Passage of effluents into oxidation tank is for

Options

A. Primary treatment
B. Secondary treatment
C. Tertiary treatment
D. Both A and B

Answer

### Step-by-Step Solution:

1. **Understanding Effluents**: Effluents are liquid waste materials that are discharged into the environment, typically from industrial processes or sewage treatment plants.

2. **Sewage Treatment Process**: The sewage treatment process is divided into three main stages:
- **Primary Treatment**: This involves the physical separation of solids from liquids. During this stage, solid waste settles at the bottom, forming sludge, while the liquid portion, known as effluent, remains on top.
- **Secondary Treatment**: This stage focuses on biological processes to further treat the effluent. The effluent from the primary treatment is passed into an aeration tank or oxidation tank, where microorganisms break down organic matter.
- **Tertiary Treatment**: This is the final stage, which involves advanced treatment processes to remove remaining impurities and contaminants from the effluent.

3. **Role of the Oxidation Tank**: The oxidation tank, also referred to as the aeration tank, is specifically designed for secondary treatment. Here, the effluent is aerated to promote the growth of aerobic bacteria, which consume organic pollutants, thereby purifying the water.

4. **Conclusion**: The passage of effluents into the oxidation tank is primarily for secondary treatment, where biological processes are employed to further reduce the organic load and improve water quality before it is discharged or subjected to tertiary treatment.

### Final Answer:
The passage of effluents into the oxidation tank is for **secondary treatment**.

---