Can a landfill ever be too sanitary? Perhaps surprisingly, the answer is yes. Some of them, it turns out, are so dry and airtight that their contents never rot. During its excavations of different landfills, the Garbage Project at the University of Arizona has encountered 15-year-old steak, with fat and meat intact, and 30-year-old newspapers, still quite legible. It concluded that in many landfills only food and garden clippings rot. Other supposedly biodegradable materials, such as paper and wood, often do not decompose at all.rnThat may sound like a good thing because it reduces methane emissions and leachate. But it also spreads out the risk of pollution over a very long period. And methane is difficult to capture in small volumes at low concentrations. So Waste Management, America's biggest waste firm, has been experimenting with a type of landfill called a "bioreactor", designed to ensure and accelerate the decay of biodegradable waste by injecting a mixture of air, water and recycled leachate. That should increase not just the amount ofrnmethane collected but also the capacity of the landfill, since waste shrinks as it rots. It should also reduce the degree of monitoring and treatment needed after closure, and allow the site to be put to another use more quickly.
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