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Ultraviolet light-emitting diodes (UV-LEDs) are among the most compact devices and safest technologies in water disinfection systems. However, the validation of different assay methods to evaluate the disinfection performance of different wavelengths (265, 280, 285, and 300 nm) of UV-LEDs toward marine microalgae remains poorly characterized. In this study, several detection assays, namely the culture-based most probable number (MPN) assay, membrane integrity-based vital stain (VS) assay, chlorophyll fluorescence assay, and photochemical efficiency assay, were compared to assess the viability of the marine microalga Tetraselmis sp., with results indicating the MPN assay to be the most sensitive. In addition, this study compared the inactivation kinetics, inactivation efficiency, and energy efficiency of Tetraselmis sp. under different UV wavelengths, as assessed by the VS and MPN assays. The fluence-response curves of Tetraselmis sp. varied with assay and wavelength, with Geeraerd's model fitting all fluence-response microalgal inactivation curves. The results showed a non-significant difference in inactivation efficiency among different wavelengths of UV-LEDs (except for 300 nm) when using the VS assay. On the contrary, significant differences among all wavelengths were observed with respect to inactivation efficiency when using the MPN assay. The wavelength of 265 nm exhibited maximum inactivation efficiency, whereas 285 nm achieved optimal energy efficiency. The UV action spectrum of Tetraselmis sp. exhibited the peak at 265 nm, a finding which matched well with the absorbance spectrum of DNA. The observations from this study provide a theoretical basis and technical support for the application of the emerging UV-LED light sources in the algicidal treatment of marine water.

Thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) are widely studied and used in the oil & gas industry for hydrate prevention. In this experimental study, we applied an...

Vertical axes of mesoscale eddies with the coherent structure were observed to tilt southwestward significantly from the sea surface to bottom in the South China Sea. The dynamic mechanism for vertical tilting of eddies, however, is not well understood. In this study, the influence of the planetary β-effect on the vertical structure of a coherent eddy is investigated based on analytical considerations and numerical results produced by the MIT general circulation model (MITgcm). Both the analytical and numerical results demonstrate that, during the westward propagation of a mesoscale eddy, the momentum advection and divergence in the inner region of the eddy impact the propagation direction of the eddy on a β-plane. In the upper layer of the mesoscale eddy, the eddy propagation is mainly controlled by the β-effect and nonlinear effect (momentum advection). In the lower layer of an anticyclonic eddy, the eddy propagation direction is dominated by the advection and divergence, which leads to the westward shift of the eddy center in the upper layer. For a cyclonic eddy, by comparison, the vertical axis tilts to eastward from surface to bottom. The tilting distance is up to 30 km in a flat bottom ocean with the β value of 2.15 × 10−11 m−1 s−1. In addition, model results indicate that vertical stratification, eddy strength, and rough topography have significant influences on the vertical structure of a mesoscale eddy.

Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations. Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from high dosing, environmental unfriendliness, corrosiveness, and economical burden. The development and use of kinetic hydrate inhibitors (KHIs), mostly polymeric compounds, with their inhibiting effects on hydrate nucleation and growth are considered an effective and economically viable chemical treatment for hydrate prevention. However, the actual performance of a KHI candidate is dependent on various factors including its chemical structure, molecular weight, spatial configuration, effective concentration, pressure and temperature, evaluation methods, use of other additives, etc. This review provides a short but systematic overview of the fundamentals of natural gas hydrates, the prevailing categories of polymeric kinetic hydrate inhibitors with proposed inhibition mechanisms, and the various synergists studied for boosting the KHI performance. Further research endeavors are in need to unveil the KHI working modes under different conditions. The conjunctive use of KHIs and synergists may facilitate the commercial application of effective KHIs to tackle the hydrate plugging problem in the oil and gas flow assurance practices.

