Accumulation and fate of selected heavy metals in a biological wastewater treatment system.

The aim of this research was to study the accumulation and removal of heavy metals (Cd, Cu, Pb, Zn) by a biological wastewater treatment system. Heavy metal contents in the influent and effluent wastewater were compared. Also, the heavy metal contents in the sludge before and after anaerobic digestion were compared. The results showed: (1) more pronounced variations in the contents of Cu and Zn than that of Cd and Pb, which showed that at 0.02 for Cd and 0.05 mg/l for Pb, the reduction in their contents was insignificant; (2) that removal of heavy metals was directly proportional to their initial contents in the influent wastewater. Corresponding to the influent contents, in increasing order, the reduction in heavy metal contents was: Cd<Pb<Cu<Zn; and (3) that anaerobic stabilization of sludge caused an increase in heavy metal contents on dry weight basis. The order of increase in heavy metal contents in digested sludge (Zn<Pb<Cu<Cd) was opposite to that of their contents removal from influent wastewater.