Résumé : Offshore wind assets have reached multi-GW scale and additional
capacity is being installed and developed. To achieve demanding
cost of energy targets, awarded by competitive auctions,
the operation and maintenance (O&M) of these assets has to become
increasingly efficient, whilst ensuring compliance and effectiveness.
Existing offshore wind farm assets generate a significant
amount of inhomogeneous data related to O&M processes.
These data contain rich information about the condition of the
assets, which is rarely fully utilized by the operators and service
providers. Academic and industrial research and development
efforts have led to a suite of tools trying to apply sensor data
and build machine learning models to diagnose, trend and predict
component failures. This study presents a decision support
framework incorporating a range of different supervised and unsupervised
learning algorithms. The aim is to provide guidance
for asset owners on how to select the most relevant datasets, apply
and choose the different machine learning algorithms and
how to integrate the data stream with daily maintenance procedures.
The presented methodology is tested on a real case example
of an offshore wind turbine gearbox replacement at Teesside
offshore wind farm. The study uses kNN and SVM algorithms to
detect the fault using SCADA data and an autoregressive model
for the CMS data. The implementation of all the algorithms has
resulting in an accuracy higher than 94%. The results of this
paper will be of interest to offshore wind farm developers and operators to streamline and optimize their O&M planning activities
for their assets and reduce the associated costs.
Résumé : DiVA portal is a finding tool for research publications and student theses written at the following 47 universities and research institutions.
Résumé : In the transition from a fossil fuel driven economy to renewable solutions, the activities in offshore wind energy are growing. Operation and maintenance costs of offshore wind turbines are high, therefore alternative methods should be developed to reduce these costs. The replacement of heavy components, like a gearbox or a generator, is a frequently occurring operation that can be improved.<br/>Currently the replacement of these components is performed by a jack-up crane vessel which has two downsides: (1) long mobilization time and (2) high operational costs. The development of systems that can replace heavy components can contribute to reduce the maintenance costs of offshore wind turbines.<br/><br/>Therefore in the first part of this thesis, developments and techniques were investigated which can do so. It was observed that different types of solutions are already available for onshore maintenance purposes like the crane developed by Liftra and the Gamesa flexifit. Furthermore new concepts are being developed by the wind turbine manufacturer Vestas and Anson, a Chinese crane builder. These developments are addressing the problem of reducing the maintenance costs, but still two important downsides are present: (1) insufficient lifting capacity for gearbox replacement and (2) most systems are designed to be used on specific turbines. <br/><br/>The current developments and available techniques were studied to generate concepts that can address these shortcomings. This resulted in a promising solution where a relatively small crane is installed on the wind turbine tower from a floating vessel. A great advantage over currently used method is that no specialised maintenance vessel is required for a gearbox replacement and thereby costs and time can be saved. <br/><br/>This crane is attached to the tower structure by use of a clamping mechanism and is kept in position by generating frictional force. To generate this force, hydraulic cylinders are pressing the pads (contact surfaces of the clamp) against the tower structure. For the applicability of this concept it is of major importance that the structural integrity of the tower is maintained, while sufficient frictional force is generated to avoid the crane from slipping down during lifting operations. Therefore, in the second part of this thesis a feasibility study is done on the application of this clamping mechanism on wind turbine towers. By use of finite element modelling a workable contact surface configuration of this clamping mechanism was found. <br/><br/>The following four variables were studied: (1) elasticity of the contact layer, (2) number of pads used, (3) width and (4) height of the pads. The latter three relate to the contact surface area and the elasticity of the contact layer influences the distribution of the forces from the clamp to the tower structure. <br/><br/>Investigating these variables, it was concluded that; the proposed solution should have a contact layer where the elasticity modulus is higher than 1200 Mpa. By adding more pads, the loading capacity increases. However, it also results in a more complex structure and therefore it is advised to reduce the number of pads and instead widen them. Considering this trade off, a four pad configuration is selected to determine the required width and height of the pad. For this set-up it is advised to use a pad width of eighty degrees and pad height of three meter to meet the requirement of replacing the gearbox, the heaviest component of the wind turbine powertrain. <br/> <br/>Furthermore, to assure this clamping mechanism works on towers of different dimensions (i.e. diameter and wall thickness combinations), the loading capacity was determined for a variety of tower dimensions. By doing so, insights are gathered on the application of this clamping mechanism on different turbines. To make the data useful for further application, tables are included which indicate the loading capacity for investigated wind turbine towers. <br/>
Résumé : To more effectively extract the vast wind energy in marine areas, offshore wind turbines have been built with slender tower and large rotor, which makes them vulnerable to the external vibration sources such as aerodynamic, sea wave and/or seismic excitations. Previous studies on the dynamic responses of offshore wind turbines normally assumed they are in the parked condition and the blades are considered as a lumped mass located at the top of the tower. In reality, the geometrical characteristics and rotational velocity of the blades can directly influence the aerodynamic loads acting on the blades. Moreover, the centrifugal stiffness generated by the rotating blades can increase the stiffness and natural frequencies of the blades, which in turn can further affect the structural responses. In this study, a detailed three-dimensional (3D) numerical model is developed to investigate the dynamic responses of the NREL 5 MW wind turbine subjected to the aerodynamic and sea wave loadings. The blades are explicitly modelled and the operating condition of the wind turbine is considered. Multiple tuned mass dampers (MTMDs) are proposed to mitigate the excessive vibrations of the tower and blades in the out-of-plane direction. The advantages of using MTMDs are discussed.
Résumé : As floating wind turbine technology matures and wind farms are considered at larger scales in deeper waters, moorings may take a larger share of the costs. In response, floating wind farms could be designed such that the moorings are shared between turbines, using interconnecting mooring lines between adjacent floating offshore wind turbine platforms and also possibly connecting multiple mooring lines to the same anchor. This may reduce the total length of mooring line, the wind farm footprint, and the number of anchors; worthwhile advantages if not overcome by increases in mooring strength requirements. A design algorithm is presented for preliminary sizing of shared mooring systems for pilot-scale floating offshore wind farms. Quasi-static modelling is used to analyze the performance of shared-mooring systems produced by the algorithm. The model accounts for steady wind thrust forces and nonlinear mooring line reactions. A four-turbine floating wind farm is designed and analyzed with three alternative shared-mooring configurations and four water depths. Results are presented in terms of platform displacements, mooring tensions, and cost, providing an initial comparison of shared mooring options and their potential for cost savings over conventional individually-moored configurations.
Résumé : ABSTRACT Currently, the development of renewable energy has become a trend with the increasing demand for energy. Wind energy, as a renewable source of energy, is also getting more attention. Increasing effort is devoted to developing floating offsh
Résumé : Coupled aero-hydro-servo-elastic simulation tools play an important role in the design of offshore floating wind turbines. For rational design of the system, accuracy of the numerical tool is important in predicting the system responses. While the load cases where the wind and wave are aligned are sometimes the largest contributor to the design, evaluation of the load cases where the wind and wave are a misaligned condition are also required in the design codes. In this study, first a series of water tank tests is performed for a 1/50 scale semisubmersible floater and results for irregular wave tests with aligned and misaligned wind were analysed. Then, an in-house numerical tool, NK-UTWind is used to model the full scale system. Results showed that measured motions in surge, heave, and pitch are similar for the aligned and misaligned cases, and these were well reproduced by the calculation. Measured sway and roll motion in the misaligned case were characterized by the components in wave frequencies, which calculation expressed well for the roll motion while underestimated several peaks for the sway motion. The characteristics of frequency distribution of measured tower-base shear force in the x direction and moment around the y axis forces were similar for both aligned and misaligned cases, which agreed approximately well with the calculation. The peak frequencies of the measured tower-base shear force in the y direction were similar for aligned and misaligned cases, and the measured tower-base moment around the x axis force included additional components in wave frequencies for the misaligned case. Calculations reproduced the natural frequency component for the tower-base moment around the x axis in both cases, while the accuracy was low for shear force in y direction.
Résumé : Continuously variable speed wind turbines (CVSWTs) without using fixed speed gearboxes continue being as viable options for modern wind power industry. CVSWTs have an infinite number of transmission ratios in contrast to specific gear ratios of a standard wind turbine. This transmission flexibility allows the generator to maintain a constant speed regardless of highly turbulent wind speeds. The development of CVSWTs has made great progress in recent years due to the high demand for renewable energy sources. Therefore, this paper serves to provide a systematic review of the CVSWTs including mechanical, hydraulic and hydro-mechanical type CVSWTs. The operating principles, design topologies and basic characteristics are described and analyzed. The comparisons and new trends of the CVSWTs are also discussed, which indicate the feasibility of applying CVSWTs in wind power industry and the high potential of using hydro-viscous transmission in megawatt CVSWTs.
Résumé : The durability and reliability of tidal energy systems can be compromised by the harsh environments that the tidal stream turbines need to withstand. These loadings will increase substantially if the turbines are deployed in exposed sites where high magnitude waves will affect the turbine in combination with fast tidal currents. The loadings affecting the turbines can be modelled using various numerical or analytical methods; each of them have their own advantages and disadvantages. To understand the limitations arising with the use of numerical solutions, the outcomes can be verified with practical work. In this paper, a Blade Element Momentum coupled with wave solutions is used to predict the performance of a scaled turbine in a flume and a tow tank. The analytical and experimental work is analysed for combinations of flow speeds of 0.5 and 1.0 m/s, wave heights of 0.2 and 0.4 and wave periods of 1.5 and 1.7 s. It was found that good agreement between the model and the experimental work was observed when comparing the data sets at high flow conditions. However, even if the average values were similar, the model tend to under predict the maximum and minimum values obtained in the experiments. When looking at the results of low flow velocities, the agreement between the average and time series was poorer.
