流動式電極電容去離子(FCDI)系統應用於氨氮去除

Flow-electrode Capacitive Deionization (FCDI) system for ammonia removal

臧培宏(Pei-Hung Tsang)

指導教授 ： 彭晴玉

淡江大學/工學院/水資源及環境工程學系碩士班/碩士(2021年)

https://doi.org/10.6846/TKU.2021.00231

摘要

電容去離子技術(Capacitive Deionization, CDI)技術是一種低能耗、無二次污染的新興脫鹽技術，藉由在兩端電極施加低電壓從水溶液中移除離子。流動式電極電容去離子技術(Flow-Electrode Capacitive Deionization, FCDI)技術，則是進一步將CDI技術中的固定電極改為流動電極，以獲得更高吸附容量及連續操作等優勢。本研究，首先進行FCDI系統的操作參數最佳化，比較不同FCDI操作模式對去除離子效能之影響，並利用CuHCF嵌入式材料應用於FCDI系統中去除地下水中之氨氮。
本研究去除1 g/L的NaCl溶液實驗中，選用最佳化流動電極流速(16 mL/min)、進流水流速(8 mL/min)、襯墊厚度(0.5 mm)並保持進流水與流動電極電解質濃度相同時，去除效率可達99.9%。提高流動電極電解質濃度可以增加系統導電能力進而促進去除效率。
兩種進流水操作模式比較之研究中，和batch-mode相比，single-pass由於有穩定高濃度離子連續供給，所以具有高處理水量、高平均鹽類脫鹽效率(ASRR)、高吸附容量、高充電效率及更快確認進流水離子平衡狀態等優勢，也不會由於濃度差擴大及系統電阻增加，而導致FCDI系統除鹽能力下降。兩種流動電極操作模式比較時，短流式封閉循環(short-circuited closed-cycle, SCC)與獨立式封閉循環(isolated closed-cycle, ICC)相比，由於可以同時進行電吸附與電極再生，所以擁有高去除效率、高ASRR、不需額外的電極脫附程序、pH穩定等優勢。但ICC模式可以推估流動電極中固液相間的離子分佈情況，且可以組建不對稱FCDI系統等優點。
使用嵌入式材料CuHCF與活性碳(AC)作為電極材料的不對稱FCDI系統，研究應用於移除地下水之氨氮可行性，相較於鉀離子，FCDI系統對於氨氮有著更高的選擇性(選擇係數SNH4+/K+=1.07，於混合Na+和K+離子溶液)。在模擬地下水實驗中，發現高濃度的鈉離子與鉀離子的加入，不僅不會因為競爭吸附而降低系統對氨氮的電吸附作用，反而會因為改善系統導電能力而增加系統對氨氮的去除效率(23.5%)並維持優異的離子選擇性，選擇係數SNH4+-N/K+ 與SNH4+-N/Na+為3.22與10.22。使用嵌入式材料CuHCF作為電極材料的不對稱FCDI系統，應用於地下水中氨氮的去除與回收深具潛力。

關鍵字

流動電極電容去離子 ； 操作模式 ； 鐵氰化銅 ； 氨氮 ； 選擇性

並列摘要

Capacitive Deionization (CDI) is an emerging desalination technology with low energy demand and without secondary pollution, which removes ions from solution by applying a low voltage between two electrodes. Flow-Electrode Capacitive Deionization (FCDI) replaces the fixing electrode in CDI with the flow electrode for better electrosorption capacity and continuous operation. In this study, we first optimized operation parameters of FCDI system, and then compared the different operation modes to analyze how different operation modes affect the FCDI system. Finally, employing copper ferricyanide (CuHCF) in the FCDI system to remove ammonia in the synthetic groundwater.
In this study, we chose the best flow rate of flow-electrode (16 mL/min), flow rate of inflow (8 mL/min), spacer thickness (0.5 mm), and same electrolyte concentration in flow electrode as the inflow to remove the 1 g/L NaCl solution. The NaCl removal efficiency can reach 99.9%. In addition, increasing the flow-electrode concentration can improve the ion transport ability of system; therefore, it can enhance the salt removal efficiency.
In the comparison of two inflow operation modes, single-pass mode has higher water treatment capacity, higher average salt removal rate (ASRR), higher electrosorption capacity, higher charging efficiency and easier to find the equilibrium condition of inflow because of stable and continuous supply of high concentration of salts. Single-pass mode can avoid the reduction of removal efficiency caused by electric resistance increasing and concentration gradient increasing.
In the comparison of two flow-electrode operation modes, SCC (short-circuited closed-cycle) mode has advantages of higher removal efficiency and ASRR, stable pH value and without regeneration process due to simultaneously electrosorption and regeneration. While ICC (isolated closed-cycle) mode can evaluate the ion distribution between liquid (flow electrode electrolyte) and solid (electrode materials) phases and can construct the asymmetric FCDI system.
When the asymmetric FCDI system using copper ferricyanide (CuHCF) and activated carbons (ACs) to explore the feasibility of removing ammonia from groundwater, the FCDI system achieved higher selectivity of ammonia to potassium (S NH4+/K+=1.07, in Na+and K+ mixture). When the system was applied to the synthetic groundwater, high concentrations of sodium and potassium in the synthetic groundwater instead of competitive adsorption to lower the electrosorption ability to ammonia, but improve the removal efficiency of ammonia (23.5%) and excellent selectivity (SNH4+-N/K+ and SNH4+-N/Na+ : 3.22 and 10.22) because they make better ion transport ability of system. Therefore, applying intercalation material CuHCF to assemble the asymmetric FCDI system has great potential to treat or recover ammonia in groundwater.

並列關鍵字

Flow-Electrode Capacitive Deionization ； Operating mode ； Copper ferricyanide ； Ammonia ； Selectivity

參考文獻

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