Read the following passage and answer the questions that follow :
Sewage is generated in large quantities in the urban areas. It is treated in sewage treatment-plants (STPs) to make it less polluted before discharging into any natural water body. Observe the flow chart given below and answer the questions that follow :Primary effluent is passed into large aeration tank
↓
Effluent is passed into settling tank to form the sediment (activated sludge)
(a) Name the two products obtained after primary treatment of sewage.
Sewage is generated in large quantities in the urban areas. It is treated in sewage treatment-plants (STPs) to make it less polluted before discharging into any natural water body. Observe the flow chart given below and answer the questions that follow :
Primary effluent is passed into large aeration tank
↓
Effluent is passed into settling tank to form the sediment (activated sludge)
(a) Name the two products obtained after primary treatment of sewage.
Show Hint
Solution and Explanation
Primary treatment is a physical process. It removes small and large particles from the sewage by filtration and sedimentation.
The grit settles first and the floating debris is filtered out.
Step 2: Products:
The settled solids form the primary sludge.
The liquid that floats above the sludge is called the primary effluent.
Final Answer:
The two products are the primary sludge (settled solids) and the primary effluent (the liquid portion).
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A laboratory assistant collected three water samples, namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant. But the laboratory attendant did not note which was which. The samples were labelled A, B and C and subjected to a BOD test. The BOD values of the three samples A, B and C were recorded as 30 mg/L, 8 mg/L and 400 mg/L respectively.
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