Satellite observations reveal many mesoscale eddies in the West Pacific Ocean (WPO) that propagate westwards and eventually interact with the Kuroshio Current. Examination of global ocean and sea ice reanalysis data in years 2008–2015 suggests trajectories of these mesoscale eddies over the Kuroshio zone can be categorized into three different patterns: ~63% of mesoscale eddies dissipating during the eddy-current interaction, ~33% moving to the north along the Kuroshio and only ~4% passing through the Kuroshio and Luzon Strait (LS) to enter to the South China Sea (SCS). A three-dimensional ocean circulation model based on the MIT General Circulation Model (MITgcm) is used to study the evolution of a westward propagating mesoscale eddy during the eddy-current interaction. Thirteen numerical experiments are conducted with the circulation model driven by currents specified at the southern and northern open boundaries to represent the influence of the Kuroshio. A mesoscale eddy is initialized to the east of the Kuroshio and the model is integrated for 70 days in each experiment. Model results suggest that the northward-flowing Kuroshio Current and the seamount topography within LS form a barrier for the westward propagating eddies to enter the South China Sea (SCS). Non-linear interactions between the Kuroshio Current, local topography and westward propagating mesoscale eddies can generate localized eddies in LS which could be shed into the SCS. Furthermore, the eddy-current interaction is found to be one of mechanisms for generating a multi-eddy structure in LS region.

A three-scale in situ observation technique combining the optical microscope, confocal microscope, and Raman spectroscopy was proposed to gain insights into the thickening growth kinetic of hydrate film formed on a gas bubble suspended in water. The evolution of the morphology and mass transfer channels of the hydrate films formed from pure CH4 or the mixture of CH4 and C2H6 during thickening growth was investigated. Results demonstrated that the morphological evolution of hydrate films during thickening growth depended on the initial morphology of the hydrate film formed in the lateral growth. The sI CH4 and sI CH4–C2H6 hydrates had the same ultimate morphology (e.g., a large number of well-defined polyhedral granular hydrates), while the sII CH4–C2H6 hydrates appeared massive. It was clearly observed that the gas pores on the hydrate film gradually vanished with the growth of hydrate film, which suggested that the predominant mass transfer channels on the film changed from the gas pores to the lattices....

Replacement of CH4 with CO2 in gas hydrates is a promising option for producing CH4 and sequestrating CO2 simultaneously, but it remains debatable if the CH4 hydrate dissociates or converts to the ...

The paper introduces a set of modeling methods to predict the failure probability of offshore wind turbines in the China coastal waters. In detail, a series of full-set three-dimensional meteorology simulations are conducted using the Weather Research and Forecast model to provide the extreme wind fields, while the extreme wave fields are predicted according to the conditional probability model. After the extreme wind and wave fields are prepared, the ultimate loads on the three critical parts of an OC4-DeepCwind semisubmersible wind turbine are simulated using the fatigue, aerodynamics, structures, and turbulence code, which in turn leads to the prediction of the failure probability. It has been found that the OC4-DeepCwind semisubmersible constructed in the Taiwan Strait has higher chance to fail under typhoon conditions than in other parts of the China coastal waters, showing a maximum failure probability of 0.6. In addition, the failure probabilities in the South and East China Sea are in the range of 0.3–0.45. The probability densities of the ultimate loads show, in some cases, a bimodal shape, which indicates that the loads as well as the failure probability are not in a simple linear relationship with the extreme wind speeds and wave heights/periods.

Harmful algal blooms (HAB), heavily influenced by human activities, pose serious hazard to aquatic ecology and human health. In this study, we monitored the physiological responses and paralytic shellfish poisoning toxins (PSTs) of the toxin-producing HAB species Alexandrium tamarense under titanium dioxide nanoparticles (nTiO2) exposure in the concentration range of 2–320 mg L−1 over a period of 13 days. The results showed the acute inhibition of nTiO2 on the algal growth, photosynthetic efficiency and esterase activity at all concentrations except 2 mg L−1. Nonetheless, they recovered after 13 days nTiO2 exposure from 20 to 80 mg L−1. The EC50 value increased from 85.1 mg L−1 in Day 4 to 140.9 mg L−1 in Day 13. The physiological recovery after prolonged exposure may result from the elimination of excess reactive oxygen species (ROS), a combined outcome of increased nTiO2 aggregation and algal antioxidant defense mechanisms. This observation is supported by the immediately increased antioxidant enzyme activities, including the superoxide dismutase (SOD) and catalase (CAT) activities upon nTiO2 exposure. Moreover, the production of PSTs in A. tamarense significantly increased by 1.41–1.76 folds after chronic nTiO2 exposure at all tested concentrations (p

