Effect and Mechanism of Polyethylene Nanoplastics on Biological Phosphorus Removal and Intracellular Polymers

Polyethylene nanoplastics, as emerging environmental pollutants, have received significant attention due to their toxicity. In this study, we investigated their effects on the performance of biological phosphorus removal and their mechanisms of action on microbial intracellular polymers. The results showed that polyethylene nanoplastics concentrations below 1 mg/L had minimal impact on biological phosphorus removal. However, as the concentration of polyethylene nanoplastics increased, the phosphate concentration in the effluent gradually rose. Analysis of microbial intracellular polymers revealed that the contents of polyphosphate (poly-P), poly-β-hydroxybutyrate (PHB), and glycogen exhibited minor fluctuations at polyethylene nanoplastics concentrations below 1 mg/L. When the polyethylene nanoplastics concentration exceeded 1 mg/L, the synthesis and degradation of both poly-P and PHB were inhibited, whereas those of glycogen were promoted. Fourier transform infrared spectroscopy (FTIR) analysis indicated that low concentrations of polyethylene nanoplastics had negligible effects on the structures of poly-P, PHB, and glycogen. At concentrations ≥10 mg/L, the degree of polymerization of the P–O–P functional groups in poly-P decreases, accompanied by a reduction in chain length; a leftward shift of the C=O peak and decreased transmittance in PHB suggested the occurrence of polyhydroxyvalerate (PHV) polymerization within microbial cells; additionally, the absorption peaks of α- and β-glycosidic bonds in glycogen showed reduced transmittance, accompanied by altered connection modes.