Understanding and Addressing Microbiologically Influenced Corrosion (MIC) Laura L

REVIEW PAPER

Understanding and Addressing Microbiologically Influenced Corrosion (MIC) Laura L. Machuca

OVERVIEW corrosion on underground pipelines [5]. We know MIC involves the interaction Microbial life is everywhere. The formation of biofilms on metals of electrochemical, environmental, Microorganisms have been found and alloys can result in corrosion rates operational, and biological factors inhabiting iced-covered lakes in in excess of 10 mm per year (mm/y) that often result in substantial Antarctica at -13°C and hydrothermal leading to equipment failure before increases in corrosion rates to metals vents at the bottom of the ocean their expected lifetime and serious in specific environments. However, at 120°C [1]. Microorganisms have environmental damage [6, 7]. The the complex and dynamic nature of inhabited our planet for billions 2006 trans-Alaskan pipeline failure, these interactions have made detailed of years before plants and animals which was attributed to microbial mechanisms elusive, i.e. the precise appeared. It was through their corrosion where 200,000 gallons of mechanism(s) of MIC is still being activities that higher forms of life crude oil leaked resulted in significant debated among corrosion specialists. could appear and thrive [2]. However, environmental pollution, lost The most challenging aspects of MIC microorganisms can also be harmful production of two million barrels and is its lack of predictability and the fact and their activities can result, under a worldwide impact on oil price [7] is a that it does not produce a distinct type certain conditions, in detrimental prime example of such issues. Incidents of corrosion or a unique morphology effects such as disease and damage like these have resulted in increased of corrosion damage, or any sort of to infrastructure. Industrial systems industry awareness and to increasing mineralogical fingerprints. Although typically create new microbial research and developments in the field some investigators claim that certain habitats that can stimulate undesired over the past 10 years. The evolution of metallurgical features are characteristic microbial activities. A notable MIC knowledge throughout these years of a MIC mechanism, e.g. deep pits example of this is microbiologically has been reviewed recently by Hashemi that are hemispherical, and cup‐ influenced corrosion (MIC) which et al. [5]. like in appearance with striation or refers to corrosion of metallic equipment and structures caused or accelerated by microorganisms. These microorganisms are mainly bacteria and archaea, but microalgae and fungi can also be important contributors in certain environments [3, 4]. In Australia, MIC represents a common threat to the oil & gas, defence and marine industries which are major components of the national economy. Deterioration and corrosion due to microorganisms drives a worldwide market for microbial control that is worth billions of dollars annually.

MIC unquestionably has always occurred in industry; however, it remains poorly understood and recognized. In the past, reluctance among corrosion professionals to acknowledge the possibility for MIC and its potential to cause equipment failure led to it being considered of less significance, therefore research to advance its understanding was less well supported. However, this has drastically changed in recent years. It is now widely recognized that MIC contributes to at least 20% of the total cost of Figure 1 Microbiologically influenced corrosion of crude line to cargo storage in a corrosion worldwide, 40% of internal Floating, Production, Storage and Offloading vessel (FPSO). Reproduced with permission corrosion and 20% to 30% of external from Machuca and Polomka (2018), Microbiology Australia 39 (3), 165-169. p.88 CORROSION & MATERIALS REVIEW PAPER

contour lines, the evidence remains The microbial ecology of a system is a steel is the most common material of largely anecdotal. In addition, MIC critical component to consider when construction due to its commercial generally occurs in conjunction with assessing the potential mechanisms attractiveness. However, carbon steel is other corrosion mechanisms. These for MIC. Microbial communities susceptible to MIC. In offshore oil and characteristics present challenges to with distinct capabilities commonly gas production systems, for instance, identifying MIC as the mechanism inhabit oil production facilities [19]. carbon steel is prone to MIC at even low of failure. In most cases, MIC These microorganisms are typically water cuts (ratio of water vs. total fluids morphologies are localized types of strictly anaerobic (oxygen is not produced) under the right combination corrosion that manifest in pitting, present