Biotreatment of cr(VI)-containing wastewater mediated by indigenous bacteria

Abstract

Indigenous Pseudomonas veronii 2E, Klebsiella oxytoca P2 and Klebsiella ornithinolityca 1P were tested as catalysts for the transformation of Cr(VI) to Cr(III) for Cr(VI)-containing wastewater biotreatments. The Cr(VI) biotransformation was assayed during bacterial growth and by using pre-grown quiescent cells. Proof of the unsuitability of a biotreatment based on Cr(VI)-reduction during bacterial growth was found: the reduction rate and the maximum Cr(VI) concentration able to be reduced were too low. On the other hand, high density suspensions of pre-grown quiescent cells presented the highest reduction rates, especially in the presence of an electron donor. The most efficient strain for Cr(VI) removal was Pseudomonas veronii 2E. Optimal pH and temperature for the biotransformation process resulted 7 and 32ºC respectively. The maximum initial reduction rate obtained in these conditions was 0.49 mg Cr(VI) h-1 g cell dry weight-1 (9.4 µmol Cr(VI) h-1 g cell dry weight-1). Proof of the feasibility and efficiency of this technology is provided by using in calcium alginate immobilized P. veronii 2E cells for the treatment of a real Cr(VI)-containing industrial wastewater.