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This study was undertaken because the literatureon enhanced softening, specifically withrespect to the role of magnesium in removingnatural organic matter (NOM), has been limited.In evaluating the fundamental chemistry of precipitatecharacteristics and their effect on NOMremoval, this research showed that NOM removalbefore magnesium hydroxide precipitation occursfrom adsorption onto calcium carbonate (andmixed magnesium-calcium carbonate) precipitatesas they form and possibly also through directprecipitations as a magnesium fulvate or humate.The authors identify three potential strategiesthat softening plants can use to enhance NOMremoval and reduce disinfection byproduct formation.Some facilities might be able to operate ata slightly higher lime dose, avoiding magnesiumhydroxide precipitation while achieving slightlygreater removal of total organic carbon. Dependingon source water characteristics, plants couldenhance NOM removal by adding magnesium. IfNOM removal is to be maximized, soda ash (ifrequired) should be added in the second stage of atwo-stage softening process. Includes 37 references, tables, figures.

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Edition: Vol. 101 - No. 4 Published: 04/01/2009 Number of Pages: 13File Size: 1 file , 750 KB