Oxygen Transfer Rate Research Articles

The Absence of Phasins PhbP2 and PhbP3 in Azotobacter vinelandii Determines the Growth and Poly-3-hydroxybutyrate Synthesis.

Phasins are proteins located on the surface of poly-3-hydroxybutyrate (P3HB) granules that affect the metabolism of the polymer, the size and number of the granules, and some also have stress-protecting and growth-promoting effects. This study evaluated the effect of inactivating two new phasins (PhbP2 or PhbP3) on the cellular growth, production, and molecular mass of P3HB in cultures under low or high oxygen transfer rates (OTR). The results revealed that under high OTRₘₐₓ conditions (between 8.1 and 8.9 mmol L-1 h-1), the absence of phasins PhbP2 and PhbP3 resulted in a strong negative effect on the growth rate; in contrast, the rates of specific oxygen consumption increased in both cases. This behavior was not observed under a low oxygen transfer rate (3.9 ± 0.71 mol L-1 h-1), where cellular growth and oxygen consumption were the same for the different strains evaluated. It was observed that at high OTR, the absence of PhbP3 affected the production of P3HB, decreasing it by 30% at the end of cultivation. In contrast, the molecular weight remained constant over time. In summary, the absence of phasin PhbP3 significantly impacted the growth rate and polymer synthesis, particularly at high maximum oxygen transfer rates (OTRₘₐₓ).

UHPLC-Q-Orbitrap metabolomics of Syrah red wines during bottle ageing: Molecular markers of evolution and cork permeability

An experiment involving the ageing of Syrah red wine was conducted over a period of 24 months, during which the impact of four different micro-agglomerated corks was examined. An untargeted UHPLC-Q-Orbitrap metabolomics analysis was performed and provided valuable insights into the chemical dynamics of red wine evolution. Forty-three specific discriminating compounds were found for non-aged wines, including various CHO and CHON-types molecules. Thirteen specific discriminating compounds were found for 24-months-aged wines including CHO, CHNOS and CHOS compounds. Among them, sulfonated flavanols and pyranoanthocyanins were identified and emerged as key molecular markers of wine ageing. This metabolomics analysis also enabled us to identify specific chemical markers of cork oxygen transfer rate (OTR) influence. Analysis revealed specific molecules linked to corks with low and high OTR such as anthocyanins and proanthocyanins respectively. This research enhances our comprehension of intricate chemical changes during red wine ageing and underscores the potential impact of cork OTR on wine composition.

Oxygen uptake rate analysis to evaluate the impact of hydrodynamic stress on the growth of the avian cell line DuckCelt®-T17

Scale-up of bioprocesses involving animal cell culture is hampered by the sensitivity of the cells to hydrodynamic stress, either from agitation or bubble bursting. Here, the hydrodynamic stress experienced by a recent cell line, the DuckCelt®-T17 avian cells, previously used for viral vaccine production, is investigated in shake flasks and in a 3 L bioreactor. Cell stress was assessed by monitoring the dissolved oxygen in the culture medium, which depends on Oxygen Transfer Rate (OTR) and Oxygen Uptake Rate (OUR) during cultivation. Classical parameters such as the maximum growth rate (µmax) and metabolite profiles were also determined. A dynamic model able to predict nutrient consumption, metabolic waste production, viable cell number and OUR was also developed and validated from the data measured in shake flasks. The experiments performed in the stirred tank bioreactor (STBR) show that OUR depended on both the cell growth phase and the stirring conditions. The oxygen consumption of the cells during the exponential growth phase (where there were no nutrient and O2 limitations) was significantly altered at average and maximum shear rates above 70 and 840 s−1, respectively, indicating highly shear-sensitive cells. OUR is a suitable tool to identify the hydrodynamic conditions for robust cell growth. The scale-up criteria to be favored for the DuckCelt®-T17 cell culture in STBRs would be the shear and/or the tip’s speed.

