In a push to produce more of its own energy, a wastewater treatment plant in Gresham, Ore., is turning to an unlikely source to generate power: the gray-white grease-filled wastewater that flows out of restaurants and other places where food is prepared.
Gresham’s plant, which serves about 120,000 people in three cities east of Portland, has been making use of the digesters’ gas byproduct since 1990. That generates all of the heat for the plant’s buildings and about half of the electricity that the facility needs each year, said Alan Johnston, a senior engineer for the city of Gresham who oversees the treatment plant.
In January 2010, the city installed an array of solar panels that currently supply about 450,000 kilowatts hours annually, or about 8 percent of the power that the plant needs each year, he said.
Now the Gresham plant is ready to feed greasy wastewater brought in from restaurants all over the Pacific Northwest by three hauling companies to its digesters, Mr. Johnston said. He expects that adding the energy-rich restaurant wastewater to the mix — a common culprit for backed-up sewers — will increase the amount of gas that the digesters release by 40 percent.