生物工程專(zhuān)業(yè)畢業(yè)設(shè)計(jì)英文翻譯

1、<p>　　High-Rate Continuous Production of Lactic Acid by Lactobacillus rhamnosus in a Two-Stage Membrane Cell-Recycle Bioreactor</p><p>　　Sunhoon Kwon, Ik-Keun Yoo, Woo Gi Lee, Ho Nam Chang, Yong Keun Ch

2、ang </p><p>　　Department of Chemical Engineering and BioProcess Engineering Research Center, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, South Korea; E-m

3、ail: hnchang@kaist.ac.kr</p><p><b>　　Abstract</b></p><p>　　It is important to produce L(+)-lactic acid at the lowest cost possible for lactic acid to become a candidate monomer mater

4、ial for promising biodegradable polylactic acid. In an effort to develop a high-rate bioreactor that provides high productivity along with a high concentration of lactic acid, the performance of membrane cellrecycle bior

5、eactor (MCRB) was investigated via experimental studies and simulation optimization. Due to greatly increased cell density, high lactic acid productivity, 21</p><p>　　Keywords: Lactobacillus rhamnosus; lacti

6、c acid; high productivity; cell recycle; membrane bioreactor </p><p>　　INTRODUCTION</p><p>　　The efficiency of the membrane cell-recycle bioreactor (MCRB) was successfully demonstrated in a numb

7、er of previous studies of the high-volumetric productivity of lactic acid. With greatly increased density of biocatalysts, i.e., microbial cells, the volumetric productivity of lactic acid could go up to 160 g L?1 h?1 as

8、 reported in the study of Ohleyer et al. (1985), which is more than 20 times higher than that of the conventional batch and chemostat processes. </p><p>　　However, the high productivity is not the only requi

9、rement for the economic feasibility of the process. Timmer and Kromkamp (1994) found that the process might be primarily influenced by production capacity and product concentration and to a lesser extent by the volumetri

10、c productivity when annual lactic acid production capacity rose to as high as 4540 metric tons. In case lactic acid concentration is significantly low, the energy cost for water removal in the downstream process offsets

11、the bene</p><p>　　Thus, to enhance the economical advantage of the MCRB process, methods that increase the lactic acid concentration along with the high-cell density are required. Some authors, who considere

12、d this persistent problem of low-product concentration, conducted studies to obtain higher lactic acid concentration in MCRB. Xavier et al. (1995) reported a lactic acid concentration of 90 g/L with a productivity of 36

13、g L?1 h?1, while Tejayadi and Cheryan (1995) achieved 89 g/L and 22 g L?1 h?1 of lactic aci</p><p>　　A typical approach to overcome the above-mentioned problem, a low-product concentration due to severe prod

14、uct inhibition, is the use of a plug-flow reactor, which can be approximated by several continuous-stirred-tank receptors (CSTRs) in series (de Gooijer et al., 1996; Keller and Gerhardt, 1975; Luedeking and Piret, 1959b;

15、 Levenspiel, 1984). The advantages of the CSTRs-in-series against a single CSTR especially in lactic acid production were revealed by others in two- and three-stage CSTRs (Ae</p><p>　　In an effort to combine

16、 the advantage of both the bioreactor configurations—MCRB and multi-staged bioreactor— Kulozik et al. (1992) investigated the performance of a seven-staged cascade reactor with cell recycle. Cells in the outflow of the l

17、ast reactor were fivefold concentrated by a microfilter and recycled back to the first reactor. In comparison with a single-stage MCRB, the cascade reactor showed 4 times higher productivity, 28 g L?1 h?1, with complete

18、utilization of 100 g/L lactose, in wh</p><p>　　In this study, the performance of a new bioreactor configuration, two MCRBs in series, was investigated aiming at the highest volumetric productivity ever obtai

19、ned along with the lactic acid concentration as high as possible. Moreover, a simulation study was conducted to estimate the performance limit of MCRB with an unstructured kinetic model, which is validated by the experim

