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501.
Neutrophilic Fe(II) oxidizing microorganisms are found in many natural environments. It has been hypothesized that, at low oxygen concentrations, microbial iron oxidation is favored over abiotic oxidation. Here, we compare the kinetics of abiotic Fe(II) oxidation to oxidation in the presence of the bacterium Leptothrix cholodnii Appels isolated from a wetland sediment. Rates of Fe(II) oxidation were determined in batch experiments at 20°C, pH 7 and oxygen concentrations between 3 and 120 μmol/l. The reaction progress in experiments with and without cells exhibited two distinct phases. During the initial phase, the oxygen dependency of microbial Fe(II) oxidation followed a Michaelis-Menten rate expression (KM = 24.5 ± 10 μmol O2/l, vmax = 1.8 ± 0.2 μmol Fe(II)/(l min) for 108 cells/ml). In contrast, abiotic rates increased linearly with increasing oxygen concentrations. At similar oxygen concentrations, initial Fe(II) oxidation rates were faster in the experiments with bacteria. During the second phase, the accumulated iron oxides catalyzed further oxidative iron precipitation in both abiotic and microbial reaction systems. That is, abiotic oxidation also dominated the reaction progress in the presence of bacteria. In fact, in some experiments with bacteria, iron oxidation during the second phase proceeded slower than in the absence of bacteria, possibly due to an inhibitory effect of extracellular polymeric substances on the growth of Fe(III) oxides. Thus, our results suggest that the competitive advantage of microbial iron oxidation in low oxygen environments may be limited by the autocatalytic nature of abiotic Fe(III) oxide precipitation, unless the accumulation of Fe(III) oxides is prevented, for example, through a close coupling of Fe(II) oxidation and Fe(III) reduction. 相似文献
502.
Mirko Trutnau Mike Petzold Lysann Mehlig Martin Eschenhagen Katja Geipel Susann M��ller Thomas Bley Isolde R?ske 《Bioprocess and biosystems engineering》2011,34(3):287-295
Modelling of activated sludge processes is a commonly used technique to design and optimize wastewater treatment processes.
Since wastewater and activated sludge is characterized by chemical oxygen demand (COD) measurements, units of state variables
describing organic matter are expressed as equivalent amounts of COD. However, current procedures for measuring it have several
drawbacks, including the production of hazardous wastes, so the utility of other variables for characterizing the organic
load in modelling, such as total organic carbon (TOC), warrant re-evaluation. Other advantages of TOC over COD are that it
provides matrix-independent analytical results and it can be readily measured online. Proposals for TOC-based models were
made in the 1990s, but they seem to have sunk into obscurity. To re-assess the value of TOC for this purpose, we have recalculated
the EAWAG module for Bio-P removal coupled to the Activated Sludge Model No. 3 on a TOC basis, and tested it against data
acquired in batch experiments with four single carbon sources (acetate, glucose, citrate and casein). The batch test-based
calibrations showed a good match with experimental data, following modifications of the model to account for the anaerobic
volumes and retention times applied in the tests. 相似文献