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Environment | Energy

King County Opens The Door For Heat Energy From Wastewater

SEATTLE — Jessie Israel looks down into an open sewage pipe at a construction site near Discovery Park. She handles resource recovery for King County’s Wastewater Utility.

Stinky water rushes beneath the construction worker’s feet. But Israel doesn’t think about it as stinky water.

“The vast majority of what’s going out to the plant is water from running our laundry, the sink, your shower this morning,” she says. “We flush a lot of hot water, a lot of energy, down the drain and you can see it right here. We’re trying to figure out how to capture that and use it in buildings.”

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Source: King County

Israel sees that warm wastewater as energy. The average temperature of the water rushing through this pipe, and hundreds of miles of sewage and wastewater pipes in the county, is a pretty constant 65 degrees.

That’s warm enough to get energy out of it. And King County is looking for partners in the private sector who want to harness that heat and use it in buildings - kinda like speed dating, Israel laughs.

“We’re essentially going to match-make places where we have pipes full of sewage, full of hot water, next to a piece of developable land, with a developer that is a deep green developer that wants to innovate and integrate new technologies.”

To be clear: King County is not paying the contractors. They’re just offering them access to their pipes. And they are one of the first counties in the nation to do so.

Another point of clarification: warm wastewater is not getting funneled around buildings to provide heat.

Lynn Mueller, president of a company in Vancouver, BC that installs systems to extract heat energy from wastewater, says to understand how this works, picture your refrigerator:

“You put warm beer in the fridge, pretty soon the beer is cold and the back of your fridge is warm? Well you’ve moved heat from that warm material in the fridge to outside of the fridge and that’s basically exactly the same system – it’s a heat pump.”

So the warm wastewater in the sewage pipe provides the heat – just like the beer in the fridge – and then that heat is used to warm up clean water in separate pipes that circulate around the building.

Systems like this have been installed in Japan, China, Canada and parts of Northern Europe - and they’re having an impact.

One of Mueller’s systems went into a building in Vancouver and lowered the building’s energy consumption by 75 percent.

“We’re operating at 600 percent efficiency,” Mueller says. “So every dollar we spend recovering the heat out of the sewer we get $6 worth of heat out.”

His company’s sales are projected to jump from $3 million this year to $50 million next year.

But wastewater energy systems won’t work on all buildings. It can be tricky to retrofit buildings that don’t already have hot water circulating systems.

King County’s Jessie Israel says the key is to get developers of new buildings thinking about incorporating this technology on the front end of their design process – in order to reap big energy saving rewards later on.

“350 billion kilowatt hours of energy are lost every year, just flushed down the drain,” she says, shakes her head. “If we’re smart about how we build cities and how we build communities and how we build buildings. Maybe 50 years from now that will be a much smaller number.”

King County will be accepting ideas for wastewater energy capture projects until the 23rd of August.

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