Environmental Engineering Reference
In-Depth Information
Over the past three decades, ecological design
has been applied to an increasingly diverse range of
technologies and innovative solutions for the man-
agement of resources (Todd et al.
2003
). Ecological
technologies are particularly considered in the field
of environmental protection and restoration due to
their sustainable nature. The conventional waste-
water treatment systems have inherent limitations
as they employ chemicals, emit foul odours, require
technical skills to operate, and are expensive
involving a lot of investment in construction and
maintenance, and moreover they are not environ-
mentally friendly (Carty et al.
2008
). If wisdom of
ecosystem be applied to the fundamental redesign
of human support technologies (Todd et al.
2003
),
it can cogently reduce the negative human footprint
on the earth up to 90 % (Hawken et al.
1999
).
The use of SF systems is extensive in North
America. These systems are used mainly for
municipal wastewater treatment with large waste-
water flows for nutrient polishing. The SF system
tends to be rather large in size with only a few
smaller systems in use.
The majority of constructed wetland treat-
ment systems are surface flow or free water
surface (SF) systems. These types utilise influent
waters that flow across a basin or a channel that
supports a variety of vegetation, and water is
visible at a relatively shallow depth above the
surface of the substrate materials. Substrates are
generally native soils and clay or impervious
geotechnical materials that prevent seepage
(Reed et al.
1995
). Inlet devices are installed to
maximise sheet flow of wastewater through the
wetland to the outflow channel. Typically, bed
depth is about 0.4 m.
2
Constructed Wetland:
Definition and Classification
2.2
Sub-Surface Flow (SSF)
System
Constructed wetlands (CWs) are engineered
wastewater treatment systems that encompass a
plurality of treatment modules including biologi-
cal, chemical and physical processes, which are
all akin to processes occurring in natural treat-
ment wetlands. CWs have now been successfully
used for environmental pollution control, through
the treatment of a wide variety of wastewaters
including industrial effluents, urban and agricul-
tural storm water run-off, animal wastewaters,
leachates, sludges and mine drainage (Scholz
2006
) using different types of potent aquatic
macrophytes and hyperaccumulator plants like
bulrush (
Scirpus
), reeds (
Phragmites
), cattail
(
Typha latifolia
) and knotweed (
Polygonum
sp.),
lotus (
Nelumbo nucifera
), nilofar (
Nymphaea
alba
),
Ceratophyllum demersum
, etc.
There are two basic types of constructed wet-
lands: surface flow and sub-surface flow systems
(Kadlec and Knight
1996
).
Sub-surface flow wetlands mostly employ gravel
as the main media to support the growth of plants;
wastewater flows vertically or horizontally
through the substrate where it comes into contact
with microorganisms, living on the surfaces of
plant roots and substrate (Cooper et al.
1996
;
Kadlec and Knight
1996
), allowing pollutant
removal from the bulk liquid. The SSF system
includes soil-based technology which is predom-
inantly used in Northern Europe, and the vege-
tated gravel beds are found in Europe, Australia,
South Africa and almost all over the world.
Sub-surface flow constructed wetlands are
further divided into two groups:
1. Vertical flow (VF)
2. Horizontal flow (HF)
Much interest has developed in recent years to
study the mechanism and possible impact of wet-
lands to remove contaminants from water,
whether it is effluent from municipal or private
waste systems and industrial or agricultural
wastewater. A constructed wetland uses natural
geochemical and biological processes in a wet-
land ecosystem to treat metals, explosives and
other contaminants in groundwater.
2.1
Surface Flow (SF)
Surface flow wetlands are similar to natural wet-
lands, with shallow flow of wastewater (usually
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