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• A novel side-aerated reactor for in-situ H 2 O 2 electrosynthesis was designed. • Side-aerated reactor coupled with a composite cathode greatly improved H 2 O 2 production. • Different aeration system and cathodes were evaluated for comparison. • Key factors for in-situ H 2 O 2 electrosynthesis were determined. The active graphite felt (GF) catalytic layer was effectively synthesized through a wet ultrasonic impregnation-calcination method, modified with CB and PTFE, and implemented in a pioneering side-aeration electrochemical in-situ H 2 O 2 reactor. The optimal mass ratio (CB: PTFE 1:4) for the modified cathode catalytic layer was determined using a single-factor method. Operating under optimum conditions of initial pH 5, 0.5 L/min air flow, and a current density of 9 mA/cm2, the system achieved a remarkable maximum H 2 O 2 accumulation of 560 mg/L, with the H 2 O 2 production capacity consistently exceeding 95 % over 6 usage cycles. The refined mesoporous structure and improved three-phase interface notably amplified oxygen transfer, utilization, and H 2 O 2 yield. Side aeration led to an oxygen concentration near the cathode reaching 20 mg/L, representing a five-fold increase compared to the 3.95 mg/L achieved with conventional bottom aeration. In the final application, the reaction system exhibited efficacy in the degradation of landfill leachate concentrate. After a 60-minute reaction, complete removal of chroma was attained, and the TOC degradation rate surpassed 60 %, marking a sixfold improvement over the conventional system. These results underscore the substantial potential of the system in H 2 O 2 synthesis and environmental remediation. [ABSTRACT FROM AUTHOR]

Gabion weir comprises porous materials packed with distinct shapes and sizes of gravel. The gabion weir is eco-friendlier than an impervious weir, as its opening enables water life and sediment materials to pass through it. Aeration is how natural processes or physical structures enhance the contact area and time between water and estranged air. This process improves the dissolved oxygen (D.O.) of water. The D.O. is one of the best determinants used for water quality measurement. This paper investigates the prediction of mass oxygen transfer over the gabion weir by ensemble models. The outputs of gabion weir oxygen mass transfer were estimated using bagging, boosting, and stacking by taking input parameters such as average size, porosity, the gabion weir height, discharge per unit width, and drop height. The dataset was taken by conducting experiments. By comparing these modeling ensembles, it was found that random forest-based bagging outperformed all proposed models. Nevertheless, all applied ensemble models were performing well, but published traditional equations were performing incredibly poorly. As sensitivity analysis suggests, the discharge per unit width was the most sensitive input. An uncertainty study was also carried out. [ABSTRACT FROM AUTHOR]

Wastewater treatment is currently focused on the development of simple, safe, cost-effective technologies for the complete destruction of persistent organic pollutants. A novel reagent-free electro-Fenton process by integrated nano-bubble aeration and sacrificial iron anode is proposed, which improves mass transferability of large content dissolved oxygen (10.55mgL−1) in the electrolyte and then quickly transported oxygen to the electrode surface. The synergistic effect of nanobubble aeration and sacrificial iron anodes can product a highly efficient hydrogen peroxide (H2O2) (310 mgL−1) and enhanced electrochemically driven reduction of Fe2+ at pH 3.5 and current density 55 mAcm−2. The degradation of phenol (100 mgL−1) with hydroxyl radicals (⋅OH) generated in situ is described by a pseudo first-order kinetics mode and was fast (0.036 min−1), which obtained a remarkable decolorization of over 58.7 % in 60 min. With nanobubble aeration and sacrificial iron anode, the catalytic decomposition of H2O2 to ⋅OH by Fe2+ was more powerful, achieving a cost-effective and green design without reagents.

This research uses an ejector bubble generator to determine water's flow structure and dissolved oxygen. The horizontal position of ejector, modified from conventional venturi, utilizes a gradual reduction in cross-section at the water inlet and contains air space before the mixing region. The bubble size distribution and the dissolved oxygen were measured experimentally, and empirical correlations were obtained from dimensional analysis, including the effect of Martinelli parameter. The characteristics of microbubble and volumetric mass transfer were investigated in the air flow range of 0.1–1.5 lpm and nozzle diameter of 1.17–3.50 mm. Bubble size distribution was obtained using image processing technique from a high-speed video camera, and dissolved oxygen was recorded using a polarographic dissolved oxygen meter. Based on the research variable, the air/water discharge ratio and nozzle diameter have a high impact on the bubble size with the power of 0.572 and 0.598 for bubble size correlation, respectively. They have power of −17.411 and 5.928 for oxygen transfer rate correlation, respectively. It shows that the air/water ratio and nozzle diameter significantly affect the bubble size and oxygen transfer rate.

