BOD (Biologocal Oxygen Demand) means the amount of oxygen (in mg/l) 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 poution in a chemical way (by adding oxidising agents and heating). In general with chemical destruction you can remove more polution than with the biological wa