Researchers Delve into Enzyme Costs

It is commonly assumed lower in literature
By Holly Jessen | April 11, 2012

In order to decrease enzyme or cellulase costs for lignocellulosic biofuel, such as wood-to-ethanol production, two important factors need to be considered, according to a paper published in the April edition of Biotechnology and Bioengineering. “The cost of cellulases is not clear in the literature and should be more widely available,” Daniel Klein-Marcuschamer, one of four researcher authors tells EPM. “In addition, research must be done to either lower the enzyme loading, or increase the yield of ethanol at the biorefinery.”

Klein-Marcuschamer, the director of technoeconomic analysis at the Joint Bioenergy Institute, joined researchers from Lawrence Berkeley National Laboratory, Sandia National Laboratories and the University of California-Berkeley, in publishing “The Challenge of Enzyme Cost in the Production of Lignocellulosic Biofuels.” The cost contribution of enzymes is a subject of debate, with some calling it a “major barrier” and others assuming the cost of enzymes will decrease with technological advances. For this paper, researchers said “the vast majority of the literature to date has significantly underestimated the contribution of enzyme costs to biofuel production.” They concluded that significant effort must be put forth to lower the cost of enzymes, and therefore, the total cost of biofuel production.

The paper examined steam-exploded poplar as a feedstock for cellulase production. “Steam explosion is a pretreatment process in which the biomass is put in contact with high-pressure steam, and when the pressure is released, the lignocellulosic components are rendered labile to attack by the cellulases that the fungus [such as Trichoderma reesi] produces.” Klein-Marcuschamer says. “As the fungus ‘eats’ the poplar, it produces an excess of cellulases that can be harvested for selling.”

After calculating the cost per kilogram of enzyme production, the researchers conceptualized the cost per gallon contribution of enzymes for a corn stover-to-ethanol process. With typical enzyme loading of filter paper unit per gram (FPU/g) of cellulose the researchers calculated a cost range of 68 cents to $1.47 per gallon of ethanol produced. If, on the other hand, enzyme loading was reduced to 5 FPU/g cellulose, the range was calculated at 34 cents to 73 cents per gallon of ethanol. Other studies pegged enzyme costs as low as 10 cents per gallon of ethanol produced to 40 cents per gallon.  —Holly Jessen