Oxygen Mass Balance Research Articles

The role of free-surface turbulence and surfactants in air–water gas transfer

Laboratory measurements of gas-transfer velocity and free-surface hydrodynamics were made for oscillating grid-stirred turbulence. Air–water gas-transfer velocities were determined from the waterside dissolved oxygen mass balance, and an innovative digital particle image velocimetry technique was used to measure the two-dimensional free-surface flow field. The impact of adventitious and purposely introduced surfactant films on free-surface turbulence and gas-transfer rates was explored quantitatively. As expected, bulk turbulence was unable to provide a unique relationship for the gas-transfer rates observed, owing predominantly to surfactant effects. However, the surface divergence computed from the free-surface velocity field was capable of reconciling the gas-transfer data. This is possible evidence confirming that the free-surface divergence is an important process involved in interfacial gas transport. A relationship for the gas-transfer velocity in terms of the surface divergence and the surface pressure is presented that successfully relates the interactions between surface renewal, surfactants, and gas transfer.

Control of starvation‐induced apoptosis in Chinese hamster ovary cell cultures

The application of the unscented Kalman filter to control starvation-induced programmed cell death—apoptosis—in Chinese hamster ovary cells was investigated. Neural network-based sensitivity analysis identified glutamine and asparagine as two major amino acids that play a key role in the suppression of apoptosis. Dynamic equations that accounted for the dependence of apoptotic cells on the concentrations of viable cells, glutamine, and asparagine were derived. These state equations were highly nonlinear and included nine state variables. An oxygen mass balance was written in the liquid phase. It served as the output equation for the unscented Kalman filter. Using the oxygen uptake rate as the observer, it was possible to estimate the states. A model predictive controller was then implemented once the apoptotic cells in the bioreactor approached a concentration of 1.5×104 cells/mL, taking into account the operating range of the flow cytometer and measurement error. The manipulated variables were the flow rates of glucose, glutamine, and asparagine. Simulation results showed that the controller was able to keep the apoptotic cells at a concentration of 1.5×104 cells/mL. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 645–657, 2002.

Control of starvation-induced apoptosis in Chinese hamster ovary cell cultures.

The application of the unscented Kalman filter to control starvation-induced programmed cell death-apoptosis-in Chinese hamster ovary cells was investigated. Neural network-based sensitivity analysis identified glutamine and asparagine as two major amino acids that play a key role in the suppression of apoptosis. Dynamic equations that accounted for the dependence of apoptotic cells on the concentrations of viable cells, glutamine, and asparagine were derived. These state equations were highly nonlinear and included nine state variables. An oxygen mass balance was written in the liquid phase. It served as the output equation for the unscented Kalman filter. Using the oxygen uptake rate as the observer, it was possible to estimate the states. A model predictive controller was then implemented once the apoptotic cells in the bioreactor approached a concentration of 1.5 x 10(4) cells/mL, taking into account the operating range of the flow cytometer and measurement error. The manipulated variables were the flow rates of glucose, glutamine, and asparagine. Simulation results showed that the controller was able to keep the apoptotic cells at a concentration of 1.5 x 10(4) cells/mL.

Practical identification of the dissolved oxygen dynamic in activated sludge plants

This paper presents the application to a full-scale waste water treatment plant (WWTP) of a practical methodology to identify the oxygen supply and consumption terms, which regulate the dynamic behaviour of the dissolved oxygen concentration (S(O)) in activated sludge reactors. This methodology is based on a periodic adjustment of the selected model for oxygen mass-transfer coefficient (K(L)a) and a continuous estimation of the oxygen uptake rate (r(O)), maintaining constant the adjusted K(L)a model, in order to uncouple the effects that the consumption and supply terms have on the S(O) concentration. The adjustment phase of the K(L)a model is based on typified excitations of the system through the aeration system of the plant, which allow the estimation of K(L)a for different values of the aeration intensity parameter, for instance, air flow rate in air diffusion systems, revolution speed in surface aerators, etc. Once the K(L)a model is adjusted, it is possible to evaluate the K(L)a value in process conditions at any time. The continuous estimation of r(O) is carried out starting from the oxygen mass balance in the activated sludge reactor. This practical methodology has been successfully verified in the Badiolegi WWTP in Azpeitia (Spain), which biological process consists of a double stage AB process, with two different aeration systems: fine pore air diffusers in the A-stage and surface aerators in the B-stage.

