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.