Biofouling and Biocorrosion in Industrial Water Systems

Corrosion associated with microorganisms has been recognized for over 50 years and yet the study of microbiologically influenced corrosion (MIC) is relatively new. MIC can occur in diverse environments and is not limited to aqueous corrosion under submerged conditions, but also takes place in humid atmospheres.

Biofouling of industrial water systems is the phenomenon whereby surfaces in contact with water are colonized by microorganisms, which are ubiquitous in our environment. However, the economic implications of biofouling in industrial water systems are much greater than many people realize. In a survey conducted by the National Association of Corrosion Engineers of the United States ten years ago, it was found that many corrosion engineers did not accept the role of bacteria in corrosion, and many of them that did, could not recognize and mitigate the problem.

Biofouling can be described in terms of its effects on processes and products such as material degradation (bio-corossion), product contamination, mechanical blockages, and impedance of heat transfer. Microorganisms distinguish themselves from other industrial water contaminants by their ability to utilize available nutrient sources, reproduce, and generate intra- and extracellular organic and inorganic substances in water. A sound understanding of the molecular and physiological activities of the microorganisms involved is necessary before strategies for the long term control of biofouling can be format. Traditional water treatment strategies however, have largely failed to address those factors that promote biofouling activities and lead to biocorrosion.

Some of the major developments in recent years have been a redefinition of biofilm architecture and the realization that MIC of metals can be best understood as biomineralization.     

The relationship between microbial metabolic activity and biocorrosion of carbon steel

The effect of metabolic activity (expressed by generation time, rate of H₂S production and the activity of hydrogenase and adenosine phosphosulphate (APS)-reductase enzymes) of the 8 wild strains of Desulfovibrio desulfuricans and of their resistance to metal ions (Hg²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Ni²⁺, Cr³⁺) on the rate of corrosion of carbon steel was studied. The medium containing lactate as the carbon source and sulphate as the electron acceptor was used for bacterial metabolic activity examination and in corrosive assays. Bacterial growth inhibition by metal ions was investigated in the sulphate-free medium. The rate of H₂S production was approximately directly proportional to the specific activities of the investigated enzymes. These activities were inversely proportional to the generation time. The rate of microbiologically induced corrosion (MIC) of carbon steel was directly proportional to bacterial resistance to metal ions (correlation coefficient r = 0.95). The correlation between the MIC rate and the activity of enzymes tested, although weaker, was also observed (r = 0.41 for APS-reductase; r = 0.69 for hydrogenase; critical value r_c = 0.30, p = 0.05, n = 40).Nous avons étudié l'influence, sur le taux de corrosion de l'acier carboné, de l'activité métabolique (durée du cycle de reproduction, taux de production d'H₂S et activité de l'hydrogénase et de l'adénosinephosphosulfate (APS)-réductase) de 8 souches de Desulfovibrio desulfuricans, et de la résistance de ces souches aux ions métalliques (Hg²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Ni²⁺, Cr³⁺).Le milieu contenant le lactate comme source de carbone et le sulfate comme accepteur d'électron a été utilisé pour l'étude du métabolisme bactérien et pour les tests de corrosion. L'inhibition de la croissance bactérienne par les ions métalliques a été étudiée en milieu sans sulfate. Le taux de production d'H₂S est approximativement directement proportionnel aux activités spécifiques des enzymes étudiées. Ces activités sont inversement proportionnelles à la durée du cycle de reproduction. Le taux de corrosion biologique (MIC, microbiologically induced corrosion) de l'acier carboné est directement proportionnel à la résistance bactérienne aux ions métalliques (coefficient de corrélation r = 0,95). Une corrélation entre les taux de MIC et ceux de l'activité enzymatique, bien que plus faible, a été aussi observée (r = 0,41 pour l'APS-réductase; r = 0,69 pour l'hydrogénase; valeur critique r = 0,30; p = 0,05; n = 40).     

Analysis for Giardia cysts and Cryptosporidium oocysts in water samples from small water systems in Taiwan

Giardia and Cryptosporidium have emerged as waterborne pathogens of concern. Twenty-six water samples were collected from small water systems in Taiwan and checked for the occurrence of both parasites. Water quality parameters and characteristics of the sampling sites were also recorded. The frequencies of occurrence for Giardia and Cryptosporidium were 46.2% for each; and their mean concentrations were 79.5 cysts/100 l and 22.1 oocysts/100 l, respectively. The concentrations of oocysts and heterotrophic bacteria exhibited the highest correlation and followed the concentrations of the two protozoa. The water samples from sites with filtration devices had a lower oocyst concentration than those from sites without filtration devices, while no significant difference was found for cysts. The level of each parasite had no direct relationship with altitude. The cyst concentrations increased proportionally with the consumer population using the water systems. Risk assessment of the parasitic infections suggests that setting up disinfection devices in the small water systems would be needed. Received: 6 September 2000 / Accepted: 10 September 2000     

Can drinking water standards be reliably derived from industrial TLVs?

