Abstract
Toxicity of heavy metals to aquatic organisms is depending on their speciation in the water environment. Free ion of the metals is known as the most toxic species in general, although the total metal concentration has been adopted in water quality standards due to the limitation of field data on metal speciation in anthropogenic discharges. This study focused on zinc, copper and nickel speciation in domestic wastewater treatment plant and their fate in the receiving water. The metals were separated into particulate, dissolved and free metals with 0.5μ m membrane and. EmporeTM Chelating Disks, a chelating disk cartridge with iminodiacetic acid sodium salt . The free zinc, copper and nickel concentrations in the treated effluents were 3.0-15μg Zn/L, ND-6.0μgCu/L and < 1.5-7.1μg Ni/L. The fraction of free ion in dissolved metal was variable in samples as 12-47% in zinc, 24-61% in copper and 16-60% in nickel. The metal speciation in the effluent from the advanced treatment processes for organic matter and nutrients removal was not significantly different from that in the conventional treatment process. A laboratory experiment to simulate the effluent discharge to a river indicated that the fraction of dissolved zinc complex decreased by mixing the treated sewage and the river water.
