Question

You have been retained to design a wastewater treatment plant using a conventional activated sludge process for a town of 40,000 people. The industrial flow contribution to the sewer system is 300,000 gallons per day. Effluent discharge standards require effluent BOD5 and total suspended solids concentration of <10 mg/l.

Assume the following design criteria are applicable:

• Domestic sewage flow = 100 gal/cap/day (including I/I)

• BOD loading = 0.18 lbs/cap/day

• TSS loading = 0.20 lbs/cap/day

• BOD removal in primary = 33% at surface overflow rate of 1,000 gpd/ft2

• BOD loading to aeration basin = 40 lb BOD/1000 ft3

• Oxygen required for aeration = 1.1 1bs O2/lb BOD applied.

• Aerator oxygen transfer rate = 2.5 lbs O2/hp-hr

• MLSS concentration = 2,750 mg/l; MLVSS conc.= 0.8 MLSS conc.

• Final clarifier surface overflow rate = 800 gpd/ft2

Question:

1. Determine the BOD loading to the aeration basin.

2. Determine the size of the aeration basin (length/width/height) for a 6-hour detention time.

3. Calculate the F/M ratio.

4. Determine aeration requirements (number and hp capacity of aerators)

Answer 1