Waste Water Engineering

251. The self-cleansing velocity of water flowing through pipe lines, is

1. 2 metres/sec
2. 1 metre/sec
3. 0.5 metre/sec
4. 0.25 metre/sec

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252. The settlement of a particle in sedimentation tank, is affected by

1. Velocity of flow
2. Viscosity of water
3. Size and shape of solid
4. All the above

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253. The settlement velocity of a solid (diameter 0.5 mm, specific gravity 1.75) in water having temperature 10°C, is

1. 213.5 cm/sec
2. 313.5 cm/sec
3. 413.5 cm/sec
4. 500 cm/sec

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254. The settling velocity of a spherical particle of diameter less than 0.1 mm as per Stock's law, is

1. V_s = 418 (G_s - G_w)d [(3T + 70)/100]
2. V_s = 418 (G_s - G_w)d² [(3T + 70)/100]
3. V_s = 218 (G_s - G_w)d² [(3T + 70)/100]
4. V_s = 218 (G_s - G_w)d [(3T + 70)/100]

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255. The settling velocity of the particles larger than 0.06 mm in a settling tank of depth 2.4 is 0.33 m per sec. The detention period recommended for the tank, is

1. 30 minutes
2. 1 hour
3. 1 hour and 30 minutes
4. 2 hours

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256. The sewage discharge in a detritus tank of a treatment plant is 576 litres/sec with flow velocity of 0.2 m/sec. If the ratio of width to depth is 2, the depth is

1. 100 cm
2. 110 cm
3. 120 cm
4. 150 cm

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257. The sewage is pumped up

1. From low lying areas
2. From flat areas
3. From basements
4. All the above

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258. The sewage treatment in septic tanks is due to

1. Anaerobic decomposition
2. Aerobic decomposition
3. Parasitic decomposition
4. None of these

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259. The sewage treatment units in which anaerobic decomposition of organic matter is used, are called

1. Imhoff tanks
2. Trickling filters
3. Sludge sedimentation tanks
4. None of these

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260. The sewer pipe which carries sewage from a building for immediate disposal is

1. House sewer
2. Lateral sewer
3. Intercepting sewer
4. Main sewer

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