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

本研究的目的是阐明通过NF膜的传质和分离特性，特别是在非常低的压力下操作，并与溶解物质的混合物interaction.As研究期间的最后一年，中试实验已在Tamagawa净水厂，东京进行。对河水的纳滤特性进行了详细的研究。具有高盐截留率的纳滤膜在半年以上的运行中既对THM前体有高截留率，又对溶解离子有高截留率。尺寸排阻、电荷和亲和性的综合作用可以解释膜分离的机理。此外，修正的扩展能斯特普朗克方程可以很好地解释正电荷膜对大部分溶解态离子的分离。然而，对于硫酸根离子，模型的计算结果与实验结果存在较大差异，对于河水离子混合物，模型还需进一步改进。在农村地区的现场试验证明，即使在3个大气压的非常低的压力下，该系统在技术上也是可行的。然而，严重砷污染的地下水通常含有三价砷化合物，NF对三价砷的保留低于五价砷，这表明需要在NF之前进行预氧化处理。这些对策措施很容易合理化的机制为导向的理解，作为本研究的结果。

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.