Reverse Osmosis

Jane Kucera is a senior technical consultant with Nalco Water, an Ecolab Company, where she designs water and wastewater use and reuse facilities. With over 40 years of experience, she has an MS in chemical engineering and has authored two books, both with Scrivener Publishing, the first and second editions of Reverse Osmosis, and the first and second editions of Desalination: Water from Water. She is active in the International Water Conference (IWC) and served as the 2023 Conference Chair. She received the 2021 Award of Merit offered by the Engineers’ Society of Western Pennsylvania for her work in the water treatment industry and contributions to the IWC. Jane has a Teaching Credential from the State of California and taught chemistry at Linfield University, Los Angeles Valley College, and Central Oregon Community College.

Preface to the 3rd Edition xxi

Acknowledgements xxiii

Section I: Fundamentals 1

1 Introduction to Reverse Osmosis: History, Challenges, and Future Directions 3

1.1 Introduction 3

1.2 A Brief History of Reverse Osmosis 5

1.2.1 Early Development 5

1.2.2 Advances 1970s–1980s 10

1.2.3 Advances from 1990s through the Early 2000s 12

1.3 Challenges and Prospects 14

1.3.1 Membrane Materials Development 15

1.3.2 Modification of Element Construction for Ultra-High Pressure or High-Temperature Operation 17

1.3.2.1 Ultra-High Pressure Spiral Wound RO 17

1.3.2.2 High-Temperature Elements 18

1.3.3 Optimization of RO Element Feed Channel Spacer 19

1.3.4 Other Advances and Future Requirements 23

1.4 Summary 26

Symbols 26

Nomenclature 27

References 27

2 Principles and Terminology 33

2.1 Semipermeable Membranes 33

2.2 Osmosis 33

2.3 Reverse Osmosis 35

2.4 Basic Performance Parameters: Recovery, Rejection, and Flux 35

2.4.1 Recovery and Concentration Factor 35

2.4.2 Rejection 38

2.4.3 Flux 41

2.4.3.1 Water Flux 41

2.4.3.2 Solute Flux 43

2.5 Filtration 43

2.5.1 Dead-End Filtration 43

2.5.2 Cross-Flow Filtration 43

2.6 Concentration Polarization 45

Symbols 47

Nomenclature 48

References 48

3 Membranes: Transport Models, Characterization, and Elements 51

3.1 Membrane Transport Models 51

3.1.1 Solution-Diffusion Transport Model 52

3.1.2 Modified Solution-Diffusion Transport Models 55

3.1.2.1 Solution-Diffusion Imperfection Model 55

3.1.2.2 Extended Solution-Diffusion Model 56

3.1.3 Pore-Based Transport Models 56

3.1.4 Models Based on Non-Equilibrium Thermodynamics 57

3.2 Polymeric Membranes 57

3.2.1 Cellulose Acetate 57

3.2.2 Linear Polyamide (Aramids) 61

3.2.3 Fully Aromatic Polyamide Composite Membranes 63

3.2.3.1 NS-100 Membrane 64

3.2.3.2 FT-30 Composite Membrane 67

3.2.4 Characterization of CA and Composite Polyamide Membranes 73

3.2.4.1 Surface Roughness 73

3.2.4.2 Zeta Potential (Surface Charge) 76

3.2.4.3 Hydrophilicity 76

3.2.5 Other Membrane Polymers 78

3.3 Membrane Elements 80

3.3.1 Plate and Frame Elements 81

3.3.2 Tubular Elements 82

3.3.3 Hollow Fine Fiber Elements 83

3.3.4 Spiral Wound Elements 84

3.4 Specialty Membranes and Elements 91

3.4.1 Specialty Membranes 91

