Test: Oxygen Demand - Civil Engineering (CE) MCQ

The full form of BOD is biochemical oxygen demand. It is measured in ppm or mg/L.

BOD is the amount of oxygen required to oxidize only organic matter in sewage. It is always less than COD as COD oxidizes both organic and inorganic matter.

ZL represents the first stage BOD from the given figure. The first stage BOD is also called as the carbonaceous demand.

BOD = Dissolved oxygen * Dilution factor.
Where Dilution factor = Volume of diluted sewage sample / Volume of undiluted sewage sample.

The carbonaceous demand occurs due to oxidation of organic matter. The carbonaceous demand is also called as the initial demand.

LP represents the second stage BOD from the given figure. The second stage BOD is also called as the nitrogenous demand.

ZP is correctly paired and it represents the combined demand, which includes both carbonaceous and nitrogenous demand.

The carbonaceous demand occurs due to oxidation of ammonia. The nitrogenous demand is also called as the final demand.

The value of deoxygenation constant is directly proportional to the temperature. It increases with increase in temperature.

As the growth rate of nitrifying bacteria is slow, the nitrogenous demand begins after 5 days.