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 20 mg / L, 8 mg / L, and 400 mg / 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 ?
BOD measures the milligrams of oxygen consumed during the biological decomposition of organic matter occurring in a litre of waste water during a specified period of time.BOD value is an indication of pollution , so if the BOD value is high the water is highly polluted and if it is low i indicates less pollution.
Untreated sewage water is most polluted as it contains high amount of human excreta, wash waters and industrial and agricultural wastes, so it has highest BOD value. River water is clean and contains less organic material, thus it has least BOD value among all. So they can be labelled as :
|
Sample
|
BOD Value
|
Type of Sample
|
|
A →
B →
C →
|
20 mg / It →
8 mg / It →
400 mg / It →
|
Secondary effluent
River water
Untreated sewage water
|
165 Views