3.4.1.1 Dry Membranes 91

3.4.1.2 Boron-Rejecting Membranes 92

3.4.2 Specialty Elements 93

3.4.2.1 Sanitary Elements 93

3.4.2.2 Disc Tube Elements 94

3.4.2.3 Vibratory Shear Enhanced Processing (VSEP) Elements and System 94

3.4.2.4 Ultra-High Pressure and High Temperature Elements 95

Symbols 95

Nomenclature 96

References 97

Section II: System Design and Engineering 103

4 Basic Design Arrangements and Concentration Polarization Guidelines 105

4.1 Arrays and Stages 105

4.1.1 Recovery per System Array 106

4.1.2 Element-By-Element Flow and Quality Distribution 108

4.1.3 Flux Guidelines 109

4.1.4 Cross-Flow Velocity Guidelines for Array Design 111

4.1.5 Concentrate Recycle 112

4.2 Passes 113

Symbols 115

Nomenclature 115

References 115

5 RO System Design Using Design Software 117

5.1 RO System Design Guidelines 117

5.2 Step-by-Step Design—Sample Problem 118

5.2.1 Step 1—Water Flux 119

5.2.2 Step 2—Membrane Selection 119

5.2.3 Step 3—Number of Elements Required 119

5.2.4 Step 4—System Array 120

5.3 Design Software 121

5.3.1 Water Application Value Engine (WAVE)— DuPont Water Solutions 123

5.3.2 IMSDesign—Hydranautics 131

5.3.3 Q+ Projection Software LGChem 135

5.4 Optimum Design Result for the Sample Problem 140

Symbols 141

Nomenclature 141

References 142

6 Design Considerations 143

6.1 Feed Water Source and Quality 143

6.1.1 Feed Water Source 143

6.1.2 Feed Water Quality and Guidelines 145

6.1.3 pH 147

6.1.3.1 pH Profile Through an RO System— Alkalinity Relationships 148

6.1.3.2 pH and Membrane Scaling Potential 148

6.1.3.3 pH Effects on Solute Rejection and Water Permeability 149

6.2 System Operations 149

6.2.1 Pressure 149

6.2.2 Compaction 151

6.2.3 Temperature 155

6.2.4 Balancing Flows 156

6.2.5 Designing for Variable Flow Demand 157

6.3 Existing RO System Design Considerations 157

6.3.1 Changing Membranes 157

6.3.1.1 Changing Membrane Area 158

6.3.1.2 Changing Membrane Types 158

6.3.1.3 Mixing Membrane Types 158

6.3.2 Increasing Recovery 159

6.3.3 Changing Feed Water Sources 160

6.3.4 Reducing Permeate Flow 161

Symbols 161

Nomenclature 161

References 162

7 RO Equipment 163

7.1 Basic RO Skid Components 163

7.1.1 Cartridge Filters 164

7.1.2 High Pressure Feed Pump 172

7.1.3 Pressure Vessels 177

7.2 Skid Design Considerations 181

7.2.1 Piping Materials of Construction 181

7.2.2 Feed Distribution Headers 183

7.2.3 Stage-by-Stage Cleaning 184

7.2.4 Sampling and Profiling/Probing Connections 187

7.2.5 Instrumentation 188

7.2.6 Controls and Data Acquisition/Analysis 193

7.2.6.1 System Control 193

7.2.6.2 Data Acquisition and Analysis 194

7.2.7 Designs for Variable Permeate Flow Demand 195

7.3 Energy Recovery Devices (ERDs) 196

7.3.1 ERD Types 196

7.3.2 ERD Applications for RO 197

7.3.2.1 Single-Stage RO 197

7.3.2.2 Multi-Stage RO 197

7.4 Clean-In-Place (CIP) Equipment 200

7.5 Mobile RO Equipment 203

Symbols 205

Nomenclature 205

References 206

Section III: Membrane Deposition and Degradation: Causes, Effects, and Mitigation via Pretreatment and Operations 207

