5 Intricate Mechanisms for Metal Removal in Wastewater
by Wetland Technology
The metals copper, selenium, and zinc are required for proper growth and functioning of plant and animal in small amounts. In higher concentrations some metals turn
toxic and cause health hazards, i.e., lead, cadmium, and mercury, generally found in
industrial. The pollutants are removed by physical, chemical, and biological processes in a wetland. We have to understand the basic processes of the removal and
potential applications and knowledge of benefits along with limitations of these
treatment systems to design constructed wetlands.
5.1 Physical Processes
In a constructed wetland, various processes like plant uptake, filtration, chemical
transformation, and adsorption can take place for removal of heavy metals from
water (Walker and Hurl 2002); however, the primary process considered is sedimentation with suspended particles. As heavy metals come in contact with wetland,
a number of removal processes may occur (Zoppou 2001).
During sedimentation, the surface water velocity turns very low through the
wetland due to plants and rate of suspended particles affecting the sedimentation
rate being proportional to the settling velocity of particle and water residence time
(DeBusk 1999). Another process, flocculation, which is a physical process, is
influenced by pH, ionic strength, suspended particles, and microorganism concentration (Droppo et al. 1997; Matagi et al. 1998; Sheoran and Sheoran 2006).
Sedimentation is generally considered as a reversible process that causes accumulation of particles and association of contaminants on the wetland soil/sediment
surface and releases them with the environmental change (DeBusk 1999). The
turbulence should be controlled as the sediment can resuspend and reenter the waters
by wind-driven turbulence and bioturbation (disturbance by animals and humans).
5.2 Biological Processes
This is the most important method for contaminant removal in wetlands as plant
uptake is considered the most widely recognized biological process. The plants can
absorb pollutants directly in water or supply oxygen to microorganisms around the
rhizosphere within the wetland.
272
M. Rastogi and M. Nandal
by Wetland Technology
The metals copper, selenium, and zinc are required for proper growth and functioning of plant and animal in small amounts. In higher concentrations some metals turn
toxic and cause health hazards, i.e., lead, cadmium, and mercury, generally found in
industrial. The pollutants are removed by physical, chemical, and biological processes in a wetland. We have to understand the basic processes of the removal and
potential applications and knowledge of benefits along with limitations of these
treatment systems to design constructed wetlands.
5.1 Physical Processes
In a constructed wetland, various processes like plant uptake, filtration, chemical
transformation, and adsorption can take place for removal of heavy metals from
water (Walker and Hurl 2002); however, the primary process considered is sedimentation with suspended particles. As heavy metals come in contact with wetland,
a number of removal processes may occur (Zoppou 2001).
During sedimentation, the surface water velocity turns very low through the
wetland due to plants and rate of suspended particles affecting the sedimentation
rate being proportional to the settling velocity of particle and water residence time
(DeBusk 1999). Another process, flocculation, which is a physical process, is
influenced by pH, ionic strength, suspended particles, and microorganism concentration (Droppo et al. 1997; Matagi et al. 1998; Sheoran and Sheoran 2006).
Sedimentation is generally considered as a reversible process that causes accumulation of particles and association of contaminants on the wetland soil/sediment
surface and releases them with the environmental change (DeBusk 1999). The
turbulence should be controlled as the sediment can resuspend and reenter the waters
by wind-driven turbulence and bioturbation (disturbance by animals and humans).
5.2 Biological Processes
This is the most important method for contaminant removal in wetlands as plant
uptake is considered the most widely recognized biological process. The plants can
absorb pollutants directly in water or supply oxygen to microorganisms around the
rhizosphere within the wetland.
272
M. Rastogi and M. Nandal