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# GATE 2025 Environment Quiz 13

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Question 1

The following data pertains to a sewage sample:

Initial D O. = 15 mg/l

Final D O. = 4 mg/l

The BOD of the given sample assuming 2% dilution will be?

Question 2

An industrial waste water enters a stream having a BOD concentration of 10 mg/l and a flow of 20 m3/sec. If the flow of waste water is 1.5 m3/sec & its BOD concentration is 250 mg/l, then the BOD concentration in the stream at a point downstream of the point of confluence of waste water with the stream will be?

Question 3

A waste water sample has a BOD of 150 mg/l and its flow is 1000 m3/day. If the domestic sewage has a BOD of 80 gm/capita/day, then the population equivalent of the waste would be?

Question 4

In two samples of water A and B, organic content was to be determined. Potassium dichromate was equally added in both the samples. Titration of A and B was done with ferrous ammonium sulphate, the volume of ferrous ammonium sulphate required in sample A was found to be less than that in sample B then

Question 5

Determine the diameter of sludge digestion tank for 40,000 people. The sludge content per capita per day is 0.068 kg. The moisture of the sludge is 94%. The specific gravity of the wet sludge is 1.02 and 3.5 percent of the digester volume is daily filled with fresh sludge, which is mixed with the digested sludge. Depth of tank is 5 m.

Question 6

Which of the statements are true?
1) The colour of fresh wastewater is colourless.
2) The false odour of the stale water is due to release of Hydrogen Sulphide.
3) Imhoff cone is used to measure the settelable solids in waste water.
4) Coagulation followed by sedimentation is used to remove the colour.
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