دانلود رایگان مقاله تولید نفت میکروبی و اتانول از آب سورگوم شیرین

Abstract

The juice extracted from sweet sorghum stalks has been previously explored to produce ethanol and also to grow oleaginous yeasts and algae with the objective of producing microbial oil. In this paper we propose a different process route in order to produce ethanol and microbial oil in two consecutive fermentation steps. Ethanol is produced first followed by the growth of oleaginous yeast employing the residual carbon and nitrogen left from the first step. Two yeasts were compared for ethanol production. Trichosporon oleaginosus was cultivated for lipid production. The yeast selection for the first step was the most important factor for achieving a high ethanol yield and the effect of inorganic nitrogen addition was not significant. The remaining sugars consisted of a mixture of sucrose and fructose and no residual glucose was detected in any of the runs. In the second step T. oleaginosus DSM 11815 grew in the pooled juices remaining from the first step for 168 h and produced biomass with 28% lipid content. Glucose showed the highest uptake rate, sucrose was utilized until low glucose values prevailed, and fructose was slowly metabolized and a substantial amount remained. Although the two step process has flexibility in choosing the proper microorganism for each step, it is necessary to look for a rapid fructose uptake strain for both fermentations.

4. Conclusion

We have proposed a different process route in order to produce ethanol and microbial oil in two consecutive fermentation steps from sweet sorghum juice. The first step consisted of ethanol production and the second step in the growth of oleaginous yeast employing the residual carbon and nitrogen left from the first step. In this paper we presented experimental data with the main objective of providing a proof of concept. The yeast selection for the first step was the most important factor for achieving a high ethanol yield and the effect of inorganic nitrogen addition was not signifi- cant. The remaining sugars consistedmainly of sucrose and fructose as no residual glucose was detected. Sucrose inversion took place during ethanol separation so that sucrose, glucose and fructose were present in the residual liquid. In the second step, T. oleaginosus DSM 11815 grew in the pooled juice remaining from the first step. The yeast took a relatively long time to grow and accumulate oil although the initial C/N ratio was acceptable. In order to consolidate process steps, no pH adjustment was made and growth took place at a pH of 4.8, no additional sterilization was performed in the residual liquid from the distillation step. Glucose showed the highest uptake rate, sucrose was utilized until low glucose values prevailed, and fructose was slowly metabolized and a substantial amount remained. Although the two step process has flexibility in choosing the proper microorganism for each step, it is necessary to look for a rapid fructose uptake strain for both fermentations.