The chemical control of biofouling in industrial water systems

Oxidising and non-oxidising biocides are commonly used in an attempt to control biofouling in industrial water systems. Many of these programmes, however, fail due to the incorrect selection and application of these chemical compounds. Knowledge of the organisms to be eliminated and system hydraulics are important operational parameters in ensuring the successful application of chemical control programmes. A further complicating factor is the build up of bacterial resistance to many of these compounds. One way of limiting resistance is the alteration of oxidising and non-oxidising biocides at the correct miminum inhibitory concentration and using these in combination with surface active compounds to dislodge any biofilm. A variety of surface monitoring techniques are in use in order to monitor the success of biofouling control programmes. Unfortunately none of these techniques are ideal and results have to be considered very carefully.     

Assessment of biofilm cell removal and killing and biocide efficacy using the microtiter plate test

Biofilm formation on surfaces has serious economic and environmental implications. Growth of biofilm within a water distribution system can lead to problems such as biocorrosion and biofouling accumulation. To prevent and control these occurrences, it is necessary to use suitable biocides to remove the biofilm and kill biofilm cells. In this study, the genera Actinobacillus, Branhamella, Bacillus, Micrococcus and Acinetobacter were isolated from biofilms formed on brass coupons exposed to a cooling water system. It was shown by the microtiter plate test that a mixed culture of the isolates and a single culture of Acinetobacter sp(2) produced high levels of biofilm formation. A microwell plate technique was applied for assessment of the ability of various biocides to remove and kill mixed-culture biofilm cells and Acinetobacter sp(2), the latter as a single-species biofilm with a high rate of biofilm production. The results showed that the mixed-culture biofilm cells had more resistance to removal and killing by some biocides, such as hydrogen peroxide and sulfathiazole, than the single-species biofilm cells (Acinetobacter sp(2)). Oxidising biocides, such as sodium hypochlorite and hydrogen peroxide, demonstrated a higher potential for biofilm removal and killing compared with non-oxidising biocides (sulfathiazole and glutaraldehyde).     

Control of biocorrosion using laboratory and field assessments

Biofouling and biocorrosion can be significant problems in oilfield water injection systems, despite extensive use of chemical biocides. This work set out to establish relevant testing and monitoring procedures to optimise microbiological control in these systems.A combination of laboratory based sessile biocide screening trials and onsite monitoring of biofilm bacteria was developed to ensure that an effective biocontrol programme was set up. It is important to use a mixed population of bacteria freshly isolated from biofilms in the system to ensure that any biocide tolerance of the system bacteria is reflected in the laboratory tests. In general, the results are borne out by the site audits of the control regime against sessile bacteria in the system.In an industrial system, biocide resistant populations develop from time to time. In practice it was found that even a small change to the biocide formulation could improve biocontrol, with concomitant reduction in corrosion rates and maintenance costs.     

Barnacles and biofouling

Biofouling, the attachment and growth of organisms on submerged, man-made surfaces, has plagued ship operators for at least 2500 years. Accumulation of biofouling, including barnacles and other sessile marine invertebrates, increases the frictional resistance of ships' hulls, resulting in an increase in power and in fuel consumption required to make speed. Scientists and engineers recognized over 100 years ago that in order to solve the biofouling problem, a deeper understanding of the biology of the organisms involved, particularly with regard to larval settlement and metamorphosis and adhesives and adhesion, would be required. Barnacles have served as an important tool in pursuing this research. Over the past 20 years, the pace of these studies has accelerated, likely driven by the introduction of environmental regulations banning the most effective biofouling control products from the market. Research has largely focused on larval settlement and metamorphosis, the development of new biocides, and materials/surface science. Increased research has so far, however, failed to result in commercial applications. Two recent successes (medetomidine/Selektope?, surface-bound noradrenaline) build on our improving understanding of the role of the larval nervous system in mediating settlement and metamorphosis. New findings with regard to the curing of barnacle adhesives may pave the way to additional successes. Although the development of most current biofouling control technologies remains largely uninfluenced by basic research on, for example, the ability of settling larvae to perceive surface cues, or the nature of the interaction between organismal adhesives and the substrate, newly-developed materials can serve as useful probes to further our understanding of these processes.     

Biofouling in water systems – cases,causes and countermeasures

Biofouling is referred to as the unwanted deposition and growth of biofilms. This phenomenon can occur in an extremely wide range of situations, from the colonisation of medical devices to the production of ultra-pure, drinking and process water and the fouling of ship hulls, pipelines and reservoirs. Although biofouling occurs in such different areas, it has a common cause, which is the biofilm. Biofilms are the most successful form of life on Earth and tolerate high amounts of biocides. For a sustainable anti-fouling strategy, an integrated approach is suggested which includes the analysis of the fouling situation, a selection of suitable components from the anti-fouling menu and an effective and representative monitoring of biofilm development.     

