Thermally aged PET microplastics disrupt methanogenic syntrophy via toxic leachates: Microbial assembly dynamics unravel biotoxicity in anaerobic digestion

Thermally aging processes for microplastics (MPs) in organic waste commonly occur before anaerobic digestion (AD), potentially influencing microbial community assembly differently compared to primal MPs. In this study, polyethylene terephthalate (PET) MPs were thermally aged under laboratory conditions. Subsequently, morphological analysis, identification of released ingredients, and toxicity assessments for both primal and thermally aged MPs within a biogas upgrading system. The results demonstrated that at a concentration of 60 mg/L, the ultimate CH₄ percentage of upgraded biogas decreased by 2.31 % and 3.43 % after aging durations of 15 and 30 days, respectively, compared to primal PET MPs. Following thermal aging, the reactive oxygen species (ROS) levels in the medium increased, and plasticizer extract of 2,4-Di-tert-butylphenol (DTBP) interacted with the acetyl-CoA decarbonylase/synthase (ACDS), CODH/ACS complex β subunit, which negatively impacted the activity of methanogenic metabolism. Microbial community assembly analysis revealed that the dominant methanogenic syntrophy shifted from acetoclastic to hydrogenotrophic methanogenesis when thermally aged MPs replaced primal MPs. These findings enhance our understanding of how MPs influence microbial metabolism under anaerobic condition, particularly regarding methanogenesis.