Removal of heavy metals from sewage sludge by acid treatment

Sludge samples were found to contain significant amounts of heavy metals (C r, Cu, Ni, Pb and Zn) and were subjected to acid treatment using either hyd rochloric, sulfuric, nitric or phosphoric acid. The optimum combination, in terms of metal removal efficiency and environmental impacts was sought thr ough a variety of tests by applying a ratio of 1:5 of sludge quantity (g) p er volume of acid (ml). The concentrations of the different acids used, wer e in the range of 5%-20% and the contact times ranged between 15 and 60 min utes. The optimum combination was achieved when the sludge samples were in contact with H2SO4 20%v/v for 60 minutes. In order to estimate the metal le achability, the heavy metal content as well as the metal distribution in th e residue were investigated and it was found that most of the heavy metal c ontent was extracted while the remaining was removed from the initial mobil e phases to the more stable ones.