Removal of cyanobacterial blooms in Taihu Lake using local soils. I. Equilibrium and kinetic screening on the flocculation of Microcystis aeruginosa using commercially available clays and minerals

Algal removal abilities of 26 clays/minerals were classified into three categories according to the 8-h equilibrium removal efficiency (Q 8h) and removal rate at a clay loading of 0.7 g/L. Type I clays (sepiolite, talc, ferric oxide, and kaolinite) had a Q 8h > 90%, a t 5 (time needed to remove 50% of the algae) < 15 min, and a t 8 < 2.5 h. Type II clays (6 clays) had a Q 8h 50-90%, a t 5 < 2.5 h, and a t 8 > 2.5 h. Type III clays (14 clays) with Q 8h < 50%, t 5 > 8 h and t 8 > 14 h had no practical value in removal of algal blooms. When the clay loading was reduced to 0.2 g/L, Q 8h for all the 25 materials decreased to below 60%, except for sepiolite whose Q 8h remained about 97%. The high efficiency for sepiolite to flocculate M. aeruginosa cells in freshwaters was due to the mechanism of netting and bridging effect. - Sepiolite was the most effective flocculant among 26 commercially available clays and minerals in removing harmful algal cells from freshwaters