Effects of groundwater flux on open‐channel estimates of stream metabolism

The open‐channel oxygen method can produce precise estimates of photosynthesis (P) and respiration (R) over a wide range of stream conditions. It is widely recognized that flux of groundwater contributes to the oxygen mass balance for a stream. However, groundwater flux is rarely considered in open‐channel estimates of stream metabolism, and no guidelines have been established regarding the conditions under which it can be ignored. The purpose of this paper is to describe a method for predicting the effect of groundwater flux on estimates of metabolism and thereby establish the conditions under which flux of groundwater can lead to large errors in estimates of metabolism. Estimation of P is not significantly affected by flux of groundwater. Ecosystem R, however, can be greatly overestimated where the oxygen concentration of groundwater is substantially lower than the concentration in the channel. Although the effects of groundwater flux on estimates of metabolism often are trivial, rates of flux can be sufficiently high in many streams, at least during some part of the year, to affect estimates of R where the oxygen concentration differs substantially between groundwater and surface water. Thus, the potential contribution of groundwater flux to oxygen mass balance should always be evaluated when the

Automated fed-batch culture of Kluyveromyces fragilis based on a novel method for on-line estimation of cell specific growth rate

A corrected feed-forward control strategy was developed for automated substrate feeding in aerobic fed-batch cultures. The control strategy incorporates a novel method for on-line estimation of specific growth rate as a performance indicator of the fed-batch culture. The estimation is based on the measurement of the maximum substrate uptake rate (MSUR) using on-line dissolved oxygen (DO) concentration data and mass balances. It allows the controller to track changes in the specific growth rate to compensate for process disturbances. The control strategy was applied to fed-batch culture of Kluyveromyces fragilis to maximize the volumetric productivity of lactase. A maximum volumetric lactase productivity of 2.98 U/ml h was achieved. The control was shown to be stable throughout the culture period even at the highest cell density of 69 g/l. This technique is applicable to various aerobic systems, especially for microbial cultures showing high specific oxygen uptake rates, since it only requires on-line measurement of DO concentration without the need for off-gas analysis. In a comparison carried out with three other fed-batch control strategies (DO-stat, exponential feeding and exponential feeding with manual feedback control), the corrected feed-forward control strategy exhibited the best performance by achieving the highest volumetric lactase and biomass productivity.

Temperature-programmed reduction and oxidation experiments with V2O5/TiO2 catalysts

Temperature-programmed reduction (TPR) and oxidation (TPO) experiments were performed with V2O5/TiO2 catalysts with vanadia loadings of 1 wt.% (Eurocat EL10V1) and 8 wt.% (Eurocat EL10V8) and with unsupported V2O5. It was possible to correlate the redox properties with the presence of different vanadia species: crystalline and polymeric vanadia species known to be present on EL10V8 were found to be the most difficult to reduce but the easiest to reoxidize. Monomeric vanadyl species known to be present on EL10V1 were the easiest to reduce but the most difficult to reoxidize. In a further set of experiments toluene was used as reducing agent under isothermal conditions at 623 K to probe the catalytic properties of the various vanadia species. In the subsequent TPO experiments the oxygen mass balance including O2, CO, CO2 and H2O was solved thus allowing us to distinguish between the oxidative degradation of adsorbates and the reoxidation of the catalyst. The O2 consumption at lower temperatures was shown to originate from the total oxidation of adsorbates, observed for all three samples, whereas the O2 consumption at higher temperatures, observed only for EL10V8 and V2O5, was caused by the reoxidation of these catalysts. Thus, monomeric vanadyl species were able to adsorb toluene dissociatively, but no oxygenated products were released into the gas phase. In contrast, fast oxygen insertion into toluene and desorption of oxygenates occurred when crystalline and polymeric vanadia species were present.

