The use of biocides to control sulphate‐reducing bacteria in biofilms on mild steel surfaces

Three different types of biocides, viz. formaldehyde (FM), glutaraldehyde (GA) and isothiozolone (ITZ) were used to control planktonic and sessile populations of two marine isolates of sulphate‐reducing bacteria (SRB). The influence of these biocides on the initial attachment of cells to mild steel surfaces, on subsequent biofilm formation and on the activity of hydrogenase enzymes within developed biofilms was evaluated. In the presence of biocides the rate and degree of colonization of mild steel by SRB depended on incubation time, bacterial isolate and the type of biocide used. Although SRB differed in their susceptibility to biocides, for all isolates the biofilm population was more resistant to the treatment than the planktonic population. GA showed highest efficiency in controlling planktonic and sessile SRB compared with the other two biocides. The activity of the enzyme hydrogenase measured in SRB biofilms varied between isolates and with the biocide treatment. No correlation was found between the number of sessile cells and hydrogenase activity.     

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor was investigated over a 10-month period in a hotel. Planktonic and sessile numbers of sulphate reducing bacteria (SRB) and heterotrophic bacteria were monitored. The corrosion rate was determined by the weight loss method. The corrosion products were analyzed by energy dispersive X-ray spectroscopy and X-ray diffraction. A mineralized, heterogeneous biofilm was observed on the coupons. Although a biocide and a corrosion inhibitor were regularly added to the cooling water, the results showed that microorganisms, such as SRB in the mixed species biofilm, caused corrosion of galvanized steel. It was observed that Zn layers on the test coupons were completely depleted after 3?months. The Fe concentrations in the biofilm showed significant correlations with the weight loss and carbohydrate concentration (respectively, p?<?0.01 and p?<?0.01).     

Extracellular Electron Transfer Is a Bottleneck in the Microbiologically Influenced Corrosion of C1018 Carbon Steel by the Biofilm of Sulfate-Reducing Bacterium Desulfovibrio vulgaris

Carbon steels are widely used in the oil and gas industry from downhole tubing to transport trunk lines. Microbes form biofilms, some of which cause the so-called microbiologically influenced corrosion (MIC) of carbon steels. MIC by sulfate reducing bacteria (SRB) is often a leading cause in MIC failures. Electrogenic SRB sessile cells harvest extracellular electrons from elemental iron oxidation for energy production in their metabolism. A previous study suggested that electron mediators riboflavin and flavin adenine dinucleotide (FAD) both accelerated the MIC of 304 stainless steel by the Desulfovibrio vulgaris biofilm that is a corrosive SRB biofilm. Compared with stainless steels, carbon steels are usually far more prone to SRB attacks because SRB biofilms form much denser biofilms on carbon steel surfaces with a sessile cell density that is two orders of magnitude higher. In this work, C1018 carbon steel coupons were used in tests of MIC by D. vulgaris with and without an electron mediator. Experimental weight loss and pit depth data conclusively confirmed that both riboflavin and FAD were able to accelerate D. vulgaris attack against the carbon steel considerably. It has important implications in MIC failure analysis and MIC mitigation in the oil and gas industry.     

Study of parameters implicated in the biodeterioration of mild steel in the presence of different species of sulphate-reducing bacteria

Two different species of sulphate-reducing bacteria, strain classified by NCIMB as Desulfovibrio desulfuricans subspecies desulfuricans New Jersey (8313) isolated from the corroding heat exchanger, and SRB species recovered from a corroding ship hull anchored off the Indonesian coast (Indo isolate) were grown as laboratory batch cultures. Several factors such as the surface finish of substratum, metabolic activity of planktonic and sessile bacterial populations, initial attachment of cells to surfaces and subsequent formation of biofilms on the process of biodeterioration of mild steel in the presence of these two different species of SRB were investigated. The corrosion rates of mild steel were estimated by weight loss measurements and correlated with the density of sessile SRB population. The yield and composition of extracellular polymers released into the bulk phase of culture media were determined and the amount of dissolved hydrogen sulphide was monitored. The results revealed differences between SRB species in their aggressiveness towards mild steel under identical growth conditions, emphasising the importance of biochemistry and physiology of SRB for the biocorrosion process. Biochemical and genetic characterisation of SRB isolates chosen for this study are currently in progress.     

Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions

Sulfate-reducing bacteria (SRB) play a major role in the precipitation of metal sulfides in the environment. In this work, biogenic copper sulfide formation was examined in cultures of SRB and compared to chemically initiated Cu sulfide precipitation as a reference system. Mixed cultures of SRB were incubated at 22, 45, and 60°C in nutrient solutions that contained copper sulfate. Abiotic reference samples were produced by reacting uninoculated liquid media with Na₂S solutions under otherwise identical conditions. Precipitates were collected anaerobically by centrifugation, frozen in liquid N₂, and freeze-dried, followed by analysis using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy. Covellite (CuS) was the only mineral found in the precipitates. Covellite was less crystalline in the biogenic precipitates than in the abiotic samples based on XRD peak widths and peak to background ratios. Poor crystallinity may be the result of slower precipitation rates in bacterial cultures as compared to the abiotic reference systems. Furthermore, bacterial cells may inhibit the nucleation steps that lead to crystal formation. Incubation at elevated temperatures improved the crystallinity of the biotic specimens.     

Influence of cathodic protection of mild steel on the growth of sulphate‐reducing bacteria at 35°C in marine sediments

In order to protect metallic structures from marine corrosion, cathodic protection using sacrificial anodes or impressed current is widely used. In aerated seawater steel is considered to be protected when a cathodic potential of — 800 mV/SCE (Saturated Calomel Electrode) is applied. However, in many cases, this potential must be lowered due to the presence and activity of microorganisms such as acid‐producing bacteria or sulphate‐reducing bacteria (SRB). SRB are obligate anaerobes using sulphate as an electron acceptor with resultant production of sulfides. Some SRB are able to use hydrogen as an electron donor causing thereby depolarization of steel surfaces.

An experiment was performed in marine sediments to determine the relationship between cathodically produced hydrogen and growth of SRB in marine sediments both at ambiant temperature (Therene, 1988) and at 35°C. Results concerning the latter experiments are reported here.

Analytical techniques included microbiological analyses, lipid biomarker studies and electrochemical measurements including AC impedance spectroscopy. Results indicated a change in the bacterial community structure both on the steel and sediment as a function of time and potential. The results also showed that cathodically‐produced hydrogen promoted the growth of SRB with the Desulfovibrio genus predominating.     

Influence of sulfate reducing bacterial biofilm on corrosion behavior of low-alloy,high-strength steel (API-5L X80)

The utilization of high strength carbon steels in oil and gas transportation systems has recently increased. This work investigates microbiologically influenced corrosion (MIC) of API 5L X80 linepipe steel by sulfate reducing bacteria (SRB). The biofilm and pit morphology that developed with time were characterized with field emission scanning electron microscopy (FESEM). In addition, electrochemical impedance spectroscopy (EIS), polarization resistance (R_p) and open circuit potential (OCP) were used to analyze the corrosion behavior. Through circuit modeling, EIS results were used to interpret the physicoelectric interactions between the electrode, biofilm and solution interfaces. The results confirmed that the extensive localized corrosion activity of SRB is due to a formed biofilm and a porous iron sulfide layer on the metal surface. Energy Dispersive Spectroscopy (EDS) revealed the presence of different sulfide and oxide constituents in the corrosion products for the system exposed to SRB.     

