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In this study, the zeta potential of Microcystis aeruginosa (cyanobacteria), Synechococcus sp. (picocyanobacteria) and Chlorella vulgaris (algae) was investigated in order to determine the zeta potential range for optimum cell removal. Algae and cyanobacteria species were treated by coagulation-sedimentation using 0-500 mg/l polyaluminum chloride (PACl). Analyses included zeta potential measurement, cell counts and turbidity removal. The role of pH on the zeta potential also investigated in this study. The pH of coagulation system was adjusted to pH 6.5 and 7.0. At pH 6.5, the optimum zeta potential bands were between -2.1 mV and +20.45 mV for Microcystis aeruginosa, +3.45 mV and +8.71 mV for Chlorella vulgaris and +7.41 mV and +13.33 mV for Synechococcus sp. The ranges were much narrower at pH 7 than at pH 6.5. The cell removal efficiencies were 98.9%, 90.6% and 55.7% for Microcystis aeruginosa, Chlorella vulgaris and Synechococcus sp, respectively. The implications of such findings are that the charge measurement can be used for controlling coagulation of algae and cyanobacteria. In addition, the type of cell species in the system was shown to a significant factor in the coagu- lation performance. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the efficiency of the coagulation process for the removal of picophytoplankton from drinking water and, in addition, to investigate the performance of simple coagulants such as alum and ferric chloride, and polymer coagulants such as PAC and PSI, in picophytoplankton removal. Two simple coagulants such as alum (Al2(SO4)3·16H2O) and ferric chloride (FeCl3·6H2O) and two polymer coagulants such as poly-silicate iron (PSI) and poly-aluminum chloride (PAC) were used in both raw water including picophytoplankton and synthetic water samples prepared by Synechococcus sp. Analyses included a picophytoplankton count, an assessment of the turbidity, dissolved organic carbon, UV254, and zeta potential and the settling time measurements. The removal efficiency of picophytoplankton during the coagulation-flocculation-sedimentation process was determined using simple and polymer coagulants. Water samples with lower coagulation pH had better picophytoplankton removal in coagulation-flocculation-sedimentation. The results indicate that even low coagulant doses of PSI in both raw water and artificial water performs better than the other three types of coagulants in terms of picophytoplankton, turbidity, UV254, and DOC removal. [ABSTRACT FROM AUTHOR]