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The Fate of Cyanotoxins in Drinking Water Sources and Treatment Processes

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2018, Doctor of Philosophy, Ohio State University, Civil Engineering.
The adsorption of microcystin-LR (MCLR) to kaolinite, illite and montmorillonite were determined and the adsorption was strongly influenced by the properties of adsorbent and adsorbate, which responded to the environmental conditions. Ca-montmorillonite, where the surface was saturated with the calcium ion, was capable of adsorbing the highest amount of MCLR and the adsorption exhibited little pH-dependence. While, kaolinite and illite, both saturated with either the sodium ion or the calcium ion, as well as Na-montmorillonite showed decreasing MCLR adsorption when the pH increased. The results fit the linear adsorption isotherm model well, and demonstrated the importance of polar groups on MCLR on the interactions with clays. MCLR adsorption was favored under Ca2+-enriched conditions, compared to Na+-enriched conditions, because the amine group on MCLR was available to have interactions with the sorbent in the Ca system, rather than intramolecular ion-pairing with one of the carboxyl groups on MCLR in the Na system. Based upon the responses of MCLR adsorption to environmental factors and adsorbent properties, ligand exchange, ion exchange reactions, electrostatic interactions, van der Waals interactions and hydrogen bonding interactions were involved in the adsorption of MCLR to clays. The effect of natural organic matter, as well as pH and electrolyte cation on additional sorption behaviors of MCLR with clays, including kinetics and desorption, were also examined. Suwannee river fulvic acid (SRFA) was used to represent natural organic matter in the system, and its influence on MCLR adsorption depends on its concentration and the interacting clays. SRFA adsorption was greatest when interacting with kaolinite, compared to illite and montmorillonite, and increasing its concentration reduced the MCLR adsorption to kaolinite at acidic condition. This indicates the competition of SRFA for sorption sites with MCLR via a ligand exchange reaction, which resulted in MCLR adsorbing tightly to kaolinite with little desorption. Little SRFA bound to illite, and it was thought to result in a complex of MCLR-SRFA forming and this complex further affected the MCLR adsorption to illite. With higher SRFA concentration in solution, more SRFA could interact with MCLR and retained MCLR in the aqueous phase, resulting in a reduction of MCLR adsorption in the presence of higher concentrations of SRFA. The presence of SRFA in the system significantly increase the dispersion of Na-montmorillonite, resulting in MCLR adsorption increasing by a factor of two when SRFA was added than the samples in the absence of SRFA. This enhancement of clay dispersion by SRFA was not observed for Ca-montmorillonite, and the influence of SRFA on MCLR adsorption to Ca-montmorillonite was little. However, a portion of SRFA was adsorbed onto Ca-montmorillonite and the surface-bound SRFA adsorbed MCLR tightly with less desorption occurring when more SRFA was added. The inconsistent effect of surface-bound SRFA on MCLR adsorption between kaolinite and montmorillonite emphasized that the properties of adsorbent plays an important role in MCLR adsorption. Lastly, enhancement of microcystins removal on activated carbon treatment of microcystins due to ozone oxidation and biodegradation were evaluated. By comparing the performance of ozone-BAC, BAC and GAC, biodegradation of microcystins by acclimated biomass on BAC was shown to improve the removal efficiency of GAC, which only involved adsorption. However, the biomass was sensitive to the toxin concentration and was selective in treating microcystin variants. Increasing toxin concentration or introducing new microcystin variants in the source water resulted in biomass decay and a reduction in removal. With pre-ozonation, microcystins were broken down to smaller and less toxic byproducts. Therefore, pre-ozonation not only reduces the concentration of microcystins entering the BAC column but also enhances the toxin biodegradation of the biomass on BAC. It resulted in less sensitivity and selectivity for biomass degrading microcystins. However, the enhancement was strongly controlled by the ratio of the ozone dosage to toxin concentration in that toxin removal by ozone-BAC and BAC was similar when the ratio was below 312 in this study. Overall, ozone-BAC and BAC provided better performance than GAC as they could keep removing microcystins over the 260-day study while the efficiency of GAC gradually decreased over time.
John Lenhart (Advisor)
Allison MacKay (Committee Member)
Andrew May (Committee Member)
Harold Walker (Committee Member)
Linda Weavers (Committee Member)
283 p.

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Citations

  • Liu, Y.-L. (2018). The Fate of Cyanotoxins in Drinking Water Sources and Treatment Processes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515021263671957

    APA Style (7th edition)

  • Liu, Yen-Ling. The Fate of Cyanotoxins in Drinking Water Sources and Treatment Processes. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1515021263671957.

    MLA Style (8th edition)

  • Liu, Yen-Ling. "The Fate of Cyanotoxins in Drinking Water Sources and Treatment Processes." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515021263671957

    Chicago Manual of Style (17th edition)