Difference Between BOD And COD

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Biochemical oxygen demand (BOD) is the amount of oxygen microorganisms require to break down organic materials. In contrast, chemical oxygen demand (COD) is the amount of oxygen required to break down the organic material via oxidation.

Read: Biological Oxygen Demand

Let us look at the differences between BOD and COD.

Biological Oxygen Demand Chemical Oxygen Demand
Definition
It is the amount of oxygen the microbes require to decompose the organic matter under aerobic conditions. It  is the total amount of oxygen required to break down the organic matter by chemical oxidation.
Test
It can be determined by putting a sealed water sample under specific temperature conditions for five days. It can be determined by placing a water sample with a strong oxidising agent under specific temperature conditions for a short period.
Value
Lower than COD. Higher than BOD.
Use
  • It is used to waste loadings in treatment plants.
  • Evaluation of BOD removal efficiency of the waste plants.
  • To quantify the amount of oxidisable pollutants found in water bodies.
  • It provides a measurement on how an effluent will affect the water body.

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Frequently Asked Questions

Q1

Is biochemical oxygen demand different from biological oxygen demand?

No, they are the same terms.

Q2

What are BOD, COD and TOC?

BOD and COD are water’s biochemical and chemical oxygen demands to break down the organic components, whereas TOC is total organic carbon found in an organic compound.

Q3

Is COD equal to BOD?

No, COD is always greater than BOD.

Q4

Why is COD higher than BOD?

COD is always higher than BOD because chemical oxidation is easier than biological oxidation.

Q5

What is a good BOD level?

A BOD supply of 1-2 ppm is an expectedd value.

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