Effect Of Gas Sparging Research Articles

Influence of two phase flow on cake layer resistance and flux enhancement in spiral wound and submerged flat sheet microfiltration membrane modules

<p>Gas sparging has emerged as an effective technique for control of particle fouling in different microfiltration membrane processes. However most of the research work carried out has been pertinent to hollow fiber and tubular membrane geometries. A little attention has been paid to evaluate the potentails of gas-liquid two-phase for control of particle fouling in spiral wound and submerged flat sheet microfiltration membranes. This study focuses on control of particle fopuling by gas sparging in open channel spiral wound and submerged flat sheet microfiltration membranes. Commercial yeast was used as test suspension. The Effect of gas sparging on membrane fouling and permeate flux was studied by analysing the cake layer characteristics like cake mass deposition, cake layer thickness and cake porosity. The filtration flux and cake properties under various operating conditions, such as cross-flow velocity, filtration pressure, particle concentration, and sparging intensity are analyzed based on hydrodynamics. The results of this study show that gas sparging is very effective in control of particle fouling for both membrane module geometries. It was found that gas bubbling reduced the deposition of particles on the membrane surface due to which cake layer thickness decreases and resultantly permeate flux increased substantially. The permeate flux increased with increase in gas sparging intensity. A maximum flux enhancement of 170 % and 284 % were observed for spiral wound and flat sheet membranes respectively when gas sparging was applied to the process.</p>

Effects of gas sparging and mechanical mixing on sonochemical oxidation activity

The effects of air sparging (0–16 L min−1) and mechanical mixing (0–400 rpm) on enhancing the sonochemical degradation of rhodamine B (RhB) was investigated using a 28 kHz sonoreactor. The degradation of RhB followed pseudo first-order kinetics, where sparging or mixing induced a large sonochemical enhancement. The kinetic constant varied in three stages (gradually increased → increased exponentially → decreased slightly) as the rate of sparging or mixing increased, where the stages were similar for both processes. The highest sonochemical activity was obtained with sparging at 8 L min−1 or mixing at 200 rpm, where the standing wave field was significantly deformed by sparging and mixing, respectively. The cavitational oxidation activity was concentrated at the bottom of the sonicator when higher sparging or mixing rates were employed. Therefore, the large enhancement in the sonochemical oxidation was attributed mainly to the direct disturbance of the ultrasound transmission and the resulting change in the cavitation-active zone in this study. The effect of the position of air sparging and mixing was investigated. The indirect inhibition of the ultrasound transmission resulted in less enhancement of the sonochemical activity. Moreover, the effect of various sparging gases including air, N2, O2, Ar, CO2, and an Ar/O2 (8:2) mixture was compared, where all gases except CO2 induced an enhancement in the sonochemical activity, irrespective of the concentration of dissolved oxygen. The highest activity was obtained with the Ar/O2 (8:2) mixture. Therefore, it was revealed that the sonochemical oxidation activity could be further enhanced by applying gas sparging using the optimal gas.

Combined oil demulsification and copper removal from copper plating plant effluents by electrocoagulation in a new cell design

In an attempt to reduce the capital and operating costs of electroplating plant effluent treatment, simultaneous oil and copper ion removal by electrocoagulation from copper plating plant effluents were studied in a new cell design, the cell anode was Al helical tube placed between two vertical cylindrical Al screen cathodes. Variable studied were current density, pH, temperatures, initial pollutant concentration, NaCl supporting electrolyte concentration, and the effect of gas sparging. Under optimum conditions, 85% of the oil was removed in one hour while the % Cu2+ removal was 98% in only 15 min. Electrical energy consumption for oil removal ranged from 4.3 × 10−3 to 5.2 kW.h/kg, while that of copper removal ranged from 5.4 × 10−3 to 7.5 kW.h/kg depending on the operating conditions. The merits of the suggested cell such as compactness and the use of the internal surface of helical coil anode as a built-in cooler to prevent the increase in solution temperature which adversely affects the efficiency of large scale electrocoagulation processes was highlighted.

