Coagulant-enhanced Sorption for In Situ Remediation of PFAS Contaminated Groundwater Systems

Dr. Matt Simcik | University of Minnesota

ER-2425

Objective

Alginate Beads Filled with PolyDADMAC

Alginate Beads Filled with PolyDADMAC

Perfluoroalkyl substances (PFASs) are a broad class of chemicals that contain a fully fluorinated carbon chain and one of several different end groups including sulfonate, carboxylate, sulfonamidoalkyls, and alcohols. Compounds of greatest relevance to this project are the perfluoroalkyl sulfonates and carboxylates. These compounds were used in mixtures of aqueous film forming foams as fire extinguishing agents, particularly on hydrocarbon fires due to their surface-active properties. As a result, these compounds were released into the environment during firefighting, both as an emergency measure and in fire training activities conducted by the military at many installations around the country. PFASs are recalcitrant in the environment and require extreme conditions to initiate chemical transformation reactions. In general, the techniques capable of destroying PFASs are not amenable to in situ remediation of contaminated groundwater.

The objective of this project is to develop a cost-effective, in situ method using coagulants to sequester the six PFASs in EPA’s Unregulated Contaminant Monitoring Rule 3 (UCMR3) list, including perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), in groundwater systems to prevent their migration to drinking water supplies. The central hypothesis is that the addition of chemical coagulants used in the drinking water industry will enhance PFAS sorption to the soil, preventing mobility. This project is expected to determine the optimal sorption enhancers (identity and dosage), the delivery mechanisms, and the capacity and limitations of the in situ PFAS retention process in groundwater systems. Furthermore, it will determine the effect, if any, of co-contaminants (e.g., fuels) on PFAS enhanced sorption and retardation.

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Technical Approach

Researchers will assess the ability of sorption enhancers to increase the sorption and retention of a suite of PFASs in simulated groundwater systems in the laboratory. A series of batch experiments will be conducted using soil excavated from Tinker Air Force Base in Oklahoma, the six PFASs on the EPA UCMR3 list, and each of four commercial coagulants: polyaluminum chloride; polyamine; polydimethylamine diallyldimethyl ammonium chloride; and a tannin-based cationic polymer. To determine the effects of co-contaminants on coagulant performance, the experiments will be repeated with diesel fuel (or another relevant co-contaminant) added at a concentration similar to that found in contaminated groundwater. As part of the batch experiments, efficiency and rate of PFAS removal and any potential re-release will be determined.

Different sorption enhancer delivery approaches will be evaluated to achieve optimal in situ sequestration. The underlying rationale for these experiments is to develop systems that are able to deliver sorption enhancers slowly over a period of time to allow for continuous PFAS removal. Three delivery systems will be evaluated, two are commercially available (osmotic pumps and floc logs) and one will be developed in the laboratory (polymer impregnated with the desired sorption enhancer).

Retention of PFASs in porous media following sorption enhancer introduction will also be evaluated in both one- and two-dimensional experimental systems. One-dimensional column studies allow controlled flow conditions, testing of multiple dosages, measurement of profiles of contaminant/sorption enhancer concentrations, assessment of the effect of co-contaminants, and evaluation of performance, including saturation and desorption issues. Two-dimensional aquifer cells will be used to mimic conditions that are representative of heterogeneous aquifer formations. The experiments will be conducted in aquifer cells that are approximately 1.5 m (horizontal length) operated under constant head flow conditions. The aquifer cells and operating protocols were developed with prior SERDP support (project ER-1612). Both column and aquifer cell studies will be performed in the presence and absence of diesel fuel as a model co-contaminant (or another appropriate co-contaminant as determined by SERDP).

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Benefits

Successful completion of this project will provide the Department of Defense and the greater scientific community with a cost-effective remediation technology for in situ treatment of PFAS-contaminated groundwater that will serve as an alternative to excavation or pump-and-treat technologies. The performance and limitations of the technology will be determined for systems representative of fire training activity sites at military installations. Of particular interest to the greater scientific community will be the improved understanding of PFAS adsorption in heterogeneous systems, the effect of co-contaminants on adsorption, and the ability of commercially available coagulants to achieve sequestration of PFAS from groundwater systems. (Anticipated Project Completion - 2019)

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Publications

Aly, Y.H., C. Liu, D.P. McInnis, B.A. Lyon, J. Hatton, M. McCarty, W.A. Arnold, K.D. Pennell, and M.F. Simcik. 2018. In Situ Remediation Method for Enhanced Sorption of Perfluoro-Alkyl Substances onto Ottawa Sand. Journal of Environmental Engineering, 144(9).

Anderson, E.L., M.P.S. Mousavi, Y. Aly, X.V. Chen, M.F. Simcik, and P. Buhlmann. 2019. Remediation of Perflurooctylsulfonate Contamination by In Situ Sequestration: Direct Monitoring of PFOS Binding to Polyquaternium Polymers. ACS Omega, 4(1):1068-1076.

 

Theses:

Aly, Y. 2016. Enhanced Sorption of Perfluoroalkyl Substances (PFASs) onto Ottawa Sand (Master’s Thesis). University of Minnesota, School of Public Health, Division of Environmental Health Sciences.

Aly, Y. 2019. Enhanced Adsorption of Perfluoroalkyl Substances in Groundwater; Development of a novel in situ Groundwater Remediation Method (PhD Thesis). University of Minnesota, Water Resource Sciences Program.

McCarty, M. 2016. Development of a Novel Perfluoroalkyl Substance Sequestration Scheme Using Alginate Macrobeads and Common Water Treatment Polymers (Master’s Thesis). University of Minnesota, Civil Environmental and Geoengineering.

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Points of Contact

Principal Investigator

Dr. Matt Simcik

University of Minnesota

Phone: 612-626-6269

Program Manager

Environmental Restoration

SERDP and ESTCP

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