Efficient Ethanol Production From Lignocellulosic Hydrolysates By Strain Adaptation And Repeated Fermentation

Lignocellulosic materials are the most abundant renewable resourcesfor bioethanol production. However, the microbial utilization oflignocellulose feedstock is limited because of the toxic compounds presentin the hydrolysate. Until now, low efficiency of fermentation and highcosts of the whole procedure are the most critical bottlenecks for industrialethanol production. For economical feasibly producing ethanol fromlignocellulose hydrolysates, it is important to develop a robustmicroorganism and design an efficient process with high titer. In currentwork, ethanol production from corncob residues （CCR） by an adaptedyeast Pichia guilliermondii was investigated to obtain an efficientfermentation technology for cellulosic ethanol production.After adaptation in defined medium and hydrolysate under the stressof several inhibitors, the adapted yeast could tolerate up to5g l^-1furfural，10g l^-15-hydroxymethylfurfural （5-HMF） and20g l^-1acetic acid in defined medium. No decrease of ethanol yield or titer was observed.Directly using CCR as feedstock, the maximum ethanol concentration of35.1g l^-1and ethanol yield of0.45g g^-1were achieved using18.7%initialsolid loading by separate hydrolysis and fermentation （SHF） withoutexternal nutrient supplementation. By feeding with concentratedhydrolysate, the final ethanol titer could further reach up to56.3g l^-1.To obtain efficient and high titer ethanol production, high cell densityculture was carried out and the yeast cells were reused in both batch andfed-batch mode. With this processing approach, fermentation period ofeach cycle was reduced to16hours and48hours during repeated batchand fed-batch fermentation, respectively. The maximum volumetricethanol productivity could reach up to2.33g l^-1h^-1and1.11g l^-1h^-1, withhighest ethanol titer of37.7g l^-1and51.2g l^-1, respectively.In the whole process, we tried to reduce the cost by omitting thepretreatment procedure and external nutrient supplementation. Our resultsindicated that this robust inhibitor-tolerant yeast and simple process werepotentially effective for commercial bioethanol production.