Date of Award
Doctor of Philosophy (PhD)
Fernando L. Rosario-Ortiz
R. Scott Summers
Diane M. McKnight
Dissolved organic matter (DOM) is a heterogeneous mixture of organic molecules derived from a variety of sources (plant and microbial) and is ubiquitous to all natural water sources. DOM removal is a core treatment objective for water treatment plants to prevent the formation of disinfection byproducts (DBPs). Due to its complex nature, current understanding of DOM and its effects on drinking water quality relies on bulk characterization methods, such as fluorescence spectroscopy. Fluorescence measures a fraction of DOM that is optically active and has the potential to absorb and reemit light. This thesis investigated how the optical properties of DOM can be used to understand and monitor drinking water treatment processes.
After a critical analysis of commonly-used fluorescence metrics, the use of fluorescence to characterize DOM removal by coagulation was investigated. Coagulation of DOM isolates demonstrated the advantages and disadvantages of following different fluorescence metrics. The results provided evidence that the association of different peak regions (A and C) with distinct DOM fractions (humic and fulvic acids) is unsupported. The study was then extended to cover 22 different waters with diverse water quality characteristics. Robust, universal relationships were developed between optical surrogates and DOM removal. Both UV absorbance and fluorescence intensities (Peaks A and C) were found to perform equally as DOM surrogates when compared on a relative basis. In contrast, specific UV absorbance (SUVA) was a better predictor of DBP yields than fluorescence compositional metrics. These differences were attributed to heterogeneity amongst non-fluorescing moieties.
Finally, fluorescence was evaluated as a potential surrogate for metabolite (e.g. Microcystin-LR, MIB and geosmin) release from cyanobacteria cells during oxidation processes within a treatment plant. Characterization of intracellular organic matter (IOM) isolates determined that IOM has a unique fluorescence signature compared to DOM, but it also shows compositional differences between species. Parallel Factor Analysis (PARAFAC) identified compositional difference in phycobiliproteins between species. Cell oxidation studies found that fluorescence index (FI) and FDOM intensity (Ex 370 nm, Em 460 nm) better capture the loss of viable cells and release of metabolites compared to absorbance and are promising monitoring tools for utilities.
Korak, Julie Ann, "Use of Fluorescence Spectroscopy to Characterize Dissolved Organic Matter" (2014). Civil Engineering Graduate Theses & Dissertations. 159.