The primary treatement of wastewater involves the removal of

Options

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

Explanation

**Step-by-Step Solution:**

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

2. **Mechanisms Involved**: The primary treatment involves two main mechanisms:
- **Sedimentation**: This process allows heavier solid particles to settle at the bottom of a tank due to gravity, forming a sludge layer.
- **Filtration**: This process involves passing the wastewater through filters to remove smaller solid particles that may still be suspended in the water.

3. **Types of Solids Removed**: During the primary treatment, various types of solids are removed, including:
- Large solids (e.g., plastics, food waste)
- Small solids (e.g., silt, sand)
- Suspended solids (solids that are not dissolved in water)

4. **Identifying What is Not Removed**: It is important to note that the primary treatment does not remove:
- Dissolved impurities (these remain in the water as they are not solid particles)
- Toxic substances (these are typically addressed in the secondary treatment)
- Harmful bacteria (also removed in the secondary treatment)

5. **Evaluating Options**: Based on the understanding of primary treatment:
- **Dissolved impurities**: Not removed.
- **Stable particles**: Correct, as these are insoluble solids removed during primary treatment.
- **Toxic substances**: Not removed; addressed in secondary treatment.
- **Harmful bacteria**: Not removed; addressed in secondary treatment.

6. **Conclusion**: The only correct option regarding what is removed in the primary treatment of wastewater is the removal of stable particles (insoluble solids).

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

---