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Revealing the Mechanisms of Polyethylene Microplastics Affecting Anaerobic Digestion of Waste Activated Sludge
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Researchers studied how polyethylene microplastics affect the anaerobic digestion of sewage sludge, a common wastewater treatment process. They found that higher concentrations of microplastics significantly reduced methane production by disrupting microbial communities and enzyme activities essential for digestion. The study reveals that microplastic contamination in wastewater systems can undermine the efficiency of sludge treatment and biogas generation.
Polyethylene (PE) microplastics retained in sewage sludge inevitably enter the anaerobic digestion system. To date, no information has been reported on the mechanisms of PE microplastics affecting anaerobic digestion of waste activated sludge (WAS). This study evaluated the mechanisms using batch and continuous tests. Short exposure to PE microplastics at lower levels (i.e., 10, 30, and 60 particles/g-TS) did not significantly affect the methane production, but higher levels of PE microplastics (i.e., 100 and 200 particles/g TS) significantly (P = 0.006 and 0.0003) decreased methane production by 12.4-27.5%, with a lower methane potential and hydrolysis coefficient. In continuous test over 130 days, feeding WAS with 200 particles PE microplastics/g TS decreased vs destruction by up to 27.3% (P = 2.18 × 10-18) and resulted in a 9.1% (P = 0.002) increase in the volume of digested sludge for disposal. Correspondingly, the microbial community was shifted in the direction against anaerobic digestion. A mechanisms study revealed that the negative effect of PE microplastics was likely attributed to the induction of reactive oxygen species (ROS) rather than the released acetyl tri-n-butyl citrate. The generation of ROS caused a 7.6-15.4% reduction of cell viability, thereby restraining sludge hydrolysis, acidification, and methanogenesis.
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