Breaking the stable carbon-fluorine bonds within per- and polyfluoroalkyl substances (PFAS) is one of the most significant challenges in mitigating persistent PFAS pollution. The Hydrothermal Alkaline Technology (HALT; diagram), invented at the Colorado School of Mines (Golden, Colo.; www.mines.edu) and commercially licensed by Aquagga, Inc. (Tacoma, Wash.; www.aquagga.com), can defluorinate PFAS using a precise combination of high temperature, pressure and alkalinity. “HALT fully mineralizes even the most recalcitrant PFAS, including short-chain and ultra-short-chain variants, which often pose significant degradation challenges for many other technologies. Unlike methods such as incineration or plasma, HALT avoids the formation of toxic volatile organic fluorine compounds, dioxins or other harmful emissions,” explains Dhileep Sivam, CEO of Aquagga.
In the HALT process (diagram), PFAS-contaminated liquid is mixed with an alkaline substance, typically NaOH. The solution is heated under high pressure to maintain a subcritical liquid state. The HALT systems then break the PFAS down, cleaving the carbon-fluorine bonds and mineralizing fluorine-to-fluoride ions. This, says Sivam, “closes the fluorine mass balance.” And since the reaction mechanism uses nucleophilic substitution, which selectively targets the C–F bond in a bulk reaction mechanism that does not rely on PFAS migrating to an electrode or interface, short- and ultra-short-chain PFAS are destroyed more reliably than with other technologies.
Sivam also points out that the HALT system can be used with very complex waste systems, and it has been used to efficiently treat high-salinity, high-organic-content waters without the corrosion or clogging issues that are usually associated with supercritical water oxidation (SCWO) or electrochemical oxidation (EO) technologies. “Additionally, compared to SCWO and plasma-based technologies, HALT operates at milder conditions (lower temperatures and pressures), significantly reducing equipment complexity and cost,” he adds.
The HALT system has seen several field installations in a variety of settings, and in 2026, the company is planning to deploy long-term installations at a large industrial complex and a solid-waste processing facility.