| Performance goal: Minimise the risk from algae, blue-green algae (cyanobacteria) and their toxins. |
|---|
| Description: Algae are a diverse group of water-living primitive plants. Freshwater algae are divided into four main groups: flagellates, green algae, diatoms and blue-green algae. High concentrations of algae in drinking water can clog water system equipment, release toxins, cause corrosion, create slime or biofilms, and deoxygenate water. Many of the Organic matter treatments will reduce algae concentrations in water. 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 realised from dead cells. It should be noted that the treatment of Cyanobacteria with algicides or disinfectants, will initially cause an increase in the toxin levels due to the toxins being released from dead cells. |
| Performance criteria: Algae risks are controlled. If algae have been identified as a problem: Best practice level: Chlorophyll a: 0–7μg/L Maximum acceptable level: Chlorophyll a: 15μg/L |
| Minimum requirements |
| Source water is filtered before storage – intact cells (and intracellular toxins) are removed: See Table 13 (below) for a comparison of treatment options for intracellular and extracellular cyanotoxins. |
| Regularly monitor source water, storage reservoir and evaporative cooling system (if used) for algae. |
| Best practice options |
| If possible: |
| Manage source water to control algae by: |
| Species and toxin identification. |
| If possible, after a severe bloom: Note: Algicides may have side effects such as killing aquatic life. They will cause plants to rot, which in turn will cause a sudden decrease in oxygen levels in water bodies which will affect aquatic life. Therefore, additional aeration and filtering may be required. When blue-green algae die they release toxins into the water which can be poisonous to animals, birds, humans and other aquatic life. |
Other information
Table 13. Cyanotoxins treatment processes and relative effectiveness (D'Anglada, 2019)
| Treatment process | Relative effectiveness |
|---|---|
| Intracellular cyanotoxins removal (intact cells) | |
| Coagulation / Sedimentation / Filtration | Effective for removing cyanobacteria cells (intracellular cyanotoxins). Ensure that captured cells accumulated in sludge are removed frequently so as not to release toxins. Ensure that sludge supernatant is not returned to the supply after sludge separation. |
| Membranes | Effective for removing cyanobacteria cells (intracellular cyanotoxins). Microfiltration and ultrafiltration are effective when cells are not allowed to accumulate on membranes for long periods (months). |
| Flotation | Flotation processes effectively remove intracellular cyanotoxins since many of the toxin-forming cyanobacteria are buoyant. |
| Extracellular cyanotoxins removal | |
| Membranes | Selection depends on the type of cyanotoxin, membrane material, membrane pore size distribution, and influent water quality. Nanofiltration is generally effective in removing extracellular microcystins. RO filtration is generally applicable for removing microcystins and cylindrospermopsin. |
| Activated carbon adsorption | Powdered activated carbon (PAC): The effectiveness of PAC adsorption varies depending on the type of carbon, pore size, type of cyanotoxin, and other water quality parameters such as natural organic matter (NOM) concentration. Granular activated carbon (GAC): The effectiveness of GAC adsorption varies depending on the type of carbon, pore size, type of cyanotoxin, and other water quality parameters such as NOM concentration. |
