Ozonation of ammonia at low temperature in the absence and presence of MgO.

Ozone oxidation and ozonation catalyzed with MgO were applied to remove ammonia in water at low temperature (10℃). Results show that pH played a critical role in both ozonation and catalytic ozonation for ammonia removal, especially in the ozonation rate of ammonia and the types of oxidation products. For single ozonation, both O3 and OH contributed to ammonia degradation. Lower pH is beneficial to high selectivity of gaseous products (N2 or N2O) in the presence of Cl-. Significantly enhanced efficiency of ammonia removal was obtained under the catalysis of MgO, which worked as a solid alkali as well as a catalyst, facilitating ammonia oxidation both in the solution and on the MgO surface. Molecular O3 dominated ammonia removal in the heterogeneous catalytic ozonation system, while the contribution of OH was not significant in quantity and a small part of ammonia was degraded by the reaction of ClOx- with NH4+. A relatively high removal efficiency (77.53%˜80.17%) of ammonia could also be achieved in the temperature range of 0℃˜10℃, which indicates that catalytic ozonation over catalysts like MgO may be a potential method to control ammonia pollution during cold weather or under other conditions difficult for biological treatment.