You are provided with the following information about a municipal wastewater treatment plant. This plant uses the traditional activated sludge process. Assume the microorganisms are 60 percent efficient at converting food to biomass, the organisms have a first order death rate constant of 0.1/day, and the microbes reach half of the maximum growth rate when the BOD5 concentration is 22 mg/L. There are 220,000 people in the community (their wastewater production is 225 L/day-capita, 0.1 kg BOD5/capita-day). The effluent standard is BOD5 = 20 mg/L and TSS = 20 mg/L. Suspended solids were measured as 4,000 mg/L in a wastewater sample obtained from the biological reactor, 16,500 mg/L in the secondary sludge, 230 mg/L in the plant influent, and 110 mg/L in the primary clarifier effluent. SRT is equal to 4.5 days.
(a) what is the design volume of the aeration basin (m3)?
(b) what is the plant’s aeration period (days)?
(c) How many kg of secondary dry solids need to be processed daily from the treatment plants?
(d) if the sludge wastage rate (Qw) is increased in the plant, will the solids retention time go up, go down, or remain the same?
(e) Determine the F/M ratio in units of kg BOD5/kg MLVSS-day.
(f) What is the mean cell residence time?