Question

Biochemical Oxygen demand in river water.

Answer 1

Hint: BOD stands for Biological Oxygen Demand. It is related to environmental issues like pollution and others.
Pollution is defined as an undesirable change in physical, chemical, biological characteristics of air, water, land or soil.

Complete Answer:
Now, let us take a look further to know what is BOD.
BOD stands for Biological Oxygen Demand. It refers to the amount of Oxygen required for microbial breakdown of biodegradable organic matter.
It is higher in polluted water and lesser in drinking water. It is used as a degree to measure the pollution. Its value is most commonly expressed in milligrams as consumed per litre.
Health workers find the amount of dissolved oxygen in water by measuring BOD. The lesser the amount of dissolved oxygen, the more polluted the water body will be. The water bodies which have a high level of BOD indicates the high pollution in them as the dissolved oxygen available in these water bodies is being used by the bacteria by which other aquatic organisms result in less oxygen availability.
It increases gradually when sewage gets mixed with river water. It resulted in the killing of aquatic organisms and disappearance of clean water organisms.

Note:
Domestic Sewage contains nutrients like Nitrogen and Phosphorus which favors the excessive growth of free-floating organisms(planktonic). It causes fish mortality and results in bad water quality.
Domestic sewage mainly contains such biodegradable organic wastes which are decomposed by decomposers hence, decomposers required more oxygen for their activity which resulted in the increase of Biochemical Oxygen Demand (BOD).
Excessive growth of unwanted things in water imbalances the water ecosystem and thus, aquatic animals die.