Enhanced Degradation of Perfluorocarboxylic Acids (PFCAs) by UV/Sulfite Treatment: Reaction Mechanisms and System Efficiencies at pH 12

Reductive defluorination with UV-generated hydrated electrons (eaq–) is a promising technology for the destruction of perfluorocarboxylic acids (PFCAs, CnF2n+1COO–). However, prior studies using pH 9–10 observed a slow reaction rate, limited defluorination percentage (deF%), and thus high energy consumption. Herein, we report on the substantially enhanced rate and extent of PFCA defluorination by operating the UV/sulfite system at the optimized pH 12. Degradation kinetics and transformation products show that at pH 12 the eaq– cleaved multiple strong C–F bonds that could not be cleaved at pH 9.5. The high pH condition also significantly favored the preferred decarboxylation pathway toward a deep defluorination. In comparison to the reactions at pH 9.5, the increase in solution pH to 12 improved the UV lamp energy efficiency by 5–22 folds, enhanced the deF% of C3–C9 PFCAs to 73%–93%, and reduced the overall consumption of chemicals.