Bioprocess strategies for enhanced performance in single‐use bioreactors for biomolecule synthesis: A biokinetic approach

AbstractSingle‐use bioreactors (SUB) have made a significant impact on the field of bioprocessing, becoming increasingly popular for biomolecule synthesis due to their many advantages, such as minimizing contamination risks and streamlining processes. Extensive research has been conducted on the hydrodynamic conditions within single‐use bioreactors, with a focus on parameters like mixing time, oxygen transfer rate, and stress levels to improve cell cultivation procedures. Several studies have demonstrated that SUB can effectively nurture various cell types, including those that generate monoclonal antibodies, yielding outcomes similar to conventional bioreactor systems, thus highlighting their adaptability and effectiveness in biomolecule processing. SUB equipped with wave mechanisms have shown to display comparable metabolic behaviors and fermentation consistency to conventional bioreactors, confirming their dependability in supporting fungal growth and metabolite generation. Mechanical stirring for agitation leads to high shear forces alongside enhanced monitoring and control, influencing microbial physiology and macro‐morphologies. This underscores the importance of operational factors such as rocking speed, rocking angle, and gas flow rate. Overall, the integration of single‐use bioreactors in biomolecule synthesis is expected to expand, driven by the need for increased yields and cost‐effective manufacturing solutions.

Impact of hydromechanical stress on CHO cells’ metabolism and productivity: Insights from shake flask cultivations with online monitoring of the respiration activity

The hydromechanical stress is a relevant parameter for mammalian cell cultivations, especially regarding scale-up processes. It describes the mechanical forces exerted on cells in a bioreactor. The maximum local energy dissipation rate is a suitable parameter to characterize hydromechanical stress. In literature, different studies deal with the effects of hydromechanical stress on CHO cells in stirred tank reactors. However, they often focus on lethal effects. Furthermore, systematic examinations in smaller scales like shake flasks are missing. Thus, this study systematically considers the influence of hydromechanical stress on CHO DP12 cells in shake flask cultivations. By utilizing online monitoring of the oxygen transfer rate, the study simplifies and enhances the resolution of examinations. Results indicate that while lethal effects are absent, numerous sub-lethal effects emerge with increasing hydromechanical stress: The process time is prolonged. The time of glucose and glutamine depletion, and the lactate switch correlate positively linear with the logarithmic average energy dissipation rate while the maximum specific growth rate correlates negatively. Strikingly, the final antibody concentration only declines at the highest tested average energy dissipation rate of 3.84Wkg-1 (only tested condition with a turbulent flow regime and therefore a higher maximal local energy dissipation rate) from about 250mgL-1 to about 180mgL-1. This study presents a straightforward method to examine the impact of hydromechanical stress in shake flasks, easily applicable to any other suspension cell line. Additionally, it offers valuable insights for scale-up processes, for example into stirred tank reactors.

Anionic and cationic co-doping to enhance the oxygen transport property of Bi0.5Sr0.5FeO3-δ as a high-performance air electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) have attracted considerable interest due to their efficient energy conversion. However, the low catalytic activity of air electrodes limits the application of RSOCs. Bi0.5Sr0.5Fe0.9Ta0.1O3-δ developed in our previous work exhibits a comparatively desirable performance and is expected to be further optimized. Herein, a novel strategy of anionic F and cationic Ta co-doped Bi0.5Sr0.5Fe0.9Ta0.1O3-δ-xFx (x = 0, 0.05, 0.10, 0.15, denoted as, BSFTF0, BSFTF5, BSFTF10, BSFTF15) materials are obtained to enhance the oxygen transport property of Bi0.5Sr0.5FeO3-δ for RSOCs. The polarization resistance (Rp) of BSFTF10 (0.017 Ω cm2) decreases by 66 % compared with that of BSFTF0 (0.051 Ω cm2) at 800 °C. In fuel cell mode, the single cell with BSTF10 reaches the maximum power density of 908 mW cm−2, which is approximately 72 % higher than the only Ta-doped BSFTF0 (527 mW cm−2) at 800 °C. In electrolysis mode, the single cell with BSFTF10 exhibits a high electrolysis current density of 1679 mA cm−2, indicating an approximately 90 % increase compared to that of BSFTF0 at 800 °C and 1.5 V with 70 % CO2-30 % CO feed gas. The bulk chemical diffusion (Dchem) of BSFTF10 is up to 5.12 × 10−4 cm2 s−1, which is 4.3 times higher than that of BSFTF0. The superior oxygen transport property of BSFTF10 is attributed to the high electronegativity of F− (4.0) and low electronegativity of Ta5+(1.8), which may weaken the chemical bonding between B-site ions and O2−, generating more oxygen vacancies and accelerating the rate of oxygen transfer. The results indicate that F and Ta co-doping is an effective strategy to develop a highly catalytically active air electrode for RSOCs featuring oxygen transport properties.

