Methane digester ready to go at Threemile Canyon Farms

Marty Myers, general manager at Threemile Canyon Farms, talks with employee Tom Chavez about the operation of the new methane digester, which is expected to reduce the farm's natural gas use.<br><i> Staff photo by Dean Brickey </i>

Marty Myers, general manager at Threemile Canyon Farms, has high hopes for the operation's new fuel plant.

Workers just completed building a $1 million methane digester near the milking barns.

Myers and Tom Chavez, the farm's waste manager, hope to begin producing methane gas from the digester in early January.

"This is a pilot project that should handle the manure from 1,000 to 1,500 cows," Myers said.

Threemile Canyon Farms has a flush dairy. That means employees use water to clean the stalls, washing animal waste into a drainage system that pumps it over revolving screens that remove large solids for composting.

The wastewater then flows into clarifiers, similar to those used in municipal wastewater systems. They allow solids to settle to the bottom, from which the waste again is pumped over the screens.

Myers said some waste from the bottom of the clarifiers eventually will go to the digester, where bacteria will decompose it, producing methane.

The rest will go through settling cells and finally into the lagoon.

"The lagoon water is then clean enough to be pumped through the irrigation system through the pivots as fertilizer," he said.

The digester isn't much to look at. Most of it is underground, comprising a 29-foot deep inverted pyramid that is 160 feet square at ground level.

Troy Green, a Kennewick engineer who helped design the digester, said it's filled with 31,000 neatly stacked tires.

Myers said he and the engineers think this digester will process manure twice as fast as a traditional digester, which takes 20-25 days.

"I think this will reduce the time to seven to 10 days because of the tires," Myers said. "They give a place for the bacteria to live."

Waste that isn't routed to the digester will go through settling cells and finally into the lagoon.

"The lagoon water is then clean enough to be pumped through the irrigation system through the pivots as fertilizer," he said.

The gas will be collected and used to fire a boiler. It will heat water for use on the 17,000-cow dairy.

This pilot project will determine the system's success. If it works, Myers plans to build up to a dozen digesters to handle manure from the entire dairy.

"It's a successful project if it produces enough gas to heat our ... water for the dairy," he said.

The dairy's propane bill runs about $120,000 per year to do that today. That's why the methane digester project is a partnership among the farm, Northwest Natural Gas and the Bonneville Environmental Foundation.

Myers expects it will be 18 months after startup before he'll know the digester's effectiveness, but he's eager to find out.

"If it's as successful as we think it is, the next eight to 12 will be lesser cost per unit."

Producing methane from cow manure could even become a revenue stream, Myers said. If the farm can't burn all the methane it produces, it might build a co-generation plant or sell methane to Portland General Electric, which has a generating plant about four miles from the farm.

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