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?
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 sewage treatment plant
B.
8 mg/L
River water
C.
400 mg/L
Untreated sewage water
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 sewage treatment plant |
|
B. |
8 mg/L |
River water |
|
C. |
400 mg/L |
Untreated sewage water |