in oil production systems), of nutrient availability, microbial crevice corrosion and under deposit thermophilic and exhibit slow growth population density and temperature. corrosion (UDC). and enhanced resistance to stress. Corrosion resistant alloys (CRA) as MIC mechanisms in these conditions opposed to carbon steel are more MIC is driven by environmental are usually related to CO2 and H2S resistant to MIC despite having similar conditions. Mechanisms that govern corrosion and electron acceptors such susceptibility to biofilm formation [21]. MIC in freshwater environments as sulphate, CO2 and nitrate are critical This is particularly the case for highly- seem to be quite different to those in supporting such mechanisms. In resistant alloys that contain higher observed in marine environments and marine environments, conversely, concentrations of alloying elements to those in oil and gas production oxygen is a key player, which not only such as chromium, nickel, molybdenum facilities [9-11]. Parameters such as drives the corrosion reactions but also and nitrogen [24]. However, in lower temperature, flow conditions, pH, light the metabolic activities of colonizing grade CRAs such as 304 and 316 and and nutrients will favour the growth species and thus, the resulting biofilm even 2205 duplex stainless steel both of particular species and restrain the composition and structure [20, 21]. the breakdown of passive films and the growth and metabolism of others on Marine bacteria typically identified propagation of localized corrosion can a particular substratum. Particularly, in corroded equipment correspond to be greatly affected by microbial activity the type of electron acceptors mesophilic species. Marine biofilms on [25]. The phenomenon of ennoblement available in a system, e.g. sulphate, steel materials can also contain other of CRAs, a shift of the corrosion CO2 and oxygen, are known to play a seawater organisms such as algae (e.g. potential (Ecorr) in the noble or anodic critical role in shaping the microbial diatoms) and barnacles [21]. However, direction, is associated with microbial community developed on the metal the structure and composition of marine activity [21, 26]. The significance of this surface, its biofilm structure and the biofilms (and surface concretions) on phenomenon lies in its influence on resulting MIC [12, 13]. In addition, steel materials depend on water depth; the susceptibility to corrosion of anode the presence of chemical inhibitors deep waters have different nutrient, materials in galvanic couples and the and additives used by the industry microbial and dissolved oxygen content initiation and propagation of localized to prevent scaling, fouling, microbial and exhibit lower temperature and corrosion [27, 28]. There is a particular activity and corrosion will also create a higher pressure when compared to risk for CRAs with MIC when exposed selective environment for and against shallow waters [22]. There is no light to environments were oxygen is present certain groups of microorganisms. in the deep ocean which restricts the or when oxygen can ingress as a result Likewise, in low velocity systems and potential activity of photosynthetic of contamination, such as during poor stagnant flow conditions, deposits organisms that can contribute to oxygen water flooding of subsea pipelines and debris can settle providing an and organic carbon generation within [29]. MIC of CRAs under oxygen- ideal niche for bacterial accumulation, biofilms if light is present [23]. free conditions appears to be of less growth and activity [14]. We have concern. However, this is a topic that recently reported MIC under oilfield MIC is also affected by material remains under debate and requires more deposits from corroded pipelines (substratum) composition. Carbon systematic investigations. which resulted in pitting rates greater than those obtained in the absence of bacteria [15]. Results indicated that bacterial extracellular polymeric substances, or EPS, on the metal surface created a diffusion barrier that entrapped chemical species within the deposit, which facilitated the formation of concentration cells on the metal surface. MIC under deposits have been reported to result in corrosion rates greater than 5 mm/y in Floating production storage and floating vessels (FPSO’s) (Personal communication)[16]. A case study in West Africa, related the predominance of high-MIC risk bacteria Thermovirga sp. in solids deposited in separation vessels with high corrosion rates, which were 30 times higher than the expected range [17]. Wang et al., suggested a synergistic effect between MIC and under-deposit corrosion resulting in more severe localized corrosion [18]. Figure 2 Scanning electron micrograph of microorganisms on corroded carbon steel (AISI 1030).

