# Waste water calculations

1. Mar 31, 2009

### Stacyg

I'm not sure where to start with these any help would be great. Not sure if this is the right place to put these questions but this site has helped before.
Thanks

1)
A treatment plant consists of a primary sedimentation tank followed by a trickling filter that removes 80% of the influent BOD. The flow is then directed to a constructed marsh system that has an influent target BOD concentration of 30 mg/l before being discharged to a small stream.

Using the following table of % BOD removal to overflow rate and calculate the dimensions of a circular sedimentation tank suitable for the imposed flow with a detention time of 1.5 hours. Assume BOD and flow of wastewater entering the plant to be 214.245 mg/l and 848 kL/day.
BOD Removal % 22.0 31.5 33.5 35.5 36.5 37.5
Overflow rate m3/m2/day 100 50 40 30 25 20

2)
A community of 200 people has its gravity main sewer discharging to a treatment plant located near the town. The water consumption rate is 280 l/h/d, all of which could be assumed to discharge to the main sewer. The domestic sewage flow contains an average BOD loading of 75 g/h/d and a suspended solids loading of 84 g/c/d.
A cheese factory situated nearby, processing milk products, is also connected to the treatment plant inlet and discharges a raw effluent with a BOD loading of 110 g/m3 and an SS loading of 130 g/m3 at an average flow rate of 10 l/s over a period of 8 hours in one day.
Calculate the combined average concentrations of BOD and SS at the treatment plant inlet.
3)
Design an activated sludge plant for the following figures given for a community
Design Population 4500 people producing 320 liters per head per day
Raw Sewage Strength BOD – 206 mg/l, SS – 320 mg/l
Contact Stabilization Time 24 minutes
Extended Aeration Time 0.07 kg BOD/m3 of tank/hr
Sedimentation Overflow 48 meters per day
Depth Of Settling Tank 3.0m
Air Requirement 4.5 m3/hour/m3 of tank volumes

Calculate the volumes of the three process tanks (CS, EA and Sedimentation tanks) and the total air flow.
b) For the same sewage flow, design a fixed growth reactor. Assume the primary sedimentation stage removes 38% of the BOD. Use the following design criteria:

4)
For a primary domestic sewage (1276 m3/day, BOD 240 mg/l), the treatment process is to be conventional activated sludge. Sketch and find the volumes of the contact tank, the aeration tank and the diameter of the settling tank, given the following design loading :
Contact Stabilization Time 1.5 hours