INOCULUM SIZE INFLUENCE IN FERMENTATIONS USING HEMICELLULOSIC ACID HYDROLYSATE

Second generation ethanol presents great potential to replace fossil fuels. However, its production at competitive prices faces challenges related to slow fermentation rates and low ethanol productivities. The presence of inhibitors, formed during the acid hydrolysis pretreatment of the lignocellulosic biomass, contributes to hamper process performance. This work aims to study the influence of inoculum size on inhibitors tolerance as well as the inhibitors influence on process performance after long exposure time. In the fermentations with low initial cell concentration, the harmful effect was observed mainly over the growth rate, hampering substrate consumption and consequent conversion to ethanol. On the other hand, in the culture with high cell population, there was a high sugar conversion in the first batch, which decreased in the sequential batches, proving the progressive negative influence of the inhibitors over the yeast cells.