Measurement Of Oxygen Transfer Research Articles

Measurement of oxygen transfer from air into organic solvents.

BACKGROUNDThe use of non‐aqueous organic media is becoming increasingly important in many biotechnological applications in order to achieve process intensification. Such media can be used, for example, to directly extract poorly water‐soluble toxic products from fermentations. Likewise many biological reactions require the supply of oxygen, most normally from air. However, reliable online measurements of oxygen concentration in organic solvents (and hence oxygen transfer rates from air to the solvent) has to date proven impossible due to limitations in the current analytical methods.RESULTSFor the first time, online oxygen measurements in non‐aqueous media using a novel optical sensor are demonstrated. The sensor was used to measure oxygen concentration in various organic solvents including toluene, THF, isooctane, DMF, heptane and hexane (which have all been shown suitable for several biological applications). Subsequently, the oxygen transfer rates from air into these organic solvents were measured.CONCLUSIONThe measurement of oxygen transfer rates from air into organic solvents using the dynamic method was established using the solvent resistant optical sensor. The feasibility of online oxygen measurements in organic solvents has also been demonstrated, paving the way for new opportunities in process control. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry.

Measurement of air–water oxygen transfer of cylindrical vortex flow regulators at a recirculating system

Hydrodynamic flow regulators are used for diversion and/or limiting excess discharge in wastewater and stormwater systems as a replacement for traditional flow throttling devices. They are highly efficient, reliable and free from common disadvantages of traditional devices. Recent research of the authors indicated that atomization of a liquid by vortex flow regulators accelerates oxygenation and prevents the putrefaction process in wastewater and storm water collection systems. The study presents experimental results of the oxygen transfer measurements for basic designs of cylindrical hydrodynamic flow regulators in a closed-circuit experimental setup at the semi-commercial scale. The oxygen mass transfer coefficient, standard oxygen transfer rate and standard aeration efficiency were determined for the range of tested configurations by the clean water test.

Oxygen Transfer Parameter Estimation: Impact of Methodology

Oxygen transfer is an important part of wastewater treatment and accounts for as much as 60% of energy consumption in the activated sludge process. Prior to 1984, no standard method for quantifying oxygen transfer existed, which created problems in the design and warranties for treatment plants. The ASCE standards for the measurement of oxygen transfer in clean water and the Standard Guidelines for In-Process Oxygen Transfer Testing have found widespread application and have reduced design variability. The standard has allowed operators and engineers to better evaluate process operation of existing treatment plants. This paper illustrates the key concepts of the standard and shows why they are important and how they reduce the variability of oxygen transfer testing. The reasons for the standard’s success are described, as are the pitfalls of earlier approaches. The paper also highlights key new areas of the revised clean water standard, including an optional correction for test water total dissolved solid...

Measurement of Oxygen Transfer from Air Bubbles to Water

This paper presents fundamental properties of concentrations of oxygen dissolved from air-bubbles pumped into water with the aim to understand aeration effects to oxygen supply in the surf zone. Fluorescence imaging experiments were performed to identify relations of the local transfer of oxygen and the bubble size distribution. It has been found that the both of spatial distributions and temporal variations of dissolved oxygen were described by the number densities of small bubbles less than 2.0 mm.

Local measurement of oxygen transfer around a single bubble by planar laser-induced fluorescence

The aim of this work is to develop a non-intrusive experimental technique to measure oxygen concentration in a liquid phase. This technique relies on the planar laser-induced fluorescence (PLIF). In its classical version, PLIF consists in viewing the presence of a fluorescent dye in a liquid phase by means of a laser sheet. Digital image analysis gives the relationship between local grey levels and the dye concentration. The principle of the oxygen concentration measurement rests on the fact that the oxygen molecules inhibit this fluorescence, in proportion to their concentration. After calibration, analysis of the grey levels gives an image of the 2D field of oxygen concentration.

