Long-term phosphate removal by the calcium-silicate material Polonite in wastewater filtration systems

The mineral-based filter material Polonite was tested for its PO4 removal capacity in column and full-scale systems using synthetic and domestic wastewater. Three long-term experiments (67, 68 and 92 wk), operated under different hydrological conditions, were compared. The best PO4 removal capacity (97%) was observed in an intermittent saturated column fed with a synthetic solution (530 L m−2 d−1) without organic matter during 68 wk. An unsaturated column system using municipal wastewater (76.7 L m−2 d−1) showed no tendency for PO4 breakthrough and effluent PO4 concentration was still low (0.2 mg L−1) after 67 wk. For a compact bed filter containing 560 kg of Polonite and fed with 70 m3 of wastewater from a single house, the average PO4 removal was 89% after 92 wk of operation. The column experiments revealed that a design volume of 1–2 kg of material of a particle size of 2–5 mm was required amount for treating 1 m3 of wastewater in on-site systems operating at target 90% P mass removal. Poor pre-treatment of the wastewater was suggested to reduce the phosphate removal capacity of Polonite in the bed filter trial, where 8 kg were required per m3. To measure pH of the treated effluent water proved not to be a simple tool for determining when the filter material is exhausted and should be replaced.