The US Department of Energy (DOE) and US Department of Agriculture (USDA) have published the results of the Biodiesel Lifecycle Inventory Study. This compared findings for a comprehensive “cradle to grave” inventory of materials used, energy resources consumed and air, water and solid waste emissions generated by petroleum diesel fuels and biodiesel in order to compare the total “lifecycle” costs and benefits of each of the fuels. This 3.5-year study followed US Environmental Protection Agency (EPA) and private industry approved protocols for conducting such research.

The study was designed to provide policy-makers with comparative information that they could use to formulate appropriate policies regarding biodiesel.

The major findings of the study are:

The total energy efficiency ratio (ie total fuel energy/total energy used in production, manufacture, transportation and distribution), the report notes, shows: “Biodiesel and petroleum diesel have very similar energy efficiencies.”

The total fossil energy efficiency ratio (ie total fuel energy/total fossil energy used in production, manufacture, transportation and distribution) for diesel fuel and biodiesel shows that biodiesel is four times as efficient as diesel fuel in utilising fossil energy – 3.215 per cent for biodiesel vs 0.8337 for diesel. The study notes: “In terms of effective use of fossil energy resources, biodiesel yields around 3.2 units of fuel product for every unit of fossil energy consumed in the lifecycle. By contrast, petroleum diesel’s life cycle yields only 0.83 units of fuel product per unit of fossil energy consumed. Such measures confirm the “renewable” nature of biodiesel. ‘The report also notes: “On the basis of fossil energy inputs, biodiesel enhances the effective utilisation of this finite energy source.”

The overall lifecycle emissions of carbon dioxide (a major greenhouse gas) from biodiesel are 78 per cent lower than the overall carbon dioxide emissions from petroleum diesel. “The reduction is a direct result of carbon recycling in soybean plants,” notes the study.

The overall lifecycle emissions of carbon monoxide (a poisonous gas and a contributing factor in the localized formation of smog and ozone) from biodiesel are 35 per cent lower than overall carbon monoxide emissions from diesel. Biodiesel also reduces bus exhaust-pipe emissions of carbon monoxide by 46 per cent. The study observes: “Biodiesel could, therefore, be an effective tool for mitigating CO.”

The overall lifecycle emissions of particulate matter (recognised as a contributing factor in respiratory disease) from biodiesel are 32 per cent lower than overall particulate matter emissions from diesel. Bus exhaust-pipe emissions of PM10 are 68 per cent lower for biodiesel compared to petroleum diesel. The study notes: “PM10 emitted from mobile sources is a major EPA target because of its role in respiratory disease. Urban areas represent the greatest risk in terms of numbers of people exposed and level of PM10 present. Use of biodiesel in urban buses is potentially a viable option for controlling both life cycle emissions of total particulate matter and exhaust-pipe emission of PM10.”

The study also finds that biodiesel reduces the total amount of particulate matter soot in bus exhaust-pipe exhaust by 83.6 per cent. Soot is the heavy black smoke portion of the exhaust that is essentially 100 per cent carbon that forms as a result of pyroysis reactions during fuel combustion. The study notes there is research confirming the relationship between exposure to diesel soot and cancerous growths. Beyond the potential public health benefit from substantially reduced soot emissions, the study also notes: “There is an aesthetic benefit associated with significantly less visible smoke observed from the exhaust-pipe. For urban bus operators, this translates into improved public relations’.

The overall lifecycle emissions of sulphur oxides (major components of acid rain) from biodiesel are 8 per cent lower than overall sulphur oxides emissions from diesel. Biodiesel completely eliminates emissions of sulphur oxides from bus exhaust-pipe emissions. The study notes: “Biodiesel can eliminate sulphur oxides emissions because it is sulphur-free.”

The overall lifecycle emissions of methane (one of the most potent greenhouse gases) from biodiesel are almost 3 per cent lower than those from diesel. The study notes: “Though the reductions achieved with biodiesel are small, they could be significant when estimated on the basis of its CO2 equivalent-warming potential.”

The bus exhaust-pipe emissions of hydrocarbons (a contributing factor in the formation of smog and ozone) are 37 per cent lower for biodiesel than diesel. The fact that biodiesel’s hydrocarbon emissions at the exhaust-pipe are lower means that the biodiesel life cycle has beneficial effects on urban pollution.

The overall lifecycle production of wastewater from biodiesel is 79 per cent lower than overall production of wastewater from diesel. The study notes: “Petroleum diesel generates roughly five times as much wastewater flow as biodiesel.”

The overall lifecycle production of hazardous solid wastes from biodiesel is 96 per cent lower than overall production of hazardous solid wastes from diesel.