20、ent results.</p><p>　　MATERIALS AND METHODS</p><p>　　Microorganism and Culture Conditions</p><p>　　Lactobacillus rhamnosus (ATCC 10863), an obligatory anaerobic homofermentative L(+

21、)-lactic acid producer, was obtained from American Type Culture Collection (Rockville, MD). One-mL stock cultures were stored at ?76°C in Lactobacilli MRS medium (Difco, Detroit, MI) with 25%(v/v) glycerol. Precultu

22、res were prepared by transferring a stock culture to 200 mL of MRS medium and incubated at 42°C for 12 h and transferred to the main culture. The culture temperature was 42°C and the culture pH was contr</p&

23、gt;<p>　　Analytical Methods</p><p>　　Cell growth was measured by a spectrophotometer (Pharmacia Ultrospec 3000, Cambridge, UK) at a wavelength of 620 nm. Dry cell concentration was calculated from the

24、 optical density (OD620) with a linear correlation factor (one OD62040.32 g-dry cell weight per liter). Concentrations of lactic acid and glucose were determined by a high performance liquid chromatography (HPLC) system

25、equipped with a refractive-index detector (Hitachi L-6000, Tokyo, Japan). An HPLC column (Aminex 87H, Bio-Rad, Richmo</p><p>　　Membrane Cell-Recycle Bioreactor (MCRB) </p><p>　　In the experiment

26、s of a single-stage MCRB, a 400-mL water-jacketed glass reactor was employed, that was equipped with a hollow-fiber filtration unit UFP-100-H-4X2TCA (100 k NMWC, 0.065 m2 filtration area; A/G Technology Corporation, MA).

27、 A peristaltic pump, 07090-40 (Cole-Parmer, IL) was used to circulate the culture broth through the membrane unit with a flow rate of ca. 100 mL/min. For the two-stage operations, two identical MCRBs were serially connec

28、ted. Each MCRB consisted of a 1-L glass rea</p><p>　　Numerical Methods</p><p>　　The least squares regression was used to estimate the parameters of the fermentation kinetics. Numerical integrati

29、on to find steady-state values and constrained multivariable optimization to find the optimal operation variables were performed with the help of a software package, Matlab 5.0 (The Mathworks, Inc., USA). The constraints

30、 utilized in the optimization were the maximum cell density (Xm) and the maximum remaining glucose concentration (S).</p><p>　　DISCUSSION</p><p>　　To increase the bioreactor performance for the

31、production of lactic acid, a continuous lactic acid fermentation system coupled with membrane cell-separation technique (MCRB) has been studied. By greatly increased cell density in the reactor volumetric productivity co

32、uld be increased over 10times than the conventional batch and continuous fermentation. However, the concentration of lactic acid produced, a major factor for economic feasibility, could not be increased higher than 95 g/

33、L beyond whic</p><p>　　In conclusion, a systematic approach with MCRBs with multistaged operation can be carried out to predict optimal performances of lactic acid production, which experimentally proved tha

34、t two stage MCRBs can produce lactic acid in a high concentration with greatly increased volumetric productivity (type A).</p><p>　　References</p><p>　　[1] Aeschlimann A, Stasi LD, von Stockar U

35、. 1990. Continuous production of lactic acid from whey permeate by Lactobacillus helveticus in two chemostats in series. Enzyme Microb Technol 12:926–932.</p><p>　　[2] Amrane A, Prigent Y. 1999. Analysis of

36、growth and production coupling for batch cultures of Lactobacillus helveticus with the help of an unstructured model. Proc Biochem 34:1–10.</p><p>　　[3] Berry AR, Franco CMM, Zhang W, Middelberg APJ. 1999. G

37、rowth and lactic acid production in batch culture of Lactobacillus rhamnosus in a defined medium. Biotechnol Lett 21:163–167.</p><p>　　[4] Bibal B, Kapp C, Goma G, Pareilleux A. 1989. Continuous culture of S

