Formatted Title
Development of a Cost-Effective and Reliable Destructive Technology for PFAS: A Promising Advanced Reduction Process
Background/Objectives
Per- and poly-fluoroalkyl substances (PFAS) are a group of man-made, fluorinated organic chemicals that include thousands of individual compounds. The ubiquitous occurrence of PFAS in the environment, links to toxic effects at low concentrations, and several high-profile court cases, have led to increased media and regulatory attention. Currently, the most widely applied methods for treating PFAS-contaminated water are separation technologies, including ex situ granular activated carbon, ion exchange resin, foam fractionation, and membrane filtration. Although these separation technologies have been demonstrated effective to certain extent in removing PFAS, each process also generates one or more residue or concentrated streams that require further treatment. Cost-effective and reliable destructive technology is needed to destroy PFAS in such concentrated streams.
Approach/Activities
An innovative technology has been developed to destroy PFAS in the concentrated waste using an advanced reductive process. This technology is primarily based on hydrated electrons that are generated in an ultraviolet (UV)/sulfite system. Hydrated electron is a strong reductant, with a standard reduction potential of −2.9 volts and has been demonstrated effective in breaking carbon-fluorine bonds. The technology development has been supported with funding provided by the Department of Defense’s (DoD) Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP) and the Air Force Civil Engineer Center. Laboratory studies have been completed and a pilot-scale destructive treatment system has been constructed. Two field demonstrations are being planned.
Results/Lessons Learned
Laboratory studies and pilot-scale reactor tests were conducted using both simulated waste samples and field samples (e.g., ion exchange regeneration still bottom, foam fractionates from both groundwater and landfill leachate treatment) to systematically investigate reductive destruction of PFAS and the effort to date has resulted in the following key findings: 1) greater than 100% defluorination was achieved for field concentrate sample tests based on fluorine mass balance and target PFAS analysis; 2) the UV/sulfite system demonstrated excellent defluorination efficiency for both short- and long-chain PFAS. The notoriously recalcitrant perfluorobutane sulfonate (PFBS) can be degraded as well, albeit a longer reaction time is needed; 3) while some oxidative technologies generate toxic byproducts such as perchlorate, bromate and chlorate, the UV/sulfite system uses a reductive mechanism and does not generate those byproducts; and 4) the electrical energy per order (EE/O) values for degradation of PFCA by UV/sulfite have been reduced to less than 1.5 kilowatt hour per cubic meter under laboratory conditions. This energy consumption is orders of magnitude lower than that for other destructive PFAS treatment technologies. Results from laboratory experiments, pilot-scale reactor testing, and potentially field demonstration will be presented.