News from the South African water sector (November 2008)

Abstract

Information ‘misleading’ The letter received from Mr J Barnard of NMMU, ‘Incorrect water treatment chemistry also causes problems’, published in the July/ August 2008 issue of Water Wheel (Vol. 7 No 4) is rather concerning. Advocating that corrosive water can be remedied by merely adding lime to raise the pH can cause further reticulation problems if not properly controlled. Even when the pH is above 7,0 (alkaline), water can be strongly corrosive. Keeping corrosion of a domestic water supply under control requires the control of both pH and alkalinity. If not properly controlled, corrosion or excessive scale (CaCO3) build-up occurs. A number of applications of Stability pH (pHs) exist: Langelier Saturation Index, Ryznar Stability Index and the Corrosivity Ratio. Control of chemical stability: Soft waters (e.g. those in the Southern and Eastern coastal areas of the Republic) are corrosive and it is important that the purification process should include steps for stabilizing the water chemically by treatment with Ca(OH)2 and CO2.

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