Effect of Gas Sparging on Fouling and Fouling Mechanism During Microfiltration of Pineapple Juice and Coconut Water

Flux reduction due to fouling is the major problem during microfiltration. This study aimed to investigate the role of gas sparging, an effective technique for flux enhancement, on fouling and fouling mechanism during microfiltration pineapple juice and coconut water. A hollow fiber membrane was used and the experiments were performed at cross flow velocity (CFV) of 1.5 m/s, transmembrane pressure (TMP) of 0.7 bar for pineapple juice and CFV of 1.6 m/s, TMP of 0.6 bar for coconut water, as varying gas injection factors (e). It was found that the fouling mechanism during microfiltration of pineapple juice and coconut water began with complete blocking, followed by an intermediate blocking and finally cake filtration. The use of gas sparging did not affect the sequence of fouling mechanism but affected both intensity duration of these fouling mechanisms. The duration of complete blocking stage was about 5-6 min at the beginning of the microfiltration for both feed. The initial points of defined cake filtration stages reduced from 1.3 to 0.9 h for pineapple juice and 1.0 to 0.67 h for coconut water when the e was varied from 0 to 0.35. Regarding fouling resistance analysis, increase in gas injection factor could significantly reduce the reversible fouling, external irreversible fouling but internal irreversible fouling.

Propionic acid production from corn stover hydrolysate by Propionibacterium acidipropionici

BackgroundThe production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries. Here, the production of propionic acid (PA), a potential building block for C3-based chemicals, from corn stover hydrolysate is investigated using the native PA-producing bacterium Propionibacterium acidipropionici.ResultsA wide range of culture conditions and process parameters were examined and experimentally optimized to maximize titer, rate, and yield of PA. The effect of gas sparging during fermentation was first examined, and N2 was found to exhibit improved performance over CO2. Subsequently, the effects of different hydrolysate concentrations, nitrogen sources, and neutralization agents were investigated. One of the best combinations found during batch experiments used yeast extract (YE) as the primary nitrogen source and NH4OH for pH control. This combination enabled PA titers of 30.8 g/L with a productivity of 0.40 g/L h from 76.8 g/L biomass sugars, while successfully minimizing lactic acid production. Due to the economic significance of downstream separations, increasing titers using fed-batch fermentation was examined by changing both feeding media and strategy. Continuous feeding of hydrolysate was found to be superior to pulsed feeding and combined with high YE concentrations increased PA titers to 62.7 g/L and improved the simultaneous utilization of different biomass sugars. Additionally, applying high YE supplementation maintains the lactic acid concentration below 4 g/L for the duration of the fermentation. Finally, with the aim of increasing productivity, high cell density fed-batch fermentations were conducted. PA titers increased to 64.7 g/L with a productivity of 2.35 g/L h for the batch stage and 0.77 g/L h for the overall process.ConclusionThese results highlight the importance of media and fermentation strategy to improve PA production. Overall, this work demonstrates the feasibility of producing PA from corn stover hydrolysate.

THE EFFECT OF OPERATING CONDITIONS ON CRITICAL FLUX AND REVERSIBLE FOULING IN MEMBRANE FILTRATION USING GAS SPARGING TECHNIQUE

Gas sparging method utilizing injection of nitrogen gas was employed during the ultrafiltration of the natural rubber effluent (latex serum). The objective of this research was to investigate the effect of gas sparging on the critical flux and the observed reversible cake layer resistance during the ultrafiltration of skim latex serum. Experiments were conducted using a 100 kDa MWCO tubular membrane (PCI Membrane System) mounted vertically. The effect of operating parameters, such as feed flow rate, concentration and transmembrane pressure were investigated. The results showed that when the feed flow rate was increased, the permeate was correspondingly increased and the reversible cake resistance decreased. In this research a feed flow rate of 1400 ml/min and transmembrane pressure of 13.00 psig resulted in the maximum total permeate flux of 70.80 L/m2h. Results from this study obtained so far showed that the use of gas sparging has been able to increase total permeate flux between 8.3% and 145.3% compared to non-gas sparged condition. Critical flux occurrence was increased to 82.63% above the value obtained for non-sparged condition and applied transmembrane pressure can be reduced to 2.4% of the non-gas sparged condition.Keyword: skim latex serum, reversible fouling, gas sparged, critical flux

Analysis of backwashing efficiency in dead-end hollow-fibre ultrafiltration of anaerobic suspensions.

