Oxygen Transfer Rate Research Articles

Energy and carbon footprint analysis of municipal wastewater treatment process integrated with food waste disposer

Household food waste (FW) management has become an emerging environmental issue affecting sustainable urban development. The application of in-sink domestic food waste disposers (FWDs) have brought significant public attentions due to its simplified waste handling process and reduced household expenses. However, the potentail negative impacts of mixing FW in the sewer system, i.e., the reduction of aeration efficiency in wastewater treatment processes (WWTPs) and corresponding increase of greenhouse gas (GHG) emission, has not been quantified. In this study, real-time oxygen transfer efficiency in processing water was measured in WWTPs receiving negligible amount of FW and compared with those receiving sewage combined with FWD effluent. WWTP receiving sewage with FW had 6–10% lower oxygen transfer rate than those without FW, resulting in extra energy consumptions of 0.25–0.30 kWh/m3 and GHG emissions of 0.35–0.41 kg CO2/m3. For estimating the substantial impacts of FWD to the carbon cycle, sludge treatment scenarios were designed among anaerobic digestion (AD), incineration, and direct landfill disposal. Compared with AD (−0.07 kWh/kg) and incineration (0.112 kWh/kg), FWD/WWTP consumed more energy (0.69–0.9 kWh/kg) and most of which (∼64%) was required by aeration. The operating costs of WWTPs also increased by 1.6–2.1 times in comparison with those did not receive FW. The application of FWD, however, could reduce the overall GHG emissions by 35.2% in comparison with direct landfilling. Decision-makers should guide householders and waste management practitioners through new policies such as carbon credits and/or waste charging scheme to support more environmental-friendly disposal methods of FW, especally when the maturity of socio-economic conditions are of concerns. Compared with AD and incineration, FWD may be a compromising alternative to control GHG emissions with existing wastewater treatment facilities especially to those regions where complete FW classification and treatment are not well-established.

The Effect of Mixing Chamber Configuration and Submersion Depth on Centrifugal Aerator Performance

Centrifugal aerators are a vital piece of equipment in water treatment. To improve the efficiency and economy of their operation, a study of their mixing chamber structure and submergence depth was carried out using a combination of numerical simulations and experiments. A centrifugal aerator dissolved oxygen (DO) test bench was built and the numerical simulation was compared with the experiment, the inlet air flow rate showing only a 2.23% error, which verifies the reliability of the numerical simulation. The results show that the capacity of oxygen dissolved in the aeration tank increases and then decreases as the relative area ratio (ð) of the mixing chamber increases, reaching the best capacity at ð = 8.38. In the case of different submergence coefficients (β), the gas volume fraction increased by 31.29% on average at β = 0.15; the standard oxygen transfer rate (SOTR) increased and then decreased with the increase of β, with an average increase of 56.6%. Moreover, the oxygenation performance of centrifugal aerators was significantly improved by the reasonable submergence depth and the structure of the mixing chamber.

Improving carboxymethyl cellulose edible coating using ZnO nanoparticles from irradiated Alternariatenuissima

In this paper, gamma-irradiation was successfully used to intensify the yield of Zinc oxide nanoparticles (ZnONPs) produced by the fungus Alternariatenuissima as a sustainable and green process. The obtained data showed that 500 Gy of gamma-irradiation increased ZnONPs’ yield to approximately four-fold. The synthesized ZnONPs were then exploited to develop active Carboxymethyl Cellulose films by casting method at two different concentration of ZnONPs 0.5% and 1.0%. The physicochemical, mechanical, antioxidant, and antimicrobial properties of the prepared films were evaluated. The incorporation of ZnONPs in the Carboxymethyl Cellulose films had significantly decreased solubility (from 78.31% to 66.04% and 59.72%), water vapor permeability (from 0.475 g m−2 to 0.093 g m−2 and 0.026 g m−2), and oxygen transfer rate (from 24.7 × 10–2 to 2.3 × 10–2 and 1.8 × 10–2) of the respective prepared films. Meanwhile, tensile strength (from 183.2 MPa to 203.34 MPa and 235.94 MPa), elongation (from 13.0% to 62.5% and 83.7%), and Yang's modulus (from 325.344 to 1410.0 and 1814.96 MPa) of these films were increased. Moreover, the antioxidant and antimicrobial activities against several human and plant pathogens the prepared of Carboxymethyl Cellulose-ZnONPs films were significantly increased. In conclusion, the prepared Carboxymethyl Cellulose-ZnONPs films showed enhanced activities in comparison with Carboxymethyl Cellulose film without NPs. With these advantages, the fabricated Carboxymethyl Cellulose-ZnONPs films in this study could be effectively utilized as protective edible coating films of food products.