Features of internal tides in the northern South China Sea are investigated using measurements of two moorings at 506 m (MR1) and 260 m (MR2) working between April and November of 2014. The diurnal internal tides at MR1 are significantly enhanced in June–July and display a regular fortnight modulation, whereas at shallower MR2, the June–July intensification is absent and the fortnight cycle becomes irregular. Fortnight cycle peaks of diurnal internal tides have a regular time-lag of ~ 2.8 days after those of diurnal barotropic tides (at MR1). We derive a mathematical relationship indicating that this time-lag of fortnight cycle peaks is around twice the time for the diurnal internal tides propagating from the generation place to the mooring site. Semidiurnal internal tides are dominated by the mode-1 (~ 70%), while diurnal internal tides exhibit multi-modal structures, with the contribution of ~ 20–30% for each of the first three modes. The diurnal mode-1 contribution varies fortnightly, and eddy passages are highly correlated with the increasing contribution of semidiurnal high modes (at MR1). Furthermore, we find that the nonlinear interaction between internal tides and near-inertial motions is weak in summer, even during periods of strong near-inertial motions (at MR2), because in summer, the shear of near-inertial currents is maximum at a depth shallower than the depth of maximum internal tide shear.

In this Review, we present a comprehensive overview of fundamental gas hydrate properties and formation theories. Key terminologies, theories and hypotheses for hydrate nucleation process were elucidated as bulletin points, while proposed hydrate growth models were categorized into groups based on variously proposed controlling mechanisms and compared in depth. Understanding and mastering these is instrumental to engineering the formation and dissociation of gas hydrates for beneficial applications. We conclude with an outlook on future research opportunities within this rapidly developing field, to facilitate future endeavors in the realm of gas hydrates.

Computational fluid dynamics (CFD) technique has been widely used in simulating dynamic responses of offshore floating wind turbines under excitations of prescribed wave and wind loads. In the simulation, the Volume of Fluid (VOF) method is generally employed to capture the free surface of the liquid, which illustratively shows the evolution of waves. The stresses at the free surface are not explicitly modeled in the VOF method, which challenge the establishment of the equilibrium marine atmospheric boundary layer (MABL) throughout the computational domain. Given the importance of the generation of the MABL in a CFD simulation of offshore wind turbines, methods for establishing sustainable wind profiles in a simulation based on the VOF method should be systematically investigated. In the present study, a virtual body force method is developed to maintain the horizontally homogeneous MABL in the VOF-based CFD simulation. The proposed method is quantitatively verified through a simulation of the equilibrium MABL with the sheared wind profile.

Microsecond molecular dynamics simulations were performed to investigate the methane hydrate formation on smooth and rough metal surface covered with water, light oil, and heavy oil with asphaltenes, respectively. The growth and crystallization of methane hydrates were characterized by the four-body order parameter and the face-saturated incomplete cage analysis. Results highlighted the priority for hydrate growth inside the groove of rough metal surface, from which the hydrate grew upwards to the outside of the groove and then to the water-gas interface. It clearly demonstrated the inhibition effects of light oil on the methane hydrate growth, which was further enhanced by adding asphaltenes. The inhibition mechanisms were elaborated during different stages of hydrate growth by gaining insights into the four-body order parameters at different locations of metal surface. To our knowledge, this was the first molecular-level study on the methane hydrate evolution on metal surface with heavy oil. It provided theoretical supports for evaluating the priority sites for the hydrate formation on pipe wall with concave and convex surfaces that might result from metal corrosion, change of pipe diameter or depositions of solid particles during the multi-phase transportation.

