Effects of Different Morphologies of PET Microplastics on Anaerobic Digestion of Sewage Sludge

• • MP inhibited total biogas production by 8.16%–9.58% across all tested concentrations (15–150 mg·g⁻¹ TS), whereas MF and MPF showed stimulation at 15–30 mg·g⁻¹ and inhibition at 75–150 mg·g⁻¹, with MPF exhibiting stronger inhibition than MF. • • MP induced the highest ROS accumulation, with increases of 9.43%–34.52% over control, indicating the most severe oxidative stress to anaerobic microbes. • • Low concentrations (15–30 mg·g⁻¹) of all PET morphologies increased cell membrane permeability, as evidenced by elevated extracellular LDH activity, and triggered differential EPS secretion (polysaccharides vs. proteins) as a protective response. • • PET morphology and concentration reshaped microbial community structure by altering the relative abundances of proteolytic bacteria, organic acid-oxidizing bacteria, and low-abundance taxa, which directly correlated with observed digestion performance variations.