The accuracy of TLV derived drinking water standards is evaluated. When using the identical TLV conversion methodology which Stokinger and Woodward (1) used in deriving the standard for barium in drinking water, standards for arsenic, cadmium, chromium and lead offer 6, 200, 60, and 10 times less protection than the present drinking water standards, respectively. However, using the same methodology, the TLV derived drinking water standard for fluoride offers greater protection than the present standard by a factor of approximately 2. Thus, the use of the TLV conversion factor should be viewed in as one of many lines of potential evidence which should be reviewed in the standard derivation process - but it should not, if at all possible, be considered alone - as in the case of barium.     

Possible role of water structure in biological magnesium systems

Magnesium chloride-water solutions have been studied by Fourier Transform Infrared Spectroscopy (FT-IR) in the near infrared region, 5000-10,000 cm-1. The effect of the concentration of magnesium chloride and temperature on the solutions has been studied from the spectra and it is concluded that magnesium chloride modifies the structure of the bulk water. The important absorption bands of water at 5200 and 7020 cm-1 may be assigned to combination vibrations and overtones. They are shifted either by increasing the magnesium chloride concentration or the temperature. The hydrated magnesium ions, [Mg(H2O)6]2+, will most probably break important hydrogen bonds in the clusters of water (H2O)n, where n = 2, 3, 4, 5, 6.../forming new hydrogen bonds in the presence of hexa-aquated magnesium cations. FAB mass spectra also suggest the formation of hydrated magnesium cations, Mg (H2O)6(2+).     

Distribution of biological particles in two-phase systems of water soluble polymers and salts

The paper discusses the problems of purification of Provachek's rickettsias used to prepare typhus vaccines and diagnostic kits. The currently available agents contain many admixtures of rickettsias products, more commonly yolk and chick embryo yolk sack cell detritus, which make it impossible to determine the true antigenic properties of rickettsias in the context of protection and diagnosis. By applying the well-known principle of distribution of biological particles in the two-phase systems of water soluble polymers, investigations were made to examine the distribution of rickettsias and their infected biological mass in the system: polyethylene glycol-6600, sodium-500 dextran sulfate, potassium phosphate, sodium chloride in order to prepare agents of pure rickettsias. It has been found that rickettsias are distributed in the polymer-enriched phase, their number and the degree of purity when isolated from the infected biological mass depends on the capacity of an interphase wherein tissue detritus sorption occurs.     

Potentially pathogenic nontuberculous mycobacteria found in aquatic systems. Analysis from a reclaimed water and water distribution system in Mexico City

We investigated the presence of nontuberculous mycobacteria (NTM) in three Mexican aquatic systems to evaluate the prevalence with the distribution of NTM species. Key physicochemical parameters of the water samples were determined to find correlations with the species’ distributions. We used multilocus sequence analysis (MLSA) based on hsp65, rpoB, and 16S rRNA fragments to determine their taxonomic affiliations. NTM were recovered from water distribution systems and reclaimed water from the Mexico City Metropolitan Area (MCMA). The isolated species were associated with a temperature of 21°C and pH >7.7. The phylogenetic analysis showed that eight of the 14 different NTM strains were unambiguously classifiable: Mycobacterium peregrinum, M. nonchromogenicum (2), M. smegmatis (2), M. fortuitum, M. avium ssp. hominissuis, M. arupense, M. gordonae, and M. chitae. One strain was tentatively identified as M. mantenni/ scrofulaceum and another strain was related to M. porcinum/M. septicum. All NTM species identified in the water distribution system were also detected in the reclaimed water, but some species from the reclaimed water were not found in the water distribution systems. Two of the identified species found in the reclaimed water, M. avium and M. fortuitum, are considered important human opportunistic pathogens.     

Comparative evaluation of health hazards associated with industrial chemicals and their derivates forming during water chlorination

Many industrial chemicals found in waste waters are able to form organochlorine by-products during water disinfection. The transformation of seven model compounds, cyclohexene, n-butanol, diphenylmethane, acetophenone, aniline, 1-methylnaphthalene, and phenylxylylethane during a reaction with active chlorine was studied. Aqueous chlorine and sodium hypochlorite were used as chlorinating agents. The products of the reaction were analyzed by means of chromatomass-spectrometry. A schematic model of diphenylmethane transformation was proposed. Comparative evaluation of hazards associated with the model chemicals and their derivates confirmed that chlorination products can be more toxic and dangerous than the initial compounds, and may possess mutagenic and cancerigenic properties.     

