Evaluation of cyanobacterial cells removal and lysis by ultrafiltration

Abstract

The aim of this study was to evaluate the ultrafiltration (UF) performance for removing Microcystis aeruginosa cells under different growthages (1, 2, 3 and 4 months old). Special attention was given to cell damaging and subsequent release of microcystins to permeate. Experiments were performed with a hollow-fibre cellulose acetate membrane (100kDa). UF achieved an absolute removal of M. aeruginosa single cells, producing chlorophyll-a free water and with a turbidity below 0.1 NTU. Cell lysis occurred at all cell growth phases although greater damage was observed for older cultures. However, the permeate quality was never deteriorated and its microcystin concentration was always identical or lower than the dissolved concentration in the feedwater. The hydrophilic UF membrane presented low adsorption of microcystins but the microcystin rejection increased in the presence of algogenic organic matter (AOM). The type rather than the overall concentration of salts and organics ruled the membrane fouling, the 1-month-old suspension (polysaccharide-rich AOM with scaling multivalentions) presenting higher fouling potential than the 3-month-old suspension (protein-rich AOM with much lower content of multivalent ions).