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|Other Titles: ||Immobilization of yeast on calcium alginate beads and its dead-end filtration characteristics|
|Authors: ||蘇炳元;Su, Ping-Yuan|
|Keywords: ||恆壓過濾;薄膜結垢;酵母菌;藻酸鈣晶球;Dead-end filtration;Membrane fouling;Ca-alginate beads|
|Issue Date: ||2013-04-13 11:52:30 (UTC+8)|
|Abstract: ||本論文旨在探討酵母菌在藻酸鈣晶球上之固定化的恆壓過濾特性。分別使用孔徑為0.025μm之醋酸纖維(MCE)膜、0.1μm之醋酸纖維(MCE)膜以及Whatman #2濾紙作為濾材，對單成份藻酸鈉(Sodium alginate)、酵母菌(Yeast)、藻酸鈣晶球(Calcium beads)及酵母菌固定化晶球(immobilized beads)進行恆壓過濾，探討不同成分物料、過濾壓差、以及鈣離子濃度對濾速、過濾阻力、薄膜結垢、濾餅及粒子之壓縮性質的影響。|
研究結果發現，當過濾單成份藻酸鈉時，藻酸鈉分子在薄膜表面上的結垢具有高壓縮性與高阻力，會導致濾速急速下降，而提高過濾壓差可以增加過濾速度。當過濾添加培養基之酵母菌，發現過濾初期濾速下降的速度較過濾藻酸鈉分子時不明顯，這是由於過濾阻力的主要來源是酵母菌細胞在膜面上堆積所形成的濾餅；但隨著過濾的進行，形成的濾餅開始受到壓縮，導致阻力增加，酵母菌形成的濾餅具有高壓縮性，增加過濾壓差會形成較緻密的結構，使得過濾比阻增加。在過濾藻酸鈣晶球時，發現在低壓操作下所得到的濾速反而較高，表示高壓下濾餅受到嚴重壓縮，導致的高阻力使濾速變得較慢。而過濾壓差越高，越容易將晶球內部的水分擠出，使濾餅重量反而下降。以較高濃度鈣離子所製備的晶球較為堅硬，其壓縮性也會較小，平均濾餅過濾比阻較低。當過濾酵母菌固定化晶球時，過濾初始時，濾餅與粒子尚未受到壓縮，過濾行為與堅固的粒子類似，dt/dv vs. v的過濾曲線接近直線；隨著過濾進行，粒子開始受到壓縮變形，使得濾餅孔隙度減小、阻力急遽增加，大部份的壓降損失於此時形成的濾餅，而在過濾後期，剩餘的壓降無法對濾餅上層新堆積的粒子產生壓縮，故濾餅阻力增加的趨勢減緩。濾餅孔隙度減小時，粒子的有效比表面積會增加，表示過濾酵母菌固定化晶球時，除了濾餅受到壓縮之外，晶球粒子本身也會受到壓縮變形，柔軟指數大約為1.5，酵母菌固定化至藻酸鈣晶球可以保持細胞活性在75 %左右。和先前文獻比較發現本篇製備的藻酸鈣晶球粒子(1 mm)比先前文獻的粒子小(3.8 mm與5 mm)，而且酵母菌活性會比先前文獻還要高。
Yeast cells are immobilized on the calcium alginate beads in this study. The alginate beads are prepared using different calcium concentrations, and their filtration characteristics, such as the retardation time for compression and softness index, are measured by a dead-end filtration system. The filter medium used in experiments include mixed cellulose acetate (MCE) membranes with mean pore sizes of 0.025 μm and 0.1 μm, and Whatman #2 filter paper. The effects of suspension materials, filtration pressure, and calcium concentration on the filtration rate, filtration resistance, and cake filtration and compression properties are discussed.
In the filtration of pure sodium alginate, the serious fouling on the membrane surface results in highly compressible cake with extremely high resistance as well as a rapid decline in filtration rate. The filtration rate increases with increasing filtration pressure. When a yeast fermentation broth is filtered, the filtration rate declines slowly at the beginning because the main source of filtration resistances is the filter cake formed by yeast cells. The filtration resistance increases quickly after a period of filtration due to the cake compression. The cake formed by yeast behaviors highly compressible. Therefore, the average specific cake filtration resistance increases significantly with increasing filtration pressure. In the filtration of calcium alginate beads, an increase in filtration pressure leads to a lower filtration rate due to severe cake and particle compressions, and leads to lighter cake mass due to the percolation of inter-particle water. The alginate beads prepared under high calcium concentration are more hardness, lower compressibility and lower specific cake filtration resistance. In the filtration of yeast immobilized beads, the filtration curves of dt/dv can be divided into three parts. The first part of filtration curve is a straight line and similar to those of incompressible particle. In the second part, the filtration resistance increases suddenly because of particle deformation and low cake porosity. Most solid compressive pressures are depleted in the cake formed in this period. The newly formed cake layer in the last part has a relatively loose structure. The increase in filtration resistance therefore becomes far smaller compared to the second part. Because the effective specific surface area of particles increases when the cake porosity decreases under high pressure, the cake compression and particle deformation occur simultaneously. The softness index of particles is measured as 1.5 for the yeast immobilized beads. The yeast activity for immobilized beads remains 75 % for a long period, which is much higher than those in free suspensions. Comparing the results of this study with those in previous literatures, the size of calcium alginate beads prepared by this study (ca 1 mm) are smaller and the yeast activity is higher than those in previous literatures.
|Appears in Collections:||[Graduate Institute & Department of Chemical and Materials Engineering] Thesis|
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