Application of Supercritical Water Oxidation for Treating Wastes Contaminated with PFAS, 6PPD-Q, and Other Emerging Pollutants

The rapid emergence of contaminants of emerging concern (CECs) in municipal and industrial waste streams has accelerated the need for treatment technologies capable of achieving verifiable destruction across a broad chemical spectrum. Supercritical Water Oxidation (SCWO) has increasingly been positioned within the landscape of 'thermal technologies,' yet is often compared-sometimes inappropriately-to systems that differ fundamentally in chemistry, operating mechanisms, monitoring requirements, and achievable performance. Current technology comparison studies typically fall into two categories: (1) comparisons to broad-treatment thermal technologies capable of addressing many or most CEC classes, and (2) comparisons to highly specialized technologies designed to target only one or a small subset of contaminants. In both cases, economic or performance comparisons often lack the foundational data needed to be meaningful. For technologies in the first bucket, comparisons are limited because regulatory monitoring and verification requirements differ widely across platforms. Many systems do not require, or are not capable of, collecting mass balance data that confirms true destruction rather than transformation or transfer of contaminants. As a result, economic comparisons fail to reflect the cost of achieving verified destruction. For the second bucket-specialized solutions developed in response to accelerated PFAS regulatory pressure-economic analyses are typically framed around PFAS alone. This narrow focus does not account for the longer-term value of a technology capable of treating diverse CECs such as pharmaceuticals, tire-derived contaminants (e.g., 6PPD-q), industrial organics, and complex waste matrices. Consequently, technology selection is often made without considering the operational and financial advantages of broad applicability. This presentation addresses the gap created by these incomplete comparisons by providing new data that illustrates how SCWO performance varies across waste types and CEC classes with only moderate adjustments to system operating parameters. Because SCWO is frequently and incorrectly grouped with incineration and other thermal destruction methods, this work clarifies the fundamental distinctions in reaction environment, destruction mechanisms, emissions profiles, effluent quality, and monitoring requirements. A detailed overview of SCWO's flexibility is presented through data generated from municipal sludges, controlled laboratory studies using spiked CEC solutions, and blended industrial waste streams. Methods: A series of waste matrices were evaluated to assess the performance of SCWO on eliminating various CECs. The contaminants tested include PFAS compounds in wastewater sludge, analytical grade 6PPD-q, and a pharmaceutical waste blend containing various solvents and organic contaminants. Variables examined include alkaline addition, reactor temperature, operating pressure, mixing intensity, and influent water content. Performance was measured using process indicators-pressure drop behavior, temperature stability, CO emissions, metals content in the liquid effluent-and by assessing physical characteristics of the resulting effluent streams. Analytical measurements of contaminant concentrations in the SCWO influent and effluent were used to determine destruction efficiency. Results PFAS in Sludge: Multiple datasets were generated by treating sludges with various concentrations of PFAS (variations on both a diurnal and seasonal level) via SCWO to determine a range of typical PFAS destruction and removal efficiencies (Figure 1). This commercial scale demonstration which showed >98% DRE for every PFAS compound detected in the influent verified the effective treatment of PFAS in biosolids using SCWO. Additionally, valuable insights on run-time and reliability were realized and allowed for optimization of the unit both mechanically and operationally. 6PPD-q: This project was conducted using a bench-scale SCWO system. The main benefits from first conducting this research at bench scale were (1) resource efficiency and (2) cost-effective identification of conditions to be scaled up to commercial SCWO systems. Analytical results showed a reduction from an inlet 6PPD-q concentration of 18 ug/L to non-detect in both of the two effluent grab samples. Considering the method detection limits of 0.64 and 0.58 ng/L (0.00064 and 0.00058 ug/L), a DRE of >99.99% was achieved. Mixed Pharmaceutical Waste: Two variables were tested – the feedstock blend and the SCWO operating temperature and pressure – to determine how versatile the SCWO system is in treating the waste should the blend vary from batch to batch. The results, using COD as a surrogate for all organic constituents, illustrated that the impact of waste blend and/or SCWO operating conditions was marginal. In all instances, >99% removal of COD was achieved, resulting in a SCWO effluent that was in compliance with the existing industrial site. Significance: The ability of SCWO technology to treat a wide range of contaminants with minimal operating adjustments suggests that the benefits of investing in the technology, may outweigh the higher OPEX of SCWO as compared to traditional waste disposal techniques such as landfilling.