Oxygen transfer and energy dissipation rate in surface aerator

The dissipation rate of turbulent kinetic energy (epsilon) is a key parameter for mixing in surface aerators. In particular, determination epsilon across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix (R) calculates the energy dissipation rate in geometrically similar unbaffled surface aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system, oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.

Oxygen transfer and energy dissipation rate in surface aerator

The dissipation rate of turbulent kinetic energy(e)is a key parameter for mixing in surface aerators. In particular, determination e across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix calculates the energy dissipation rate in geometrically similar unbaffled surface aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system,oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.

Oxygen transfer in circular surface aeration tanks

Surface aeration systems employed in activated sludge plants are the most energy-intensive units of the plants and typically account for a higher percentage of the treatment facility's total energy use. The geometry of the aeration tank imparts a major effect on the system efficiency. It is said that at optimal geometric onditions, systems exhibits the maximum efficiency. Thus the quantification of the optimal geometric conditions in surface aeration tanks is needed. Optimal geometric conditions are also needed to scale up the laboratory result to the field installation. In the present work, experimental studies have been carried out on baffled and unbaffled circular surface aeration tanks to ascertain the optimal geometric conditions. It is found that no optimal geometric conditions exist for the liquid/water depth in circular surface aeration tanks; however, for design purposes, a standard value has been assumed. Based on the optimal geometric conditions, a scale-up equation has been developed for the baffled circular surface aeration tanks.

Fermentation medium and oxygen transfer conditions that maximize the xylose conversion to ethanol by Pichia stipitis

The xylose conversion to ethanol by Pichia stipitis was studied. In a first step, the necessity of supplementing the fermentation medium with urea. MgSO(4) x 7H(2)O, and/or yeast extract was evaluated through a 2(3) full factorial design. The simultaneous addition of these three nutritional sources to the fermentation medium, in concentrations of 2.3, 1.0, and 3.0 g/l, respectively, showed to be important to improve the ethanol production in detriment of the substrate conversion to cell. In a second stage, fermentation assays performed in a bioreactor under different K(L)a (volumetric oxygen transfer coefficient) conditions made possible understanding the influence of the oxygen transfer on yeast performance, as well as to define the most suitable range of values for an efficient ethanol production. The most promising region to perform this bioconversion process was found to be between 2.3 and 4.9 h(-1), since it promoted the highest ethanol production results with practically exhaustion of the xylose from the medium. These findings contribute for the development of an economical and efficient technology for large scale production of second generation ethanol. (C) 2011 Elsevier Ltd. All rights reserved.

Comparing oxygen transfer performance between three membrane oxygenators: effect of temperature changes during cardiopulmonary bypass

Recently, a new oxygenator (Dideco 903 [D903], Dideco, Mirandola, Italy) has been introduced to the perfusion community, and we set about testing its oxygen transfer performance and then comparing it to two other models. This evaluation was based on the comparison between oxygen transfer slope, gas phase arterial oxygen gradients, degree of blood shunting, maximum oxygen transfer, and diffusing capacity calculated for each membrane. Sixty patients were randomized into three groups of oxygenators (Dideco 703 [D703], Dideco; D903; and Quadrox, Jostra Medizintechnik AG, Hirrlingen, Germany) including 40/20 M/F of 68.6 +/- 11.3 years old, with a body weight of 71.5 +/- 12.1 kg, a body surface area (BSA) of 1.84 +/- 0.3 m(2), and a theoretical blood flow rate (index 2.4 times BSA) of 4.4 +/- 0.7 L/min. The maximum oxygen transfer (VO(2)) values were 313 mL O(2)/min (D703), 579 mL O(2)/min (D903), and 400 mL O(2)/min (Quadrox), with the D903 being the most superior (P < 0.05). Oxygen (O(2)) gradients were 320 mm Hg (D703), 235 mm Hg (D903), and 247 mm Hg (Quadrox), meaning D903 and Quadrox are more efficient versus the D703 (P < 0.05). Shunt fraction (Qs/Qt) and diffusing capacity (DmO(2)) were comparable (P = ns). Diffusing capacity values indexed to BSA (DmO(2)/m(2)) were 0.15 mL O(2)/min/mm Hg/m(2) (D703), 0.2 mL O(2)/min/mm Hg/m(2) (D903), and 0.18 mL O(2)/min/mm Hg/m(2) (Quadrox) with D903 outperforming D703 (P < 0.0005). During hypothermia (32.0 +/- 0.3 degrees C), there was a lower absolute and relative VO(2 )for all three oxygenators (P = ns). The O(2) gradients, DmO(2) and DmO(2)/m(2), were significantly lower for all oxygenators (P < 0.01). Also, Qs/Qt significantly rose for all oxygenators (P < 0.01). The oxygen transfer curve is characteristic to each oxygenator type and represents a tool to quantify oxygenator performance. Using this parameter, we demonstrated significant differences among commercially available oxygenators. However, all three oxygenators are considered to meet the oxygen needs of the patients.

