Insights into the microbial response of anaerobic granular sludge during long-term exposure to polyethylene terephthalate microplastics.

The negative effects of ubiquitous microplastics on wastewater treatment have attracted increasing attention. However, the potential impacts of microplastics on anaerobic granular sludge (AGS) remain unknown. To fill this knowledge gap, this paper investigated the response of AGS to the exposure of model microplastics (polyethylene terephthalate (PET-MPs)) and provided insights into the mechanisms involved. The 84 days' long-term exposure experiments demonstrated that PET-MPs, at relatively low level (15 MP L−1) did not affect AGS performance during anaerobic wastewater treatment, while 75–300 MP L−1 of PET-MPs caused the decreases of COD removal efficiency and methane yields by 17.4–30.4% and 17.2–28.4%, accompanied with the 119.4–227.8% increase in short-chain fatty acid (SCFA) accumulation and particle breakage. Extracellular polymeric substances (EPS) analysis showed that dosage-dependent tolerance of AGS to PET-MPs was attributed to the induced EPS producing protection role, but PET-MPs at higher concentrations (75–300 MP L−1) suppressed EPS generation. Correspondingly, microbial community analysis revealed that the populations of key acidogens (e.g., Levilinea sp.) and methanogens (e.g., Methanosaeta sp.) decreased after long-term exposure to PET-MPs. Assessment of the toxicity of PET-MPs revealed that the leached di-n-butyl phthalate (DBP) and the induced reactive oxygen species (ROS) by PET-MPs were causing toxicity towards AGS, confirmed by the increases in cell mortality and lactate dehydrogenase (LDH) release. These results provide novel insights into the ecological risk assessment of microplastics in anaerobic wastewater treatment system. Image 1 • Long-term exposure of PET microplastics decreased AGS performance in anaerobic wastewater treatment. • PET microplastics inhibited AGS ability and EPS secretion, causing granule breakage. • Populations of key acidogens and methanogens reduced after the exposure of PET microplastics. • PET microplastics carried on their toxic effect mainly through the leaching DBP and excess oxidative stress. [ABSTRACT FROM AUTHOR]