Efficiently destroy short-chain PFAS
UFZ team develops process for removing perfluorobutanoic acid from water
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Short-chain perfluorinated and polyfluorinated alkyl compounds (PFAS) such as perfluorobutanoic acid (PFBA) are increasingly entering the environment via various pathways and polluting groundwater and drinking water. Because they are very mobile, they have so far been very difficult to remove. A research team from the Helmholtz Center for Environmental Research (UFZ) has now developed a new technology using a two-stage electrochemical process. As the UFZ researchers write in the Chemical Engineering Journal, the new process is more environmentally friendly and consumes less energy.
In the course of the UFZ process, the PFAS are first separated and enriched by electrosorption (step 1) and then destroyed by electrooxidation (step 2). What remains is mainly CO2 and fluoride.
Susan Walter-Pantzer / UFZ
There are currently around 10,000 PFAS substances, of which 4,000 to 5,000 are used industrially - in the manufacture of outdoor clothing, food packaging, pans, cosmetics and much more. Numerous PFAS, for example in fire extinguishing foams, are released into the environment and break down very slowly or not at all. They pose a risk to human health as they affect metabolism, hormone balance, reproduction and the immune system and are suspected of being carcinogenic. Numerous PFAS with long carbon chains have therefore already been regulated by the Stockholm Convention, meaning that their production and use is banned or restricted. As a result, the industry has increasingly replaced them with short-chain PFAS - with the result that short-chain PFAS such as perfluorobutanoic acid (PFBA) are increasingly being detected in the environment. PFBA has only four carbon atoms and has a carboxyl group at the end of the molecule, which strongly attracts water. "This is why PFBA dissolves very well in water and is very mobile. In conventional methods such as activated carbon adsorption, PFBA is therefore difficult to remove from water," says UFZ chemist and author Dr. Anett Georgi.
In order to eliminate PFBA from water, the UFZ research team has developed a two-stage electrochemical purification process in which the PFBA is first enriched and then destroyed. This is how it works: In the first step, large quantities of water containing PFBA are passed through a flow-through cell with an electrode made of a textile-like activated carbon fiber fleece by means of electro-adsorption. This becomes slightly positively charged. "As a result, the negatively charged PFBA is deposited on the surface of the activated carbon," explains first author and UFZ environmental engineer Dr. Navid Saeidi. By reversing the polarity of the voltage, PFBA is then dissolved from the surface again, rinsed out with a small volume of water and collected as a concentrate. The PFBA concentration can be increased by a factor of up to 40. This enrichment can be repeated several times using a cascade-like arrangement of electro-sorption cells. In the second process step, PFBA is destroyed by electro-oxidation on a boron-doped diamond electrode - i.e. by chemical purification of the water, which is triggered by an electric current. The anode has a strong oxidizing effect and causes PFBA to decompose. The main decomposition product that remains is fluoride, which is easy to separate.
"All steps can be carried out on site, which reduces transportation costs and the energy required is low," says Anett Georgi, naming two advantages of the process. As the adsorption of PFBA is controlled by applying an electrical voltage, the adsorption fleece made of activated carbon can be regenerated again and again and can therefore be used several times, unlike other processes in which the PFAS-enriched activated carbon has to be disposed of in waste incineration plants or restored at great energy expense. "This not only conserves fossil resources, but also reduces CO2 consumption, as activated carbon is often obtained from hard coal and is mainly imported from Asia," adds Anett Georgi.
The UFZ scientists see potential applications for their process, for which a patent application has already been filed, particularly wherever PFAS needs to be removed from municipal and industrial wastewater streams - for example at airports, where the groundwater is contaminated with short- and long-chain PFAS due to the use of fire-fighting foams. "As operators have to comply with increasingly strict PFAS limits, there is a need for more efficient and sustainable technologies for its removal that are reliable, environmentally friendly and affordable like our method. It could supplement the classic activated carbon adsorbers for complex PFAS contamination and capture the short-chain PFAS," says co-author and UFZ chemist Dr. Katrin Mackenzie. This would mean a significantly longer operating time and thus cost savings for the entire adsorber unit.
Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.
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