Total environmental impact is best calculated by doing a full Life Cycle Inventory (LCI [pdf]) on each biodiesel production method, as resource consumption and energy usage can vary drastically. The most in depth LCI of BD versus PD was completed in 1998 in a joint project with the US DOA and the US DOE. The study concluded that total LCI usage for soy based BD compared to PD was 95% less. The comparison was made for BD and PD consumption in the US transportation industry, specifically urban buses.
Resource and energy consumption differ for planting, growing and harvesting different crops. Transportation costs can vary based on where crops are located in relation to the production facilities. Production of oils, in this case crushing the soybeans, varies by crop. Conversion to a standard BD chemistry, like ASTM D-6571, can also vary because plant chemistry can vary. Post production, the impact of BD from different sources would be the same because transportation to the location of end use, and the use itself would be very similar.
Because of strict standards, the chemical and physical properties of the end BD products upon final delivery are nearly identical. ASTM D-6751 requires that “the product[s] shall undergo chemical analysis for flash point, methanol, water and sediment, kinematic viscosity, sulfated ash, oxidation stability, sulfur, copper strip corrosion, cetane number, cloud point, acid number, carbon residue, total and free glycerin, phosphorus, reduce pressure distillation temperature, atmospheric equivalent temperature, combined calcium and magnesium, and combined sodium and magnesium,” and must meet standards at time and place of delivery.
Over the entire life cycle, soy based BD reduces total CO2 emissions by 78.45%, compared to petroleum diesel.2 The use of B100 over PD reduces the total emissions of particulate matter (TPM) 32.4%, carbon monoxide (CO) 34.5% and sulfur oxides (SOx) 8%. Unfortunately, one of the trade offs is that nitrous oxide emissions are increased by 13.35%.2 Total hydrocarbon (THC) emissions are also increased by 35.9% in the total life cycle of soy based BD because hexane is released in production.
Published LCI studies with algae based BD have not been as thorough because study has been focused on production, rather than combustion. Since production methods are not standardized, it is not yet possible to do a full life cycle inventory that represents all algae based BD. However, since algae based BD is essentially CO2 neutral, it saves 22.2 pounds of CO2 per gallon of diesel fuel it displaces.
