Page 19 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

xviii Contents

13.1.2 Attributes .................................................................................................................................... 395
13.1.2.1 Selection Criteria......................................................................................................... 395
13.1.2.2 Effectiveness ............................................................................................................... 395
13.1.2.3 Economy ..................................................................................................................... 396
13.1.2.4 Labor........................................................................................................................... 396
13.1.2.5 Materials...................................................................................................................... 397
13.1.2.6 Contextual Factors ...................................................................................................... 397
13.1.3 History ........................................................................................................................................ 397
13.1.3.1 James Simpson and the Start of Slow Sand............................................................... 398
13.1.3.2 Evolution of Practice .................................................................................................. 398
13.2 Slow Sand as a Process ........................................................................................................................... 399
13.2.1 Removal Mechanisms ................................................................................................................ 399
13.2.1.1 Schmutzdecke and Its Role in Straining ..................................................................... 399
13.2.1.2 Depth Filtration........................................................................................................... 400
13.2.2 Hydraulics................................................................................................................................... 401
13.2.2.1 Darcy’s Law................................................................................................................ 401
13.2.2.2 Instrinsic Hydraulic Conductivity............................................................................... 401
13.2.2.3 Hydraulic Profile and Headloss .................................................................................. 403
13.3 Design...................................................................................................................................................... 403
13.3.1 Filter Box.................................................................................................................................... 404
13.3.1.1 Hydraulic Loading Rate and Area.............................................................................. 404
13.3.1.2 Number of Cells.......................................................................................................... 405
13.3.1.3 Layout ......................................................................................................................... 405
13.3.1.4 Depth of Box .............................................................................................................. 405
13.3.1.5 Structural Design ........................................................................................................ 406
13.3.2 Hydraulics................................................................................................................................... 406
13.3.2.1 Backfilling after Scraping ........................................................................................... 407
13.3.2.2 Air Binding ................................................................................................................. 408
13.3.2.3 Distribution of Raw Water Inflow Kinetic Energy .................................................... 408
13.3.2.4 Drainage System......................................................................................................... 408
13.3.2.5 Underdrain Manifold Design...................................................................................... 408
13.3.2.6 Depth of Sand............................................................................................................. 408
13.3.2.7 Sand Size .................................................................................................................... 409
13.3.2.8 Gravel Support............................................................................................................ 410
13.3.3 Support Systems......................................................................................................................... 411
13.3.3.1 Flow Measurements.................................................................................................... 411
13.3.3.2 Piezometers ................................................................................................................. 411
13.3.3.3 Turbidimeters.............................................................................................................. 411
13.3.3.4 Flow Control............................................................................................................... 411
13.3.3.5 Tailwater Control........................................................................................................ 411
13.3.3.6 Pipe Gallery ................................................................................................................ 412
13.3.3.7 Access to Filters.......................................................................................................... 412
13.3.3.8 Plumbing Functions .................................................................................................... 412
13.3.3.9 Hydraulic Profile......................................................................................................... 412
13.3.3.10 Headroom.................................................................................................................... 412
13.3.3.11 Designing to Avoid Freezing...................................................................................... 412
13.3.3.12 Sand Recovery System ............................................................................................... 413
13.4 Pilot Plant Studies.................................................................................................................................... 413
13.4.1 Pilot Plant Construction.............................................................................................................. 414
13.4.2 Case Study.................................................................................................................................. 414
13.4.2.1 Context........................................................................................................................ 414
13.4.2.2 Pilot Plant Setup ......................................................................................................... 414
13.4.2.3 Results......................................................................................................................... 415
13.4.2.4 Discussion................................................................................................................... 415