(592e) Production of Butanol From Corn Fiber Hydrolysate by Clostridium Acetobutylicum in a Fibrous Bed Bioreactor

Butanol is an important industrial solvent as well as an excellent candidate of performance fuel. Due to the limited supply of fossil fuels and the surging price of crude oil, there has been an increased interest in producing butanol through acetone-butanol-ethanol fermentation (ABE fermentation) by Clostridia instead of petrochemical routes. Moreover, bioconversion of lignocellulosic biomass into fuels and chemicals through fermentation has been a focus in recent years. In this study, corn fiber and corn steep liquor (CSL), two by-products of the corn refinery industry, are used as the carbon source and nitrogen source, respectively, in the media supplemented with butyric acid at a level of 3-4 g/L to induce solventogenesis in the ABE fermentation.

Using 50 g/L glucose along with CSL, 83% of glucose was consumed in 72 hours resulting in 10.2 g/L butanol and a total ABE yield of 0.4 g/g. This indicated that CSL alone can replace all the traditional P2 minerals and vitamins to serve as the sole nutrition source sufficiently. It was also found that without detoxicification, the dilute sulfuric acid treated corn fiber hydrolysates (CFH) hindered sugar consumption and severely inhibited cell metabolism in conventional free-cell fermentation, resulting in less than 1 g/L butanol and a low cell density. However, when cells were first immobilized onto a fibrous bed bioreactor (FBB), the inhibition caused by the CFH was largely reduced. By attaching and immobilizing cells onto the fibrous matrix in the FBB, cells were able to adapt to the relatively harsh environment caused by the undetoxified CFH and 3.3 g/L butanol was produced using pure CFH containing 23.8 g/L glucose, which was lower than 4.9 g/L butanol produced in P2 medium containing 25 g/L glucose. However, the inhibition effect caused by CFH can be significantly reduced by diluting CFH in the medium and supplementing some glucose. It is thus concluded that Clostridium acetobutylicum can use undetoxcified hydrolysates as the carbon source to produce butanol because the employment of FBB significantly reduced the inhibition caused by furfural and ferulic compounds present in the hydrolysates. This would allow economic use of agricultural residues such as corn fiber for biofuels production. By converting waste by-products of the corn refinery industry into biofuel, not only additional value is added but also the net emission of greenhouse gases is reduced, benefiting the society and environment.