Question

What are oxygen-demanding wastes? Define BOD. How is it determined?

Answer 1

Hint: Oxygen-demanding wastes are the second category of water pollutants and these are the wastes that can be decomposed by oxygen requiring bacteria. The amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic conditions at a specific temperature is known as Biochemical oxygen demand or BOD.

Complete answer:
Oxygen demanding wastes are those substances which oxidize in the receiving body of water with the consumption of dissolved oxygen. Major sources of oxygen demanding wastes are:
The Biodegradable organic substances which are found in municipal wastewater, which is mainly human waste and food Residue and Industrial wastewater such as from tannery, textile, paper & pulp and food processing industries.
Minor Sources such as crop residue, decaying plants and leaves, animal, droppings, oxidation at certain inorganic compounds
Strength of oxygen demanding wastes are mainly measured using two methods:
BOD (Biological Oxygen Demand)
COD (Chemical Oxygen Demand)
The amount of oxygen required for microbial metabolism of organic compounds in water is termed as the biochemical oxygen demand. Depending upon the temperature, nutrient concentrations, and the enzymes available for indigenous microbial populations, this demand occurs over some variable period of time.
The biochemical oxygen demand can be computed based upon the difference between initial and final dissolved oxygen. Here, dilution water and a known amount of sample in an \[250 - 300{\text{ }}ml\] incubation bottle is used. When microbial activity may not be present, a small number of seeds is added to the sample. The initial dissolved oxygen is measured using a probe and the bottle is stored at \[20^\circ C\]. After five days, the final dissolved oxygen is measured and the difference is taken.

Note:
Total biological oxygen demand or total BOD is the amount of oxygen required to completely oxidize the organic compounds to carbon dioxide and water through generations of microbial growth, death, decay, and cannibalism. The measurement of total BOD is of more significance to the food webs than to water quality. In response to a large amount of organic material, the dissolved oxygen depletion is most likely to become evident during the initial aquatic microbial population explosion.