Pure Pedantry

A study in the newest PNAS seeks to quantify the efficiency and resource utilization for various types of biofuels:

The first comprehensive analysis of the full life cycles of soybean biodiesel and corn grain ethanol shows that biodiesel has much less of an impact on the environment and a much higher net energy benefit than corn ethanol, but that neither can do much to meet U.S. energy demand.

The study will be published in the July 11 Proceedings of the National Academy of Sciences.

The researchers tracked all the energy used for growing corn and soybeans and converting the crops into biofuels. They also looked at how much fertilizer and pesticide corn and soybeans required and how much greenhouse gases and nitrogen, phosphorus, and pesticide pollutants each released into the environment.

“Quantifying the benefits and costs of biofuels throughout their life cycles allows us not only to make sound choices today but also to identify better biofuels for the future,” said Jason Hill, a postdoctoral researcher in the department of ecology, evolution, and behavior and the department of applied economics and lead author of the study.

The study showed that both corn grain ethanol and soybean biodiesel produce more energy than is needed to grow the crops and convert them into biofuels. This finding refutes other studies claiming that these biofuels require more energy to produce than they provide. The amount of energy each returns differs greatly, however. Soybean biodiesel returns 93 percent more energy than is used to produce it, while corn grain ethanol currently provides only 25 percent more energy.

Still, the researchers caution that neither biofuel can come close to meeting the growing demand for alternatives to petroleum. Dedicating all current U.S. corn and soybean production to biofuels would meet only 12 percent of gasoline demand and 6 percent of diesel demand. Meanwhile, global population growth and increasingly affluent societies will increase demand for corn and soybeans for food.

The authors showed that the environmental impacts of the two biofuels also differ. Soybean biodiesel produces 41 percent less greenhouse gas emissions than diesel fuel whereas corn grain ethanol produces 12 percent less greenhouse gas emissions than gasoline. Soybeans have another environmental advantage over corn because they require much less nitrogen fertilizer and pesticides, which get into groundwater, streams, rivers and oceans. These agricultural chemicals pollute drinking water, and nitrogen decreases biodiversity in global ecosystems. Nitrogen fertilizer, mainly from corn, causes the ‘dead zone’ in the Gulf of Mexico.

This study agrees with what I was saying before: that biofuels are definitely part of the solution but we need to be smart about it. 1) We need to be selective about how we produce them. It looks like soybeans are a must better deal than corn. 2) No one alternative fuel is the complete answer. No one can pretend that biofuels will meet all our energy needs.