3.2.5. Simple model for ethanol yield prediction
We found there was a correlation between ethanol yield and silage pH, thus two regressions were built for ethanol yield prediction as shown in Fig. 5. The pH predicted the ethanol yield of washed alfalfa stems better than for the unwashed stems. The pH had a negative effect on ethanol yield, due to a higher pH would treat biomass less, and thus the cellulose accessibility was less improved.
4. Conclusions
Ethanol was produced from alfalfa stems with ambient-temperature sulfuric acid pretreatment, ensiling, and washing. The cellulose and hemicellulose contents of ensiled alfalfa stems decreased, while the ash and water-soluble carbohydrates contents increased with increasing sulfuric acid during pretreatment. The air-dry process had a negative effect on ethanol production. The ambienttemperature sulfuric acid pretreatment and washing greatly improved ethanol production from alfalfa stems. We theorize that sulfuric acid at ambient temperature partially degraded hemicellulose and ash, and altered cell wall structure during long-term ensiling, and washing removed soluble ash in substrates that could inhibit the simultaneous saccharification and fermentation.
Acknowledgements
This material is based upon work support by the National Institute of Food and Agriculture, United States Department of Agriculture, under ID number WIS01664. The authors are also grateful to the Wisconsin Energy Institute at the University of Wisconsin- Madison, for financial support of this work. Additionally, the authors want to thank Mary Becker of USDA-ARS, U.S. Dairy Forage Research Center (Madison,WI) for silage analysis, and Nathan Felix of the Department of Biological System Engineering of University of Wisconsin at Madison for his assistance.