Functional role of mixed-culture microbe in photocatalysis coupled with biodegradation: Total organic carbon removal of ciprofloxacin

Ciprofloxacin is an extensively used fluoroquinolone antibiotic, which exists in aquatic environment, causing detrimental effects to the aquatic ecosystem and thus, indirectly to humans. Thus, an efficient and rapid removal method for ciprofloxacin is urgently needed. Intimately coupled photocatalysis and biodegradation has proven to be highly efficient, low-cost, and eco-friendly. In this study, cube polyurethane sponges modified with visible light-responsive g-C3N4 and mixed culture microbes were used to increase the ciprofloxacin removal efficiency. Subsequently, 94% of ciprofloxacin was removed by photocatalytic-biodegradation and 12 degradation products and possible degradation pathways were analyzed. Photocatalytic-biodegradation had a 1.57 times higher total organic carbon (TOC) removal rate than photocatalytic degradation. The microbial community structure after 72 h of photocatalytic biodegradation was examined. High microbial richness, evenness, and functional dominant species belong to Proteobacteria, which were closely associated with the utilization of antibiotics, may be majorly responsible for the highly efficient removal degradation process. Additionally, microbes retarded the interaction of photogenerated electrons and holes, which may contribute to the increasing mineralization. The findings demonstrated the potential ability of photocatalytic biodegradation in degrading bio-recalcitrant compounds and provide new insights into photocatalytic coupled with biodegradation for removal of ciprofloxacin.