In The Netherlands, Belgium and other European countries, manganese is removed from groundwater by aeration followed by rapid (sand) filtration. Although manganese removal from groundwater has been studied extensively, the mechanisms that control the ripening of filter media are not yet fully understood. This thesis highlights the role of the formation of a manganese oxide coating on virgin filter media. Characterization and identification of the media revealed that Birnessite was the manganese oxide responsible for effective manganese removal. This study confirmed that Birnessite formed at the beginning of the ripening process was of biological origin. As filter ripening progressed, the origin of the Birnessite became predominantly physico-chemical, although biological manganese oxidation still contributed to the overall removal of manganese. The formation of Birnessite at the start of filter media ripening was negatively influenced by a high filter back wash frequency. Molecular DNA analyses showed that Pseudomonas species are most likely involved at the start of the manganese oxide formation process. Based on the knowledge that manganese removal in conventional groundwater treatment is initiated biologically, long ripening times may be reduced by creating conditions favouring the growth of manganese oxidizing bacteria, e.g., by limiting the back wash frequency and/or intensity. Finally it was shown that the use of freshly prepared manganese oxide, containing Birnessite, can completely eliminate the need for filter media ripening. The results of this research enable the development of an innovative manganese removal process to shorten or completely eliminate long periods of ripening of virgin filter media, as well as significantly prolonging the lifetime of the filter media. @en

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.@en