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Several MIC mechanisms have known as a corrosive gas) [35-37]. media, i.e. produced water inoculated been described including direct and Methanogens have not been widely with active SRB, raw produced water indirect mechanisms. Comprehensive detected in corroded facilities since containing field bacteria and Postage review papers on MIC mechanisms they are very difficult to grow under B medium inoculate with active SRB are available elsewhere [30, 31]. For laboratory conditions. However, [46]. Results indicated that biocide decades, specific microbial groups such DNA based analysis has shown that efficiency was affected by growth as sulphate‐reducing bacteria (SRB) and methanogens are widespread in medium. Overall biofilms formed in acid‐producing bacteria (APB) have oilfield environments and are typically Postgate B medium exhibited more been identified as the main culprits of detected in biofilms associated with resistance to biocides compared to MIC and their metabolites, sulphide corrosion. MIC research involving biofilms formed using produced water and organic acids, respectively, have methanogens has demonstrated that from field. This could be due to the been directly associated with corrosion. these microorganisms can accelerate fact that Postgate medium is very Such MIC mechanisms, in which corrosion via EMIC mechanisms [38]. nutritious and results in the formation corrosion is accelerated by production of more robust biofilms. Also, Postgate of corrosive microbial metabolites, are A concerning aspect in the B medium contains yeast extract (YE) known as chemical MIC, or CMIC, and understanding of the MIC risk is the which is a very complex nutrient have been reviewed extensively in the typical assignment of specific metabolic source that contains organics, proteins literature [32, 33]. However, the list functions to individual microbial and vitamins. YE can form complexes of microorganisms that can influence populations. One example is the on the surface and potentially corrosion is constantly growing. assumption that the sole presence of SRB react with biocide compounds. The Particularly with the advent of new species is enough evidence for sulphide- potential impact of YE on the biotic sequencing technologies that allow associated corrosion. Microorganisms are reactions in MIC experiments has been identification of non-culturable species significantly versatile, with the potential discussed previously [47]. Ideally, MIC present in corroded equipment that to use different metabolic pathways experiments should be designed to have not previously been associated than those commonly attributed to use field samples directly, or synthetic with corrosion. them, depending on the environmental medium of very similar composition, conditions and the availability of and to replicate the field environment In recent years, novel MIC mechanisms nutrients [39]. For instance, the (temperature, material, gas atmosphere, involving direct electron transfer (DET) detection of fermenting microbes, which etc) to grow and study biofilm activity between bacteria and steel have been are widely distributed in oil production and its inhibition on metals. revealed and are now the focus of a facilities, is typically associated with the great deal of scientific work [34]. This risk of acid corrosion. Some of these BIOFILM: THE COMPLEX mechanism is known as electrical MIC, microorganisms are known to be able CULPRIT BEHIND MIC or EMIC. Typically, corrosion rates to reduce sulphur compounds such as Regardless of the particular reactions obtained in laboratory experiments elemental sulphur and thiosulphate and processes governing MIC in involving CMIC mechanisms are as electron-sink reactions that different environments, there is much lower than those reported prevent accumulation of inhibitory agreement among researchers that in field. It appears that one of the concentrations of the fermentation biofilm formation is the critical step reasons for this persistent outcome product molecular hydrogen [40, 41]. in MIC [48]. Thus, MIC is not only is that most laboratory experiments This will result in sulphide production; the result of complex corrosion involving SRBs generate H2S and iron therefore, some fermenting microbes reactions but also, the result of a sulphide films that are protective can also become sulphide-producing series of flawless events involved in and uniformly distributed on the bacteria. Likewise, some microorganisms the construction of a biofilm, the surface of a test coupon [32]. This can switch from one electron acceptor to most intricate, highly-organised scenario cannot be compared with another if the first one becomes depleted and successful mode of life for field conditions were in metres of and another one becomes available [42]. microorganisms. Biofilms consist pipe only a few pits are present (small