Economic feasibility of microalgae as a source of biodiesel: Techno-economic and sustainability analyses

Microalgae receive rising attention because of their capacity to generate biofuels. Cultured either in ponds or photobioreactors, they have a high growth rate, occupy smaller cultivation land area than other biofuel-generating land crops and use CO2 as a substrate making them promising alternative to fossil fuels. Numerous techno-economic analyses (TEA) have assessed economic viability of the different options for microalgae cultivation, harvesting and conversion. A small meta-study of representative TEA and associated sensitivity analysis led us to identify factors that have the most influence on the outcomes of microalgae biomass use. Biological parameters such as lipid content and growth rate are commonly identified as two critical productivity parameters. Another consensus from several TEA studies is the commercial interest to produce a range of high-value co-products including animal feed and crop fertilizers that may actually compensate high costs of biodiesel production from microalgae. In parallel, recent life cycle analysis (LCA) studies gave us some insights on the inputs and outputs of microalgae-to-biodiesel supply chain that impact on sustainability. They reveal that net energy ratio is not favorable as the production of inorganic nutrients to feed algae and bioreactor consumption in particular require a lot of energy. Greenhouse gas are also generated along the processes of biomass production and lipid extraction, making microalgae-based biofuel production less carbon-neutral than initially thought. Finally, one common favorable parameter identified as critical by TEA and LCA is wastewater, the use of which to grow microalgae can indeed reduce the costs of biodiesel production and further support sustainability. Altogether these data indicate that the economic viability of biofuel production from microalgae remains challenging and requires the implementation of supportive policies from governments and supra-national organizations. Also, while filling the gap left by fossil fuels shortage was the initial trigger of microalgae use to produce biodiesel, their potential to contribute mitigating climate changes is today their greatest asset and warrants further R&D efforts.