Engineered nanomaterials display a variable interaction with anoxygenic photoelectrogenic biofilm for pharmaceutical pollutants degradation

Engineered nanomaterials (ENMs) have been reported to facilitate extracellular electron transfer (EET) by increasing the electrical conductivity of electroactive biofilms. However, the mechanisms between different ENMs and anoxygenic photoelectrogenic bacteria for degrading organic pollutants remain unclear. In this study, we investigated the mechanism of metronidazole (MNZ) degradation by different concentrations of carbon nanotubes (CNTs), Iron (III) oxide (Fe3O4) NPs, and titanium dioxide (TiO2) NPs in Rhodopseudomonas palustris based photoelectrogenic biofilms. At low concentrations, CNTs enhanced the electrochemical activity and EET capacity of the biofilm, possibly by increasing the DNA concentration and cellular activity in the cathodic biofilm. However, the ecological toxicity of CNTs at high concentrations damaged the activity of R. palustris, resulting in a decline in the MNZ degradation rate (0.29179 h−1 at 185 μg/L and 0.27801 h−1 at 370 μg/L). A high TiO2 NPs concentration (370 μg/L) significantly boosted the MNZ degradation rate (133 % increase) via photocatalytic activity. But it affected the biofilm activity and EET. Overall, Fe3O4 NPs demonstrated superior performance. At 185 μg/L, the photosynthetic current and MNZ degradation rate increased by 138 % and 142 %, respectively. Despite a slowdown in the utilization rate of Fe (III) and EET at high concentrations, the biofilm exhibited sustained high activity, indicating that Fe3O4 NPs can significantly enhance the metabolism of R. palustris. These findings were not only important for optimizing the performance of anoxygenic photoelectrogenic biofilms but also for regulating the ecological impact of ENMs in natural environments.