Bio-fuel production by using integrated anaerobic fermentation.

Abstract

Saccharification is one of the most critical steps in producing lignocellulose-based bio-ethanol through consolidated bioprocessing (CBP). However, extreme pH and high ethanol concentrations are commonly considered potential inhibitors for the application of Clostridium sp. in CBP. The fermentation of several saccharides derived from lignocellulosics was investigated with a co-culture consisting of Clostridium themocellum and Clostridium thermolacticum with or without immobilization. Alkali environments proved to be more favorable for ethanol production. Fermentation inhibition was observed at high ethanol concentrations (>8g/L) and extreme pH (>10). However, low levels of initial ethanol addition resulted in an unexpected stimulatory impact on the final ethanol productions for all cultures under selected conditions. The co-culture was able to actively ferment glucose, xylose, cellulose and micro-crystallized cellulose (MCC). The ethanol yield observed in the co-culture was higher (up to two-fold) than in mono-cultures, especially in MCC fermentation. The highest ethanol yield (as a percentage of the theoretical maximum) observed were 75% (w/w) for MCC and 90% (w/w) for xylose. Immobilization technique using sodium alginate is efficient in improve the ethanol production during co-culture fermentation, although the immobilization is not able to change the ethanol sensitivity of this co-culture. The ethanol yield through the use of immobilized technique increased to 97% of the theoretical efficiency for glucose. For cellobiose and MCC under optimized condition, the ethanol yields were approaching 85% of the theoretical efficiency. In order to examine the feasibility of this immobilization co-culture on lignocellulosic biomass conversion, untreated and pretreated aspen fermentations were performed. The immobilization co-culture shows clear benefit in bio-ethanol production in CBP process. With a 3h, 9% NaOH pretreatment, the aspen powder fermentation yield approached 78% of the maximum theoretical efficiency, which is almost twice the yield of the untreated aspen fermentation. Keywords: Consolidated bioprocessing, Clostridium sp., Fermentation, Co-culture, Lignocellulosic ethanol, Immobilization, Alginate gel.