After the atmospheric hydrochloric acid leaching method is used to treat laterite ore and initially purify it, the extract that results often contains a significant amount of Fe2+ impurities. A novel metallurgical process has been proposed that utilizes microbubble aeration to oxidize Fe2+ ions in laterite hydrochloric acid lixivium, facilitating subsequent separation and capitalizing on the benefits of microbubble technology, including its expansive specific surface area, negatively charged surface attributes, prolonged stagnation duration, and its capacity to produce active oxygen. The study examined the impacts of aeration aperture, stirring speed, oxygen flow rate, pH value, and reaction temperature. Under optimized experimental conditions, which included an aeration aperture of 0.45 µm, stirring at 500 rpm, a bubbling flow rate of 0.4 L/min, pH level maintained at 3.5, and a temperature range of 75–85 °C, the oxidation efficiency of Fe2+ surpassed 99%. An analysis of the mass transfer process revealed that microbubble aeration markedly enhances the oxygen mass transfer coefficient, measured at 0.051 s−1. The study also confirmed the self-catalytic properties of Fe2+ oxidation and conducted kinetic studies to determine an apparent activation energy of 399 kJ/mol. At pH values below 3.5, the reaction is solely governed by chemical reactions; however, at higher pH values (>3.5), both chemical reactions and oxygen dissolution jointly control the reaction. [ABSTRACT FROM AUTHOR]

One-dimensional oxygen transport relation is indispensable to study the oxygen distribution in the LBE-cooled system with an oxygen control device. In this paper, a numerical research is carried out to study the oxygen transport characteristics in a gas-phase oxygen control device, including the static case and dynamic case. The model of static oxygen control is based on the two-phase VOF model and the results agree well with the theoretical expectation. The model of dynamic oxygen control is simplified and the gas-liquid interface is treated as a free surface boundary with a constant oxygen concentration. The influences of the inlet and interface oxygen concentration, mass flow rate, temperature, and the inlet pipe location on the mass transfer characteristics are discussed. Based on the results, an oxygen mass transport relation considering the temperature dependence and velocity dependence separately is obtained. The relation can be used in a one-dimensional system analysis code to predict the oxygen provided by the oxygen control device, which is an important part of the integral oxygen mass transfer models.

Aeration and stir are vital steps in wastewater treatment plants (WWTPs) to enhance dissolved oxygen (DO) concentration in water. In laboratories, aerated stirred reactors (ASRs) are commonly utilized to cultivate activated sludge and degrade pollutants in sewage. The performance of the ASR depends mainly on the gas-liquid distribution and hydrodynamics. The current study investigated a lab-scale ASR using computational fluid dynamics (CFD) modeling and simulation. The experimental data were used to validate the CFD model. Then, the validated model was used to investigate the effect of impeller types on gas-liquid mixing quality and oxygen mass transfer efficiency. This investigation aimed to select suitable and efficient impeller types for different needs in ASRs. The predictions suggested the Pitched 30° impeller is excellent in mass transfer and gas-liquid mixing besides needing more power. Simulation results of oxygen transfer shown that the gas holdup and bubble diameter mainly determined the oxygen mass transfer coefficient in ASRs. Rushton impeller and Folded impeller offer good oxygen transfer but also higher power consumption. Pitched 45° impeller and Pitched 60° impeller offer more uniform gas holdup than other impellers and have lower energy consumption. [ABSTRACT FROM AUTHOR]

The paper presents the results of analysis of the main existing theories of oxygen mass transfer in dynamic water– air disperse systems. A theoretical model has been developed for the process of oxygen mass transfer, making it possible to account for the effect of deformation of air bubbles rising in turbulent regimes. A new calculation procedure has been proposed for the process of oxygen mass transfer developed on the basis of hydrodynamic characteristics of air bubble floating regimes. The use of obtained mathematical dependences will make it possible to take into account the effects of geometric parameters of air bubbles with a changed shape rising in turbulent regimes and, on this basis, to achieve higher accuracy of identifying technological characteristics of mass transfer processes. [ABSTRACT FROM AUTHOR]

Conventional electrosynthesis of H 2 O 2 through a two-electron oxygen reduction reaction (2e− ORR) requires continuous O 2 feeding as the reactant, which is produced by oxygen evolution reaction (OER) in water electrolysis. In principle, H 2 O 2 can be directly synthesized from water once the 2e− ORR is coupled with OER in one electrode. Unfortunately, such effective coupling has not yet been established. Herein, we created a cyclic oxygen exhalation-inhalation for on-demand and on-site H 2 O 2 production by coupling the OER and 2e− ORR with a facile alternating-current (AC) electrocatalytic process. By ingeniously manipulating the reaction interfaces and operating voltage, we achieved efficient and stable in-situ H 2 O 2 production. The rapid oxygen transfer in the localized three-phase interface favors the sufficient electrochemical reactions. The AC-electrocatalytic system exhibits highest performance including H 2 O 2 production rate of 90.16 mmol h−1 g cat −1. Moreover, such AC-electrocatalysis inspires a new strategy to combine multiple electrocatalytic reactions into one electrode for fundamental study and practical applications. [Display omitted] • OER and 2e− ORR have been cascaded by AC-electrocatalysis. • The system exhibits high performance for on-site and on-demand H 2 O 2 production. • This work provides a new chance to integrate different electrochemical reactions. [ABSTRACT FROM AUTHOR]

The effect of aeration on the stability of glucose oxidase in the reaction of glucose oxidation to gluconic acid was investigated by determining the operational stability decay rate constant in the process conditions. Eupergit C as a porous carrier was chosen for the enzyme immobilization. To evaluate glucose oxidase operational stability during process conditions, experiments of glucose oxidation were carried out in the repetitive batch reactor with and without continuous aeration at different aeration levels. It was found that the decay rate of the free enzyme linearly depended on the air flow rate. Immobilization of glucose oxidase on Eupergit C significantly enhanced enzyme stability at higher aeration rates. Kinetics of the free and immobilized enzyme was also determined. The mathematical model of glucose oxidation catalysed by free and immobilized glucose oxidase in the batch reactor was developed.

