A decade-old industry that recycles old rubber tires into fuel is chipping away at the stockpile of 1 billion retired tires in the U.S. But the laudable recycling effort is balanced by a negative impact on air pollution, as the U.S. EPA’s clean-air regulations for burning solid waste include a loophole loosening requirements for facilities that “recover energy.” Now a recent appeals-court decision in favor of environmental groups is forcing the U.S. EPA to come up with a new definition of “solid waste” — if tires are included, it may have a huge impact on the industry, which touts tire-derived fuel as a huge money-saver. Indeed, the world’s second-largest cement maker, Holcim, saves more than $100 million a year by using tire fuel instead of coal; cement kilns, the biggest users of the alternative fuel, burn as many as 60 million tires a year.

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