Oxygen Transfer Rate Coefficient Research Articles

Effect of Gas Sources on the Oxygen Transfer Efficiency Produced by Fine Bubbles Generator

Fine bubbles (micro to nanometer-sized) have rapidly gained popularity in academia and industry due to their unique properties, such as their high surface area, stability, and longevity. In this study, the performance of oxygen transfer rate efficiency in fine bubbles with high purity oxygen and atmospheric air was analyzed. In this study, the developed fine bubbles generator with power requirement 300 watt was used to evaluate the production of fine bubbles and oxygen transfer efficiency at two type gas sources i.e., ambient air and high-purity oxygen in the small bench aqueous media (5 L water tank). The fine bubbles generator was set up at the pressure in 50 psi and gas flow rate at 0.3 L/min to produce fine bubbles in water medium. The effect of water recirculation process in the bubbles production was measured using particles size analyzer (PSA), zeta potential and dissolved oxygen (DO) meter to measure temperature and dissolved oxygen on the water. Dissolved Oxygen (DO) measurement shows the saturation value of oxygen concentration in water, for high purity oxygen is 30 mg/L higher than air which has a value of 8.64 mg/L. This causes the efficiency of gas transfer in high-purity oxygen to reach 72.09% higher than ambient air at 35.39%. The particle size distribution shows that the mean size of bubbles after 10 minutes recirculation was 465.5 nm and 599.9 nm correspondingly for ambient air and oxygen gas source. High purity oxygen also affect to the zeta potential value tends to be more negative than in ambient air. The type of high-purity oxygen gas can increase the efficiency of the oxygen transfer rate so that the gas containing high-purity oxygen increases the volumetric oxygen transfer rate coefficient which is 2 times higher than using ambient air.

Development of a Model to Determine the Baseline Mass Transfer Coefficient in Bioreactors (Aeration Tanks).

Over 60 percent of all wastewater treatment plants in the developed countries use the activated sludge process as their secondary treatment system. About 50 to 85 percent of the total energy consumed in a biological wastewater treatment plant is in aeration. The activated sludge process, the most common such process, is performed in large aeration basins to provide air for microorganisms to remove nutrients and pollutants through biodegradation. Designs for the air supply often fail to meet sustained peak organic loading, which may lead to unsatisfactory treatment performance and even plant failure. On the other hand, excessive safety factors used in design for the air supply may similarly lead to unsatisfactory treatment performance and energy wastage. Improper sizing of the aeration system is primarily due to inability to estimate the mass transfer coefficient (KL a) correctly for different tank depths, leading to improper blower design and to inappropriate operation, among other things. In general, the efficiency of porous fine-bubble diffuser systems varies from 10 to 30 percent or more, depending on tank depth. The term KL a is used in ASCE/EWRI Standard 2-06 to define the apparent volumetric mass transfer coefficient in a non-steady-state clean water test in an aeration tank. This parameter is a function of tank depth, due to the variation of oxygen gas depletion with depth. The objective of this paper is to introduce a baseline oxygen mass transfer coefficient (KL a0 ), a hypothetical parameter defined as the oxygen transfer rate coefficient at zero depth, and to develop new models relating KL a to the baseline KL a0 as a function of temperature, system characteristics (e.g., the gas flow rate, the diffuser depth Zd ), and oxygen solubility (Cs ). Results of this study on data extracted from the literature indicate that a uniform value of KL a0 that is independent of tank depth can be obtained experimentally. Using the baseline, a family of rating curves for KL a20 (the standardized KL a at 20 °C) can thus be constructed for various gas flow rates applied to various tank depths. The new model relating KL a to the baseline KL a0 is an exponential function, and (KL a0 )T is found to be inversely proportional to oxygen solubility in water (Cs )T to a high degree of correlation. Using a predetermined baseline KL a0 , the new model predicts oxygen transfer coefficients KL a20 for any tank depth to within 1-3% error compared to observed measurements, and similarly for the standard oxygen transfer efficiency. The discovery of a standard baseline (KL a0 )20 determined from shop tests is important for predicting the KL a20 value for any other aeration tank depth and gas flowrate, and this finding can be used in the development of energy optimization strategies for wastewater treatment plants. This work may also improve the accuracy of aeration models used for aeration system evaluations.

