biological wastewater treatment : principles, modelling
TRANSCRIPT
Biological Wastewater Treatment
Principles, Modelling and Design
2nd edition
Guanghao Chen
Mark CM. van Loosdrecht
George A. Ekama
Damir Brdjanovic
DMAPUBLISHING
Table of contents
1. WASTEWATER TREATMENT DEVELOPMENT 1
1.1 Global drivers for sanitation 1
1.2 History of wastewater treatment 2
2. BASIC MICROBIOLOGY AND METABOLISM 11
2.1 Introduction 11
2.1.1 Microorganisms in biological wastewater treatment 11
2.1.2 Microbial growth as a functional unit 12
2.1.3 Microbial community engineering 12
2.1.4 Analytical methods for microbial ecology 12
2.1.5 Mathematical models of microbial growth 13
2.2 Basic aspects of microbiology and metabolism 13
2.2.1 Prokaryotes, eukaryotes and viruses 13
2.2.2 Cell structure and components 16
2.2.2.1 Cell structures ofprokaryotes and eukaryotes 16
2.2.2.2 Elemental composition of biomass 16
2.2.2.3 Cellular macromolecules 19
2.2.2.4 Intracellular storage biopolymers 20
2.2.2.5 Extracellular polymeric substances (EPS) and biofilms 21
2.2.3 Metabolism and regulation 22
2.2.3.1 Breakdown ofpolymeric substrates and biosynthesis of biomass macromolecules.. 22
2.2.3.2 Dissimilation and assimilation of substrates: catabolism and anabolism 22
2.2.3.3 Metabolic regulation in microbial cells: ATP, NADH, and NADPH 25
2.2.3.4 Molecular regulation in microbial cells: DNA, RNA, proteins and metabolites 25
2.2.4 Trophic groups and metabolic diversity 26
2.2.4.1 Trophic structure in microbiology and links to environmental engineering 27
2.2.4.2 Illustration ofmicrobial trophic groups 30
2.2.4.3 Predominant guilds of microorganisms involved in BNR from wastewater 30
2.2.5 Microbial physiology and environmental gradients 34
2.2.5.1 Environmental factors 34
2.2.5.2 Microbial niche establishment across gradient systems 35
2.3 Microbial ecology and ecophysiology methods 35
2.3.1 Black to grey and white-box analysis ofmicrobiomes 36
2.3.2 Informational molecules from microorganisms 36
2.3.3 Classifications of microorganisms: morphotypes, phenotypes, and genotypes 37
2.3.3.1 rPvNA genes for taxonomic classification at high resolution 38
2.3.3.2 Taxonomic classification and levels 38
2.3.4 Culture-dependent vs. culture-independent methods 39
2.3.4.1 Analysing taxa and functions: choosing the right method(s) 39
2.3.5 Microscopy, isolation, and counting methods 40
2.3.6 Molecular biology and fingerprinting methods 43
2.3.7 High-throughput 'omic' methods 46
2.3.8 Ecophysiology methods 50
2.3.9 From microbial ecology analyses to microbial community engineering 50
2.4 Microbial growth basics 51
2.4.1 Microbial growth 51
2.4.2 Bacterial bioenergetics 52
2.4.3 Redox reactions 53
2.4.4 Thermodynamics basics 55
2.5 Stoichiometry of microbial growth 58
2.5.1 Anabolism 58
2.5.2 Catabolism 60
2.5.3 Metabolism 61
2.5.4 Generalized method to estimate the maximum biomass yield 63
2.6 Kinetics ofmicrobial growth 65
2.6.1 Substrate consumption rate: the Herbert-Pirt relation 65
2.6.2 Substrate consumption rate: saturation kinetics 67
2.6.3 Outlook 69
3. WASTEWATER CHARACTERISTICS 77
3.1 Wastewater types and their characteristics 77
3.1.1 Sources of wastewater 77
3.1.2 General overview ofwastewater constituents 78
3.2 Physical and chemical occurrence ofwastewater components 79
3.2.1 Soluble versus colloidal versus particulate constituents 79
3.2.2 Organic versus inorganic constituents 81
3.3 Microorganisms81
3.4 Organic matter82
3.4.1 Characterization: BOD versus COD 82
3.4.2 COD fractionation 83
3.5 Nitrogen86
3.6 Phosphorus87
3.7 Sulphur88
3.8 Cellulose89
3.9 Micropollutants90