Microbiologically influenced corrosion in petroleum product pipelines--a review

Microbiologically influenced corrosion is responsible for most of the internal corrosion problems in oil transportation pipelines and storage tanks. One problematic area in treating gas lines is the occurrence of the stratification of water in the line. Under these conditions, corrosion inhibitors do not come into contact properly and oil and inhibitors undergo degradation. The role of bacteria on oil degradation, the consequences of oil degradation in fuel systems and its influence on corrosion have been explained in detail. Besides, factors influencing on degradation of oil and corrosion inhibitors have also been discussed. Mechanism of microbiologically influenced corrosion in oil pipeline has been explained. Many of the misapplication of biocides/inhibitors occur mainly because the characteristics of biocides/inhibitors are not considered before use in pipeline industry. List of biocides and monitoring programme have been collected from literature and presented.     

硫酸盐还原细菌生物被膜的形成与调控研究进展

硫酸盐还原细菌(sulfate-reducing bacteria,SRB)形成的生物被膜是微生物导致金属锈蚀行为的主要原因,同时也是重金属污水微生物修复技术的关键因子。生物被膜形成及调控机制研究对SRB的防治和利用均十分重要。本文综述了近年来SRB生物被膜的研究进展,包括SRB生物被膜的胞外多聚物组成和控制因子,并着重阐述了目前已知的调控因子对SRB生物被膜形成的影响。     

Kinetics of conditioning layer formation on stainless steel immersed in seawater

Adhesion of microorganisms to surfaces in marine environments leads to biofouling. The deleterious effects of biofilm growth in the marine environment are numerous and include energy losses due to increased fluid frictional resistance or to increased heat transfer resistance, the risk of corrosion induced by microorganisms, loss of optical properties, and quality control and safety problems. Antifouling agents are generally used to protect surfaces from such a biofilm. These agents are toxic and can be persistent, causing harmful environmental and ecological effects. Moreover, the use of biocides and regular cleaning considerably increase the maintenance costs of marine industries. An improved knowledge of bio‐film adhesion mechanisms is needed for the development of an alternative approach to the currently used antifouling agents. The aim of this study is to characterise the chemical composition of the molecules first interacting with stainless steel during the period immediately following immersion in natural seawater and to elucidate the kinetics of the adsorbtion process. Proteins are shown to adhere very rapidly, closely followed by carbohydrates. The distribution on the surface of organic molecules is also examined. The ad‐sorbate on the surface is not a continuous film but a heterogeneous deposit, whose average thickness varies widely. The cleaning procedures used affect the adsorption kinetics. In particular, cleaning with hexane results in slower adsorption of nitrogen‐containing species than does cleaning in acetone.     

Microbe-surface interactions in biofouling and biocorrosion processes.

The presence of microorganisms on material surfaces can have a profound effect on materials performance. Surface-associated microbial growth, i.e. a biofilm, is known to instigate biofouling. The presence of biofilms may promote interfacial physico-chemical reactions that are not favored under abiotic conditions. In the case of metallic materials, undesirable changes in material properties due to a biofilm (or a biofouling layer) are referred to as biocorrosion or microbially influenced corrosion (MIC). Biofouling and biocorrosion occur in aquatic and terrestrial habitats varying in nutrient content, temperature, pressure and pH. Interfacial chemistry in such systems reflects a wide variety of physiological activities carried out by diverse microbial populations thriving within biofilms. Biocorrosion can be viewed as a consequence of coupled biological and abiotic electron-transfer reactions, i.e. redox reactions of metals, enabled by microbial ecology. Microbially produced extracellular polymeric substances (EPS), which comprise different macromolecules, mediate initial cell adhesion to the material surface and constitute a biofilm matrix. Despite their unquestionable importance in biofilm development, the extent to which EPS contribute to biocorrosion is not well-understood. This review offers a current perspective on material/microbe interactions pertinent to biocorrosion and biofouling, with EPS as a focal point, while emphasizing the role atomic force spectroscopy and mass spectrometry techniques can play in elucidating such interactions.     

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.     

Prevention and control of biocorrosion

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.     

