Non-thermal Plasma and Foaming-based Remediation with Enhanced chemical Screening for PFAS Pollution COntrol

Intermediate results:

Analytical Techniques

The analytical support provided by VITO to the pFRESCO project enables the evaluation of the performance of the applied remediation technologies. Standard PFAS analytical methods are used to quantitatively measure the PFAS compounds present in the samples. To investigate potential transformations of PFAS compounds, non‑targeted analysis (NTA) and a Total Oxidisable Precursor Assay (TOPA) were also conducted.

The presence of foam‑forming compounds appeared to have a very limited impact on PFAS measurements in the samples, particularly in the foam concentrate. This may be explained by the applied dilution or by the use of solid‑phase extraction with an anion‑exchange sorbent. On the one hand, further dilution reduces the concentration of matrix components, potentially decreasing their influence on the measurement. On the other hand, a sample clean‑up step is included—initially using an anion‑exchange sorbent and later a combination of an anion‑exchange sorbent and GCB (graphitized carbon black). This clean‑up procedure effectively reduces matrix background interference, enabling robust and reliable measurements.

Foam Fractionation

1/ Test Setup

The test consisted of a continuous flow experiment in which both the effluent and the foam stream were collected. Throughout the test, non‑variable operational parameters were continuously monitored and adjusted to ensure stability. The key parameters were the hydraulic residence time in the reactor, the injected air flow rate, and the foam‑to‑influent ratio.

The test was carried out in three consecutive stages:

• Step 1: Foam fractionation of the raw extracted groundwater.
• Step 2: Foam fractionation of the effluent obtained in Step 1.
• Step 3: Foam fractionation of the foam generated in Steps 1 and 2.

2/ Results of Test 1

• The results from Step 1 show that foam fractionation without additives achieves high removal efficiencies for 6:2 FTS, PFHxS, PFOA, and PFOS. In Step 2, these same components are again removed with high efficiency. The PFAS compounds that proved problematic for foam fractionation without additives were PFPeA, PFHxA, PFBA, and PFHpA.
• Foam fractionation applied to the settled primary foam fraction (from Steps 1 and 2) resulted in good concentration performance for most PFAS. The components that showed poor concentration in Steps 1 and 2 again displayed limited concentration in Step 3. The composition of the effluent after Step 3 is comparable to the original extracted groundwater (influent of Step 1). Consequently, this effluent is suitable for recirculation to the influent. Overall, the bulk of the PFAS is concentrated into 5% of the original volume.
• Ultrashort‑chain PFAS (<C4) were not removed during the foam fractionation batch tests without dosing.
• PFCA precursors were efficiently concentrated in the foam during foam fractionation. This is an important finding, as these precursors can, over time, lead to the formation of PFAS carboxylic acids.

3/ Results of Test 2

Non‑thermal Plasma

The laboratory tests using non‑thermal plasma destruction were successful. The main PFAS components were almost completely degraded and mineralised, and the smaller breakdown products were mineralised to a high degree using NTP Max. The use of NTA provided additional insight into the analyses, enabling the replacement of a seal in the laboratory/test setup. Other analyses of specific PFAS components still need to be examined in closer detail together with project partner VITO, which performs these analyses, as certain results may be outliers, unexpected, or simply chemically impossible.

The results of the laboratory tests make it possible to further refine and adjust the settings and operational parameters in preparation for the planned pilot tests.

Conclusions: The results also show that the combination of foam fractionation and NTP can serve as an effective treatment train; all values are below the (expected) discharge limits for the individual PFAS components.