The work in this paper focuses on the examination of the effect of variable stiffness distributions on the kinematics and propulsion performance of a tuna-like swimmer. This is performed with the use of a recently developed fully coupled fluid-structure interaction solver. The two different scenarios considered in the present study are the stiffness varied along the fish body and the caudal fin, respectively. Our results show that it is feasible to replicate the similar kinematics and propulsive capability to that of the real fish via purely passive structural deformations. In addition, propulsion performance improvement is mainly dependent on the better orientation of the force near the posterior part of swimmers towards the thrust direction. Specifically, when a variable body stiffness scenario is considered, the bionic body stiffness profile results in better performance in most cases studied herein compared with a uniform stiffness commonly investigated in previous studies. Given the second scenario, where the stiffness is varied only in the spanwise direction of the tail, similar tail kinematics to that of the live scombrid fish only occurs in association with the heterocercal flexural rigidity profile. The resulting asymmetric tail conformation also yields performance improvement at intermediate stiffness in comparison to the cupping and uniform stiffness.

Research on fish locomotion has made extensive progress towards a better understanding of how fish control their flexible body and fin for propulsion and maneuvering. Although the biologically flexible fish fins are believed to be one of the most important features to achieve optimal swimming performance, due to the limitations of the existing numerical modeling tool, studies on a deformable fin with a non-uniformly distributed stiffness are rare. In this work, we present a fully coupled fluid–structure interaction solver which can cope with the dynamic interplay between flexible aquatic animal and the ambient medium. In this tool, the fluid is resolved by solving Navier–Stokes equations based on the finite volume method with a multi-block grid system. The solid dynamics is solved by a nonlinear finite element method. A sophisticated improved IQN-ILS coupling algorithm is employed to stabilize solution and accelerate convergence. To demonstrate the capability of the developed Fluid–Structure-Interaction solver, we investigated the effect of five different stiffness distributions on the propulsive performance of a caudal peduncle-fin model. It is shown that with a non-uniformly distributed stiffness along the surface of the caudal fin, we are able to replicate similar real fish fin deformation. Consistent with the experimental observations, our numerical results also indicate that the fin with a cupping stiffness profile generates the largest thrust and efficiency whereas a heterocercal flexible fin yields the least propulsion performance but has the best maneuverability.

Gas hydrate plugging in oil and gas transportation pipelines is a knotty problem for flow assurance practices. The nucleation mechanism of methane hydrate on corroded iron pipeline surface is still unclear. In this work, both smooth and corroded iron particles were packed into a hydrate reactor to investigate the relationship between the induction time of methane hydrate and the liquid-metal contact area. Experimental results indicated an insignificant difference among the particles of varied specific surface areas when submerged in the aqueous phase. However, the induction time was reduced by more than 60% when the particles were located above the gas-liquid interface and further shortened by 80% if the particles were corroded. Molecular dynamics simulations indicated that decreased interlayer spacing between the iron layers would facilitate methane hydrate formation in the initial period. Based on our energy analysis, this was ascribed to an increased curvature of the gas-liquid interface, causing a decrease of energy barrier by 54% for a methane molecule to transfer from the interface into the bulk liquid and subsequently, an increase of methane concentration in solution. Meanwhile, two layers of water molecules were observed to adsorb on the iron surface stably and no hydrate cages formed in such region throughout the simulation time. The microscopic phenomenon agreed well with the experimental results, which highlighted the influence of the gas-liquid-metal three-phase interface other than the liquid-metal contact area upon methane hydrate nucleation. The results shed new insights on predicting the prioritized locations of methane hydrate formation in metallic pipelines to reduce the potential hydrate plugging risk.

Nowadays, the combination of natural gas hydrates exploitation and CO2 storage is considered of excellent application. In this work, we explored reservoir reformation technology to enhance gas recovery from the unsealed water-saturated hydrate-bearing deposits in a large-scale tridimensional simulator. Firstly, recurrent CO2 injection into the overburden was to gradually form CO2 hydrate and reduce its permeability. Then traditional depressurization operations were conducted to compare the influences of overburden thickness and additional reservoir reformation on the evolution of pressure distribution and the gas/water production. The results showed that reservoir reformation could effectively improve the mining efficiency, reaching ∼2–4 times of gas production and ∼3–5 times of gas–water ratio compared with the direct depressurization. After a long-term reformation, CH4 recovery ratio was increased from 24.5% to 84.9%. Additionally, we further demonstrated the complete spatiotemporal evolution mechanism of the initial CH4 hydrate and artificial overlying CO2 hydrate during depressurization. A large amount of CO2 was ultimately stored in the depleted reservoir in the form of CO2 hydrate and the CO2 storage ratio was up to 79.5%. Therefore, this reservoir reformation approach is greatly promising for high-efficient and safe exploitation of marine hydrate and CO2 storage.

