When polyethylene terephthalate microplastics meet Perfluorooctane sulfonate in thermophilic biogas upgrading system: Their effect on methanogenesis

Microplastics (MPs) and Perfluorooctane sulfonate (PFOS) are two hard -biodegradable pollutants widely existing in the waste streams treated by anaerobic digestion. However, their synergistic effect on methanogenic metabolism is still unknown. This study investigated the impact of polyethylene terephthalate (PET) MPs alone and co -existing with PFOS on CO2 conversion to CH4 in a thermophilic biogas upgrading system. The results showed that either PET MPs addition alone or coexisting with PFOS improved the ultimate CH4 percentage and increased CO2 utilization rate. When Fe0 was added into the reactors with PET to enhance the interspecies electron transfer, a potential defluorination was observed with a defluorination rate of 15.88 +/- 1.53%. Exposure of the reactor to PFOS of 300 mu g/L could change the methanogenic pathway, resulting in a newly emerged Methanomassiliicoccus with dominance of 16%. Furthermore, under the exposure of PFOS, the number of predicted genes regulating enzymes in methanogenic steps from CO2 increased. These results suggest that the co -existence of PET MPs and PFOS will not inhibit the activity of hydrotrophic methanogenes, and a portion of PFOS may be biodegraded during the methanogenesis under Fe0 regulation.