Significant enhancement on ammonia removal by thermal/peroxymonosulfate system with bromide ion: Performance, influencing factors and mechanism

Although thermal-activated peroxymonosulfate (PMS) system possesses good performance on the removal of organic pollutants, thermal/PMS system exhibited poor capacity to remove ammonia nitrogen (NH 4 + -N). This study demonstrated the huge enhancement on the removal of NH 4 + -N by thermal/PMS system with the commonly coexistent bromide ion (Br - ). The elimination of NH 4 + -N by thermal/PMS/Br - system fitted the pseudo -zero-order kinetics model well, while the corresponding k obs in the presence of 200 μM Br - was 5.76 times greater than that by thermal/PMS system. Bromine (HBrO) was confirmed as the dominant oxidant responsible for removing NH 4 + -N and TN, while the radicals of HO ⋅ , SO 4 ⋅- and Br ⋅ were also generated but made minor contribution to removing NH 4 + -N. HBrO was mostly produced by PMS reacting directly with Br - , while these radicals were produced from the cleavage of the O-O bond in PMS and the reaction between PMS and HBrO under high temperature. Thermal/PMS/Br - system exhibited superior performance on TN removal (up to 90 %) than that by thermal/PMS system (less than 5 %) and Cl - -enhanced system (about 80 %). The main removal product of NH 4 + -N was identified as the environmentally friendly gas of N 2 , although nitrate was also detected. Neutral pH condition was the optical pH for NH 4 + -N removal. Increasing reaction temperature, PMS dosage and Br - concentration were beneficial to accelerating the removal of NH 4 + -N. Cations of Cu 2+ and Fe 3+ , anions of SO 4 2- , CO 3 2 - and NO 3 - , humic acid and the actual water matrix of landfill leachate negligibly influenced the removal of NH 4 + -N, while Cl - exhibited strong enhancement on NH 4 + -N removal. In summary, this study provided an effective method to improve the oxidizing capacity of thermal/PMS system, especially for NH 4 + -N removal in wastewater containing Br - .