Unraveling the impact of pH, sodium concentration, and medium osmolality on Vibrio natriegens in batch processes

BackgroundVibrio natriegens, a halophilic marine γ-proteobacterium, holds immense biotechnological potential due to its remarkably short generation time of under ten minutes. However, the highest growth rates have been primarily observed on complex media, which often suffer from batch-to-batch variability affecting process stability and performance. Consistent bioprocesses necessitate the use of chemically defined media, which are usually optimized for fermenters with pH and dissolved oxygen tension (DOT) regulation, both of which are not applied during early-stage cultivations in shake flasks or microtiter plates. Existing studies on V. natriegens’ growth on mineral media report partially conflicting results, and a comprehensive study examining the combined effects of pH buffering, sodium concentration, and medium osmolality is lacking.ResultsThis study evaluates the influence of sodium concentration, pH buffering, and medium osmolality on the growth of V. natriegens under unregulated small-scale conditions. The maximum growth rate, time of glucose depletion, as well as the onset of stationary phase were observed through online-monitoring the oxygen transfer rate. The results revealed optimal growth conditions at an initial pH of 8.0 with a minimum of 300 mM MOPS buffer for media containing 20 g/L glucose or 180 mM MOPS for media with 10 g/L glucose. Optimal sodium chloride supplementation was found to be between 7.5 and 15 g/L, lower than previously reported ranges. This is advantageous for reducing industrial corrosion issues. Additionally, an osmolality range of 1 to 1.6 Osmol/kg was determined to be optimal for growth. Under these optimized conditions, V. natriegens achieved a growth rate of 1.97 ± 0.13 1/h over a period of 1 h at 37 °C, the highest reported rate for this organism on a mineral medium.ConclusionThis study provides guidelines for cultivating V. natriegens in early-stage laboratory settings without pH and DOT regulation. The findings suggest a lower optimal sodium chloride range than previously reported and establish an osmolality window for optimal growth, thereby advancing the understanding of V. natriegens’ physiology. In addition, this study offers a foundation for future research into the effects of different ions and carbon sources on V. natriegens.

The influence of water turbulence on surface deformations and the gas transfer rate across an air–water interface

We present experimental results of a study on oxygen transfer rates in a water channel facility with varying turbulence inflow conditions set by an active grid. We compare the change in gas transfer rate with different turbulence characteristics of the flow set by four different water channel and grid configurations. It was found that the change in gas transfer rate correlates best with the turbulence intensity in the vertical direction. The most turbulent cases increased the gas transfer rate by 30% compared to the low turbulence reference case. Between the two most turbulent cases studied here, the streamwise turbulence and largest length scales in the flow change, while the gas transfer rate is relatively unchanged. In contrast, for the two less turbulent cases where the magnitude of the fluctuations normal to the free surface are also smaller, the gas transfer rate is significantly reduced. Since the air–water interface plays an important role in the gas transfer process, special attention is given to the free-surface deformations. Despite taking measures to minimise it, the active grid also leaves a direct imprint on the free surface, and the majority of the waves on the surface originate from the grid itself. Surface deformations were, however, ruled out as a main driver for the increase in gas transfer because the increase in surface area is < 0.25%, which is two orders of magnitude smaller than the measured change in the gas transfer rate.

Five-day Wearable Respiratory Support With a Novel Ambulatory Pulmonary Assist System in an Awake Ovine Model.

