The effect of dissolved natural organic matter on the rate of removal of ferrous iron in fresh waters

The ease of removal of iron in water treatment is determined principally by the form of iron present. If iron is complexed to natural organic matter (NOM) and present in dissolved form, it is quite difficult to remove by conventional deep-bed filtration methods while if present as particulate iron oxyhydroxides it is readily removed. A major source of iron in reservoirs is the benthic sediments which, on becoming anoxic, release ferrous iron (Fe(II)) to the water column. This Fe(II) may either bind to NOM and be retained in dissolved form or may form inorganic hydroxyl complexes which oxidize to Fe(III) species which typically precipitate rapidly. In this paper, we report on studies of the kinetics of Fe(II) removal from solution in the presence and absence of the IHSS standard Suwannee River Fulvic Acid (SRFA). Oxidation of inorganic Fe(II) by oxygen is negligible at low pH but addition of organics changes the kinetics of removal of Fe(II) remarkably, reducing the half life of Fe(II) from hours to minutes. Increasing the concentration of SRFA also enhances the degree of Fe(II) removal. Experimental results obtained over a wide range of conditions are successfully described using a kinetic model which accounts for the transformations between Fe(II) and Fe(III) species.