PDF《博士学位论文》

5 L helical stirring reactor. Temperature characteristics of S. cerevisiae DQ1 was firstly evaluated in YPD medium. The results indicated the strain could grow at

44 o C while the ethanol yield and grow ability of the strain were reduced greatly when cultured at the temperature over

40 o C. SSF experiments at different temperature without prehydrolysis were conducted when solid loadings and enzyme loading were

20 %(w/w),

5 FPU/g DM. The results indicated that S. cerevisiae could be employed in SSF at

40 o C which gave better performance than SSF at 30-37 o C. However, the fermentation was slowed or stuck when SSF experiments at

40 o C without prehydrolysis as increased solid loadings (~ 30%) and/or increased enzyme loadings (~

15 FPU/g DM). This may due to the weak growth ability of S. cerevisiae DQ1 at

40 o C, and the inhibition of the inhibitors and cellulase were augmented as increased solid and/or enzyme loadings. Even supplementation with external nutrients into SSF experiments could not enhance the fermentation performance of S. cerevisiae DQ1 at

40 o C. The modes of SSF could significantly affect the fermentation performance. And SSF with temperature swing could overcome the problems related with SSF without prehydrolysis at

40 o C. SSF with temperature swing conducted at 30% solids loading with an enzyme loading of

15 FPU/g DM gave ethanol concentration

48 g/L and ethanol yield 61%. The research demonstrated that S. cerevisiae DQ1 could be used for ethanol fermentation from lignocellulose at elevated temperatures. Furthermore, the stain for cellulosic ethanol fermentation at elevated temperatures should be capable of robust growth and stress tolerance at high temperature and tested in the practical lignocellulose and conditions. The main innovative point of the research was using a thermotolerant Saccharomyces strain for SSF of high loadings of the practical lignocellulosic substrate at elevated temperatures. At the part three of the research was on the discovery and isolation of a thermophilic lactate producing bacterium and its application in the SSF of corn stover for lactate production. The phenomomena of lactate formation was observed when studying the ethanol fermentation from the bioabated dilute acid pretreated corn stover at high temperature. A thermophilic lactate producing was isolated from cellulosic ethanol broth and identified belong to Pediococcus acidilactici, named as DQ2. The SSF of bioabated corn stover using P. acidilactici DQ2 for lactate production could be conducted at the temperature up to

48 o C, and lactate concentration

73 g/L and yield 63% were obtained. With the characteristics of high 华东理工大学博士学位论文 第IV 页temperature tolerance, anaerobic fermentation, low nutrients requirements and lignocellulose-dependence, P. acidilactici DQ2 brought a great opportunity for the SSF of lignocellulose for lactate production. The main innovative point of the research was the first report of a thermophilic lactate producing Pediococcus strain souring from the lignocellulose and high titre lactate procuction by SSF of the dilute acid corn stover using P. acidilactici DQ2 at high temperature. In this thesis, the SSFof the dilute acid pretreated corn stover at high temperatures using S. cerevisiae DQ1 and P. acidilactici DQ2 was carried out. The ethanol titer of

48 g/L and the lactate titre of

75 g/L were obtained, respectively, which provided the fundamental technology for the biorefinery of the lignocellulose and had great significance for application to the high temperature fermentation of lignocellulose. Keywords: Corn stover;