The United States plans to produce 70 billion liters of advanced biofuels by 2020. In 2007, the global production of all biofuels roughly matched this amount, and the US used 24% of its corn to produce its share of the ethanol included in those 70 billion liters. Even given this impressive amount of corn used for ethanol, American corn ethanol only accounted for 1.3% of the US’ national liquid fuel consumption. An increase in either corn harvests or ethanol production efficiency is clearly necessary if the US is to meet the 2020 goal with corn alone. Given the significant drawbacks to producing more corn, and the unlikelihood of efficiency increasing enough to meet requirements, it would be more prudent to invest in second- and third-generation, or advanced, biofuels.
These biofuels, such as ethanol made from cellulose, biogas, or hydrocarbon fuels converted from biomass to liquid (BtL) are made from feedstock rich in cellulose like grass and wood. Advanced biofuels have better environmental profiles than what are referred to as first generation biofuels (e.g. ethanol produced from corn or sugarcane) because they generally require less land and are converted from biomass more efficiently—the processes also use less energy and water than ethanol since they do not involve distillation. A biofuel’s emissions depend largely on land considerations, nativity to the region, and feedstock technology. If land was converted from forest or prairie, the feedstock was not native to the region, and the feedstock required excessive fertilizers to grow, then GHG emissions are higher.
Corn often meets all these criteria, and in addition the nitrogen-rich runoff from cornfields is the largest contributor to hypoxia in the Gulf of Mexico, further reducing corn’s beneficial effects as a feedstock. This is not to say that corn is necessarily always a worse fuel option. With the right land practices (using abandoned or fringe land, for example) corn ethanol gives between 30% and 50% savings of GHG emissions relative to fossil fuels. Growing corn also provides the US with food security, which some advanced biofuels do not, and a massive infrastructure and agribusiness model is already in place for corn production, reducing the investment costs of converting to advanced biofuels.
However, growing more corn is not the most sustainable option, given its high pesticide, fertilizer, and water requirements. Instead of producing more of a certain feedstock, perhaps looking to something with already high yields is more economical and ecological. Consider the steep consumption of meat in the US: some farms host thousands of cows and pigs in relatively small spaces. Livestock dung, which yields methane gas, can have up to 170% reductions in GHG emissions compared to fossil fuels. Biogas provides the service of converting this fecal waste into not only fuel but also compost that can fertilize crops. Given the huge quantities of organic waste available without additional investment, biogas production from animal waste may be a good advanced biofuel alternative to fossil fuels and corn ethanol. Perhaps urban areas can contribute with human waste as well. After all, stationary processing of biomass is more energy efficient than converting biomass to a liquid fuel (as with ethanol), so producing biogas for city use may save more CO2 at lower costs. Further research will be needed to determine whether harnessing the current waste production will be enough to satisfy the US goal of 70 billion liters by 2020. In my next post I’ll look at the biofuels of Brazil.
Howarth, R.W., S. Bringezu, M. Bekunda, C. de Fraiture, L. Maene, L. Martinelli, O. Sala. 2009. Rapid assessment on biofuels and environment: overview and key findings. Pages 1-13 in R.W. Howarth and S. Bringezu (eds), Biofuels: Environmental Consequences and Interactions with Changing Land Use. Proceedings of the Scientific Committee on Problems of the Environment (SCOPE) International Biofuels Project Rapid Assessment, 22-25 September 2008, Gummersbach Germany. Cornell University, Ithaca NY, USA.
Bringezu, S., H. Shultz, M. O’Brien, L. Kauppi, R. W. Howarth. 2009. Towards sustainable production and use of resources: assessing biofuels. Report to the United Nations Environment Programme. 36 pp. Paris, France.