . . . . . . . . . . . . . . . . . . . 1792.4.2. Advanced wastewater treatment . . . . . . . . . . . . 190

3 The Role of Organisms 1913.1. Stoichiometry and Kinetics . . . . . . . . . . . . . . . . . . . . 191

3.1.1. Stoichiometry . . . . . . . . . . . . . . . . . . . . . . 1953.1.2. Bacterial kinetics . . . . . . . . . . . . . . . . . . . . 2043.1.3. The BOD test . . . . . . . . . . . . . . . . . . . . . . 217

3.2. Energy Metabolism . . . . . . . . . . . . . . . . . . . . . . . . 2233.3. Aerobic Heterotrophic Micro-organisms . . . . . . . . . . . . . 230

3.3.1. The organisms . . . . . . . . . . . . . . . . . . . . . . 2303.3.2. Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . 2453.3.3. Environmental factors . . . . . . . . . . . . . . . . . . 2533.3.4. Inhibition . . . . . . . . . . . . . . . . . . . . . . . . 257

3.4. Anaerobic Heterotrophic Micro-organisms . . . . . . . . . . . 2593.4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2593.4.2. Presence in the treatment plant . . . . . . . . . . . . 2603.4.3. Anaerobic digestion . . . . . . . . . . . . . . . . . . . 2623.4.4. Sulphide production . . . . . . . . . . . . . . . . . . . 2713.4.5. Denitrication . . . . . . . . . . . . . . . . . . . . . . 2723.4.6. Redox potential . . . . . . . . . . . . . . . . . . . . . 275

3.5. Autotrophic Micro-organisms . . . . . . . . . . . . . . . . . . 2773.5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2773.5.2. Nitrication . . . . . . . . . . . . . . . . . . . . . . . 282

3.6. Assessing Treatability, Toxicity, and Biodegradability . . . . . 2903.6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2903.6.2. Biochemical tests . . . . . . . . . . . . . . . . . . . . 2913.6.3. Bacterial tests . . . . . . . . . . . . . . . . . . . . . . 2973.6.4. Other approaches . . . . . . . . . . . . . . . . . . . . 3173.6.5. Continuous simulation tests . . . . . . . . . . . . . . 3203.6.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 324


Contents xiii

4 Fixed-Film Reactors 3254.1. Percolating Filters . . . . . . . . . . . . . . . . . . . . . . . . 326

4.1.1. Design and operation . . . . . . . . . . . . . . . . . . 3304.1.2. Process modications . . . . . . . . . . . . . . . . . . 3564.1.3. The organisms and their ecology . . . . . . . . . . . . 3644.1.4. Factors aecting performance . . . . . . . . . . . . . 4174.1.5. Nitrifying lters . . . . . . . . . . . . . . . . . . . . . 440

4.2. Rotating Biological Contactors . . . . . . . . . . . . . . . . . 4414.3. Submerged Fixed Film Systems . . . . . . . . . . . . . . . . . 450

4.3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4504.3.2. Fluidised bed reactors . . . . . . . . . . . . . . . . . . 4514.3.3. Biological aerated ooded lters . . . . . . . . . . . . 4554.3.4. Submerged aerated lters . . . . . . . . . . . . . . . . 4604.3.5. Moving bed biolm reactor . . . . . . . . . . . . . . . 462

5 Activated Sludge 4655.1. Flocculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4695.2. Operating Factors . . . . . . . . . . . . . . . . . . . . . . . . . 477

5.2.1. Process control . . . . . . . . . . . . . . . . . . . . . 4775.2.1.1. Mixed liquor suspended solids . . . . . . . 4775.2.1.2. Sludge residence time or sludge age . . . . 4785.2.1.3. Plant loading . . . . . . . . . . . . . . . . . 4795.2.1.4. Sludge settleability . . . . . . . . . . . . . . 4835.2.1.5. Sludge activity . . . . . . . . . . . . . . . . 4845.2.1.6. Recirculation of sludge . . . . . . . . . . . 487

5.2.2. Factors aecting the process . . . . . . . . . . . . . . 4885.2.3. Aeration methods . . . . . . . . . . . . . . . . . . . . 496

5.2.3.1. Surface aeration . . . . . . . . . . . . . . . 4975.2.3.2. Air diusion . . . . . . . . . . . . . . . . . 5045.2.3.3. Testing aerators . . . . . . . . . . . . . . . 511

5.3. Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . 5165.3.1. Conventional activated sludge processes . . . . . . . . 517

5.3.1.1. Plug-ow systems . . . . . . . . . . . . . . 5195.3.1.2. Completely mixed systems . . . . . . . . . 5285.3.1.3. Sequencing batch reactor technology . . . . 530

5.3.2. Extended aeration . . . . . . . . . . . . . . . . . . . . 5325.3.2.1. Oxidation ditches . . . . . . . . . . . . . . 5325.3.2.2. Packaged plants . . . . . . . . . . . . . . . 539

5.3.3. High-rate activated sludge processes . . . . . . . . . . 5415.3.3.1. AB process . . . . . . . . . . . . . . . . . 543


xiv Contents

5.3.4. Advanced activated sludge systems . . . . . . . . . . 5445.3.4.1. ICI Deep Shaft process . . . . . . . . . . 5455.3.4.2. Pure oxygen systems . . . . . . . . . . . . 548

5.4. Sludge Problems . . . . . . . . . . . . . . . . . . . . . . . . . . 5565.4.1. Deocculation . . . . . . . . . . . . . . . . . . . . . . 5585.4.2. Pin-point oc . . . . . . . . . . . . . . . . . . . . . . 5605.4.3. Foaming . . . . . . . . . . . . . . . . . . . . . . . . . 5615.4.4. Filamentous bulking . . . . . . . . . . . . . . . . . . . 5695.4.5. Identifying problems . . . . . . . . . . . . . . . . . . 5835.4.6. Non-lamentous bulking . . . . . . . . . . . . . . . . 5925.4.7. Denitrication . . . . . . . . . . . . . . . . . . . . . . 592

5.5. Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5935.5.1. Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . 5965.5.2. Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . 5995.5.3. Protozoa . . . . . . . . . . . . . . . . . . . . . . . . . 5995.5.4. Other groups . . . . . . . . . . . . . . . . . . . . . . . 615

5.6. Nutrient Removal . . . . . . . . . . . . . . . . . . . . . . . . . 6185.6.1. Denitrication . . . . . . . . . . . . . . . . . . . . . . 6225.6.2. Phosphorus removal . . . . . . . . . . . . . . . . . . . 628

6 Natural Treatment Systems 6416.1. Land Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 643

6.1.1. Purication process . . . . . . . . . . . . . . . . . . . 6446.1.2. On-site subsurface inltration . . . . . . . . . . . . . 6466.1.3. Slow rate land application . . . . . . . . . . . . . . . 6516.1.4. Rapid inltration land treatment systems . . . . . . . 6546.1.5. Overland ow . . . . . . . . . . . . . . . . . . . . . . 656

6.2. Macrophyte-Based Systems . . . . . . . . . . . . . . . . . . . 6586.2.1. Algae and submerged macrophytes . . . . . . . . . . 6606.2.2. Floating macrophytes . . . . . . . . . . . . . . . . . . 6636.2.3. Emergent macrophytes . . . . . . . . . . . . . . . . . 673

6.3. Stabilisation Ponds . . . . . . . . . . . . . . . . . . . . . . . . 6976.3.1. Anaerobic ponds and lagoons . . . . . . . . . . . . . 7006.3.2. Oxidation ponds . . . . . . . . . . . . . . . . . . . . . 7046.3.3. Aeration lagoons . . . . . . . . . . . . . . . . . . . . . 731

7 Anaerobic Unit Processes 7357.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7357.2. Flow-Through Systems (Digestion) . . . . . . . . . . . . . . . 743

7.2.1. Combined systems . . . . . . . . . . . . . . . . . . . . 744


Contents xv

7.2.2. Digestion . . . . . . . . . . . . . . . . . . . . . . . . . 7547.3. Contact Anaerobic Systems . . . . . . . . . . . . . . . . . . . 777

