Formatted Title
Application of Supercritical Water Oxidation to Treat Concentrated Per- and Polyfluorinated Substances (PFAS)-Impacted Water
Background/Objectives
The PFAS Annihilator™, a supercritical water oxidation (SCWO) technology, has been demonstrated to achieve a high degree of per- and polyfluoroalkyl substances (PFAS) removal (>99.99%) in aqueous media including landfill leachate, investigation derived waste (IDW), groundwater, and aqueous film forming foam (AFFF), among others. The PFAS Annihilator™ differentiates itself from other PFAS remediation technologies in that it completely mineralizes PFAS to produce carbon dioxide, water, and inert salts, requires a less than 10 second residence time, is effective on short- and long-chain compounds, is not inhibited by organic co-contaminants, is not likely to generate high temperature reaction byproducts (e.g., SOx and NOx), and effectively treats dilute and highly concentrated PFAS-impacted streams.
Reverse osmosis (RO) is a readily available technology that can be used to remove PFAS from a variety of impacted aqueous sources. RO produces a reject (concentrate) stream that contains concentrated PFAS, and other ions, and any contaminants that may be present in the feed source. This concentrated stream must be treated to remove PFAS and any other compounds and/or disposed of off-site in accordance with local requirements.
The objective of this field demonstration is to evaluate a treatment train approach that combines SCWO with RO to achieve a high degree of PFAS removal while minimizing operating cost ($/pound of PFAS removed/destruction efficiency).
Approach/Activities
The Active Fire Training Area (AFTA) at Peterson Space Force Base is part of a recirculation system used during training exercises to capture and store water. Although PFAS-containing AFFF is no longer used, residual PFAS in soil and groundwater has impacted the water in the tank. Historical levels of PFAS in the AFTA tank are 15 micrograms per liter (µg/L) PFOA, 188 µg/L PFOS, and 447 µg/L total PFAS. In addition, other chemicals commonly encountered at fire fighting training facilities, including petroleum hydrocarbon constituents and chlorinated ethenes are present.
A bench-scale study was performed using water from the AFTA tank to evaluate PFAS destruction and identify any issues that could impact field operation. Unconcentrated, 50% and 90% concentrates generated using RO, were tested. Testing results were used to determine required treatment chemical dosage, rate of vapor generation, and liquid and vapor effluent polishing requirements for the field demonstration.
A field demonstration of the PFAS Annihilator™ will be performed at the AFTA to demonstrate the efficacy of SCWO to destroy PFAS in RO concentrate. The demonstration will commence November 2023. A PFAS Annihilator™, which can treat 350 gallons per day and is equipped with a field-scale RO system, will be mobilized to the site. The PFAS Annihilator™ will be operated to treat, unconcentrated, 50% concentrate, and about 90% concentrate. Operation will be performed continuously for about 48 hours for each feed processed.
Results/Lessons Learned
Results of the bench tests indicated that PFAS can be destroyed effectively with close to 100% removal in the 90% concentrate. Vapor data indicated that little vapor will be generated during the field demonstration (less than 1.5 m3/day) and that concentrations of PFAS in the vapor will be negligible. Bench test results also indicated that 20% hydrogen peroxide or less can be used for the field demonstration mitigating fire and safety concerns associated with higher concentrations. Furthermore, no feed-specific issues were identified during the bench test that would be expected to adversely impact the field demonstration.
Results of the field demonstration will be presented. The cost (dollars per 1,000 gallons treated per treatment efficiency) and performance to continuously treat aqueous PFAS-impacted media at the planned concentrations will be discussed. Results of a fluorine mass balance will be included to confirm that PFAS is destroyed rather than being transferred to another media. Lessons learned and any technological challenges based on data and observations made during the demonstration also will be discussed.