Anaerobic Digestion173

5.1 Introduction, 174

5.1.1 Advantages and Disadvantages, 174

5.1.2 Theory of Anaerobic Digestion, 175

5.2 Environmental Factors, 176

5.2.1 Solids and Hydraulic Retention Times, 177

5.2.2 Temperature, 177

5.2.3 pH and Alkalinity, 179

5.2.4 Toxic Materials, 180

5.3 Process Variations, 182

5.3.1 Low-Rate Digestion, 182

5.3.2 High-Rate Digestion, 183

5.3.3 Thermophilic Digestion, 185

5.3.4 Two-Stage Digestion, 185

5.3.5 Two-Phase Digestion, 186

5.4 Process Design, 188

5.4.1 Per Capita Basis, 188

5.4.2 Solids Loading, 189

5.4.3 Solids Retention Time, 189

5.4.4 Volatile Solids Reduction, 190

5.4.5 Gas Production, 190

5.5 System Component Design, 191

5.5.1 Tank Design, 191

5.5.2 Digester Covers, 193

5.5.3 Mixing, 193

5.5.4 Heating, 197

5.5.5 Gas Usage, 200

5.6 Operational Considerations, 205

5.6.1 Reactor Performance, 205

5.6.2 Odor Control, 207

5.6.3 Supernatant, 207

5.6.4 Struvite, 209

5.6.5 Digester Cleaning, 210

6 Alkaline Stabilization 213

6.1 Introduction, 213

6.1.1 Advantages and Disadvantages, 214

6.1.2 Process Theory, 215

6.2 Process Application, 217

6.2.1 Liquid Lime Stabilization, 217

6.2.2 Dry Lime Stabilization, 218

6.2.3 Advanced Alkaline Stabilization Technologies, 220

6.3 Process Design, 221

6.3.1 Sludge Characteristics, 221

6.3.2 Contact Time and pH, 222

6.3.3 Lime Dosage, 222

6.3.4 Alkaline Material Storage, 223

6.3.5 Lime Feeding, 224

6.3.6 Liquid Lime Mixing, 226

6.3.7 Dry Lime Mixing, 227 6.4 Process Performance, 231

6.4.1 Odor Reduction, 231

6.4.2 Pathogen reduction, 232

6.4.3 Dewatering Characteristics, 233

7 Composting 235

7.1 Introduction, 236

7.1.1 Composting Process, 236

7.1.2 Composting Methods, 237

7.1.3 Advantages and Disadvantages of Composting, 239

7.1.4 Zoological Characteristics of Compost, 239

7.2 Process Description, 240

7.2.1 Factors Influencing Composting, 240

7.2.2 Windrow Process, 243

7.2.3 Aerated Static Pile Process, 244

7.2.4 In-Vessel Process, 246

7.2.5 Design Considerations, 249

7.3 Theoretical Aspects of Composting, 252

7.4 New Technology in Composting, 259

7.4.1 Organic Content, 259

7.4.3 Temperature and Moisture, 261

7.4.4 Composting Mixture, 262

7.4.5 Composting Process Control, 263

7.5 Examples of Composting in Europe, 267

7.6 Examples of Composting in the United States, 272

8 Thermal Drying and Incineration 277

8.1 Introduction, 278

8.2 Thermal Drying, 278

8.2.1 Methods of Thermal Drying, 278

8.2.2 Design Considerations, 287

8.3 Incineration, 290

8.3.1 Methods of Incineration, 291

8.3.2 Design Considerations, 298

9 Comparison of Energy Consumption 304

9.1 Introduction, 304

9.2 Anaerobic Digestion, 304

9.3 Incineration, 306

9.4 Composting, 309

9.5 Comparison of Thermal Drying and Composting, 310

9.6 Conclusion, 313

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