Résumé : For purpose of studying the influence of wave on the wind turbines, the causes of aerodynamic load fluctuation and the aerodynamic torque ripple of hydrodynamic frequency is analysed in the mechanism by using the wave model. According to the formation mechanism, the existence of the ripples is verified on GH Bladed platform. To reduce the ripples caused by wind shear, tower shadow and waves of offshore wind turbine, a pitch control strategy is presented in this paper. Firstly, the integral gain of the top tower vibration acceleration signal is combined with the reference pitch angle value to reduce the uniform pitch. Then designing a low-pass filter to filter out the 3P output power ripple of the wind turbine, and converted into adjustment of individual pitch angles of three blades according to rotor azimuth, and superimposed with the changed uniform pitch angle at last. Simulation results indicate that the designed pitch control strategy can not only alleviate the 1P aerodynamic load ripple, but also suppress the aerodynamic torque and output power ripples at 3P and hydrodynamic frequency. The proposed pitch control strategy can reduce wind turbine fatigue loads and improve the output power quality.
Résumé : DTU Wind Energy continues the experimental investigation of the wind turbine blades to assess innovative designs of long and slender blades. This paper presents an experimental structural dynamics identification and structural model validation of the 14.3m long research blade. Unique feature of the blades is that its internal layup design has been highly optimized w.r.t. stretching the rotor and substantial mass reduction at the same time. As the result, the blade is more flexible than the traditional one. The results of the modal tests following analyses were performed: (i) Uncertainty Quantification of the experimental modal parameters for the blades, (ii) non-linearity assessment, (iii) numerical model correlation – frequencies and mode shapes of the experimental model comparison with those from Finite Element (FE). Finally, the outlook for the future experimental blade research activity is outlined.
Résumé : The paper investigates the linear-elastic and nonlinear stiffnesses of a suction caisson used as monopod foundation for an Offshore Wind-Turbine (OWT). Starting from caissons at low working stresses, in which case the linear elastic theory provides an adequate engineering model for soil, analytical expressions for the elastic stiffness matrix of a flexible skirted foundation are proposed and validated. To account for the nonlinear foundation response, the paper proposes a simplified equivalent linear iterative approach where the effective foundation stiffness is expressed in terms of deformation amplitude. To this end, utilizing results from a 3D finite element parametric study, non-dimensional charts have been produced for caissons ranging from perfectly rigid to flexible with variable embedment ratios. To deal with uncertainty on the conditions at the soil-skirt interface, three idealized interface scenarios – “fully-bonded”, “tensionless”, “frictionless” – are implemented. Reduced values of foundation stiffness are computed for a frictionless contact. On the contrary, the impact of a “tensionless” interface, whilst trivial in elastic problems, is intensified with progressing soil inelasticity resulting in severely reduced stiffnesses and capacities. Moreover, with increasing relative skirt flexibility, the elastic stiffnesses of deep suction caissons tend to recede substantially, but the rate of stiffness degradation is fairly attenuated.
Résumé : One of the most important technical problems among the different challenges of offshore wind farms is to obtain a suitable turbine model for a particular site. Designers of offshore plants can take into account several aspects, such as wind class of the selected site, environment requirements, height restrictions, turbinés price, power capacity, energy production and wake effect/electrical losses. This paper clarifies the concept of power density applied to offshore turbines and shows the correlation between the power density and the selection of the site. Different commercial offshore turbines are analyzed for three different class wind sites. Recently commissioned offshore wind farms and offshore wind turbines are included in the study. The results show greater energy production for low power density turbines and this parameter is more reliable than the capacity factor to select the turbines that match with the site.
Résumé : This paper presents the modeling and the simulation of a hybrid marine current-hydrogen power generation system. The marine current power generation system consists of a fixed pitch marine current turbine directly coupled to a permanent magnet synchronous generator (PMSG). The generator is connected to a DC link capacitor via a controlled rectifier, which has two modes of operation. The first mode is the maximum power point tracking (MPPT) by using torque control when the generator runs below the rated speed. The second mode is the power limitation (at the rated value) when the generator runs above the nominal speed. The generated power is transferred from the DC-link to the load via an inverter to run the system in a stand-alone operation mode. An energy storage system must cover the difference between the generation and the consumption for this scheme. The hydrogen, compared with the different energy storage systems, exhibits characteristics more applicable for marine current power generation systems. When the generated power is higher than the load requirements, a Megawatt-scale proton exchange membrane (PEM) electrolyzer consumes the surplus energy for hydrogen generation. The generated hydrogen is stored in tanks to feed a PEM fuel cell system to generate power in case of shortage. Based on this topology and operation procedure, the overall system is called an active power generation system. The MW scale PEM electrolyzer model is presented based on state of the art and the literature of different scales PEM electrolyzer system modeling.
Résumé : Offshore marine renewable energy installations (MREI) introduce structure into the marine environment and can locally exclude destructive, bottom tra
Résumé : The wind power industry has experienced rapid growth over the past few decades, but the operation and maintenance costs have become huge challenges to achieve better economic returns and enhance the market competitiveness. In this paper, an opportunistic maintenance strategy for wind turbines considering stochastic weather conditions and spare parts management is proposed. The Markov chain model is adopted to generate wind speed time series and obtain the maintenance wait time owing to weather restrictions. The opportunistic maintenance threshold is a dynamic value related to the wind speed to reduce power generation losses. Moreover, the (s, S) inventory policy, with the reorder stock level s and maximum stock level S , is employed. Numerical examples are used to illustrate the economic advantages of the proposed strategy. Compared with a static opportunistic maintenance strategy and a strategy not considering opportunistic maintenance, the life cycle operation and maintenance cost for the proposed dynamic opportunistic maintenance strategy shows a decline of 10.927% and 18.304%, respectively. The optimal maintenance and inventory strategy is obtained with the decision variables of opportunistic maintenance reliability threshold and reorder stock level, and the effects of various applied parameters are described.
Résumé : Offshore wind turbines and their foundations experience loading from varying directions, yet understanding of the effect of changes in the direction of applied cyclic loading on foundation response remains limited. This study investigates the behaviour of a suction caisson foundation in sand over clay under various types of multidirectional cyclic loading. The findings are significant: although the caisson rotation (or tilt) is affected by changes in load direction, the caisson rotation is less than that in a unidirectional test with the same cyclic load magnitude and symmetry, meaning that a unidirectional test may serve as a conservative estimate of caisson rotation for multidirectional loading. This contrasts with previous findings for monopiles in sand, where prediction of the accumulated displacement based on unidirectional cyclic loading was substantially un-conservative for multidirectional loading. Changes in unloading stiffness due to changes in load direction are slight, varying by an amount that is no greater than the change measured over the course of a unidirectional test. Foundation stiffness and ultimate capacity following multidirectional cyclic loading are largely unaffected, unlike unidirectional cyclic loading, where consolidation of the clay layer improves both the stiffness and capacity.
Résumé : The Ocean has provided a new way in the quest for renewable energy. One potential source of energy is the tidal current. The objective of this paper is to carry out a review of systems for the recovery of tidal energy and its conversion into electricity which represents one of the most interesting renewable energy resources precisely Marines Current Turbine MCT. In the first part of this work, a comprehensive description of marine current is performed, in which the physics of tide, the marine current prediction and the tidal Current Kinetic energy extraction models are given. In the second part, a detailed assessment of various state of art MCT systems (horizontal axis, vertical axis, and oscillating Hydroplane Systems), along with their classification and qualitative comparison, is presented. In the last part of this work, an outline of direct-drive electrical generator topologies is sketched in order to identify suitable generator concepts for direct-drive MCT. The comparison of different generator systems in literature is discussed with the criteria based on the energy yield, cost, weight and maintenance problem.
Résumé : The current study systematically analyzes the impact of solidity (σ) and number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines (VAWTs). Solidity varies within the wide range of 0.09–0.36. A large number of operational parameters, i.e., tip speed ratio (λ), Reynolds number (Re), turbulence intensity and reduced frequency (K) are investigated to provide a deeper insight into the impact of σ and n on the dynamic loads on blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that the turbine optimal tip speed ratio (λopt) is invariant to a newly-introduced parameter ‘σλ3’, regardless of the turbine geometrical and operational characteristics. In addition, a new correlation is derived to estimate λopt as a function of σ, which can also be employed to predict the optimal σ for a turbine with a given λ. It is also found that: (i) for constant-speed urban VAWTs, which due to the low mean wind speed in the urban environment, frequently operate at moderate to high λ, a relatively-low σ is optimal; (ii) an optimal VAWT is a moderately-high-solidity variable-speed rotor maintaining a relatively-low λ, where due to the large blade chord length the resulting Re and K are favorably high; (iii) within the turbine optimal operational range, turbine power coefficient (CP) is almost independent of n. The present findings support the optimal aerodynamic design of small-to large-scale VAWTs.
Résumé : Early in an offshore wind farm development, the project developer needs to determine which type of offshore wind foundations are suitable to its site. At that stage, only a limited amount of site-specific data is available. However this conceptual study is critical to estimate a preliminary cost target and assess the techno-economic viability of an offshore wind farm at that location.In this context, INNOSEA has developed a user-friendly preliminary design tool for foundations (monopile, jacket and gravity-based foundation) named PREDIN. This numerical software tool is able to perform semi-automatically: the conceptual design, the planning of the installation phase, the cost estimate of fabrication, transport and installation of foundations and substations for sound decision-making. The software features a lean graphical user interface which provides an integrated vision: from foundation design to planning and key cost drivers. PREDIN is adapted for uninitiated users, by providing guidelines and standards values, and for specialist users by enabling a total control of the process.The foundation design methodology is based on a two-step approach: General conception, mainly based on verification of the dynamics of the structure; Local sizing: PREDIN interfaces with a standard structural software from the offshore industry: ANSYS Structural. This two-step approach therefore makes it possible to be able to rapidly iterate on the foundation design.The transport and installation module methodology relies on 4 different functions: Weather Data extraction, Marine Spread selection, Operabilities and T&I planning.The cost estimate methodology is based on a Monte Carlo probabilistic approach, integrating the projects uncertainties in order to generate the probability distribution of the final cost.This study highlights the capabilities of PREDIN software to efficiently deliver a preliminary design and EPCI cost of offshore wind foundations for project developers, relying on extensive metocean, turbine, foundation and cost databases.
