Phytocapping: an alternative technique for landfill remediation

An alternative technique of landfill remediation known as 'Phytocapping' was trialled at Rockhampton, Australia. Twenty one tree species were established on two types of phytocaps (thick cap; 1400 mm soil and thin cap; 700 mm). The trial was monitored for plant growth, transpiration loss, canopy rainfall interception and methane oxidation. The results show that the tree species can intercept ca. 30% of the rainfall and they transpire 1-2 mm day−1. The phytocaps also lowered methane emission by 4-5 times compared to an adjacent non-vegetated landfill. The HYDRUS 1D simulation revealed a percolation rate of 16.7 mm yr−1 in thick phytocap and 23.8 mm yr−1 in thin phytocap. These values are significantly lower than those expected from compacted clay capping (78 mm yr−1; i.e. 10% of the rainfall). Overall, this study demonstrated that the phytocaps are effective in minimising percolation of water into buried waste. Further research is being conducted (http://www.wmaa.com.au/aacap/aacap.html), to seek approval of regulatory authorities to use phytocapping as an alternative technique of landfill remediation.