P12-48 Streamlining the Ames mutagenicity test by online monitoring of the oxygen transfer rate in 96-well microplate scale

P12-48 Streamlining the Ames mutagenicity test by online monitoring of the oxygen transfer rate in 96-well microplate scale

Enhancement in oxygen transfer rate of CuMn2O4 oxygen carrier via selective dopants: Role of dopant effects on O migration for chemical looping combustion

Chemical looping combustion technology has been widely studied because this platform can convert fossil fuels efficiently into sustainable energy with an in situ carbon capture capability. The redox property of the oxygen carrier (usually a transition metal oxide) plays a critical role in determining the kinetics of the combustion process. This study investigated computationally and experimentally methane oxidation on spinel structure of Mn–Cu bimetallic oxygen carriers due to its facile oxygen uncoupling (Mn and Cu) with high durability in the reduction cycle. Our simulation predicted that the mechanism of complete methane oxidation on CuMn2O4 involved two competitive rate-limiting steps: 1) thermodynamic controlled step of CH2O* formation (CH3O* + O → CH2O* + OH) and 2) kinetic controlled step of CO formation (CHO* + O → CO* + OH). Multiple dopants (Co, Cr, Fe, Ni, Ti, V, and Zn) to the activation barriers of the rate-limiting steps were tested to enhance the performance of oxygen carriers by improving the oxygen transfer rate. Ni-doped CuMn2O4 and V-doped CuMn2O4 showed promising results computationally (significant decrease in ∆E of rate limiting steps). The enhanced oxygen transfer rate of Ni-doped CuMn2O4 was confirmed experimentally. On the other hand, experimentally, V-doped CuMn2O4 provided a lower oxygen transfer rate than the other CuMn2O4 materials, which is inconsistent with the computational predictions. Computation studies showed that the lower oxygen transfer rate stems from the hindrance of O migration by surface V dopants; surface V atom energetically hampers O migration from the subsurface to the top surface. This behavior adversely affects the oxygen transfer rate, resulting in a lower net oxygen transfer rate. These results suggest that the effects of dopants on O migration should be carefully considered when designing enhanced oxygen carriers using a dopant strategy.

An experimental study of venturi aeration system

Aeration with a venturi aerator is efficient method to increase the dissolved oxygen (DO) concentration in water sources like rivers, waterways, ponds and water treatment plants. It is employed in aquatic animals' respiration and other biological processes as well as the removal of dissolved gases, dissolved metals, and volatile organic chemicals (VOC) in water. Aeration system efficiency is a crucial design factor, as aeration systems often account for the most energy draw and consumption. The study aims to evaluate the standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), volumetric oxygen transfer coefficient (KLa20) of venturi aeration system, air velocity and airflow rates at different water levels of the tank. Venturi aerator designed by Green Pumps and Equipments was used for experimentation. Air entrainment hole was fixed to 25 mm and 66 mm water inlet diameter. It was discovered that the rate of air flow rises as the tank's water level falls. The KLa20 was achieved at a rate of 2.58 h−1, SOTR at a rate of 0.323191 kgO2/hr, and SAE at a rate of 0.293594 kgO2/KWh, respectively. The findings suggest that venturi aeration may have a considerable impact on air entrainment and aeration efficiency. As a result, the venturi aeration system can be employed as an efficient aerator in aeration procedures.