Résumé : The global development of the offshore renewable energy sector has been driven by extensive investment and research in the utilization of offshore renewable energies, mainly at the regional level. However, for mid to long-term marine energy development planning, a comprehensive assessment of the global potential for the exploitation of the main offshore resources is required. This work developed and implemented an innovative methodological approach to identify potential zones for wind and wave energy exploitation at the global level, using long-term data series with fine spatial and temporal resolution. The proposed methodology was based on a five-step approach comprised of: (i) a resource assessment, to identify the zones with favorable conditions for energy exploitation; (ii) a structural survivability assessment, to identify feasible areas which would likely ensure the integrity and durability of the wind and wave devices; (iii) a logistics assessment, to evaluate the possibility of carrying out installation, operations, and maintenance activities; (iv) an assessment of the distance to consumer centers, to estimate the feasibility of transmission to the main urban areas; and (v) an estimate of the extractable power of the identified potential zones. For wind power, the United Kingdom (with 1470 TWh/month using a 10-MW turbine) and the United States (1079 TWh/month) were the countries with the highest estimated energy output of the identified potential zones. For wave energy, Brazil and New Zealand presented good opportunities for the development of the wave energy industry, with an estimated extractable power of 372 TWh/month and 286 TWh/month, respectively. The unique preliminary global analysis presented in this work provides guidelines to assist in the development of wave and offshore wind industries, in addition to supporting the management of marine spaces. Moreover, the methodologies can be replicated for other marine activities.
Résumé : An experimental marine current power station has been deployed in So¨derfors, Sweden. It comprises a vertical axis turbine directly connected to a permanent magnet synchronous generator rated at 7.5 kW. The generator is controlled by a Back-To-Back 2L-3L Cascaded H-Bridge full scale bi-directional Power Converter located on shore. This paper presents the ﬁrst test results of the power converter, including grid connection. The startup of the turbine, power extraction and initial active power injection to the grid, at 50 % of rated power, operated as predicted by laboratory experiments and simulations. After 40 seconds of grid connection the safety system disconnect the grid converter due to high currents injected to the grid. The problem is mostly likely associated with the current controller in the dq0 frame. Further tuning of the PI regulators and the potential addition of an anti-windup could mitigate the control issue.
Résumé : This paper addresses a fundamental study of a floating type shrouded wind turbine on the design, mathematical model and motion analysis. Several novel concepts are introduced to the system for cost reduction: a revolute hinge is applied between the tower and the nacelle to maintain the orientation of the nacelle even in a large tower inclination, a swashplate mechanism with cyclic control is employed for blade pitch regulation to improve the system controllability, a novel mooring system with a slewing bearing is utilized to build the passive yawing system, and an advanced spar-type floater is used to obtain high restoring performance with a short spar. Firstly, the design aspects of the main components of the system are given. Then, the numerical model including the structural model, hydrodynamic/aerodynamic model, and the control system is presented. The static and dynamic responses under both the operational situation and survival conditions are finally studied. The paper illustrates the probability of the shrouded wind turbine on floating offshore application, and can provide critical information for the optimization design in next stage.
Résumé : This paper presents the development of an open-source object-oriented program, named OpenMOOR, for static and dynamic analyses of mooring systems in ocean renewable energy applications, including offshore wind turbines and wave energy devices. The program is developed for cross-platform applications. It can be used as a standalone software or a dynamic linking library for developing coupled models of the moored structures/devices. A finite difference model of mooring cables is adopted for solving the motion of a single cable which can deal with the hydrodynamic effect, cable bending/torsional stiffness and nonlinear strain-tension relationship. Parallel computing is implemented for efficient analysis of a mooring system consisting of multiple cables, as common in the practice. OpenMOOR has then applied to analyse a single mooring cable under forced harmonic motions at the top end. The cable responses are found to agree well with the experimental data in the literature, which validates OpenMOOR.
Résumé : Offshore wind farm operations and maintenance costs currently total 6 m€/year, or 25–28% of total costs. For wave and tidal energy converters, this cost is projected to be twice that of offshore wind, but has high levels of uncertainty. As the wave and tidal energy industries mature, decreasing O&M costs through reliability-based design optimization is critical to increasing feasibility and competitiveness with other energy technologies. In this paper, we will synthesize existing information on reliability-based optimization in systems analogous to offshore renewable energy systems. We will conclude by highlighting opportunities for future work in this field.
Résumé : Cost of energy is one of the main reasons why wind power generation hasn’t been able to compete with fossil fuels. However, in the past decade wind energy field has made quite a big leap in making this way of energy generation cheaper and more competitive. As a result, the price of onshore wind energy has already reached the price of fossil fuel power generation. The progress has been made with offshore wind turbine technology as well, however ever increasing energy demand has forced industry to push the limits even further. Attempts are being made to build wind farms further offshore where wind resource is much higher and where more space is available. This on the other side requires new technological development and finding new ways to decrease the cost of energy.<br/>This thesis is a part of a larger project (DOT - Delft Offshore Turbine) which represents one such attempt to make the offshore wind energy much more competitive by combining wind turbine and hydraulic turbine technology. DOT company works on the development of the fluid power transmission in offshore wind turbines, using seawater as medium. The idea is that every wind turbine drives a hydraulic pump. Each turbine thus creates a flow of water under high pressure which is converted to electricity using a Pelton turbine generator. The main objective of this thesis is to identify and try to overcome challenges in design of Pelton turbines for high water pressures, variable flow rates and<br/>seawater conditions. In order to accomplish this objective, theoretical, experimental and numerical approach was used.<br/>Theoretical approach was used to develop a tool for initial Pelton turbine design. Small program was developed in Python programming language which enabled faster and easier turbine dimensioning for any operating conditions based on standard Pelton turbine design procedure. Next, test rig was designed and built as part of the experimental investigation. Test was divided in two phases. Phase I was meant to show the influence of the flow rate, pressure and pressure fluctuations on the development and quality of the water jet. Pressure is measured at the inlet of the injector and flow visualization of the jet was conducted with the high speed camera. Experimental set-up for Phase<br/>II was concluded while performing experimentation has been left out for a future research project. As last step, CFD simulation of the designed model was conducted using Ansys CFX commercial solver and results were presented and discussed.<br/>Although, all three approaches are conducted independently each of them contributed to answering the research questions and giving a better insight in problem definition. Furthermore it helped identifying the differences between the standard Pelton turbine design and the DOT concept. The research brings<br/>us one step closer to making DOT concept a viable sustainable energy solution for the future.
Résumé : Biofouling is the unwanted attachment of organisms and microorganisms to a submerged surface. It is a natural phenomenon that results in negative impacts on man-made industries such as the marine industry, food industry, water treatment among others. Studies have shown that the application of surface topography with varied geometries and sizes have the potential to prevent biofouling. This research aims to assess microtopographies of varied geometries and shape in relation to biofouling control. The size and dimensions of the topographies were kept the same at 150 µm. This research is computational where simulations of flow in three-dimensional (3D) models were performed with ANSYS Fluent, a Computational Fluid Dynamics (CFD) software. With the aid of CFD, simulations of fluid flow in 3D models that consist of surface topographies with varied geometries and defined boundary conditions were conducted. The topographies investigated include pillars, octagonals, cross shaped grooves and square grooves. Hydrodynamic variations of interest that were analysed upon completion of the simulations include wall shear stress and velocity. Analysis of simulations show that the presence of topographies disrupt uniform flow and creates hydrodynamic fluctuations that discourage biofouling settlement. Simulations indicate that the pillars topography would likely have the best antifouling potential because it is the least likely to result in the formation of many vortices and also because shear stresses at the peaks of this topography are the highest among the four investigated topographies.
Résumé : The growing awareness of climate change and the recognised need to secure energy production has been a driving force behind the expansion of the offshore wind industry across the world. Benefits from offshore wind farms (OWFs) may extend further than low CO2 energy production. Wind turbine substructures introduce hard surfaces that are rapidly colonised by epibenthic marine organisms, altering biomass and biodiversity within the local ecosystem. Biodiversity plays a critical role in supporting ecosystem processes and functions that maintain ecosystem services. As offshore wind development continues to grow and modify marine habitats, changes in biodiversity could affect the provision of ecosystem services. In this context, this review sets out to capture the current understanding of epibenthic biodiversity change following the installation of OWFs and attempt to link these changes in biodiversity with marine ecosystem services through the associated processes and functions.
Résumé : In nature, microbes tend to form synergistic biofilms on a wide range of materials using extracellular polymeric substances to embed sessile cells. Problematic biofilms provide environments conducive to the occurrence of microbiologically influenced corrosion (MIC) in many industries. MIC includes corrosion caused by microbes as well as corrosion by another pre-existing corrosion agent that is accelerated by microbes. There are several distinct types of MIC mechanisms associated with different microbial species and metabolism types. Biofilms employ different defense mechanisms to protect themselves from environmental hazards. This makes sessile cells in biofilms much more resistant to treatment than planktonic cells. Biofilms are often treated with biocides together with physical scrubbing. Various approaches have been developed to boost biocide efficacy. New emerging technologies such as bacterial phages, quorum sensing inhibitors, and special chemicals to enhance biocides have been proposed in recent years. This review evaluates these different treatment methods and various techniques used to assess biocide treatment outcome including microbiology, molecular biology, corrosion testing and electrochemical methods.
Résumé : Corrosion and clogging are hidden hazards in various engineered systems dealing with water as storage or heat transfer medium.
The related efficiency and serviceability losses may entail expensive remedial measures and costs up to the range of millions (e).
Especially modern low-exergy installations are affected. They may suffer from oxygen ingress through capillary tubes, higher
microbial activity due to moderate temperatures and increased vulnerability of complex components to particulate corrosion products.
This field study presents in-situ investigations of chemical and microbial water quality and corrosion in pipes of different
non-residential buildings. It identifies processes and recommends measures to prevent corrosion. Causes of corrosion and clogging
were found to be i.a. related to operational errors.
