Ques. 1AIPMT 2007
In which one of the following the BOD (Biochemical Oxygen Demand) of sewage (S), distillery effluent (DE), paper mill effluent (PE) and sugar mill effluent (SE) have been arranged in ascending order?
- SE < PE < S < DE
- SE < S < PE < DE
- PE < S < SE < DE
- S < DE < PE < SE
Answer
(3) PE < S < SE < DE
Solution
As per NCERT, BOD is the amount of oxygen needed by micro-organisms to decompose the biodegradable organic matter in one litre of water; the greater the organic load, the higher the BOD.
Typical BOD values of untreated wastes:
Paper mill effluent (PE) ≈ 190 mg L-1
Domestic sewage (S) ≈ 200–400 mg L-1
Sugar mill effluent (SE) ≈ 1000–1500 mg L-1
Distillery effluent (DE) ≈ 40000 mg L-1 (spent wash, extremely rich in organic matter)
∴ Ascending order of BOD: PE < S < SE < DE
Answer: (3)
Out of syllabus