Waste Water Engineering

171. Skimming tanks are

1. Used to remove the grease and oil
2. Those from which sludge is skimmed out
3. Tanks provided with self-cleansing screens
4. Improved version of grit chambers

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172. Sludge banks are formed if sewage is disposed of in

1. Rivers
2. Seas
3. Lakes
4. None of these

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173. Stone ware pipes are

1. Highly resistant to sulphide corrosion
2. Highly impervious
3. Hydraulically efficient because of their smooth interior surface
4. Especially suited to pressure pipes

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174. Stoneware sewers are available in size

1. 10 cm
2. 15 cm
3. 20 cm
4. All the above

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175. The algae dies out in the zone of

1. Degradation
2. Active decomposition
3. Recovery
4. Cleaner water

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176. The amount of oxygen consumed by the aerobic bacterias which cause the aerobic biological decomposition of sewage, is known

1. Bio-Chemical Oxygen Demand (B.O.D.)
2. Dissolved Oxygen (D.O.)
3. Chemical Oxygen Demand (C.O.D.)
4. None of these

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177. The angle subtended by the surface of sewer water with partial flow, at sewer centre is 120°, the depth of sewerage is

1. 20 cm
2. 25 cm
3. 40 cm
4. 50 cm

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178. The arrangement made for passing the sewer line below an obstruction below the hydraulic gradient lines called

1. Inverted syphon
2. Depressed sewer
3. Sag pipe
4. all of these

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179. The asbestos cement pipes are generally laid

1. Horizontally
2. Vertically
3. At an angle of 30°
4. At an angle of 60°

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180. The asbestos cement sewers are

1. Light in weight
2. Not structurally strong to bear large compressive stress
3. Susceptible to corrosion by sulphuric acid
4. All the above

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