Advanced bioethanol production from olive tree biomass using different bioconversion schemes

In this work, olive tree biomass (OTB) was pretreated with sulfuric acid at previously optimized conditions according two different criteria optimization. Then, two schemes of saccharification and fermentation were tested to evaluate the potential of bioethanol production from olive tree biomass pretreated under both optimal conditions. The best results of ethanol production were achieved from OTB pretreated at 15% solids, 164ºC and 0.89% H2SO4. However, when OTB was pretreated at 35% solids, 160ºC, and 1.72% H2SO4, more concentrated sugar solutions were obtained but the ethanologenic microorganism was not capable of assimilating all sugars in the medium. Therefore, the highest ethanol yield, 0.45 g ethanol/g sugar (88% of the theoretical ethanol yield), corresponding to 14.4 g ethanol/100 g raw OTB was achieved when OTB was pretreated at 15% solids using a new bioconversion scheme for this feedstock. It consisted of the enzymatic hydrolysis of the whole slurry from the pretreatment followed by the co-fermentation of cellulosic and hemicellulosic sugars by a recombinant ethanologenic Escherichia coli MM160.