Gas hydrates in marine sediments are promising energy resources, while an effective recovery of methane from clay pores relies on a comprehensive appreciation of the hydrate evolution inside and outside the pore especially at a saline environment. Molecular dynamics simulations were conducted to investigate the methane hydrate formation and dissociation in the sodium montmorillonite (Na-MMT) interlayer with fresh water and saline water, respectively, by characterizing the distribution and transportation of methane and ions (K+, Na+, and Ca2+), the overall and local four-body structural order parameter, and the radial distribution functions. Results indicated that it was much easier to form methane hydrates in the bulk water than in the pore water, while the hydrates in the pore region were more readily dissociated than in the bulk region. The effects of salt ions on the hydrate formation were opposite in these two regions, which highlighted the role of the salting-out effect and the ion exchange between b...

The development of subsea injection water disinfection systems will enable the novel exploration of offshore oilfields. Ultraviolet light emitting diodes (UV-LEDs) with peak wavelengths at 255 nm, 280 nm, 350 nm, and combinations of 255 nm and 350 nm, and 280 nm and 350 nm were investigated in this study to determine their efficiency at disinfecting saprophytic bacteria, iron bacteria, and sulfate reducing bacteria. Results show that UV-LEDs with peak wavelengths at 280 nm were the most practical in this domain because of their high performance in both energy-efficiency and reactivation suppression, although 255 nm UV-LEDs achieved an optimal germicidal effect in dose-based experiments. The use of combined 280 nm and 350 nm wavelengths also induced synergistic bactericidal effects on saprophytic bacteria.

Molecular dynamics (MD) simulations and optical contact angle measurements were performed to shed light on the microscopic mechanisms for the dynamic wetting of heavy oil on rough silica surfaces. The surface wetting process was characterized by interaction energy, wettability transition, density profile, and penetration of each oil fraction, while competitive adsorption between oil and water droplets on rough surfaces was also investigated. Results highlighted the role of asphaltenes on the distribution and penetration of resins and aromatics, which might become either a driving force or mass transfer resistance for the wettability transition on rough surfaces. The competitive adsorption process was divided into three steps including water bridge formation, water penetration, and oil penetration. Water penetration promoted oil penetration by providing a channel for asphaltene invading. The overall tendency of simulation results agreed with experimental observations. To our knowledge, this was the first a...

An improved dynamic downscaling method is introduced in the present study to discern the spatial variations in offshore wind resources over the China coastal waters. In the improved method, the authors develop a novel pre-processing technique to provide the lateral boundary and initial conditions for the main dynamic downscaling process. In detail, the multivariate orthogonal decomposition is employed, at first, to extract the time-independent componential wind fields from the 30-year regional ECMWF meteorology data, which are then used to run the Weather Research and Forecast (WRF) model to produce the offshore wind field with high spatial resolutions from dynamic downscaling. Given the contribution of each componential wind field estimated in the decomposition, the WRF simulation results are subsequently recomposed into the final wind field showing wind resources along the coast of China. It has been found that the offshore wind resources are abundant over the South and East China Sea, especially in the Taiwan Strait where the maximum annual wind power density ∼ 800 W / m 2 is observed at the 90 m height. Via the improved dynamic downscaling method, the small-scale features of the localized offshore wind fields are improved by ∼13% after comparing to the raw ERA-Interim data, which is used to facilitate the siting of offshore wind farms.

Gas hydrate formation and asphaltene aggregation are two major concerns for flow assurance in the petroleum industry, whereas the atomistic understanding of their interactions remains limited, especially in the oil-dominated systems. Microsecond molecular dynamics simulations were performed to investigate the combined effects of solvent type, water droplet size, and asphaltenes on methane hydrate formation in a model water-in-oil emulsion by characterizing the four-body structural order parameter, molecular configurations, and evolution of hydrate cages. The results indicated the faster hydrate formation in a small water droplet with n-heptane because of the decreased interfacial curvature. Meanwhile, hydrate growth was promoted in a large water droplet with toluene because of the occurrence of a vertical water channel, which provided an extra growth site. The results also demonstrated the inhibition effect of asphaltenes on hydrate formation, which was more pronounced in a small droplet with n-heptane or...

