Hector A. Videla

Prevention and control of biocorrosion

Abstract Microbial colonization of metals and alloys of industrial usage takes place through the formation of biofilms made of bacteria, extracellular polymeric substances (EPS) and mainly water. These biological deposits can drastically modify the corrosion behavior of structural metals and alloys enhancing localized alterations in the type and concentrations of ions, pH, and oxygen levels. However, biofilms also facilitate the formation of diffusional barriers to the exchange of chemical species from and towards the metal/solution interface. Problems due to biocorrosion and biofouling of industrial systems range from heavy microbiological contamination with consequent energy and efficiency losses to structural failures owing to corrosion. The use of appropriate monitoring strategies complemented with field and laboratory microbiological techniques is necessary to reach a proper understanding of the effects derived from microbiological activity and the role of biofilms in the corrosion reaction to later implement effective control and preventive countermeasures. It must be emphasized that this assessment should be made for each industrial system, considering its previous history, present operational conditions, physicochemical composition of the intake water and the number and identity of microbial contaminants. Cleaning procedures, most relevant biocides and other methods for prevention and control of biocorrosion like coatings, and cathodic protection are successively described. Updated information about monitoring strategies is also included in the final part of the paper.

Biofouling and microbially influenced corrosion

Abstract Biofouling and microbially influenced corrosion (MIC) are mediated by micro-organisms attached to the metal surface and/or embedded in a gelatinous organic matrix (the biofilm). Microbial adhesion processes lead to an important modification of the metal/solution interface, inducing changes in the type and concentrations of ions, pH, oxygen levels, flow velocity and buffering capacity of the liqud microenvironment or the interface. This feature drastically changes the classical concept of electrochemical interface used in corrosion studies. Metal dissolution at a biofouled surface will be conditioned by two different processes occurring at the metal/solution interface: passivity, directed from the metal to the solution, and biofouling settlement, oriented towards the metal substratum. Electrochemical concepts, adapted to the characteristics of the biologically conditioned interface to interpret the corrosion process, and process analysis to interpret biofouling, are used in a unified approach for understanding biofilms, MIC and their interactions.

Biodeterioration of Mayan archaeological sites in the Yucatan Peninsula, Mexico

Many of the monuments of the Mayan civilization are suffering deterioration caused by environmental factors (high temperatures and relative humidities), increasing contamination from natural and anthropogenic sources, and by the action of micro- and macro-biological communities. Archaeological sites and historical monuments in the Mayan area were constructed with different limestones which offer different resistances to degradation by the various types of contamination. Two different sampling sites were chosen at the archaeological site of Uxmal in the Yucatan Peninsula, Mexico. Heterotrophic bacteria, cyanobacteria and different fungi were isolated and classified taxonomically. The other archaeological site chosen for this study was the fortress of Tulum, located at the side of the Caribbean Sea and exposed to chloride of marine spray and sand erosion. In this case, heterotrophic aerobic and anaerobic bacteria, cyanobacteria and fungi were isolated from the four sampling areas selected. In both archaeological sites crust deposits were observed by using light microscopy, SEM and ESEM. Surface analyses were made by means of EDAX and electron microprobe. Possible mechanisms of stone decay, based on the type of microorganisms isolated, the physico-chemical characteristics of the constructional materials and environmental factors are discussed.

Biodeterioration of Mayan buildings at uxmal and tulum, Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.

Use of dissolved ozone for controlling planktonic and sessile bacteria in industrial cooling systems

Abstract Cooling water treatment requires effective, environmentally-safe biocides compatible with system operation. The unique combination of high biocidal activity during use with no toxic discharge, could render dissolved ozone a safe biocide for cooling water treatment. Planktonic and sessile cells of Pseudomonas fluorescens (a frequent microbial contaminant of industrial systems) were used in this work to assess the biocidal effectiveness of ozone. Dissolved ozone showed to be effective at concentrations between 0.1 and 0.3 ppm, to eliminate completely the levels of planktonic cells used in this paper (10 7 –10 8 cell/ml) within a range of contact times between 10 and 30 min. However, ozone at 0.15 ppm was only able to diminish sessile cell population by two or three orders of magnitude. This minor biocidal effectiveness of ozone against bacterial biofilms is discussed in this paper, taking into account recent concepts on structure and dynamics of biofilms. Different metallic substrata were assayed to verify if there was any effect of metal nature on the biocidal action. Open circuit potentials vs. time experiments and potentiodynamic polarization curves were made for assessing the effect of dissolved ozone on the corrosion behavior of the metals tested.

