Gravel is a crucial component in various water treatment processes. Key points include:

1. Definition: Small, rounded rock fragments, typically 2-64 mm in size.
2. Primary use: As a filter media in water filtration systems.
3. Applications:
   • Rapid sand filtration
   • Slow sand filtration
   • Biofiltration systems
   • Constructed wetlands
   • Septic drain fields
4. Functions:
   • Physical filtration of suspended particles
   • Support for beneficial microorganisms in biological filtration
   • Improves water distribution in filtration beds
5. Advantages:
   • Durable and long-lasting
   • Chemically inert
   • Cost-effective
   • Easily cleaned and maintained
6. Gravel layers:
   • Often used in graduated layers of different sizes
   • Supports finer filter media like sand
7. Types:
   • River gravel (rounded)
   • Crushed stone (angular)
8. Size selection:
   • Varies based on specific treatment process requirements
   • Proper sizing ensures optimal flow and filtration
9. Maintenance:
   • Periodic backwashing to remove trapped particles
   • Occasional replacement or replenishment
10. Environmental impact:
    • Natural material with minimal ecological footprint
    • Can be recycled or repurposed after use
11. Compatibility:
    • Works well with other filter media and treatment processes