3.10 Other characteristics91
3.10.1 Metals 91
3.10.2 Physical properties ofwastewater 91
3.10.3 Toxic organic components92
3.11 Typical wastewater characteristics 92
3.11.1 Population equivalent 92
3.11.2 Municipal wastewater composition 93
3.11.3 Importance ofratios 93
3.11.4 Domestic wastewater sub-streams 94
3.11.5 Non-domestic sewage components 96
3.11.6 Internal loads in wastewater treatment plants 97
3.11.7 Non-sewered (onsite) sanitation flows 98
3.12 Dynamics ofwastewater characteristics 101
3.13 Calibration protocols for activated sludge modelling 103
4. ORGANIC MATTER REMOVAL111
4.1 IntroductionHI
4.1.1 Transformations in the biological reactor Ill
4.1.2 Steady-state and dynamic-simulation models 113
4.2 Activated sludge system constraints 113
4.2.1 Mixing regimes113
4.2.2 Sludge retention time (SRT) 114
4.2.3 Nominal hydraulic retention time (HRTn) 115
4.2.4 Connection between sludge age and hydraulic retention time 115
4.3 Some model simplifications 116
4.3.1 Complete utilization ofbiodegradable organics 116
4.4 Steady-state system equations 116
4.4.1 For the influent 117
4.4.2 For the system 118
4.4.3 Reactor volume and retention time 120
4.4.4 Irrelevance of HRT 120
4.4.5 Effluent COD concentration 120
4.4.6 The COD (or e ) mass balance 121
4.4.7 Active fraction ofthe sludge 122
4.4.8 Steady-state design 123
4.4.9 The steady-state design procedure 123
4.5 Design example 124
4.5.1 Temperature effects 125
4.5.2 Calculations for organic material degradation 125
4.5.3 The COD mass balance 128
4.6 Reactor volume requirements 130
4.7 Determination of reactor TSS concentration 131
4.7.1 Reactor cost 131
4.7.2 Secondary settling tank cost 132
4.7.3 Total cost 133
4.8 Carbonaceous oxygen demand 134
4.8.1 Steady-state (daily average) conditions 134
4.8.2 Daily cyclic (dynamic) conditions 134
4.9 Daily sludge production 135
4.10 Food-to-Microorganism (F/M) ratio and Load Factor 136
4.11 Capacity estimation of AS systems 138
4.12 System design and control 141
4.12.1 System sludge mass control 142
4.12.2 Hydraulic control ofsludge age 145
4.13 Selection of sludge age 146
4.13.1 Short sludge ages (1 to 5 days) 146
4.13.2 Intermediate sludge ages (10 to 15 days) 149
4.13.3 Long sludge ages (20 days or more) 151
4.13.4 Dominant drivers for activated sludge system size 152
4.13.5 Some general comments 154
5. NITROGEN REMOVAL 161
5.1 Introduction to nitrification 161
5.2 Biological kinetics 162
5.2.1 Growth 162
5.2.2 Growth behaviour 164
5.2.3 Endogenous respiration 164
5.3 Process kinetics 164
5.3.1 Effluent ammonia concentration 164
5.4 Factors influencing nitrification 166
5.4.1 Influent source 16V
5.4.2 Temperature 167
5.4.3 Unaerated zones 168
5.4.4 Dissolved oxygen concentration 170
5.4.5 Cyclic flow and load 171
5.4.6 pH and alkalinity 172
5.5 Nutrient requirements for sludge production 175
5.5.1 Nitrogen requirements 175
5.5.2 N (and P) removal by sludge production 177
5.6 Design considerations 178
5.6.1 Effluent TKN 178
5.6.2 Nitrification capacity 179
5.7 Nitrification design example 181
5.7.1 Effect of nitrification on mixed liquor pH 181
5.7.2 Minimum sludge age for nitrification 182
5.7.3 Raw wastewater N concentrations 182
5.7.4 Settled wastewater 183
5.7.5 Nitrification process behaviour 183
5.8 Biological nitrogen removal 186
5.8.1 Interaction between nitrification and nitrogen removal 186
5.8.2 Benefits of denitrification 186
5.8.3 Nitrogen removal by denitrification 188
5.8.4 Denitrification kinetics 189
5.8.5 Denitrification systems 189
5.8.6 Denitrification rates 191
5.8.7 Denitrification potential 194
5.8.8 Minimum primary anoxic sludge mass fraction 196
