Waste Water Engineering

11. A nuisance is experienced in diluting water if dilution factor is less than

1. 100
2. 60
3. 40
4. 20

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12. A rain sanitary sewer is constructed to carry

1. Sanitary sewage
2. Storm sewage
3. Surface water
4. Ground water

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13. A rainfall may be classified as acidic if its pH value is less or equal to

1. 6
2. 7
3. 5
4. 6.5

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14. A safety lamp when inserted in the upper portion of a manhole causes flames. It indicates the presence of

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

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15. A sewer pipe contains 1 mm sand particles of specific gravity 2.65 and 5 mm organic particles of specific gravity 1.2, the minimum velocity required for removing the sewerage, is

1. 0.30 m/sec
2. 0.35 m/sec
3. 0.40 m/sec
4. 0.45 m/sec

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16. A sewer running partially full and hurried with back filled, fails in compression due to

1. Weight of the pipe
2. Weight of the back fill
3. Superimposed traffic loads
4. All the above

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17. A well oxidized sewage contains nitrogen mainly as

1. Nitrates
2. Nitrites
3. Free ammonia
4. None of these

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18. Acid regression stage of sludge digestion at a temperature 21°C extends over a period of

1. 15 days
2. 30 days
3. 60 days
4. 90 days

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19. Aerobic activity is maximum

1. In freshly produced sewage
2. At sewer pipes
3. In sewer treatment plants
4. None of these

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20. Aerobic bacterias

1. Flourish in the presence of free oxygen
2. Consume organic matter as their food
3. Oxidise organic matter in sewage
4. All the above

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