Hydroxylation of naphthalene by aromatic peroxygenase from Agrocybe aegerita proceeds via oxygen transfer from H2O2 and intermediary epoxidation

Agrocybe aegerita peroxidase/peroxygenase (AaP) is an extracellular fungal biocatalyst that selectively hydroxylates the aromatic ring of naphthalene. Under alkaline conditions, the reaction proceeds via the formation of an intermediary product with a molecular mass of 144 and a characteristic UV absorption spectrum (A(max) 210, 267, and 303 nm). The compound was semistable at pH 9 but spontaneously hydrolyzed under acidic conditions (pH<7) into 1-naphthol as major product and traces of 2-naphthol. Based on these findings and literature data, we propose naphthalene 1,2-oxide as the primary product of AaP-catalyzed oxygenation of naphthalene. Using (18)O-labeled hydrogen peroxide, the origin of the oxygen atom transferred to naphthalene was proved to be the peroxide that acts both as oxidant (primary electron acceptor) and oxygen source.

Oxygen-transfer performance of a newly designed, very low-volume membrane oxygenator.

OBJECTIVES Oxygenation of blood and other physiological solutions are routinely required in fundamental research for both in vitro and in vivo experimentation. However, very few oxygenators with suitable priming volumes (<2-3 ml) are available for surgery in small animals. We have designed a new, miniaturized membrane oxygenator and investigated the oxygen-transfer performance using both buffer and blood perfusates. METHODS The mini-oxygenator was designed with a central perforated core-tube surrounded by parallel-oriented microporous polypropylene hollow fibres, placed inside a hollow shell with a lateral-luer outlet, and sealed at both extremities. With this design, perfusate is delivered via the core-tube to the centre of the mini-oxygenator, and exits via the luer port. A series of mini-oxygenators were constructed and tested in an in vitro perfusion circuit by monitoring oxygen transfer using modified Krebs-Henseleit buffer or whole porcine blood. Effects of perfusion pressure and temperature over flows of 5-60 ml × min(-1) were assessed. RESULTS Twelve mini-oxygenators with a mean priming volume of 1.5 ± 0.3 ml were evaluated. With buffer, oxygen transfer reached a maximum of 14.8 ± 1.0 ml O2 × l(-1) (pO2: 450 ± 32 mmHg) at perfusate flow rates of 5 ml × min(-1) and decreased with an increase in perfusate flow to 7.8 ± 0.7 ml ml O2 × l(-1) (pO2: 219 ± 24 mmHg) at 60 ml × min(-1). Similarly, with blood perfusate, oxygen transfer also decreased as perfusate flow increased, ranging from 33 ± 5 ml O2 × l(-1) at 5 ml × min(-1) to 11 ± 2 ml O2 × l(-1) at 60 ml × min(-1). Furthermore, oxygen transfer capacity remained stable with blood perfusion over a period of at least 2 h. CONCLUSIONS We have developed a new miniaturized membrane oxygenator with an ultra-low priming volume (<2 ml) and adequate oxygenation performance. This oxygenator may be of use in overcoming current limitations in equipment size for effective oxygenation in low-volume perfusion circuits, such as small animal extracorporeal circulation and ex vivo organ perfusion.