The pulmonary assist system (PAS) is a wearable respiratory support system that is currently under development for patients with chronic lung disease as a bridge to lung transplantation or as destination therapy. This study evaluates the long-term performance and biocompatibility of the PAS in a 5-d awake, ovine model. The PAS was attached to normal sheep in venovenous configuration. Components of the PAS included a 0.9 m2 surface area oxygenator and a lightweight, battery-powered axial flow pump. The system was also tested using the Abbott PediMag as the control pump. Each sheep was supported on the PAS for 5 d with 2 L/min blood flow and 4 L/min sweep gas. Activated clotting times of 200-240 s were maintained using intravenous heparin. Pump performance, oxygen transfer, oxygenator resistance, and hematologic parameters were measured throughout the support. The PAS, either using the axial flow pump or PediMag (n = 4 each), was well tolerated by the sheep without signs of device-related organ damage or hemolysis. All the studies achieved the full, 5-d study duration. The oxygenator resistance remained consistent without significant clot formation in all experiments with an average resistance of 2.55 ± 0.10 mm Hg/(L/min). The system achieved an average oxygen transfer rate of 116.4 ± 5.5 mL/min, with an average Hb concentration of 9.2 ± 0.6 g/dL. White blood cell, platelet, and hematocrit levels also remained stable and within normal limits throughout the study period. The PAS provided 5 d of uncomplicated ambulatory respiratory support with minimal clot formation, stable gas exchange, blood flow resistance, and hematologic parameters.

Improving the transfer of dissolved oxygen in a biological Fe2+ oxidation process using a venturi jet as an intensive aeration system

The low bio-production of Fe3+ as a leaching agent is one of the main limitations to implementing industrial bio-processes at feasibility conditions. The main limitation of the bio-oxidation process of Fe2+ is the low oxygen transfer to the aqueous phase because of the low oxygen solubility. This study assesses the effectiveness of the venturi jet as an innovative and intensive aeration device for overcoming the oxygen limitation in a continuous ferrous oxidation process in a fixed-bed reactor with immobilized acidithiobacillus ferrooxidans, in contrast to the conventional diffuser aeration device. Firstly, the influence of the airflow and the influence of the medium concentration were determined for the following parameters for both aeration devices; Volumetric mass transfer coefficient (kLa), Standard Oxygen Transfer Rate (SOTR), Standard Aeration Efficiency (SAE), and Standard Oxygen Transfer Efficiency (SOTE). Then, both aeration devices were compared in a continuous bio-oxidation process in an up-flow packed bio-reactor (UFPB). The system performance was assessed by monitoring temperature, pH, oxidation-reduction potential, and dissolved oxygen concentration for 69 days. Findings displayed that when aerating with the diffuser, the ferrous oxidation rate was restricted by the low dissolved oxygen availability, being about 1 ppm (1 mg L−1). Under these oxygen-limiting conditions, the maximum ferrous (Fe2+) oxidation rate was 9.09 g L−1 h−1. However, when aerating with the venturi jet, the dissolved oxygen concentration increased up to 2.70 mg L−1, achieving a maximum of 29.11 g L−1 h−1. So, this study has demonstrated that the change in the aeration device has resulted in an improvement in the process, achieving a 3.5-fold increase in the oxidation rate. Furthermore, the venturi jet offered additional advantages over the diffuser, such as requiring less power to deliver the same amount of air, being unaffected by jarosite precipitates, and not requiring a supply of compressed air.

Efficient Bio-Oxidation of Cellobiose with Engineered Gluconobacter oxydans to Provide Highly Concentrated Cellobionic Acid