Scale-Up to Pilot of a Non-Axenic Culture of Thraustochytrids Using Digestate from Methanization as Nitrogen Source.

The production of non-fish based docosahexaenoic acid (DHA) for feed and food has become a critical need in our global context of over-fishing. The industrial-scale production of DHA–rich Thraustochytrids could be an alternative, if costs turned out to be competitive. In order to reduce production costs, this study addresses the feasibility of the non-axenic (non-sterile) cultivation of Aurantiochytrium mangrovei on industrial substrates (as nitrogen and mineral sources and glucose syrup as carbon and energy sources), and its scale-up from laboratory (250 mL) to 500 L cultures. Pilot-scale reactors were airlift cylinders. Batch and fed-batch cultures were tested. Cultures over 38 to 62 h achieved a dry cell weight productivity of 3.3 to 5.5 g.L−1.day−1, and a substrate to biomass yield of up to 0.3. DHA productivity ranged from 10 to 0.18 mg.L−1.day−1. Biomass productivity appears linearly related to oxygen transfer rate. Bacterial contamination of cultures was low enough to avoid impacts on fatty acid composition of the biomass. A specific work on microbial risks assessment (in supplementary files) showed that the biomass can be securely used as feed. However, to date, there is a law void in EU legislation regarding the recycling of nitrogen from digestate from animal waste for microalgae biomass and its usage in animal feed. Overall, the proposed process appears similar to the industrial yeast production process (non-axenic heterotrophic process, dissolved oxygen supply limiting growth, similar cell size). Such similarity could help in further industrial developments.

Influence of Gelatin-Based Coatings Crosslinked with Phenolic Acids on PLA Film Barrier Properties

Single-use plastics are a major source of pollution and biodegradable polymers could be the best substitute, as they possess similar barrier and functional properties. Aiming at improving barrier properties and providing antioxidant bioactivity, PLA (PolyLactic Acid) films were coated with a crosslinked suspension of plasticized gelatin incorporating phenolic compounds. The coating process induced weak modifications of PLA properties due to plasticization by moisture and glycerol from the coating suspension. Indeed, a double glass transition was displayed. The water vapor barrier properties of the PLA-coated films were not significantly affected. Phenolic compounds induced a crosslinking of the gelatin network, slightly decreasing the moisture sensitivity and surface hydrophilicity. Therefore, the mechanical properties of PLA were maintained after coating and their barrier properties were highly improved, with up to a 600-fold reduction of the oxygen transfer rate. These results make possible new applications for oxidation-sensitive foods, and even for semi-moist foods.

Gas transfer model for a multistage vortex aerator: A novel oxygen transfer system for dissolved oxygen improvement

A novel aerator for enhancing the oxygen transfer rate and efficiency, named multistage vortex aerator (MVA), was developed. It uses vortex flow in repeated stages to increase the gas-liquid interfacial area and to decrease the thickness of the stagnant layer at the interface between the two phases. The basic characteristics of oxygen transfer using this aerator were investigated using the American Society of Civil Engineers standard procedure. The MVA could rapidly transfer oxygen to water to a concentration higher than 40 mg/L in 60 min owing to the effect of high purity oxygen, additional pressure induced by water and gas, and vortex flow dynamics. A gas transfer model was developed for describing the non-steady state operation of the aerator. This model is based on the mass and molar balances of oxygen in gas and water. It could successfully simulate the DO change inside the aerator. This study can help better understand the oxygen transfer mechanism and evaluate the performance of the new aerator at the various temperatures, pressures, and gas compositions found in diverse environmental systems.

