Lignocellulosic biomass offers the potential to provide sustainable sugar streams from a variety of materials including agricultural and forest residuals, and high-yielding bioenergy crops.  However, if cropland is diverted from feed production to produce energy crops there will still be an impact on food prices, and as these energy crops have little alternative use, they represent a high risk for farmers.  Therefore, biomass production systems that are coupled with instead of replacing traditional farming systems should be considered.  One such system being studied is alfalfa fractionation where the high protein leaf fraction is used for animal feed, and the remaining stalks are converted to biofuels.  Alfalfa, like other legumes, contains nitrogen fixing bacteria in its root nodules, thus requiring little fertilizer and improving the soil fertility for other crops after it in the crop rotation. In our work, we furthered the concept of fractionating alfalfa, looking at on-farm storage that can double as pretreatment for saccharification.  Alfalfa stems, which have high carbohydrate content but relatively low protein content, were separated from alfalfa leaves and stored through ensilage (anaerobic wet storage) using either the natural lactic acid produce, or added sulfuric acid.  The pretreatment was done at room temperature and held there for several months mimicking the storage process that would be used on farms.  The alfalfa stems were then neutralized, chemically characterized and then used to produce ethanol using simultaneous saccharification and fermentation (SSF) on either unwashed or washed samples.Results showed that acid pretreatment reduced structure hemicellulose and cellulose content, and increased water soluble carbohydrates (WSCs) of alfalfa stems. Wet storage of alfalfa stems did not affect ethanol yield over dry storage, though with additional acid the pretreatment could improve ethanol yield.  Washing before SSF also improved ethanol yield likely due to inhibitory effect.

Producing ethanol from alfalfa stems with an acid ensilage pretreatment

248th National Meeting (2014)

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