Biodegradation Of The Lignocellulose Derived Inhibitor Substrances In The Pretreatment Process And Its Photo-fermentation For Hydrogen Production

The degradation products from lignocellulose pretreatment, such as furfural, 5-hydroxymethylfurfural (5-HMF), acetic acid, formic acid, levulinic acid etc, are the typical inhibitors for the cellulase enzymes and ethanol fermentation strains. Efficient degradation of these inhibitors ("biodetoxification") is required for the following fermentation process. Biodegradation by microorganism is one of the most effective ways for inhibitors degradation. In this thesis, we isolated three fungi with the degradation capacity for the inhibitors by the two screening procedures in both the synthetic medium and the pretreated corn stovers. The strains were identified as Amorphotheca resinae ZN1, Penicillium polonicum ZN2, and Penicillium turbatum ZN3 using the 16sDNA molecular identification method. A. resinae ZN1 grows well at the pH 3-8,20-32℃, with or without oxygen when the inhibitors concentrations are not very high. The maximum concentrations at 10% solid loading hydrolysate degraded by the A. resinae ZN1 strain were acetic acid 8g/l; formic acid 9g/l; furfural 4g/l; 5-HMF 5g/l. The hydrolysate at 30% solid loading using the typical dilute acid pretreated corn stover contains glucose 65g/l, xylose 34g/l, acetic acid 9.0g/l, formic acid 2.7g/l, levulinic acid 3.2g/l, furfural and 5-HMF 0.8 g/1. The Saccharomyces cerevisiae DQ1 could not grow in this hydrolysate at 37℃without detoxification. After the ptreated corn stover was detoxificated by A. resinae ZN1 for 4 days, the simultaneous saccharification and fermentation (SSF) by S. cerevisiae DQ1 at the same condition could be carried out and 43g/l of ethanol was obtained. In the second section of the thesis, organic acids (acetic acid, formic acid, levulinic acid) derived from the lignocellulose are not only produced during the pretreatment but also fermentation process. Using these organic acids for hydrogen production can combine the treatment of waste water and hydrogen production. In our study, we choose the Rhodobacter sphaeroides ZX-5 for the photo-fermentation using the effluent from lipid fermentation based on lignocellulose. The study show that:at 30℃and 45001ux light intensity, R. sphaeroides ZX-5 could degrade the all residual sugar and organic acids with hydrogen yield 8ml H2/ml effluent.