Gas Sparging Rate Research Articles

Macroalgal biochar synthesis and its implication on membrane fouling mitigation in fluidized bed membrane bioreactor for wastewater treatment

The intensification of biochar into fluidized bed membrane bioreactor was investigated to mitigate membrane fouling. Different biochars from algal biomass were produced and used as biomaterials for wastewater treatment. In this study, different macroalgal biochar was synthesized at different pyrolysis temperatures and characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Brunauer Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FTIR) techniques to implicate their effect on membrane fouling reduction in fluidized bed membrane bioreactor. The combined effect of macroalgal biochars and biocarriers with gas sparging was evaluated for fouling mitigation. Macroalgal biochar curtailed membrane fouling effectively at low gas sparging rate. Transmembrane pressure (TMP) was reduced to 0.053 bar; under the fluidization of biochar-650 and biocarriers with gas sparging; from 0.27 bar (gas sparging only). Combined effect of gas sparging, biocarriers and biochar-650 instigated 92.1% fouling reduction in comparative to gas sparging alone. Mechanical scouring driven by biocarriers could reduce fouling due to removing surface deposit of foulants from membrane surface effectively and biochar can efficiently adsorb foulants because of its active functional groups resulting in reduction of colloidal fouling. The addition of divalent ions (Ca2+) further enhanced the fouling reduction in fluidized bed membrane bioreactor.

Modelling of bubble breakage and coalescence in stirred and sparged bioreactor using the Euler-Lagrange approach

Gas-liquid systems are commonly used in industry to carry out biochemical reactions. Such process must be carried out to ensure sufficient mass transfer while there is no damage to the living cells/microorganisms. This is given mainly by the bubble size distribution (BSD) and process parameters such as the impeller speed and gas sparging rate. The correct prediction of BSD is crucial to choosing the optimal process parameters and meeting the requirements of a given culture. This work aimed to use computational fluid dynamics (CFD) to predict the breakage and coalescence of individual bubbles and therefore to predict the whole BSD under broad range of process parameters. The gas-liquid system of the stirred and sparged bioreactor was modelled utilizing the Euler-Lagrange (EL) approach. The continuous phase was modelled as a 3D time-dependent problem using the Reynolds-averaged Navier-Stokes (RANS) method with a realizable k-ε model for the description of turbulence. The motion of discrete Lagrangian bubbles was tracked by Newton's equation of motion. Both the breakage and coalescence of individual bubbles were implemented. For bubble coalescence, the model developed by Prince and Blanch and further modified by Sommerfeld and Sungkorn for use in the Lagrangian approach to bubbles was used. For breakup, a model developed by Martínez-Bazán was used. There, the effect of daughter distribution function (DDF) on the resulting gas dispersion was studied. Experiments and simulations were performed in the Minifors stirred and sparged bioreactor with a working volume of 3.5 L. The impeller speeds ranged from 200 to 500 rpm (corresponding to Reynolds number in the range from 10,889 to 27,222), while the gas feed rate was constant and reached a value of 1.2 L min–1. To validate the whole CFD model, we compared the BSDs obtained from the simulations against experimentally determined BSDs. There, for all cases, the simulations matched the experimental data relatively well. Subsequently, a general characterization of the system studied was performed in terms of the volumetric mass transfer coefficient (kLa) and the maximum hydrodynamic stress (τVS) to which the cell could be exposed. Also in this case, under all tested conditions, we achieved satisfactory agreement with experiments.

Impact of permeate flux and gas sparging rate on membrane performance and process economics of granular anaerobic membrane bioreactors

