Treatment of perfluorooctane sulfonic acid (PFOS) using a large-scale sonochemical reactor

(Per)fluorochemicals are highly persistent in the environment and need to be treated before discharge. Sonochemical treatment is most efficient for removal of recalcitrant pollutants such as (per)fluorochemicals. Many laboratory-scale studies have highlighted the importance of sonochemical method for removal of (per)fluorochemicals. In the present work, treatment of perfluorooctane sulfonate (PFOS) using a large sonochemical reactor of 91-L capacity was investigated. The reactor was provided with nine 1-MHz and three 500-kHz transducers and variable power dissipation with maximum rating of 12,000 W. De-fluorination and mineralization of PFOS was evaluated based on release of fluoride and sulfate ions and removal of TOC for varying initial PFOS concentration and solution pH, addition of salt, and frequencies. It has been observed that release of fluoride and sulfate ions increased with an increase in initial PFOS concentration from 0.32 to 2.6 mM and a decrease in pH of the solution from 8.5 to 4.0. The maximum concentration of fluoride and sulfate ions released after 240 min of sonication was 102.2 ± 0.2 µM and 76.6 ± 0.1 µM, respectively, for an initial PFOS concentration of 2.6 mM at pH 4. The addition of sodium chloride and sodium carbonate decreased the rate of defluorination. The present investigation is useful for the development of a sonochemical process for industrial scale operations.