Oxygen Transfer Efficiency Research Articles

The Impact of Organic Contamination on the Dynamic Equilibrium of Dissolve Oxygen in Selected Water Bodies in South East Sri Lanka

Domestic and other related waste disposals lead to degrade the rate of equilibrium ofdissolved oxygen (DO) in the water bodies. The aim of this study is to investigate thecontributions of the organic contamination throughout the measured parameters of dissolvedsulfide, chemical oxygen demand (COD), nutrient level and salinity in dynamic equilibriumof DO. The selected parameters were observed over a period of six month and thecorrelations were studied among them for randomly selected two water bodies (WB) withdifferent type of waste effluents. Results indicated that the measured DO has good negativecorrelation with COD (r2 > 0.8), dissolved sulfide and nutrient levels in the both stationsimplies a strong impact on the dynamic equilibrium of DO. Also, the measured DOdemonstrated poor negative correlations (r2 < 0.5) with salinity indicate salinity as a lessimportant parameter for the dynamic equilibrium of DO.The measured data were utilised in estimating the oxygen transfer efficiency, α and β values.Particularly, in Karaivahu (WB) and Allai (WB) exhibited low levels of partial pressuresimply higher level of α and lower β values. However, which were found to be in the range of8.67 – 16.88 and 0.99 – 1.02 respectively. The nutrient and COD values were observed in therange of 0.0 - 10.0 mg/L and 0 - 900 mg/L respectively. This concluded that the COD levelsignificantly contributes to the variation of DO throughout the surface active substance in thewater bodies.

Energy-efficient wastewater treatment via the air-based, hybrid membrane biofilm reactor (hybrid MfBR).

We used modeling to predict the energy and cost savings associated with the air-based, hybrid membrane-biofilm reactor (hybrid MfBR). This process is obtained by replacing fine-bubble diffusers in conventional activated sludge with air-supplying, hollow-fiber membrane modules. Evaluated processes included removal of chemical oxygen demand (COD), combined COD and total nitrogen (TN) removal, and hybrid growth (biofilm and suspended). Target concentrations of COD and TN were based on high-stringency water reuse scenarios. Results showed reductions in power requirements as high as 86%. The decrease mainly resulted from the dramatically lower air flows for the MBfR, resulting from its higher oxygen-transfer efficiencies. When the MBfR was used for COD and TN removal, savings up to US$200/1,000 m(3) of treated water were predicted. Cost savings were highly sensitive to the costs of the membrane modules and electrical power. The costs were also very sensitive to membrane oxidation flux for ammonia, and the membrane life. These results suggest the hybrid MBfR may provide significant savings in energy and costs. Further research on the identified key parameters can help confirm these modeling predictions and facilitate scale-up.

Promotion and inhibition of oxygen transfer under fine bubble aeration by activated sludge

AbstractThe promotion and inhibition of inactivated and activated sludge on oxygen mass transfer (OMT) were studied using lab‐scale experiments. The results showed that the α‐values and oxygen transfer efficiency (OTE) decreased with increasing mixed liquor suspended solids (MLSS) concentration (1–10 g/L). Although OMT promotion rate by microbial respiration in activated sludge system increased from 39.8–97.5% for the α‐values and OTE, the two parameters were found to fall sharply when MLSS concentration was over 5 g/L. This indicated that the sludge concentration is a major influence factor on OMT in activated sludge system. Such results provide valuable knowledge for the operating optimization of the aeration system in wastewater treatment process.

Oxygen air enrichment through composite membrane: application to an aerated biofilm reactor

A highly permeable composite hollow-fibre membrane developed for air separation was used in a membrane aerated biofilm reactor (MABR). The composite membrane consisted of a porous support layer covered with a thin dense film, which was responsible for oxygen enrichment of the permeate stream. Besides oxygen enrichment capability, dense membranes overcome major operational problems that occur when using porous membranes for oxygen transfer to biofilms. Air flow rate and oxygen partial pressure inside the fibres were the variables used to adjust the oxygen transfer rate. The membrane aerated biofilm reactor was operated with hydraulic retention times (HRT) ranging from 1 to 4 hours. High organic load removal rates, like 6.5 kg.m-3.d-1, were achieved due to oxygen transfer rates as high as 107 kg.m-3.d-1. High COD removals, with improved oxygen transfer efficiency, indicate that a MABR is a compact alternative to the conventional activated sludge process and that the selected membrane is suitable for further applications.

