Experimental investigation of oil-in-water microfiltration assisted by Dielectrophoresis: Operational condition optimization

Membrane filtration is an efficient method in treating oily waste water containing fine oil droplets. However rapid fouling of membrane and decay in process performance has resulted in limited industrial application of membrane processes for oily waste water treatment. In this paper, electric field is used as an assisting force to improve oil in water microfiltration performance. An electrically safe membrane module is fabricated and used for microfiltration studies in the presence of electric field. A statistical study is developed for conducting necessary experiments to identify optimum processing conditions in the presence of an AC electric field. Two response functions of stable flux and oil rejection are defined and optimized with response surface methodology and central composite design. The effects of trans membrane pressure, cross flow velocity, feed concentration and applied voltage on stable permeate flux and oil rejection are studied for an emulsion of 1.93 μm oil droplets in water in a microfiltration system with cellulose acetate membrane of 0.45 μm pore size. Results reveal that induction of electric field can considerably improve process performance. Variation in studied factors results in the flux ranging from 64 to 140 L/m2hr while rejection varies between 85% and 97%. Quadratic models are suggested for flux and rejection with 0.93 and 0.83 R2 values respectively. Optimum conditions are predicted at 136.2 L/m2hr for flux and 94.1% for rejection, observed at 360 V, 1.1 m/s, 900 ppm and 2.5 bar. The real values for flux and rejection are 131.8 L/m2hr and 88.7% respectively representing −3.4% and −6.0% relative errors for the correlations.