Browsing by Author "Lee, Whonchee"

Now showing 1 - 14 of 14

Anaerobic srb biofilms in industrial water systems: a process analysis
(1993) Okabe, Satoshi; Jones, Warren L.; Lee, Whonchee; Characklis, William G.
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 under an anaerobic biofilm
(Montana State University - Bozeman, College of Letters & Science, 1990) Lee, Whonchee; Chairperson, Graduate Committee: William G. Characklis; Eric Grimsrud (co-chair)
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.
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.
Dissolved oxygen and pH microelectrode measurements at water-immersed metal surfaces
(1989-02) Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Little, Brenda J.
Dissolved oxygen (DO) and pH were measured at metal/artificial seawater interfaces using microelectrodes in biotic and abiotic systems. Measurements in a closed system proved that presence of electrochemical and/or biological reaction products substantially influence the conditions at the metal surface. For long-term studies, only open (e.g., continuous flow) reactors should be used. An open channel flow reactor suitable both for microbiological and electrochemical measurements has been constructed and successfully tested.
Electrochemical interactions of biofilms with metal surfaces
(1997) Lewandowski, Zbigniew; Dickinson, Wayne H.; Lee, Whonchee
Two mechanisms of microbially influenced corrosion (MIC) are discussed and compared: corrosion modified by the presence of (1) sulfate-reducing bacteria (SRB) and (2) manganese-oxidizing bacteria (MOB). It is demonstrated that the nature of MIC in both cases depends on the nature of inorganic materials precipitated at the metal surface, iron sulfides and manganese oxides. Those materials are electrochemically active and, therefore, modify the electrochemical processes naturally occurring at the metal-solution interface. Some of these modifications may lead to accelerated corrosion.
Impact of biofouling on the electrochemical behavior of 304 stainless steel in natural seawater
(1991-02) Little, Brenda J.; Ray, Richard; Wagner, Patricia A.; Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Mansfeld, Florian
Biofilm formation on 304 stainless steel (S30400) does not necessarily result in an ennoblement of the corrosion potential. Instead, biofilms composed of aerobic and anaerobic bacteria from Gulf of Mexico water formed an anaerobic biofilm/metal interface and caused the corrosion potential to move in the negative direction. Biofilms from the same source containing photosynthetic diatoms in the presence of light produced aerobic biofilm/metal interfaces and a positive shift (ennoblement of the corrosion potential). Corrosion potentials of stainless steels exposed in natural seawater cannot be predicted without an understanding of the composition of the biofilm and its impact on interfacial chemistry. In this paper, measurements of corrosion potential, interfacial pH and dissolved oxygen have been correlated with SEM/EDAX surface analyses to evaluate the electrochemical behaviour of stainless steels exposed to Gulf of Mexico water. The interfacial chemistries that influence the corrosion potential are also discussed.
Interactions between process waters, microbial biofilms, and metal substrata
(1990) Characklis, William G.; Lee, Whonchee; Peyton, Brent M.; Lewandowski, Zbigniew
Microbial corrosion of mild steel in a biofilm system
(1993) Lee, Whonchee; Lewandowski, Zbigniew; Characklis, William G.; Nielsen, P. H.
Oxygen and ph microprofiles above corroding mild steel covered with a biofilm
(1995-05) Lee, Whonchee; de Beer, Dirk
O2 and pH microprofiles were measured above corroding mild steel covered with a biofilm. The pH in the anodic areas (tubercles) ranged from 5 to 7 and was always 9.45 at the surface of the cathodic areas. After 1 month of biofilm development, O2 was depleted at the anodic area but could reach the cathodic surface where it was reduced. Consequently, differential O2 concentration cells were the driving force for corrosion. The O2 microprofiles indicated that O2 was consumed in the tubercles, probably by microbial activity, while O2 was reduced electrochemically in the cathodic areas. It was concluded that O2 transfer to the cathodic surface was the rate limiting step for the corrosion process.
pH at polarized metal surfaces: theory, measurement and implications for mic
(1990) Lewandowski, Zbigniew; Lee, Whonchee; Characklis, William G.; Little, Brenda J.
Role of sulfate-reducing bacteria in corrosion of mild steel: a review
(1995-03) Lee, Whonchee; Lewandowski, Zbigniew; Nielsen, P. H.; Hamilton, W. A.