Report No FR0491

J Hart

Nov 1994


Blooms of blue-green algae can give rise to the production of toxins that may contaminate freshwaters used as sources for potable water. Toxicological studies carried out on behalf of the FWR and in Australia suggest thate toxin concentrations of low micrograms per litre would give an adequate margin of safety for human consumption.

WRc has undertaken several studies under contract to the Foundation for Water research, to investigate the removal of algal toxins from drinking water. These studies have included both laboratory and pilot scale tests to assess treatment options for the removal of microcystin-LR and anatoxin-a. These toxins were chosen as representatives of the toxins produced by the common blue-green algae in the United Kingdom.

This report summarises the results of the previous studies, with the objective of providing guidelines for the treatment of potable water supplies at risk from algal toxins.

The treatment options given in the report are specified as being suitable for the removal of the toxins that have been released into the water. They are not specified on the basis of their suitability for removing algae, oras ameans of preventing algal blooms.

Algae removal is an important aspect of treatment. Typically, an algal cell will contain 10-12g of toxin. Algal concentrations of 1000cells/ml could thus result in a toxin concentration of 1 g/l. The algal counts of treated water should be below 1000 cells/ml, so that the risk of algae cells containing toxin entering supply is minimised.

Copies of the Report are available from FWR, price 15 less 20% to FWR Members.