Continuous Acetone-Butanol-Ethanol Fermentation From Low-Value Sugar-Based Feedstocks

In this study, the acetone-butanol-ethanol （ABE） fermentation by Clostridiumsaccharobutylicum DSM13864using glucose as substrate was conducted firstly, and then, inorder to replace glucose, the low-value sugar based feedstocks including cane molasses andcorn stover hydrolysate （CSH） were utilized for acetone-butanol-ethanol （ABE） fermentation.After48h fermentation in a3-L stirred fermenter using optimized glucose medium, totalsolvent titer of18.20g/L （butanol11.53g/L）, ABE yield of0.314g/g, and productivity of0.379g/L/h were achieved. In continuous fermentation, ABE titer of R1and R4were9.14g/L（butanol5.96g/L） and11.57g/L （butanol7.29g/L） at the dilution rate of0.05h^-1.Consequently, the solvent productivity in R1was calculated to be0.457g/L/h, representing a20.58%increase compared with that of batch fermentation. In temperature-shiftingcontinuous fermentation, when fermentation temperatures of R1&R2and R3&R4werecontrolled at37℃and33℃respectively, total ABE titer of13.69g/L （butanol8.36g/L） andABE productivity of0.171g/l/h were reached.Using cane molasses medium in3-L bioreactor, maximum ABE titer16.50g/L （butanol10.09g/L） was reached at36h, and ABE yield and productivity were0.336g/g and0.458g/L/h, respectively. The ABE titer of17.85g/L and productivity of0.496g/L/h were obtainedusing a two-stage pH control strategy, in which the culture pH was controlled at5.5for thefirst24h of fermentation and then adjusted to5.1until the end of fermentation. In continuousfermentation with gradient dilution rates of0.15,0.15,0.125and0.1h^-1in R1R4, theaverage ABE titers of7.15,12.24and13.75g/L and ABE productivity of1.072,0.574and0.439g/L/h were obtained for R1, R3, and R4, respectively, and the ABE productivity of R1was enhanced by134.1%compared with that of batch fermentation. In continuousfermentation by immobilized C. saccharobutylicum cells on bricks, ABE concentrations （R4）of15.76g/L （butanol9.61g/L） and13.69g/L （butanol8.00g/L） and ABE productivities of0.394g/L/h and0.513g/L/h were obtained at the dilution rates of0.1h^-1and0.15h^-1,respectively. The continuous fermentation process could be stably operated for264h.During the preparation of corn stover hydrolysate, the cellulase dosage and solid-liquidratio were optimized to be30FPIU/g corn stover and8g corn stover/80ml water. The ABEtiter of16.03g/L （butanol10.56g/L） was attained at48h, and the ABE yield and productivitywere0.312g/g and0.334g/L/h, respectively. In continuous fermentation with dilution rates of0.05h^-1,0.1h^-1and0.15h^-1, ABE titer （R4） of10.14g/L,13.44g/L and11.30g/L, and ABEproductivity of0.127g/L/h,0.336g/L/h and0.424g/L/h were achieved respectively. Atdilution rate of0.15h^-1, ABE productivity was enhanced for26.95%compared with that ofbatch fermentation.Our results show continuous acetone-butanol-ethanol （ABE） fermentation fromlow-value sugar-based feedstocks have great potential in industrial application of biobutanolproduction.