Pilot-scale ultrafiltration of an emulsified oil wastewater

Abstract

Wastewater from a household appliance factory containing emulsified oil was treated using a separation method based on an ultrafiltration membrane. Initial wastewater characteristics were a chemical oxygen demand (COD) of 1500 mg of O2/L and a total hydrocarbon concentration (HC) of 170 mg/L. The cross-flow pilot-scale study was performed with two commercial spiral-wound membrane modules having a molecular weight cutoff of 35 000 (M2 membrane) and of 2000 (M1 membrane). The M1 membrane showed COD and HC rejection performance higher than the M2 membrane. The M1 permeate flux and solute rejection were investigated in relation to the membrane pressure drop (ΔP= 100-400 kPa), temperature (20-35 °C), and feed cross-flow rate (2-5 m3/h). The permeate flux was in good agreement with the expression of Darcy's law, where the end-of-permeate flux is directly proportional to both applied pressure and temperature. Results indicate that the fouling layer resistance of the membrane was the dominant resistance and that it was mainly caused by the emulsified oil adsorption on the surface and/or in the pore wall of the membrane. For design purposes, correlations to estimate both permeate flux and COD-HC concentration in the retentate or permeate at any operational conditions (temperature, pressure, solution viscosity, concentration factor) have been obtained. Experimental pilot-scale tests had shown that an M1 ultrafiltration membrane is effective for removing emulsified oil and achieving up to 90.1% and 99.7% removal of COD and HC, respectively, with a permeate flux of 20 L h-1 m-2 at ΔP = 400 kPa and 35 °C. It is pointed out that by optimizing the process design utilizing this membrane module, it is possible to successfully apply the ultrafiltration membrane technology to the treatment of industrial emulsified oil waste effluents.