Cellobionic acid (CBA) can be obtained through the oxidation of cellobiose, the monomer of cellulose. CBA serves as a plant-based alternative to its stereoisomer lactobionic acid, which is used in the pharmaceutical, cosmetic, and food industries. Gluconobacter oxydans is a well-established whole-cell biocatalyst with membrane-bound dehydrogenases (mDH) for regio-specific oxidations. As G. oxydans wildtype cells show low cellobiose oxidation activities, the glucose mDH from Pseudomonas taetrolens was overexpressed in G. oxydans BP9, a multi mDH deletion strain. Whole-cell biotransformation studies were performed with resting cells of the engineered G. oxydans in stirred tank bioreactors. Initial biomass specific cellobionate formation rates increased with increasing cellobiose concentrations up to 190 g L−1, and were constant until the solubility limit. The maximal volumetric CBA formation rates and the oxygen uptake rates increased linearly with the concentration of engineered G. oxydans. This enables the estimation of the maximum biocatalyst concentration limited by the maximum oxygen transfer rate of any bioreactor. Thus, 5.2 g L−1 G. oxydans was sufficient to produce 502 g L−1 CBA with &gt;99% yield in a simple aerobic batch process. The highly concentrated CBA will reduce downstream processing costs considerably after cell separation.

Advancing precision fermentation: Minimizing power demand of industrial scale bioreactors through mechanistic modelling

Minimizing power consumption in large-scale aerobic fermentation is essential for cost-effective operations. A mechanistic model of aerobic precision fermentation was developed integrating microbial growth parameters, thermodynamic data, and bioreactor properties. Results showed that agitation power dominated energy consumption at low oxygen transfer rates (OTR), shifting to aeration power (70 % of total) at high cell growth rates. In high OTRs, mixing time reduced to 60 s from an initial value of 211 s. Scale-up from 5 m³ to 100 m³ decreased total specific power by 88 %. Operating at elevated headspace pressure lowered agitation speed, reducing total power consumption at high OTR. Impeller to bioreactor diameter ratio impacted the required agitation speed without significantly altering total power demand. Experimental data in a 100 L case study indicated a 0.43 kW.m⁻³ average power requirement across a 96-hour fermentation period. Our model demonstrates effective strategies for minimization of power consumption in industrial-scale aerobic fermentations.

Diffusion-driven fed-batch fermentation in perforated ring flasks

PurposeSimultaneous membrane-based feeding and monitoring of the oxygen transfer rate shall be introduced to the newly established perforated ring flask, which consists of a cylindrical glass flask with an additional perforated inner glass ring, for rapid bioprocess development.Methods A 3D-printed adapter was constructed to enable monitoring of the oxygen transfer rate in the perforated ring flasks. Escherichia coli experiments in batch were performed to validate the adapter. Fed-batch experiments with different diffusion rates and feed solutions were performed.ResultsThe adapter and the performed experiments allowed a direct comparison of the perforated ring flasks with Erlenmeyer flasks. In batch cultivations, maximum oxygen transfer capacities of 80 mmol L−1 h−1 were reached with perforated ring flasks, corresponding to a 3.5 times higher capacity than in Erlenmeyer flasks. Fed-batch experiments with a feed reservoir concentration of 500 g glucose L−1 were successfully conducted. Based on the oxygen transfer rate, an ammonium limitation could be observed. By adding 40 g ammonium sulfate L−1 to the feed reservoir, the limitation could be prevented.Conclusion The membrane-based feeding, an online monitoring technique, and the perforated ring flask were successfully combined and offer a new and promising tool for screening and process development in biotechnology.

On the Oxygenation Efficacy of Geoengineered Artificial Downwelling in the Estuarine Ecosystem

AbstractThis study examines the oxygenation efficacy of geoengineered artificial downwelling (AD) in the hypoxia zone of the Pearl River Estuary (PRE) using a fine‐resolution coupled physical‐biogeochemical model. Like many estuaries worldwide, the PRE experiences summer hypoxia because of intense stratification and eutrophication. AD provides a potential solution for short‐term hypoxia relief via the mixture of surface and bottom water, but its oxygenation efficacy relying on both local hydrodynamics and biogeochemistry is largely uncertain. Our simulations suggest that AD has extremely low oxygenation efficacy in the PRE during the hypoxia period. The estimated oxygen transfer efficiency (OTE), defined as the rate of oxygen transfer per unit of power needed for pumping, varies between −0.81 and +0.92 kg O2 kWh−1. This is an order of magnitude less than the previous estimate of 10–100 kg kWh−1 in closed lakes and fjords. Moreover, a negative OTE means that AD sometimes backfires and exacerbates hypoxia in the bottom water. The above results remain unchanged when different values of engineering parameters including downwelling rate and discharging depth are used. Extremely low oxygenation efficacy is attributed to strong subtidal advection in the estuary as well as the engineering side effects including reduced vertical diffusion.

