Feasibility study of novel dual-step process combining physical and biological methods for long-chain PFAS degradation
Date
2021
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
To date, there are no standalone chemical, biological, or physical processes known to completely mineralize per- and poly-fluoroalkyl substances (PFASs). With military and industrial stockpiles of PFAS-containing coatings and firefighting foams and industrial usage of PFASs still allowed, there are needs for both environmental and industrial remediation of PFAS pollution. The current methods for directly removing PFASs from environmental samples do not effectively degrade them. These methods can also be extremely costly and be needed in perpetuity when PFAS sources are not remediated or removed. In this project, we intended to determine the feasibility of a dual step process combining, in series, physical and biological degradation of long-chain PFASs to smaller, innocuous products. Our proposed method would use inexpensive materials and be scalable to an industrial magnitude, allowing for availability to a greater population. The physical degradation step of this project determined the feasibility of synthesizing aluminum nanoparticles at diameters sub-100 nm and using them as conduits of energy via light activation to break bonds within long-chain PFASs. The goal was to break apart long-chain PFASs into smaller fluorinated molecules. These smaller molecules, which would likely be more easily utilized by bacteria, would then be fed to microbes enriched from environments known to be contaminated with PFASs in the hopes of continuing the degradation process. This method, if successful, could be applied to degradation of concentrated stockpiles of PFASs, as well as potential side streams to current water treatment processes. ☐ Working with experts in the University of Delaware Nanofabrication Facility, we generated aluminum nanoparticles in organized arrays with consistent diameters and shape. Chapter 2 delves into the process by which this synthesis was performed, as well as the use of the nanoparticles through light activation for potential degradation of PFOA (the long-chain PFAS studied in this project). While the data from the first round of nanoparticle experiments was not entirely conclusive due to insufficient replicate measurements, there appeared to be lower PFOA concentrations in samples using the nanoparticles compared to the negative and positive controls. This loss of PFOA over the course of the experiments indicated potential degradation of the long-chain PFAS. ☐ Microbial interactions with PFASs were also studied in this project. We used PFAS growth media enriched with samples from PFAS-contaminated environments to grow microbial cultures in search of potential microbes or communities able to utilize and degrade shorter-chain PFASs. While we saw growth in all enrichment cultures and on agar plates containing PFASs as the only added carbon sources, we were unable to culture isolates able to grow on only the studied PFASs. However, the robust growth of a variety of colonies on all PFASs used indicated the potential for microbial growth on PFASs. ☐ While the microbial enrichments were used to search for microbes able to degrade PFASs, we also wanted to determine the effect that PFASs would have on growth of model microbes. Through growth experiments outlined in Chapter 4, we found that PFASs do not appear to inhibit growth of E. coli or Bacillus velezensis, representative of Gram negative and Gram positive bacteria, respectively.
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Keywords
Degradation, Nanoparticles, PFAS, PFOA, Water treatment