枯草桿菌懸浮液之微過濾結垢特性

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Title:	枯草桿菌懸浮液之微過濾結垢特性
Other Titles:	Fouling characteristic in microfiltration of bacillus subtilis suspension
Authors:	王鐘逸;Wang, Chung-yi
Contributors:	淡江大學化學工程與材料工程學系碩士班黃國楨;Hwang, Kuo-jen
Keywords:	枯草桿菌;蛋白質;多醣體;生化分離;Bacillus subtilis;Protein;Polysaccharide;bio-separation
Date:	2010
Issue Date:	2010-09-23 17:32:29 (UTC+8)
Abstract:	本研究在探討枯草桿菌(Bacillus subtilis)之微過濾結垢特性，實驗採用恆壓系統分別對未添加培養基與添加培養基之枯草桿菌懸浮液進行過濾實驗，了解生物發酵槽產品之過濾行為的差異。實驗結果發現，未添加培養基之懸浮液之過濾曲線可區分為三個階段：第一階段：過濾一開始呈線性關係；第二階段：隨著過濾進行則變成一先凹再凸的反曲曲線；第三階段：過濾後期則又大致呈線性關係，且斜率則與第一段之斜率相當。此現象表示在第二階段之阻力急遽上升，是因為此時於薄膜表面上的粒子受到壓縮變形，並且形成一緻密層(skin layer)，使得大部分的壓降損失於此濾餅層，所以當在此層形成後，剩餘的壓降不足以再對隨後輸送至膜面的粒子產生壓縮，後期所形成的濾餅結構於是較為鬆散，該時期與第一階段相同，濾餅的阻力係來自於枯草桿菌細胞的堆積與重排。而過濾添加培養基之枯草桿菌懸浮液可發現，其過濾曲線會隨懸浮液中菌體以及膠羽濃度而有所不同。於低濃度下，當操作壓力越大時，其過濾曲線(dt/dv vs. v) 之切線斜率增加的趨勢越明顯，由經驗式所求得的壓縮係數分別為n=1.09與β=0.11，顯示出此濾餅具有很高的壓縮性。實驗結果亦顯示：欲收集相同的濾液體積，高壓操作所需要的時間反而越長，這表示在懸浮液中有膠羽存在時，影響濾速的不止有壓力，濾餅的性質也是重要的影響因子。由於濾餅在高壓下被壓縮的更緊密，使得濾速反而會隨著壓力之增加而下降。當培養天數增加、懸浮液中膠羽量變多時，可發現在不同過濾壓力下之過濾曲線幾乎重疊，這是因為在高膠羽濃度下，透膜壓差之增加會使得濾餅孔隙度降低，而導致過濾總阻力隨之上升，抵消了因透膜壓差增加所提升的過濾驅動力。此外，並進行懸浮液與濾液端之蛋白質與多醣體的濃度分析。結果可發現，原懸浮液中蛋白質/多醣體的比例約為0.1~0.3。蛋白質在過濾過程中的阻擋率高達100%，表示懸浮液中的蛋白質都會被薄膜阻擋；而多醣體的阻擋率介於0.01~0.1%之間，表示懸浮液中大多數的多醣體皆能穿透薄膜。為了解過濾阻力來源，先藉由離心將原懸浮液分為上清液與殘留粒子，並各自重新懸浮後進行實驗。實驗結果顯示：殘留粒子懸浮液主要組成為菌體以及膠羽，其主要成分為萃取性胞外高分子物質(extractable EPS)，其中絕大多數為蛋白質，由阻力串聯模式可知，殘留粒子懸浮液之濾餅阻力佔了將近99%。而上清液懸浮液之主要成分為可溶性胞外高分子物質(soluble EPS)，其中絕大部分為多醣體，實驗結果顯示：上清液之濾餅阻力約佔了55%，而不可逆阻力約佔27%。此外，殘留粒子懸浮液之濾餅阻力比上清液懸浮液之濾餅阻力大了將近100倍，故過濾之主要阻力來源為菌體以及膠羽所構成之濾餅層。 Fouling characteristic in microfiltration of bacillus subtilis suspension was studied. In order to understand the filtration behavior of fermentation bio-products. Bacillus subtilis suspensions were prepared under two different culture conditions, and used in dead-end cake filtration. In the condition of no culture medium addition, the trend for filtration curve of dt/dv vs. v can be divided into three distinct parts. In the early period of filtration, the filtration curve is a straight line. This reveals that the average specific cake filtration resistance is constant. The increase in filtration resistance is caused by the cake formation and the rearrangement of particles in cake. The tangent slope of filtration curve drastic increases in the second period. This is because the deformation and compression of bacillus subtilis cells result in a sudden decrease in cake porosity and consequently an increase in filtration resistance. A skin layer with compact structure may be formed next to the membrane surface. Because most solid compressive pressures are depleted by the skin layer, the filtration curve in the third period is then similar to that in the first period. The filtration curve significantly varies with the concentrations of Bacillus subtilis and floc when medium is added during culture. The tangent slope of filtration curve becomes sharper under higher filtration pressure at low cell concentration, the compressibility factors obtained by empirical equations are n=1.09 and β=0.1, respectively. These indicate that the cakes have extremely high compressibility. The results also show that the filtration time should be longer to receive a given filtrate volume under higher filtration pressure. When flocs exist in the suspension, the filtration flux is affected by not only filtration pressure but also the cake properties. Because the cake is compressed to be more compact under higher pressure, the flux contrarily decreases with increasing pressure. At high floc concentration, the filtration curves almost overlap whatever the pressure is. An increase in transmembrane pressure leads to lower cake porosity and to higher total filtration resistance. The increase in driving force by increasing pressure is therefore offset by the resistance increase. Besides, the concentrations of protein and polysaccharide in the suspension and filtrate are analyzed. The ratio of protein/polysaccharide in the original suspension is ca 0.1 - 0.3. The rejection of protein is as high as 100%, while that of polysaccharide ranges from 0.01 to 0.1%. These results indicate that all proteins will be retained by the membrane, but most polysaccharides can penetrate through the membrane into filtrate. In order to understand the sources of filtration resistances, the original suspension is separated into supernatant and residue using centrifuge. The major components in the residue are cells and flocs, in which contain a significant amount of proteins. According to the resistance-in-series model, the cake resistance for the residue suspension is nearly 99% of the overall resistance. The major components existed in the supernatant suspension is soluble extracellular polymer substances (EPS), most of which is polysaccharides. The cake resistance is 55% and the irreversible resistance is 27% of the overall resistance for the supernatant suspension. However, the cake resistance for the residue suspension is ca 100 times higher then that for supernatant suspension. It could be said that the major resistances in the filtration of bacillus subtilis suspension is causing by the cake layer formed by cells and flocs.
Appears in Collections:	[Graduate Institute & Department of Chemical and Materials Engineering] Thesis

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