Response of biofilm structure to long-term exposure to CeO2 nanoparticles in a trickling bioreactor for the removal of phenol, nitrogen, and phosphorus

The long-term exposure of cerium oxide nanoparticles (CeO₂ NPs) at 5, 20, and 50 mg/L to the biofilm and its impact on the treatment of synthetic wastewater, containing phenol, in a trickling bioreactor (TBR) were examined. An increase of 38.1 % in the reactive oxygen species (ROS) production and 29.0 % in the lactate dehydrogenase (LDH) release indicated that CeO₂ NPs were toxic to the microorganisms at 50 mg/L and disrupted the integrity of the microbial membrane within the community. Phenol biodegradation, total nitrogen (TN), and total phosphorus (TP) removal slightly changed from 98.6, 53.7, and 13.0 % in the absence of NPs to respectively 96.5, 49.7, and 9.0 % in the presence of 50 mg/L CeO₂ NPs. High-throughput sequencing after prolonged 30-day exposure to CeO₂ NPs showed that the microbial community could self-regulate the population by adjusting species composition in response to the presence of NPs. The relative abundance of some sensitive species such as Castellaniella defragrans declined from 39.5 to 0.6 % in the presence of NPs. However, other species such as Comamonadaceae bacterium thrived and became more prevalent. The TBR effectively removed phenol, TN, and TP in the presence of CeO₂ NPs, benefiting from the cells immobilization that limited the access of NPs to the deep layers of biofilm.