treatment providing integrated sludge accumulation and mineralization, thus
avoiding the need for additional sludge dewatering equipment (Stefanakis and
Tsihrintzis 2012; Stefanakis et al. 2014; Morvannou et al. 2015; Stefanakis 2020).
VFCWs also have lower area demand than horizontal subsurface flow CWs
(HSFCW). Moreover, over the last years, a new design modification has been tested
and applied, that of the artificially aerated constructed wetlands (ACW). In these
systems, artificial means are used to maximize the air supply to the system in order to
improve the oxygen availability. For this, an air pump (a blower or injector) is used
to provide compressed air to the CW bed. This design mode has been tested in
HSFCWs where oxygen availability is limited (Ouellet-Plamondon et al. 2006;
Chazarenc et al. 2009; Stefanakis et al. 2009, 2011; Zhang et al. 2010; Uggetti
et al. 2016), as well as in VFCW systems (Dong et al. 2012; Stefanakis et al. 2014,
2019; Murphy et al. 2016; Liu et al. 2019).
Although wastewater aeration is a common practice in other treatment methods
(e.g., in activated sludge systems and membrane bioreactors), aeration of gravel beds
is not that old. In tanks and ponds, aeration creates air bubbles, creating this way a
hydrodynamic mixing effect, which results in a more uniform distribution of the
dissolved oxygen at a considerable distance from the air diffuser (Nivala et al. 2012;
Stefanakis et al. 2014). Therefore, aeration in conventional wastewater treatment
methods is provided via high-volume devices. On the contrary, in subsurface flow
CWs containing gravel media, the hydrodynamic mixing is limited and the distance
an air bubble can reach does not exceed approx. 30–40 cm. For this reason, effective
aeration in subsurface flow CWs can be implemented with uniform distribution of
small air quantities across the bottom of the bed. The main advantage of bottom
additional aeration especially in VFCWs is that the combined action of the vertical
downward drainage of the wastewater with the upflow movement of air bubbles
results in a very good water mixture within the bed (Stefanakis 2015). Additional
aeration of the bed has been promoted as a positive alternative to enhance nitrogen
removal, especially in cold climate systems where ambient temperatures are not
favourable for nitrification (Wallace et al. 2000). Artificial aeration has shown a
tremendous treatment potential with significantly reduced area requirements (Dong
et al. 2012; Wu et al. 2014), indicating that they reach high levels of organic
degradation and enhanced nitrogen removal.
The existing international published literature already focuses on the investigation of the various operational parameters and the functions of these advanced
designs. The optimization of the system’s efficiency is of course always the goal.
Such information can be derived, however, only through the verification of experimental designs in full-scale systems operating under real conditions. Under this
frame, the technological status of CWs indicates that the combination of two
different wetland designs, i.e. of a VFCW and an ACW, could be a new approach
to wetland technology, providing an advanced wetland design with further enhanced
benefits. This concept aims at a dual target: (a) integrating sludge mineralization
within the system without the need for additional sludge dewatering equipment and
(b) minimizing the area demand using the aerated wetland system to provide a
treated effluent of high quality. Hence, this chapter presents one of the first
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A. I. Stefanakis
avoiding the need for additional sludge dewatering equipment (Stefanakis and
Tsihrintzis 2012; Stefanakis et al. 2014; Morvannou et al. 2015; Stefanakis 2020).
VFCWs also have lower area demand than horizontal subsurface flow CWs
(HSFCW). Moreover, over the last years, a new design modification has been tested
and applied, that of the artificially aerated constructed wetlands (ACW). In these
systems, artificial means are used to maximize the air supply to the system in order to
improve the oxygen availability. For this, an air pump (a blower or injector) is used
to provide compressed air to the CW bed. This design mode has been tested in
HSFCWs where oxygen availability is limited (Ouellet-Plamondon et al. 2006;
Chazarenc et al. 2009; Stefanakis et al. 2009, 2011; Zhang et al. 2010; Uggetti
et al. 2016), as well as in VFCW systems (Dong et al. 2012; Stefanakis et al. 2014,
2019; Murphy et al. 2016; Liu et al. 2019).
Although wastewater aeration is a common practice in other treatment methods
(e.g., in activated sludge systems and membrane bioreactors), aeration of gravel beds
is not that old. In tanks and ponds, aeration creates air bubbles, creating this way a
hydrodynamic mixing effect, which results in a more uniform distribution of the
dissolved oxygen at a considerable distance from the air diffuser (Nivala et al. 2012;
Stefanakis et al. 2014). Therefore, aeration in conventional wastewater treatment
methods is provided via high-volume devices. On the contrary, in subsurface flow
CWs containing gravel media, the hydrodynamic mixing is limited and the distance
an air bubble can reach does not exceed approx. 30–40 cm. For this reason, effective
aeration in subsurface flow CWs can be implemented with uniform distribution of
small air quantities across the bottom of the bed. The main advantage of bottom
additional aeration especially in VFCWs is that the combined action of the vertical
downward drainage of the wastewater with the upflow movement of air bubbles
results in a very good water mixture within the bed (Stefanakis 2015). Additional
aeration of the bed has been promoted as a positive alternative to enhance nitrogen
removal, especially in cold climate systems where ambient temperatures are not
favourable for nitrification (Wallace et al. 2000). Artificial aeration has shown a
tremendous treatment potential with significantly reduced area requirements (Dong
et al. 2012; Wu et al. 2014), indicating that they reach high levels of organic
degradation and enhanced nitrogen removal.
The existing international published literature already focuses on the investigation of the various operational parameters and the functions of these advanced
designs. The optimization of the system’s efficiency is of course always the goal.
Such information can be derived, however, only through the verification of experimental designs in full-scale systems operating under real conditions. Under this
frame, the technological status of CWs indicates that the combination of two
different wetland designs, i.e. of a VFCW and an ACW, could be a new approach
to wetland technology, providing an advanced wetland design with further enhanced
benefits. This concept aims at a dual target: (a) integrating sludge mineralization
within the system without the need for additional sludge dewatering equipment and
(b) minimizing the area demand using the aerated wetland system to provide a
treated effluent of high quality. Hence, this chapter presents one of the first
198
A. I. Stefanakis