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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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5.1 Conclusions

The removal mechanisms of zinc and chromium by water hyacinth plants showed that the plant concentrated a high amount of metals. The aquatic plant water hyacinth have shown promising potential for the removal of Cr (VI) and Zn (II) from industrial synthetic wastewater of three different concentrations (1, 3 and 6 mg / L).

Zn (II) was much more mobile than Cr (VI) due to their sizes and charges. The accumulation of metals in the roots and shoots of water hyacinth has been shown in laboratory experiments in which water hyacinth was used as a biological adsorbent. It was recoded that Zn (II) was more accumulated (leaves<roots<petioles) in petioles whereas Cr (VI) was more accumulated in roots (leaves<petioles<roots). This phenomenon can explain by the mobility of Zn (II) when compare to Cr (VI) and also Zn (II) at low concentration contributes to the plants cells building.

It was observed the Bioconcentration factor decreases while the Zn (II) and Cr (VI) concentrations increase. This expresses that aquatic macrophytes water hyacinths are able to accumulate Zn (II) at low concentration and which contributes particularly to plant cells building. The bioconcentration factor of Cr (VI) shows the same trend as for Zn (II) that the increasing in concentration reduces the ability of the plant to accumulate more trace elements of Cr (VI) and looks to be stagnant independently to the initial concentration.

The translocation ability of aquatic macrophytes water hyacinth plants look to be high for Zn (II) in petioles whereas is high in roots for Cr (VI) due to size of elements and their respective charges.

5.2 Recommendations

Further research is necessary to establish a practical scale demonstration system. The information from the laboratory pilot scale research should also be used to establish a best practice environment for integrated wastewater treatment by aquatic plants and to study also the effects of decrease in pH after 48 h on metal removal as the solution becomes more acidic and a release of trace metals can be expected;

The experiments conducted in this research were carried out using a laboratory synthetic wastewater. It is important to repeat the experiments with a real industrial wastewater on field and to assess the treatment performance.

Further experiments with other heavy metals and other aquatic macrophytes could be more benefits to optimize the mechanisms involved in heavy metals by aquatic macrophytes.

A combination of different types of macrophytes plants could be useful in order to increase the contact between the polluted water and the bioadsorbent for metal fixation.

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