A novel dead-end mode operation for filtering anaerobic suspensions was investigated. In this mode, the filtration system automatically adjusted backwashing frequency to a preselected transmembrane pressure set-point. This paper discusses the effectiveness of the backwashing conditions on membrane fouling. Anaerobic suspensions from a conventional wastewater treatment plant digester were used as model suspensions for the trials carried out at lab-scale. Gas sparging aided backwashing significantly enhanced membrane cleaning efficiency. No effect of gas sparging on internal fouling was detected. Also, the cleaning efficiency linearly decreased with permeate flux. Nevertheless, due to a high increase in the reversible fouling, a reasonable net permeate flux (7.2-6.8 L/h m(2)) can be achieved when intermediate fluxes (12-16 L/h m(2)) were imposed and the higher transmembrane pressure set-point value (50 kPa) was applied. Both backwashing duration and flux exhibited similar influence on cake fouling removal for a given volume of permeate produced.

Mitigation of Flux Decline in the Cross-Flow Nanofiltration of Molasses Wastewater under the Effect of Gas Sparging

Gas sparging has been shown to significantly affect the performance of nanofiltration of molasses wastewater using a hydrophilized polyamide membrane (molecular weight cut-off 250) in a flat sheet module. Sparging of nitrogen at two different gas velocities was capable of appreciable alleviation of permeate flux decline over a period of time under the present experimental conditions when compared with the conventional unsparged nanofiltration. Critical flux (Jcrit), limiting flux (Jlim), and shear stress number (Ns) were determined at different cross-flow velocities for both the cases in the presence and absence of gas sparging. Increase in Ns with increasing cross-flow velocity was more pronounced in presence of gas sparging. Almost 1.5-2 fold increase in Ns was observed using cross-flow velocity of 0.8 ms−1 with gas sparging, compared to the case of “no sparging.” However, there was no significant improvement of rejection behavior of the solutes in presence of gas sparging. The value of mass transfer coefficient was considerably higher with increasing cross-flow velocity, while gas sparging was on, as against the case of “no sparging.” In terms of percentage increase in permeate flux with increase in trans-membrane pressure (TMP), gas sparging could achieve higher enhancement where concentration polarization is expected to be severe, that is, at high TMP and high feed concentrations. Some practical issues and technical limitations of gas sparging are also discussed.

Gas sparged gel layer controlled cross flow ultrafiltration: A model for stratified flow regime and its validity

Gas sparging is one of the techniques used to control the concentration polarization during ultrafiltration. In this work, the effects of gas sparging in stratified flow regime were investigated during gel layer controlling cross flow ultrafiltration in a rectangular channel. Synthetic solution of pectin was used as the gel forming solute. The liquid and gas flow rates were selected such that a stratified flow regime was prevalent in the channel. A mass transfer model was developed for this system to quantify the effects of gas flow rates on mass transfer coefficient (Sherwood number). The results were compared with the case of no gas sparging. Gas sparging led to an increase of mass transfer coefficient by about 23% in this case. The limitation of the developed model was also evaluated and it was observed that beyond a gas flow rate of 20 l/h, the model was unable to explain the experimental observation, i.e., the decrease in permeate flux with flow rate.

