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 (this refers to the yield coefficient), 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 activated sludge basin (so this is volatile suspended solids), 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 (the activated sludge basin) (m3)? (b what is the plant’s aeration period (the hydraulic retention time) (days)? (c) How many kg of secondary dry solids (solids removed from the secondary clarifier to waste) 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 mg BOD5/mg VSS-day. (f) What is the mean cell residence time?
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 (this refers to the yield coefficient), 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 activated sludge basin (so this is volatile suspended solids), 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 (the activated sludge basin) (m3)?
(b what is the plant’s aeration period (the hydraulic retention time) (days)?
(c) How many kg of secondary dry solids (solids removed from the secondary clarifier to waste) 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 mg BOD5/mg VSS-day.
(f) What is the mean cell residence time?
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