Predicting high recombinant protein producer strains of Pichia pastoris MutS using the oxygen transfer rate as an indicator of metabolic burden

The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is a widely used host for recombinant protein production. In this study, a clonal library of P. pastoris MutS strains (S indicates slow methanol utilization) was screened for high green fluorescent protein (GFP) production. The expression cassette was under the control of the methanol inducible AOX promoter. The growth behavior was online-monitored in 48-well and 96-well microtiter plates by measuring the oxygen transfer rate (OTR). By comparing the different GFP producing strains, a correlation was established between the slope of the cumulative oxygen transfer during the methanol metabolization phase and the strain’s production performance. The correlation corresponds to metabolic burden during methanol induction. The findings were validated using a pre-selected strain library (7 strains) of high, medium, and low GFP producers. For those strains, the gene copy number was determined via Whole Genome Sequencing. The results were consistent with the described OTR correlation. Additionally, a larger clone library (45 strains) was tested to validate the applicability of the proposed method. The results from this study suggest that the cumulative oxygen transfer can be used as a screening criterion for protein production performance that allows for a simple primary screening process, facilitating the pre-selection of high producing strains.

Techno-Economic Analysis as a Driver for Optimisation of Cellobiose Lipid Fermentation and Purification.

Cellobiose lipids (CL) are glycolipids synthesized by Ustilaginaceae species with potential application as detergents or in cosmetics. This study identified process optimisation potential for CL fermentation based on process modelling and techno-economic analysis. Using a stoichiometric equation based on laboratory data, we calculated the maximum possible CL yield YP/S of 0.45 gCL·gglucose −1 at the biomass yield of 0.10 gBiomass·gglucose −1 with an Ustilago maydis strain. Due to substrate inhibition that may occur at high glucose concentrations, a fed-batch process to increase biomass and CL concentrations was considered in our model. Simulation of different process scenarios showed that the choice of aeration units with high oxygen transfer rates and adaptation of power input to oxygen uptake can significantly decrease electricity consumption. We further assessed scenarios with different fermentation media and CL purification methods, suggesting additional process optimisation potential. Here the omission of vitamins from the fermentation medium proved to be a possible mean to enhance process economy, without compromising CL productivity.

A new approach to estimating oxygen off-gas fraction and dynamic alpha factor in aeration systems using hybrid machine learning and mechanistic models

The aeration process is the largest energy consumer in wastewater treatment plants (WWTP), and the optimization of the process based on computational models can offer significant savings for the plant. Recent theoretical developments have revealed that many of the parameters commonly assumed as constants in aeration modelling have a dynamic nature; however, there still lacks a universal way to model these factors accurately. This work proposed a new framework and optimal time scale for building hybrid machine learning-mechanistic oxygen transfer rate models. The data used for the modelling were from existing sensors in a full-scale WWTP supplemented by a two-month field sampling campaign for collecting 15 min of dynamic data, including off-gas air fraction. Two machine learning (ML) models were built: the first set was a novel hybrid ML-mechanistic model developed to estimate the off-gas aeration fraction from wastewater parameters and calculate dynamic alpha per the off-gas method. The second ML model directly estimated dynamic alpha from wastewater process and operation parameters. The performance of the ML models was compared with recalibrated published regression-based models. Results showed that the hybrid ML-mechanistic alpha model (NSE = 0.96 and RMSE = 0.03) were more accurate than the direct ML alpha (NSE = 0.67 and RMSE = 0.07) and recalibrated regression (NSE < 0 and RMSE = 0.18 to 0.28) models, and therefore could be efficiently applied to predict dynamic alpha factor of an activated sludge plant. In addition to typical surfactant indicators such as MLSS and COD, other parameters like temperature and aeration ammonia concentration were substantial in dynamic off-gas and alpha estimation.

Boosting hydrogen peroxide accumulation by a novel air-breathing gas diffusion electrode in electro-Fenton system

Electro-Fenton (EF) is a promising electrochemical technology in degrading recalcitrant organic pollutants. However, the technology faces problems of high energy consumption, low cathodic oxygen transfer rate and low H2O2 production efficiency. Therefore, a novel air-breathing gas diffusion electrode (GDE) with multiform hydrophobic layers was prepared by a facile method. The novel GDE allows the air to diffuse to the triphase interface spontaneously, eliminating the cost of aeration. Also, the multiform hydrophobic layers can greatly improve the oxygen transfer rate and expand the triphase interfaces in the GDE, resulting in a high H2O2 accumulation of 44.30 mg L−1 cm−2 h−1 without aeration, which was 18 times higher than that of the virgin cathode. A 100% degradation efficiency of sulfadiazine (SDZ) was achieved with the fabricated GDE in 10 min in EF system. Moreover, theoretical calculations were performed for accurately elucidating the SDZ degradation mechanism and pathway.

