176. The clarigesters are circular septic tanks
A. rectangular septic tanks
B. circular Imhoff double tanks with bottom hoppers
C. circular Imhoff double storey tanks without bottom hoppers.
D. none of these.

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177.  The coagulant which is generally not used for treating the sewage, is
A. alum
B. ferric chloride
C. ferric sulphate
D. chlorinated copperas.

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178. The coagulant widely used for sewage treatment, is
A. alum
B. ferric chloride
C. ferric sulphate
D. chlorinated copperas.

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179.  The moisture content of a sludge is reduced from 90% to 80% in a sludge digestion tank. The percentage decrease in the volume of sludge, is
A.25%
B.50%
C.10%
D. 5%.

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180.  Pick up the incorrect statement from the following :
A. The process of decomposing the organic matter under controlled anaerobic conditions, is called sludge digestion
B. Sludge digestion is carried out in sludge tank
C. The gases produced in sludge digestion process. contain 75% carbon dioxide
D. The gases produced in sludge digestion process, contain 75% methane.

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181.  The first stage of neutral process of sludge digestion, is
A. acid fermentation
B. acid regression
C. alkaline fermentation
D. none of these.

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182.  Acid regression stage of sludge digestion at a temperature 21?C extends over a period of
A. 15 days
B. 30 days
C. 60 days
D. 90 days.

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