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,

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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.

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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.

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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.

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236.  Sluge banks are formed if sewage is disposed of in
A. rivers
B. seas
C. lakes
D. none of these.

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237. The recommended detention period for grit chambers is
A. 1 minute
B. 2 minutes
C., 3 minutes
D. 5 minutes.

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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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