Pretreatments and Enzymatic Hydrolysis of Grass Straws for Ethanol Production in the Pacific Northwest U.S.

Abstract

Increasing energy demand and rising petroleum prices necessitate development of alternative energy resources. Bioethanol, an important renewable transportation fuel, has been considered as one of the most promising alternatives to petroleum. The grass seed production industry in the Pacific Northwest produces about 2 Mt per year of grass straw as a coproduct. Various species of grasses, with yields of up to 5 tons per acre and containing up to 35% cellulose, are potential feedstocks for ethanol production. Three common grass seed crops, perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb) and bentgrass (Agrostis sp.), were investigated as feedstocks for ethanol production. Composition analysis was performed using standard NREL laboratory analytical procedures. The grasses were pretreated at 10% solid loading at 180C for 15 min using hot water, dilute acid, or dilute alkali. Scanning electron microscope (SEM) images of untreated and pretreated grasses were used to visually analyze structural changes in the biomass after pretreatment. Both untreated and pretreated grass straw was enzymatically hydrolyzed at 50C for 120 h. All pretreatments were effective in increasing enzymatic digestibility of pretreated straw compared to untreated samples. For all experimental conditions investigated, most of the hydrolysis (>80%) was completed in the first 48 h. No single pretreatment gave the maximum hydrolysis yield for all grasses. Potential maximum ethanol yields for tall fescue, perennial ryegrass, and bentgrass were 360, 297, and 276 L ton-1 of biomass, respectively.