Question

“Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body.” Explain.

Answer 1

Hint: The demand for biochemical oxygen (BOD) is the quantity of dissolved oxygen supplied by aerobic biological organisms in a particular water sample to break down organic material after a certain temperature within a certain period of time. Most generally, the BOD value is expressed in milligrammes of oxygen absorbed per liter of sample at $20^{o}$ during 5 days of incubation. It is also used as a surrogate for the extent of organic water contamination.

Complete answer: A calculation of the amount of oxygen used by microorganisms (e.g. aerobic bacteria) in the oxidation of organic matter is the biological oxygen demand. Normal bodies of water contain a certain amount of organic substances that microbes act on and decompose. The amount of organic content in it is established by evaluating the BOD of the water body.
Biological activity is intensified by the presence of more organic waste, leading to algal blooms.
The reduction in BOD is used as an indicator of the efficacy of wastewater treatment plants. To demonstrate the short-term effects on the oxygen levels of the receiving water, BOD of wastewater effluents is used. In terms of chemical oxygen demand (COD) analysis, the BOD approach is similar in function, in that both calculate the amount of organic compounds in water.

Note:
Tiny amounts of organic compounds are found in most natural water. To use some of these compounds as food, aquatic microorganisms have evolved. Dissolved oxygen is used by microorganisms living in oxygenated water to dissolve organic compounds, releasing energy that is used for growth and reproduction. In proportion to the amount of food available, the populations of these microorganisms begin to increase.