Mechanism of heterogeneous reduction of NO over graphite-supported single-atom Fe catalyst: DFT study

The mechanism of nitrogen oxide (NO) reduction over graphite carbon-supported single-atom iron (Fe) catalyst (Fe/G) was investigated by density functional theory (DFT) and transition state theory (TST). The catalyst deactivation was also analyzed. The results revealed that the NO reduction, based on the Eley-Rideal (E-R) mechanism, underwent four stages including N2O formation and release as well as N2 formation and release. However, the NO reduction only involved two stages according to Langmuir-Hinshelwood (L-H) mechanism: N2 formation and release. Furthermore, for the E-R mechanism, the rate-controlling step was NO reduction, where a NO molecule was adsorbed on an Fe atom with an N, O-down structure with energy barrier of 15.5 kJ/mol, lower than that of other paths. Energy barrier analysis indicated that the energy barrier for the reduction of reactive oxygen species was higher than that for the formation of N2. Reactive oxygen species remaining on the surface of Fe atoms after NO decomposition inhibited the adsorption and reduction of NO, leading to catalyst deactivation due to the absence of active sites. The single-atom Fe species promoted the NO reduction. Kinetic analysis results suggested that, upon increasing the reaction temperature, the NO reduction rate increased more significantly than the reactive oxygen transfer rate.

Improving the performance of microbubble through the modification and optimization of venturi-type generator

Venturi-type generators are recognized as one of the most promising microbubble generators with potential in various fields. However, there is still room for further optimization of their performance to meet the requirements of real applications, such as aeration systems or water treatment applications. This research modified the geometry of a venturi-type generator with specific dimensions: a length of 80 mm, an inside diameter of 26 mm, a throat diameter of 7.2 mm, a convergent nozzle angle of 30°, a divergent diffuser angle of 30°, and an airflow inlet diameter of 6 mm. By varying the water flow rates (i.e., 22 L/min, 26 L/min, and 30 L/min) and air flow rates (i.e., 0.1 L/min, 0.2 L/min, and 0.3 L/min), the study observed the average diameter, size distribution, Standard Oxygen Transfer Rate (SOTR), and Standard Aeration Efficiency (SAE) of the generated microbubbles. This study aims to improve the performance of a microbubble generator, particularly by optimizing the relative size, distribution, and main parameters for real applications. The proposed modification and optimization successfully produced microbubbles with an average diameter of 180-450 μm. Furthermore, the optimal combinations of water and air flow rates (i.e., 30 L/min of water and 0.1 L/min of air) produced approximately 60% of microbubbles with a diameter of no more than 200 μm. These combinations also enable the delivery of a SOTR and SAE values of 0.94 kgO2/h and 1.73 kgO2/kWh, respectively.

Online monitoring of the respiration activity in 96-deep-well microtiter plate Chinese hamster ovary cultures streamlines kill curve experiments.

Cell line generation of mammalian cells is a time-consuming and labor-intensive process, especially because of challenges in clone selection after transfection. Antibiotics are common selection agents for mammalian cells due to their simplicity of use. However, the optimal antibiotic concentration must be determined with a kill curve experiment before clone selection starts. The traditional kill curve experiments are resource-intensive and time-consuming due to necessary sampling and offline analysis effort. This study, thus, explores the potential of online monitoring the oxygen transfer rate (OTR), as a non-invasive and efficient alternative for kill curve experiments. The OTR is monitored using the Transfer-rate Online Measurement (TOM) system and the micro(μ)-scale Transfer-rate Online Measurement (μTOM) device, which was used for mammalian cells first. It could be shown that the OTR curves for both devices align perfectly, affirming consistent cultivation conditions. The μTOM device proves effective in performing kill curve experiments in 96-deep-well plates without the need for sampling and offline analysis. The streamlined approach reduces medium consumption by 95%, offering a cost-effective and time-efficient solution for kill curve experiments. The study validates the generalizability of the method by applying it to two different CHO cell lines (CHO-K1 and sciCHO) with two antibiotics (puromycin and hygromycin B) each. In conclusion, the broad application of OTR online monitoring for CHO cell cultures in 96-deep-well plates is highlighted. The μTOM device proves as a valuable tool for high-throughput experiments, paving the way for diverse applications, such as media and clone screening, cytotoxicity tests, and scale-up experiments.