Therefore, assigning specific microbial of communities of microorganisms anodes) with large areas outside populations to a specific corrosion attached to the metal surface and the pits being covered by sulphide mechanism or associated risk can result embedded in self-produced EPS, films (large cathode), which results in erroneous interpretations. proteins, lipids and extracellular in greater corrosion rates. However, DNA [49]. However, far from this studies involving EMIC mechanisms In addition, transposing a field simple explanation, biofilms represent have shown that DET can result in environment to a laboratory a set of properties, functions and corrosion rates as severe as those environment to investigate MIC is structures that are highly dynamic and reported in field (>5 mm/y), which one of the biggest challenges in the imperative for the long-term survival suggests that this novel mechanism field. The effect of feeding nutrients of biofilm cells. Within biofilms, can be significant in industrial systems in the laboratory at concentrations a variety of interactions including [34]. Hitherto, only a few species have and compositions different to the field chemical and electrical signals, been demonstrated to have the ability fluids on the growth of biofilms, and social cooperation, differentiation to induce EMIC. However, only a the activity of bacteria in the biofilm as and highly controlled expression few studies have looked into natural well as the influence that the nutrients of genes and proteins, occur as a biofilm consortia and the potential may have on the corrosion and MIC response to exposure conditions [50]. of different microbial populations process, remains a big limitation Even though biofilms are comprised to carry out DET has not been fully [43]. Investigators have shown that of individual bacterial cells, it is investigated. Methanogens represent a test media can have an impact on recognized that microbes within group of microbes of increasing interest bacterial attachment and the outcome biofilms exhibit different properties in MIC despite not being associated of MIC tests [44, 45]. We studied SRB than planktonic cells and that their with corrosion via production of a biofilm growth on carbon steel and its response to environmental cues is the corrosive metabolite (methane is not inhibition by biocides in three different result of community interactions that p.90 CORROSION & MATERIALS REVIEW PAPER

cannot be predicted by only studying Biofilm-surface interactions are involved in MIC and that different free-living bacteria or single-species also spatially heterogeneous and mechanisms can occur simultaneously biofilms [50]. In addition, biofilms are can result in localized gradients on metal surfaces. Synergistic and multi-layered so stratified cell-cell and and microenvironments across the antagonistic (competing) relationships cell-medium interactions on the metal surface. This implies that more than can emanate among biofilm species, surface are also expected. one microbial mechanism has to be which can in turn affect the structure and function of biofilms. Therefore, it is not a steady state “corrosion product” formed on the surface but a dynamic system that responds to its environment (nutrient availability, hydrodynamic shear, temperature, etc.). An interesting feature of these biofilms is that metallic ions can become adsorbed in biofilms preventing microbial exposure to toxic compounds [48]. This means that localized precipitation of metals can take place within biofilms and can potentially affect the surface electrochemistry, e.g. creating galvanic cells on the surface. This can represent one of the most important yet understudied mechanisms of MIC.

Understanding the effect of nutrients on MIC represents another challenge. This is because even though nutrients are known to be essential to microbial reproduction and activity, microbial cross-feeding within biofilms can be used to overcome nutrient scarcity in a particular system [51]. For instance, microbes can exchange metabolic by- products in biofilms and interspecies electron transfer can provide pathways Figure 3 Scanning electron micrograph of a microbial cell secreting EPS on the surface of for energy generation; even dead cells stainless steel at the early stages of biofilm formation. can provide nutrients to other cells. In addition, microorganisms can enter into dormancy and viable but no-cultivable states which results in survival in times of starvation [52]. Likewise, binding sites within biofilms, including both anionic and cationic exchangers, can facilitate the entrapment and storage of substances for future consumption by cells in the biofilm. In terms of hydration, it has been demonstrated that the development of biofilms prevents dehydration (retaining water and preventing evaporation) which has been proven critical to withstand desiccation periods [50].

