Dissolved Oxygen Probe Research Articles

Gas/Liquid Mass Transfer in Hot Sparged Systems

AbstractUnderstanding the effect of temperature on the volumetric mass transfer rate is of vital importance for the design of chemical reactors operated at elevated temperatures. The present study is motivated by a poor understanding of this effect due to previous limited investigations. Such an effect has been studied at the CSIRO Energy & Thermofluids Engineering Laboratory in a mechanically agitated air‐water mixing tank with operating temperatures in the range of 20‐80d̀C at atmospheric pressure. The oxygen concentration of the liquid is measured by a dissolved oxygen probe. The volumetric mass transfer rate is estimated using a dynamic method. It has been found that the saturated oxygen concentration of the liquid does not change significantly with the gas sparging rate and impeller speed. The change of temperature affects the saturated oxygen concentration significantly. The volumetric mass transfer rate increases with the increase of liquid temperature in the range of 18‐60d̀C. Beyond 60d̀C, the transfer rate decreases. Such a decrease is mainly due to the dramatic drop in the gas void fraction.

Statistical Comparison of Multiple Methods for the Determination of Dissolved Oxygen Levels in Natural Waters

The following experiment reinforces students’ working knowledge of statistics by utilizing the t test to compare the results of two independent methods for the determination of dissolved oxygen (DO). In this experiment students utilize a dissolved oxygen probe to determine the levels of DO in natural waters at two sampling locations while obtaining samples of water from the laboratory for analysis using the classic Winkler titration. The importance of using proper sampling methods and techniques to obtain representative samkples is a large focus of the prelaboratory discussion and is continually stressed during fieldwork. After analyzing the water samples by the DO mete and the Winkler titration, students pool the class data and are asked to determine if the two methods for dissolved oxygen agree at each sampling location. The students are then asked to determine if the DO levels at the different sampling locations are statistically different or not. The students are asked to consider why their results agree or differ from the theoretical value they calculate using Henry’s law.

A lab-built respirometer for plant and animal cell culture.

A very simple off-line respirometer was developed to measure oxygen consumption rates of low respiring and shear-sensitive cell suspensions. The respirometer is composed of a 10 mL glass syringe in which the plunger was substituted with a polarographic dissolved oxygen probe. Mechanical agitation is provided by means of a magnetic stirring bar inside the measuring chamber and a stir plate placed below the respirometer. Abiotic oxygen fluxes occurring in the measurement chamber such as oxygen diffusion and probe oxygen consumption were investigated. The apparent oxygen uptake rate was then corrected for abiotic oxygen fluxes, leading to accurate measurements of respiration rates ranging from 0.5 to 25.0 mM x h(-1). Additionally, the effect of the stirring bar shape and of the test length on the integrity of plant (Eschschzoltzia californica) and animal (NS0) cells was evaluated. Animal cells showed a higher resistance to mechanical stirring inside the respirometer compared to plant cells (0% of broken cells and 78.1% respectively for a polygonal stirring bar and a 15 min test). For plant cells, cell damage inside the measurement chamber was reduced by optimizing the stirring bar shape and reducing the test length to 5 min or less. This very simple design was shown to provide reliable and low-cost quantification of the oxygen uptake rate of plant and animal cells and can be use even for more demanding measurements such as oxygen affinity studies.

Simple Tests for Rapid Assessment of the Quality of Raw Milk

Simple and inexpensive tests are described for rapid qualitative assessment of the microbiological quality of raw milk. These tests included the monitoring of dissolved oxygen levels and changes in the color of raw milk with time in a slightly modified methylene blue test using 16 ppm of dye concentration. The initial bacterial population in raw milk determined by standard plate count could be estimated with coefficients of determination (r2) of about 0.697 and 0.613 from the respective normalized voltage outputs of the dissolved oxygen probe and light-sensing probes at selected time intervals in less than 1 h. However, a comparison of experimental and estimated initial bacterial populations in raw milk showed correlation coefficients (r) of about 0.754 and 0.616 for the dissolved oxygen probe and light-sensing probe, respectively. These results clearly indicated the potential and need for improving such empirical models for grading raw milk with both types of probes.

