摘要:台灣目前有兩處地區其地下水及土壤因遭受人為砷汙染,而被公告為控制或整治場址,另外,台灣以濁水溪沖積扇、嘉南平原、屏東平原與蘭陽平原,為地下水砷含量較高之地區。針對上述砷汙染,因應的處理方式是利用各種水處理技術,如薄膜法、吸附劑吸附法與化學沉澱等進行砷移除作業。惟現有之處理方法各有其應用之限制,如薄膜法成本高且表面易積垢,而砷於地下水體中的低濃度特性亦使得各種水處理技術對砷之移除效率偏低。因此,開發創新性的砷移除技術,提升砷的處理效能,以提升國內農業灌溉用水與飲用水之用水品質與安全性,同時對被污染之場址進行整治工作,有其必要性與急迫性。
本研究團隊於104年接受環保署土汙基管會補助,執行「以電容去離子技術移除地下水中砷之研究」,成功證實電容去離子技術(Capacitive Deionization, CDI),可以電吸附方式去除水體中砷,並可適用於抽取處理法。本研究團隊亦證實CDI技術可有效處理含砷地下水,並對低濃度(<200 ppb)砷污染之水體亦有良好的處理效果,故CDI技術可作為移除砷汙染之新穎地下水處理技術,具有持續發展之潛力。惟目前CDI技術尚未有以實場應用為最終目標之先驅試驗或實地模場計畫,亦無針對CDI技術於實場應用時可能遭遇之問題與干擾提出討論,如受砷汙染之地下水中含有懸浮固體、微生物、有機巨分子等非溶解性物質,可能造成CDI電極堵塞而影響砷移除能力;或受砷汙染之地下水中所含之溶解性基質(鹼(土)金屬族與鹽類、重金屬、與鐵錳離子)對電吸附機制移除砷可能造成之干擾行為等。
綜上所述,本研究計畫之目的在於考量CDI技術於地下水整治之實場應用時可能遭遇之干擾與困難,建構電容去離子技術系統整合模組,進行CDI技術處理含砷地下水之先驅試驗。主要工作內容為(1)含砷地下水之基質特性分析,了解地下水鹼(土)金屬族與鹽類、重金屬、與鐵錳離子等溶解性基質含量,(2)結合CDI技術與微過濾薄膜技術(microfiltration, MF),建構電容去離子技術系統整合模組(MF-CDI);(3)以該系統模組進行實驗室模場試驗,評估移除水體砷汙染之成效,並進一步探討地下水中溶解性基質對於CDI技術以電吸附機制移除水體中砷汙染時,可能造成之干擾行為;同時,擬將由高孔隙與比表面積的活性碳材所製備而成的奈米孔洞碳電極,以表面修飾技術增加電極對砷的吸附容量與選擇性;(4)最後進行成本效益評估。本研究計畫兼具學術貢獻與應用價值,可對含砷地下水提供一創新性綠色整治技術。
Abstract: Arsenic contaminated groundwater in Taiwan have caused a serious problem of safe drinking water since 1960s. However, traditional water treatments, such as adsorption, reverse osmosis, and electrocoagulation, could be restricted for the removal of arsenic from aqueous solutions at low concentrations. Therefore, development of innovative, effective, energy-saving, and environmentally friendly separation techniques to remove arsenic from groundwater is a promising issue.
Capacitive deionization (CDI) technology is an innovative electrosorption method for removal of ionic species from aqueous solutions. In principle, by imposing an external electrostatic field on a pair of porous carbon electrodes, CDI technology can separate ions from bulk solutions onto the electrode surface, in which an electrical double layer (EDL) that acts as capacitance is formed at the electrode-solution interface. Thus the separated ions can be stored in the porous carbon electrodes and removed from aqueous solution. Recently, CDI technology has shown great application potential to the removal of arsenic from groundwater. The feasibility of using CDI technology to remove arsenic from groundwater at the ppb level (<200 ppb) has been proven by our research groups. However, the effects of non-dissolved matter (suspended solids, microbial, organic matters, etc.) and dissolved substances (such as alkali metal ions, alkaline-earth metal ions, salt, heavy metals, manganese ions and iron ions) in natural groundwater on the CDI performance have not been well studied in literatures.
The objective of this study is to develop an integrated module system by coupling microfiltration (MF) and CDI technology for remediation of arsenic contaminated groundwater. This is a preliminary study (lab-scale module test) to evaluate the feasibility of using integrated MF-CDI module system for in situ remediation of arsenic-contaminated groundwater. In addition, surface modification of porous carbon electrode could be conducted to improve the electrosorpion performance and selective removal of arsenic over others substrates (i.e., sodium chloride and heavy metal ions). Cost-benefit analysis of implementing groundwater remediation using the integrated MF-CDI module system will be also studied. The obtained results can provide useful information to develop CDI system for the future pilot study in groundwater remediation.