There has been very limited knowledge on the biodegradation of per-polyfluoroalkyl substances (PFAS), particularly the C−F bond cleavage from the perfluoroalkyl acids (PFAAs). The main objectives of this project are to: (1) construct and characterize reductive defluorinating enrichments from a dechlorinating microbial community, (2) identify the defluorinating microorganisms/genes, (3) elucidate structure specificity of the defluorinating microorganisms and the pathways of defluorination and biotransformation of PFAS, and (4) examine the potential of biological treatment combined with chemical treatment as a treatment train to efficiently and cost-effectively treat aqueous film forming foam (AFFF)-impacted water.

Complete decay and significant defluorination of a series of branched and unsaturated PFAAs in an anaerobic microbial community capable of reductive dichlorination has been observed. However, the microorganisms responsible for PFAA degradation were not the known dominant dechlorinating bacteria Dehalococcoides in this community. In this project, PFAA-defluorinating microorganisms from this community will be enriched and the physiological characteristics of the enrichments, such as defluorination rates, suitable electron donor types, and the effect of corrinoid cofactors and methanogenic activities will be determined. Using omics tools and anaerobic isolation techniques, the PFAA-defluorinating microorganisms and the key functional genes from the enrichments will be identified. The substrate specificity and structure-activity relationships of the defluorinating microorganisms will be examined using LC-High Resolution MS/MS and the underlying biotransformation mechanisms and pathways will be disentangled using the molecular and analytical tools. Also, adaptive evolution will be conducted to obtain acclimated enrichments and/or microorganisms capable of defluorinating more structurally diverse PFAAs, particularly those typically found in AFFF-impacted environments. Additionally, the potential of the defluorinating microbial communities to achieve cost-effective defluorination of AFFF-impacted water in combination with other treatment approaches, such as chemical oxidation and/or reduction, will be tested.

The results of this project will benefit DoD and the scientific community by: (1) advancing the knowledge on the phylogenetic and physiological characteristics of anaerobically defluorinating microorganisms, their distribution in natural and engineered environments, as well as the potential and limitation of microbial cleavage of C−F bonds under anaerobic conditions; (2) serving as a fundamental basis leading to more cost-effective ex situ and/or in situ biological treatment or treatment train systems, which will significantly contribute to DoD’s management and remediation of AFFF-impacted sites; and (3) providing valuable insights on the design of readily biodegradable fluorinated surfactants for enhanced environmental sustainability and green chemistry of the development of future fluorochemicals.