The major part of the organic matter in the sewage water is decomposed in :

Options

A. Primary treatment
B. Aeration tank/oxidation pond
C. Anaerobic sludge digester
D. Tertiary treatment

Answer

To solve the question regarding where the major part of the organic matter in sewage water is decomposed, we can break down the sewage treatment process step by step.

### Step-by-Step Solution:

1. **Understanding Sewage Water Treatment**:
- Sewage water contains a significant amount of organic matter that needs to be treated before being released into the environment.

2. **Primary Treatment**:
- The first step in sewage treatment is the primary treatment. This involves the removal of floating materials and grit (soil and small pebbles) through filtration and sedimentation.
- The result of this process is called primary sludge (the sedimented material) and primary effluent (the remaining liquid).

3. **Aeration Tank**:
- The primary effluent is then transferred to an aeration tank.
- In this tank, air is pumped in, which promotes the growth of aerobic bacteria.

4. **Decomposition of Organic Matter**:
- The aerobic bacteria in the aeration tank play a crucial role in degrading the organic matter present in the primary effluent.
- This process is where the majority of the organic matter is oxidized or decomposed.

5. **Formation of Secondary Sludge**:
- As the aerobic bacteria break down the organic matter, secondary sludge is formed, which contains the biomass of the bacteria and any remaining organic material.

6. **Conclusion**:
- Therefore, the major part of the organic matter in sewage water is decomposed in the aeration tank, also known as the oxidation pond.

### Final Answer:
The major part of the organic matter in sewage water is decomposed in the **aeration tank**.

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