Linked Redox Precipitation of Sulfur and Selenium under Anaerobic Conditions by Sulfate-Reducing Bacterial Biofilms

A biofilm-forming strain of sulfate-reducing bacteria (SRB), isolated from a naturally occurring mixed biofilm and identified by 16S rDNA analysis as a strain of Desulfomicrobium norvegicum, rapidly removed 200 μM selenite from solution during growth on lactate and sulfate. Elemental selenium and elemental sulfur were precipitated outside SRB cells. Precipitation occurred by an abiotic reaction with bacterially generated sulfide. This appears to be a generalized ability among SRB, arising from dissimilatory sulfide biogenesis, and can take place under low redox conditions and in the dark. The reaction represents a new means for the deposition of elemental sulfur by SRB under such conditions. A combination of transmission electron microscopy, environmental scanning electron microscopy, and cryostage field emission scanning electron microscopy were used to reveal the hydrated nature of SRB biofilms and to investigate the location of deposited sulfur-selenium in relation to biofilm elements. When pregrown SRB biofilms were exposed to a selenite-containing medium, nanometer-sized selenium-sulfur granules were precipitated within the biofilm matrix. Selenite was therefore shown to pass through the biofilm matrix before reacting with bacterially generated sulfide. This constitutes an efficient method for the removal of toxic concentrations of selenite from solution. Implications for environmental cycling and the fate of sulfur and selenium are discussed, and a general model for the potential action of SRB in selenium transformations is presented.     

Microbiologically influenced corrosion: looking to the future.

This review discusses the state-of-the-art of research into biocorrosion and the biofouling of metals and alloys of industrial usage. The key concepts needed to understand the main effects of microorganisms on metal decay, and current trends in monitoring and control strategies to mitigate the deleterious effects of biocorrosion and biofouling are also described. Several relevant cases of biocorrosion studied by our research group are provided as examples: (i) biocorrosion of aluminum and its alloys by fungal contaminants of jet fuels; (ii) sulfate-reducing bacteria (SRB)-induced corrosion of steel; (iii) biocorrosion and biofouling interactions in the marine environment; (iv) monitoring strategies for assessing biocorrosion in industrial water systems; (v) microbial inhibition of corrosion; (vi) use and limitations of electrochemical techniques for evaluating biocorrosion effects. Future prospects in the field are described with respect to the potential of innovative techniques in microscopy (environmental scanning electron microscopy, confocal scanning laser microscopy, atomic force microscopy), new spectroscopic techniques for the study of corrosion products and biofilms (energy dispersion X-ray analysis, X-ray photoelectron spectroscopy, electron microprobe analysis) and electrochemistry (electrochemical impedance spectroscopy, electrochemical noise analysis).     

The use of magnesium peroxide for the inhibition of sulfate-reducing bacteria under anoxic conditions

Sulfate-reducing bacteria (SRB), which cause microbiologically influenced material corrosion under anoxic conditions, form one of the major groups of microorganisms responsible for the generation of hydrogen sulfide. In this study, which is aimed at reducing the presence of SRB, a novel alternative approach involving the addition of magnesium peroxide (MgO₂) compounds involving the use of reagent-grade MgO₂ and a commercial product (ORC™) was evaluated as a means of inhibiting SRB in laboratory batch columns. Different concentrations of MgO₂ were added in the columns when black sulfide sediment had appeared in the columns. The experimental results showed that MgO₂ is able to inhibit biogenic sulfide. The number of SRB, the sulfide concentration and the sulfate reducing rate (SRR) were decreased. ORC™ as an additive was able to decrease more effectively the concentration of sulfide in water and the SRB-control effect was maintained over a longer time period when ORC™ was used. The level of oxidation–reduction potential (ORP), which has a linear relationship to the sulfide/sulfate ratio, is a good indicator of SRB activity. As determined by fluorescence in-situ hybridization (FISH), most SRB growth was inhibited under increasing amounts of added MgO₂. The concentration of sulfide reflected the abundance of the SRB. Utilization of organic matter greater than the theoretical SRB utilization rate indicated that facultative heterotrophs became dominant after MgO₂ was added. The results of this study could supply the useful information for further study on evaluating the solution to biocorrosion problems in practical situations.     

