Analysis of greenhouse gas emissions from microalgae-based biofuels

Energy supply for transportation causes a major part of the anthropogenic greenhouse gas (GHG) emissions responsible for climate change. Therefore, several governments have introduced measures to promote biofuels based on agricultural feedstock in order to decrease greenhouse gas emissions and to reduce the import dependency of fossil fuel energy. However, due to the land requirement for the cultivation of agricultural feedstock and the conflict between the use of biomass for food and fuel, the generation of biofuel from microalgae as a promising alternative is discussed more and more. Against this background, the goal of this paper is to estimate the GHG emissions for the provision and use of biodiesel, bioethanol and biomethane from microalgal feedstock. These biofuels have the possibility to reduce the pressure on agricultural land because of the higher area-specific biomass yields. Nevertheless, the energy demand needed for the provision of biofuels from microalgae according to the concepts investigated here is responsible for no significant reduction in greenhouse gas emissions compared with fossil fuels or even for a high increase in emissions. From the investigated options, the cultivation in open ponds seems to be more promising than the cultivation in photo-bioreactors, and the provision of biodiesel and biomethane from microalgae shows advantages over the ethanol generation from a greenhouse-gas-reduction point of view.