Supercritical Water Oxidation (SCWO) processing is a transformative treatment technology that utilizes the unique properties of water above its critical point (374 °C and 218 atm). At these conditions in the presence of abundant oxygen, all organic molecules are rapidly oxidized to inorganic species including CO2 and water, without a catalyst, and without the accumulation of potentially toxic intermediates. We have demonstrated that SCWO breaks the carbon-fluorine bonds within PFAS molecules when SCWO is conducted at medium- to high temperatures (&gt;550 °C and reaction times exceeding ~5 seconds), resulting in full mineralization of organofluorine to inorganic fluoride. Depending on the conditions, destruction efficiencies can exceed 99.99%. SCWO is effective for all PFAS species (ionic, non-ionic, high and low molecular weight), and does not result in accumulation of lower molecular weight PFAS or volatile PFAS species. We have investigated PFAS elimination from wastes at different scales, using a continuous process pilot system that can handle up to 1 ton of waste per day for treatability studies (e.g., with aqueous film-forming foam dilutions, decontamination rinsates, PFAS-contaminated sludge, and PFAS-contaminated groundwater) as well as in the laboratory, using a bench-scale system for kinetic and fundamental studies. In this presentation, we will discuss recent results detailing the kinetics of PFAS destruction using a variety of oxidants and experimental conditions during SCWO in our benchtop system. This includes the destruction of individual PFAS species, rinsates containing PFAS, and AFFF formulations as a function of temperature and reaction time, fluorine balances demonstrating complete mineralization of the PFAS destructed, and kinetic modeling of the oxidation process. The implications for treatment of PFAS in various matrices will be discussed.

Kinetics of PFAS destruction by supercritical water oxidation

ACS Spring 2022

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