PFAS are harmful chemicals that we humans are exposed to, for example, drinking water. Due to its water and fat repellent properties, PFAS are used in everything from clothes to fire fighting foam. The substances are difficult to break down and today PFAS is found in the blood of almost every human being on earth.
- Here in Uppsala, PFAS are present in a large amount of the groundwater that will be used to produce drinking water. This is due to several decades of use of fire foam during fire drills, says Vera Franke, a PhD student in the research group organic environmental chemistry at SLU. In her project, she is working on developing more effective methods for removing PFAS from drinking water.
Nanofiltration provides contaminated residual water
One method used today in purifying drinking water is nanofiltration, that is, the water passes through a membrane with extremely small pores. This type of purification is very effective. The method is used to filter out, among other things, pharmaceuticals and organic material, but PFAS also get stuck in the membrane.
The disadvantage of nanofiltration is that about ten percent of the water does not pass through the membrane. The remaining water is called "retentate" and contains all substances that are too large to pass through the membrane, such as PFAS. When retentate water is contaminated with PFAS, it needs to be treated before it can be discharged.
- In our studies, we have joined nanofiltration with further purification of the retentate water through different types of filters. The idea is that PFAS stick to the filters so that the retentate water is purified and released. The filters are then sent for incineration or reused, says Vera Franke.
Coal and ion exchangers capture PFAS
The researchers have tested, among other things, carbon filters and ion exchange resin as filter material. In a carbon filter, PFAS get stuck on the carbon particles. An ion exchange resin works instead by capturing PFAS molecules from the water and in exchange releasing harmless ions present on the resin.
- We saw that the carbon filters and ion-exchange resins provided an effective purification. However, both materials become saturated and need to be replaced quite often, which becomes expensive in the long run. We are therefore constantly looking for even more effective filter material, says Vera Franke.
SLU helps with new drinking water treatment plant
In the year 2021, Uppsala Water and Waste AB will start building a new drinking water plant in Uppsala to fill the need for more drinking water as the municipality grows. Vera Franke's research group is collaborating closely with the company and is involved in developing purification methods to be used in the new drinking water plant.
- They will use nanofiltration as the main step in the drinking water treatment in the new plant. The other stages of purification are not yet fully established, says Vera Franke.
Text: Ylva Sjöblom