Simultaneous preservation and pretreatment of perennial grasses for fuel ethanol production

Agricultural residues and herbaceous perennials will be important biomass feedstocks as the world moves toward renewable energy production. The logistics of harvesting, storing, and transporting the immense quantities of biomass needed is a great challenge. Most of the research on and economic analysis of biomass conversion assumes the feedstocks will be harvested and stored dry. However, wet storage methods have recently been proposed for feedstock preservation and on-farm storage because of harvest, transportation and storage advantages over a dry system. Wet storage systems may also present a unique opportunity to add value to the feedstock through chemical or biological pretreatment. In-storage pretreatments at ambient temperature and pressure but with prolonged reaction times may lower total pretreatment costs and provide better return for producers.;This research investigates the ability of on-farm pretreatments using dilute acid or alkali to improve enzymatic degradability of cellulose and hemicelluloses in biomass at the biorefinery. To this end, switchgrass ( Panicum virgatum L.) and reed canarygrass (Phalaris arundinacea L.) were pretreated under ambient conditions with sulfuric acid and calcium hydroxide at laboratory, pilot and farm scale. Pretreated and untreated samples were fermented to ethanol by Saccharomyces cerevisiae D5A in the presence of a commercially available cellulase (Celluclast 1.5L) and beta-glucosidase (Novozyme 188). Xylose yields were also measured following fermentation because xylose is not metabolized by S. cerevisiae .;After acid pretreatment and anaerobic storage, conversion of cell wall glucose to ethanol ranged from 22 to 83% of total cellulose for reed canarygrass and from 16 to 46% for switchgrass. Storage duration had a positive effect on conversion, but that effect was mitigated with increased chemical loadings. Glucose conversion after calcium hydroxide pretreatment and anaerobic storage ranged from 21 to 55% and 18 to 54% for reed canarygrass and switchgrass, respectively. Although significant levels of acetate and lactate were observed in the biomass after storage, activity of S. cerevisiae was not found to be inhibited at a 10% solids loading.;Chemical costs for biomass pretreatment applied at a rate of 50 g(kg DM)-1 were estimated to be as low as...