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Unpacking compaction: Effect of hydraulic pressure on alginate fouling
Journal of Membrane Science ( IF 9.5 ) Pub Date : 2017-12-01 , DOI: 10.1016/j.memsci.2017.09.010
Emily W. Tow , John H. Lienhard V

Abstract High pressure is often considered to be the cause of the high fouling propensity of reverse osmosis (RO) relative to forward osmosis (FO). Several experimental studies have shown that alginate fouling is more susceptible to cleaning in FO than in RO, but the theory that foulant compaction causes this disparity seems to be contradicted by the incompressibility of alginate hydrogels. In addition, the effect of hydraulic pressure on fouling in osmotic membrane desalination has never been experimentally isolated, because fixed-flux comparisons at different hydraulic pressures require different draw solution osmotic pressures. In this study, a new approach to isolating the effect of hydraulic pressure on alginate fouling and cleaning is introduced: operating FO with elevated but equal feed and draw hydraulic pressures. The same concentration of sodium chloride is used as the draw solution in all trials to eliminate possible effects of draw solution osmotic pressure on membrane fouling or cleaning. Theoretical modeling of the effect of alginate foulant compaction on flux reveals that foulant compaction should accelerate flux decline with low salinity feeds but retard flux decline at high salinity. However, in low-salinity alginate fouling trials, for which foulant compaction should accelerate flux decline, the measured flux decline rate was not affected by hydraulic pressure. Furthermore, when fouled membranes were cleaned by increasing the feed velocity and reducing the draw osmotic pressure, there was no apparent relationship between hydraulic pressure and cleaning effectiveness. Finally, in situ visualization of foulant removal during the cleaning process revealed no difference in foulant removal mechanisms between different hydraulic pressures. These findings demonstrate that alginate gel compaction by high feed hydraulic pressure does not occur and suggest that other explanations should be sought for FO's high fouling resistance relative to RO.

中文翻译:

拆包压实:液压对藻酸盐污染的影响

摘要 高压通常被认为是反渗透 (RO) 相对于正向渗透 (FO) 具有高结垢倾向的原因。几项实验研究表明,FO 中的藻酸盐污垢比 RO 中更容易清洁,但污垢压实导致这种差异的理论似乎与藻酸盐水凝胶的不可压缩性相矛盾。此外,液压对渗透膜海水淡化中结垢的影响从未在实验中被分离出来,因为不同液压下的固定通量比较需要不同的驱动溶液渗透压。在这项研究中,引入了一种隔离液压对藻酸盐污垢和清洁影响的新方法:以升高但相等的进料和排出液压操作 FO。在所有试验中都使用相同浓度的氯化钠作为汲取溶液,以消除汲取溶液渗透压对膜污染或清洁的可能影响。藻酸盐污垢压实对通量影响的理论模型表明,污垢压实应加速低盐度进料的通量下降,但延迟高盐度的通量下降。然而,在低盐度海藻酸盐污垢试验中,污垢压实应加速通量下降,测得的通量下降率不受液压的影响。此外,当通过增加进料速度和降低抽吸渗透压来清洁污染膜时,液压和清洁效果之间没有明显的关系。最后,清洁过程中污垢去除的原位可视化显示,不同液压压力之间污垢去除机制没有差异。这些发现表明不会发生由高进料液压引起的藻酸盐凝胶压实,并表明应该寻找其他解释来解释 FO 相对于 RO 的高抗污染性。
更新日期:2017-12-01
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