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Question
Differentiate the following:
BOD and COD
Solution
- Biochemical oxygen demand (BOD):
- The total amount of oxygen (in milligrams) consumed by microorganisms in decomposing the waste in one litre ut water at 20°C for a period of 5 days is called biochemical oxygen demand (BOD).
- its value is expressed in ppm.
- DOD is used as a measure of the degree of water pollution.
- BOD is only a measurement of consumed oxygen by microorganisms to decompose the organic matter.
Clean water would have BOD value less than 5 ppm.
Chemical oxygen demand (COD):
- Chemical oxygen demand is defined as the amount of oxygen required by the organic matter in a sample of water for its oxidation by a strong oxidizing agent like K7Cr2O7 in an acidic medium for a period of 2 hours.
- Its value is expressed in mg/litre.
- COD is a measure of the amount of organic compounds in a water sample.
- COD refers to the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents.
- Clean water would have COD value greater than 250 mg/litre.
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