R. Schmitz
374Water,
United States
Keywords: supercritical water oxidation, SCWO, AFFF, PFAS, biosolids, foam fractionation, remediation, ion-exchange resin
Summary:
Supercritical Water Oxidation (SCWO) is emerging as the technology of choice for treating a wide range of wastes containing recalcitrant hazardous chemicals including PFAS. SCWO leverages the reactivity and transport properties of water above its critical point (374 °C and 218 atm). In oxygenated supercritical water, organics are completely oxidized to carbon dioxide, clean water and benign inorganic salts in <1 minute. 374Water operates full- and bench-scale SCWO reactors capable of comprehensive mineralization of diverse PFAS-impacted materials in liquid or slurried matrices. PFAS-impacted matrices include industrial streams, contaminated environmental matrices, and concentrated media from PFAS remediation. Each matrix presents unique processing requirements. We present case studies for processing PFAS-laden aqueous film-forming foam (AFFF), municipal biosolids, ion exchange resin (IX) and foamate. 374Water’s bench-scale SCWO reactors (≤1 L/hr throughput) enable rapid process optimization. Our full-scale reactors (~100+ L/hr) can be deployed to waste generation sites or centralized treatment facilities and process PFAS streams at commercially relevant scales. AFFF represents a major source of PFAS contamination, millions of gallons of AFFF are stockpiled in the US. We received stockpiled AFFF for destruction testing. In a bench-scale reactor, AFFF was processed at 0.06 L/hr to evaluate the impact of residence time and temperature, demonstrating a PFAS destruction and removal efficiency (DRE) of 99.9999%. A full-scale SCWO reactor demonstrated AFFF destruction at 48 L/hr with a DRE of 99.9999%. Municipal biosolids are under increasing regulatory scrutiny due to PFAS contamination. We partnered with the City of Orlando to process PFAS-impacted biosolids from wastewater treatment. Biosolids (~7.2% total solids) were processed in full-scale reactors at 96 L/hr, with PFAS DREs between 98.6% and 99.9999%. Bench-scale biosolid testing includes optimization of mineral recovery and feedstock formulation. Remediating PFAS-impacted environmental matrices like groundwater or leachate typically utilizes a PFAS concentration step, producing a solid or liquid PFAS-enriched stream. 374Water has processed various solid and liquid PFAS-concentrate media, including IX and foamate from foam fractionation. IX is increasingly used in PFAS remediation and can be tailored to optimize PFAS sorption. We received spent IX from groundwater remediation with PFAS levels in the 500 mg/kg range. At bench-scale, IX was processed at 45 g/hr and demonstrated a PFAS DRE of 99.99999%. Bench-scale testing elucidated the roles of temperature, residence time and oxygen/waste ratios on the extent of mineralization of target PFAS. A full-scale reactor processed IX at 3 kg/hr with a PFAS DRE of 99.98%. Foam fractionation is applied directly to dilute matrices such as groundwater, or to pre-concentrated streams, such as reverse-osmosis reject. 374Water received foamate with a PFAS load of 5.6 mg/L. Bench-scale processing at 0.48 L/hr demonstrated a DRE of 99.999% and indicated the impact of foaming additives on reactor process control. A full-scale reactor destroyed 90-100 L/hr of foamate with a DRE of 99.9998%. 374Water has also demonstrated destruction of ultrashort-chain PFAS species and other persistent contaminants including 1,4-dioxane and 6PPD-Q. Detailed system performance including conversion of organics and emerging contaminants, and materials and energy balances will be presented at the conference.