Adsorption - Catalytic ozonation of ammonia nitrogen in drinking water by alkali-modified NaX zeolites

Ammonia nitrogen (NH4+-N) is one of the regular indexes and the most important contaminants in drinking water. However, it is still a great challenge to remove low concentration NH4+-N from drinking water in a safe way. Here we used NaX zeolite and alkali-modified NaX zeolite (NaX-A) as adsorbents and catalysts for ozonation to remove NH4+-N in water without adding any chemicals. The zeolites present significant adsorption of NH4+-N with Freundlich adsorption affinity of 2.10–3.27 mg1-n·L-n·g−1 by ion-exchange on the bridged Si-O-Al groups. The NaX-A catalytic ozonation achieves 26.7 % of NH4+-N removal and up to 75.0 % of gaseous products selectivity in 20 min. The NH4+-N oxidation rate constant is raised by 10.7 times over O3/NaX-A compared with single ozonation. The alkali modification stimulates the formation of acid sites in NaX-A, and thus improve the adsorption of NH4+-N and the decomposition of O3 into hydroxyl radicals (·OH) for the conversion of NH4+-N to gaseous products. This study provides new insights into catalytic ozonation by alkali-modified zeolites to remove NH4+-N in water via coupling adsorption with catalytic ozonation.