Comparison of Oxygen Transfer Parameters Determined from the Steady State Oxygen Uptake Rate and the Non-Steady-State Changing Power Level Methods

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test.     

Data Interpretation for In Situ Measurements of Cohesive Sediment Erosion

Methods for interpreting data from in situ flume measurements of cohesive sediment dynamics are evaluated and a technique for estimating various erosion parameters using in situ measurements is proposed. There is currently a lack of uniformity in analysis techniques for cohesive erosion data collected in flumes and with in situ instruments and the proposed technique resolves some of these inconsistencies. The data set used in this study was derived from field experiments conducted with a straight benthic in situ flume in different aquatic environments in New Zealand. The experiments with stepwise increases in flow velocity revealed that peaks in the erosion rate at the beginning of each velocity step are most likely associated with heterogeneous bed structure, as transient hydrodynamic effects due to the experimental procedure were found to be insignificant. The field data showed an exponential decay of the erosion rate with time that is indicative of depth-limited erosion. These data are used to illustrate methods for the parameterization of the proposed semiempirical erosion equation, taking into account the time dependency of the erosion process.     

Use of In Situ Air Flow Measurements to Study Permeability in Cracked Clay Soils

The work describes in situ measurements of crack induced permeability as a function of depth, (down to ～ 1.75?m), in clay soils at two field sites, using the gas flow technique described in an earlier study. The gas flow response to applied pressure was found to exhibit a significant nonlinearity at all depths indicating non-Darcian flow despite the fact that the flow was likely to be well within the laminar flow regime. Application of three-dimensional finite-element models to describe the gas flow revealed that the nonlinearity is likely to be an intrinsic behavior related to the soil-gas flow interaction. The Forchheimer compressible flow equation successfully simulated the behavior at all depths. The viscous and inertial permeability parameters obtained from this analysis showed a wide range of values which were closely correlated to the pore-water content of the soil medium, clearly showing the influence of ped swelling on the contraction of macrovoid channels in the structured clay soil.     

In Situ Neutron Diffraction Measurements During Annealing of Deformed Beryllium With Differing Initial Textures

The recovery of deformed beryllium was studied with mechanical testing and in situ neutron diffraction measurements. The initial texture of the material and the deformation rate were manipulated to produce four distinct deformation microstructures. The dislocation density was determined from line profile analysis of the neutron diffraction data collected as a function of temperature during annealing to a maximum homologous temperature of 0.53 following deformation. Mechanical testing was completed after the in situ annealing to determine the extent of the recovery of the flow stress. Both the dislocation density and flow stress recovered significantly by a relatively low homologous temperature of 0.3. A comparison with model calculations using a dislocation-based hardening law indicates that it is forest-type dislocations that annihilate during the relatively low temperature anneal; the dislocation substructure was stable at these temperatures. Finally, the motion of the dislocations during annealing prevented the development of intergranular thermal stresses due to the crystallographically anisotropic thermal expansion of beryllium.     

Water-Circulating Aerator: Optimizing Structure and Predicting Water Flow Rate and Oxygen Transfer

Thermal stratification is a common phenomenon in deep lakes and reservoirs, which often results in water-quality deterioration, including such problems as hypolimnetic anoxia, the release of pollutants from sediments, and algal blooms. Hypolimnetic oxygenation and destratification are the two commonly used methods for resolving these water-quality problems. A new water-quality improvement device, the water-circulating aerator, was designed to destratify lakes and reservoirs, by circulation and oxygenation of upper and lower layers of water. The design of the structure of the water-circulating aerator is detailed. Three mathematical models were built to optimize this structure, estimate the rate of water flow in the aerator, and calculate the rate of oxygen transfer from air bubbles to water in the aerator. These models were verified by experiments. The water-circulating aerator system has been successfully applied in a stratified reservoir to increase dissolved oxygen to reduce the releasing of ammonia-nitrogen from sediments under anoxic conditions.     

Modeling and Control of Oxygen Transfer in High Purity Oxygen Activated Sludge Process

A dynamic mathematical model for the high purity oxygen activated sludge process, which incorporates structured biomass, gas–liquid interactions and control systems, was developed. The model was calibrated using pilot plant data associated with the development of the West Point Treatment Plant near Seattle, Wash. The calibrated model was used to simulate oxygen transfer rates for various operating conditions. Simulations showed that an optimal control system can reduce aerator power by 33% as compared to a conventional design, and reduce average oxygen feed gas by as much as 18%. Vent gas purity control dramatically reduced the peak aerator horsepower required to maintain set point dissolved oxygen concentration during high loadings. Step feed operation reduced the stag-to-stage variation in aerator horsepower and also reduced the required peak power. Predicted power savings for a 605,000?m3/day plant were $500,000 per year at current power costs.     

