Impact of Tire Microplastics on Aerobic Granular Sludge Structure and EPS Composition Under Continuous and Intermittent Aeration

Tire microplastics (TMPs) are a widespread pollutant with growing concern due to their diverse sources, persistence, and potential risks to the environment and human health. This study investigated the impact of TMPs (50–500 mg/L) on the sludge structure, activity, and extracellular polymeric substance (EPS) dynamics in granular sequencing batch reactors (GSBRs) under continuous aeration (CA) and intermittent aeration (IA) conditions. Increased TMP concentration reduced granule size and increased the specific surface area under CA, but under IA, it increased granule size and lowered specific surface area. Total EPS declined as TMP concentration increased in both aeration regimes, but the reduction was more pronounced under CA. Protein levels in the soluble EPS fraction were consistently higher during IA than CA across all GSBRs. Aeration regimes had contrasting effects on EPS polysaccharides, as TMP dose increased; polysaccharide content increased during IA and decreased during CA. During CA, TMP presence enhanced dehydrogenase activity to over five times that of the control, while during IA, activity remained stable despite TMP addition. Overall, biomass under IA showed greater tolerance to TMP stress than CA, as evidenced by enhanced granulation, stable dehydrogenase activity, and preserved EPS.