Fumihiko Takeda

A comparison of zeta potentials and coagulation behaviors of cyanobacteria and algae

Abstract 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...

Water quality comparison of secondary effluent and reclaimed water to ambient river water of southern Okinawa Island via biological evaluation

The objective of this work was to evaluate the biological effect of the secondary effluent (SE) of a wastewater treatment plant and reclaimed water treated via ultrafiltration (UF) followed by either reverse osmosis (RO) membrane filtration or nanofiltration (NF) to be used for environmental use by comparing the results of algal growth inhibition tests of concentrated samples of the SE and permeates of RO and NF with those of six rivers in southern Okinawa Island. Although the SE water had no adverse effects on the growth of the algae Pseudokirchneriella subcapitata, it could lead to water quality degradation of rivers in terms of its toxic unit value, whereas the use of RO and NF permeates would not lead to such degradation. The recharge of rivers, into which domestic wastewater and livestock effluents might be discharged in southern Okinawa Island, with reclaimed water subjected to advanced treatment could dilute the concentrations of chemicals that cause biological effects and improve the water quality of the rivers, based on the results of the bioassay using P. subcapitata. Comparing the results of bioassays of reclaimed water with those of the ambient water at a site might be effective in assessing the water quality of reclaimed water for environmental use at the site.