同©大学 2ation Tongji University SLOW SAND FILTER EFFLUENT FLOW RAW WATER HEAD SPACE CONTROL STRUCTURE VENT SUPERNATANT WATER SUPERNATANT ADJUSTABLE WATER DRAIN WEIR SCHMUTZDECKE SAND MEDIA DRAIN TILE TO FILTER DRAIN CLEARWELL & SUPPORT FIOW CONTROL BACKFILLING GRAVEL METER VALVE Fig.2 Slow sand filter and effluent control Slow sand filter removal of microorganisms,inorganic particles; Schmutzdecke:removal of dissolved organic matter;
Tongji University (2) Slow filtration Fig. 2 Slow sand filter and effluent control Slow sand filter : removal of microorganisms, inorganic particles; Schmutzdecke: removal of dissolved organic matter;
同海大学 inlet pipe used to introduce backwater for Tongji University sand cleaning filter gravel 3)Rapid filtration outlet under drain Replaced slow sand filters in 20th century; Much higher loading rate than slow sand filters,more than 100 X,typically 5-15 m/hour; Media are coarser,more uniform,(often multiple); Removal is not by physical straining on the surface as primary mechanism; Conceptually,rapid filtration is like sedimentation; Particles need pre-treatment with a coagulant to destabilize electrical charge;Destabilized particles adhere to grains in filter medium and are removed; Turbidity of outflow changes with time;
Tongji University (3) Rapid filtration • Replaced slow sand filters in 20th century; • Much higher loading rate than ; slow sand filters, more than 100 X, typically 5-15 m/hour; • Media are coarser, more uniform, (often multiple); • Removal is not by physical straining on the surface as primary mechanism; • Conceptually, rapid filtration is like sedimentation; • Particles need pre-treatment with a coagulant to destabilize electrical charge; Destabilized particles adhere to grains in filter medium and are removed; • Turbidity of outflow changes with time;
同燎大学 ③)ration WASH-WATER TROUGH FILTER TANK 24-301N. SAND SURFACE WASH 10-12 IN.GRAVEL PRECAST FILTER BOX FLOW DURING BACKWASH FILTERED WATER (WATER TO WASTE) FLOW DURING FILTRATION FLOW (RAW WATER) DURING BACKWASH Fig.3 Typical gravity rapid rate filter system
Tongji University (3) Rapid filtration Fig.3 Typical gravity rapid rate filter system
同©大学 ③ration Filter Influent Waste(or Spent)Filter Backwash(FBW) Water Above Filter Filter Media Filtration Rate Control Equal(Constant)Rate Underdrain Filter Effluent Declining Rate System Backwash Water Supply Filter to Waste (Backwash Air Supply) Fig.4 A typical gravity filter cross section
Tongji University (3) Rapid filtration Fig.4 A typical gravity filter cross section
同海大学 Tongji University Head loss in filter increases with time as filter clogs and Ripening gets low hydraulic conductivity Breakthrough Good Removal At end of filter run,filter is "back washed". Strong flow sent back through porous medium, mobilizing grains,and washing solids off of Clean Bed medium Filter Run Time
Tongji University • Head loss in filter increases with time as filter clogs and gets low hydraulic conductivity • At end of filter run, filter is “back washed”. • Strong flow sent back through porous medium, mobilizing grains, and washing solids off of medium