Electrochemical mineralization mechanisms of perfluorooctanoic acid in water assisted by low frequency ultrasound

Abstract

The mineralization of perfluorooctanoic acid (PFOA) was investigated in electrochemical oxidation process (EC) with the assistance of low frequency ultrasound (US). The electrochemical degradation of PFOA was enhanced under the synergic effects of Ti/SnO2–Sb/Ce–PbO2 anode and US (20 kHz and 52 W). The influences of PFOA initial concentrations on its degradation were studied in EC and US-EC systems, while the effects of applied current densities were investigated in US-EC system. With the assistance of US, the increases of pseudo-first-order kinetic rate constant from 0.017 to 0.031 min−1, defluorination efficiency from 75.9% to 87.9%, mineralization efficiency from 71.9% to 86.1% and mineralization current efficiency from 0.66% to 0.77% were obtained at current density of 15 mA cm−2 and PFOA initial concentration of 60 mg L−1 during the reaction time of 180 min. The production and quenching of •OH were tested to emphasize the function of US in electrochemical mineralization of PFOA. In US-EC system, the electrochemical degradation performance of PFOA was enhanced not because of cavitation under US, but possibly because of the collapse of bubbles, anode surface cleaning, fast electron transfer on anode and higher •OH production under the assistance of US.