Carbon footprint analyses of microalgae cultivation systems under autotrophic and heterotrophic conditions

Among different biofuel feedstocks, algal biodiesel is seen as a promising feedstock. Different research papers have assessed the sustainability of algal biofuel production, but it is always difficult to have a better sense of the results since comparing them with all the differences in data sources, life cycle assumptions, functional units and environmental metrics measured is difficult. The present study develops a comparative life cycle assessment of algal biofuel production under autotrophic and heterotrophic conditions with different inputs. SimaPro 8 was used considering five different scenarios for microalgae cultivation to compare environmental impacts, energy demand and damage analysis associated with water scarcity methodology. Open ponds with three different assumptions of using fresh water, recycled water and waste water, and photobioreactor and heterotrophic technologies are considered. Results were analyzed per energy basis—the functional unit of 1 MJ of energy produced. Results of total GHG emissions show that algae cultivated in pond with wastewater and heterotrophic culture are competitive with tradition fossil fuels. Also the use of algae as the source of energy might increase the energy demand, whereas it does not have adverse impact on the environment, health and climate. The results of the water scarcity indicator show the competiveness of algae oil. This study presents an overview of environmental impacts throughout the full life cycle of a product through different pathways in cultivation stage which demonstrates the importance of decision-making process for further investment.