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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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1.2 Problem description

Rwanda is facing problem of pollution in general. In many cases the pollution ends in the water bodies. That pollution contains diverse toxic pollutants (organic and inorganic compounds) coming from household and factories. Heavy metals from factories but also from other sources such as agriculture are the toxic compounds of our interest because they are not only polluting the water sources used for drinking, agricultural and fisheries purposes but they are also entering the food chain and therefore endangering human life.

Wastewater contaminated by heavy metals need an effective and affordable technological solution. In general wastewater from industrial activities must not be allowed to be discharged into our water reservoir. In order to stop the pollution at the production site, the on site treatment of wastewater is the best option recommended for such waste. Several studies indicate that aquatic plants have large potential for removal of organic and inorganic pollutants from wastewater.

Diverse industrial wastes have aggravated the problem of water pollution. This problem
becomes complex because of the differences in pollution according to the industrial
activities and also due to the non-biodegradability of inorganic pollutants like heavy

metals (Srivastav, et al., 1994). Heavy metals produce undesirable effects, even if they are present in extremely small quantities on human and animal life.

1.3 Objectives

The general objective of this study is to investigate on the major mechanisms responsible for Cr (VI) and Zn (II) removal form the water phase by macrophyte plants. Water hyacinth have been used in the remediation process in the present work because this plant has elaborate roots system providing much binding sites for heavy metals.

The specific objectives are:

· Assessment of the Cr (VI) and Zn (II) concentrations adsorbed on the outer surfaces of the roots;

· Assessment of the Cr (VI) and Zn (II) concentrations taken up by water

hyacinths;

· Assessment of the mobility and translocation of Cr (VI) and Zn (II) within water hyacinths.

1.4 Research questions

In order to achieve the above mentioned objectives some research questions need to be addressed:

· Which part of water hyacinth has much contributed in Cr (VI) and Zn (II) removal?

· Which heavy metal between Cr (VI) and Zn (II) have been preferably fixed by water hyacinth plant?

· What was the effect of metals concentration on water hyacinth growth and how was the bioaccumulation factor?

1.5 Hypotheses

· Cr (VI) and Zn (II) are adsorbed, taken up and translocated by water hyacinth. When saturation of binding sites is reached, the plant will no longer be efficient in Cr (VI) and Zn (II) removal.

· Zn (II) is preferably adsorbed and taken up by water hyacinth when compared to Cr (VI) because of the smallest size and his positive charge.

· High metal concentration is toxic to the growth of water hyacinth plant therefore the bioaccumulation factor will increase with a low metal concentration and decrease with the increasing of the metal concentration.

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