Studies On Efficient Bioproduction Of Lactic Acid And Butyric Acid With Immobilized Cells In Fibrous-bed Bioreactor

L-lactic acid and butyric acid are two important bulk chemicals which are mainly produced by the multiple chemical reactions from the downstream of petrochemical products. Due to the non-renewable and quick consumption of fossil resources, the production of these bulk chemicals by economic microorganisms with renewable resources has became an increasing attracts in industry.Hydrolysate of Jerusalem artichoke was applied for the production of L-lactic acid by immobilized Lactococcus lactis cells in a fibrous bed bioreactor system. Preliminary experiments had indicated that the high quality hydrolysate, which was derived from the40minutes’mild acid treatment at95℃and pH1.8, was sufficient to support the cell growth and synthesis of L-lactic acid. After the basal settlement of hydrolysate based fermentation, the batch mode and the fed-batch mode fermentation were carried out in the free cell system and the fibrous bed bioreactor system, respectively. The achieved maximum concentration of L-lactic acid was142g/1in the fed-batch mode. Subsequent repeated-batch fermentation of the fibrous bed bioreactor system had further exhibited the persistence and stability of this system for the high production of L-lactic acid in a long term. Our work suggested the great potential of the fibrous bed bioreactor system and hydrolysate of Jerusalem artichoke in the economical production of L-lactic acid at industrial scale.Using non-grain raw materials as the substrate for fermentation of butyric acid in fibrous bioreactor(FBB) is significant to reduce the cost in anaerobic fermentative production of butyric acid. In our work, saccharification liquid of cassava starch was used as substrate for fermentation of Clostridium tyrobutyricum in batch and fed-batch mode. The results showed that the maximum butyric acid concentration was20.9g/L and the yield was0.34g/g using cassava hydrolysate in batch mode with free cell fermentation, and the fermentation efficiency of butyric acid was further improved in immobilized fermentation using fibrous bioreactor, the concentration, yield and productivity of butyric acid was increased by29%,35%and29%respectively. Based on this, nutrient efficiency of hydrolysate was tested by addition of yeast extract in repeated-batch fermentation of FBB. By using low concentration of nitrogen source, the butyric acid concentration was greatly increased to65.1g/L in FBB with saccharification liquid of cassava starch feeding strategy. These preliminary results revealed the potentials of saccharification liquid of cassava starch as the substrate for economic production of butyric acid with a higher production and efficiency.The cells of Clostridium tyrobutyricum were immobilized on fibrous matrix which was packed in porous levitated sphere carriers. Each carrier was packed with fiber quantity of2cm-6cm/0.42g and was rotated in a stirred-tank fermentor at100rpm to providing pH and temperature controls. Batch and repeated-batch fermentations were carried out to efficiently produce butyric acid with a high yield (0.48g/g). Subsequent fed-batch fermentation using MFBB resulted in a high concentration of butyric acid (65.4g/L). Moreover, this novel MFBB could be employed to produce high concentration of butyric acid (64.2g/L) by simple repeated-batch addition of high concentration of glucose (142g/L).This thesis presented a series of research work about the applications of fibrous bed bioreactor system for the microbial production of important bulk chemicals. The improvement of such two organic acids, as well as the development of novel fibrous bed bioreactor styles, shall accelerate the anaerobic fermentative production of this group of bulk chemicals.