The use of aqueous film-forming foam in fire suppression has resulted in hundreds of sites impacted with per- and polyfluoroalkyl substances (PFAS). Investigations determining the extent of PFAS continue to generate large quantities of investigation-derived waste (IDW) that are typically disposed through landfilling or incineration. This project aims to develop a cost-effective alternative to landfilling or incineration by assessing the efficacy of an integrated field scale approach of soil washing and plasma-based destruction for the treatment of PFAS-impacted IDW. This integrated approach could permit unrestricted disposal and/or discharge of IDW on-site in a mobile and easily deployable system and allow for more cost effective and practical field-scale IDW treatment systems. 

This project was conducted in two phases, with testing of the proof-of-concept of the technology under Phase I. Under Phase II, key challenges that will be evaluated and addressed include (1) potential limitations of PFAS mass transfer, and its impact on wash solution volume and contact time; (2) the potential to mobilize solids during the wash process, which could negatively impact follow-on destructive PFAS treatment operations; (3) the potential need for additional pre-treatment steps prior to PFAS destruction by plasma; (4) the ability to reuse wash solutions; and (5) potential challenges with upscaling for field implementation. 

This work will have two key focus areas: 

1. Improving on-site disposal and/or discharge of IDW through soil washing, targeting PFAS in relation to PFAS and IDW properties. 
2. Improving the development and implementation of a field-scale PFAS-IDW management system by the optimization of design and operational characteristics of IDW washing followed by plasma-based destructive treatment of concentrated PFAS.

In Phase I of this project, field site IDW was obtained from several Department of Defense 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.

Phase II of this project focuses on evaluating field-like and field-scale IDW washing informed by literature and current data for the removal of PFAS from up to four characterized (total organic carbon and pH) IDW samples. IDW wash tests will be conducted under field-like conditions, followed by plasma treatment for the destruction of PFAS. The feasibility of regeneration of wash solutions will also be assessed for follow-on IDW washes. The optimized wash solutions will move forward to field-scale testing in order to develop an integrated approach for treating containerized PFAS-impacted IDW.

Phase I Results

Results of Phase I demonstrated that 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 only 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 ten-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. The results of these Phase I studies are available in the Phase I Final Report.

The goal of this study is to apply an integrated approach to manage PFAS-impacted IDW to simplify the process of addressing IDW generated and stored on site, reduce the cost of managing IDW through on-site treatment, and minimize the risk of off-site transportation of PFAS-impacted IDW. This work will pave the way for on-site unrestricted disposal and/or discharge of IDW with lower costs and lower life cycle impacts associated with the treatment of PFAS-impacted media in comparison to current disposal methods and offers a permanent solution to PFAS remediation efforts. (Anticipated Phase II Completion - 2024)

Theses

Miceli, J. 2021. Removal of PFAS from Investigation Derived Waste through Soil Washing (Master's Thesis). Clarkson University.