Deciphering the inhibitory mechanisms of polystyrene microplastics on thermophilic methanogens from the insights of microbial metabolite profiling and metagenomic analyses

Abstract

Due to the utilization of food packaging bags, a substantial amount of polystyrene microplastics (PS MPs) are introduced into the food waste (FW) treatment system during the pre-treatment process, potentially impacting the subsequent biochemical treatment system. In order to investigate the mechanism by which PS MPs affect anaerobic methanogenesis metabolism in thermophilic condition, this study analyzed the characteristics of methanogenesis in thermophilic anaerobic digestion (AD) of FW under different concentrations of PS MPs (100 μm, 10–200 mg/L). The results revealed a negative correlation between PS MPs concentration and methane (CH₄) yield from FW. When the concentration of PS MPs reached 200 mg/L, CH₄ yield decreased by 47.8 %. Further mechanistic investigations revealed that while the presence of PS MPs at lower concentrations could alleviate its adverse impact on methanogenesis by enhancing EPS content, the accumulation of reactive oxygen species (ROS) persisted with increasing PS MPs concentration, thereby inhibiting the activities of key enzymes involved in solubilization and acidification metabolisms (e.g., acetate kinase and F420). Metagenomics analysis indicated that the presence of PS MPs down-regulate abundance of genes for quorum sensing and CH₄ metabolism pathways. These findings not only unveil potential detrimental effects of PS MPs on AD systems but also provide novel insights into comprehending and controlling the impact of MPs pollution on environmental preservation and energy recovery processes.