18
Mar
2013
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Overview of the Water Process

The Water Process

07
Nov
2012
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Links to Educational Material

South Africa

International:

21
Aug
2012
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Water is life

12
Oct
2007
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Abstraction of raw water from Vaal River

Due to extensive utilization of water from the Vaal River upstream of Midvaal’s abstraction point, water in this stretch of river is typically high in dissolved solids and contains high amounts of dissolved organic carbon and plant nutrients like phosphate and nitrate. This indicates that the water is “hard” or mineralized (due to the levels of salts like calcium, magnesium, sodium, chloride and sulphate) and contains numerous types of algae and other nuisance water plants like water hyacinths and water grass (due to the high levels of phosphates and nitrates).

The quality of the river water varies seasonally, as rainfall impacts on the turbidity, mineral levels and on the nutrient levels.

Raw water is abstracted from the Vaal River by means of large pumps, situated in the intake tower, and pumped through pipelines to the treatment plant for purification.

12
Oct
2007
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Chemical Addition

The type of chemicals added to the water in the treatment process has to comply with nationally approved standards for water purification for human consumption. The quality of raw water at the time of abstraction determines the amount of chemicals to be added to treat the water to the required standard. At Midvaal, the following chemicals are used.

Type of Chemical Example Purpose
Flocculants** Ferric chloride, aluminum sulphate Coagulates suspended particles into floes
Flocculant aid Anionic and cationic polymers Assists with removal of very fine particles and are used mainly during rainy seasons when high turbidity water is experienced.
Stabilization/pH correction Hydrated lime To ensure that the treated water is neither scale forming nor corrosive
Oxidation Ozone gas Removes algae, dissolved metals like iron and manganese, removes color, tastes and odors
Disinfection Chlorine gas Kills harmful bacteria and other micro-organisms

** Flocculation involves the stirring of water to which a coagulant has been added at a slow rate, causing the individual particles to “collide” with each other and with the floes formed by the coagulant. The destabilized individual colloidal particles are agglomerated and incorporated into the larger floc particles

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