Impact of agitation and aeration on hydraulics and oxygen transfer in an aeration ditch: Local and global measurements

In urban waste water treatment plants one of the most developed processes to treat pollutants is the activated sludge basin. The aim of this paper is to present results on the hydraulics and aeration performance of an aerated basin at pilot plant scale. Local gas retention, gas velocity and bubble size have been measured and linked to the classical global measurements of oxygen transfer coefficient and of horizontal liquid velocity. Different operating conditions have been tested to show the impact of each parameter on hydraulics and aeration performance. The increase of air flow rate induces an increase of the local gas retention, of the gas velocity as well as of the Sauter diameter. Changes in these local parameters do exhibit a strong impact on the oxygen transfer coefficient. Hence these local measurements are used to discuss and gain a deeper understanding of the oxygen transfer phenomena. An augmentation of the horizontal liquid velocity results in higher values for the global oxygen transfer coefficient. This is confirmed by observation and local measurements, which show a stronger inclination of the air plume with increasing velocity. This translates to a larger course for the bubbles to cover before reaching the surface. With respect to global oxygen transfer measurements, the optimal position of the agitator was found to be near the bottom of the reactor for the type of pilot plant studied. In addition it can be stated that the horizontal position of the impeller has a large impact on the liquid horizontal velocity. Improved understanding is gained through local investigations, which reveal the increased inclination of the air plume as one major cause.

Specific SBR population behaviour as revealed by comparative dynamic simulation analysis of three full-scale municipal SBR wastewater treatment plants

Three full-scale municipal sequential batch reactor (SBR) wastewater treatment plants (WWTPs) were investigated by dynamic simulation studies using ASM1. All three WWTPs showed similar kinetic and stoichiometric conditions in the SBR population behaviour after calibration of the models. The simulation results detected only a discrepancy to the ammonia online data during and shortly after shock loading under anoxic and anaerobic conditions that so far could not be adjusted by the ASM1 model. However, these differences did not severely affect the quality of the simulations nor the effluent flows. Additionally, in all cases a dynamic alpha factor curve occurred during the aeration phases that was verified by further oxygen transfer measurements. This might reveal new aspects for the process control, design and simulation of SBR WWTPs. A short lag phase was detected in many cases at the beginning of the first aeration phase.

Application of the off-gas method to the measurement of oxygen transfer in biofilters

To determine the oxygen mass transfer in clean water in biofilters, a method based on the follow up of the oxygen fraction in the off gas during the oxidation of sulphite in excess has been evaluated and applied to a pilot-scale unit (250 L, superficial gas velocity from 0 to 5.6 × 10 - 3 m N s - 1 , superficial liquid velocity from 0 to 2.5 × 10 - 3 m s - 1 ). Tests performed on a two-phase reactor showed that, without any cobalt addition, standard oxygen transfer efficiencies (SOTE) obtained from the proposed method are not statistically different from those issued from the standardised method. A relationship has been proposed to express SOTE values as a function of the conductivity, and the influence of the gas and liquid velocities on SOTE and k L a has been investigated.

Experimental Study of a Ceramic Microsparging Aeration System in a Pilot-Scale Animal Cell Culture

The oxygen supply of cell cultures with the aid of free gas bubbles is an efficient process strategy in pharmaceutical production. If the cell-damaging impact of gas bubbles is reduced, direct aeration becomes a practical solution with scale-up potential and comparatively high oxygen transfer rates. In this paper a microsparging aeration system made of porous ceramic was compared with bubble-free membrane aeration. The sparging system was used for the long-term cultivation of mammalian cells in 2- to 100-L scale bioreactors and produced bubble sizes of 100-500 microm in diameter. Using a scale of 2.5 and 30 L, a cell density of 2.6 x 10(6) cells/mL was attained. When a 100-L scale was used, a density of 1.1 x 10(6) cells/mL was achieved, whereas a comparable membrane-aerated system showed a cell density of 2.2 x 10(6) cells/mL. At relatively low agitation rates of less than 70 rpm in the sparged bioreactors, a homogeneous and constant oxygen concentration was kept in the medium. As a result of the different foam-forming tendency caused by the lower gas flow of the ceramic sparger compared to that of the standard aeration systems, we were able to develop an appropriate process control strategy. Furthermore, oxygen transfer measurements for the common stainless steel sparger and the ceramic sparger showed a 3-fold higher oxygen transfer coefficient for the ceramic sparger.