In Situ Characterization of Resuspended-Sediment Oxygen Demand in Bubbly Creek, Chicago, Illinois

Sediment oxygen demand (SOD) can be a significant oxygen sink in various types of water bodies, particularly slow-moving waters with substantial organic sediment accumulation. In most settings in which SOD is a concern, the prevailing hydraulic conditions are such that the impact of sediment resuspension on SOD is not considered. However, in the case of Bubbly Creek in Chicago, the prevailing slack water conditions are interrupted by infrequent intervals of very high flow rates associated with pumped combined sewer overflow (CSO) during intense hydrologic events. These events can cause resuspension of the highly organic, nutrient-rich bottom sediments, resulting in precipitous drawdown of dissolved oxygen (DO) in the water column. To address this issue, a new in situ experimental apparatus designed to achieve high flow velocities was implemented to characterize SOD, both with and without sediment resuspension. In the case of resuspension, the suspended sediment concentration was analyzed as a function of bed shear stress, and a formulation was developed to characterize resuspended-sediment oxygen demand (SODR) as a function of suspended sediment concentration in a form similar to first-order biochemical oxygen demand (BOD) kinetics with the DO term in the form of Monod kinetics. The results obtained can be implemented into a model containing hydrodynamic, sediment transport, and water-quality components to yield oxygen demand varying in both space and time for specific flow events. The results are used to evaluate water quality improvement alternatives that take into account the impact of SOD under various flow conditions.     

关于降低本钢氧气放散率的探讨

介绍了国内特大型钢铁企业近年来氧气放散率情况及本钢氧气放散的经济损失．闸述了本钢氧气放散率高的原因，指出了降低氧气放散应采取的措施．     

Cold Simulation of Oxygen Transfer Rate in BOF

 By measuring the mass transfer coefficient of between water and oil, the oxygen transfer rate of bath in the BOF smelting process is researched, and the influence of top and bottom blowing gas flow rate on the mechanism of mass transfer between metal and slag is discussed. The results show that when the bottom blowing gas flow rate increases on the conditions of top blowing, the mass transfer rate evidently increases, and the influence ratio of top blowing on the mass transfer is 10 percent of bottom blowing; The relation among top gas flow rate, bottom gas flow rate and lance height are established by the stirring power density. The equation between the mass transfer coefficient between metal and slag is formed, which furnishes reference for optimizing process parameters of BOF. The relation between the emulsification ratio between water and oil and the bottom blowing gas flow rate on the condition of top and bottom blowing is obtained. The result shows that with the increase of the bottom blowing gas flow rate the emulsification ratio increases in linearity, which increases the mass transfer rate of benzoic acid between water and oil.     

Effect of Nonsteady state H2O2 Tests on Oxygen Transfer Rate in Enhanced Biological Phosphorus Removal Process

A laboratory scale enhanced biological phosphorus removal process was operated in the University of Cape Town configuration to study the variations in alpha and oxygen transfer efficiency (OTEf) under different process conditions. As part of this investigation, process oxygen transfer parameters were determined using the steady state oxygen uptake rate (OUR) and the nonsteady state hydrogen peroxide addition (HPA) methods, as per the American Society of Civil Engineers guidelines. The results indicated that the oxygen transfer parameters [volumetric mass transfer coefficient (KLaf), oxygen transfer rate (OTRf), α and OTEf)] were higher when both methods were applied on the same day, compared to the subsequent period, when only the steady state OUR method was employed, under similar operating conditions. The difference in the oxygen transfer parameters appears to be due to the addition of H2O2 that generates reactive oxygen species in the nonsteady state HPA test. Based on the findings, it was concluded that the HPA test was not a suitable technique to measure oxygen transfer under process conditions. Further, a conceptual model hypothesizing the impacts of H2O2 addition on activated sludge process is presented.     