Field measurements and numerical simulations demonstrate the existence of an upper saline plume in tidally dominated beaches. The effect of tides on the saltwater-freshwater mixing occurring at both the upper saline plume and lower salt wedge is well understood. However, it is poorly understood whether the tidal driven force acts equally on the mixing behaviours of above two regions and what factors control the mixing fluctuation features. In this study, variable-density, saturated-unsaturated, transient groundwater flow and solute transport numerical models are proposed and performed for saltwater-freshwater mixing subject to tidal forcing on a sloping beach. A range of tidal amplitude, fresh groundwater flux, hydraulic conductivity, beach slope and dispersivity anisotropy are simulated. Based on the time sequential salinity data, the gross mixing features are quantified by computing the spatial moments in three different aspects, namely, the centre point, length and width, and the volume (or area in a two-dimensional case). Simulated salinity distribution varies significantly at saltwater-freshwater interfaces. Mixing characteristics of the upper saline plume greatly differ from those in the salt wedge for both the transient and quasi-steady state. The mixing of the upper saline plume largely inherits the fluctuation characteristics of the sea tide in both the transverse and longitudinal directions when the quasi-steady state is reached. On the other hand, the mixing in the salt wedge is relatively steady and shows little fluctuation. The normalized mixing width and length, mixing volume and the fluctuation amplitude of the mass centre in the upper saline plume are, in general, one-magnitude-order larger than those in the salt wedge region. In the longitudinal direction, tidal amplitude, fresh groundwater flux, hydraulic conductivity and beach slope are significant control factors of fluctuation amplitude. In the transverse direction, tidal amplitude and beach slope are the main control parameters. Very small dispersivity anisotropy (e.g., α L / α T 5 ) could greatly suppress mixing fluctuation in the longitudinal direction. This work underlines the close connection between the sea tides and the upper saline plume in the aspect of mixing, thereby enhancing understanding of the interplay between tidal oscillations and mixing mechanisms in tidally dominated sloping beach systems.

The typhoon-resistant design should be given priority when constructing offshore wind farms in China coastal waters, where typhoons pose serious threats on the safety of offshore structures. A classical power-law model with the specific exponent of ${\text{0.11}}$ has been recommended by the code (IEC 61400-3 2009) to estimate the profile of extreme wind speed versus ${\text{50}}$ years return period. Its use in the typhoon-resistant design of offshore wind turbines in China coastal waters has, however, not been validated. In the present study, a series of full-set three-dimensional meteorology simulations are conducted to provide the artificial typhoon wind fields for the evaluation of code recommendations. The simulations reveal that the classical power-law with the exponent of ${\text{0.11}}$ is inadequate to estimate the extreme wind speed profile over China coastal waters. Based on the simulated typhoon wind fields, an empirical correction ratio and a scale factor are developed to adjust the classical power-law model to estimate the vertical variation of extreme wind speeds with any desired return periods over China coastal waters. More specifically, the correct ratio revises the power-law model to provide more accurate estimates of 50 years return period extreme wind speed profiles while the scale factor projects extreme wind speeds with other desired return periods.

Molecular dynamics simulation was performed to investigate the adsorption and aqueous extraction of oil contaminants on silica surface with various roughness. The oil dispersion and immersion were characterized by molecular configuration, adsorption energy and contact angle, while the oil detachment in water and cyclodextrin solution was evaluated by the overall extractability, extractability from individual groove and free energy analysis. Results demonstrated that the main resistance for oil release from the relatively shallow grooves was the strong intermolecular interactions among the oil molecules orderly stacked inside the grooves. It highlighted the role of cyclodextrin in breaking through the energy barrier for pulling out one oil molecule from the tightly stacked oil structure, which resulted in the fast release of the remaining oil. Previous studies attributed the oil extraction to the sequestration of oil into the hydrophobic cavity of cyclodextrin, while our results demonstrated that such incl...

