Graduation Date

Fall 2019

Document Type

Thesis

Program

Master of Science degree with a major in Environmental Systems, option Environmental Resources Engineering

Committee Chair Name

Dr. Margarita Otero-Diaz

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. David Baston

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Eileen Cashman

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. Brad Finney

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Environmental Resources Engineering

Abstract

Harmful Algal Blooms (HABs) are commonly caused by the rapid growth of cyanobacteria in fresh waterways, which many people rely on for drinking water. When a HAB occurs, a variety of cyanotoxins can be produced and released into sources of drinking water, which can make people sick or die if not properly treated. Two of the most common toxins are microcystin-LR (MC-LR) and anatoxin-a (A-a), for which the World Health Organization (WHO) recommends a maximum allowable concentration of 1 µg/L in drinking water to avoid health risks. The recommendation for maximum allowable concentration was calculated specifically for microcystins, but is currently used as a limit for all cyanotoxins due to a lack of research on other toxin varieties. Treatment of drinking water to remove cyanotoxins requires special knowledge and equipment that may not be available to people who do not have access to a community-scale water system and use a small-scale treatment system such as a slow-sand filter. The lack of special training and equipment leaves members of underserved communities, such as the Hoopa and Yurok tribes in Humboldt County, at risk of drinking untreated water contaminated with cyanotoxins. The purpose of this project was to assess the effectiveness of using ultra-violate (UV) light for the treatment of two of the most prevalent cyanotoxins (MC-LR and A-a) in a small-scale drinking water treatment system.

MC-LR and A-a were each dissolved separately in solutions of Nanopure water and water from the Klamath River after being treated by a slow-sand filter at concentrations of 1, 10, 100, 1000, and 5000 µg/L. Each concentration of toxin was then exposed to UV light focused at a wavelength of 254 nm. Doses of UV light applied were: 60, 750, 1500, and 4000 mJ/cm2. A successful UV dose would lower MC-LR and A-a concentrations to below 1 µg/L, which means a 4-log removal for the highest concentrations. The concentration of MC-LR and A-a in each sample was determined using ELISA test kits, which are specific to microcystin congeners and anatoxin congeners, respectively. The work reported here showed that the highest doses of UV light applied could not achieve even a 2-log removal and showed a pattern of diminishing returns between 1500 and 4000 mJ/cm2. When the starting concentration of toxins was 10 µg/L or less, then the highest dose of UV light was sufficient to degrade the cyanotoxins below the WHO guideline. The results of this study suggest that UV treatment may require prohibitively high doses to be relied upon for treatment of cyanotoxins on its own, but may be an effective polishing step after some other primary treatment has occurred. Further testing is required to find the optimal UV dose to provide treatment in a small-scale drinking water treatment system.

Citation Style

ASCE

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