Undoubtedly, the most detrimental aspect about biofilms and perhaps one of the most difficult challenges about MIC control is the fact that biofilms provide a physical barrier that protects microbes against antimicrobial components. It is known that the efficiency of a chemical biocide is significantly reduced in the presence of biofilms [53]. The more mature a biofilm is, the more difficult to inactivate and inhibit. Different microbial mechanisms have been described that lead to isolation of toxic antimicrobial compounds Figure 4 Scanning electron micrograph of complex mature biofilms on stainless steel. within biofilms to prevent these toxic

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compounds from reaching and harming relate these microbes with a corrosion data for corrosion engineers. Even microbial cells [54]. The problem problem. There are reports of systems for experienced microbiologists, this lays with this process resulting in sub where MIC remains insignificant despite type of data represents a challenge for lethal concentration of chemicals detection of corrosion-related microbes interpretation since it is difficult to reaching biofilms cells, which can in the system, i.e. the paradox of there associate taxonomic groups to specific result in enhanced resistance of the being possible microbial contamination corrosion outcomes. We intend to microorganisms to chemical treatments. but no MIC activity remains (Personal overcome this limitation by conducting communication) [16]. Likewise, isolation of microorganisms from A NEW ERA OF MIC DIAGNOSIS microorganisms other than the ones corroded equipment and field samples AND ASSESSMENT typically associated with corrosion to sequence their genomes and further It has always been difficult to establish have also the potential to cause MIC. characterize their metabolic and MIC a direct association between biological An additional limitation of cultivation capabilities. There is a clear and present activity and corrosion failure as MIC techniques is that stress factors such as need for coordination and integration of does not produce a unique type of the presence of chemical treatments can such data into a national MIC database. corrosion. For this reason, MIC is often lead to slow growth rates and a viable- misdiagnosed. MIC investigations are but-not-culturable (VBNC) state or other Other challenges involved in NGS complex and involve interdisciplinary forms of dormancy in microorganisms analysis include bias due to the many science that includes microbiology, which will prevent them from being processing steps in the generations of chemistry, metallurgy, and corrosion. detected via MPN method despite being NGS data (including DNA extraction) No single analysis can be used to present in the system [58]. and the susceptibility of samples to diagnose MIC or to measure the risk microbial composition changes during of MIC in a particular system. Typical Molecular microbiological methods sampling, preservation and shipping analyses to investigate MIC include have received increasing recognition prior to analysis in the laboratory [65]. microscopic examination and chemical as essential identification tools for MIC Generating reliable and accurate data and microbiological characterization assessment to overcome the limitations via NGS represents a top priority in the of corrosion products and fluids [55]. of cultivation techniques [59, 60]. current environment that urges close Importantly, microbiological data A review of molecular microbiology communication and collaboration should be gathered from more than techniques applied to MIC assessment between sampling personnel, analysts one method, and interpretation of is provided elsewhere [61]. In particular, and project leaders. results requires the integration of this next generation sequencing (NGS) information within the context of allows accessing genetic blueprints Whereas DNA provides information of field conditions. In the case of failure that provides insight into microbial all the microbial populations present analysis, it is important to demonstrate communities and their potential in a sample, including those dead and a spatial association of the biological activities including identification of inactive, gene expression and functional components with the observed microbes that have not been cultured analysis based on RNA examinations corrosion, i.e. a biofilm or bacteria and studied before [62]. These methods provide a more accurate assessment of should be present on the metal surface are rapid and have become easily the active microbial component in a at the point where corrosion took accessible and cost-efficient providing system. Previously, NGS of microbial place. An association between the type microbial diversity information from 16S rRNA has been used to assess the of corrosion products formed and the complex environmental systems diversity and composition of the active predominant active bacteria present in [63, 64]. We can now reveal which component of microbial communities the corroded area should also exist. organisms are present, what they are [66, 67]. Novel metatranscriptomics doing and how they are doing it. analysis in combination with An accurate diagnosis of MIC metagenomics is a revolutionary involves strict sampling, storage and Nevertheless, novel techniques come approach that will provide MIC preservation regimes, comprehensive with new limitations and challenges. scientists with better ways to laboratory analysis and a good Environmental samples may contain understand complex MIC mechanisms understanding of the operation in excess of 10,000 microbial species, and the microbial artillery involved in