Due to their high stability, per- and polyfluoroalkyl substances (PFAS) are environmentally persistent and bioaccumulative, leading to their detection in soils and sediments, aquatic environments, plants, animals, and humans. The rationale that underlies this research is the need to develop in situ and ex situ PFAS treatment technologies that are both effective and sustainable. The central hypothesis of the project is that a cost-efficient green remediation technology can be developed repurposing a solid waste feedstock informed by the fundamental knowledge of adsorptive processes at solid-water interface, which will provide an improved technique for restoration of PFAS-impacted media.

Aluminum-based water treatment residue (Al-WTR) is a non-hazardous solid waste generated during alum coagulation in drinking water treatment plants (DWTP). Because of their amorphous character, Al-WTR have high specific surface area and high density of reactive surface functional groups that make them efficient adsorbents of both organic and inorganic chemicals of concern. The objective of this project is to investigate the potential of repurposing Al-WTR as a green remediation method for cost-effective treatment of soil and water impacted with PFAS. This study will address the following key knowledge gaps that currently:

• Surface coordination of the PFAS on variably-charged Al/Fe-oxide/hydroxide phases and organic carbon (that are well-known perfluorooctanoic acid and perfluorooctanesulfonic acid scavengers);
• The mechanisms of PFAS adsorption on them;
• The role of soil chemistry in PFAS bioaccessibility; and
• The impact of Al-WTR treatment on lowering PFAS uptake and reducing chemical stress in plants grown in PFAS-impacted soils.

The effectiveness of Al-WTR to chemically immobilize PFAS in soils and as a filter media in stormwater and groundwater treatment will be investigated in a series of laboratory- and greenhouse-based experiments that will focus on the following:

• Explore the extents and mechanisms of adsorption of PFAS on Al-WTRs;
• Explore the adsorption and bioaccessibility of PFOA and PFOS on soils amended with Al-WTRs; and
• Explore PFAS removal from impacted water using granulated Al-WTR-based filter media.

The mechanisms of PFAS adsorption on the Al-WTR will be investigated using macroscopic and microscopic techniques. The issue of heterogeneity of feedstock between various DWTP and batch-by-batch variability within a DWTP and their impact on PFAS adsorption will also be addressed.

Data gathered from these experiments will be used to develop mechanistic predictive models for predicting PFAS adsorption that will be verified by surface spectroscopic studies. Adsorption isotherm studies will be used to assess the retention capacity of PFAS by unamended and Al-WTR-amended soils having a range of common physicochemical properties.

This project will deliver two green technologies, one for in situ remediation of PFAS-impacted soils, and the other for treatment of PFAS-impacted water. Both technologies are easy-to-implement, easy-to-use, and easy-to-maintain. The technologies are “green” from both ecological and economic perspectives because they utilize a non-hazardous solid waste as a source material, which can be obtained and processed cost-effectively using green chemical methods. Given the mechanistic nature of the research, the technologies will not be site-specific and can be universally applied. Thus, the results of this research will benefit all DoD end users who can use these technologies to cost-effectively remediate any PFAS-impacted military site. (Anticipated Project Completion – 2026)