Ahmmed, Sohel creator Preeda Pakpian Chairperson Eckhardt, Ing. Heinz Examination committee Apisit Eiumnoh Examination Committee The Royal Danish Government Scholarship donor text th Bangkok Asian Institute of Technology 1998 monographic eng 104 leaves Sewage sludge usually contains significant heavy metals that may limit its land application. Heavy metals in sewage sludge have been shown to be less plant available and low concentration prior to the incubation process. In the present research DTP A test was conducted for metal bioavailability whereas sequential step extraction was employed to investigate metal speciation (into exchangeable, bound to carbonate, to Mn and Fe oxides, to organic matter and in residue phase) and the effect of high moisture (flooded sludge) as well as low moisture (wet and dry) content on metal speciation in incubation of Huay Kwang sewage sludge for heavy metal. The flooded sludge under specified period of time (10, 30 and 60 days) generally reduces bioavailability of metal except Mn, which was quite constant (20% of total heavy metal). The exchangeable and carbonated fractions (plant available) are also reduced and therefore the potential hazard of releasing metals from sludge through adsorption and complexation of the metals onto inorganic components to different extents for the different metals. Zn and Pb had distinct affinity to oxides whereas for Mn and Cd, dominant fractions were exchangeable or carbonated. Cu, Ni and Cr were associated mainly with organic or residual form (both of the forms are sparingly available). The present of fecal coliform (2 - 5 x 104 MPN/g dry wt.) indiGates the safe use in agricultural land but it should be monitored regularly. During the period of wet and dry condition (9 - 12% moisture content) the dry sludge releases more plant available metal due to stimulation of microor~anism and longer residual period. The bioavailability of Pb was found highest 54% in 30 C. In contrast the plant available fractions (exchangeable and carbonated) were found less in comparison with original one (except Zn and Cu), indicating safe use in agricultural purpose. Mn was decreased significantly in this condition. The residual fraction (mainly sulfides) was observed quite high amount for almost all metals from original or flooded sludge, indicating stable metal mineral complex and less threatening to plant. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development Thesis (M.Eng.) - Asian Institute of Technology, 1998 Heavy metals Bioavailability Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B12740 http://203.159.5.9/ait-thesis/detail.php?q=B12740 011298 20260817171417.0