Oxygen-transfer performance of a newly designed, very low-volume membrane oxygenator

Gebiet: Chirurgie Biomedizintechnik Biophysik Transplantationsmedizin Kardiologie Abstract: OBJECTIVES: – Oxygenation of blood and other physiological solutions are routinely required in fundamental research for both in vitro and in vivo experimentation. However, very few oxygenators with suitable priming volumes (<2-3 ml) are available for surgery in small animals. We have designed a new, miniaturized membrane oxygenator and investigated the oxygen-transfer performance using both buffer and blood perfusates. – – METHODS: – The mini-oxygenator was designed with a central perforated core-tube surrounded by parallel-oriented microporous polypropylene hollow fibres, placed inside a hollow shell with a lateral-luer outlet, and sealed at both extremities. With this design, perfusate is delivered via the core-tube to the centre of the mini-oxygenator, and exits via the luer port. A series of mini-oxygenators were constructed and tested in an in vitro perfusion circuit by monitoring oxygen transfer using modified Krebs-Henseleit buffer or whole porcine blood. Effects of perfusion pressure and temperature over flows of 5-60 ml × min(-1) were assessed. – – RESULTS: – Twelve mini-oxygenators with a mean priming volume of 1.5 ± 0.3 ml were evaluated. With buffer, oxygen transfer reached a maximum of 14.8 ± 1.0 ml O2 × l(-1) (pO2: 450 ± 32 mmHg) at perfusate flow rates of 5 ml × min(-1) and decreased with an increase in perfusate flow to 7.8 ± 0.7 ml ml O2 × l(-1) (pO2: 219 ± 24 mmHg) at 60 ml × min(-1). Similarly, with blood perfusate, oxygen transfer also decreased as perfusate flow increased, ranging from 33 ± 5 ml O2 × l(-1) at 5 ml × min(-1) to 11 ± 2 ml O2 × l(-1) at 60 ml × min(-1). Furthermore, oxygen transfer capacity remained stable with blood perfusion over a period of at least 2 h. – – CONCLUSIONS: – We have developed a new miniaturized membrane oxygenator with an ultra-low priming volume (<2 ml) and adequate oxygenation performance. This oxygenator may be of use in overcoming current limitations in equipment size for effective oxygenation in low-volume perfusion circuits, such as small animal extracorporeal circulation and ex vivo organ perfusion. – – © The Author 2015. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

Predicting the effect of mixing on oxygen transfer and nutrient removal in activated sludge basins

