聚偏氟乙烯微過濾膜於廢水處理應用 之污塞機制研究

Study of the Organic Fouling Mechanism of Polyvinylidene Fluoride Microfiltration Membrane for Wastewater Treatment Applications

林念蓉(Nien-Jung Lin)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2009年)

https://doi.org/10.6840/cycu200901268

摘要

微過濾與超過濾薄膜程序已廣泛地應用於各類的水處理中。然而此程序卻因為薄膜污塞的問題，使得操作成本增加且處理效能下降。為了減少薄膜污塞的發生，可藉由操作參數的調整以及薄膜特性的改變來降低污塞現象的產生。
因此，本研究中利用電漿改質來改變其PVDF膜材表面之親水與官能基特性，以簡單的基本組成來模擬廢水中污染物質，如蛋白質、多醣體與腐植酸溶液進行掃流過濾試驗作為初步評估，將產生的阻塞現象藉由雷射共軛焦顯微鏡分析以及探討其透過量衰減情形。
研究結果發現，薄膜在進行電漿改質後，隨著薄膜親水程度的增加，其接觸角明顯地下降，表面型態的差異較小。對於疏水性薄膜而言，因BSA之疏水性官能基外露，使得BSA在接觸疏水性薄膜表面時，容易堆積於膜面並造成BSA團聚現象形成緻密濾餅層，導致過濾阻力增加通量因而下降。而藉由電漿改親水之PVDF-p-HPI薄膜可有效降低膜表面上不可逆吸附的比例，使得內部阻力值下降。對於HA溶液過濾而言，其分子量範圍分布廣泛，在大分子部分易沉積於膜面使得濾餅迅速生成導致透過量衰退；而小分子部分則會穿透薄膜在孔道內阻塞，因此整個過濾機制可分為濾餅過濾以及孔洞阻塞。
在BSA-DEX的混料進料下，可發現過濾初期主要是由BSA與DEX共同阻塞於孔道內使得通量的下降，隨著過濾時間的增加，之後則改為BSA濾餅的生成而導致濾速迅速的衰退。對於BSA-HA的進料中，BSA與HA的混合會使濾餅的生成更為緻密，因此造成透過量迅速地衰退。
過濾阻力分析方面，在各進料系統中，主要還是以濾餅過濾為主，其值至少高達90%以上。另外，藉由相對透過量衰退率值可看出DEX物質最容易造成內部阻塞，使得其值較其他兩者高。此外，操作於掃流速度為0.05 m/s下，可加速濾餅的生成因而降低內部阻塞的比例，相較於掃流速度為0.11 m/s時，其相對透過量衰退率數值都較低。
最後，在三成份混合溶液系統中，主要是由BSA以及HA主導其過濾機制。在pH=5時，因BSA不帶電性故容易透過薄膜，導致內部阻力增加。此外，利用電漿接枝之PVDF-g-PRGMA薄膜，可有減緩透過量衰退的情形，並可降低其內部阻塞的發生。

關鍵字

PVDF微過濾薄膜 ； 有機污塞物 ； 掃流過濾

並列摘要

The microfiltraion (MF) and ultrafiltration (UF) were also widely used in various water purification processes. However, although the MF and UF membrane processes have already widely applied in various water treatment processes, the fouling problems during filtration reduce the performance to raise the operation cost. To reduce the membrane fouling, adjustment of the operation parameters and the membrane characteristic modifications were regarded as useful methods.
Hence, in this study, the surface hydrophilicity and functional group characteristics of polyvinylidene fluoride (PVDF) membrane was modified using the plasma modification technique. Later, the simplified simulated wastewater composed of protein, polysaccharide, and humic acid, respectively, was adopted to process the crossflow filtration through the PVDF membrane for initial estimation of the wastewater treatment. The membrane fouling phenomena were analyzed through the laser scanning confocal microscope technique and filtration flux decay analysis.
The results revealed that the enhancement in hydrophilicity of the as-modified membrane leads to the decrease in the corresponding contact angles after plasma modification of the membrane. For the hydrophobic membrane, because of the exposure of the hydrophobic functional group of BSA, BSA was easily deposited on the surface to form the BSA clusters, resulting in the development of the dense cake layer. This caused the increase in the filtration resistance, and the decrease in the filtration flux. The hydrophilic PVDF-p-HPI membrane modified by plasma could effectively reduce the ratio of irreversible adsorption on the membrane surface, leading to lower the inner resistance. As for the filtration of HA solution, we divided into two parts by the molecular weight, the large and small molecular weight of HA, due to its wide molecular weight distribution. The larger ones were easily deposited on the membrane surface to subsequently produce the cake layer, resulting in the flux decline. On the other hand, the small ones partially blocked the pores during the permeation of the membrane. Consequently, the filtration mechanism could be separated into the cake filtration and pore blocking in this study.
It was found that the BSA and DEX co-blocked the pores to result in permeability decline in the initial period of filtration under the feed solution of BSA-DEX mixture. As increasing the filtration time, the permeability rapidly declined due to the formation of BSA cake layer. As for the feed solution of BSA-HA mixture, the growth of the cake layer would be more denser, leading to the permeability decline rapidly.
In the analysis of filtration resistance, the filtration resistance was mainly controlled by the cake filtration in all of feed solution. The resistance of the cake layer was more than 90% of the total filtration resistances. Furthermore, the relative flux reduction (RFR) values could imply that the DEX substance easily causes the pore blocking than the other two substances, BSA and HA. In addition, the faster formation of cake layer would reduce the pore blocking and the RFR values under the cross-flow velocity operated at 0.05 m/s, as compared to that operated at 0.11 m/s.
At last, BSA and HA dominated the filtration mechanism in the triple mixture. At pH 5 of the feed solution, the neutral BSA was easy to permeate though the membrane pore, leading to the increase in the pore blocking. Furthermore, the grafted PVDF-g-PRGMA membrane would reduce the flux decline and the pore blocking.

並列關鍵字

PVDF Microfiltration Membrane ； Orangic fouling ； Cross-flow Filtratiion

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