Field performance of a phytocap at Lakes Creek landfill, Rockhampton, Australia

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 small and medium sized landfills (< 100,000 tonnes/annum) and the use of clay caps have proved 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 depths (700 mm and 1400 mm) of soil cover and 21 tree species. Methane emissions at the surface as well as at various depths (300 mm – 900 mm) 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 of the same landfill. Results demonstrate that the phytocapping technique can reduce surface methane flux by 75% - 85% in comparison to the adjacent non-vegetated landfill site.