The principle of sand and gravel filter

1. **Sand and Gravel Filtration Principle**

- Utilizes sand and charcoal as the filter layer, with thickness adjusted based on water turbidity (typically 70–100 cm).

- Filter layers, arranged from top to bottom: fine stones, coarse sand, charcoal, fine sand, and medium sand.

- **Filtration Rate**: 5–10 m/h.

- Removes suspended impurities, solids, iron, manganese, microorganisms, and residual chlorine from raw water.

2. **Filtration Mechanism**

- **Deep Filtration**:

- Resistance retention: Traps particles within the filter layers.

- Gravity sedimentation: Settles heavier particles.

- Contact coagulation: Aggregates smaller particles for easier removal.