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Poop power? Sewage turned into electricity

It's not as neat as spinning gold from hair, but in the world of sewage treatment what Greg Bush gets to do is pretty magical: turning filth into fuel.
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It's not as neat as spinning straw into gold, but what Greg Bush gets to do in the world of sewage treatment is pretty magical: making electricity from what's flushed down the sewer. And he does it using fuel cells, technology that's cleaner and more efficient than traditional power generation.

It's also still a lot more expensive, but that's the point of the $22 million project -- to build a power plant that can then be replicated at lower cost at sewage treatment plants across the United States, and there are hundreds of them. The power would be used inside the treatment plants and any excess could be sold to the power grid.

Day in and day out, some 700,000 people send 86 million gallons of sewage, mostly toilet and kitchen waste, to the King County treatment plant in Renton, a Seattle suburb.

Little do they know that 30 million of those gallons are producing enough methane gas to run the 1 megawatt, fuel-cell power plant that was built here this year. The system can power 1,000 homes, but in this case all the electricity is going to help run the treatment plant, which needs about 7.5 MW per hour a day on average.

How it works
The largest project of its type in the world, the process goes like this: Biodegradable solid waste is sent to large tanks, called digesters, that provide a home for three to four weeks. There bacteria eat away at the waste, releasing methane gas and further reducing the amount of solid waste.

The fuelcell power plant at the waste water treatment plant in Renton, WA. Four large digester tank are shown in backgound.
The fuelcell power plant at the waste water treatment plant in Renton, WA. Four large digester tank are shown in backgound.James Cheng

"We maintain a nice little environment for bacteria: warm and wet," says Bush, program manager for the project, which is funded by the U.S. Environmental Protection Agency, FuelCell Energy and King County.

Most treatment plants flare off the methane, and a few burn it to get electricity for their sites. But the Renton plant captures the gas and sends it to a fuel cell system, where the methane is broken down into hydrogen and carbon dioxide. The carbon dioxide is recirculated to produce carbonate.  The carbonate then combines with the hydrogen to produce electricity, water, carbon dioxide and heat.

Fuel cells operate like a battery, and methane or any other fuel containing hydrogen can be used to power the process. A key advantage to fuel cells is that they are much more efficient at generating electricity than the combustion process found in today's cars and power plants.

Long, hard road it's been
King County had been looking to start the project six years ago, and was set to go when the first fuel cell company it partnered with went bankrupt.

FuelCell Energy, a company based in Danbury, Conn., eventually stepped in, and has a team of four helping prep the project. Eventually, the system should be stable enough to monitor it remotely from Danbury.

The fuel cell technology used is different than that being developed for cars. Even though no combustion is involved, FuelCell Energy's stacks reach temperatures up to 1,200 degrees Fahrenheit.

"You wouldn't want to drive around with 1,200 degrees in your car," says Dan Beachy, project leader for FuelCell Energy.

Will it make economic sense?
Even with all the effort, there's no guarantee that the pilot project will make sense economically. For one, the fuel cell stacks need to be replaced every four years or so, and that's one of the pricier parts of the system.

The fuel cell industry does expect costs to come down as production ramps up.

Steve Eschbach, FuelCell Energy's communications director, says typically with each new power plant delivered "we're able to lower the cost by 25-35 percent" due to lessons learned from previous plants.

The company, one of several in the field, has 30 other fuel cell systems installed and a 40-unit backlog, he adds. Four installed units in California and Japan are similar but smaller to the one in Renton.

Bush, for his part, acknowledges that without the EPA grant and FuelCell Energy's partnership, the system probably wouldn't have been feasible. "It's not going to pencil out on a cost/benefit formula," he says.

On the other hand, he adds, this is just a pilot project and "the next one ... is going to come in with a different set of economics."

The project also has a significant environmental benefit: less pollution.

Combustion power plants emit nitrogen oxides, which combine with sunlight to create smog, and sulfur dioxide, which creates acid rain. But a fuel cell nearly eliminates these because no fuel is burned. And carbon dioxide emissions, which many scientists fear are contributing to global warming, are cut in half.

A bonus feature for waste treatment plants is that instead of burning off the methane, another gas tied to global warming, it can be used to create electricity.

Not built for spikes
A big drawback to fuel cells, however, is that they can't ramp up quickly for sudden spikes in electricity demand. At the treatment plant, that typically happens during a big storm, when waste water flows faster into the plant and more electricity is needed to pump the extra water out to the ocean once it's treated.

As a result, King County is planning a more traditional power plant, one that burns methane and can be ramped up quickly. "You need to think dual fuel," says Eddie Tate, construction manager for both projects.

The fuel cell project will also be scrutinized by an outside committee, whose members include Gordon Bloomquist, a program director at the Washington State University Energy Program. He says he'll be watching to see if methane proves compatible with fuel cells and just how reliable the system is.

As for the economics of fuel cells, he says, "it's not clear how the cost effectiveness is going to work out, but this project is a major step forward in terms of determining that."

For King County, the numbers work because it put up just $2 million of the $22 million project, and it is allowed to keep the fuel cell system after the two-year project. "That's the plan if everything goes well," says Bush. "It fits in with our overall goal of being as energy independent as possible."