Degradation Of Lignocellulose And L-lactic Acid Fermentation Technology

At present, there are four major bottleneck problems that constraint high cost of L-lactic acid production:First, the high cost of raw materials;secondly, production process generated waste and environmental pollution; thirdly, low enzymatic hydrolysis yield in cellulase enzymatic hydrolysis stage, resulting in a low concentration of reducing sugar in the hydrolyzate;last, low lactic acid fermentation efficiency due to the inhibition of lactic acid in lactic acid bacteria, resulting in high cost of production of L-lactic acid.Agricultural and forestry wastes were used for raw materials in this paper, physical chemical pretreatment processes and the applications of Compound Mutation breeding for L-lactic acid production strains with some acid resistance of and the comprehensive utilization of pretreatment wash water to optimize the fermentation process to explore L-lactic acid production from the cellulose of agricultural and forestry wastes. It has achieved some initial results through extensive testing in this paper, including the following aspects:(1) The pretreatment process of lignocellulosic biomass. Five different pretreatments of dilute acid, dilute alkali, low-temperature dilute acid, acid and microwave, and alkali combined with microwave have been studied the effect of pretreatment on the main component of larch, corn stalks and soybean straw, thereby increasing the efficiency of enzymatic hydrolysis. Corn stalks and soybean straw which were sufferd that2%NaOH in solid-liquid ratio1:10,100℃, for the reaction of60min, and then were added alkali to the solid-liquid ratio1:15,100℃under microwave treatment6min with speed800r/min, have been identified as the enzymatic hydrolysis of raw materials through a comparison between the different pretreatment processes and raw materials.(2) Enzymatic Hydrolysis of corn stalks and soybean straw. On the basis of single factor analysis, the optimal operation variables for the enzymatical hydrolysate from pretreatment on corn stalk and soybean straw were described through orthogonal experiment:substrate concentration5%, enzyme dosage35FPIU/g (stalk), pH4.8, temperature50℃, and hydrolysis time36h. The experiment of cellulose enzymes hydrolysis were processed in the optimum technolog y conditions, the result showed that alkali microwave preprocessing corn stalks enzymes hydrolysis rate was38.09%, increased by about24.52%for soybean straw enzymes hydrolysis rate.(3) Breeding of L-lactic acid producing strains with some acid resistance from Compound Mutation and the biological characteristics of strains. Diethyl sulfate combined with UV mutagenesis technology was used to filter out a strong strain with some acid resistance for L-lactic acid production. It was achieved that final lactic acid concentration of19.41g/L, and lactic acid volume yield(Qp) of0.404g/L· h by mutant in the fermentation of48h, increased by80.36%than the original strain, the unit cell dry weight of lactic acid production increased by1.32times than the original strain, for2.313g/g. Under laboratory conditions, the mutant growth limits of pH to3.2, the acid resistance more than the original strain,, the mutant bacteria increased by12.94times of OD value than the original parent strain under the same glucose concentration with xylose existing, it was indiscated that the mutant is easier to use xylose than the original strain, which has shown good potential for production and application prospects.(4) Lactic acid fermentation process from corn stalks enzymatic hydrolyzate with alkali and microwave pretreatment. The effect of the amount of CaCO3, of CaCO3adding time, fermentation time, inoculum size and the fermentation temperature of the fermentation process was studied to identify optimal values for each condition. According to the results of single factor experiments, the amount of CaCO3, inoculum size, fermentation temperature and CaCO3adding time were selected as factors for orthogonal optimization. Optimal fermentation conditions were determined ultimately as CaCO3addition of70g/L, inoculum size of5%, fermentation temperature40℃, CaCO3added12h.(5) The utilization of mutant of wash water from corn stalks with alkali microwave pretreatment and the fermentation capacity of mutant. Through the use of the medium, mutants can adapt to the hydrolysate with a high osmotic pressure, better use of sugar in wash water for similar fermentation parameters to control pure sugar fermentation. Under optimal fermentation conditions, the mutant with enzymatic hydrolysate medium for fermentation72h, lactate concentration in the batch fermentation broth is32.13g/L, lactic acid production (Yp/s) was0.863g/g, higher than the original strains of8.42%; volume yield (Qp)0.446g/L·h, increased by6.70percent than the original strain; unit cell dry weight of lactic acid production (Yp/x) was6.40g/g, increased by66.23%than the original strain, with the optical purity of92.8%.(6) lactic acid fermentation kinetics of mutant from enzymatic hydrolyzate. The kinetics model of operation the mutant cell growth, product synthesis, and substrate consumption were studied under optimal fermentation conditions for batch fermentation, and the model parameters were determined to build fermentation kinetics model.Cell growth kinetic model:Product to generate dynamic model: Glucose consumption kinetics model:...