The aim of this study was to investigate the influence of humic substances (HS) on volumetric oxygen‐transfer coefficient (KLa) under different turbulence intensities at the air–water interface. The experiments were carried out in an oscillating grid tank which provided three levels of turbulence intensities (Reynolds numbers of 5,116, 10,316, and 15,433). For each turbulence level, 15 different HS concentrations were tested and the KLa was estimated. The results showed that, regardless of the turbulence level in the tank, HS reduces KLa. The maximum reduction was 17%. The barrier effect, produced by the occupation of HS molecules at the interface, was the main phenomenon responsible for the reduction in the oxygen transfer. A relationship between the oxygen transfer velocity and turbulent kinetic energy showed that in the presence of HS, the air–water interface behaves like an immobile surface, reducing the oxygen diffusion and surface renewal. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel constant velocity gas diffusion electrode (CVGDE) was fabricated. • CVGDE exhibited high performance for two-electron oxygen reduction reaction. • Gas flow rate significantly affected the 2e− ORR performance of the GDE. • The dynamic equilibrium of TPI was achieved by the electric field and air flow. Mass transfer of oxygen is a critical issue in the two-electron oxygen reduction reaction (2e− ORR) for the generation of hydrogen peroxide (H 2 O 2). In this study, a novel constant velocity gas diffusion electrode (CVGDE) that can control the gas flow rate through the catalyst layer was fabricated, and the effect of the gas flow rate on three-phase interfaces (TPIs) formation and the mass transfer of oxygen in gas diffusion electrode (GDE) was investigated. In CVGDE, oxygen mass transfer was significantly improved, and the yield of H 2 O 2 reached up to 73.65 mg cm−2 h−1 at 200 mA cm−2, which was 74.3 % higher than that of conventional GDE. Furthermore, the oxygen utilization efficiency of CVGDE reached 22.4 %, and the aeration energy consumption was decreased to 5.48 Wh kg−1, which was 1000 times less than the energy consumption required for H 2 O 2 electrosynthesis. The experiments and theoretical calculations showed that the dynamic equilibrium state of TPI was achieved by the influence of both the electric field and air flow in the catalyst layer, which leading to a substantial increase in oxygen mass transfer and H 2 O 2 yield. Finally, CVGDE was utilized in the electro-Fenton process for the degradation of organic contaminants. This study will contribute to the understanding of the oxygen mass transfer process in GDE. [ABSTRACT FROM AUTHOR]

Bubble aeration is a significant consumer of energy in wastewater treatment processes. Optimizing oxygen transfer, from an energy usage perspective, is crucial in the development of clean production techniques and for the stimulation of the circular economy. Although large efforts have been made in enhancing this process, particularly in ameliorating bubble diffusers, a main problem lies in energy wastage due to over-pursuing ultra-fine bubble generation. In this study, a dynamic model, that integrated both bubble expansion and detachment at submerged orifices, and consequential oxygen utilization during the uprising, was developed in order to better facilitate energy savings during the control of bubble generation. We demonstrate through calibrated models that bubble formation is governed by many factors including gas flow rate, orifice radius, surface tension, liquid viscosity, and surface wettability. Small bubbles are more prone to form when subjected to conditions of high wettability, small orifice size and low flow rate, since the bubbles are easily detached by the increasing upward forces in these scenarios. The oxygen transfer during the rising process was calculated as a function of bubble size, gas type and water depth. Bubbles with a radius smaller than a threshold value can shrink and collapse while below the water surface and thus provide 100% oxygen utilization. The threshold values of bubble radius are determined to be 150 μm and 250 μm at 5 m and 15 m initial water depth, respectively. The parameter set for bubble generation in order to obtain the desired bubble size may then be inversely determined by our bubble formation model, and it's considered as optimal aeration strategy to realize precise aeration. With these results, our study highlights the viability of the approach employing the proposed model in order to direct energy-efficient bubble generation. • Developed a model that integrates the formation, rise and oxygen transfer of bubble. • Quantify the coupling effect of various factors on bubble formation. • Determine the optimal bubble size for aeration at specific water depth. • Inversely determine the best parameter set for generating optimal bubble. • Assessed the aeration efficiency and energy consumption of different scenarios. [ABSTRACT FROM AUTHOR]

We studied new micro-perforated diffuser concepts for the aeration process in wastewater treatment plants and evaluated their aeration efficiency. These are micro-perforated plate diffusers with orifice diameters of 30 µm, 50 µm and 70 µm and a micro-perforated tube diffuser with an orifice diameter of 50 µm. The oxygen transfer of the diffuser concepts is tested in clean water, and it is compared with commercial aerators from the literature. The micro-perforated tube diffuser and micro-perforated plate diffusers outperform the commercial membrane diffusers by up to 44% and 20%, respectively, with regard to the oxygen transfer efficiency. The most relevant reason for the improved oxygen transfer is the fine bubble aeration with bubble sizes as small as 1.8 mm. Furthermore, the more homogenous cross-sectional bubble distribution of the micro-perforated tube diffuser has a beneficial effect on the gas mass transfer due to less bubble coalescence. However, the pressure drop of micro-perforated diffusers seems to be the limiting factor for their standard aeration efficiencies due to the size and the number of orifices. Nevertheless, this study shows the potential for better aeration efficiency through the studied conceptual micro-perforated diffusers.

