Wollastonite as reactive filter medium for sorption of wastewater ammonium and phosphorus

The utilisation of reactive filter media to remove ammonium and phosphorus can improve the effluent water quality of wastewater treatment systems. The objective of this study was to estimate the ammonium and phosphorus sorption capacity of wollastonite, a calcium meta silicate (CaSiO3) that is distributed worldwide. Phosphorus sorption mechanisms were also investigated. Batch sorption experiments with agitating bottles were carried out and both phosphate and ammonium solutions as well as wastewater were used. The results showed minor ammonium adsorption, with only 3-15% of the ammonium in the solutions being adsorbed to the wollastonite. Neither the reaction time (0.5-20 h) nor the initial concentrations of phosphorus and ammonium (11-114 mg l(-1) NH4-N) were of importance. For high initial phosphate concentrations, phosphate was greatly sorbed to the wollastonite (850 mg kg(-1) at an initial phosphate concentration of 61 mg l(-1) PO4-P). However, phosphate sorption was minor when the initial phosphate concentration was low. This study showed that sorption reactions were important when phosphate was removed by wollastonite, and indicated precipitation of phosphate on the wollastonite surfaces as one possible mechanism for phosphate retention. The results from this study indicated that the wollastonite investigated may not be suitable for municipal wastewater treatment applications due to the low phosphorus sorption capacity for low initial phosphorus concentrations.