02702nas a2200241 i 450000500170000000800410001703500150005810000230007324500760009626000520017230000220022449000270024650001560027350200580042952016510048765000280213870000350216670000440220170000480224571000430229381000590233685600650239520260819085215.0271098s1982    th  u m rtt   0|  a1eng d  a.b107435831 aIslam, Md. Serajul10aTreatment of tannery waste-effects of trivalent and hexavalent chromium  aBangkok :bAsian Institute of Technology,c1982  a67 leaves :bill.1 aThesis ;vno. EV-82-25  aA thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development  aThesis (M.Eng.) - Asian Institute of Technology, 1982  aThe 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. 0aTanningxWaste disposal0 aSamorn Muttamara,eChairperson1 aVigneswaran, S.,eExamination Committee0 aChongrak Polprasert,eExamination Committee2 aBelgium Government,eScholarship Donor2 aAsian Institute of Technology.tThesis ;vno. EV-82-25  3Full-Textuhttp://203.159.5.9/ait-thesis/detail.php?q=B21207