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Question

When huge amount of sewage is dumped into a river, the BOD will

A
Increase
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B
Remain unchanged
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C
Slightly decrease
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D
Decrease
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Solution

The correct option is A Increase
Decomposition of organic matter by microbes requires oxygen. Degree of impurities of water due to organic matter is measured in terms of 'Biological Oxygen Demand' (BOD). BOD is the oxygen required by microorganisms to metabolise organic wastes. When sewage is dumped into river the BOD increases. Low pollution levels are indicated by BOD below 1500 mg per litre, medium pollution levels are indicated by BOD between 1500 and 4000 mg per litre and high organic pollution is indicated by BOD level above 4000 mg per litre.

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