Surface analysis and biocorrosion properties of nanostructured surface sol-gel coatings on Ti6Al4V titanium alloy implants

Surfaces of biocompatible alloys used as implants play a significant role in their osseointegration. Surface sol-gel processing (SSP), a variant of the bulk sol-gel technique, is a relatively new process to prepare bioreactive nanostructured titanium oxide for thin film coatings. The surface topography, roughness, and composition of sol-gel processed Ti6Al4V titanium alloy coatings was investigated by atomic force microscopy (AFM) and X-ray electron spectroscopy (XPS). This was correlated with corrosion properties, adhesive strength, and bioreactivity in simulated body fluids (SBF). Electroimpedance spectroscopy (EIS) and polarization studies indicated similar advantageous corrosion properties between sol-gel coated and uncoated Ti6Al4V, which was attributed to the stable TiO2 composition, topography, and adhesive strength of the sol-gel coating. In addition, inductive coupled plasma (ICP) and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) analysis of substrates immersed in SBF revealed higher deposition of calcium and phosphate and low release rates of alloying elements from the sol-gel modified alloys. The equivalent corrosion behavior and the definite increase in nucleation of calcium apatite indicate the potential of the sol-gel coating for enhanced bioimplant applications.     

Extracellular polymeric substances mediate bioleaching/biocorrosion via interfacial processes involving iron(III) ions and acidophilic bacteria

Extracellular polymeric substances seem to play a pivotal role in biocorrosion of metals and bioleaching, biocorrosion of metal sulfides for the winning of precious metals as well as acid rock drainage. For better control of both processes, the structure and function of extracellular polymeric substances of corrosion-causing or leaching bacteria are of crucial importance. Our research focused on the extremophilic bacteria Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, because of the "simplicity" and knowledge about the interactions of these bacteria with their substrate/substratum and their environment. For this purpose, the composition of the corresponding extracellular polymeric substances and their functions were analyzed. The extracellular polymeric substances of both species consist mainly of neutral sugars and lipids. The functions of the exopolymers seem to be: (i) to mediate attachment to a (metal) sulfide surface, and (ii) to concentrate iron(III) ions by complexation through uronic acids or other residues at the mineral surface, thus, allowing an oxidative attack on the sulfide. Consequently, dissolution of the metal sulfide is enhanced, which may result in an acceleration of 20- to 100-fold of the bioleaching process over chemical leaching. Experiments were performed to elucidate the importance of the iron(III) ions complexed by extracellular polymeric substances for strain-specific differences in oxidative activity for pyrite. Strains of A. ferrooxidans with a high amount of iron(III) ions in their extracellular polymeric substances possess greater oxidation activity than those with fewer iron(III) ions. These data provide insight into the function of and consequently the advantages that extracellular polymeric substances provide to bacteria. The role of extracellular polymeric substances for attachment under the conditions of a space station and resulting effects like biofouling, biocorrosion, malodorous gases, etc. will be discussed.     

Strain-gauge versus water plethysmography description of simplified systems and analysis of differences and accuracy

Recently developed water and strain-gauge plethysmographs are compared on the same forearm. They do not differ systematically in absolute blood-flow values at different steady-state levels, provided that the strain gauge is applied at the middle, muscular, part of the forearm. The accuracy of the water and strain-gauge plethysmograph is identical, and the two instruments closely follow random variations in blood flow. The water plethysmograph is a reliable integrator of blood flow in a segment of a limb, and the strain-gauge described here can be used as an adequate substitute, when placed in the middle of the limb segment examined. However, the results from the strain-gauge plethysmograph are dependent on the actual location of the strain gauge.     

Prevalence of Legionella pneumophila serogroup 1 in water distribution systems in Izmir province of Turkey

Legionella pneumophila serogroup 1 occurrence has been investigated in 168 hot water samples from 24 hotels, situated in 6 counties in Izmir province of Turkey, from 15 June to 30 September of the year 2000. Sampling was carried out at 15-day intervals and seven samples were taken from each of the hotels' hot water reservoirs and hot water networks. The samples were (1 L) concentrated using polycarbonate filters (mesh size 0.22 microm). Isolation was achieved using selective medium, GVPC agar. The samples were concentrated by membrane filtration, divided into three portions and cultured without pretreatment, after acid treatment, and after heat treatment, on GVPC agar. One hundred and ten isolates were identified as L.pneumophila sg 1 using the Legionella Latex Test (Oxoid). Arbitrarily primed PCR (AP PCR) was employed to assess the clonal relationship between Legionella pneumophila sg 1 isolates from the hot water samples of the hotels. Three genotypes of L. pneumophila sg 1 isolates were identified. With a high prevalence of type A, 22 hotels were found to be colonized with L. pneumophila serogroup 1, while only 2 were free from the bacteria.     

On the existence of bound water in biological systems as probed by dielectric spectroscopy

Results of dielectric relaxation studies in this laboratory on binary aqueous solutions are summarized to look for indications of the presence of bound water. The solutes include simple inorganic and organic electrolytes, polyelectrolytes, small organic molecules and polymers. It is shown that even simple solutions exhibit a great variety of dielectric effects. It therefore appears to be impossible to unambiguously discuss dielectric spectra of complex biological tissues in which different polarization mechanisms overlap. The results for solutions taken as models for biological systems indicate two types of affected water which might be considered 'bound': dielectrically saturated water in strong electric fields and water in regions with a high concentration of other molecules. Characteristics of both states of water in mixtures are presented.