Catalytic ozonation of ammonia nitrogen removal in wastewater: A review

Ammonia nitrogen (NH4+-N) is the most common pollutant in wastewater, which consumes dissolved oxygen in water and causes eutrophication in water bodies, and is an important control indicator in wastewater treatment. Biological process is not suitable for wastewater with poor biodegradability and difficult to meet increasing strict discharge standards. Physical-chemical methods such as ion exchange, fold-point chlorination and Fenton oxidation would introduce new substances to wastewater, leading to potential pollutants. Catalytic ozonation technology can effectively remove ammonia nitrogen without introducing other substances, and improve the nitrogen selectivity of reaction products by controlling the reaction conditions. However, studies on catalytic ozonation of ammonia nitrogen were scattered, and systematic induction was necessary. In this paper, the removal effect, product distribution and reaction mechanism of metal oxide catalyst, composite metal catalyst and activated carbon catalyst in catalytic ozonation for ammonia nitrogen were summarized. Catalyst is one of the keys to achieve high nitrogen selectivity by catalytic ozonation of ammonia, and the nitrogen selectivity was compared for different catalysts in this paper. Besides, based on literatures, the figures for mechanism of catalytic ozonation by several catalysts were drawn to help others understand easily. According to the discussion of literatures, the emphasis in future studies were proposed. It is important to study the catalytic mechanism in depth, further improve the removal efficiency of ammonia nitrogen and nitrogen selectivity in products, explore the effect of the actual composition of the wastewater on catalytic ozonation of ammonia nitrogen, and pay attention to the catalyst loss rate.