Henning Jørgensen, Forest and Landscape Denmark, University of Copenhagen, Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark and Jan Larsen Sr., Inbicon, Klippehagevej 22, DK-7000 Fredericia, Denmark.
Ethanol fermentation at high solids concentrations in traditional starch based processes is known to induce stress in the yeast due high sugar and ethanol concentrations. This can negatively affect the performance with respect to productivity and yield. In ethanol production from lignocellulosic materials, the presence of toxic inhibitors from the pretreatment is a further important stress factor. In addition, lignocellulosic materials such as straw are naturally low in 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.Addition of various nutrients such as vitamins and nitrogen sources is known to improve the fermentation performance of the yeast. However, the nutrient requirements might depend on the mode of operation – SHF or SSF. In SHF the yeast will be exposed to high initial sugar concentration and productivity is dependent on the fermentation rate, whereas in SSF the sugar concentration is low and rate is mainly depending on the release of sugars by the enzymes. In this study, hydro-thermally pretreated wheat straw from the DONG Energy IBUS pilot plant in Denmark has been used for hydrolysis at very high dry matter (above 25% DM). The 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. In addition the impact of nutrients has also been studied in SSF experiments at 25% DM.