Antifouling activity of enzyme‐functionalized silica nanobeads

The amelioration of biofouling in industrial processing equipment is critical for performance and reliability. While conventional biocides are effective in biofouling control, they are potentially hazardous to the environment and in some cases corrosive to materials. Enzymatic approaches have been shown to be effective and can overcome the disadvantages of traditional biocides, however they are typically uneconomic for routine biofouling control. The aim of this study was to design a robust and reusable enzyme‐functionalized nano‐bead system having biofilm dispersion properties. This work describes the biochemical covalent functionalization of silica‐based nanobeads (hereafter referred to as Si‐NanoB) with Proteinase K (PK). Results showed that PK‐functionalized Si‐NanoB are effective in dispersing both protein‐based model biofilms and structurally altering Pseudomonas fluorescens biofilms, with significant decreases in surface coverage and thickness of 30.1% and 38.85%, respectively, while increasing surface roughness by 19 % following 24 h treatments on bacterial biofilms. This study shows that enzyme‐functionalized nanobeads may potentially be an environmentally friendly and cost effective alternative to pure enzyme and chemical treatments. Biotechnol. Bioeng. 2016;113: 501–512. © 2015 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.     

Approaches to prevention, removal and killing of biofilms

Biofilms contribute to hygiene problems in the food industry and in the medical field. Biofilms are diverse and due to the development of special phenotypes, biofilm organisms are not as susceptible to biocides as planktonic microorganisms. Biofilms may be prevented by regular disinfection. Since the attachment of microbes to surfaces and the development of biofilm phenotypes is a very fast process, it is, however, almost impossible, to prevent biofilm formation completely. The removal and killing of established biofilms requires harsh treatments, mostly using oxidising biocides. Depending on the nature of the biofilms, different biocides may be useful and the best biocide for a specific biofilm still has to be determined under practical conditions. Another approach is the prevention of biofilm formation by selection of materials that do not support the attachment of microorganisms. Some materials like glass and stainless steel show less biofilm formation than others. The ranking of materials, however, depends on the conditions, under which they are tested. A novel approach is biofilm inhibition by supplementation of systems with nutrients, to inhibit attachment. First results on inhibition of biofouling in reversed osmosis systems are presented.     

Analysis of biocide transport limitation in an artificial biofilm system

An alginate gel bead artificial biofilm system was used to assay biofilm susceptibility to four biocides and to analyse the extent to which each agent penetrated the biofilm. Chlorine, glutaraldehyde, an isothiazolone, and a quaternary ammonium compound were tested on alginate-entrapped Enterobacter aerogenes in gel beads ranging from 1·8 to 6 mm in diameter. Gel-entrapped bacteria were less susceptible to all four antimicrobial agents than were planktonic micro-organisms. The degree of kill measured in artificial biofilm gel beads depended on the size of the gel bead and the cell density at which it was loaded. Disinfection efficacy decreased as gel bead radius or cell density increased. The manifest dependence of biofilm disinfection efficacy on the physical properties of the artificial biofilm (radius and cell density) suggests the impingement of transport limitation of biocide transport into the biofilm. A previously developed theory of biocide reaction and diffusion in biofilm was tested by calculating an appropriate Thiele modulus. In accordance with the theory, the efficacy of all four biocides decreased, albeit noisily, as the Thiele modulus exceeded 1. This result demonstrates that transport limitation can impact antimicrobial performance against biofilms not only of oxidizing biocides but also of non-oxidizing agents.     

Growth of Sessile Sphaerotilus natans in a Tubular Recycle System

The growth of sessile Sphaerotilus natans was measured in a continuous-flow recycle system. Four methods were used to confirm that the growth of the biofilm was a linear function that increased with time. Of the methods used, one monitored in situ biofouling (increased fluid frictional resistance), two indicated biomass (ATP and DNA per square centimeter), and one allowed the direct observation of replaceable test surfaces by scanning electron microscopy. The filamentous growth of S. natans caused an increase in the fluid frictional resistance. The increase in biofouling was directly proportional to the increase in biomass.     

Biological control of microbial attachment: a promising alternative for mitigating membrane biofouling

Microbial attachment to a solid surface is a universal phenomenon occurring in both natural and engineering systems and is responsible for various types of biofouling. Membrane systems have been widely applied in drinking water production, wastewater reuse, and seawater desalination. However, membrane biofouling is the bottleneck that limits the development of membrane systems. In this review, some biological control strategies of microbial attachment which would have great potential in alleviating membrane biofouling are discussed, including inhibition of quorum sensing system, nitric oxide-induced biofilm dispersal, enzymatic disruption of extracellular polysaccharides, proteins, and DNA, inhibition of microbial attachment by energy uncoupling, use of cell wall hydrolases, and disruption of biofilm by bacteriophage. It appears that biological control of microbial attachment would be a novel and promising alternative for mitigating membrane biofouling and would be a new research niche that deserves further study.     

