Wastewater treatment: biological treatment

Introduction to Biological Treatment Approximate composition of average sanitary wastewater (mg/l) based on 450 liter/capita/day Parameter Raw Wastewater After primary settling After biological treatment Total solids 800 680 530 TVS 440 340 220 TSS 240 120 30 VSS 180 100 20 BOD 200 130 30 Inorganic N 22 22 24 Soluble phosphorous-P 4 Total phosphorous-P Average characteristics of selected industrial wastewater Parameter Milk processing Meat packaging Synthetic Chlorophenolic textile manufacturer BOD, mg/l 1000 1400 1500 4300 COD, mg/l 1900 2100 3300 5400 TS, mg/l 1600 3300 8000 53000 TSS, mg/l 300 1000 2000 1200 Nitrogen, mg N/l 50 150 30 Phosphorous, mg P/l 12 16 0 pH 7 Temp oC 29 28 - 17 Grease, mg/l - 500 - - Chloride, mg/l - - - 27000 Phenols, mg/l - - - 140 Loadings on treatment plants are commonly expressed in units of pounds of BOD per day or pounds of solids per day in addition to the flow rate For example, each person contributes about 0.2 lb BOD/day in domestic wastewater Pounds per day = concentration (mg / l ) × Q (million gal per day ) × 8.34 Pounds per day = concentration (mg / l ) × Q (million ft per day ) × 62.4 Example: Industrial wastewaters have a total flow of 2,930,000 gpd, BOD of 21,600 lb/day and suspended solids of 13,400 lb/day Calculate the BOD and suspended solids concentration Answer: BOD= 884 mg/l SS= 548 mg/l Wastewater flow rate and BOD loading Example: The sanitary and industrial waste from a community consists of domestic wastewater from a sewered population of 7500 persons; potato processing waste of 30000 gpd containing 500 lb BOD; and creamery wastewater flow of 120,000 gpd with a BOD concentration of 1000 mg/l Estimate the combined wastewater flow in gallons per day and BOD in mg/l Assume domestic wastewater flow is 120 gpcd and BOD loading is 0.2 lbpcd Answer: Source Flow (gpd) BOD loading (lb/day) Domestic 120×7500= 900,000 30,000 0.2×7500= Potato Creamery Sum 120,000 1,050,000 1,500 500 1000 ×0.12 ×8.34=1,000 3,000 3000 lb / d BOD conc = = 342.6 mg / l 1.05 million gal / d × 8.34 Biological Reactions Adopted from Rittman and McCarty, Environmental Biotechnology Applications, 2001 Bacteria Growth Versus Substrate Decay in Batch Culture (Biomass (X Declining Stationary growth phase phase Concentration Lag phase Log growth Endogenous phase (Substrate (S Time Monod Kinetic Growth Function µ = µ max Biomass specific growth rate S KS + S Substrate concentration Halfsaturation constant Maximum specific growth rate Environmental Factors Affecting Growth Temperature range (oC) (1) Temperature k T = k 20θ Overall Optimal Psychrophilic 10-30 12-18 Mesophilic 20-50 25-40 Thermophilic 35-75 55-65 (T − 20 ) (2) pH: Best range is 6.5-7.5 but growth could still occur at pH as low as or as higher as (3) Dissolved oxygen • Aerobic (DO> 1.5-2.0 mg/l) • Anoxic (DO[...].. .Treatment Processes  Primary treatment  Secondary treatment  Advanced treatment Primary Treatment Disinfectant Wastewater influent Screens Grit Chamber Primary Contact tank Settling tank Thickner Anaerobic digester Effluent Dewatering Sludge disposal Primary treatment removes about 35% BOD and 60% SS Secondary Treatment Biological treatment can be conducted by one... following methods: Activated sludge Rotating biological contactors Trickling filters Wastewater Grit influent Chamber Screens Disinfectant Primary Settling tank Thickner Secondary Biological treatment Anaerobic digester Settling tank Dewatering Overall removal after secondary treatment is 90% BOD and 90% SS Sludge disposal Contact tank Effluent Advanced Treatment May include: Activated carbon to remove... Sludge disposal Contact tank Effluent Advanced Treatment May include: Activated carbon to remove organic contaminants Filter to capture suspended solids Nitrate removal Overall removal after advanced treatment is >95% BOD and > 95% SS Zakher WWTP Flow Sheet Diagram