Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Fernando L. Rosario-Ortiz

Second Advisor

Diane McKnight

Third Advisor

JoAnn Silverstein

Fourth Advisor

R. Scott Summers

Fifth Advisor

Djanette Khiari

Abstract

Drinking water utilities often begin the treatment process by using an oxidation process to meet different water quality objectives (e.g. disinfection, control of invasive species, oxidation of organic or inorganic contaminants). If cyanobacteria cells are not removed prior to oxidation, cell damage or lysis may result in the release of intracellular organic matter (IOM) into the water supply. The objective of this research was to determine the effect of common preoxidants used during drinking water treatment on the integrity of cyanobacteria cells, and to evaluate the subsequent release of toxic metabolites, odorous metabolites, and/or disinfection byproduct (DBP) precursors.

Three cyanobacteria (i.e. Microcystis aeruginosa (MA), Oscillatoria sp. (OSC), and Lyngbya sp. (LYN)) were selected based upon (1) occurrence in source water supplies, (2) availability of an axenic culture, (3) ability to produce odorous or toxic metabolites, and (4) morphology. In order to evaluate cell degradation, digital flow cytometry in combination with chlorophyll-a measurements provided an assessment of cyanobacteria cell damage and lysis after oxidation using ozone, chlorine, chlorine dioxide, and chloramine. The release of toxic (i.e. microcystin-LR (MC-LR)) or odorous metabolites (i.e. 2-methylisoborneol (MIB), geosmin) was evaluated after oxidation of cyanobacteria cells added to Colorado River water. The formation of DBPs was evaluated during the chlorination and chloramination of IOM extracted from the different cyanobacteria.

Results showed that cyanobacteria cell damage occurred without complete lysis or fragmentation of the cell membrane under the conditions tested. The unicellular morphology of MA was more susceptible to oxidation than the filamentous morphology of OSC and LYN. Cell damage resulted in the release of IOM, which contained MC-LR, MIB, geosmin, and DBP precursor material. Subsequent oxidation of released (or extracellular) metabolites (i.e. MC-LR, MIB, and geosmin) coincided with kinetic information found in the literature. The yield of DBPs from IOM was identified for carbonaceous DBPs (i.e. trihalomethanes, haloacetic acids) and nitrogenous DBPs (haloacetonitriles, trichloronitromethane, and nitrosamines). Utilities can use this research to better manage their pretreatment conditions in order to minimize the risk of releasing toxic metabolites, odorous metabolites, or DBP precursors.

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