Effect of gas sparging on flux enhancement and phytochemical properties of clarified pineapple juice by microfiltration

Membrane fouling is a major obstacle in the application of microfiltration. Several techniques have been proposed to enhance the permeate flux during microfiltration. Gas sparging is a hydrodynamic method for improving the performance of the membrane process. In this study, a 0.2 μm hollow fiber microfiltration membrane was used to study the effect of cross flow velocity (CFV) and gas injection factor ( ε) on the critical and limiting flux during microfiltration of pineapple juice. In addition, the phytochemical properties of clarified juice were investigated. In the absence of gas sparging, the critical and limiting flux increased as the CFV or shear stress number increased. The use of gas sparging led to a remarkable improvement in both the critical and limiting flux but it was more effective at the lower CFV (1.5 m s −1), compared to those at higher CFV (2.0 and 2.5 m s −1). When the gas injection factor was applied at 0.15, 0.25 and 0.35 with a CFV of 1.5 m s −1, the enhancement of 55.6%, 75.5% and 128.2% was achieved for critical flux, while 65.8%, 69.7% and 95.2% was achieved for limiting flux, respectively. The results also indicated that the use of gas sparging was an effective method to reduce reversible fouling and external irreversible fouling rather than internal irreversible fouling. In addition, the CFV and gas sparging did not affect pH, total soluble solids, colour, total phenolic content and the antioxidant property of the clarified juice. The l-ascorbic acid and total vitamin C were significantly decreased when the higher CFV and high gas injection factor were applied. The results also indicated that the use of gas sparging with low CFV was beneficial for flux enhancement while most of the phytochemical properties of the clarified juice was preserved.

Augmentation of the Performance of Batch Electrocoagulation Unit by Using Gas Sparging

The present work investigates the effect of gas sparging in improving the performance of a batch electrocoagulation unit used to treat wastewater generated from the dyeing industry. Monopolar cylindrical aluminum electrodes were used. Many variables were investigated such as superficial gas velocity, current density, initial dye concentration, area ratio (cathode/anode), time of operation and the effect of adding chemical coagulant as FeSO4. The results show that the percentage of dye removal has been increased by a factor ranging from 2.52 to 5.14 by increasing the gas flow rate from 0.4 to 0.8 liter/min respectively and that about 93.5 percent of the dye can be removed within 60 minutes. Also it was found that using gas sparging is more efficient than adding chemical coagulant as ferrous sulfate for the removal of dye from wastewater. The power consumption for the unit was measured for different gas flow rates and different current densities; the results show that lower gas flow rate can improve the economy of the process.

Augmentation of the Performance of Batch Electrocoagulation Unit by Using Gas Sparging

The aim of the present work is to investigate the effect of gas sparging in improving the performance of a batch electrocoagulation unit used for the treatment of wastewater generated from dyeing industry. Monopolar cylindrical aluminum electrodes were used. Many variables were investigated such as superficial gas velocity, current density, initial dye concentration, area ratio (cathode/anode), time of operation and the effect of adding chemical coagulant as Fe (SO4). The results show that the % dye removal has been increased by a factor ranging from 2.52 to 5.14 by increasing the gas flow rate from 0.4 to 0.8 liter/min, respectively, and that about 93.5% of the dye can be removed within 60 minutes. Also it was found that using gas sparging is more efficient than adding chemical coagulant as ferrous sulphate for the removal of dye from wastewater. The power consumption for the unit was measured for different gas flow rates and different current densities; the results show that lower gas flow rate can improve the economy of the process.

