Infrastructure Associated Emissions for Renewable Diesel Production from Microalgae

Greenhouse gas (GHG) emissions for microalgae biofuel infrastructure are sometimes neglected during a life-cycle analysis (LCA). Construction materials were found for a baseline facility designed to produce renewable diesel in the United States. Material use was amortized over the material lifetime of thirty years and then, using emission factors available in GREET 2, energy use and GHG emissions were found per MJ of renewable diesel (MJ RD). For the baseline, infrastructure GHG emissions were 8.9gCO₂e/MJ RD. Plastic and concrete had the largest emissions, and the growth ponds used the most materials of any unit operation. Fossil fuels comprised 97% of all energy use, which came predominately from natural gas at 0.090MJ/MJ RD. A sensitivity analysis showed that changes to the pond liner thickness and material lifetime had the largest effects with the lifetime increasing the GHG emissions 28% over the baseline. Increasing the productivity (up to 50g/m²/d) or lipid content (up to 50wt.%) decreased the emissions. Infrastructure emissions were compared to those from the fuel-cycle of a reduced emission scenario, showing that infrastructure related emissions ranged from 17% to 57% of the fuel-cycle emissions, with higher values at lower productivities.