7.3.1. Anaerobic activated sludge process . . . . . . . . . . 7797.3.2. Sludge blanket process . . . . . . . . . . . . . . . . . 7817.3.3. Static media lter process . . . . . . . . . . . . . . . 7837.3.4. Fluidised and expanded media . . . . . . . . . . . . . 790

8 Sludge Treatment and Disposal 7938.1. Sludge Characteristics and Treatment . . . . . . . . . . . . . . 793

8.1.1. Treatment options . . . . . . . . . . . . . . . . . . . . 7988.1.2. Disposal options . . . . . . . . . . . . . . . . . . . . . 819

8.2. Land Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . 8298.2.1. Sludge disposal to land sites . . . . . . . . . . . . . . 8298.2.2. Sludge utilisation to farmland . . . . . . . . . . . . . 834

8.3. Sea Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8648.3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 8648.3.2. Legislative control . . . . . . . . . . . . . . . . . . . . 8668.3.3. Dumping sites . . . . . . . . . . . . . . . . . . . . . . 8718.3.4. Environmental impact . . . . . . . . . . . . . . . . . 872

9 Public Health 8859.1. Disease and Water . . . . . . . . . . . . . . . . . . . . . . . . 8859.2. Water-Borne Diseases . . . . . . . . . . . . . . . . . . . . . . . 888

9.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 8889.2.2. Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . 8899.2.3. Viruses . . . . . . . . . . . . . . . . . . . . . . . . . . 9069.2.4. Protozoa . . . . . . . . . . . . . . . . . . . . . . . . . 9149.2.5. Parasitic worms . . . . . . . . . . . . . . . . . . . . . 929

9.3. Indicator Organisms . . . . . . . . . . . . . . . . . . . . . . . 9319.3.1. Escherichia coli and coliforms . . . . . . . . . . . . . 9419.3.2. Faecal streptococci . . . . . . . . . . . . . . . . . . . 9539.3.3. Faecal coliform/faecal streptococci (FC/FS) ratio . . 9599.3.4. Clostridium perfringens . . . . . . . . . . . . . . . . . 9629.3.5. Bacteriophage . . . . . . . . . . . . . . . . . . . . . . 9649.3.6. Bidobacteria . . . . . . . . . . . . . . . . . . . . . . 9679.3.7. Rhodococcus spp. . . . . . . . . . . . . . . . . . . . . 9689.3.8. Heterotrophic plate count bacteria . . . . . . . . . . . 9699.3.9. Other indicator organisms . . . . . . . . . . . . . . . 9719.3.10. Chemical indicators . . . . . . . . . . . . . . . . . . . 974

9.4. Hazards Associated with Wastewater and Sludge . . . . . . . 976


xvi Contents

9.4.1. Water pollution . . . . . . . . . . . . . . . . . . . . . 9769.4.2. Land Pollution . . . . . . . . . . . . . . . . . . . . . . 9969.4.3. Atmospheric pollution . . . . . . . . . . . . . . . . . 10089.4.4. Antibiotic resistance in enteric bacteria . . . . . . . . 1011

9.5. Removal of Pathogenic Organisms . . . . . . . . . . . . . . . . 10139.5.1. Environmental factors and survival . . . . . . . . . . 10139.5.2. Treatment processes . . . . . . . . . . . . . . . . . . . 10219.5.3. Sterilization and disinfection methods . . . . . . . . . 1040

10 Biotechnology and Wastewater Treatment 105710.1. The Role of Biotechnology . . . . . . . . . . . . . . . . . . . . 105710.2. Resource Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . 1060

10.2.1. Fertiliser value . . . . . . . . . . . . . . . . . . . . . . 106010.2.2. Reuse of euents . . . . . . . . . . . . . . . . . . . . 106110.2.3. Metal recovery . . . . . . . . . . . . . . . . . . . . . . 106710.2.4. Phosphorus recovery . . . . . . . . . . . . . . . . . . 1078

10.3. Biological Conversion . . . . . . . . . . . . . . . . . . . . . . . 108310.3.1. Bio-energy . . . . . . . . . . . . . . . . . . . . . . . . 108310.3.2. Single-cell protein and biomass . . . . . . . . . . . . . 109910.3.3. Composting . . . . . . . . . . . . . . . . . . . . . . . 1124

10.4. Environmental Protection . . . . . . . . . . . . . . . . . . . . 115410.4.1. Breakdown of recalcitrants . . . . . . . . . . . . . . . 115510.4.2. Bioscrubbing . . . . . . . . . . . . . . . . . . . . . . . 116010.4.3. Bioaugmentation . . . . . . . . . . . . . . . . . . . . 116410.4.4. Immobilised cells and biosensors . . . . . . . . . . . . 1169

11 Sustainable Sanitation 117911.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117911.2. The Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . 118011.3. Sustainable Options . . . . . . . . . . . . . . . . . . . . . . . . 1190

11.3.1. Source contamination . . . . . . . . . . . . . . . . . . 119011.3.2. Treatment . . . . . . . . . . . . . . . . . . . . . . . . 119611.3.3. Final disposal . . . . . . . . . . . . . . . . . . . . . . 1203

11.4. Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . 1212

References 1219

Index 1395


Preface to the Second Edition

Since writing the rst edition of Biology of Wastewater Treatment thewastewater industry has changed quite dramatically. While the basic con-cepts remain the same, the processes and the industry that design, buildand operate treatment systems have all radically altered. So why has waste-water technology changed so much since 1990? In Europe the introductionand rapid implementation of the Urban Wastewater Treatment Directivehas to be a major factor. Nutrient removal, especially biological phosphorusremoval, is now commonplace. This in turn has forced us back to the use ofthe original batch reactor designs for activated sludge. The large increasein sludge production has required the development of integrated disposalstrategies linked with better recovery and reuse technologies. The rapidexpansion of wastewater treatment is allowing manufacturers to experimentwith new innovative designs and processes, and for the rst time in nearlyhalf a century new sewage treatment plants are being built rather thanexisting plants merely being upgraded or retrotted. Privatisation in theUK has also been hugely inuential bringing into play the often-conictingfactors of cost, especially operational cost, and accountability. Better regu-lation and control in all countries, coupled with better process managementhas resulted in better treatment overall. The concept of sustainability hasalso become an important factor, although it is still to have any real in-uence on long-term design or planning. Growing urbanization, climatechange, and new analytical techniques that are constantly allowing us toidentify new pollutants and understand the fate of others during treatmentand subsequently in receiving waters, have all signicantly inuenced thewastewater industry. However, many fear that wastewater treatment will

xvii


xviii Preface

eventually reach crisis point where existing technologies will prove to betoo expensive and energy dependent to be able to satisfy all the needs ofa modern society. Also, long-term planning is dicult with legislation andregulation constantly changing. So now is the time to stand back and takea new look at the whole concept of the wastewater cycle from productionat the household level through to treatment. Our highly diluted waste-waters, heavily contaminated with metals, pharmaceutical drugs, oestro-gen mimicking compounds, more varied and dangerous pathogens, and analarmingly wide range of trace organic compounds is simply too dicultto treat eectively in a manner that is going to be sustainable. Ratherthan developing better and more ecient process designs we need to startby looking at the basic concepts of treatment and redesign the system asthough starting from scratch. For, example new separation technologiesand water reuse at the household level is reducing wastewater loadings.New advances with in-sewer treatment have been very successful in reduc-ing organic loads to treatment plants and at the same time creating a moretreatable wastewater entering the wastewater treatment plant. Localisedtreatment plants rather than centralized systems are now thought to bemore ecient. Removing pollutants at source rather than at the treatmentplant is making euents and sludges in particular less hazardous. Whatis clear is that wastewater treatment will have to become a joint venturebetween all the stakeholders, with every person having to take some re-sponsibility for their waste.

I have tried to retain as much of the original text as possible, but due tothe rapid changes that have occurred over the past decade then considerablerevision was necessary. All sections have been updated with many expandedto reect the new importance or popularity of processes. There is also a newchapter on sustainability.

It is often forgotten by environmentalists, and the public in general,what an important role wastewater treatment plays in protecting both theenvironment and the health of the public. Without it there would be nodevelopment and growth, without it our environment and our very liveswould be at risk. It is a huge credit to all those involved in the industrythat this vital service is carried out in such a discreet and professionalmanner. For all those of you who have made it your career, thank you. Forthose who would like to, then welcome and I hope that you will also nd itequally as rewarding and exciting as I have.

