Such a method is still theoretical but once developed it could help address some of the recent backlash against grain-derived biofuels, which are blamed for raising the wholesale price of corn and ultimately boosting the cost of food.

"This decouples the food problem from the transportation problem," said Rakesh Agrawal, a chemical engineer at Purdue and lead author of a study that appeared in the journal the Proceedings of the National Academy of Sciences.

Biofuels are made from biomass, which is basically any plant material -- grains, soybeans, flaxseed, sugar cane -- or any plant-derived material, which could include manure, food leftovers and even human sewage.

In conventional methods of converting biomass to fuel, about two-thirds of the material is lost as carbon dioxide released into the atmosphere.

Agrawal and colleagues propose a system that would recycle that lost carbon dioxide into usable fuel by forcing it to react with hydrogen, which suppresses the formation of carbon dioxide.

The result, he said, would be a completely efficient system that could vastly reduce the amount of materials needed to produce biofuels.

BOOSTING EFFICIENCY

Agrawal cited a recent US Department of Energy study suggesting that using conventional methods, it would take 1.366 billion tons of biomass, or about the current annual supply, to make enough fuel to supply 30 percent of the US transportation system.

Agrawal and colleagues believe that by boosting the efficiency of biofuel production through a hydrogen-carbon system, the United States could use that same amount of biomaterial to supply the entire US transportation system.

"Nations such as the United States can produce enough transportation fuels without worrying about the implications of what is happening to food production," he said in a telephone interview.

By using hydrogen derived from an alternate energy source, such as solar or nuclear energy, the system would actually have a positive environmental effect, he maintained.

Agrawal said carbon dioxide absorbed by grasses, grains, and such would balance out the carbon dioxide released into the atmosphere from cars and trucks running on biofuel.

"You take carbon dioxide from the atmosphere and you release it to the atmosphere," he said. "The challenge, though, is to make cheap hydrogen from solar or nuclear sources."

That will take more research, he said. "The hydrogen economy will not happen without that," he said.

Right now the method is just a theory, but he and his team at Purdue are doing research on how to make low-cost solar cells. They are also working on making a gasifier to covert biomass into fuel.