What do you mean by biological …

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.

• 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.