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

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 systemic 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 they achieve some of the effects 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.
Macrophyte Treatment Systems (MaTS)
The discharge of wastewaters into natural watercourses, ponds and wetlands is
an ancient and long-established practice, though rising urbanisation led to the
development of more engineered solutions, initially for domestic sewage and then
later, industrial effluents, which in turn for a time lessened the importance of the
earlier approach. However, there has been a resurgence of interest in simpler,
more natural methods for wastewater treatment and MaTS systems, in particular,
have received much attention as a result. While there has, undoubtedly, been a
strong upsurge in public understanding of the potential for environmentally har-
monious water cleaning per se , a large part of the driving force behind the newly
found interest in these constructed habitats comes from biodiversity concerns.
With widespread awareness of the dwindling number of natural wetlands, often
a legacy of deliberate land drainage for development and agricultural purposes,
the value of such manufactured replacements has become increasingly apparent.
In many ways it is fitting that this should be the case, since for the majority
of aquatic macrophyte systems, even those expressly intended as 'monocultures'
at the gross scale, it is very largely as a result of their biodiversity that they
function as they do.
These treatment systems, shown diagrammatically in Figure 7.2, are charac-
terised by the input of effluent into a reservoir of comparatively much larger vol-
ume, either in the form of an artificial pond or an expanse of highly saturated soil