Using Calculator-Based Laboratory Technology to Conduct Undergraduate Chemical Research

Calculator-based laboratory (CBL) technology can be used to initiate a viable undergraduate research program and at the same time teach ethical behavior in science and research. One research project, utilizing buckminsterfullerene, is described as a prototype of the quality and scope of such chemical research programs. Eight original research project ideas are presented for undergraduates to pursue using readily available materials and pH, colorimeter, relative humidity, temperature, light, carbon dioxide, and dissolved oxygen probes.

Avoiding acetate accumulation in Escherichia coli cultures using feedback control of glucose feeding.

An automated glucose feeding strategy that avoids acetate accumulation in cultivations of Escherichia coli is discussed. We have previously described how a probing technique makes it possible to detect and avoid overflow metabolism using a dissolved oxygen sensor. In this article these ideas are extended with a safety net that guarantees that aerobic conditions are maintained. The method is generally applicable, as no strain-specific information is needed and the only sensor required is a standard dissolved oxygen probe. It also gives the highest feed rate possible with respect to limitations from overflow metabolism and oxygen transfer, thus maximizing bioreactor productivity. The strategy was implemented on three different laboratory-scale platforms and fed-batch cultivations under different operating conditions were performed with three recombinant strains, E. coli K-12 UL635, E. coli BL21(DE3), and E. coli K-12 UL634. In spite of disturbances from antifoam and induction of recombinant protein production, the method reproducibly gave low concentrations of acetate and glucose. The ability to obtain favorable cultivation conditions independently of strain and operating conditions makes the presented strategy a useful tool, especially in situations where it is important to get good results on the first attempt.

A Comparison of Manometric and Membrane-Electrode Procedures for Measuring Rates of Leaf Decay

Two instruments were compared for consistency of decay-rate measurements of four leaf types: Lolium perenne, Typha domingenesis, Casuarina cunninghamiana and Eucalyptus polyanthemos, via progressive biological oxygen demand (BOD). The instruments were (a) a dissolved oxygen probe (i.e. an oxygen-selective membrane electrode) used in two different modes: (1) measurements of sacrificial samples that were successively discarded, and (2) repeated measurements of the same sample, and (b) a mercury free manometer. Measurements of D-glucose:glutamic acid standards were similar for both instruments, and corresponded with values expected after five days of decay. During five days decay of the four leaf types, progressive measurements obtained by both applications of the dissolved oxygen probe were similar, and could be related linearly. Progressive leaf-decay measurements obtained by the manometer and dissolved oxygen probe could be related linearly also. Decay measurements obtained by both instruments were nearly identical for C. cunninghamiana and E. polyanthemos, but there were slight differences in the slopes of linear relationships for L. perenne and T. domingenesis. These comparisons indicate the feasibility of using both instruments for obtaining comparable measurements of leaf decay rates. It is also feasible to briefly reopen the same glass bottle to facilitate temporal BOD measurements with the dissolved oxygen probe. However, because slight differences in decay rates were evident in two comparisons, care should be exercised to derive and verify the association of data between instruments.

Measurement of Gas-Liquid Mass Transfer in an Agitated Vessel. A Comparison between Different Impellers.

Measurement of mass transfer rate was carried out in an agitated vessel with gas sparging. The performance of mass transfer of several commonly used impellers (i.e. Lightnin A315 and A310, 45° pitched blade turbine, concave blade turbine, Rushton turbine, and Rushton turbine with holes) were examined systematically under the same fluid and tank conditions. A dynamic gassing-out method was used to measure the mass transfer rate of oxygen from gas to the de-ionised water. The variation of the dissolved oxygen concentration of the water was measured by a polarographic dissolved oxygen probe (ORION PCM800). The present data shows reasonable agreement with that in previous publications such as those of Linek et al. (1987), Hickman (1988), Warmoeskerken and Smith (1989), Martin et al. (1994), and Chen and Chen (1999). All the data collected here shows that van’t Riet’s (1979) expression, i.e.: kLa = α(P/V)0.4Us0.5 represents reasonably, well (to within ± 30%) the correlation of kLa with specific power P/V and superficial gas velocity Us. However, the present data seem to indicate that the radial flow impellers provide slightly higher (17%) mass transfer rate than the axial flow impellers.