Laser induced fluorescence measurements of dissolved oxygen concentration fields near air bubble surfaces

This article describes a laser-induced fluorescence (LIF) technique for measuring dissolved oxygen concentration gradients in water near the surface of an air bubble. Air bubbles are created at the tip of a needle in a rectangular bubble column filled with water that contains pyrenebutyric acid (PBA). The fluorescence of the PBA is induced by a planar pulse of nitrogen laser light. Oxygen transferring from the air bubble to the deoxygenated water quenches the fluorescence of the PBA. Images of the instantaneous and two-dimensional fluorescence field are obtained by a UV-intensified charge-coupled device (CCD) camera. Quenching of fluorescence intensity is determined at each pixel in the CCD image to measure dissolved oxygen concentration. Two-dimensional concentration fields are presented for a series of measurements of oxygen transfer from 1.6 mm bubbles suspended on the tip of a needle in a quiescent fluid. The images show the spatially varying concentration profiles, gradients, and boundary layer thicknesses at positions around the bubble surfaces. These direct and local measurements of concentration behavior within the mass transfer boundary layer show the potential of this LIF technique for the development of general and mechanistic models for oxygen transport across the air–water interface.

Oxygen transfer in agitated silica and pyrite slurries

Oxygen transfer measurements in agitated mineral slurries were carried out in a 671 laboratory tank. Two impellers (a Rushton turbine and a Lightnin A315) and two types of solid particles (silica, d 50=13 μm, and pyrite, d 50=14 μm) were investigated. Next to the volumetric oxygen transfer rate k La local bubble sizes, the overall gas hold-up in the tank, and the power input were measured. The silica and pyrite slurries behaved remarkably different with respect to the oxygen transfer as a function of the solids fraction. The pyrite particles increase ka, whereas silica impairs oxygen transfer. The bubble size measurements indicate that the increased k La in pyrite slurries is related to an increased interfacial area in the tank.

A New Approach for Measuring the Effect of a Monolayer on Molecular Transfer across an Air/Water Interface Using Scanning Electrochemical Microscopy

A new approach is described for the quantitative study of the effect of a monolayer on solute transfer rates across an air/water interface. The technique is illustrated through measurements of oxygen transfer across a monolayer of 1-octadecanol as a function of compression. The experimental approach uses an inverted ultramicroelectrode (UME), positioned in the water phase in a Langmuir trough close to the air/water interface to induce the transfer of oxygen from air to water via the reduction (and depletion) of oxygen. The steady-state current response, measured as a function of UME−interface separation at various monolayer compressions, demonstrates that the rate of oxygen transfer is governed primarily by the accessible free area of the interface.

Predictive Capabilities in Oxygen Transfer at Hydraulic Structures

Field measurements of oxygen transfer at four types of hydraulic structures are compared to predictions by 12 equations in the literature. The hydraulic structures were divided into weirs, spillways (gated and ungated), gated sills, and gated conduit outlets. For weirs, it was found that Avery and Novak's equation provides the best prediction of oxygen transfer. Rindels and Gulliver's equation and Wilhelms's equation provide the best prediction for spillways and gated sills, respectively. No equation provided an acceptable prediction of oxygen transfer at gated conduit outlets, probably because of the variety of hydraulic conditions that exist in these structures. The prediction of the transfer of other compounds from these equations also was discussed. It appears that it is currently possible to predict the transfer of another volatile compound from these oxygen transfer equations at these types of hydraulic structures, as long as the dimensionless Henry's law constant is greater than 10. The uncertainty of the prediction, however, would increase.

Oxygen Mass Transfer Fundamentals of Surface Aerators

The use of surface aerators as oxygen transfer devices in biological wastewater treatment systems has been commonplace for at least several decades. The current state-of-the-art oxygen mass transfer analysis for surface aerators is essentially limited to the first-order, exponential model employed in the ASCE Standard for the Measurement of Oxygen Transfer in Clean Water. This simple model has been used for several decades to characterize the oxygen mass transfer performance of surface aerators as well as many other types of aerators. This study develops a more fundamentally rigorous oxygen mass transfer model for surface aerators which provides a more physically realistic description of the actual oxygen transfer mechanisms. This new oxygen mass transfer model separates the oxygen transfer process into a liquid spray mass transfer zone and a surface reaeration mass transfer zone. The model independently analyzes the oxygen transfer process within these two distinctively separate zones and provides the methodology and techniques for quantitatively determining the oxygen transfer rate within each of these important, but fundamentally different, oxygen mass transfer zones.

