Ferric chloride coagulation of two types of natural dissolved organic matter was studied. The molecular weight distribution of Suwannee River humic substances currently used as an international standard was characterized using fast atom bombardment mass spectrometry (FABMS). The molecular weight distributions were characterized before and after coagulation. Ferric chloride dosage and pH domains on the iron coaglation diagrams were developed for removal of these humic substances and for determination of the resulting trihalomethane formation potentials (THMFP) of the treated water. The results indicate that it is possible to maximize the removal of dissolved organic matter and minimize trihalomethanes by coagulation only under very specific conditions of pH and ferric chloride dosage.

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