Hazen-Adams CyanoTOX Model and Applications
- Elisa Arévalo EI, Ben Stanford PhD, Allison Reinert EI, Erik Rosenfeldt PE, PhD - Hazen and Sawyer
- Craig Adams - Utah State University
Cyanotoxins are compounds produced by cyanobacteria, sometimes referred to as blue-green algae. Overgrowths of cyanobacteria can cause harmful algal blooms that seem to be ubiquitous and highly persistent, causing numerous problems for water treatment plants in terms of maintaining treatment performance, managing DBPs, and dealing with the potential presence of the cyanotoxins themselves. Both natural and anthropogenic sources can lead to algal toxins in water, including excess of nutrients in the water, seasonal changes in temperature, still water conditions, and extreme weather events.
Due to recent harmful algal blooms and effects on water qualities across the nation, the USEPA issued health advisories, in June 2015, for two cyanotoxins: microcystins and cylindrospermopsin. These non-regulatory advisories are concentrations at which no adverse health impacts are expected and are voluntary for utilities, in most states, to follow. For children under six, the health advisory is 0.3 µg/L for microcystin and 0.7 µg/L for cylindrospermopsin, while for everyone else it is 1.6 µg/L for microcystin and 3.0 µg/L for cylindrospermopsin.
In an effort to provide guidance to utilities in managing cyanotoxin events, AWWA released an Excel-based spreadsheet tool that was developed through a collaborative effort between Hazen and Sawyer and Utah State University. The Hazen-Adams CyanoTOX model is based on the best available information on cyanotoxin oxidation from peer-reviewed literature, and its purpose is to provide water utilities with a means to assess how changes in their existing treatment (e.g., pH, oxidant dose, contact time) will influence the degradation of specific cyanotoxins or groups of cyanotoxins. Additional guidance was also provided on protocols for oxidant dose testing and for testing powdered activated carbon as a possible control strategy, thereby facilitating the evaluation of different treatment alternatives and their responses to elevated levels of cyanotoxins. Specifically, this tool can be used to assess the removal of extracellular cyanotoxins by free chlorine, ozone, monochloramines, chlorine dioxide, and permanganate.
This presentation will illustrate the Hazen-Adams CyanoTOX model capabilities through several case studies, which shall demonstrate how system specific parameters and water quality goals entered into the tool generate graphic and tabulated outputs. The outputs illustrate the efficacy of specific treatment alternatives to mitigate or reduce cyanotoxin concentrations. Overall, the tool can also be used to evaluate different treatment scenarios during water treatment plants decision-making processes, allowing plant managers and operators to make informed decisions about which and how much oxidant is needed to meet their water quality goals.
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