Sensitivity of Effluent Variables in Activated Sludge Process

Abstract The quality of a treated effluent changes when there is a sudden variation in the influent flow to the wastewater treatment plant during dry, rain, and storm weather conditions. In this study, various influent flow conditions in an activated sludge process are considered that affect the sensitivity of effluent variables such as chemical oxygen demand (COD), biological oxygen demand (BOD), nitrate nitrogen (SNO), ammonical nitrogen (SNH), and total nitrogen (TN) with respect to varying internal recycle flow rate (Qa), sludge recycle flow rate (Qr), sludge wastage flow rate (Qw) and oxygen transfer rate co-efficient of aerobic tanks (KLa(3,4,5)). The analysis has been carried out based on benchmark simulation model no.1 (BSM 1) plant layout which comprises of two models namely activated sludge model no.1 (ASM 1) and simple one dimensional (Simple 1-D) Takacs model. Based on the present analysis, it is observed that the changes in influent flow rate have larger impact on the effluent variables. This variation can be subdued by introducing additional tanks to smoothen the perturbations or using internal recycle rate from the fifth tank in order to maintain the flow around the optimal influent flow rate. The sludge wastage rate has a greater impact on all effluent variables except nitrogenous variables during maximum flow conditions.

Development of a model to determine mass transfer coefficient and oxygen solubility in bioreactors.

The objective of this paper is to present an experimentally validated mechanistic model to predict the oxygen transfer rate coefficient (Kla) in aeration tanks for different water temperatures. Using experimental data created by Hunter and Vogelaar, the formula precisely reproduces experimental results for the standardized Kla at 20 °C, comparatively better than the current model used by ASCE 2–06 based on the equation Kla20 = Kla. ()(20−T) where T is in °C. Currently, reported values for range from 1.008 to 1.047. Because it is a geometric function, large error can result if an incorrect value of is used. Establishment of such value for an aeration system can only be made by means of series of full scale testing over a range of temperatures required. The new model predicts oxygen transfer coefficients to within 1% error compared to observed measurements. This is a breakthrough since the correct prediction of the volumetric mass transfer coefficient (Kla) is a crucial step in the design, operation and scale up of bioreactors including wastewater treatment plant aeration tanks, and the equation developed allows doing so without resorting to multiple full scale testing for each individual tank under the same testing condition for different temperatures. The effect of temperature on the transfer rate coefficient Kla is explored in this paper, and it is recommended to replace the current model by this new model given by:where T is in degree Kelvin, and the subscripts refer to degree Celsius; E, ρ, σ are properties of water. Furthermore, using data from published data on oxygen solubility in water, it was found that solubility bears a linear and inverse relationship with the mass transfer coefficient.

Highly efficient production of hyaluronic acid by Streptococcus zooepidemicus R42 derived from heterologous expression of bacterial haemoglobin and mutant selection.

During Streptococcus zooepidemicus fermentation, most carbon sources are used to synthesize lactic acid, which can inhibit strain growth and hyaluronic acid production. Here, we expressed bacterial haemoglobin (Vhb) in Strep.zooepidemicus. Due to highly efficient oxygen use, only 15·26gl(-1) lactic acid was produced, which is 0·73 times the quantity produced by the control strain. Compared with the control strain (1·61gl(-1) ), hyaluronic acid (HA) production in this strain did not substantially increase, only to 2·16gl(-1) . Next, we used a series of N-methyl-N'-nitro-N-nitroso-guanidine (NTG) treatments and selection programmes. Finally, we generated a hyaluronidase-negative and rifampin-resistant mutant strain that produces high levels of HA. The optimum carbon concentration for maximum hyaluronic acid production is only 30gl(-1) of sucrose, which is lower than the control strain (60gl(-1) ). The oxygen transfer rate coefficient KL a increased significantly to 372±53h(-1) from 18±4h(-1) of the control. The optimum carbon source for this strain is 21gl(-1) of sucrose, 9gl(-1) of maltose and 5gl(-1) of glutamic acid. Hyaluronic acid accumulated at 6·7gl(-1) in the culture broth. However, the molecular weight of HA decreased from 1835KDa (Control) to 429kDa. The prepared low-molecular weight HA could function as potential antiangiogenic substances, antiviral and antitumour agents to possibly be used as functional food ingredients. Hyaluronic acid (HA) has been used for a wide range of applications in health, cosmetic and clinical fields. During fermentation of Streptococcus to produce HA, 80-85% of the carbon source is used to produce lactic acid and acetic acid, and only approx. 5 and 10% of the carbon source is used to produce HA and biomass respectively. Here, we expressed bacteria haemoglobin (Vhb) in Streptococcus zooepidemicus, which can dramatically inhibit lactic acid production. After NTG treatments and selection programmes, we identified a mutant strain with highly efficient hyaluronic acid production (6·7gl(-1) ) under economic fermentation conditions.

