P46: Overliming Detoxification of Pyrolytic Sugars for Direct Fermentation of Levoglucosan to Ethanol

Pyrolysis process is a promising new method to release fermentable substrates from lignocellulosic biomass to produce biofuel. However, this application is challenged by the presence of inhibitory contaminant compounds in the pyrolytic sugar syrup. Inhibition by these contaminants is so severe that only 0.25% sugars can be used in the fermentation medium. In this study, overliming was tested as a simple detoxification method for pyrolytic sugar. Our previously-modified E. coli KO11+ lgk was used to directly convert levoglucosan into ethanol. After treatment with at least 14.8 g/L of Ca(OH)2, fermentation with 2% (w/v) pyrolytic sugar syrup was observed with no inhibition of ethanol production relative to pure glucose control. Further investigation of treatment time and temperature showed that 8-16 hours of treatment at 20 °C, and 1-4 hours of treatment at 60 °C are necessary to obtain consistent ethanol production. The samples treated with 18.5 g/L Ca(OH)2 at 60°C for 4 hours showed no inhibition at 2.5%, which is 10 times improvement from untreated sample. Multiple contaminants removed by the overliming treatment were identified. This study demonstrates that overliming is a promising method for detoxification of pyrolytic sugars for fermentation.