38、treptococcus cremoris on lactose using various medium conditions. Appl Microbiol Biotechnol 32:155–159.</p><p>　　[5] Bibal B, Vayssier Y, Goma G, Pareilleux A. 1991. High concentration cultivation of Lactoco

39、ccus cremoris in a cell-recycle reactor. Biotechnol Bioeng 37:746–754.</p><p>　　[6] Bo¨rgardts P, Krischke W, Tro¨sch W, Brunner H. 1998. Integrated bioprocess for the simultaneous production of la

40、ctic acid and dairy sewage treatment. Bioprocess Eng 19:321–329.</p><p>　　[7] Bruno-Ba´rcena JM, Ragout AL, Cordoba PR, Sin?eriz F. 1999. Continuous production of L(+)-lactic acid by Lactobacillus casei

41、 in two-stage systems. Appl Microbiol Biotechnol 51:316–324.</p><p>　　[8] Cheryan M. 1998. Ultrafiltration and microfiltration handbook. Lancaster, PA: Technomic Publishing Company. 467 p.</p><p&g

42、t;　　[9] de Gooijer CD, Bakker WAM, Beeftink HH, Tramper J. 1996. Bioreactors in series: An overview of design procedures and practical applications. Enzyme Microb Technol 18:202–219.</p><p>　　[10] Dutta SK,

43、Mukherjee A, Chakraborty P. 1996. Effect of product inhibition on lactic acid fermentation: Simulation and modelling. Appl Microbiol Biotechnol 46:410–413.</p><p>　　[11] Gonc¸alves LMD, Xavier AMRB, Alm

44、eida JS, Carrondo MJT. 1991. Concomitant substrate and product inhibition kinetics in lactic acid production. Enzyme Microb Technol 13:314–319.</p><p>　　[12] Keller AK, Gerhardt P. 1975. Continuous lactic ac

45、id fermentation of whey to produce a ruminant feed supplement high in crude protein. Biotechnol Bioeng 17:997–1018.</p><p>　　[13] Kulozik U, Hammelehle B, Pfeifer J, Kessler HG. 1992. High reaction rate cont

46、inuous bioconversion process in a tubular reactor with narrow residence time distributions for the production of lactic acid. J Biotechnol 22:107–116.</p><p>　　[14] Kulozik U, Wilde J. 1999. Rapid lactic aci

47、d production at high cell concentrations in whey ultrafiltrate by Lactobacillus helveticus. Enzyme Microb Technol 24:297–302.</p><p>　　[15] Kwon S, Lee PC, Lee EG, Chang YK, Chang HN. 2000. Production of lac

48、tic acid by Lactobacillus rhamnosus with vitamin-supplemented soybean hydrolysate. Enzyme Microb Technol 26:209–215.</p><p>　　[16] Levenspiel O. 1980. The Monod equation: A revisit and a generalization to pr

49、oduct inhibition situations. Biotechnol Bioeng 22:1671–1687. Levenspiel O. 1984. Chemical reaction engineering. New York: John Wiley & Sons. p 124–157.</p><p>　　[17] Litchfield JH. 1996. Microbiological

50、production of lactic acid. In: Neidleman SL, Laskin AI, editors. Advances in applied microbiology. Vol 42. San Diego: Academic Press. 69 p.</p><p>　　[18] Luedeking R, Piret EL. 1959a. A kinetic study of the

51、lactic acid fermentation. Batch process at controlled pH. J Biochem Microbiol Technol Eng 1:393–412.</p><p>　　[19] Luedeking R, Piret EL. 1959b. Transient and steady states in continuous fermentation. Theory

52、 and Experiment. J Biochem Microbiol Technol Eng 1:431–459.</p><p>　　[20] Major NC, Bull AT. 1985. Lactic acid productivity of a continuous culture of Lactobacillus delbrueckii. Biotechnol Lett 7:401–405.<