Mechanisms of the Microbial Corrosion of Aluminum Alloys

Abstract Pitting potential was used recently to asses the aggressiveness of the biological species in the microbial corrosion of aluminum alloys in fuel-water systems. This parameter is analyzed he...

Comparative study of the electrochemical behaviour of glucose and other compounds of biological interest

Abstract The electro-oxidation of glucose and related compounds was studied in phosphate buffered media using a smooth platinum working electrode at different temperatures. A comparative analysis of the electrochemical behaviour of glucose and gluconic acid was made. Different electrochemical responses were found in the hydrogen adatom and in the PtO layer formation potential regions. Potentiostatic and potentiodynamic measurements with inositol, fructose, xylose, arabinose and glucose-1-phosphate were also performed in an attempt to find a relation between the electrochemical behaviour and the structural characteristics of these molecules. Our results suggest that the hemiacetalic group of the glucose molecule seems to play an important role in the electro-oxidation process. The electro-oxidation order of the different carbohydrates and derivatives resembles to some extent the electrochemical conversion order already established for other organic compounds.

An overview of mechanisms by which sulphate-reducing bacteria influence corrosion of steel in marine environments.

This communication provides an overview of the literature on the biocorrosion of steel in marine media, influenced by the presence of sulphate‐reducing bacteria (SRB). Electrochemical aspects, microbial interactions within biofilms, the significance of medium composition and the role of iron sulphides, and hydrogen effects are discussed. A brief description of recent experiments involving the use of electrochemical techniques for corrosion assessment, surface studies employing energy dispersive X‐ray analysis (EDAX), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD) and electron microprobe complemented with electron microscopy observations, as well as the application of novel techniques, such as micro sensors and atomic force microscopy, is given. The growth of SRB in marine environments causes significant modifications of many physicochemical parameters at the steel/seawater interface, including local changes in pH and redox potential values, variations in anion and cation concentrations and alteration of the composition and structure of corrosion products. Complex chemical and biological reactions and equilibria are also markedly altered during bacterial proliferation. These effects, which are absent in abiotic media, often lead to significant changes in the corrosion behaviour of steel. The complicated nature of the local environment at the steel/seawater interface is enhanced in the presence of microorganisms and their extracellular polymeric substances (EPS). As a consequence of biofilm heterogeneity, areas with different ion concentrations are formed and the development of corrosion product layers of dissimilar protective characteristics occurs.

Technical Note: Assessment of Corrosion and Microfouling of Several Metals in Polluted Seawater

It has been widely acknowledged in the literature that fouling of metal surfaces in contact with seawater is the main cause of several technical problems and economic loss in industry. Corrosion of metal surfaces is one of the principal events affecting the performance of structural metals. Copious literature is available with reference to fouling initiation and progression on metal structures immersed in the marine environment. Nevertheless, the information on the relation of fouling to corrosion is by no means complete. Previous attempts to correlate fouling with corrosion of the metal base have generally been made under conditions when important biomass had already accumulated. It is important to emphasise that corrosion and fouling of metals exposed to seawater occur within the same time scale, beginning immediately after the immersion of the specimens in the aqueous environment. The aim of this paper is to assess comparatively the corrosion behaviour of several metal surfaces in contact with polluted harbour seawater during the early stages of microfouling formation. The effect of the length of exposure of the metal samples, their surface finish, and the degree of water pollution on microbial settlement were examined by scanning electron microscopy (SEM). Corrosion of the metal substrate was studied in the laboratory by means of potentiodynamic polarisation experiments and open circuit records in artificial and natural filtered seawater. In situ measurements of open circuit potentials were made with metal samples placed in the water supply intake of a power plant. In both cases, SEM observations were complemented with energy dispersive x-ray analysis (EDXA) of corrosion products. The results obtained with the different solutions used in this paper may warn against conclusions drawn from laboratory experiments made with membrane-filtered seawater or artificial solutions used to replace in situ measurements with natural seawater.

The electrooxidation of glucose on platinum electrodes in buffered media

Abstract Kinetic studies of glucose electrooxidation are of special interest in fundamental and applied electrochemistry. The electrochemical reaction on bright Pt electrodes is investigated through the application of combined potential/time perturbation programs and electrolytes of different compositions at temperatures ranging from 30 to 64°C. The electrooxidation of glucose should occur through the formation of several intermediate species and the overall reaction pathway should consist of different stages considering electroadsorption, chemical and electrochemical processes. The influence of potential perturbation conditions, anion adsorption, inhibition reactions of products and temperature are analysed through changes in U/I profiles.