Abstract
Anaerobic digestion (AD) is a reducing environment with high microbial diversity and potential for biotransformation of PFAS. Yet, their fate and impact on the microbial community remains poorly understood. This study evaluated the long-term impact (100 d) of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) spiked at10 mg/L (low) and 100 mg/L (high), respectively. Although resilient to complete system failure, high PFAS concentrations disrupted AD, evidenced by 25-50 % reduction in methane content, 45 -48 % reduction in cumulative biogas production, and accumulation of butyric acid. No significant decrease in PFAS concentration was observed in the liquid fraction after 100 d relative to the kill controls, indicating PFAS adsorption behavior. However, PFAS concentrations were temporally variable. Microbial community analysis revealed enrichment of notable AD groups, such as Firmicutes, Synergistetes, and Methanomassillicoccus phyla in high PFAS reactors, which underscores the potential for the microbiome adaptation and informs future strategies for PFAS-contaminated sludge treatment.