Effect of orifice diameter, depth of air injection, and air flow rate on oxygen transfer in a pilot-scale, full lift, hypolimnetic aerator

A pilot-scale, full lift, hypolimnetic aerator was used to examine the effect of diffuser pore diameter, depth of diffuser submergence, and gas flow rate on oxygen transfer, using four standard units of measure for quantifying oxygen transfer: (a) KLa20 (h -1 ), the oxygen transfer coefficient at 20 8C; (b) SOTR (g O2� h -1 ), the standard oxygen transfer rate; (c) SAE (g O2� kWh -1 ), the standard aeration efficiency and (d) SOTE (%), the standard oxygen transfer efficiency. Dif- fuser depth (1.5 and 2.9 m) exerted a significant effect on KLa20, SOTR, SAE, and SOTE, with all units of measure in- creasing in response to increased diffuser depth. Both KLa20 and SOTR responded positively to increased gas flow rates (10, 20, 30, and 40 Lmin -1 ), whereas both SAE and SOTE responded negatively. Orifice diameter (140, 400, and 800 mm) exerted a significant effect on KLa20, SOTR, SAE, and SOTE, with all units of measure increasing with decreas- ing orifice size. These experiments demonstrate how competing design factors interact to determine overall oxygen transfer rates in full lift hypolimnetic aeration systems. The practical application for full lift hypolimnetic aerator design is to max- imize the surface area of the bubbles, use fine (i.e., ~140 mm) pore diameter diffusers, and locate the diffusers at the max- imum practical depth.

Correct manipulation method of MBR operating parameters in membrane fouling studies

In this study, various parameter manipulation methods, variable sludge retention time (SRT)-variable mixed liquor suspended solids (MLSS) concentration, constant SRT-variable MLSS concentration and variable SRT-constant MLSS concentration, were compared based on the interrelationships among the following membrane bioreactor operating parameters: SRT, food to microorganisms (biomass) (F/M) ratio, MLSS concentration, volumetric organic loading rate (OLR) and membrane flux. Although it is the most applied method, concurrent change of SRT (or F/M ratio) and MLSS concentration is not a good parameter manipulation method because it causes unnecessary changes in many other parameters such as viscosity, oxygen transfer efficiency and oxygen utilization rate. The method of constant SRT-variable MLSS concentration has similar disadvantages to the method of variable SRT-variable MLSS concentration. The best alternative parameter manipulation method to study membrane fouling is the method of variable SRT-constant MLSS concentration because this method eliminates unnecessary changes in other parameters. In addition, while changing OLR or hydraulic retention time (HRT), contrary to the common application, membrane flux should be kept constant because any change in flux overrides changes in other parameters. Accordingly, required changes in OLR or HRT should be made by adjusting membrane area rather than membrane flux.

Analysis of Design Factors Influencing the Oxygen Transfer of a Pilot-Scale Speece Cone Hypolimnetic Aerator

The objective of this research was to characterize the performance of a pilot scale downflow bubble contact (DBCA) hypolimnetic aerator, the Speece Cone. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of oxygen transfer, was examined: (a) the oxygen transfer coefficient, KLa, corrected to 20°C, KLa20 (h−1); (b) the standard oxygen transfer rate, SOTR (g O2·h−1); (c) the standard aeration efficiency, SAE (g O2·kW h−1); and (d) the standard oxygen transfer efficiency, SOTE (%). Two sources of oxygen, pressure swing adsorption (PSA) oxygen (87% purity oxygen) and air (∼21% oxyzen) were compared. KLa20, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SOTE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Experimental treatments with air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa20, SOTE, SAE, and SOTE, when compared to treatments with PSA oxygen. The best oxygen transfer performance was achieved with an inlet water velocity of 6.9–7.6 m·s−1 and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66–72%. Further experimentation with inlet water velocity is required to increase oxygen transfer performance to the >95% range which has been reported in the literature for Speece Cone oxygenation systems.

