Ammonium assists orthophosphate removal from high-strength wastewaters by natural zeolite

• Phosphorus and nitrogen were simultaneously recovered from water by zeolite alone.
• In P only tests, pH > 9 is favorable to P recovery by natural zeolite.
• N assists recovery of P-recovery by releasing Ca2+ ions from the zeolite lattice.
• Implications to practice of zeolite treatment were discussed.

Nutrients discharge correlates to eutrophication of receiving waters. Phosphorus (P) and nitrogen (N), if recovered from wastewaters, can be applied to land as essential nutrients for plant growth. This study used natural zeolite in batch and continuous tests to simultaneously remove P and N from orthophosphate and ammonium-nitrogen laden wastewaters at pH 3–11. In P only tests, pH > 9 is favorable to P removal. When ammonium was also present, P removal was significantly enhanced. Ammonium was first adsorbed onto the zeolite via ion exchange to release Ca2+ ions from the zeolite lattice. This ion exchange reaction was independent of the presence of P. Then the released Ca2+ ions precipitated the dissolved phosphate, which was greatly dependent on the concentration of ammonium. Zeolite column could effectively remove P and N from fermentation liquor with minimal adsorption of volatile fatty acids. Implications to practice of zeolite treatment were discussed.