A sewage treatment plant involves the following steps in its working :

Answer

### Step-by-Step Solution for the Question:

1. **Collection of Wastewater**: The process begins with the collection of wastewater from homes and industries. This wastewater is then transported to the sewage treatment plant.

2. **Bar Screen**: Once the wastewater reaches the treatment plant, it passes through a bar screen. This screen is designed to catch large debris and rubbish, preventing them from entering the treatment process.

3. **Grit and Sand Removal**: After the bar screen, the wastewater flows into a grit and sand removal tank. Here, smaller particles like sand and grit settle down due to gravity, allowing cleaner water to move on to the next stage.

4. **First Sedimentation Tank**: The wastewater then enters the first sedimentation tank. In this tank, heavier solids settle at the bottom, forming sludge. The lighter materials, such as oils and grease, float to the top and can be skimmed off.

5. **Digester Tank**: The sludge collected from the first sedimentation tank is transferred to a digester tank. In this tank, anaerobic bacteria break down the organic matter in the sludge, producing biogas (mainly methane, CH4) and reducing the volume of sludge.

6. **Aeration Tank**: Next, the partially treated water moves to the aeration tank. Here, air is pumped into the water to encourage the growth of aerobic bacteria, which further break down organic pollutants.

7. **Second Sedimentation Tank**: After aeration, the water flows into a second sedimentation tank. Here, any remaining solids settle out again, and the treated water is separated from the sludge.

8. **Final Treatment and Disposal**: The clean water that is left can then be discharged into rivers, lakes, or reused for irrigation. The digested sludge can be used as manure for agricultural purposes.

### Summary of Steps:
1. Collection of wastewater
2. Bar screen for large debris removal
3. Grit and sand removal tank
4. First sedimentation tank
5. Digester tank for sludge treatment
6. Aeration tank
7. Second sedimentation tank
8. Final treatment and disposal of clean water and sludge

---