Utilization of enhanced electrolytic bubbles in electrooxidation for efficient refractory organics removal

Although electrooxidation can remove refractory organics, a significant amount of energy is required for non-selective oxidation, and the oxygen evolution reaction (OER) contributes little to the process. In this study, the conventional electrolytic bubbles were enhanced to improve the performance of organic matter removal. Using humic acid as a model recalcitrant organic pollutant, a membrane electrochemical reactor (MER) was designed to separate mixed bubbles (e.g., H₂ and O₂) produced during electrooxidation with a diaphragm, thereby dividing the individual MER O₂ and MER H₂. The bubbles stability of MER O₂ was higher than that of conventional electrooxidation and aeration, which facilitated the removal of humic acid. Surfactants with different electrical characteristics were further used to enhance the interaction between the bubbles and humic acid. After the addition of cetyltrimethylammonium bromide (CTAB 80 mg/L), the positive charge of the MER O₂ bubbles intensified, inducing the removal of 92.8 % humic acid (250 mg/L) with an oxidation rate <3.7 %. Moreover, CTAB could be reused after foam fractionation. Using zeta potential distribution theory, the initial electrical properties of MER O₂ (+) and MER H₂ (-) were clarified, as well as the charge intensification by CTAB on MER O₂ bubbles. Besides, the acidification by MER imparted initial electrical properties to the bubbles and led to the aggregation of humic acid, and the humic acid adhering to the bubbles further isolated the merging of the bubbles. The application of enhanced electrolytic bubbles offers a novel approach to reducing energy consumption in humic acid removal via electrooxidation systems.