Ethanol production using complex anaerobic inoculum: Effect of PH on the fermentation profile of Glucose and Xylose

The regulatory and political context in France and Europe gives strong incentives for the development of transportation biofuels during the ten coming years (EU Directive 2003/30/CE). The environmental benefit of using first generation biofuels (agro-fuels) is however questionable (Kalogo et al., 2007). In this framework, the development of bioethanol from other organic resources such as household waste has been reported to be more economically and environmentally attractive. We are therefore working on the coupling of an ethanol production reactor to existing anaerobic digestion processes. Household waste being a complex and heterogeneous matrix, yeast fermentation would require energy-intensive pretreatments.

Further Authors:
M. Bouix, L. Mazeas, C. Madigou, C.M. RichardA. Guenne, T. Labatut

We have consequently focussed on ethanolic fermentation by complex anaerobic microbial communities which are able to cope with a wider range of substrates without pretreatment. In particular, lignocellulosic waste constitute a major fraction of household waste. It is composed of cellulose and hemicellulose. The first one is a polymer of glucose (C6) and the second one contains many different sugar monomers, xylose (C5) being present in the largest amount. In this study, we focus on the influence of pH, being reported in the litterature as a key element for ethanol production by mixed anaerobic cultures (Ren et al. ,2001 and Temudo et al., 2007), on the fermentation profile of these two substrates. Experiments were carried out in batch with glucose or xylose under anaerobic conditions. A concentration of 4 g/L was used for the two sugars. We have tested six different pH, in triplicate (ranging from 4.5 to 7). We have shown that the production of ethanol was possible from glucose and xylose. For each sugar, the greatest ethanol concentration was obtained at pH 7 at day 2: around 500 mg/L which represents 12.5% of the initial carbon. From day 3, ethanol is degraded and at day 7 no ethanol can be quantified anymore. We have also observed that ethanol degradation is slower for pH under 6. Moreover, according to pH, we have seen that the microorganisms' populations have evolved differently which could explain the differences in ethanol production and degradation. This knowledge could be very useful to adjust parameters to optimize ethanol production. Ethanol production from simple sugar is one step of the development of biofuels from household waste. Experiments are under progress to study optimal pH operation strategies, evolution of microbial populations and their functionalities.

Copyright: © European Compost Network ECN e.V.
Source: Orbit 2012 (Juni 2012)
Pages: 6
Price: € 6,00
Autor: Théodore Bouchez

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