Hydrogen-supported biodefluorination of unsaturated perfluorinated carboxylic acids.
PFMeUPA (i.e., (E)-perfluoro(4-methylpent-2-enoic acid) is a unsaturated perfluorohexanoic acid wtih emerging concern due to its potential to cause developmental toxicity. Here, we investigate the sustainable biological treatment of PFMeUPA under anoxic conditions by delineating batch degradation potential and continuous-flow reactor dynamics using hydrogen (H2) as the sole electron donor. In batch assays inoculated with anaerobic digestion sludge, an enriched hydrogenotrophic consortium achieved near-complete removal of 50 μM PFMeUPA over 90-days with a stoichiometric release of 125 μM fluoride (F-), representing a 26% defluorination extent that corresponds to the cleavage of two C-F bonds per molecule. The continuous-flow H₂-based membrane biofilm reactor (MBfR) harboring this enriched anaerobic biofilm was operated for 130 days, achieving 100% removal of 5 μM PFMeUPA and 20% of defluorination at a hydraulic retention time (HRT) = 6 h. Transformation product identification using high-resolution mass spectrometry suggests dominance of reductive defluorination and a shift toward hydrogenated byproducts at later stages. Metagenomic results indicate the enrichment of microbial taxa including Hydrogenophaga (hp_bin.22) and and Azonexus (hp_bin.19) genomes, which carry genes for hydrogen metabolism (hoxH) and fluoride efflux pumps (crcB). This work demonstrates the feasibility of hydrogen-supported biological treatment for unsaturated perfluorinated carboxylic acids from contaminated water. SYNOPSIS: We demonstrate reductive defluorination of branched PFAS by a H2-fed biofilm, with co-occurring hydrogenase and fluoride exporter genes in Hydrogenophaga and Azonexus as potential biodefluorination biomarkers.