4-10: Improved xylose utilization by integration of first and second generation bioethanol based on separate hydrolysis and fermentation

Commercialization of second generation (2G) bioethanol has still not been realized due to several factors, including poor biomass utilization and high production cost. Integration of 2G ethanol with first generation bioethanol can facilitate the introduction of 2G technology. The capital cost per ton fuel produced and the energy demand of 2G ethanol production can be diminished and a better utilisation of the biomass can be achieved.

It is generally accepted that to reduce the production cost the most important parameters are the ethanol yield and the ethanol concentration in the fermentation broth. One way to increase the concentration and the yield is to increase xylose consumption during fermentation. TMB3400 is a genetically modified yeast strain, which has the ability to co-ferment glucose and xylose. Also, xylose uptake rate is very much enhanced when the glucose concentration is low.

In the current study, SHF of steam-pretreated wheat straw (SPWS) combined with wheat-starch hydrolysate feed was performed in two different process configurations. First, a one-hour fermentation of SPWS hydrolyzate was performed; thereafter, supernatant of the enzymatically hydrolysed (20% WIS) unwashed solid fraction and wheat-starch hydrolyzate was fed to the fermenter. The yield of ethanol and xylose consumption reached 83% and 60%, respectively. However, traditional SHF resulted in 92% yield after fermentation based on glucose and xylose and almost complete xylose consumption when only wheat starch hydrolysate was fed.

The study has now been continued with high (20 g/L) cell density in fermentation. The results of these experiments will also be presented.