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How a bio-digester works

1. Organic waste is decomposed in a liquid mixture maintained under controlled, oxygen-free conditions within a vessel.
2. The gaseous byproduct, methane, of the decomposition process is further processed to upgrade its heating value to that of natural gas so it can be used to create electricity.
3. Solid byproducts of the process are typically disposed of in a sanitary landfill.

Source: Animal Byproduct Technology Assessment and Market Analysis: Options for Oregon prepared by Cascade Economics LLC

Nearly every weekday, a truck carries several cow carcasses from Tillamook to a landfill in Corvallis. Transportation of the thriving dairy industry’s dead cows is costly and harmful to the environment. But now a possibility exists for the dead cows to become sources of renewable energy.

The Tillamook Creamery Association, the Port of Tillamook Bay and other project partners are preparing for a feasibility study to see if cow carcasses can be disposed via a bio-digester, a machine that converts organic waste into methane gas, which can be converted into electricity.

Currently, the Tillamook Creamery Association trucks 20 loads of cow carcasses per month to Coffin Butte landfill in Corvallis – at 160 miles per round trip, according to Jennifer Purcell, solid waste coordinator for Tillamook County. The Tillamook Creamery Association pays $125,000 annually for carcass disposal, said Shawn Reiersgaard, the company’s director of environmental and political affairs.

The state of Oregon no longer has any rendering facilities, which convert animal tissue into useful byproducts, such as lard. All of Oregon’s rendering facilities were privately owned, and experienced a decrease in profitability due to mad cow disease and other issues. The notoriously smelly facilities also drew many city complaints. Finally, Oregon’s last rendering facility, in Redmond, closed several years ago.

“Our waste now goes to landfills, which are not required by law to take this waste, so it’s a tenuous partnership,” Reiersgaard said. “Our industry and others are looking for alternatives to dispose of carcasses and butcher waste. One option that has risen to the top is the idea of digesting carcasses to generate methane.”

At the Port of Tillamook Bay, manure from 4,000 dairy cows is broken down into methane gas at the Hooley Digester, a bio-digester constructed at the port in 2003. The methane gas is converted into electricity, which is then sold to the Tillamook Public Utility District.

The largest challenge in getting the Hooley Digester online, according to Michele Bradley, general manager of the port, was to acquire the proper permits through the Oregon Department of Environmental Quality.

No one in Oregon has used a bio-digester for carcasses, so DEQ permitting issues would be explored during the feasibility study.

The DEQ did not respond by press time to a call seeking comment.

“I assume many of the growers in the area will want to ensure that the facility is operated in a way that’s protective of animal health,” said Stephanie Page, renewable energy specialist at the Oregon Department of Agriculture. “Working closely with the Department of Environmental Quality will be necessary. Not having rendering facilities in the state is forcing people to look at creative options.”

Bradley said the Hooley Digester’s existing infrastructure could make the site a good option for housing a bio-digester.

Like the manure, the electricity produced from the carcasses would be sold to the Tillamook Public Utility District. But cow carcasses alone would not produce enough feedstock to make the bio-digester project worthwhile.

“We’re hoping there are other commercial-grade feedstock that could be used in the bio-digester from places like the school district and commercial food processing plants,” Bradley said. “We already have the infrastructure from the manure digester, and we’d be taking trucks off the road.”

Project partners are hoping to soon issue a request for proposals for the feasibility study. They’re waiting for a $50,000 grant award from the U.S. Department of Agriculture.

“Obviously, cows are high methane producing creatures,” Purcell said. “This is a big opportunity for the county, and also for neighboring jurisdictions with potential feedstock sources.”