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Removal of Microcystin-LR from Drinking Water Using Granular Activated Carbon

Villars, Kathryn E, Villars
http://orcid.org/0000-0002-9990-766X
http://rave.ohiolink.edu/etdc/view?acc_num=osu1532007603377473

Abstract Details

2018, Master of Science, Ohio State University, Civil Engineering.
Our surface water drinking water sources are increasingly hosting “harmful algal blooms” of cyanotoxin-producing cyanobacteria, which presents a challenge to public water systems. The most common toxin class, microcystins, are liver toxins which can cause a range of symptoms from abdominal pain and headaches to internal bleeding and organ failure. Conventional treatment (coagulation, flocculation, sedimentation, and filtration) can remove cyanobacteria, but does not address extracellular toxin. Following two instances of `do not drink’ advisories in Ohio in 2013 and 2014, the Ohio EPA requires public water systems to develop and submit treatment optimization protocols when microcystins are detected in raw water above 1.6 µg/L. Water utilities and regulatory agencies are, therefore, seeking effective and implementable treatments to optimize cyanotoxin removal and destruction. Although many advanced processes are being explored, utilities without the ability to make large capital investments are focusing on optimizing existing adsorption processes. Granular activated carbon (GAC) is an increasingly utilized unit process, often installed to meet disinfection byproduct regulations, which can also reduce the extracellular toxin concentration to below health affect levels. Most quantifications of the capacity and kinetics of MC-LR onto activated carbon were not conducted under matrix conditions or experimental designs that are most relevant to GAC contactors. These contactors differ from PAC applications in that they are typically installed after conventional coagulation/flocculation/sedimentation processes at different pH and natural organic matter (NOM) conditions and operate under different kinetics. Therefore, this study specifically examines the congener microcystin-LR (MC-LR) and developed equilibrium isotherms and rapid small scale column test (RSSCT) breakthrough curves for a variety of GAC products under different matrix conditions. Equilibrium isotherms were developed for six different GAC products from four different carbon source materials (hardwood, lignite, bituminous coal and coconut) both with and without the presence of NOM. Experiments were conducted in model water with an initial concentration of 50 ug/L of MC-LR and 5mg/L of Suwanee River Fulvic Acid. Further, a series of proportional diffusivity rapid small scale column tests (PD-RSSCTs) were designed to compare MC-LR and NOM breakthrough for three different GAC source materials (bituminous coal, lignite and hardwood) and at a pH range of relevance to GAC unit processes (pH = 7.8 and 9.5). PD-RSSCT were conducted in a 0.38cm inner diameter column with GAC bed depths packed to 1.5 cm. Model water with ~100ug/L of MC-LR and 5mg/L of Suwanee River Fulvic Acid was fed at ~0.32mL/min to generate a full scale empty bed contact time of 15minutes. From the results it appears that material type does have an effect on the adsorption capacity; however, other factors such as activation method likely also have an influence. The addition of 5mg/L Suwannee River Fulvic Acid as competitive NOM decreased the maximum adsorption capacity for the GAC products tested as expected. MC-LR breakthrough exceeded the Ohio EPA action level of 0.3 µg/L MC-LR for bituminous coal, lignite and hardwood GAC in 1000, 9700, and 9800 treated bed volumes respectively, and the MC-LR breakthrough curve was most gradual for the wood based GAC and steepest for the bituminous coal based GAC. The varying pH trial was conducted on the bituminous product only and the volume treated prior to breakthrough for MC-LR was similar at the 1.6 µg/L MC-LR Ohio EPA action level (1600 to 1900 bed volumes). However, the slope of the pH 9.5 curve was more gradual than the pH 7.8 curve likely due to decreased interaction between the GAC and competitive NOM. Any interpretation of these reported full scale breakthrough times must consider that this study was conducted at an unrealistically high influent MC-LR concentration (100µg/L) in order to obtain quantifiable data. These findings indicate that the most commonly used GAC media in Ohio (bituminous coal) is not as effective as other source material carbons for removal of MC-LR and that some lignite products may be comparable with wood. However, this cannot be extrapolated to its suitability for other contaminants of concern such as MIB, geosmin, disinfection byproduct precursors or other organic molecules, and further, there are operational reasons for public utilities to choose a particular manufacturer.
John Lenhart (Advisor)
Allison MacKay (Committee Member)
Linda Weavers (Committee Member)
113 p.
Engineering; Environmental Engineering; Water Resource Management
microcystin; adsorption; granular activated carbon; GAC; cyanotoxin; HAB; harmful algal bloom; water treatment; RSSCT; rapid small scale column test;

Recommended Citations

Citations

  • Villars, Villars, K. E. (2018). Removal of Microcystin-LR from Drinking Water Using Granular Activated Carbon [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532007603377473

    APA Style (7th edition)

  • Villars, Villars, Kathryn. Removal of Microcystin-LR from Drinking Water Using Granular Activated Carbon. 2018. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1532007603377473.

    MLA Style (8th edition)

  • Villars, Villars, Kathryn. "Removal of Microcystin-LR from Drinking Water Using Granular Activated Carbon." Master's thesis, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532007603377473

    Chicago Manual of Style (17th edition)

osu1532007603377473
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This open access ETD is published by The Ohio State University and OhioLINK.