In the Eastern corridor of Northern region of Ghana, 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 this part of Ghana and it’s spatial distribution. Treatment of the fluoride-contaminated groundwater by adsorption is also hampered by the lack of suitable adsorbents that are locally available.
Based on principal component analysis, and saturation indices calculations, this thesis highlights that, the predominant mechanisms controlling the fluoride enrichment probably include calcite precipitation and Na/Ca exchange processes, both of which deplete Ca from the groundwater, and promote the dissolution of fluorite. The mechanisms also include F-/OH- anion exchange processes, as well as evapotranspiration processes which concentrate the 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.
The thesis further highlights that, modifying the surface of indigenous materials by an aluminium coating process, is a very promising approach to develop a suitable fluoride adsorbent. Aluminum oxide coated media reduced fluoride in water from 5. 0 ± 0.2 mg/L to ≤ 1.5 mg/L (which is the WHO health based guideline for fluoride), in both batch and continuous flow column experiments in the laboratory. Kinetic and isotherm studies, thermodynamic calculations, as well as analytical results from Fourier Transform Infrared Spectroscopy and Raman spectroscopy, suggest the mechanism of fluoride adsorption onto aluminium oxide coated media involved both physisorption and chemisorption processes.
Field testing in a fluoritic community in Northern Ghana showed that the adsorbent is also capable of treating fluoride-contaminated groundwater in field conditions, suggesting it is a promising defluoridation adsorbent. The adsorbent also showed good regenerability potential that would allow re-use, which could make it practically and economically viable. Additional research is, however, required to further increase the fluoride adsorption capacity of developed adsorbent.
1 General introduction
1.2 Groundwater, fluoride contamination, the benefits and pathophysiology
1.3 High fluoritic regions
1.4 Available fluoride removal technologies
1.5 Aim and scope of the study
1.6 Research objectives
1.7 Outline of the thesis
2 Fluoride occurrence in groundwater in the Northern region of Ghana
2.2 Occurrence and hydrogeochemistry of fluoride
2.3 The study area
2.4 Study methodology
2.5 Results and Discussions
3 Drinking water defluoridation using aluminium (hydr) oxide coated pumice: Synthesis, equilibrium, kinetics and mechanism
3.2 Materials and Methods
3.3 Results and discussions
4 Laboratory-scale column filter studies for fluoride removal with aluminum (hydr) oxide coated pumice, regeneration and disposal
4.2 Material and methods
4.3 Results and Discussions
4.4 Modeling of breakthrough profiles
4.5 Fluoride adsorption performance of RAOCP and comparison with that of AOCP
4.6 Leaching test for waste (spent) AOCP for safe disposal
4.7 FTIR and thermodynamic analysis for insight into fluoride removal mechanism by RAOCP
5 Fluoride removal from drinking water using granular aluminium-coated bauxite as adsorbent: Optimization of synthesis process conditions and equilibrium study
5.2 Material and Methods
5.3 Results and discussion
6 Aluminol (Al-OH) fuctionalized wood charcoal for treatment of fluoride-contaminated groundwater: Effect of wood source, particle size, surface acidity-basicity and field assessment
6.2 Materials and Methods
6.3 Results and Discussion
7 General Conclusions
7.1 Overall conclusions and perspective
7.2 Fluoride occurrence in groundwater in the Northern region of Ghana
7.3 Drinking water defluoridation using aluminum (hydr)oxide coated pumice: Synthesis, equilibrium, kinetics and mechanism
7.4 Laboratory-scale column filter studies for fluoride removal with aluminum (hydr)oxide coated pumice: Filter runs with freshly synthesized and regenerated adsorbent and options for disposal of fluoride-saturated adsorbent
7.5 Fluoride removal from drinking water using granular aluminum-coated bauxite as adsorbent: Optimization of synthesis process conditions and equilibrium study
7.6 Groundwater defluoridation using aluminol (Al-OH) fuctionalized wood charcoal: Effect of wood source, particle size and field assessment
7.7 General outlook, limitations and recommendations
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.