Given below are the steps involved in sewage treatment. Arrange them in proper sequence and select the correct option.
A. Passage of primary effluent into large aeration tanks for mechanical agitation and pumping of air.
B. Passage of secondary effluent and formation of activated sludge.
C. Physical removal of particles through filtration and sedimentation
D. Release of effluent from the secondary treatment plant into natural water bodies.
E. Growth of useful aerobic microbes into flocs which significantly reduce the BOD.

Options

A. A,C, B, E, D
B. A,B,C,D,E
C. C,A,E,B,D
D. C,E,A,B,D

Answer

To arrange the steps involved in sewage treatment in the correct sequence, we can analyze each step provided in the question:

1. **C. Physical removal of particles through filtration and sedimentation**: This is the primary treatment step where solid waste is physically removed from sewage.

2. **A. Passage of primary effluent into large aeration tanks for mechanical agitation and pumping of air**: After primary treatment, the primary effluent is sent to aeration tanks for secondary treatment.

3. **E. Growth of useful aerobic microbes into flocs which significantly reduce the BOD**: In the aeration tanks, aerobic microbes grow and form flocs, which help in reducing the Biological Oxygen Demand (BOD) of the sewage.

4. **B. Passage of secondary effluent and formation of activated sludge**: The flocs settle down, and the remaining liquid is referred to as secondary effluent, which also leads to the formation of activated sludge.

5. **D. Release of effluent from the secondary treatment plant into natural water bodies**: Finally, the treated effluent is released into natural water bodies.

Putting these steps in order, we get the sequence: **C, A, E, B, D**.

### Final Sequence:
1. C - Physical removal of particles through filtration and sedimentation
2. A - Passage of primary effluent into large aeration tanks for mechanical agitation and pumping of air
3. E - Growth of useful aerobic microbes into flocs which significantly reduce the BOD
4. B - Passage of secondary effluent and formation of activated sludge
5. D - Release of effluent from the secondary treatment plant into natural water bodies

### Correct Option:
C, A, E, B, D

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