Butanol and Hydrogen Production From Xylan By Clostridium Sp. BOH3: Simultaneous Saccharification and Fermentation

Title

Butanol and hydrogen production from xylan by Clostridium sp. BOH3: simultaneous saccharification and fermentation

Abstract

Butanol and hydrogen are recognized as fossil-fuel alternatives. They can be simultaneously produced from anaerobic fermentation of simple sugars. Recently, a new strain Clostridium sp. BOH3 was observed to produce butanol and hydrogen from xylan. While the most of solventogenic Clostridia spp. require simple fermentable sugars such as glucose for the production of butanol, sp. BOH3 utilizes xylan (10 g/l) effectively because of its high level xylanase expression. In the present study, a medium is designed for the production of xylanase, butanol and hydrogen using response surface methodology. The medium is composed of two major components, xylan as carbon source and ammonium sulphate as nitrogen source. With the help of central composite design, the direct and interactive effects of xylan and ammonium sulphate on xylanase, butanol and hydrogen production were analysed. The optimized medium, which supports maximum production of xylanase, butanol and hydrogen, contained 49.4 g/l of xylan and 19.8 g/l of ammonium sulphate. It supports the production of 6.1 U/ml of xylanase, 7.6 g/l of butanol and 16.2 ml/l.h of hydrogen. Apparently, simultaneous saccharification and fermentation (SSF) of xylan by using BOH3 is possible, thanks to the expression of xylanse by BOH3. To improve this SSF process, xylanase produced by BOH3 was purified by using one-step Q-anion column chromatography and supplemented into the next batch. Every attempt of purification yields 43±1.5% of enzyme, and its supplementation to the next batch results the xylanase activity of 2.5±0.1 U/ml at the beginning of fermentation. Due to this addition of xylanase, production of butanol and hydrogen is increased to 16.05±0.5 g/l and 28.3±0.8 ml/l.h respectively. The butanol and hydrogen yields are increased to 0.33±0.01 g/g and 0.58±0.008 ml/l.h/g respectively. These results suggest that improved SSF process enhances the butanol and hydrogen yield about 2 fold. This approach would also facilitate the effective recycling of potential enzyme produced in the fermentation process.