Optimum Of Bioleaching Of Heavy Metals In Sewage Sludge And Research On Reaction Mechanism

The bioleaching process, which causes 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 bacterium for bioleaching.In this paper, the optimum parameters of bioleaching of sewage sludge with isolated Thiobacilli (T. thiooxidans and T. ferrooxidans) are basically reviewed. Based on their theoretical similarity and analogy, the reaction mechanism is studied. The purposes of the study are to quantitatively and qualitatively 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.The significance of starting pH, the solids concentration and the energy source in bioleaching are evaluated in a bench-scale reactor. Results show that the metal removal efficiency increases when using Fe2+ and S as the energy source, comparing to using them individually. Adjusting starting pH is unnecessary. Due to the buffering capacity of sludge solids, the rates of pH reduction, ORP rise and metal solubilization are reducing with the increase of the solids concentration. When the solids concentration is 4% (w/v), high efficiencies of metal solubilization are achieved. It is observed that solubilization of Zn from sludge is highly pH-dependent.The bioleaching process starts when pH of sludge reaches to 4.Amongst various physical stimuli methods for speeding up the bioleaching process, the application of ultrasound is proved to be of considerable interest for rapidly intensifying the performance of live biocatalysts. The use of power ultrasound in combination with bioleaching (referred to as sonobioleaching) has been studied and is shown to be beneficial in the recovery of heavy metal from sewage sludge. With a controlled level, the use of ultrasound can speed up the bioleaching process. The removal rates of Cu and Zn can reach to 99.3% and 88% with 1 min of sonication at 20kHz frequency and 20% swing .