Implementation of Perforated Concentric Ring Walls Considerably Improves Gas-Liquid Mass Transfer of Shaken Bioreactors.

Since their first use in the 1930s, shake flasks have been a widely used bioreactor type for screening and process development due to a number of advantages. However, the limited gas-liquid mass transfer capacities—resulting from practical operation limits regarding shaking frequency and filling volumes—are a major drawback. The common way to increase the gas-liquid mass transfer in shake flasks with the implementation of baffles is generally not recommended as it comes along with several severe disadvantages. Thus, a new design principle for shaken bioreactors that aims for improving the gas-liquid mass transfer without losing the positive characteristics of unbaffled shake flasks is introduced. The flasks consist of cylindrical glass vessels with implemented perforated concentric ring walls. The ring walls improve the gas-liquid mass transfer via the formation of additional liquid films on both of its sides, whereas the perforations allow for mixing between the compartments. Sulfite oxidation experiments revealed over 200% higher maximum oxygen transfer capacities (OTRmax) compared to conventional shake flasks. In batch cultivations of Escherichia coli BL21 in mineral media, unlimited growth until glucose depletion and oxygen transfer rates (OTR) of up to 138 mmol/L/h instead of an oxygen limitation at 57 mmol/L/h as in normal shake flasks under comparable conditions could be achieved. Even overflow metabolism could be prevented due to sufficient oxygen supply without the use of unconventional shaking conditions or oxygen enrichment. Therefore, we believe that the new perforated ring flask principle has a high potential to considerably improve biotechnological screening and process development steps.

A Non‐Invasive Method to Estimate Pulmonary Oxygen Transfer Rate

ObjectiveIneffective transfer of oxygen from the atmospheric air to the circulation is associated with low cardiorespiratory fitness and increased disease risk. Unfortunately, measuring the efficiency of gas exchange requires invasive and expensive procedures. We first sought to develop a parameter (Do) that reflects the capacity to move oxygen from air to the arterial circulation using non‐invasive methods. We then tested the utility of Do to detect changes in pulmonary oxygen transfer rate under differing conditions of oxygen supply and demand. Last, we compared Do with the Oxygen Deficit (OD) method, a non‐invasive way to estimate gas‐exchange impairment.MethodsHeart rate (ECG), tidal volume (pneumotachometer), respiratory rate (pneumobelt), and oxygen saturation (finger pulse oximeter) were measured in 25 young healthy adult participants (13 males, 12 females; 25 ± 4 years of age). Participants completed 4 trials: 1) Resting normoxia, 2) Steady‐state hypoxia (80% SpO2, SSH), 3) Cold pressor test (CPT, to increase oxygen demand), and 4) SSH + CPT. Do was derived by engineering analysis considering the biophysics of the 3 major process essential for effective oxygen transfer (i.e., ventilation, alveolar gas exchange, hemoglobin binding). Do was estimated for each condition and results were compared with the OD method.ResultsDoincreased during SSH (5.13±1.07×10‐2L/min/kPa) and CPT (2.91±1.03 ×10‐2L/min/kPa) when compared to resting normoxia (2.24±0.66×10‐2 L/min/kPa, p&lt;0.05). Dowas further increased during SSH+CPT (5.71±1.52×10‐2L/min/kPa) when compared to SSH alone (p&lt;0.05). Applicability of the OD method was limited to SpO2&lt;95%; thus OD could only be calculated in 40% of participants (n=10). OD was lower during SSH (2.18±0.63 kPa) and CPT (2.48±1.56 kPa) versus normoxia (3.15±1.3 kPa, p&lt;0.05). In contrast, OD increased during SSH+CPT (2.42±0.59 kPa) when compared to SSH alone (p&lt;0.05).ConclusionApplication of the novel parameter, Donot only showed the ability to respond to changes in supply and demand of oxygen but exhibited advantages over a conventional measure (OD). Specifically, Do showed consistent effect of CPT under normoxic and hypoxic conditions, whereas: 1) OD could only be determined in 40% of study participants, and 2) OD exhibited a paradoxical increase during SSH+CPT, despite a decrease during SSH and/or CPT alone. Future studies seek to test the utility of Do in cardiopulmonary patients.