Prediction of penetration depth in a plunging water jet using soft computing approaches

The flow characteristics of the plunging water jets can be defined as volumetric air entrainment rate, bubble penetration depth, and oxygen transfer efficiency. In this study, the bubble penetratio...

Impact of Groundwater Salinity on Bioremediation Enhanced by Micro-Nano Bubbles.

Micro-nano bubbles (MNBs) technology has shown great potential in groundwater bioremediation because of their large specific surface area, negatively charged surface, long stagnation, high oxygen transfer efficiency, etc. Groundwater salinity, which varies from sites due to different geological and environmental conditions, has a strong impact on the bioremediation effect. However, the groundwater salinity effect on MNBs’ behavior has not been reported. In this study, the size distribution, oxygen transfer efficiency and zeta potential of MNBs was investigated in different salt concentrations. In addition, the permeability of MNBs’ water through sand in different salt concentrations was studied. The results showed that water salinity has no influence on bubble size distribution during MNBs generation. MNBs could greatly enhance the oxygen transfer efficiency from inner bubbles to outer water, which may greatly enhance aerobic bioremediation. However, the enhancement varied depending on salt concentration. 0.7 g/L was found to be the optimal salt concentration to transfer oxygen. Moreover, MNBs in water salinity of 0.7 g/L had the minimum zeta potential. The correlation of zeta potential and mass transfer was discussed. The hydraulic conductivities of sand were similar for MNBs water with different salt concentrations. The results suggested that salinity had a great influence on MNBs performance, and groundwater salinity should be taken into careful consideration in applying MNBs technology to the enhancement of bioremediation.

Microbial activity catalyzes oxygen transfer in membrane-aerated nitritating biofilm reactors

The remarkable oxygen transfer efficiencies attainable in membrane-aerated biofilm reactors (MABRs) are expected to favor their prompt industrial implementation. However, tests in clean water, currently used for the estimation of their oxygen transfer potential, lead to wrong estimates once biofilm is present, significantly complicating reactor modeling and control. This study shows for the first time the factors affecting oxygen mass transfer across membranes during clean water tests and reactor operation via undisturbed microelectrode inspection and bulk measurements. The mass transfer resistance of the liquid boundary layer developed at the membrane–liquid interface during clean water tests accounted for two thirds of the total mass transfer resistance, suggesting a strong underestimation of the oxygen transfer rates when it is absent (e.g. after biofilm growth). Reactor operation to attain partial nitritation showed that predicted oxygen transfer rates are enhanced up to six times with biofilm activity. The higher availability of ammonia at the biofilm base drives this process. Such behavior can be captured with the addition of two terms (depending on system characteristics and reactor loading) to existing model structures. Overall, we provide tools to better estimate, model, and optimize oxygen transfer supporting a more energy-efficient approach to MABR operation.

Long-Term Low DO Enriches and Shifts Nitrifier Community in Activated Sludge

In the activated sludge process, reducing the operational dissolved oxygen (DO) concentration can improve oxygen transfer efficiency, thereby reducing energy use. The low DO, however, may result in incomplete nitrification. This research investigated the long-term effect of low DO on the nitrification performance of activated sludge. Results indicated that, for reactors with 10 and 40 day solids retention times (SRTs), complete nitrification was accomplished after a long-term operation with a DO of 0.37 and 0.16 mg/L, respectively. Under long-term low DO conditions, nitrite oxidizing bacteria (NOB) became a better oxygen competitor than ammonia oxidizing bacteria (AOB) and, as a result, no nitrite accumulated. Real-time PCR assays indicated that the long-term low DO enriched both AOB and NOB in activated sludge, increasing the sludge nitrification capacity and diminishing the adverse effect of low DO on the overall nitrification performance. The increase in the population size of nitrifiers was likely resulted from the reduced nitrifier endogenous decay rate by a low DO. Under long-term low DO conditions, Nitrosomonas europaea/eutropha remained as the dominant AOB, whereas the number of Nitrospira-like NOB became much greater than Nitrobacter-like NOB, especially for the 40 day SRT sludge. The enrichment and shift of the nitrifier community reduced the adverse effect of low DO on nitrification; therefore, low DO operation of a complete nitrification process is feasible.