Process calorimetry on composting of municipal organic wastes

Composting of organic wastes saves environmental resources and helps to recover valuable constituents for agricultural purposes. Composting is a large scale bioprocess, which inherently is operated unisothermally for reasons of large scale and high oxidative metabolic activity. The autothermal pattern of internal heat generation affects the microbiology during the process. In this paper we demonstrate the impact of calorimetric approaches to composting in the laboratory and deduced implications for large scale installations, where oxygen supply, mass balances and heat dissipation calls for a thorough understanding. A comprehensive characterization of a lab-scale composting reactor was performed and the results and methodology transferred to the plant scale. Using these tools we estimated oxycaloric coefficients and mass to enthalpy ratios. Calorimetry provided a robust and reliable tool to study the bulk-kinetics of composting.

Summer Transports of Nutrients in the Gulf of St. Lawrence Estimated by Inverse Modelling

In this paper, we use an inverse methodology to parameterize box models of the Estuary and Gulf of St. Lawrence (GSL) to study carbon, oxygen and nutrient exchanges and transports during the summer period. Three models were developed and compared: a purely physical model A1 and two models including biogeochemical processes (new production, particle sedimentation, remineralization, and burial): a ‘high-flux’ model A2 and a ‘low-flux’ model A3, named in reference to shallow particle flux measurements. Even though the best fits for oxygen, phosphate, and nitrate mass balances were obtained with the low-flux model A3, our results show that a model based only on advection and diffusion fluxes gives a good representation of all the nutrient patterns in summer. However, the use of nutrient and other biogeochemical processes improved the water, heat, and salt balances relative to using only physical data. Moreover, the use of biogeochemical processes allows model A3 more flexibility to reproduce oxygen and nutrient patterns in the deep layer. Without the biogeochemical processes, the deep circulation along the Laurentian Channel and the upward fluxes into the upper layers were reduced below expected values due to the incapacity of the model to balance deep inflows of nutrients with surface outflows through Cabot Strait. The low-flux model A3 estimated higher velocities in the deep layer since the deep nutrient inflows could then be balanced by biological removal in the upper layers. The resulting flow pattern indicated that the St. Lawrence system can be characterized by two main regions: the western region (Estuary, Gaspé Current and Northwestern Gulf), where high biological production is associated with a cyclonic and upwelling circulation, and the eastern region (Laurentian Channel Central, Jacques Cartier Passage, Esquiman Channel and Cabot Strait), where low production is associated with an anticyclonic and downwelling circulation. The Southern Gulf or Magdalen Shallows is mainly influenced by the Gaspé Current, which transports nutrients and production towards Cabot Strait.

Refinement of predictive reaeration equations for a typical Indian river

AbstractDissolved oxygen mass balance has been computed for different reaches of River Kali in western Uttar Pradesh (India) to obtain the reaeration coefficient (K2). A total of 270 field data sets have been collected during the period from March 1999 to February 2000. Eleven most popular predictive equations, used for reaeration prediction and utilizing mean stream velocity, bed slope, flow depth, friction velocity and Froude number, have been tested for their applicability in the River Kali using data generated during field survey. The K2 values computed from these predictive equations have been compared with the K2 values observed from dissolved oxygen balance measurements in the field. The performance of predictive equations have been evaluated using error estimation, namely standard error (SE), normal mean error (NME), mean multiplicative error (MME) and correlation statistics. The equations developed by Smoot and by Cadwallader and McDonnell showed comparatively better results. Moreover, a refined predictive equation has been developed using a least‐squares algorithm for the River Kali that minimizes error estimates and improves correlation between observed and computed reaeration coefficients. Copyright © 2001 John Wiley & Sons, Ltd.