This research investigated the impact of permeate flux and gas sparging rate on membrane permeability, dissolved and colloidal organic matter (DCOM) rejection and process economics of granular anaerobic membrane bioreactors (AnMBRs). The goal of the study was to understand how membrane fouling control strategies influence granular AnMBR economics. To this end, short- and long-term filtration tests were performed under different permeate flux and specific gas demand (SGD) conditions. The results showed that flux and SGD conditions had a direct impact on membrane fouling. At normalised fluxes (J20) of 4.4 and 8.7 L m−2 h−1 (LMH) the most favourable SGD condition was 0.5 m3 m−2 h−1, whereas at J20 of 13.0 and 16.7 LMH the most favourable SGD condition was 1.0 m3 m−2 h−1. The flux and the SGD did not have a direct impact on DCOM rejection, with values ranging between 31 and 44%. The three-dimensional excitation-emission matrix fluorescence (3DEEM) spectra showed that protein-like fluorophores were predominant in mixed liquor and permeate samples (67–79%) and were retained by the membrane (39–50%). This suggests that protein-like fluorophores could be an important foulant for these systems. The economic analysis showed that operating the membranes at moderate fluxes (J20 = 7.8 LMH) and SGD (0.5 m3 m−2 h−1) could be the most favourable alternative. Finally, a sensitivity analysis illustrated that electricity and membrane cost were the most sensitive economic parameters, which highlights the importance of reducing SGD requirements and improving membrane permeability to reduce costs of granular AnMBRs.

Production of recombinant butyrylcholinesterase from transgenic rice cell suspension cultures in a pilot-scale bioreactor.

Producing recombinant proteins in transgenic plant cell suspension cultures in bioreactors provides controllability, reproducibility, scalability, and low-cost production, although low yields remain the major challenge. The studies on scaling-up to pilot-scale bioreactors, especially in conventional stainless-steel stirred tank bioreactors (STB), to produce recombinant proteins in plant cell suspension cultures are very limited. In this study, we scaled-up the production of rice recombinant butyrylcholinesterase (rrBChE), a complex hydrolase enzyme that can be used to prophylactically and therapeutically treat against organophosphorus nerve agents and pesticide exposure, from metabolically regulated transgenic rice cell suspension cultures in a 40-L pilot-scale STB. Employing cyclical operation together with a simplified-process operation (controlling gas sparging rate rather than dissolved oxygen and allowing natural sugar depletion) identified in lab-scale (5 L) bioreactor studies, we found a consistent maximum total active rrBChE production level of 46-58 µg/g fresh weight in four cycles over 82 days of semicontinuous operation. Additionally, maintaining the overall volumetric oxygen mass transfer coefficient (kL a) in the pilot-scale STB to be equivalent to the lab-scale STB improves the maximum total active rrBChE production level and the maximum volumetric productivity to 85 µg/g fresh weight and 387 µg L-1 day-1 , respectively, which are comparable to the lab-scale culture. Here, we demonstrate pilot-scale bioreactor performance using a metabolically regulated transgenic rice cell culture for long-term, reproducible, and sustained production of rrBChE.

Identification of gas sparging regimes for granular anaerobic membrane bioreactor to enable energy neutral municipal wastewater treatment

In this study, conventional and novel gas sparging regimes have been evaluated for a municipal wastewater granular anaerobic MBR to identify how best to achieve high sustainable fluxes whilst simultaneously conserving energy demand. Using continuous gas sparging in combination with continuous filtration, flux was strongly dependent upon shear rate, which imposed a considerable energy demand. Intermittent gas sparging was subsequently evaluated to reduce energy demand whilst delivering an analogous shear rate. For a flux of 5 L m−2 h−1, a fouling rate below 1 mbar h−1 was sustained with low gas sparging frequency and gas sparging rates. However, to sustain low fouling rates for fluxes above 10 L m−2 h−1, a gas sparging frequency of 50% (i.e. 10 s on/10 s off) and an increase in gas sparging rate is needed, indicating the importance of shear rate and gas sparging frequency. An alternative gas sparging regime was subsequently tested in which filtration was conducted without gas sparging, followed by membrane relaxation for a short period coupled with gas sparging, to create a pseudo dead-end filtration cycle. Fouling characterisation evidenced considerable cake fouling rates of 200–250 mbar h−1 within each filtration cycle. However, long term fouling transient analysis demonstrated low residual fouling resistance, suggesting the cake formed during filtration was almost completely reversible, despite operating at a flux of 15 L m−2 h−1, which was equivalent or higher than the critical flux of the suspension. It is therefore asserted that by operating filtration in the absence of shear, fouling is less dependent upon the preferential migration of the sub-micron particle fraction and is instead governed by the compressibility of the heterogeneous cake formed, which enables higher operational fluxes to be achieved. Comparison of energy demand for the three gas sparging regimes to the energy recovered from municipal wastewater AnMBR demonstrated that only by using dead-end filtration can energy neutral wastewater treatment be realised which is the ultimate ambition for the technology.

