Iron-rich sludge biochar triggers sodium percarbonate activation for robust sulfamethoxazole removal: Collaborative roles of reactive oxygen species and electron transfer

Abstract

The efficient removal of sulfamethoxazole (SMX) from swine farming wastewater is a major emerging environmental issue. This study successfully developed Fe-rich sludge biochar (Fe-BC) from dewatered iron-containing sewage sludge cake, in order to activate sodium percarbonate (SPC) for rapid SMX degradation in swine farming wastewater. Under optimal conditions of 0.5 g/L Fe-BC and 0.3 mM SPC at pH of 3.0, Fe-BC/SPC process achieved highly efficient SMX degradation within 5 min, reaching 100 % SMX degradation efficiency with kobs of 1.1439 min−1. The Fe-BC/SPC process exhibited recyclability and a high level of resistance to natural wastewater conditions. The main mechanism included adsorption and oxidation process. The SMX was probably adsorbed on the Fe-BC surface. Also, SPC activation by Fe-BC for SMX degradation was found to include a radical-driven pathway dominated by •OH and a non-radical pathway governed by direct electron transfer. Furthermore, the high rate of SMX degradation in the Fe-BC/SPC process was attributed to Fe2+ generation via the Fe3+/Fe2+ cycle and efficient electron transfer through oxygenated functional groups. Four SMX degradation pathways (i.e., hydroxylation, –NH2 group oxidation, ON bond and NS bond cleavage reactions) were proposed. The Fe-BC/SPC process exhibited high SMX removal performance and low-toxicity with swine farming wastewater. Overall, this study shows that the development of Fe-BC/SPC as a promising and efficient system for SMX degradation in practical swine farming wastewater treatment applications.