and peri-urban and rural areas. Hence, over the last years an alternative approach of
wastewater treatment has risen, the so-called decentralized approach.
CWs belong to this category and serve this philosophy as point-of-use treatment
systems that deliver effluents of the desired quality. CWs can be installed in most
areas and regions with reduced overall costs. It should be noted that the technology
of constructed wetlands should not be viewed as a direct competitor of conventional
treatment systems. A total replacement of centralized facilities with CWs and/or
other natural treatment systems is practically infeasible, given that the required land
area would be very high (Stefanakis 2015). Such a demand cannot be met in large
densely populated urban areas. However, CW systems can be an ideal solution for
small and medium communities, small cities, villages, single households or block of
flats and generally rural, mountainous and remote areas, where sewer network does
not exist, and the construction of a conventional treatment plant is economically
unfeasible.
CWs are in general easy to build and provide treatment that is robust to flow
fluctuations and pollutant concentrations. Among the advantages of wetland technology are also its simple and easy operation and minimal mechanical equipment
(Stefanakis et al. 2014). CW facilities do not include large and multiple mechanical
parts. The only mechanical equipment is usually pumps installed to transfer the
wastewater from one stage to the other, which can even be avoided with a proper
design and exploitation of the topography of the installation area. All these translate
to minimum operational costs, which probably represent the main advantage of CW
technology (Stefanakis 2015). In CWs, the energy input needed is very small,
usually only for any pumps that may exist in the facility. Energy requirements for
the treatment processes are covered by renewable energy sources used by plants
(solar, wind energy). Maintenance needs are also low, since the operation of a CW
facility is practically autonomous; at the stage of full operation, a typical maintenance scheme applied is one visit at the site on a monthly basis. Additionally, there is
limited need for specialized personnel to run the CW facility. Global experience
indicates that operational costs of CW facilities can be up to 90% lower compared to
conventional treatment methods. Moreover, CWs operate without the need for the
addition of any chemical substances, which is not the case in conventional treatment
plants.
Based on the above, it is obvious that these various and multiple characteristics of
CW provide this treatment technology an ecological character. They are often
characterized as sustainable systems due to the low energy consumption and the
use of natural materials (gravel, soil, sand and plants). The minimum energy
consumption in CW facilities saves natural resources and minimizes pollution
generation, especially when the energy source is non-renewable (e.g. fossil fuels).
These environmental benefits can be translated to low levels of greenhouse gas
emissions (CO 2 , CH 4 and N 2 O) (Langergraber 2013; Stefanakis et al. 2014;
Stefanakis 2019).
The main limitation of CW technology is the higher area demand compared to
mechanical solutions. However, continuous research and development can now
deliver improved designs in terms of area demand and operational mode. The type
of vertical flow constructed wetlands (VFCW) is widely used for raw wastewater
7 A Two-Stage Constructed Wetland Design Integrating Artificial Aeration and. . .
197
wastewater treatment has risen, the so-called decentralized approach.
CWs belong to this category and serve this philosophy as point-of-use treatment
systems that deliver effluents of the desired quality. CWs can be installed in most
areas and regions with reduced overall costs. It should be noted that the technology
of constructed wetlands should not be viewed as a direct competitor of conventional
treatment systems. A total replacement of centralized facilities with CWs and/or
other natural treatment systems is practically infeasible, given that the required land
area would be very high (Stefanakis 2015). Such a demand cannot be met in large
densely populated urban areas. However, CW systems can be an ideal solution for
small and medium communities, small cities, villages, single households or block of
flats and generally rural, mountainous and remote areas, where sewer network does
not exist, and the construction of a conventional treatment plant is economically
unfeasible.
CWs are in general easy to build and provide treatment that is robust to flow
fluctuations and pollutant concentrations. Among the advantages of wetland technology are also its simple and easy operation and minimal mechanical equipment
(Stefanakis et al. 2014). CW facilities do not include large and multiple mechanical
parts. The only mechanical equipment is usually pumps installed to transfer the
wastewater from one stage to the other, which can even be avoided with a proper
design and exploitation of the topography of the installation area. All these translate
to minimum operational costs, which probably represent the main advantage of CW
technology (Stefanakis 2015). In CWs, the energy input needed is very small,
usually only for any pumps that may exist in the facility. Energy requirements for
the treatment processes are covered by renewable energy sources used by plants
(solar, wind energy). Maintenance needs are also low, since the operation of a CW
facility is practically autonomous; at the stage of full operation, a typical maintenance scheme applied is one visit at the site on a monthly basis. Additionally, there is
limited need for specialized personnel to run the CW facility. Global experience
indicates that operational costs of CW facilities can be up to 90% lower compared to
conventional treatment methods. Moreover, CWs operate without the need for the
addition of any chemical substances, which is not the case in conventional treatment
plants.
Based on the above, it is obvious that these various and multiple characteristics of
CW provide this treatment technology an ecological character. They are often
characterized as sustainable systems due to the low energy consumption and the
use of natural materials (gravel, soil, sand and plants). The minimum energy
consumption in CW facilities saves natural resources and minimizes pollution
generation, especially when the energy source is non-renewable (e.g. fossil fuels).
These environmental benefits can be translated to low levels of greenhouse gas
emissions (CO 2 , CH 4 and N 2 O) (Langergraber 2013; Stefanakis et al. 2014;
Stefanakis 2019).
The main limitation of CW technology is the higher area demand compared to
mechanical solutions. However, continuous research and development can now
deliver improved designs in terms of area demand and operational mode. The type
of vertical flow constructed wetlands (VFCW) is widely used for raw wastewater
7 A Two-Stage Constructed Wetland Design Integrating Artificial Aeration and. . .
197