OPERATIONAL STRATEGY FOR METAL BIOLEACHING BASED ON PH MEASUREMENTS

An advanced operational strategy was developed in this study for a batch microbial leaching process, employing sulfur oxidation for heavy metal removal from sewage sludge, to terminate the batch operation at its best moment. Due to the practical difficulties associated with on-line measurement of soluble metal concentrations during the leaching operation, the present methodology is based on pH measurements in the reacting system. To monitor the metal solubilization, the bioleaching process model was developed, corresponding with the activity of the less-acidophilic bacteria and the acidophilic bacteria. An advanced on-line predicting system was then implemented; it employed the techniques of extended Kalman filtering and the neural net-based model that was based on a large amount of experimental observations in our laboratory to predict concentrations of six heavy metals in the bioleaching system's liquid phase. Finally, a case study illustrating the application is presented.