Activated carbon is considered a standard technology for the removal through adsorption of PFAS molecules from raw drinking water or wastewater without formation of potentially toxic by-products. Thermal reactivation, a well-established high temperature process, mineralises the PFAS molecules adsorbed on the activated carbon to remove these persistent contaminants from the water cycle. During this process the spent activated carbon can be recovered and thus be reused. The reactivation of spent carbon containing PFOS, PFOA, and other PFAS has been practiced for over 15 years.
Calgon Carbon processes the saturated carbon in dedicated thermal reactivation furnaces at high temperature to regain the activity levels of adsorption required for the application and to mineralise the adsorbed organic species. These thermal reactivation furnaces are specifically engineered units for the purpose, meeting the local environmental requirements.
Difference between the reactivation process and regeneration process:
Reactivation: spent carbon is reactivated in a multi-hearth furnace or rotary kiln by volatilizing and destroying the adsorbed contaminants and restoring the activated carbon to a virgin-like state. Reactivation temperature and feed throughput requirements may vary depending upon the adsorbate loading characteristics of the spent carbon being processed; Industrial Reactivation furnace temperatures are generally around 900-950°C, similar to incineration conditions but in a low oxygen environment.
Spent activated carbon is subjected to quality control to establish the proper reactivation conditions for those types of used activated carbon.
- The current operating procedure for reactivation of PFAS loaded activated carbon is regularly reviewed and can be summarized below:
- The destruction of adsorbates on spent activated carbon is a two step process. First, the adsorbates are volatilized or desorbed from the carbon surface. Some of the desorbed contaminants are destroyed in the reactivation furnace. Adsorbates that are removed and not destroyed in the furnace are drawn through an abatement system, which consists of a thermal oxidizer/afterburner, an acid gas scrubber, and a baghouse. The abatement system is designed to destroy organics to at least 99% efficiency, to neutralize acid gases formed during the process, and to capture particulates. Efficiency and functionality of the abatement system is verified by agency approved and verified stack testing.
Regeneration: our reactivation process differs greatly from the “regeneration” process. Carbon regeneration does not have the same temperature requirements as Calgon Carbon’s reactivation process and could be performed with steam or hot N2 that rarely gets above 100°C. As a result, activated carbons that have gone through a regeneration process remain partially spent and contain some, and potentially all, of the original adsorbates.
There are a number of literature references and third-party data that support the destruction of PFAS at temperatures similar to our reactivation conditions. Here are some examples for reference:
- A study of spent carbon used in drinking water treatment that contained PFAS found that no PFAS remained on the carbon at temperatures above 700°C in nitrogen.[i]
- A number of studies indicate that PFAS and fluoropolymers are effectively destroyed under conditions similar to reactivation.[ii],[iii]
- PFOA and its various salts have been shown to be completely destroyed at temperatures of 350°C[iv],[v]
- PFOS is reported to be completely destroyed at 600°C.[vi],[vii]
- A study on the thermal stability of PFAS on spent GAC concluded, “…effective thermal destruction of PFAS during GAC reactivation in CO2/N2 or during incineration / combustion of materials laden with PFAS (e.g., municipal solid wastes) is very likely provided high temperatures (≥ 700°C) are used.”[viii]
- The porous and electron structure of the activated carbon is reported to increase the degree of decomposition of adsorbed PFAS during thermal processing.[ix]
Based on significant R&D work completed both internally, by third parties, and various literature references, we are confident that PFAS are desorbed and abated through Calgon Carbon’s reactivation process. If you have any questions or concerns, please do not hesitate to contact us at info(at)chemviron(dot)eu.
i Watanabe, N., Takemine, S., Yamamoto, K., Haga, Y., Takata, M. Residual organic fluorinated compounds from thermal treatment of PFOA, PFHxA and PFOS adsorbed onto granular activated carbon (GAC). Journal of Material Cycles and Waste Management, 2016, 18:625–630.
ii Yamada, T., Taylor, P. H., Buck, R. C., Kaiser, M. A., Giraud, R. J. Thermal degradation of fluorotelomer treated articles and related materials. Chemosphere, 2005, 61(7), 974 – 984.
iii Lemieux, P. M., Strynar, M., Tabor, D. G., Wood, J., Cooke, M., Rayfield, B., Kariher, P. Emissions of fluorinated compounds from the combustion of carpeting. Proceedings of the 2007 International Conference on Incineration and Thermal Treatment Technologies, Phoenix, AZ.
iv Krusic, P. J., and Roe, D. C. Gas-phase NMR technique for studying the thermolysis of materials: Thermal decomposition of ammonium perfluorooctanoate. Analytical Chemistry, 2004, 76(13), 3800–3803.
v Krusic, P. J., Marchione, A., Roe, D. C. Gas-phase NMR studies of, the thermolysis of perfluorooctanoic acid. Journal of Fluorine Chemistry, 2005, 126(11-12), 1510–1516.
vi Office of Pollution Prevention & Toxics, Docket AR226-1366, ed. Laboratory-Scale Thermal Degradation of Perfluorooctanyl Sulfonate and Related Substances. Washington DC: US Environmental Protection Agency, 2003, 13.
vii Office of Pollution Prevention & Toxics, Docket AR226-1367, ed. Final Report: Laboratory-Scale Thermal Degradation of Perfluoro-Octanyl Sulfonate and Related Substances. Washington DC: US Environmental Protection Agency, 2003, 142.
viii Xiao, F., Sasi, P. C., Yao, B., Kubatova, A., Golovko, S. A., Golovko, M. Y., Soli, D. Thermal stability and decomposition of perfluoroalkyl substances on spent granular activated carbon. Environmental Science & Technology Letters, 2020, 7, 343-350.
ix Baghirzade B.S., Zhang y., Reuther J.F., Saleh N.B. Venkatesan A.K., Apul O. G. Thermal regeneration of spent granular activated carbon to break the forever PFAS Cycle. Environmental Science & Technology, 2021, 55, 9, 5608 – 5619.