5.8.9 Denitrification - influence on reactor volume and oxygen demand 197
5.9 Development and demonstration of design procedure 197
5.9.1 Review of calculations 198
5.9.2 Allocation ofunaerated sludge mass fraction 199
5.9.3 Denitrification performance ofthe MLE system 199
5.9.3.1 Optimum a-recycle ration 199
5.9.3.2 The balance MLE system 205
5.9.3.3 Effect ofinfluent TKN/COD ratio 207
5.9.3.4 MLE sensitivity diagram 210
5.10 System volume and oxygen demand 212
5.10.1 System volume 212
5.10.2 Daily average total oxygen demand 213
5.11 System design operation and control 214
5.12 Novel nitrogen removal processes 215
5.12.1 Impact of side-stream processes 216
5.12.2 The nitrogen cycle 217
5.12.3 Nitrite-based N removal 220
5.12.4 Anaerobic ammonia oxidation 222
5.12.5 Bio-augmentation 227
6. ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL 239
6.1 Introduction 239
6.2 Principles of enhanced biological phosphorus removal (EBPR) 240
6.3 EBPR microbiology 242
6.4 EBPR mechanisms 243
6.4.1 Background 243
6.4.2 Prerequisites 243
6.4.3 Observations 244
6.4.4 Biological P-removal mechanism 244
6.4.4.1 In the anaerobic reactor 244
6.4.4.2 In the subsequent aerobic reactor 246
6.4.4.3 Quantitative anaerobic-aerobic PAO model 247
6.4.5 Fermentable COD and slowly biodegradable COD 248
6.4.6 Functions ofthe anaerobic zone 248
6.4.7 Influence of recycling oxygen and nitrate on the anaerobic reactor 248
6.4.8 Denitrification by PAO 249
6.4.9 Relationship between influent COD components and sludge components 249
6.5 Factors impacting EBPR process performance 249
6.5.1 Total influent COD (CODi) 249
6.5.2 Raw or settled sewage 251
6.5.3 Influence of influent RBCOD fraction 252
6.5.4 Influence of recycling nitrate and oxygen on the anaerobic reactor 252
6.5.5 The effects ofthe SRT 253
6.5.6 Influence of the anaerobic stage 254
6.5.6.1 Effect of the anaerobic mass fraction 254
6.5.6.2 Effect of the number of anaerobic reactors (n) 255
6.5.7 Presence ofGAO 255
6.5.9 Carbon sources 256
6.5.10 Influent COD/P ratio 257
6.5.11 pH effects 258
6.5.12 Temperature effects 258
6.5.12.1 Short-term temperature effects on the physiology of EBPR 259
6.5.12.2 Long-term temperature effects on the EBPR process 260
6.5.13 Dissolved oxygen and aeration 260
6.5.14 Inhibitory compounds 260
6.6 EBPR process configurations 261
6.6.1 Phosphorus removal optimization principles 261
6.6.2 EBPR process discovery 262
6.6.3 PhoStrip® system 263
6.6.4 Modified Bardenpho 263
6.6.5 Phoredox or anaerobic/oxic (A/O) system 267
6.6.7 University of Cape Town (UCT, VIP) system 268
6.6.8 Modified UCT system 269
6.6.9 Johannesburg (JHB) system 269
6.6.10 Biological-chemical phosphorus removal (BCFS® system) 270
6.6.11 Side-stream EBPR (S2EBPR) systems 271
6.7 Model development for EBPR 271
6.7.1 Early developments 271
6.7.2 Readily biodegradable COD 272
6.7.3 Parametric model 272
6.7.4 Comments on the parametric model 273
6.7.5 NDEBPR system kinetics 273
6.7.6 Enhanced PAO cultures 274
6.7.6.1 Enhanced culture development 274
6.7.6.2 Enhanced culture kinetic model 274
6.7.6.3 Simplified enhanced culture steady state model 277
6.7.7 Steady-state mixed-culture NDEBPR systems 277
6.7.7.1 Mixed-culture steady-state model 277
6.8 Mixed-culture steady-state model 280
6.8.1 Principles ofthe model 280
6.8.2 Mass equations 281
6.8.2.1 PAOs 281
6.6.2.2 OHOs 281
6.8.2.3 Inert mass 282
6.8.3 Division of biodegradable COD between PAOs and OHOs 282
6.8.3.1 Kinetics ofconversion offermentable organics to VFAs 282
6.8.3.2 Effect of recycling nitrate or oxygen 283
6.8.3.3 Steady-state conversion equations 283
