"There's no such thing as garbage," says Bill Chambers, president of Stahlbush Island Farms. "Only underutilized resources."

That's the philosophy behind the farm's new biogas digester, which is turning vegetable waste from Stahlbush's busy food processing operation into methane. The gas fuels a generator that can crank out 1.6 megawatts of electricity - enough to power 1,100 homes.

The farm needs only about half that much, so the rest goes out onto the grid - and the electric company sends Stahlbush a check.

"Pacific Power is now my customer," said Karla Chambers, Bill's wife. "I never would have dreamed I'd ever be in the energy business. I can't imagine not being in it now."

It's the latest example of a small but growing trend to turn farm waste into green energy.

Oregon is offering a variety of incentives to encourage more farmers to go into the energy business.

"It has potential, it really does," said Rick Wallace, the biofuels coordinator for the Oregon Department of Agriculture. "We're hoping we see quite a few more of these."

Feeding the machine

Most biogas digesters use a biochemical process called anaerobic digestion to break down biomass in an oxygen-free environment. Here's how it works:

A feedstock (vegetable waste, animal manure, straw, wood chips, etc.) is fed into an airtight chamber. The digester is heated to between 68 and 150 degrees. Bacteria gradually break down the feedstock - first into sugars and amino acids, then into other acids that become hydrogen, carbon dioxide and acetate. Finally, these byproducts are converted into methane and other gases.

The system installed by Stahlbush Island Farms is an Austrian-designed hybrid that conducts the first part of the digestion process in an aerobic environment.

The methane is burned in a generator to produce electricity to power the food processing plant and other farm operations, with the excess sold back to Pacific Power under a net-metering agreement.

Waste heat from the generator is put to use in the food processing plant, producing steam for blanching vegetables, hot water for space heating and hot air for drying pumpkin seeds.

Finally, the nutrient-rich solid waste recovered from the digester is used on the farm as fertilizer.

"We really try not to let anything get away from us," Bill Chambers said.

Stahlbush managed to capture its share of government green energy incentives.

A business energy tax credit from the state Department of Energy and a federal producer's tax credit will cover about half the cost of the $10 million project, Chambers said, and a pair of grants from the Energy Trust of Oregon paid about half of a $50,000 feasibility study.

Despite the hefty initial investment, Chambers thinks the plant will pay for itself fairly quickly.

"We think it's going to be on the order of four or five years," he said.

Old world idea

Biogas technology is widely used in Europe, which has more than 400 commercial digesters, but America has been slow to follow suit.

Most biogas digesters in the United States are at municipal wastewater treatment plants, where they tend to be used more for waste management than power generation. Landfills have been more successful at capturing methane to run electrical turbines. (Coffin Butte is one example.)

In recent years the technology has spread to confined-animal feeding operations - mainly dairies and pig farms - which have large amounts of manure to use as feedstock. They also face powerful regulatory pressures to reduce odor and effluent runoff.

According to the Environmental Protection Agency, 135 commercial-scale digesters now are operating on U.S. farms. Another 22 are under construction, and 64 more are in the planning stages.

The agency estimates these operations produce about 244,000 megawatt-hours of electricity per year while preventing the emission of 36,000 metric tons of methane, one of the most potent greenhouse gases.

State sees potential

The idea is catching on in Oregon, which can boast four digesters running on agricultural waste since the Stahlbush plant went online June 2. All the others are at dairy farms, and eight more dairy-based digesters are in various stages of planning or construction.

Cow manure makes a dandy feedstock for digester-based power plants, according to Mike Gamroth, a dairy specialist with the Oregon State University Extension Service.

"What we talk about is 2 kilowatts per cow per day," Gamroth said. "A 700-cow dairy can do 700 homes."

But he also sees some untapped potential at food-processing plants like Stahlbush Island Farms - as long as they are producing enough biomass themselves or can truck it in from other sources.

"It is a technology of size," Gamroth said. "You need to have a certain amount of material to really make it go."

Building an

energy portfolio

Digesters can be tricky to operate, sometimes requiring lengthy shutdowns to clean the tanks and fine-tune the process.

Nor is it a completely green technology. Burning methane to make electricity produces emissions comparable to those of a natural gas-fired power plant, including greenhouse gases such as carbon dioxide. But as bad as it is, experts say carbon dioxide is much less harmful than methane, one of the most powerful contributors to global warming.

And methane is a renewable energy source, unlike oil, coal and natural gas - finite resources that sequester carbon until they're burned, then turn it loose to heat up the planet.

For electric utilities such as Pacific Power, digesters help meet state-mandated goals to market more energy from alternative sources. Combined with power from other renewables such as wind, solar and geothermal, they can also reduce the need to build regional generating plants that run on coal or gas.

Thanks to a slew of government financial incentives, "they're producing energy at prices that are competitive in the market (now)," said Tom Gauntt, a Pacific Power spokesman. "They'll become part of the larger mix."

Jumpstarting a variety of alternative technologies is the whole idea behind Oregon's green power initiative, said the Department of Energy's Wallace, and he thinks biogas plants have the potential to be a significant part of the state's energy mix.

"We think there's a future for these kinds of facilities," Wallace said.

"It's a technology that's really finding its own legs, and as energy gets more expensive, it's going to look better and better."

Bennett Hall can be reached at 758-9529 or bennett.hall@lee.net.