Effect of acid treatment on the removal of heavy metals from sewage sludge

In this paper, sludge samples that were collected from the municipal wastewater treatment plant in Psittalia (Athens, Greece) were subjected to acid treatment using sulphuric acid. Furthermore, a sequential extraction scheme was applied in order to determine the chemical forms of Ni, Cu, total Cr, Pb and Zn in sewage sludge. The optimum combination was achieved through a variety of tests by applying a ratio of 1:5 of sludge quantity (g) per volume of acid (mL). The concentration of the acid used was in the range of 10–20% at two different temperatures (25–80°C) and the contact times ranged from 1 to 60 min. The optimum combination was achieved when the sludge samples were in contact with H2SO4 (20%) for 30 min at 80°C, as these experimental conditions resulted in the highest heavy metal removal efficiency. In addition, the metal distribution in the residue was investigated and the heavy metal partitioning was found to be different after acid treatment.