Energy production from microalgae biomass: carbon footprint and energy balance

Bioenergy sources are promising alternatives for sustainable energy production. Nevertheless, significant research and detailed analysis are necessary to identify the circumstances under which such energy sources can contribute to sustainability. This paper reviews the literature of Life Cycle Assessment (LCA) of microalgae-to-energy technologies and focuses in two categories, Greenhouse Gas (GHG) emissions and Net Energy Ratios (NER). The analysis is illustrated with a case study of microalgae biomass combustion to produce heat and compares the influence of different electricity sources with respect to GHG emissions and NER along the supply chain. Selected fossil energy sources were used as reference conditions. The methodology was LCA based on ISO 14044 standard, and most of the data used were extracted from a review of relevant scientific publications. Heat production from microalgae showed higher GHG emissions than those from fossil fuels with United States' electricity grid, but lower than those with the Brazilian one. The NER of heat from microalgae combustion life cycle is still disadvantageous compared to most of fossil options. However, the observation that fossil fuel options performed slightly better than microalgae combustion, in the two categories analyzed, must be understood in the context of a mature fossil energy technology chain. The fossil technology has less potential for improvements, while microalgae technology is beginning and has significant potential for additional innovations. (C) 2014 Elsevier Ltd. All rights reserved.