Fermentation of Lignocellulosic Biomass

Fermentation is a biological process in which enzymes produced by microorganisms catalyze chemical reactions. An enormous variety of bacteria, yeasts, and fungi exist to ferment these sugars. These microorganisms digest sugars to produce the energy and chemicals they need for survival while giving off byproducts such as carbon dioxide, organic acids, hydrogen, ethanol, and other products. Producing commercial products through fermentation of lignocellulosic material is a multi-step process involving pre-treatment and hydrolysis of the material with acid to release fermentable simple sugars, fermentation of these sugars by living organisms to produce hydrocarbons, recovery from the fermentation broth of the desired products, and utilization of the byproducts (Van Hoek et al. 2003).

Biorefineries are examining a wide variety of bacteria, yeasts, and fungi because they are capable of producing dozens of chemicals with significant market potential (Energetics 2003). In addition to ethanol, fermentation is already producing commercial levels of therapeutic and research enzymes, antibiotics, and many more intermediate and specialty chemicals to produce even more industrial and consumer products. The byproducts of lignocellulosic fermentation are nearly as valuable as the target products. Residual cellulose and lignin serve as boiler fuel for electricity or steam production and gases such as carbon dioxide are often captured for sale to the beverage industry. Some recovery methods generate large volumes of solid materials such as gypsum that is used as a soil amendment. Very promising research has shown that ethanol production, by means of lignocellulosic fermentation, has an energy output to input ratio of 2.6 to 1 with respect to short rotation woody crops (Lorenz and Morris 1995).

Large-scale fermentation of ethanol from lignocellulose has been possible for decades but has only proven to be commercially attractive during times of shortage, such as wartime. Intense research is being conducted in two critical needs areas: the need to develop cost-efficient processes for hydrolyzing fermentable sugars from cellulose and the need for robust microorganisms to ferment non-glucose sugars from hemicellulose (Gantz 2003, Kerr 2004, LaPlaza and Jeffries 2004).

Iogen operates a demonstration facility in Ontario, Canada that is proposing a US$250 million plant that can handle all functions involved in lignocellulosic fermentation from a variety of biomass feedstocks.