Waste Water Engineering

141. In the activated sludge process

1. Aeration is continued till stability
2. Aeration is done with an admixture of previously aerated sludge
3. Sludge is activated by constant stirring
4. Water is removed by centrifugal action

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142. In trickling filter, B.O.D. is reduced to

1. 30 to 40%
2. 40 to 60%
3. 60 to 80%
4. 80 to 90%

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143. In very first stage of decomposition of the organic matter in sewage

1. Nitrites are formed
2. Nitrates are formed
3. Carbondioxide is formed
4. Ammonia is formed

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144. Inter-distance between ventilation columns in a sewer line is kept

1. 25 to 50 m
2. 50 m to 100 m
3. 100 m to 150 m
4. 150 m to 300 m

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145. It is customary to design a sewer for D.W.F. on the basis of

1. Average demand
2. Twice the average demand
3. Thrice the average demand
4. Four times the average demand

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146. Kjeldahl nitrogen is a mixture of

1. Ammonia and nitrogen
2. Nitrogen and organic nitrogen
3. Organic nitrogen and ammonia
4. All the above

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147. Large diameter sewers subjected to external pressure alone, are reinforced

1. Near the inner surface of the pipe
2. Near the outer surface of the pipe
3. Both (a) and (b)
4. With elliptical cage

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148. Lead acetate test in sewer manhole is done to test the presence of

1. Methane gas
2. Hydrogen sulphide
3. Carbondioxide gas
4. Diesel vapours

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149. Lead caulked joints are used for laying

1. Stone ware pipes
2. Earthenware pipes
3. C.I. pipes
4. G.I. pipes

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150. Maximum permissible velocity 1.5 m/sec, is adopted in drains

1. With beds of rocks and gravels
2. Lined with stones
3. Both (a) and (b)
4. Neither (a) nor (b)

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