The antioxidant effects of pomegranate extract on local and remote organs in a mesenteric ischemia and reperfusion model

Objectives: We investigated whether pomegranate extract plays a protective antioxidant role against mesenteric ischemia–reperfusion injury (IR), which can lead to a systemic response and damage distant organs, such as the lung, liver, and kidney.

Methods: Forty female Wistar–Albino rats were separated into four groups: laparotomy, laparotomy?+?PG, mesenteric IR, and mesenteric IR and pomegranate (IR?+?PG). In the laparotomy?+?PG and IR?+?PG groups, pomegranate (225?mg/kg) was given by oral gavage at the beginning of the study. Ischemia was induced for 30 minutes, and reperfusion was subsequently allowed for 60 minutes in the IR and IR?+?PG groups. The malondialdehyde (MDA) and total antioxidant activity (AOA) levels were evaluated in blood samples. Additionally, all tissues were removed for the measurement of AOA and total oxidant status as well as for subsequent histopathological evaluation. The oxidative stress index was calculated.

Results: Histopathological changes in all organs were significantly higher in the IR group and significantly lower in the IR?+?PG group vs. the other groups. Serum MDA levels were significantly lower in the IR?+?PG group than in the IR group. No significant difference was found in AOA levels of the groups.

Discussion: These data may explain the positive protective effects of pomegranate based on the histopathologic findings in ischemic conditions in an intestinal IR injury model.     

硫酸盐还原菌Desulfotomaculum reducens ZTS1厌氧降解昭通褐煤

[目的] 以云南昭通褐煤为研究对象,从矿井水富集产物中分离得到SRB菌株Desulfotomaculum reducens ZTS1厌氧降解褐煤,分析研究SRB菌株处理褐煤前后的物化性质变化。[方法] 采用工业和元素分析、XRD、FT-IR、SEM和低温液氮吸附法比较研究SRB厌氧降解褐煤前后矿物组成、有机官能团、表面形貌和孔隙结构变化。[结果] D.reducens ZTS1厌氧降解褐煤后灰分和挥发分略有降低,碳、氮和硫元素的含量降低,氧的含量增加,煤中硫代硫酸钠消失,FT-IR结果表明褐煤长链烃上的甲基和亚甲基团增多,游离羟基减少。煤表面粗糙度增加,小孔径的孔隙增多,孔径比表面积增大。[结论] D.reducens ZTS1可以厌氧降解昭通褐煤,厌氧降解后煤的物化性质发生变化。     

Thermal effects on microbial composition and microbiologically induced corrosion and mineral precipitation affecting operation of a geothermal plant in a deep saline aquifer

The microbial diversity of a deep saline aquifer used for geothermal heat storage in the North German Basin was investigated. Genetic fingerprinting analyses revealed distinct microbial communities in fluids produced from the cold and warm side of the aquifer. Direct cell counting and quantification of 16S rRNA genes and dissimilatory sulfite reductase (dsrA) genes by real-time PCR proved different population sizes in fluids, showing higher abundance of bacteria and sulfate reducing bacteria (SRB) in cold fluids compared with warm fluids. The operation-dependent temperature increase at the warm well probably enhanced organic matter availability, favoring the growth of fermentative bacteria and SRB in the topside facility after the reduction of fluid temperature. In the cold well, SRB predominated and probably accounted for corrosion damage to the submersible well pump and iron sulfide precipitates in the near wellbore area and topside facility filters. This corresponded to lower sulfate content in fluids produced from the cold well as well as higher content of hydrogen gas that was probably released from corrosion, and maybe favored growth of hydrogenotrophic SRB. This study reflects the high influence of microbial populations for geothermal plant operation, because microbiologically induced precipitative and corrosive processes adversely affect plant reliability.     

