Combination of electric field and medium coalescence for enhanced demulsification of oil-in-water emulsion

Currently, the green and efficient demulsification of oil-in-water (O/W) emulsion is a challenging problem in the treatment of oily wastewater. This work describes a nonchemical method for recovering oil from emulsions. A novel attempt to enhance the demulsification of O/W emulsions using the combination of an electric field and medium coalescence was carried out, and the combined treatment significantly improved the separation performance compared with medium coalescence or electrical demulsification alone. The electrohydrodynamic (EHD) effects could drive fine droplets to migrate and collide with the medium. The demulsification effects under various electric field parameters and medium properties were investigated. As the voltage increased, the EHD motion of oil droplets increased, and the demulsification effect was significantly improved. Under the same voltage, the demulsification effect of the DC electric field (DCEF) was better than that of pulsed electric field, but the current of bidirectional pulsed electric field (BPEF) is smaller. BPEF was more efficient at low frequencies less than 25 Hz. As the frequency increased, EHD motion was inhibited, especially when the frequency exceeded 1000 Hz, and the demulsification effect was poor. The particle size of the coalescence medium was also a key factor. The bed packed with small-sized particles showed a better demulsification effect whereas the wettability of the particles showed relatively little effect.