Long-term effect of polyethylene microplastics on the bioelectrochemical nitrogen removal process

Nitrogen pollution in wastewater has been considered a worldwide risk to ecosystems. Bioelectrochemical technologies have been developed recently to remove nitrogen. In addition to nitrogen, microplastics, as emergency pollutants in wastewater, could potentially affect nitrogen removal efficiency due to their toxic effects on the activity of microorganisms. This study explored how microplastics would influence nitrogen removal in the bioelectrochemical process. It was found that nitrogen removal declined following the addition of microplastic during a long-term exposure experiment. With exposure to microplastics, the biofilm viability and the content of EPS declined significantly. Microbial community structure shifted significantly following the addition of microplastics. As the most abundant genera and denitrifier, Thiobacillus shrank largely with the addition of microplastics. Moreover, the reduction of the total abundance of the denitrification bacteria and the denitrification-related functional genes was also observed. The results unveil the mechanisms of how microplastics inhibit nitrogen removal and offer insights into the application of bioelectrochemical in nitrogen removal from wastewater rich in microplastic.