6.8.3.4 Implications ofconversion theory 284
6.8.4 P release 285
6.8.5 P removal and effluent total phosphorus concentration 285
6.8.6 VSS and TSS sludge masses and P content of TSS 287
6.8.6.1 Actual P content in active PAO biomass 287
6.8.6.2 VSS sludge mass 287
6.8.6.3 FSS sludge mass 287
6.8.6.2 TSS sludge mass and sludge VSS/TSS ratio 288
6.8.6.4 P content ofTSS 288
6.8.7 Process volume requirements 289
6.8.8 Nitrogen requirements for sludge production 289
6.8.9 Oxygen demand 289
6.8.9.1 Carbonaceous oxygen demand 289
6.8.9.2 Nitrification oxygen demand 290
6.8.9.3 Total oxygen demand 290
6.9 Design example 291
6.9.1 Steady-state design procedure 291
6.9.2 Information provided 291
6.9.3 Calculations 294
6.10 Influence of operational factors on full-scale EBPR WWTP 302
6.10.1 Influence on volatile and total suspended solids and oxygen demand 302
6.10.2 P/VSS ratio 304
6.11 Integrated design ofNDEBPR systems 304
6.11.1 Background 304
6.11.2 Denitrification potential in NDEBPR systems 306
6.11.2.1 Denitrification potential of the primary anoxic reactor 306
6.11.3.2 Denitrification potential of the secondary anoxic reactor 307
6.11.3 Principles of denitrification design procedures for NDEBPR systems 307
6.11.4 Analysis ofdenitrification in NDEBPR systems 308
6.11.4.1 UCT System 309
6.11.5 Maximum nitrate recycled to anaerobic reactor 309
6.12 Conclusions 310
7. INNOVATIVE SULPHUR-BASED WASTEWATER TREATMENT 327
7.1 Introduction 327
7.2 Sulphate-reducing bioprocess 329
7.2.1 Fundamental ofthis bioprocess 329
7.2.2.1 Sulphate-reducing pathways 329
7.2.1.2 Biochemical reactions involved in sulphate-reducing bioprocesses 332
7.2.2 Key microorganisms driving sulphate reduction 333
7.2.3 Electron donors for sulphate-reducing bioprocess 335
7.2.4 Application domain and model parameter 338
7.2.4.1 Sulphur-laden wastewater treatment 338
7.2.4.2 Bioremediation oftoxic metals 339
7.2.4.3 Process kinetic parameters 340
7.2.5 Factors that affect sulphate reduction 340
7.3 Sulphur-driven autotrophic denitrification 342
7.3.1 Introduction 342
7.3.2 Biochemical reactions in the SdAD process 343
7.3.3 Microorganisms in the SdAD process 344
7.3.4 Biochemistry of the SdAD process 346
7.3.4.1 Sulphur-oxydizing enzymes 346
7.3.4.2 Nitrogen-reducing enzymes 347
7.3.4.3 Electron distribution and competition in the SdAD process 348
7.3.5 Operational conditions governing the SdAD process 349
7.3.6 Implications ofthe SdAD process 351
7.4 SANI® Process development, modelling and application 351
7.4.1 Introduction 351
7.4.1.1 The Hong Kong water tale 351
7.4.1.2 Principle ofthe SANI® process 352
7.4.2 SANI® process development 354
7.4.2.1 Laboratory study 354
7.4.2.2 Pilot-scale study 355
7.4.3 SANI® process demonstration 356
7.4.4 Steady-state modelling ofthe SANI® plant 358
7.4.4.1 Stoichiometry equations 359
7.4.4.2 Kinetic equations 361
7.4.5 The SANI® plant design approach 363
7.4.5.1 Steady-state plant-wide model 363
7.4.5.2 Design calculation of SANI® reactors 363
7.5 Sulphur conversion-based resource recovery 365
7.5.1 Introduction 365
7.5.2 Metal sulphides 365
7.5.3 Elemental sulphur recovery and reuse 367
7.5.4 Metabolic intermediate recovery 367
7.6 Conclusions and perspectives 369
8. WASTEWATER DISINFECTION 381
8.1 Background 381
8.2 Indicator organism concept 382
8.3 Disinfection with halogens (chlorine) 382
8.3.1 Physical chemistry of chlorine 383
8.3.2 Disinfection mechanisms: chlorine 386
8.4 Disinfection with peracids (peracetic acid) 387
8.4.1 Physical chemistry of peracids 388
8.4.2 Disinfection mechanisms: peracids 388
