Paris sewers to heat schools, president's palace
* Energy from effluence under Paris to provide heating
* Presidential palace next on list to use technology
PARIS, April 5 (Reuters Life!) - The Paris sewers -- whose murky labyrinths have been reviled and romanticized through history -- are at the centre of a renewable energy experiment to harness heat for buildings, including the presidential palace.
Paris wants green sources to fuel 30 percent of its energy needs by 2020 and a new heating project at a primary school is the city's first using power from sewers, where temperatures average between 12 and 20 degrees Celsius (53 to 68 Fahrenheit).
The technology takes advantage of the warm waste water flowing into the sewers from showers, dishwashers and washing machines. A steel plate containing heat-conveying fluid is submerged in the waste and feeds a heat exchanger pump -- in this case located in the school's cellar -- which circulates heat through an existing network of radiators.
Engineers say the process is safe, non-polluting and -- more importantly, does not smell.
"It's very modern, intelligent from the point of view of sustainable energy and it's really a hallmark of the dynamism of Paris," said Paris Mayor Bertrand Delanoe, outside Wattignies school on the city's southeastern side.
Paris is not the first place to turn to sewage as a source of energy -- the technology has been used elsewhere in France, as well as in Norway, Japan and Canada, where it helped heat the 2010 Olympic Village -- but it is one of the most high profile.
Indeed another future beneficiary of sewer-generated heat in Paris will be none other than President Nicolas Sarkozy, whose Elysee Palace plans to use its own sewer heat system from mid-2011, a spokeswoman there told Reuters.
Home in the 19th century to rats, pickpockets, intrepid tour groups and the odd corpse, the Paris sewers were described by Victor Hugo as "the conscience" of the teeming city and were immortalised in his epic novel Les Miserables, as well as in Gaston Leroux's "The Phantom of the Opera" a few years later.
Today, the sewers pump 285 million cubic meters (10 billion cubic feet) of waste water per year through a vast maze some 2,400 km (1,491 miles) in length, and tourists still descend into the city's bowels to view the system first hand.
The heating technology is not universally applicable, however, as the harnessed heat can only be used within 200 metres (656 feet) of its source -- making it impractical for city districts lying far away from the sewage network.
That means that only 10 percent of Paris could be heated through sewer energy, said Denis Penouel, the city's head of water and sanitation.
Another challenge for developers is the big initial cost of setting up the infrastructure. "It's a project that consumes a lot of capital," said Thierry Franck de Preaumont, president of CPCU, the local heating utility involved in the project.
The Wattignies school project, which cost 400,000 euros ($568,360), will take care of 70 percent of its heating needs.
Next up are a handful of similar projects at a municipal swimming pool and a local town hall. (Reporting by Alexandria Sage; Editing by Catherine Bremer and Paul Casciato)