In situ microbubble electroflotation enhanced emulsion separation and membrane antifouling ability for durable oil-in-water emulsion separation

Abstract

For membrane separation of emulsified oil wastewater, the aggregation of oil-in-water (O/W) emulsions on the membrane surface leads to the formation of a filter cake layer and seriously weakens separation flux. Herein, a Co₃O₄-coated titanium foam separation membrane with improved wettability, high electrochemical stability and excellent oxygen evolution reaction (OER) activity is developed. During the electroflotation coupled membrane separation (ECM) process, electro-generated microbubbles are rapidly generated and in situ released from the membrane surface, forming triple physical barriers consisting of a hydrophilic layer, electrostatic repulsion layer and microbubble layer to prevent the adsorption of oil fouling. Moreover, the electro-generated microbubbles can spontaneously adsorb and lift oil droplets for oil/water separation, while also accumulating inside the oil fouling adhered to the surface and removing it via increased buoyancy force. Therefore, the ECM strategy can eliminate flux decline induced by membrane fouling with improved separation flux (7.54 ± 0.30 kL m⁻² h⁻¹ bar⁻¹) and efficiency (99.9%), thus achieving long-term self-cleaning ability for O/W emulsion separation. In a 400 min continuous separation, the ECM process can recover its initial separation flux via intermittent microbubble-mediated antifouling, while the separation efficiency is consistently maintained above 99.8%, verifying the effectiveness and stability.