Performance of a phytocapped landfill in a semi-arid climate

Landfills have been the major repositories of urban wastes, and they will continue to be built, so long as the humans live in communities. The costs of construction, maintenance and remediation of landfills have escalated over the years and research is therefore required to identify alternative techniques that will not only minimise the costs, but also demonstrate increased environmental performance and community benefits. This chapter discusses the alternative landfill capping technique known as ‘Phytocapping’ (establishment of perennial plants on a layer of soil placed over the waste), which was trialed 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 rate of percolation of water was modelled using HYDRUS 1D for two different scenarios (with and without vegetation) for the thick (1400 mm) and thin (700 mm) covers respectively. Evidence and simulations incorporating 15 years of meteorological data showed percolation rates of 16.7 mm yr-1 in thick cover and 23.8 mm yr-1 in thin cover, both of which are markedly lower than those expected from a clay cap.