8.5 Disinfection with ultraviolet radiation 389
8.5.1 Laws of photochemistry 389
8.5.2 Principles ofphotochemical kinetics 390
8.5.3 Mechanisms ofmicrobial inactivation: UV irradiation 392
8.5.4 Sources of germicidal UV radiation 393
8.6 Disinfection kinetics 395
8.6.1 Disinfection kinetics: chemical disinfectants 395
8.6.2 Disinfection kinetics: UV irradiation 398
8.6.3 Comparisons of disinfection kinetics among common disinfectants 400
8.7 Process models 403
8.7.1 Deterministic process models 403
8.7.2 Probabilistic (stochastic) process models 404
8.8 Disinfection applications in wastewater treatment 409
8.8.1 Chemical disinfection systems 410
8.8.2 UV disinfection systems 412
8.9 Future directions 413
8.10 Final remarks 414
9. AERATION AND MIXING 419
9.1 Aeration fundamentals and technology 419
9.1.1 Fundamentals and metrics 419
9.1.1.1 Oxygen transfer in clean water 419
9.1.1.2 Oxygen transfer in process water 421
9.1.1.3 The mysterious alpha factor 423
9.1.2 Fine bubbles, coarse bubbles and droplets 425
9.1.3 Inside the aeration tank 426
9.1.3.1 Bubble aeration 428
9.1.3.2 Mechanical aeration 431
9.1.4 Air blowers 434
9.1.4.1 Centrifugal blowers 435
9.1.4.2 Positive displacement blowers 437
9.1.5 The 'elephant in the room': I IPO processes 439
9.2. Mixing in activated sludge 441
9.2.1 Mixing quantification and design 443
9.2.2 Mixing equipment 445
9.3 Factors affecting oxygen transfer 446
9.3.1 Sludge retention time 447
9.3.2 Roleofselectors 447
9.3.3 Airflow rate 450
9.3.4 Diffuser density 450
9.3.5 Reactor depth 450
9.3.6 Diffuser fouling, scaling, and cleaning 450
9.3.7 Mixed-liquor concentrations 454
9.3.8 Temperature and pressure 455
9.3.9 Impact of hydrodynamics 4^5
9.3.10 Daily dynamics and alpha 456
9.4 Design algorithm 4^7
9.4.1 Verification/upgrade algorithm 460
9.5 Aeration and energy 4f>l
9.6 Sustainable aeration practice 4f>l
9.6.1 Aeration diagnostics 4f>l
9.6.2 Mechanically-simple aerated treatment systems 465
9.6.3 Energy-conservation strategies 466
10. BULKING SLUDGE 475
10.1 Introduction 475
10.2 Historical aspects 477
10.3 Relationship between morphology and ecophysiology 478
10.3.1 Microbiological approach 478
10.3.2 Morphological-ecological approach 480
10.4 Filamentous bacteria identification and characterisation 481
10.4.1 Microscopic characterisation versus molecular methods 481
10.4.2 Physiology of filamentous bacteria 481
10.5 Current general theories to explain bulking sludge 483
10.5.1 Diffusion-based selection 483
10.5.2 Kinetic selection theory 483
10.5.3 Storage selection theory 485
10.6 Remedial actions 485
10.6.1 Selector 485
10.6.1.1 Aerobic selectors 485
10.6.1.2 Non-aerated selectors 486
10.6.1.3 Anoxic selectors 487
10.6.1.4 Anaerobic selectors 488
10.7 Mathematic modelling 491
10.8 Granular sludge 49210.9 Conclusions 493
11. AEROBIC GRANULAR SLUDGE 497
11.1 Introduction 49711.2 Important considerations for selecting aerobic granular sludge 500
11.2.1 Gradients 500
11.2.2 Microbial selection 501
11.2.3 Physical selection 50211.2.4 Shear 50211.2.5 Plug-flow feeding 502
11.2.6 Effect ofsubstrate and feeding regime on granule morphology 503
11.3 Kinetics of aerobic granular sludge 505
11.3.1 Carbon removal 50511.3.2 Nitrogen removal 505
11.3.3 Biological phosphorus removal 506
11.3.4 Granular sludge properties 507
11.3.5 Reactor operation aspects 50711.4 Process control 508
11.4.1 The Nereda®cycle 508
11.4.2 Batch scheduling 509
11.4.3 Nutrient removal 510
11.4.4 Effluent suspended solids 511
11.4.5 Solids retention time 512
11.5 Design considerations 512
11.5.1 Plant configuration 512
11.5.2 Design volume 513
