During waste water treatment, trickling filter is used for :

Options

A. Primary treatements
B. Secondary aerobic treatements
C. Secondary anaerobic treatement
D. Tertiary treatement

Answer

### Step-by-Step Solution:

1. **Understanding Wastewater Treatment**:
- Wastewater treatment, also known as sewage treatment, involves various processes to remove contaminants from wastewater.

2. **Identifying Treatment Stages**:
- Wastewater treatment typically consists of three main stages: primary treatment, secondary treatment, and tertiary treatment.
- **Primary Treatment**: This stage involves physical processes such as filtration and sedimentation to remove large solids and settleable organic matter.
- **Secondary Treatment**: This stage focuses on biological processes to further reduce organic matter and pollutants.

3. **Exploring Trickling Filters**:
- A trickling filter is a type of secondary treatment process.
- It consists of a bed of stones or other media where wastewater is distributed over the surface.
- Microorganisms (bacteria) grow on the media and break down organic matter in the presence of air (aerobic conditions).

4. **Determining the Correct Option**:
- The question asks specifically about the role of trickling filters in wastewater treatment.
- Since trickling filters are designed to promote the aerobic decomposition of organic matter, they are classified under secondary aerobic treatment.
- Therefore, the correct answer is **Option 2: Secondary Aerobic Treatment**.

5. **Conclusion**:
- Trickling filters are essential in the secondary treatment stage of wastewater treatment, where they help reduce biochemical oxygen demand (BOD) by breaking down organic pollutants.