Question

The amount of oxygen required by the microbes in the decomposition of organic matter is called:
A) Chemical oxygen demand
B) Biochemical oxygen demand
C) Total oxygen demand
D) Dissolved oxygen

Answer 1

Hint:
The primary liquid waste is moved to big aeration tanks and it is continually flustered mechanically and the air is put into it. That allows vigorous growth of useful aerobic microbes into flocs(masses of bacteria associated with fungal filaments to form mesh-like structures).

Complete answer:
Microbes are grown for the decomposition of organic matter, microbes consume a major part of organic matter in the effluent while growing. This significantly reduces the (biochemical oxygen demand) BOD of the effluent. The dissolved oxygen that is required by aerobic microorganisms in a water body to dissociate organic matter in the water for a specific period of time and temperature is called biological oxygen demand or BOD. Until the BOD is reduced sewage water is treated. Hence, indirectly, BOD measures the organic matter present in water. More the BOD of liquid waste more polluted it will be. Once the BOD of sewage water is reduced significantly the effluent is then passed into a settling tank where bacterial flocs are allowed to sediment. This sediment is called activated sludge.
Therefore the correct answer is biochemical oxygen demand.

Option ‘B’ is correct

Note:
(Chemical oxygen demand) COD is the test that measures oxygen required to oxidize the organic and inorganic materials such as ammonia and nitrite that are present in water. Total oxygen demand is the measurement of continuous analysis of the concentration of oxygen in a combustion process gas effluent. The decrease in oxygen resulting from the introduction of the sample into the combustion zone is a measure of oxygen demand.