Coagulation: its effect on organic matter

Removal of natural aquatic dissolved organic matter (DOM) by conventional coagulation using ferric chloride was investigated. Reverse osmosis was used to isolate DOM from the Suwannee River in southern Georgia and from Lake Allatoona in northwestern Georgia. The two most significant differences between the source waters are pH and organic carbon concentration. Extensive jar-testing identified regions of removal based on initial concentration of DOM, coagulant dosage,, and pH conditions. Fast atom bombardment mass spectrometry was used to characterize the molecular-weight distributions of DOM before and after coagulation. Trends in the shape of the mass spectra correlated well with data for DOM removal and suggested that the mechanism for DOM removal varies with the pH and coagulant dosage. At higher pH conditions and lower coagulant dosages, masses up to 1,000 daltons (D) were detected in the mass spectra after coagulation. At lower pH conditions and higher coagulant dosages, no masses above 750 D appeared in the mass spectra.