Degradation mechanisms and microbial community analysis of cefalexin in the intimately coupled photocatalytic and biodegradation system

The widespread contamination of the aquatic environment by cefalexin (CEX) has attracted extensive attention. Intimately coupled photocatalysis and biodegradation (ICPB) is considered as a promising green technology that provides a new approach for the degradation of this pollutant. Using TiO2 with high active {001} crystal facets exposed as photocatalyst and activated sludge as microbial inoculation source, we successfully constructed the ICPB system for the treatment of cefalexin wastewater. The results demonstrated that ICPB could accomplish rapid and stable contaminant degradation when using various concentrations of CEX to domesticate ICPB system and single biofilm system, which was superior to single biodegradation. The contributions of CEX removal in the ICPB system were photocatalytic (PC), bio-degradation (B), photolysis (P) and adsorption of the carrier (AD) in descending order. UPLC-MS analysis indicated that the ICPB system could convert contaminants into small molecules for microbial utilization or complete mineralization. Microbial community analysis revealed that the abundance of diverse bacteria in the ICPB system changed significantly after CEX addition. Proteobacteria, Firmicutes and Bacteroidetes gradually be-came the dominant genera and could deeply mineralize and utilize CEX as well as its intermediates. This study provides a new strategy for the effective treatment of antibiotic-contaminated domestic wastewater. (c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).