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Zinc and Chromium removal mechanisms from industrial wastewater by using water hyacinth, eicchonia crassipes

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par John Gakwavu Rugigana
National University of Rwanda - Master's in WREM (water resources and environmental management) 2007

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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).

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