matter needed to run the biogeochemical processes and ensure the availability of
organic compound through exudation from roots (Jenssen et al. 1993). In acid mine
drainage, the substrate and water are categorized by low pH and high metal concentrations. This leads to release of dissolved iron and protons, which, in turn, leads to
the release of other metallic ions, such as Mn, Ni, Zn, Cu, and Cd. Because of the
extreme conditions of acid mine drainage (Holmstrom 2000), the formation of acid
mine drainage can be prevented by limiting contact between mining wastes and
oxygen. One attractive and efficient solution for reducing O 2 diffusion is to construct
a wetland as a cover over mine waste (Stoltz and Greger 2005).
Erosion and Sedimentation The macrophyte plant species (Phragmites australis)
encourage suspended solids and sedimentation and also stop erosion by reducing
flow rates of water by increasing the surface area per length of the hydraulic
pathways through the structure (Lee and Scholz 2007). Surface flow system shows
different behaviors; sometimes, it shows static behavior in which there is no flow and
another is dynamic behavior in which the flow is high in static condition, and the
flow is negligible and behaves like stagnant pond in which displacement effects
caused by submerged plant mass decrease retention times. Under dynamic conditions, active flow-through and stem drag are increased and are more important than
displacement of volume (Matagi et al. 1998).
Retention times become high with increasing vegetation resulting in increased
sedimentation, but it is possible after floc formation, but it may absorb metal and
other types of suspended material. Flocculation can be improved by high pH, high
ionic strength, high vegetation density, and high concentration of suspended material. A key point that is often overlooked is the supply of organic matter by plants.
Organic matter derived from plants in wetlands constantly provides carbon sources
for bacterial metabolism as well as metal sorption thus encouraging long-term
operation (Marchand et al. 2010).
Plant plays an important role in wetlands for wastewater treatment. Though,
handling with contaminated saline wastewater importance must be given to the
selection process of plants as they should be tolerable to salt and show resistant in
active CW system (Brix 1997). Klomjek and Nitisoravut (2005) assessed the
feasibility of CWs to remove contaminants through eight plant species from saline
wastewaters. They stated that Typha angustifolia is best for nitrogen accumulation
and plant growth, whereas Digitaria bicornis was best for BOD5 removal when
linked to other species (Brachiaria mutica, Cyperus corymbosus, Vetiveria
zizanioides, Leptochloa fusca, Spartina patens, and Echinodorus cordifolius).
Emergent Plants Various types of emergent plants are used in constructed wetlands and result in different metal removals of widely used species Phragmites
australis (Vymazal et al. 2007). Other used species are Typha domingensis, Typha
latifolia, and Phragmites karka (Juwarker et al. 1995). In constructed wetlands,
numerous emergent plants particularly Phragmites australis have been tested
achieving variable metal removal rates (Vymazal et al. 2007). Phalaris arundinacea
shows same capabilities like Typha domingensis, Phragmites australis, Phragmites
karka, and Typha latifolia (Juwarker et al. 1995) as shown in Table 6.2. Toxic metals
and suspended organic matter are removed mainly by rhizosphere immobilization
138
S. Khan et al.
organic compound through exudation from roots (Jenssen et al. 1993). In acid mine
drainage, the substrate and water are categorized by low pH and high metal concentrations. This leads to release of dissolved iron and protons, which, in turn, leads to
the release of other metallic ions, such as Mn, Ni, Zn, Cu, and Cd. Because of the
extreme conditions of acid mine drainage (Holmstrom 2000), the formation of acid
mine drainage can be prevented by limiting contact between mining wastes and
oxygen. One attractive and efficient solution for reducing O 2 diffusion is to construct
a wetland as a cover over mine waste (Stoltz and Greger 2005).
Erosion and Sedimentation The macrophyte plant species (Phragmites australis)
encourage suspended solids and sedimentation and also stop erosion by reducing
flow rates of water by increasing the surface area per length of the hydraulic
pathways through the structure (Lee and Scholz 2007). Surface flow system shows
different behaviors; sometimes, it shows static behavior in which there is no flow and
another is dynamic behavior in which the flow is high in static condition, and the
flow is negligible and behaves like stagnant pond in which displacement effects
caused by submerged plant mass decrease retention times. Under dynamic conditions, active flow-through and stem drag are increased and are more important than
displacement of volume (Matagi et al. 1998).
Retention times become high with increasing vegetation resulting in increased
sedimentation, but it is possible after floc formation, but it may absorb metal and
other types of suspended material. Flocculation can be improved by high pH, high
ionic strength, high vegetation density, and high concentration of suspended material. A key point that is often overlooked is the supply of organic matter by plants.
Organic matter derived from plants in wetlands constantly provides carbon sources
for bacterial metabolism as well as metal sorption thus encouraging long-term
operation (Marchand et al. 2010).
Plant plays an important role in wetlands for wastewater treatment. Though,
handling with contaminated saline wastewater importance must be given to the
selection process of plants as they should be tolerable to salt and show resistant in
active CW system (Brix 1997). Klomjek and Nitisoravut (2005) assessed the
feasibility of CWs to remove contaminants through eight plant species from saline
wastewaters. They stated that Typha angustifolia is best for nitrogen accumulation
and plant growth, whereas Digitaria bicornis was best for BOD5 removal when
linked to other species (Brachiaria mutica, Cyperus corymbosus, Vetiveria
zizanioides, Leptochloa fusca, Spartina patens, and Echinodorus cordifolius).
Emergent Plants Various types of emergent plants are used in constructed wetlands and result in different metal removals of widely used species Phragmites
australis (Vymazal et al. 2007). Other used species are Typha domingensis, Typha
latifolia, and Phragmites karka (Juwarker et al. 1995). In constructed wetlands,
numerous emergent plants particularly Phragmites australis have been tested
achieving variable metal removal rates (Vymazal et al. 2007). Phalaris arundinacea
shows same capabilities like Typha domingensis, Phragmites australis, Phragmites
karka, and Typha latifolia (Juwarker et al. 1995) as shown in Table 6.2. Toxic metals
and suspended organic matter are removed mainly by rhizosphere immobilization
138
S. Khan et al.