Degradation of microplastics by electrocoagulation technology: Combination oxidation and flocculation effects

Electrocoagulation (EC) technology features a promising prospect for coping with the formidable microplastics (MPs) pollution challenge, albeit the underlying abatement mechanism still needs to be further clarified. Accordingly, in this work, we evaluated the removal performance by EC for four typical MPs, including polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), and polyethylene (PE). The Fourier transform infrared spectroscopies of MPs confirmed the presence of electrochemical oxidation during EC process, owing to its hydroxyl radical generation ability as demonstrated by the detected fluorescence spectroscopies and electron paramagnetic resonance results, which has been rarely reported in other works. Specifically, 21.2 ± 0.8 %, 10.8 ± 1.8 %, 15.6 ± 1.6 %, and 7.6 ± 1.4 % abatement efficiency for PVC, PS, PP, and PE, respectively, originated from the oxidation effect, and these values for flocculation effect were 77.2 ± 0.8 %, 74.0 ± 1.6 %, 70.8 ± 1.2 %, and 69.2 ± 1.2 %, successively. Many factors influence these differences, especially the MPs' hydrophilicity, as it facilitates the mass transfer efficiency between MPs (like PVC and PP) and the generated flocs or radicals. To lay a foundation for practical application, we also optimized the operation parameters, demonstrating the wise choice of pH 7 to maintain a balance between the oxidation and flocculation effect. Therefore, we believe our work provides a good reference for promoting MPs abatement efficiency and elucidating the corresponding mechanism, especially the contribution of the oxidation part by EC.