8 Membrane Scaling 211

8.1 What is Membrane Scale? 211

8.2 Effects of Scale on Membrane Performance 212

8.3 Hardness Scales 215

8.3.1 Types of Hardness Scale 215

8.3.1.1 Carbonate-Based Hardness Scales 215

8.3.1.2 Sulfate-Based Hardness Scales 216

8.3.1.3 Other Calcium Scales: Calcium Phosphate and Calcium Fluoride 218

8.3.2 Mitigation of Hardness Scales 219

8.3.2.1 Chemical Pretreatment—Acid and Antiscalant Dosing 220

8.3.2.2 Non-Chemical Pretreatment—Sodium Softening and Nanofiltration 221

8.3.2.3 Operational Techniques—Flushing, Reverse Flow, and Closed Circuit Desalination 225

8.4 Silica Scale 226

8.4.1 Forms and Reactions of Silica 227

8.4.2 Factors Affecting Silica Scale Formation 228

8.4.3 Mitigation of Silica Scale 232

8.5 Struvite 236

8.5.1 What is Struvite? 236

8.5.2 Mitigation of Struvite 238

8.6 Scaling Mitigation Guidelines—Summary 239

Symbols 240

Nomenclature 240

References 240

9 Generalized Membrane Fouling 249

9.1 What is Membrane Fouling? 249

9.2 Classification and Measurement of Potential Foulants 250

9.2.1 Settleable and Supra-Colloidal Particulates 251

9.2.2 Colloids 252

9.2.2.1 Measurement of Colloids for RO Applications—Silt Density Index (SDI15) 252

9.2.2.2 Measure of Colloids—Modified Fouling Indices 255

9.2.2.3 Summary of Colloidal Fouling Indices 257

9.2.3 Natural Organic Material (NOM) 257

9.2.4 Other Organics 259

9.2.5 Other Foulants: Cationic Coagulants and Surfactants, and Silicone-Based Antifoams 259

9.2.6 Metals: Aluminum, Iron, Manganese, and Sulfur 259

9.2.6.1 Aluminum 259

9.2.6.2 Iron and Manganese 261

9.2.6.3 Hydrogen Sulfide 262

9.3 Effects of Fouling on Membrane Performance 265

9.3.1 Effects of Inorganic Foulants 266

9.3.1.1 Fouling with Larger Settleable and Supra-Colloidal Solids 266

9.3.1.2 Cake Layer Surface Fouling with Colloids 266

9.3.1.3 Feed Channel Fouling 268

9.3.1.4 Summary of Fouling Effects of Inorganic Particulates and Colloids 271

9.3.2 Effects of NOM and Other Organics 273

9.3.2.1 Effects of NOM—Humic Acids 273

9.3.2.2 Effects of Hydrocarbons 276

9.3.2.3 Effects of Cationic Coagulants and Surfactants 278

9.3.2.4 Summary of the Effects of Organic Surfactant and Antifoam Fouling on Membrane Performance 279

9.4 Pretreatment to Minimize Membrane Fouling 279

9.4.1 Primary Pretreatment—Clarification for Colloids and Organics (NOM) Removal 280

9.4.1.1 Coagulation 280

9.4.1.2 Flocculation 283

9.4.2 Pressure Filtration: Particles, SDI15 , and Organics Removal 283

9.4.2.1 Multimedia Pressure Filters: Suspended Solids Removal 283

9.4.2.2 Catalytic Filters: Soluble Iron, Manganese, and Hydrogen Sulfide Removal 287

9.4.2.3 Carbon Filters: TOC Removal 292

9.4.2.4 Walnut Shell Filters: Hydrocarbon Oil Removal 296

9.4.2.5 Cartridge Filters: What is Their Purpose? 299

9.4.3 Membrane Filtration Turbidity, SDI 15 , and Metal Hydroxide Removal 300

9.4.3.1 Membrane Materials and Elements 301

9.4.3.2 Membrane Filtration Operations— Polymeric Membranes 306

9.4.3.3 Membrane Filtration as Pretreatment for RO 311

9.4.4 Nanofiltration (NF): Organics and Color Removal 321

9.5 Feed Water Quality Guidelines to Minimize Membrane Fouling 323

Symbols 324

Nomenclature 324

References 326

10 RO Membrane Biofouling 335

10.1 What is RO Membrane Biofouling? 335

10.2 Factors Affecting Membrane Biofouling 339

10.2.1 Polyamide RO Membrane Characteristics 339

10.2.1.1 Membrane Surface Roughness 339

10.2.1.2 Surface Charge and Zeta Potential 339

10.2.1.3 Membrane Hydrophilicity 339

10.2.2 Feed Water Matrix 340

10.2.2.1 Concentration of Microorganisms and Nutrients 340

10.2.2.2 Feed Water Ionic Strength and pH 341

