Application of granular activated carbon and iron oxide coated sand for the removal of iron and manganese from ground water point sources

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Groundwater remained the most important source of water supply for rural communities in Ghana. Currently, over 95% of the domestic water needs of rural communities are obtained from this resource. The occurrence of high concentrations of minerals, in particular iron and manganese above acceptable levels is a limiting factor in the choice of this resource. In the Eastern Region of Ghana, drilling records have shown that about 30 percent of all boreholes drilled for domestic water supplies to rural communities contain iron, manganese or both metals in concentrations above World Health Organization (WHO) acceptable limits for drinking water. Although new techniques are available for the removal of these metals, the operation, management and maintenance procedures are complex and capital intensive, and are thus more suitable for conventional systems rather than for point systems in rural communities. In Ghana sand filters installed on wells to reduce the levels of these metals have not been successful. These filters (plants) have been designed to operate under aerobic conditions, using aeration processes to transform soluble compounds of iron and manganese to the insoluble forms through oxidation (gas transfer). The experience has been that the rate of transformation of the soluble metal compounds into the insoluble forms is slow and thus affects the filtered water quality. Similarly, the iron and manganese oxide flocs formed clogs the filter media, thus resulting into short filter run. This study has revealed that the communities soon become overburdened with the frequency of rejuvenation of the filter media, leading to the system either being abandoned or the community going back to the untreated surface water sources. This study focus mainly on investigating the performance of the existing sand filters installed for iron and manganese removal on point sources in the Eastern Region, and also determining the suitability of applying granular activated carbon (prepared from charcoal), and iron oxide coated sand as filter media in the removal of these metals from groundwater point sources. Results of the study show that, the application of the combined effect of granular activated carbon and iron oxide coated sand as filter media in separate treatment chambers in a new plant developed, named Mwacafe is effective in removing over 98 percent of iron and 80 percent of manganese from groundwater point sources, and with longer filter run in excess of four (4) months. The plant has provided high removal efficiency of not only iron and manganese, but also other minerals such as nitrates and fluorides, which are difficult to remove even in conventional water treatment plants. This new knowledge would be very useful in reducing the resources that would have been lost when wells are abandoned because of their excess mineral content.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Science degree in Water Supply and Environmental Sanitation, 2002