Removal of Intact Cyanobacterial Cells by Water Treatment
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report no. UWRAA 134
Cyano bacteria produce toxins and tastes and odours which can significantly impair water quality. The removal of cyanobacterial cells without cell damage would significantly reduce the concentration of taste, odour and toxic cell metabolites present in the treated water. The aim of this project was to determine the effect of available water treatment systems on cyanobacterial cells and their noxious products. Two cyanobacteria, hepatotoxic Microcystis aeruginosa and odorous Anabaena circinalis, were selected as test organisms in this study. The effects of conventional water treatment(coagulation/ flocculation – sedimentation – filtration) and membrane filtration on cultured cyanobacteria were evaluated. For conventional water treatment, the study investigated the impact of coagulation toxicity, mechanical stirring and the total flocculation process using both laboratory jar test apparatus and a small pilot plant. Treatment chemicals, aluminium sulphate and ferric chloride, dosed at concentrations used in water treatment practice and the mechanical actions, pumping and stirring, occurring in the water treatment plant did not appear to cause lysis of cells of cultured M. aeruginosa and A. circinalis. More importantly no additional release of cell metabolites, microcystin and geosmin, was found after the experiments. The same conclusion also applied to the flocculation study. In the pilot plant study, we have further confirmed that conventional water treatment cannot remove extracellular toxin, however, it can remove cyanobacterial cells from the water (99.9% removal) under normal operating conditions. The cells removed were in good condition and no additional cell metabolites were found in the treated water.
Membrane filtration is a relatively new technique in water treatment. The work conducted was a preliminary study on the effect of membrane filtration on cyanobacterial cells. In general, both the selected microfiltration and ultrafiltration membranes effectively removed the algal cells in good condition with no additional release of cell metabolites in the treated water.