Development of Bioreactor System for the Treatment of Chromate Wastewater and the Recycle of Chromium using Chromate Reducing Bacteria Enterobacter cloacae HO-1

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A novel bioreactor system was developed for the simultaneous treatment of toxic and mutagenic hexavalent chromium (chromate) and high strength organic pollutants by introducing chromate-resistant and chromate-refucing bacteria Enterobacter cloacae strain HO-1. Growth and chromate reducing characteristics of E.cloacae HO-1 were extensively investigated. To enrich the active E.cloacae HO-1 in the bioreactor, the acrated cultivation with oxidation-reduction potential (ORP) control was successfully applied. Characteristics of the bioreactor system were studied to optimize its operating condition. Based upon the growth and chromate reducing kinetics of HO-1, a mathematical model to simulate the change of chromate removal rate per unit volume of bioreactor and that per unit cell mass under the fed-batch operation was proposed. Effects of repeated cultivation of HO-1 with ORP-controlled acration and the cumulative chromate reduction perunit cell mass on the microbial activity were investigated to represent the kinetic expression of chromate reduction. By using the mathematical model developed through the present research, relationship between the operating conditions and the chromate reduction rate in the bioreactor weas simulated and the model was verified by comparing with the observed data. Thus the optimal operating conditions to give the higher reduction rate and the longer operating interval with and without actated cultivation of HO-1 were extensively discussed. This bioreactor can be used for the treatment of chromate wastewater provided that some high concentration organic wastes are available. The specific rate of chromate reduction is as high as 500 mg-chromate/g-microbes.The rate of chromate reduction in the bioreactor is around 10-15 g-Cr^<6+>/m^3h. Chromium hydroxide, products of biological chromate reduction, can be recycled for green-color pigment after the incineration of the sludge removed from the effluent.