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Environment & Health

Question
50 out of 72
 

Strength of sewage is expressed in terms of all except:



A E.coli count
B Suspended particles

C COD
D BOD

Ans. A E.coli count Ref: Park; 22nd edi, Pg –708

The "strength" .of the sewage is expressed in terms of

A. BIOCHEMICAL OXYGEN DEMAND (BOD) : It is the most important test done on sewage. It is defined as the amount of oxygen absorbed by a sample of sewage during a specified period, generally 5 days, at a specified temperature, generally 20 deg.C for the aerobic destruction or use of organic matter by living organisms. BOD values range from about 1 mg per litre for natural water to about 300 mg per litre for untreated domestic sewage. If the BOD is 300 mg/l and above, sewage is said to be "strong"; if it is 100 mg/l, it is said to be "weak"

B. CHEMICAL OXYGEN DEMAND (COD): The COD test measures the oxygen equivalent of that portion of the organic matter in a sample which is susceptible to oxidation by a strong chemical oxidiser. If wastes contain toxic substances, this test may be the only practical method for determining the organic load.

C. SUSPENDED SOLIDS: The suspended solids are yet another indicator of the "strength" of sewage. The amount of suspended solids in domestic sewage may vary from 100 to 500 p.p.m. (mg/I). If the amount of suspended solids is 100 mg/l, the sewage is said to be weak: if the amount is 500 mg/l the sewage is said to be strong.

Environment & Health Flashcard List

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