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Stayton-based Slayden Construction, a subsidiary of global firm MWH Constructors, has broken ground on a $13.9 million project to upgrade the Willow Lake Cogeneration Facility at Salem’s wastewater treatment plant.

The existing cogeneration system, in operation since 1988, 鈥済enerates power from biogas produced as a byproduct of wastewater treatment processes,鈥� according to the city’s website. However, the system 鈥渋s at the end of its useful life and is undersized,鈥� the city states.

A new cogeneration building will be constructed to house a Peterson-Caterpillar diesel generator for burning surplus methane and producing electricity. This new system will double the power output at Willow Lake to 1.2 megawatts. It’s expected to save the city up to $300,000 annually in energy costs.

鈥淗ow the process typically works is they bring in raw sewage, clean it up and run it into the digesters,鈥� Slayden project manager Ryan Imel said. 鈥淭hey’re just stomachs; they live off bacteria, and when it decomposes they start to off-gas methane. It’s a dirty, wet methane, and what they’ve found is with a little bit of effort you can treat that methane and burn it.鈥�

Construction of the plant expansion won’t be technically difficult, Imel said.

鈥淭hey use large diesel generators to burn that off-gas and make electricity for the plant,鈥� he said. 鈥淎nd our project is to construct a new building for the (cogeneration) system and install a new diesel engine. That will double the output of the plant, and I believe the plant is set up to consume that power, so they power their own gear with that.鈥�

The plant improvements also will reduce the amount of pollution released into the air by an estimated 5,000 metric tons annually.

While the construction method may be orthodox, scheduling and organization pose challenges, Imel said.

鈥淚t’s definitely a puzzle,鈥� he said. 鈥淏ecause while we’re doing this, everything has to remain running. You cannot interrupt service. So a lot of that puzzle that has to be figured out before we dive in and start disconnecting things.鈥�

Construction began earlier this month and is expected to finish by mid-summer 2020. As general contractor, Slayden will handle the entire project scope and self-perform demolition, civil, concrete, mechanical and piping work.

Project funding partners include the cities of Salem and Keizer as well as Portland General Electric and the Energy Trust of Oregon.