Effect of composition and pretreatment processes on hydrolysis yield from grass straws in Pacific Northwest US

In last few decades, due to a huge increase in energy demands, bioethanol has been considered as one of the most promising alternatives to petroleum. Unlike fossil fuels, bioethanol is a renewable energy source, which is produced by fermentation of sugars. Abundance of lignocellulosic feedstocks, which have high amount of cellulose and hemicellulose, makes this alternative more attractive. Grass seed production industry in Pacific Northwest produces about 2 Mt/year of grass straw as a coproduct. In this study, three common grass seed crops, Perennial Ryegrass (Lolium Perenne), Tall Fescue (Festuca arundinacea Schreb) and Bentgrass (Agrostis Sp.) were investigated as feedstocks for ethanol production. The grasses were pretreated at 10% solid loading at 180°C for 15 min. using hot water, dilute acid or dilute alkali. Composition analysis was performed using standard NREL protocols. . Both untreated and pretreated grass straws were enzymatically hydrolyzed at 50°C for 120h. All pretreatments were found effective in increasing enzymatic digestibility of pretreated straws compared to untreated samples. For all experimental conditions investigated, most of the hydrolysis (>80%) was completed in first 48 h and hydrolysis yield was relatively constant after 48h. No single pretreatment gave the maximum hydrolysis yield for all grasses. The efficiency of pretreatment process cannot be explained only on basis of hemicellulose and lignin removed. A better explanation is possible by considering structural changes. Potential maximum ethanol yields were for tall fescue, perennial rye and bent grass were 360, 297 and 276 L/ton of biomass respectively.