IN SITU REMEDIATION OF PFAS-CONTAMINATED GROUNDWATER

Abstract

An in situ remediation process for a PFAS-contaminated site includes sub-surface injection of slurry containing activated carbon in combination with a substances that promotes formation of an activated carbon emulsion and retention of PFAS by a solid matrix at said site, thereby removing said PFAS from groundwater.

Claims

1. A method comprising carrying out in situ remediation of a PFAS-contaminated site by carrying out sub-surface injection of a slurry that contains activated carbon in combination with a substance that promotes formation of an activated carbon emulsion and retention of PFAS by a solid matrix at said site, thereby removing said PFAS from groundwater.

2. The method of claim 1, further comprising selecting said substance to be a polymer coagulant.

3. The method of claim 1, further comprising selecting said substance to be polyDADMAC.

4. The method of claim 3, further comprising selecting said slurry to have a 5,000 milligrams per liter of polyDADMAC and 1 gram per liter of activated carbon.

5. The method of claim 1, further comprising selecting said substance to be polyamine.

6. A composition comprising a slurry, said slurry comprising activated carbon mixed a substance that promotes formation of an activated carbon emulsion and retention of PFAS by a solid matrix at said site, thereby preventing said PFAS from entering groundwater.

7. The composition of claim 6, wherein said substance comprises said substance comprises a polymer coagulant.

8. The composition of claim 6, wherein said substance comprises polyDADMAC.

9. The composition of claim 8, wherein said slurry has 5,000 milligrams per liter of polyDADMAC and 1 gram per liter of activated carbon.

10. The composition of claim 6, wherein said substance comprises polyamine.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0018] FIG. 1 shows a site undergoing in situ remediation; and

[0019] FIG. 2 shows compares sequestration of a representative PFAS species (perfluorooctanoic acid, PFOA) onto porous media (Ottawa sand) with and without pre-injection of a slurry containing both activated carbon and a coagulant polymer.

DETAILED DESCRIPTION

[0020] FIG. 1 shows a slurry-injector 10 injecting coagulating slurry 12 into a subsurface 14 above a water table 16 contaminated with PFASs. The coagulating slurry 12 includes powdered activated-carbon mixed with a coagulant polymer. A suitable coagulant polymer is polyDADMAC.

[0021] The presence of coagulant polymer creates a stable emulsion that allows the activated carbon to remain in suspension during injection. This contributes to the sorption and sequestration of PFASs.

[0022] To establish the effectiveness of the method, an Ottawa sand column was used to simulate groundwater flow through porous media. The sand was first saturated with 10 mM NaCl and then a slurry containing PAC and polyDADMAC was injected into the column. Results were compared to a control experiment where no PAC/polyDADMAC was injected. Next, simulated contaminated groundwater containing 50 ppb of PFAS, and in particular, with perfluorooctanoic acid (PFOA), hereafter referred to as the pollutant, was injected into the column. FIG. 2 shows a breakthrough curve of the pollutant, plotted as the measured PFOA concentration in effluent samples (C) divided by the influent concentration (C.sub.0) versus time, expressed as dimensionless pore volumes (PVs).

[0023] For the column with no PAC/coagulant polymer, very little PFOA retention is observed, with pollutant breakthrough occurring just after 1 PV and reaching C/C.sub.0. In contrast, the pre-injection of a slurry having both PAC and coagulant polymer promoted sequestration of the pollutant, with very little breakthrough (C/C.sub.0 less than 0.1). In FIG. 2, it can be seen that the pre-injection of the PAC/coagulant polymer slurry results in as much as 95% greater removal of pollutant from the simulated groundwater than the activated carbon acting alone.

[0024] From the results shown in FIG. 2, it is possible to infer that PFAS is strongly adsorbed by the PAC that was retained within the column, and that the adsorbed coagulant could also form complexes with PFASs, further enhancing the sorption capacity of the PAC+coagulant treatment.

[0025] The relative amounts of coagulant polymer used and the manner of injection can be expected to vary depending on site-specific properties. However, the general principle of using a coagulant polymer to promote retention of the pollutant by solid matrix is expected to be applicable across multiple sites.

[0026] In the experimental results shown in FIG. 2, the coagulant polymer was polyDADMAC and 3.5 PVs of the slurry containing 5,000 milligrams per liter of polyDADMAC and 1 gram per liter of activated carbon was pre-injected. The PFOA pollutant was injected at a concentration of 50 micrograms per liter and at a flow rate of 0.12 milliliters per minute to simulate a pore water velocity of 1 meter per day. The dashed line shows the breakthrough of a non-reactive tracer made of 10 mM NaBr.

[0027] Although polyDADMAC is used in the above example, other coagulants made by used. One example is a polyamine coagulant, such as a co-polymer comprised of epichlorohydrin and dimethylamine.