Characterisation and Chemical Removal of Organic Matter in South African Coloured Surface Waters

Feb 2004


By far the highest priority for further research on the treatment of coloured water in South Africa was found to be the need for characterisation and removal of unwanted organic compounds in these waters. Little information is available on the true character and properties of the local coloured waters, and more specifically of its high variability in locality and time (spatial and temporal), as well as the many complexes that it forms with other substances, notably metals. There is also a lack of knowledge on the effect of treatment processes, and in particular coagulation, on the removal of the different constituents of the coloured water. There was, therefore, a need for a more fundamental characterisation of natural organic matter (NOM) in South African coloured waters and classifying the coloured surface water sources, and to use this for establishing the treatability of the different classes of coloured water.

Considerable work on the characterisation of organic matter in coloured waters has been done overseas, notably in the UK (Water Research Centre (Wrc); Severn Trent Water), USA (AWWA Research Foundation), Australia (Australian Water Quality Centre, CSIRO and Monash University) and Norway (Norwegian Institute of Water Research). These included land use (catchment) studies, colour and organic matter characterisation, bench-scale treatability studies and continuous flow studies. A study at the University of Cape Town has, however, shown that South African coloured waters have considerably higher colour levels than in these countries, and that especially in standing waters (such as dams and lakelets), the colour intensity is very high by international standards. The results of the NOM characterisation performed overseas can hence not be applied directly to local waters to assess its treatibility by existing processes or new processes that are being developed.

A project was therefore undertaken to characterise the natural organic matter in South African coloured surface waters and to develop operational coagulation diagrams for the removal of the organic matter, in order to improve the effectiveness and cost-efficiency of treatment of these coloured waters.

The aims of the project were as follows:

The overall conclusions of this study are that, for the waters of the study area:

Based on the findings of this study, the following recommendations are made for further research on characterization and treatment of South African coloured surface waters:

  1. Investigate the occurrence of metals (iron, manganese and aluminium) in colour removal treatment plants, and draw up guidelines for removal and control of the metals, both at the treatment plant and in the distribution system.
  2. Perform desk studies on how alternative non-chemical treatment technologies can be used either together with chemical treatment or on its own to improve the quality of the final water, and be able to do this in a sustainable and affordable manner.
  3. Investigate the beneficial use of chemical sludges from colour removal treatment plants (research on management and use of water works sludges generally is currently being carried out by the University of Natal in Pietermaritzburg).