Question

The primary effluent is to be treated by two parallel trains of the complete mix activated sludge process. The average daily wastewater design flows of 2.0 MGD and assume that the primary sedimentation process removes 60% of the suspended solids and 40% of the BOD5 of the raw sewage. The following data are given:

• Plant effluent BOD₅ of 8 mg/L

• Biomass yield of 0.55 kg biomass / kg BOD

• Endogenous decay rate (kd) = 0.04 day^-1

• Solids Retention Time (θ_C) = 8 days

• MLVSS concentration in the aeration tank of 3000 mg/L

• Waste and recycle solids concentration of 12,000 mg/L   

a) Determine the aeration tank volume in cubic meters.

b) Determine the mass and volumetric flow rates (kg/day and m³ day) of wasted sludge.

c) Determine the return (recycle) flow rate in cubic meters per day (and in MGD).

d) Determine the volumetric BOD loading to the aeration tank in lb BOD per 1000ft³.  

e) Determine the food to microorganism ratio (F/M) for the aeration tank in kg BOD/day/kg

f) Determine the design hydraulic detention time (θ) in hours.

Answer 1