Environmental contamination by per- and polyfluoroalkyl substances (PFASs) is a major public health concern because of the wide range of toxic effects that have been associated with exposure to these persistent chemicals. Due to the strong stability of the C-F bond, very few microorganisms have been found capable of degrading PFASs, and the biodegradation is very slow and incomplete. Often, bioremediation efforts result in the formation of shorter chain PFASs that remain toxic, persistent, and highly mobile in the environment. Current abiotic treatment technologies can be more effective, but have very high energy requirements. Therefore, this research proposes an innovative remediation strategy that couples a pre-treatment step using catalytic hybrid nanomaterials with biodegradation using enriched microbial communities to achieve more efficient and complete destruction of PFASs without the formation of toxic by-products. Multifunctional reduced graphene oxide-metallic nanohybrids (e.g. rGO-nZVI-TiO2) that are capable of catalyzing defluorination and oxidation of PFASs will be synthesized and characterized for their efficiencies in converting highly stable PFASs to more biodegradable forms. Pure cultures (e.g. Dehalococcoides sp. and Dehalobacter sp.) and enriched microbial consortia collected from PFAS-contaminated sites and anaerobic wastewater treatment plants will be used to degrade different types of PFASs and measure their removal efficacy. Using metagenomic and transcriptomic tools, the microorganisms responsible for degradation, their functional characteristics, and the genes being transcribed during defluorination will be identified. By-products formed at each step of the pre-treatment reaction, and during the course of the microbial degradation of PFASs will be characterized using liquid chromatography with high- resolution mass spectrometry, 19F-nuclear magnetic resonance spectroscopy, and ion chromatography to obtain information on the identities of PFASs transformation products, degradation kinetics, and mass balance. Molecular modeling will be used to bring mechanistic insight into specific PFAS-surface and PFAS-enzyme interactions. The effect of the structural features of PFASs (i.e. branching, chain-length, type of head groups) on their biodegradability will be systematically evaluated, first by molecular modeling, and then by experimental validation. Knowledge from the chemical characterization of PFASs degradation by-products combined with in silico site-directed mutagenesis will facilitate the tuning of enzymatic activities and discovery of novel bacteria that are efficient degraders of PFASs from the natural environment. These insights will guide the systematic design of highly efficient nano-enhanced bioremediation systems for complete microbial degradation of PFASs.
Per- and polyfluoroalkyl substances (PFASs) are highly stable and toxic chemicals that can cause adverse human health effects (e.g. increased risk of Type 2 diabetes and liver cancer). The goal of this proposal is to develop a treatment system that combines nanotechnology with microbial degradation to achieve complete destruction of PFASs without the production of toxic byproducts. The fundamental knowledge obtained from this study will provide critical information needed in developing efficient strategies to eliminate deleterious effects of PFAS in the environment.
