Initial O2 Concentration Research Articles

Absorption kinetics of oxygen scavengers

The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or −1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over‐wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half‐life when compared with those at higher temperatures, e.g. O2 half‐lives of 7.1 and 1.0 h at −1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half‐lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half‐lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over‐wrapped trays within bags had up to 12 times longer O2 half‐lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2).

Cu2+ -induced low density lipoprotein peroxidation is dependent on the initial O2 concentration: an O2 consumption study.

Atherosclerotic plaques form in the arterial intima, where low density lipoprotein (LDL) is thought to be oxidatively modified at sites which may contain catalytic amounts of copper in the presence of low O2 tension. We have investigated O2 consumption during LDL peroxidation induced by Cu2+ ions in vitro and found two phases: a lag phase followed by a phase of rapid O2 consumption. The length of the lag phase was dependent on Cu2+ and on initial O2 concentrations; increasing either decreased the lag time; however, LDL. concentration had no effect. LDL-induced Cu2+ reduction, however, was not affected by low initial O2 concentrations, suggesting that O2 is not required for LDL-mediated reduction of Cu2+. Following the lag phase, O2 consumption was dependent upon LDL or initial O2 concentrations; Cu2+ concentrations had little effect, suggesting that the propagation phase is more dependent on the presence of LDL lipids and O2 as substrates for the reaction. In summary, LDL peroxidation takes place in the presence of Cu2+ at low O2 tension; however, the reaction is dependent upon initial O2 concentrations; increases shorten the lag phase and accelerate O2 consumption.

Physical versus Biological Hydrocarbon Removal during Air Sparging and Soil Vapor Extraction

Although physical removal of contaminants may account for the majority of mass of petroleum hydrocarbons (PH) removed using air sparging and soil vapor extraction (AS/SVE), biological processes contribute to mass removal both during system operation and during system shutdown. Biodegradation rates are difficult to measure during active AS/SVE due to the forced entry of air. This study examined the relative rates of physical and biological removal of PH during AS/SVE. Before system startup, soil gas CO2 and O2 were measured to estimate biodegradation rates based stoichiometrically on the mass of hexane. Biodegrada tion rates calculated from average CO2 production (0.08% d-1) were 1.3 times less than those based on average O2 utilization (0.26% d-1). A simulation model (Stella II) incorporating air injection and microbial respiration measured during AS/SVE shutdown predicted initial O2 concentrations during AS/SVE well but overestimated steady-state O2 by up to 2.5% potentially because respiration may be underestimated if more O2 depletion occurred during AS/SVE than was measured when the system was off. Although biodegradation accounted for 77 times less contaminant mass removal than physical removal, biological contaminant removal may be underestimated using standard respiration tests.

Oxygen Consumption and Carbon Dioxide Production Rates of `Red Gold' Nectarines as Affected by Gas Composition and Storage Temperature

The effects of gas composition and temperature on both the O2 consumption (RRO2) and CO2 production (RRCO2) rates of `Red Gold' nectarines were investigated. Three temperatures (0, 10, and 20 °C) and six gas combinations of initial O2 (1%, 5%, and 20%) and CO2 (0 and 15%) with the balance N2 were used. Triplicate glass jars containing two fruits each were flushed with the respective certified gas mixtures and stored in environmental chambers maintained at 0, 10, and 20 °C. Head space O2 and CO2 concentrations were monitored until O2 levels dropped to 1% or less. Both RRO2 and RRCO2 showed significant increases (P < 0.05) as temperature increased from 0 to 20 °C at the gas concentrations tested. The RRO2 increased slightly (P < 0.05) as initial O2 concentration increased while showing no changes at the range of initial CO2 concentrations used in the study. For RRCO2, no significant changes (P < 0.05) were observed as gas concentrations varied at constant temperatures. This information is useful in establishing empirical models for modified atmosphere packaging predictions.

Spatial variability in the naphthalene mineralization response to oxygen, nitrate, and orthophosphate amendments in MGP aquifer sediments

The feasibility of aerobic in situ bioremediation isbeing investigated for use in a strategy to controlsubsurface coal tar contamination at the site of aformer manufactured gas plant. As part of thisinvestigation, anoxic aquifer sands collected between11 and 25 m below ground surface were assayed in batchmicrocosms to measure the singular and combinedeffects of O2, NO3 -, andPO4 3- on 14C-naphthalenemineralization. The influence of these additivesvaried considerably between sediments. A high initialconcentration of O2 (21 mg/L) promoted thegreatest extent of mineralization in the majority ofactive sediments. NO3 - (85 mg/L) wasobserved to enhance, inhibit, or have no effect on therate of naphthalene mineralization, althoughsignificant denitrification was observed in nearly allthe active sediments. Data suggest thatPO4 3- complexation and/or precipitation withsediment cations limited P bioavailability. Thesediments that were incapable of mineralizingnaphthalene were characterized by low pH (< 4.1),high SO4 2- (> 500 mg/L), and moderate tohigh dissolved Fe(II) (30–265 mg/L) whenequilibrated aerobically with water. Fe(II) likelyexerted a significant O2 demand that reduced theO2 available as an electron acceptor forbiodegradation. These experiments demonstrate thatwhile aeration/oxygenation can be an effectivestrategy for enhancing subsurface bioremediation ofaromatic hydrocarbons, the biodegradation response toaeration/oxygenation and nutrient addition may varyconsiderably within an aquifer.

