Geographical assessment of open pond algal productivity and evaporation losses across the United States

This study presents a geographical and temporal assessment of the evaporation losses for commercial-scale production of algae biomass through a dynamic integrated thermal and biological modeling framework. Evaporation losses were calculated through a validated dynamic thermal model which predicts temperature with an accuracy of −0.96 ± 2.72 °C and evaporation rates with a 1.46 ± 5.92% annual accuracy. The biological model was validated with experimental data representing the current state of technology and shows an average error of −4.59 ± 8.13%. The integrated thermal growth model was then utilized to simulate the evaporation losses for biomass production of a 400-hectare algae farm at 198 different locations across the United States over a period of 21 years. This foundation is integrated with life cycle methodology to determine the blue water footprint of algal biomass, proteins, and biofuels. Results show the water consumption of cultivation can be reduced through cultivation in the Gulf Coast region compared to other US locations, where the average blue water footprints of the three simulated pathways were determined to be 155 m3 water tonne−1 biomass, 371 m3 water tonne−1 algal proteins, and 11 m3 GJ−1 biofuel. The blue water footprints of algal biomass were found to be comparable to those of wheat, sorghum, and corn. In terms of proteins, algal proteins are the least water-intensive being two times more water-efficient than proteins from soybeans. When compared to petroleum-based fuels, results emphasize the need for more water-efficient strategies to reduce the blue water footprint of algal biofuel production. This work also incorporates a novel temperature tolerance assessment to identify the geographically specific temperature limits for algal strains in a commercial-scale facility. Results highlight the importance of high temporal and spatial resolution when modeling culture temperature, evaporative loss, and algae growth rate.