Résumé : Anaerobic, aerobic, and facultative bacteria are all present in corrosive environments. However, as previous studies to address corrosion in the marine environment have largely focused on anaerobic bacteria, limited attention has been paid to the composition and function of aerobic and facultative bacteria in this process. For analysis in this study, ten samples were collected from rust layers on steel plates that had been immersed in seawater for different periods (i.e., six months and eight years) at Sanya and Xiamen, China. The cultivable aerobic bacterial community structure as well as the number of sulfate-reducing bacteria (SRB) were analyzed in both cases, while the proportion of facultative SRB among the isolated aerobic bacteria in each sample was also evaluated using a novel approach. Bacterial abundance results show that the proportions are related to sea location and immersion time; abundances of culturable aerobic bacteria (CAB) and SRB from Sanya were greater in most corrosion samples than those from Xiamen, and abundances of both bacterial groups were greater in samples immersed for six months than for eight years. A total of 213 isolates were obtained from all samples in terms of CAB community composition, and a phylogenetic analysis revealed that the taxa comprised four phyla and 31 genera. Bacterial species composition is related to marine location; the results show that Firmicutes and Proteobacteria were the dominant phyla, accounting for 98.13% of the total, while Bacillus and Vibrio were the dominant genera, accounting for 53.06% of the total. An additional six facultative SRB strains were also screened from the isolates obtained and were found to encompass the genus Vibrio (four strains), Staphylococcus (one strain), and Photobacterium (one strain). It is noteworthy that mentions of Photobacterium species have so far been absent from the literature, both in terms of its membership of the SRB group and its relationship to corrosion.
Résumé : In the present investigation, Polyalthia longifolia plant extract (PLAE) was used as biocide to control corrosion in the presence of sulfate-reducing bacteria (SRB). Transmission electron microscopy showed the damage of SRB outer cell membrane which lead to cell destruction and disturbed membrane permeability. The scanning electron microscopy also confirmed the cell shrinkage due to green biocide, and energy-dispersive Fourier transform infra-red spectroscopy indicated the decrease in sulfide concentration in the presence of biocide. Potentiodynamic polarization of mild steel showed the lower in corrosion rate due to the decrease in cathodic reduction kinetics of SRB in the presence of biocide PLAE. The gravimetric mass loss also showed corrosion rate dropped from 0.064 millimeter per year (mm/year) to 0.013 mm/year with and without biocide. The present study showed that P. longifolia extract could be a novel biocide against the growth of the SRB to control corrosion in oil and gas industries.
Résumé : Oil reservoir souring and associated materials integrity challenges are of great concern to the petroleum industry. The bioengineering strategy of nitrate injection has proven successful for controlling souring in some cases, but recent reports indicate increased corrosion in nitrate-treated produced water re-injection facilities. Sulfide-oxidizing nitrate-reducing bacteria (soNRB) have been suggested to be the cause of such corrosion. Using the model oil field soNRB Sulfurimonas sp. strain CVO we conducted a detailed analysis of soNRB-induced corrosion at initial nitrate to sulfide (N/S) ratios relevant to oil field operations. The activity of strain CVO caused severe corrosion rates of up to 0.27 mm y−1 and up to 60 µm deep pitting within only nine days. The highest corrosion during growth of strain CVO was associated with production of zero-valent sulfur during sulfide oxidation, and accumulation of nitrite, when initial N/S ratios were high. Abiotic corrosion tests with individual metabolites confirmed biogenic zero-valent sulfur and nitrite as the main causes of corrosion under the experimental conditions. Mackinawite (FeS) deposited on carbon steel surfaces accelerated abiotic reduction of both sulfur and nitrite, exacerbating corrosion. Based on these results a conceptual model for nitrate-mediated corrosion by soNRB is proposed.
IMPORTANCE Ambiguous reports of corrosion problems associated with the injection of nitrate for souring control necessitate a deeper understanding of this frequently applied bioengineering strategy. Sulfide-oxidizing nitrate-reducing bacteria have been proposed as key culprits, despite the underlying microbial corrosion mechanisms remaining insufficiently understood. This study provides a comprehensive characterization of how individual metabolic intermediates of the microbial nitrogen and sulfur cycles can impact the integrity of carbon steel infrastructure. The results help explain the, at times, dramatic increases in corrosion rates observed during nitrate injection in field and laboratory trials and point to strategies for reducing adverse integrity-related side effects of nitrate-based souring mitigation.
Résumé : Various anaerobic environments exist in the Earth’s ecosystem, which can produce a great deal of organic matter each year. In anaerobic habitats, bacterial sulfate reduction may occur due to the action of sulfate-reducing bacteria. As a result, hydrogen sulfide (H2S) is formed. This paper focuses on sulfatereducing bacteria and the revision of the activity characteristics of these bacteria in the reducing environment. It discusses the metabolic process of sulfate-reducing bacteria using sulphate and organosulfur compounds as sulfur source, the mechanism of bacterial sulfate reduction and H2S formation mechanism. There are two main ways of H2S formation in sulfate-reducing bacteria, the production of metabolic sulphate and the metabolic organo-sulfur compounds (mainly cysteine). The paper, combined with the activity characteristics of sulfate-reducing bacteria and the pathway of metabolic formation of H2S, also discusses the circulation of sulfur in the environmental system of the Earth due to the action of sulfate-reducing bacteria, concerning the redox zone division in submarine sedimentary strata and landfills, the biogas formation phase of sulfate-reducing bacteria metabolism in sedimentary formations, and the bacterial sulfate reduction action in salt lakes (seawater) systems. Moreover, the production of hydrogen sulfide and the formation model of dolomite are both presented here. The findings support that sulfate-reducing bacteria are the most important biological source of H2S production. The study of the physiological characteristics of sulfate-reducing bacteria and the formation mechanism of H2S due to bacterial sulfate reduction can provide useful reference for the exploration of the laws of sulfur geochemical cycle and the rules of the ecological environment, which is essential for the protection of the natural environment and the restoration of polluted ecosystems, and can also provide a useful reference for the control of aerobic microorganisms.
Résumé : A method for determining the susceptibility of a material to corrosion includes generating, via an inlet in a monitoring device, a laminar flow of material comprising a plurality of microorganisms. The plurality of microorganisms comprises at least one microorganism type. The method also includes forming, inside the monitoring device, in response to the laminar flow, a biofilm comprising at least one microorganism type. In addition, the method includes applying a voltage to the first and second electrodes during the laminar flow.
Résumé : Electron mediators are redox active compounds capable of mediating electron transfer from a donor to acceptor. In microbial systems, electron mediators play a key role in extracellular electron transfer processes to assist the bacteria to thrive under unusual environmental conditions. Electron mediators are known to facilitate electron transfer from the bacterial cells to their electron acceptors which are insoluble (e.g. Fe3+, Mn4+) or toxic (e.g. oxygen for anaerobes). Interspecies electron transfer between different microbial species is also known to be driven by electron mediators. In this case, one species uses the oxidized mediator as electron acceptor and reduces it while the other species uses the reduced mediator as electron donor. The involvement of electron mediators in these electron transfer processes has led to extensive investigation to elucidate their contribution in microbial ecosystems.
The aim of this thesis is to investigate the role of microbially produced electron mediators in facilitating microorganisms to thrive in selected environments that are of human concern. In this study, a novel electrochemical tool was developed that allows characterization of the electron mediators more effectively than the conventional techniques. The proposed method offered much better sensitivity and resolution compared to the conventional technique in detecting electron mediators.
Conventional electrochemical studies use the three-electrode electrochemical cell which is equipped with only one controllable working electrode (WE). The other two electrodes serve as counter and reference electrodes. The traditional one-WE setup is based on the oxidation or reduction of the target molecule at different time interval as for example used in cyclic voltammetry. Having only one WE does not allow mimicking redox condition of the microbial systems where oxidation and reduction occur simultaneously.
In order to test for the presence of redox active mediators, a new apparatus and technique was developed that consists of two independently controllable WEs which enable the generation of redox gradient between the WEs to allow simultaneous oxidation and reduction of the target redox active mediator. By using this redox gradient generating property, a new method was developed that characterizes electron mediators within a thin layer microscale (250 μm) system without the need of a bulk solution and associated mass transfer.
Electrochemical properties of electron mediators were characterized by stepwise shifting a “voltage window” (maintaining 0.05 V potential difference between two WEs) within a range of potentials (between –1 V and +0.5 V vs. Ag/AgCl) and monitoring the establishment of steady equilibrium current in both WEs. The resulting current difference between two WEs was recorded for each voltage step of the “voltage window”. Results indicated that this technique enabled identification (by the distinct peak locations at the potential scale) and quantification (by the peak of current) of individual mediators as well as several mediators in an aqueous mixture. This technique enabled the precise determination of the mid-potential of hexacyanoferrate (HCF), riboflavin (RF) and two mediators from the pyocyanin-producing P. aeruginosa (WACC 91) culture. The capability of Twin-WE approach in detecting unknown electron mediators from a microbial culture confirms its suitability in studying microbial extracellular electron transfer (EET) processes.
The Twin-WE electrochemical cell was used to investigate the role of the bacterial mediator PYO in electron transfer processes accomplished by its producer P. aeruginosa (PA), a high impact bacterium from human health perspective. Pyocyanin (PYO) is a redox active compound present in the biofilm of P. aeruginosa and believed to mediate an electron transfer from PA cells to oxygen for assisting PA to respire under oxygen limited condition. In contrast to widely held belief, this study shows that reduced PYO v
(RedPYO) is not readily oxidized by oxygen unless catalyzed by living cells. The results are supportive to a scenario in which PYO can extract electrons from other living cells by oxidizing their NADH. The resulting RedPYO can be utilized as electron donor for oxygen or nitrate respiring PA cells. While this PYO mediated electron transfer resembles syntrophic interspecies electron transfer, it suggests, in this case, the existence of a not yet described form of energy parasitism. The discovery of this parasitic life style puts a new perspective on the role of PYO in biofilms, its natural soil environment and host infections.
