Despite legislative pressures to reduce landfill use, in certain parts of the world, it remains the most economical and simplest method of waste disposal.
Biodegradation of organic matter in a landfill site occurs most rapidly when water comes into contact with the buried waste, according to Kartik Venkatraman and Nanjappa Ashwath of the Department of Molecular and Life Sciences, at Central Queensland University (CQU), Rockhampton, Australia.
They point out that conventional approaches to reducing this effect involve placing compacted clay over the top of a landfill to form a cap that minimizes percolation of water into the landfill.
But, according to researchers, the use of clay capping has generally proved ineffective in trials in the US.
Hence, a new technique, known as phytocapping, which involves placing a layer of top soil and growing dense vegetation on top of a landfill, was successfully trailed at Rockhampton's Lakes Creek Landfill.
This research was conducted by Venkatraman and Ashwath, in conjunction with the Rockhampton Regional Council and Phytolink Pty LTD.
Selected plant species are established on an unconsolidated soil placed over the waste. The soil acts both as "storage" and "sponge" and the plants as "bio-pumps" and "rainfall interceptors".
For an effective site water balance, it is important that appropriate plant species are chosen and the soil depth optimized.
As such, the team has investigated the effects of different ranges of species as well as soil depth.
The team's studies of the benefits of a landfill phytocap show that the approach can reduce surface methane emission four to five times more than the adjacent un-vegetated site.
They found that a cap of 1400 mm thickness also reduces surface methane emissions 45 percent more than a cap half as thick.
The benefits of phytocapping include, cutting in half the cost of landfill remediation and providing biodiversity corridors along which wild species can travel.
The process also inverts the aesthetic qualities of landfills adjacent to urban communities, and in some cases, introduces economical benefits such as timber and fodder.
"The establishment of phytocaps would offer an additional and economical way of reducing methane emission from landfills," the researchers concluded.