全球暖化將導致水源短缺問題更趨嚴重，因應未來水資源問題，減少用水風險，因此中鋼公司需要提升水回收再用之能力，並有效規劃與推動未來的近零排放目標。本研究以鋼鐵酸洗之廢水在經過逆滲透 (Reverse osmosis, RO) 脫鹽程序後，產生之濃水 (被薄膜阻擋) 為研究對象，探討資源化回收之可行性。研究中以雙極膜電透析膜(Bipolar membrane electrodialysis, BMED)技術，將廢水中之「NaCl」，資源化成HCl、NaOH以再利用。
本研究首先建立雙極膜電透析模組，進行模組操作參數建立及薄膜於操作時之影響因子評估，測試之操作參數包含電流密度、模組數及通量，並依操作參數結果作電費成本計算。為提升研究應用性，研究中並評估停留時間(不同回流率)、酸/鹼提濃方法、及低濃度回用於製程適用性、薄膜阻塞之影響、阻塞後清洗方法、減少阻塞之前處理評估、及薄膜汰換時機。
本研究於實驗室建立半批次連續BMED操作模組，主要單元及參數如下：1. 陽極：DSA、2. 隔板：塑膠隔板、3. 薄膜：SF膜、4. 模組數：1 cell 、5. 電流密度：100 A/m2，由此操作方法，測試出最適產酸、鹼濃度(酸：1.38 % ；鹼：1.44 %)。以此模組進行RO濃排廢水作BMED測試，若以未經前處理之RO濃排廢水作BMED進流水，在180分鐘內BMED之操作電壓從7急升至28V，顯示水質需要適當前處理。薄膜表面分析顯示，鈣為主要造成阻塞因素。後續以軟化將鈣降低至10 mg/L以下後，BMED操作前三次循環操作穩定，經鹼洗、酸洗和純水清洗薄膜後，可穩定進行多次批次試驗。以軟化後之水樣再利用奈米過濾(NF)去除RO濃排中之有機物至10mg/L以下，可使BMED對於產HCl的電流效率大大提高，並且能在更短的時間內將RO濃排之氯鹽去除。

成本計算以過量軟化和軟化合併NF去有機物這兩種前處理方式作評估。BMED回收RO濃排廢水，考量電費、藥品費支出，及產酸、產鹼收入，其總成本計算結果如下: 過量軟化法處理一噸RO濃排廢水需要221.35 $NTD的支出 ，而軟化合併NF處理一噸RO濃排廢水會有84.8 $NTD/m3的收益。

Global warming will lead to a more serious shortage of water resources. In response to future water issues and reduce water risks, China Steel company needs to improve its ability to recycle water. Also effectively plan and promote future approximate zero emissions targets. In this study, the wastewater from steel pickling was subjected to reverse osmosis (RO) desalination process and the concentrated water (blocked by the membrane) was used as the research object to explore the feasibility of resource recycling. In the study, the "NaCl" in the wastewater was converted into HCl and NaOH for reuse by Bipolar membrane electrodialysis (BMED) technology.
In this study, the bipolar membrane electrodialysis module was first established to establish the module operating parameters and the impact factor evaluation of the membrane during operation. The operating parameters of the test included current density, module number and flux. The electricity cost was calculated according to the operating parameter results. In order to improve the applicability of the study, the study evaluated the residence time (different reflux rate), the acid/base concentration ascending method, and the low concentration for the process suitability, the effect of the membrane blockage, the post-blocking cleaning method, the pretreatment evaluation for reducing the membrane fouling problems and the timing of membrane replacement.
This study established a semi-batch continuous BMED operation module in the laboratory. The main units and parameters are as follows: 1. Anode: DSA, 2. Partition: plastic separator, 3. membrane: SF membrane, 4. Number of modules: 1 Cell, 5. Current density: 100 A/m2. The optimum acid and alkali concentration (acid: 1.38 %; base: 1.44%) was tested by this method. This module is used for the BMED test of raw RO concentrated wastewater. If the raw RO concentrated wastewater is used as the BMED influent water, the operating voltage of BMED will rise from 7 to 28V in 180 minutes, indicating that the water quality needs proper pretreatment. Surface analysis of the membrane showed that calcium was the main cause of blockage. After softening to reduce calcium to less than 10 mg/L, the three cycles of the BMED operation are stable. After washing the membrane with alkali, acid and pure water, multiple batch tests can be carried out stably. By using nanofiltration (NF) to remove the organic matter in the RO concentration to below 10mg/L, the BMED can greatly improve the current efficiency of HCl production. Also the chlorine salt in the RO concentrate can be removed in a shorter time.
Cost calculations were evaluated in two pre-treatments, excessive softening method and softening combined with NF de-organic method. BMED recovers RO concentrated wastewater, considers electricity cost, chemical expenses, the income of the acid and alkali production. The total cost calculation results are as follows: excessive softening method for treating one ton of RO concentrated wastewater requires 221.75 NTD$ expenditure, while softening combined NF method for treating one ton of RO concentrated wastewater will have a gain of 84.8 $NTD.

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