Mass Transfer Effects on Kinetics of Dibromoethane Reduction by Zero-Valent Iron in Packed-Bed Reactors

Mass transfer effects on the kinetics of 1,2-dibromoethane (EDB) reduction by zero-valent iron (ZVI) in batch reactors, a laboratory scale packed-bed reactor, and a pilot scale packed-bed reactor are described. EDB was debrominated by ZVI to ethylene and bromide. EDB sorption to the cast iron surface was nonlinear and was described by a Langmuir equation. Laboratory scale column studies showed a nonlinear dependence of EDB removal on flow rate and initial EDB concentration. A nonequilibrium model of EDB sorption and reaction dependent on mass transfer was constructed using the laboratory scale data. The model was verified using data from a larger pilot scale packed-bed reactor that was used to remove EDB from contaminated groundwater. The data showed two distinct removal processes, an initial rapid phase dominated by mass transfer followed by a slower phase where surface reactions dominated. The model successfully predicted the transition from mass transfer controlled to surface reaction controlled conditions in the pilot scale data.     

某矿通风系统的测定与评价及其优化改造实践

通过对某硫化矿矿井通风系统的全面测定与评价，得出其存在的主要问题，并提出行之有效的优化改造措施。此结果对其他地下矿山的通风系统改造具有一定的参考价值。     

Gas Transfer During Bubbler Destratification of Reservoirs

In this paper, dimensional analysis has been carried out to derive general equations that predict: the total gas transferred to the ambient reservoir water from an air bubbler, total volume entrained, and total energy consumed for a known or equivalent linear stratification. The equations are tested by comparison with a one-dimensional bubbler model developed by the authors. It is shown that the oxygen transfer to the water column can be significant if small bubbles are used. The mechanical destratification efficiency ηmech (%), destratification time per unit surface area Γ?(s/m2), oxygen dissolution efficiency Ω (%), and oxygen transferred per unit input energy are examined as functions of bubble size. It is concluded that an average bubble radius of 1?mm should be considered for design purposes. However, if oxygen transfer from the bubbler is not considered important, then a bubble size of up to 4?mm is acceptable for destratification purposes.     

In Situ Measurement of Nonlinear Shear Modulus of Silty Soil

A new field test method to evaluate in situ nonlinear shear modulus of soils was developed. The method utilizes a drilled shaft as a cylindrical, axisymmetric source for shear loading of soil at depth. The applicability of the test method was studied by conducting small-scale, prototype experiments at a “calibration” field site in Austin, Texas. Numerous conventional in situ and laboratory measurements were performed to characterize the soil at the field site. The “small-scale” nature of the tests involved using a 381?mm (15?in.) diameter, 3.7?m (12?ft) long drilled shaft. Experimental results from this field study provided an opportunity to compare laboratory and field measurements of the G?log?γ and G/Gmax?log?γ curves. This comparison was used to investigate the accuracy of common procedures relating field and laboratory modulus reduction curves. Nonlinear modulus measurements were performed at depths of 1.8?to?2.1?m (6?to?7?ft) in a silt (ML). The field G/Gmax?log?γ curve for this soil at low confining pressures are in general agreement with the laboratory curve from an intact specimen as well as empirical curves.     

Relationships between In Situ and Roller-Integrated Compaction Measurements for Granular Soils

To evaluate compaction meter value and machine drive power roller-integrated compaction technologies, a field study was conducted with 30-m test strips using five granular materials. The test strips were compacted using a prototype CS-533E vibratory smooth drum roller and tested for various compaction parameters using in situ test methods (e.g., nuclear moisture density, dynamic cone penetrometer, plate load tests, etc.). To characterize the roller machine-ground interaction, soil testing focused on measuring soil compaction parameters of the compaction layer, to a depth not exceeding 300?mm. The experimental testing of five test strips provided roller data and in situ measurements for several stages of compaction that were used in performing statistical regression analyses. The relationships between data from the roller-integrated compaction technologies were investigated with special consideration for the relative variation that was observed for each measurement system. Statistical averaging mitigated measurement variability and revealed statistically significant (R2>0.9) relationships between in situ and roller-integrated compaction measurements. This research demonstrates statistical analysis techniques for which calibration procedures using roller-integrated compaction technologies may be developed.     

3D In Situ Imaging of Aluminium Alloys During Solidification

X-ray tomography has become a widely used 3D characterisation technique in materials science either using laboratory tomographs or large X-rays facilities. The advantage of large X-rays facilities is the high photon flux which allows fast tomography to be performed. With fast acquisition CCD cameras, it is possible to obtain a 3D image of the material in less than 30?s with a spatial resolution of the order of 1 or 2???m. We will show that this allows to study the influence of copper addition on the formation of intermetallics formation in Al?CSi?CFe?CCu alloys: we will show that copper seems to have beneficial effects. With CMOS cameras it is possible to reduce acquisition times down to values of about 0.15?s. We will show that this allows to obtain in situ 3D information on the early stage of solidification in aluminium alloys, only accessible up to now using radiography : the solidification front rate was measured on several individual dendrites an Al?C20wt%Cu alloy and estimated to be around 10???m/s.     

