[Effects of ionic strength on the flocculation and removal of cyanobacterial cells of Microcystis aeruginosa by clays].

The effect of ionic strength on the flocculation and removal of Microcystis aeruginosa by clays and chitosan-modified clays were studied. High ionic strength was beneficial to the removal of algae cells by clays due to the reduction of the thickness of electrical double layer that enhanced the collision probability of the granules. In contrast to normal clays, chitosan-modified clays showed a higher removal efficiency of Microcystis aeruginosa cells under low ionic strength. The removal efficiency was reduced from more than 90% to 70% by sepiolite, but promoted from 70% to 95% by modified sepiolite when the ionic strength decreased from 0.17mol/L to 0 mol/L. This is because the repulsion of positive charged groups in chitosan molecule chain were shielded by large number of ions at higher ionic strength that reduce the extensibility of the chitosan molecule, leading to the reduction of bridging and netting between particles. Chitosan-modified clays were therefore suitable for removal cyanobacterial cells in fresh waters such as lakes, reservoirs and rivers.