Chemical Decomposition Combined with Physical Adsorption for the Treatment of Investigation-Derived Waste Containing PFASs
Hyeok Choi | The University of Texas at Arlington
This proof-of-concept study will develop innovative approaches for treatment of per- and polyfluoroalkyl substances (PFASs) in investigation-derived waste (IDW). Considering the heterogeneous nature of components in IDW and the presence of PFASs and many other co-contaminants with different chemical reactivities and affinities, combining multiple treatment technologies known to be effective for various contaminants might be needed to address the chemical stability of PFASs and the real-world complexities of treating IDW. In particular, physical adsorption ensures a fail-less approach while chemical decomposition means a destructive method. Most importantly, PFASs, once defluorinated via initial reductive defluorination, become much more vulnerable to chemical oxidation in subsequent steps.
The overall objective of this project is to integrate various effective treatment technologies, including physical adsorption, advanced oxidation, and reductive defluorination, into one engineered system to synergistically remove and degrade PFASs in IDW under ambient conditions. This project will determine whether the integrated system is effective to physically adsorb and chemically decompose PFASs and other co-contaminants in IDW enough for safe disposal and release of the treated IDW.
To decompose PFASs (and potentially co-contaminants later) in IDW effectively, this work will investigate the use of an engineered system that combines advanced oxidation technologies with reductive defluorination methods. Such an integrated system can synergistically harness the two complementary chemical approaches and overcome their limitations. Highly segregated nanoscale zerovalent iron (nZVI) will be coupled with common oxidants such as hydrogen peroxide, persulfate, and peroxymonosulfate, where electrons, hydrogens, and superoxide radical anions generated in situ function as strong reducing species while simultaneously hydroxyl radicals and sulfate radicals serve as strong oxidizing species. The integrated system will leverage various decomposition pathways and routes to reductively cleave C−F bonds, which then undergo subsequent downstream oxidation, eventually mineralizing PFASs. In addition, the chemical decomposition of PFASs will be combined with their physical adsorption by utilizing nZVI impregnated into the porous structure of granular activated carbon, so-called reactive activated carbon (RAC). Considering (i) activated carbon is effective for adsorption of PFASs; (ii) reductive defluorination of PFASs on nZVI results in, at best, formation of defluorinated PFASs; (iii) PFASs are resistant to chemical oxidation due to the strong C−F bonds; and (iv) PFASs, once defluorinated, become more vulnerable to chemical decomposition, the suggested strategy might have high potential to synergistically remove and degrade PFASs (hypothesis). As a result, the reactivity and treatability of the integrated RAC/oxidant system will be experimentally tested in a laboratory-scale batch reactor containing a variety of PFASs including perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorobutanesulfonic acid, and perfluorononanoic acid.
The ultimate treatment procedure would be largely composed of (i) mixing IDW with RAC granules, (ii) letting them react in the presence of oxidants injected, and then (iii) disposing of the treated IDW. Considering the heterogeneous nature of components in IDW and the presence of PFASs and many other co-contaminants with different chemical reactivities and affinities, the integrated approach employing various reactive oxidizing and reducing species might help to address the real-world complexities of treating IDW. The mineralization capability of the integrated system via advanced oxidation is significant because most of other chemical methods end up with short-chain PFASs that have unknown toxicity and treatability. Knowledge obtained for the decomposition of PFASs could be potentially expanded to treat many other problematic halogenated chemicals (e.g., short-chain PFASs) in a real-world matrix. (Anticipated Completion - February 2019)