整合薄膜電容去離子與逆滲透技術應用於再生水處理系統之效能提升

Abstract

近年來，由於人口蓬勃發展以及快速的經濟發展，水資源的需求日益增加，使得水資源匱乏的問題在世界各地受到重視。然而，河流，湖泊和地下水等淡水的來源不足以供應人們的日常需求。因此，目前已開發許多淨水技術，用於從海水，微鹹水和工業用水中脫鹽以發展替代水資源。 逆滲透(Reverse osmosis, RO)為常見的淨水技術，常用於半鹽水/海水脫鹽、超純水製備及工業廢水處理。由於較高的壓力需求，逆滲透技術的能耗普遍偏高。然而，電容去離子(Capacitive deionization, CDI)為目前具有前瞻性的淨水技術，透過施加低電壓於兩側多孔碳電極上，使溶液中的離子受電場吸引而儲存於孔洞中，進而達到脫鹽的目的。此技術具有低能耗，操作簡易及環境友好的優點。進一步地，薄膜電容去離子(Membrane capacitive deionization, MCDI)透過將離子交換樹脂薄膜(Ion exchange membranes, IEMs)放置於電極表面，藉由IEM的電性選擇特性，於電吸附過程中減緩同離子(co-ion)效應的影響，因而提升整體的去除容量及電荷效率。 此研究目的為評估以MCDI提升RO平板過濾模組的處理效能，透過於MCDI放電階段施加反向電壓以及調控幫浦靜置時間進行程序控制，並找出MCDI最佳運行條件，進而降低整體比能耗、提高整體水回收率及提升產品水水質以符合Class A的再生水水質標準。首先，以濃度2000 mg/L的氯化鈉溶液模擬工業用水，作為兩級RO系統和RO-MCDI混合系統的進流，再以實際工業用水作為進流。由實驗結果得知，在最佳操作模式下，MCDI能達成去除率99.99%，且水回收率達75%。再者，由兩級RO系統和RO-MCDI混合系統處理工業用水之結果，其導電度分別降至94.83 μS/cm和12.27 μS/cm，總水回收率分別為4.25％和15.57％，總比能耗分別為3.272 kWh/m3和2.819 kWh/m3。顯示出MCDI能提升整體RO產品水水質，提高整體水回收率並降低整體比能耗且具有應用於工業之再生水處理之潛力。 由於MCDI系統具有良好之去離子效能，同時，處理過程中僅需較低之比能耗。因此，在最佳操作模式下能有效提升水回收率，進而提高整體RO系統之水回收率與產水水質，使透過MCDI優化之RO系統於再生水處理流程中具備良好的應用潛力，可作為一清淨節能之再生水處理流程。

The demand of fresh water has increased over the past decades around the worldwide due to the rapid population and economic development, and the sources of fresh water such as rivers, lakes and groundwater are insufficient for daily consumption. Many water purification technologies have been developed for water desalination from seawater, brackish water and industrial water. Reverse osmosis (RO) is a common technology for fresh water production from seawater or brackish water. Due to the high pressure demand, the RO system shows high specific energy consumption. Capacitive deionization (CDI), is a promising technology for water desalination, has advantages in low energy consumption, easy operation and environmental friendliness. Recently, membrane capacitive deionization (MCDI) has been developed, using ion exchange membranes on the electrodes to block the co-ions effect. Hence, the removal capacity and charge efficiency of MCDI is better than CDI. The objective of this study is to enhance the performance of RO system with MCDI, by applying the reverse voltage and adjusting the standing time of the pump during the discharge process, and figuring out the optimal operating conditions of MCDI system to further reduce the overall specific energy consumption, enhance the overall water recovery, improve the permeate water quality to meet the Class A reuse water standard. Firstly, for industrial water simulation experiment, the concentration of 2000 mg/L sodium chloride is used as influent for two-pass RO system and RO-MCDI hybrid system. From the experimental result of MCDI under optimal operating conditions, the water recovery increases to 75%, the rejection rate reaches to 99.99%. Furthermore, from the results which use the industrial water as influent for two systems, the conductivity of two-pass RO system decreases to 94.83 μS/cm whereas that of RO-MCDI hybrid system decreases to 12.27 μS/cm. The overall water recovery of the former system is 4.25% while the latter one is 15.57%. And the overall specific energy consumption of both systems are 3.272 kWh/m3 and 2.819 kWh/m3, respectively. It can be shown that the use of MCDI system can reduce the overall specific energy consumption, enhance the overall water recovery, improve the permeate water quality. Furthermore, it is feasible to apply to industrial water treatment. Due to the MCDI system has good deionization performance under optimal operating condition, it can enhance the overall performance of RO, and consume lower energy, enhance the overall water recovery and have good application potential in the reclaimed water treatment.