This paper presents a comparative experimental study of different configurations of mechanical surface aerators used in wastewater treatment plants. A laboratory scale tank equipped with different configurations for aeration process was installed to compare the standard aeration efficiency and power consumption of curved blade impellers with 3, 6, 9, and 12 blades. Different parameters thought to have significant effects on standard aeration efficiency (SAE) and power consumption, such as submergence depth and rotating speed were studied. Results show that an optimum configuration (9 blades) has the highest aeration efficiency (2.60 Kg. O 2 /KW.hr) at 500 rpm. Also, a submersion depth ratio of 0.35 was optimum, giving the highest standard aeration efficiency, as increasing submergence depth ratio above this value causes drop in standard aeration efficiency as a result of inevitable increase in input power consumption in this case. [ABSTRACT FROM AUTHOR]

Rocking disposable bioreactors are a newer approach to smaller‐scale cell growth that use a cyclic rocking motion to induce mixing and oxygen transfer from the headspace gas into the liquid. Compared with traditional stirred‐tank and pneumatic bioreactors, rocking bioreactors operate in a very different physical mode and in this study the oxygen transfer pathways are reassessed to develop a fundamental mass transfer (kLa) model that is compared with experimental data. The model combines two mechanisms, namely surface aeration and oxygenation via a breaking wave with air entrainment, borrowing concepts from ocean wave models. Experimental data for kLa across the range of possible operating conditions (rocking speed, angle, and liquid volume) confirms the validity of the modeling approach, with most predictions falling within ±20% of the experimental values. At low speeds (up to 20 rpm) the surface aeration mechanism is shown to be dominant with a kLa of around 3.5 hr−1, while at high speeds (40 rpm) and angles the breaking wave mechanism contributes up to 91% of the overall kLa (65 hr−1). This model provides an improved fundamental basis for understanding gas–liquid mass transfer for the operation, scale‐up, and potential design improvements for rocking bioreactors. [ABSTRACT FROM AUTHOR]

Abstract The removal of toxic hydrogen sulfide (H 2 S) from the air at pilot-scale with elemental sulfur recovery was evaluated using Fe-EDTA chelate as a single treatment at a pH of about 8.5. This was later combined with a compost biofiltration process for polishing the pre-treated air. Experiments were performed in a unique container system that allowed deploying either Fe-EDTA chelate or Fe-EDTA chelate/biofiltration treatment (hybrid system). The results showed the feasibility of H 2 S removal at concentrations between 200 and 5300 ppmv (H 2 S loading rates of 7–190 g m−3 h−1) present in fouled air. The Fe-EDTA chelate as a single treatment was able to remove nearly 99.99% of the H 2 S at inlet concentrations ≤ 2400 ppmv (107 g m−3 h−1), while the hybrid system archived undetectable outlet H 2 S concentrations (<1 ppmv) at inlet levels of 4000 and 5300 ppmv. At 5300 ppmv, the Fe-EDTA chelate process H 2 S removal efficiency decreased to 99.20% due to the limitation of oxygen mass transfer in the Fe(III) regeneration reaction. Under the previous conditions, the pH was required to be controlled by the addition of NaOH, due to the likely occurrence of undesirable parallel reactions. The elemental sulfur yield attained in the physicochemical module was 75–93% with around 80% recovered efficiently as a solid. Graphical abstract Image 1 Highlights • A hybrid system: Fe-EDTA chelate/compost biofiltration was evaluated at pilot scale. • H 2 S concentrations up to 5300 ppmv were successfully removed from air. • The compost biofilter module polished the remained H 2 S from physicochemical module. • Under oxygen limitation the Fe-EDTA chelate system reduced its H 2 S removal efficiency. • The elemental sulfur produced in chelate Fe-EDTA module had > 99% purity. [ABSTRACT FROM AUTHOR]

Aerator is the largest part of the energy consumption of oxidation ditch. In order to reach the goal of saving energy and reducing consumption, in this study a series of experimental studies on aeration and oxygenation performance were conducted in tap water. Based on the theoretical model of oxygen mass transfer, the influence of operating conditions such as aeration rate, the arrangement of aerators and the strength of lateral flow on mass transfer were investigated. The oxygen mass transfer coefficient increased when there exists transverse flow in the ditch, but the system power efficiency was not positively related to transverse flow. The oxygenation capacity increased 35% using uniform arrangement of the micro-pore aerator. With the increase of aeration rate, oxygen volume mass transfer coefficient increased, but the changes in oxygen utilization rate behaved opposite. Combining with the volumetic mass transfer coefficient and the dynamic efficiency of the system, the research on oxygen transport performance of micro-porous aerator can provide theoretical basis for the purpose of saving energy and reducing consumption and optimizing operation conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different functional groups modifying WO 3 /R-MOFs (R = NH 2 , C 5 H 11 , C 5 F 11) were designed. • Hydrophobic WO 3 /C 5 F 11 -MOF improves oxygen mass transfer. • The formation of electron-deficient region in WO 3 /C 5 F 11 -MOF prolongs the relaxation time of electrons. The solar-driven photocatalytic degradation of persistent organic pollutants is considered as a promising water treatment approach. Nevertheless, the activity of photocatalytic degradation of pollutants is still limited by the rapid carrier recombination and sluggish oxygen mass transfer. Herein, we designed different functional groups modified WO 3 /R-MOF (MOF: MIL-125-Ti, R = NH 2 , C 5 H 11 , C 5 F 11) heterojunction to overcome the aforementioned limitations. Among them, WO 3 /C 5 F 11 -MOF exhibited an excellent degradation efficiency of 91.6 % for 4-chlorophenol pollutants, which was seven and two times higher than that of WO 3 /NH 2 -MOF and WO 3 /C 5 H 11 -MOF, respectively. The WO 3 /C 5 H 11 -MOF and WO 3 /C 5 F 11 -MOF exhibited hydrophobic and formed microscopic triphase interface, which increased oxygen transfer. Furthermore, strong electron-withdrawing property of fluorine in the C 5 F 11 - ligand generated electron-deficient regions, increasing the transfer rate of photo-generated electrons and prolonging the relaxation time of electrons. Thus, hydrophobic WO 3 /C 5 F 11 -MOF not only regulates the catalytic interface microenvironment, but also effectively inhibits the recombination of photo-generated carrier. This study provides an efficient strategy to achieve excellent photocatalytic activity via interfacial engineering. [ABSTRACT FROM AUTHOR]

