Phytocapping of landfills : an Australian experience

Landfills have been the major repositories of urban wastes and they will continue to be built so long as the humans live in the communities. The costs of construction, maintenance and remediation of landfills have escalated over the years and research is therefore required to identify alternative technologies that will not only minimise the costs but also demonstrate increased environmental performance and community benefits. An alternative landfill capping technique known as 'Phytocapping' (establishment of perennial plants on a layer of soil placed over the waste) was trialled in Rockhampton, Australia. In this technique, trees were used as 'bio-pumps' and 'rainfall interceptors' and soil cover as 'storage' of water. Tree performance was measured based on their canopy rainfall interception and water uptake potential. The percolation rate was estimated using HYDRUS 1D for two different scenarios (with and without vegetation) for the thick and thin covers respectively. Results from the simulations incorporating 15 years of meteorolgical data showed percolation rates of 16.7mm yr-1 in thick cover and 23.8mm yr-1 in thin cover, both of which are markedly lower than those expected from a clay cap.