Immobilization Of Heavy Metals In Dewatered Sludge Conditioned By Skeleton Builders

Landfill is the main approach to sewage sludge disposal in China. However, heavymetals in sludge may release to the landfill leachate and then cause pollution in thegroundwater environment. Based on our previous research about sludge dewatering anddisposal based on skeleton builders, immobilization of hevy metals under differentconditions such as standard curing, steam curing and accelerated carbonation is carried outin this thesis. The main contents are presented as follows:1. Study on characteristics analysis and dewaterability of sludgeStudy on characteristics analysis and dewaterability of Longwangzui, Shahu, Sanjintan,Tangxunhu and Zhuankou sludge in four quarters is carried out.The resluts indicate thatmoisture content and VSS/SS are low and SS, COD, SCOD, SRF, CST are high for Shahusludge, while Longwangzui, Tangxunhu and Sanjintan sludge have similar properties. Thedewaterability of sludge could affacted by COD, SCOD, SRF and CST.2. Leaching properties of heavy metalsReference to the U.S. EPA Toxicity characteristics leaching procedure （TCLP）, astandard agitated leaching test is devoloped to simulate the process of heavy metalsleached from solidified sludge by the landfill leachate; Same batch of specimens under thecolumn leaching is the comparative experiments. Considering the local situation of Wuhanrainfall, leachates of relevant L/S are collected. pH and the heavy metal contents aredetermined to study the dynamic leaching behavior and long-term leachingcharacteristics.The resluts indicate leaching percentage of heavy metals decreases with theincrease of curing age. In column leaching test, extraction percentage and pH of leachateshow a good correlation. After a column leaching which is equivalent to landfilling for70a, leaching percentages of Cr, Cd, Pb, Cu and Zn are3.1%,2.4%,2.4%,3.9%and2.3%.3. Speciation distribution of heavy metals and microstructural characterization ofspecimensSequential extraction procedure proposed by Tessier is used to analysed the speciationdistribution of heavy metals; X-ray diffraction （XRD） and Scanning electron microscope（SEM） are used to explore the microstructural characterization of specimens.The resluts indicate that the main compounds of dewatered sludge are SiO₂, CaCO₃and Ca（OH）₂. Themobility of heavy metals in specimens decreases with the incease of curing age.Morphologies of dewatered sludge after different curing days illustrates that ettringitephase formed and a compacter structure generates in dewatered sewage sludge.This thesis carries out the studies on immobilization of heavy metals in dewateredsludge after conditioning with skeleton builders. Influence of curing and extractionconditons to the leaching is also disscussed. The results in this thesis provide a theoreticalbasis for long-term security of heavy metals in sludge landfill disposal.