Select the correct statement.
A. 5 day BOD is the ultimate BOD
B. 5 day BOD is greater than 4 day BOD keeping other conditions same
C. 5 day BOD is less than 4 day BOD keeping other conditions same
D. BOD does not depend on time
Answer: Option C
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5day BOD=0.68 ultimate BOD whereas 4day BOD =0.601 ultimate BOD
In 5 day BOD ,micro-organisms have more time to consume O2and hence dissolved oxygen demanded will be less after 5days whereas in 3day BOD micro-organisms have less time to consume O2 to decompose organic matter and after 3day dissolved oxygen demanded will be more to decompose organic matter.so BOD 5 is less than BOD 3 (compare dissolved oxygen demanded or required) thanks
In 5 day BOD ,micro-organisms have more time to consume O2and hence dissolved oxygen demanded will be less after 5days whereas in 3day BOD micro-organisms have less time to consume O2 to decompose organic matter and after 3day dissolved oxygen demanded will be more to decompose organic matter.so BOD 5 is less than BOD 3 (compare dissolved oxygen demanded or required) thanks
Correct answer is B, 5 day BOD greater than 4 day BOD