The Foundation And Process Optimization Of The Two-step Mixed Fermentation On Straw

The crops straw is an important biological resource. Because of its particular composition and structure, the hardly-degradation is always the problem of straw conversion and application. The biological treatment of straw is deemed to be the best method at present, because this treatment has many advantages, such as low pollution, high efficiency and benefit for industrial production. However, in the long-term experiments and production practice, people found that the straw degradation was accomplished by a series of enzymes produced in the microbial metabolism process. These enzymes need to have a synergistic effect on the degradation of straw. The single enzyme has a low degradation ability, nevertheless the series of enzymes have strong capability. The different straw degradation strains have strong interaction to each other. The combined degradation ability of cellulose-decomposing microorganisms and lignin funguses is higher than that of single strain. So the degradation effect of mixed microorganisms is better in the practical processing.This paper selected the best strain from existing lignin funguses, then fermented with Trichoderma koningii to degrade straw. Finally the optimization experiment of mixed fermentation technology was carried. Through the studies we get the conclusion as follows:1) The best strain which had growth advantage and yielded high activity lignin-degrading enzymes is selected from 6 common white-rot funguses. The average grow rate of mycelium is 0.97cm/d; the biomass achieves to the maximum value 0.4418g; the highest enzyme activity of Laccase produce in the liquid shake culture and the solid-state straw fermentation are 934.20U/mL 648.39U/mL.2) Through the antagonistic experiment of Pteurorus ostreatus and Trichoderma Koningii, we found that Trichoderma Koningii had stronger growth advantage and competitive inhibition to Pteurorus ostreatus. So we carried the two-step mixed fermentation to degrade straw by the two strains. Through the different combination ways, we found that H₆-T₁₀ group can get the best straw degradation result. The lignin degradation rate reached 34.77%, and the cellulose degradation rate was 41.48%. 3) Through single factor experiments, the effect factors related to fermentation was studied. Finally we get the optimum fermentation conditions as follows: the particle size of straw is 50mesh, total inoculum amount is 10%, the inoculum ration of Pteurorus ostreatus and Trichoderma koningii is 3:2, the fermentation temperature is 26℃, initial pH is5.5, the water content of is 60%.4) The fermentation temperature , initial pH and the inoculum ration of Pteurorus ostreatus and Trichoderma koningii are screened from 8 single factors by Plackett-Burman. Through the Response surface methodology, the best fermentation conditions are as follows: the best fermentation temperature is 24.80℃, the best initial pH is 4.88, the interval of two inoculations is 6.53 days.5) The structure of straw which fermented in optimum conditions are analysed by IR and SEM. We can see that the mixed fermentation can degrade the cellulose, hemicellulose and ligin.