Degradation of sulfamethoxazole by ferrous iron activated peroxymonosulfate: Elucidation of the degradation mechanism and influence of process parameters

In this research, the activation of peroxymonosulfate (PMS) by ferrous iron (Fe2+) was investigated as a technique for the degradation of sulfamethoxazole (SMX). First, the influence of the Fe2+:PMS molar ratio on the obtained degradation efficiency was investigated and an excess of Fe2+ was found to result in a decrease in SMX degradation efficiency, while, for the investigated molar ratios, an excess of PMS was found to enhance the degradation efficiency. To obtain a higher degradation efficiency, the dosing strategy of the reagents was altered: from direct dosing (introducing the reagents all at once) to sequential dosing (adding the same total amount of reagent, but divided over specific time intervals) and continuous dosing (adding the same total amount of reagent, but continuously over 30 min reaction time). Continuous dosing of both Fe2+ and PMS was found to be the optimal strategy, with a SMX degradation efficiency of 67% in 50 min reaction time. By performing scavenging experiments, the reactive species (•OH, •SO4- and Fe(IV) present in this process were identified. It was found that the contribution of •OH to the degradation of SMX increased when changing from direct to continuous dosing. Lastly, the formed degradation products were identified, and differences in reaction pathway depending on the reactive species present were elucidated.