Lab results and flow rate for an activated sludge are listed below under the known column. Information helpful to the operator in controlling the process is listed in the unknown column. The aerator or aerator tank volume is 70600 cuft.

Known
Mixed Liquor Suspended Solids (MLSS) = 1,800 mg/L
Mixed Liquor Volatile Content = 76%
Thirty –Minute Settleable solids Test = 170 ml/L, or 17%
Primary Effluent BOD = 140 mg/L
Primary Effluent Suspended solids = 110 mg/L
Flow Rate = 2.0 MGD

1. Find Sludge Volume Index

2. Pounds of Solids in the Aerators

3. Aerator Loading, lbs BOD/day

4. Sludge age, days

Answers:

1. Sludge Volume Index, ml/gm = (Settleable Solids, % X 10,000) / (MLSS, mg/L) OR
SVI, ml/gm = (Settleable Solids, ml/L X 1,000) / (MLSS, mg/L)
(17 % X 10,000) / (1,800 mg/L) = 94 OR (170 X 1,000) / (1,800 mg/L) = 94

2. Aerator Solids, lbs = Tank Vol, MG X MLSS, mg/L X 8.34 lbs/gal
70600 cuft X 7.48 gal/cuft = 528,088 gal
(528,088 gal) / (1,000,000) = 0.5 MG
0.5 MG X 1,800 mg/L X 8.34 lbs/gal = 7,500 lbs

3. Aerator Loading, lbs BOD/day = Flow, MGD X Pri Eff BOD, mg/L X 8.34 lbs/gal
2.0 MGD X 140 mg/L X 8.34 lbs/gal= 2,335 lbs BOD/day applied to aerator

4. (Mixed Liquor Suspended Solids, lbs) / (Primary Effluent Solids, lbs/day) OR
(Tank Vol, MG X MLSS, mg/L X 8.34 lbs/gal) / (Flow, MGD X Pri Eff SS, mg/L X 8.34 lbs/gal)
(0.5 MG X 1,800 mg/L X 8.34 lbs/gal) / (2.0 MGD X 110 mg/L X 8.34 lbs/gal)
(7,500 lbs) / (1,835 lbs/day) = 4.1 days