10.2.2.3 Pretreatment Antiscalants 341

10.2.2.4 Feed Water Organic Concentration and Fouling 341

10.2.3 RO System Hydrodynamics 341

10.3 Effects of Biofouling on Membrane Performance 342

10.3.1 Scale Formation 342

10.3.2 Hydrodynamic Effects on Performance 342

10.4 Measurement of Biofouling 343

10.4.1 Predictive Techniques 343

10.4.1.1 Assimilable Organic Carbon (AOC) 343

10.4.1.2 Adenosine Triphosphate (ATP) and the Biofilm Formation Rate (BFR) 344

10.4.2 Plate Counts 344

10.4.2.1 Heterotrophic Plate Counts (HPC) 344

10.4.2.2 Total Direct Counts (TDC) 345

10.5 Mitigation Techniques 345

10.5.1 Pretreatment 346

10.5.1.1 Reduction of Feed Water Nutrients and Microorganisms 346

10.5.2 Disinfection 348

10.5.2.1 Physiochemical Disinfection Method— Ultraviolet (UV) Light 348

10.5.2.2 Chemical Disinfection—Oxidizing Biocides 353

10.5.2.3 Chemical Disinfection—Non-Oxidizing Biocide 368

10.5.2.4 Biocides Not Recommended for Use with Polyamide RO Membranes 370

10.5.2.5 Chemical Disinfection—Prospective Biocides for RO 370

10.5.3 Membrane Cleaning for Biofouling Removal 373

10.5.4 Membrane “Sterilization” 375

10.5.5 Biocide Flushing 375

10.6 Biofouling and Mitigation Summary 376

Symbols 378

Nomenclature 378

References 379

11 Membrane Degradation 387

11.1 Chemical Degradation 388

11.1.1 Polyamide Layer Degradation—Oxidation 388

11.1.1.1 Chlorine 388

11.1.1.2 Chloramine 396

11.1.1.3 Chlorine Dioxide 398

11.1.2 Polysulfone Support Layer Degradation 400

11.1.3 Polyester Fabric Degradation—Hydrolysis 402

11.1.4 Prevention of Chemical Damage 402

11.1.4.1 Removal of Oxidizers 402

11.1.4.2 Protection of Membrane Support Layers 404

11.2 Mechanical Damage 404

11.2.1 Physical Membrane Damage Due to Abrasion 404

11.2.2 Physical Membrane Damage Resulting from Operational Factors 407

Symbols 412

Nomenclature 412

References 412

Section IV: System Monitoring, Normalization, and Troubleshooting 417

12 Data Collection and Normalization 419

12.1 Data Collection 419

12.2 Data Normalization 422

Symbols 427

Subscripts 428

Nomenclature 428

References 428

13 Membrane Issues and Troubleshooting 431

13.1 Observed Performance Issues 432

13.1.1 High Permeate Solute Concentration 432

13.1.1.1 Increase in Feed Water Concentration of Ions 433

13.1.1.2 Hardness Scaling 433

13.1.1.3 Membrane Damage 434

13.1.1.4 Temperature Increase/Pressure Decrease 435

13.1.1.5 System Operations and Mechanical Issues 438

13.1.2 Changes in Permeate Flow 439

13.1.3 Changes in Feed Pressure 439

13.1.4 High Differential Pressure 440

13.2 Common Causes of Performance Failures 445

13.2.1 Mechanical Failures 445

13.2.2 RO Equipment Design 445

13.2.3 Operational Problems 446

13.2.4 Feed Water Quality Issues 446

13.2.5 Membrane Issues 446

13.3 Troubleshooting Techniques 447

13.3.1 Mechanical Inspection 447

13.3.2 Cartridge Filter Inspection 447

13.3.3 Water Analyses 448

13.3.4 RO Projections 449

13.3.5 Profiling and Probing 449

13.3.5.1 Profiling 449

13.3.5.2 Probing 452

13.3.6 Normalized Data Analysis 455

13.3.7 Autopsy 457

13.3.7.1 Visual Inspection—External 458

13.3.7.2 Visual Inspection—Internal 459

Symbols 471

Nomenclature 471

References 472

Section V: Off-Line Activities: Membrane Cleaning, Flushing, and Layup 475

14 Membrane Cleaning 477

14.1 When to Clean 478

14.2 Cleaning Chemicals 479

14.2.1 High pH Cleaning 480

14.2.2 Low pH Cleaning 481

14.3 Cleaning Equipment Design 483

14.3.1 Design of the RO Skid for Effective Cleaning 483

14.3.2 Design of the Cleaning Skid 484

14.3.2.1 Cleaning Tank 484

14.3.2.2 Cartridge Filters 486

