A Possible Industrial Solution to Ferment Lignocellulosic Hydrolyzate to Ethanol: Continuous Cultivation with Flocculating Yeast

Abstract

The cultivation of toxic lignocellulosic hydrolyzates has become a challengingresearch topic in recent decades. Although several cultivation methods have been proposed,numerous questions have arisen regarding their industrial applications. The current workdeals with a solution to this problem which has a good potential application on anindustrial scale. A toxic dilute-acid hydrolyzate was continuously cultivated using a high-cell-density flocculating yeast in a single and serial bioreactor which was equipped with asettler to recycle the cells back to the bioreactors. No prior detoxification was necessary tocultivate the hydrolyzates, as the flocks were able to detoxify it in situ. The experimentswere successfully carried out at dilution rates up to 0.52 h-1. The cell concentration insidethe bioreactors was between 23 and 35 g-DW/L, while the concentration in the effluent ofthe settlers was 0.32 ± 0.05 g-DW/L. An ethanol yield of 0.42-0.46 g/g-consumed sugarwas achieved, and the residual sugar concentration was less than 6% of the initialfermentable sugar (glucose, galactose and mannose) of 35.2 g/L.