Analysis on the removal of ammonia nitrogen using peroxymonosulfate activated by nanoparticulate zero-valent iron

Nanoparticulate zero-valent iron (Fe⁰) was used to activate peroxymonosulfate (PMS) to remove low concentration of ammonia nitrogen in the aqueous system. The removal process was investigated under various conditions. It was indicated that the removal of \({\text{NH}}_{4}^{ + }\) followed the pseudo-first-order kinetic model for the initial reactions. The removal rate increased with the ascending of pH and Fe⁰ dosage, while declined with the ascent of initial \({\text{NH}}_{4}^{ + }\) concentration. The existence of nitrogenous compounds would inhibit the reactions, especially for the compounds with carboxyl structure functional groups. The identification of free radical proved that \(\cdot {\text{SO}}_{4}^{ - }\) is the main radical in Fe⁰/PMS for the removal of ammonia nitrogen. The inorganic products including \({\text{NO}}_{2}^{ - }\), \({\text{NO}}_{3}^{ - }\), Fe²⁺ and Fe³⁺ were detected with the detailed mechanism proposed. The results demonstrated that Fe⁰/PMS process was more effective on ammonia removal compared to single Fe⁰, Fe⁰/persulfate and Fe⁰/H₂O₂. This study proposed a cost-effective process for \({\text{NH}}_{4}^{ + }\) removal at very low concentration of sulfate radicals.