Wastewater - Questions

1. A town of 11,000 people (130 gpcd) has its own primary treatment plant.
a) What mass of total solids should the treatment plant expect?
b) If the town is 5 mi from the treatment plant and 425 feet above it in elevation. What minimum pipe size should be used, assume the pipe flow full?

2. The BOD of raw sewage of a plant serving 21,000 is 350 mg/L. The BOD loading is 0.18 lbm/day. 25% of the BOD is removed by settling. One single stage high rate trickling filter is to be used to reduce effluent to 75 mg/L. Recirculation is from the filter to the primary settling effluent. Ten States’ Standards is in effect.
a) What is the design flow rate?
b) Using the above design flow rate, what is the total organic load on the filter?
c) What is the plant efficiency?

3. Waste water from a city with a population of 44,000 has daily average flow of 4.0 MGD

BOD5 at 20°C – 150 mg/L
COD = 850 mg/L
Total Solids = 950 mg/L
Suspended solids = 190 mg/L
Volatile solids = 330 mg/L
Settleable solids = 9 mg/L
pH = 7.9

Wastewater is treated with primary settling and secondary trickling filtration. Settling basins are circular, 9 feet deep and designed to a standard overflow rate of 1500 gal/day-ft^2

a) assume 2 basins in parallel, find the diameter in order to remove 35% BOD
b) What is the detention time?
c) What is the weir loading?

4. 35 m^3/day of thickened sludge with a suspended solids content of 4% and 15 m^3/day of anaerobic digester sludge with a suspended solids content of 8% are produced in a wastewater treatment plant.
a) What is the effect of the use of a filter press to increase solids content of thickened sludge to 25%?
b) What volume of digester sludge must be disposed of from sand drying beds that increase the solids concentration to 34%?