Content and Chemical Speciations of Cu, Zn, Pb, Cr, Ni and Mn in Sewage Sludge from Guangzhou, China

Sludge can be used in agriculture as a fertilizer and soil conditioner. But heavy metals are one of the important factors affecting the sludge for agricultural purpose. In this study, the concentration of Zn, Cu, Pb, Cr, Mn and Ni in seven kinds of sludge from Guangzhou were analyzed and the chemical speciation of heavy metals in the five kinds of sludge were studied. The results showed that the concentration of Cu, Zn, Mn, Ni were higher, but Pb, Cr much lower. Although the contents of heavy metals were higher than the background values of Pearl River Delta crop soil, except for Cu contents in the selected sludge, the other elements meet the controlled standards of pollutants in sludge for agricultural uses (GB18918-2002). Different heavy metals in different selected sludge had different phrases. In the industrial sludge, Cu, Cr existed mainly in reduction phrases, but Pb and Fe were in the reducible and residual phrases. In the domestic sewage sludge, the heavy metals exist mainly in oxidizable and residual phrases, but the percentage of Mn in the exchangeable phrase and Zn in the reducible phrase were largest. In all, the active proportion of Cu, Zn and Mn was larger and their potential transformation was strong. Compared with the background crop soils, the sludge was valuable in agricultural usage characterized by higher organic matters, N and P, and lower K, but the potential transference and biological toxicity of the selected heavy metals deserved the most attention in agriculture use.