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 solve the question regarding the proper sequence of sewage treatment steps, we will arrange the given steps logically based on the sewage treatment process. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Physical Removal of Particles**:
- The first step in sewage treatment is the physical removal of particles through filtration and sedimentation. This is known as primary treatment, where solids settle down and are separated from the liquid waste.
- **Step C**: Physical removal of particles through filtration and sedimentation.

2. **Passage of Primary Effluent**:
- After the primary treatment, the primary effluent (the liquid that remains after solids have settled) is passed into large aeration tanks. Here, mechanical agitation and the pumping of air occur to promote the growth of aerobic bacteria.
- **Step A**: Passage of primary effluent into large aeration tanks for mechanical agitation and pumping of air.

3. **Growth of Aerobic Microbes**:
- In the aeration tanks, useful aerobic microbes grow into flocs, which are aggregates of bacteria and fungi. These microbes consume organic matter, significantly reducing the Biological Oxygen Demand (BOD).
- **Step E**: Growth of useful aerobic microbes into flocs which significantly reduce the BOD.

4. **Formation of Activated Sludge**:
- The mixture then moves to settling tanks where the flocs settle down, forming activated sludge. Some of this sludge is returned to the aeration tanks to maintain the microbial population.
- **Step B**: Passage of secondary effluent and formation of activated sludge.

5. **Release of Treated Effluent**:
- Finally, the treated effluent is released from the secondary treatment plant into natural water bodies, completing the sewage treatment process.
- **Step D**: Release of effluent from the secondary treatment plant into natural water bodies.

### Final Sequence:
The correct order of the steps is:
- C → A → E → B → D