Analyzing of hydrodynamic stress and mass transfer requirements of a fermentation process carried out in a coaxial bioreactor: a scale-up study.

Fluid hydrodynamic stress has a deterministic effect on the morphology of filamentous fungi. Although the coaxial mixer has been recognized as a suitable gas dispersion system for minimizing inhomogeneities within a bioreactor, its performance for achieving enhanced oxygen transfer while operating at a reduced shear environment has not been investigated yet, specifically upon scale-up. Therefore, the influence of the impeller type, aeration rate, and central impeller retrofitting on the efficacy of an abiotic coaxial system containing a shear-thinning fluid was examined. The aim was to assess the hydrodynamic parameters, including stress, mass transfer, bubble size, and gas hold-up, upon conducting a scale-up study. The investigation was conducted through dynamic gassing-in, tomography, and computational fluid dynamics combined with population balance methods. It was observed that the coaxial bioreactor performance was strongly influenced by the agitator type. In addition, coaxial bioreactors are scalable in terms of shear environment and oxygen transfer rate.

Manipulating dissolved oxygen concentration to control the partitioning between carbon oxidation and redirection in the A-stage high rate activated sludge process

The adsorption/bio-oxidation (A/B) process has emerged as a remedy to the significant energy use from wastewater treatment plants. In such a process, the A-stage's objective is to balance maintaining high COD redirection towards recovery streams with achieving high effluent quality to facilitate energy savings in the B-stage. While SRT was intensively investigated to control A-stage performance, this study investigates the use of dissolved oxygen (DO) concentration under two adverse conditions: short and long residence times (SRT and HRT). The findings indicate that excessive oxidation is impeded at short residence times, meanwhile, high DO concentration (>2 mgO2/L) is required for enhanced substrate utilization and high removal efficiencies. Conversely, low DO concentration (< 0.5 mgO2/L) is needed at long residence times to control the system's oxidative status and partition more COD towards redirection instead of oxidation. Whereas, high removal efficiency is governed by the long residence times. Notably, this study implies that the low COD removal efficiencies in existing A-stage systems can be referred to the need to deliver oxygen at rates beyond the maximum achievable oxygen transfer rates in full-scale systems. Novelly, this study demonstrates that systems operated at lower rates coupled with low DO concentration can achieve higher COD removal efficiencies while maintaining high COD diversion.

Designing a self-breathing electrode modulated by spatial hydrophobic microenvironments with stabilized H2O2 generation for wastewater treatment

A novel self-breathing air-diffusion rod graphite electrode (ADE-RG) engineered with spatial hydrophobic microenvironments was developed to enhance H2O2 production without external air aeration. The microenvironments, created through thermal shaking-induced turbulence and centrifugal effect, significantly improved the air-diffusion capability. This innovation led to the increase in H2O2 generation (3.36 times higher than that in the unmodified system) due to a locally enhanced electric field, increased oxygen transfer rate, and improved selectivity for two-electron transfer process. Furthermore, incorporating polyepoxysuccinic acid into the electrolyte not only prevents electrode scaling but also minimizes H2O2 decomposition, culminating in the H2O2 concentration of 50.64 ± 2.92 mg L−1 cm−2. Notably, the system performed prominently in treating industrial rifampicin wastewater, achieving a degradation efficiency of 95.29 ± 0.47%, even under high-loading conditions (initial COD was 22,898.50 ± 405.17 mg L−1). These results indicate the significant potential of the self-breathing ADE-RG system in broad-scale wastewater treatment applications.