AWWA JAW60509

Oxidation of ferrous iron, Fe(II), to ferric iron, Fe(III), is an important reaction in drinking water treatment and distribution systems, and the ferric particles that form are a major source of consumer complaints about colored water. Ferrous iron is found naturally in many groundwaters and can be released from distribution system materials. Bench-scale experiments were conducted to study the effects of pH, oxidant type (oxygen, chlorine, and chlorine dioxide), and oxidant concentration on the properties of Fe(III) particles and suspensions formed from Fe(II) oxidation. The color and turbidity per unit mass of iron of suspensions formed from oxygen were more than twice those of suspensions formed from chlorine and chlorine dioxide at all pH values. Similar observations were made during tests with oxygen and chlorine using natural groundwaters at two field locations. Particles formed from chlorine and chlorine dioxide were less dense and had a greater capacity to adsorb orthophosphate. Experimental observations were explained using a model that considers differences in Fe(III) particle formation and growth pathways. These research findings have practical implications related to both water treatment (iron removal) and distribution system issues. Includes 39 references, tables, figures.