2 LITERATURE REVIEW
2.1 Overview on use of macrophytes in metal removal
Aquatic plants have been used now for decades to remove heavy
metal in polluted water (Rai et al., 1995; Denny et al.,
1995; Mungur et al., 1997; Zhihong et al., 1997; Obarska,
2001; Cheng et al., 2002; Keskinkan, 2005). These aquatic plants
commonly called macrophytes plants belong to different plant species. In
general these aquatic plants showed the capacity to remove heavy metal from
polluted water by accumulation in their roots or by simple uptake by the plants
(Lubberding et al., 1999; Lubberding et al., 2000; Awuah
et al., 2000; Lubberding et al., 2001). Many investigations
on metal removal have been conducted with the principal aim of cleaning the
environment from these dangerous metals. No particular attention to the
mechanism involved in the removal process had been investigated to explain what
is really occurring in the solution and what should be do to enhance the
removal efficiency when macrophytes plants cannot accumulate anymore heavy
metal in its roots or leaves.
Considerable interest has developed in the removal of heavy
metal in water using macrophytes plants (Prasad and Freitas, 2003). This method
of extracting heavy metal from polluted water bodies is called phytoextraction.
Plants are used to accumulate and uptake heavy metal from soil, sludge or
water. It has been reported that the removal accumulation process occurs via
adsorption, uptake and translocation processes (Abdel-Rahman, 1999; Kelderman,
2000; Leman, 2000; Babu, 2001; Meggo, 2001 and Alick, 2002).
Figure 2.1: Common aquatic plants (source: Aquatics,
2005)
In all reported investigations, it has been demonstrated that
adsorption was the main mechanism involved in the removal of heavy metal. In
some cases uptake and translocation have been observed. (Hasan et al.,
2006)
Different species have the ability to remove coliforms,
bacteria, metals from wastewater such as Nasturtium officinale to
accumulate Copper, Zinc and Nickel (Kara, 2005), the ability of water hyacinth
(Eichhornia crassipes) to remove Aluminum by constructed wetland grown
under different nutritional conditions is excepted (Jayaweera et al.,
2007), by different mechanisms. Vesk et al. (2006) confirm the metal
localization within and around roots of water hyacinth growing in a wetland
receiving urban run-off.
Several publications (Sarabjeet and Dinesh, 2005; Liu et
al., 2007, etc.) shown different plants able to treat wastewater in terms
of heavy metals removal such as Lemna minor, Myriophyllum aquaticum,
Ceratophyllum demersum, Azolla filiculoides, Salvinia natans, Acanthopanax
sciadophylloides, Ilex crenata, Clethra barbinervis, Acanthopanax
sciadophylloides, Pieris japonica, Ilex crenata, Rhododendron semibarbatum Acer
sieboldianum, Acer rufinerve, Acer micranthum, Lindera erythrocarpa, Clethra
barbinevris Macadamia neurophylla, M. augustifolia, Betula verrucosa, Sorbus
aucuparia, Clethra barbinervis.
2.2 Water hyacinth (Eichhornia crassipens (Mart.)
Solms.
Water hyacinth (E. crassipens) is fast growing
perennial aquatic macrophyte (Reddy
and Sutton, 1984). It is a member of
pickerelweed family (Pontederiaceae) and its name
Eichhornia was derived from well-known 19th century
Prussian politician J.A.F. Eichhorn (Aquatics, 2005). The plants can double its
population in only twelve days (APIRIS, 2005). Water hyacinth is also known for
its ability to grow in severe polluted waters (So et al., 2003).
E. crassipens is well studied as an aquatic plant that can improve
effluent quality from oxidation ponds and as a main component of one integrated
advanced system for treatment of municipal, agricultural and industrial
wastewaters (U.S. EPA, 1988; Sim, 2003). Water hyacinth is often described in
literature as serious invasive weed on the world (U.S. EPA, 1988; Maine et
al., 1999; Wilson et al., 2005).
| 
