Speciation Analysis of Heavy Metals in Sludge from a Wastewater Treatment Plant

The Tessiers five-stage sequential extraction procedure for extractable heavy metals determination was applied to sludge samples collected from wastewater treatment plant of Yanan city, Shaanxi province, China. According to the Tessiers guidelines, Copper (Cu), Zinc (Zn), Nickel (Ni), Cadmium (Cd) and Chromium (Cr) were determined by atomic absorption spectrometry (AAS). The heavy metal concentrations from high to low are Cu > Zn > Ni > Cr > Cd, which are lower than maximum permitted levels for agricultural use in relation to current international legislation. As shown in the speciation experiment, Cu mainly exists in organic form and sulfides, which is relatively stable. Zn with potentially hazards mainly exists in iron/manganese form. Ni mainly exists in insoluble form, which is stable and not easy to migrate to the environment. Cd with potential biological effectiveness mainly exists in acid soluble form and is easy to migrate to the environment.