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.
| 
