Abstract

In the Eastern corridor of the Northern region of Ghana, the presence of high fluoride concentration in the groundwater has made many drilled boreholes unusable for drinking. Little is, however, known about the factors contributing to the occurrence of high fluoride in the groundwater. Fluoride-contaminated groundwater can be treated by adsorption, but is hampered by the lack of suitable adsorbents that are locally available. Based on principal component analysis, and saturation index calculations, this thesis highlights that, the predominant mechanisms controlling the fluoride enrichment in the groundwater probably include calcite precipitation and Na/Ca exchange processes, both of which deplete Ca from the groundwater, and promote dissolution of fluorite. The mechanisms also include F-/OH- anion exchange as well as evapotranspiration, which concentrate fluoride ions, hence increasing its concentration in the groundwater. Spatial mapping showed that the high-fluoride groundwaters occur predominantly in the Saboba, Cheriponi and Yendi districts in the Northern region of Ghana. The thesis further highlights that, modifying the surface properties of locally available materials by aluminium coating, is a very promising approach to develop a novel fluoride adsorbent. Aluminium oxide coated media reduced fluoride in water from 5. 0 ± 0.2 mg/L to ? 1.5 mg/L (WHO guideline), in both batch and continuous flow column experiments in the laboratory. Kinetic and isotherm adsorption modelling, thermodynamic calculations, as well as Fourier Transform Infrared and Raman spectroscopy studies, suggest the mechanism of fluoride adsorption onto aluminium oxide coated media involved both physisorption and chemisorption processes. Field testing in Northern Ghana showed that the adsorbent is also capable of treating fluoride-contaminated groundwater in field conditions. The adsorbent also showed good regeneration potential making it a promising defluoridation adsorbent in practical applications in developing countries.

*Read the full thesis online at http://fluoridealert.org/wp-content/uploads/salifu.unesco-dissertation.2017.pdf

Corporate: UNESCO-IHE Institute for Water Education (Netherlands), Delft University of Technology (Netherlands), Wageningen University (Netherlands)
ISBN: 978-0-8153-9207-1
Collation: 276 pages : illustrations
Document type: doctoral thesis
Degree granting institution: Delft University of Technology
Publisher: CRC Press / Balkema – Taylor & Francis Group