Filtration Process
Following clarification, the water enters the Filtration stage. This marks the shift from chemical treatment to physical removal of particles.
Filter Design
The plant utilizes Rapid Sand Filters constructed of reinforced concrete (approx. 34' x 50'). Each filter acts as a physical barrier to remove remaining suspended solids and pathogens (like Giardia and Cryptosporidium).
| Layer | Material | Function |
|---|---|---|
| Top Layer | Anthracite Coal | Traps larger floc particles |
| Bottom Layer | Sand | Polishes water by trapping fine particles |
| Support | Gravel | Supports media and distributes backwash water |
Operational Standards
- Capacity: Each filter can process up to 4 Million Gallons Per Day (MGD).
- Turbidity Goal: Must be $\le 0.3$ NTU in 95% of samples.
- Absolute Limit: Turbidity must never exceed 1 NTU.
The Backwash Cycle
When filter media becomes clogged with trapped solids, efficiency drops and the filter must be cleaned.
- Backwash: Clean water and air (scour) are forced backward through the filter to lift the bed and scrub the media.
- Filter-to-Waste: Before returning to service, the filter runs to waste for a short period. This allows the media to settle and ensures no loose particles pass into the clearwell.
!!! warning "Turbidity Spike" Rules allow for a temporary increase in turbidity for 4 hours immediately following a backwash, as the filter "seasons" itself.