Lignocellulosic ethanol can provide an environmentally-friendly alternative to petroleum-based fuels. By utilizing locally-produced feedstocks as carbon sources for transportation fuel, ethanol can substantially alter the energy profile of transportation fuels, reducing geopolitical implications and dependence on foreign energy supplies. Obtaining fermentable sugars in a cost-effective fashion is the central barrier to realizing the commercial potential of lignocellulosic ethanol. The costs associated with hydrolysate conditioning, nutrients, and enzymes, which were projected at 45% of the total processing cost, must be reduced to improve the overall economics.

Feedstock pretreatment has pervasive impacts on downstream processes, particularly on fermentation. On a comparable basis, Ammonia Fiber Expansion (AFEX)-pretreated biomass is significantly more fermentable than that from dilute acid pretreatment. This study confirmed that fermentation of AFEX-pretreated corn stover using Saccharomyces cerevisiae eliminated the requirement for washing of pretreated biomass, detoxification and nutrient supplementation. Overall ethanol yield at 191 g/kg (64 gal/ton) corn stover was achieved at a final titer of 40 g/L. Fermentations were completed within 72 hr in a high-cell-density fermentation. Fermentations can be conducted with similar effectiveness with the recycled cells, for at least another three generations without the addition of fresh cells.

The proposed integrated cellulosic ethanol production utilizes AFEX-pretreated biomass as the exclusive source of carbon, nitrogen and nutrients for ethanol fermentation and cellulase production. The carbon (sugar) source is divided between ethanol and enzyme production at a weight ratio of 4:1. Maximum ethanol yield under this carbon partition scheme is 267 g EtOH/kg CS or 90 gal/ton. About 60% of the extractable nitrogen and nutrients from AFEX-pretreated corn stover is projected to be used for enzyme production. This in-house production would be self-sustained if 12% of the bioavailable nitrogen source was assimilated for saccharolytic enzyme production and to provide optimal set of activities for biomass deconstruction.