Browsing by Author "Nielsen, P. H."

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Characterization of thermophilic consortia from two souring oil reservoirs
(1996-09) Mueller, Robert Franz; Nielsen, P. H.
Corrosion of mild steel in an alternating oxic and anoxic biofilm system
(1993-12) Nielsen, P. H.; Lee, Whonchee; Lewandowski, Zbigniew; Morrison, Michael L.; Characklis, William G.
The effect of alternating oxic and anoxic conditions (12 h oxic‐12 h anoxie) on sulfate reducing activity, iron‐sulfur chemistry and the corrosion of mild steel, has been studied in biofilm reactors. During the experiment (35 d) an increasing activity of sulfate reducing bacteria was observed. A part of the produced sulfide and iron sulfide (FeS) was oxidized during oxic periods and resulted in a mixture of acid volatile sulfides (mainly mackinawite, FeS), chromium reducible sulfur (mainly pyrite, FeS2) and elemental sulfur (S°). At the end of the experiment an amount of total S corresponding to 157 umol cm−3 was found within the deposit. Corrosion rates were measured electrochemically during the experiment and were found in the range of 3–5 mpy after 7 d to 120–160 mpy after 34 d. An extended aeration of the biofilm system for 1 month without addition of any organics showed that the pools of Fe‐S compounds in the deposit and the corrosion rate remained high. Microsensor studies of dissolved oxygen penetration through the biofilm and the deposit showed that even after 1 month of aeration oxygen did not penetrate to the metal surface. The limited oxygen penetration was caused by a very high oxygen consumption rate due to oxygénation of reduced chemical species originating from the dissolution of metal by the corrosion process (approximately 66 mmol Fem−2 h−1). Measurements of in situ sulfate reducing activity revealed high sulfate reduction rates within the anoxic part of the deposit and suggested that SRB activity was important as electron carrier from the metal surface to the oxic interface.
Corrosion of mild steel underneath aerobic biofilms containing sulfate-reducing bacteria. part i: at low dissolved oxygen concentration
(1993-11) Lee, Whonchee; Lewandowski, Zbigniew; Okabe, Satoshi; Characklis, William G.; Avci, Recep; Nielsen, P. H.
The sulfate‐reducing bacteria (SRB)‐enhanced corrosion of mild steel in the presence of 1.5 mg·l−1 dissolved oxygen (DO) in bulk liquid was investigated. The biofilm process analysis was combined with microelectrode measurements, electrochemical measurements, and surface analysis. In the early stages of biofilm accumulation, the cathodic polarization and the decreasing corrosion rate were attributed to DO consumption by aerobic bacteria. During that time, limited SRB activity was observed. The DO concentration near the steel surface was between 0.6 and 1 mg·l−1. After total depletion of dissolved oxygen near the steel surface, the cathodic depolarization and the increased corrosion rate were associated with the proliferation of SRB near the steel surface. Auger electron spectroscopy analysis indicated localized sulfide attack. High pit density appeared where the coincidence of oxygen and sulfur occurred. The bottom of the pit was enriched with sulfur.
Corrosion of mild steel underneath aerobic biofilms containing sulfate-reducing bacteria. part ii: at high dissolved oxygen concentration
(1993-11) Lee, Whonchee; Lewandowski, Zbigniew; Morrison, Michael L.; Characklis, William G.; Avci, Recep; Nielsen, P. H.
Microbial biofilms containing sulfate‐reducing bacteria (SRB) and general anaerobic bacteria (GAB) were grown in a closed flow channel reactor in air‐saturated bulk liquid. The SRB proliferated within anaerobic microniches even when dissolved oxygen penetrated the entire biofilm at some locations. Corrosion of mild steel during aerobic/anaerobic biofilm accumulation was classified as aerobic corrosion and SRB‐enhanced corrosion. Aerobic corrosion dominated during the early stages of biofilm accumulation. The corrosion rate decreased as the biofilm became more uniform over the surface. SRB‐enhanced corrosion occurred after the SRB community was established within the deposits and significant amounts of iron sulfides contacted the bare steel surface. The initiation and propagation of SRB‐enhanced corrosion in an aerobic/anaerobic biofilm system was explained through the establishment of an FeS/Fe galvanic cell.
Deflocculation of activated sludge by the dissimilatory fe(III)-reducing bacterium Shewanella alga BrY
(1996-04) Caccavo, Frank; Frolund, B.; Van Ommen Kloeke, Fintan; Nielsen, P. H.
