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Item 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.Item Corrosion of mild steel under anaerobic biofilm(1993-03) Lee, Whonchee; Characklis, William G.Corrosion of mild steel under completely anaerobic conditions in the presence of a mixed population biofilm, including sulfate-reducing bacteria (SRB), has been studied in a continuous flow system. The closed channel flow reactor was continuously fed with low concentration substrate at different dilution rates that influenced biofilm accumulation. No direct correlation was observed between corrosion and SRB activity in the absence of ferrous iron. Furthermore, corrosion of mild steel in the SRB environment was determined by the nature of the metal and environmental conditions such as dissolved iron concentration. When formation of an iron sulfide film on mild steel was prevented before the biofilm accumulated, the metal surface retained its scratch lines after a 21-day experiment (SRB at 2.6 × 109/cm2). However, when the iron sulfide film was formed before the accumulation of biofilm, visible localized corrosion appeared after 14 days and increased up to 21 days. Intergranular and pitting attack was found in the localized corrosion area. Inclusions (Al, Mn, and Fe) and grain boundary triple points were also found in the localized corrosion area. At high iron concentration (approximately 60 mg/L in the bulk water), all biogenic sulfide was precipitated and corrosion had significantly enhanced. Intergranular attack was found over the entire metal surface.Item Biofilm laboratory methods: the use of flow reactors(1992) Bryers, James D.; Characklis, William G.Investigations of biofilm formation and persistence require a fundamental approach in the collection and analysis of data, irrespective of the specific environment or application. This approach must be based upon the principles of process analysis (see Bryers and Characklis, this volume) and the concomitant need to provide comprehensive and compatible data with which to evaluate appropriate mass balance equations. Experimental reactor systems employed in either (a) controlled laboratory environments, (b) field applications, or (c) in vivo biomedical situations should be designed and operated in order provide the appropriate data under known conditions to facilitate this mass balance approach.Item Biofilm accumulation and activity: a process engineering analysis(1992) Bryers, James D.; Characklis, William G.Process Analysis refers to the application of systematic methods to recognize, define and clarify problems and to develop methodologies for their solution. Biofilm formation and persistence in both natural and engineered systems is governed by a collage of complex physical, chemical, and biological processes; each process dependent on a unique set of system parameters. Process analysis applied to biofilm formation provides an integrated approach which incorporates microbial physiology, reaction engineering, and transport phenomena to understand, control, and exploit biofilm processes. Application of process analysis allows one to (a) interpret the operation of an existing biofilm system, (b) design new biofilm reactor systems, and (c) understand the complexities of natural biofilm systems. It is increasingly apparent that research into biofilm processes which does not comprise microbial, chemical, and fundamental engineering aspects is incomplete.Item Centers, new technologies focus on biofilm heterogeneity(1992) Geesey, Gill G.; Characklis, William G.; Costerton, J. WilliamItem Interspecies competition in colonized porous pellets(1994-04) Sturman, Paul J.; Jones, Warren L.; Characklis, William G.Packed-bed bioreactors filled with diatomaceous earth (D.E.) pellets were used to evaluate the effects of competition between inoculated and invading microbial species on the spatial and temporal distribution of microorganisms within an individual pellet. The (D.E.) pellets were cylinders 6 mm in diameter and 5–10 mm long with a mean pore diameter of 20 μm. Bench-scale experiments evaluated competition between two distinct microbial species: Pseudomonas aeruginosa, a motile, obligate aerobe (μmax = 0.4 h−1) and Klebsiella pneumoniae, a non-motile, facultative organism (μmax = 2.0 h−1). Organism growth rate appeared to be more important than motility or order of introduction in determining organism spatial and temporal distribution within the pellets. Pilot-scale experiments used pellets colonized with a pseudomonad growing on chlorobenzene as the sole carbon and energy source. Organic-rich ground water containing benzene, chlorobenzene and a population of indigenous microorganisms was used as feed. Pellet concentrations of the inoculated pseudomonad dropped from 109 to 106 colony forming units (cfu) ml−1 pellet volume over 15 days. These experiments demonstrate that inoculated organisms within porous packing media may undergo significant loss in colonization numbers when faced with competition from faster growing organisms.Item 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.Item 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.Item 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.Item Microbial corrosion of mild steel in a biofilm system(1993) Lee, Whonchee; Lewandowski, Zbigniew; Characklis, William G.; Nielsen, P. H.