Impact of anaerobic dynamic membrane bioreactor configuration on treatment and filterability performance

Submerged and external anaerobic dynamic membrane bioreactors (AnDMBRs) have been compared in terms of removal efficiency, filtration characteristics and microbial community structure. High COD removal efficiencies were obtained with both submerged and external AnDMBRs. To obtain an effective dynamic membrane (DM) layer enabling high quality permeate, longer time was required in the external AnDMBR configuration compared to the submerged one. A difference in microbial community structure was identified using pyrosequencing analyses between the submerged and external AnDMBRs. The number of archaeal types decreased in the bulk sludge of the external AnDMBR. External sludge recirculation might have had a negative effect on the archaeal community in the bulk sludge of the external AnDMBR. However, the sludge recirculation in the external AnDMBR configuration led to a filtration at lower total filtration resistance and TMP in comparison to the submerged one at the same gas sparging rate. Results showed that the submerged AnDMBR system can provide a shorter start-up period, slightly better permeate quality in terms of COD concentration, and higher biogas production in comparison to the external one in gas-lift mode.

MS-2 and T4 phage removal in an anaerobic membrane bioreactor (AnMBR): effect of gas sparging rate.

BACKGROUNDThe enhanced removal of viruses in wastewater treatments plant is important due to concerns about public health. Bacteriophages (or phages) are often used to model the behavior of pathogenic human viruses as they are similar in size, structure and behavior. This study investigated the removal of phages MS‐2 (25 nm) and T4 (200 nm) in an anaerobic membrane bioreactor (AnMBR) with a membrane pore size of 0.4 µm.RESULTSThe membrane reactor without biomass was assessed and its log removal was 0.7 ± 0.4 log for the MS‐2 phage, and 2.3 ± 0.2 log for the T4. When anaerobic biomass was added to the reactor the log removal for both phages increased, and this was thought to be due to a complex relationship with the biofilm on the membrane.CONCLUSIONSOverall MS‐2 rejections ranged from 1.75 up to 5.5 log, with the highest rejections observed at the highest sparging rates after extensive fouling had occurred. For T4, removal in the AnMBR ranged from 5 log up to complete removal (>log 7). © 2014 Society of Chemical Industry

Application of bioreactor design principles and multivariate analysis for development of cell culture scale down models.

A bench scale cell culture model representative of manufacturing scale (2,000 L) was developed based on oxygen mass transfer principles, for a CHO-based process producing a recombinant human protein. Cell culture performance differences across scales are characterized most often by sub-optimal performance in manufacturing scale bioreactors. By contrast in this study, reduced growth rates were observed at bench scale during the initial model development. Bioreactor models based on power per unit volume (P/V), volumetric mass transfer coefficient (kL a), and oxygen transfer rate (OTR) were evaluated to address this scale performance difference. Lower viable cell densities observed for the P/V model were attributed to higher sparge rates and reduced oxygen mass transfer efficiency (kL a) of the small scale hole spargers. Increasing the sparger kL a by decreasing the pore size resulted in a further decrease in growth at bench scale. Due to sensitivity of the cell line to gas sparge rate and bubble size that was revealed by the P/V and kL a models, an OTR model based on oxygen enrichment and increased P/V was selected that generated endpoint sparge rates representative of 2,000 L scale. This final bench scale model generated similar growth rates as manufacturing. In order to take into account other routinely monitored process parameters besides growth, a multivariate statistical approach was applied to demonstrate validity of the small scale model. After the model was selected based on univariate and multivariate analysis, product quality was generated and verified to fall within the 95% confidence limit of the multivariate model.