Performance of coal fly-ash based oxygen carrier for the chemical looping combustion of synthesis gas

The performance of coal fly-ash based oxygen carriers for chemical looping combustion of synthesis gas has been investigated using both a thermogravimetric analyser and a packed bed reactor. Oxygen carriers with 50wt% active metal compounds, including copper, nickel and iron oxides, supported on coal fly-ash were synthesised using the deposition–precipitation method. Copper oxide and nickel oxide supported on fly-ash showed high oxygen transfer efficiency and oxygen carrying capacity at 800°C. The fly-ash based nickel oxide was effective in reforming hydrocarbons and for the conversion of carbon dioxide into carbon monoxide; a nickel complex with silicate was identified as a minor phase following the reduction reaction. The fly-ash based iron oxide showed various reduction steps and resulted in an extended reduction time. The carbon emission at the oxidation stage was avoided by reducing the length of the exposure to the reduction gas.

Transferência de massa em sistemas de aeração por jatos bifásicos

A injeção de misturas de ar e água na forma de jatos bifásicos é bastante usada para a aeração artificial em tanques e corpos hídricos. No presente trabalho, foram realizados experimentos para investigar a transferência de massa induzida por estes jatos em um tanque de aeração. Os resultados forneceram eficiências de transferência de oxigênio padrão variando entre aproximadamente 5 e 9%. Combinando-se os dados obtidos nesta pesquisa com os disponíveis na literatura, foram geradas correlações adimensionais para o coeficiente de transferência de massa em função da fração volumétrica de ar e do número de Froude densimétrico. Finalmente, os resultados foram aplicados a situações práticas envolvendo sistemas de aeração por jatos bifásicos.

Biotrickling filters for biogas sweetening: Oxygen transfer improvement for a reliable operation

An industrial-scale biotrickling filter for the removal of high concentrations of H2S is described in this work. The system has been operating at H2S inlet concentrations between 1000 and 3000ppmv at acidic conditions. A decrease of pH from 2.6 to 1.8 did not affect the biological activity inside the biofilter while reducing the water make-up consumption up to 75%. The current oxygen supply system, based on direct injection of air to the liquid phase, has demonstrated to be inefficient for a long-term operation leading to elemental sulfur accumulation in the packing material (i.e. promoting clogging episodes). The present study demonstrates it is possible to partially remove (40.3%) the deposited elemental sulfur by bio-oxidation when biogas is not fed. In normal operation conditions, the implementation of an aeration system based on jet-venturi devices has shown quite promising results in terms of oxygen transfer efficiency and robustness. Such improvement of oxygen transfer was translated in a better conversion of H2S to sulfate, which increased around 17%, prolonging the lifespan operation at low-pressure drop.

Optimization of Oxygen Transfer through Membrane Diffusers for Biological Sweetening of Biogas

AbstractBiological techniques for the removal of gaseous pollutants such as hydrogen sulfide (H2S) have proved to be effective, environmentally friendly, and economically viable. However, when high concentrations of H2S are treated, the process is severely restricted by the oxygen deficit in the liquid phase. The oxygen transfer efficiency provided by a membrane diffuser is evaluated under typical pressure and salinity conditions used for the biological treatment of H2S in biogas. The optimal operating parameters for enhanced oxygen transfer were determined. The addition of pure oxygen with a membrane diffuser to increase the oxygen transfer rate and the use of a nonaqueous phase to improve oxygen transfer in a bioscrubber system are also evaluated.