Antagonistic activity of <Emphasis Type="Italic">Bacillus</Emphasis> sp. obtained from an Algerian oilfield and chemical biocide THPS against sulfate-reducing bacteria consortium inducing corrosion in the oil industry

The present study enlightens the role of the antagonistic potential of nonpathogenic strain B21 against sulfate-reducing bacteria (SRB) consortium. The inhibitor effects of strain B21 were compared with those of the chemical biocide tetrakishydroxymethylphosphonium sulfate (THPS), generally used in the petroleum industry. The biological inhibitor exhibited much better and effective performance. Growth of SRB in coculture with bacteria strain B21 antagonist exhibited decline in SRB growth, reduction in production of sulfides, with consumption of sulfate. The observed effect seems more important in comparison with the effect caused by the tested biocide (THPS). Strain B21, a dominant facultative aerobic species, has salt growth requirement always above 5% (w/v) salts with optimal concentration of 10–15%. Phylogenetic analysis based on partial 16S rRNA gene sequences showed that strain B21 is a member of the genus Bacillus, being most closely related to Bacillus qingdaonensis DQ115802 (94.0% sequence similarity), Bacillus aidingensis DQ504377 (94.0%), and Bacillus salarius AY667494 (92.2%). Comparative analysis of partial 16S rRNA gene sequence data plus physiological, biochemical, and phenotypic features of the novel isolate and related species of Bacillus indicated that strain B21 may represent a novel species within the genus Bacillus, named Bacillus sp. (EMBL, FR671419). The results of this study indicate the application potential of Bacillus strain B21 as a biocontrol agent to fight corrosion in the oil industry.     

Chelators enhanced biocide inhibition of planktonic sulfate-reducing bacterial growth

Biocides are currently the primary mitigation method to control sulfate-reducing bacteria (SRB) in biofouling, reservoir souring and microbiologically influenced corrosion. Increasingly restrictive environmental regulations and safety concerns on biocide uses demand more efficient dosing of biocides. Chelators have been known to enhance antibiotics because of their properties such as increasing the permeability of the outer cell membrane of Gram-negative bacteria. Two readily biodegradable chelators, ethylenediaminedisuccinate (EDDS) and N-(2-hydroxyethyl)iminodiacetic acid (HEIDA) disodium salts that are touted as potential replacements of ethylenediaminetetraacetic acid (EDTA), were evaluated as potential biocide enhancers for glutaraldehyde and tetrakis hydroxymethyl phosphonium sulfate (THPS) in their inhibition of planktonic SRB growth. Desulfovibrio vulgaris ATCC 7757 and Desulfovibrio desulfuricans ATCC 14563 were grown in modified ATCC 1249 medium and in enriched artificial seawater, respectively. Laboratory tests in 100 ml anaerobic vials showed that EDDS or HEIDA alone did not inhibit SRB growth. However, when EDDS or HEIDA was combined with glutaraldehyde or THPS, each of them enhanced the biocide inhibition of planktonic SRB growth.     

Manganese biofouling and the corrosion behavior of stainless steel

Manganese- and iron-oxidizing bacteria (MFOB) are widely implicated in microbially influenced corrosion, often in association with sulfate-reducing bacteria (SRB). Traditionally MFOB have been assigned a passive role in the corrosion process, promoting differential aeration cells, and providing oxygen depleted conditions conducive to the growth and corrosive attack of SRB. Recent work, summarized in this article, demonstrates that manganese biofouling alters the electrochemical behavior of stainless steel (SS), and suggests that MFOB are more active in localized corrosion than traditionally held. The paper discusses the chemistry and potentially corrosive impact of manganese and iron oxides on SS, explores the possible relationship between MFOB and SRB, and proposes a model to describe the synergistic influence these organisms may exert in the corrosion process.     

