Unstable secondary oil water emulsion treatment using ultrafiltration: fouling control by backflushing

Ceramic membranes with different characteristics and pore size distributions were evaluated for the treatment of an unstable secondary emulsion. The experimental studies were undertaken to investigate the optimum operating conditions (forward and reverse backflushing time, pressure, velocity and feed concentration) to obtain the best permeate flux. Backflushing was applied to reduce the formation of a gel polarization layer and membrane fouling. The optimum forward filtration and reverse filtration time were found to be 1 min and 0.7 s, respectively. Applied pressure, velocity and feed concentration also have an important influence on the flux. With hydrophobic membranes, flux was found to be lower than with hydrophilic membranes, indicating that oil was easily wetted on the hydrophobic membrane surface and induced more fouling of the membrane. The contamination of the permeate with oil was observed when using 0.5 mu m pores as the operating pressure was then higher than capillary pressure. Moreover, oil droplet sizes were bigger than in the feed as a result of the coalescence of oil drops as they passed through the membrane pores. (C) 1999 Elsevier Science B.V. All rights reserved.