232. For the COD test of sewage, organic matter is oxidised by K2Cr207 in the presence of
A. H2SO4
B. HNO3
C. HC1
D. none of these,
233. Bio-chemical oxygen demand (BOD) for the first 20 days in generally referred to
A. initial demand
B. first stage demand
C. carbonaceous demand
D. all of these.
234. 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/1. After 5 day-incubation at 20?C, the DO. concentration was 5 mg,/1. The BOD of raw sewerage is
A. 100 mg/1
B. 200 mg/1
C. 300 mg/1
D. 400 mg/l.
235. If a 2% solution of sewage sample is incubated for 5 days at 20?C and the dissolved oxygen depletion was found to be 8 mg/I. The BOD of the sewage is
A. 100 mg/1
B. 200 mg/1
C. 300 mg/1
D. 400 mg/I.
236. Sluge banks are formed if sewage is disposed of in
A. rivers
B. seas
C. lakes
D. none of these.
237. The recommended detention period for grit chambers is
A. 1 minute
B. 2 minutes
C., 3 minutes
D. 5 minutes.
238. The rate of accumulation of sludge in septic tanks is recommended as
A. 30 litres/person/year
B. 25 litres/person/year
C. 30 litres/person/month
D. 25 litres/person/month.
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