process, material performance and giving genetic techniques the potential such process. This approach allows the corrosion mechanisms. For decades to produce large amounts of sequence identification of the expressed genes MIC assessment has relied on the use data, which is complex to process in microbial communities and the of standard culture medium and most and to discern which are the key construction of metabolic profiles in a probable number (MPN), or serial organisms that are giving rise to the particular system including community dilution technique, for detection and series of corrosion issues. These massive metabolic shifts in response to enumeration of corrosion-related data sets can only be processed using environmental cues [68]. For instance, microbes in a particular system [56]. advanced bioinformatics that require corrosion studies can be designed to However, standard culture techniques skilled and trained analysists and vast assess community gene expression can only detect a minor fraction (0.1 to computational power. With novel, fluctuations associated with corrosion 10%) of the microorganisms in nature uncultured and numerous species being events such as pitting initiation, which hence this method underestimates frequently detected in field samples, the can potentially lead to elucidation of microbial diversity and provides an potential complexity of the problem novel genes and mechanisms involved inaccurate assessment of the microbial increases. These new species can in MIC. In this fashion, we will be able community in a system if used alone potentially reveal new MIC mechanisms, to elucidate how biofilms on metals [57]. It is also known that the mere and complex antagonistic or synergistic develop, adapt and respond. The isolation or identification of MIC related relationships among populations in a application of this novel, sophisticated microorganisms (typically categorized sample which are difficult to interpret in molecular techniques in combination based on their capability to produce the context of corrosion risk. Reporting with localized electrochemical and corrosive metabolites) from a particular hundreds of species in a sample surface methods will become the basis environment is not sufficient to creates uncertainty and meaningless of leading-edge MIC multidisciplinary p.92 CORROSION & MATERIALS REVIEW PAPER

research, which will ultimately result of such improved prediction tool will cells are capable of resisting common in superior technologies for managing be based on field and experimental antimicrobial regimes effective against MIC. However, there is a need to observations from studying the planktonic bacteria [74]. develop improved protocols to process relationship between the functional DNA and RNA from difficult samples activities of microbial communities and Recently, we have studied the effect of such as iron concretions, field deposits, their association with corrosion. a chemical biocide, one of the most corrosion products and corrosion widely used treatments to control coupons with limited biomass and with MIC MITIGATION: FROM TOXIC microbial activity in industrial systems, excessive metallic ions and polymerase BIOCIDES TO ECO-FRIENDLY against oilfield biofilms developed chain reaction (PCR) inhibitors that APPROACHES on steel under laboratory conditions interfere with nucleic acid extraction There are available treatments to (unpublished data). The biocide, and downstream analysis [69]. There is restrict the activity of microbes and evaluated at the manufacturer's a big limitation regarding RNA analysis reduce the risk of MIC. The selection recommended concentration, exhibited because of the greater susceptibility of of a specific anti-microbial treatment 99.9% killing efficacy against planktonic RNA molecules to degrade and change. will depend on the particulars of the (free-living) cells but was only able to In particular, messenger RNA (mRNA), system and what is permitted to use inactivate half of the population when the type of RNA used to determine in the field environment situation. the same cells were present in the form which genes are expressed in a cell Typical treatments to prevent of biofilms (attached to the surface). at different stages of development MIC include chemical biocides, The additional presence of deposits and under different environmental chlorination, UV-irradiation, filtration, (acid-cleaned sand) on the surface, conditions, undergoes an exponential mechanical cleaning (e.g. pigging and resulted in an even more resilient decay with an average of 1.3 min at flushing), velocity control, cathodic biofilm which was negligibly affected 37 °C [70]. There is also a requirement protection, protective coatings with by the same biocide treatment, i.e. only for high quality and quantity of RNA anti-bacterial and corrosion inhibitor 1-log reduction in the total number of in a sample to be able to apply RNA compounds and combinations of biofilm cells was observed. Deposits and methods to identify functional and these treatments [72]. In order to set biofilms (embedded in EPS) resulted gene expression profiles of the entire up a good microbial control program, in a very robust bio-deposit that acted microbial community. If RNA analysis is the chemistry, microbiology and as a strong physicochemical barrier applied to MIC diagnosis or monitoring dynamics of the system need to be that prevented diffusion of chemical purposes, strict protocols need to be considered. Any selected control compounds through the biofilms. It followed by sampling personnel and treatment should not affect the has been demonstrated that bacteria the analysis needs to be performed performance of the material under in