Pichia stipitis를 이용한 모자반 가수분해물로부터의 bioethanol 생산 시 최적 surface aeration rate

We investigated the optimal surface aeration rate during bioethanol production from the hydrolysate of seaweed Sargassum sagamianum using Pichia stipitis. It was observed that, when the working volume was 880 mL in 2.5-L lab-fermentor, the surface aeration rates of 30 to 100 mL/min were the optimal values for bioethanol production, in which this surface aeration rate corresponded to less than 0.05 (1/min) as the oxygen transfer rate coefficient (<TEX>$k_La$</TEX>). In addition, during repeated-batch operation was carried out, we examined whether those surface aeration rates were the optimal for bioethanol production. It was also observed that the surface aeration rates of 30 to 100 mL/min in the working volume of 880 mL were the optimal values in terms of the cumulative bioethanol producrion and bioethanol yield. On the basis of the oxygen transfer rate coefficient it is probable that those surface aeration rates will be applied to the large-scale bioethanol production from the hydrolysate of seaweed Sargassum sagamianum.

Influence of hyaluronidase addition on the production of hyaluronic acid by batch culture of Streptococcuszooepidemicus

Enhancement of hyaluronic acid (HA) production by Streptococcus zooepidemicus through increasing oxygen transfer rate via degradation of HA by hyaluronidase was investigated. Dissolved oxygen (DO) level became a limiting factor for HA production during 8–16h, and thus hyaluronidase (0.05, 0.10, 0.15, 0.20, 0.25g/l) was added at 8h to degrade HA. Oxygen transfer rate coefficient and DO level during 8–16h increased with increased hyaluronidase concentration. Compared to 5.0±0.1g/l of the control without hyaluronidase addition, HA production was increased from 5.0±0.1g/l to 6.0±0.1g/l when hyaluronidase concentration was 0.15g/l. Further increase of hyaluronidase concentration had no effect on HA production. The molecular weight of HA decreased with the increased hyaluronidase concentration and decreased to 21kDa when hyaluronidase concentration was 0.25g/l from 1300kDa of the control. The prepared low molecular weight HA (LMW-HA) could function as potential anti-angiogenic substances, antiviral and anti-tumor agents to possibly be used as functional food ingredients.

A pH-based fed-batch process for the production of a chimeric recombinant infectious bursal disease virus (IBDV) structural protein (rVP2H) in insect cells

For the production of a rVP2H vaccine, to protect young chickens from infection by an infectious bursal disease virus (IBDV), Trichoplusia ni (Hi-5) cells were cultured in a 500-ml spinner flask to evaluate the productivity of the rVP2H protein. The spinner flask, with a working volume of 500 ml, was equipped with a sparger to bubble the air at a flow rate of 0.134 vvm to provide adequate oxygen transfer. The oxygen transfer rate coefficient, k L a, was 24/h under these conditions. Hi-5 cells were grown and then infected with a recombinant rVP2H expressing baculovirus in spinner flasks. The Hi-5 cells generated a higher rVP2H yield at a low cell density (1×10 6 cells/ml) than at higher cell density (2–3×10 6 cells/ml). Nutrient depletion, especially glucose and glutamine, caused a decrease in specific productivity (i.e. production per cell) with increase in cell density at infection. A pH-based fed-batch culture method, in which the increase in pH, signalled by a ‘metabolic switch’, was used as an indicator for initiating supplemental glucose and glutamine application. By applying this method, the production of rVP2H was increased from 25 to 54 mg/l when the Hi-5 cells were infected at a cell density of 2×10 6 cells/ml. This feeding strategy was carried out with simple instruments and could facilitate a significant increased-yield of rVP2H protein in spinner flasks. This technique should be beneficial in research laboratories employing the Hi-5 cells/baculovirus expression system as a rapid and efficient system for the production of foreign proteins.