Understanding the Alpha factor: Studies of the rheological properties of sludge and their effect on oxygen transfer efficiencies from Full Scale Systems

Understanding the Alpha factor: Studies of the rheological properties of sludge and their effect on oxygen transfer efficiencies from Full Scale Systems

Evaluation of Different Wastewater Treatment Processes and Development of a Modified Attached Growth Bioreactor as a Decentralized Approach for Small Communities

This study was undertaken to evaluate the potential future use of three biological processes in order to designate the most desired solution for on-site treatment of wastewater from residential complexes, that is, conventional activated sludge process (CASP), moving-bed biofilm reactor (MBBR), and packed-bed biofilm reactor (PBBR). Hydraulic retention time (HRT) of 6, 3, and 2 h can be achieved in CASP, MBBR, and PBBR, respectively. The PBBR dealt with a particular arrangement to prevent the restriction of oxygen transfer efficiency into the thick biofilms. The laboratory scale result revealed that the overall reduction of 87% COD, 92% BOD5, 82% TSS, 79% NH3-N, 43% PO4-P, 95% MPN, and 97% TVC at a HRT of 2 h was achieved in PBBR. The microflora present in the system was also estimated through the isolation, identification, and immobilization of the microorganisms with an index of COD elimination. The number of bacterial species examined on the nutrient agar medium was 22 and five bacterial species were documented to degrade the organic pollutants by reducing COD by more than 43%. This study illustrated that the present PBBR with a specific modified internal arrangement could be an ideal practice for promoting sustainable decentralization and therefore providing a low wastage sludge biomass concentration.

Studies on biodegradation of vegetable-based fat liquor-containing wastewater from tanneries

Fat liquoring, a post-tanning operation is carried out on tanned leather using oils, fats, or greases in emulsion form to make soft leathers and to improve the physical characteristics of the finished products during leather manufacturing. Around 10–15 % of un-exhausted fat liquor is discharged in the process water as wastewater. The major components of vegetable fat liquor are triacylglycerols, which primarily consist of glycerol molecules esterified with long chain fatty acids. The presence of fats, grease, and oils not only causes choking of wastewater conveyance mains but also interferes with the oxygen-transfer efficiency in aerobic treatment process. The aim of the present study is to assess the rate of biodegradability of vegetable-based fat liquor-containing wastewater generated from tanneries for various food to microbial (f/m) ratio, i.e., 0.35, 0.25, and 0.15 g biochemical oxygen demand (BOD5)/g volatile suspended solids (VSSs) day. The f/m ratio and reaction time were investigated in detail in aerobic batch reactor to arrive at the optimum ratio needed for biodegradation of vegetable fat liquor. From the aerobic biodegradation studies, it was established that at an f/m ratio of 0.15 and a reaction time of 24 h, BOD5 and chemical oxygen demand removals were 97.24 and 89.58 %, respectively. It was evident from Fourier transform infrared spectrometry and electrospray ionization–mass spectroscopy analysis that the triglycerides present in vegetable fat liquor were degraded effectively.

미세기포 산기장치를 적용한 타워형 생물반응기의 산소전달 및 수력학적 특성

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient (KLa20) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, KLa20 was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

Fouling characteristics in pure oxygen MBR process according to MLSS concentrations and COD loadings

A submerged MBR with a pure oxygen system was operated at high COD loading conditions to find out how high a level of COD loading can be treated consistently in an aerobic condition. Pure oxygen was supplied with circulated MLSS to the aerobic tank by a two-phase nozzle to increase oxygen transfer efficiency. Tested COD loadings ranged from 2 to 10kgCOD/m3 day. And the effect of MLSS concentration on the membrane fouling was investigated from 5000 to 25,000mg/L. The membrane fouling rates and filtration resistance were tested to evaluate the effect of COD loadings and MLSS concentrations. Over the range of COD loading tested (2.0–10kgCOD/m3 day), the effluent qualities ranged from 35 to 69mg/L and the COD removals ranged from 99.1 to 99.7 for synthetic wastewater. The membrane fouling rates increased seven-fold over a five-fold increase in COD loadings. And the fouling rates increased almost nine-fold over a three-fold increase in MLSS concentration. The membrane fouling in high COD loading conditions was more sensitive to MLSS concentration than COD loading. The specific EPS productions in this test ranged from 6.9 to 10.9mgEPS/gVSS, and the specific polysaccharide and protein productions were 9.2mgPolysaccharide/gVSS and 1.8mgProtein/gVSS, respectively.