281. Ventilating shafts are provided to a sewer line at every
A. 100 m
B. 150 m
C. 200 m
D. 300 m

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282.  Aerobic activity is maximum la in freshly produced sewage
A.in freshly produced sewage
B. at sewer pipes
C. in sewer treatment plants
D. none of these.

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283. During putrifaction process of sewage the gas given off, is
A. carbon dioxide
B. hydrogen
C. ammonia
D. all the above.

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284. Oxidation process results in the formation of
A. carbon dioxide
B. nitrates
C. sulphates
D. all the above.

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285.  Fresh sewage may become stale in
A. one hour
B. two to three hours
C. three to four hours
D. six hours.

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286. Water content of sewage is about
A.90%
B.95%
C.99%
D. 9.9%.

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287. For evaporation and measurement of settlable solids, the apparatus used, is
A. a jar
B. a breaker
C. a test tube
D. an Imhoff cone.

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