A Novel Mock Circuit to Test Full-Flow Extracorporeal Membrane Oxygenation.

Extracorporeal membrane oxygenation (ECMO) has become an important therapeutic approach in the COVID-19 pandemic. The development and research in this field strongly relies on animal models; however, efforts are being made to find alternatives. In this work, we present a new mock circuit for ECMO that allows measurements of the oxygen transfer rate of a membrane lung at full ECMO blood flow. The mock utilizes a large reservoir of heparinized porcine blood to measure the oxygen transfer rate of the membrane lung in a single passage. The oxygen transfer rate is calculated from blood flow, hemoglobin value, venous saturation, and post-membrane arterial oxygen pressure. Before the next measuring sequence, the blood is regenerated to a venous condition with a sweep gas of nitrogen and carbon dioxide. The presented mock was applied to investigate the effect of a recirculation loop on the oxygen transfer rate of an ECMO setup. The recirculation loop caused a significant increase in post-membrane arterial oxygen pressure (paO2). The effect was strongest for the highest recirculation flow. This was attributed to a smaller boundary layer on gas fibers due to the increased blood velocity. However, the increase in paO2 did not translate to significant increases in the oxygen transfer rate because of the minor significance of physically dissolved oxygen for gas transfer. In conclusion, our results regarding a new ECMO mock setup demonstrate that recirculation loops can improve ECMO performance, but not enough to be clinically relevant.

Insights into Streptomyces coelicolor A3(2) growth and pigment formation with high-throughput online monitoring.

Streptomyces species are intensively studied for their ability to produce a variety of natural products. However, conditions influencing and leading to product formation are often not completely recognized. Therefore, in this study, high-throughput online monitoring is presented as a powerful tool to gain in-depth understanding of the cultivation of the model organism Streptomyces coelicolor A3(2). Through online measurements of oxygen transfer rate and autofluorescence, valuable information about availability of nutrients and product formation patterns of the pigments actinorhodin and undecylprodigiosin can be obtained and explained. Therefore, it is possible to determine the onset of pigmentation and to study in detail the influencing factors thereof. One factor identified in this study is the filling volume of the cultivation vessel. Slight variations led to varying pigmentation levels. By combining optical and metabolic online monitoring techniques, the correlation of the filling volume with pigmentation could be explained as a result of different growth trajectories caused by varying specific power inputs and their influence on the pellet formation of the filamentous system. Finally, experiments with the addition of supernatant from unpigmented and pigmented cultures could highlight the applicability of the presented approach to study quorum sensing and cell-cell interaction.

Experimental characterization of an oxygen transfer model of a fine pore diffuser aerator

Dissolved oxygen (DO) is an important aspect of water quality in aquaculture. To prevent oxygen deficiency, aeration is used to improve DO and increase yields in aquaculture farms. However, the experimental quantification of standard oxygen transfer rate (SOTR) of aerators is highly case dependent and varies under different aerator operational conditions. Hence, using SOTR for modeling, simulation, and aerator design purposes tends to be unreliable. This work validates an existing theoretical oxygen transfer model of an economical fine-pore diffuser using a bench-scale aeration system. Modifications were made to the model to account for physical conditions and to relate the model to SOTR. Aeration tests were conducted using various airflow rates and diffuser depths for three water volumes (137 L, 160 L, 192 L). As a parameter to the model, bubble diameters were determined for each experiment using an automated image processing tool developed for this study. The percentage error between the theoretical and experimental oxygen transfer coefficients range from 12.87% to 19.99% and are well within the 95% confidence interval of both respective results. The oxygen transfer coefficient and rate increased with diffuser submergence and airflow rate. However, standard aeration efficiency decreased exponentially with increasing airflow rates. The use of this model provides an approximate estimate of oxygen transfer rates in different conditions, which can be used to optimally design aerators and strategically create cost-saving practices for both intensive and extensive aquaculture applications.

