Sewage to Electricity
Paging King Midas ... Well, maybe. Getting energy from sewage and sludge has a lot in common with King Midas' ability to turn everything he touched into gold. And if you think about the ways that traditional electricity comes into our homes, there's a lot to like about sewage treatment energy.
Too much of our country's electricity is tied into the burning of coal. While we're all focused on driving down our dependency on foreign oil, domestic coal is a source that won't tie us down to the fortunes of the Middle East, but it will damage the environment.
So how does it work? Let's look at the example of a plant in Renton, Washington, a suburb of Seattle. Each day, about 700,000 residents flush an average of 86 million gallons of kitchen and bathroom waste down the drain, right to this plant. About a third of this waste goes into a system that extracts the methane gas and uses it to power a fuel-cell power plant that generates a full megawatt. The energy supplements the power plant's own needs, powering about 14% of the plant's electrical needs.
The waste goes into digesters, which are giant tanks that hold it for up to a month. Bacteria feast on the filth, getting rid of the solid matter and releasing methane as a by-product. This isn't that different from the way that most treatment plants work, but what the Renton plant does is the revolutionary part.
Instead of burning the methane, the Renton plant cycles it through a fuel-cell system, and the methane breaks down into carbon dioxide and hydrogen. The system turns the carbon dioxide into carbonate and then combines it with hydrogen to make water, carbon dioxide- and heat and electricity.