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年度	108	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	副教授
專案中文名稱	開發二氧化錳/生物炭之循環經濟材料於地下水砷吸附之研究
中文關鍵字	砷, 生物碳, 二氧化錳, 地下水整治, 吸附, 循環經濟
專案英文名稱	Fabrication of Manganese Dioxide Modified Biochar for Arsenic-Contaminated Groundwater Removal and Circular Economy
英文關鍵字	Biochar, Circular Economy, Manganese Dioxide, Arsenic, Groundwater Remediation
執行金額	1,200,000元
執行期間	2019/1/1 至 2019/12/31
計畫中文摘要	砷於水環境中多以無機砷存在，其中，因受環境的氧化還原電位及pH值影響，常以砷酸鹽(arsenate, As(V))與亞砷酸鹽(arsenite, As(III))為主要物種存在，而一般的地下水環境處於還原條件，砷物種多以As(III)存在。值得注意的是，As(III)之毒性、可溶解性及可移動性等特性皆高於As(V)，並具有整治策略困難及處理成效不彰之劣勢。傳統上，砷整治策略包含吸附、氧化、混凝、離子交換及薄膜法等，但於實場應用時仍受許多因素限制；因此，持續精進含砷地下水整治技術的可行性、有效性及新穎性，並結合具備節能減碳、資源再生與回收再利用的生物資源循環技術，促進前瞻永續與循環經濟，就現今處理技術的開發而言十分重要。生物炭(biochar, BC)的優勢在於可將生物質固體廢棄物轉換為具有經濟價值或吸附能力的材料，同時達到環境友善及資源循環的雙重目標，且其具備高比表面積及多孔隙結構的特性，並常帶有豐富的官能基，經改質後更可進一步改善孔隙結構及表面積，進而對特定離子具化學吸引力，於本研究中可有效增加砷的吸附效能。另一方面，二氧化錳(manganese oxides, MnO2)可把毒性高且移動性高的As(III)轉化成毒性低且移動性低的As(V)，實為良好之活性材料。因此，本研究主要目的係以循環材料BC為基底，利用化學沉積法將MnO2批覆於生物炭表面，製備出MnO2/BC複合材料以進行地下水砷污染之處理。研究成果顯示，MnO2/BC複合材料表面所披覆之MnO2提供大量的中孔結構及更多的活性點位，有助於促進三價砷的氧化反應，亦進一步提升總砷的吸附效能。而相比於BC材料的吸附容量，MnO2/BC複合材料對三價砷的吸附容量提高約10倍；對五價砷的吸附容量則提高約5.1倍。其成果可歸因於MnO2對三價砷的強氧化活性，促使三價砷轉化成五價砷的效率提升。然而，隨著pH提高，砷物種受靜電排斥比例提高，導致吸附能力下降。值得一提的是，本研究開發之MnO2/BC複合材料，其羧基(−COOH)、羥基(−OH)，以及經MnO2披覆後形成之Mn−OH鍵結，可增進吸附作用，促進錯合反應之發生，同時提高複合式材料對三價砷及五價砷的吸附效能。最終，於MnO2/BC複合材料應用於模擬地下水砷污染之試驗結果顯示，約有96%的總砷從溶液中被移除，處理水質可符合飲用水水質標準與農業灌溉用水水質標準。綜上而言，本研究計畫已完成MnO2/BC複合材料於地下水砷污染之可行性研究，將有助於未來發展以廢棄物資源化及循環經濟為基礎的地下水整治技術。
計畫英文摘要	The problem of arsenic contamination in groundwater has been a challenge of many countries in the world and has attracted a great deal of research because of its serious effects on human health. Arsenic exists mainly in four oxidation states, consists of arsenate (As(V)), arsenite (As(III)), arsenic (As(0)), and arsine (As(-III)) and its solubility depends on the pH and ionic environment. Among them, As(V) being the most stable form and As(III) is usually more toxic than As(V). As(V) is the thermodynamically stable state in aerobic water, while As(III) is predominantly in the reduced redox environment. Many methods have been applied to treat arsenic in natural water sources such as coagulation/direct filtration, ion exchange, adsorption, and reverse osmosis. Adsorption process is known as a most simple operational and cost-effective technique applying in many research and sites. Rice husk biochar (BC) has seen significant advancement to remove different contaminants from water streams, thus providing a low-cost and eco-friendly solution for contaminant immobilization in water. It can be used as a sorbent of many heavy metals for diminishing contaminant transport and bioavailability in wastewater due to its remarkably relative high surface area, and negative charge for adsorbing organic functional groups on its surface. Manganese dioxide (MnO2) has been widely applied as oxidizing materials by its ability to convert As(III) to more stable As(V) form. Moreover, hierarchical porous MnO2 with plentiful active sites correlated with mesopores and micropores cause an increase in effective contact area with pollutants, thus leading boost the water treatment efficiency. The aim of this study is to develop a cost-effective method for As removal from groundwater. Hierarchical MnO2 modified-rice husk biochar is synthesized and controlled physiochemical properties to enhance As removal by precipitation method by the different time and temperature reactions. The improvement of As removal efficiency is estimated by a series of batch adsorption experiments, including pH effect, kinetic and isotherm tests for biochar and modified biochar samples. The excellent performance for the arsenic removal may be attributed to the 3D-structure characteristics of highly accessible surface and improved active sites. The X-ray diffraction, scanning electron microscopy, nitrogen adsorption–desorption isotherms and Fourier transform infrared spectroscopy are employed to determine the structure properties and verify the successful synthesis of MnO2 onto biochar surface. X-ray photoelectron spectroscopy analysis is used to explain the adsorption mechanism and enhancement of the adsorbents after modification. The co-existence of oxidation and physical adsorption are important mechanisms for the enhancement of As(III) removal efficiency, in which manganese dioxide is mainly responsible for converting As(III) to As(V) form. Herein, MnO2/BC prepared by in situ chemical precipitation method is to oxidize As(III) to As(V) to enhance the adsorption of As. The increase in the mass ratio of MnO2 on MBC provided a better porosity structure and larger activated sites. Noteworthy, MBC enhanced the adsorption of As(III) of 10 times compared to the pristine BC, which is much higher than 5.1 times for adsorption of As(V). This finding is due to the powerful oxidation of MnO2 coated on MBC with As(III), forming As(V). The oxidation reaction was simultaneously occurred with the reduction of Mn(IV) to Mn(III) and Mn(II) during adsorption process. Noteworthy, with the increase in pH, the adsorption capacity decreased, while the oxidation ratio increased. The adsorption mechanisms of As(III) and As(V) on MBC surface was governed by the surface complexation of functional groups, i.e., carboxyl (COOH), hydroxyl (OH) on rice husk biochar and hydroxyl bonded to Mn (Mn−OH) formed by MnO2 modification. MBC testing done with the simulated groundwater showed almost 100% removal capacity of arsenic. Most especially, the concentrations of arsenic and released Mn(II) in the final solution met the drinking water standard.