Waste Water Engineering

81. Hume steel pipes are

1. Steel pipes
2. Steel shell coated from inside with cement mortar
3. Steel shell coated from outside with cement mortar
4. Both (B) and (C)

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82. Hydraulic mean radius is

1. Mean radius of sewer
2. Difference in heads between two points in circular pipes
3. Mean of radii in a pipe line of varying cross-sections
4. Cross-sectional area/wetted perimeter

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83. If 2% solution of a sewage sample is incubated for 5 days at 20°C and depletion of oxygen was found to be 5 ppm, B.O.D. of the sewage is

1. 200 ppm
2. 225 ppm
3. 250 ppm
4. None of these

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84. If a 2% solution of sewage sample is incubated for 5 days at 20°C and the dissolved oxygen depletion was found to be 8 mg/l. The BOD of the sewage is

1. 100 mg/l
2. 200 mg/l
3. 300 mg/l
4. 400 mg/l

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85. If a paper moistened with lead acetate for five minutes when placed in manhole turns black. The sewer certainly contains

1. Hydrogen sulphide
2. Carbon dioxide
3. Methane
4. Oxygen

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86. If D is the diameter of a circular sewer and D' is the top horizontal diameter of an equivalent egg shaped section, the relationship which holds good, is

1. D' = 0.64 D
2. D' = 0.74 D
3. D' = 0.84 D
4. D' = 0.94 D

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87. If 'D' is the diameter of upper circular portion, the area of cross-section of a standard egg shaped sewer, is

1. [(10 + 5π)32] D²
2. [(12 + 5π)15] D²
3. [(18 + 5π)16] D²
4. [(82 + 5π)32] D²

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88. If 'D' is the diameter of upper circular portion, the overall depth of New Egg shaped sewer section, is

1. 1.250 D
2. 1.350 D
3. 1.425 D
4. 1.625 D

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89. If D.O. concentration falls down to zero in any natural drainage, it indicates the zone of

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

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90. If is the diameter of upper circular portion, the overall depth of a standard egg shaped section, is

1. D
2. 1.25 D
3. 1.5 D
4. 1.75 D

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