December 12th, 2008 · No Comments

By John DeFore

Despite efforts to increase recycling, landfills aren’t going away any time soon. But a process called “phytocapping” might drastically reduce their impact on the environment, according to a paper published in the first 2009 issue of the International Journal of Environmental Technology and Management. (The full paper can only be seen if purchased, but it is summarized here.)

Organic materials in landfills produce the greenhouse gases methane and carbon dioxide as they decay, and this decay happens most rapidly when rainwater reaches the material. Today, many sites attempt to counter this by covering heaps of trash with impacted clay, which is intended to keep water from “percolating” into the heap. But clay is ineffective in many areas because heat and dry conditions cause cracks that let rain through; other attempts to regulate methane, like gas-collection devices, can be prohibitively expensive.

Kartik Venkatraman and Nanjappa Ashwath of Central Queensland University just conducted a study of a much more natural solution: placing layers of plants and trees on the top of the decaying junk.

In addition to the obvious aesthetic improvement, the authors have found that these plants and the soil they hold in place can stop water from seeping into the mound, with plants using it for their own growth processes. In trials at a landfill in Rockhampton (where their university is located), the researchers found that the water barrier had a dramatic effect on subsequent emissions: “Phytocaps can reduce surface methane emission 4 to 5 times more than the adjacent un-vegetated site,” they reported, going on to note that of two caps tested, a thicker one (almost a meter and a half) was 45% more effective than a thin one.

The team used 19 different species of trees at the site, boosting their conclusion that, in addition to the atmospheric benefits, phytocapping plans could help encourage biodiversity zones in areas that are now wastelands.

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