Removal Of The Cu,Zn,Ni Form The Urban Sewage Sludge By Bioleaching

With the popularization of the national sewage treatment facilities,the sludge output is increasing day by day,which causes serious sludge problem. As the sludge contains abundant nutrient elements,such as nitrogen,phosphoros and kalium, the agricultural utilization of sewage sludge has become an important topic in today's research. However, the heavy metals in sewage sludge are the key restricted factor to the utilization of sewage sludge in agriculture. Therefore, research on the removal of the heavy metal and the utilization of sewage sludge in agriculture is of great significance. The sewage sludge from Taiyuan Hexi sewage treatment plant is studied. The research aims to reduce the poisonous heavy metals and search for an effective method of using the sewage sludge as resources by microbe treatment.Bioleaching is used to reduce the heavy metals in sewage sludge. It has been paid great attention in recent years due to its low cost,high efficiency and good dehydration capability after bioleaching. The major miroorganisms responsible for bioleaching are a variety of acidophilic and chemoautolithotrophic bacteria such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans,which oxidize the insoluble metal sulfides into metal sulfates in direct or indirect way. The insoluble metal sulfides are solubled after separation from liquid. At present, research on bioleaching has just started and not complete on inoculum sizes,reactor etc.This article will firstly introduce some important techniques national and international to deal with sludge briefly, and provide some necessarity in land application. Then the basic methods and theories are introduced.The second part of this article will mainly introduce the features of bacteria for bioleachingthe reaction mechanism of bioleaching, and the factors influencing the metal removal efficiency during bioleaching.The third part of this article will mainly measure the total sum of heavy metals included in concentrated sludge in the sewage treatment plants located in north and mid Taiyuan, and will analyze the chemical speciations. The result shows that the sludge of this sewage treatment plants doesn't exceed the standard of alkalescent soil; only the content of Zn and Cu has exceeded the standard of acidic soil. In the meantime, the unsteady chemical speciations of element Zn takes a common high percentage in sludge. So before sludge in agriculture are taken use of, dealing with the heavy metals is more and more necessary.In the forth part, Thiobacillus thiooxidans is used to bioleaching. Influnce on removal effect with different inoculum sizes is started. The result shows the efficency can be better with inoculum sizes of 3%.The removal rates of Cu, Zn andNi are 93.9%, 83.4%和55.6% separately;The higher of sulfur concentration is,the faster the pH falls down. The pH value will be 1.8 finally with sulfur concentration of 3g/L and 5g/L.3g/L is choosen.Simple bioleaching reactor is made in the fifth part. Better result-18days can be achieved in Continuous Stirring Tank Reactor(CSTR) without adding inoculum during first period. Time needed with higher removal rates is shorter and shorter in the later periods. This is because acclimation time of Thiobacillus thiooxidans is shortened.The last part concludes the whole paper and proposes to the later research: efficency of different kinds of sludge and relation between best inoculum sizes and shortest bioleaching time; nutrition comonents loses after bioleaching;land application;reasonable collection measures of filtrate etc.