11. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
Biological oxygen demand (BOD) is the method of determining the amount
of oxygen required by micro-organisms to decompose the waste present in
the water supply. If the quantity of organic wastes in the water supply is
high, then the number of decomposing bacteria present in the water will also
be high. As a result, the BOD value will increase.
Therefore, it can be concluded that if the water supply is more polluted, then
it will have a higher BOD value. Out of the above three samples, sample C
is the most polluted since it has the maximum BOD value of 400 mg/L.
After untreated sewage water, secondary effluent discharge from a sewage
treatment plant is most polluted. Thus, sample A is secondary effluent
discharge from a sewage treatment plant and has the BOD value of 20 mg/L,
while sample B is river water and has the BOD value of 8 mg/L.
Hence, the correct label for each sample is:
|
Label BOD value Sample |
||
|
A. |
20 mg/L |
Secondary effluent discharge from a sweage treatment plant |
|
B. |
8 mg/L |
River water |
|
C. |
400 mg/L |
Untreated sewage water |
© 2024 GoodEd Technologies Pvt. Ltd.
