Page 10 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Contents ix

6.6.2 Final Settling as Affected by Limiting Flux Density................................................................. 108
6.6.2.1 Activated Sludge......................................................................................................... 109
6.6.2.2 Final Settling Basin Processes.................................................................................... 109
6.6.2.3 Mass Balance Relations.............................................................................................. 109
6.6.2.4 Limiting Flux Density................................................................................................. 110
6.6.2.5 Limiting Flux Density: Evaluation Procedure............................................................ 110
6.6.2.6 Example of Limiting Flux Density Using Plots......................................................... 111
6.7 Hydraulics of Settling Basins.................................................................................................................. 112
6.7.1 Flow Patterns and Short Circuiting............................................................................................ 113
6.7.2 Density Currents......................................................................................................................... 113
6.7.3 Dispersion Tests Using a Tracer ................................................................................................ 113
6.7.3.1 Results of Dispersion Tests ........................................................................................ 113
6.7.4 Computational Fluid Dynamics.................................................................................................. 114
6.8 Design Practice........................................................................................................................................ 114
6.8.1 Categories of Basins................................................................................................................... 114
6.8.2 Examples of Designs.................................................................................................................. 115
6.8.2.1 Horizontal Flow .......................................................................................................... 115
6.8.2.2 Up-Flow ...................................................................................................................... 115
6.8.2.3 Data from Real Basins................................................................................................ 115
6.8.3 Guidelines and Criteria for Design ............................................................................................ 115
6.8.3.1 Discrete Particle Suspensions: Type I ........................................................................ 118
6.8.3.2 Flocculent Suspensions: Type II................................................................................. 118
6.8.3.3 Flocculent Suspensions–Hindered Settling: Type III ................................................. 118
6.8.3.4 Compression Settling: Type IV .................................................................................. 118
6.9 Real Basins .............................................................................................................................................. 118
6.9.1 Inlet Design ................................................................................................................................ 119
6.9.2 Outlet Design.............................................................................................................................. 121
6.9.3 Summary Notes for Practical Design......................................................................................... 122
6.10 Plate Settlers and Tube Settlers............................................................................................................... 122
6.10.1 Plate Settlers ............................................................................................................................... 122
6.10.1.1 Particle Path: Analysis................................................................................................ 122
6.10.1.2 Sludge Removal.......................................................................................................... 123
6.10.1.3 Plate Settler Systems................................................................................................... 123
6.10.1.4 Sizes of Units.............................................................................................................. 124
6.10.1.5 Surface Overflow Rates .............................................................................................. 124
6.10.1.6 Theory......................................................................................................................... 124
6.10.2 Tube Settlers............................................................................................................................... 127
Problems............................................................................................................................................................. 128
Acknowledgments .............................................................................................................................................. 130
Glossary.............................................................................................................................................................. 130
References .......................................................................................................................................................... 132

Chapter 7 Grit Chambers .................................................................................................................................................... 135
7.1 Grit........................................................................................................................................................... 135
7.2 Horizontal Flow Grit Chambers .............................................................................................................. 135
7.2.1 Theory......................................................................................................................................... 135
7.2.1.1 Ideal Basin .................................................................................................................. 135
7.2.1.2 Scour ........................................................................................................................... 135
7.2.2 Horizontal Velocity Control....................................................................................................... 137
7.2.2.1 Proportional Weir........................................................................................................ 137
7.2.2.2 Parshall Flume ............................................................................................................ 138
7.2.2.3 Rectangular Section .................................................................................................... 142
7.2.2.4 Parabolic Section ........................................................................................................ 146
7.2.3 Practice—Horizontal Flow Grit Chambers ................................................................................ 147
7.2.3.1 Design and Performance—Examples ......................................................................... 147
7.2.3.2 Removal Equipment ................................................................................................... 148