In this work, effects of anionic surfactant on the oxygen transfer is investigated in a cylindrical reactor. For the first time, a systematic study in a wide surfactant concentration range, below and above the critical micellar concentration, is shown. A maximum reduction in the volumetric mass transfer coefficient (KLa) was observed for a surfactant concentration of 0.07 mM, before the CMC. Results are discussed based on the molecular interactions among water, air bubbles, and surfactant molecules. To better understand the experimental findings, a mathematical model was developed based on the estimated volumetric mass transfer coefficient. Predictions agree very well with the experimental results and point to a maximum reduction of 41% in the KLa, regardless of the inlet airflow rate in the reactor. We believe that our model can be used to predict future experimental results. In addition, this work can also be useful to better design an aerobic system. [ABSTRACT FROM AUTHOR]

Highlights • Hydrodynamic characteristics of orifice type microbubble generator were investigated. • The bubbles diameter distribution is approached by the beta distribution function. • The liquid flow rate takes part an important role on the the volumetric mass transfer. • The empirical correlations of hydrodynamic parameters of the microbubbles were proposed. Abstract The aim of this work was to investigate the characteristics of oxygen dissolution into water in aeration using an orifice type microbubble generator (MBG). The analysis was conducted using dimensional analysis by taking into account bubble diameter distribution and oxygen mass transfer rate. The characteristics of microbubbles produced by MBG were affected by the combination of air and water flow rates through the MBG. In this study, the ranges of air and water flow rates were set at 0.1–1.0 l/min and 30.0–80.0 l/min, respectively. The microbubbles were captured by a high-speed camera using shadow photographic technique to obtain the bubbles size distribution as well as the average diameter of the bubbles. The volumetric mass transfer coefficient of oxygen was measured using dynamic physical absorption model. The results verified that the size of microbubble depend on air and water flow rates. The increase of the gas flow rate increased the average bubble diameter. On the other hand, the increase of the water flow rate decreased the average bubble diameter. Furthermore, the increase of water flow rate increased the oxygen volumetric mass transfer coefficient. Finally, by using dimensional analysis, the empirical correlation of volumetric mass transfer coefficient, average bubble diameter, and bubble diameter distribution, was proposed. The correlation showed that liquid Reynolds number played most important role in average bubble diameter and oxygen mass transfer rate obtained in MBG aeration. [ABSTRACT FROM AUTHOR]

O2‐dependent whole‐cell bioprocesses, such as C−H oxyfunctionalizations, are constrained by technically limited O2 mass transfer and biocatalyst‐inherent O2 respiration. In large‐scale bioprocesses, this restricts the maximum achievable productivity to 5.6 gproduct L−1 h−1 assuming a resting cell concentration of 9.4 gCDW L−1. This concept paper discusses strategies to enhance the O2 availability for biocatalytic oxyfunctionalizations with a focus on the in situ generation of O2 from water. This promising approach was addressed recently by the exploitation of microbial photosynthesis for light‐driven C−H oxyfunctionalization. Via intracellular O2 evolution, phototrophic biocatalysts increase the maximum achievable productivity well beyond technical boundaries. This fundamental advantage over O2‐respiring biocatalysts now awaits scale‐up evaluations, combining established cultivation technologies for phototrophic organisms with bioprocessing techniques for heterotrophic organisms. DIY: O2‐dependent whole‐cell bioprocesses are constrained by a limited net O2 accumulation rate in the applied bioreactor system. Photosynthetically active biocatalysts can overcome this limitation by in situ O2 evolution via photosynthetic water‐oxidation. This fundamentally opens up the process boundary towards higher productivities. [ABSTRACT FROM AUTHOR]

The effect of aeration on the stability of glucose oxidase in the reaction of glucose oxidation to gluconic acid was investigated by determining the operational stability decay rate constant in the process conditions. Eupergit C as a porous carrier was chosen for the enzyme immobilization. To evaluate glucose oxidase operational stability during process conditions, experiments of glucose oxidation were carried out in the repetitive batch reactor with and without continuous aeration at different aeration levels. It was found that the decay rate of the free enzyme linearly depended on the air flow rate. Immobilization of glucose oxidase on Eupergit C significantly enhanced enzyme stability at higher aeration rates. Kinetics of the free and immobilized enzyme was also determined. The mathematical model of glucose oxidation catalysed by free and immobilized glucose oxidase in the batch reactor was developed. [ABSTRACT FROM AUTHOR]

Oxygen transfer can be a limiting step in aerobic biodegradation processes. Therefore, this process has been widely investigated for wastewater treatment, but only few research works have been done on soil slurry systems. This study focuses on the gas-liquid oxygen mass transfer in clay slurry conditions in an aerated and agitated reactor using a marine propeller. Conversely to most studies on oxygen transfer, pneumatic power input is not negligible compared to mechanical power input. Clay presence has a negative impact on the oxygen transfer. However, the effect of agitation and aeration on this process remains unaffected at the clay concentrations tested. Three different phases explaining the depletion in the oxygen transfer rate are hypothesized. A model to predict the oxygen transfer coefficient in slurry reactors, including the three operational parameters tested within their respective ranges, is proposed. [ABSTRACT FROM AUTHOR]