A mushroom ( Agaricus bisporus) tissue homogenate based alcohol oxidase electrode for alcohol determination in serum

To construct homogenized tissue based biosensors by using plant tissue materials is a relatively new development in the biosensor technology. In this study, a homogenized mushroom ( Agaricus bisporus) tissue based electrode in which alcohol oxidase activity was developed by immobilizing with gelatin and cross-linking agent glutaraldehyde at dissolved oxygen probe for determination of ethyl alcohol. The electrode response depends linearly on ethyl alcohol concentration between 0.2 and 20 mM. In the optimization studies, phosphate buffer (pH 7.5, 50 mM) and 35°C were obtained as the optimum conditions. By using the electrode prepared we have made approximately 60 measurements in 10-h period, and response time of the electrode is 2 min for each measurement.

Gas-Liquid Mass Transfer Using Surface-Aeration in Stirred Vessels, with Dual Impellers

Mass transfer is calculated, for air-water systems, using measurements from a dissolved oxygen probe with a simple model.Most measurements are taken at the 20 litre scale, but successful mass transfer measurements have also been made at the 5000 litre scale. The full-scale designs are illustrated for a number of different processes, and examples given of the reduction in cycle-time achievable by a change of impeller configuration. The effects of geometry and gassed-power input on the mass transfer coefficient are also discussed.

On-line measurement of oxygen uptake in cell culture using the dynamic method

Measurement of oxygen uptake rate is useful in assessing growth, viability, and metabolic activity. In cell culture, however, the oxygen demand is extremely small (typically 0.1-0.3 mM O(2)L-h) and is very difficult to measure accurately using conventional offgas analysis. In many industrial submerged cell culture systems, dissolved oxygen levels are controlled between preset limits by intermittent sparging of air or oxygen. This article describes a computational method for the automatic online determination of oxygen uptake from the dynamic dissolved oxygen probe response. Experimental measurements show that for a typical hybridoma culture, specific oxygen demand is 0.15 mM O(2)/10(9) cells/h. (c) 1996 John Wiley & Sons, Inc.

A new enzyme electrode based on ascorbate oxidase immobilized in gelatin for specific determination of l-ascorbic acid

A biosensor for the specific determination of l-ascorbic acid in fruit juices and vitamin C tablets was developed using ascorbate oxidase (EC 1.10.3.3) from cucumber ( Cucumis sativus L.) in combination with a dissolved oxygen probe. Ascorbate oxidase immobilized with gelatin using glutaraldehyde and fixed on pretreated teflon membrane served as an enzyme electrode. The phosphate buffer (50 mM, pH 7.5) and 35°C were established as providing the optimum conditions. The biosensor response depends linearly on l-ascorbic acid concentration between 5.0×10 −5 and 1.2×10 −3 M with a response time 45 s. The biosensor is stable for more than 2 months, while more than 200 assays were performed. The results obtained for fruit juices and tablets were compared with DCIP (2,6 dichlorophenolindophenol) method.

A novel biosensor for specific determination of hydrogen peroxide: catalase enzyme electrode based on dissolved oxygen probe

A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved oxygen probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35°C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0×10 −5 and 3.0×10 −3 M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed.