biofilms can resist antimicrobial by skilled analysts with advanced routine operations, i.e. it should not compounds at concentrations up to knowledge of molecular biology and be corrosive and should not interfere 1000 times higher than those active bioinformatics. with production. In the case of potable on the same bacteria in the planktonic water systems treatments that present state. This supports the practise of Importantly, microbiological data toxicity concerns and health hazards implementing regular physical cleaning should always be correlated to cannot be applied. Monitoring of the methods such as pigging, if economical key performance indicators for a treatment efficiency using corrosion and practical, to remove the biofilms given system. That means, MIC risk coupons, probes and sensors, as well from the steel surface. However, this is assessment should always integrate as inspection and review programs not always possible. In this area, we are results from both corrosion and that include recurrent chemical and currently studying the role of bacteria microbiological analysis. There could microbiological analysis over the life in under-deposit corrosion and the be occasions where high-risk microbial of the asset are crucial to prevent performance of corrosion inhibitors species are detected in a system; MIC‐induced failures [73]. It is also in the presence of microbial cells and however the system does not experience important to identify specific locations deposits. It is widely recognized that significant corrosion [71]. It is likely in the system where risks exist and corrosion inhibitors can adsorb onto that such species remain inactive if where particular remediation strategies deposits reducing inhibitor availability, control strategies and field operations should be implemented. Establishing thus leading to inadequate inhibition are not conducive of microbial activity. a multidisciplinary team involving beneath the deposits [75]. In the In this case, MIC is not considered industry (facilities operation) and presence of bacteria and deposits, an immediate concern. However, academics with the right expertise in complex organic deposits can be formed care must be taken to ensure field oilfield microbiology, MIC, chemistry, on metal surfaces and interact with an operations remain under control and corrosion and materials is the ultimate inibitor in a way that their inhibition the microbiology of the system is not approach for MIC management. perfomance is significanlty reduced. altered. This will allow cost savings on unnecessary excessive dosages The main challenges in protecting In recent years, environmental concerns of chemical treatments. However, equipment from microbial corrosion have led to legislation that encourages this requires adequate industry and lies in how fast bacteria in fluids can the replacement of toxic chemical academic engagement to make sure form biofilms on the metal surface since compounds with environmentally- the system is properly monitored. biofilms afford protection from external friendly antimicrobial treatments that We are currently developing a MIC harsh conditions and create a more are less harmful to the environment. prediction tool in collaboration with sustainable environment for survival Consequently, there is a growing industry that will integrate corrosion and proliferation. The great difficulty interest in the application of green and microbiological data, considering with eradicating microbial corrosion approaches to control biofouling not only high-risk species but also caused by biofilm-forming bacteria has and MIC. Most of these methods are incorporating RNA-based microbial received increasing attention over the being investigated and implemented functional activity information for the last decades. It is recognized that once within the water industry, e.g. first time. Data for the development established on a metal surface biofilm wastewater treatment and potable water

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applications. However, these approaches bacteria but also on sessile bacteria to advanced experimental and diagnostic may also be suitable for microbial obtain information on the minimum methods in combination with high control within the oil and gas industry. biofilm eradiation concentration performance bioinformatics tools Microorganisms suspended in water (M.B.E.C) [84, 85]. It is also important to MIC research would substantially for instance, may be controlled by the to understand that even though improve our understanding of MIC application of ultraviolet light (UV), some of these methods can inactivate processes. Notably, future MIC studies which under certain conditions can be biofilms monitoring of such efficiency should focus on mixed-species, or very effective. We studied the effect of over time is very important to ensure community level biofilms, since most filtration along with (UV-C) irradiation MIC control is achieved in the long natural biofilms exist as very diverse to mitigate MIC [21]. This approach term. As discussed in previous sessions, communities. This is one of the most showed promise in the mitigation of microorganisms can develop diverse problematic issues involved in MIC biofilm growth-associated effects on survival strategies when exposed to research which has been traditionally corrosion resistant alloys. However, the enduring stress conditions, which conducted using planktonic microbes suitability of applying this method, can result in mitigation approaches or single-species biofilms that do not particularly for long-term preservation, being only able to inactivate microbial represent the more complex naturally needs further investigation. cells