Breeding Of A High Butanol Producing Strain And Butanol Fermentation With Wheat Starch Wastewater And Cassava

With the depletion of fossil resources, people paid attention to using renewable resources. Butanol is an important organic solvent and chemical material. As a promising new biofuel, butanol is better than ethanol. However, raw materials price almost accounts for 60%～70% of the total production costs. As butanol is toxic to the bacteria, solvent and productivity are only 18～20g/L and 0.34g/g respectively. When competing with chemical synthesis, fermentation had no advantage because of low solvent yield and high production cost. In this paper, high butanol tolerance and butanol-yielding strains were bred after high concentration of butanol soaking and N+ beam implantation. Using wheat starch wastewater and cassava instead of corn as raw materials for butanol fermentation, production costs were reduced, competitivity was improved accordingly.A high butanol tolerance strain BR30-2 was bred after high concentration butanol soaking, and the output of butanol reached 11.77g/L, increasing by 16.65% compared with the original strain. Using BR30-2 as original strain for N+ beam implantation, a higher butanol-yielding strain BH-9 was bred, of which butanol and total solvent were up to 14.51g/L and 23.14g/L, increasing by 43.81% and 38.28% respectively compared with BR30-2. And BH-9 had a good stability.Effects of electron transfer mediator, acetate, butyrate, pH buffers, reducing agents, agitation and ventilation on butanol fermentation were studied. Resazurin (<0.50%o) could be used as a indicator for breeding high reducing strains. Neutral red increased the ratio of butanol significantly; methylene blue had little effect on solvent production while toluidine blue inhibited growth strongly. Acetate and butyrate increased solvents. When added 0.30% sodium acetate or 0.10% sodium butyrate, butanol reached 16.20g/L and 16.59g/L respectively. K2HPO4 stimulated the formation of solvent, and butanol reached 16g/L when its concentration was 0.40%; CaCO3, two buffer salts (Na2HPO4:KH2PO4=1:1) were not conducive to butanol fermentation. Na2S, Vc and L-cysteine hydrochloride as reducing agents were not good for solvent production either. Intermittent agitation had little effect on solvent; Ventilation had different effects in different fermentation periods. During the same period, the inhibition effect from oxygen was increased while extending ventilation time.Using wheat starch wastewater and cassava as raw materials for butanol fermentation, the optimal fermentation medium and conditions were gotten through uni-factor test and orthogonal design. The optimal medium compositions were:cassava power 5%, protein A 3%, butyric acid sodium 0.10% and K2HPO4 0.10%. The optimal culture conditions were: temperature 37℃, initial pH7, seed age 24h, inoculum 3%, medium volume 110mL/250mL, fermentation time 80h. Under the optimal conditions, butanol and total solvent reached 19.32g/L and 32.34g/L respectively, solvent and productivity increased 61.70% and 21.91% compared with corn, and production costs were decreased remarkably.