Emerging Contaminants Summit

Spring 2020

thoresonKristen Thoreson
Director of Research & Development

Dr. Thoreson leads the chemical research and product development program at REGENESIS. She is trained as a chemist, and her graduate and post-doctorate research focused on mechanistic investigations of chlorinated ethene degradation pathways using molecular models and compound specific isotope analysis (CSIA) for both biotic and abiotic systems. She obtained her BSc in chemistry from the University of Wisconsin, La Crosse, and her PhD in inorganic chemistry from the University of Minnesota. She also spent time as a postdoctoral associate at the Helmholtz

Zentrum in Munich, Germany as a part of the Research Unit for Environmental Organic Isotope Chemistry.



In Situ Containment of PFAS using Colloidal Activated Carbon

With the increasing awareness to the widespread contamination associated with PFOA, PFOS, and other PFAS compounds, there is an established need for new and lower cost treatment options that can address the large, dilute plumes that these contaminants commonly form.  At the present time, the accepted remediation method for these contaminants is to use pump and treat systems equipped with activated carbon. The costs associated with running these systems and replacing the carbon can be quite high. For that reason, the ability to implement an in situ barrier of activated carbon that can cut off and contain these plumes for many years with a single application affords a beneficial means to decrease or avoid the operating and maintenance costs in the existing above ground systems. This paper examines the use of a colloidal activated carbon that readily distributes within the subsurface, providing a method for injecting an in situ barrier of activated carbon for PFAS treatment.

Laboratory batch studies were conducted to measure the relative adsorption of PFOS, PFOA, PFHpA and PFBS with a distributable form of colloidal activated carbon. The adsorption data were then used in an adapted version of the BioChlor model 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. 

Results of these studies demonstrated that a field relevant dose of the colloidal activated carbon could reduce 100 g/L of each PFAS compound tested by at least 99.9% and the relative adsorption followed in the order: PFOS > PFOA > PFHpA > PFBS, as has been observed with other activated carbons. In these experiments PFOS and PFOA were reduced to below the 2016 revised EPA health advisory limits of 70 ng/L. Using the measured isotherm parameters within the BioChlor model, it was shown that a 5 g/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 over 50 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. 

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