An improved interface model for molten corium–concrete interaction

In the field of research for Severe Accidents of PWRs, calculation results are needed to estimate when corium achieves basemat melt-through. In this framework, knowledge of the heat transfer coefficient as well as the temperature at the interface between the melt and the solid are key issues. It has been previously emphasized that physico-chemistry of the melt (composition) affects the temperature. However, the effect of gas sparging and liquid concrete release on the mechanical stability of the solid layer and on the interface temperature has not been analysed in detail. ARTEMIS 1D tests were launched to analyse the phenomenology at the interface. A general conclusion for all these tests is that a solid medium enriched in refractory species exists at the interface between the pool and the concrete. Tests 2 and 6, which are close to reactor representative conditions, could be well described with the assumption T interface = T liquidus. The analysis of tests 3 and 4 revealed that the interfacial medium is thicker by a factor of 4–5 times than calculated with the assumption of pure conduction heat transfer. Detailed analysis leads to the conclusion that the interfacial medium is made of a porous layer of refractory particles embedded in a liquid phase. The liquid density difference, between the porous medium and chimneys, results in recirculation of the liquid in the porous layer. This recirculation is responsible for a convective contribution to heat transfer through the porous layer. The convective heat flux is partly linked to cooling of the recirculating liquid, but also to its partial solidification. The solidification results in gradual plugging and enrichment of the porous layer in refractory species and in the increase of the resistance to heat transfer. The phenomena have been modelled and ARTEMIS tests 3 and 4 are well reproduced. The complete plugging of the porous medium, associated with thermodynamic equilibrium at the interface between the solid medium and the pool leads naturally to the solid crust model implemented in TOLBIAC-ICB. The latter model appears, thus, as a simplification of the porous medium approach described here. Thick interfacial layers, which have composition between refractory and corium mixture, have been observed in ACE and MACE tests with LCS (Limestone–Common Sand) or Limestone concrete and can be explained with the proposed model approach. For siliceous concrete, convection within a porous medium is not possible due to the large viscosity.

Effect of gas sparging on continuous fermentative hydrogen production

The effect of gas sparging on continuous fermentative H 2 production was investigated in completely stirred-tank reactors (CSTR) using internal biogas, N 2 and CO 2 with various flow rates (100, 200, 300 and 400 ml/min). The sparging with external gases of N 2 and CO 2 showed higher H 2 yield than the control of no sparging and internal biogas sparging. It indicated that the decrease of H 2 partial pressure by external gas sparging had a beneficial effect on H 2 fermentation. Especially, CO 2 sparging was more effective in the reactor performance than N 2 sparging, accompanied by higher production of H 2 and butyrate. The best performance was obtained by CO 2 sparging at 300 ml/min, resulting in the highest H 2 yield of 1.68 mol H 2 / mol hexose consumed and the maximum specific H 2 production rate of 6.89 L H 2 / g VSS/day. Compared to N 2 sparging, there might be another positive effect in CO 2 sparging apart from lowering H 2 partial pressure. High CO 2 partial pressure had little effect on H 2 -producing bacteria but inhibitory effect on other microorganisms such as acetogens and lactic acid bacteria which were competitive with H 2 -producing bacteria. Only H 2 -producng bacteria, such as Clostridium tyrobutyricum, C. proteolyticum and C. acidisoli were isolated under CO 2 sparging conditions based on 16S rDNA analysis by PCR-DGGE.

Effect of Gas Sparging on the Rate of Mass Transfer at Horizontal Cylinders

The rate of mass transfer was studied at (i) a single horizontal cylinder cathode and (ii) a vertical array of closely spaced horizontal cylinders and an array of separated cylinders. The mass transfer coefficients were obtained by measuring the limiting current of the cathodic reduction of alkaline potassium ferricyanide. Variables studied were: cylinder diameter, physical properties of the solution, and nitrogen flow rate. The mass transfer coefficient was found to increase with increasing nitrogen superficial velocity. Decreasing the diameter was found to increase the mass transfer coefficient. The mass transfer data were correlated by the following equations: For single horizontal cylinder cathode: J = 2.138 (Re. Fr) -0.24 For an array of closely spaced cylinders: J = 50.118 (Re.Fr) -0.32 For an array of separated cylinders: J = 100 (Re.Fr) -0.28 Possible practical application of gas sparged array of horizontal cylinders in building electrochemical reactors are discussed.

Effect of gas sparging on the rate of mass transfer during electropolishing of vertical plates

Rates of electropolishing of vertical copper plates in phosphoric acid using a gas sparged rectangular cell were measured under different conditions of superficial gas (N 2) velocity, workpiece height, physical properties of the solution and macroroughness of the surface. The limiting current was found to increase with increasing N 2 superficial velocity to the power of 0.24 while increasing workpiece height ( L) was found to decrease the limiting current ( I) according to the equation, I= aL −0.19. The data were correlated by the equation j=0.235(Re Fr) −0.253 L d e −0.19 Where j, Re and Fr are the mass transfer j factor, Reynolds number and Froude number, respectively. Macroroughness was found to increase the limiting current by a modest amount depending on the peak-to-valley height of the roughness elements. The economic importance of using gas sparging in mass transfer controlled metal finishing processes is pointed out.

