Reactor performance and microbial responses of sulfate-reducing bacteria sludge under stepwise polyvinyl chloride...

Plastic pollution, particularly microplastic contamination, poses potential risks to biological wastewater treatment processes. However, the response of sulfate-reducing bacteria (SRB) sludge systems to polyvinyl chloride (PVC) microplastics remains poorly understood. In this study, a laboratory-scale sulfate-reducing up-flow sludge bed (SRUSB) reactor was operated under stepwise PVC microplastic exposure at 0, 20, 100, and 500 particles/L. COD removal and sulfate reduction showed limited changes at 20 and 100 particles/L, whereas 500 particles/L caused transient inhibition followed by gradual recovery within the same reactor. PVC exposure increased intracellular reactive oxygen species (ROS) levels and lactate dehydrogenase (LDH) release, while live/dead staining indicated no marked increase in cell mortality across the operational stages. Stepwise PVC exposure was also accompanied by enrichment of protein-rich loosely bound extracellular polymeric substances (LB-EPS) and accumulation of PVC-derived additives, including BPA and ATBC. Microbial community analysis showed that the relative abundance of SRB-related genera increased from 8.7% to 24.9%, mainly involving increased abundances of Desulfobacter, Desulfococcus, and Desulforhabdus. Metagenomic annotation further revealed genes associated with EPS precursor supply, polysaccharide assembly/export, protein secretion, antioxidant response, aromatic metabolism, ester-bond hydrolysis, and dissimilatory sulfate reduction. Overall, this study provides a longitudinal characterization of reactor performance and associated physiological, chemical, microbial, and community-level genetic responses of SRB sludge under stepwise PVC microplastic exposure, offering useful insights for evaluating sulfate-reducing saline wastewater treatment systems facing microplastic contamination.