Utilisation of a packed-bed biofilm reactor for the determination of the potential of biofilm accumulation in water systems

An experimental system has been developed that allows the monitoring of biofilm development on supports exposed to water of different characteristics. The system consists of a series of packed-bed reactors filled with glass beads, and by periodically removing biofilm attached to these beads for off-line analyses this provides a means for monitoring biofilm development. Despite its reduced dimensions (6.9 cm long and 1.58 cm in diameter), the experimental system used has a sampling surface of 90.3 cm2 (including only the surface of the glass beads). This allows reproducible and representative samples to be taken from different water systems, providing a reliable and economic method for evaluating in situ the formation of biofilms from different environments. The set-up of the entire experimental system was constructed to meet the demands of field experiments in a well-defined hydrodynamic environment and to allow easy removal of samples for biomass quantification and microscopic observation. Data obtained using this device can be used as an indicator of the risk of biofilm formation in different water systems. This indicator, "the biofilm accumulation potential", represents an effective and representative tool for the monitoring of biofilm development in an integrated antifouling strategy, in order to help keep biofouling, scaling and microbial risks under control. According to the experiments with the packed-bed reactors used with a high flow regime, the ratio TCN/HPC could provide an indication of the state of the biofilm, and lower ratios could indicate a higher biofilm accumulation potential.     

Biofilm formation and biocide susceptibility testing of Mycobacterium fortuitum and Mycobacterium marinum

The ability of non-tuberculous mycobacteria to form biofilms may allow for their increased resistance to currently used biocides in medical and industrial settings. This study examines the biofilm growth of Mycobacterium fortuitum and Mycobacterium marinum, using the MBEC trade mark assay system, and compares the susceptibility of planktonic and biofilm cells to commercially available biocides. With scanning electron microscopy, both M. fortuitum and M. marinum form biofilms that are morphologically distinct. Biocide susceptibility testing suggested that M. fortuitum biofilms displayed increased resistance over their planktonic state. This is contrasted with M. marinum biofilms, which were generally as or more susceptible over their planktonic state.     

Utilisation of a packed-bed biofilm reactor for the determination of the potential of biofilm accumulation in water systems

Abstract

An experimental system has been developed that allows the monitoring of biofilm development on supports exposed to water of different characteristics. The system consists of a series of packed-bed reactors filled with glass beads, and by periodically removing biofilm attached to these beads for off-line analyses this provides a means for monitoring biofilm development. Despite its reduced dimensions (6.9 cm long and 1.58 cm in diameter), the experimental system used has a sampling surface of 90.3 cm² (including only the surface of the glass beads). This allows reproducible and representative samples to be taken from different water systems, providing a reliable and economic method for evaluating in situ the formation of biofilms from different environments. The set-up of the entire experimental system was constructed to meet the demands of field experiments in a well-defined hydrodynamic environment and to allow easy removal of samples for biomass quantification and microscopic observation. Data obtained using this device can be used as an indicator of the risk of biofilm formation in different water systems. This indicator, “the biofilm accumulation potential”, represents an effective and representative tool for the monitoring of biofilm development in an integrated antifouling strategy, in order to help keep biofouling, scaling and microbial risks under control. According to the experiments with the packed-bed reactors used with a high flow regime, the ratio TCN/HPC could provide an indication of the state of the biofilm, and lower ratios could indicate a higher biofilm accumulation potential.     

Advances in the treatment of problematic industrial biofilms

In nature, microorganisms tend to form biofilms that consist of extracellular polymeric substances with embedded sessile cells. Biofilms, especially mixed-culture synergistic biofilm consortia, are notoriously difficult to treat. They employ various defense mechanisms against attacks from antimicrobial agents. Problematic industrial biofilms cause biofouling as well as biocorrosion, also known as microbiologically influenced corrosion. Biocides are often used to treat biofilms together with scrubbing or pigging. Unfortunately, chemical treatments suppress vulnerable microbial species while allowing resistant species to take over. Repeated treatment cycles are typically needed in biofilm mitigation. This leads to biocide dosage escalation, causing environmental problems, higher costs and sometimes operational problems such as scale formation. New treatment methods are being developed such as enhanced biocide treatment and bacteriophage treatment. Special materials such as antibacterial stainless steels are also being created to combat biofilms. This review discussed some of the advances made in the fight against problematic industrial biofilms.