Improved Ethanol Production Through Anaerobic Thermophilic Co-Culture From Various Carbohydrates
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Saccharification of fermentable sugars is one of the most critical steps in producing bio-ethanol from lignocellulosics through Consolidate Bioprocessing (CBP). However, the extreme pH and ethanol concentration are commonly considered to be the potential inhibitory factors for the application of clostridium sp. in CBP. The fermentation of several saccharides derived from lignocellulosic biomass was investigated in an anaerobic thermophilic co-culture consisting of Clostridium themocellum and Clostridium thermolacticum under various fermentation conditions. Alkali proved to be more favorable for the ethanol production utilizing lignocellulosics. Inhibitions of fermentation were observed at high ethanol concentrations and extreme pH values. However, the addition of low levels of ethanol showed an unexpected stimulatory impact on final ethanol productions for co-culture under selected conditions. This co-culture was able to actively ferment glucose, xylose, cellulose hemicellulose and micro-crystallized cellulose (MCC). The ethanol yield observed in co-culture is higher than in their mono-cultures. Especially in MCC fermentation, over two-fold increase was observed in ethanol production as compared to the mono-cultures. The highest ethanol yield was observed as 75% (w/w) for MCC and 90% (w/w) for xylose of the theoretical maximum yield.