Thermal Treatment of PFAS with Gasification, Pyrolysis, Incineration, and Supercritical Water Oxidation (SCWO) - What is the Current Status?

PFAS has become a major concern in wastewater treatment. Thermal processes offer an opportunity to treat PFAS using different technologies such as gasification, pyrolysis, incineration, thermal oxidation, and supercritical water oxidation (SCWO). There have been several promising pilot and bench scale studies resulting in high removal efficiencies of PFAS from biosolids. This technical paper presents and compares the results of the most recent studies on PFAS treatment using thermal technologies. Pyrolysis, gasification, and incineration technologies have been compared in a technical paper by Winchell (2023). Based on the results, pyrolysis and gasification were shown to be promising alternate technologies to incineration in terms of lower capital cost at lower feed rates, relaxed emission limits compared to incineration requiring less equipment for the air pollution control system, and the potential use of char, which is a by-product of pyrolysis and gasification process. A study by Williams (2023) confirmed that pyrolysis had the potential to reduce or eliminate the measurable concentration of PFAS in biochar. PFAS emissions testing was also performed at the stack outlet of the wastewater solids gasification and thermal oxidation demonstration scale installation in Loganholme, Australia (Loganholme City Council, 2021). Gasification systems operate similar to pyrolysis units except some oxygen gets introduced to the thermal reactor to further refine the off-gas and biochar products. The thermal oxidizer operated at a two seconds residence time at 800-850°C. In this case, the total mass of 28 PFAS in the outlet measured 47 ng/Nm3 over a 100-hour sample event. This emission level translated to an over 94% PFAS treatment efficiency across the thermal process train. Another study by 374Water (Sudhakar, 2023) indicated that SCWO technology could achieve more than 99.99% PFSA removal efficiency using proprietary AirSCWOTM process to treat PFAS from lime stabilized PFAS laden sludge. A lab scale study by Veolia (Mocock, 2023) confirmed that almost complete destruction of PFAS was possible using thermal oxidation at a combustion temperature of 1150°C at two different gas residence times (two and four seconds). Higher gas residence time (four seconds) at the same combustion temperature (1150°C) resulted in lower PFOA and PFOS air emissions during the lab scale tests. Bench and pilot scale studies by Laub (2023) indicated that pyrolyzed biosolids did not have any measurable levels of PFAS. Results of these studies have been presented at conferences such as WEF/IWA Residuals and Biosolids and WEFTEC in 2023. In this technical paper, PFAS test results from the most recent pilot and bench scale studies are being presented and compared to each other to determine the current status of PFAS treatment efficiencies for gasification, pyrolysis, thermal oxidation, and SCWO.