DESOTEC and VITO develop an accurate method for the measurement of PFAS level adsorbed on activated carbon

DESOTEC therefore decided to develop a more accurate and reliable way to measure PFAS level on spent activated carbon to:

• Enable customers to identify the most appropriate way of treating their activated carbon PFAS waste to protect the environment and human health.
  
• Allow companies to demonstrate legal compliance, giving them confidence that their measurements will match those taken by the environmental authorities, thus avoiding hassle, fines or other enforcement action.
• Protect customers’ reputations, as the issue of PFAS is in the spotlight.
• Enable our R&D teams to assess installation performance and compare different carbon grades for various PFAS molecules.

The six-month project consisted of two broad challenges:

Step 1: Optimising extraction. PFAS adsorbed onto activated carbon is a solid matrix. Therefore, an extraction step is necessary; this needs to be as efficient as possible in order to get as much PFAS out of the carbon as possible. DESOTEC’s expertise in activated carbon was crucial here.

Once extracted and transferred into a liquid phase, the PFAS was measured using liquid chromatography tandem mass spectrometry (LC-MS). Here, VITO’s expertise and equipment were critical.

Step 2: Validation experiments. VITO’s expertise was invaluable in defining a set of experiments to assess five parameters: detection, accuracy, linearity, reproducibility and uncertainty.

There were four rounds of experiments to test different solvents and conditions to optimise extraction. In each round, the recovery for the different methods was calculated, determining which method was used in the following rounds.

Round 1:

• Two solvents : acetonitrile and methanol.
• Sonication versus shaking for extraction.
• Length of time for shaking/ sonication.
• One carbon type.
• One fixed concentration.

Round 2:

• Two different spiking concentrations.
• Length of sonication.
• Addition of acid and base (formic acid and ammonium acetate) to the solvent.

Round 3:

• Three spiking concentrations.
• Isotopes to evaluate accuracy of extraction methods.
• Two-step extraction method using one solvent and a binary mixture (only acetonitrile, or acetonitrile/hexane (50:50), or acetonitrile + hexane).
• Two carbon types: one coconut and one coal-based.

Round 4:

• Three solvents (acetonitrile + hexane (two steps) or alkaline methanol (NH₃)).
• Three activated carbon grades: two coal-based and one coconut-based.
• One concentration.

Two initial validations were conducted: one at VITO, and an internal validation at DESOTEC. Activated carbon samples were also sent to commercial laboratories for further validation.

See the method in this infographic:

Two existing methods used in Flanders are:

1. CMA/3/D: for soils and sediments.

2. CM/A3/O: for soil improvers.

Both use one extraction step followed by one concentration step, followed by measurement on LC/MS device.

Our new method uses three extraction steps and one concentration step, followed by the same LC/MS measurement as in the existing methods above. The solvents used are the same.

This ensures that as much PFAS is extracted from the activated carbon as possible, giving far more reliable and accurate results, and providing reassurance to our industrial customers on how best to treat their PFAS-waste.