The existence of a similar electron extracting mechanism of PYO was also investigated in microbially influenced corrosion (MIC). MIC is a complex bio-electrochemical process where the exposure of the metal to microorganisms and their metabolic products causes dissolution of metal ions. Corrosion of steel occurs due to the existence of simultaneous anodic and cathodic reactions on the steel surface. At the cathodic site, steel loses electrons which consequently causes the dissolution of ferrous ions at the anodic site. Under aerobic condition, steel loses electrons from the cathodic site to oxygen. MIC has been described as bacteria rely on mediators to use electrons from the cathode under anaerobic conditions. The potential role of bacterial mediators to influence corrosion in the presence of oxygen has not been investigated yet.
The capability of PYO to extract electrons from living cells was translated to electron extraction from corroding steel. Results showed that PYO can more efficiently harness electrons from the steel than oxygen alone. The reduced PYO thus generated (RedPYO) subsequently can transfer electrons to oxygen. The corrosion rate as determined by the release of dissolved iron was increased by two-fold when carbon steel was exposed to PYO compared to the exposure to a PYO free electrolyte under oxygen saturated environment. This increase in corrosion rate can be explained by the existence of a PYO mediated electron flow from the steel to the oxygen which accelerated the cathodic half reaction. PA cells can also benefit from this electron flow to generate cellular energy (ATP) using RedPYO as the electron donor for oxidative phosphorylation. Hence, PA and PYO containing biofilms could be described as catalyst of the cathodic reaction of corroding iron. To our knowledge, this is the first study to demonstrate the role of a biological electron mediator in influencing aerobic corrosion by cathodic stimulation.
Overall, this thesis has contributed towards improving the understanding of microbial mediators, their detection and possible role in microbial consortia and in interaction of microbes with reducing surfaces such as steel constructions.
Résumé : This study presents the corrosion and microbiologically influenced corrosion processes of steels in the highly mineralized geothermal water of Polish Lowland. The geothermal sediments were studied using various techniques to confirm the presence of sulphate-reducing bacteria, to determine the chemical composition of deposits and to describe their morphology. On-site and laboratory electrochemical tests were carried out to determine the corrosion rate of selected steels and the influence of sulphate-reducing bacteria to the electrochemical processes.
Résumé : Corrosion degradation was observed in a nuclear power plant spent fuel cooling system. A systematic and comprehensive investigation program was developed to reveal the root cause of the degradation. Series of corrosion tests, mechanical, microstructural and microbiological investigations were carried out. Also, simulations of the operating conditions and welding parameters were performed. Based on the results, the major contributors to the degradation process were identified and a possible degradation mechanism was proposed.
Résumé : Steel corrosion is a global problem in marine engineering. Numerous inhibitory treatments have been applied to mitigate the degradation of metallic materials; however, they typically have a high cost and are not environmental-friendly. Here we present a novel and “green” approach for the protection of steel by a marine bacterium Pseudoalteromonas lipolytica. This approach protects steel from corrosion in seawater via the formation of a biofilm followed by the formation of an organic-inorganic hybrid film. The hybrid film is composed of multiple layers of calcite and bacterial extracellular polymeric substances, exhibiting high and stable barrier protection efficiency and further providing in situ self-healing activity. The process involving the key transition from biofilm to biomineralized film is essential for its lasting anti-corrosion activity, which overcomes the instability of biofilm protection on corrosion. Therefore, this study introduces a new perspective and an option for anticorrosion control in marine environments.
Résumé : In this work, microbiologically influenced corrosion (MIC) of an X52 pipeline steel in thin layers of simulated soil solution in the presence of sulfate-reducing bacteria (SRB) under a disbonded polyethylene coating was investigated. The steel MIC depends heavily on the thickness of the solution layer. In the present testing system, there exists a critical solution layer thickness, i.e., 150 μm, where a maximum corrosion rate is reached. Pipeline corrosion in thin layers of solution containing SRB trapped under disbonded coating is resulted from the synergism of MIC and the film formation on the steel surface.
Résumé : Purpose
The purpose of this study is to investigate microbial influenced corrosion of steel because of iron oxidizing bacteria (IOB).
Carbon steel was selected for this study. Winogradsky media was used for isolation of IOB and as test solution for corrosion measurements. Electrochemical tests and immersion test were conducted to estimate the corrosion rate and extent of pitting. The corroded surface was analysed by SEM and corrosion products formed over the metal surface were identified by XRD and Fourier transformed infrared. Biofilm formed over the corroded metal was analysed by UV-visible spectroscopy for its extracellular polymeric substances (EPS) constituents.
Presence of IOB in Winogradsky medium enhances corrosion. Uniform and localized corrosion increases with increased bacterial concentration and EPS constituents of the biofilm. Iron sulphite formation as one of the corrosion products has been suggested to be responsible for increased corrosion attack in the inoculated media in comparison to control media where corrosion product observed is iron hydrogen phosphate which is protective in nature.
This work correlates increased corrosion of steel in the presence of bacteria with the nature of corrosion products formed over it in case of IOB. Formation of corrosion products is governed by various electrochemical reactions; hence, inhibition of such reactions may lead to reduce or stop the formation of such products which enhances corrosion and thereby may reduce the extent of microbial induced corrosion
Résumé : At present, most Microbiologically Influenced Corrosion (MIC) models used in the petroleum industry are risk based, and predict the likelihood of MIC. It is imperative that the industry adopts mechanistic models to accurately quantify MIC in pipes/facilities. This paper summarizes the findings of a literature review of mechanistic MIC models available in the public domain. The results indicated that most of the models reviewed consider Sulphate Reducing Bacteria (SRB) as the main players in MIC, and very few models consider biofilm formation and transport phenomena. Furthermore, no models were found to accurately correlate sessile and planktonic bacteria.
Résumé : The influence of aerobic halophilic archaea Natronorubrum tibetense on the corrosion of Q235 carbon steel was investigated. In immersion tests, more serious corrosion was observed in the N. tibetense-inoculated medium than in the sterile medium. Compared with the uniform corrosion morphologies in the sterile medium, severe localized corrosion occurred in the inoculated medium. After 14 days of immersion, the presence of N. tibetense caused a weight loss of 0.051 g/cm2 of the steel, which was about two times larger than that in sterile medium (0.026 g/cm2). The starved N. tibetense exhibited more aggressive MIC against the steel when organic sources were deficient.
Résumé : The large number of metallic systems developed for last few decades against both general uniform corrosion and localized corrosion. Among all microbiological induced corrosion (MIC) is attractive, multidisciplinary and complex in nature. Many chemical processing industries utilizes fresh water for fire service to nullify major/minor fire. One such fire water service line pipe attacked by micro-organisms leads to leakage which is industrially important from safety point of view. Also large numbers of leakage reported in similar fire water service of nearby food processing plant, paper & pulp plant, steel plant, electricity board etc...In present investigation one such industrial fire water service line failure analysis of carbon steel line pipe was analyzed to determine the cause of failure. The water sample subjected to various chemical and bacterial analyses. Turbidity, pH, calcium hardness, free chlorine, oxidation reduction potential, fungi, yeasts, sulphide reducing bacteria (SRB) and total bacteria (TB) were measured on water sample analysis. The corrosion rate was measured on steel samples and corrosion coupon measurements were installed in fire water for validating non flow assisted localized corrosion. The sulphide reducing bacteria (SRB) presents in fire water causes a localized micro biological corrosion attack of line pipe.
Résumé : This review evaluates the analytical methods used for detecting microbiologically influenced corrosion (MIC), which is an aggressive microbiota-facilitated degradation of engineering materials, and discusses their advantages and limitations. The challenges presented by the lack of a comprehensive mechanistic understanding on MIC detection, which include the need to use a combined array of morphological, chemical, electrochemical and biological characterization for MIC detection, are thoroughly discussed using multiple case studies from the literature. The paradigm shifts and research necessary for the early and real-time monitoring of MIC are presented.
Résumé : The influence of sulfate-reducing bacteria (SRB) on the corrosion of L245NS carbon steel was investigated in a medium containing H2S by various surface characterizations and electrochemical measurements. The addition of H2S will totally inhibit the planktonic SRB in the medium. However, the sessile SRB in the corrosion crust can survive under the protection of the biofilm. Pitting corrosion is found under the corrosion crust, which is caused by the sessile SRB. The pitting corrosion rate is 1.1 mm/a. Additionally, the corrosion rate increases with the corrosion time. The SRB influenced corrosion mechanism of the steel is discussed.
Résumé : One of the cause of corrosion is the attachment of bacteria or commonly called as bio-corrosion or Microbial Influenced Corrosion (MIC). This aim of the research was to determine effect of heat treatment process on the bio-corrosion rate of API 5L steel. The treatments were namely, without heat treatment as a control, and with the heat treatment (austempering process). The austenizing process was conducted before the austempering process. All specimens without and with the heat treatment were be used on bio-corrosion test. The bio-corrosion testing was conducted with immersion corrosion test method with artificial seawater salinity of 35‰. Three of species bacteria were be used, Escherichia coli, Pseudomonas fluorescens, and Thiobacillus ferrooxidans. The result showed the corrosion rate on API 5L steel without bacteria was 2.7558 mpy, but it reached 3.4273, 3.6062 and 3.7699 mpy after addition with E. coli, P. fluorescens, and T. ferrooxidans, respectively. It was indicating that bacteria can accelerate the corrosion rate. The highest bio-corrosion rate due to T. ferrooxidans without heat treatment process was 3.7699 mpy. Meanwhile, the bio-corrosion rate due to T. ferrooxidans with austempering process was 3.5046 mpy. It was indicating that heat treatment can decrease the bio-corrosion rate.
Résumé : Cu corrosion by Desulfovibrio vulgaris, an example of sulfate reducing bacteria (SRB), was investigated. D. vulgaris was first pre-grown in full-strength ATCC 1249 medium with coupons for three days. Then, the medium was switched to fresh media with decreased levels of carbon source. Unlike microbiologically influenced corrosion (MIC) of carbon steel by D. vulgaris, carbon starvation reduced Cu corrosion during the additional seven days of incubation. Experimental data and a thermodynamic analysis indicated that Cu MIC by SRB was caused by secreted sulfide rather than by electron harvesting for energy production, unlikely in the carbon steel MIC by SRB.