11.5.3 Sludge treatment 516
11.5.4 Mixed liquor suspended solids 516
11.6 Resource recovery 516
12. FINAL SETTLING 523
12.1 Introduction 523
12.1.1 Objective of settling 523
12.1.2 Functions ofa secondary settling tank 524
12.1.2.1 Clarification in secondary settlers 524
12.1.2.2 Thickening in secondary settlers 524
12.1.2.3 Sludge storage in secondary settlers 524
12.2 Settling tank configurations in practice 525
12.2.1 Circular clarifiers with radial flow pattern 525
12.2.2 Rectangular clarifiers with horizontal flow pattern 527
12.2.3 Deep clarifiers with vertical flow pattern 528
12.2.4 Improvements common to all clarifier types 528
12.2.4.1 Flocculation well 528
12.2.4.2 Scum removal 529
12.2.4.3 Baffles 529
12.2.4.4 Lamellae 529
12.2.5 Operational problems 530
12.2.5.1 Shallow tanks 530
12.2.5.2 Uneven flow distribution 530
12.2.5.3 Uneven weir loading 530
12.2.5.4 Effect ofwind 530
12.2.5.5 Sudden temperature changes 530
12.2.5.6 Freezing in cold weather 531
12.2.5.7 Recycle problems 531
12.2.5.8 Algae on weirs 531
12.2.5.9 Anaerobic clumps 532
12.2.5.10 Birds•
532
12.2.5.11 Bulking sludge 532
12.2.5.12 Rising sludge 532
12.3 Measures of sludge settleability 532
12.3.1 Sludge Volume Index 532
12.3.2 Other test methods 533
12.4 Flux theory for estimation of settling tank capacity 533
12.4.1 Zone Settling Velocity test 533
12.4.2 Discrete, flocculent, hindered (zone) and compression settling 534
12.4.3 The Vesilind settling function 534
12.4.4 Gravity, bulk and total flux curves 537
12.4.5 Solids handling criteria limits ofthe clarifier 538
12.4.6 State Point Analysis 539
12.5 Overview ofthe use of flux theory and other methods for design and operation 543
12.5.1 Design using flux theory 544
12.5.2 Empirical design 545
12.5.3 WRC design 545
12.5.4 ATV design 546
12.5.5 STOWA design 547
12.5.6 Comparison of settlers designed using different methods 548
12.6 Modelling of secondary settlers 548
12.6.1 Zero dimensional models 548
12.6.2 One-dimensional models 549
12.6.3 Computational Fluid Dynamic models 550
12.7 Design examples 551
13. MEMBRANE BIOREACTORS 559
13.1 Membrane separation principles 559
13.2 Introduction to membrane bioreactors 559
13.2.1 Membrane bioreactor history 559
13.2.2 Membrane bioreactor features 559
13.2.3 Membrane bioreactor configuration 560
13.2.4 Membrane materials and modules 561
13.2.5 Commercial membrane module makers 562
13.2.5.1 Immersed HF products 563
13.2.5.2 Immersed FS products 566
13.2.5.3 Tubular products 568
13.3 Wastewater treatment performance and effluent quality 569
13.3.1 Ordinary pollutant removal 569
13.3.2 Hygiene water quality 571
13.3.3 Emerging pollutant removal 572
13.3.4 Energy recovery 574
13.4 Membrane fouling and control 575
13.4.1 Definition of membrane fouling 575
13.4.2 Characterization ofmembrane fouling 576
13.4.3 Comprehensive control strategies for membrane fouling 577
13.4.4 Optimization ofmembrane operation conditions 577
13.4.4.1 Feed pretreatment 577
13.4.4.2 Enhancement of hydrodynamic conditions 578
13.4.4.3 Optimization of membrane flux 578
13.4.5 Cleaning fouled membranes 578
13.4.5.1 Physical cleaning 578
13.4.5.2 Chemical cleaning 579
13.4.6 Improving the filterability of mixed liquor 580
13.4.7 Other potential fouling control methods 580
13.4.7.1 Biological methods 580
13.4.7.2 Electrically-assisted approaches 581
13.4.7.3 Potential fouling mitigation using nanomaterials-based membranes 581
13.5 MBR plant design, operation and maintenance 582
13.5.1 Process composition 582
13.5.2 Pretreatment 583
13.5.3 Biological treatment units and kinetic parameters 584
