Single and binary metal systems were employed to investigate the removal characteristics of Pb2+, Cu2+, Cd2+, and Zn2+ by Chlorella sp. HA-1 that were isolated from a CO2 fixation process. Adsorption test of single metal systems showed that the maximum metal uptakes were 0.767 mmol Pb2+, 0.450 mmol Cd2+, 0.334 mmol Cu2+ and 0.389 mmol Zn2+ per gram of dry cell. In the binary metal systems, the metal ions on Chlorella sp. HA-1 were adsorbed selectively according to their adsorption characteristics. Pb2+ ions significantly inhibited the adsorption of Cu2+, Zn2+, and Cd2+ ions, while Cu2+ ions decreased remarkably the metal uptake of Cd2+ and Zn2+ ions. The relative adsorption between Cd2+ and Zn2+ ions was reduced similarly by the presence of the other metal ions. (C) 2009 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.