Sprawling beneath the streets of Paris is a 1,491-mile long network of sewers, famed as a tourist attraction and setting for novels, films and various other forms of entertainment aside from fulfilling its regular duties. Well, not to pile on, but the sewers of Paris are about to take up a new role in the sustainable future. If a pilot project proves succcessful, they are going to act as a home-brewed, renewable geothermal energy system for up to 10 percent of their host city.
Sewage, Sewers and Renewable Energy
Sewage treatment plants are gradually making the transition from waste dumps to genuine resource recovery centers. You can even mine gold in sewage, though more typically the fruits of sewage recycling consist of renewable biogas and a natural soil enhancer. Bioplastics and liquid biofuel are two other areas of exploitation. As for the sewers themselves, harvesting hydrokinetic energy is one possibility, and geothermal is another.
Geothermal Energy from Paris’s Sewers
As reported by Alexandria Sage of Reuters, average temperatures in the sewers of Paris range up to 68 degrees Fahrenheit. As with any other geothermal system, you can pipe a special heat-conveying fluid through the warm sewage, then extract energy from the heated fluid. It’s a closed system, so nothing stinky leaves the sewer. The system is currently being tested at school, and in an interesting twist the Elysee Palace will be one of the next buildings in line to get geothermal sewer energy, along with a town hall and a public swimming pool. Sage notes that the system is only effective up to about 600 feet of its source, which is why its potential extends only to about ten percent of Paris.
Geothermal Energy and the U.S.
The U.S. military has estimated that there is enough geothermal energy under its facilities to provide for its own energy needs, with some left over for the national grid – and that’s just a fraction of the total U.S. geothermal capacity. Given these resources, and assuming the development of a modern national energy grid, it’s not necessarily the case that the widespread use of geothermal sewer systems would make sense in the U.S. – but then again, you never know.
Image: Paris sewer by Bogdan Migulski on flickr.com.
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