Natural gas hydrate is a promising energy resource, but it is challenging to recover methane from the clay pores rich with sediment organic matter due to the inadequate information on hydrate evolution in the organoclay complex. Molecular dynamics simulations were conducted to investigate the methane hydrate formation and dissociation in the sodium montmorillonite interlayer (Na-MMT) with fatty acids by characterizing the four-body structural order parameter, radial distribution functions, and cage types. Results demonstrated the slight inhibition of fatty acid types (butyric and isovaleric acid) at molar concentrations (0.6% and 1.5%) on the methane hydrate formation in the context of this study. This finding was a result of several main processes including the formation of “quasihydrate” water structures around the hydrophobic carbon chains of fatty acids, the disruption of hydrogen bond networks by the hydrophilic carboxyl of fatty acids, and the restriction on the thermal motion of the sodium ions by ...

Unwanted proliferation of and adhesion by microalgae, as involved in fouling and species invasion, are important problems across many maritime operations and coastal industrial activities. The algicidal mechanisms of ultraviolet light-emitting diodes (UV-LEDs) and the synergistic algicidal effects between UV-LEDs and chlorine treatments in seawater were investigated in this study. Tetraselmis sp. was employed as the challenge organism. Five UV wavelengths (265, 280, 285, 300 and 315 nm) and three chlorine dosages (0.6, 0.8 and 1 mg L−1) were examined in a factorial experiment to optimize the disinfection performance achieved by combined UV-LED/chlorine treatments in seawater. Overall, the combined treatments showed a more effective inactivation of the microalgae than did the single treatments. Treatment with UV285 combined with 0.8 mg L−1 chlorine resulted in 3.12-log inactivation at 100 mJ cm−2 (i.e. 2.34 Einsteins L-1, 67 s). This optimal combination showed a higher inactivation rate constant and lower energy consumption (EE,2) than did the other treatments. The contribution of UV-LEDs, chlorine and hydroxyl radical (·OH) in the inactivation of Tetraselmis sp. by the combined UV-LED/chlorine disinfection process was investigated to illustrate the mechanism of this synergistic process, the results indicated that ·OH generated by photolysis were not the only contributors to the inactivation of the microalgae. Although a UV300/chlorine treatment demonstrated the highest chlorine photolysis rate, the inactivation constant of this treatment was lower than that of UV285/chlorine. These results demonstrated a synergistic algicidal effect of the combined disinfection system caused by exposure to the 285 nm UV-LED and low dosages of chlorine, which could provide an important basis for further developments and possibly industrial applications in the future.

CH4 hydrate have been considered as the future clean energy resource. Recovery of CH4 from natural gas hydrates by CO2 replacement is a promising method for energy harvest and CO2 sequestration. Field production tests have proved the feasibility of gas production by CO2 replacement in the permafrost region. However, most of the hydrate reservoirs are located at marine conditions where pressure and temperature conditions are not favorable for the replacement process. In this work, we identified a possible marine condition, where mixed hydrates could potentially form. We investigated the technical feasibility of CH4 recovery by a depressurization process followed by the injection of CO2-N2 gas. To quantify the dynamic behavior of mixed hydrates formation and dissociation, we developed a numerical method to estimate the phase partitioning during the replacement process. The effects of mixed gas compositions in the reactor on the replacement efficiency were investigated. Our experimental results showed that rapid co-growth of mixed hydrates occurs when the injected gas composed of a lower N2 concentration (

Cyclodextrins were used as environmentally friendly additives to overcome the slow kinetics of hydrate formation that limited the industrial application of gas hydrate technology. Microsecond molecular dynamics simulations were performed to identify the degree and the underlying mechanisms of the cyclodextrin effects on the methane hydrate formation rate by the four-body order parameter and molecular configurations and to clarify the hydrate structure in the presence of cyclodextrin by face-saturated incomplete cage analysis. Overall results indicated that the addition of β-cyclodextrin in water facilitated the hydrate growth rate, promoted the formation of thermodynamically stable hydrate structure, and enhanced the methane storage capacity. It highlighted the role of cyclodextrin to facilitate the formation of water channel bridging hydrate and water (at low ratio of gas to water) and to increase the gas–water interfacial curvature (at high ratio of gas to water) on the accelerated kinetics of hydrate g...