Microscopic modeling of critical pressure of permeation in oily waste water treatment via membrane filtration

Abstract

Membrane pore blockage is a great concern during membrane processes in oily water treatment. In this paper, microfluidic science through the CFD technique was used to recognize this blocking mechanism. The behavior of a sample droplet was modeled on a membrane surface to observe the droplet deformation schematically. The theoretical torque balance and similar experimental data in the literature were applied to validate the modeling results. The critical permeation pressure concept was developed to enable quantitative study of membrane pore blockage. Subsequently, central composite design and the response surface methodology were employed for pressure modeling and optimization. Five variables were selected and studied, which resulted in critical pressures ranging from 5000 to 330 000 Pa. A quadratic model (R² = 0.99) for critical pressure was suggested, with maximization results under the optimum process conditions of 660 000 s⁻¹ shear rate, 0.01 N m⁻¹ surface tension, 120° contact angle, 0.47 μm pore diameter and 1.44 μm droplet diameter. CFD results under the optimum conditions predicted 355 kPa critical pressure, which is in 96.2% agreement with the quadratic correlation, representing the ability of this correlation to adjust trans-membrane pressure for the microfiltration of oil in water. On the other hand, the effectiveness order of the variables indicates that contact angle and interfacial tension are the most effective variables; therefore, the best remedy to overcome membrane fouling is membrane surface treatment by increased hydrophilicity along with an increase in interfacial tension.