The Study Of New Process For L-lactic Acid Production Based On Inexpensive Biomass

L-lactic acid, which is one of bio-based bulk chemicals, has been widely applied. Against the background of food shortage and growing demand for environmental protection, the use of non grain raw material in the fermentation of L-lactic acid has been one important way to both reduce production cost and carry out the policy of environmental protection, and it also helps to maintain food security of a country. Thus,this paper focus on the efficient utilization of agricultural by-products for L-lactic acid fermentation and providing practical and reliable technical support for industrial production. The main points of this study are listed as follows:1. As one byproduct in the oil extraction of rice bran, defatted rice bran is rich of starch, protein and salts. In the study of L-lactic acid fermentation based on defatted rice bran hydrolysate, the hydrolysate of defatted rice bran was proved to be an efficient alternative to mMRS medium. In the batch fermentation conducted in a 5L fermentor, the productivity and product titer reached 3.63 g L-1 h-1 and 142 g L-1, and the yield of L-lactic acid was 94.5%. L-lactic acid fermentation cost of DRB medium was compared with those media containing com starch, YE and CSP. The total fermentation cost of DRB medium was $0.684 per kilogram lactic acid, which is 57.72% of the cost with starch and YE medium, and 87.8% of the cost with starch and CSP medium. In addition,64.0% of DRB fermentation cost can be re-earned by protein feed which is an byproduct in the process studied.2. As representative of starch materials, defatted rice bran and corn bran were used in the simultaneous saccharification and fermentation of L-lactic acid, and the product titer reached 82.7 g Kg-1 and 85.5 g Kg-1 fermentation broth, respectively. White rice bran was furtherly used in L-lactic acid production by open simultaneous saccharification and fermentation, and the thermophilic bacteria B.coagulans LA-15-2 was used as L-lactic acid producer. In batch fermentation, 117 g L-1 lactic acid was obtained, and the productivity and yield reached 2.79 g L-1 h-1 and 98.75%, respectively. No complicated pretreatment or sterilization was needed before fermentation, and the process studied showed an efficient and simplified way to produce L-lactic acid from white rice bran with a low fermentation cost which is 36.2% and 56.7% of conventional corn starch & YE medium and corn starch & CSLP medium, respectively.3. Sweet sorghum bagasse as an important lignocellulosic biomass was used by Bacillus coagulans LA1 507 in open simultaneous saccharification and fermentation, and the effect of cellulase concentration and stover loading on L-lactic acid fermentation was studied. The optimized cellulase concentration and initial stover loading were 25 FPU g-1 pretreated sweet sorghum bagasse and 10% (w/v),respectively. In the fed-batch SSF process with a stepwise controlled pH,a cellulase dose of 25 FPU g-1 pretreated SSB and 15 g L-1 corn steep liquor powder (CSLP) were used to produce L-lactic acid from 17.5%(w/v) stover, and B.coagulans LA 1507 provided a balanced result which contained a product titer of 111 g L-1, a yield of 0.437 g g-1 crude SSB and an average productivity of 1.59 g L-1 h-1. Based on a mass balance of the experimental process, a L-lactic acid yield of 0.437 g g-1 crude SSB was obtained by fed-batch SSF under unsterilized conditions.4. Sweet sorghum stalk was used as the carrier for immobilization of L. rhamnosus LA-04-1 in the repeated batch fermentation of L-lactic acid. Fifteen batches of fermentation were conducted, and the L-lactic acid titer were 80-90g L-1 with a productivity ranging from 3.8-4.0 g L-1 h-1.5. As an invertase-active Lactobacillus strain, Lactobacillus rhamnosus LA-04-1 was used for L-lactic acid fermentation from sweet sorghum juice, and a membrane integrated repeated batch fermentation was developed for productivity improvement and cell recycling.Simultaneous utilization of sugars from sweet sorghum juice was realized to overcome CCR effect. When sweet sorghum juice was used as carbon source, L-lactic acid productivity was increased significantly from 1.45 g L-1 h-1 (batch 1) to 17.55 g L-1 h-1 (batch 6), and the final cell density(OD620) reached 42.3. The L-lactic acid concentration of each batch was near 60 g L-1, and the yield reached 0.954 g g-1.6. To improve the efficiency of open fermentation by Lactobacillus rhamnosus based on sweet sorghum juice and to overcome sucrose utilization deficiency of Bacillus coagulans, a mixed fermentation was developed. Besides, the optimization of pH, sugar concentration and fermentation medium were also studied. With an optimized sugar concentration and a stepwise-controlled pH, the L-lactic acid titer, yield and productivity reached 121 g L-1, 94.6% and 2.18 g L-1 h-1, respectively. By the analysis of the constituents of metal ions,phosphorus and amino acids of different raw materials, CSP with SSJ was proved to be an efficient alternative of YE & salts, and a L-lactic acid titer of 118 g L-1 was achieved, with a yield of 92.1%, and a productivity of 1.84 g L-1 h-1.7. In the cogeneration of ethanol and L-lactic acid based on corn stover, a two-stage fermentation mode was adopted. The efficient conversion of fermentable sugars deriving from corn stalk hydrolysate was achieved in the biological refining process, and the disability of wild saccharomyces cerevisiae in using xylose was overcomed to improve the utilization rate of subatrate. Finally, 50.3 g L-1 ethanol and 24.25 g L-1 L-lactic acid were obtained from the corn stalk hydrolysate containing 120 g L-1 glucose and 33 g L-1 xylose.8. An in situ product removal process for magnesium lactate production based on crystallization was developed. The crystallization was carried out at 42 ?, avoiding the addition of seed crystal. The product concentration, productivity and yield of fermentation coupled with in situ product removal (ISPR) reached 143 g L-1, 2.41 g L-1 h-1 and 94.3%. In four cycles of crystallization, the average reuse rate of fermentation medium and removal rate of product reached 64.0% and 77.7%. At the same time, ISPR fermentation saved 40% water, 41%inorganic salts and 43% yeast extract as compared to fed-batch fermentation. The process introduces an effective way to reduce the amount of waste water and the raw material in magnesium lactate fermentation, which contributes to the environmentally friendly production of L-lactic acid.9. The amplification of L-lactic acid fermentation based on defatted rice bran was studied. Using the supernatant of defatted rice bran hydrolysate as substrate, a L-lactic acid titer of 145 g L-1 was achieved in the level of 150 L fermentor, and the productivity and yield reached 2.38 g L-1 h-1 and 94.9%, respectively. A pilot platform was furtherly constructed to lay the foundation for industrial production. In the synchronous saccharification fermentation of L-lactic acid, a 500 L fermentor was used. A product titer of 88 g L-1 was obtained, and the productivity and yield reached 2.46 g L-1 h-1 and 87.65%, respectively. In the output level of 2000 t year-1 L-lactic acid, the process design of separated hydrolysis and fermentation (SHF) and synchronous saccharification fermentation (SSF) was conducted.