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THE EFFECT OF ORTHO- AND POLY-PHOSPHATES ON THE PROPERTIES OF IRON PARTICLES AND SUSPENSIONS FORMED FROM THE OXYGENATION OF FERROUS IRON
Citation:
Lytle*, D A. AND V. L. Snoeyink. THE EFFECT OF ORTHO- AND POLY-PHOSPHATES ON THE PROPERTIES OF IRON PARTICLES AND SUSPENSIONS FORMED FROM THE OXYGENATION OF FERROUS IRON. AWWA Annual Conference, New Orleans, LA, 06/16-20/2002.
Description:
"Red water" describes the appearance of drinking water that contains suspended particulate iron although the actual suspension color may be light yellow to brown depending on water chemistry and particle properties. Iron can originate from the source water and from distribution system materials. The relatively soluble +II oxidation state is the dominant form of iron in anoxic environments including some groundwaters, the hypolimnion of eutrophic reservoirs, drinking water distribution system dead ends, and beneath thick iron corrosion scales. Upon exposure to oxygen or disinfectant during water treatment and distribution, Fe(II) is oxidized to the insoluble Fe(III) form, which readily precipitates and is responsible for colored water.
Colored water problems can be reduced by removing source water iron, controlling corrosion and iron release from corrosion scales, and controlling the form of iron precipitates. Chemicals such as silicate or polyphosphate may be used to reduce the amount of noticeable iron precipitate. This approach may be used to reduce the impacts of both source water iron and iron released from distribution system materials. Corrosion may be controlled by proper control of pH, alkalinity and hardness, as well as through the use of corrosion inhibitors such as orthophosphate. The objective of this research was to evaluate the effect of orthophosphate and several polyphosphates on the properties of iron particles and aqueous iron suspensions formed from the oxygenation of Fe(II).