Biochemical oxygen demand
Also called: BOD · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT
Meaning
Biochemical oxygen demand (BOD) is the amount of oxygen that microbes (tiny living things such as bacteria) use up to break down organic matter in water. Organic matter includes sewage and rotting plant and animal waste. When there is more waste, microbes use more oxygen, so BOD rises. High BOD leaves less oxygen for fish and other water life. This makes BOD a key sign of sewage pollution. Water fit for outdoor bathing should have a BOD of 3 mg per litre or less.
Example
In 2022, the Central Pollution Control Board marked 311 stretches on 279 Indian rivers as polluted because their BOD was above 3 mg/l. Maharashtra had the most such stretches (verify current).
Don't confuse with
- Dissolved oxygen: this is the oxygen actually present in the water. BOD is the oxygen that microbes need to use up. High BOD usually means low dissolved oxygen.
Related concepts
- Water pollution
- Water-borne diseases
- Polluted river stretches
- Sewage treatment gap
- Water (Prevention and Control of Pollution) Act 1974