Optimization Of Parameter During The Removal Of Heavy Metals By Bioleaching

Bioleaching has great potential of the emerging biotechnology, which is an effective way to the removal of heavy metals in sludge. It has paid great international concern in recent years because of its low cost and high removal efficiency and good dehydration capability after bioleaching. Through the solid-liquid separation to achieve the purpose of removing heavy metals, sludge bioleaching mainly used Thiobacillus to oxidize the sludge of insoluble metal sulfides to metal sulfate stripping directly or indirectly. With the development of wastewater treatment facilities ,the production of excess sewage sludge increased substantially.Although land application was economically feasible, but sludge heavy metals has potential threat on the ecological environment and to human health.so,at this time,bioleaching technology was particularly important.Now, the sludge heavy metal bioleaching technology research has just started, then the use of sulfur bacteria leaching studies as well as the contents of the reactor and other research was not yet completed. In order to its efficient and economical operation,so optimal process parameters was of great significance.In this paper, Taiyuan Hexi Central sewage treatment plant sludge was used as the research enrichment, and we use bioleaching to remove heavy metals in sludge, at the same time the bioleaching process parameters were optimized. Then, on this basis, we have run dynamic bioleaching experiments. In order to further lay the foundation for agricultural and forestry use, the purpose of this paper is to remove and reduce the cities of toxic heavy metals in sludge effectively, and to achieve the resource usage.First of all, it briefly describes the characteristics and nature of the sludge, as well as the current domestic and sludge treatment and disposal of the main techniques at home and abroad.Then we propose the effect of sludge agricultural resource and environmental effects and finally it focuses on the basic treatment of heavy metals in sewage sludge method.Secondly, we focuses on the study of biological leaching status, including the characteristics of bioleaching bacteria, bioeaching of heavy metals in sludge removal by the biological reaction mechanism and efficiency factors which impact of removing heavy metals by bioleaching, then put forward the improvement of biological leaching and its prospects.When we determined of total heavy metals, it was found that the sludge of this sewage treatment plants didn't exceed the standard of alkalescent soil, only Zn and Cu element has exceeded the acid soil standards.At the same time, the unsteady chemical speciations of Zn element took a common high percentage in sludge and the generally high proportion of unstable form,which all exceeded the use of sludge acid soil standards. Therefore, the treatmen to heavy metals in sewage sludget before agriculture is very necessary.By the way of comparing the rate of heavy metal leaching using two different media which were ferrous sulfate and elemental sulfur,and because of high Zn content of Taiyuan Hexi Central sewage treatment plant,the test chose the sulfur as the substrate. Then, mix sulfer bacteria inoculums was used to bioleaching static experiments.Removal effects of heavy metals under different sludge concentration and substrate concentration and the amount of inoculum as well as the different initial pH values of leaching were researched .It was found that a 3% of the inoculum size had better leaching effects, then the best sludge concentration was 5%, the best initial pH value was 4, lastly the best substrate concentration was 5g/L. Finally, continued stirring bioleaching reactor (CSTR) was used to run two ways bioleaching dynamic test, namely, continuous flow and intermittent, which batch bioleaching tests carried out three batches. It was found that continuous flow intermittent removal better than the same time. At the same time, the leaching effect was good and in addition to Cd, Cu and Zn removal efficiency was better than those in static tests.In the last part, it was recommended to improve bacteria and reduce leaching cycle. We shoule do more in-depth study to the dynamic experiment and in order to keep the fertilizer and utilization of sludge after agricultural, we must determine the content of the nutrients whenever necessary. Lastly, the heavy metal in the filtrate should be recycled.