| considering the current development of fuel ethanol industry in China and according to the status of potato production in Gansu Province, the ethanol fermentation technology by potato waste was explored in this paper the aim of this investigation was to expand the scope of raw materials for fuel ethanol production and reduce ethanol production costs as well as resolve the problems of value-added exploitation of potato residues and environmental pollution due to potato residues.On the fiber structure of potato residues, the mechanism of potato cellulose decomposition by cellulase, and the mechanism of ethanol fermentation, ethanol was produced by yeast fermentation using potato residues, liquefied, saccharified, and treated with complex enzymes. The studies were carried on as following:1.Mutagen by UV irradiation and screening methods were applicated on yeast strains, impact factors of mutagenesis and cell fusion were optimized, and growth characteristics of different strains were also observed.2.Factors affecting on the growth of immobilized yeast, simultaneous saccharification and fermentation of immobilized yeast technology were explored.3.Batch ethanol fermentation conditions on lab scale and pilot scale were studied, fermentation temperature, dissolved oxygen, pH changes in fermentator were analyzed.The results showed that:(1) Yeast mutagenesis and screening. The growth rate of Yeast KYB208 was greater than the control Yeast K1. The survival rate of Yeast KYB208 after UV irradiation for 5 min was 1.79% of the control group. The mutation rate of Yeast KYB208 after UV irradiation for 4 min was 16.67% of the control group. Therefore, the UV treatment was beneficial to the yeast strains for getting mutation. Ethanol fermentation capacities of 3 mutagenesis strains were greater than 1# Yeast K1 control strain, producing ethanol yield of the 8 # Yeast KYB208 strain was up to 14.% of the higest, which was 2.2% higher than control after fermentation with the same raw material. Technology of UV mutagenesis, screening and culture was available to screening high-efficiency ethanol fermentation yeast.(2) Fusion and fermentation of yeast strains. Using 40-60% of concentration of 6000 PEG to treat parent strains of yeast, good effects of cell fusion were achieved. The optimum conditions for the protoplast formation were at strain age of 24 h,0.25%(w/v) snail enzyme, osmotic pressure stabilizers of 20%(w/v) of sucrose solution, and growth medium with YEPD. Under this condition, parent strain protoplast formation rate was 92.7%, the regeneration rate was 30.5%. The ethanol production capacities of two parent strains were 3.0%(v/v) and 5.6% (v/v) after incubating 5 d, respectively, and the fermentation capacity of fussion cell was up to 8.7%(v/v). The results demonstrated that the fussion strain was a high-yield ethanol strains of yeast.(3) Immobilized yeast and simultaneous saccharification and fermentation. The fermentation rates of immobilized yeasts were greater than the others with potato residues at the simultaneous saccharification and fermentation. In the fermentation mash, the residual sugar content tended to increase first and then decrease with the fermentation time. After 64 h fermented, resedual sugar content in fermentation mash by the Yeast immobilized K1B reduced to less than 3.5%, and as to Yeast A1B reduced to below 2.7%. Ethanol content in fermentor increased with the fermentation time, alcohol content in mash of immobilized Yeast KIB was up to 2.3%(v/v), and Yeast A1B attained to 3.1%(v/v).(4) Batch fermentation of the potato residues in the fermentor of pilot experiments. With the same quantity of 2000 g of raw materials in fermentor, different amount of complex enzyme added, the reducing sugar contents were 1# of 31.8%,2# of 28.6%,3# of 21.3%,4# of 27.5%, respectively. Added equal amounts of yeast KYB208, alcohol contents were 1# of 11.0%,2# of 11.4%,3# of 8.7%,4# of 11.9%, respectively. The fermentation efficiencies were 1# of 69.44%, 2# of 64.07%,3# of 56.41%,4# of 78.91%, respectively. As the alcohol content in the culture reached 11.0%, it would inhibit fermentation, yeast was unable to continue to use sugar for producing ethanol, this cause fermentation rate being from 64.07% to 78.9%. Different treaments in potato residues pilot fermentation, isometric saccharomycetes added,30.0% of starch, the alcohol contents were 1# of 8.1%,2# of 7.9%, and fermentation rate 1# of 47.47%,2 #of 46.21% after fermentation, respectively. With the same residues content of 37.45% of potato residues, alcohol contents were 3# of 6.2%,4# of 6.4%, and fermentation rate 3# of 43.07%,4# of 44.31% after fermentation, respectively. The fermentation results showed when the alcohol content achieved on a certain degree, the saccharomycetes cannot continue using the sugar to produce the alcohol, so that the starch fermentation rate was of 46.21-47.47%, the potato residues ferments rate was of 43.07-44.31%. |
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