Effect of biomineralized manganese on the corrosion behavior of c1008 mild steel
(2000-01) Olesen, Bo H.; Nielsen, P. H.; Lewandowski, Zbigniew
The possibility that biomineralized manganese dioxide (MnO2) might serve as an efficient cathodic reactant in mild steel corrosion was studied using stainless steel (SS) covered with microbially or electrochemically deposited MnO2 and galvanically coupled to mild steel and mild steel covered with microbially deposited MnO2. Biofilms of the manganese-oxidizing bacteria, Leptothrix discophora SP-6, were used to deposit biomineralized MnO2. When MnO2 was biologically deposited on the SS, the corrosion rate of the galvanically coupled mild steel was initially about eight times higher than that in a control experiment without depositing manganese. After a few minutes, the MnO2 discharged and the corrosion rate of the mild steel decreased to values comparable with biofouled cathodes without manganese. When MnO2 was electroplated on SS, a linear relation between the amount of MnO2 and the duration of the elevated corrosion rate of mild steel was observed. However, when MnO2 was biologically deposited directly onto the mild steel, the corrosion rate did not increase, possible because the corrosion product buildup on the mild steel surface prevented electrical contact between the manganese oxide and the underlying metal.
Estimation of cellular and extracellular carbon contents in sulfate-reducing bacteria biofilms by lipopolysaccharide assay and epifluorescence microscopic techni
(1994-11) Okabe, Satoshi; Nielsen, P. H.; Jones, Warren L.
Measurement of cellular and extracellular carbon contents of sulfate-reducing bacteria (SRB) is essential and important in studies of the role of SRB in corrosion and biofouling. An epifluorescence (EPI) microscopic technique and a lipopolysaccharide (LPS) assay were used to quantify cellular and extracellular carbon contents in Desulfovibrio desulfuricans biofilms. The average contents of lipopolysaccharide (LPS) and cellular carbon were 7.3 ± 2.8 (fg LPS) cell−1 and 39.9 ± 9.9 (fg cellular-C) cell−1, respectively, in a D. desulfuricans chemostat culture. A ratio of cellular carbon content to LPS content was 6.5 ± 2.8, and was used to estimate cellular carbon contents in a D. desulfuricans biofilm. The LPS and EPI methods gave comparable results for suspended samples, but not for biofilm samples.
Factors affecting microbial sulfate reduction by desulfovibrio desulfuricans in continuous culture: limiting nutrients and sulfide concentration
(1992-09) Okabe, Satoshi; Nielsen, P. H.; Characklis, William G.
The effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (μmax), half-saturation coefficients (Ksul), and cell yield (Yc/Lac) of 0.344 ± 0.007 and 0.352 ± 0.003 h −1, 1.8 ± 0.3 and 1.0 ± 0.2 mg/L, and 0.020 ± 0.003 and 0.017 ± 0.003 g cell/g lactate, respectively, were obtained under sulfate-limiting conditions at 35°C and 43°C. Maintenance energy requirements for D. desulfuricans were significant under sulfate-limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also ivestigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process.
Microbial corrosion of mild steel in a biofilm system
(1993) Lee, Whonchee; Lewandowski, Zbigniew; Characklis, William G.; Nielsen, P. H.
Role of sulfate-reducing bacteria in corrosion of mild steel: a review
(1995-03) Lee, Whonchee; Lewandowski, Zbigniew; Nielsen, P. H.; Hamilton, W. A.
Sulfide product inhibition of desulfovibrio desulfuricans in batch and continuous cultures
(1995-02) Okabe, Satoshi; Nielsen, P. H.; Jones, Warren L.; Characklis, William G.
Sulfide product inhibition kinetics for growth and activity of Desulfovibrio desulfuricans was investigated in batch and continuous cultures at pH = 7.0. A non-competitive inhibition model adequately described sulfide product inhibition kinetics. Inhibition coefficient (Ki) for maximum specific growth rate (μinhmax) was 251 mg l−1 S in a batch experiment. Cell yield determined in a chemostat was reduced in half by a sulfide concentration of about 250 mg l−1 S, which was very close to the Ki value for the batch growth. Maximum specific growth rate (μinhmax) and cell yield (YcLac) were strongly inhibited by high levels of sulfide concentrations, whereas specific lactate utilization rate increased with increasing sulfide concentrations. The results indicated an increase in the relative energy needed for maintenance to overcome sulfide inhibition and uncoupling growth from energy production. However, D. desulfuricans to some extent could recover from the shock of high sulfide concentrations. Stoichiometry for catabolic reactions (energy producing) did not change at high sulfide concentrations, while anabolic reactions (cellular synthesis) were strongly inhibited by high sulfide concentrations. These results suggested that separation of sulfide product inhibition into growth (cell yield) and activity (substrate utilization rate) was important to incorporate the sulfide product inhibition kinetics in a variety of applications.