National Geographic : 2014 Jan
U.S. METHANE EMISSIONS by source 37.5%* Natural gas and petroleum industry 21.5% Animal digestion 16% Landfills 2% Wastewater treatment 5% Other 8% 11% Coal mining Manure storage O2 O2 O2 Acetate Acetate Acetate Acetate CH4 Methane CO2 Carbon dioxide O2 Cover vegetation Topsoil Protective cover soil Drainage layer Liner Compacted clay Daily cover material Waste Collection layer for liquid waste from organic breakdown Filter Transport system for liquid waste from organic breakdown Liner Compacted clay Foundation Waste LINING THE BOTTOM Layers of clay, rubber, and plastic liners are impenetrable to sharp objects and prevent leaks into aquifers. CAPPING IT OFF A series of seals keep out precipitation, which could cause erosion or flooding. They also prevent gases from escaping. Next The Afterlife of a Landfill As the U.S . population has grown, so too has its collective output of waste—a quantity that last year topped 250 million tons. At modern landfills, waste managers compress and sculpt rising heaps of garbage in order to maximize capacity. With the dirty work also comes an opportunity. As garbage breaks down, the organic material produces carbon dioxide and methane, a potent gas that can be burned to produce large amounts of energy. At existing landfill plants, that method has been used to create nearly 15 billion kilowatt-hours, enough to power roughly one million homes for a year. More than 600 energy projects at landfills pipe the gases to the surface, in every U.S . state except Alaska and Hawaii. California has the most, with 75. The Environmental Protection Agency has categorized landfill gas alongside wind and solar as an environmentally efficient way to produce power. Seeking new revenue sources, some states and private companies have invested in technologies to turn garbage into other valuable substances, like crude oil or ethanol. “The goal is to extract the maximum value from everything that passes through these facilities,” says waste company executive Lynn Brown. Other countries are testing similar strategies. A partnership in Belgium plans to harness gases from a landfill dating from the 1960s. Proving that garbage can be valuable, Sweden has already begun importing waste from Norway for incineration to feed a growing energy demand. —Daniel Stone CRUSHING THE HEAP To minimize a landfill’s volume, vehicles with steel wheels spread waste evenly and then compact it. Maintaining the structural integrity of the pile can prevent unexpected landslides and cave-ins. SORTING RAW TRASH Landfill operators want less waste, not more. Separating out recyclable materials can bring additional revenue and reserve valuable space in the heap.