Bacterial Transport in Gas-Sparged Porous Medium

To improve the feasibility of soil-aquifer remediation using bioaugmentation, more efficient meth- ods are needed to widely disperse pollutant-degrading bacteria in porous media. Under water-saturated condi- tions, bacteria readily adhere to soil particles, but under unsaturated conditions, bacteria preferentially accumulate at the air-water interface. Air sparging a saturated porous medium produces a mobile water interface that was hypothesized to facilitate bacterial transport. To investigate whether gas sparging increased bacterial transport relative to saturated-water conditions, the transport of three strains of bacteria and negatively charged micro- spheres of different relative hydrophobicities RH was measured in saturated and gas-sparged quartz-packed columns. Gas sparging increased (>60%) the bacterial transport in only one case (Pseudomonas fluorescens P17; RH = 27%). Transport of the other two strains were either unaffected by gas sparging (Mycobacterium vaccae JOB5; RH = 33%), or was reduced (Pseudomonas aeruginosa ; RH = 75%) relative to water-saturated conditions. Microspheres were the most hydrophobic (RH = 98%) and the most retained of all particles under saturated conditions, but microsphere transport was unaffected by gas sparging. These preliminary results suggest that the effect of gas sparging on colloid transport is particle specific and not predictable from measurement of relative hydrophobicity.

Enhancement of ultrafiltration by gas sparging with flat sheet membrane modules

Gas sparged ultrafiltration has been applied to a flat sheet membrane module and the enhancing effect from the injected bubbles is examined experimentally. Two membranes, polysulphone (PS) and polyethersulfone (PES), were used in the experiments, and four proteins, human serum albumin (HSA), human immunoglobulin G (IgG), bovine serum albumin (BSA) and lysozyme (Lys), were chosen as the test media. The effects of gas sparging on permeate flux, single protein transmission and protein fractionation have been investigated. Experimental results show that gas sparging can increase permeate flux and improve the efficiency of protein fractionation.

Fractionation of BSA and lysozyme using ultrafiltration: Effect of gas sparging

AbstractFractionation of proteins by ultrafiltration is an interesting challenge. With a particular membrane, the protein – protein and protein – membrane interactions largely decide which protein passes through and which is retained. System hydrodynamics also affects protein fractionation as the transmission behavior of a protein is altered by concentration polarization. Therefore, disruption of the concentration polarization layer would help to maintain the native selectivity of the membrane and hence aid in protein fractionation. An attempt is made to use gas sparging, a technique proven effective in controlling concentration polarization to enhance the selectivity of separation of BSA (MW 67,000) and lysozyme (MW 14,100). The effects of gas flow rate, liquid flow rate and feed concentration on the selectivity of fractionation are examined. Gas sparging enhances protein fractionation; under suitable solution conditions, nearly complete separation of BSA and lysozyme was achieved with gas sparged ultrafiltration. The permeate flux was also increased by gas sparing. The mechanism of enhancement is explained in terms of disruption of the concentration polarization layer and enhanced mass transfer due to bubble‐induced secondary flow.

Liquid—solid mass transfer at vertical screens in bubble columns

AbstractThe effect of gas sparging on the rate of mass transfer at a vertical single screen was studied by an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide. Variables studied were screen characteristics, physical properties of the solution and gas superficial velocity. Screen characteristics, e. g., mesh number and wire diameter were found to have little effect on the rate of mass transfer. The data at different screens were correlated in terms of the superficial gas velocity by the equation St Sc0.5 = 0.095 (Re Fr)−0.272, where St is Stanton number, Sc is Schmidt number, Re is Reynolds number and Fr is Froude number.Comparison of the present data with previous results obtained with different transfer geometries has shown that screens produce higher rates of mass transfer than other geometries. The importance of the present work to catalytic and electrochemical reactor design was noted.