Nick GrayTCDJanuary 2004


To you its just crap, to me its bread and butter.Spike Milligan

Recollections of the latrine orderly


1

How Nature Deals with Waste

1.1. Introduction

1.1.1. The wastewater problem

Each day, approximately 1106m3 of domestic and 7106m3 of industrialwastewater is produced in the UK. This, along with surface runo frompaved areas and roads, and inltration water, produces over 20 106m3of wastewater requiring treatment each day. To cope with this immensevolume of wastewater there were, in 1999, some 9260 sewage treatmentworks serving about 95% of the population (Water UK 2001). The sizeof these plants varies from those serving small communities of < 100, toplants like the Crossness Sewage Treatment Works operated by ThamesWater which treats the wastewater from over 1.7 million people living in a240 km2 area of London.

In terms of volume or weight, the quantity of wastewater treated annu-ally in the UK far exceeds any other product (Table 1.1) including milk,steel or even beer (Wheatley 1985), with vast quantities of wastewater gen-erated in the manufacture of most industrial products (Fig. 1.1). The costof wastewater treatment and pollution control is high, and rising annually,not only due to ination but to the continuous increase in environmentalquality that is expected. During the period 19941999, the ten main watercompanies in England and Wales invested 16.55bn into its services. Overhalf of this was on wastewater provision. In the year 1998/1999, 1.9bnwas spent on new wastewater treatment plants alone as compliance withthe European Union UrbanWastewater Treatment Directive continues. Theindustry is extremely large, with the income for these water companies for

1


2 How Nature Deals with Waste

Table 1.1. The quantity of sewage treated in the UK far exceedsthe quantity of other industrial products processed. Comparativevalues are based on 1984 sterling values (Wheatley 1985).

Product Tonnes/annum (106) Price (/tonne)

Water as sewage 6500 0.10

Milk 16 25

Steel 12 300

Beer 6.6 280

Inorganic fertilizer 3.3 200

Sugar 1.0 350

Cheese 0.2 1300

Bakers yeast 0.1 460

Citric acid 0.015 700

Penicillin 0.003 45000

Fig. 1.1. Tonnes of water required in the manufacture of some products that produceorganic euents.

1998/1999 in excess of 6,000m with operating costs approaching 4,000m(Water UK 2001).

There are two fundamental reasons for treating wastewater: to preventpollution, thereby protecting the environment; and, perhaps more impor-tantly, protecting public health by safeguarding water supplies and prevent-ing the spread of water-borne diseases (Sec. 2.1).

The safe disposal of human excreta is a pre-requisite for the supply ofsafe drinking water, as water supplies can only become contaminated wheredisposal is inadequate. There are many infectious diseases transmitted in


Introduction 3

excreta, the most important being the diarrhoeal diseases cholera, typhoid,and schistosomiasis. The faeces are the major source of such diseases withfew infections, apart from schistsosomiasis, associated with urine. Amongthe most common infectious water-borne diseases are bacterial infectionssuch as typhoid, cholera, bacillary dysentery, and gastro-enteritis; viral in-fections such as infectious hepatitis, poliomyelitis, and various diarrhoealinfections; the protozoal infections cryptosporidiosis, giardiasis, and amoe-bic dysentery, and the various helminth infections such as ascariasis, hook-worm, and schistosomiasis (bilharzia). Although the provision of clean wa-ter supplies will reduce the levels of infection in the short term, in thelong term it is vital that the environment is protected from faecal pollution(Feachem and Cairncross 1993; Mara 1996). Adequate wastewater treat-ment and the disinfection of water supplies has eectively eliminated thesewater-borne diseases from developed countries, but they remain endemic inmany parts of the world, especially those regions where sanitation is poor ornon-existent (Chap. 9). In developed countries where there are high popula-tion densities, such as the major European cities, vast quantities of treatedwater are required for a wide variety of purposes. All the water suppliedneeds to be of the highest quality possible, although only a small propor-tion is actually consumed. To meet this demand, it has become necessary toutilise lowland rivers and groundwaters to supplement the more traditionalsources of potable water such as upland reservoirs (Gray 1997). Where thewater is reused on numerous occasions, as is the case in the River Severnand the River Thames Sec. 10.2.2, adequate wastewater treatment is vitalto ensure that the outbreaks of waterborne diseases that were so prevalentin the eighteenth and nineteenth centuries do not reoccur (Chap. 9).

In terms of environmental protection, rivers are receiving large quan-tities of treated euent while estuaries and coastal waters have vastquantities of partially or completely untreated euents discharged intothem. Although in Europe, the Urban Wastewater Treatment Directivehas caused the discharge of untreated wastewater to estuarine and coastalwaters to be largely phased out. Apart from organic enrichment endan-gering the ora and fauna due to deoxygenation, treated euents rich inoxidised nitrogen and phosphorus can result in eutrophication problems.Where this is a particular problem, advanced or tertiary wastewater treat-ment is required to remove these inorganic nutrients to protect rivers andlakes (Sec. 2.4). Environmental protection of surface waters is therefore amajor function of wastewater treatment. In 1998, 30% of all rivers surveyedin England and Wales (12,241 km) were classied as having doubtful, orworse, quality (i.e. class D, E and F using the Environment Agency General



Table 1.2. The river quality in England and Wales based on the EnvironmentAgency GQA systems.

River length (%) in each quality grade

A B C D E F Total km

Chemical GQA

19881990 17.7 30.1 22.8 14.4 12.7 2.3 34161

19931995 26.8 32.7 21.3 10.2 8.1 0.9 40227

19941996 27.1 31.5 21.2 10.4 8.8 1.0 40804

Biological GQA

1990 24.0 31.6 21.6 9.8 7.3 5.7 30001

1995 34.6 31.6 18.4 8.1 5.4 1.9 37555

Nutrient GQA

1990 8.0 17.7 10.2 13.1 28.0 22.9 23003

19931995 14.7 22.6 11.0 13.1 27.3 11.0 34864

Quality Assessment (GQA) chemical classication system) (EnvironmentAgency 1998; Gray 1999; Water UK 2001) (Table 1.2). As in Ireland, thereis an increasing trend in eutrophication of surface waters (EPA 2000). Thecost of rehabilitating rivers, as was seen with the River Thames in the pe-riod 19601980, is immense. The River Mersey for example, now Britainsmost polluted river, will cost an estimated 3,700m over the next quarterof a century to raise to a standard suitable for recreation (Department ofthe Environment 1984).

1.1.2. Legislation

Environmental legislation relating to wastewater treatment and receiv-ing water quality is based largely on quality standards that are relatedto suitability of water for a specic use, the protection of receivingwaters, or emission limits on discharges. Standards are usually manda-tory with maximum permissible concentrations based on health criteriaor environmental quality standards. Table 1.3 lists the key Directivesconcerning the aquatic environment that govern legislation in countries(Member States) comprising the European Union. The principal Direc-tives are those dealing with Surface Water (75/440/EEC), Bathing Waters(76/160/EEC), Dangerous Substances (76/464/EEC; 86/280/EEC), Fresh-water Fish (78/659/EEC), Ground Water (80/68/EEC), Drinking Water


Introduction 5

Table 1.3. EU Directives concerning inland waters by year of introduction.

