Waste Water Engineering
3.0 ml of raw sewage is diluted to 300 ml. The D.O. concentration of the diluted sample at the beginning of the test was 8 mg/l. After 5 day-incubation at 20°C, the D.O. concentration was 5 mg/l. The BOD of raw sewerage is

300 mg/l
400 mg/l
100 mg/l
200 mg/l

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Waste Water Engineering
Skimming tanks are

Tanks provided with self- cleansing screens
Improved version of grit chambers
Those from which sludge is skimmed out
Used to remove the grease and oil

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