Activated sludge monitoring with combined respirometric–titrimetric measurements

A short review of different respirometric methods is presented, and advantages and disadvantages of different principles are discussed. In this study a combined respirometric–titrimetric set-up was applied to monitor the degradation processes during batch experiments with activated sludge. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber. It is operated with two oxygen probes resulting in two sources of information on the oxygen uptake rate; both collected at a high frequency. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value through the addition of acid and/or base. The cumulative amount of added acid and base serves as a complementary information source on the degradation processes. Interpretation of respirometric data resulting from validation experiments (additions of acetate and urea as ammonium source) showed that the set-up provided reliable data. Data interpretation was approached in two ways: (1) via a basic calculation procedure, in which the oxygen uptake rates were obtained by an oxygen mass balance over the respiration chamber, and (2) via a model-based procedure in which substrate transport was included for a more accurate data interpretation. Simulation examples showed that the presence of substrate transport in the model may be crucial for a correct data interpretation, since experimental conditions (e.g. low flow rate) and/or the biodegradation kinetic parameters (e.g. high K S) may otherwise lead to data interpretation errors. Earlier studies already pointed out that titrimetric data can be related to nitrification, and this was also confirmed in this study. However, in addition, it was shown here for experiments with acetate that the amount of acid dosed was clearly related to the amount of acetate degraded. This indicates that the titrimetric data can be used to study the carbon source degradation. For the titrimetric data in this study, a model-based analysis was however only applied for the nitrification process. For an experiment with ammonium, it was illustrated that the estimation of biodegradation kinetics on a combined respirometric–titrimetric data set significantly improves confidence intervals of the parameters compared to the parameter estimation based on respirometric or titrimetric data separately.

A general model of the activated sludge reactor with dispersive flow—I. model development and parameter estimation

A general dynamic model, including biological processes, hydraulics, oxygen transfer and temperature, was developed for the activated sludge reactor. Transport of wastewater constituents was described by the 1-D advection–dispersion equation with a source term written principally according to the Activated Sludge Model No. 1 (ASM1). Oxygen transfer was strongly related to the air flowrate and this feature was included in the oxygen mass balance. The temperature model was based on a heat balance of the reactor. Experimental methods for parameter estimation were demonstrated. The dispersion coefficient and the oxygen transfer coefficient were estimated from tracer studies and off-gas measurements, respectively. Values of the kinetic and stoichiometric coefficients estimated from batch experiments were generally found to agree with the default values used in the ASM1.

DETERMINING OXYGEN EXCHANGE FROM GAS-SIDE ANALYSIS IN ARTIFICIAL LUNGS

Blood flow rates and blood tension values are difficult to attain during an invivo test of an intravascular artificial lung. As a result, a gas-side oxygen measurement technique is needed This study will discuss two techniques used to make these gas-side measurements, the simple mass balance approach and the Haldane correction approach, and make suggestions on their usage. The simple oxygen mass balance approach involves measuring both oxygen flow and oxygen concentration of both the gas inlet and gas outlet to the artificial lung. On the other hand, the Haldane correction approach couples an additiona mass balance of a tracer gas with the simple oxygen mass balance equations to eliminate the need for one of the oxygen gas flow measurements. Using the simple mass balance approach and single sample uncertainty analysis, the oxygen gas exchange error is quite large at ± 90%. Using the Haldane correction approach, assuming that there is no tracer gas mass transfer, the single sample error is reduced to ± 40% However, small amounts of tracer gas mass transfer can significantly diminish the accuracy of the Haldane correction approach; a tracer gas mass transfer rate equivalent to only 1.0% of the carbon dioxide transfer rate can increase the oxygen exchange error to ± 60%. Due to the inherent Haldane correction approach sensitivity to small amounts of tracer gas mass transfer, oxygen gas exchange analysis of artificial lungs should be done using blood-side analyis with ex-vivo testing

Influence of nutrients and mixing on the primary production and community respiration in the Gulf of Riga

