The bacterial reaction of ammonium oxidation coupling with iron reduction (Feammox) has been discovered recently. To improve the ammonium removal efficiency from wastewater of Feammox bacteria, magnetic chitosan hydrogel beads (MCHBs) were prepared via sodium hydroxide co-precipitating-sol-gel method, Feammox bacteria were immobilized to 1-5 mm MCHBs, and the ammonium removal efficiency by MCHBs-Feammox bacteria was compared to free-Feammox bacteria. In addition, the influences of initial ammonium concentration, pH and temperature were assessed. The results showed that the MCHBs were ferromagnetic and exhibited high crystallinity, with the magnetization of saturation of 29.46 emu·g-1. The average rates of ammonia oxidation and iron reduction increased by 42.96% and 20.75% after Feammox bacteria immobilization, respectively, and the most significant effect was observed on 1-2 mm MCHBs-Feammox bacteria (P<0.05). Furthermore, 1-2 mm MCHBs immobilized bacteria worked in less favorable matrix concentrations, temperatures, and pH. Particularly, it could maintain high ammonium removal efficiency with 60.00 mg·L-1 initial ammonium concentration, 25℃ temperature and 4.50 pH. In addition, nitrate and ferrous ions were detected in the system. The highest ammonium removal rate occurred on day 16, reaching 53.62%. These results indicated that MCHBs immobilization can improve the ammonium removal efficiency of Feammox.
Keywords: ammonium oxidation coupling with iron reduction (Feammox); ammonium removal; immobilization; iron reduction; magnetic chitosan hydrogel beads (MCHBs).