Extracellular cyanotoxin treatment

Performance goal: Minimise risk from blue-green algae (cyanobacteria) and their toxins.
Description: There are many different varieties of blue-green algae that can release toxins that can cause liver, kidney and nervous system damage and have severe health implications for meat chickens. Toxins and other metabolites can be described as either intracellular (in a live cell) or extracellular (external to the cell). Extracellular metabolites can be released during stress, as by-products of intracellular reactions or released from dead cells. Many of the conventional treatments that remove live algal cells are ineffective for extracellular toxin removal due to their smaller size. It should be noted that the treatment of blue-green algae with algicides or disinfectants, will initially cause an increase in the toxin levels due to the toxins being released from dead cells. Toxins can be inactivated with oxidant disinfection; however, the effectiveness depends on the toxin and disinfectant type. The ADWG only has a guideline value for microcystins. However, other toxins are produced from blue-green algae, so this may not be the most ideal indicator for all blue-green algae. To allow for targeted inactivation of toxins, it is recommended that blue-green algae species and toxins are identified. This disinfection performance criterion is ideally measured after all pre-treatment performance criteria have been meet and water has been disinfected.
Performance criteria: Risks from blue-green algae controlled. If algae toxins have been identified as a problem: Best practice level: microcystins: 0–1.3μg/L, species and toxin identified Maximum acceptable level: microcystins: 1.3μg/L
Minimum requirements
Disinfection concentration is increased to a concentration that will inactivate toxins.
Best practice options
Species and toxin are identified.
A disinfectant is used that is effective against the species and toxin identified. See Tables 21 and 22 (below) for a comparison of the effectiveness of treatments against cyanotoxins.

Table 21. Extracellular cyanotoxin disinfection treatment processes and relative effectiveness (reproduced from D'Anglada, 2019)

Treatment process	Relative effectiveness
Potassium permanganate	Effective for oxidizing microcystins and anatoxins. Further research is needed for cylindrospermopsin. Not effective for oxidising saxitoxin.
Ozone	Very effective for oxidizing microcystins, anatoxin-a, and cylindrospermopsin. Not effective for oxidising saxitoxin.
Chloramines	Not effective.
Chlorine dioxide	Not effective at doses typically used in drinking water treatment.
Free Chlorine	Effective for oxidising microcystins as long as the pH is below 8. Effective for oxidising cylindrospermopsin and saxitoxin. Not effective for oxidising anatoxin-a.
Advanced oxidation (UV radiation with ozone or hydrogen peroxide)	UV radiation alone is not effective at oxidising microcystins and cylindrospermopsin at doses typically used in drinking water treatment. When UV radiation is coupled with ozone or hydrogen peroxide (called ‘advanced oxidation’), the process is effective at oxidising anatoxin-a, cylindrospermopsin, and with high UV doses, microcystins.

Table 22. Disinfection treatment effectiveness for specific extracellular microcystins, cylindrospermopsin, anatoxin and saxitoxin toxin removal (reproduced from Greenstein, 2019)

Cyanotoxins	Microcystins	Cylindrospermopsin	Anatoxin	Saxitoxin
Free chlorine	Moderate	Effective	No	Effective
Monochloramine	No	No	No	Unknown
Chlorine dioxide	No	No	No	Unknown
Potassium permanganate	Effective	No	Moderate	No
Ozone	Effective	Effective	Effective	No
Advanced oxidation processes (AOP)	Effective	Effective	Effective	Unknown
UV	No	No	Unknown	Unknown

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