53、;/p><p>　　利用鼠李糖乳桿菌在兩級(jí)細(xì)胞膜循環(huán)</p><p>　　生物反應(yīng)器中高速連續(xù)生產(chǎn)乳酸</p><p>　　——作者：Sunhoon Kwon，Yong Keun Chang</p><p>　　單位：韓國(guó)高等科學(xué)技術(shù)學(xué)院，化學(xué)與生物工程研究中心，E-mail: hnchang@kaist.ac.kr</p><

54、;p><b>　　摘　　要</b></p><p>　　眾所周知，乳酸是可生物降解材料聚乳酸的主要原料，所以找到以一種以最低的成本來(lái)生產(chǎn)L（+）－乳酸的方法具有非常重大的意義。為了找到一種可以高速地生產(chǎn)高濃度乳酸的生物反應(yīng)器，我們對(duì)膜循環(huán)生物反應(yīng)器（ MCRB ）的性能進(jìn)行了研究，并進(jìn)行了實(shí)驗(yàn)仿真優(yōu)化。由于大大增加了細(xì)胞濃度，這個(gè)反應(yīng)器的乳酸生產(chǎn)力可達(dá)到21.6gL- 1 h - 1。

55、但乳酸濃度卻不能超過(guò)83 g/L，當(dāng)額外增加一個(gè)連續(xù)攪拌反應(yīng)釜（ CSTR）附到MCRB旁邊時(shí)，可以大幅度的提高生產(chǎn)速率，乳酸濃度也可以提高到87 g / L，當(dāng)兩個(gè)MCRBs串聯(lián)在一起時(shí)， 乳酸的生產(chǎn)力速率達(dá)到57gL- 1 h - 1，最終溶液中的乳酸濃度為92 g / L，這比以前所報(bào)道的使用葡萄糖基生產(chǎn)L （ + ）乳酸濃度超過(guò)85 g / L的最高的生產(chǎn)率還要高。此外，研究乳酸發(fā)酵動(dòng)力學(xué)產(chǎn)生了以鼠李糖乳桿菌發(fā)酵生產(chǎn)乳酸為代表的

56、成功典范，該模型被認(rèn)為是適用于大多數(shù)現(xiàn)有的MCRBs的數(shù)據(jù) ，并且很好地吻合了Levenspiel的產(chǎn)品抑制模型，Luedeking-Piret產(chǎn)品形成動(dòng)力學(xué)方程似乎是有效的代表發(fā)酵動(dòng)力學(xué)。然而具有生產(chǎn)潛力的細(xì)胞（細(xì)胞密度相關(guān)參</p><p>　　© 2001 John Wiley ＆ Sons出版公司 生物 Bioeng 73 ： 25-34 ， 2001 。</p><p>

57、;　　關(guān)鍵詞：鼠李糖乳桿菌;乳酸;高生產(chǎn)力;細(xì)胞循環(huán);膜生物反應(yīng)器</p><p><b>　　1　前　　言</b></p><p>　　膜細(xì)胞循環(huán)生物反應(yīng)器（ MCRB ）的生產(chǎn)效率成功地證實(shí)了一些以往關(guān)于高容積生產(chǎn)乳酸的研究。Ohleyer等的研究報(bào)告指出，通過(guò)大量增加生物催化劑，即微生物細(xì)胞，乳酸的生產(chǎn)力可高達(dá)160 g L?1 h?1。 （ 1985年） ，這

58、比常規(guī)批次和恒化的生產(chǎn)工藝高出20倍以上。然而，高生產(chǎn)力并不是唯一的要求，這種工藝還必須在經(jīng)濟(jì)上有可行性。Timmer and Kromkamp （ 1994年）發(fā)現(xiàn)，這一工藝可能主要受生產(chǎn)能力和產(chǎn)品的集中的影響，在較小程度時(shí)當(dāng)年這種工藝生產(chǎn)乳酸的產(chǎn)能上升到高達(dá)4540噸。如乳酸濃度顯著低，能源成本中的水在去除抵消下游過(guò)程的好處，提高了生產(chǎn)力。從這個(gè)角度上講， MCRB有一個(gè)重要的問(wèn)題有待解決：在乳酸濃度顯著低相比，間歇過(guò)程的乳酸濃度1

