and storage in the roots by plant species (Lesage et al. 2007). Research work has
shown that heavy metals such as Cr, Zn, and Ni are efficiently accumulated in the
whole plants (Cheng et al. 2002). The leading capacity of root-exuded organic acids
arises in soil as anions such as oxalate, acetate, malate, citrate, fumarate, and
malonate. The phytotoxicity can be decreased because the anions can chelate
metallic ions to variable degrees (Ryan et al. 2001).
Floating Plants Floating plants absorb metals, i.e., Eichhornia crassipes, Salvinia
herzogii, and Pistia stratiotes. In contrast, floating plants store metals in their
biomass and then absorb it in to subtract (Vymazal et al. 1998). Eichhornia crassipes
biomass doubles in 6 days under promising situations (Mitchell 1976). Some of the
plant takes up high amounts of P and N in the roots. This supports microorganism
that degrades organic matter and releases oxygen into the E. crassipes that permits a
significant P removal rate in a short duration after harvesting from water (Maine et al.
2006).
Submerged Plants The submerged marine plants such as Hydrilla verticillata,
Ceratophyllum demersum, Potamogeton spp., and Myriophyllum spicatum have
been used frequently for wastewater treatment (Bunluesin et al. 2007). Besides the
experiments performed, batch experiment studies have been useful, but their implementation in large-scale constructed wetlands is ambiguous, mainly due to their little
winter performance, biomass and, maintenance of efficient system (Kivaisi 2001).
To stabilize acid mine drainage, plantation of submerged plant species is preferred in
wastewater because these plants accumulate more metals as compared to emergent
macrophytes (Nyquist and Greger 2009).
Submerged macrophytes are possibly not appropriate for wastewater in excessive Fe precipitation, because it constrains light distribution and photosynthesis
(Nyquist and Greger 2009). The system in which the contaminants entered the
plants and transpired through the plant leaves is called phyto-volatilization (Interstate 2003). Besides this, plants play a significant role in removal of heavy metals
through adsorption, filtration, and cation. Plant species play a vital role in uptake
and removal of heavy metals, and some plant species have the capability to
accumulate more heavy metals than others, such as Lemna gibba, Salix Alba L,
Lemna minor, Phragmites australis, and Typha latifolia (Zayed et al. 1998).
According to Stottmeister et al. (2003), the extreme circumstances to treat
wastewater through rhizosphere in wetlands can be summarized as (1) extremely
condensed situation (Eh up to <_200 mV, particularly in horizontal subsurface flow
systems) encouraging the development of CH 4 and H 2 S; (b) pH values (acidic or
alkaline) in certain wastewaters; (c) Contaminated components of wastewater such
as heavy metals, phenols and biocides etc.; and (d) salinity.
The listed plant species are commonly used for the treatment of wastewater in
constructed wetlands (Greenway and Bolton 1996): Typha latifolia L. (broadleaved cattail); Scirpus spp. (bulrushes); Juncus spp. (rushes); Phragmites
australis (Cav.) Trin. ex Steud. (common reed); Typha angustifolia L. (narrowleaved cattail); Iris pseudacorus L. (yellow flag); Glyceria maxima (Hartm.)
Holmb. (reed grass); Carex spp. (sedges), and Acorus calamus L. (sweet flag).
6 Constructed Wetlands: A Clean-Green Technology for Degradation and. . .
139
shown that heavy metals such as Cr, Zn, and Ni are efficiently accumulated in the
whole plants (Cheng et al. 2002). The leading capacity of root-exuded organic acids
arises in soil as anions such as oxalate, acetate, malate, citrate, fumarate, and
malonate. The phytotoxicity can be decreased because the anions can chelate
metallic ions to variable degrees (Ryan et al. 2001).
Floating Plants Floating plants absorb metals, i.e., Eichhornia crassipes, Salvinia
herzogii, and Pistia stratiotes. In contrast, floating plants store metals in their
biomass and then absorb it in to subtract (Vymazal et al. 1998). Eichhornia crassipes
biomass doubles in 6 days under promising situations (Mitchell 1976). Some of the
plant takes up high amounts of P and N in the roots. This supports microorganism
that degrades organic matter and releases oxygen into the E. crassipes that permits a
significant P removal rate in a short duration after harvesting from water (Maine et al.
2006).
Submerged Plants The submerged marine plants such as Hydrilla verticillata,
Ceratophyllum demersum, Potamogeton spp., and Myriophyllum spicatum have
been used frequently for wastewater treatment (Bunluesin et al. 2007). Besides the
experiments performed, batch experiment studies have been useful, but their implementation in large-scale constructed wetlands is ambiguous, mainly due to their little
winter performance, biomass and, maintenance of efficient system (Kivaisi 2001).
To stabilize acid mine drainage, plantation of submerged plant species is preferred in
wastewater because these plants accumulate more metals as compared to emergent
macrophytes (Nyquist and Greger 2009).
Submerged macrophytes are possibly not appropriate for wastewater in excessive Fe precipitation, because it constrains light distribution and photosynthesis
(Nyquist and Greger 2009). The system in which the contaminants entered the
plants and transpired through the plant leaves is called phyto-volatilization (Interstate 2003). Besides this, plants play a significant role in removal of heavy metals
through adsorption, filtration, and cation. Plant species play a vital role in uptake
and removal of heavy metals, and some plant species have the capability to
accumulate more heavy metals than others, such as Lemna gibba, Salix Alba L,
Lemna minor, Phragmites australis, and Typha latifolia (Zayed et al. 1998).
According to Stottmeister et al. (2003), the extreme circumstances to treat
wastewater through rhizosphere in wetlands can be summarized as (1) extremely
condensed situation (Eh up to <_200 mV, particularly in horizontal subsurface flow
systems) encouraging the development of CH 4 and H 2 S; (b) pH values (acidic or
alkaline) in certain wastewaters; (c) Contaminated components of wastewater such
as heavy metals, phenols and biocides etc.; and (d) salinity.
The listed plant species are commonly used for the treatment of wastewater in
constructed wetlands (Greenway and Bolton 1996): Typha latifolia L. (broadleaved cattail); Scirpus spp. (bulrushes); Juncus spp. (rushes); Phragmites
australis (Cav.) Trin. ex Steud. (common reed); Typha angustifolia L. (narrowleaved cattail); Iris pseudacorus L. (yellow flag); Glyceria maxima (Hartm.)
Holmb. (reed grass); Carex spp. (sedges), and Acorus calamus L. (sweet flag).
6 Constructed Wetlands: A Clean-Green Technology for Degradation and. . .
139