Author(s)

C. S. SHIBAMBU, J. R. GUMBO & W. M. GITARI

Abstract

Constructed and natural wetlands have been used successfully in the treatment and polishing of municipal wastewater all over the world, including in South Africa. Here we report on the heavy metal removal in a natural wetland that is receiving municipal sewage discharge, Limpopo province, South Africa. The natural wetland is located downstream of Makhado oxidation ponds and is dominated by the reed plant Phragmites australis. The changes in the metal variation from discharge of oxidation ponds to middle section and downstream of the natural wetland was analysed for heavy metals by ICP-MS over a 12 month period. The annual rainfall data were obtained from Agricultural Research Council. The following heavy metals: total chromium, zinc, cadmium and lead were effectively reduced during the passage through the wetland, to levels below the Department of Water & Sanitation (DWS) guidelines for waste water discharge. In contrast, the manganese and iron was reduced slightly above the DWS guideline value during the drier season and was higher during the wet season indicating a contribution of soil and water erosion. With copper it was effectively reduced during the wet and dry seasons with the exception in April, June and September when the downstream section was three times higher than the DWS guideline value. Thus the natural wetland was able to reduce considerable the heavy metals in the municipal discharge during its passage in the wetland. This is able to render the water in downstream of the wetland safe for rural communities to use the water for irrigation purposes.

Keywords

drinking water, heavy metal reduction, natural wetland, phragmites australis rural communities