59、22 g / L的是容易實(shí)現(xiàn)的。此外，還有一份報(bào)告顯示以84 g L?1 h?1 的生產(chǎn)速率得到的D（+）L乳酸最終濃度為117 g/L （ Mehaia和Cheryan ， 1987年） ，而除部分MCRB工藝生產(chǎn)出的乳酸濃度低于90/g/L外所有其他的大多數(shù)生產(chǎn)的濃度低于60 g / L的（Cheryan ，1998年;里</p><p>　　因此，為加強(qiáng)MCRB工藝的經(jīng)濟(jì)優(yōu)勢(shì)的方法有，隨著高密度的要求增加乳

60、酸濃度。一些考慮到這個(gè)長(zhǎng)期存在的低濃度產(chǎn)品問(wèn)題的作者對(duì)他進(jìn)行了研究，并通過(guò)MCRB工藝獲得了較高濃度的乳酸。哈維爾等人。 （ 1995年）和Tejayadi和Cheryan （ 1995年）分別發(fā)表了以36 g L?1 h?1的生產(chǎn)速率得到濃度為90 g / L的乳酸和以22g L?1 h?1的生產(chǎn)速率得到濃度為89 g / L的乳酸的報(bào)道。</p><p>　　產(chǎn)品的濃度低是由于乳酸菌受到了嚴(yán)重抑制，這里有一個(gè)

61、很好的辦法來(lái)克服上述問(wèn)題，我們可以通過(guò)使用推流反應(yīng)器，它類(lèi)似于很多連續(xù)化攪拌式受體（ CSTRs ）結(jié)合在一起（日Gooijer等。996年; Keller和戈哈德，1975年;Luedeking和Piret，1959年 ; Levenspiel ，1984年）。CSTRs的優(yōu)勢(shì)在一系列針對(duì)單一CSTR中特別是在乳酸生產(chǎn)中所揭示的其他兩個(gè)和三個(gè)階段CSTRs （艾緒里曼等人。1990年;布魯諾- Ba'rcena等。1999年;

62、根等。1991年）通過(guò)部分分離細(xì)胞的生長(zhǎng)和乳酸生產(chǎn)階段提高乳酸的生產(chǎn)力和濃度，增加乳酸產(chǎn)量為代價(jià)的生物形成的后期;高純度的乳酸異構(gòu)體長(zhǎng)，L（ + ）乳酸菌通過(guò)增加新鮮細(xì)胞的數(shù)量;同時(shí)減少使用昂貴的養(yǎng)分——酵母膏。</p><p>　　為了結(jié)合雙方的優(yōu)勢(shì)，生物反應(yīng)器的配置MCRB和多階段生物反應(yīng)器Kulozik等。（1992）進(jìn)行了一項(xiàng)七級(jí)聯(lián)反應(yīng)器與細(xì)胞循環(huán)的研究。最后一個(gè)反應(yīng)器中流出的細(xì)胞溶液通過(guò)收集器集中再生回

63、到第一座反應(yīng)器中，相對(duì)于單級(jí)MCRB ，梯級(jí)反應(yīng)器得到的生產(chǎn)率要高出4倍。達(dá)到 28克L- 1 h - 1，乳糖完整的利用率為100 g / L，其中的細(xì)胞濃度保持在20 g / L和的乳酸濃度約為72g/ L。</p><p>　　在這項(xiàng)研究中，對(duì)新型生物反應(yīng)器的配置，即兩個(gè)MCRBs串聯(lián)的性能進(jìn)行了研究，旨在在最高容積生產(chǎn)力的情況下不斷得到乳酸且其濃度盡可能高。此外，對(duì)估計(jì)MCRB的性能極限與非結(jié)構(gòu)化的動(dòng)力學(xué)

