Adsorptive removal of arsenic and manganese from groundwater

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Groundwater remains 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 source. In some localities, the quality of groundwater is affected by the occurrence of Arsenic (As) and Manganese (Mn) in concentrations above tough and 0.1mg/l respectively which are the World Health Organization (WHO) acceptable limits for drinking water. This is a limiting factor in the choice of this resource. Water supply companies are currently seeking to improve the process of As and Mn removal from groundwater. In this study, Adsorption capacity of locally available filter media namely, laterite and Iron Oxide Coated Sand (ICS) were investigated for removal of As and Mn from synthetic water. Batch studies were conducted under aerobic and anaerobic conditions. Changes in concentrations of As and Mn were determined using the Atomic Adsorption Spectrometer (AAS) and Graphite furnace AAS. Adsorption isotherms were prepared using different concentrations of Mn. Isotherms were not prepared for As due to constraints of time. The effect of pH on adsorptive trends was also investigated into. The filter media was then used for treatment of real groundwater seeded with different concentrations of Mn and As from Ayeduase Township. Results of the study show that adsorption under conditions of anaerobic and aerobic is comparable prior to the attainment of equilibrium by the anaerobic case. However the aerobic adsorption process continues slowly and consistently probably because the adsorbed Mn2+ gets oxidized to form manganese oxides and manganese oxyhydroxide complexes. These complexes form a new external coating round the media and facilitate further adsorption of Mn2+ ions, The anaerobic adsorption data of both ICS and laterite fined well with the Freundlich’s Isotherm. The results revealed that, iron oxide coated sand has higher adsorption capacity than laterite. This may be due to higher iron and manganese oxide content in the coating of the coated sand as compared to the amount in the laterite. The iron oxide coated sand also had higher adsorption intensity as compared to the laterite. Better adsorption trends were realized at higher pH for both media.
A thesis submitted to the School of Engineering, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of in Water Supply and Environmental Sanitation, 2005