This project’s objectives were to investigate the use of an integrated approach of soil washing and destructive treatment using plasma for treatment of investigation derived waste (IDW) impacted with per- and polyfluoroalkyl substances (PFAS). The combination of systems could permit unrestricted disposal and/or discharge of IDW on-site. Information from this study and ongoing PFAS research efforts will serve as a foundation for the development of fully developed field-scale systems for the treatment of PFAS-impacted IDW. These systems would be mobile and easily deployable, minimizing the spatial footprint and mobilization time and effort and allow cost effective treatment compared to current disposal methods.
Field site IDW was obtained from several Department of Defense (DoD) sites. Removal of PFAS from the IDW by soil washing was evaluated using a variety of solutions including water alone, water plus solvent, and water plus solvent and salt. Destruction of PFAS in these concentrated soil washing solutions using the enhanced contact electrical discharge plasma reactor was then verified.
An optimized wash solution of 50% water and 50% methanol with 1% NaCl was found to be the most effective wash; however, for soils with low organic carbon content and for short-chain PFAS, water alone was somewhat effective. Single washes removed the vast majority of compounds from the IDW samples. Removal was fast, taking minutes; however, the soil was pulverized in these experiments and vessels were completely mixed, thus kinetic limitations were largely eliminated. Plasma treatment of distilled (to recover methanol) solution (i.e., brine still bottoms) resulted in >99.6% destruction of precursors qualified by the total oxidizable precursor assay, >99% destruction of long and short-chain perfluorinated alkyl acids (except perfluorobutanoic acid (PFBA)) and of identifiable precursors, with a 10-fold dilution of the concentrated still bottoms. Two sequenced reactors for high concentration followed by low concentration treatment were required for effective treatment. The addition of cationic surfactant resulted in greater removal of short-chain compounds, treating all except PFBA (260 ng/L) to below detection.
Cost-effective and efficient technologies for treatment of IDW from PFAS investigations will improve the ability of Remedial Project Managers (RPMs) to manage these sites. On-site options that treat the waste and destroy PFAS will result in significant cost reductions compared to off-site disposal and incineration. (Anticipated Phase II Completion - 2024)
Miceli, J. 2021. Removal of PFAS from Investigation Derived Waste through Soil Washing (Master's Thesis). Clarkson University.