Q.What do you mean by Biochemical Oxygen Demand (BOD)?

Biochemical Oxygen Demand (BOD) is defined as the amount of oxygen (usually expressed in milligrams of O2 per litre, or ppm) required by microorganisms (mainly bacteria) to biochemically decompose (oxidise) the organic matter present in a given sample of water, under aerobic conditions, over a specified time period — conventionally measured over 5 days at a temperature of 20°C.

Significance: BOD is one of the most important indicators of the degree of organic pollution of a water body. The more organic waste (sewage, industrial organic effluent, decaying plant/animal matter) present in water, the more oxygen the bacteria need to decompose it, and hence the higher the BOD. A high BOD means bacteria are consuming a large amount of dissolved oxygen, which leaves less oxygen available for fish and other aquatic organisms, potentially causing them to die.

Typical values:

• Clean water: BOD less than about 5 ppm.
• Highly polluted water: BOD of 17 ppm or more. …

State the precise definition of BOD (oxygen consumed by bacteria decomposing organic matter, over 5 days), then explain its significance as an indicato …

• Confusing BOD with COD (Chemical Oxygen Demand), which measures oxygen needed for chemical oxidation of both organic and inorganic matter, not just biological/bacterial decomposition. …