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/kLa) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredkLa values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.

Fate of volatile organic compounds in municipal activated sludge plants

ABSTRACT: The fate of volatile organic compounds (VOCs) in municipal activated sludge plants was investigated at pilot and full scale. More than 80% of the mass flow of nonchlorinated compounds was observed to be biodegraded while less than 20% was removed by stripping. Conversely, 46% of the mass flow of chlorinated compounds was biodegraded and 47% was removed by stripping. Adsorption of VOCs onto waste sludge was not a significant removal mechanism. The pilot plant employed was found to effectively emulate the liquid‐gas phase partitioning and overall compound removals observed in a full‐scale plant. Little difference in liquid‐gas phase partitioning was observed for coarse and fine pore diffusers in spite of differing mass‐transfer characteristics as demonstrated by oxygen‐transfer measurements. This implies that equilibrium between the liquid and gas‐phase concentrations was achieved with both diffuser types. Stripping of VOCs was observed to increase with airflow; however, the extent of stripping increased at a declining rate.

Biocarbone Aerated Filters - Ten Years After: Past, Present, and Plenty of Potential

About ten years ago, the first full scale Biocarbone aerated filter went into service in Soissons (France) for a capacity of 40 000 population equivalents. This compact wastewater treatment system combines aerobic biodegradation and filtration in one unit, eliminating the need for clarifiers and achieving high removal rates through fixed biomass. Since, a number of independent investigations have been performed to establish dimensioning criteria and process performance. This article summarises the reports of the US EPA, the Japanese JSWA, and the British WRC, as well as experiences acquired by cities and water authorities. In pilot and demonstration scale, reactor kinetics, sludge production and energy consumption was measured. Most reports agree on removal rates up to 4 kg BOD/m3 d or nitrification rates around 0.6 kg N/m3 d. Sludge yields ranged consistently around 0.8 kg SS / kg BOD removed, but oxygen transfer measurements varied from 7 % to 15 %. Full scale experience confirms these values, and operation results from large plants in North America are given. Several examples of using the Biocarbone process for low pollution residuals are demonstrated, including plants in Britain, Denmark and Switzerland. As tertiary installation fed with clarified secondary effluent, final residuals below 1 mg/l N-NH4 and 5 mg/l for SS and BOD can be achieved in a hydraulic detention time around one hour. On settled sewage, two hours detention time results in advanced secondary effluent quality below 5 mg/l N-NH4 and around 10 mg/l for BOD and SS. If an anoxic reactor is added, total nitrogen residuals below 10 mg/l can be achieved in about three and a half hours.

Oxygen Transfer Measurements and Air Distribution for an Aeration Basin with Fine Bubble Diffusers

The off-gas method was used to study oxygen transfer efficiency in a long, narrow activated sludge basin. The basin was equipped with square, ceramic, fine pore diffuser plates arranged in a uniform longitudinal pattern at a depth of 4.3 m. Oxygen transfer efficiency, at 20°C and zero dissolved oxygen concentration, during the second and third years following diffuser cleaning, was between 15 and 17%. A uniform distribution of air to the tank was compared with a tapered air supply (more air at the inlet end and less at the outlet). The tapered air supply gave lower dissolved oxygen at the outlet and did not increase overall oxygen transfer. With a 3 to 5-fold variation in air flow, at either the inlet or outlet zone of the basin, the oxygen transfer efficiency, adjusted for zero dissolved oxygen, stayed constant.

Oxygen transfer into a medium with extracellular polysaccharide

Measurement of oxygen transfer into a pseudoplastic solution of agrobacteran yielded the correlationKLa ≈Re1.013 (100Re 600). A possible method of estimation of changes inKLa, in dependence on agrobacteran concentration is presented.