Gresham system turns sewage into electricity

Soon, they'll flip the switch on the city's latest methane-powered generator, a machine that produces electricity by burning gases produced during the biological breakdown of sewage.

The equipment, which replaces an older methane-powered generator in use since 1991, is expected to produce 3 million kilowatt hours of electricity every year - the equivalent needed to serve about 275 homes, says Guy Graham, the city's wastewater services manager.

"It's pretty straightforward - you take the sewage, you treat it, you burn the gas, and you get electricity," he says. "It's cool."

It is also expected to save the city at least $183,000 in energy costs annually, Graham says.

Graham expects the $1.1 million 400-kilowatt generator to go online by mid-October and cover about half of the wastewater treatment facility's electrical needs. That facility processes about 12 million gallons of wastewater a day, serving about 100,000 customers in Gresham, Fairview and Wood Village.

Before the advent of methane "co-generation," which began showing up at treatment facilities and methane-producing landfills in the 1990s, gases that built up were burned off as a useless byproduct. Now, Graham says, they are being harnessed as "green energy."

The new system's eight-cylinder engine is much more fuel- efficient than the old one, he said, and unlike the old one, it will continue to run when the power goes out. It can run on natural gas if needed. The city managed to recoup $5,000 by selling the old generator, which had started to break down, Graham said.

"We should be able to utilize better than 80 percent of our gas," Graham said, adding that the system should be in use almost continuously.

The system is designed and built by California Power Partners Inc. Part of its cost is covered by a $82,379 grant from the Energy Trust of Oregon for renewable resource projects and a $270,000 business energy tax credit from the Oregon Department of Energy.