Fermentation Of 2,3-butanediol From Corn Stover Hydrolysate

2,3-butanediol is a valuable chemical feedstock and liquid fuel.Biological production of 2,3-butanediol from biomass is a feasible alternative for traditional chemical synthesis.Because of the increasing shortage of oil resources,fermentatve production of 2,3-butanediol from cheap lignocellulose materials become more and more competive and practicable.This article studies the key technical parameters in pretreatment,cellulose hydrolysis,batch fermentation,fed-batch fermentation, simultaneous saccharification and fermentation and other aspects using corn stover as the initial raw materials,the results have some significance in promoting biotransformation of no-grain biomass.Pretreatment of corn stover has been studied.The results show that acid treatment can remove most of the hemi-cellulose,while in alkali treatments a large proportion of the lignin is removed.Enzymatic hydrolysis of cellulose experiments show that hydrolysate from alkali treatment residue contains more monosaccharide,mainly due to the high lignin removal rate.In addition,the cellulose component is easily hydrolyzed after wetting and expansion.Dilute alkali pretreatment is an effective pretreatment method.Pretreatment process would introduce inorganic salts to hydrolysate and Na₂SO₄ is a typical one.Sodium sulfate concentration under 20 g/L in corn stover hydrolysate has no significant influence on subsequent fermentation;acetic acid and ethanol,as the main byproducts,affects the fermentation as the concentration exceeds 20 and 5 g/L respectively.The optimal initial pH is 6.0～6.5 and the initial total sugar concentration is 80～100 g/L.Batch fermentation on hydrolysate by Klebsiella oxytoca ZU-03 shows when the total sugar concentration is 80 g/L,the cultures are shaking at 30℃for 64 h, a 2,3-butanediol concentration of 37.20 g/L is achieved and 99.36%of the total sugar is consumed with the yield of 0.468 g/g,which reached 93.6%of the theoretical maximum.Common utilization of pentose and hexose from semi-cellulose and cellulose is achieved in this process.The substrate inhibition bottleneck in batch fermentation can be overcomed by fed batch operation.Study shows substrate supplement should start at 12 h and appropriate addition mount is 15 g/L each time.The proper supplemental carbon nitrogen ratio is 16.2,3-butanediol concentration reached 100.14 g/L in 204 h and maximum output is 108.13 g/L which increased 190.7%to the batch fermentation. High product concentration generated by fed batch fermentation has a value for saving the cost of downstream separation of 2,3-butanediol.Simultaneous saccharification and fermentation(SSF) of 2,3-butanediol integrates two major segments:hydrolysis and fermentation and saved the hydrolysate processing step,which improves production efficiency and lowers costs.The optimal initial pH of SSF by Klebsiella oxytoca ZU-03 is 6.0 and suitable temperature is 31℃. The appropriate cellulase and cellobiase dosage in SSF is 25 FPIU/g and 12.5 CBIU/g, respectively.2,3-butanediol concentration reached 23.30 g/L with the yield 0.23 g/g after 36 h fermentation.Fermentative production of 2,3-butanediol makes the reuse of agricultural waste possible.Bio-conversion process is relatively mild compared with chemical synthesis, therefore,the wastage of equipments and energy consumption is lower.A useful compound 2,3-butanediol is obtained in the process.This study promotes transformation of biodegradable waste and opens a new direction.