Evidence for simultaneous abiotic-biotic oxidations in a microbial-Fenton's system.

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.

Microbial dynamics in an extractive membrane bioreactor exposed to an alternating sequence of organic compounds.

Wastewaters containing organic compounds have been treated using extractive membrane bioreactors (EMBs). During treatment, a biofilm normally develops on the surface of the membrane, on the biological side. This study investigates the dynamics of biofilm growth in an EMB exposed to an alternating sequence of organic compounds. Microbial dynamics of both suspended and attached cultures were investigated experimentally in a single-tube extractive membrane bioreactor (STEMB), which comprised a continuous stirred-tank bioreactor (CSTB) coupled to eight single-tube extractive membrane modules (STEMMs) via a recirculating biomedium. A model microbial culture consisting of a Burkholderia sp. strain JS150 (ATCC No. 51283), able to degrade monochlorobenzene, and a Xanthobacter autotrophicus sp. strain GJ10 (ATCC No. 43050), able to degrade 1, 2-dichloroethane, was used. Both microbial strains exhibited exclusive degradative capabilities. The CSTB was monitored by quantification of individual strains and by product and organic compound evolution. To investigate the biofilm growth dynamics, eight STEMMs were run in parallel with the same operating conditions. Every week, STEMMs were stopped for biofilm analysis and the organic compound in the wastewater was changed. Biofilm growth was investigated by quantification of individual strains, by evaluation of the overall biofilm growth, and by microscopic analysis. A biofilm composed of both strains was developed and maintained during the whole experiment in the STEMMs. The biofilm that developed on the membrane improved the response of the system to changes in the wastewater.