1973Council Directive on the approximation of the laws of the Member States relating todetergents (73/404/EEC)Council Directive on the control of biodegradability of anionic surfactants (73/405/EEC)1975Council Directive concerning the quality required of surface water intended for the ab-straction of drinking water in the Member States (75/440/EEC)1976Council Directive concerning the quality of bathing waters (76/160/EEC)Concil Directive on pollution caused by certain dangerous substances discharged intothe aquatic environment (76/464/EEC)1977Council decision establishing a common procedure for the exchange of information onthe quality of surface in the Community (77/795/EEC)1978Council Directive on titanium oxide waste (78/178/EEC)Council Directive on quality of fresh waters needing protecting or improvement in orderto support sh life (78/659/EEC)1979Council Directive concerning the methods of measurement and frequencies of samplingand analysis of surface water intended for the abstraction of drinking water in the Mem-ber States (79/869/EEC)Council Directive in the quality required for shellsh wates (79/923/EEC)1980Council Directive on the protection of ground water against pollution caused by certaindangerous substances (80/68/EEC)Council Directive on the approximation of the laws of the Member States relating to theexploitation and marketing of natural mineral waters (80/777/EEC)Council Directive relating to the quality of water intended for human consumption

(80/778/EEC)1982Council Directive on limit values and quality objectives for mercury discharges by thechlor-alkali electrolysis industry (82/176/EEC)Council Directive on the testing of the biodegradability of non-ionic surfactants(82/883/EEC)Council Directive on the monitoring of waste from the titanium oxide industry(82/883/EEC)1983Council Directive on limit values and quality objectives for cadmium discharges(83/513/EEC)1984Council Directive on limit values and quality objectives for discharges by sectors otherthan the chlor-alkali electrolysis industry (84/156/EEC)Council Directive on limit values and quality objectives for discharges of hexachlorocy-clohexane (84/491/EEC)1985Council Directive on the assessment of the eects of certain public and private projectson the environment (85/337/EEC)



Table 1.3. (Continued)

1986Council Directive on the limit values and quality objectives for discharge of cer-tain dangerous substances included in List I of the Annex to Directive 76/464/EEC(86/280/EEC)1987Council Directive on the preventation and reduction of environmental pollution by as-bestos (87/217/EEC)1988Council Directive amending Annex II to the Directive 86/280/EEC on limit values andquality objectives for discharges of certain dangerous substances included in List I of the

Annex to Directive 76/464/EEC (88/347/EEC)1990Council Directive amending Annex II to the Directive 86/280/EEC on limit values andquality objectives for discharges of certain dangerous substances included in List I of theAnnex to Directive 76/464/EEC (90/415/EEC)1991Council Directive concerning urban waste water treatment (91/271/EEC)Council Directive concerning the protection of waters against pollution caused by nitratesfrom agricultural sources (91/676/EEC)1992Council Dirrective on pollution by waste from the titanium oxide industry (92/112/EEC)1996Council Directive on integrated pollution prevention control (96/61/EEC)1998Council Directive on the quality of water intended for human consumption (98/83/EEC)2000Council Directive establishing a framework for community action in the eld of waterpolicy (00/60/EC)

(80/778/EEC), Urban Waste Water Treatment (91/271/EEC), Nitrates(91/676/EEC), Integrated Pollution Prevention Control (96/61/EEC), andWater Framework (00/60/EEC). The Directive controlling sewage sludgedisposal to agricultural land (86/278/EEC) is discussed in Chap. 8. In mostDirectives both guide (G) and imperative, or mandatory, (I) values aregiven. The G values are those which Member States should be working to-wards in the long term. In most cases, nationally adopted limit values arethe I values although occasionally more stringent values are set.

The Dangerous Substances Directive (76/464/EEC) requires licensing,monitoring and control of a wide range of listed substances dischargedto the aquatic environment. List I (Black List) substances have been se-lected mainly on the basis of their toxicity, persistence and potential forbioaccumulation. Those that are rapidly converted into substances that arebiologically harmless are excluded. List II (Grey List) substances are consid-ered to be less toxic, or the eects of which are conned to a limited area


Introduction 7

Table 1.4. List I and List II substances dened by the EU Dangerous Substances Di-rective (76/464/EEC).

List no. 1 (black list)Organohalogen compounds and substances which may form such compounds in theaquatic environmentOrganophosphorus compoundsOrganotin compoundsSubstances, the carcinogenic activity of which is exhibited in or by the equatic environ-ment (substances in List 2 which are carcinogenic are included here)Mercury and its compoundsCadmium and its compoundsPersistent mineral oils and hydrocarbons of petroleumPersistent synthetic substances

List no. 2 (grey list)The following metalloids/metals and their compounds:Zinc, copper, nickel, chromium, lead, selenium, arsenic, antimony, molybdenum, tita-nium, tin, barium, beryllium, boron, uranium, vanadium, cobalt, thalium, tellurium,silverBiocides and their derivatives not appearing in List 1Substances which have a deleterious eect on the taste and/or smell of products forhuman consumption derived from the aquatic environment and compounds liable togive rise to such substances in waterToxic or persistent organic compounds of silicon and substances which may give rise tosuch compounds in water, excluding those which are biologically harmless or are rapidlyconverted in water to harmless substancesInorganic compounds of phosphorus and elemental phosphorusNon-persistent mineral oils and hydrocarbons of petroleum originCyanides, uoridesCertain substances which may have an adverse eect on the oxygen balance, particularlyammonia and nitrites

which is dependent on the characteristics and location of the water intowhich they are discharged (Table 1.4). Member States are in the process ofestablishing environmental quality standards (EQS) for surface and groundwaters. These will be used as maximum permissible concentrations in wa-ters receiving discharges containing such compounds (Table 1.5).

Water policy in the EU has recently been rationalized into three keyDirectives: Drinking Water (80/778/EEC), Urban Waste Water Treatment(91/271/EEC), and the Water Framework Directive (2000/60/EEC).

The Water Framework Directive (2000/60/EEC) brings together the ex-isting Directives on water quality of surface fresh water, estuaries, coastalwaters and ground water. It covers all aspects of aquatic ecology and wa-ter quality, including the protection of unique and valuable habitats, theprotection of drinking water resources and the protection of bathing wa-ters. It achieves this by managing all water resources within River Basin



Table 1.5. Environmental quality standards for List I and List II substances in Englandand Wales (Environment Agency 1998).

List I substances Statutory EQSa (g/l) Number of discharges

Mercury and compounds 1 752

Cadmium and compounds 5 2196

Hexachlorocyclohexane (all isomers) 0.1 123

DDT (all isomers) 0.025 15

DDT (pp isomers) 0.01 1

Pentachlorophenol 2 88

Carbon tetrachloride 12 51

Aldrin 0.01 35

Dieldrin 0.01 58

Endrin 0.005 37

Isodrin 0.005 7

Hexachlorobenzene 0.03 20

Hexachlorobutadience 0.1 14

Chloroform 12 73

Trichloroethylene 10 48

Tetrachloroethylene 10 51

Trichlorobenzene 0.4 31

1,2-dichloroethane 10 87

aStandards are all annual mean concentrations

List II substances Operational EQSa (g/l) Measured as

Lead 10 AD

Chromium 20 AD

Zinc 75 AT

Copper 10 AD

Nickel 150 AD

Arsenicb 50 AD

Boron 2000 AT

Iron 1000 AD

pH 6.09.0 P

Vanadium 20 AT

Tributyltinb 0.02 MT

Triphenyltinb 0.02 MT

PCSD 0.05 PT

Cyuthrin 0.001 PT


Introduction 9


List II substances Operational EQSa (g/l) Measured as

Sulcofuron 25 PT

Flucofuron 1 PT

Permethrin 0.01 PT

Atrazine and simazineb 2 A

Azinphos-methylb 0.01 A

Dichlorvosb 0.001 A

Endosulphanb 0.003 A

Fenitrothionb 0.01 A

Malathionb 0.01 A

Triuralinb 0.1 A

Diazinon 0.01 A

Propetamphos 0.01 A

Cypermethrin 0.0001 A

Isoproturon 2.0 A

A = annual average, P = 95% of samples, D = dissolved, T = total, M = maximum.aStandards quoted for metals are for the protection of sensitive aquatic life at hardness100150 mg/l CaCO3, alternative standards may be found in DoE circular 7/89.bStandards for these substances are from the Surface Waters (Dangerous Substances)(Classication) Regulations 1997, Sl 2560 in which case these are now statutory.

Districts for which management plans will be drawn up using environmentalquality standards (EQSs) (Table 1.5). The Directive sets clear monitoringprocedures and lists specic biological, hydromorphological and physico-chemical parameters to be used for rivers, lakes, estuaries and coastal wa-ters. For each of these resource groups, denitions of high, good and fairecological quality are given for each specied parameter.

