1.3.2 Description of the experiments

Bioethanol production from wheat straw was investigated. Several improvements, particularly one washing step and the recirculation strategy, were made. The washed wheat straw was named inhibitor-controlled wheat straw. These improvements increase both the sugar concentration and the bioethanol yield by up to 7%(vol). Also, the lignocellulose — containing substrate corn stover was tested for its potential in bioethanol production. Furthermore, recirculation of bioethanol was performed to ultimately raise the end concentration of bioethanol. Therefore, ethanol was added during the pretreatment process and a possible effect on the hydrolysis and fermentation steps was examined.

The enzyme mixture Accellerase TM1000 from Genencor® was used with enzyme activities of 775 IU cellulase (CMC)/g solids and 138 IU beta-glucosidase/g solids. Suspensions with various dry substances (10-20%) were produced with the pretreated substrate in citrate buffer (50 mM, pH 5.0) and incubated at 50°C for 96 hours in a shaking incubator (100 rpm). The hydrolysis of pretreated substrate was repeated three times in a recirculation process. Sample analysis was performed with HPLC. Diverse salts were added to the straw hydrolysate for fermentation. A wild-type strain of Saccharomyces cerevisiae was used exclusively for all experiments. The fermentation process was conducted at 30°C in a shaking incubator for one week (110 rpm).