京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20692号 / 工博第4389号 / 新制||工||1682(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 田中 宏明, 教授 高岡 昌輝, 教授 藤井 滋穂 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In Taiwan, more than 25% of all water uses comes from groundwater, and thus groundwater is a very valuable water resource for both domestic and industrial uses. However, groundwater at many existing former industrial sites and disposal areas was contaminated by halogenated organic compounds that were released into the environment. The chlorinated solvent trichloroethene (TCE) is one of the most ubiquitous of these compounds. In this laboratory-scale feasibility study, a hybrid two-stage process combining fiber filtration (FF) and nanofiltration (NF) was applied to remove to suspended solids (SS) and TCE from contaminated groundwater for water purification. In this study, a man-made kaolin solution was used to simulate groundwater purification using FF system. Then, microfiltration (MF), ultrafiltration (UF), and NF systems were applied for TCE removal. The hybrid membrane process using FF and NF units was used to evaluate the feasibility on TCE removal. The scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) were used to investigate membrane morphology and structure after use. A 3-D excitation emission fluorescence matrix (EEFM) was used to evaluate the potential of membrane organic fouling. Results show that the optimization filtration velocity of FF was 15.3 m/hr, and the observed TCE and SS removal efficiencies were 80% and 60%, respectively. Removal mechanisms for MF and UF were mainly sieving, and the removal mechanism for NF was mainly electrostatic repulsion. Results indicate that NF had the highest TCE removal efficiency (98.2%). When initial TCE concentration was 1 mg/L, NF membrane pore might shrink caused increased TCE removal (rejection). When TCE concentration was higher 1 mg/L, membrane damage and pore enlargement was observed with decreased TCE removal efficiency. The observed SS, sulfate, and hardness removal efficiencies were 99.8%, 98.7%, and 98.7% respectively, when FF and NF hybrid process was used. Higher TCE concentration might enlarge membrane pore, which caused decreased membrane separation and increased flux. Approximately 46% of flux drop was observed when NF was used alone compared to the hybrid membrane process using FF as the first treatment stage. Membrane analyses show that residual TCE was adsorbed on the membrane. Low zeta potential of groundwater was observed due to the compressed electric double layer, which caused aggregation of particle. High zeta potential of permeate was due to the particle dispersive through hybrid process. Results from SEM analysis show that membrane morphology was damaged by TCE, and heavy metal in groundwater deposited on membrane. Results of EEFM analysis indicate that groundwater contained humic acid (HA) and soluble microbial by-product (SMP). HA and SMP might be adsorbed on fiber filter, and extracellular polymeric substances (EPS) that attached on fiber filter might be washed out. The organic powders on the surface of the fiber filter might be washed out causing the increased in NPDOC concentrations. Humic acid could be removed through NF process, and SMP might be adsorbed in membrane pore caused organic fouling, and SMP might be washed out after treatment by the FF+NF hybrid process. Results indicate that FF as pre-treatment can maintain higher flux. Higher TCE concentration caused membrane destruction and decreased membrane separation. TCE contaminated groundwater can be affectively treated by the hybrid membrane system to meet the groundwater standard and reclaimed water standard. Reclaimed water could be used for industrial cooling water and irrigation purposes.