Oxygen mass transfer in a membrane blood oxygenator (MBO) surrogate system has been addressed in this work. It consists of a slit for water circulation as a surrogate blood flow channel and a constant pressure oxygen chamber separated by an integral asymmetric hemocompatible polyurethane‐based membrane. The oxygenated stream enters a well‐mixed reservoir of constant volume, V, for the oxygen average concentration, C O 2, measurement as a function of time, t. In a range of short times, the linearity of C O 2 vs. t allows the direct determination of the permeation fluxes J O 2, with no recourse to dimensionless correlations for the determination of mass‐transfer coefficients. The experimental fluxes are in very good agreement with the predictions based in unidimensional axial convection and unidimensional transversal diffusion. This custom‐made benchmark system allows the optimization of the flow and oxygen mass transfer for the design of a novel flat‐sheet MBO. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3756–3763, 2018 [ABSTRACT FROM AUTHOR]

Jet loop reactors (JLRs) are an alternative reactor type for the intensification of aerobic bioprocesses which are normally carried out in stirred tank reactors (STR). A JLR is capable to generate the same oxygen transfer rate ( OTR ) at a higher efficiency compared to a STR. If the ejector nozzle of a JLR is used for headspace pressurization, the oxygen mass transfer can be increased even further. However, intensified mass transfer usually requires increased power inputs while mass transfer efficiencies are decreased. In this respect, the energy efficiency of a JLR designed for intensification of an industrial bioprocess was evaluated. Compared to a STR, the JLR achieved a 70% higher mass transfer rate at identical power input. Based on the results obtained for mass transfer performance, an increase in aerobic biomass formation up to 100% can be expected for the JLR in comparison to the STR. [ABSTRACT FROM AUTHOR]

Respirometric techniques are useful tools to evaluate bacterial activities in activated sludge processes due to their fast execution and the possibility to obtain several kinetic parameters from a single test. Using such techniques in microalgae-bacteria consortia treating wastewater could allow a better understanding of mutual interactions between the microbial populations as a function of environmental parameters. This work aims at developing and testing a novel experimental respirometric protocol to determine oxygen uptake rates and oxygen production rates by a microalgae-bacteria consortium. The defined protocol is characterized by alternating light/dark regimes and by dosing substrates/inhibitors to selectively activate/inactivate microalgal and bacterial metabolisms. The protocol was then applied on microalgal and bacterial consortia, which were grown on the liquid fraction of black water from biogas plants fed on agricultural and municipal waste sludge. Results elucidate the presence and activity of microalgae and nitrifying bacteria in the tested systems, suggesting that the respirometric tests could be included into monitoring procedures of photobioreactors/algal ponds. [ABSTRACT FROM AUTHOR]

Corrosion of steels in lead bismuth eutectic (LBE) cooled reactors can be mitigated by forming a protective oxide layer on the steel surfaces. The amount of oxygen necessary to ensure continuous oxide layer formation on fuel cladding depends on the characteristics of the steel and on the local temperature, local oxygen concentration and velocity of the LBE in contact with the steel. The most critical areas from a corrosion point of view are high temperature and low oxygen concentration regions. Wire-wrapped fuel assemblies (FAs) which are foreseen to be used in LBE cooled reactors, are characterized by hot spots and quasi-stagnant areas where oxygen could be depleted. Experimental measurements to verify whether the oxygen concentration in those critical areas is sufficiently elevated for oxide layer formation, are practically impossible. This information can be however obtained by numerical modeling. This paper focuses on the development of a numerical model of oxygen mass transfer in a 19-pin scaled fuel assembly (FA) representative of the MYRRHA reactor core. Oxidation of steels and oxygen transport from the bulk of the LBE to the surface of steels were simulated simultaneously. The simulations provide a local oxygen concentration mapping at steel/LBE interface enabling to identify the regions of the core which could be prone to corrosion due to oxygen depleted LBE. Operation recommendations for the MYRRHA reactor were given based on the simulation results. [ABSTRACT FROM AUTHOR]

We have experimentally found a pumping-up mechanism, where the thin liquid film flow goes up fully upward along the outer surface of a rotating cone. The mechanism is applied to the atomization of the liquid and to the transportation of oxygen from the air to the water through the atomized water droplets. We measure the dissolved oxygen concentration and axial torque for varying the immersed radius, the total volume of water and the rotation rate. The correlation between the unit volume power consumption and the oxygen mass transfer is examined. It is found that the oxygen transfer increases in power law relationship with the unit volume power consumption. Eventually, an empirical correlation function of the oxygen mass transfer against the power consumption is obtained. [ABSTRACT FROM AUTHOR]

