Fuel Ethanol Production From Food Waste With Microorganism

In recent years, the world’s fossil fuels were inevitable depleted and the current demandsfor energy were increasing, bioethanol was considered as one of the most important substitutesof fuels, and was widely used to relieve the energy crisis. Food waste as the residual organicsolid waste is discharged from restaurants containing lots of free sugar and starchiness, andthere is at least60million tons in China every year. Because of its rich carbon content, it is agood raw material for producing ethanol and has the huge development potential. In this study,a recombinant Sacharomyces cerevisiae strain co-expressing glucoamylase and α-amylase wasconstructed and a consolidated bioprocessing (CBP) was established to produce ethanol byusing this recombinant yeast. To assess the feasibility of CBP, some influencing factors wereexplored, and it provided the basis for further reseach.Firstly, the δ (delta) DNA fragment was amplified from the genomic DNA ofSaccharomyces cerevisiae As2.489using PCR, and it was inserted into the expression vectorpScIKP, to construct a new δ DNA-mediated integrated expression vector, designated aspδRCMB. Then an α-amylase and a glucoamylase gene expression cassettes were inserted intothe expression vector pδRCMB to construct a recombinant plasmid pδRCMB/amy/ga. Therecombinant plasmid was then transformed into the Saccharomyces cerevisiae As2.489strainby electroporation. The recombinant yeast named As2.489/pδRCMB/amy/ga was obtained byG418resistance screening, starch transparent circle and SDS-PAGE. The recombinant yeastshowed α-amylase and glucoamylase activities of1.03IU/ml and1.95IU/ml.In order to study the feasibility of CBP,7.86%food waste (dry weight) were used insimultaneous saccharification and fermentation (SSF) for ethanol production. The resultsshowed that the ethanol yield of CBP (16.2g/L) was lower than the SSF’s (18g/L). However,considering the price of commercial enzymes and the cost of production, SSF may be difficultto be widely applied in the industry of food waste treatment. So the CBP technique was choosedto be the focus in this study.Based on the CBP mentioned above, a series of fermentation factors, such as nitrogensource, nutrients, and substrate concentration were explored. The results indicated that nitrogensource and nutrients were invalid to improve ethanol yield, but the substrate concentration had an obvious influence on ethanol fermentation. The ethanol yield and conversion rate of26.2%food waste was65.2g/L and0.25g/g (dry weight), higher than that of7.86%food waste (16.2g/L and0.206g/g), which was more suitable for ethanol production.In conclusion, the recombinant yeast strain co-expressing glucoamylase and α-amylase,and the CBP from food waste to bioethanol were successfully constructed. It shows goodpotential applications.