奈米薄膜對水中新興污染物的去除機制與模式探討

Elucidation of Rejection Mechanisms and Models for PPCPs/EDCs in aqueous solution by Nanofiltration Membrane

吳海翔(Hai-Hsiang Wu)

指導教授 ： 蔣本基

國立臺灣大學/工學院/環境工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02992

摘要

本研究使用九種個人保健藥品(PPCPs)或內分泌干擾物質(EDCs)來系統化的研究奈米薄膜(NF)的去除機制。目標化合物被分成三組：第一組(G1)為親水性中性物質；第二組(G2)為帶負電物質；第三組(G3)為疏水性中性物質。為了要區分電荷斥力的效果，奈米薄膜過濾實驗在pH 3 和pH 8 的條件下進行。而區分吸附的效果，奈米薄膜過濾實驗初始的去除率和最終去除率比較。
本研究評估薄膜特性與操作條件對去除率的影響。薄膜孔徑的減少會顯著的增加去除率，而薄膜厚度的增加會少量的增加去除率。透膜壓力的增加會使去除率呈線性上升，而增加掃流速度使去除率先上升接著達到穩定的去除率。
G1 化合物去除率隨著溶質大小(分子量)的增加而增加。G1 和G3 在pH 8 和pH 3 的去除率的差距不顯著，但G2 在pH 8 的去除率比pH 3 來得高，原因為電荷斥力作用。G3 化合物由於有吸附作用，濃度與去除率會隨著時間降低，且最終的去除率可能會低於相似大小的G1。本研究中定量三個去除機制對去除率的貢獻，結果顯示G1 的去除率僅由分子篩除所控制，但在pH 3 trimethoprim 有電荷斥力作
用；G2 的去除率由電荷斥力和分子篩除所控制；G3 的去除率由分子篩除和吸附所控制。
本研究使用 Irreversible thermodynamics 及extended Nerst-Planck 模式來預測去除率。預測結果在小分子情況下較為準確，大分子則有高估情況。改變掃流速度與透膜壓力會改變濃度極化因子，雖然濃度極化因子對於去除率是有影響，但是其數值很可能有估算錯誤的情況，因而造成去除率的估算有誤差。

關鍵字

奈米薄膜 ； 去除機制 ； 個人保健藥物(PPCPs) ； 內分泌干擾物質(EDCs) ； 分子篩除 ； 電荷斥力 ； 吸附 ； 去除模式

並列摘要

The rejection mechanism of nine PPCPs/EDCs by nanofiltration membrane was systematically studied. Target compounds were classified into three groups: Group 1
(G1) was hydrophilic neutral compounds; Group 2 (G2) was negatively charged compounds; Group 3 (G3) was hydrophobic neutral compounds. To distinguish electrostatic repulsion, filtration experiments were conducted at pH 3 and pH 8. To
differentiate adsorption effect, initial rejection and final rejection were compared. Adsorption experiment was conducted to validate the effect of adsorption.
The effect of membrane characteristic and operating condition on rejection was evaluated. The decrease in membrane pore radius significantly increased the rejection,
whereas the increase in membrane thickness only slightly increased the rejection. Rejection increased as the transmembrane pressure increased, whereas rejection slightly
increased and reach stable rejection as cross flow velocity increased.
The rejections of G1 solutes increased as the solute size (or molar weight) increased. The rejections of G1 and G3 solutes have almost the same at pH 8 and at pH 3, except
for trimethoprim. However, the rejections of G2 solutes were higher at pH 8 than at pH 3 due to electrostatic repulsion. G3 solutes had adsorption effect, and the initial
rejections were higher than the final rejection and decreased in the feed concentration with time. The contribution of the three rejection mechanisms was quantified. The rejections of G1 solutes were governed only by size exclusion, except for trimethoprim at pH 3. The rejections of G2 were governed by electrostatic repulsion and size exclusion at pH 8. The rejections of G3 solutes were governed by adsorption and size exclusion.
The irreversible thermodynamics model and the extended Nerst-Planck model were used to predict rejection. The predicted rejection is more accurate for relatively small
and medium compounds. However, it is overestimated for relatively larger compounds. The deviation may cause by the non-uniform of the membrane pore size. By comparing
the effect of the cross flow velocity and the transmembrane pressure on predicted rejections and experimental rejections, results showed that the concentration
polarization factor may play a role on rejection, but the value of the concentration polarization factor may not be calculated correctly.

並列關鍵字

Nanofiltration membrane ； Pharmaceutical and personal care products ； Rejection mechanism ； Endocrine disruptor chemicals ； size exclusion ； electrostatic repulsion ； adsorption ； rejection model.

參考文獻

Bellona, C., Drewes, J. E., Xu, P., Amy, G., 2004. Factors affecting the rejection of organic solutes during NF/RO treatment—a literature review. Water Research 38, 2795-2809.

Bowen, W.R., Mohammad, A.W., Hilal, N., 1997. Characterisation of nanofiltration membranes for predictive purposes — use of salts, uncharged solutes and atomic force microscopy. Journal of Membrane Science 126, 91-105.

Braeken, L., Bettens, B., Boussu, K., Van De Meeren, P., Cocquyt, J., Vermant, J., Van der Bruggen, B., 2006. Transport mechanism of dissolved organic compound in aqueous solution during nanofiltration. Journal of Membrane Science 279, 311-319.

Bungay, P.M., Brenner, H., 1973. The motion of a closely fitting sphere in a fluid-filled tube. Int. J. Multiph. Flow 1, 25-56.

Comerton, A.M., Andrews, R.C., Bagley D.M., Yang, P., 2007. Membrane adsorption of endocrine disrupting compounds and pharmaceutically active compounds. Journal of Membrane Science 303, 267-277.