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 usin g 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-stead y-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 func tion of an increase in the quasisteady-state H2O2 concentration. Central co mposite rotatable experimental designs were used to determine the condition s that provide maximum simultaneous abiotic-biotic oxidations, which were a chieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NT A. These results demonstrate that heterotrophic bacterial metabolism can oc cur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbi al oxygen source or as a source of chemical oxidants. In addition, hybrid a biotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.