AWWA WQTC57136

"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. The oxidation of Fe(II) is the basis for iron removal treatment of iron-containing groundwaters, and an important step in iron corrosion byproduct development and red water formation in drinking water distribution systems. The relationships between redox potential, and aqueous iron chemistry and iron mineralogy are well known. No research, however, has considered the effect of oxidant type on the properties of Fe[III] particle suspensions formed following the oxidation of Fe[II]. The objective of this research was to study the effect of oxidant (oxygen and free chlorine) on the properties of iron particles and suspensions formed from the oxidation of Fe[II] over a broad pH range. Particle properties including size, electrophoretic mobility, and suspension properties including turbidity and color were studied. Iron particle suspensions formed following the oxidation of Fe(II) by oxygen and free chlorine have dramatically different color and turbidity properties independent of pH. Suspension property differences indicated that differences in the iron particles existed. The particle properties examined in this investigation (size, zeta potential and crystalline nature), however, did not show notable differences in particles formed in oxygen and chlorine systems. Additional particle analysis including density measurements and particle image analysis will be performed to identify particle differences. Includes 3 references, figures.