Résumé : Herein, a schematic model was established to assess the combined effect of deposited CaCO3 and thermophilic sulfate-reducing bacteria (SRB), at high CO2 and low O2 dissolution levels on the corrosion behavior and growth of corrosion scale on X65 pipeline carbon steel. Field emission scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, confocal laser scanning microscopy, open circuit potential, and electrochemical impedance spectroscopy were used to characterize the corrosion pattern of water injection pipe. The results showed that a synergistic effect exists between CaCO3 and thermophilic SRB, both uniform and localized corrosion of CaCO3-coated X65 steel were promoted when inoculated with SRB. The corrosion process was comprised of three stages depending on the metabolism of SRB.
Résumé : Here, a heterogeneous Bacillus cereus (B. cereus) biofilm on the surface of 316 L stainless steel (SS) was observed. With electrochemical measurement and surface analysis, it was found that B. cereus biofilm could inhibit SS pitting corrosion, attributing to the blocking effect of bacterial biofilm on extracellular electron transfer (EET). Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) results also showed that B. cereus biofilm clearly impeded the EET. The proposed mechanism for the decreased corrosion rates of SS involves the interactions of extracellular polymeric substance (EPS) with SS and biofilm formation blocking electron transfer, preventing the passive layer from destroying. After biofilm formation following initial attachment of cells and EPS, electron transfer between SS and the cathodic depolarizer (oxygen) was hindered.
Résumé : Mature sulfate reducing archaeon (Archaeoglobus fulgidus) biofilm at 80 °C was found more corrosive against C1018 carbon steel under organic carbon starvation. After 3-day pre-growth in enriched artificial seawater medium (EASW), C1018 coupons with biofilms were placed in fresh EASW with reduced carbon source levels for an additional 7 days of incubation. Coupon weight losses were 0.9 mg/cm2, 2.0 mg/cm2 and 1.4 mg/cm2 for this subsequent 7-day starvation period, corresponding to 0%, 90% and 100% carbon source reductions, respectively. Electrochemical tests corroborated the weight loss data, providing evidence for the utilization of elemental iron as electron donor through extracellular electron transfer.
Résumé : This chapter focuses on the various approaches to combat biofouling/biocorrosion. First, we present the vastness of the problem, along with known mechanisms of biofouling. This is followed by numerous molecular approaches (such as a surface assembled monolayer) to affect a biocidal substrate surface. Various measurement techniques, such as fluorescence labeling followed by microscopy AFM, XPS, SEM, etc.), along with standard electrochemical corrosion rate techniques to monitor surface microbiological fouling and its control are discussed with multiple case studies.
Résumé : Microbiologically influenced corrosion (MIC) is a big threat to the strength and safety of many metallic materials used in different environments throughout the world. The metabolites and bioactivity of the microorganisms cause severe deterioration on the metals. In this study, MIC of pure Ti was studied in the presence of a highly corrosive aerobic marine bacterium Pseudomonas aeruginosa. The results obtained from electrochemical test showed that Ti was corrosion resistant in the abiotic culture medium after 14 d, while the increased corrosion current density (icorr) obtained from polarization curves and the decreased charge transfer resistance (Rct) from electrochemical impedance spectroscopy (EIS) indicated the accelerated corrosion of Ti caused by Pseudomonas aeruginosa biofilm. For further confirmation of the above results, the surface of Ti was investigated using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). According to the XPS results, TiO2 was formed in both abiotic and biotic conditions, while unstable oxide Ti2O3 was detected in the presence of Pseudomonas aeruginosa, leading to the defects in the passive film and localized corrosion. Pitting corrosion was investigated with the help of CLSM, and the largest pit depth found on Ti surface immersed in Pseudomonas aeruginosa was 1.2 μm. Ti was not immune to MIC caused by Pseudomonas aeruginosa.
Résumé : Microbiologically influenced corrosion (MIC) is a major concern in a wide range of industries, with claims that it contributes 20% of the total annual corrosion cost. The focus of this present work is to review critically the most recent proposals for MIC mechanisms, with particular emphasis on whether or not these make sense in terms of their electrochemistry. It is determined that, despite the long history of investigating MIC, we are still a long way from really understanding its fundamental mechanisms, especially in relation to non-sulphate reducing bacterial (SRB) anaerobes. Nevertheless, we do know that both the cathodic polarization theory and direct electron transfer from the metal into the cell are incorrect. Electrically conducting pili also do not appear to play a role in direct electron transfer, although these could still play a role in aiding the mass transport of redox mediators. However, it is not clear if the microorganisms are just altering the local chemistry or if they are participating directly in the electrochemical corrosion process, albeit via the generation of redox mediators. The review finishes with suggestions on what needs to be done to further our understanding of MIC.
Résumé : Microbiology Australia, bringing Microbiologists together
Résumé : The worst nightmare of the oil and gas industry which must not be taken lightly is the issue of corrosion which affects the pipes used for transportation of oil and gas. Corrosion problems need to be properly understood in order to prescribe the necessary kind of treatment that will ensure a long life span for the
pipeline. This paper gives a comprehensive review of corrosion problems in API 5L steel pipeline and the ways to mitigate the corrosion problems. Proper control and prevention of corrosion in API 5L steel would ensure long life span of the pipe, uninterrupted flow of products, reduction in shutdown time and generate more revenue for the industry. Oil and gas materials last longer when both inhibitors and protective coatings are used together or when protective
coating is used together with cathodic protection
Résumé : Environmental concerns have been changing the way of looking for solutions to problems. The hydrosphere, together with its biosphere, has been feeling the impact of many pollutants, used for instance in the marine industry for economic reasons or lack of knowledge of their effects. In particular biocides, applied as coatings in paints, are released into the waters becoming toxic and persistent extending their action to an area far beyond the initial coated surface they should protect. In order to minimize these side effects, two biocides, Irgarol (I) and Econea (E), were covalently attached to polyurethane (PU) and foul-release silicone based (PDMS) marine paints through an isocyanate linker. Their antifouling bioactivity was better in PDMS coatings, both for single (Econea) and combined biocides (E/I ratio = 1.5) with contents lower than 0.6 wt%. The treated samples remained almost clean after more than one year immersion in the Portuguese shore of the Atlantic Ocean, and after about 24 weeks under the tropical conditions of Singapore (Fouling rate < 1%). Complementary biofilm adhesion susceptibility tests against Pseudoalteromonas tunicata D2 showed adhesion reduction higher than 90% for PU formulations containing single biocides and close to 100% for PDMS with combined biocides. The eco-toxicity assessment evidenced a low environmental impact, in accordance with the European standards. In addition, shipping field trial tests showed the best antifouling performance for the Econea-based PDMS formulations (E = 0.6 wt%), which remained clean for about nine months in open seawaters, proving the efficacy of this non-release strategy, when applied under dynamic conditions.
Résumé : Biofouling on artificial and biotic solid substrata was studied in several locations in the Baltic Sea brackish water (Gulf of Gdansk) during a three-year period with contact angle wettability, confocal microscopy and photoacoustic spectroscopy techniques. As a reference, the trophic state of water body was determined from chemical analyses according to the following parameters: pH, dissolved O2, phosphate, nitrite, nitrate, ammonium etc. concentrations and further correlated to the determined biofilm characterizing parameters by means of Spearman’s rank correlation procedure. Biofilm adhesive surface properties (surface free energy, work of adhesion etc.) were obtained with the contact angle hysteresis (CAH) approach using an automatic captive bubble solid surface wettability sensor assigned for in-situ, on-line and quasi-continuous measurements of permanently submerged samples (Pogorzelski et al., 2013, Pogorzelski and Szczepańska, 2014). Structural and morphological biofilm features (biovolume, substratum coverage, area to volume ratio, spatial spreading, mean thickness and roughness) were determined from confocal reflection microscopy (COCRM) data. Photosynthetic properties (photosynthetic energy storage (ES), photoacoustic amplitude and phase spectra) of biofilm communities exhibited a seasonal variability as indicated by a novel closed-cell type photoacoustic spectroscopy (PAS) system. That allowed mathematical modeling of a marine biofilm under steady state, in particular the specific growth rates μi, and the conditioning or induction times λi to be derived from simultaneous multitechnique signals. A set of the established biofilm structural and physical parameters could be modern water body trophic state indexes.
Résumé : Bioinspired superhydrophobic and oil-infused surfaces have been recognized as interesting and promising materials for a wide range of applications correlated with water environment, such as corrosion and biofouling inhibition. Which material is the better choice still waits to reveal. In this study, taking stainless steel as the substrate, superhydrophobic and oil-infused surface based on Cu(OH)2 matrix with prickly chestnut husk morphology is respectively obtained via successive steps. During the preparation of superhydrophobic surface, firstly, discrete Cu particles are electrodeposited onto stainless steel. After that, oxidation of the as-deposited Cu particles leads to the prickly Cu(OH)2 following a dissolution-crystallization mechanism. Under a mild condition, dodecanethiol vapor modifies prickly matrix to achieve superhydrophobicity by anchoring the long-chain organic moiety onto Cu(OH)2 surface. Since superhydrophobic matrix is intrinsically superoleophilic, oil-infused surface is finally constructed onto stainless steel. Taking typical marine fouling organisms including sulfate-reducing bacteria (SRB) and diatoms as the representatives, oil-infused surface can steadily prevent the biofouling on stainless steel, showing the better performance than superhydrophobic surface for biofouling inhibition. Using epoxy resin as the artificial fouling agent, the pulling force to remove the glued solid on oil infused surface is much lower than that on bare stainless steel, illustrating oil layer acting as the separation cushion between fouling agent and underneath substrate.
Résumé : Biofilm represents a non-uniform distribution of flexible microorganisms over a surface with variable density and height, it can be modified and displaced due to the flow. Therefore, the modelling of the flow and the assessment of resistance for surfaces covered with biofilm are problematic. Presently, there is no generally accepted method for the evaluation of the effects of a given biofilm on the resistance. Within this paper, roughness function models for surfaces covered with diatomaceous biofilm are established utilizing the experimental data presented in the literature. These roughness function models are then implemented within the wall function of the commercial software package STAR-CCM+. Numerical simulations of the rough plates in the turbulent channel flow are performed and the results are verified and validated against the experimentally obtained results presented in the literature. Utilizing the roughness length scale, proposed in the literature, and the proposed roughness function models, the effects of the biofilm on the resistance of any arbitrary body can be assessed using only roughness measurements. Finally, the increase in the frictional resistance and effective power due to the presence of the biofilm is determined using the validated roughness function models.
