Second-Generation Biofuel Production from Corn-Ethanol Industry Residues

Abstract

Net ethanol production per unit mass of corn kernel can be significantly improved by utilizing fibrous co-products to produce cellulosic ethanol. Corn fiber is a good cellulosic feedstock to produce second-generation biofuel. A biorefinery concept is introduced to convert fibrous residue, corn fiber, into fermentable sugars at a lower temperature with minimal use of chemicals. Laboratory-scale consolidated fermentation system comprised of on-site fungal enzyme production system and simultaneous saccharification and fermentation (SSF) yielded 7.1, 8.6 and 4.1 g ethanol per 100 g corn fiber when saccharified with the white-, brown-, and soft-rot fungi, respectively. The highest corn-to-ethanol yield (8.6 g ethanol/100 g corn fiber) was equivalent to 42% of the theoretical ethanol yield from starch and cellulose in corn fiber. This is equivalent to 120 l of ethanol per metric ton of corn fiber. With process optimization, conversion of over 70% of corn fiber carbohydrate content into ethanol can generate as much as 13x109 l of ethanol per year, which is equivalent to 25% of the current annual ethanol production (52x109 l) in the US, additional $8.65 billion annual revenue and reduction in corn acreage by 3 mha. It is also possible to convert the carbohydrates to a fuel oil using a secondary oleaginous fungal process. The residual fiber enriched with fungal protein can still be utilized as animal feed without unbalancing the feed market/supply.