Media Selection Guide
Four questions to a recommended bed
Answer these the way you would describe the duty to an engineer. The recommendation comes back with the reasoning, not just a parts list.
Recommended bed
- Filter anthracite500 mm
0.8 – 1.6 mm
- Silica filter sand400 mm
0.5 – 1.0 mm
- Support gravel100 mm
2 – 4 mm
- Support gravel100 mm
4 – 8 mm
- Support gravel100 mm
8 – 16 mm
- Support gravel150 mm
16 – 32 mm
Why this bed
A coarser anthracite cap converts the bed to depth filtration — large floc is captured near the surface instead of blinding the top of the sand. At variable influent turbidity this typically extends filter runs by 50–100%.
The four-layer gravel set maintains roughly a 1:4 size progression between adjacent layers, which is what stops sand migrating into the underdrain and keeps backwash distribution even across the bed.
Relevant applications
These are sizing aids for enquiry and budgeting, not a filter design. Final layer depths, freeboard and backwash rates follow from the underdrain type, design filtration rate and target effluent quality.
This is a starting point. Let us check it.
A recommendation from four questions is a good first pass. A design needs the influent analysis, the vessel and the backwash regime — send those and we will do it properly.