Abstract
An alternative landfill capping technique known as ‘Phytocapping’ (establishment of perennial plants on a layer of soil placed over the waste) was trailed in Rockhampton, Australia. In this technique, trees were used as ‘bio-pumps’ and ‘rainfall interceptors’ and soil cover as ‘storage’ of water. The environmental performance of the phytocapping system was measured based on its ability to minimise water percolation into the waste. The percolation rate was modelled using HYDRUS 1D for two different scenarios (with and without vegetation) for the thick and thin caps, respectively. Results from the modelling showed percolation rates of 16.7 mm year−1 in thick cover and 23.8 mm year−1 in thin cover, both of which are markedly lower than those expected from a clay cap. Results from monitoring and observations showed that 19 trees out of 21 tree species grew well in the harsh landfill environment. Top ten performing species have been identified and are recommended to be grown on phytocaps in the Central Queensland region.
Highlights
Deposition of wastes in landfills has adverse environmental impacts such as leachate generation and methane emission (El-Fadel and Massoud 2000)
The environmental performance of the phytocapped site was measured by evaluating the tree species with regards to their growth, transpiration rates and canopy interception potential
Results from this study demonstrate that selection of the right species is very important for the sustainability of the phytocapping system
Summary
Deposition of wastes in landfills has adverse environmental impacts such as leachate generation and methane emission (El-Fadel and Massoud 2000). To reduce the impact of landfills on the environment, various technologies such as leachate collection systems (Rittmann et al 1998), compacted lay liners (Aliston et al 1997), composite liners (Halse et al 1990), geosynthetic clay liners (GCLs; Benson 2000), compacted clay covers (Khire et al 1997) and composite covers (high density polyethylene, HDPE; Khire et al 1997; Levin and Hammod 1990) have been introduced and practiced. Conventional capping systems made of compacted clay (Othman et al 1994), GCL (Benson 2000), polyvinyl chloride (Levin and Hammond 1990) and HDPE (Simon and Muller 2004) have been used extensively in developed and many developing countries. A typical compacted clay cap recommended in Queensland contains 200 to 300 mm of earthen cover at the bottom, followed by a 500-mm layer of low permeability clay (Ks
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