The Urban Waste Water Treatment Directive (91/271/EEC) makes sec-ondary treatment mandatory for sewered domestic waste waters and alsoall biodegradable industrial (e.g. food processing) waste waters. Minimumeuent standards have been set at BOD 25 mg l1, COD 125 mg l1 andsuspended solids 35 mg l1. Those receiving waters that are consideredto be at risk from eutrophication are classied as sensitive so that dis-charges require more stringent treatment to bring nutrient concentrationsof nal euents down to a maximum total phosphorus concentration of2 mg l1 for P and a total nitrogen concentration of 1015 mg l1 for N(Table 1.6). Due to the cost of nutrient removal, the designation of receiv-ing waters as sensitive has signicant cost implications for Member States.



Table 1.6. The Urban Wastewater Treatment Directive (91/271/EEC) sets dis-charge limits for wastewater treatment plants. Values for total phosphorus andnitrogen only apply to discharges > 10, 000 population equivalents (PE) discharg-ing to surface waters classed as sensitive (e.g. those subject to eutrophication).

Parameter Minimum concentration Minimum percentage reduction

BOD5 25 mg O2 l1 7090COD 125 mg O2 l1 75Suspended solids 35 mg l1 90Total phosphorus 1 mg P l1a 80

2 mg P l1b 80Total nitrogen 10 mg N l1a 7080

15 mg N l1b 7080

a10000100000 PE.b>100000 PE.

Strict completion dates have been set by the Commission for the provisionof minimum treatment for waste waters entering freshwater, estuaries andcoastal waters. For example, full secondary treatment (Sec. 2.1) includingnutrient removal for all discharges to sensitive waters with a populationequivalent (PE) >10,000 must be completed by the end of 1998. By 31December 2005 all waste waters from population centres


Introduction 11

Fig. 1.2. The implementation of the EU Urban Wastewater Directive, with dates forcompliance by Member States.

metals or listed substances which may categorise it as a hazardous wasteunder the EU Directive on Hazardous Waste (91/689/EEC).

Industrial euents have in the past been a major cause of pollution.The discharge of industrial euents is generally governed by two objec-tives: (1) the protection of environmental water quality, and (2) the needto protect sewers and wastewater treatment plants (Table 1.7). To meetthese objectives, discharge standards are required that are a compromisebetween what is needed to protect and improve the environment and thedemands of industrial development. Most industrialists accept that the ap-plication of the best practical technology (i.e. euent treatment using thebest of current technology to meet local environmental requirements atthe lowest nancial cost) is a reasonable way to comply with the euentdischarge standards set. However, where discharges contain dangerous ortoxic pollutants which need to be minimised, then the application of thebest available technology is required (i.e. euent treatment using the bestof current technology to minimise local environmental change, especiallythe accumulation of toxic materials, where nancial implications are sec-ondary considerations). Where euent standards are necessary that areeven unobtainable using the best available technology, then of course in-dustries can no longer continue at that location.



Table 1.7. Typical euent standards for discharges to sewers (Gledhill 1986).

Parameter Standard Reasons

pH 6 to 10 Protection of sewer and sewage works fabric

from corrosion.Suspended solids 200400 mg l1 Protection from sewer blockages and extra

load on sludge disposal system.BOD5 No general limit Local authorities would be concerned with

large loads on small sewage works and bal-ancing of ows may be required in ordernot to overload treatment units.

Oils/fats/grease 100 mg l1 Prevention of fouling of working equipmentand safety of men. Soluble fats, etc. can beallowed at ambient temperature.

Inammables, hy-drocarbons, etc.

Prohibited Prevention of hazards from vapours in sewers.

Temperature 43C Various reasons promotes corrosion, in-creases solubility of other pollutants, etc.

Toxic metals 10 mg l1 Prevention of treatment inhibition. The solu-ble metal is more toxic and dierent met-als can be troublesome. Total loads with alimit on soluble metals more realistic.

Sulphate 5001000 mg l1 Protection of sewer from sulphate corrosion.Cyanides 01 mg l1 Prevention of treatment inhibition. Much

higher levels can also cause hazardousworking conditions due to HCN gas accu-mulation in sewer.

The integrated pollution prevention and control (IPPC) Directive(96/61/EEC) was adopted in September 1996. Integrated pollutionprevention and control is a major advance in pollution control in that alldischarges and environmental eects to water, air and land are considered,together with the Best Practicable Environmental Option (BPEO) selectedfor disposal. In this way, pollution problems are solved rather than trans-ferred from one part of the environment to another. In the past, licensingof one environmental media (i.e. air, water or land) created an incentive torelease emissions to another. Integrated pollution prevention and controlalso minimises the risk of emissions crossing over into other environmentalmedia after discharge (e.g. acid rain, landll leachate). There is only one li-cence issued under IPPC covering all aspects of gaseous, liquid, solid wasteand noise emissions, so that the operator only has to make one applicationas well as ensuring consistency between conditions attached to the licence inrelation to the dierent environmental media. In Europe, IPPC applies tothe most complex and polluting industries and substances (e.g. large chem-ical works, power stations, etc.). In England and Wales, the Environment


Introduction 13

Agency issues guidance for such processes to ensure that the BPEO is car-ried out. The aim of IPPC is to minimise the release of listed substancesand to render substances that are released harmless using Best AvailableTechniques Not Entailing Excessive Cost (BATNEEC). The objective of theguidance notes is to identify the types of techniques that will be used bythe Agency to dene BATNEEC for a particular process. The BATNEECidentied is then used as a base for setting emission limit values (ELVs).Unlike previous practice in the identication of BATNEEC, emphasis isplaced on pollution prevention techniques such as cleaner technologies andwaste minimisation rather than end-of-pipe treatment. Other factors forimproving emission quality include in-plant changes, raw material substi-tution, process recycling, improved material handling and storage practices.Apart from the installation of equipment and new operational proceduresto reduce emissions, BATNEEC also necessitates the adoption of an on-going programme of environmental management and control which shouldfocus on continuing improvements aimed at prevention, elimination andprogressive reduction of emissions.

The selection of BATNEEC for a particular process takes into account(i) the current state of technical knowledge, (ii) the requirements of environ-mental protection, and (iii) the application of measures for these purposeswhich do not entail excessive costs, having regard to the risk of signicantenvironmental pollution. For existing facilities, the Agency considers (i) thenature, extent and eect of the emissions concerned, (ii) the nature and ageof the existing facilities connected with the activity and the period duringwhich the facilities are likely to be used or to continue in operation, and(iii) the costs, which would be incurred in improving or replacing these ex-isting facilities in relation to the economic situation of the industrial sectorof the process considered. Thus, while BATNEEC guidelines are the ba-sis for setting licence emission standards, other factors such as site-specicenvironmental and technical data as well as plant nancial data are alsotaken into account. In Ireland, similar IPPC licensing procedures are op-erated by the Environmental Protection Agency (EPA 1994), and like theEnvironment Agency in England and Wales, public registers of all licencesare maintained.

The introduction of the polluter which pays charging system through-out Europe and the USA is an attempt to achieve such environmentalobjectives, at least in terms of the cost to the community, by reinforcingthe philosophy that the polluter is responsible for all aspects of pollutioncontrol in relation to its own euent (Deering and Gray 1987). Two distincttypes of charges exist: euent charges are levied by local authorities for



discharges directly to surface waters, whereas user charges are levied for theuse of the authoritys collective treatment system (Table 1.16). By charg-ing industry for treating their euents in terms of strength and volume, itencourages them to optimise production eciency by reducing the volumeand strength of their euent. Most important of all, such charging systemsensure that euent disposal and treatment costs are taken into account bymanufacturers in the overall production costs, so that the cost of the nalproduct reects the true cost of production (Deering and Gray 1986).

Wastewater treatment is not solely a physical phenomena controlled byengineers, it also involves a complex series of biochemical reactions involv-ing a wide range of micro-organisms. The same micro-organisms that occurnaturally in rivers and streams are utilised, under controlled conditions, torapidly oxidise the organic matter in wastewater to innocuous end productsthat can be safely discharged to surface waters. Compared with other indus-tries which also use micro-organisms, such as brewing or baking, wastewa-ter treatment is by far the largest industrial use of micro-organisms usingspecially constructed reactors. As treatment plants that were constructedduring the early expansion of wastewater treatment in the late nineteenthand early twentieth centuries now near the end of their useful lives, it isclear that the opportunities for the biotechnologists to apply new technolo-gies, such as genetic manipulation combined with new reactor designs, topollution control are enormous (Chap. 10). In the future, cheaper, more ef-cient, and more compact processes will be developed, with the traditionalaims of removing organic matter and pathogens to prevent water pollu-tion and protect public health replaced with a philosophy of environmentalprotection linked with conservation of resources and by-product recovery(Chap. 11).

