Assessment of dissolved organic matter fluorescence PARAFAC components before and after coagulation-filtration in a full scale water treatment plant

Fluorescence monitoring of the raw and treated water after coagulation-filtration in a drinking water treatment plant in Northeast Ohio was conducted during a period of 32 months. Principal fluorophore groups present in the dissolved organic matter (DOM) of the raw, treated, raw-treated combined water and differential fluorescence data sets comprising over 680 samples were determined through Parallel Factor (PARAFAC) analysis. Four components (two humic-like and two with protein nature) were identified in each model and their degree of similarity was evaluated using the Uncorrected Matrix Correlation (UMC), a measure of spectral overlapping. Results show that spectral characteristics of the components in the independent models are comparable (average UMC > 0.98), indicating that from a PARAFAC perspective, components in the raw water are not experiencing major transformations beyond removal through the treatment process and new fluorescent components are not being formed. Coagulation assessment based on PARAFAC application to the differential excitation-emission matrices (ΔEEM), representing the portion of fluorescence removed after treatment, is introduced in this paper along with the volumetric evaluation of the components present in a sample as an alternative approach to determine their relative contribution. Volumetric analysis revealed a predominance of humic components, constituting about 80% in the raw and treated water. Results of the ΔEEM model indicated that the most amenable component to be removed by coagulation (removal ≈ 50%) at full scale operation is a humic-like fluorophore with predominance in the raw water, while removal of the protein-like components was about 30%. Results also show that the PARAFAC sample loadings exhibit a higher association with the total EEM signal in the raw and treated water samples when compared with alternative analysis techniques. These results support the analysis of the PARAFAC components present in the raw and treated samples as a viable measure for assessment of the coagulation process in a drinking water treatment plant.