Energy consumption during the manufacture of nutrients for algae cultivation

The effect of nutrient production on life cycle analysis (LCA) of energy use and greenhouse gas emissions for algal biofuels can be significant, yet recent algal biofuel LCAs vary significantly in their estimates for contributions from fertilizer production. Given the uncertainty in emissions associated with fertilizer manufacturing and the possibility that they play a significant role in algae LCA, this report examined nitrogen and phosphorus fertilizer production in the U.S. by way of a detailed examination and analysis of published data. We found that the energy use and emissions of algae fertilizers derive from the manufacturing of just a few key reagents, namely ammonia and phosphoric acid. Under the assumption that large-scale algae growth will utilize commodity chemicals, the life cycle inventory centers on a few processes. We report relatively consistent values in the literature for these processes, suggest representative values to use in future LCA work, and discuss proper handling of fossil carbon in urea.