(266c) Geographically Specific Life Cycle Assessment of Biofuels from Wastewater Microalgae
Geographically specific variables can significantly influence the sustainability of algal biofuels. Recently published geographic analyses have shown how climatic variables and resource collocation demands can affect potential algal biofuel feedstock production, but they do not compare the life cycle environmental impacts of production between regions within their area of study. To meet this research need and to more accurately reflect the spatially heterogeneity of environmental impacts, life cycle assessments (LCAs) of algal biofuels should incorporate geographic factors that influence land use change impacts, algal productivity, and transportation needs.
An LCA for a functional unit of 1 GJ of bio-jet fuel produced through hydrothermal liquefaction of microalgae grown in wastewater effluent is performed for each Level II ecoregion in the continental United States. The biofuel production steps analyzed are algal cultivation at a municipal WWTP, algal harvesting by gravity sedimentation, algal dewatering by centrifuge, hydrothermal liquefaction, transportation of algal biocrude to a refinery, upgrading to bio-jet fuel, transportation of the fuel to an airport, and combustion in a jet engine. In addition to these fuel production steps, the life cycle greenhouse gas emissions of land use change impacts are included in this analysis. The climate change impacts of land use change include the impacts of changing the surface albedo of an area; changing the carbon flux between vegetation, soils, and the atmosphere; and removing the original carbon stored over an area. Models for these land use change components and an algal growth model with site-specific GIS variables are used to determine the LCA input parameter ranges aggregated by ecoregion. The site-specific parameters are defined over land that is less than 2% sloped and that is categorized as barren land, developed open space, grassland, shrubland, or pasture land within a 5-km radius from the center of municipal WWTPs within each ecoregion. This methodology which incorporates land use change impacts and geographic factors produces more applicable LCA results to guide future siting decisions for algal biofuel feedstock production.