Page 9 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

viii Contents

5.2.1.3 Screenings..................................................................................................................... 80
5.2.1.4 Bar Size......................................................................................................................... 80
5.2.1.5 Hydraulic Design ..........................................................................................................81
5.3 Comminutors ............................................................................................................................................. 82
5.3.1 Design........................................................................................................................................... 82
5.4 Fine Screens............................................................................................................................................... 83
5.4.1 Drum Screens and Disk Screens ..................................................................................................83
5.4.2 Wedge-Wire Static Screens.......................................................................................................... 83
5.4.2.1 Mathematical Relationships.......................................................................................... 85
5.4.2.2 Theory........................................................................................................................... 85
5.4.2.3 Design ........................................................................................................................... 85
5.5 Microscreens.............................................................................................................................................. 86
5.5.1 Equipment and Installation........................................................................................................... 86
5.5.2 Applications.................................................................................................................................. 86
5.5.3 Performance.................................................................................................................................. 86
5.5.4 Operation ...................................................................................................................................... 86
5.5.5 Sizing............................................................................................................................................ 87
5.5.6 Operating Data.............................................................................................................................. 87
5.5.7 Microscreen Model....................................................................................................................... 88
5.5.7.1 Interpretation of Model Results.................................................................................... 91
Problems............................................................................................................................................................... 92
Bar Screens................................................................................................................................................ 92
Acknowledgments ................................................................................................................................................ 93
Glossary................................................................................................................................................................ 93
References ............................................................................................................................................................ 93

Chapter 6 Sedimentation ....................................................................................................................................................... 95
6.1 Key Notions in Design.............................................................................................................................. 95
6.2 Particle Settling.......................................................................................................................................... 95
6.2.1 Particle Settling Principles............................................................................................................ 95
6.2.2 Stokes’ Law.................................................................................................................................. 95
6.2.3 Suspensions .................................................................................................................................. 97
6.2.3.1 Type I: Discrete Particle Suspensions .......................................................................... 97
6.2.3.2 Type II: Flocculent Suspensions................................................................................... 98
6.2.3.3 Type III: Hindered Settling........................................................................................... 98
6.2.3.4 Type IV: Compression Settling .................................................................................... 99
6.3 Settling Basins ........................................................................................................................................... 99
6.3.1 The Ideal Basin............................................................................................................................. 99
6.3.1.1 Camp’s Conditions for the Ideal Basin......................................................................... 99
6.3.1.2 Overflow Velocity......................................................................................................... 99
6.3.1.3 Significance of Overflow Velocity ............................................................................. 101
6.3.1.4 Insignificance of Detention Time ............................................................................... 101
6.3.1.5 Partial Removals for Particles with Fall Velocities, v s < v o ...................................... 101
6.4 Characterizing Suspensions..................................................................................................................... 103
6.4.1 Characteristics of Discrete Particle Suspensions and Removal Analysis .................................. 103
6.4.2 Graphic Depiction of Size Fraction Removed ........................................................................... 103
6.4.3 Mathematics of Removal............................................................................................................ 104
6.4.4 Up-Flow Basins: A Special Case............................................................................................... 105
6.4.5 The Role of Ideal Settling Basin Theory ................................................................................... 105
6.5 Flocculent Suspensions (Type II)............................................................................................................ 106
6.5.1 Settling Test for a Flocculent Suspension.................................................................................. 106
6.5.2 Determining Percent Removals.................................................................................................. 106
6.6 Hindered and Compression Settling (Type III and Type IV Suspensions) ............................................ 107
6.6.1 Settling Velocity as Affected by Solids Concentration ............................................................. 108
6.6.1.1 Settling Tests............................................................................................................... 108
6.6.1.2 Characterizing Settling Velocity................................................................................. 108