胞外高分子物質對枯草桿菌之掃流微過濾的影響

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Title:	胞外高分子物質對枯草桿菌之掃流微過濾的影響
Other Titles:	Effects of extracellular polymeric substances on the cross-flow microfiltration of bacillus subtilis
Authors:	蔡明修;Tsai, Ming-Hsiu
Contributors:	淡江大學化學工程與材料工程學系碩士班黃國楨
Keywords:	枯草桿菌;微過濾;掃流過濾;胞外聚合物;阻擋率;Bacillus subtilis;microfiltration;Cross-flow filtration;Extracellular polymeric substances;Rejection
Date:	2011
Issue Date:	2011-12-28 18:50:29 (UTC+8)
Abstract:	本研究旨在探討枯草桿菌培養液中胞外高分子物質與操作條件對掃流微過濾性能之影響。實驗採用平板式掃流微過濾系統，使用平均孔徑為0.22 μm的聚二氟乙烯(PVDF)濾膜，過濾不同培養天數的枯草桿菌培養液，探討透膜壓差、掃流速度對過濾速度、過濾阻力、蛋白質和多醣體的阻擋率、濾餅性質等之影響。研究結果發現，培養時間越久的菌體尺寸越大，從培養1天平均尺寸200 μm增加到5天的229 μm；胞外聚合物的濃度亦會隨培養時間而增加，更容易在膜面形成積垢，造成過濾阻力上升。經由過濾阻力分析，可得知濾餅阻力佔總阻力的90%以上；將離心後之上層澄清液與原菌液之過濾速度做比較，發現原菌液中的膠羽是造成過濾初期濾速急速下降的原因。膠羽粒子容易在膜表面形成積垢，而胞外聚合物則會在積垢的縫隙中進行填補，使得阻力增加、濾速降低。研究結果亦顯示，濾速會隨掃流速度與透膜壓差之增加而增加，當掃流速度由0.1增加至0.3 m/s，濾速最多增加1.7倍，而透膜壓差由20增加至120 kPa，濾速最多增加1.2倍；然而濾速卻隨培養天數之增加而減少，當掃流速度與透膜壓差固定時，培養時間由1天增加至5天，濾速皆會降低60%。此外，培養天數增加，胞外聚合物濃度的增加會導致濾餅更緻密，造成多醣體與蛋白質阻擋率的上升。多醣體與蛋白質的阻擋率皆會隨掃流速度之增加而增加，掃流速度由0.1增加至0.3 m/s，二者的阻擋率皆增加1.4倍，而蛋白質與多醣體的阻擋率受透膜壓差的影響不大。由枯草桿菌所形成的濾餅具高壓縮性，雖然壓縮係數隨掃流速度之增加並無明顯變化，然而卻隨透膜壓差之增加而增加，也隨培養天數之增加而增加，培養時間由1天增加至5天，濾餅壓縮係數會由0.60增加至0.88。 The effects of extracellular polymer substances (EPS) in Bacillus subtilis broth and operating conditions on the performance of cross-flow microfiltration are studied. A two-parallel-plate cross-flow system is used in experiments, and a 0.22 μm membrane made of polyvinylidene fluoride is used as the filter medium. The effects of culture time, transmembrane pressure and cross-flow velocity on the filtration rate, filtration resistance, rejections of proteins and polysaccharides and cake characteristics are discussed. The results show that a larger size of bacteria is observed for longer culture time, the mean size increases from 200 to 229 μm when the culture time increases from 1 to 5 days. An increase in culture time also leads to higher EPS concentration and higher filtration resistance caused by the fouling on the membrane surface. Analysis of filtration resistance indicates that the cake resistance is over 90% of the overall filtration resistance. Comparing the filtration data of the upper supernatant after centrifugation and the original Bacillus subtilis broth, the rapid decline in filtration rate at the early periods of filtration is attributed to the floc existence in the Bacillus subtilis broth. The packing of EPS in the filter cake which is formed by the floc causes to significant increase in filtration resistance and decrease in filtration rate. The filtration rate increases with increasing cross-flow velocity or transmembrane pressure. The filtration rate increases 1.7-fold when cross-flow velocity increases from 0.1 to 0.3 m/s and increases 1.2 times if transmembrane pressure increases from 20 to 120 kPa. However, the filtration rate decreases with increasing culture time. the filtration rate decreases 60% when culture time increases from 1 to 5 days under the same cross-flow velocity and transmembrane pressure. Furthermore, the increase in EPS concentration for longer culture time results in more compact cake, as a result, in higher rejections of polysaccharides and proteins. The rejections of polysaccharides and proteins also increase with increasing cross-flow velocity. Both the rejections increase 1.4-fold when cross-flow velocity increases from 0.1 to 0.3 m/s. However, the transmembrane pressure has a trivial effect on the rejections of proteins and polysaccharides. The cake formed by Bacillus subtilis exhibits highly compressible behavior. Although the effect of cross-flow velocity on the cake compressibility factor is not obvious, the cake compressibility increases significantly with increasing transmembrane pressure and culture time. The cake compressibility factor increases from the 0.60 to 0.88 when the culture time increases from 1 to 5 days.
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