Due to their water and dirt repellent properties, PFAS chemicals (polyfluorinated and alkyl-resistant compounds) are often used in products such as coated pans, rain gear, baking paper or pizza boxes. The group of substances includes more than 10,000 compounds with different properties. They are extremely long lasting, hardly degradable in nature and accumulate in groundwater and soil. Many of them are very toxic, especially for the development of children, and are associated, for example, with the development of organ damage and cancer.
Researchers are investigating the effectiveness of combustion processes
A research team led by Dr. Checked by Hans-Joachim Gehrmann from the KIT Institute for Technical Chemistry (ITC). In collaboration with the Indian company Gujarat Fluorchemicals, a manufacturer of fluoropolymers, the scientists investigated the Brenda power plant pilot combustion chamber (combustion chamber with a steam boiler) at KIT. Fluoropolymers were burned and the PFAS concentrations in the wash water, ash and exhaust gas were then determined. The aim of the experiments was to clarify the temperatures and combustion conditions at which the most complete destruction of PFAS can be achieved.
A representative mixture of fluoropolymers
The researchers tested two different temperature conditions: 860 degrees Celsius, in accordance with European standards for household waste incineration, and 1,095 degrees Celsius, as in hazardous waste incineration. In both cases, the minimum residence time for the exhaust gases in the combustion chamber was two seconds. “We were able to show that under combustion conditions of 860 degrees Celsius and a residence time of two seconds, a fluorine degradation rate of more than 99.99 percent can be achieved. This means that almost complete mineralization of the fluoropolymers was achieved under conditions similar to those in a household waste incinerator,” reports Gehrmann. “Combustion at 1,095 degrees Celsius did not significantly increase the amount of degradation. This suggests that mineralization of fluoropolymers is not significantly affected by higher temperatures.”
For the combustion chamber experiments, the team selected a representative mix of fluoropolymers covering 80 percent of the world’s commercially used fluoropolymers, including polytetrafluoroethylene (PTFE, also known as Teflon), polyvinylidene fluoride (PVDF), perfluoroalkoxy polymers (PFA), and fluorocarbons (FKM).
Sampling was taken at several points in the combustion process: at the exit from the afterburning chamber, after the boiler and in the exhaust gas at the chimney. The team also analyzed samples from the wash water and ash. PFAS were precisely identified and quantified using analytical methods such as gas chromatography mass spectrometry. “The results are good news for the almost complete disposal of fluoropolymers by incineration of household waste according to European standards,” says Gehrmann, assessing the results of the research. “However, PFAS also enter the environment through other pathways that remain to be studied and evaluated.”
The study was published in the journal Chemosphere. DOI: 10.1016/j.chemosphere.2024.143403