GATE Exam Questions - Engineering

Q1:

A waste water sample diluted to 100 times with aeration water had an initial dissolved oxygen (DO) of 7.0 mg/l and after 5 days of incubation at 20°C, the DO was zero. The BOD of waste water is :

A 700 mg/l

B 100 mg/l

C cannot be determined

D 7mg/l

ANS:A - 700 mg/l

Even I think the answer should be C because at what time do become 0 is not known. It becomes after 5 days because reading is taken after 5 days but maybe at the 3rd to 4th day it became 0.

So, the answer cannot be determined.