Kinetics of the reaction of nitric oxide with oxygen in aqueous solutions.

An understanding of the rate of reaction of nitric oxide (NO) with oxygen in aqueous solutions is needed in assessing the various actions of NO in the body. A novel approach was developed for studying the kinetics of this reaction, which permitted simultaneous and continuous measurements of the concentrations of NO and the principal product, nitrite (NO2-). Nitric oxide was measured using a chemiluminescence detector, with continuous sampling achieved by diffusion of NO through a membrane fitted into the base of a small, stirred reactor. The results with various initial NO and O2 concentrations confirmed that the rate of reaction is second-order in NO and first-order in O2. The rate of reaction of NO was described by the expression 4k1 [NO]2[O2], where k1 was (2.1 +/- 0.4) x 10(6) M-2 s-1 at 23 degrees C and (2.4 +/- 0.3) x 10(6) M-2 s-1 at 37 degrees C. The value of k1 was the same at pH 4.9 and 7.4. The rate of formation of NO2- equaled the rate of reaction of NO (within experimental uncertainty of a few percent), and there was no detectable formation of nitrate (NO3-). This confirmed that NO and NO2- were the only NOx species present in significant amounts and supported the validity of pseudo-steady-state assumptions for NO2 and N2O3, which are intermediates in the conversion of NO to NO2-.(ABSTRACT TRUNCATED AT 250 WORDS)

711 PB 385 EFFECTS OF TEMPERATURE, GAS COMPOSITION, AND STORAGE ON THE O2CONSUMPTION OF `RED GOLD' NECTARINES

The influence of 3 temperatures (1, 10 and 25°C). 9 combinations of initial O2 (5, 10 and 20%) and CO2 (0, 10 and 20%) concentrations, and 3 storage durations at 1°C (2, 13 and 24 days) on the O2 consumption of `Red Gold' nectarines was investigated. Fruits were sealed in glass jars, flushed with respective gas mixtures and stored in dark incubators maintained at 1, 10 or 25°C. Head space O2 concentration was monitored at selected intervals until it dropped down to 1% or less. The oxygen consumption rate decreased significantly with decrease in temperature and initial O2 concentration. The O2 consumption rate increased as storage duration increased. The range of initial CO2 concentrations used in this study had no effect on O2 consumption rate. An empirical model was developed to estimate O2 consumption rate of `Red Gold' nectarines as a function of temperature, initial O2 and CO2 concentrations and storage duration.

Effect of Initial Oxygen Concentration on Diacetyl and Acetoin Production by Lactococcus lactis subsp. lactis biovar diacetylactis

The production of aroma compounds (acetoin and diacetyl) in fresh unripened cheese by Lactococcus lactis subsp. lactis biovar diacetylactis CNRZ 483 was studied at 30 degrees C at different initial oxygen concentrations (0, 21, 50, and 100% of the medium saturation by oxygen). Regardless of the initial O(2) concentration, maximal production of these compounds was reached only after all the citrate was consumed. Diacetyl and acetoin production was 0.01 and 2.4 mM, respectively, at 0% oxygen. Maximum acetoin concentration reached 5.4 mM at 100% oxygen. Diacetyl production was increased by factors of 2, 6, and 18 at initial oxygen concentrations of 21, 50, and 100%, respectively. The diacetyl/acetoin concentration ratio increased linearly with initial oxygen concentration: it was eight times higher at 100% (3.3%) than at 0% oxygen (0.4%). The effect of oxygen on diacetyl and acetoin production was also shown with other lactococci. At 0% oxygen, specific activity of alpha-acetolactate synthetase (0.15 U/mg) and NADH oxidase (0.04 U/mg) was 3.6 and 5.4 times lower, respectively, than at 100% oxygen. The increasing alpha-acetolactate synthetase activity in the presence of oxygen would explain the higher production of diacetyl and acetoin. The NADH oxidase activity would replace the role of the lactate dehydrogenase, diacetyl reductase, and acetoin reductase in the reoxidation of NADH, allowing accumulation of these two aroma compounds.

