Direct oxidation of ammonia to dinitrogen through persulfate activation by coal-based activated carbon: Selectivity and mechanism

• A novel PS/AC/MgO process was developed for selective oxidation of NH 4 +. • More than 90 % NH 4 + -N was selectively converted to nitrogen gas. • The oxidation of NH 4 + -N mainly occurred through non-radical pathways. • PS/AC/MgO process could resist the interference from actual water/wastewater matrix. • The AC exhibited good stability and reusability for long-term operation. Removal of ammonia nitrogen (NH 4 + -N) from water and wastewater with low C/N ratios by advanced oxidation processes (AOPs) is crucial for guaranteeing the safety of drinking water and preventing eutrophication in aquatic environment. Conventional AOPs tend to over-oxidize NH 4 + -N to nitrite or nitrate and potentially interfere with the water and wastewater matrix. Herein, we proposed a strategy for direct oxidation of NH 4 + -N to N 2 through activating persulfate (PS) by coal-based activated carbon (AC) in the presence of MgO . In the AC/MgO/PS process, NH 4 + -N oxidation mostly occurred via non-radical pathways ( 1 O 2 and electron transfer). The high selectivity of direct oxidation of NH 4 + -N was due to the following four reasons: (1) MgO made NH 4 + -N exist predominantly in the form of NH 3 in solution; (2) electronic shuttle function of AC enhanced the electron transfer from NH 3 /N 2 H 4 to PS to form N 2 ; (3) AC surface contains various functional groups, such as C=O, which may catalyze the conversion of N 2 H 4 and NO intermediates to form N 2 ; (4) sulfur components in AC reduced the nitrite/nitrate product to N 2 . AC/MgO/PS process could be used to oxidize NH 4 + -N in polluted groundwater. This work offers a new AOP for chemical treatment of NH 4 + -containing water and wastewater.