Water Pollution and BOD

Biochemical oxygen demand (BOD) is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by micro-organisms.
A higher BOD value means that the water sample is more polluted by biodegradable organic matter.
Distillery effluent (spent wash) is extremely rich in organic matter and has the highest BOD of the four, of the order of 40,000 mg/L.
Sugar mill effluent also carries a heavy load of sugars and other organic matter, so its BOD is high, though far below that of distillery effluent.
Domestic sewage and paper mill effluent have much lower values; taking the figures used in the source, paper mill effluent is the lowest and sewage comes next.
So the ascending order of BOD is PE < S < SE < DE.

BOD (biochemical oxygen demand) is the amount of oxygen required by micro-organisms to oxidise the organic matter present in one litre of water; it is a measure of organic pollution.
Effluents with a high BOD use up the dissolved oxygen of the receiving water and kill the aquatic life.
So waste water must be treated to bring down its BOD before it is released into rivers and lakes.
The Central Pollution Control Board (CPCB) has prescribed that the BOD of industrial and municipal waste water discharged into natural surface waters should be less than 30 ppm (30 mg/L).
Clean water has a BOD of less than about 5 ppm, while untreated sewage has a BOD of a few hundred ppm.
So the prescribed limit is less than 30 ppm.