Terrestrial Phyto-Systems (TPS)
The importance of pollution, contaminated land and the increasing relevance of bioremediation have been discussed in previouly. Phytoremediation methods offer significant potential for certain applications and, additionally, permit much larger sites to be restored than would generally be possible using more traditional remediation technologies. The processes of photosynthesis described earlier are fundamental in driving what is effectively a solar-energy driven, passive and unengineered system and hence may be said to contribute directly to the low cost of the approach.
A large range of species from different plant groups can be used, ranging from pteridophyte ferns, to angiosperms like sunflowers, and poplar trees, which employ a number of mechanisms to remove pollutants. There are over 400 differ-ent species considered suitable for use as phytoremediators. Amongst these, some hyperaccumulate contaminants within the plant biomass itself, which can subse-quently be harvested, others act as pumps or siphons, removing contaminants from the soil before venting them into the atmosphere, while others enable the biodegradation of relatively large organic molecules, like hydrocarbons derived from crude oil. However, the technology is relatively new and so still in the development phase. The first steps toward practical bioremediation using various plant-based methods really began with research in the early 1990s and a number of the resulting techniques have been used in the field with reasonable success.
In effect, phytoremediation may be defined as the direct in situ use of living green plants for treatment of contaminated soil, sludges or groundwater, by the removal, degradation, or containment of the pollutants present. Such techniques are generally best suited to sites on which low to moderate levels of contamination are present fairly close to the surface and in a relatively shallow band. Within these general constraints, phytoremediation can be used in the remediation of land contaminated with a variety of substances including certain metals, pesticides, solvents and various organic chemicals.