Membrane fouling in ultrafiltration of latex paint

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Ultrafiltration (UF) is a membrane separation process used in a wide range of applications, such as: water/wastewater treatment, water pre-treatment for reverse osmosis, separations in food, chemical and biochemical industries. With the developement of low-pressure membranes, membrane applications, including ultrafiltration, have been growing exponentially in recent years. However, a major challenge in the application of ultrafiltration is membrane fouling by the solutes in the feed solution. Membrane fouling causes a reduction of the filtrate flux with time, and hence, a low filtration efficiency.** In the manufacture of paint products, a large amount of wastewater is generated from cleaning of reactors and mixing basins. The wastewater contains a wide variety of substances, such as: organic and inorganic pigments, latex, solvents and emulsifying agents. The treatment of latex-paint wastewater by ultrafiltration can serve not only for pollution control but also for latex recovery. One of the benefits of treating water-based paint effluent by ultrafiltration over other processes such as electrochemical oxidation or Fenton oxidation is the potential to reclaim the solid in the effluent as well as to reuse the filtrate as process or cleaning water. However, membrane fouling causes a significant increase in the hydraulic resistance, manifested as a permeate flux decline or a transmembrane pressure increase. The energy consumption in the filtration process thus increases. Membrane fouling also increases the complexity of membrane filtration operation since the system has to be halted frequently to restore the filtrate flux by back-washing. Over a long period of operation, membrane fouling might not be totally reversible by back-washing. In order to regain the membrane efficiency, chemical cleaning is often used. This results in an increased operational cost. In addition, chemical cleaning reduces the membrane lifetime. These make UF less economically feasible for some applications. Therefore, a thorough understanding of this phenomenon and the development of novel techniques to reduce or eliminate membrane fouling are of important.************