Phytocapping : an innovative technique to 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. Various techniques such as clay capping are used to minimise percolation of water into the waste and gas flaring and gas recovery systems are installed to reduce methane emission into the atmosphere. Flaring and recovery systems for reducing methane gas are very expensive for smaller and medium sized landfill (< 100,000 tonnes/annum) and the use of clay cap has proven to be ineffective in avoiding percolation of water which controls methane emission. 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 two phytocaps were monitored. Results from this study show that Phytocaps can reduce surface methane emission 4 to 5 times more than the adjacent un-vegetated site, and the thick cap (1400 mm) reduces surface methane emission 45% more than the thin cap (700 mm). The root zone effects of 19 tree species on methane emission were also examined. The study also compared methane flux between phytocaps and non-vegetated sections ofthe same landfill. Results demonstrate that phytocapping technique can reduce surface methane flux by 75% - 85% compared to its adjacent non-vegetated site.