but inefficient at killing them. developed multi-species biofilms. The risk of this lies in the possibility Therefore, studies on the effect of Further promising and exciting non- that biofilm cells recover their antimicrobial substances on the biofilm toxic approaches to mitigate biofilm activity very quickly in the event of phenotype are urgently needed. The formation include the application treatment failure. In this context, future holds much promise for this of antimicrobial surface coatings it is also important to bear in mind area of research, where MIC researchers and recalcitrant surfaces [76, 77], that in difficult conditions, some will increasingly be able to resolve, membrane technologies to decrease microorganisms enter a dormant state at the molecular and biochemical the nutrient content in the water [78], in which they induce their metabolic levels, interspecies relationships and a range of enzymatic and biochemical functions to slow and eventually mechanisms of cell-cell and cell- technologies [79, 80] and ultrasonic shut down completely. Then when metal interactions and how these treatment [81]. Other natural the surrounding environmental processes are associated with corrosion compounds including herbal extracts, conditions improve, they resume and its inhibition. In addition, MIC natural antimicrobial peptides and normal metabolism. In this fashion, experiments should be designed to use molecules of microbial origin have been we have recently studied thermophilic the field environment, or the closest studied. In particular, the potential biofilms on carbon steel and the effect field simulating environment, to grow of developing new molecules based of exposing them to cold temperatures and study biofilms and MIC. The on plant derivatives as inexpensive, (10°C). This temperature is considered outcome of these studies will greatly eco-friendly alternatives to toxic an aggressive environment for enhance our understanding of the chemicals for the control of MIC thermophiles, potentially resulting in ecological factors that drive community should be assessed. We have recently lysis of biofilm cells. Results showed function in industrial systems and move reported garlic extract (GAE) as an that even though thermophilic us towards developing appropriate effective corrosion inhibitor which also biofilms remain inactive (or exhibited management solutions. exhibits antimicrobial activity [82]. extremely low metabolic activity) GAE effectively reduced viable cells during exposure to low temperature, MIC control has traditionally relied in multispecies biofilms developed on and even some biofilms cells died on the application of toxic chemical steels and was demonstrated to mitigate upon exposure to cold conditions, compounds incorporated into coatings MIC on both carbon steel and stainless a significant portion of the biofilm or biocide products. Even though such steels in conditions closely simulating cells remained live and were able to chemical treatments have shown broad hypersaline oilfield environments. re-establish activity upon exposure to efficiency, environmental concerns Corrosion inhibition and anti-microbial the original thermophilic conditions. regarding their application represent properties of the GAE were attributed Similar results were obtained by an ongoing challenge to industry, to organo-sulphur compounds present Weaver et al. [86] after evaluating particularly with the advent of offshore in GAE. Bacterial cooperative traits the effect of desiccation on microbial developments and floating processing such as cell-cell signalling used to activity. Microorganisms were exposed facilities where operations may involve coordinate biofilm dispersal are also to long desiccation periods during disposal of chemical treatments to the being explored for the control of which microbial activity was not ocean. Therefore, increased attention is biofilm-related problems [83]. However, detected. However, microorganisms being paid to develop and implement the effectiveness and applicability of were able to recover activity once novel, eco-friendly approaches to these approaches to industrial systems they were in contact with water even mitigate MIC. These approaches remains uncertain, mainly because after four months of desiccation include membrane technologies to of the unrealistic conditions used for highlighting the capabilities of remove critical nutrients, application their laboratory validation. In addition, microorganisms to withstand exposure of natural corrosion and antimicrobial many of these approaches fulfil their to harsh environments. inhibitors such as plant materials as purpose as antifouling methods but well as peptides and molecules of remain inacceptable economically CONCLUDING REMARKS microbial origin. Special attention and environmentally. The use of these The oil & gas, marine and defence should be paid to identifying new technologies for the preservation of industries are a major component of antibacterial molecules that specifically oil and gas equipment has yet to be the Australian economy. It is therefore target the biofilm state, i.e. anti- investigated. essential to respond to the scientific biofilm substances. In this fashion, challenge of MIC by developing and any alternative methods proposed for Regardless of the technology applying new knowledge to every aspect the control MIC should be screened developed, it is important to assess of our exploration and production on sessile bacteria (biofilms) to achieve their efficiency not only on planktonic processes. The application of relevant values on the minimum p.94 CORROSION & MATERIALS REVIEW PAPER

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