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What is The biological oxygen demand indicates ? and explain in detail?
Ans. is 'a' i.e., Organic matter Biochemical Oxygen demand It is the most impoant 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 Pr the aerobic destruction or use of organic matter by living organisms. BOD value ranges from about 1 mg per litre far natural waters to about 300 mg per litre for untreated domestic sewage. If the HOD is 300 mg/1 and above, sewage is said to be strong ; if it is 100 mg/1, it is said to be weak".