Activated sludge basins (ASBs) are a key-step in wastewater treatment processes that are used to eliminate biodegradable pollution from the water discharged to the natural environment. Bacteria found in the activated sludge consume and assimilate nutrients such as carbon, nitrogen and phosphorous under specific environmental conditions. However, applying the appropriate agitation and aeration regimes to supply the environmental conditions to promote the growth of the bacteria is not easy. The agitation and aeration regimes that are applied to activated sludge basins have a strong influence on the efficacy of wastewater treatment processes. The major aims of agitation by submersible mixers are to improve the contact between biomass and wastewater and the prevention of biomass settling. They induce a horizontal flow in the oxidation ditch, which can be quantified by the mean horizontal velocity. Mean values of 0.3-0.35 m s-1 are recommended as a design criteria to ensure best conditions for mixing and aeration (Da Silva, 1994). To give circulation velocities of this order of magnitude, the positioning and types of mixers are chosen from the plant constructors' experience and the suppliers' data for the impellers. Some case studies of existing plants have shown that measured velocities were not in the range that was specified in the plant design. This illustrates that there is still a need for design and diagnosis approach to improve process reliability by eliminating or reducing the number of short circuits, dead zones, zones of inefficient mixing and poor aeration. The objective of the aeration is to facilitate the quick degradation of pollutants by bacterial growth. To achieve these objectives a wastewater treatment plant must be adequately aerated; thus resulting in 60-80% of all energetic consummation being dedicated to the aeration alone (Juspin and Vasel, 2000). An earlier study (Gillot et al., 1997) has illustrated the influence that hydrodynamics have on the aeration performance as measure by the oxygen transfer coefficient. Therefore, optimising the agitation and aeration systems can enhance the oxygen transfer coefficient and consequently reduce the operating costs of the wastewater treatment plant. It is critically important to correctly estimate the mass transfer coefficient as any errors could result in the simulations of biological activity not being physically representative. Therefore, the transfer process was rigorously examined in several different types of process equipment to determine the impact that different hydrodynamic regimes and liquid-side film transfer coefficients have on the gas phase and the mass transfer of oxygen. To model the biological activity occurring in ASBs, several generic biochemical reaction models have been developed to characterise different biochemical reaction processes that are known as Activated Sludge Models, ASM (Henze et al., 2000). The ASM1 protocol was selected to characterise the impact of aeration on the bacteria consuming and assimilating ammonia and nitrate in the wastewater. However, one drawback of ASM protocols is that the hydrodynamics are assumed to be uniform by the use of perfectly mixed, plug flow reactors or as a number of perfectly mixed reactors in series. This makes it very difficult to identify the influence of mixing and aeration on oxygen mass transfer and biological activity. Therefore, to account for the impact of local gas-liquid mixing regime on the biochemical activity Computational Fluid Dynamics (CFD) was used by applying the individual ASM1 reaction equations as the source terms to a number of scalar equations. Thus, the application of ASM1 to CFD (FLUENT) enabled the investigation of the oxygen transfer efficiency and the carbon & nitrogen biological removal in pilot (7.5 cubic metres) and plant scale (6000 cubic metres) ASBs. Both studies have been used to validate the effect that the hydrodynamic regime has on oxygen mass transfer (the circulation velocity and mass transfer coefficient) and the effect that this had on the biological activity on pollutants such as ammonia and nitrate (Cartland Glover et al., 2005). The work presented here is one part to of an overall approach for improving the understanding of ASBs and the impact that they have in terms of the hydraulic and biological performance on the overall wastewater treatment process. References CARTLAND GLOVER G., PRINTEMPS C., ESSEMIANI K., MEINHOLD J., (2005) Modelling of wastewater treatment plants ? How far shall we go with sophisticated modelling tools? 3rd IWA Leading-Edge Conference & Exhibition on Water and Wastewater Treatment Technologies, 6-8 June 2005, Sapporo, Japan DA SILVA G. (1994). Eléments d'optimisation du transfert d'oxygène par fines bulles et agitateur séparé en chenal d'oxydation. PhD Thesis. CEMAGREF Antony ? France. GILLOT S., DERONZIER G., HEDUIT A. (1997). Oxygen transfer under process conditions in an oxidation ditch equipped with fine bubble diffusers and slow speed mixers. WEFTEC, Chicago, USA. HENZE M., GUJER W., MINO T., van LOOSDRECHT M., (2000). Activated Sludge Models ASM1, ASM2, ASM2D and ASM3, Scientific and Technical Report No. 9. IWA Publishing, London, UK. JUSPIN H., VASEL J.-L. (2000). Influence of hydrodynamics on oxygen transfer in the activated sludge process. IWA, Paris - France.

Continuous oxygen ion transfer medium as a catalyst for high selective oxidative dehydrogenation of ethane

An oxygen permeable mixed ion and electron conducting membrane (OPMIECM) was used as an oxygen transfer medium as well as a catalyst for the oxidative dehydrogenation of ethane to produce ethylene. O2- species transported through the membrane reacted with ethane to produce ethylene before it recombined to gaseous O-2, so that the deep oxidation of the products was greatly suppressed. As a result, 80% selectivity of ethylene at 84% ethane conversion was achieved, whereas 53.7% ethylene selectivity was obtained using a conventional fixed-bed reactor under the same reaction conditions with the same catalyst at 800 degreesC. A 100 h continuous operation of this process was carried out and the result indicates the feasibility for practical applications.

