239. . Which one of the following statements regarding septic tanks is wrong :
A. a gap of 7.5 cm between the bottom of the covering slab and the top level of scum is provided
B. the outlet invert level is kept 5 to 7.5 cm below the inlet invert level
C. the minimum width of septic level is 90 cm
D. the depth of tank is kept equal to its width.

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240.  The ratio of design discharge to the surface area of a sedimentation tank is called
A. surface loading
B. overflow rate
C. overflow velocity
D. all of these.

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241. The flow velocity in detritus tanks is
A. 0.05 m/sec
B. 0.09 m/sec
C. 1.25 in/sec
D. none of these.

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242. The sewage treatment units in which anaerobic decomposition of organic matter is used, are called
A. imhoff tanks
B. trickling filters
C. sludge sedimentation tanks
D. none of these.

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243.  The sewage treatment in septic tanks is due to
A. anaerobic decomposition
B. aerobic decomposition
C. parasitic decomposition
D. none of these,

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244. To maintain aerobic biological activity, the moisture content of the compost mass should be about
A.45%
B.50%
C.55%
D. 60%.

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245.  Pick up the correct statement from the following :
A. Indore method of composting involves decomposition under aerobic conditions
B. Bangalore method of composting involves decomposing under anaerobic conditions
C. Fully stabilised refuse by the Bangalore method of compositing is a powdery mass called humus
D. all of these.

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