Question

Differentiate the following:

BOD and COD

Answer 1

• Biochemical oxygen demand (BOD):

1. 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).
2. its value is expressed in ppm.
3. DOD is used as a measure of the degree of water pollution.
4. 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):

1. 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.
2. Its value is expressed in mg/litre.
3. COD is a measure of the amount of organic compounds in a water sample.
4. COD refers to the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents.
5. Clean water would have COD value greater than 250 mg/litre.