Difference between Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)

Dissolved oxygen (DO) is the amount of dissolved oxygen present in a water body. Biochemical oxygen demand (BOD) is the amount of oxygen required by the microorganisms to break down the organic materials, whereas chemical oxygen demand (COD) is the amount of oxygen required to break down the organic material via oxidation.

Dissolved oxygen in the water body depends on the temperature, sediment, and the oxygen input and output. Oxygen is given back to the water through photosynthesis and stream flow, whereas oxygen is lost from the water through respiration and decayed organisms.

Read: Biological Oxygen Demand

Let us look at the differences between BOD and COD.

Biological Oxygen Demand

Chemical Oxygen Demand


It is the amount of oxygen required by the microbes 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.


It can be determined by putting a sealed water sample under specific temperature and conditions for five days.

It can be determined by putting a water sample with a strong oxidizing agent under specific temperature and conditions, for a short period of time.


Lower than COD.

Higher than BOD.


  • It is used to waste loadings in treatment plants.
  • Evaluation of BOD removal efficiency of the waste plants.
  • To quantify the amount of oxidizable 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

Is biochemical oxygen demand different from biological oxygen demand?

No, they are the same terms.

What is BOD, COD and TOC?

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

Is COD equal to BOD?

No, COD is always greater than BOD.

Why is COD higher than BOD?

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

What is a good BOD level?

A BOD supply of 1-2 ppm is a standard value.

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