Thermal hydrolysis intensifies the targeted inhibition of polyethylene terephthalate microplastics on anaerobic methanogenesis in sludge: Path identification and quantitative mechanism research

Polyethylene terephthalate microplastics (PET MPs) inhibit anaerobic digestion (AD) of waste activated sludge, and thermal hydrolysis (TH) intensifies this inhibition. However, the relative contributions of PET MP-induced transformation pathways remain unquantified. In this study, a quantitative attribution framework was firstly developed by integrating biochemical methane potential assays, microbial community profiling, and variance decomposition analysis. After TH at 170 °C for 60 min, 10 mg/g TS PET MP increased cumulative methane-yield inhibition from 11.68 % to 32.61 %. Inhibition was concentrated in acidogenesis, where the inhibition magnitude was 356.45 % greater than without thermal hydrolysis. Variance decomposition attributed 54 % of total inhibition to additive leaching, 35 % to particle-size reduction, and 11 % to surface-property changes. Leachates detected by GC-MS that dominated by oleanitrile, dibutyl phthalate, and cyclohexasiloxane selectively suppressed acidogenic consortia (Synergistota and Firmicutes) and reduced activities of enzymes central to volatile fatty acid formation, thereby limiting substrate supply to methanogens. Size refinement to nano/submicron plastics amplified oxidative stress and membrane damage in functional bacteria, further reducing methane production. These results establish a quantitative, pathway-resolved basis for understanding PET MP risks in thermal-hydrolysis-coupled AD and provide actionable guidance for monitoring and managing microplastics to protect methane recovery and sustain resource-recovery operations.