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 Sewage Treatment**: Sewage treatment is a process that involves the removal of contaminants from wastewater. It is typically divided into three main processes: primary, secondary, and tertiary treatment.

2. **Primary Treatment**: In the primary treatment phase, physical processes are employed to remove solid waste. This includes the removal of soil, grit, and other debris. During this stage, solids settle down to form what is known as primary sludge, while the liquid that remains is referred to as effluent.

3. **Effluent Definition**: The effluent is the liquid waste that has been separated from the solid waste during the primary treatment. It contains dissolved and suspended organic matter that still needs further treatment.

4. **Secondary Treatment**: The effluent is then passed into an oxidation tank, which is part of the secondary treatment process. This stage is also known as biological treatment.

5. **Aeration Tanks**: In the aeration tanks, the effluent is exposed to air, which promotes the growth of microorganisms that consume the organic matter present in the effluent. This process helps in breaking down the remaining contaminants biologically.

6. **Conclusion**: Therefore, the passage of effluent into the oxidation tank is primarily for the purpose of secondary treatment, which is aimed at further purifying the wastewater by biological means.

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

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