Simultaneous removal of acetaminophen, sulfamethoxazole, and iohexol from real wastewater in continuous mode by an immobilized sulfur-doped Bi2O3/MnO2 photocatalyst†

Abstract

Advanced oxidation processes like heterogeneous photocatalysis can degrade recalcitrant compounds. However, the overall potency of most semiconductor-based photocatalysts in continuous operation and real wastewater matrices remains inadequate. This study investigates the simultaneous removal of three contaminants, namely, acetaminophen (ACT), sulfamethoxazole (SMX), and iohexol (IOX), from actual municipal wastewater (MWW) and hospital wastewater (HWW) by utilizing a moving bed biofilm system coupled with a filtration unit, followed by a continuous photocatalytic reactor. Here, a sulfur-doped Bi₂O₃/MnO₂ Z-scheme heterojunction photocatalyst immobilized over low-cost and eco-friendly clay beads (2S-BOMO CCB) was employed to degrade an ACT–SMX–IOX mixture in a continuous photocatalytic reactor. Under optimal conditions, removal efficiencies of 87.1 ± 1.4%, 82.6 ± 1.9%, and 77.5 ± 2.3% were attained for ACT, SMX, and IOX, respectively. The feasibility of reusing the spent photocatalyst was also investigated over ten consecutive cycles. Further, this study confirmed that the superoxide anion, hydroxyl radical, and singlet oxygen were dominant oxidative species for ACT–SMX–IOX degradation. However, the removal efficiency of ACT–SMX–IOX by 2S-BOMO CCB was significantly reduced due to the presence of various interfering agents in real wastewater. Nonetheless, when the hybrid system was employed, approximately 93.8 ± 2.7% and 89.4 ± 3.6% of ACT, 89.6 ± 1.8% and 83.7 ± 1.1% of SMX, and 84.5 ± 1.7% and 81.5 ± 3.3% of IOX were eliminated from MWW and HWW, respectively. These results endorse the applicability of the developed integrated technology for removing pharmaceutical contaminants from real wastewater.