PFAS Treatment Strategies: Challenges and Solutions
Citation:
Sahle-Demessie, E. PFAS Treatment Strategies: Challenges and Solutions. U C Graduate Seminar, Cincinnati, OH, February 24, 2023.
Impact/Purpose:
Supercritical water oxidation (SCWO) is a destructive technology that uses unique properties of water above its critical point at 374°C and 3200 psi. Thus, SCWO is a moderate temperature and pressure technology that offers essential environmental advantages for treating industrial wastes and sludges. SCWO, or hydrothermal oxidation (HTO), has homogeneous reaction conditions between oxidizing materials and added oxygen or hydrogen peroxide as the oxidizing agent creates an aggressive oxidative environment. The reaction of SCWO can also be heterogeneous when the organic material is a solid or, in the case of heterogeneous catalytic SCWO. EPA-vendor studies show high removal efficiencies with no measurable fluorinated emission.
Description:
Communities are searching for technologies to remove and destroy toxic per- and polyfluoroalkyl substances (PFAS), especially when these chemicals are in their drinking water. PFAS have been used in applications such as fire-fighting foam, cosmetics, water- and fire-resistant clothing, and aerospace equipment. Their durability makes them environmentally persistent, and some forms of PFAS are toxic and linked to health problems. Supercritical Water Oxidation (SCWO) process for hazardous waste destruction uses the temperature and pressure of water above the critical point (374 oC, and 22.1 MPa) to degrade hazardous organic pollutants into CO2, water, SO42-, and other benign compounds. We have tested SCWO technology the removal and destruction efficiency of (PFAS) within aqueous film-forming foam (AFFF). The complete miscibility of hazardous pollutants with oxidizing gases in a single phase at moderate temperature and molecular densities affords high destruction efficiencies with a residence time of less than 30 sec. Aqueous film-forming foam mixed with water at ratios (34 to 212) was fed to the SCWO reactor at an average rate of 9.1 L/min. Samples were collected from both influent and effluent streams – including gaseous emissions. In all tests, PFAS and total organic carbon (TOC) destruction efficiencies were > 99.99%, of targeted PFAS compounds, with high levels of fluoride ion detected, and no non-target PFAS above the background level in the gas analyses. The effluent from the process is water, with dissolved HF and gas consisting of CO2, O2, and oxidation products of the diesel used for energy generation with less than 10 ppm of CO. The study confirmed safe, complete, and reliable destruction of PFAS is within our reach, thus solving the most fundamental issue that comes with PFAS.