In Situ Measurements of Settling Velocity near Baimao Shoal in Changjiang Estuary

At the South Branch of the Changjiang Estuary near Baimao Shoal, two in situ approaches were used to estimate the settling velocity, ws, of suspended, fine-grained sediments. The first approach was used when the current was less than 1.5??m/s and was based on measurements from an optical backscatter sensor (OBS-3A) and a laser in situ scattering and transmissometer (LISST-100, Type C). A modification, using the measured ratio of volume concentration for each floc size class to the total volume concentration as a weighting factor. To improve a previously published approach, a better algorthim was implemented to estimate ws. Results of the modified approach (0.4 to 4.6??mm/s) are about twice those of the original approach, which assumes that all sizes of flocs have the same floc density. The second approach used the Rouse equation to estimate the depth-averaged ws when the current was strong and nearly steady around maximum ebb. Results from the second approach show a much greater depth-averaged ws (4–8.5??mm/s). This is attributed to the large bed shear stresses (between 3 and 3.6?Pa) bringing large sediments into the water column.     

Oxygen Transfer Model for a Flow-Through Hollow-Fiber Membrane Biofilm Reactor

A mechanistic oxygen transfer model was developed and applied to a flow-through hollow-fiber membrane-aerated biofilm reactor. Model results are compared to conventional clean water test results as well as performance data obtained when an actively nitrifying biofilm was present on the fibers. With the biofilm present, oxygen transfer efficiencies between 30 and 55% were calculated from the measured data including the outlet gas oxygen concentration, ammonia consumption stoichiometry, and oxidized nitrogen production stoichiometry, all of which were in reasonable agreement. The mechanistic model overpredicted the oxygen transfer by a factor of 1.3 relative to the result calculated from the outlet gas oxygen concentration, which was considered the most accurate of the measured benchmarks. A mass transfer coefficient derived from the clean water testing with oxygen sensors at the membrane-liquid interface was the most accurate of the predictive models (overpredicted by a factor of 1.1) while a coefficient determined by measuring bulk liquid dissolved oxygen underpredicted the oxygen transfer by a factor of 3. The mechanistic model was found to be an adequate tool for design because it used the published diffusion and partition coefficients rather than requiring small-scale testing to determine the system-specific mass transfer coefficients.     

Analysis of Lightweight Deflectometer Test Based on In Situ Stress and Strain Response

The lightweight deflectometer (LWD) is gaining acceptance and popularity as an in situ spot-testing device for quality control/quality assurance of earthwork compaction. Little research has been conducted to investigate the stress–strain response within the soil during LWD testing. Similarly, little research has been performed to examine the appropriateness of using homogeneous, isotropic, linear elastic half-space theory to estimate soil modulus (ELWD) from LWD results. With this aim, an array of vertical stress and strain sensors was placed within the soil to measure the stress–strain response during LWD loading. Measured in situ stress values matched well with stresses predicted using homogeneous, isotropic, linear elastic half-space theory. In situ stress data revealed that the contact stress distribution between the soil surface and loading plate is a function of the soil type. Measured in situ strain values did not correspond well with strains predicted using homogeneous, isotropic, linear elastic elasticity. An exponentially increasing modulus function was required to match experimental with theoretical elastic strains. The results indicate that the commonly used form to predict ELWD is inappropriate if the goal is to extract constitutive soil properties. Analysis of strain data suggests the LWD depth of influence (measurement depth) is 0.9–1.1 times the plate diameter.     

Air/Water Oxygen Transfer in a Biological Aerated Filter

The oxygen-transfer characteristics of an upflow biological aerated filter filled with angular clay media were determined over a wide range of gas and liquid flow rates. Liquid-side, oxygen-transfer coefficients (KLa) were measured using a nitrogen gas stripping method under abiotic conditions and were found to increase as both gas and liquid superficial velocity increases, with values ranging from 12 to 110?h?1 based on empty bed volume. The effect of gas and liquid velocity, wastewater to clean water ratio, and temperature dependence was correlated to within ±20% of the experimental KLa value. Stagnant gas holdup is roughly double in wastewater compared to clean water, but the dynamic gas holdup is the same. The oxygen-transfer coefficient is directly proportional to the dynamic gas holdup. Stagnant gas holdup does not influence the rate of oxygen transfer. The results suggest that dynamic gas holdup largely determines the specific interfacial area (a), whereas the interstitial liquid velocity largely controls the oxygen-transfer coefficient (KL).