Decontamination and Surface Analysis of PFAS-Contaminated Fire Suppression System Pipes: Effects of Cleaning Agents and Temperature

Per- and polyfluoroalkyl substances (PFAS)-containing firefighting foam have been used in stationary fire suppression systems for several decades. However, there is a lack of research on how to decontaminate PFAS-contaminated infrastructure and evaluate treatment efficiency. This study assessed the removal of PFAS from stainless steel pipe surfaces using different cleaning agents (tap water, methanol, and aqueous solutions containing 10 and 20 wt % of butyl carbitol (BC)) at different temperatures (20 °C, 40 °C, and 70 °C). The content of the remaining fluorine (F)-containing compounds on the pipe surfaces was evaluated for the first time using time-of-flight elastic recoil detection (ToF-ERD). The results showed that a 20% BC aqueous solution heated to 70 °C removed up to 40 μg/cm² ∑PFAS from surfaces via soaking (targeted analysis). Treatment with 20% BC was 2- to 8-fold more effective than tap water at 70 °C and 10- to 20-fold more effective than tap water at 20 °C. Total fluorine analysis determined by combustion ion chromatography showed a 2- to 8-fold higher F-equivalent compared to targeted analysis in the cleaning solution after treatment, indicating the presence of a significant amount of polyfluoroalkyl PFAS. Surface analysis with ToF-ERD confirmed partial F removal from pipe surfaces throughout consecutive soaking intervals, with residual F remaining on pipe surfaces after treatment, leaving the risk of PFAS rebound into F-free firefighting foams. Furthermore, supramolecular assemblies of PFAS with at least 70 PFOS molecules/nm² were identified by ToF-ERD on pipe interior surfaces.