Improved, High-Moisture Ensiled Crop Feedstocks for Cellulosic Ethanol

As grain ethanol production capacity becomes constrained by the available supply of corn grain, production of ethanol from lignocellulosic biomass is widely seen as necessary to meet the surging demand for fuel ethanol. However, the high cost of biomass pretreatment and enzymatic hydrolysis make cellulosic ethanol too expensive. This project will develop technology to improve the quality of ensiled biomass, thus reducing both downstream pretreatment and hydrolysis costs. The approach builds on past research in which ensiled biomass was inoculated with cellulases and other enzymes to increase saccharification (sugar content) and digestibility, thereby improving feed quality for livestock. Analogously, energy crops will be engineered to express such enzymes in plant tissues, with the enzymes activated during ensilement. In Phase I, two crops, switchgrass and corn stover, were bioengineered to produce a cellulase in their leaves and stems. Ensilement increased the level of fermentable sugars in each crop relative to unensiled control crops. In Phase II, three crops ¿ corn, switchgrass, and sorghum ¿ will be bioengineered to produce cellulases in leaves and stems, then grown, harvested, and ensiled. The ensiled crops then will be tested for saccharification levels, improvements in ethanol yield, and reductions in processing cost relative to the control crops. Following Phase II, the technology will be applied to a DOE-supported, pilot-scale cellulosic-ethanol biorefinery in St. Joseph, MO. Commercial Applications and other Benefits by the awardee: By ensiling crops that produce enzymes, the downstream processing costs of cellulosic ethanol can be reduced. Pricing models have indicated that even slight increases in the levels of fermentable sugars can substantially reduce overall production costs. The new technology will create value-added revenue opportunities for agricultural producers and ethanol cooperatives, and reduce fuel costs for consumers.