Division of Environmental and Water Resources Engineering, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore 637141, Singapore; Singapore Membrane Technology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore 637141, Singapore.
Water Res. 2013 Nov 1;47(17):6618-27. doi: 10.1016/j.watres.2013.08.037. Epub 2013 Sep 10.
Alginate has been commonly used as a model foulant in studies of membrane organic fouling. As a complex polymer, alginate is composed of two different monomers, namely M ((1 → 4) linked β-D-mannopyranuronic acid) and G ((1 → 4) linked α-L-gulopyranuronic acid) which are randomly arranged into MG-, MM- and GG-blocks. So far, little information is available about fouling propensity of each block in microfiltration. In this study, microfiltration experiments were conducted respectively with MG-, MM- and GG-blocks separated from alginate under defined conditions. Results showed the severest fouling in the filtration of MG-block, and the least flux decline in the filtration of MM-block. The initial pore blocking was found to be responsible for the fouling observed in MG-block filtration, while the cake layer formed on membrane surface during the MM-block filtration could serve as a pre-filter that prevented membrane from further pore blocking. In order to look into fouling mechanisms, the effects of transparent exopolymeric particles (TEP) on membrane fouling were also studied. TEP were found to form through aggregation or cross-link of alginate blocks. As TEP were bigger than original alginate blocks, they could facilitate the formation of cake layer on membrane surface. It was observed that more TEP were produced from MM-blocks than from MG-blocks in solutions. This in turn explained why cake resistance was dominant in the filtration of MM-blocks as compared to MG-blocks. The analysis by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further revealed that MM-blocks had lowest cohesive interaction energy among all three alginate blocks, which favoured aggregation of MM-blocks, and ultimately leading to the formation of more TEP. This study provided insights into the roles of different alginate blocks in development of membrane fouling, and suggested that the membrane fouling would be related to molecular structure of alginate.
海藻酸盐通常被用作膜有机污染研究中的模型污染物。作为一种复杂的聚合物，海藻酸盐由两种不同的单体组成，即 M（（1→4）连接的β-D-甘露糖醛酸）和 G（（1→4）连接的α-L-古洛糖醛酸），它们随机排列成 MG-、MM-和 GG- 嵌段。到目前为止，关于微滤中海藻酸盐中每个嵌段的污染倾向的信息很少。在这项研究中，分别在定义的条件下用从海藻酸盐中分离出来的 MG-、MM- 和 GG- 嵌段进行微滤实验。结果表明，在 MG-嵌段的过滤中污染最严重，而在 MM-嵌段的过滤中通量下降最小。发现初始孔堵塞是导致 MG-嵌段过滤中观察到的污染的原因，而在 MM-嵌段过滤过程中在膜表面形成的滤饼层可以作为预过滤器，防止膜进一步的孔堵塞。为了研究污染机制，还研究了透明胞外聚合物 (TEP) 对膜污染的影响。TEP 被发现通过海藻酸盐嵌段的聚集或交联形成。由于 TEP 比原始海藻酸盐嵌段大，因此它们可以促进膜表面滤饼层的形成。观察到在溶液中 MM-嵌段比 MG-嵌段产生更多的 TEP。这反过来解释了为什么在 MM-嵌段的过滤中，滤饼阻力比 MG-嵌段的过滤更占主导地位。扩展的德加古因-兰德劳-韦尔拜克（XDLVO）理论分析进一步表明，在所有三种海藻酸盐嵌段中，MM-嵌段具有最低的内聚相互作用能，这有利于 MM-嵌段的聚集，并最终导致形成更多的 TEP。这项研究深入了解了不同海藻酸盐嵌段在膜污染发展中的作用，并表明膜污染与海藻酸盐的分子结构有关。
