Intimately coupled photocatalysis and biodegradation for effective simultaneous removal of sulfamethoxazole and COD from synthetic domestic wastewater

The inefficiency of conventional biological treatment for removing sulfamethoxazole (SMX) is posing potential risks to ecological environments. In this study, an intimately coupled photocatalysis and biodegradation (ICPB) system consisting of Fe3+/g-C3N4 and biofilm was fabricated for the treatment of synthetic domestic wastewater containing SMX. The results showed that this ICPB system could simultaneously remove 96.27 ± 5.27% of SMX and 86.57 ± 3.06% of COD, which was superior to sole photocatalysis (SMX 100%, COD 4.2 ± 0.74%) and sole biodegradation (SMX 42.21 ± 0.86%, COD 95.1 ± 0.18%). Contributors to SMX removal in the ICPB system from big to small include LED photocatalysis, biodegradation, LED photolysis, and adsorption effect of the carrier, while COD removal was largely ascribed to biodegradation. Increasing initial SMX concentration inhibits SMX removal rate, while increasing photocatalyst dosage accelerates SMX removal rate, and both had no impact on COD removal. Our analysis of biofilm activity showed that microorganisms in this ICPB system maintained a high survival rate and metabolic activity, and the microbial community structure of the biofilm remained stable, with Nakamurella and Raoultella being the two dominant genera of the biofilm. This work provides a new strategy to effectively treat domestic wastewater polluted by antibiotics.