Way back in 2006, when gasoline cost just $2.50 a gallon, President Bush called for home-grown biofuels to replace three-quarters of oil imports from the Persian Gulf – or about 72 billion gallons – by 2025.

How to achieve that goal is still a question. Corn-based ethanol production is expected to be 12 billion to 15 billion gallons in coming years.

But with gas now at $4 a gallon and critics hammering corn ethanol for helping to pump up global food prices, it is clear that the holy grail of biofuels – cellulosic ethanol – needs to make its entrance soon.

Driven by a growing political consensus to shift toward nonfood biofuels, the high price of oil, and gains in technology, a flood of public and private investment has poured into the development of cellulosic ethanol.

“Actual marketplace production of cellulosic ethanol is zero – there’s not a gallon being produced [commercially] right now,” says Thomas Foust, biofuels research director at the National Renewable Energy Laboratory in Golden, Colo. “But with all these plants coming on line ... by 2010 or 2011 we will start to see millions of gallons.”

At least 30 cellulosic ethanol “biorefineries” with solid sources of funding – including 13 with federal funding – are now active in the development pipeline, according to the Biotechnology Industry Organization, a Washington trade organization.

Not all these facilities will ultimately be built. But a high proportion will be, given investor confidence, according to Dr. Foust. Cellulosic ethanol is on track – or perhaps even ahead of schedule – to produce up to 60 billion gallons by 2030, he says.

There seem as many varieties of cellulosic technology as there are companies trying to produce it on a commercial scale. Most, however, fall into two broad categories: Thermochemical processes use heat and pressure to extract sugars from plant material – sugar that is then turned into ethanol. Biochemical proces­ses mostly use enzymes to do the same thing.

A big step forward came last week with the opening of the nation’s first ­demonstration-scale cellulosic ethanol plant in Jennings, La. The facility, built by Cambridge, Mass.-based Verenium Corp., will use high-tech enzymes to make 1.4 million gallons per year of ethanol from the cellulose in sugar cane bagasse, a waste product.

That plant will be used to tweak the technology and validate cost and performance measures, putting the company on track for a 30-million-gallon commercial plant by the middle of next year.

“This is a first for the US, and as we take the next step toward commercialization, we are breaking new ground and setting new standards,” said Carlos Riva, president of Verenium, in a statement.

Despite the financial shock wave from the housing credit crunch and the subsequent closing of wallets on Wall Street, investor interest in cellulosic continues to be strong. Developments popping up rapid-fire include:

• DuPont and Genencor’s deal last month to form a $140 million joint venture to make cellulosic ethanol from corn stover (husks and leaves) and bagasse.

• General Motors last month said it would make a major investment in Mascoma Corp., a cellulosic ethanol company based in Boston that hopes to use more powerful enzymes to break down material in a single step.

• Range Fuels, a Broomfield, Colo., company, announced that in April it raised more than $100 million to help finish construction of its Soperton, Ga., cellulosic ethanol plant. With completion slated for 2009, that plant is designed to turn logging residue into 20 million gallons of ethanol a year using a thermochemical process.

• BlueFire Ethanol’s announcement last month that it will break ground soon on its first commercial cellulosic-ethanol plant. The company says it will use a different process using wood and garden waste from a landfill in Lancaster, Calif., to begin producing 3.1 million gallons annually by 2009.

Adding fuel to the cellulosic fire, the new farm bill passed by Congress last month includes $384 million in new tax credits to spur cellulosic development. The US Department of Energy also is investing about $385 million in six commercial-scale projects to be built over the next four years.

The plants will have a combined capacity of 130 million gallons.

“Just three years ago, people would tell me: ‘Oh, professor, things are not that bad [with the nation’s fuel situation]; there’s not a need for that kind of radical change,” says Lee Lynd, a cellulosic pioneer who is a professor of engineering at Dartmouth College in Hanover, N.H., and chief technology officer for Mascoma.

But now with food supply, climate change, and gas-price issues, “all of a sudden we have this attitude emerging that the markets [for cellulosic] are very real,” Dr. Lynd says.

Often seen as a technological “silver bullet,” cellulosic ethanol promises to require far less energy to refine than corn ethanol does. It does not require land that might otherwise provide food, as its feedstock is nonfood agricultural waste.

On that basis, cellulosic ethanol could reduce greenhouse-gas emissions up to 87 percent if used broadly in the United States for transport fuel, the US Department of Energy reports.

The potential of cellulosic biofuels to meet world demand is suggested by the current impact of corn-based ethanol, biodiesel, and other biofuels. Biofuels will account for 63 percent of oil supply growth from non-OPEC countries this year, taking global production of crop-based fuel to more than 1.5 million barrels a day, according to the International Energy Agency.

Output is projected to grow by 425,000 barrels a day this year, a 57 percent increase from a year ago, the agency reported.

“We feel like things have accelerated much more quickly in the past six months than they have in the past five years,” says Brent Erickson, vice president for industrial and environmental technology at the Biotechnology Industry Organization, a Washington trade group that includes a number of cellulosic-ethanol companies.

Still, some environmentalists are hesitant about endorsing cellulosic technology without qualification, since there could be “good cellulosic and bad cellulosic,” says Nathanael Greene, senior policy analyst at the Natural Resources Defense Council in New York.

Basing government funding and tax incentives on the environmental performance of a technology – supporting technologies that use the least water, land, and other resources while cutting more CO2 emissions – is the key, he says.

“We’ve got to pay attention to the performance of new biofuels, not give credentials out for who produces the most gallons,” he says, “but who produces the best in terms of water use, water quality, soil erosion, wildlife and habitat enhancement – and greenhouse-gas emissions.”