| Cellulosic ethanol is so renewable and carbon-neutral that many researchers have made huge efforts in its production.Unfortunately,the bioethanol production with a low loading of cellulase hydrolyzing the lignocellulosic substrate into fermentative sugars is still far from ethanol economic distillation requirements(ethanol titer>40 g·L-1,fermentation productivity>1g·L-1·hr-1)level that the conventional starchy ethanol industry has reached.Accordingly,this thesis was proposed in the laboratory to enhance the level of the present cellulosic ethanol fermentation at high solid content with a low cellulase loading.The experiment involves three points as below.First,the experiment was carried out to run semi-simultaneous saccharification and fermentation?semi-SSF?of alkali-catalyzed atmospheric glycerol organosolv?al-AGO?pretreated sugarcane bagasse.With single-factor and orthogonal experiments,some key variables were obtained as follows:initial pH 4.8,15%of solid content,6 FPU·g-1 dry mass of cellulase loading and 30 mg·g-1 of Tween 20 addition at the saccharification stage;16 g·L-1 of yeast extract,10%?v/v?of inoculum size,39°C of fermentation temperature and 150 r·min-1of rotary speed for the subsequent ethanol fermentation.After 48 hr of pre-hydrolysis,the glucose content released from the al-AGO pretreated substrate was 76.5 g·L-1 with 81%of the hydrolysis yield.And the subsequent ethanol production was 36.8 g·L-1 after 48 hr.These results indicated that it is feasible to implement cellulosic ethanol fermentation from al-AGO pretreated sugarcane bagasse.Then,the study tried to enhance the cellulosic ethanol production with fed-batch high-solid enzymatic hydrolysis and fermentation of al-AGO pretreated sugarcane bagasse.Result showed that with the reasonable fed-batch mode was 18%of initial solid content,4%,5%,4%and 4%of the total substrate was fed consecutively at 12 hr,18 hr,24 hr and 30 hr,respectively.At 48 hr of pre-hydrolysis,the high-solid enzymatic hydrolysis yielded 57%with 122 g·L-1 of glucose content.And the subsequent ethanol fermentation produced 59 g·L-1 of the ethanol titer at 72 hr with 54%of the cellulose-ethanol conversion.Finally,some strategies?accessary enzymes,mechanic stirring hydrolysis,etc?were adopted to facilitate the high-solid saccharification and fermentation to further the cellulosic ethanol production level.The key variables of these strategies were optimized as below:0.7mg·g-1 of xylanase addition,0.1 mg·g-1 of Lytic polysaccharide monooxygenases Auxiliary Activity 9?AA9?addition,15 mg·g-1 of bovine serum albumin.With the 18%substrate used for initial solid content,the mechanic stirring(180 r·min-1)prehydrolysis released 153 g·L-1 of glucose concentration at 48 hr.The subsequent ethanol fermentation achieved 75 g·L-1 after 72hr,and thus the cellulose-ethanol conversion and fermentation productivity were 68.5%and1.04 g·L-1·hr-1,respectively,which reached remarkably the basic requirements of economic ethanol distillation(ethanol production>40 g·L-1,the productivity>1 g·L-1·hr-1).This research work has pushed cellulosic bioethanol fermentation forward,which has made a great clue to the ongoing cellulosic ethanol production industrially from lignocellulosic biomass. |
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