Waste incineration destroys PFAS chemicals

PFAS chemicals (perfluorinated and polyfluorinated alkyl compounds) are often used in products such as coated pans, rainwear, baking paper or pizza boxes due to their water and dirt-repellent properties. This group of substances comprises more than 10,000 compounds with different properties. They are extremely persistent, hardly degradable in nature and accumulate in groundwater and soil. Many of them are highly toxic, especially for the development of children, and are associated with the development of organ damage and cancer, for example.

Researchers investigate the effectiveness of combustion processes

A research team led by Dr. Hans-Joachim Gehrmann from the Institute of Technical Chemistry (ITC) at KIT has now investigated whether and to what extent the compounds are also released into the environment via waste incineration. In cooperation with the Indian company Gujarat Fluorchemicals, a manufacturer of fluoropolymers, the scientists carried out tests on the power plant pilot combustion chamber Brenda (combustion chamber with steam boiler) at KIT. Fluoropolymers were burned and the PFAS concentrations in the wash water, ash and exhaust gas were subsequently determined. The tests were intended to clarify at which combustion temperatures and conditions the most complete destruction of PFAS can be achieved.

Representative mixture of fluoropolymers

The researchers tested two different temperature conditions: 860 degrees Celsius, corresponding to the European standards for household waste incineration, and 1,095 degrees Celsius, as in the incineration of hazardous waste. In both cases, the minimum residence time for the exhaust gases in the combustion chamber was two seconds. "We were able to show that at combustion conditions of 860 degrees Celsius and two seconds dwell time, a fluorine-related 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 household waste incineration," reports Gehrmann. "Incineration at 1,095 degrees Celsius did not significantly increase the degree of degradation. This suggests that a higher temperature has no significant influence on the mineralization of the fluoropolymers."

For the experiments in the combustion chamber, the team selected a representative mixture of fluoropolymers covering 80 percent of the fluoropolymers used commercially worldwide, including polytetrafluoroethylene (PTFE, also known as Teflon), polyvinylidene fluoride (PVDF), perfluoroalkoxy polymers (PFA) and fluorororubber (FKM).

Samples were taken at several points in the combustion process: at the exit of the post-combustion chamber, after the boiler and in the flue gas at the chimney. The team also analyzed samples from the wash water and the ash. Using analytical methods such as coupled gas chromatography-mass spectrometry, PFAS were precisely identified and quantified. "The results are good news for the virtually residue-free disposal of fluoropolymers via household waste incineration in accordance with European standards," says Gehrmann, assessing the research results. "However, PFAS also enter the environment in other ways that still need to be investigated and evaluated."

The study was published in the journal Chemosphere. DOI: 10.1016/j.chemosphere.2024.143403