Traditional single-media rapid sand filters suffer from a fundamental hydraulic drawback: during fluidizing backwash cycles, the finest sand grains settle at the top of the bed while coarse grains sink to the bottom. As a result, suspended solids are trapped entirely within the top 2 to 5 centimeters, causing rapid head loss, short filter runs, and frequent water-wasting backwash cycles.
The Dual-Media Hydraulic Advantage
Anthracite coal media solves this stratification problem. Because anthracite has a lower specific gravity (~1.45–1.60 g/cc) compared to quartz sand (~2.65 g/cc), larger anthracite granules (0.8–2.0 mm) naturally settle on TOP of smaller, denser quartz sand (0.5–1.0 mm) after hydraulic backwashing.
Core Performance Metrics
- Specific Gravity: 1.40 – 1.60 g/cm³
- Fixed Carbon Content: > 85% to 92% pure low-volatile carbon
- Acid Solubility: < 2.0% (ASTM B100 compliant)
- Hardness: 3.0 to 3.5 Mohs scale for low attrition during fluidization
Operational Benefits
- True Coarse-to-Fine Filtration: Floc and larger particulates are captured deep within the high-void anthracite layer, while fine sub-micron turbidity is polished by the underlying quartz sand.
- Higher Filtration Velocities: Hydraulic flow rates increase from 8–10 m/h in single-sand filters up to 15–25 m/h in dual-media beds without breakthrough.
- Extended Filter Cycles: Filter run times are doubled or tripled, cutting backwash wastewater loss by up to 40%.
Repuls Anthracite Availability:
We supply premium graded anthracite (>85% carbon, low acid solubility <2%) in standard mesh fractions: 0.8–1.6mm, 1.0–2.0mm, and 1.5–2.5mm.
