Simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash as influenced by salt treatment.

To develop an effective technique for enhancing the removal efficiency of ammonium and phosphate at low concentrations without losing potential removal capacity, Na-ZFA (zeolite synthesized from fly ash) was converted into Ca-, Mg-, Al-, and Fe-ZFA by salt treatment and the simultaneous removal of ammonium and phosphate by ZFA saturated with different cations was investigated. It was shown that Al3+-ZFA had the highest removal efficiencies (80-98%) for ammonium, followed by Mg2+ (43-58%), Ca2+ (40-54%), Na+ (<20%), and Fe3+ (<1%). Both alkaline pH values (in the cases of Na+, Ca2+, Mg2+) and acidic pH value (in the case of Fe3+) inhibited the sequestration of ammonium. At low initial phosphate concentrations, the efficiency of phosphate removal by Al3+- and Fe3+-ZFA approached 100%, followed by Ca2+ (60-85%), Na+ (<25%), and Mg2+ (<5%). The difference in phosphate removal efficiency was explained by the adsorption mechanisms. It was concluded that ZFA could be used in simultaneous removal of NH4+ and phosphate at low concentrations with presaturation by an appropriate cation such as Al3+ through salt treatment.