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The impact of microplastics and nanoplastics on biological nitrogen removal processes: Exacerbating the greenhouse effect
Summary
This review examines how microplastics and nanoplastics accumulate in wastewater treatment plants and interfere with the biological processes that remove nitrogen from water. The disruption leads to increased emissions of nitrous oxide, a powerful greenhouse gas, making the problem both an environmental health concern and a climate issue. The findings suggest that microplastic contamination in wastewater is undermining treatment effectiveness while simultaneously contributing to global warming.
The widespread presence of microplastics/nanoplastics (MPs/NPs) in various environments poses a significant threat to the ecological environment. Wastewater treatment plants (WWTPs) serve as significant reservoirs of MPs/NPs, wherein a substantial quantity of these are adsorbed by activated sludge in the biological treatment system and continuously accumulated, thereby jeopardizing the stable operation of biological nitrogen removal (BNR) processes. Consequently, it is imperative to comprehensively summarize the impacts of MPs/NPs on BNR process performance and elucidate their underlying mechanisms of action. This review paper provides an overview of the sources and types of MPs/NPs found in WWTPs, examines their effects on different BNR processes, and summarizes several inhibition mechanisms associated with MPs/NPs exposure. The findings indicate that the inhibitory effect exerted by MPs/NPs on BNR processes is closely correlated with their polymer type, size, concentration, and duration of exposure. Anaerobic ammonium oxidation processes exhibit higher sensitivity towards MP/NP exposure. Furthermore, analysis reveals that MPs/NPs influence microbial activity through protein secretion inhibition, competition for substrate adsorption sites, obstruction of substrate transport channels, attenuation of extracellular electron transfer processes, and induction of reactive oxygen species production. Additionally, MPs/NPs will expedite the migration of toxic and deleterious substances, such as heavy metals and antibiotics, towards microbes. Finally, molecular docking simulation experiments demonstrate that PS-MPs exhibit superior binding energy with key enzymes involved in nitrogen removal functionality. Nor functional enzymes display high binding energy levels when interacting with diverse types of MPs. The presence of MPs/NPs leads to accumulation of NO and NO, greatly exacerbating the greenhouse effect. The article offers new insights into the impact of MPs/NPs on BNR process and lays the groundwork for developing strategies to mitigate this impact.