Abstract:
People in several regions of the Rift Valley of Ethiopia are suffering from skeletal and nonskeletal fluorosis as result of consuming water containing excessive fluoride. Several methods
are available to remove fluoride ion from water but they are not feasible due to social, financial,
economic, environmental and technical reasons. In an attempt to suggest an action oriented
solution to the challenges mentioned above, Fluoride bio sorption using seeds of cabbage tree
(Moringa stenopetala) has been investigated.
Batch experiments were conducted on ground water samples and aqueous solution as a function
of contact time, pH, initial fluoride ion concentration, and biomass dosage. By changing the
initial concentration of F
from 1 to 25 mg/l-fluoride ion removal efficiency was reduced from
100 to 76%. The maximum sorption capacity was achieved during the first 30 minutes. Fluoride
sorption was also found to be dependent on the aqueous phase pH and the fluoride uptake was
observed to be greater at pH 9.It was found that increasing the adsorbent dose from 0.1 g.l-1 to
40 g.l-1 resulted in an increase in removal efficiency from 75 to 100%. The maximum sorption
capacity of fluoride was 33mg.g−1.
Isothermal data fitted well with Fredulich adsorption model (R
2
=0.87). Only 6% of the F- was
regenerated by 0.02 M KCl, the remaining 94% was strongly bound with the biomass, suggesting
that chemisorption as the possible mechanism of fluoride-Moringa binding. Cabbage tree
(Moringa stenopetala) seeds are the promising biosorbent for removing excess fluoride ions from
water at economically feasible cost. The biosorption mechanism and the surface morphology of
this biosorbent were not well investigated due to the limited scope of this study.
