A review of microplastics stress on nitrogen conversion and nitrous oxide emissions from biological wastewater treatment: Efficiency, mechanism and prospects

Microplastics, as an emerging pollutant ubiquitous in aquatic systems, are commonly detected in wastewater treatment plants. They not only pose risks to human health but also impact nitrogen cycling and nitrous oxide (NO) emissions. In recent years, research on the interaction between microplastics and nitrogen has gained considerable attention. However, comprehensive analysis on the overall influence of microplastics on emissions of the potent greenhouse gas NO during wastewater treatment are still limited, with knowledge gaps remaining-particularly in elucidating the underlying mechanisms and regulatory processes. This review aims to synthesize and discuss the effects of microplastics on nitrogen cycling and NO emissions in wastewater treatment systems. It was summarized current research findings and provided an in-depth examination of the mechanisms by which microplastics affect nitrogen transformation, identifying key enzymes, functional microorganisms, and genes as the main factors influencing these processes. Furthermore, integrated strategies for regulating nitrogen cycling and NO emissions were suggested, including physicochemical methods, biochemical approaches, operational parameter adjustment, and the integration of machine learning with modeling simulations. This review offered new insights into the reduction of greenhouse gases in the biological treatment of wastewater containing microplastics, and aims to promote its development in engineering applications.