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Full text release has been delayed at the author's request until August 10, 2025

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Tracking Cyanobacteria Cell Integrity through Chemical and Mechanical Stressors in the Water Treatment Process

Elliott, Dane
http://orcid.org/0000-0002-0417-2374
http://rave.ohiolink.edu/etdc/view?acc_num=osu1658411375895179

Abstract Details

2022, Master of Science, Ohio State University, Civil Engineering.
As source waters for Ohio drinking water treatment plants are increasingly subject to algal blooms, treatment utilities must employ methods to remove resulting cyanotoxins. Cyanotoxins exist in two forms: intracellular and extracellular. Intracellular toxins are contained within a living cyanobacteria cell, whereas extracellular toxins are dissolved in water after cell death. Treatment for each form of cyanotoxin varies and can result in a conflicting outcome. Strategies like pre-oxidation, which are employed to remove extracellular toxins, can adversely affect the living cyanobacteria cells. If the oxidant damages the cell wall, the cyanobacteria cell can lyse and release toxins. Thus, there is potential for higher levels of extracellular toxins later in the drinking water treatment process. Our work aimed to discern where cyanobacteria cells are subjected to stressors that cause damage within the drinking water treatment process. We employed a bench- scale simulation to focus on chemical treatments and mechanical shear that occur during the water treatment process. The study considered Microcystis (MC) and Planktothrix (PT), which are two types of microcystin-producing cyanobacteria that are prominent in Ohio with different morphological characteristics. Our first objective was to understand the effect that chemical oxidant treatments have on cyanobacteria cells. Potassium permanganate and sodium hypochlorite (chlorine) are oxidants that are used in water treatment for their destructive capabilities. Treatment utilities often employ pre-oxidants near the water intake to remove extracellular toxins, but there is concern that pre-oxidation damages cells and leads to release of additional cyanotoxins. In this study, we tested different dosages of chlorine and permanganate on cyanobacteria cells to determine the impact of these oxidants on cell integrity. We found that chlorine caused complete lysis by a dosage of 2 mg/L for both species, but PT showed higher sensitivity to lower doses than MC. We also found that permanganate did cause lysis at high dosages (20 mg/L) for MC but had no effect on PT. It is likely that the presence and type of DOM in PT samples contributed to the lower sensitivity to permanganate. Our second objective aimed to understand the effect of mechanical shear on cyanobacteria cells. Shear stress in the treatment process, such as by rapid mixing, may cause damage to cells, particularly when the cells have been weakened by preceding chemical treatments. This study aimed to quantify the cell lysis that occurs when cyanobacteria cells are exposed to mechanical shear with and without pre-oxidation. We found that shear did not have a significant negative impact on cells in three of four cases but did cause an increase in extracted phycocyanin, particularly when a viable population was initially present (e.g., at low oxidant dosages). The only case to show that shear negatively impacts cells was PT cells after permanganate oxidation, which may be due to the mechanism of permanganate attack and the morphology of PT. The final objective of this work was to develop a method to quantify cell lysis that can be used by treatment utilities. Guidelines, such as the Ohio Environmental Protection Agency and American Water Works Association White Paper on Cyanotoxin Treatment, identify potential concerns but lack detailed protocols to assess cell lysis potential in suggested treatments. In this study, cell lysis is quantified by using measures of phycocyanin, a protein that exists inside cyanobacteria, using affordable benchtop equipment. We extracted intracellular phycocyanin after a chemical or mechanical treatment to quantify the amount of phycocyanin that remained as a proxy for living cells in the sample. We quantified the extracted phycocyanin using fluorescent spectroscopy. We validated this method using membrane integrity staining and confirmed that intracellular phycocyanin analysis is a valid method to evaluate how treatment strategies affect cell integrity. We concluded this method can be adapted by utilities to independently identify whether a treatment is causing cell damage that leads to toxin release.
Allison MacKay (Advisor)
John Lenhart (Committee Member)
Natalie Hull (Committee Member)
112 p.
Civil Engineering; Environmental Engineering
Cyanobacteria; harmful algal blooms; drinking water treatment; phycocyanin; microcystis; planktothrix; cell damage; lysis; chemical oxidants; permanganate; chlorine; mechanical shear

Recommended Citations

Citations

  • Elliott, D. (2022). Tracking Cyanobacteria Cell Integrity through Chemical and Mechanical Stressors in the Water Treatment Process [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658411375895179

    APA Style (7th edition)

  • Elliott, Dane. Tracking Cyanobacteria Cell Integrity through Chemical and Mechanical Stressors in the Water Treatment Process. 2022. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1658411375895179.

    MLA Style (8th edition)

  • Elliott, Dane. "Tracking Cyanobacteria Cell Integrity through Chemical and Mechanical Stressors in the Water Treatment Process." Master's thesis, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658411375895179

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.