The growth parameters of Leptothrix discophora SP-6 were quantified on the basis of the steady-state concentrations and utilization rates of pyruvate, dissolved oxygen, and concentration of microorganisms in a chemostat operated at 25 degrees C, pH 7.2, and an agitation rate of 350 rpm. The results showed that the microbial growth was limited by both pyruvate and dissolved oxygen. A combined growth kinetics model using Monod growth kinetics for pyruvate and Tessier growth kinetics for oxygen showed the best correlation with the experimental data when analyzed using an interactive multiple substrate model. The growth kinetics parameters and the respective confidence limits, estimated using the Monte Carlo simulation, were mu(max) = 0.576 +/- 0.021 h(-1), K(sMp) = 38.81 +/- 4.24 mg L(-1), K(sTo) = 0.39 +/- 0.04 mg L(-1), Y(X/p) = 0.150 (mg microorganism mg(-1) pyruvate), Y(X/o) = 1.24 (mg microorganism mg(-1) oxygen), the maintenance factors for pyruvate and oxygen were m(p) = 0.129 (mg pyruvate consumed mg(-1) microorganism h(-1)) and m(o) = 0.076 (mg oxygen consumed mg(-1) microorganism h(-1)), respectively.
The noble shift in corrosion potential to values between +300 and +400 mVSCE and the accompanying increase in cathodic current density and polarization slope at mild cathodic potentials that develop during microbial colonization of passive metals, are collectively known as ennoblement. This phenomenon is of concern as the noble shift in the corrosion potential may lead to pitting corrosion. We have demonstrated, by growing pure cultures of manganese oxidizing bacteria (MOB) Leptothrix discophora SP-6 under well defined conditions, that microbial deposition of manganese oxides causes ennoblement of 316L stainless steel (SS). Exposing 316L corrosion coupons in lakes and streams supported this conclusion; the rate and extent of ennoblement were positively correlated with the rates of deposition and the amounts of biomineralized manganese oxides deposited on the surfaces of the SS corrosion coupons. X-ray photoelectron spectroscopy (XPS) analyses of the deposits from the ennobled coupons revealed a mixture of manganese oxides, as expected. Many natural waters can support growth of MOB. When manganese-oxidizing biofilms accumulate on surfaces of passive metals there is a potential for manganese redox cycling on the metal surface. This process is initiated by depositing minute amounts of manganese oxides on the metal surface. These microbially deposited manganese oxides are then reduced by the electrons derived from anodic dissolution of the metal; the metal is corroding and the manganese oxides are reduced to divalent manganese ions. However, since the manganese ions are liberated within the manganese-oxidizing biofilm, the manganese ions are immediately reoxidized, and the cycle continues.
During the past few years, biomineralized manganese has been shown to cause ennoblement of various stainless steels to open circuit potentials of 300 ± 400 mV/SCE. We have demonstrated that ennoblement, caused by biologically deposited manganese minerals, along with a relatively low stainless steel pitting potential, caused by the presence of chloride, is sufficient to initiate and drive active pitting corrosion. Stainless steel samples (type 304L), chemically or microbiologically ennobled with manganese dioxide, were exposed to a 0.35% w/v NaCl solution; an environment otherwise not corrosive against the 304L stainless steel. In the first case, steel samples were ennobled by electroplating the sample with a thin film of manganese dioxide, except for a small anodic area. In the latter case, the manganese dioxide was deposited on the steel within biofilms of the manganese oxidizing bacterium Leptothrix discophora SP-6. After 24 h exposure to the chloride solution the samples were investigated by atomic force microscopy (AFM). Both types of ennobled samples were found severely pitted, whereas reference samples (w/o manganese minerals) had remained intact.In den letzten Jahren hat es sich gezeigt, dass biomineralisiertes Mangan die Veredelung von nichtrostendem Stahl zu freien Korrosionspotentialen von 300 ± 400 mV/SCE verursachen kann. Wir haben gezeigt, dass die Veredelung von nichtrostendem Stahl durch mikrobiologisch gebildete Manganminerale kombiniert mit einem relativ niedrigen Lochkorrosionspotential des nichtrostenden Stahls in chloridhaltigem Wasser hinreichend ist, um aktive Lochkorrosion zu initiieren. Proben von nichtrostendem Stahl (Typ 304L), chemisch oder mikrobiologisch veredelt mit Manganoxid, wurden einer 0,35% w/v NaCl-Lo Èsung ausgesetzt; ein Milieu, das normalerweise bei 304L nichtrostendem Stahl keine Korrosion herbeifu Èhren kann. In dem ersten Experiment wurden die Stahlproben mit Ausnahme von einem kleinen anodischem Bereich mit einem du Ènnen Manganoxidfilm veredelt. In dem zweiten Experiment wurde das Manganoxid in Biofilmen, bestehend aus dem Mangan-oxidierenden Bakterium Leptothrix discophora SP-6, auf dem Stahl abgelagert. Nach 24 h in der Chloridlo Èsung wurden die Proben mit Rasterkraftmikroskopie (AFM) untersucht. Bei beiden Typen von Veredelung wurden wesentliche Lochkorrosionsangriffe gefunden, gleichzeitig waren Kontrollproben (ohne Manganminerale) intakt.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.