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Revision of Surveying : Part 2 (Hindi)
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Simran Kapoor is teaching live on Unacademy Plus

Simran Kapoor
* STAR EDUCATOR * I B.Tech l Civil Engineer l@simranunacademy l Teaching is my Passion l ex Content writer of Grade up l learn and Enjoy✌| B

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BOD (Biological/Biochemical Oxygen Demand) means the amount of oxygen (in mg/l) microorganisms like bacteria need to 'eat' the organic pollution (sugars, fat, proteins, ...). Note that not all pollution can be removed (eaten) by bacteria. BOD value in polluted water is normally higher than the fresh water. Increased BOD can be resulted due to domestic sewage, petroleum residues and wastes of animals and crops. COD (Chemical Oxygen Demand) is the amount of oxygen required to degenerate all pollution in a chemical way (by adding oxidising agents and heating). In general with chemical destruction you can remove more pollution than with the biological way. As BOD is only a measurement of consumed oxygen by aquatic microorganisms to decompose or oxidize organic matter and COD refers the requirement of dissolved oxygen for the oxidation of organic and inorganic constituents both. Hence COD must be greater than BOD.