5. CONCLUSIONS AND RECOMMENDATIONS
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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