Microplastics reshape frozen algal-bacterial granular reactivation: Decoding structural collapse and microbial drivers of nutrient removal

The storage of mature algal-bacterial granular sludge (ABGS) offers a sustainable solution for its large-scale wastewater applications. This study investigates the post-effects of co-existing polyethylene terephthalate, polyvinyl chloride and polyethylene microplastics (MPs) on the reactivation of frozen ABGS, focusing on structural integrity, nutrient removal, and microbial dynamics. Results demonstrated that moderate MPs stress (12 mg/L) enhanced granular compactness, achieving superior nitrogen and phosphorus removal. However, elevated MPs (120 mg/L) deteriorated the systematic stability leading to declined structural integrity and settling capability through suppression of tightly bound extracellular polymeric substances and quenching of protein-like EPS components. Notably, photosynthetic pigments surged by 122 % under moderate MPs, but plummeted at high MPs correlating with suppressed metabolic activity. Microbial profiling linked enhanced nitrogen/phosphorus removal to enriched Nitrospirota and Candidatus Competibacter, while high MPs disrupt the functional consortia. This work pioneers MPs thresholds for ABGS preservation and provides insights for optimizing reactivation in MPs-contaminated environments.