Simultaneous abiotic reduction–biotic oxidation in a microbial-MnO 2-catalyzed Fenton-like system

Abstract

The possibility of simultaneous activity of superoxide-mediated transformations and heterotrophic aerobic bacterial metabolism was investigated in catalyzed H 2O 2 propagations (CHP; i.e., modified Fenton's reagent) systems containing Escherichia coli. Two probe compounds were used: glucose for the detection of heterotrophic metabolism of E. coli, and tetrachloromethane (CCl 4) for the detection of superoxide generated in a MnO 2-catalyzed CHP system. In the MnO 2-catalyzed CHP system without bacteria, only CCl 4 loss was observed; in contrast, only glucose degradation occurred E. coli systems without CHP reagents. In combined microbial-MnO 2 CHP reactions, loss of both probes was observed. Glucose assimilation decreased and CCl 4 transformation increased as a function of H 2O 2 concentration. Central composite rotatable experimental designs were used to determine that the conditions providing maximum simultaneous abiotic–biotic reactions were a biomass level of 10 9 CFU/mL, 0.5 mM H 2O 2, and 0.5 g MnO 2. These results demonstrate that bacterial metabolism can occur in the presence of superoxide-mediated transformations. Such coexisting reactions may occur when H 2O 2 is injected into MnO 2-rich regions of the subsurface as a microbial oxygen source or for in situ oxidation; however, process control of such coexisting transformations may be difficult to achieve in the subsurface due to heterogeneity. Alternatively, hybrid abiotic reduction–biotic oxidation systems could be used for the treatment of industrial effluents or dilute solvent wastes that contain traces of highly halogenated compounds.