Résumé : The settlement and growth of marine organism increased sharply with the ships in a static environment, although the release rate of antibacterial agent decreased smoothly. Besides of a rapid release rate of the antibacterial agents, a destruction of films by sand and rocks restricted the long-term antibacterial efficiency of antifouling films on voyage. In this work, intelligent bacterial-triggered multilayer films are prepared via adding pH responsive nanocapsules to control releasing of antifouling agents during bacterial growth. Chitosan (CS) has a capability to change the swelling of capsules by amino protonation and deprotonation upon the change of the environmental pH. It is combined with capsaicin (CAP) to form nanocapsules for accomplishing a pH responsive behavior. The intelligent CAP@CS nanocapsules are added in polydopamine/sodium alginate (PDA/Alg)m PEM multilayer films to enable the (PDA/Alg-CAP@CS-n)m films with a pH-triggered antifouling agents (CAP) releasing performance. The results demonstrate that there are outstanding pH-triggered activities for the (PDA/Alg-CAP@CS-8)20 multilayer films. The released CAP concentration decreased by nearly 42% from pH 4 to pH 8.5. The bacteriostatic percentages of (PDA/Alg-CAP@CS-n)m against S. aureus and P. aeruginosa are 79% and 74%, respectively, after 60 days of immersion in pH 8.5 PBS buffer solutions. The amino deprotonation of CS in alkaline condition prevents the CAP release, resulting in an extended antibacterial performance. The electrostatic interaction between Alg and PDA in solutions leads to (PDA/Alg-CAP@CS-n)m films to exhibit the self-healing behaviors since the ions penetrate and free chins transfer in artificial seawater solutions after mechanical scratching.
Résumé : Biofouling as a global problem has made detrimental impact on many fields, especially for marine industry. Polydimethylsiloxane-based coatings are environment-friendly and exhibiting good fouling release performance in the marine coating application. However, their intrinsic low surface energy and high hydrophobic character lead to poor fouling resistance property and weak adhesion to substrate. In this work, we firstly fabricate self-adhesive PDMS-based amphiphilic cross-linked coatings with good anti-biofouling performance via synthesizing dopamine methacrylamide which then copolymerized with mercaptopropyl methylsiloxane- dimethysiloxane, poly (ethylene glycol) diacrylate under UV photo-cross-linking. The coating exhibits devisable heterogeneous nanoscale mosaic chemical surfaces caused by micro phase segregation, effectively resistance to nonspecific protein adsorption and marine fouling organism (P. tricornutum) attachment which are mainly ascribed to the unique surface topography and chemical heterogeneity. Moreover, the resulting coatings exhibit significantly improved adhesion to substrates, due to complex interfacial catechol chemistry reaction. This simple design provides a novel methodology for preparing an efficient and eco-friendly anti-biofouling PDMS-based amphiphilic coating.
Résumé : ABSTRACT The attachment of marine fouling organisms is harmful to any marine structure such as ship hulls, fishing nets, jetties and platforms. Marine antifouling coating is still the widely commercial used solution for marine antifouling in shippin
Résumé : Abstract. The introduction of artificial hard substrates in an area dominated by a sandy seabed increases habitat available to epifouling organisms. To investi
Résumé : In order to prevent the formation of a biofilm on the surface of materials in an aqueous environment various strategies could be developed. Notably following an electrochemical route it is possible to apply a potential which could lead to (i) oxidation of halide anions leading to the formation of biocidal molecules, (ii) O2 reduction leading to H2O2, (iii) water reduction leading to H2 bubbles or (iv) a low-intensity electric potential. Moreover an electrochemical method could be used to nano or microstructure the material surface or to deposit on the material a coating which would avoid protein adsorption or microorganism attachment and therefore the formation of a biofilm, this coating could be of an inorganic or an organic film.
Résumé : Biofilms and biofouling as important ecological phenomena have important implications affecting the development of invertebrates on surfaces in aquatic ecosystems, with economic impacts in several industries. Microbial biofilms on the surfaces of materials also affect the properties, longevity, and performance. The process of fouling and its prevention has been a major scientific challenge for many decades. Biofilms and fouling on surfaces affects the integrity of the substrutam materials from metals to inorganic and composites. Biodegradation and biodeterioration of materials are discussed here with information on relevant testing techniques tailored to material types. Biodeterioration by microorganisms is also discussed and prevention strategies offered to allow effective management of selective environmental conditions to ensure material integrity.
Résumé : Marine biotechnology is an emerging field in Brazil and includes the exploration of marine microbial products, aquaculture, omics, isolation of biologically active compounds, identification of biosynthetic gene clusters from symbiotic microorganisms, investigation of invertebrate diseases caused by potentially pathogenic marine microbes, and development of antifouling compounds. Furthermore, the field also encompasses description of new biological niches, current threats, preservation strategies as well as its biotechnological potential. Finally, it is important to depict some of the major approaches and tools being employed to such end. To address the challenges of marine biotechnology, the Brazilian government, through the Ministry of Science, Technology, Innovation, and Communication, has established the National Research Network in Marine Biotechnology (BiotecMar) (www.biotecmar.sage.coppe.ufrj.br). Its main objective is to harness marine biodiversity and develop the marine bioeconomy through innovative research.
Résumé : Habitat destruction is one of the main causes of the decline of biodiversity and of fishery resources in the marine environment. An artificial reef (AR) could be a tool for protecting or restoring these habitats and their declining biodiversity, and also help to enhance sustainable fisheries. The goal is to design non-polluting structures that best mimic the complexity of natural habitats in order to improve their service to the community. To date, the assessment of reef performance has been mostly focused on fish assemblages and species of ecological and/or socio-economic interest, and has disregarded the biofilm communities that determine the first level of an AR’s trophic network. In this work, we used biofilm formation to compare the quality of substrates used as building parts for an AR, in order to optimize an eco-friendly material that will be used to design a new generation of ARs produced by giant 3D printers. The structure of the photosynthetic communities has been identified using pigment biomarkers and their production of exudates has been analysed. These polymeric substances were quantified in terms of total sugar and protein concentrations. They were further analysed in terms of amino acid content. We found no significant differences between the micro-algae communities developed on the different substrates. These photosynthetic communities were mainly composed of diatoms, prasinophytes, haptophytes, and dinoflagellates. However, we showed that the material for ARs is crucial for biofilm development, especially with regard to its secretions of sugar. The choice of an appropriate substrate for AR construction is thus of particular importance since biofilm secretions determine the organic substrate on which sessile macro-organisms will settle.
Résumé : In this study, the antifouling (AF) performance of different carbon nanotubes (CNTs)-modified polydimethylsiloxane (PDMS) nanocomposites (PCs) was examined directly in the natural seawater, and further analyzed using the Multidimensional Scale Analyses (MDS) method. The early-adherent bacterial communities in the natural biofilms adhering to different PC surfaces were investigated using the single-stranded conformation polymorphism (SSCP) technique. The PCs demonstrated differences and reinforced AF properties in the field, and they were prone to clustering according to the discrepancies within different CNT fillers. Furthermore, most PC surfaces only demonstrated weak modulating effects on the biological colonization and successional process of the early bacterial communities in natural biofilms, indicating that the presence of the early colonized prokaryotic microbes would be one of the primary causes of colonization and deterioration of the PCs. C6 coating seems to be promising for marine AF applications, since it has a strong perturbation effect on pioneer prokaryotic colonization.
Résumé : Marine biofouling is an increasing problem from both economic and environmental points of view in terms of increased resistance, increased fuel consumption, increased GHG emissions and transportation of harmful non-indigenous species. Marine coatings are prevalently used to mitigate biofouling and smooth the surfaces of hulls. This paper aims at introducing new horizons and novel approaches in marine antifouling coatings. Firstly, marine biofouling and fouling prevention methods are briefly introduced. Afterwards, latest research in coating/fouling hydrodynamics is presented. Biomimetic approach to antifouling technology, bio-inspired antifouling strategies and the challenges in designing bio-inspired antifouling coatings are then discussed in detail. It is believed that, the on-going research in marine coatings will lead to an effective mitigation of marine biofouling while maintaining the harmony between man-made structures and marine life.
Résumé : The manufacture and preliminary testing of a drag-reducing riblet texture with fouling-control properties is presented. The commercial fouling-release product Intersleek® 1100SR was modified to manufacture riblet-textured coatings with an embossing technology. Hydrodynamic drag measurements in a Taylor–Couette set-up showed that the modified Intersleek® riblets reduced drag by up to 6% compared to a smooth surface. Barnacle settlement assays demonstrated that the riblets did not substantially reduce the ability of Intersleek® 1100SR to prevent fouling by cyprids of Balanus amphitrite. Diatom adhesion tests revealed significantly higher diatom attachment on the riblet surface compared to smooth Intersleek® 1100SR. However, after exposure to flow, the final cell density was similar to the smooth surface. Statically immersed panels in natural seawater showed an increase of biofilm cover due to the riblets. However, the release of semi-natural biofilms grown in a multi-species biofilm culturing reactor was largely unaffected by the presence of a riblet texture.
Résumé : A hydrosound marine anti-fouling system with a microcontroller monitoring and modifying, as desired, hydrosound pulse rate, output frequencies and volume level. This allows hydrosound pulse rate, output frequency and volume to be adjusted to levels determined to be effective with local marine growth. By adding a sensor to monitor hydrosound pulse rate, output frequencies and volume, an automatic testing process can be instituted at timed intervals and monitored by the microcontroller to confirm the hydrosound marine anti-fouling system is fully functioning.
Résumé : Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water, and how such structures change while exposing to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property while other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.
