Removalof Intact Cyanobacterial Cells by Water Treatment

ReportNo WSAA 134

December 1997

 

SYNOPSIS

 

Cyanobacteriaproduce toxins and tastes and odours which can significantly impair waterquality. The removal of cyanobacterial cells without cell damage wouldsignificantly reduce the concentration of taste, odour and toxic cellmetabolites present in the treated water. The aim of this project was todetermine the effect of available water treatment systems on cyanobacterialcells and their noxious products. Two cyanobacteria, hepatotoxic Microcystis aeruginosa and odorous Anabaena circinalis, were selected astest organisms in this study. The effects of conventional water treatment(coagulation/ flocculation sedimentation filtration) and membrane filtrationon cultured cyanobacteria were evaluated. For conventional water treatment, thestudy investigated the impact of coagulation toxicity, mechanical stirring andthe total flocculation process using both laboratory jar test apparatus and asmall pilot plant. Treatment chemicals, aluminium sulphate and ferric chloride,dosed at concentrations used in water treatment practice and the mechanicalactions, pumping and stirring, occurring in the water treatment plant did notappear to cause lysis of cells of cultured M.aeruginosa and A. circinalis.More importantly no additional release of cell metabolites, microcystin andgeosmin, was found after the experiments. The same conclusion also applied tothe flocculation study. In the pilot plant study, we have further confirmedthat conventional water treatment cannot remove extracellular toxin, however,it can remove cyanobacterial cells from the water (99.9% removal) under normaloperating conditions. The cells removed were in good condition and noadditional cell metabolites were found in the treated water.

 

Membranefiltration is a relatively new technique in water treatment. The work conductedwas a preliminary study on the effect of membrane filtration on cyanobacterialcells. In general, both the selected microfiltration and ultrafiltrationmembranes effectively removed the algal cells in good condition with noadditional release of cell metabolites in the treated water.

 

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