Life cycle assessment of novel technologies for algae harvesting and oil extraction in the renewable diesel pathway

Abstract

There are many challenges and technical barriers to implementation of a viable commercial process to produce algae-based biofuels. Biofuels made from algae must typically go through a complicated series of unit processes for algae cultivation, harvesting, dewatering, oil extraction, conversion, and other logistical steps. The National Alliance for Advanced Biofuels and Bioproducts (NAABB) was developed to produce new technologies to be implemented by the algal biofuel industry in an effort to improve the process economics and environmental benefits associated with algae fuels. This LCA study investigated the environmental impacts associated with four harvesting and two extraction technologies developed by NAABB researchers. Gate-to-gate LCA results show that all novel technologies appear to have the potential to provide at least modest decreases in greenhouse gas (GHG) emissions compared to current default algae process technologies. 14 scenarios of different combinations of harvesting and extraction unit operations were further evaluated in the context of the full life cycle for producing algae-based renewable diesel. Results indicate that selection of a particular technology for a unit operation can have consequences that affect other stages of the full biofuels life cycle, both upstream and downstream from the unit operation in question. Considering material and energy inputs, operation efficiency, impacts on on-site recycled energy, and co-products credits, acoustic harvesting followed by acoustic oil extraction give the best performance on the overall lifecycle, which reduce the GHG emissions by roughly 45% compared to the base case. LCA modeling also demonstrates that co-products produced at various points of the value chain, for use within or outside the algae biofuels system boundary, considerably affect the LCA results beyond harvesting and extraction unit processes.