Dual oxidant strategy involving calcium peroxide and peroxydisulfate for waste activated sludge recycling: Removal of sulfamethoxazole and hydrocortisone

Abstract

In this study, the removal of sulfamethoxazole (SMX) and hydrocortisone (HC) from waste activated sludge (WAS) was explored using a dual oxidant strategy involving calcium peroxide (CaO2) and peroxydisulfate (PDS). Synergistic effects were observed between CaO2 and PDS at 0.1 g/g TS (total solids), leading to 89 % and 54 % removal of SMX and HC, respectively, in 8 min in sludge. Ca2+, Ca(OH)2, H2O2, and SO42– from CaO2 and PDS hydrolysis promoted pollutant removal. SMX removal was mainly driven by 1O2, which had a 78 % contribution to the removal rate, while HC removal was mainly due to OH and SO4–, with an overall 79 % contribution. Furthermore, removal pathways for SMX and HC during CaO2/PDS were proposed. SMX, HC, and their intermediates with high toxicity transformed into less toxic or nontoxic products during CaO2/PDS oxidation. Moreover, the dewatering ability and solubility of sludge increased after CaO2/PDS treatment. Furthermore, the production of volatile fatty acids during anaerobic fermentation of sludge pretreated with CaO2/PDS increased by 1.8 times relative to the control, with a 13 % increase in acetic acid content. The altered relative abundance of Firmicutes and Proteobacteria played a key role in promoting the recovery of carbon sources from the sludge.