Per- and polyfluoroalkyl substances (PFAS) are persistent environmental chemicals of concern, particularly at sites where aqueous film-forming foams (AFFF) were used. The objective of this demonstration was to evaluate the effectiveness of a mobile supercritical water oxidation (SCWO) system, the PFAS Annihilator®, to destroy PFAS in four types of concentrated aqueous waste streams including surface active foam fractionate, AFFF, and two ion exchange (IX) regenerant distillates. The study aimed to determine if SCWO could achieve >99.9% PFAS destruction, meet regulatory discharge requirements, minimize byproduct formation, and provide a robust, cost-effective solution for field-scale PFAS remediation.

SCWO is a high-temperature, high-pressure process that mineralizes PFAS into innocuous products such as carbon dioxide, water, and salts. The PFAS Annihilator^® operates above the supercritical point of water, enabling rapid oxidation of PFAS and co-occurring chemicals. The system is containerized for field deployment and incorporates advanced features for salt separation, corrosion resistance, and automated process control. The demonstration was conducted at the Clean Earth Centralized Water Treatment Facility in Detroit, MI, treating real-world PFAS-impacted waste streams generated from remediation activities.

The PFAS Annihilator^® achieved >99.9% removal of PFAS from all tested media before sorbent polishing, with actual destruction rates (accounting for PFAS in brine and vapor) ranging from 94% to 97%. Effluent concentrations for most regulated PFAS met federal and state maximum contaminant levels after granular activated carbon (GAC) polishing, with minor exceedances for perfluorooctanesulfonic acid attributed to operational issues with the GAC system. Operability exceeded 90% for most feed types.

A quantitative mass balance was performed for fluorine during treatment of each media type. The majority of fluorine introduced as PFAS was accounted for in the effluent streams, supporting the conclusion that the technology achieves substantial mineralization rather than merely transferring PFAS to another phase. Mass recoveries ranged from 83% to 169% across feed types, consistent with or better than previous SCWO studies. Percent defluorination, representing the conversion of organofluorine to inorganic fluoride, ranged from 78% to 167% across the tested feed types, further confirming substantial PFAS mineralization during SCWO treatment.

Energy efficiency was measured using the electric energy per order (EEO) metric, which is the electrical energy needed to remove one order of magnitude of PFAS. The feeds treated by the PFAS Annihilator^® had an EEO range of 263 to 1,412 kWh/m³, which is similar to other PFAS destruction technologies. When adjusting for dilution due to the oxidant and water introduced into the system EEO was found to be inversely related to the total PFAS concentration, such that high PFAS concentrations resulted in low EEO values.

Operational costs varied by feed type and PFAS concentration, ranging from approximately $30 to $154 per gallon of feed treated. Labor was the dominant cost driver (between 85 and 95% of total costs), followed by chemicals and electricity. The technology is most cost-effective for high-concentration waste streams, offering value through on-site destruction and reduced long-term liability compared to incineration or landfilling.

Key implementation challenges included managing salt precipitation (salt plugging), some corrosion of reactor materials, which did not impact performance, and ensuring proper configuration and maintenance of post-treatment polishing units (GAC and IX). The demonstration highlighted the importance of preventive maintenance, automation, and environmental controls (e.g., protection from weather and debris). Recommendations for future deployments include increasing automation, optimizing chemical dosing, and enhancing system throughput to further reduce costs and improve operational resilience. Such advancements in large-scale PFAS remediation and destruction contributes to sustainment of force readiness and the operational capacity of the defense industrial base, preventing disruptions to production and supply chains. (Project Completion - 2025)