Efficient degradation of venlafaxine using intimately coupled high-active crystal facets exposed TiO2 and biodegradation system: Kinetic studies, biofilm stress behavior and transformation mechanism

Abstract

Intimately coupled photocatalysis and biodegradation (ICPB) system is a potential wastewater treatment technology, of which TiO₂-based ICPB system has been widely studied. There are many ways to improve the degradation efficiency of the ICPB process, but no crystal facet engineering method has been reported yet. In this work, a new ICPB system coated with NaF-TiO₂ exposing high energy facets was designed to degrade biorecalcitrant psychotropic drug - venlafaxine (VNF). Initially, the TiO₂ crystal surface was modified with NaF, resulting in the formation of NaF-TiO₂ with a 14.4% increase in the exposure ratio of (001). The contribution rate of ·OH was increased by 9.5%, and the contribution rate of h⁺ was increased by 33.2%. Next, NaF-TiO₂ was loaded onto the surface of the sponge carrier, and then the ICPB system was constructed after about 15 days of biofilm formation. After the ICPB system was acclimated with VNF, the removal rate of COD decreased significantly (the lowest was 62.7%), but that of ammonia nitrogen remained at 50.5 ± 6.0% and the extracellular polymeric substance (EPS) secretion increased by 84.1 mg/g VSS. According to the high throughput results, at the phylum level, Proteobacteria and Chloroflexi together maintain the nitrogen removal capability and structural stability of the ICPB system. The relative abundance of Bacteroidota was significantly increased by 14.2%, suggesting that there may be some correlation between Bacteroidota and certain metabolites of the anti-depressant active ingredients. At the genus level, the Thauera (3.1%∼11.5%) is the major bacterial group that secretes EPS, protecting biofilm against external influences. Most of the changes in microorganisms are consistent with the decontamination properties and macroscopic appearance of EPS in the ICPB system. Finally, the degradation efficiency of ICPB system for VNF was investigated (92.7 ± 3.8%) and it was mostly through hydroxylation and demethylation pathways, with more small molecular products detected, providing the basis for biological assimilation of VNF. Collectively, the NaF-TiO₂ based ICPB system would be lucrative for the future degradation of venlafaxine.

Keywords: Biofilm; High-active crystal facets; Intimately coupled photocatalysis and biodegradation; Venlafaxine.