Vegetable, fruit waste can produce electricity

Think about all the fruit and vegetable waste left behind during harvest, lying unused and unwanted in farm fields and processing plants. Not only does it literally go to waste, it often takes time and labor to get rid of it.

But what if all that unused produce could be turned into energy? A grower or processor could take care of its waste problems and pay its energy bills at the same time.

Two West Coast vegetable processors are doing just that. The Oregon and California companies both recently opened power plants fueled by waste produce.

Stahlbush Island Farms

Bill and Karla Chambers, owners of Stahlbush Island Farms, a grower and processor in Corvallis, Oregon, spent $10 million and 14 months building a biogas plant that turns fruit and vegetable byproducts into thermal and electrical energy.

The new plant officially joined the power grid in June and could save the farm half a million dollars per year in electricity and natural gas costs, Bill said.

Even with all that savings and help from state and federal incentives, $10 million was a huge investment. But Bill and Karla knew biogas plants were common investments in Europe, and they still think such plants could play a key role in American energy independence.

Using waste to create energy also fit Bill and Karla’s goal of complete sustainability for their farm. And since the fruit and vegetable byproducts won’t be consumed anyway, they aren’t taking away from the food market to feed the energy market, Karla said.

“We see waste as an underutilized resource,” she said. “We felt this would close a significant loop and help us move toward a carbon-negative footprint.”

Stahlbush Island Farms encompasses more than 4,000 acres of fruits and vegetables in the Willamette Valley, some of those acres certified organic. Much of the farm’s produce is processed on-site, destined for its own product lines or to be used as ingredients for other food companies, according to the farm’s website.

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All that growing and processing leaves a lot of excess produce lying around. That “waste” is a highly efficient energy creator, capable of releasing a “remarkable amount of electricity,” Bill said.

When describing how the new biogas plant works, Bill compares it to a cow. Whatever you feed to a cow you can feed to a biogas plant; the end result for both is methane gas.

Once collected, the corn silage, pumpkin waste and other organic material is ground up and placed in an anaerobic digester, where it turns into a soupy liquid. Bacteria convert the waste to volatile fatty acids, and a second set of bacteria converts those fatty acids to methane. The methane bubbles up through the liquid waste and is collected at the top of the digester, where it’s fed to an internal combustion engine that runs a generator to produce electricity, Bill said.

Anaerobic digestion is a biological process that can’t be turned off. The plant has to run continuously, so they stockpile fruit and vegetable waste for the winter months. The same amount of waste is fed to the plant every day, he said.

When the plant is in full gear, it should produce almost twice as much power as the farm needs (enough to power more than 1,000 homes). The excess electricity will be sold back to the power grid, making the power company a customer rather than a vendor, he said.

Karla said other growers or processors could try building their own biogas plants, but the circumstances need to be right and they need to have the right waste stream. Bill said it’s too early for recommendations.

“We don’t know enough yet,” he said. “This is a big adventure.”

Gills Onions

In Oxnard, California, a fresh-onion processor is using onion juice to make fuel. Thanks to its new advanced energy recovery system, Gills Onions will reduce the solid waste coming out of its processing plant (300,000 pounds per day) by 75%, said co-owner Steve Gill.

The Gills Onions Web site describes the energy recovery process: The onion waste is turned to liquid and put through an anaerobic digester, which converts the juice to methane. The methane is burned cleanly to power 600 kilowatt fuel cells, which supply the processing facility with enough electricity to power 460 homes and can reduce its greenhouse gas emissions by up to 30,000 tons a year.

About a decade ago, Steve started investigating how to solve Gills Onions’ waste problem, which was growing along with the company. With initial help from the University of California, Davis, he found a solution in the advanced energy recovery system, which is based on European technology.

Designing and financing the system took about three years, and construction started about a year ago. The system came on line in June, he said.

The total cost was $9.5 million, but federal and state incentives paid almost a third of that. Steve estimated that the energy system would pay for 30 to 40% of Gills Onions’ needs — about $700,000 worth of electricity per year.

All vegetable waste — with its solids and sugars that bacteria love to eat — has potential as a renewable energy source, Steve said. Growers and processors studying their waste streams might be surprised at the hidden value they find.



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