Phytotechnology and Photosynthesis - Environmental Biotechnology: Theory and Application - page 155

One area where phytoremediation could have a particular role to play, and
one which might be amenable to early acceptance is as a polishing phase in
combination with other clean up technologies. As a finishing process follow-
ing on from a preceding bioremediation or non-biological method first used to
deal with 'hot-spots', plant-based remediation could well represent an optimal
low-cost solution. This has already been successful in small scale trials and con-
sequently techniques have been suggested to treat deeply located contaminated
ground water by simply pumping to the surface and using it as the irrigant for
carefully selected plant species, allowing them to biodegrade the pollutants. The
lower levels of site intrusion and engineering required to achieve this would
bring clear benefits to both the safety and economic aspects of the remedia-
tion operation, if the planned larger scale investigations are found to support
the idea.
Aquatic Phyto-Systems (APS)
Aquatic phyto-systems (APS) are principally used to process effluents of one
form or another, though manufactured wetlands have been used successfully
to remediate some quite surprising soil contaminants, including TNT residues.
Though the latter type of application will be discussed in this section, it is prob-
ably best considered as an intergrade between the other APS described hereafter
and the Terrestrial Phyto-Systems (TPS) of the previous. Many of the aspects of
the bio-treatment of sewage and other wastewaters have already been covered
in the previous chapter and so will not be restated here. The major difference
between conventional approaches to deal with effluents and phytotechnological
methods is that the former tend to rely on a faster, more intensively managed
and high energy regime, while in general the stabilisation phase of wastewaters
in aquatic systems is relatively slow. The influx and exit of effluent into and out
of the created wetland must be controlled to ensure an adequate retention period
to permit sufficient residence time for pollutant reduction, which is inevitably
characterised by a relatively slow flow rate. However, the efficiency of removal
is high, typically producing a final treated off-take of a quality which equals,
or often exceeds, that of other systems. Suffice it to say that, as is typical of
applications of biological processing in general, there are many common sys-
temic considerations and constraints which will obviously affect phyto-systems,
in much the same way as they did for technologies which rely on microbial
action for their effect.
Many aquatic plant species have the potential to be used in treatment systems
and the biological mechanisms by which some of the effects they achieve will
already be largely familiar from the preceding discussion of terrestrial systems.
There are a number of ways in which APS can be categorised but perhaps the
most useful relates to the natural division between algae and macrophytes, which
has been adopted, accordingly, here.