Characterization of Natural Organic Matter Removal During Coagulation Using Fluorescence Spectroscopy

Coagulation is an important component of conventional drinking water treatment systems used to remove microbiological contaminants, turbidity and natural organic matter (NOM) that causes colorization and disinfection byproducts (DBPs) in the water. Fluorescence spectroscopy can be used in characterizing NOM through various methods including indexing and parallel factor analysis (PARAFAC) and peak picking. The fluorescence index (FI) characterizes the aromaticity of the NOM and the humification index (HIX) characterizes the NOM based in the degree of humification. For this study, these analysis methods were applied to characterize the removal of NOM through coagulation. A range of natural waters from reservoirs and large lakes were collected and the change in NOM character during coagulation could be followed throughout the jar tests. Total organic carbon (TOC), total nitrogen (TN), specific UV absorbance (SUVA), haloacetic acid formation (HAA), and trihalomethane formation (THM) measurements were taken from samples before and after coagulation. Fluorescence spectroscopy produced excitation-emission matrices (EEMS) for each sample using an excitation wavelength of 250 – 450 nm and an emission wavelength range of 300–560 nm. As NOM is removed, the FI increases and the HIX decreases showing that the aromatic, hydrophobic and more humified NOM is preferentially removed. A decrease in the redox index in the 2005 Cory-McKnight PARAFAC model is observed explaining that the reduced quinones are preferentially removed over the non-reduced quinones. As the coagulant dose is increased, the protein concentration increases relative to the other components. Further analysis will be related to the DBP and carbon-nitrogen ratio.