(116c) Fermentation of Xylose to Carboxylic Acids Under Low pH Conditions

Lignocellulosic biomass has been perceived to be a promising and widely available resource for conversion to bioethanol. Lignocellulosic materials contain both cellulose and hemicellulose in significant quantities which upon hydrolysis produces both C5 and C6 sugars. The inability of microorganisms to efficiently utilize xylose, the principal C5 sugar, results in significant sugar wastes from bioethanol production that impacts upon the economics of the cellulosic ethanol process. A biorefinery concept that promotes the comprehensive utilization of the hemicellulose and lignin component of biomass will favorably impact the economics of biomass to biofuel processes. In this work, the utilization of xylose in the production of lactic and acetic acids is explored using bacteria that can ferment xylose at pH ~ 4. Fed-batch fermentation studies have shown that ~ 67 g/L of lactic acid and 32 g/L of acetic acid can be produced from a feed containing ~ 80 g/L of xylose. The low pH of fermentation allows for the efficient extraction of the acids from the broth. Batch and continuous fermentation data will be presented along with a model that can predict acid productivities as a function of dilution rate.