Natural scientists, whether they are trained as microbiologists, bio-chemists, biologists, biotechnologists, environmental scientists or any otherallied discipline, have an important role in all aspects of public health en-gineering. They already have a signicant function in the operation andmonitoring of treatment plants, but their expertise is also needed in theoptimisation of existing plants and in the design of the next generation ofwastewater treatment systems.

1.2. Nature of Wastewater

Although there has been a steady increase in the discharge of toxic in-organic and organic materials, it is still the biodegradable organic wastes


Nature of Wastewater 15

that are the major cause of pollution of receiving waters in Britain andIreland (Gray and Hunter 1985; DETR 1998; Environment Agency 1998,1999; EPA 2000). Organic waste originates from domestic and commercialpremises as sewage, from urban runo, various industrial processes and agri-cultural wastes. Not all industrial wastes have a high organic content thatis amenable to biological treatment, and those with a low organic content,insucient nutrients, and which contain toxic compounds, require specicchemical treatment, such as neutralisation, chemical precipitation, chemi-cal coagulation, reverse osmosis, ion-exchange, or adsorption onto activatedcarbon (Table 1.8) (Casey 1997).

This book concentrates on non-toxic wastewaters. It is these that areof particular interest to the biologist and biotechnologist in terms ofreuse, conversion, and recovery of useful constituent materials. Primar-ily sewage containing pathogenic micro-organisms is considered, althoughother wastewaters, such as agricultural wastes from intensive animal rearingand silage production, food processing wastes, and dairy industry wastesare also briey reviewed.

1.2.1. Sources and variation in sewage ow

The absolute minimum quantity of wastewater produced per person (percapita), without any excess water, is 4 litres per day. At this concentration,the wastewater has a dry solids content in excess of 10%. However, in mostcommunities that have an adequate water supply this minimum quantity isgreatly increased. In those countries where technology and an almost un-limited water supply has led to the widescale adoption of water-consumingdevices many of which are now considered to be standard, if not basic,human requirements the volume of wastewater produced has increasedby a factor of 100 or more. Flush toilets, baths, showers, automatic washingmachines, dishwashers and waste disposal units all produce vast quantitiesof diluted dirty (grey) water with a very low solids content and all requiringtreatment before being discharged to surface waters. For example, a ushtoilet dilutes small volumes of waste matter (< 1 litre) to between 10 or30 litres each time it is used. Domestic sewage is diluted so much that it isessentially 99.9% water with a dry solids content of less than 0.1%. Con-ventional sewage treatment aims to convert the solids into a manageablesludge (2% dry solids) while leaving only a small proportion in the naleuent (0.003% dry solids).

The total volume of wastewater produced per capita depends on thewater usage, the type of sewerage system used and the level of inltration.



Table 1.8. Main chemical and biological unit processes employed in wastewatertreatment.

Process Description

Chemical unit processes

Neutralisation Non-neutral waste waters are mixed either with an alkali (e.g.NaOH) or an acid (e.g. H2SO4) to bring the pH as close to neu-tral as possible to protect treatment processes. Widely used inchemical, pharmaceutical and tanning industries

Precipitation Dissolved inorganic components can be removed by adding an acidor alkali, or by changing the temperature, by precipitation as asolid. The precipitate can be removed by sedimentation, otationor any other solids removal process

Ion-exchange Removal of dissolved inorganic ions by exchange with another ionattached to a resin column. For example Ca and Mg ions canreplace Na ions in a resin, thereby reducing the hardness of thewater

Oxidation reduction Inorganic and organic materials in industrial process waters can bemade less toxic or less volatile by subtracting or adding electronsbetween reactant (e.g. aromatic hydrocarbons, cyanides, etc.)

Biological unit processes

Activated sludge Liquid waste water is aerated to allow micro-organisms to utilise

organic polluting matter (95% reduction). The microbial biomassand treated euent are separated by sedimentation with a portionof the biomass (sludge) returned to the aeration tank to seed theincoming waste water

Biological ltration Waste water is distributed over a bed of inert medium on whichmicro-organisms develop and utilise the organic matter present.Aeration occurs through natural ventilation and the solids arenot returned to the lter

Stabilisation ponds Large lagoons where waste water is stored for long periods to al-low a wide range of micro-organisms to break down organic mat-ter. Many dierent types and designs of ponds including aerated,non-aerated and anaerobic ponds. Some designs rely on algae toprovide oxygen for bacterial breakdown of organic matter. Sludgeis not returned

Anaerobic digestion Used for high strength organic euents (e.g. pharmaceutical, foodand drink industries). Waste water is stored in a sealed tank whichexcludes oxygen. Anaerobic bacteria breakdown organic matterinto methane, carbon dioxide and organic acids. Final euent stillrequires further treatment as has a high BOD. Also used for thestabilisation of sewage sludge at a concentration of 27% solids

The volume of wastewater varies from country to country depending onits standard of living and the availability of water supplies (Table 1.9).Generally, the volume and strength of the sewage discharged in a particularcountry can be predicted fairly accurately. For example, the mean dailyvolume of wastewater, excluding industrial waste but including inltration,



Table 1.9. Specic water consumption in Europe (IWSA 1995).

Household and Industry

small businesses and others Total

1980 1993 1980 1993 1980 1993

Austria 155 170 100 92 255 262

Belgium 104 120 59 37 163 157

Denmark 165 155 96 74 261 229

France 109 157 58 58 167 215

Germany1 137 136 74 41 211 177

Hungary 110 121 107 63 217 184

Italy 211 251 69 78 280 329

Luxembourg 183 178 76 83 259 261

Netherlands 142 171 37 32 179 203

Norway 154 180 247 340 401 520

Spain 157 210 58 90 215 300

Sweden 195 203 120 73 315 276

Switzerland 229 242 163 120 392 362

United Kingdom 154 2 100 2 254 331

1Includes former GDR.

2UK values not available in this format.

produced per capita in England is 180 l d1, compared 230 l d1 in Irelandand 250 l d1 in Scotland. The equivalent volume of sewage produced inthe USA is on average 300 l per capita per day (100 US gallons d1).The amount of wastewater produced per capita can be estimated quiteaccurately from the specic water consumption.

The variation in volume depends on a number of variables includingthe amount of inltration water entering the sewer. The higher volume ofwastewater produced in Scotland is primarily due to the widescale use ofa larger ushing cistern, 13.6 l compared with 9.0 l in England and Wales,although other factors also contribute to this variation. Guidelines fromthe Department of the Environment in England and Wales stipulate thatall new cisterns manufactured after 1993 should have a maximum ushingvolume of 7.5 l. However, the reliance of water closets which function on asiphon rather than a valve to release water restricts the minimum opera-tional volume to between 45 l (Pearse 1987). The Building Research Es-tablishment (1987) highlights the potential water saving from the adoptionof new cistern designs and suggests the need for new British Standards.



Comparative studies were carried out using a standard turd, which is a43 mm diameter ball of non-absorbent material with a relative density of1.08, and with a cohesive shear strength, coecient of friction, and adhesiveproperties very close to the real thing.

In rural areas, where water is drawn from boreholes or from small com-munity water schemes, water may be at a premium, so the necessary con-servation of supplies results in reduced volumes of stronger sewage. Occa-sionally, the water pressure from such rural supplies is too low to operateautomatic washing machines or dishwashers and results in an overall reduc-tion in water usage and subsequent wastewater discharge.

In the home, wastewater comes from three main sources. Approximatelya third of the volume comes from the toilet, a third from personal washingvia the wash basin, bath, and shower, and a third from other sources suchas washing up, laundry, food and drink preparation (Tables 1.10 and 1.11).Outside the home, the strength and volume of wastewater produced percapita per day will uctuate according to source, and this variation mustbe taken into account when designing a new treatment plant. For example,the ow per capita can vary from 50 l d1 at a camping site to 300 ld1 at a luxury hotel (Table 1.11). More detailed tables of the volume ofwastewater produced from non-industrial sources, including the strengthof such wastewater, are given by Hammer (1999) and also by Metcalf andEddy (1991).

