Phytocaps reduce methane emission from landfills

Greenhouse gases such as methane and carbon dioxide are produced from landfill when the waste comes in contact with water. With a view to reducing methane emissions, techniques such as clay capping is used to minimise percolation of water into the waste or gas recovery systems are installed to reduce methane emission into the atmosphere. The use of clay cap has proven to be ineffective in avoiding percolation of water (Albright et al. 2004) Thus an alternative technique known as ‘Phytocapping’ was trialled at Rockhampton’s Lakes Creek Landfill using two soil depths of (700 mm and 1400 mm) of soil cover and 21 tree species. Methane emissions at the surface as well as at various depths of the phytocaps were monitored. The study also compared methane flux between vegetated and un-vegetated sections of the landfill. Results demonstrate that phytocapping technique can reduce surface methane flux by 75% - 85% compared to its adjacent un-vegetated site. Methane flux ranged between < 0.0007 g m-2 d-1 to >0.0009 g m-2 d-1 in phytocaps as compared to >0.0036 g m-2 d-1 in the adjacent un-vegetated landfill site. Depth-wise changes in methane concentrations in both 700 mm and 1400 mm soil covers were also monitored. Methane concentrations at 900 mm depth were up to 240 ppm which decreased to less than 0.1 ppm at the surface. Methane oxidation occurred through out the soil depth (0 mm to 900 mm). Root zone methane concentrations significantly varied between tree species, with the highest reduction occurring in the root zones of Ficus macrocarpa var. hillii.