School of Civil and Environmental Engineering, Nanyang Technological University, Singapore.
Adv Colloid Interface Sci. 2011 May 11;164(1-2):126-43. doi: 10.1016/j.cis.2010.10.007. Epub 2010 Oct 31.
Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of colloidal fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling colloidal fouling of both RO and NF membranes. Major colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for colloidal fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter≪100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF colloidal fouling are also identified in the current paper.
胶体是指粒径在 1-1000nm 范围内的细微颗粒。在压力驱动的膜系统中，这些细微颗粒极易污染膜，导致水透过率显著下降，并且常常使产品水质恶化。在过去三十年中，针对反渗透（RO）和纳滤（NF）膜的胶体污染问题已经开展了大量的系统性研究，人们对胶体污染的认识也取得了显著进展。本文综述了 RO 和 NF 膜胶体污染的机理和控制因素。总结了主要胶体污染物（包括刚性无机胶体和有机大分子）及其特性。这些胶体颗粒在 RO 或 NF 膜上的沉积形成滤饼层，由于 1）滤饼层水力阻力和/或 2）滤饼增强渗透压，会对膜通量产生不利影响。详细讨论了进水成分、膜特性和水动力条件对无机胶体、天然有机物、多糖和蛋白质等胶体污染物的影响。一般来说，通过考虑膜表面附近的传质和胶体-膜（或胶体-胶体）相互作用，可以很容易地解释这些影响。最初为多孔膜胶体污染开发的临界通量和极限通量概念也适用于 RO 和 NF 膜。对于小胶体（直径≪100nm），极限通量可能由两种不同的机制导致：1）扩散-溶解（凝胶形成）控制机制和 2）表面相互作用控制机制。前者机制可能在浓溶液中起主导作用，而后者机制在稀溶液中可能更为重要。本文还确定了 RO 和 NF 胶体污染的未来研究需求。
