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1、 High-Rate Continuous Production of Lactic Acid by Lactobacillus rhamnosus in a Two-Stage Membrane Cell-Recycle Bioreactor Sunhoon Kwon, Ik-Keun Yoo, Woo Gi Lee, Ho Nam Chang, Yong Keun Chang Department of Chemical Engineering and BioProcess Engineering Research Center, Korea Advanced Institute of S

2、cience and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, South Korea； E-mail: hnchangkaist.ac.kr Abstract It is important to produce L(+)-lactic acid at the lowest cost possible for lactic acid to become a candidate monomer material for promising biodegradable polylactic acid. In an effo

3、rt to develop a high-rate bioreactor that provides high productivity along with a high concentration of lactic acid, the performance of membrane cellrecycle bioreactor (MCRB) was investigated via experimental studies and simulation optimization. Due to greatly increased cell density, high lactic aci

4、d productivity, 21.6 g L1 h1, was obtained in the reactor. The lactic acid concentration, however, could not be increased higher than 83 g/L. When an additional continuous stirred tank reactor (CSTR) was attached next to the MCRB a higher lactic acid concentration of 87 g/L was produced at significa

5、nt productivity expense. When the two MCRBs were connected in series, 92 g/L lactic acid could be produced with a productivity of 57 g L1 h1, the highest productivity among the reports of L(+)-lactic acid that obtained lactic acid concentration higher than 85 g/L using glucose substrate. Additionall

6、y, the investigation of lactic acid fermentation kinetics resulted in a successful model that represents the characteristics of lactic acid fermentation by Lactobacillus rhamnosus. The model was found to be applicable to most of the existing data with MCRBs and was in good agreement with Levenspiels

7、 product-inhibition model, and the Luedeking-Piret equation for product-formation kinetics appeared to be effective in representing the fermentation kinetics. There was a distinctive difference in the production potential of cells (cell-density-related parameter in Luedeking-Piret equation) as lacti

8、c acid concentration increases over 55 g/L, and this finding led to a more precise estimation of bioreactor performance. 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 73: 2534, 2001. Keywords: Lactobacillus rhamnosus； lactic acid； high productivity； cell recycle； membrane bioreactor INTRODUCTION Th

9、e efficiency of the membrane cell-recycle bioreactor (MCRB) was successfully demonstrated in a number 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

10、to 160 g L1 h1 as 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. However, the high productivity is not the only requirement for the economic feasibility of the process. Timmer and Kromkamp (1994) found t

11、hat the process might be primarily influenced by production capacity and product concentration and to a lesser extent by the volumetric 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 cos

12、t for water removal in the downstream process offsets the benefits of the increased productivity. From this point, MCRB has an important problem to be tackled: The concentrations of lactic acid are significantly low when compared with batch processes where the lactic acid concentration above 120 g/L

13、 is easily attainable. Except for a report showing 117 g/L D()-lactic acid with a volumetric productivity of 84 g L1 h1 (Mehaia and Cheryan, 1987), all other MCRB operations resulted in lactic acid concentrations of less than 90 g/L and, moreover, most of them had concentrations below 60 g/L (Cherya

14、n, 1998； Litchfield, 1996； Ohleyer et al., 1985). The microorganisms cannot grow above a certain range of lactic acid concentration and the MCRBs are run under continuous manner with continuous bleeding of cells to prevent the loss of fluidity that occurs when cell concentration goes too high. 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 considered this persistent problem of low-product concentration,