A simple respirometric technique for assessing compost stability

Stability is an important compost quality characteristic, but also one that is difficult to measure. A simple respirometric technique for the assessment of compost stability (SOUR test) was developed, that utilises a dissolved oxygen probe to measure changes in the oxygen concentration in an aqueous compost extract, under conditions ensuring optimum microbial activity and maximum reaction rates. A fully automated procedure is described and possible problems are discussed. The method was used to follow changes in stability of sewage sludge composts from a commercial plant using the windrow composting system. Two different batches of material were monitored. Results were compared with three other stability tests, a respirometric method utilising solid compost samples and the COD and optical density of compost water extracts. Both respiration tests indicated increasing compost stability with processing time and gave significant correlation both with compost age and with each other. The SOUR of the raw mixture was different for the two batches (9.3 and 18.4 mg O 2/g VS/h), but after composting and maturation both dropped to about 1 mg O 2/g VS/h. Measuring the respiration rate of an aqueous compost suspension rather than a solid compost sample offers certain advantages: the test is not affected by variations in the matric water potential of the samples; there is immediate contact between substrate, microbes and oxygen leading to maximum reaction rates; and the gas–liquid barrier for oxygen diffusion at the surface of the compost particles is omitted. The COD and the optical density of the water extracts did not show clear trends and did not allow any conclusions about compost stability to be drawn.

A model for multicomponent biosensing and its application to a dead cell-based BOD biosensor

The sensor response of a biofilm-modified dissolved oxygen probe in a multicomponent organic solution was described mathematically with respect to the mass transfer and biooxidation rate processes of the organic solutes and the dissolved oxygen in the biosensor. The model was used to interpret and define mathematically the biochemical oxygen demand (BOD 5) of an organic solution with respect to the universally accepted BOD check solutions containing equal mass concentrations of glucose and glutamic acid. The model was also extended to describe the effect of cell population immobilized in the biofilm and substrate temperature on the BOD-sensing sensitivity. The model showed that the sensing characteristics for a given solute in a solution depends on the stoichiometric ratio of its diffusivity to that of oxygen in the biofilm. This parameter was determined for a number of single organic solutes using a BOD biosensor with immobilized thermally killed Bacillus subtilis cells. The single solute parameters were used to verify the application of the model to the sensing of multicomponent organic mixtures with respect to their compositions and their biochemical oxygen demand. The model’s description of the sensor response for multicomponent organic mixture and its interpretation and description of its biochemical oxygen demand were well substantiated experimentally. The model is useful for the characterization, design and fabrication of a bio-oxidation-based biosensor for monitoring multicomponent organic solutions and their biochemical oxygen demands.

Power consumption and mass transfer in agitated gas‐liquid columns: A comparative study

AbstractPower consumption, gas holdup and oxygen mass transfer in agitated gas‐liquid columns have been studied for an air‐water system. Measurements have been carried out in a reciprocating plate reactor using five different types of perforated plates and in a stirred tank reactor with one, two and three Rushton turbines, a helical ribbon impeller with and without surface baffles. Each mixing vessel had an identical geometry with a working volume of 17 L. For reciprocating plate stacks, the gas holdup is a complex function of the perforation diameter, the frequency of agitation and the gas superficial velocity. For radial‐type mixing devices, the gas holdup increases more rapidly with the speed of rotation for the helical ribbon. The power imparted to the fluid by the mixing device is independent of the gas superficial velocity for the plate stacks and the helical ribbon impeller for a given frequency or speed of agitation whereas it decreases for Rushton turbines. The correlation of the power consumption obtained for all mixing devices plotted against the reciprocating frequency or speed of rotation to the third power shows a linear fit. KLa values were correlated very well with the power input per unit volume and superficial gas velocity for all mixing devices. At lower power input per unit volume, KLa is a function of only the gas superficial velocity. At higher input power per unit volume, KLa increases rapidly with an increase in the intensity of agitation. Reciprocating plates with larger diameter perforations led to higher KLa values whereas the lowest KLa were obtained with the helical ribbon impeller. Correlations for one and three Rushton impeller assemblies were almost identical whereas measured KLa were much higher for the two‐impeller assembly due to the presence of a highly mixed zone in the vicinity of the dissolved oxygen probe.

