Effect mechanism of polyethylene nanoplastics on biological phosphorus removal and microbial extracellular polymers

Polyethylene nanoplastics (PE-NPs) are emerging wastewater contaminants that may disrupt biological phosphorus removal (BPR). To assess their effects on BPR, experiments with PE-NPs at 0-20 mg/L were conducted. With increasing PE-NPs, phosphorus removal declined from 96.16% to 83.97% and effluent COD increased from approximately 20-43.04 mg/L. At 20 mg/L PE-NPs, anaerobic PHA synthesis and aerobic PHA consumption were measured at 83.19% and 82.74% of the control values, respectively. Total EPS dropped from 136.78 to 118.26 mg/g MLVSS alongside a minor increase in the PN/PS ratio, and intracellular ROS levels reached about 128% of those in the control. Fluorescence excitation-emission matrix and Fourier-transform infrared spectroscopy analyses indicated a reduction in aromatic protein and microbial by-product signals, alterations in N-H/O-H and amide-I hydrogen bonding environments, and a shift in EPS protein conformation from α-helix to β-sheet/aggregate-rich structures. High-throughput sequencing revealed a microbial community shift, marked by a decrease in phosphorus-accumulating organisms (PAOs, e.g., <i>Acinetobacter</i> and <i>Candidatus Accumulibacter</i>) and an increase in glycogen-accumulating organisms (GAOs, notably <i>Candidatus Competibacter</i>). This shift intensified carbon competition, limiting PAOs energy storage and phosphate uptake. These combined effects-oxidative stress, altered EPS, and microbial shift-decouple carbon-phosphorus metabolism, accelerating BPR deterioration.