Living Lab: PFAS Remediation

Per- and polyfluoralkyl substances (PFAS9) are man-made substances which are very difficult (almost impossible) to decompose. These chemicals are very versatile because they have water-repelling, grease-repelling and dirt-repelling properties, and are used in many products. From cooking gear, clothing, textiles and cosmetics to packaging materials for food products. The abundant prevalence of these chemical substances and the difficult natural decomposition process have resulted in serious contamination of soil and the environment. On top of that, PFAS have been found throughout the entire world and in most ecosystems, and in most adults, animals and even newborn children.

UU creates living labs on its own campus, in which staff members, students and societal partners experiment in co-creation, and come up with solutions to sustainable challenges in the process. In these living labs, education, research, operational management and societal partners meet. The PFAS Remediation Living Lab came about when Frank Kooiman, who works at Campus & Facilities (C&F) at Utrecht University, was appointed project leader for the remediation of a PFAS-contaminated field in Utrecht Science Park. The university really wanted to investigate whether or not this PFAS field could be remediated in a sustainable way. Together with researchers and students from two different faculties, C&F and the municipality of Utrecht as the commissioner, people are working on experimental remediation methods and testing them in the living lab.

PFAS are also called forever chemicals. So far, destroying PFAS has been proven to be practically impossible. As they do not decompose by themselves, they keep circulating in our systems. Traces of PFAS can currently be found almost everywhere. As they are toxic substances, it is important that we limit or even completely abandon the use of PFAS in production processes, and try to remediate it as much as possible besides that.

The classic method to remediate a contaminated plot of land is dig and dump. You measure how deep the PFAS go, excavate that top layer and dump the soil somewhere else.

There are alternative remediation techniques such as phytoremediation (by means of growing plants which supposedly help in the removing, degrading and converting these chemical substances). In Belgium, hemp is used in a research project to remove PFAS from the ground. How effective this is, depends on how deep in the ground the PFAS are. The used plant also has to be capable of growing deep roots.

PFAS are also widely spread in our water. Several drinking water companies in The Netherlands apply a filtration technique which remove PFAS from our drinking water: reverse osmosis. However, the produced brine from this method including its PFAS, is discarded in some cases via a sewage treatment system on the surface water. Meaning PFAS is being removed from drinking water this way but not from the environment.

You can also try to have bacteria break it down. That is called bioremediation.

You also see the dig and treat method more and more often, in which people try to remove some additional PFAS out of that collected soil. Like with active carbon. That works a bit like Norit. You have carbon which is very porous, which results in much PFAS attaching themselves to the carbon. If you upturn the ground and mix this active carbon in it, the PFAS are immobilised. What is in the carbon will no longer end up in the plants or in the ground water. However, most of these dig and treat methods do not really decompose the PFAS: if you treat it with active carbon, it remains. If you burn it, part of it is released into the air. If you wash it, it ends up in the waste water.

Experiments to find methods to destroy the PFAS are being carried out. Such as the method of supercritical water oxidation. The idea in this is that you bring contaminated groundwater to extreme temperatures under extreme pressure, which degrades the PFAS. In the laboratory, that works at temperatures higher than 600 degrees Celsius and a pressure of 240 bar. However, a large amount of energy has to be used in order to scale up this method.

Another way to destroy PFAS is mechanical destruction. Contaminated ground is crushed, as it where, in a barrel of small metal balls and a shovel of sand. The crushing process increases the pressure on the PFAS so much that the fluorine atoms disconnect from the carbon and attach themselves to the silicon sand consists of. All that remains is powder which you can safely dump somewhere. In this experiment, the PFAS were decomposed for 99.88 percent. The question again remains whether or not this technique can be scaled up, also in regards to the required amount of energy.

Stefanie Lutz, Alraune Zech, George Kowalchuk and Johan van Leeuwen are currently involved in this living lab. Each of them also supervises one or more Master's students and three PhD researchers who will also participate in the research will be appointed.

One obstacle is that with this method, it is currently impossible to destroy PFAS. It serves as a method to extract PFAS and get them out of the soil.

• The extraction can take long and an effective method can be specific to a location; what works on one field, might not work elsewhere and the roots have to reach deep enough into the soil.