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 (e(aq)(-)) 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 e(aq)(-) 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.