Predicting End-of-Summer Oxygen Profiles in Stratified Lakes

Mean end-of-summer dissolved oxygen profiles in the hypolimnion of oligotrophic and oligomesotrophic thermally stratified lakes were accurately predicted with a multivariate regression model. The model integrates the effects of lake morphometry, total phosphorus concentration (TP), and initial O2 concentrations at spring turnover to predict mean end-of-summer O2 concentration within individual hypolimnetic strata. Lake morphometry exerts a large influence on O2 profiles and this influence is particularly evident in shallow (&lt; 20 m maximum depth) oligotrophic lakes. Predictions of O2 profiles are sensitive to changes in TP concentrations, with all study lakes predicted to have severely O2-depleted hypolimnions by the end of summer at an epilimnetic TP of only 15 μg∙L−1.

Kinetic studies of the deactivation of O2(1Σg+) and O(1D)

AbstractThe kinetics of the deactivation of O2(1Σg+) is studied in real time. O2(1Σg+) is generated in this system by the O(1D) + O2 reaction following O3laser flash photolysis in the presence of excess O2, and it is monitored by its characteristic emission band at 762 nm. Quenching rate constants were obtained for O2, O3, N2, CO2, H2O, CF4and the rare gases. Since O(1D) is the precursor for the formation of O2(1Σg+), the addition of an O(1D) quencher effectively lowers the initial concentration of O2(1Σg+). By measuring the initial intensity of the 762 nm fluorescence signal, the relative quenching efficiencies were determined for O(1D) quenching by N2, CO2, Xe, and Kr with respect to O2; the results are in good agreement with literature values.

Fireflooding a High-Gravity Crude in a Watered-Out West Texas Sandstone

Summary This paper describes the results, operational problems encountered, and the ongoing technical evaluation of an in-situ combustion pilot project in the North Ward-Estes field in Ward County, TX (Fig. 1). This sandstone reservoir was discovered in 1929 and has been under waterflood since 1955. Even though the reservoir characteristics were marginal in comparison with the screening criteria for in-situ combustion, laboratory tests indicated that this process could be viable. Introduction The North Ward-Estes field is an anticlinal structure of lagoonal deposition 18 miles (28.9 km) long and 4 miles (6.4 km) wide, trending north to south along the western edge of the central basin platform. The Yates formation is located at a depth of 2,400 to 2,800 ft (732 to 853 m). This Permian age reservoir consists of seven sand members trapped by dense dolomites and is limited a really by shales and evaporites. Approximately 10% of the rock volume consists of clay: montmorillonite, 80 to 85%; illite, 5 to 10%; chlorite, 1 to 5%. Some minor evidence of fracturing has been indicated, and a northwest-southeast directional permeability is also present. The G.W. O'Brien Well 4 was drilled in April 1929 by Gulf Oil Exploration and Production Co. After this discovery well, approximately 2,000 wells producing from the Yates and Queen formations were drilled over an area of about 30,000 acres (121 × 10(6) m2). By 1955 most of the primary oil was depleted by solution gas drive. At that time, a waterflood was initiated that still remains in operation. Production and injection have been from open hole multi sand completions, which do not lend themselves to reliable calculations of oil saturation. Approximately 350 million bbl (55 × 10(6) m3) of oil have been produced from this reservoir since discovery. A dry forward in-situ combustion pilot was initiated on April 11, 1978. This project, known as the Section 10 combustion project, was implemented in the J-2 sand, which is the lowest of seven Yates sand members (Fig. 2). The rock and fluid properties are given in Table 1. Comparison of project parameters with various screening criteria indicated that the reservoir oil saturation was marginal (Table 2). All other parameters were within the minimum criteria. Laboratory experiments using produced fluids and preserved core demonstrated the applicability of an in-situ combustion process in this watered-out reservoir. We initiated a pilot project to substantiate these tests and to answer four major objectives:Can ignition be obtained and can combustion be propagated in a light-gravity crude?Can flue gas be isolated from other producing sands?Can produced flue gas be disposed of readily?Will the oil-production rate be increased? This pilot was implemented in two phases. We conducted Phase 1 in an inverted 10-acre (40 469-m2) five- spot pattern. High O2 and low CO2 concentrations in gas samples from offset producing wells indicated marginal bum quality. Rapid flue gas migration and the evidence of a low-quality bum caused this phase to be terminated in April 1979. In Nov. 1978, we began Phase 2 in an inverted 40-acre (161 875-m2) nine-spot pattern west of the Phase 1 pilot in a location having a thicker sand section. The initial O2 and CO2 concentrations in the produced flue gas indicated a better burn quality in this area. An observation well was dulled and cored behind the calculated location of the combustion zone to determine whether ignition was obtained and whether combustion propagation was possible in this formation. Another observation well was drilled and cored in an attempt to locate the leading edge of the combustion zone and to determine whether an oil bank was developing. JPT P. 2244^

Ventilatory CO2 response in endurance-trained rats.

