comparative studies on the bioremediation of hexavalent and trivalent chromium using citrobacter freundii: part i-effect of parameters controlling biosorption

the potential of citrobacter freundii, a gram negative bacteria for the remediation of hexavalentchromium (cr(vi)) and trivalent chromium (cr(iii)) from aqueous solutions was investigated. bioremediationof cr(vi) involved both biosorption and bioreduction processes, as compared to only biosorption processobserved with respect to cr(iii) bioremediation. in the case of cr(vi) bioremediation studies, about 59 %biosorption was achieved at an equilibrium time of 2 h, initial cr(vi) concentration of 4 mg/l, ph 1 and abiomass loading of 5x1011 cells/ml. the remainder, 41 %, was found to be in the form of cr(iii) ions owing tobioreduction of cr(vi) by the bacteria resulting in the absence of cr(vi) ions in the residue, there by meetingthe usepa specifications. similar studies were carried out using cr(iii) solution for an equilibrium time of 2h, cr(iii) concentration of 4 mg/l, ph 3 and a biomass loading of 6.3x1011 cells/ml, wherein a maximumbiosorption of about 30 % was achieved.