Production of indole-3-acetic acid by Bacillus circulans E9 in a low-cost medium in a bioreactor

Bacillus circulans E9 (now known as Niallia circulans) promotes plant growth-producing indole-3-acetic acid (IAA), showing potential for use as a biofertilizer. In this work, the use of a low-cost medium containing industrial substrates, soybean, pea flour, Solulys, Pharmamedia, yeast extract, and sodium chloride (NaCl), was evaluated as a substitute for microbiological Luria Broth (LB) medium for the growth of B.circulans E9 and the production of IAA. In Erlenmeyer flasks with pea fluor medium (PYM), the maximum production of IAA was 7.81 ± 0.16μgmL-1, while in microbiological LB medium, it was 3.73 ± 0.15μgmL-1. In addition, an oxygen transfer rate (OTR) of 1.04kg O2 m-3 d-1 allowed the highest bacterial growth (19.3 ± 2.18 × 1010CFUmL-1) and IAA production (10.7μgmL-1). Consequently, the OTR value from the flask experiments was used to define the conditions for the operation of a 1L stirred tank bioreactor. The growth and IAA production of B.circulans cultured in a bioreactor with PYM medium were higher (8 and 1.6 times, respectively) than those of bacteria cultured in Erlenmeyer flasks. IAA produced in a bioreactor by B.circulans was shown to induce the root system in Arabidopsis thaliana, similar to synthetic IAA. The results of this study demonstrate that PYM medium may be able to be used for the mass production of B.circulans E9 in bioreactors, increasing both bacterial growth and IAA production. This low-cost medium has the potential to be employed to grow other IAA-producing bacterial species.

Experimental study on design and operational performance of solar-powered venturi aeration system developed for aquaculture – A semi-floating prototype

Venturi-type injectors have been used usually due to the practical use and modular design that allows for quick configuration, ready-to-use, and low-cost solutions in the last years. This study aims to design a solar-powered venturi aeration system (SVAS) and determine its flow characteristics, standard, and real-time operational performance parameters. SVAS has a design providing the maximum vacuum and air velocity at air inlets and allowing for all technical measurements. Moreover, a solar-powered experimental apparatus having a weather station, a pool station, and a data logger station was constructed. Experiments were carried out using a plastic pool with a capacity of 4000 L, a diameter of 3 m and a depth of 0.75 m, four venturi injectors, and a submersible pump of 0.3 kW operated at the constant water flow regime of 4.1 m3 h-1. According to flow tests, the oxygen mass flow rates ranged from 2.77 to 2.84 kg h−1. The specific energy consumption values are 263.2 kJ per cubic meter for water flow and 380 kJ per kg for oxygen transfer.Standard performance experiments were repeated four times. The maximum overall oxygen mass transfer coefficient obtained during the experiments was 5.58 h−1. The maximum values of standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), and standard oxygen transfer efficiency (SOTE) were 0.206 kgO2 h−1, 0.681 kgO2 kWh−1, and 7.32%, respectively. The pool conditions were simulated using de-oxygenation and mixing systems to determine the operational performance. For simulation experiments, six procedures and two processes were applied. Throughout operational experiments of four days, real-time dissolved oxygen levels fluctuated between 1.05 mg L−1 and 6.65 mg L−1. The maximum performance values were 0.143 kgO2 h−1 for the actual oxygen-transfer rate, 0.474 kgO2 kWh−1 for aeration efficiency, and 5.1% for oxygen transfer efficiency.