Estimation of respirometric activities in bioprocesses

In biotechnical and biological wastewater treatment processes the availability of real-time information about the biological activity is of crucial importance, and for aerobic processes this is represented by the oxygen uptake rate (OUR). Although several respirometric equipments are commercially available, the associated cost and maintenance needs have prevented their widespread use. As an alternative, computer codes are been developed to be used as software sensors for the estimation of the respirometric activity, based on simple dissolved oxygen measurements. The aim of this paper is to present the design techniques of such sensors to monitor both OUR and the related oxygen transfer rate coefficient K L a. This paper assesses the problems incurred into when both OUR and K L a are estimated concurrently and shows how to overcome the limits of conventional least-squares techniques, which yield biased estimates. Several structural modifications to the basic scheme are proposed and evaluated, including a discrete-time model with a piecewise linear approximation of both quantities. This approach yields a good estimation of OUR, but the K L a estimate is still slightly biased, if linear approximations are used. After showing the limits of this approach, a better result is obtained with a more accurate approximation of the dissolved oxygen derivative. This new approach eliminates the bias on the K L a estimate and provides an algorithm which is much more robust with respect to process conditions.

Adaptive estimation of bioactivities in the activated sludge process

In biotechnical processes the availability of real-time information about the biological activity is of crucial importance, and this is represented by the oxygen uptake rate (OUR). The aim of this paper is to design and evaluate a real-time estimator both for this quantity and for the related oxygen transfer rate coefficient. The design is based on linear approximations of these unknown variables and nonlinear system dynamics, and relies on a careful choice of probing signals. It is found that a maximum length binary sequence (MLBS) can be successfully used as an alternative to a switching sequence resulting from an on/off control. Later, estimation in the closed loop is considered, coupling the previous estimator with a self-tuning PID regulator. Given the nonlinear nature of the system the analysis is carried out mostly by simulation, and the results confirm that in all cases efficient estimates can be obtained. The performance compares very well with previous literature results.

An experimental investigation of the performance of a stirred aerator having an axial flow pump in inner casing.

A tested aerator are consisted of a vertical cylindrical vessel with a coaxial inner casing, and an axial flow impeller is arranged in an inner casing. As a circulatory flow is built up between the inner tube and the outer annulus, there isn't any dead zone in the flow area in this new-type stirred aerator. Moreover, a high efficiency of the impeller may be expected compared with the conventional stirred vane. First, the effect of the existence of inner casing on the performance of aeration, and secondly, the effects of the air supply position, air flow rate, impeller speed and the diameter of air bubbles on the oxygen transfer rate coefficient are studied. Moreover, the dissolution efficiency of the oxygen and the power consumption are investigated.

The dissolved oxygen profile—A valuable tool for control of the activated sludge process

Control of activated sludge process based on measurement of the dissolved oxygen profile has the distinct advantage of using sensors of proven reliability. These measurements, when coupled with the power of an on-line computer, permit the calculation of important variables which cannot be measured directly. The features of the profile which are of major significance are the position of the maximum slope, the value of the maximum slope, the DO concentration at the reactor outlet, the slope of the profile close to the outlet, and the second derivative of the profile towards the outlet. This paper demonstrates that the above mentioned features reflect both the hydraulic and organic loading, reaction rates, and degree of completion of the reactions in the activated sludge process. Simulations are presented to show how these features may be controlled by manipulating the mass of sludge in the reactor and the overall oxygen transfer rate coefficient.

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter: I. Influence of viscosity

AbstractThe effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min−1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m3) and sufficient coefficient KLa (160–200 h−1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min−1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m3 and the coefficient KLa ∼ 50 h−1.

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter. I. Influence of viscosity

AbstractThe effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min−1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m3) and sufficient coefficient KLa (160–200 h−1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min−1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m3 and the coefficient KLa ∼ 50 h−1.