Membrane fouling in ultrafiltration of latex paint

超滤（UF）是一种膜分离工艺，应用广泛，例如：水/废水处理，反渗透水预处理，食品，化学和生物化学工业中的分离。近年来，随着低压膜的发展，膜的应用，包括超滤，呈指数增长。然而，超滤应用中的主要挑战是进料溶液中的溶质造成的膜污染。膜污染导致滤液通量随时间降低，因此过滤效率低。** 在涂料产品的生产过程中，清洗反应器和混合池会产生大量废水。废水中含有各种各样的物质，如：有机和无机颜料、乳胶、溶剂和乳化剂。采用超滤法处理乳胶漆生产废水，既可治理污染，又可回收乳胶。通过超滤处理水基涂料流出物相对于其他方法如电化学氧化或芬顿氧化的益处之一是回收流出物中的固体以及将滤液再利用为工艺水或清洁水的潜力。然而，膜污染导致水力阻力显著增加，表现为渗透通量下降或跨膜压力增加。因此，过滤过程中的能量消耗增加。膜污染也增加了膜过滤操作的复杂性，因为系统必须频繁地停止以通过反冲洗恢复滤液通量。在长期运行中，膜污染可能无法通过反冲洗完全逆转。为了恢复膜的效率，经常使用化学清洗。这导致增加的操作成本。此外，化学清洗会缩短膜的使用寿命。这使得UF在某些应用中不太经济可行。因此，深入了解这一现象并开发新的技术来减少或消除膜污染是非常重要的。

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.************