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A wastewater treatment plant that treats wastewater to secondary treatment standards uses a primary sedimentation process...

A wastewater treatment plant that treats wastewater to secondary treatment standards uses a primary sedimentation process fol

You have gathered data below from the plant flowmeters, and the construction drawings. Primary Sedimentation Process The foll

16. What is the secondary clarifiers detention time? (answer will be given in the unit of (hr)) 17. Are the processes operat

A wastewater treatment plant that treats wastewater to secondary treatment standards uses a primary sedimentation process followed by conventional activated sludge process composed of covered aeration tanks and secondary clarifiers. You are asked to calculate the different operation parameters to make sure that the system is operated within normal process ranges listed in the reference tables below. Table 5-20 Typical design information for primary sedimentation tanks U.S. customary units Item Unit Range Typical Primary sedimentation tanks followed by secondary treatment Detention time 1.5-2.5 20 Overflow rate Average flow gal/142- 800-1200 1000 Peak hourly flow gal/l-d 2000-3000 2500 Weir loading gal/Itd 10,000-40,000 20,000 h TABLE 12.3 General Loading and Operational Parameters for Activated-Sludge Processes BOD Loading Ib BODI 1000 ft day Ib BODI day/lb of MLSS Average Return Sludge Rates (5) Aeration Period (hr) Sludge Age (days) 5-15 5-15 Process 30-50 30-40 0.2-0.5 0.2-0.5 5.0-7.0 6.0-75 50 30 Step aeration Conventional (tapered aeration) Contact stabilization Extended aeration High-purity oxygen 30-50 10-30 120+ 0.2-0.5 0.05-0.2 0.6-1.5 5-15 20+ 5-10 6.0-9.0 20-30 1.0-3.0 100 100 30 1.0 lb/1000 ft/day - 16 g/ m.d.
You have gathered data below from the plant flowmeters, and the construction drawings. Primary Sedimentation Process The following Instrument data are given: Plant influent flow, MGD 60 The following laboratory data are given: Primary influent TSS, mg/L Primary effluent TSS, mg/L Primary influent BOD, mg/L Primary effluent BOD, mg/L Primary sludge %TS concentration, % 280 110 230 150 3% The following plant construction data are given: Number of primary sedimentation tank Primary tank volume, Mgal each Primary tank surface area, ft2 each Weir length, ft each 6 0.75 7,500 500 Activated Sludge Process The following Instrument data are given: Plant influent flow, MGD Returned activated sludge flow, MGD Waste activated sludge Flow, MGD 60 35 1.0 110 150 The following laboratory data are given: Aeration process influent TSS, mg/L Aeration process influent BODs, mg/L Mixed Liquor TSS, mgTSS/L Mixed liquor %VS RAS TSS, mgTSS/L RAS %VS Final effluent TSS, mg/L Final effluent BOD5, mg/L 3000 85% 8,000 82% 10 12 The following plant construction data are given: Number of aeration tank 8 Aeration tank volume, Mgal each 2.5 Number of secondary clarifiers 6 Secondary clarifier volume, Mgal each 2 Surface area, ft2 each 20,000 Weir length, each 500
16. What is the secondary clarifiers' detention time? (answer will be given in the unit of (hr)) 17. Are the processes operated under normal range? 18. Would the activated sludge F/M ratio increase or decrease if the primary clarifiers were not in operation and the plant influent was fed directly into the activated sludge process? 19. Would the oxygen demand increase or decrease if the primary clarifiers were not in operation and the plant influent was fed directly into the activated sludge process?
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Answer #1

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16, 17

Page 16 GivenamG Detention time is given by De= Volume of one clasifier one Clarifies # total flowetz GOMGD Flow over #flow o

18,19

18 Flm ratio is Food/micoo organisms It is amount of sludge recieing into the aeration Colo activated sludge unit. = when the

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