Stimulatory Effect And Adsorption Behavior Of Rhamnolipid On Lignocellulose Degradation System

Energy shortage is an important problem which restricts sustainable development in our country. As a sustainable way, using straws of crops to produce bioethanol has been much attracted nowadays. It showed that the production of reducing sugar could be improved by adding biosurfactants, such as rhamnolipid. Thus, rice straw and Trichoderma reesei was chosen as degradation substrate and fermentation bacteria, respectively, and the acceleration effect and mechanism of rhamnolipid on rice straw fermentation process was investigated in our study.The effect of fermentation factors on reducing sugar yield were optimized by single factor test. The results showed that the optimal conditions of fermentation were solid to liquid ratio 2:100, pH 5.5,30 ℃, dirhamnolipid 12 mg-L"1 and mixed rhamnolipid 15 mg·L-1. Through orthogonal test, the effect of pH, temperature and rhamnolipid concentration on reducing sugar yield were analyzed. As for dirhamnolipid, the optimal fermentation condition was pH 7.5,30℃ and dirhamnolipid 10 mg·L-1, and the influence degree of these factors were pH> dirhamnolipid concentration> temperature. As for mixed rhamnolipids, the optimal fermentation condition was pH 5.5,30℃ and mixed rhamnolipid 15 mg·L-1, and the influence degree of these factors were temperature> mixed rhamnolipid concentration> pH. The main components of reducing sugars after fermentation were detected in the optimal fermentation condition. It was showed that glucose, xylose and arabinose were the main contents, and the proportion of each was 55%-60%,22%-26% and 16%-18%, respectively. Compared to reducing sugars in the fermentation broth without rhamnolipid addition, the xylose was reduced 7.9% and glucose yield was increases 16.2% after adding mixed rhamnolipid.The adsorption behavior and adsorption pattern of dirhamnolipid and mixed rhamnolipids were observed. It was showed that the adsoption of rhamnolipids on Trichoderma reesei was larger than that of rice straw in single adsorption system, and the adsorption pattern was consistent with Langmuir adsorption pattern. Meanwhile, the total adsorption amount in the rice straw-Trichoderma reesei compound system was not the summation of the adsorption amount in the two single systems. The adsorption curves of rhamnolipid were simulated by SPSS analysis. The results showed that the cubic equation was the fittest, and its fitting coefficient could reach 0.995. The linear and quadratic rate equations were used to simulate the dynamic adsorption model of rhamnolipid. It was found that the fitting effect of quadratic rate equations is better than that of linear rate equations, whose fitting coefficient could reach 0.977. The simulated equation was y=0.2428x+7.1781 and y=0.3261x+7.6461.Finally, the morphology changes in the fermentation system were observed and analyzed by SEM and FTIR. The surface morphology of rice straw in different degradation period was observed by SEM. It was found that the surface of rice straw was severely damaged after 30 days, and half/full breakdown holes were observed. The damage of rice straw was more serious after adding rhamnolipid than that of without rhamnolipid. By FTIR spectra we could see that partial functional groups were decreased after degradation in 30 days. There was no new compound synthesized between rhamnolipid and cellulose after adding rhamnolipid.