Abstract
Conventional water treatment technologies for the removal of fluoride ion may not be feasible for developing countries due to their high investment and operational costs. The aim of this study was therefore, to investigate the fluoride biosorption potential of the seeds of the cabbage tree (Moringa stenopetala). The influence of Moringa dosage, pH, contact time, and initial concentration of fluoride ion was investigated. The maximum fluoride sorption capacity was found to be 1.32 mg.g-1 of dry weight of Moringa seeds at a biomass dosage of 2 g L-1, pH 7.00, initial fluoride ion concentration of 10 mg.L-1 and a contact time of 60 min. The fluoride level was reduced from 10 to 3.4 mg L-1. The adsorption of fluoride ion onto Moringa powder was best described by the pseudo-second-order kinetic model (R2 = 0.99). The adsorption equilibrium data have been fitted well to Langmuir as well as Freundlich adsorption models (R2≥0.97 for both models). The distribution constant (Kd) and maximum adsorption capacity (Bmax) were significantly influenced by the amount of Moringa and equilibrium fluoride ion concentration (p<0.05). The desorption tests indicated that only 20% of the initially bound fluoride ion was regenerated, while the remaining 80% were bounded with the Moringa powder. This suggests that chemisorption was the possible mechanism of fluoride removal. Key words: Biosorption, chemisorption, desorption, fluoride, isotherm, Moringa stenopetala.
Highlights
Fluoride related health hazards are a major environmental problem in many regions of the world
At pH below 7, the decrease in fluoride adsorption efficiency and fluoride adsorption capacity might be due to the formation of hydrofluoric acid, which would reduce the coulombic attraction between adsorbent surface and the fluoride ion (Kagne et al, 2009)
The results of this study revealed that application of M. stenopetala seeds as a biosorbent introduces a less expensive and environmentally friendly method for removal of fluoride ion from aqueous media
Summary
Fluoride related health hazards are a major environmental problem in many regions of the world. Studies revealed that Ethiopia is among the 25 nations around the globe, where health problem occurs due to the consumption of fluoride contaminated water (Ayoob and Gupta, 2006). Out of 10 million people living in Rift Valley region of Ethiopia, 8.5 million people are exposed for high fluoride contamination. Ground and surface water fluoride concentration varies from 0.5 to 264 mg.L-1 (up to 26 mg.L-1 in drinking water sources) (Tekle-Haimanot, 2006). Over 80% of the children in the rift valley areas have developed varying degrees of dental fluorosis (Kebede et al, 2016). The public health and economic importance of fluorosis is significant in many endemic areas in view of the occurrence of debilitating skeletal fluorosis in humans
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