Suitability of Local Materials to Purify Akaki Sub-Basin Water

  • Autor:

    Haile Tolera, H.

  • Quelle:

    Dissertation, Karlsruher Mineralogische und Geochemische Hefte / Band 33 (2007)

Kurzfassung (Abstract)

The drinking water quality of the southern margins of Addis Ababa is a crucial problem at present day. Dissolved and suspended particulate matter (SPM) bound Cu, Zn, Ni, As, Pb, Mn, and Fe are common pollutants in surface and groundwater. Drinking water contaminated by these heavy metals and some other inorganic pollutants such as nitrates account for high rate of health hazards. This work (1) presents results of the hydrochemical characterization of surface and groundwater in the Akaki Sub-basin and (2) evaluates an innovative approach for removing heavy metals from polluted water using natural materials. Local materials such as DQ scoria, KVA volcanic ash, EBF laterites, MnR sediment and PYC pyroclastic were tested. Water quality data shows that dissolved concentrations of Mn, Fe, Zn, and Pb in groundwater are at the critical limit of the US EPA MCL while surface water show elevated Mn, Fe, and Ni exceeding the limit. Most water samples have higher concentration of U well above the critical limit. Comparison of SPM bound concentrations of Cu, Pb and Zn with the LAWA classes indicates that groundwater samples are moderately to strongly contaminated whereas surface water samples show moderate contamination. The removal capacities of the filter media for dissolved and SPM bound Cu, Zn, Ni, As, and Pb show that the average retentions of Cu, Zn, and Pb were above 90%. However, Ni retention was variable (69-98 %) depending on the filter substrate used. Arsenic was poorly retained by all media except MnR sediment (97%), DQ scoria and EBF laterite (50%). Removal mechanisms of Zn, Cu and Ni mainly involve weak sorption and surface precipitation on the filter media and/or montmorillonite. Overall, the project adequately demonstrates the potential applicability of natural materials and their weathering products as filter media, and it appears that the filter media are appropriate for testing at a larger scale.