Study of the pathway of heavy metals in a sewerage system

Halday, Ismail (2007-03)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007.


This thesis reports on an exploratory investigation of proposed sludge guideline limits of heavy metal (cadmium, chromium, copper, nickel, lead and zinc) concentrations for South Africa. The purpose of the study is to determine allowable heavy metal concentrations in sludge for use as fertilizer in agriculture that can be attained and is practically possible without being detrimental to the environment. This determination was done by investigating the potential sources and concentrations of these heavy metals at the Potsdam Wastewater Treatment Works (WWTW) and also the efficiency of the treatment works in removal of these heavy metals. A heavy metal mass balance of both the influent at the Potsdam WWTW and the wastewater through the treatment works was calculated. This study also proposes possible interventions to minimize the levels of these heavy metals. Results for the heavy metal mass balance of the influent showed that a large quantity of some metals were unaccounted for, this implies that either industries discharge illegally after hours or the present monitoring undertaken by the City of Cape Town is inadequate. The large percentage of unaccounted cadmium suggests another source, which should be further investigated. The mass balance of the wastewater through Potsdam WWTW concluded that all these heavy metal limits were attainable, and that in some cases can be lowered even more. The treatment works has a high removal efficiency of these heavy metals, and a substantial reduction of these limits is justified. In the period of this study, the area under investigation gradually expanded, as more industries were established in it. Although the works was performing beyond its capacity it nevertheless was able to attain the rigorous heavy metal limits in sludge that are envisaged. There has also been a reduction in limits of heavy metals for discharge of final effluent into waterbodies; this study shows that these limits are also attainable.

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