Life cycle assessment on microalgal biodiesel production using a hybrid cultivation system

• Life cycle assessment was performed on a putative algal biodiesel production plant.
• Hybrid cultivation system couples airlift tubular bioreactors with raceway ponds.
• Environmental impact of algal biodiesel was considerably lower than fossil diesel.
• Algal cultivation and drying of wet biomass were the two largest energy input.
• Sustainability of algal biodiesel depends on efficient utilization of co-products.

A life cycle assessment (LCA) was performed on a putative biodiesel production plant in which the freshwater alga Chlorella vulgaris, was grown using an existing system similar to a published commercial-scale hybrid cultivation. The hybrid system couples airlift tubular photobioreactors with raceway ponds in a two-stage process for high biomass growth and lipid accumulation. The results show that microalgal biodiesel production would have a significantly lower environmental impact than fossil-derived diesel. Based on the functional unit of 1 ton of biodiesel produced, the hybrid cultivation system and hypothetical downstream process (base case) would have 42% and 38% savings in global warming potential (GWP) and fossil-energy requirements (FER) when compared to fossil-derived diesel, respectively. Sensitivity analysis was performed to identify the most influential process parameters on the LCA results. The maximum reduction in GWP and FER was observed under mixotrophic growth conditions with savings of 76% and 75% when compared to conventional diesel, respectively.