Low-Voltage Electrical Demulsification of Oily Wastewater

Many industrial processes generate oily waste-waters, characterized by low volume fractions of micrometerscale, oil-in-water droplets that are difficult to separate by mechanical or chemical means. High dc voltages are traditionally applied for the electrical demulsification of water-in-oil emulsions. In this work, we demonstrate that oil-in-NaOH contaminated wastewater emulsions respond to low-voltage, low-frequency oscillatory fields by aggregating near the electrodes. Optical microscopy shows that droplets initially separate upon the application of an similar to 10 Hz oscillatory field but slowly form aggregates over longer time scales of several minutes. The rate of aggregation varies nonmonotonically with the applied field strength, exhibiting a peak near 3 V(pp )and decreasing at higher strengths. Finally, we demonstrate that a combination of low-frequency fields with a small dc offset induces coalescence to break the emulsion. These results point toward a low-energy, nonchemical method for recovering oils from oily wastewaters.