Phytocapping To Rehabilitate Landfills, Reduce Greenhouse Emissions

rehabilitated landfill montreal photo
Image: Former landfill and limestone quarry near Montreal now being mined for its methane (by frigate on Flickr)

Though it's changing, the human species still largely lives in "disposable" societies — with the pinnacle of the life cycle ending up in the landfills, which generate large amounts of greenhouse gases as waste decays. But according to Australian scientists, these emissions can be reduced significantly with a process called "phytocapping," where a thick layer of soil is laid over the landfill and planted with specific tree and plant species.

Typically, buried organic matter in landfills degrades most quickly when it comes into contact with water. The usual method to combat unwanted percolation is to layer compacted clay over the top. This approach fares poorly in arid areas as the clay cracks, allowing water to seep through. However, other landfills skip the percolation shield altogether and opt instead to install systems to trap the methane released — a much more expensive option.

Phytocapping however, which employs a thick layer of soil and growing a dense buffer of vegetation, not only proves to be more efficient at trapping greenhouse gases, but also comes with a host of other potential advantages for the environment.The Central Queensland University (CQU) researchers' findings, published in the International Journal of Environmental Technology and Management, concluded that phytocapping could reduce surface methane emission four to five times more than an uncapped landfill.

But that's not all: "the establishment of phytocaps would offer an additional and economical way of reducing methane emission from landfills," adds Kartik Venkatraman and Nanjappa Ashwath, authors of the study.

Depth of soil layer and root systems a factor
In the study, the soil layer, which acts as "storage" and "sponge" was tested at different depths to see its effectiveness in reducing percolation and emissions, while nineteen species of endemic plants were tested for their suitability to maintaining water balance. Plants' root systems act as "bio-pumps" and "rainfall interceptors".

Overall, the study showed that phytocaps have great promise in rehabilitating landfill sites and transforming them into biodiversity corridors, connecting and enlarging habitats for isolated wild species. There's even the possibility of fringe economic benefits from providing timber and fodder to neighbouring communities.

So while landfills remain a problem, nothing says they cannot be rethought, whether that means mining them or harnessing landfill gases as energy or using landfill ooze as fertilizer. The least that can certainly be done is to beautify them with a bit of living green, or to completely transform them into green spaces where the public also has a stake in them.

Environmental News Network
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