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System-dependent effects and mechanisms of microplastics/nanoplastics on nitrogen and phosphorus removal from wastewater treatment and N2O emission
Summary
Researchers reviewed the system-dependent effects of microplastics and nanoplastics on nitrogen and phosphorus removal efficiency across various wastewater treatment systems, including activated sludge, constructed wetlands, and membrane bioreactors. The study found that these plastic particles also impact nitrous oxide emissions, with effects varying significantly depending on the treatment technology used.
The pervasive presence of microplastics/nanoplastics (MNPs) threatens the efficiency of nitrogen (N) and phosphorus (P) removal and impacts nitrous oxide (N₂O) emissions in wastewater treatment plants. However, the current understanding of their impacts across different treatment systems remains limited. This review evaluates the effects of MNPs on N and P removal and NO emissions across various treatment systems, including activated sludge, constructed wetlands, granular sludge, membrane bioreactors, biofilm, and bioelectrochemical systems. The results demonstrated that MNPs toxicity is governed by polymer type, size, concentration, and exposure duration. Nanoplastics exhibit greater toxicity than microplastics, and the risks posed by non-biodegradable plastics differ markedly from those of biodegradable plastics. Compared to nitrification and phosphorus removal, denitrification shows higher sensitivity under MNPs exposure. These impacts are primarily mediated via alterations in extracellular polymeric substances, microbial enzyme activity, oxidative stress levels, and community structure induced by MNPs. Future studies should integrate realistic multi-pollutant exposure, long-term monitoring, multi-omics, isotope tracing, and machine learning to decipher mechanisms and predict outcomes. This work provides critical insights for developing strategies to maintain treatment performance and reduce N₂O emissions under escalating MNPs pollution.