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

•Fe-rich dewatered sludge cake could be successfully converted into Fe-rich biochar.•SMX could be rapidly degraded in a wide adaptability manner with Fe-BC/SPC treatment.•Hydroxyl radical and electron transfer jointly contributed in sulfamethoxazole degradation.•Fe-BC accelerated Fe2+/Fe3+ cycle and promoted reactive species production.•Fe-BC/SPC system effectively treated real swine farming wastewater with high stability.