3-11: Integrating dry matter losses and direct gas emissions during biomass storage into life cycle inventory models of switchgrass and Miscanthus based ethanol production

Accurate estimates of greenhouse gas emissions from biofuel production are necessary to ensure the economic and environmental sustainability of the biofuels industry and to meet government mandates for low-carbon fuel production.  Biomass storage represents a critical gap in many biofuel life cycle assessment (LCA) methodologies, and may have a large impact on production and transportation logistics for biofuel feedstocks, in addition to greenhouse gas emissions.  In this study, 143 laboratory-scale bales made from switchgrass and Miscanthus grown at Purdue University were stored in insulated boxes.  Initial moisture content and bulk density were varied among the bales (11.8 – 34.2% w.b., and 103 – 308 kg/m3, respectively) and dry matter loss was tracked for each treatment combination over three months of storage.  22 additional laboratory-scale switchgrass bales at 9.9%, 14.1%, and 18.6% moisture (w.b.) were stored at 4°C, 23°C, and 40°C under controlled aeration to monitor the direct emissions of the greenhouse gasses CO₂, CH₄, and N₂O during storage.  Relationships between biomass moisture and rates of dry matter loss, and between moisture, temperature, and direct greenhouse gas emissions, were used to model the potential impacts of biomass storage on biomass supply logistics and net global warming potential of ethanol from switchgrass and Miscanthus at the biorefinery scale.