Integrated Cost and Environmental Life Cycle Analysis of Biomass Supply Systems for Biofuels and Bioenergy

Abstract

The production of six regionally important cellulosic biomass feedstocks, including pine, eucalyptus, unmanaged hardwoods, forest residues, switchgrass, and sweet sorghum, was analyzed using consistent life cycle methodologies and system boundaries to identify feedstocks with the lowest cost and environmental impacts. Supply chain analysis models were created for each feedstock calculating costs and supply chain requirements for the production 453,592 dry tonnes of biomass per year. Cradle-to-gate environmental impacts from these supply systems were quantified for nine mid-point indicators using SimaPro 7.2 LCA software. Conversion of grassland to managed forest for bioenergy resulted in large reductions in GHG emissions, due to carbon sequestration associated with direct land use change. However, converting forests to energy cropland resulted in large increases in GHG emissions. Production of forest-based feedstocks for biofuels resulted in lower delivered cost, lower greenhouse gas (GHG) emissions and lower overall environmental impacts than the studied agricultural feedstocks. Forest residues had the lowest environmental impact and delivered cost per dry tonne. Using forest-based biomass feedstocks instead of agricultural feedstocks would result in lower cradle-to-gate environmental impacts and delivered biomass costs for biofuel production in the southern U.S. Introduction. Production of cellulosic biofuels and other bio-based products are expected to increase national energy independence, improve rural economies, and reduce greenhouse gases (GHG) compared to conventional transportation fuels (Demirbas 2008). To ensure greenhouse gas (GHG) emission reductions and a sustainable bioenergy industry, the Energy Independence and Security Act (EISA) established the life cycle greenhouse gas (GHG) thresholds (percent reduction) compared to the 2005 base line, with reductions of 20% for renewable fuels, 50% for advance fuels, 50% for biomass-based fuels and 60% for cellulosic biofuels (EPA 2012). The feedstock type used for biofuels conversion can play a central role in determining the overall GHG emissions as well as the financial and technological feasibility of a renewable biofuel. This study evaluated six potential biomass supply system scenarios for renewable energy production (liquid and/or solid fuels) in the southern U.S. Supply chain logistics, delivered cost and environmental burdens of these biomass feedstocks were qualified and quantified from cradle-to-gate. Feedstocks analyzed included loblolly pine, eucalyptus, unmanaged hardwood, forest residues, switchgrass and sweet sorghum. Previous studies have revealed feedstock production and delivery as the single largest contributor to the financial feasibility of bioenergy Proceedings of the International Symposium on Sustainable Systems and Technologies (ISSN 2329-9169) is published annually by the Sustainable Conoscente Network. Melissa Bilec and Jun-ki Choi, co-editors. ISSSTNetwork@gmail.com. Copyright © 2013 by Jesse S. Daystar, Carter W. Reeb, Ronalds Gonzalez, Richard A. Venditti. Licensed under