UNIT 1

1	The sewage system in Paris, France, carries about 340 billion liters of wastewater per year.  But this underground system of pipes might also be one of the largest unused sources of renewable energy, or energy that doesnft disappear, in the whole city.  Some scientists and city planners want to use this energy to heat a local school.
2	The energy people use mostly comes from nonrenewable resources \\ sources that will someday disappear.  Some, such as oil and coal, also release large amounts of pollution into the air, which can harm the environment.  Greenhouse gases, which may bring about widespread climate change, are another consequence of burning oil and coal for energy.  So the city of Paris has set a goal to reduce its dependence on these resources.  By 2020, 30 percent of the cityfs energy needs have to be met with green, or environment-friendly, energy.  Thatfs where the sewer comes in.
3	Warm wastewater from hot baths and showers, dishwashers, and kitchen sinks flows into the sewers every day.  As a result, temperatures in the cityfs sewer system can be as high as 20 degrees.  Engineers plan to run a pipe through the sewer, filled with a special fluid that can collect heat.  The fluid then flows into a machine in the schoolfs basement that circulates heat throughout the school.
4	Because the fluid is enclosed in a pipe, no waste ever leaves the sewer.  That means that, despite its smelly source, the heating should not have a bad smell. 
5	This project should meet 70 percent of the schoolfs heating needs.  If it is successful, other buildings will be fitted for the sewer treatment, including the presidential palace, the home of French President Nicolas Sarkozy.
6	The plan has problems.  First, it is expensive.  In addition, the sewer is 2,400 kilometers long, but the heating system can work only roughly 550 meters away from the sewer source.  That means only 10 percent of the city could benefit from this energy. 
7	This form of energy has been used successfully before.  Canada used this energy source to heat the Olympic Village in Vancouver in 2010.  Sewers are good sources of other energy as well.  Biogas, a renewable fuel source, and soil fertilizer can be taken from sewers.  There are still numerous energy problems to solve, but Paris might just have found an underground answer to one of them.
