The impacts of ZnO/g-C3N4/Fe3O4-mediated photocatalytic degradation products of norfloxacin on Chlorella vulgaris in a photocatalyst-microalgae synergistic system

Norfloxacin (NFX) is a widely used antibiotic that poses a persistent threat to aquatic ecosystems. The combination of photocatalysis and microalgae has emerged as a promising strategy for antibiotic removal. However, current research predominantly focuses on optimizing photocatalytic conditions and overall system efficiency, often neglecting the dynamic physiological state of microalgae when exposed to the photocatalytic degradation products of NFX (PDPN), which is the mixture of intermediates after 2 h ZGF photocatalysis of 8 mg/L NFX. This study constructed a synergistic degradation system employing a ZnO/g-C 3 N 4 /Fe 3 O 4 (ZGF) composite photocatalyst and Chlorella vulgaris for PDPN removal. Within this synergistic system, our primary focus was on the microalgal activity when cultured in a medium prepared from the PDPN. The results indicated the degradation rate of PDPN reached 82.1% in the synergistic degradation system. Transcriptomic analysis revealed that microalgae exhibited enhanced adaptability to these products, which were generated from ZGF photocatalytic pre-treatment of NFX. Key functional categories, including catalytic activity, oxidoreductase activity, and cytochrome P450 drug metabolism were significantly upregulated. This study indicates that the ZGF/microalgae system simultaneously achieves efficient pollutant degradation and maintains high metabolic potential as revealed by transcriptomic profiling, providing crucial insights for developing stable and sustainable bioremediation technologies.