Algal Toxins in Drinking Water

Water Treatment Approaches for Algal Toxins in Drinking Water- an Interview

InWater Technology's "Professor POU/POE - October 2014" Technical Editor Dr. Joseph Cotruvo discussesalgaltoxins in drinking water as a result of algal blooms and various water treatment options available.

• Conventional treatment that includes coagulation, flocculation, sedimentation and chlorinedisinfectioncan remove most of the algal cells, buttoxinremoval is more problematic. It is essential to remove the algal cells byfiltrationprior to the addition of any oxidant such as chlorine. The oxidant will lyse the cells and release the toxins into thedrinking water.
• Oxidants/disinfectants such as chlorine, chloramine, chlorine dioxide, ozone, potassium permanganate andultraviolet (UV)light are frequently available in a water treatment facility, or can be added, and provide a range of efficacies against the toxins. The following relate to Microcystin-LR, which is a common form of an algal toxin and among the most potent:
  • Ozone will rapidly lyse the cells; it is effective against the toxin atozonedoses of five ppm or less and at very low concentration-time values (CT in mg-min/l). CT means concentration in mg/l x time in minutes, so for example, a concentration of one mg/l for 10 minutes would be the same as 10 mg/l for one minute. Elimination of Microcystin-LR is virtually instantaneous.
  • Potassium permanganate will lyse the cells and is also a very effective, rapid treatment for the toxin. The CT value for complete elimination is about 25 mg-min/l.
  • Free chlorine will lyse the cells and it is very effective, achieving nearly complete elimination at CT of about 60 mg-min/l. Chlorine is present in almost every surface water treatment plant and probably functions both as an oxidizing and chlorinating agent.
  • Chlorine dioxide is a good disinfectant and lyses cyanobacteria cells, but it has no reactivity toward the toxin.
  • Monochloramine has some reactivity against the cells but not towards the toxin.
  • UV light irradiation at high doses has a destructive effect on the cells but does not affect toxin concentrations.
• Membranes such asreverse osmosis (RO), nanofiltration, ultrafiltration and microfiltration are all effective for the removal of cells. Pretreatment and frequent cleaning could be necessary. RO and nanofiltration, but not microfiltration, would be effective for toxin removal.

Source: Water Technology

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Taxonomy

• Algae
• Water Supply
• Drinking Water