What is Biological Oxygen Demand? (BOD)

Biological Oxygen Demand is defined as the amount of dissolved oxygen required by aerobic microorganisms to breakdown the organic materials in a sample of water at a specific temperature & timeframe. In simpler words, The amount of oxygen needed by biological organisms such as bacteria in a given water sample for a breakdown of organic matter by oxidation process is called the Biochemical Oxygen Demand.

Why is this method used?

  • BOD is the biological method used for the measurement of the total amount of dissolved oxygen (DO) used by microbes in the biological process of metabolizing organic molecules present in water.
  • The total amount of oxygen gas present in the water is called the dissolved oxygen (DO). The non-compound oxygen present in water may either be a by-product of the photosynthesis of the aquatic plants or the dissolved atmospheric oxygen gas.


  • BOD measures the amount of oxygen utilized by microorganisms for the process of decomposition of the organic matters in the water bodies.
  • It symbolizes the amount of organic pollution present in an aquatic ecosystem.
  • Also regulates the chemical oxidation (COD) of inorganic matter.
  • Used in sewage treatment or wastewater treatment to destroy and decay organic wastes through the aerobic organisms.
  • Determines the amount of organic matter present in soils, sewages, sediment, garbage, sludge, etc.
  • Detects the rate of respiration in living beings.
  • Used in the medicinal & pharmaceutical industries to test the oxygen consumption of cell cultures.
  • Biological oxygen demand can be used as an indicator of the level of environmental pollution. For instance, the higher the levels of organic matter (in polluted water bodies or sewage), the greater the BOD.
  • Consequently, a high Blood Oxygen Demand level means the amount of dissolved oxygen available for other marine organisms such as fish is low.
  • From an ecological perspective, wastewater treatment plants aim to lower their BOD before discharging the affluents into a water body.




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