Rates of plankton community production and respiration in relation to wind, solar radiation, biomass and nutrients were measured in the mixed layer during a late spring, a mid-summer and an early autumn situation in the Gulf of Riga. System metabolism was estimated by the in vitro oxygen method and from oxygen mass balance directly in the water. Gross production (GPP) remained fairly stable throughout the investigation periods with a mean of 1.8 g C m −2 day −1 (range: 0.5–3.9 g C m −2 day −1). Community respiration varied from 0.5 to 6.4 g C m −2 day −1 during the two summer studies (the high respiration rates ranging from 3.0 to 10.4 g C m −2 day −1 found during the autumn cruise were probably overestimates). Respiration rates generally exceeded GPP indicating that the system was apparently net-heterotrophic during the three investigation periods. The predominant limiting factor for phytoplankton growth were nutrients during spring and summer. In autumn the combination of low light levels and high vertical mixing due to wind lead to conditions of light limitation. However, growth conditions were affected by the stabilizing (solar heating) and destabilizing (wind) forces acting on the water column in all three situations. Depending on the relative strength of these forces, day-to-day primary production could vary considerably. Under conditions of nutrient limitation mixing may increase photosynthesis; this is a consequence of improved exploitation of incident light and of available nutrients in the mixed layer. The strong dependency of mixing on primary production implies that measurements based on in vitro incubations may underestimate “real” production.

Oxygen and carbon dioxide mass balance for the estuarine‐intertidal marsh complex of five rivers in the southeastern U.S.

We measured dissolved O2 concentrations, pCO2 values, and respiratory rates in five estuaries of the southeastern U.S. in October 1995 and July 1996. In the low‐salinity sections of the coastal plain rivers, dissolved O2 saturation states were typically only 50%, while pCO2 values were over 4,000 matm. Respiratory rates measured concurrently in estuarine water averaged 8 and 23 mmol m−3 d−1 in October 1995 and July 1996, but they showed little variability either within or among the five estuaries. Benthic chamber incubations in the adjacent intertidal marshes indicated fluxes of 30–40 mmol m−2 d−1 and 50–120 mmol m−2 d−1 for O2 and total dissolved inorganic carbon (DIC), respectively. For the Satilla River estuary, simple calculations revealed that neither respiratory activity in estuarine waters and sediments nor any other within‐estuary process (not including the intertidal marsh system) was sufficient to account for the observed O2 concentrations and pCO2 values. Dissolved oxygen concentrations in four other southeastern U.S. estuaries fit the same general pattern as the Satilla, and likewise, within‐estuary processes could not explain observed gas concentrations. Measured O2 concentrations, pCO2 values, pelagic respiratory rates, and benthic fluxes were used to construct a mass‐balance model, focusing on the influence of the extensive intertidal marshes on O2 and CO2 mass balance and water‐atmosphere gas exchange in the five estuaries. Results indicate that respiratory activity in the sediments and overlying water of the marshes during high tide leaves a signal that is funneled back to the estuary during ebb tide and can account for the estuarine gas concentrations and fluxes. Both experimental and modeling approaches argue that the intertidal marshes of the southeastern U.S. export considerable amounts of inorganic respiratory products to the estuaries and that “outwelling” of organic matter to the estuaries is a minor process by comparison. The DIC exported to the coastal ocean, however, is only a small fraction of the total gas mass flow between the marsh, estuary, and atmosphere.

Direct comparison of four different biomass estimation techniques against conventional dry weight measurements

Many indirect biomass estimation techniques have been discussed in the literature; however, a comparison of the applicability of these methods for bioprocess control purposes has not been discussed comprehensively. In this paper, four different uncomplicated biomass measurement techniques were directly compared with the conventional biomass dry weight measurement, and the possibilities of their implementation in process control environments is discussed. These techniques are estimations based on laser turbidimeter signals, measurement of cell numbers and sizes, estimations based on the oxygen mass balance, and, finally, estimations based on the base consumption during pH control. All these techniques led to essentially the same quality of estimations. The comparisons were performed in experiments with two bacteria strains. Cross-validation analyses showed that all measurements are sufficiently accurate for process supervision and control purposes. The final decision about implementation of one of the techniques discussed must be made under consideration of the available equipment, the microorganisms to be cultivated and the cultivation conditions.

