Effect of chain length, electrolyte composition and aerosolization on the removal of per- and polyfluoroalkyl substances during electrochemical oxidation

Abstract

Electrochemical oxidation processes (eAOP) are a promising approach for the remediation of per- and polyfluoroalkyl substance (PFAS) due to its ease of operation, low energy needs and lack of auxiliary chemicals. In this study, we designed and utilized a boron-doped diamond anode in a two-electrode system to investigate the impact of the electrolyte composition and PFAS chain length on the eAOP performance. We varied the supporting anions (Na2SO4, NaCl, NaNO3) and electrical conductivity (500-2000 μS cm−1, constant current), and found no effect of supporting anions on PFAS removal. Varying the supporting anions, while maintaining constant electrical conductivity did not significantly vary the anodic voltage (p value = 0.99). We found a strong correlation between PFAS removal and their log n-octanol-water partitioning coefficient (r = 0.8), suggesting that PFAS sorption onto the electrode was a critical step in the degradation of PFASs. It was also demonstrated, for the first time for eAOPs, that gas bubbles generated in the system could capture and transport PFASs from the solution to the water surface, leading to loss of PFASs by electrochemical aerosolization (2-85%) after the bursting of bubbles. Fluorine mass balance for the treatment of PFOA and 6 : 2 FTS revealed ∼68% recovery post treatment, with the inorganic fluorine (48%) released during treatment being the primary component and ∼20% fluorine, unaccounted for. Results from this study highlight the impact of the supporting electrolyte and PFAS aerosolization on the treatment efficiency and provide insight into the mechanisms and system design to improve removal of PFASs utilizing an eAOP.