AWWA ACE58229

Researchers have noted that Mg(OH)2 solids reduce natural organic matter (NOM) concentrations significantly more efficiently than CaCO3 solids. To date, enhanced softening research indicates magnesium plays an important role in NOM removal even at pH values below that required for precipitation of Mg(OH)2, possibly due to the formation of mixed Mg- CaCO3 precipitates. Unfortunately, little is known about these minor precipitates formed in softening, and hence the positive impact cannot be systematically taken advantage of in operating treatment plants. This research attempts to close the gap in softening research by: determining the chemical composition and structure of solids formed under various softening conditions (e.g., Ca:Mg ratio of the raw water and pH of softening); and, investigating the capability of removing natural organic matter depending on the chemical and surface characteristics of the solids formed (e.g., degree of incorporation of minor constituents in solids, surface charge, shape). Includes 10 references, table, figures.