Quorum sensing involved in regulating biological phosphorus removal under two different addition modes of polystyrene microplastics

Microplastics (MPs) impair wastewater treatment by lowering pollutant removal and accumulating in systems, yet their effects on microbial metabolic interactions remain largely unexplored. This study investigated the effects of polystyrene MPs (PS-MPs) on granular sludge and elucidated the effects of quorum sensing (QS) across two modes of low-dose chronic addition and high-dose acute addition. Using sequencing batch reactors, changes in phosphorus removal, extracellular polymeric substances (EPS), QS molecules, and microbial community, and key genes were monitored. Results showed that, under continuous exposure to 10 mg/L and acute exposure to 100 mg/L PS-MPs, anaerobic phosphorus release decreased from 16.91 mg/L to 7.72 mg/L and from 10.92 mg/L to 5.54 mg/L, respectively. Concurrently, phosphorus removal efficiency dropped from 87.52% to 53.83% and from 88.17% to 58.14%, respectively. Notably, continuous dosing with 10 mg/L PS-MPs led to more persistent inhibition of phosphorus metabolism. EPS of granular sludge increased steadily from 85.18 to 145.59 mg/g SS in the 10 mg/L group, whereas acute dosing with 100 mg/L PS-MPs has no significant effect on EPS. Microbial community indicated that chronic exposure decreased the abundance of the dominant community polyphosphate-accumulating organisms (PAOs) and increased the species diversity, confirming that PS-MPs affect community structure related to phosphorus removal and EPS. A strong positive correlation was observed between QS molecules (C8-HSL and 3OC8-HSL) and EPS components, particularly polysaccharides (PS) and proteins (PN) (P < 0.05). Metatranscriptomic analysis further revealed that continuous exposure to 10 mg/L PS-MPs can increase EPS secretion and inhibit carbon-phosphorus metabolisms of dominant community PAOs through phbB, ppk and ppx. These findings offer the novel insights for sustaining phosphorus removal and enhancing resilience against the different exposure mode of MPs.