Six pilot-scale studies evaluating the in situ treatment of PFAS in groundwater

  • 15 maart 2021

In situ PFAS treatment: testing the waters

The use of in situ approaches for the treatment of contaminated groundwater is well established. The three most frequently applied in situ methods are in situ chemical oxidation, In situ chemical reduction and enhanced bioremediation, with each approach offering advantages over other in situ and ex situ technologies. With the growing awareness of PFAS in the environment, a greater focus is being applied to potential technologies to treat PFAS both ex situ and in situ.

Although the use of in situ methods for the treatment of PFAS potentially offers several advantages over extraction technologies, only limited testing of reagents for the in situ treatment of PFAS have been conducted. In order to fill this gap, a series of pilot tests were conducted to evaluate the effectiveness of 6 reagents in a permeable reactive zone configuration (PRZ). The reagents tested were sodium persulfate, hydrogen peroxide, powdered activated carbon (PAC), colloidal activated carbon (CAC), biochar and ion exchange resin (IER).

Pilot tests methodology

To evaluate the effectiveness of the reagents, six pilot tests were conducted in an unconfined sandy aquifer. The tests involved injecting reagents and subsequently monitoring the groundwater. Groundwater samples were collected before injection of the reagents (to establish a baseline concentration) and postinjection for up to 549 days. Groundwater samples were collected for analysis of 23 selected PFAS compounds. Pre-injection analysis detected six compounds at concentrations greater than their respective detection limits.

Results

Posttreatment groundwater monitoring over 1,5 years within the six PRZ’s indicated that the PFAS was not effectively treated by either persulfate nor hydrogen peroxide and, in some cases, individual PFAS increased in concentration. Concentrations of PFAS in groundwater sampled within the PAC, CAC, IER and biochar PRZ’s immediately after injection decreased to below their respective detection limits. Over time concentrations of individual PFAS within the groundwater sampled from the PAC, IER and biochar PRZ’s, however, exhibited partial or complete breakthrough. The only PRZ that completely attenuated the PFAS analyzed was the CAC PRZ. The increase in treatment performance for the CAC compared to the other adsorption based PRZ’s is attributed to better distribution of the CAC  and increased capacity for the adsorption of the PFAS compared with the IER, PAC and biochar used in this study.

The article “Six pilot-scale studies evaluating the in situ treatment of PFAS in groundwater” by Rick McGregor was published in “Remediation” (volume 30, issue 3, pages 39-50).