14.3.2.3 Cleaning Pump 486

14.4 Cleaning Techniques 487

14.4.1 Conventional Cleaning 487

14.4.2 Two-Phase Cleaning 489

14.4.3 Reverse Cleaning 490

14.4.4 Preventative Cleaning 490

14.4.4.1 Extrapolative Preventative Cleaning 491

14.4.4.2 Direct-Osmosis High-Salinity (DO-HS) On-Line Cleaning Technique 491

14.5 Determining the Efficacy of Cleaning 493

14.6 Clean-In-Place (CIP) Versus Offsite Cleaning 494

14.6.1 CIP 494

14.6.2 Off-Site Cleaning 494

14.7 Membrane Disinfection 495

14.7.1 Hydrogen Peroxide/Peroxyacetic Acid 495

14.7.2 Non-Oxidizing Biocides 497

14.7.2.1 DBNPA 497

14.7.2.2 Isothiazolones—CMIT/MIT 499

14.7.2.3 Other Non-Oxidizing Biocides 500

Symbols 500

Nomenclature 500

References 501

15 Controlling Off-Line Membrane Deposition via Flushing and Layup 505

15.1 Membrane Flushing 505

15.1.1 End of Service Flush 506

15.1.2 Stand-By Flush 506

15.1.3 Return to Service Flush 507

15.2 Membrane Layup 508

15.2.1 Short-Term Layup 508

15.2.2 Long-Term Layup 508

15.2.2.1 Sodium Metabisulfite (SMBS) 508

15.2.2.2 DBNPA 510

15.2.2.3 CMIT/MIT 510

15.3 Membrane Preservation 510

Nomenclature 512

References 512

Section VI: Sustainability and Future Prospects 515

16 Concentrate Management 517

16.1 Discharge 517

16.1.1 Discharge to Surface Waters 517

16.1.2 Discharge to Sewer 518

16.1.3 Discharge to On-Site Treatment Facility 518

16.1.4 Deep Well Injection 518

16.2 Land Application 519

16.2.1 Irrigation 519

16.2.2 Evaporation Ponds 519

16.3 Reuse 519

16.3.1 Direct Reuse 520

16.3.1.1 Wash Down Systems 520

16.3.1.2 Cooling Tower Make-Up 520

16.3.2 Treated Concentrate for Reuse—Brine Minimization 520

16.3.2.1 Recovery RO Systems 520

16.3.2.2 Zero Liquid Discharge (ZLD) 522

16.4 Off-Site Disposal 523

16.5 Emerging Technologies for Concentrate Management 523

16.5.1 Membrane Distillation (MD) 524

16.5.2 Forward Osmosis (FO) 526

Symbols 529

Nomenclature 529

References 529

17 High-Recovery Reverse Osmosis 531

17.1 Single-Step High Recovery Processes 531

17.1.1 Closed Circuit RO (CCRO) 531

17.1.1.1 Managing Scale Formation 533

17.1.1.2 Managing Membrane Fouling 535

17.1.1.3 Energy Savings 536

17.1.2 Osmotically-Assisted RO (OARO) 538

17.1.3 Pulse Flow RO (PFRO ™) 542

17.1.4 Feed Flow Reversal (FFR) 545

17.2 Enhanced High Recovery Processes with Interstage Solute Precipitation 548

17.2.1 Intermediate Concentrate Demineralization (ICD) 549

17.2.2 Accelerated Seeded Precipitation (ASP) 551

17.3 Multi-Step High Recovery Membrane Processes 552

17.3.1 Toward Zero Liquid Discharge (ZLD) 552

17.3.2 Challenging Waters and Wastewaters 553

17.3.3 Commercialized Multi-Step, High-Recovery RO Processes 553

17.3.3.1 Optimized Pretreatment and Unique Separation (OPUS®) 554

17.3.3.2 High Efficiency Reverse Osmosis (HERO®) 556

Symbols 558

Nomenclature 558

References 559

18 New and Alternative Membrane Materials For Sustainability 565

18.1 Specific Requirements to Improve Sustainability 566

18.1.1 Membrane Performance 566

18.1.2 Fouling Resistance 568

18.1.3 Chlorine (Oxidant) Tolerance 570

18.1.4 Energy-Water Nexus 570

18.2 Membrane Materials to Meet RO Demineralization Challenges 571

18.2.1 Modification of Polyamide Interfacial Polymerization (IP) Preparation Chemistries and Techniques 572

18.2.2 Membrane Surface Modifications 575

18.2.3 Nanotechnology and Nanoparticle Membranes 578

18.2.3.1 Carbon Nanotube (CNT) Nanocomposite Membranes 578

18.2.3.2 Thin Film Nanoparticle (TFN) Membranes 584

18.2.4 Graphene Oxide (GO)-Based Membranes 586

18.2.5 Biomimetic Aquaporin Membranes 591

Symbols 594

Nomenclature 594

References 595

Index 601