COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised. This includes chemicals toxic to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing.

Is COD greater than BOD?

BOD can be higher than COD determined by dichromate oxidation in a few cases. The most common is a sample with very degradable organic matter and high organic nitrogen or ammonium such as wastewater from fish processing. ... In this case, measured BOD can be higher than measured COD.

Why is COD value high?

The higher the COD value, the more serious the pollution of organic matter by water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g., lakes and rivers) or wastewater (Davidson, 2001; Sara and Goncaloglu, 2008).