Objective
The physical and chemical properties of per- and polyfluoroalkyl substances (PFASs) make them difficult to remove from groundwater using traditional treatment technologies. Designing treatment systems for AFFF-impacted sites is further complicated by the frequent presence of co-contaminants and the fact that PFAS composition can vary significantly according to AFFF manufacturer and production year. However, in situ chemical oxidation (ISCO) and bioremediation can provide effective, relatively inexpensive and less energy intensive alternatives, especially when used in combination. That is, chemical oxidation can quickly transform large masses of a variety of contaminants and then bioremediation can remove residual contaminants, or, alternatively, bioremediation prior to ISCO could decrease the amount of oxidants required to achieve remedial goals by decreasing the mass of reduced organics.
The objective of this study is to develop knowledge leading to an in situ groundwater remediation strategy for PFASs with chlorinated compounds and 1,4-dioxane as potential co-contaminants. This strategy aims to integrate chemical oxidation for PFAS removal with bioremediation for organic mass degradation. The effects of biostimulation and/or bioaugmentation will be determined prior to ISCO technologies as well as the effects of ISCO on the viability of aquifer microorganisms critical to AFFF co-contaminants degradation. The overall goal is to establish optimal combinations of ISCO and bioremediation processes to clean up multiple contaminants.
Technical Approach
The hypothesis of this study is that in situ remediation of AFFF with co-contaminants can be achieved by sequentially applying ISCO based on persulfate chemistry in combination with bioremediation strategies. The most effective and efficient strategies require a fundamental understanding of the interplay of these technologies. Further, it is hypothesized that the initial treatment of PFASs and common co-contaminants with heat activated persulfate ISCO will remove chemical inhibitors of aquifer microorganisms and that subsequent downstream microbial activity for in situ mixed contaminants degradation will be stimulated. In addition, bioremediation of organics in AFFF and potential co-contaminants prior to ISCO can decrease the amount of oxidants needed for contaminant removal. Overall, elucidating the significance of the possible effects of ISCO on aquifer bacteria as well as the effects of bioremediation on subsequent ISCO could substantially improve the performance of remedial scenarios that combine ISCO with bioremediation. The research will evaluate the following areas:
- Evaluate the transformation of source-zone AFFF and its co-contaminants, chlorinated solvents and 1,4-dioxane, during persulfate-based ISCO in the presence of aquifer solids.
- Determine the effects of source-zone ISCO treatment of AFFF on co-contaminant degrading bacteria, and assess the feasibility of downgradient plume control via bioremediation after ISCO.
- Evaluate the feasibility of employing bioremediation prior to persulfate based ISCO treatment to increase its effectiveness and decrease reagent requirements.
Benefits
This study will result in an improved understanding of key factors that determine the potential outcome of combined ISCO and bioremediation for the treatment of multiple contaminant sites. These results will provide a foundation for the advancement of technologies for in situ remediation of AFFF, dioxane, and TCE mixtures.
By determining the transformation products of AFFF by heat-activated persulfate at different reagent loads, we can probe both the efficacy of ISCO on AFFF in the presence of co-contaminants and aquifer solids as well as the risks of generating more toxic or more persistent fluorinated compounds. A greater understanding of the effects of the heat-activated persulfate ISCO at AFFF contaminated sites on co-contaminant biodegrading microorganisms will help to guide engineers responsible for remediation of military sites in deciding the likelihood of success if biostimulation and bioaugmentation is employed following ISCO. Sequential batch studies investigating chemical oxidation (persulfate dose, timing, etc.) in combination of pre- or post-bioremediation strategies with aquifer solids will inform engineers of vital factors for designing and implementing effective combined in situ chemical oxidation and bioremediation. Taken together, the information gained from this research will address the military’s need to achieve site closure by means of timely and cost effective remediation.
