Concentration-dependent effects of polystyrene microplastics on methanogenic activity and microbial community shifts in sewer sediment

Microplastics (MPs) are emerging environmental contaminants that interfere with microbial processes, yet their effects on methanogenesis in anaerobic systems remain insufficiently understood. This study investigates the impact of polystyrene microplastics (PS-MPs) on methanogenesis, microbial community structure, and metabolic pathways in simulated sewer sediment systems, with exposure concentrations of 5, 50, and 250 mg·L⁻¹. The results revealed a concentration-dependent effect of PS-MPs on methanogenesis: a 222.2 % increase at 5 mg·L⁻¹, and 72.2 % and 88.9 % increases at 50 mg·L⁻¹ and 250 mg·L⁻¹, respectively, indicating a non-linear response. PS-MPs exposure enhanced coenzyme F420 (F420) activity, a key indicator of methanogenic activity, but also inhibited methyl coenzyme M reductase (Mcr), disrupting critical methanogenic pathways. At lower concentrations, PS-MPs promoted the abundance of hydrogenotrophic methanogens, whereas higher concentrations suppressed overall methanogenic activity. Furthermore, PS-MPs had a dose-dependent effect on CH₄ oxidation, influencing the structure of methanotrophic communities. These findings establish a clear dose–response relationship between PS-MPs concentration and CH₄ dynamics in anaerobic systems, highlighting the complex role of microplastics in methanogenesis and microbial interactions. This research provides valuable insights into the environmental implications of microplastics in wastewater systems and their potential impacts on biogas production and CH₄ mitigation, aligning with the objectives of environmental bioengineering and sustainable waste management.