RESUMEN
Heavy metals in municipal sewage sludge can limit the utilization of sludge resources, due to their recalcitrant characteristics and harmful effects. Here, ICP-MS was used to determine the total and special content of Pb, As and Cd in the sewage sludge from G and Q Wastewater Treatment Plants, Beijing. The air-dried samples were dissolved in HNO3-HClO4 before the total content determination, or, sequentially extracted with BCR three-step method before special content determination for the heavy metals. The total contents are 19.60, 37.96 and 1.34 mg x kg(-1) dry weight (DW) for Pb, As and Cd in the sewage sludge from G Plant; respectively; or, 19.58, 23.46 and 2.30 mg x kg(-1) DW in that from Q Plant, respectively. Pb and Cd decreased dramatically in the total contents, compared to the corresponding data in the late 20th century. Both G and Q sludge samples show similar patterns in the species distribution for the three heavy metals: most of Pb and As are HAc soluble, and least are H2O2 oxidative; while Cd mainly exists in NH2OH-HCl reductive state, seldom in HAc soluble state. Species with high ecotoxicity account for a major part (over 70%) of the three species for all the metals on the whole. The authors' results provide basic data for the ecological risk assessment and utilization of municipal sewage sludge from Beijing.
