Simultaneous abiotic reduction-biotic oxidation in a microbial-MnO2-catalyzed Fenton-like system

Abstract

The possibility of simultaneous activity of superoxide-mediated transformations and heterotrophic aerobic bacterial metabolism was investigated in catalyzed H(2)O(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(2)O(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, 0.5mM H(2)O(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(2)O(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.