Phosphorus Sorption Capacity of Concrete Waste, Natural Sorbents, Alum Residuals from Water Supply Sludge, and Ceramic Material for Tertiary Treatment in Onsite Systems

The phosphorus (P) sorption capacity was determined for concrete waste, alum residuals from water treatment sludge, and natural sorbents (shells, clay, kaolin, and mordenite) from various parts of Thailand. The material showing the best P sorption capacity (shells) was selected for preparing a ceramic material to support the growth of nitrifying bacteria. The ceramic material, consisting of shells (50% by weight), alum residuals sludge (40% by weight) and a soil (10% by weight) heat at 750°C for about one hour, was studied for its P sorption capacity. Langmuir and Freundlich sorption isotherms yielded similar relative maximum P sorption capacities for the sorbents. The results from the Langmuir calculations showed the following maximum P sorption capacities: 32.26 g P/Kg shells, 31.25 g P/Kg concrete waste, 7.19 g P/Kg alum residuals sludge, 290 mg P/Kg clay, 80 mg P/Kg kaolin, and 30 mg P/Kg mordenite. The P sorption capacity for the prepared ceramic material at grain size 12 mm was 4.85 g P/kg. This result suggests that the ceramic material could be used for P sorption while providing growth support for nitrifying bacteria, similar to the well documented a popular P sorption material: light expanded clay aggregate (LECA) from Sweden.