Biomedical Engineering Reference
In-Depth Information
Clearly, the metallurgists would have to be assured that it was a worthwhile
exercise - and with the price of metals on the global market being a notoriously
cyclical thing, the dimension of time-sensitivity would also need to be factored
into the discussion. The recycling question is, then, a long way from being a
workable solution, but potentially it could offer a highly preferable option to the
landfill route.
Rhizofiltration
Rhizofiltration is the absorption into, or the adsorption or precipitation onto,
plant roots of contaminants present in the soil water. The principle difference
between this and the previous approach is that rhizofiltration is typically used
to deal with contamination in the groundwater, rather than within the soil itself,
though the distinction is not always an easy one to draw. The plants destined
to be used in this way are normally brought on hydroponically and gradually
acclimatised to the specific character of the water which requires to be treated.
Once this process has been completed, they are planted on the site, where they
begin taking up the solution of pollutants. Harvesting takes place once the plants
have become saturated with contaminants and, as with the phytoextraction, the
collected biomass requires some form of final treatment. The system is less widely
appreciated than the previous technology, but it does have some very important
potential applications. Sunflowers were reported as being successfully used in a
test at Chernobyl in the Ukraine, to remove radioactive uranium contamination
from water in the wake of the nuclear power station accident.
Phytostabilisation
In many respects, phytostabilisation has close similarities with both phytoextrac-
tion and rhizofiltration in that it too makes use of the uptake and accumulation
by, adsorption onto, or precipitation around, the roots of plants. On first inspec-
tion, the difference between these approaches is difficult to see, since in effect,
phytostabilisation does employ both extractive and filtrative techniques. How-
ever, what distinguishes this particular phytoremediation strategy is that, unlike
the preceding regimes, harvesting the grown plants is not a feature of the pro-
cess. In this sense, it does not remove the pollutants, but immobilises them,
deliberately concentrating and containing them within a living system, where
they subsequently remain. The idea behind this is to accumulate soil or ground
water contaminants, locking them up within the plant biomass or within the rhi-
zosphere, thus reducing their bioavailability and preventing their migration off
site. Metals do not ultimately degrade, so it can be argued that holding them in
place in this way is the best practicable environmental option for sites where
the contamination is low, or for large areas of pollution, for which large scale
remediation by other means would simply not be possible.
A second benefit of this method is that on sites where elevated concentrations
of metals in the soil inhibits natural plant growth, the use of species which have
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