Phytotechnology and Photosynthesis - Environmental Biotechnology: Theory and Application - page 156

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 sim-
pler, more natural methods for wastewater treatment and Macrophyte Treatment
Systems (MaTS), 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 harmonious water cleaning per se ,alargepartof
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 devel-
opment 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
volume, either in the form of an artificial pond or an expanse of highly satu-
rated soil held within a containment layer, within which the macrophytes have
been established. Less commonly, pre-existing natural features have been used.
Although wetlands have an innate ability to accumulate various unwanted chem-
icals, the concept of deliberately polluting a habitat by using it as a treatment
system is one with which few feel comfortable today. A gentle hydraulic flow is
established, which encourages the incoming wastewater to travel slowly through
the system. The relatively long retention period that results allows adequate
time for processes of settlement, contaminant uptake, biodegradation and phyto-
transformation to take place.
The mechanisms of pollutant removal are essentially the same, irrespective of
whether the particular treatment system is a natural wetland, a constructed mono-
culture or polyculture and independent of whether the macrophytes in question
Figure7.2 Diagrammaticmacrophytetreatmentsystem(MaTS)