Study on occurrence state and bioavailability of heavy metals in municipal sludge

On the basis of analyzing the physical and chemical properties of sludge, the selective sequential extraction procedures developed by Tessier was used to study the chemical forms and the bioavailability of heavy metals (Cu, Zn, Pb, Ni, Cd and Cr) in municipal sludge. The experimental result indicated that the content of organic matter in the sludge reached 45.62 %, the contents of N, P and K were 1.55 %, 4.26 % and 1.01 %, respectively, and the contents of heavy metals were lower than those of the control standard of sludge. The proportions of effective forms of Cu, Zn and Ni were 2.65 %, 1.24 % and 46.01 %, respectively. The potential effective forms of Cu and Zn were 36.52 % and 10.71%, respectively, and theunavailable forms of Cu, Zn, Pb and Ni were 60.83 %, 88.05 %, 100 % and 53.99 %, respectively.Metals Cd and Cr were not detected in the sludge. The heavy metals mainly exist in the forms of non-exchange state, and the bioavailability is low, which is very beneficial to the use of composting processin agriculture.