Supercritical Water Oxidation (SCWO) for Complete PFAS Destruction
Dr. Marc Deshusses | Duke University
There are unprecedented challenges caused by the extensive use of aqueous film forming foam (AFFF) containing significant quantities of per- and polyfluoroalkyl substances (PFAS). As a result, SERDP and ESTCP are funding a broad portfolio of research and demonstration projects aimed at a) finding benign replacements for fluorinated AFFFs, b) developing technologies for the cleanup of firefighting equipment that contained PFAS, and c) developing and demonstrating treatment technologies to remediate PFAS-laden materials. The remediation of such materials is rendered particularly challenging by the extremely low lifetime health advisories that have been implemented or proposed by the U.S. EPA for PFAS. These require extraordinarily effective treatment technologies.
The overall objective of this project is to demonstrate the technical feasibility of using supercritical water oxidation (SCWO) for the complete destruction of PFAS in a variety of relevant waste streams and to determine and optimize the treatment cost effectiveness.
SCWO processing is a transformative treatment technology that utilizes the unique properties of water above its critical point (704 °F and 3200 pounds per square inch). At these conditions, when air is injected, all organics are rapidly oxidized to carbon dioxide and water, without a catalyst, and without the formation of harmful by-products. The project team has shown that PFAS can be very effectively destroyed by SCWO in preliminary experiments, with effluent streams well below health advisory limits. Success in this project will be measured by the ability to consistently treat wastes to below the Regional Screening Levels (RSLs) or 40 part per trillion for perfluorooctanoic acid (PFOA) + perfluorooctanesulfonic acid (PFOS) and individual PFOA and PFOS while remaining within cost constraints.
This one-year demonstration will include treatability studies to be conducted in an existing and state of the art pilot SCWO system at Duke University that can treat about 1 ton (or 260 gallons) per day. PFAS-containing rinsates, residues derived from cleaning processes, rinsates and residues, spent adsorption matrices will be processed and the PFAS destruction efficacy will be quantified and optimized under a range of selected operating conditions. The fate of fluorine atoms will be tracked to show destruction of PFAS to harmless end-products. Data intelligence will help determine the factors that affect treatment performance for the different PFAS which will help with optimizing the operating conditions for maximum PFAS destruction. In parallel, a detailed techno-economic analysis will be conducted for typical DoD scale scenarios that will serve to optimize the cost of using SCWO for the destruction of PFAS-laden wastes at DoD facilities.
SCWO treatment offers many advantages and will lead to cost savings for the DoD. It is extremely fast (treatment occurs in seconds) and thus systems will have a very small footprint. In addition, it does not require catalysts, nor are there harmful residues or emissions of NOx, SOx. The SCWO treatment is scalable with high destruction efficiency (>99.99%). It is also very versatile as it can co-treat all types of wastes.