Question

ANSWER as much as possible:

Design an activated sludge process consisting of a complete mix flow through aeration tank followed by final settling tanks. The sizing of the reactor and all appurtenances should be based on a solids retention time, (SRT), of 4 days and the particulates given below.

Biological characteristics: K_s = 20 mg/L COD, k_d = 0.1 per day, mu_max = 3 gVSS/gVSS-day,

   Y = 0.4 gVSS/gCOD

Primary settling Tank Effluent Characteristics:

Q= 20MGD, biodegradable COD, bCOD = 300 mg/L, SS = 100 mg/L of which 20 mg/L are inert solids, (i.e. non-biodegradable).

Aeration Tank: SVI = 125 ml/gram MLSS, MLVSS:MLSS ratio = 0.80, T = 20^oC

Final Settling Tanks: Operating at an overflow rate = 600 gpd/sq.ft, Solids Loading Rate = 10 lb SS/ day-sq.ft., Final Settling Tank Effluent, (FSTE), SS = 20 mg/L

Calculate/ Estimate: (Questions 1-9, 5-pts. each, Questions 10 & 11, 10pts. each)

1. The soluble bCOD in the final settling tank, (FST), effluent in mg/L ____, estimate the total COD in the effluent _____________
2. The Q_RAS in MGD ___________
3. The concentration of MLVSS in mg/L ____________ and the MLSS in mg/L ___________. Hydraulic retention time, HRT, in the aeration tank in hrs ______
4. The net growth rate in lb VSS/ day _______________
5. The flow rate of the waste activated sludge, WAS, taken from the RAS line in gpd _____
6. The oxygen demand in lb/day ______________________
7. The specific oxygen uptake rate in: g oxygen / g MLVSS-day ______________
8. The value of K_La that will enable the aeration tank to be operated at a DO concentration of 2 mg/L, in hours^-1 _______
9. If the aeration rate being applied equals 14,835 standard cubic feet/ minute, scfm, Calculate the oxygen transfer efficiency in % ________________
10. Estimate the number of diffusers required for aeration_______________________

(Use Sanitaire Silver Series II diffusers- disk shape)

1. Sketch to scale the process flow block diagram of the activated sludge process that should include two common wall, four-pass aeration tanks followed by four common wall rectangular aeration tanks. In a separate sketch show a plan view of the bottom of one aeration tanks and the actual number of diffusers that were selected. Aeration tank dimensions: Depth=20 feet and width= 40 feet, Length = ?

Answer 1