253. If G is the specific gravity of particles of diameter d, the velocity of settlement Vin still water at T?C, according to Stoke's law, is

A. V = 418 (G ? 1) d2( 3T + 70 100

B. V = 418 (1 ? G)d 3T ? 70 100

C. V = 418(1 G)2T + 70 100

D. V =. 418 (G ? 1) d3 3T11007?

254. In plain sedimentation tanks under normal conditions, impurities are removed upto

A.60%

B.70%

C.80%

D. 90%.

255. The ratio of discharge and plan area of a continuous flow type settling tank, is known

A. surface loading

B. overflow

C. overflow rate

D. all the above.

256. Normal values of overflow rate for plain sedimentation tank, is

A. 250 to 500 litres/hr/m2

B. 500 to 750 litres/hr/m2

C. 750 to 1000 litres/hr/m2

D. 1000 to 1250 litres/hr/m2

257. Normal values of overflow rate for plain sedimentation tank using coagulants, is

A. 750 to 1000 litres/hr/m2

B. 1000 to 1250 litres/hr/m2

C. 1250 to 1500 litres/hr/m2 1500 litres/hr/m2.

D.

258. Detention period of a settling tank is

A. average theoretical time required for water to flow through the tank

B. time required for flow of water to fill the tank fully

C. average time for which water is retained in tank

D. all the above.

259. Detention time for plain sedimentation tank usually ranges from

A. 2 to 4 hours

B. 4 to 8 hours

C. 6 to 10 hours

D. 8 to 12 hours

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