Application of Supercritical Water Oxidation to Effectively Destroy Per- and Polyfluoroalkyl Substances in Aqueous Matrices

Abstract

Supercritical water oxidation (SCWO) is a destruction technology to treat per- and polyfluoroalkyl substance (PFAS)-impacted groundwater, investigation-derived waste, and other aqueous matrices such as landfill leachate and aqueous film-forming foam. A SCWO system, Battelle’s PFAS AnnihilatorTM, was optimized with a goal of reducing all measured PFAS to non-detect levels. Laboratory-prepared and field-collected samples with inlet PFAS concentrations up to 50 ppm were consistently destroyed to less than 70 ppt for all PFAS, when running at the determined optimal operating conditions (≥600 °C and 3500 pounds per square inch). We investigated the correlation between temperature and flowrate of the system, finding that reactor temperatures ≥450 °C destroy perfluorinated carboxylic acids, but temperatures of ≥575 °C are necessary to destroy perfluorosulfonic acids. A continuous 5-log reduction in concentration of PFAS (99.999% destruction) is demonstrated for 3 h at steady-state operation. The destruction efficiency is not impacted by the addition of co-contaminants such as petroleum hydrocarbons, and volatile organic compounds. The treated effluent is largely composed of complete combustion products including carbon dioxide, water, and the corresponding anion acids; hence, the treated liquid can be released back into the environment after neutralization.

Available and emerging liquid treatment technologies for PFASs

“…Supercritical water is achieved at temperatures and pressures above its critical point (374°C and 22.1 MPa). At higher temperatures, around 575°C–650°C, nearly all PFASs can be mineralized with a residence time of 25 s (Li, Austin, et al, 2023; McDonough et al, 2022; Scheitlin et al, 2023). Destruction percentages are largely impacted by the temperature of the reactor (Scheitlin et al, 2023).…”

“…At higher temperatures, around 575°C–650°C, nearly all PFASs can be mineralized with a residence time of 25 s (Li, Austin, et al, 2023; McDonough et al, 2022; Scheitlin et al, 2023). Destruction percentages are largely impacted by the temperature of the reactor (Scheitlin et al, 2023). Commercial SCWO reactors are operated at temperatures >500°C to ensure complete destruction and reduce the residence time.…”

“…Commercial SCWO reactors are operated at temperatures >500°C to ensure complete destruction and reduce the residence time. SCWO has been reported to oxidize and mineralize PFASs by up to 99.9% (Krause et al, 2022; Li, Austin, et al, 2023; Scheitlin et al, 2023). In addition to treating aqueous materials, SCWO has the potential to treat spent treatment media such as IX resin and GAC in a slurry form (Chiang et al, 2023), and has been considered for treatment of biosolid slurries.…”

Decomposition of Organic Pollutants in Subcritical Water under Moderate Conditions

“…The authors confirmed the previously established fact that the pressure did not significantly affect the efficiency of the process. Groundwaters contaminated with polyfluoroalkyl compounds (PFAS) were treated at high temperatures (≥600 • C) with supercritical water oxidation (SCWO), achieving complete combustion and producing carbon dioxide, water, and corresponding anion acids, and were considered safe after neutralization [9]. In steady conditions, after 3 h of treatment, the concentration of PFAS dropped from ~50 ppm level to an almost undetectable level (70 ppt).…”