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年度	104	專案性質	實驗性質
專案類別	研究專案	研究主題	整治
申請機構	國立臺灣大學	申請系所	環境工程學研究所
專案主持人	侯嘉洪	職等/職稱	助理教授
專案中文名稱	以電容去離子技術移除地下水中砷之研究
中文關鍵字	電容去離子技術, 砷污染, 地下水整治
專案英文名稱	Capacitive Deionization Technology for the Removal of Arsenic from Groundwater
英文關鍵字	Capacitive Deionization, Arsenic, Groundwater Remediation
執行金額	999,790元
執行期間	2014/12/1 至 2015/11/30
計畫中文摘要	砷的毒害是一種全球性的地下水污染問題，而台灣現有之地下水質砷污染來源包含土壤污染列管場址，因土壤中砷傳輸至地下水體，導致地下水中砷濃度超過地下水污染管制標準，以及砷來源主要來自於岩層的西南沿海與宜蘭地區地下水，若農業及漁業用水引用當地地下水做為水源，造成對生物或人體的潛在危害性。電容去離子技術(Capacitive Deionization, CDI)為一種節能、清淨、無需使用化學藥劑，且不產生二次污染物之新穎電化學處理技術，其原理是利用外加電場的控制與奈米孔洞碳電極的高比表面積，基於電荷分離機制，先以外部供電方式充電，在處理水體中產生電場，利用庫倫作用力將水中離子電吸附於電極表面上，在奈米孔洞間形成電雙層，進而產出乾淨水體。值得注意的是，與傳統的砷處理技術相比，CDI更適合處理含低濃度污染物之水體，恰符合砷在天然水體中低濃度之特性，且處理過程中能源需求低、無須添加化學藥劑，不會產生二次污染物，且電極可重覆使用。故與傳統的砷處理技術相比，利用CDI去除水中砷相當具有競爭優勢與應用潛力。 本研究計畫之目的在於評估CDI技術於移除地下水中無機砷之可行性，顯著提升對於五價砷與三價砷的去除效能，達到其與水體分離的目的。研究內容包含研析五價砷與三價砷之去除機制與移除效率，瞭解電場對於砷型態間的轉變之影響，與地下水體中不同物質的存在對於砷選擇性之影響，並發展實驗室規模CDI模組系統，應用於處理含砷地下水體，評估CDI技術應用於模擬/實場水體中移除砷之發展潛力。本研究試驗結果顯示，CDI對於水中低濃度的砷(如0.2 mg/L)具有良好的移除效果，其中五價砷以帶有負電荷之H2AsO4－或HAsO42－型態存在溶液中，在電場作用下(1.2 V)，容易以電吸附方式被去除；三價砷則是在電場作用下，與陽極反應被氧化成五價砷，再電吸附於電極表面而被去除。故五價砷之因其帶電荷型態，CDI對其有較佳的去除效率。另外，三價砷與五價砷在CDI系統中之吸附行為，皆符合傳統之Langmuir 與Freundlich等溫吸附模式，以及擬一階動力學。在CDI的單元連續式實驗中，活性碳電極具有良好的再生性與穩定性，且藉由對連續吸脫附實驗後之電極表面進行分析，證實砷於電容去離子系統中主要是以電吸附機制被去除，電沉積還原機制並不顯著。再者，於競爭性分析中可知含砷溶液中其它物質，如氯化鈉或天然有機物質皆會對砷之電吸附效果造成影響。研究中進一步使用實驗室規模的電容去離子技術模組系統處理實場含砷地下水(含有天然有機物質及多種溶解性離子)時，砷去除率達70.5%，可使砷濃度從0.138 mg/L降至符合飲用水水源標準及農業灌溉用水標準(0.05 mg/L)之下，故以電容去離子技術處理含砷地水體具有良好之移除效率與穩定性，具有發展潛力。
計畫英文摘要	Arsenic poisoning via groundwater is one of worldwide problems. Arsenic can be introduced in groundwater through nature sources and anthropogenic sources. Importantly, it is found that in some areas of Taiwan, the arsenic concentrations are much higher than the groundwater quality standards. However, traditional water treatments, such as adsorption, reverse osmosis, and ion exchange, have many limits for the removal of arsenic from aqueous solutions at low concentrations. Capacitive deionization (CDI), or referred to electrosorption process, has been regarded as a novel water purification technology, which has many advantages including low operating pressure, low energy consumption, no secondary waste, and easy regeneration. The mechanism behind CDI to remove ionic species from water is based on the charge separation, in which nanoporous carbon electrodes are charged and discharged to store and to release large quantities of ions, respectively. As evidenced by this study, CDI process can applied to effectively separate arsenic at low concentrations (0.2 mg/L) from aqueous solutions under an external electric field of 1.2 V. The removal capacity of activated carbon electrodes strongly depends on the applied voltage and initial arsenic concentration. Arsenate (As(V)) can be directly removed by electrosorption process at 1.2 V because of its negative charge. The mechanism of arsenite (As(III)) removal in CDI system could be involved with the oxidation of As(III) to As(V), and thereby they can be further removed by electrosorption process. The electro-sorption/desorption experiments and electrode surface analysis provided evidence that the arsenic removal can be mainly attributed to electrosorption rather than electrodeposition in this electrochemically assisted process. However, the presence of sodium chloride or natural organic matter cuases a significant derease in aresnic removal. For remediating a natural groundwater, 70.5% removal efficiency of arsenic can be achieved, and the treated groundwater can reach the dring water resource standard and agricultural irrigation water standard (< 0.05 mg/L). The results provide a fundamental understanding of the removal mechanisms for arsenic in an electrosorption process, which is beneficial for the practical application of CDI techniques for the remediation of arsenic-contaminated groundwater.