The diluted nature of wastewater has led to the development of thepresent system of treatment found in nearly all the technically-developedcountries, which is based on treating large volumes of weak wastewater.In less developed communities, the high solids concentration of the waste

Table 1.10. Comparison of the percentage consumption of water for various pur-poses in a home with an oce; indicating the source and make-up of wastewaterfrom these types of premises (Mann 1979).

Total water Total water

Home (sources) consumed (%) Oce (sources) consumed (%)

WC ushing

Washing/bathing

35

25

WC ushing

Urinal ushing

43

20

}63

Food preparation/drinking 15 Washing 27

Canteen use 9

Laundry 10 Cleaning 1

Car washing/garden use 5a

aMay not be disposed to sewer.



Table 1.11. Daily volume of wastewater produced per capita from variousnon-industrial sources (Mann 1979).

Volume of sewage

Source category (litres/person/day)

Small domestic housing 120

Luxury domestic housing 200

Hotels with private baths 150

Restaurants (toilet and kitchen wastes per customer) 3040

Camping site with limited sanitary facilities 80120

Day schools with meals service 5060

Boarding schools: term time 150200

Oces: day work 4050

Factories: per 8 hour shift 4080

Table 1.12. Comparison of the concentration of various compounds reported in urbanruno with precipitation, strictly surface runo from roads and with combined seweroverow (Pope 1980). All units are in mg l1 unless specied. Those marked with arein mg kg1 and in kg curb km1.

Reported concentration range (mg l1)

Parameter Precipitation Road/street Urban Combined

runo runo sewer overow

COD 2.5322 300 53100 932636

BOD 1.1 25165 1700 15685

Total solids 1824 4741070 40015322 1502300

Volatile total solids 3786 121600

Suspended solids 213 115500 211300 201700

Volatile suspended solids 616 1001500 121268 113

Settleable solids 0.55400

Total dissolved solids 6633050 9574

Volatile dissolved solids 1630 160

Conductance (mho cm1) 8395 10000 5.520000

Turbidity (JTU) 47 370

Colour (Pt-Co units) 510 5160

Total organic carbon 118 5.349 14120

Total inorganic carbon 02.8 1.17

Oils/hydrocarbons 28400 0110

Phenols 010




Reported concentration range (mg l1)

Parameter Precipitation Road/street Urban Combined

runo runo sewer overow

Total nitrogen N 0.59.9 0.184.0 1.16.2 4.063.3

Organic N 0.10.32 0.183.23 0.116 1.533.1

Inorganic N 0.69 1.0

Ammonia N 0.010.4 12 0.114.0 0.112.5

Nitrate N 0.025.0 0.312.62 0.12.5

Nitrite N 00.1 0-1.5

Total phosphorus 0.0010.35 0.30.7 0.094.4 1.026.5

Hydrolysable phosphorus 0.80.24 0.110

Aldrin trace

Dieldrin 0.003 6.8 106 trace p, p-DDD 18.9 106 p, p-DDD 17.2 106 Heptachlor 0.04 trace Lindane trace

PCB 311 106 Bromide 5

Chloride 0.11.1 470000 225000

Cadmium 0.0130.056 0.0020.01 0.0060.045

Chromium 0.0230.08 0.0181.0 0.0127.0

Copper 0.060.48 0.0072.55 0.0410.45

Iron 03.05 5440 05.3

Lead 0.02410.4 1113 0.0114.5

Mercury 0.029

Nickel 0.021.5

Zinc 0.024.9 115 0.015.23

Total coliform (ml1) 24099100

Total coliform

(organisms km1) 15.9 1010 Faecal coliform (ml1) 550011200

Faecal coliform

(organisms km1) 0.9 1010 Faecal streptococcus

(ml1) 12020000



makes it dicult to move to central collection and treatment sites, while themore diluted wastewater ows easily through pipes, and can be transportedeasily and eciently via a network of sewers to a central treatment works.In isolated areas or underdeveloped countries, human waste is normallytreated on-site, due to its smaller volume and less uid properties (Feachemand Cairncross 1993; Mara 1996).

The collection and transport of sewage to the treatment plant is via anetwork of sewers. Two main types of sewerage systems are used, combinedand separate. Combined sewerage systems are common in most towns inBritain. Surface drainage from roads, paved areas, and roofs are collectedin the same sewer as the foul wastewater and piped to the treatment works.This leads to uctuations in both the volume and the strength of sewagedue to rainfall, and although the treatment works is designed to treat up tothree times the dry weather ow of wastewater (DWF), problems arise if therainfall is either heavy or continuous. During such periods, the wastewaterbecomes relatively diluted and the volume too great to be dealt with bythe treatment works. Excess ow is, therefore, either directly discharged toa watercourse as storm water or stored at the treatment works in stormwater tanks. The stored wastewater can be circulated back to the start ofthe treatment works once capacity is available. However, once the tanksbecome full, and then the settled wastewater passes into the river withoutfurther treatment where the watercourse, already swollen with rainwater,can easily assimilate the diluted wastewater because of the extra dilutionnow available.

A separate sewerage system overcomes the problem of uctuations insewage strength and volume due to rain, by collecting and transportingonly the foul wastewater to the treatment works, and surface drainage isdischarged to the nearest water course. Such systems are common in newtowns in Britain and are mandatory in Canada and the USA. This typeof sewerage system allows more ecient and economic treatment works tobe designed as the variation in the volume and strength of the wastewateris much smaller and can be more accurately predicted. A major drawbackwith separate systems is that the surface drainage water often becomespolluted. All stormwater is contaminated to some degree because of contactduring the drainage cycle: it passes over paved areas along roadside gulliesto enter the sewer via a drain with a gully pot, which catches and removessolids that might otherwise cause a blockage in the sewer pipe (Bartlett1981). The quality of urban runo is extremely variable and biochemicaloxygen demand (BOD) values have been recorded in excess of 7,500 mgl1 (Mason 1991; Lee and Bang 2000). It is the rst ush of storm water



that is particularly polluting as it displaces the anaerobic wastewater, richin bacteria, that has been standing in the gully pots of the roadside drainssince the last storm (Butler and Memon 1999). The runo from roads isrich in grit, suspended solids, hydrocarbons including polycyclic aromatichydrocarbons (Krein and Schorer 2000), heavy metals, pesticides such asthe herbicide atrazine (Appel and Hudak 2001), and, during the winter,chloride from road-salting operations. Surprisingly, it also contains organicmatter, not only in the form of plant debris such as leaves and twigs, butalso dog faeces (Table 1.12). It has been estimated that up to 17 g m2

y1 of dog faeces are deposited onto urban paved areas and that the dog

Table 1.13. Chemical characteristics of treated euents from three UKsewage treatment plants.

Source

Constituenta Stevenage Letchworth Redbridge

Total solids 728 640 931

Suspended solids 15 51

Permanganate value 13 8.6 16

BOD 9 2 21

COD 63 31 78

Organic carbon 20 13

Surface-active matter

Anionic (as Manoxol OT) 2.5 0.75 1.4

Non-ionic (as Lissapol NX) 0.4

Ammonia (as N) 4.1 1.9 7.1

Nitrate (as N) 38 21 26

Nitrite (as N) 1.8 0.2 0.4

Chloride 69 69 98

Sulphate 85 61 212

Total phosphate (as P) 9.6 6.2 8.2

Sodium 144 124

Potassium 26 21

Total hardness 249 295 468

pH value 7.6 7.2 7.4

Turbidity (ATU)b 66

Colour (Hazen units) 50 43 36

Coliform bacteria (no./ml) 1300 3500

aResults are given in mg l1, unless otherwise indicated.bAbsorptiometric turbidy units



