Life cycle assessment of algal biofuels: Influence of feedstock cultivation systems and conversion platforms

Abstract

Commercial technology is available for producing high quality fuels from algae-derived feedstocks, but questions persist about the environmental implications of producing and processing algae through a range of potential routes. In this study, a life-cycle assessment approach was used to investigate the impacts of combining different algae cultivation techniques (raceway vs. effluent cultivation) and fuel conversion pathways (whole cell pyrolysis vs. oil extraction and hydrotreatment). Material and energy input data for the cradle-to-grave study was compiled from peer-reviewed literature, government reports, and confidential commercial processing studies. Results indicated that a wide range of potential greenhouse gas (GHG) emissions and life cycle fossil energy demand results are possible for different algal fuels produced with various unit operations combinations, highlighting the potential for substantial emissions reductions or increases compared to fossil petroleum fuels. The fuel conversion stage is not a large source of GHG emissions (15–20g CO2eq/MJ fuel), compared to algae cultivation (25–87g CO2eq/MJ) or dewatering (60–150g CO2eq/MJ) unit operations. Results indicate that in cases where a portion of the algae biomass is not available for internal heat and power generation, favorable environmental results can be obtained when algae cultivation operations are used to offset current nutrient management activities, such as biological nutrient removal at a wastewater treatment plant. Current estimates suggest that nutrient sources other than municipal wastewater treatment effluents will have to be explored in order for this style of algae cultivation to produce commercially significant quantities of biofuel.