Sunday, April 29, 2007

Optimisation of medium for fermentation of wheat straw at very high dry matter content

Henning Jørgensen1, Mai Østergaard Petersen2, Jan Larsen2, and Claus Felby1. (1) Danish Center for Forest and Landscape, Faculty of Life Sciences, Copenhagen University, Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark, (2) DONG Energy, Kraftværksvej 53, DK-7000 Fredericia, Denmark

It is well known from the fuel ethanol industry that in VHG-fermentations stress of the yeast due to high sugar and ethanol concentrations can result in sluggish fermentations and loss of fermentation capacity. Some yeast strains are more tolerant to stress but it has also been proven that supplementation of the medium with nutrients, especially nitrogen or amino acids, can improve the tolerance and performance of the yeast.

In the ethanol production from lignocellulosic materials, the presence of toxic inhibitors arising from the pretreatment is a further very important stress factor for the yeast. In addition, lignocellulosic materials like straw are naturally low in the content of nutrients and nitrogen. Operating the fermentation of lignocellulosic materials at very high dry matter (20-30 % DM) is therefore expected to put significant stress on the yeast and thereby result in reduced fermentation performance.

In this study, wheat straw hydro-thermally pretreated in a continuous counter-current washing process on the IBUS (Integrated Biomass Utilisation System) pilot plant has been used for hydrolysis at very high dry matter (above 25 % DM). The undiluted hydrolysate has then been used as substrate for fermentation with Saccharomyces cerevisiae and the effect of supplementation with various nutrients on fermentation performance has been investigated.