Study On Extractive Fermentation Conditions And Using Wheat Starch Wastewater To Improve Butanol Production

Due to the increasing consumption of fossil energy discovered and deterioration ofecological environment, the development of new sustainable and environment-friendly energyhas become one of the important directions in energy research. As a new kind of green energy,biobutanol has many advantages, such as more moderate production conditions comparedwith chemical synthesis method and it could be directly used in place of petrol to the currenttransport vehicle. These superiority makes it an ideal energy in the future. But there areobvious limitations of high substrate concentration and solvent concentration, so this paperadopts extractive fermentation method to overcome butanol inhibition effect. In addition, thehigh cost of biobutanol is the biggest obstacle to its industrialization. Therefore using starchwaste water as substrate could reduce production cost. On the basis of the optimization ofstarch waste water medium, the method of liquid-liquid extraction fermentation can furtherreduce the toxicity of organic solvents on bacteria in order to improve the production of totalsolvent.In this paper, the selection of extractive agent, ratio of extractant to water, substrateconcentration and some other factors were investigated. The results showed that thebiocompatibility of oleyl alcohol and soybean oil biodiesel was better than other extractant.Bacause of high price of oleyl alcohol, thus soybean oil biodiesel was regarded as the bestextraction solvent and oil/water ratio was3:5. Static fermentation is more appropriate forbutanol extractive fermentation while turbulence and stirring results in a decline of ABEoutput. The time of adding extractant had a negligible effect on ABE yield. To streamline theoperation, extractant was added to broth in the beginning of fermentation.The optimum concentration of corn and cassava substrate was identified as100g·L-1bycomparing the influence of different concentration of raw material to butanol fermentation. Inthe process of extractive fermentation with corn substrate, the production of butanol and totalsolvent were18.17g·L-1and29.31g·L-1, respectively. In the process of extractivefermentation with cassava as raw material, the yield of butanol and total solvent increased48.69%and51.80%respectively than traditional fermentation.Using high concentration of wheat starch wastewater(starch6.86%) as raw material forbutanol fermentation, after adding a small amount of inorganic salts and nitrogen source, thefinal butanol and total solvent yield can reach12.40g·L-1and21.66g·L-1, respectively.However, with low concentration of starch wastewater (starch1.89%) as auxiliary materialand cassava as the main raw material, then adding70g·L-1cassava,2g·L-1yeast extractpowder，1g·L-1K2HPO4and pH6.0gave better performance, the yield of butanol and totalsolvent with optimized medium fermentation increased35.17%and38.03%respectively.Extractive fermentation with starch wastewater as fermentation auxiliary material can solvethe problem of high residual sugar, as final butanol and total solvent production can reach19.63g·L-1and30.86g·L-1using9%cassva, respectively. The substrate yield of butanol andtotal solvent reached0.28g·g-1and0.33g·g-1, respectively.Strain fermentation performance was investigated in7L fermentation tank. With optimized wastewater-cassava mixed medium as fermentation medium, butanol and totalsolvent production were13.5g·L-1and23.13g·L-1, respectively. Productivity of butanol was0.19g·L-1·h-1. The yield of butanol and total solvent increased44.42%and58.33%respectively than pure cassava fermentation. The residual sugar reduced55%accordingly.