In Situ Containment of PFOA/PFOS using Colloidal Activated Carbon
Laboratory studies were conducted to measure the adsorption isotherms for PFOA and PFOS with a distributable form of colloidal activated carbon. The isotherm data was then used in an adapted version of the BioChlor model in order to estimate the expected adsorption longevity that a barrier of the colloidal carbon can provide for PFOA and PFOS considering the flux and the concentration. Additionally, a 16-foot sand column experiment was conducted to determine the ability of the colloidal activated carbon to flow and deposit in an aquifer.
The measured PFOA and PFOS isotherms were fit to the Freundlich equation and the isotherm parameters were determined. The isotherm measurements included a demonstration that a dose of the colloidal activated carbon could reduce 100 mg/L of PFOA and PFOS to below the 2016 revised EPA health advisory limits of 0.07 mg/L. Using the measured isotherm parameters within the BioChlor model, it was shown that a 50 mg/L plume of either PFOS or PFOA traveling with a velocity of 120 ft/yr could be contained and meet EPA limits with a single barrier of the colloidal activated carbon for up to 8 years. While this timeframe will also depend on other water components, for example TOC and additional contaminants present, the containment time can be increased with multiple barriers or a higher dose of the colloidal carbon.