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Reactor performance and microbial responses of sulfate-reducing bacteria sludge under stepwise polyvinyl chloride microplastic exposure
Summary
Scientists tested how tiny PVC plastic particles (the kind found in some plastic products) affect bacteria used in wastewater treatment plants to clean up sulfate-polluted water. They found that at high microplastic levels, the treatment process temporarily struggled but bounced back as bacteria adapted, though the plastic also caused mild cell stress and released chemical additives like BPA (a compound linked to hormone disruption in humans). This matters because it shows that microplastic pollution could disrupt the wastewater treatment systems we rely on to keep our water clean, and it may also release additional harmful chemicals into the environ
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.