Enhanced Electrochemical Destruction of Perfluorooctanoic Acid (PFOA) Aided by Overlooked Cathodically Produced Bubbles

Perfluorooctanoic acid (PFOA) electrochemical elimination systems usually focus on anodic processes, while the cathodic reactions are generally neglected. In this study, an anodic oxidation system aided by cathodically produced bubbles was proposed for enhanced PFOA oxidation, by simply rotating the electrode orientation by 90 degrees with the cathode at the bottom and the anode at the top (abbreviated as AO/ Rotation). In the AO/Rotation system, hydrogen bubbles that were inevitably generated at the cathode could concentrate PFOA and bring it to the anode for further oxidation; thus, PFOA removal increased by 50% at 4.5 V/standard hydrogen electrode. The first-order rate also increased from 2.7 x 10-2 h-1 cm-2 for anode oxidation alone to 3.8 x 10-2 h-1 cm-2 for AO/Rotation. N2 sparging promoted the defluorination rate from 31% to 100% (100 mL/min) at 3 h, further proving the dominant contribution of bubble enrichment. The aerosol release is negligible in this system according to fluoride mass balance. Energy consumption of this new system was only 7 kWh center dot m-3 center dot log-1, half of that in the direct AO process. These results demonstrate that cathodically produced bubbles for improved mass transfer should be well-utilized during the reactor design for energy-efficient PFOA removal.