Inhibiting mild steel corrosion from sulfate-reducing bacteria using antimicrobial-producing biofilms in Three-Mile-Island process water

Biofilms were used to produce gramicidin S (a cyclic decapeptide) to inhibit corrosion-causing, sulfate-reducing bacteria (SRB). In laboratory studies these biofilms protected mild steel 1010 continuously from corrosion in the aggressive, cooling service water of the AmerGen Three-Mile-Island (TMI) nuclear plant, which was augmented with reference SRB. The growth of both reference SRB (Gram-positive Desulfosporosinus orientis and Gram-negative Desulfovibrio vulgaris) was shown to be inhibited by supernatants of the gramicidin-S-producing bacteria as well as by purified gramicidin S. Electrochemical impedance spectroscopy and mass loss measurements showed that the protective biofilms decreased the corrosion rate of mild steel by 2- to 10-fold when challenged with the natural SRB of the TMI process water supplemented with D. orientis or D. vulgaris. The relative corrosion inhibition efficiency was 50–90% in continuous reactors, compared to a biofilm control which did not produce the antimicrobial gramicidin S. Scanning electron microscope and reactor images also revealed that SRB attack was thwarted by protective biofilms that secrete gramicidin S. A consortium of beneficial bacteria (GGPST consortium, producing gramicidin S and other antimicrobials) also protected the mild steel.     

Polysomnography in AF patients without prior diagnosis of obstructive sleep apnea reveals significant sleep abnormality: A strong case for screening in all patients with atrial fibrillation?

BackgroundObstructive sleep apnea (OSA) and atrial fibrillation (AF) are known to often coexist together. However, whether all patients with AF should be screened for sleep abnormalities is not clear. No previous study has examined the association of asymptomatic OSA with AF.ObjectiveThis study sought to determine the prevalence of asymptomatic OSA in patients with persistent AF and whether asymptomatic OSA is an independent risk factor for atrial fibrillation.MethodPatients with persistent AF without a prior diagnosis of OSA and asymptomatic for sleep abnormalities were prospectively enrolled over 12 months. All patients underwent polysomnography after informed consent. Patients without AF or OSA who underwent polysomnography during the same period served as controls.ResultsA total of 97 patients were studied; 50 were in the case group (patients with persistent AF) and 47 were in the control group (patients in sinus rhythm). Asymptomatic OSA was diagnosed on polysomnography in 72% of patients in the AF group and 17% of the control population. Multivariable analysis of factors including diabetes, hypertension, coronary artery disease, hypothyroidism, prior MI, and asymptomatic OSA, suggested asymptomatic OSA as an independent factor associated with AF.ConclusionA significant proportion (72%) of patients with persistent AF have underlying asymptomatic OSA. Sleep abnormality thus has a strong association with AF even in patients who are asymptomatic for OSA. Screening for OSA may be advised for all patients with AF, as this may have significant implications for management.     

Axenic aerobic biofilms inhibit corrosion of copper and aluminum

The corrosion behavior of unalloyed copper and aluminum alloy 2024 in modified Baar's medium has been studied with continuous reactors using electrochemical impedance spectroscopy. An axenic aerobic biofilm of either Pseudomonas fragi K or Bacillus brevis 18 was able to lessen corrosion as evidenced by a consistent 20-fold increase in the low-frequency impedance value of copper as well as by a consistent four- to seven-fold increase in the polarization resistance of aluminum 2024 after six days exposure compared to sterile controls. This is the first report of axenic aerobic biofilms inhibiting generalized corrosion of copper and aluminum. Addition of the representative sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris (to simulate consortia corrosion behavior) to either the P. fragi K or B. brevis 18 protective biofilm on copper increased the corrosion to that of the sterile control unless antibiotic (ampicillin) was added to inhibit the growth of SRB in the biofilm. Received: 24 May 1999 / Received revision: 6 July 1999 / Accepted: 1 August 1999     

Marine ‘copper-tolerant’ sulphate reducing bacteria and their effects on 90/10 copper-nickel (CA 706)

Copper and nickel ‘tolerant’ marine sulphate reducing bacteria (SRB) were isolated from 90/10 copper-nickel and shown to attach and grow on the alloy. Their effects upon the corrosion resistance of the alloy, using energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and electrochemical polarisation analyses, were shown to be identical to those produced by synthetic addition of sulphide to test solutions reported by others. Thus attached SRB may have a role in 90/10 copper-nickel corrosion as long as they also possess transient oxygen tolerance.