Islam, Md. Serajul creator Samorn Muttamara Chairperson Vigneswaran, S. Examination Committee Chongrak Polprasert Examination Committee Belgium Government Scholarship Donor text series technical report th Bangkok Asian Institute of Technology 1982 continuing eng 67 leaves : ill. The purpose of this research work was to study the effect of trivalent and hexavalent chromium on the activated-sludge treatment of tannery waste. A complete characteristics analysis and treatability study of tannery waste was performed. Since Cr-III toxicity is a direct function of Cr-III in soluble form and solubility is a function of pH alkalinity and waste characteristics; particular emphasis was given on the study of the solubility of trivalent chromium. In case of Cr-VI, an effort was made to investigate the uptake of hexavalent chromium by activated sludge for consequent removal. Results of the research work showed that 81% of the COD can be removed from tannery waste by activated-sludge process in a detention time of 12 hrs. The trivalent chromium toxicity is due to its soluble form. At any influent Cr-III concentration, the available soluble Cr is less than 4 mg/t and the rest is retained with MLSS in the reactor in precipitated form (pH= 6.8 - 9.0). A daily addition of 100 mg/t of Cr-III for 10 days with a gross accumulation of 576 mg/t (28.8% of MLSS on dry wt. basis) of precipitated Cr-III and 4 mg/t of soluble Cr-III, the laboratory activated-sludge units showed no loss in efficiency. The hexavalent chromium toxicity is a function of only MLSS concentrations at and above F/M ratio of 0.25. A metal to biomass ratio, i.e. Cm/Cx; ratio of 0.005, is the safe limit for Cr-VI. Below F/M ratio of 0.25, the toxicity is a function of both substrate and MLSS concentrations and increases with the decrease of substrate and MLSS concentrations. A maximum uptake of 45 mg of Cr-VI is possible with 2 gm of MLVSS. 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, 1982 Tanning Waste disposal Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B21207 http://203.159.5.9/ait-thesis/detail.php?q=B21207 271098 20260819085215.0