MASS TRANSFER MECHNISM AND SEPARATION CHARACTERISTICS OF NANOFILTRATION MEMBRANES UNDER VERY LOW PRESSURE OPERATION AND WITH MIXTURE OF DISSOLVED SUBSTANCES INTERACTION

本研究旨在阐明纳滤膜的传质和分离特性，特别是在极低压操作和溶解物质混合物相互作用下。作为研究期的最后一年，在东京玉川净水厂进行了一项试点实验。对河流水的纳滤特性进行了详细的研究。具有高盐潴留的纳滤膜在半年以上的操作中具有高THM前体潴留和高溶解离子潴留。排粒径、电荷和亲和的共同作用可以解释膜分离的机理。此外，还证明了一个修正的扩展能普朗克方程可以很好地解释大部分溶解离子被带正电的膜分离的现象。然而，硫酸盐离子的理论与实验存在一定的差异，需要对河流水中的离子混合物进行进一步的改进。人工驱动的纳滤系统已应用于孟加拉国地下水中的砷去除。在农村地区的现场试验证明，即使在3atm的极低压力下，该系统在技术上也是可行的。然而，受砷严重污染的地下水通常含有三价砷化合物，而纳滤水对三价砷的保留比五价砷的保留要低，这表明在纳滤水之前需要进行预氧化处理。本研究的结果是，这些对策很容易被机制导向的理解合理化。

This study aims to elucidate mass transfer and separation characteristics through NF membranes especially at operations under very low pressure and with mixture of dissolved substances interaction.As the last year of the research periods, a pilot experiment has been carried out at Tamagawa Water Purification Plant, Tokyo. Nanofiltration characteristics of river water was investigated in details. A NF membrane with a high salt retention gave both a high retention of THM precursors and a high retention of dissolved ions for more than a half year operation. The combined effects of size-exclusion, electric charge, and affinity could explain the mechanism of membrane separation. In addition, it is shown that a modified Extended Nernst Plank Equation could well explain the separation of most of dissolved ions by a positively charged membrane. However, a discrepancy between theoretical and experimental was observed for sulfate ions, a further improvement of the model is required for the ion mixture of river water.A manually driven nanofiltration system has been applied to arsenic removal from groundwater in Bangladesh. The field tests in the rural area has proven the system is technically feasible even at a very low pressure of 3 atm. However, the groundwater heavily contaminated with arsenic typically contains trivalent arsenic compounds and NF gives a lower retention of trivalent arsebnic than that of pentavalent one, suggesting a need of pre-oxidation process prior to NF. These couter measures are easily rationalized by mechanism-oriented understandings as a result of this study.