School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Singapore Membrane Technology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore 637141, 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. 2015 Oct 15;83:248-57. doi: 10.1016/j.watres.2015.06.008. Epub 2015 Jun 9.
Alginate, a linear copolymer, is composed of 1,4-linked β-d-mannuronic acid (M) and α-l-guluronic acid (G), which are combined into homopolymeric blocks (MM-block and GG-block) and heteropolymeric block (MG-block). It has been widely used as a model foulant in various studies of membrane fouling, thus this study investigated the impacts of calcium ion on MG-, MM- and GG-blocks of alginate and the filtration behaviors of the three types of alginate blocks at different concentrations of calcium ion. Results showed that calcium ion had the most serious effects on GG-blocks and significantly promotes the formation of transparent exopolymeric particles (TEP) from GG-blocks which in turn led to rapid formation of thick cake layer on membrane surface during the filtration of GG-blocks. As for MM-blocks, it was found that the formation of TEP was proportional to the Ca(2+) concentration in MM-blocks solution, while the membrane fouling was enhanced by Ca(2+) in the filtration of MM-blocks solution. Unlike MM- and GG-blocks, MG-blocks were nearly not affected by addition of calcium ion, as the result, there was no significant increase in TEP. The initial fouling rates and the mass of foulants deposed on the membrane surfaces further revealed a close correlation between the TEP concentration and the membrane fouling propensity. The observations by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM) further confirmed the formation process of the cake layer by TEP on the membrane surface. This study offers deep insights into the development of membrane fouling by different alginate blocks in the presence of calcium ion, and suggests that TEP formed from alginate blocks played a very significant role in the fouling development.
藻酸盐是一种线性共聚物，由 1,4 连接的 β-d-甘露糖醛酸（M）和 α-l-古洛糖醛酸（G）组成，这些糖醛酸结合成均聚物块（MM 块和 GG 块）和杂聚物块（MG 块）。它已被广泛用作各种膜污染研究中的模型污染物，因此本研究调查了钙离子对藻酸盐中的 MG、MM 和 GG 块的影响，以及在不同钙离子浓度下三种类型的藻酸盐块的过滤行为。结果表明，钙离子对 GG 块的影响最严重，显著促进了 GG 块中透明胞外聚合物颗粒（TEP）的形成，从而导致 GG 块过滤时在膜表面迅速形成厚的滤饼层。对于 MM 块，发现 TEP 的形成与 MM 块溶液中的 Ca（2+）浓度成正比，而 MM 块溶液过滤时 Ca（2+）会增强膜污染。与 MM-和 GG-块不同，MG-块几乎不受钙离子添加的影响，因此 TEP 没有明显增加。初始污染速率和沉积在膜表面上的污染物质量进一步表明 TEP 浓度与膜污染倾向之间存在密切相关性。场发射扫描电子显微镜（FESEM）和原子力显微镜（AFM）的观察结果进一步证实了 TEP 在膜表面上形成滤饼层的过程。本研究深入了解了在钙离子存在下不同藻酸盐块对膜污染的发展，表明藻酸盐块形成的 TEP 在污染发展中起着非常重要的作用。
