Full-scale On-farm Pretreatment of Perennial Grasses with Dilute Acid for Fuel Ethanol Production
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Full-scale On-farm Pretreatment of Perennial Grasses with Dilute Acid for Fuel Ethanol Production Matthew Francis Digman & Kevin J. Shinners & Richard E. Muck & Bruce S. Dien
Published online: 27 April 2010 # US Government 2010
Abstract Biorefineries that rely on lignocellulosic feedstocks require dependable and safe methods for storing biomass. Storing biomass wet in the presence of sulfuric acid and the absence of oxygen has been shown to preserve carbohydrates and enhance cellulose conversion but has not been demonstrated at farm-scale. To that end, switchgrass (Panicum virgatum L.) and reed canarygrass (Phalaris arundinacea L.) were pretreated with 18N sulfuric acid with two methods: during bagging (on-line) and thoroughly mixed in a commercial feed mixer (mixed) and both stored for 90 days. The two methods, applied at rates from 28 to 54 g(kg DM)−1 not only helped to preserve biomass substrates under on-farm conditions (anaerobic, ambient temperature and pressure) through inhibition of microbial activity but also enhanced conversion of cellulose to ethanol by simultaneous saccharification and fermentation (SSF) using Saccharomyces cerevisiae. Acid-pretreated substrate yielded 19 and 7 percentage points higher ethanol
M. F. Digman : R. E. Muck US Dairy Forage Research Center, United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Madison, WI 53706, USA M. F. Digman (*) : K. J. Shinners Department of Biological Systems Engineering, University of Wisconsin-Madison, 460 Henry Mall, Madison, WI 53706, USA e-mail: [email protected] B. S. Dien National Center for Agricultural Utilization Research, United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Peoria, IL 61604, USA
conversion efficiencies than fresh reed canarygrass and switchgrass, respectively. The on-line method of pretreatment out-yielded the mixed method both as a preservative and as an agent for enhanced cell wall degradation. This result was thought to be an outcome of more uniform acid application as indicated by the on-line method’s more consistent pH profile and decreased fermentation products, as compared to the mixed method. Although significant levels of acetate and lactate were present in the biomass following storage, concentrations were not sufficient to inhibit S. cerevisiae in SSFs with a 10% solids loading. Keywords Pretreatment . Biomass storage . Energy crop . Perennial grass . Switchgrass . Reed canarygrass . Ethanol
Introduction There is considerable interest in developing agricultural residues and herbaceous perennials as feedstocks for ethanol production. The logistics of harvesting, storing, and transporting the immense quantities of biomass needed to supply cost-competitive biorefineries is a great challenge [1]. Most research on biomass conversion assumes the crops will be harvested and stored dry. Such dry harvesting and packaging requires many operations that do not add value to the biomass when considering most conversion processes use wet biomass. These dry harvesting ope
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