Intensification of chemical processes has surfaced many challenging but promising areas. Enhancement of Oxygen Mass Transfer (OMT) is one such area in aqueous chemical processes. Several attempts made to alleviate OMT limitation, however, remains futile in lowering energy and material requirement. In this regard, the use of n- Dodecane, an Oxygen Vector, could be a radically promising route for enhancing OMT. The present work explores the use of n- Dodecane (Oxygen Vector) for the enhancement of OMT, corroborated with the Classical Molecular Dynamic (MD) simulations. The results showed that 2.5% (v/v) n- Dodecane addition in aqueous systems (‘Na 2 SO 3 solution – n- Dodecane’ and ‘H 2 O – n -Dodecane’) would lead to enhancement up to 750%. MD simulation results confirm the transfer of oxygen from n- Dodecane-to-aqueous medium with diffusivity of 10 −8  m 2 /s, thus becomes the dominating route for the enhancement in OMT. In addition, it has been found that n- Dodecane fraction, temperature and the rate of oxygen consumption reaction are the dictating parameters for enhancement. The concept of Oxygen Vector for enhancing OMT has been successfully exploited for cleaner leaching of metals (>95 % Cu, Ni and Co) from refractory complex sulfides at moderate temperature-pressure conditions (T∼ 95 °C and pO 2 ∼3 Bar), which would have otherwise been possible at T > 200 °C and pO 2  > 10 Bar. In addition, recyclability of n -Dodecane, Oxygen Vector, in leaching system is an added advantage. Thus, this study offers a promising route in enhancing kinetics of oxidative aqueous processes and provides suggestive insights for lowering the material and energy requirements. [ABSTRACT FROM AUTHOR]

The Rotary Biological Contact (RBC) reactor has a unique aeration system that provides a moving bed for easy and efficient oxygen transfer within the system to overcome the limitations of stationary culture in bacterial cellulose (BC) production. In most cases, oxygen mass transfer is the limiting factor of an aerobic process, hence the changes in the oxygen mass transfer coefficient within the system have been given special attention. In this study, the RBC bioreactor producing BC was modeled based on one-dimensional oxygen mass transfer in the direction perpendicular to the surface of the discs. The Monod kinetic model has been used to express cell growth. Simulation of the mathematical model was done based on the numerical solution with finite difference method in MATLAB software. Sensitivity analysis was performed to investigate the effect of changing different system parameters in RBC modeling. The simulation results showed that with the increase in angular velocity, the oxygen transfer coefficient and subsequently the mass transfer rate increase. Also, at a certain angular velocity, the oxygen mass transfer coefficient increases with the increase of immersion depth. The best disk rotation speed considering other parameters as well as the laboratory results was 13 rpm with a 45% indentation percentage and the optimal distance between the disks was 1.5 cm. [Display omitted] • RBC bioreactor producing BC was modeled based on one-dimensional O 2 mass transfer. • mass transfer was modeled in the direction perpendicular to the surface of discs. • mathematical model was simulated with finite difference method in MATLAB software. • increasing of angular velocity increases the K L a and mass transfer rate of O 2. • at a certain angular velocity, K L a of O 2 increases by immersion depth increasing. [ABSTRACT FROM AUTHOR]

Abstract: Microbial fuel cells (MFCs) are a sustainable technology for the direct conversion of biodegradable organics in wastewater into electricity. In most MFCs, the oxygen reduction reaction (ORR) is used as the cathode reduction reaction. Aerobic biocathodes, which use bacteria as biocatalysts to catalyze the cathode ORR, provide self‐sustained, robust and highly active alternatives to chemical catalysts. However, further study of the effect of oxygen mass transfer to the biofilm and cathode materials design is needed. In the current work, two aerobic biocathodes were enriched in half‐cells, and oxygen mass transfer to the biofilm and the biofilm distribution in the porous electrode structure were investigated. It was found that mass transfer of oxygen to the aerobic biocathode was a significant factor affecting cathode ORR, evidenced by a strong correlation between the air flow rate and current. Additionally, it was found that the biofilm penetrates between 20–30% into the porous carbon electrode structure, which is likely due to oxygen mass transfer limitations. The performance of a MFC with biocatalysts at both anode and cathode (64 µW cm−2 peak power at an air flowrate of 1 L min−1) showed strong correlation with air flowrate, confirming the observation in the half‐cell system. [ABSTRACT FROM AUTHOR]

Gas-liquid mass transfer of gaseous reactants is a major limitation for high space-time yields, especially for O2-dependent (bio)catalytic reactions in aqueous solutions. Herein, oxygenic photosynthesis was used for homogeneous O2 supply via in situ generation in the liquid phase to overcome this limitation. The phototrophic cyanobacterium Synechocystis sp. PCC6803 was engineered to synthesize the alkane monooxygenase AlkBGT from Pseudomonas putida GPo1. With light, but without external addition of O2, the chemo- and regioselective hydroxylation of nonanoic acid methyl ester to ω-hydroxynonanoic acid methyl ester was driven by O2 generated through photosynthetic water oxidation. Photosynthesis also delivered the necessary reduction equivalents to regenerate the Fe2+ center in AlkB for oxygen transfer to the terminal methyl group. The in situ coupling of oxygenic photosynthesis to O2-transferring enzymes now enables the design of fast hydrocarbon oxyfunctionalization reactions. [ABSTRACT FROM AUTHOR]

In this work, CFD is used to simulate the gas-liquid dispersion coupled to the kinetics of the iron(II) removal from drinking water by aeration process in a split-rectangular airlift reactor. The model aims to describe oxidation of iron(II) into insoluble iron(III) species in water treatment, so that hydrodynamics, oxygen mass transfer, chemical reactions, and pH change can be taken into account. In comparison to the abundant literature using CFD on airlift reactors, this work focuses on a particular reactor in which a highly non-uniform primary gas distribution is ensured by a 3.5 mm diameter single-orifice nozzle located at the bottom center of the riser. This makes convergence more difficult, as local gas velocity is high near the nozzle. A multiphase Euler-Euler model with a unique bubble size and a standard k – ε model of turbulence are used. The 3-D CFD simulations are able to predict the liquid circulation velocity and the average gas holdup both in the riser and the downcomer. The model can also identify the transition from the gas flow regimes without bubbles and with stationary bubbles in the downcomer, while predicted k L a values agree with reoxygenation experiments. Finally, the simulations also predict accurately the oxidation of iron(II) vs. time without or in the presence of iron(III) as a catalyst, and they are also able to detect where local heterogeneities in dissolved oxygen concentration can emerge when pH and/or the amount of catalyst is increased. [ABSTRACT FROM AUTHOR]

