Effects of Different Morphologies of PET Microplastics on Anaerobic Digestion of Sewage Sludge
Microplastics in sewage sludge, owing to their diverse physicochemical properties, can differentially affect subsequent anaerobic digestion. This study focused on polyethylene terephthalate (PET) microplastics, systematically investigating the effects of particle (MP), fiber (MF), and film (MPF) morphologies at concentrations of 0–150 mg·g⁻¹ (based on total solids) on sludge digestion performance and microbial community structure. Results showed that MP inhibited total biogas production at all concentrations (inhibition rates 8.16%–9.58%), whereas MF and MPF exhibited low-concentration stimulation and high-concentration inhibition, with MPF exerting stronger inhibition than MF. All MP concentrations induced significant reactive oxygen species (ROS) accumulation (increases of 9.43%–34.52%), indicating the strongest oxidative stress. Low concentrations of PET generally enhanced cell membrane permeability, prompting microbes to secrete different extracellular polymeric substances (EPS) to resist stress. The morphology and concentration of microplastics regulated the relative abundances of key functional bacteria (e.g., proteolytic bacteria and organic acid-oxidizing bacteria) and low-abundance bacteria, ultimately leading to differences in digestion performance. This study provides a theoretical basis for efficient treatment of sludge containing microplastics.