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Revealing How Polyvinyl Chloride Microplastic Physicochemically Affect the Anaerobic Digestion of Waste Activated Sludge
Summary
PVC microplastics in sewage sludge change the surface chemistry of sludge flocs, raising the energy barrier between sludge and the microbes that break it down and causing microbial communities to reorganise. At low concentrations PVC initially increases contact efficiency, but at higher concentrations it coats sludge surfaces and blocks microbial access, ultimately reducing methane production in anaerobic digesters — a finding relevant to the performance and safety of wastewater treatment plants receiving plastic-contaminated sludge.
Recent studies have shown that the microplastics in waste activated sludge (WAS) can directly reduce the microbial activity and influence the performance of anaerobic digestion. Unfortunately, few studies paid attention on the interactions between WAS and MPs, since MPs could impact the contact between sludge flocs and microorganisms. We found that PVC-MP changed the interfacial energy properties of the WAS surface and affected methane production. Low concentration (40 mg/L) of PVC-MP changed the water affinity and greatly reduced the energy barrier of interfacial reaction. Simultaneously, WAS surface charge characteristics changed with increasing MPs concentration, which made the sludge difficult to contact with microorganisms. The change process of WAS surface functional groups also indicated that PVC-MP first cover the sludge surface to prevent from being utilized by microorganisms, and then affect the surface protein structure before toxic substances leaching. Our study provides new insights into how MPs affect anaerobic digestion.