64、模型，進(jìn)行了模擬研究，通過(guò)這個(gè)實(shí)驗(yàn)驗(yàn)證了結(jié)果。</p><p><b>　　2　材料與方法</b></p><p>　　2.1 微生物培養(yǎng)法及培養(yǎng)條件</p><p>　　鼠李糖乳桿菌（ ATCC 10863 ） ，一種同型發(fā)酵的具有極強(qiáng)的厭氧性的L （ + ）乳酸生產(chǎn)菌，它是從美國(guó)特種培養(yǎng)物保藏中心獲得的（位于美國(guó)馬里蘭州羅克維爾市） 。一毫

65、升庫(kù)乳桿菌菌種與（培養(yǎng)基，底特律， MI ）和的25 ％ （ V / V ）的甘油混合后在-76 ° C的條件下保存，Precultures準(zhǔn)備通過(guò)在MRS培養(yǎng)基中，在42°C的條件下培養(yǎng)12小時(shí)，將菌株培養(yǎng)到200毫升，并轉(zhuǎn)移到主要化。控制培養(yǎng)溫度為42 ℃和通過(guò)使用氨水調(diào)節(jié)pH到6.0，MCRB工藝的培養(yǎng)基要有以下組成部分每升： 0.2Na3-Citrate·2H2O，1.0 g KH2PO4, 0.2

66、 g MgSO4·7H2O, 0.03 g MnSO4·H2O, 0.03 g FeSO4·7H2O, 和0.015mL硫酸。糖的濃度和酵母提取物將在結(jié)論中指出。除酵母提取物是單獨(dú)滅菌15分鐘外，所有培養(yǎng)基一起在121°C的條件下滅菌100分鐘。在結(jié)論中談到的培養(yǎng)體積包括循環(huán)流體培養(yǎng)基的體積。</p><p><b>　　2.2 分析方法</b><

67、;/p><p>　　細(xì)胞生長(zhǎng)可通過(guò)分光光度計(jì)在波長(zhǎng)為620納米時(shí)測(cè)定（法瑪西亞Ultrospec 3000 ，英國(guó)劍橋）一般可由干細(xì)胞濃度與光密度（OD620）的線(xiàn)性相關(guān)系數(shù)（1 OD62040.32克，干重每公升） 計(jì)算出來(lái)。乳酸的濃度和葡萄糖含量可由配備了折射率檢測(cè)器系統(tǒng)的高效液相色譜儀（HPLC）（日立L型6000 ，日本東京） 測(cè)定。HPLC柱使用時(shí)（ Aminex 87H ，酶標(biāo)儀，里奇蒙， CA ）以0.

68、005M硫酸為流動(dòng)相，在洗脫速度為0.6毫升/分鐘，而柱溫保持在50 ° C的濃度標(biāo)準(zhǔn)為1.0米乳酸（鹽，布克斯，瑞士）和10 g / L的葡萄糖（六西格瑪，圣路易斯，密蘇里州）用于高效液相色譜分析中。</p><p>　　2.3 膜細(xì)胞循環(huán)生物反應(yīng)器（ MCRB ）</p><p>　　在單級(jí)MCRB的實(shí)驗(yàn)中， 要應(yīng)用到如下實(shí)驗(yàn)器材：一；400毫升水套，它采用玻璃反應(yīng)器并配備了

69、中空纖維超微粒過(guò)濾裝置- 100 - H的4X2TCA（100 k NMWC，0.065平方米過(guò)濾面積;阿/ g技術(shù)公司，馬）。二：蠕動(dòng)泵， 07090-40型（科爾- Parmer ，白細(xì)胞介素）CA以100毫升/分鐘的速度推動(dòng)發(fā)發(fā)酵液通過(guò)膜單元。 在兩個(gè)階段的行動(dòng)，兩個(gè)相同的MCRBs是串行連接。每個(gè)MCRB包括一個(gè)1一L玻璃反應(yīng)堆附有板和幀過(guò)濾單元， 一個(gè)Pellicon 2 BIOMAX 100V的（ 100 k NMWC ，

