Question

In: Chemistry

Why do COD and BOD measurements give different result for same waste?

Why do COD and BOD measurements give different result for same waste?

Solutions

Expert Solution

the definition of COD ie., the chemical oxygen demand can be defined as 'The measure of total quantity of oxygen required for oxidation of organic and inorganic wastes present in one litre of waste water sample'.

whereas the definition of BOD ie., the Biochemical oxygen can be defined as the amount of oxygen that would be consumed if all the organics in one liter of water were oxidized by bacteria and protozoa

For both experiments the purpose will be same but the procedures were different. both were used to measure the waste present in the water released by industries.

The COD and BOD mesrements will give different result for same waste because. in BOD  the oxygen used by microorganisms to decompose this waste. so if more waste is present then more bacteria is also present inorder to decompose the waste. usually the In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed in the water, BOD levels will begin to decline.

whereas in COD we will be using chemicals if strong organic agents are present then we use strong oxidising agents like acidified K2Cr2O7 and silver chloride as catalysts and we proceed the experiment so on.

the above reaction represents COD experiment.

for the BOD experiment the typical reaction is

organic matter + micro organisms+ O2 + nutrients -----> CO2 + H2O + microorganisms.

as we can observe that the efficent work can be achevied by the COD experiment compared to BOD experiment.

so certainely there will be diffents results will be obtained.


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