Environmental sustainability of emerging algal biofuels: A comparative life cycle evaluation of algal biodiesel and renewable diesel

Abstract

Holistic evaluation via a life cycle based approach is critical for guiding the environmentally conscious development of emerging microalgal biofuel pathways. This study models the energy return on investment (EROI) and life cycle greenhouse gas (GHG) emissions for producing algal derived biodiesel and renewable diesel under different production pathways—consisting of a combination of algal cultivation, harvesting, extraction, and coproduct utilization scenarios. The results indicate that in the base‐case scenario(s) the EROI for microalgae fuels range from 0.26 to 1.20 with GHG emissions ranging from 50 to 240 gCO2 equivalent/MJ‐fuel depending on the choice of cultivation variables, coproduct utilization options, and processing technologies. In the improved scenario(s), algal fuels have an EROI ranging from 0.81 to 2.01 and GHG emissions ranging from 30 to 90 gCO2 eq./MJ‐fuel. Furthermore, improved scenarios with favorable EROI and GHG emissions profile for microalgal biofuels are plagued with high technological uncertainty. This suggests that broad advances in algal technologies are required if algal fuels are to be competitive with other leading second generation and advanced biofuels. The choice of fuel conversion technology was found to have a comparatively small impact on overall life‐cycle energy use and GHG emissions. Therefore, the choice of fuel product may be based on other criteria such as fuel storage stability and compatibility with transportation fuel infrastructure. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 926–936, 2013