Life Cycle Assessments of Algal Biofuels: Influence of Alternative Uses of Lipid-Extracted Algae

Algae-based biofuels have received considerable interest due to the potential for large volumes of biofuel production using relatively small amounts of idle or retired agricultural lands. When algae oil is extracted for fuel production, the lipid-extracted algae (LEA) generated as a co-product of algae biofuel has considerable value as a source of heat, power, and nutrients if re-used on site after anaerobic digestion. However, LEA is also feasible to be exported to substitute for the use of animal feed. Our recent work within the National Alliance for Advanced Biofuels and Bioproducts (NAABB) research consortium has focused on conducting environmental life-cycle assessment (LCA) studies to investigate key potential scenarios concerning algal biofuels development. Here, we present LCA study results on the environmental impacts of algae biofuel when evaluating several potential uses for LEA as animal feeds, and compared with the base case which uses this LEA on site as a source of nutrients and energy. The baseline approach was to assume that LEA could to be used as a 1:1 (mass basis) replacement for soybean meal, rapeseed meal, fish meal, or trout feed. All algae cultivation nutrients lost in LEA export were replaced with chemical fertilizers; electricity and heat previously generated on-site were replaced with US grid electricity and with natural gas heat. Important trade-offs were assessed in terms of Greenhouse Gas (GHG) emissions for algae renewable diesel with LEA displacement credits for certain feed ingredients. Results indicates that the benefit from displacing animal feed does not outweigh the burdens associated with replacing the requirements that LEA currently satisfies and therefore results in a worse GHG emissions profile for algae fuels life cycle.