98/01459 Projected application and modelling of combustion furnace system in a boiler: Hu, T. et al. Ranshao Kexue Yu Jishu, 1997, 3, (3), 286–292. (in Chinese)

A dynamic mathematical model has been developed which predicts the transient temperature response of circulating fluidized bed (CFB) combustors as well as the corresponding transient carbon and oxygen concentrations in the bed. The model includes mass balances of oxygen and carbon, energy balances, as well as sub-models for the gas-solid flow structure, combustion, and heat transfer from the bed to both the refractory walls and to a waterwall located in the fast bed section. Model validation was successfully completed against data obtained from tests performed on the 0.3 MWt CFB pilot plant located at the Technical University of Nova Scotia in Halifax, Nova Scotia.

A model for prediction of transient response to the change of fuel feed rate to a circulating fluidized bed boiler furnace

A dynamic mathematical model has been developed which predicts the transient temperature response of circulating fluidized bed (CFB) combustors as well as the corresponding transient carbon and oxygen concentrations in the bed. The model includes mass balances of oxygen and carbon, energy balances, as well as sub-models for the gas-solid flow structure, combustion, and heat transfer from the bed to both the refractory walls and to a waterwall located in the fast bed section. Model validation was successfully completed against data obtained from tests performed on the 0.3 MWt CFB pilot plant located at the Technical University of Nova Scotia in Halifax, Nova Scotia.

Oxygen isotope evidence for extensive crustal contamination in the Okenyenya igneous complex, Namibia

Oxygen isotope data are presented for silicate minerals separated from a variety of rock types from the 130 Ma Okenyenya igneous complex of northwestern Namibia. These rock types include a tholeiitic suite ranging from olivine gabbro to quartz monzodiorite and syenite, and an alkaline suite including gabbro, syenite, nepheline syenite, and essexite. In general, the difference in δ18O values between coexisting feldspar, pyroxene, and biotite are consistent with equilibrium at high temperatures and preclude significant interaction with magmatic or external fluids.The δ18O values of pyroxene can be used to model magmatic processes and show a systematic increase from 7.1–9.0‰ along a transect through a tholeiitic olivine gabbro-quartz monzodioritic body, corresponding to a systematic decrease in Mg#. Pyroxene δ18O values also show a strong correlation with initial strontium and neodymium isotope ratios, with the alkaline suite having lower δ18O values, lower initial strontium-isotope ratios, and higher initial neodymium isotope ratios than the tholeiitic suite. Simple oxygen mass balance calculations suggest that the extremes of isotope composition resulted from at least 60% contamination by material of similar isotope composition to the nearby southern Etendeka quartz latites. Assimilation/crystal fractionation models of oxygen, strontium, and neodymium isotope data suggest that the rate of assimilation was high and may have approached simple mixing. The contaminated tholeiitic olivine gabbro-quartz monzodioritic body was the earliest to crystallize in the complex and this was followed by relatively uncontaminated silica-undersaturated magmas.

Chemical tracers of productivity and respiration in the subtropical Pacific Ocean

We determine annual rates of net biological oxygen production in the euphotic zone and respiration in the upper thermocline of the subtropical North Pacific ocean using mass balances of oxygen, argon, and nitrogen measured at the U.S. Joint Global Ocean Flux Study time series station ALOHA. Net evasion of nitrogen and argon to the atmosphere caused by warming of surface waters is balanced by supply primarily from cross‐isopycnal transport. Mixing rates between the euphotic zone and the top of the permanent thermocline required to balance the inert gas flux are 1–2 cm2 s−1 when transformed to units of an eddy diffusion coefficient. Application of mixing rates derived from the inert gas mass balance to the oxygen field yields a net annual euphotic zone production rate of 1.4±1.0 moles O2 m−2 yr−1, one half of which is lost to the atmosphere, with most of the rest mixed into the top of the thermocline. Since cross‐isopycnal gradients of dissolved organic carbon (DOC) are about half to those of oxygen, we estimate that at least one quarter of the carbon flux out of the euphotic zone is via DOC. Because surface ocean dissolved organic matter has a relatively high C/N ratio, the stoichiometry among O2, C, and inorganic N in the upper ocean should be different than that observed in deeper waters.