In this study, the dependency of energy recovery on separator characteristics applied in microbial fuel cells (MFCs) was sought by testing an emerging class of membranes (supported ionic liquid membranes (SILMs), prepared with [hmim][PF 6 ] and [bmim][NTf 2 ] ionic liquids) comparatively with well-known proton exchange (Nafion N115) and microfiltration (PVDF) counterparts. Crucial membrane features such as O 2 and substrate (acetate as the sole carbon source) crossovers were assessed and as a result, mass transfer as well as diffusivity coefficients of these compounds ( k O , k A , D O , D A , respectively) were determined. The experiments showed that SILM-operated MFCs could work in a reliable way and among them, the [bmim][NTf 2 ]-based one produced higher specific energy yield ( Y S = 9.78 kJ g −1 CODin m −2 ) than the Nafion-MFC ( Y S = 8.25 kJ g −1 CODin m −2 ) used as an important reference. This outcome was found to be associated with the membrane-cross oxygen shuttle properties of the membranes ( k O = 1.25 cm s −1 and 1.31 cm s −1 , respectively). As for the two SILMs, significant differences in terms of the energy yield, mass transfer and diffusion coefficients were noted, however, it has appeared from cell polarization measurements that the internal resistances of the SILM-MFCs were nearly the same. The evaluation of the SILM-operated MFCs’ power production was complemented by measuring the dielectric traits of ionic liquids that can be related with the ion conductivity of these materials. It turned out that the [hmim][PF 6 ] IL had an order of magnitude lower ionic conductivity. [ABSTRACT FROM AUTHOR]

In wastewater treatment plants (WWTPs) using the activated sludge process, two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strategy. Aeration efficiency is closely linked to sludge characteristics (such as concentrations of mixed liquor suspended solids (MLSS) and microbial communities) and operating conditions (such as air flow rate and operational dissolved oxygen (DO) concentrations). Moreover, operational DO is closely linked to effluent quality. This study, which is in reference to WWTP discharge class A Chinese standard effluent criteria, determined the growth kinetics parameters of nitrifiers at different DO levels in small-scale tests. Results showed that the activated sludge system could meet effluent criteria when DO was as low as 0.3 mg/L, and that nitrifier communities cultivated under low DO conditions had higher oxygen affinity than those cultivated under high DO conditions, as indicated by the oxygen half-saturation constant and nitrification ability. Based on nitrifier growth kinetics and on the oxygen mass transfer dynamic model (determined using different air flow rate ( Q ′ air ) and mixed liquor volatile suspended solids (MLVSS) values), theoretical analysis indicated limited potential for energy saving by improving aeration diffuser performance when the activated sludge system had low oxygen consumption; however, operating at low DO and low MLVSS could significantly reduce energy consumption. Finally, a control strategy coupling sludge retention time and MLVSS to minimize the DO level was discussed, which is critical to appropriate setting of the oxygen point and to the operation of low DO treatment technology. [ABSTRACT FROM AUTHOR]

A new metallurgical process via aeration for the decomposition of vanadium slag in concentrated NaOH solution was proposed. The improvement of oxygen mass transfer coefficient when using aeration at different NaOH concentration was studied and the effects of critical reaction parameters on vanadium extraction were systematically investigated. The optimal condition was determined to be: alkali concentration of 60%, reaction temperature of 130 °C, alkali-to-ore mass ratio of 6:1, stirring speed of 500 rpm. The yield of vanadium could reach to 97.41% after reacting for 6 h under this reaction condition. The reaction temperature in this new method is 50–270 °C lower than the current liquid oxidation methods reported in the literatures, and the medium alkaline concentration declined from 85% to 60%, exhibiting significant advantages in energy consumption as well as reactor design. Kinetics study indicated that the extraction of vanadium was governed by internal diffusion, and the apparent activation energy was calculated to be 17.57 kJ/mol. [ABSTRACT FROM AUTHOR]

In this work, an easily implemented and cost-effective activated carbon (AC) enhanced technique was proposed for C5 sugar acid production from corncob hemicellulose hydrolysates. The optimum AC detoxification conditions were obtained by response surface methodology, and the fermentation kinetics behaviors were comparatively evaluated using two fermentation modes: separate detoxification and fermentation (SDF) and in-situ detoxification and fermentation (In-situDF). An investigation of the AC function demonstrates it offers synchronous detoxification and oxygen transfer enhancement, with a final increase of XA fermentation yield and productivity. This study shows a potential of detoxification and oxygen transfer enhancement in one-pot in C5 sugar acid production, which may smooth the way for commercial utilization of C5 sugars from lignocellulosic biomass in the future. • A novel integrated process was developed to produce C5 sugar acid by AC addition. • 100% removal of furfural and HMF coupled with 6.4% xylose loss was achieved. • AC acted as an oxygen transfer enhancement additive, in addition to a detoxifier. • XA production in the in-situDF process reached that of the SDF process. [ABSTRACT FROM AUTHOR]