02988cas|a2200241 i 450000500170000000800410001703500150005810000220007324500770009526000520017230000140022449000270023850001550026550200580042052018750047865000470235370000350240070000470243570000400248271001000252281000590262285600650268120260817172545.0230399s1994    th  uzm rtt  00|  a1eng d  a.b101361131 aAli, Syed Murtuza10aChemical and biological heavy metal dissolution process of sewage sludge  aBangkok :bAsian Institute of Technology,c1994  a64 leaves1 aThesis ;vno. EV-94-01  aA thesis submitted in partial fulfillment of the requirements for the degree of Master of  Engineering, School of Environment, Resources & Development  aThesis (M.Eng.) - Asian Institute of Technology, 1994  aSequential extraction was performed to find out exchangeable, adsorbed, organic, carbonate  and residual forms of the metals in the sludge under consideration. Each metal showed binding  characteristics of its own. Zn had distinct affinity to the organic ligands present in the sludge,  whereas for Cd, Cr, Cu and Ni, dominant form was residual. Pb and Mn were associated mainly  with the organic and carbonate forms. Chemical leaching experiments were carried out for five  days by varying the pH to 1.5, 2.5 and 3.5. Chemical leaching of different forms were also  dependent on metal characteristics. In general; metals in adsorbed, organic and carbonate forms  were solubilized more easily than that of residual form. Exchangeable form increased to a  considerable extent after leaching.  Different forms of metals remained after leaching for the specified period of time was  found out and compared to investigate the chemical leaching process. Formation of stable  complexes with humic substances, mineral constituents and buffer action due to release of ligands  by H+ from metal-ligand complexes were considered responsible for the remaining of different  metal forms even after leaching for 5 days at a very low pH 1.5.  Solubilization rate of different heavy metals by the bacterium Thiobacillus ferrooxidans  was found very fast compared to chemical leaching at the same pH. Other than sulfides; metals  in adsorbed, organic and carbonate forms also were found solubilized due to bacterial activity.  This solubilization however, was considered either the result of production of excess H2S04  during bacterial leaching process or due to dissociation of metal-ligand complex by bacteria.  Metals in residual form, which was mainly sulfides were not leached completely by bacteria which  indicated the presence of very stable metal-mineral complex in this form. 0aSewagexPurificationxHeavy metals removal1 aUmita, Teruyuki, eChairperson1 aReutergardh, Lars, eExamination Committee1 aStoll, Uwe, eExamination Committee2 aSwedish International Development Authority (SIDA),  Government of Sweden., eScholarship Donor2 aAsian Institute of Technology.tThesis ;vno. EV-94-01  3Full-Textuhttp://203.159.5.9/ait-thesis/detail.php?q=B15600