Second-generation biofuels can reduce emissions, report suggests

Second-generation biofuel crops like the perennial grasses Miscanthus and switchgrass can efficiently meet emission reduction targets without significantly displacing cropland used for food production, according to a new study.

Researchers from the University of Illinois and collaborators published their findings in the inaugural edition of the journal Nature Energy.

The researchers call it the most comprehensive study on the subject to date.

The US Environmental Protection Agency's Renewable Fuel Standard sets an annual production goal of 16 billion gallons of second-generation biofuel—fuels from plant stems and leaves rather than from fruit or grains—and 15bn gallons of ethanol by 2022.

The study found that even though previous emission reduction estimates were overly optimistic, meeting the federal biofuels goal will reduce annual US transportation emissions by 7%.

'Viable path forward to energy security'

"Greenhouse gas savings from bioenergy have come under varying levels of attack, and this paper goes a long way to showing that contrary to what some are saying, these savings can be potentially large if cellulosic biofuels from dedicated energy crops meet a large share of the mandate," said Evan DeLucia, a professor of plant biology at the University of Illinois and the study's author.

He added: "This is a viable path forward to energy security, reducing greenhouse gases and providing a diversified crop portfolio for farmers in the US."

Second-generation biofuels are much cleaner than corn ethanol thanks to a number of biological characteristics, said DeLucia.

In a 2011 study, DeLucia used a model to show what would happen if the land being used to grow corn for ethanol production was instead converted to Miscanthus and switchgrass.

"Our results were staggering," DeLucia said. "Since both of those plants are perennial, you don't till every year, so you release less carbon to the atmosphere. The grasses also require less fertiliser, which is a source of nitrous oxide, and they store more carbon in the ground than corn."

According to DeLucia, switching from using 40% the corn crop for ethanol production to using the same land to grow biofuel grasses "changed the entire agricultural Midwest from a net source of greenhouse gas emissions to the atmosphere, to a net sink."

He called the new research an improvement of those findings because it applies realistic, economic constraints to the model.

The new study assumes farmers won't take their most productive farmland and use it for bioenergy crops, but they may use low-yielding land—for example, low-quality pastures in the West, which already host perennial grasses.