| The bioleaching process, which leads to acidification and solubilization of heavy metals, is recommended as an economical and effective process for the removal of heavy metal from sewage sludge. Thiobacilli is a group of organisms recommended as effective bacteria for bioleaching. In this paper, the optimum parameters of bioleaching of sewage sludge with isolated Thiobacilli (T.thiooxidans and T. ferrooxidans) were basically reviewed. Based on their theoretical similarity and analogy, the reaction mechanisms were studied. The purposes of the study are quantitatively and qualitatively to investigate the relationship between various physicochemical parameters and metal leaching and to provide a better understanding for the treatment of heavy metal from sewage sludge.Influences of the ratio of sulfur addition to the total solid in sewage sludge (SA/TS) were studied on the bioleaching of heavy metals using mixed T.thiooxidans liquor. The results show that higher SA/TS significantly accelerates the acidification of sludge and increases the efficiency of heavy metal bioleaching.The optimal SA/TS ratio is 2.5, under which 66.2% of Cu and 63.9% of Zn are leached out after 8 days and 30.8% of Pb is leached out after 16 days. Cu mainly exists as organic-Cu both before and after the bioleaching. A high percentage of oxides bound Zn is solubilized.After 16 d bioleaching, oxides bound Pb decreases while organic bound Pb increases. A higher SA/TS ratio improves the utilization of sulfur, insignificantly impacts the preservation of nitrogen, but promotes the loss of phosphorous.Xiawangang Stream was seriously polluted by heavy metals. Its sediment was very special because of the high alkalinity and the high content of heavy metals. Experiments were carried out to assess the influence of initial pH of the system on bioleaching of zinc, copper and cadmium. Results show that the bioleaching can not start-up effectively, when the initial pH is 7. For Cu, Zn and Cd solubilization, similar bioleaching efficiency was reached when setting the initial pH at 6, 5, 4, but the initial pH 6 seemes to be the best one for bioleaching. Taking heavy metals removal and economic costs into account, the initial pH 6 is optimal. The loose sediments become massive after bioleaching, which improves its dewatering performance significantly. |