13.5.3.1 Overview ofthe biological treatment units 584
13.5.3.2 Calculation of tank volumes and recirculation flow rates 585
13.5.3.3 Calculation of excess sludge production 586
13.5.3.4 Calculation of aeration demand for biological reactions 587
13.5.4 Membrane filtration system 588
13.5.4.1 Flux 588
13.5.4.2 Membrane area 589
13.5.4.3 Aeration demand 589
13.5.4.4 Chemical cleaning procedure 590
13.6 Practical application 591
13.6.1 Overall MBR applications 591
13.6.2 Four full-scale cases of MBR application 591
13.6.3 Latest developments in MBR systems 597
13.6.3.1 The high-loaded MBR (HL-MBR) concept 597
13.6.3.2 Applications of the HL-MBR system 599
13.7 Future trends in MBR technology 602
14. MODELLING ACTIVATED SLUDGE PROCESSES 613
14.1 What is a model? 613
14.2 Why modelling? 618
14.3 Modelling basics 620
14.3.1 Model building 620
14.3.2 General model set-up 620
14.3.3 Stoichiometry 622
14.3.4 Kinetics 623
14.3.5 Transport 624
14.3.6 Matrix notation 626
14.4 Stepwise development of the biokinetic model: ASM1 627
14.5 Activated sludge models 634
14.6 The ASM toolbox 642
14.7 Challenges for ASM and future trends 644
14.8 Conclusions 652
15. PROCESS CONTROL 666
15.1 Driving forces and motivations for control 666
15.1.1 ICA system features 668
15.1.2 Driving forces 669
15.1.3 Outline of the chapter 670
15.2 Disturbances in wastewater treatment systems 670
15.3 The role ofcontrol and automation 674
15.3.1 Setting the priorities 675
15.4 Instrumentation and monitoring 676
15.4.1 Sensors and instruments 67615.4.2 Monitoring 677
15.5 The importance ofdynamics 680
15.6 Manipulated variables and actuators 68215.6.1 Hydraulic variables 68215.6.2 Chemical addition 684
15.6.3 Carbon addition 684
15.6.4 Air or oxygen supply 68415.7 Basic control concepts 68515.8 Examples of feedback in wastewater treatment systems 686
15.9 Operating cost savings due to control 692
15.10 Integration and plant-wide control 69315.11 Concluding remarks 694
16. ANAEROBIC WASTEWATER TREATMENT 70116.1 Sustainability in wastewater treatment 701
16.1.1 Definition and environmental benefits of anaerobic processes 70116.2 Microbiology ofanaerobic conversions 704
16.2.1 Anaerobic degradation of organic polymers 704
16.2.1.1 Hydrolysis 70516.2.1.2 Acidogenesis 70616.2.1.3 Acetogenesis 707
16.2.1.4 Methanogenesis 710
16.3 Predicting the CH4 production 71116.3.1 COD 712
16.4 Impacts ofalternative electron acceptors 715
16.4.1 Bacterial conversions under anoxic conditions 715
16.4.1.1 Sulphate reduction 71516.4.1.2 Denitrification 717
16.5 Working with the COD balance 719
16.6 Immobilisation and sludge granulation 720
16.6.1 Mechanism underlying sludge granulation 72116.7 Anaerobic reactor systems 723
16.7.1 High-rate anaerobic systems 723
16.7.2 Single-stage anaerobic reactors 725
16.7.2.1 The anaerobic contact process (ACP) 72516.7.2.2 Anaerobic filters (AF) 72516.7.2.3 Anaerobic sludge bed reactors (ASBR) 727
16.7.2.4 Anaerobic expanded and fluidized-bed systems (EGSB and FB) 729
16.7.2.5 Advanced sludge liquid separation 73316.7.2.6 Other anaerobic high-rate systems 734
16.7.2.7 Anaerobic membrane bioreactors 734
16.7.2.8 Acidifying and hydrolytic reactors 735
16.7.2.9 Current market trends in anaerobic high-rate reactor sales 73616.8 Upflow anaerobic sludge blanket (UASB) reactor 737
16.8.1 Process description 737
16.8.2 Design considerations ofthe UASB reactor 737
16.8.2.1 Maximum hydraulic surface loading 73716.8.2.2 Organic loading capacity 73816.8.2.3 Internal components of the reactor 740
16.8.3 UASB septic tank 740
16.9 Anaerobic process kinetics 741
16.10 Anaerobic treatment ofdomestic and municipal sewage 742
