[Show abstract][Hide abstract] 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.
Full-text · Article · Nov 2010 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: Destruction of a dense nonaqueous phase liquid (DNAPL) by soluble iron (III)-catalyzed and pyrolusite (ß-MnO2)-catalyzed Fenton's reactions (hydrogen peroxide and transition metal catalysts) was investigated using carbon tetrachloride (CT) as a model contaminant. In the system amended with 5 mM soluble iron (III), 24% of the CT DNAPL was destroyed after 3 h while CT dissolution in parallel fill-and-draw systems was minimal, indicating that CT was degraded more rapidly than it dissolved into the aqueous phase. Fenton's reactions catalyzed by the naturally occurring manganese oxide pyrolusite were even more effective in destroying CT DNAPLs, with 53% degradation after 3 h. Although Fenton's reactions are characterized by hydroxyl radical generation, carbon tetrachloride is unreactive with hydroxyl radicals; therefore, a transient oxygen species other than hydroxyl radicals formed through Fenton's propagation reactions was likely responsible for CT destruction. These results demonstrate that Fenton-like reactions in which nonhydroxyl radical species are generated may provide an effective method for the in situ treatment of DNAPLs. Journal of Environmental Engineering
No preview · Article · Jul 2005 · Journal of Environmental Engineering
[Show abstract][Hide abstract] ABSTRACT: The toxicity of hydrogen peroxide, hydroxyl radical, and superoxide radical anion to Escherichia coli was investigated as a basis for understanding the effects of hydrogen peroxide when it is injected into the subsurface for in situ bioremediation or in situ chemical oxidation. Hydrogen peroxide toxicity was evaluated by maintaining its steady state concentration at a series of concentrations ranging from 0.7 to 3.0 mM in the presence of E. coli. Hydroxyl radical toxicity was studied by conducting parallel reactions of equal steady state concentrations of hydrogen peroxide, but using an iron (III)–nitrilotriacetic acid complex to decompose hydrogen peroxide to hydroxyl radicals. Superoxide was also generated from equal steady state concentrations of hydrogen peroxide, but with the addition of pyrolusite (manganese oxide) to catalyze its decomposition to superoxide radical. Hydrogen peroxide was toxic to E.coli at all concentrations investigated. The generation of hydroxyl radicals in hydrogen peroxide solutions showed no increase in toxicity relative to hydrogen peroxide toxicity, indicating minimal additional toxicity of the hydroxyl radicals. Hydrogen peroxide solutions of equal concentrations in which superoxide was generated showed less toxicity relative to hydrogen peroxide systems. The results indicate that toxicity of hydrogen peroxide to microorganisms may be lower when it is injected to subsurface systems containing high manganese oxide contents.
Full-text · Article · Jun 2003 · Advances in Environmental Research
[Show abstract][Hide abstract] ABSTRACT: Hydrogen peroxide (H2O2) catalyzed by soluble iron or naturally occurring soil minerals, (i.e., modified Fenton's reagent) was investigated as a basis for mineralizing sorbed and NAPL-phase benzo[a]pyrene (BaP), a hydrophobic and toxic polycyclic aromatic hydrocarbon, in two soils of different complexity. 14C-Benzo[a]pyrene was added to silica sand and a silt loam soil, and mineralization was investigated using three-level central composite rotatable experimental designs. The effects of H2O2 concentration, slurry volume, and iron(II) amendment were investigated in the silica sand systems. In a Palouse loess silt loam soil, the variables included H2O2 concentration, slurry volume, and pH, with H2O2 catalyzed by naturally occurring iron oxyhydroxides. Regression equations generated from the data were used to develop three-dimensional response surfaces describing BaP mineralization. Based on the recovery of 14C-CO2, 70% BaP mineralization was achieved in the sand within 24 h using 15 M H2O2 and an iron(II) concentration of 6.6 mM with a slurry volume of 0.3 x the field capacity of the sand. For the silt loam soil, 85% mineralization of BaP was observed using 15 M H2O2, no iron amendment, and a slurry volume of 20 x the soil field capacity. The balance of the radiolabeled carbon remained as unreacted BaP in the soil fraction. Gas-purge measurements over 5 d confirmed negligible desorption under nontreatment conditions. However, oxidation reactions were complete within 24 h and promoted up to 85% BaP mineralization, documenting that the natural rate of desorption/dissolution did not control the rate of oxidation and mineralization of the BaP. The results show that catalyzed H2O2 has the ability to rapidly mineralize sorbed/NAPL-phase BaP and that partitioning, which is often the rate-limiting factor in soil remediation, does not appear to limit the rate of vigorous Fenton-like treatment.
[Show abstract][Hide abstract] ABSTRACT: The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.
No preview · Article · Aug 2001 · Environmental Science and Technology