Provision of a final landfill cover is a legislative requirement under State Government Guidelines and Regulations. Phytocapping is an alternative option to traditional clay and/or composite liner capping methods for closed landfills towards effective leachate management.
What is Phytocapping?
“Phytocapping is a capping technique that utilises vegetation as a natural pumping system to reduce water being stored in the soil and then gravity fed into the covered waste. This in turn reduces the amount of water reacting with the buried waste and being released as leachate”
How does it work?
Trees extract water through the soil that they grow in for their development. The key process that uses this water is photosynthesis. This process is where plants absorb carbon dioxide and water to produce oxygen and essential sugars for their function and growth. Excess water that is not used in this process is released into the atmosphere through transpiration through the leaf surface. Some water received via rainfall is also stored in the canopy and directly evaporated into the atmosphere without reaching the ground. Vegetation that has a high capacity for respiration through photosynthesis is preferable for Phytocapping.
What are the benefits of Phytocapping?
There are economic, environmental and social benefits to Phytocapping. Financially, establishing and managing a vegetative cap costs less than delivery and management of traditional clay based cap. Cost savings shown as we move away from a traditional cap where spend per m2 is approximately halved (depending on availability of resources and distance).
Environmentally, increased vegetation can assist with provision of habitat for all species and can often provide key linkages within the natural landscape. Phytocaps are most beneficial where the potential evapotranspiration (PET) rate exceeds the average annual rainfall.
Social benefits are also available if recreational aspects can be built into the redevelopment of the site. This is particularly applicable in urban areas, with land previously unusable for recreational benefits becomes newly available. It is beneficial in areas where there is a lack of suitable clay material for capping; where locally available material will suit Phytocapping.