以乙二胺四乙酸二鈉和磷酸三鈉作為前驅滲透驅動液之研究

A Study of Disodium Ethylenediaminetetraacetate and Trisodium Phosphate as Draw Solutions in Forward Osmosis Process

黃國哲(Kuo-Zhe Huang)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2014年)

https://doi.org/10.6841/NTUT.2014.00827

摘要

前驅滲透（Forward osmosis, FO）是新興薄膜分離程序，為利用溶液自然滲透壓差驅動的薄膜技術，相較於傳統薄膜程序如逆滲透（Reverse osmosis, RO），有著低成本、無需外加壓力、低耗能就能使污染物達到高截留之效益…等優點。過去大多文獻以 NaCl 等傳統單價鹽類作為驅動液，但是有驅動液反滲透的問題。因此，本研究以使用乙二胺四乙酸二鈉（EDTA-2Na）和磷酸三鈉（Na3PO4）高價數溶液作為驅動液，並經由FO程序稀釋後之高價數驅動液可以奈米過濾（Nanofiltration , NF）來濃縮回收再利用。
本研究主要以FO/NF用於污泥濃縮脫水及回收驅動液之再利用，使用美國HTI公司製造之三乙酸纖維膜（Cellulose triacetate, CTA）及複合式膜（Thin-film Composite, TFC）進行測試。實驗分為兩部份：第一部份FO程序以CTA膜應用於驅動液EDTA-2Na進行污泥濃縮脫水，隨後使用稀釋後之驅動液透過4種不同NF膜來做回收截留效率之比較；第二部份FO程序以TFC膜於驅動液Na3PO4 進行污泥濃縮脫水，並使用稀釋後驅動液於NF-TS80膜來進行濃縮回收。
第一部份使用EDTA-2Na驅動液進行實驗，研究結果顯示，與傳統鹽類（NaCl）做為驅動液相比，產生較高水通量及低鹽反滲透量，在操作時間16小時後，MLSS 濃度從初始濃度8000 mg/L上升至32000 mg/L，且對污泥中有機物與營養鹽去除率分別為 NH4+-N：97%、NO3--N：90%、NO2--N：97%及PO43--P：99%，此外，在 NF 回收過濾程序中，在4片分別為 NF-XN45膜、NF-DL膜、NF-TS80 膜及 NF-DK 膜中，在操作壓力80 psi下，以 NF-TS80 膜截留率來的最好 (93%)。第二部份，以驅動液 Na3PO4 分別在 FO mode (active layer facing the feed solution)及 PRO mode (active layer facing the draw solution) 進行污泥脫水研究，結果顯示，FO mode 較 PRO mode 來的更有效率，並產生較高的水通量（FO mode Jw = 7.09 LMH；PRO mode Jw = 6.71 LMH)，在操作時間15小時後， MLSS 濃度從初始濃度3500 mg/L上升至19800 mg/L（PRO mode)及22000 mg/L（FO mode），此外奈米薄膜回收程序中，應用NF-TS80膜，在操作壓力120 psi下，其截留率可達90.88%。本研究亦證明了以高價數溶液較傳統單價鹽類作為驅動液產生較高水通量、低鹽反滲透量。

關鍵字

前驅滲透 ； 驅動液 ； 污泥脫水

並列摘要

Forward osmosis (FO) is an emerging membrance separation process of water driven by the natural osmotic pressure difference across the semipermeable membrane without the aid of external energy. Unlike traditional membrane process such as Reverse Osmosis (RO), the no/less energy consumption of FO makes it possible to be a promising technology. However, so far, the development of FO technology is still hindered by the unavailability of suitable draw solutions and the exploration of new draw solutes is vital for future FO applications. As presented in some literatures, used traditional inorganic univalent salt (NaCl) as the draw solution in FO process but still has reverse salt problem. Therefore, this research used high valence charged species draw solution such as trisodium phosphate (Na3PO4) and disodium ethylenediaminetetraacetate (EDTA-2Na) are proposed, since these complexes can be removed by nanofiltration.
In this study, a hybrid forward osmosis – nanofiltration (FO/NF) process was designed for dewatering high nutrient containing sludge and recovering draw solution. In this work, two novel solutions - disodium ethylenediaminetetraacetate (EDTA-2Na) and trisodium phosphate (Na3PO4) by utilizing commercial asymmetric cellulose triacetate (CTA) membrane and new FO – thin film composite (TFC) membrane. Since, TFC is new published membrane and using CTA membrane in FO processes , this study divided into two parts. In first part, was proposed EDTA-2Na as the draw solution (DS) by CTA membrane. In Second part, Na3PO4 was proposed as DS and using TFC as FO membrane.
In first part, results show that using EDTA-2Na produced higher water flux and lower reverse salt flux when compared to conventional inorganic salt (NaCl) at pH 8 . The final sludge concentration reached 32000 mg/L from initial 8000 mg/L after 16 h of operation. Moreover, nutrient compounds in sludge were successfully removed by the FO membrane with a removal efficiency of approximately 97% of NH4+-N , 90% of NO3--N , 97% of NO2--N and 99% of PO43--P.The NF recovery of EDTA-2Na indicated that all NF membrane performed well and TS-80 was the best among the tested membrane. In second part, the result showed that FO tests achieved high water flux and low reverse salt flux at pH9 of Na3PO4 DS due to increase in high complex formation between Na+ and HPO42- and Donnan effect. Final sludge concentration reached 19800 mg/L in PRO mode and 22000 mg/L in FO mode after 15 hours of operation. The NF recovery of Na3PO4 salt indicated that NF-TS80 was achieved the highest Na3PO4 rejection of 90.88% at operating pressure of 120 psi. This study also demonstrated that high valence charged species draw solution is more suitable than traditional inorganic salt.

並列關鍵字

Forward osmosis ； Draw solution ； Sludge dewatering

參考文獻

1. N. T. Hau, S.-S. Chen, N. C. Nguyen, K..Z. Huang, H.H. Ngo, and W. Guo, 'Exploration of EDTA sodium salt as novel draw solution in forward osmosis process for dewatering of high nutrient sludge'. Journal of Membrane Science, Vol. 455, 2014, pp. 305-311.

2. C. Boo, M. Elimelech, and S. Hong, 'Fouling control in a forward osmosis process integrating seawater desalination and wastewater reclamation'. Journal of Membrane Science,Vol.444, 2013, pp. 148-156.

3. N. C. Nguyen, S.S. Chen, H.Y. Yang, and N.T. Hau, 'Application of forward osmosis on dewatering of high nutrient sludge'. Bioresource Technology, Vol.132, 2013, pp. 224-229.

4. T.-S.Chung, X. Li, R.C. Ong, Q. Ge, H. Wang, and G. Han, 'Emerging forward osmosis (FO) technologies and challenges ahead for clean water and clean energy applications.' Current Opinion in Chemical Engineering, Vol.1, 2012, pp. 246-257.

5. H. Zhu, L. Zhang, X. Wen, and X. Huang, 'Feasibility of applying forward osmosis to the simultaneous thickening, digestion, and direct dewatering of waste activated sludge'. Bioresource Technology, Vol.113, 2012, pp. 207-213.