| 摘要: | 納濾膜(Nanofiltration, NF)在海水淡化、廢水回收及其他工業分離應用中發揮著重要作用，逐漸替代逆滲透膜(Reverse osmosis, RO)，因此預計廢棄(End-of-life, EOL)膜的數量將在未來急劇增加。為了延長使用壽命，可以對膜進行化學處理(例如氯暴露)以恢復滲透通量和脫鹽能力。目前大部分研究主要針對EOL-RO膜，而本研究主要是評估次氯酸鈉(Sodium hypochlorite, NaOCl)再生EOL-NF膜，並基於超聲波(Ultrasound, US)處理加速反應進行，探討最佳的操作條件。
本研究所使用的EOL-NF膜為半芳香族聚醯胺膜(semi-aromatic polyamide membranes)，且表面存在疏水性複合型積垢，不可逆污染導致其滲透通量下降而脫鹽率維持在95%以上，故再生考慮保留其良好脫鹽能力的情況下，儘可能的提升滲透通量。EOL-NF膜在使用濃度為3,000 ppm NaOCl靜態浸泡20小時恢復最佳的再生性能，使其滲透通量提升15.51%且脫鹽率維持在95.87%。但使用乙醇預處理並未有更高的效能提升，反而增加化學藥品的消耗。而後利用US (1 W/cm2)輔助化學氧化(3,000 ppm NaOCl)，大幅節省膜再生時間，從20 h縮短至45 min (約27倍)，使EOL膜的滲透通量提升17.84%且脫鹽率維持在95.01%。但值得注意的是過高功率(1.4 W/cm2)的US會對膜造成物理損傷。
本研究最佳操作條件之再生膜在實際廢水(都市污水二級處理出流水)長達168小時的長期實驗中，不僅達到穩定的滲透通量(6.61 Lh-1m-2bar-1)，同時對導電度、濁度、UV254 (紫外光照射254 nm波長)皆有較高的去除效率，分別為66-67%、90-96%、88-94%。且能截留多種離子，其中對二價陽離子(Ca2+、Mg2+)的去除率高達85%以上，對硫酸根離子甚至可以達到99%的去除。其出水水質均可符合目前較為嚴苛的冷卻水回用標準，且離子濃度遠低於基準值。
廢棄膜的再利用已成為循環經濟框架中重要的可持續替代方案。本研究評估了使用超聲波輔助化學氧化法處理EOL-NF膜用於處理生活二級廢水以獲得具有冷卻水標準質量的回收水之可行性，展示了一種能將廢棄納濾膜快速再利用的新方法，從而為解決廢棄膜組件的處置問題提供了實用的解決方案。;Nanofiltration membranes (NF) play an important role in seawater desalination, wastewater recycling, and other industrial separation applications, gradually replacing reverse osmosis membranes (RO), so the number of end-of-life (EOL) membranes is expected to increase dramatically in the future. To extend service life, membranes can be chemically treated (e.g., chlorine exposure) to restore permeate flux and desalination capacity. Most current research focuses on EOL-RO membranes, and this study mainly evaluates the regeneration of EOL-NF membranes with sodium hypochlorite (NaOCl), accelerates the reaction based on ultrasonic (US) treatment, and explores the best operating conditions.
This study uses a semi-aromatic polyamide EOL-NF membrane, which has a hydrophobic complex fouling on its surface. Its permeability decreases due to irreversible fouling, while the salt rejection stays over 95%. Regeneration therefore takes into account raising the permeability as much as feasible while maintaining its strong desalination ability. After 20 hours of statically immersed in 3,000 ppm NaOCl, the EOL-NF membrane regained its optimal regeneration capability, with a 15.51% increase in permeability and a 95.67% salt rejection rate. Nevertheless, applying ethanol pretreatment raises the amount of chemicals used without increasing efficiency. The EOL membrane′s permeability increases by 17.84% and the desalination rate is maintained by using the US (1 W/cm2) to assist with chemical oxidation (3,000 ppm NaOCl). This significantly reduces the membrane regeneration time from 20 hours to 45 minutes (about 27 times). It should be noted, however, that using the US at too high a power (1.4 W/cm2) will cause physical damage to the membrane.
Under ideal operating conditions, the regenerated membrane in this study not only improved conductivity but also reached a stable permeability (6.61 Lh-1m-2bar-1) in a 168-hours long experiment with real wastewater (urban sewage secondary treatment effluent). The removal efficiencies of degree, turbidity, and UV254 are 66–67%, 90–96%, and 88–94%, respectively. It has the ability to intercept a wide range of ions, with the removal rate of divalent cations (Ca2+, Mg2+) reaching over 85% and the removal rate of sulfate ions reaching 99%. Its ion concentration is significantly below the standard value, and its effluent water quality satisfies the more demanding cooling water reuse regulations that are in place at present.
Reusing waste membranes has emerged as a significant sustainable alternative in the framework of the circular economy. This study assesses the feasibility of treating EOL-NF membranes for the treatment of domestic secondary wastewater using ultrasonic-assisted chemical oxidation in order to produce recycled water with cooling water standard quality. A novel technique for the rapid repurposing of EOL membranes is presented, offering a workable resolution to the EOL membrane module disposal issue. |