70、0.1平方米過(guò)濾面積，超純水，貝德福德，馬）與隔膜泵， 和一個(gè)P - 07090 -40 （科爾 Parmer ）的細(xì)胞再生裝置，其CA流速為600毫升/分鐘。 MCRB在接種前需要用含50 ％ （ V / V ）乙醇的無(wú)菌水徹底清洗。在操作過(guò)程中，需不斷向發(fā)酵罐中加入新的培養(yǎng)基同時(shí)排出產(chǎn)物。為了防止細(xì)胞密度去超過(guò)一定限度，造成過(guò)濾功能下降，需要從發(fā)酵罐中不斷抽出少量的發(fā)酵液 。在這兩個(gè)階段發(fā)酵過(guò)程中，從第一階段流出的發(fā)酵液用于第二階段

71、中。</p><p>　　2.4 數(shù)值分析方法</p><p>　　發(fā)酵動(dòng)力學(xué)的參數(shù)可以用最小二乘回歸來(lái)估算。利用Matlab 5.0 （ MathWorks公司，公司，美國(guó)） 軟件進(jìn)行數(shù)值積分找到穩(wěn)態(tài)值和約束多變量?jī)?yōu)化以尋找到最佳操作變量。限制利用的優(yōu)化是最大的細(xì)胞密度（Xm）和最大其余血糖濃度（s） 。</p><p><b>　　討 論<

72、/b></p><p>　　為了提高生物反應(yīng)器產(chǎn)乳酸的性能，我們對(duì)連續(xù)乳酸發(fā)酵系統(tǒng)加上膜細(xì)胞分離技術(shù)（ MCRB ）進(jìn)行了研究。大大增加在固定體積發(fā)酵罐中的細(xì)胞密度，生產(chǎn)率比傳統(tǒng)的間歇和連續(xù)發(fā)酵提高了10倍以上。然而，乳酸實(shí)際生產(chǎn)中，最主要因素經(jīng)濟(jì)上的可行性，此方法乳酸濃度高于95 g / L時(shí)，細(xì)胞的生長(zhǎng)幾乎完全受到抑制。在初步單MCRB實(shí)驗(yàn)中 ，即使在細(xì)胞密度保持在高于90 g / L時(shí)，得到的乳酸濃度

73、仍然很低，約51政/ L，（圖4 ）。當(dāng)加入一個(gè)體積比MCRB大9的CSTR時(shí)，在放出細(xì)胞液之前如果讓它在在MCRB反應(yīng)器中停留更長(zhǎng)的時(shí)間， 則乳酸濃度會(huì)明顯提升，會(huì)達(dá)到87 g / L圖6 ） 。由此我們可以得出這樣的結(jié)論：在第二個(gè)反應(yīng)器CSTR與另一MCRB 相連并且兩個(gè)階段的生物反應(yīng)器與細(xì)胞循環(huán)同在這兩個(gè)階段前提下，可以高速生產(chǎn)高濃度的乳酸，如果使用兩個(gè)MCRBs系列，則可以以57 g L?1 h?1 的生產(chǎn)速率生產(chǎn)出濃度達(dá)到 9

74、2 g / L的乳酸（圖12 ） 。</p><p>　　最后，通過(guò)優(yōu)化多步驟MCRBs反應(yīng)器，可以得到預(yù)期想得到的最優(yōu)生產(chǎn)乳酸的方法，實(shí)驗(yàn)證明，利用兩階段MCRBs反應(yīng)器可以高速生產(chǎn)高濃度的乳酸，從而使固定容積反應(yīng)器的生產(chǎn)效率大大提高（ A型） 。</p><p><b>　　參考文獻(xiàn)</b></p><p>　　[1] Aeschliman

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