Ozonation, biofiltration and the role of membrane surface charge and hydrophobicity in removal and destruction of algal toxins at basic pH values

This study was directed at the investigation of technologies for treatment of water containing algal toxins at basic pH values. Ozonation, biofiltration and membrane filtration were examined for the removal of algal toxins, specifically microcystin-LR (MC-LR). Results indicate that, as expected, ozonation completely destroyed MC-LR in water, while biofiltration using naturally-occurring bacteria did not show a significant reduction in MC-LR concentration after eight days of contact time. More compelling were the membrane filtration results, which showed that water-affinity interactions were not the only governing factor influencing the removal of MC-LR by membranes. It was found that charge interactions between membranes and MC-LR played an important role in the rejection. MC-LR was completely removed from the feed water only by hydrophobic neutrally and positively charged membranes. Furthermore, due to charge interactions, MC-LR reversibly adsorbed to neutral hydrophobic membranes, but it irreversibly adsorbed to positive hydrophobic membranes.