AWWA JAW31569

Ozonation may alter the functional group composition, molecular weight (MW), and behavior of natural organic matter (NOM) in reactions of significance for drinking water treatment. In this work, the transformation of NOM by ozone was monitored by acid-base titrations, ion chromatography, and gel-permeation chromatography (GPC). The results led to an improved understanding of how ozonation affects NOM and how ozonated NOM affects the solubility of freshly precipitated iron and aluminum hydroxides. Organic acidity increased substantially during ozonation, and most of the newly produced organic acid groups were ionized at pH 4.0. Of 27 simple organic acids assayed in ozonated NOM, oxalic acid was dominant. The concentration of oxalate produced upon ozonation increased with ozone dose, solution pH, and Fe(II) concentration. Ozonation of NOM destroyed compounds of high and low apparent MW as determined by GPC and increased the concentration of compounds with intermediate apparent MW. Within the group of compounds formed with intermediate apparent MW, however, the dominant identifiable compounds were low-MW organic acids such as oxalic and formic acids. Based on this and other observations, changes in the chromatograms of NOM as a result of ozonation appear to reflect changes in functional group composition and polarity of the molecules more--and true MW changes less--than previously recognized. At relatively high ozone doses and slightly acidic pH values, oxalic acid produced upon ozonation of NOM can complex and solubilize significant concentrations of aluminum. The concentration of soluble metal that formed in the presence of ozonated NOM can be predicted reasonably well by considering oxalate as the only metal-complexing ligand present in such systems. Includes 40 references, tables, figures.