Résumé : An antifouling coating composition contains a silyl ester (co)polymer and medetomidine and is used to prevent the fouling of substrates by aquatic organisms and which can form antifouling coating films exhibiting outstanding antifouling properties over a long period and also has good storage stability. The antifouling coating composition includes a silyl ester (co)polymer (A) and medetomidine (B), the silyl ester (co)polymer (A) including structural units derived from a monomer (a) represented by the general formula (I): R1—CH═C(CH3)—COO—(SiR2R3O)n—SiR4R5R6, and structural units derived from an unsaturated monomer (b) copolymerizable with the monomer (a).
Résumé : One of the most important research areas in the marine industry is to investigate new and effective anti-biofouling technologies. In this study, high voltage pulse electric field (HPEF) mediated by carbon fiber (CF) composite coating was utilized to prevent the fouling of bacteria, microalgae and barnacle larvae in seawater. The plate count, 2, 3, 5-triphenyl-tetrazolium chloride (TTC) reduction assay and neutral red (NR) staining and larval motility detection showed that the inactivation rates were at the highest levels, which reached 99.1%, 99.9%, 99.7%, 98.7% and 85% respectively for Pseudomonas sp., Vibrio sp., iron bacteria, Navicula sp. and the second stage nauplii of Balanus reticulatus, under the HPEF with 19 kV pulse amplitude, 23.15 kHz frequency and 0.5 duty cycle. The field-emission scanning electron microscopy (FE-SEM) of Navicula sp. revealed that the HPEF brought about the cell lysis and the cell organic matter release on the coating, which could be the mechanism of the inactivation by the HPEF. Additionally, the FE-SEM and Raman spectroscopy indicated that the HPEF hardly damaged the coating.
Résumé : There is an important need for the development of new “environmentally-friendly” antifouling molecules to replace toxic chemicals actually used to fight against marine biofouling. Marine biomass is a promising source of non-toxic antifouling products such as natural antimicrobial peptides produced by marine organisms. The aim of this study was to demonstrate the efficiency of antimicrobial peptides extracted from snow crab (SCAMPs) to reduce the formation of marine biofilms on immerged mild steel surfaces. Five antimicrobial peptides were found in the snow crab hydrolysate fraction used in this study. SCAMPs were demonstrated to interact with natural organic matter (NOM) during the formation of the conditioning film and to limit the marine biofilm development in terms of viability and bacterial structure. Natural SCAMPs could be considered as a potential alternative and non-toxic product to reduce biofouling, and as a consequence microbial induced corrosion on immerged surfaces.
Résumé : Abstract Corrosion and biofouling control is an important consideration for offshore oil structures. Corrosion rates for steel exposed to seawater immersion and brine air can easily exceed 10 mils per year if left unprotected in the splash zone, whi
Résumé : There is a need for the development of antifouling materials to resist adsorption of biomacromolecules. Here we describe the preparation of a novel zwitterionic block copolymer with the potential to prevent or delay the formation of microbial biofilms. The block copolymer comprised a zwitterionic (hydrophilic) section of alternating glutamic acid (negatively charged) and lysine (positively charged) units and a hydrophobic polystyrene section. Cryo-TEM and dynamic-light-scattering (DLS) results showed that, on average, the block copolymer self-assembled into 7-nm-diameter micelles in aqueous solutions (0 to 100 mM NaCl, pH 6). Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and contact angle measurements demonstrated that the block copolymer self-assembled into a brush-like monolayer on polystyrene surfaces. The brush-like monolayer produced from a 100 mg/L block copolymer solution exhibited an average distance, d, of approximately 4–8 nm between each block copolymer molecule (center to center). Once the brush-like monolayer self-assembled, it reduced EPS adsorption onto the polystyrene surface by ∼70% (mass), reduced the rate of bacterial attachment by >80%, and inhibited the development of thick biofilms. QCM-D results revealed that the EPS molecules penetrate between the chains of the brush and adsorb onto the polystyrene surface. Additionally, AFM analyses showed that the brush-like monolayer prevents the adhesion of large (>d) hydrophilic colloids onto the surface via hydration repulsion; however, molecules or colloids small enough to fit between the brush polymers (
Résumé : Biofouling causes huge economic loss and generates serious ecological issues worldwide. Marine coatings incorporated with antifouling (AF) compounds are the most common practices to prevent biofouling. With a ban of organotins and an increase in the restrictions regarding the use of other AF alternatives, exploring effective and environmentally friendly AF compounds has become an urgent demand for marine coating industries. Marine microorganisms, which have the largest biodiversity, represent a rich and important source of bioactive compounds and have many medical and industrial applications. This review summarizes 89 natural products from marine microorganisms and 13 of their synthetic analogs with AF EC50 values ≤ 25 μg/mL from 1995 (the first report about marine microorganism-derived AF compounds) to April 2017. Some compounds with the EC50 values < 5 μg/mL and LC50/EC50 ratios > 50 are highlighted as potential AF compounds, and the preliminary analysis of structure-relationship (SAR) of these compounds is also discussed briefly. In the last part, current challenges and future research perspectives are proposed based on opinions from many previous reviews. To provide clear guidance for the readers, the AF compounds from microorganisms and their synthetic analogs in this review are categorized into ten types, including fatty acids, lactones, terpenes, steroids, benzenoids, phenyl ethers, polyketides, alkaloids, nucleosides and peptides. In addition to the major AF compounds which targets macro-foulers, this review also includes compounds with antibiofilm activity since micro-foulers also contribute significantly to the biofouling communities.
Résumé : The bacterial and eukaryotic communities forming biofilms on six different antifouling coatings, three biocidal and three fouling-release, on boards statically submerged in a marine environment were studied using next-generation sequencing. Sequenced amplicons of bacterial 16S ribosomal DNA and eukaryotic ribosomal DNA internal transcribed spacer were assigned taxonomy by comparison to reference databases and relative abundances were calculated. Differences in species composition, bacterial and eukaryotic, and relative abundance were observed between the biofilms on the various coatings; the main difference was between coating type, biocidal compared to fouling-release. Species composition and relative abundance also changed through time. Thus, it was possible to group replicate samples by coating and time point, indicating that there are fundamental and reproducible differences in biofilms assemblages. The routine use of next-generation sequencing to assess biofilm formation will allow evaluation of the efficacy of various commercial coatings and the identification of targets for novel formulations.
Résumé : An experimental study was carried out by a dynamic fouling monitor system to investigate the fouling process in convective heat transfer by ultrasonic treatment. During the experiment, the cooling water in heat exchanger was used as working fluid with the inlet temperature of 22.5 °C and 44 °C and the initial hardness of 300 mg/L and 500 mg/L, respectively. For all cases the inlet temperature of hot water was kept at 70°C, and the flowrates of cooling water and hot water were set at 0.77 m3/h and 0.81 m3/h, respectively. In this experimental setup, a double-tube heat exchanger was served as a test section of heat transfer, in which hot water flows inside the inner copper tube and cooling water flows in the annular gap between the two tubes, thus forming a counter-flow situation. Further, an ultrasonic device was installed for water treatment with a frequency of 20.7 kHz and power ranging from 0 to 75 W. The results showed that the fouling resistance for hard water increased evidently with increasing of water temperature and hardness. With the ultrasonic treatment, the fouling resistance decreased remarkably compared with the untreated case, and the asymptotic fouling resistance decreased monotonously with increasing of the ultrasonic power. Subsequently, the crystal morphology of calcium carbonate was observed in microscopic view and the transform of crystal from the vaterite to aragonite and calcite was analyzed based on the theory of the formation energy. It was confirmed that the ultrasonic treatment may have significant effect on the crystal shape, and more aragonites appeared with increasing powers of ultrasound.
Résumé : The invention provided herein presents a novel family of antifouling agents based on hydroxylated and fluorinated compounds.
Résumé : Membrane fouling, which arises from the nonspecific interaction between the membrane surface and foulants, significantly impedes the efficient application of membrane technology. Antifouling and antimicrobial materials are important classes of functional materials for the surface modification of reverse osmosis and nanofiltration membranes. Applications of various organic and inorganic materials having different characteristics such as size, surface charge, hydrophilicity, functionality and biocidal activity, provide protective/sacrificial layers to the membrane surface against different foulants and microorganisms. This review summarizes the properties and applications of organic and inorganic materials, antifouling mechanisms, and surface modification of pre-formed membranes. Materials such as zwitterionic polymers, neutral polymers, polyelectrolytes, amphiphilic polymers, quaternary ammonium polymers, biopolymers, hydrophilic polymers, polydopamine, inorganic salts, and nanomaterials have shown great potential in reducing foulant adhesion and/or proliferative microbial growth on membrane surfaces.
Résumé : The present invention is directed to bioactive microcapsules and to the process for their production. More in particular, the present invention relates to the production of bioactive microcapsules, or porous microspheres by a water-in-oil (W/O) microemulsion method combined with interfacial polymerization, involving the full or partial covalent immobilization of biocides and/or modified biocides within the microcapsules shell, or porous microspheres. In addition, the present invention further relates to the use of said bioactive microcapsules/microspheres for controlled release of biocides in antifouling application and their incorporation in matrices such as marine coatings.
Résumé : Abstract This chapter contains sections titled: Introduction Antifouling Options Problem Statement Coatings with Special Wettability and Performance Against Biofouling General Discussion Summary
Résumé : Persistent protein resistance is critical for marine antibiofouling. We have prepared copolymer of 2-methylene-1,3-dioxepane (MDO), tertiary carboxybetaine ester (TCB), and 7-methacryloyloxy-4-methylcoumarin (MAMC) via radical ring-opening polymerization, where MDO, TCB, and MAMC make the polymer degradable, protein resistible, and photo-cross-linkable, respectively. Our study shows that the polymer can well adhere to the substrate with controlled degradation and water adsorption rate in artificial seawater (ASW). Particularly, the polymer film can generate zwitterions via surface hydrolysis in ASW. Quartz crystal microbalance with dissipation measurements reveal that such hydrolysis-induced zwitterionic surface can effectively resist nonspecific protein adsorption. Moreover, the surface can inhibit the adhesion of marine bacteria Pseudomonas sp. and Vibrio alginolyticus as well as clinical bacterium Escherichia coli.