Purifying wastewater of PFOS and other PFAS

This chemical production company has facilities in several countries. At its main Belgian location, it operates a water purification system on behalf of several chemical firms that share the site.

After this treatment, the company found PFAS in the water of around 300 nanograms per litre. Of this, about 160 ng are perfluorooctane sulfanate (PFOS): one of the best-known long-chained type of PFAS molecules that are especially persistent. The water also contains less than 100 mg of organic components measured as total organic carbon (TOC).

As the treated water is discharged directly to the nearby river, it must have a high level of purity. Initially, the company faced a PFAS limit of 500 nanograms per litre, but this was later reduced to just 100 ng/l due to a regulation update in June 2023. PFOS limits were also cut from 100 ng/l to 20 ng/l.

As the company did not know where the PFAS originated, it sought an end-of-pipe polishing solution. It already had activated carbon filters on site for other applications, so conducted some pilot tests to estimate how long they would last before saturation.

Once it had established that activated carbon was a viable technology, the company approached DESOTEC. We were selected thanks to the quality of our competitive offer, willingness to engage and collaborate with the customer, and ability to see the bigger picture.

The client is now fully compliant with the new lower PFAS limits. With a reliable solution in place, it has turned its attention to tracing the source of the PFAS, which has turned out to be mainly groundwater due to historic contamination, and is considering how best to address this in the longer term.

The client carries out measurements after both the first and second filters to determine when to exchange them. The front filters, saturated with organics, last 1-2 months. The second filters, saturated with PFAS, last 4-5 months.

After swift exchange, DESOTEC transports the closed saturated filters away from the customer’s site to our own facilities for analysis and treatment if possible. There, we measure the level of PFAS and PFOS adsorbed on the carbon.

If PFAS levels are too high, we are not allowed to reactivate the carbon and must send it to an external specialised company for incineration. According to the EU POPs regulation, the limits are 50 ppm for PFOS, and 1 ppm for two other types of PFAS: perfluorooctanoic acid (PFOA) and perfluorohexanesulfonic acid (PFHxS).

For this customer, analyses confirmed the PFAS concentration on the spent carbon was below the POPs regulation limits, so we can guaranty that the waste coming from our clients will be treated in full compliance with the POPs regulation. The thermal treatment destroys PFAS completely by breaking down the molecules, reducing them to their elemental building blocks such as water, CO₂ and hydrogen fluoride.

The gases and impurities generated by this process, including the hydrogen fluoride which is formed during the PFAS destruction are neutralised via our flue gas treatment, making sure all contaminants are destroyed. DESOTEC takes the utmost care to ensure that no PFAS is emitted in the reactivation process, and carries out multiple measurements to ensure this is the case.

The reactivated carbon is completely free of pollutants and suitable for reuse for high-quality filtration. This circular approach drives down costs and cuts the amount of virgin carbon used, boosting sustainability and helping our customers meet their green goals.