The primary treatment of waste water in- volves the removal of

Options

A. dissolved impurities
B. stable particles
C. toxic substances
D. harmful bacteria

Answer

### Step-by-Step Solution:

1. **Understanding Primary Treatment of Wastewater**:
- The primary treatment of wastewater is the first step in the wastewater treatment process. It primarily focuses on the physical removal of impurities from the wastewater.

2. **Types of Impurities in Wastewater**:
- Wastewater contains various types of impurities, including dissolved impurities, stable particles, toxic substances, and harmful bacteria.

3. **Processes Involved in Primary Treatment**:
- The primary treatment involves two main processes: **filtration** and **sedimentation**.
- **Filtration**: This process removes floating debris and larger particles from the wastewater.
- **Sedimentation**: This process allows smaller solid particles to settle down, forming sludge.

4. **Focus on Stable Particles**:
- In primary treatment, the focus is on removing stable particles (both large and small) rather than dissolved impurities. Dissolved impurities remain in the water after primary treatment.

5. **Formation of Effluent**:
- After the filtration and sedimentation processes, the remaining liquid is called effluent, which is then sent for secondary treatment.

6. **Conclusion**:
- Therefore, the primary treatment of wastewater primarily involves the removal of stable particles, while dissolved impurities, toxic substances, and harmful bacteria are not significantly removed during this stage.

### Final Answer:
The primary treatment of wastewater involves the removal of **stable particles**.

---