What with the microbial waste-water fuel cells, the London Science Museum using human waste as a power source, and spread of biogas plants, it seems more and more people are getting on the "turn sewage into power" bandwagon. Next up, a 1 megawatt fuel cell running on the methane from the King County, Washington, sewage treatment plant -- used to help power that very facility.

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.

"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.

The King County plant is an experiment in converting waste into power via fuel cells instead of simple combustion: a cleaner, more sophisticated, but technically more challenging project. The $22 million cost would likely not have been feasible without EPA support, but the lessons learned from the pilot facility will help bring down the cost of future sewage-fuel cell power plants. It may not end up being the path to a sustainable future, but it's certainly one worth following for a bit.