Investigating Potential of AC Electrocoagulation for Removal of Microplastics

Alternating current electrocoagulation (AC-EC) has been proposed as an alternative to conventional Direct current electrocoagulation (DC-EC) as it mitigates cathode passivation. This is due to the polarity reversal in an AC system preventing the buildup of the unwanted metal oxide layer on the cathode. AC has shown higher removal efficiencies and lower energy consumption in studies involving heavy metals and dyes. This study aimed to replicate those results with microplastics (MPs). A kinetic study of AC-EC with varying NaCl concentrations was conducted to find optimal concentration, which was then used to conduct a DC-EC experiment to compare the removal efficiencies of AC and DC. An AC–DC cycle experiment—run back-to-back without cleaning electrodes—was also performed to compare the effects on cathode passivation. Contrary to expectations, AC showed lower removal efficiency and higher energy consumption. SEM images further revealed greater cathode passivation in electrodes used for AC than DC. A possible reason could be that the frequency of the AC was too high, causing concentration polarization of the coagulants near the electrodes without diffusion into the bulk solution to sufficiently interact with the MPs. Further research should explore AC-EC of microplastics at varying frequencies while optimizing other critical parameters.