Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7d. Ex Situ PFAS Water Treatment Technologies

Formatted Title:

Evaluation of PFAS Removal by Surface Activated Foam Fractionation of Low Foaming Groundwater and High Foaming Surface Water

Background/Objectives:

Filtration methods are commonly used for the large-scale treatment of PFAS-impacted water, resulting in the transfer of PFAS to a solid media which must be reactivated or disposed. Surface activated foam fractionation (SAFF) provides an alternative solution to filtration by injecting air into the water to generate foam. Removal of the foam results in large reductions in PFAS concentrations in the water and a highly concentrated, small volume waste stream that could be treated by numerous PFAS destruction technologies. The purpose of this study was to evaluate the effectiveness of SAFF with impacted surface and groundwater in the eastern Saint Paul, Minnesota metro area and determine if SAFF was a feasible technology to address impacted waters in a full-scale treatment system. The results will be incorporated into a feasibility study to address PFAS impacts present in surface water and multiple bedrock aquifers which are used for drinking water in the area.

Approach/Activities:

A pilot study was conducted with a SAFF®20 (OPEC Systems, Australia) to determine the PFAS removal efficiency in treatment of impacted surface water and groundwater from the Shakopee and Jordan Aquifers. Operational settings including air injection frequency and treatment time were varied to evaluate the effect on removal efficiency during primary fractionation with each water source. Variations in the effluent were then evaluated over at least one week at the optimal settings. Surface water PFOS and PFOA concentrations were approximately 1500 ng/L and 800 ng/L. PFOS and PFOA concentrations were approximately 800 ng/L and 300 ng/L, respectively, in the Shakopee Aquifer and 5 ng/L and 40 ng/L, respectively, in the Jordan Aquifer. The groundwater sources contain lower total organic carbon concentrations compared to the surface water, providing a comparison for the removal efficiency in water sources without other organic compounds that could promote the formation of foam. In addition to the analysis of specific PFAS compounds, total adsorbable organofluorine, total oxidizable precursors, total organic carbon, and select ions and metals were periodically analyzed. The volume of SAFF concentrate produced, energy consumption, and daily treatment volumes were documented to evaluate the potential to use SAFF in full-scale operations to address PFAS impacts at the site.

Results/Lessons Learned:

SAFF was demonstrated to be effective at removing PFOS and PFOA, which were the primary PFAS of concern at the site, from the three water sources tested. As was expected, surface water easily foamed and removal efficiencies of PFOS and PFOA were greater than 99%, resulting in PFOS and PFOA effluent concentrations were less than 1 ng/L. The groundwater did not readily foam and required oscillating the air injection frequency between higher and lower settings to achieve higher removal efficiencies. Even without the formation of foam during primary fractionation, removal efficiencies of over 99% for PFOS and PFOA were observed during treatment of the Shakopee Aquifer with PFOS and PFOA effluent concentrations were less than 2 ng/L. PFAS concentrations in the Jordan Aquifer are lower, especially for PFOS, but PFOS and PFOA effluent concentrations were below detection limits and less than 5 ng/L, respectively. Through this pilot test, 30,000-50,000 gallons of water were treated each day but less than 1 gallon/day of concentrated PFAS waste was produced with PFOS and PFOA concentrations above 6 mg/L and 2 mg/L respectively. These results show that SAFF is an effective technology at removing PFAS from surface water and low foaming groundwater, including groundwater from drinking water aquifers.

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Laura Lewis