population of a city the size of Manchester will produce an organic loadequivalent to the human population of a small town of 2530,000 people. InNew York, the dog population deposits over 68,000 kg of faeces and 405,000 lof urine onto the streets each day, much of which is washed by storm waterinto local streams and rivers (Feldman 1974). The degree of contaminationof urban runo during a specic storm depends on: (i) the intensity andduration of the rainfall; (ii) the length of the preceding dry period, whichcontrols the build up of pollutants on roads and in the quality of waterstored in gully pots and gutters; (iii) seasonal variations that occur in therainfall pattern and temperature which aects the degradation of organicmatter; including leaf fall and the use of grit and salt during the winter, and(iv) the eectiveness of local authorities to clean roadside gullies and gullypots (Helliwell 1979). Unlike drainage from land, runo from roads andpaved areas is very rapid due to the short length of surface water sewers. Thecontaminated wastewater, therefore, reaches the receiving watercourse veryquickly and before the dry weather ow has increased, so that any pollutantsentering will receive minimum dilution. Where there is an accidental ordeliberate spillage of chemicals or noxious wastes on roads, or in privateyards, serious pollution of receiving waters is bound to occur. However, withcombined sewerage systems such spillages can be conned at the treatmentworks and recovered or treated before reaching the watercourse (Sec. 2.1.1).During storm events, it is possible for combined sewers in particular tobecome overloaded, leading to the operation of sewer overow systems.Combined sewer overows (CSOs) discharge a mixture of wastewater andsurface runo that causes severe pollution in receiving waters (Balmforth1990; Field et al. 1994). Extensive work has been undertaken to reduce thenumber of storm water overows within sewer networks and to reduce theamount of storm water entering the sewer by using interception systemssuch as swales, percolation areas, porous roads and wetlands (Field et al.1994; Debo and Reese 1995; Shutes et al. 1997; Sieker 1998; Adams andPapa 2000).

It is common, in both separate and combined sewers, for water notdischarged as wastewater to enter the sewer via joints and cracks in thepipework. Inltration water is normally from ground water sources and canbe especially high during periods of rainfall. Few estimates of the extent ofthe problem are available, although some studies have found inltration tobe as high as 80% of the total volume in badly deteriorated sewers. In theUSA, it is estimated that a mean value is 70 m3d1 per km of sewer (30,000US gallons per day per mile of sewer) (Clarke et al. 1971), although Grace(1979) recorded mean values some 50% less. As groundwater is generally



very clean, inltration has the eect of diluting the strength of wastewaterand at the same time increasing the volume requiring treatment.

The ow rate of wastewater to treatment works is extremely variable,and although such ows follow a basic diurnal pattern, each treatmentworks tends to have a characteristic ow pattern. This pattern is controlledby such factors as: the time taken for sewage to travel from householdsto the treatment works, which is itself a function of sewer length; the de-gree of inltration; the presence of stormwater and the variability in thewater consumption practices of communities (Gower 1980). Industrial in-puts obviously have a profound eect on ow rates, and industrial practicessuch as discharging wastes after 8-hour shifts can completely alter the ex-pected normal ow pattern to a treatment plant. The basic ow patternfor a domestic wastewater treatment plant is shown in Fig. 1.3 with theminimum ow normally occurring in the early hours of the morning whenwater consumption is lowest and the ow consists largely of inltrationwater. Flow rate rapidly increases during the morning when peak morn-ing water consumption reaches the plant, followed by a second peak in the

Fig. 1.3. Example of the hourly variation in ow to a sewage treatment plant.



early evening. When inltration, storm water, and the water used for non-sewered purposes such as garden use, are removed from a basic model ofconsumption and discharge, then the water supplied is essentially equiv-alent to the wastewater discharged to the sewer (Lenz 1983a). Thus, thewastewater discharge curve, as measured at the sewage treatment works,will closely parallel the water supply curve, as measured at the waterworks,with a lag of several hours.

Inltration and storm water tend to distort the basic shape of the hydro-graph of diurnal ow. Inltration, while increasing the total daily volume,does not alter its characteristic shape. Storm water, however, can alter theshape of the hydrograph by hiding peaks and troughs or adding new peaksas the rainfall causes rapid increases in the ow. Hourly uctuations are lessclear in large catchments due to the diversity of activities taking place dur-ing the 24-hour period and the presence of industry. The variable distanceof households from the treatment works normally results in the hydrographof the diurnal pattern becoming attened and extended so that only onetrough and one peak is seen daily (Clark et al. 1977; Escritt and Haworth1984). Many problems at small to moderate sized treatment works are as-sociated with the diurnal variation in ow, which is especially serious atthe smallest works where often there is no ow at all during the night.Smaller variations of the average daily ow rate are recorded at treatmentworks serving large catchments (50200%) compared with smaller commu-nities (20300%) (Painter 1958; Water Pollution Control Federation 1961).Many works overcome the problem of ow variation by using ow balanc-ing, where the wastewater is stored at times of high ow and allowed toenter the works at a constant rate, or by recirculating treated nal euentduring periods of low ow.

Variation between weekday ows is negligible, except in those areaswhere the household laundry is done on specic days. However, with theadvent of automatic washing machines this practice has become largely ex-tinct. With changing work patterns, many homes are now only occupiedat night and on the weekends, leading to changes in diurnal and daily owcharacteristics. Also, automatic washing of household laundry and dishesis increasingly done at night to take advantage of cheaper o-peak elec-tricity taris. Although summer discharges normally exceed winter owsby 1020%, up to 2030% in the USA, seasonal variations in ow are duemainly to variation in population, as is the case at holiday resorts, schools,universities, and military camps. Other seasonal variations in ow are dueto inltration, which is linked to rainfall pattern and groundwater levels,and seasonal industrial activities such as food processing.



1.2.2. Composition of sewage

Wastewater is dened as domestic (sanitary) or industrial (trade). Domes-tic wastewater comes exclusively from residences, commercial buildings,and institutions such as schools and hospitals, while industrial wastewatercomes from manufacturing plants. Inevitably, large towns and cities havea mixture of domestic and industrial wastewaters which is commonly re-ferred to as municipal wastewater, and normally includes euents from theservice industries such as dairies, laundries, and bakeries, as well as a vari-ety of small factories. It is unusual for modern municipal treatment plantsto accept wastewater from major industrial complexes, such as chemicalmanufacturing, brewing, meat processing, metal processing, or paper mills,unless the treatment plant is specically designed to do so. The practice inall European countries is now for water authorities to charge industry forthe treatment and disposal of their wastewater. Thus, the current trend isfor industry to treat its own waste in specically designed treatment plants.In many cases, it is not cost-eective for an industry to provide and oper-ate its own treatment plant, although most industries partially treat theirwaste to reduce the pollution load before discharge to the public sewer, inorder to reduce excessive treatment charges.

It is of prime importance for the designer and operator of a treatmentplant to have as much knowledge of the composition of the wastewater to betreated as possible. This is particularly important when new or additionalwastes are discharged to existing plants. A full analysis of the wastewaterwill, for example:

(i) determine whether pretreatment is required;(ii) determine whether an industrial waste should be treated alone or with

sewage and, if so, in what proportions;(iii) determine whether an industrial waste would attack the sewer;(iv) permit a better selection of the most appropriate treatment process;(v) allow an assessment of the toxicity or disease hazards;(vi) provide indication of the resultant degree of eutrophication or organic

enrichment in the form of sewage fungus in the receiving water (i.e.impact assessment); and

(vii) an assessment of the recoverable or reusable fractions of thewastewater.

Although there is considerable similarity in the basic content of sewage,the precise volume and characteristics will vary not only from country tocountry because of climatic conditions and social customs, but also within



Table 1.14. Volume and composition of human faeces and urine(Gloyna 1971).

Faeces Urine

Moist weight per capita per day 135270 g 1.01.3 kg

Dry weight per capital per day 3570 g 5070 g

Moisture content 6680% 9396%

Organic matter content (dry basis) 8897% 6585%

Nitrogen (dry basis) 5.07.0% 1519%

Phosphorus (as P2O5) (dry basis) 3.05.4% 2.55.0%

Potassium (as K2O) (dry basis) 1.02.5% 3.04.5%

Carbon (as dry basis) 4055% 1117%

Calcium (CaO) (dry basis) 45% 4.56.0%

individual countries due to supply water characteristics, water availability,population size, and the presence of industrial wastes. Data on wastewatersis normally limited to BOD5 (the ve day biochemical oxygen demand test),COD (ch

Biology of-wastewater-treatment-vol 4

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