[Effect of growth phase on the flocculation of algal cells using clays]

Four different growth phases, late lag phase, middle logarithmic phase, late logarithmic phase and early senescence phase of Microcystis aeruginosa 469 were studied for their surface hydrophobicity (xylene-water system) and surface charge (Zeta potential), followed by flocculation tests with sepiolite of 0.2 g/L. The results showed that the values of hydrophobicity were 64%, 48%, 58% and 70%, and the algal removal efficiencies after 60 min were 97%, 87%, 81% and 99% respectively, indicating a good relationship between surface hydrophobicity and removal efficiency (R = 0.7-0.8), but not the surface charge. Surface hydrophobicity and removal efficiency for the algal cells of Microcystis aeruginosa both varied with growth phase in a sequence of senescence phase > lag phase > logarithmic phase.