Figure 4. The Pilot Trial Unit (rendered drawing – final lay-out).

Figure 5. The Control Panel.

Next Steps

Soil washing is really about controlling partitioning, i.e., the equilibrium ratio between solute concentrations in soil and in water phase, under saturated (or partially saturated) conditions. It involves complex mass transfer mechanisms, especially when PFAS are involved, as these are a mixture of many compounds with different water affinity behaviours.

Many parameters can affect partitioning, however the pilot trials will focus on optimising the following:

• Permeability, which in the case of the process depicted in Figure 1 can be translated to:
  • Clay/Sand ratio; and
  • Homogeneity.
• Solvent concentration, which will impact:
  • The amount of brine generated at the end of the process; and
  • The volumes of solvent lost via volatilisation along the process.
• Electro-conductivity, which can be controlled by the addition of ions to the ethanol solution; and
• pH, which can be controlled by the addition of buffering solutions to the ethanol solution.

References

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• Darlington et al. (2018) The challenges of PFAS remediation. The Military Engineer 110, 58–60. 10.1007/978-1-4419-1157-5_1. [PubMed: 29780177]
• ITRC (2009) Evaluating LNAPL Remedial Technologies for Achieving Project Goals. Interstate Technology Regulatory Council, LNAPLs Team, Washington, D.C.
• Meng at al. (2017) Effect of hydro-oleophobic perfluorocarbon chain on interfacial behavior and mechanism of perfluorooctane sulfonate in oil-water mixture. Scientific Reports | 7:44694 | DOI: 10.1038/srep44694.
• Ross et al. (2018) A review of emerging technologies for remediation of PFASs. Remediat. J. 28, 101–126. 10.1002/rem.21553.
• Schröder (2003) Determination of fluorinated surfactants and their metabolites in sewage sludge samples by liquid chromatography with mass spectrometry and tandem mass spectrometry after pressurised liquid extraction and separation on fluorine-modified reversed-phase sorbents. J. Chromatogr. A 1020, 131–151. 10.1016/S0021-9673(03)00936-1. [PubMed: 14661764]
• Senevirathna et al. (2021) In situ soil flushing to remediate confined soil contaminated with PFOS- an innovative solution for emerging environmental issue, Chemosphere 262.
• Zhang et al. (2019) Adsorption of perfluoroalkyl and polyfluoroalkyl substances (PFASs) from aqueous solution-A review. Sci. Total Environ. 694, 133606 10.1016/j.scitotenv.2019.133606. [PubMed: 31401505]