A hybrid respirometric method for more reliable assessment of activated sludge model parameter

A novel hybrid respirometric principle is proposed that is particularly suited to sludge and wastewater characterisation in the context of activated sludge process models. Advantages of two respirometric principles are combined and their disadvantages eliminated to increase measuring frequency and precision. Emphasis is put on decreasing the bias in parameter estimates that results from the use of unreliable sensor constants in the calculation of respiration rates. To this end checks for dissolved oxygen probes, aeration systems and pumps are built into the respirometer's operation. Checks are to be run while the respirometric batch experiment is conducted so that between-experiment variation is eliminated and within-experiment variation is minimised. It is also stressed that a combined sensor/process model should be used to estimate the process parameters rather than a sequential procedure in which the sensor constants are first used to calculate respiration rates, that are subsequently used for sludge and wastewater characterisation. Finally, three possible practical implementations of the new principle are discussed in relation to maximising parameter estimation accuracy.

RESPONSE CHARACTERISTICS OF A DEAD-CELL BOD SENSOR

Bacillus subtilis cells, thermally killed by exposing dried cells to 280°C for 2.5 mins, were used for fabricating the biofilm attached to a dissolved oxygen probe. The dead cell biosensor showed good sensing characteristics for the BOD of aqueous organic solutions and wastewaters in regard to its response and recovery times, reproducibility and stability. It has a significantly long life span of several months, requiring only simple storage at room temperature in phosphate buffer in between measurements and even over extended idling periods for which microbial sensors would normally require food and nutrient additions for their sustenance. The sensitivity of the biosensor towards 24 organic solutes were generally comparable with biosensors using living Bacillus subtilis cells and the American Public Health Association (APHA) method of measurement using activated sludge. The high diffusion resistance of the membranes was experimentally verified to have caused the long response time for soluble starch. The BOD 8 of some real wastewater and synthetic water samples were determined and compared with the BOD 5 obtained by the APHA method. The deviation of the biosensor values from the APHA values depends on the difference in the sensitivity of the device and the microbial system towards the compounds in the test sample. Nevertheless the deviation was similar to those generally observed among the APHA values reported for a given substrate by different analysts and laboratories.

A Novel Catechol Oxidase Enzyme Electrode for the Specific Determination of Catechol.

An enzyme electrode for the specific determination of catechol was developed by using catechol oxidase (EC 1.10.3.1) from eggplant (Solanum melangena L.) in combination with a dissolved oxygen probe. Optimization studies of the prepared catechol oxidase enzyme electrode established a phosphate buffer 50 mM at pH 7.0 and 35°C to provide the optimum conditions for affirmative electrode response. The enzyme electrode response depended linearly on a catechol concentration range of 5•10(-7)-30•10(-5) M with a response time of 25 sec and substrate specificity of the catechol oxidase electrode of 100%. The biosensor retained its enzyme activity for at least 70 days.

A hybrid respirometric method for more reliable assessment of activated sludge model parameter

A novel hybrid respirometric principle is proposed that is particularly suited to sludge and wastewater characterisation in the context of activated sludge process models. Advantages of two respirometric principles are combined and their disadvantages eliminated to increase measuring frequency and precision. Emphasis is put on decreasing the bias in parameter estimates that results from the use of unreliable sensor constants in the calculation of respiration rates. To this end checks for dissolved oxygen probes, aeration systems and pumps are built into the respirometer's operation. Checks are to be run while the respirometric batch experiment is conducted so that between-experiment variation is eliminated and within-experiment variation is minimised. It is also stressed that a combined sensor/process model should be used to estimate the process parameters rather than a sequential procedure in which the sensor constants are first used to calculate respiration rates, that are subsequently used for sludge and wastewater characterisation. Finally, three possible practical implementations of the new principle are discussed in relation to maximising parameter estimation accuracy.