A CO2 rebreathing technique was used to assess possible changes in the ventilatory response to CO2 in rats following a 14-week swim training program. Over the final 9 weeks, the rats swam 1 hr per day with a weight of 2.5% of the body weight attached to the tail. Ventilation was measured by a barometric method in awake, restrained rats in a total body plethysmography at CO2 concentrations of 0, 2, 4, 6, and 8%, with an initial O2 concentration of approximately 100%. Ventilation increased in the trained rats with increasing CO2 from 775ml . min-1 . kg-1 at 0% CO2 to 1,387 ml . min-1 . kg-1 at 8% CO2. This increase was a consequence of a 34% increase in tidal volume and a 32% increase in breathing frequency. In comparison with a group of sedentary control rats, there was a significantly higher ventilation and tidal volume at 0% CO2; however, this difference disappeared with increasing levels of CO2. A significantly lower resting heart rate was observed in the exercised (296 +/- 44 beats . min-1, mean +/- SD) compared to the sedentary control rats 380 +/- 42). It was concluded that, while the normal training response of resting bradycardia was observed following this duration and intensity of training, endurance swimming had no significant effect on the ventilatory response to CO2 in the rat.

Isolation and pure culture of a freshwater magnetic spirillum in chemically defined medium.

A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of iron and carbon, respectively. Nonmagnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less iron and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent guanine plus cytosine content, growth characteristics, nutrition, and physiology, the two types were similar. The isolate reduced nitrate without accumulating nitrite and produced ammonia during growth. Nitrate or ammonium ions served as a nitrogen source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less.

Kinetics of particle growth VII. NH4NO3from the NH3‐O3 reaction in the presence of air and water vapor

AbstractOur earlier work on the formation of particulate NH4NO3 in the NH3O3 reaction at 25°C is extended to include air as a diluent and H2O vapor as an additive. More extensive data at different values of [NH3]/[O3]0 were obtained also, where [O3]0 is the initial O3 concentration. In our earlier work we concluded that NH4NO3 vapor was dissociated to NH3 + HNO3 and that the HNO3 was removed by diffusion to the walls with a rate coefficient kdiff = 0.4 min−1 or by condensation on the suspended particles. Particles were nucleated by 8 NH3HNO3 pairs when their concentration product reached 5.8 × 1027 molec2/cm6 with a rate coefficient knucl of 6.2 × 10−224 cm45/min and removed by coagulation with a rate coefficient kcoag of 1.3 × 10−7 cm3/min. A corrected calculation modifies the number of pairs required to 6–7 with a correspondingly changed value of knucl.With the more extensive data of the present study the indications are that the vapor‐phase NH4NO3 monomer is not dissociated and that its diffusion constant for loss to the walls varies between 0.3 and 0.9 min−1 for different reaction conditions. Nucleation occurs when the NH4NO3 vapor concentration reaches 1.0 × 1012 molec/cm3 via. where r is 9 and the nucleation rate coefficient knucl is 3 × 10−108 cm24/min. With 5.0 or 9.5 torr of H2O vapor present, there is an excess of particles produced over that expected from this rate coefficient, indicating an additional nucleation step in which H2O vapor participates directly to produce a hydrated salt. The coagulation coefficient of (1.87 ± 0.14) × 10−7 cm3/min found here is in good agreement with that found previously.

Efficiency of a soil Mycobacterium during growth on hydrocarbons and related substrates.

Hydrocarbon-utilizing bacteria retained the ability to readapt to propane utilization after prolonged transfer on a non-hydrocarbon substrate. The organism studied most thoroughly (Mycobacterium vaccae strain JOB5) required 12–15 hr to readapt to propane oxidation. The amount of growth with propane as substrate by strain JOB 5 was proportional to the initial propane concentration when neither O2 nor substrate was limiting. Maximal cell yields were attained with an initial atmospheric O2 concentration of 40% when the propane concentration was 50%. The generation time for strain JOB 5 was 5 hr with propane and 3.5 hr with propionate as substrate. The molar growth yield with strain JOB 5 on gaseous alkanes and related substrates was consistently lower than predicted values.

Efficiency of a soil Mycobacterium during growth on hydrocarbons and related substrates

AbstractHydrocarbon‐utilizing bacteria retained the ability to readapt to propane utilization after prolonged transfer on a non‐hydrocarbon substrate. The organism studied most thoroughly (Mycobacterium vaccae strain JOB5) required 12–15 hr to readapt to propane oxidation. The amount of growth with propane as substrate by strain JOB 5 was proportional to the initial propane concentration when neither O2 nor substrate was limiting. Maximal cell yields were attained with an initial atmospheric O2 concentration of 40% when the propane concentration was 50%. The generation time for strain JOB 5 was 5 hr with propane and 3.5 hr with propionate as substrate. The molar growth yield with strain JOB 5 on gaseous alkanes and related substrates was consistently lower than predicted values.