Test: Population Equivalent & Relative Stability - Civil Engineering (CE) MCQ

BOD of industrial sewage kg/day /(0.08kg/person/day) where 0.08 represents the average standard BOD of domestic sewage.

The average standard BOD of domestic sewage is measured in 0.08Kg per person per day.

The expression of relative stability at 37ºC is given by S = 100 (1-(0.630)^T37) where T37 represents the incubation period at 37ºC.

The expression of relative stability at 20ºC is given by S=100 (1-(0.794)^T20) where T20 represents the incubation period at 20ºC.

Relative stability at 37ºC is given by, S = 100 (1-(0.630) ^T37) = 100 (1-(0.630)⁵) = 90.08% which is approximately 90%.

BOD of industrial sewage in kg/day = Population equivalent * Average standard BOD of domestic sewage = 6000*0.08 = 480kg/day.

COD is abbreviated as chemical oxygen demand. It is measured in ppm or mg/L.

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

5 days BOD at 20ºC is the standard BOD which is 68% of total demand, whereas 10 days BOD at 20ºC is 90% of total demand.

In COD test, oxidization of organic matter takes place by potassium dichromate in the presence of sulphuric acid using ferroin as indicator.