Industrial by-products and natural substrata as phosphorus sorbents

The efficiency of phosphorus (P) removal in ecologically-engineered wastewater treatment facilities, such as artificial wetlands and sand filters, can be improved by using a reactive sorbent. The sorbent must therefore have a high P-sorption capacity and an adequate hydraulic conductivity. Several filter materials have been tested here in regard to their P-sorption capacity. In this study, three natural materials - opoka (a bedrock found in south-eastern Poland) limestone and the B horizon of a forest soil, plus two artificial materials - blast furnace slag (crystalline and amorphous, in two particle sizes (0-0.125 mm and 0.25-4 mm), and fly ash were investigated. Phosphate sorption and isotherm studies were performed. In addition, physical and chemical properties of the materials were also investigated. The P-sorption experiment showed that all materials were capable of sorbing P to various extents. The coarse crystalline slag had the highest P-sorption capacity followed in order by the fine crystalline slag, the fine amorphous slag, the B horizon, the limestone, the coarse amorphous slag, the ash and the opoka. The isotherm studies showed that the B horizon was the most efficient P retainer, followed in order by the coarse crystalline slag,the fine crystalline slag, the fine amorphous slag and the coarse amorphous slag, with opoka and limestone showing the poorest retention. It was concluded that the crystalline slags had the highest P-sorption capacities, and that coarse crystalline slag possessed the highest hydraulic conductivity, suggesting that this material is the most suitable for use in ecological wastewater treatment systems.