16.11 Anaerobic treatment ofblack water in new sanitation systems 748
17. MODELLING BIOFILMS 757
17.1 What are biofilms? 757
17.2 Motivation for modelling biofilms and how to choose modelling approaches 758
17.3 Modelling approach for a biofilm 760
17.3.1 Basic equations 761
17.3.2 Solutions ofthe diffusion-reaction biofilm equation for different rate expressions 762
17.3.2.1 First-order substrate removal rate within the biofilm 762
17.3.2.2 Zero-order substrate removal rate within the biofilm 764
17.3.2.3 Monod kinetics within the biofilm 766
17.3.3 Summary ofanalytical solutions for a single limiting substrate 768
17.3.4 Derivation of the reaction diffusion equation from a mass balance within the biofilm 768
17.3.5 Overview of AQUASIM 770
17.4 Example of how Jlf = f(SuO can be used to predict biofilm reactor performance 771
17.4.1 Analytical solution 772
17.4.2 Trial and error or iterative approach 772
17.4.3 Graphical solution 772
17.4.4 Numerical solution (e.g. using AQUASIM) 773
17.5 Effect of external mass-transfer resistance 773
17.5.1 Substrate flux for first-order reaction rate with external boundary layer 774
17.5.2 Substrate flux for zero-order reaction rate with external boundary layer 774
17.5.3 Substrate flux for Monod kinetics inside the biofilm with an external boundary layer 775
17.6 Multi-component diffusion 776
17.6.1 Two-component diffusion ofan electron donor and acceptor 776
17.6.2 General case of multi-component diffusion 779
17.6.3 Complications for multiple processes inside the biofilm 779
17.7 Combining Growth and decay with detachment 780
17.7.1 Influence of detachment on the steady-state biofilm thickness and the substrate flux 781
17.7.2 Attachment and fate of particles 783
17.8 Biofilm reactor modelling in practice 784
17.8.1 Collection ofexamples 785
17.8.2 Step-by-step approach to evaluating biofilm reactors 791
17.9 Derived parameters 793
17.9.1 Solids retention time 793
17.9.2 Lowest effluent substrate concentration supporting biomass growth (Smin) 794
17.9.3 Characteristic times and non-dimensional numbers to describe biofilm dynamics 795
17.9.3.1 Application of characteristic times to estimate response times 796
17.9.3.2 Non-dimensional numbers: Da11, 3>, G, Bi and Pe 797
17.10 How does 2D/3D structure influence biofilm performance? 798
17.11 Model Parameters 800
17.11.1 Biofilm biomass density (Xf) 800
17.11.2 Diffusion coefficients (Dw, Df) 800
17.11.3 External mass transfer (Ll, Rl) 801
17.11.4 Biofilm thickness (Lf) and biofilm detachment (ud,s, ud,v, Ud,M) 802
17.11.5 Caution when using parameters from other types of models 803
17.12 Modelling tools 803
18. BIOFILM REACTORS 813
18.1 Biofilm reactors 813
18.1.1 Types ofreactors 814
18.1.1.1 Trickling filters 815
18.1.1.2 Rotating biological contactors 817
18.1.1.3 Submerged fixed-bed biofilm reactors 817
18.1.1.4 Fluidized and expanded-bed biofilm reactors 819
18.1.1.5 Granular sludge reactors 820
18.1.1.6 Moving-bed biofilm reactors 821
18.1.1.7 Hybrid biofilm/activated sludge systems 822
18.1.1.8 Membrane-attached biofilm reactors 823
18.1.2 Choosing from different biofilm support material options 824
18.2 Design parameters 825
18.2.1 Substrate flux and loading rates 825
18.2.2 Hydraulic loading 826
18.3 How to determine maximum design fluxes or design loading rates 827
18.3.1 Model-based estimation ofthe maximum substrate flux 827
18.3.2 Empirical maximum loading rates 829
18.3.3 Design examples 829
18.4 Other design considerations 833
18.4.1 Aeration 833
18.4.2 Flow distribution 834
18.4.3 Biofilm control 834
18.4.4 Solids removal 834