Ethanol-dependent oxygen consumption and acetaldehyde formation during vanadyl oxidation by H2O2

Sequential addition of vanadyl sulfate to a phosphate-buffered solution of H2O2 released oxygen only after the second batch of vanadyl. Ethanol added to such reaction mixtures progressively decreased oxygen release and increased oxygen consumption during oxidation of vanadyl by H2O2. Inclusion of ethanol after any of the three batches of vanadyl resulted in varying amounts of oxygen consumption, a property also shared by other alcohols (methanol, propanol and octanol). On increasing the concentration of ethanol, vanadyl sulfate or H2O2, both oxygen consumption and acetaldehyde formation increased progressively. Formation of acetaldehyde decreased with increase in the ratio of vanadyl:H2O2 above 2:1 and was undetectable with ethanol at 0.1 mM. The reaction mixture which was acidic in the absence of phosphate buffer (pH 7.0), released oxygen immediately after the first addition of vanadyl and also in presence of ethanol soon after initial rapid consumption of oxygen, with no accompanying acetaldehyde formation. The results underscore the importance of some vanadium complexes formed during vanadyl oxidation in the accompanying oxygen-transfer reactions.

Oxygen relationships in intermittent sand filtration of wastewaters

A model for some of the many physical-chemical and biological processes in intermittent sand filtration of wastewaters is described and an expression for oxygen transfer is formulated.

The model assumes that aerobic bacterial activity within the sand or soil matrix is limited, mostly by oxygen deficiency, while the surface is ponded with wastewater. Atmospheric oxygen reenters into the soil after infiltration ends. Aerobic activity is resumed, but the extent of penetration of oxygen is limited and some depths may be always anaerobic. These assumptions lead to the conclusion that the percolate shows large variations with respect to the concentration of certain contaminants, with some portions showing little change in a specific contaminant. Analyses of soil moisture in field studies and of effluent from laboratory sand columns substantiated the model.

The oxygen content of the system at sufficiently long times after addition of wastes can be described by a quasi-steady-state diffusion equation including a term for an oxygen sink. Measurements of oxygen content during laboratory and field studies show that the oxygen profile changes only slightly up to two days after the quasi-steady state is attained.

Results of these hypotheses and experimental verification can be applied in the operation of existing facilities and in the interpretation of data from pilot plant-studies.

Estimation of the volumetric oxygen tranfer coefficient (KLa) from the gas balance and using a neural network technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relatin Dissolved Oxygen Concentration to Fish Distribution in Jarecki Lake

Abstract Water temperature and dissolved oxygen (DO) profiles were measured once every month from mid July to mid February in a relatively deep sand-pit lake in southeast Nebraska. These profiles showed depleted DO concentrations below the thermocline during summer stratification indicating areas fish will likely avoid in summer months. Colder temperatures in fall caused complete mixing of the water column allowing fish to inhabit all depths of the lake. An inverse temperature stratification occurred directly below the ice during winter months as ice cover cooled the surface water to below 4 degrees Celsius. Ice cover also blocked air – water oxygen transfer and reduced light for photosynthesizing algae. Associated with winter ice cover, DO concentrations in the hypolimnion decreased significantly, once again reducing available fish habitat. It is likely anglers will have a higher success rate catching fishing in water above 6 meters (m) (~20 feet) in a eutrophic sandpit lake during hot summer months and below ice cover in winter. Fish can utilize all depths of the lake during fall turnover and could theoretically be caught by anglers anywhere in the lake.

Hydrodynamics and mass transfer coefficient in three-phase air-lift reactors containing activated sludge

This study was to investigate the impacts of operating conditions and liquid properties on the hydrodynamics and volumetric mass transfer coefficient in activated sludge air-lift reactors. Experiments were conducted in internal and external air-lift reactors. The activated sludge liquid displayed a non-Newtonian rheological behavior. With an increase in the superficial gas velocity, the liquid circulation velocity, gas holdup and mass transfer coefficient increased, and the gas residence time decreased. The liquid circulation velocity, gas holdup and the mass transfer coefficient decreased as the sludge loading increased. The flow regime in the activated sludge air-lift reactors had significant effect on the liquid circulation velocity and the gas holdup, but appeared to have little impact on the mass transfer coefficient. The experimental results in this study were best described by the empirical models, in which the reactor geometry, superficial gas velocity and/or power consumption unit, and solid and fluid properties were employed. (c) 2006 Elsevier B.V. All rights reserved.