Impact on reactor configuration on the performance of anaerobic MBRs: Treatment of settled sewage in temperate climates

The treatment efficiency and membrane performance of a granular and suspended growth anaerobic membrane bioreactor (G-AnMBR and AnMBR respectively) were compared and evaluated. Both anaerobic MBRs were operated in parallel during 250 days with low strength wastewater and under UK weather conditions. Both systems presented COD and BOD removal efficiencies of 80–95% and >90% respectively. Effluent BOD remained between 5 and 15 mgBOD L−1 through the experimental period while effluent COD increased from 25 mg L−1 to 75 mg L−1 as temperature decreased from 25 °C to 10 °C respectively indicating the production of non biodegradable organics at lower temperatures. Although similar levels of low molecular weight organics were present in the sludge supernatant, recycling of the mixed liquor from the membrane tank to the bioreactor at a low upflow velocity enhanced interception of solids in the sludge bed of the G-AnMBR limiting the solid and colloidal load to the membrane as compared to the suspended system. Results from flux step test showed that critical flux increased from 4 to 13 L m−2 h−1 and from 3 to 5 L m−2 h−1 with gas sparging intensities varying from 0.007 m s−1 to 0.041. Additional long term trials in which the effect of gas sparging rate and backwashing efficiency were assessed confirmed the lower fouling propensity of the G-AnMBR.

Hydrogen supersaturation in extreme-thermophilic (70 °C) mixed culture fermentation

Hydrogen supersaturation in extreme-thermophilic (70°C) mixed culture fermentation (MCF) was demonstrated for the first time by membrane inlet mass spectrometry. It was found that hydrogen supersaturation ratio (RH2) increased dramatically (from 1.0 to 20.6) when H2 partial pressure (PH2) was reduced by N2 flushing or sparging. The distribution change of metabolites was insignificant under low PH2 (<0.30atm) due to the high value of RH2, which indicated that it was more relevant to the concentration of dissolved H2 (H2aq) rather than PH2. To explain the cause of hydrogen supersaturation, the overall volumetric mass transfer coefficients (KLa) for H2 were calculated. KLa changed slightly (∼7.0/h) with N2 flushing, while it increased from 7.4 to 10.2/h when N2 sparging rate increased from 0.3 to 17.9mL/min/L. However, the required KLa values were orders of magnitude higher than the experimental ones when maintaining low RH2 by gas sparging, which indicated that hydrogen supersaturation was likely inevitable in MCF. Moreover, to improve the hydrogen yield of MCF, the gas sparging rate was suggested as 2–10times of the hydrogen production rate.

Influence of gas sparging on clarification of pineapple wine by microfiltration

A microfiltration process with a tubular ceramic membrane was applied for clarification of pineapple wine. The process was operated with the membrane pore size of 0.2 μm at transmembrane pressure of 2 bar and crossflow velocity of 2.0 m/s. The effects of gas sparging on permeate flux, fouling and quality of clarified wine were studied. It was found that a relatively low gas sparging rate could increase permeate flux up to 138%. Further increase of the gas sparging rate did not improve permeate flux compared with that without gas sparging. Gas sparging affected the density of cake layer. Increasing gas sparging rate led to an increase in specific cake resistance. It was observed that increasing gas sparging rate could reduce reversible fouling rather than irreversible fouling. The turbidity of pineapple wine was reduced and a clear product with bright yellow color was obtained after microfiltration. The negative effect of gas sparging which caused a loss of alcohol content in the wine was also observed.

Chloride leaching of a complex matte: comparison of oxidants

The leaching of a complex matte in chlorine and chloride media was studied. The matte was prepared from manganese nodules by the reduction smelting-sulfidation route. From XRD analysis, the major phases of the matte were identified as CuFeS2, CuS2, (FeNi)9S8, (FeNi)S2, Ni9S8, Ni3S2, (CoFeNi)9S8 and Co metal. Investigated were the chlorine, hydrochloric acid, hydrochloric acid-oxygen, ferric chloride, ferric chloride-oxygen, cupric chloride and cupric chloride-oxygen systems. The results are discussed in terms of reagent concentration retention time, leach temperature and gas sparging rate. The chlorination process resulted >99% metal extraction efficiency within a short retention time and at atmospheric temperature. However, there were no preferential extractions of Cu, Ni and Co with respect to Fe. The cupric chloride-oxygen system produced leach liquors with the lowest Fe content and with a high base-metal extraction. Sulfide sulfur was converted to mixtures of elemental sulfur and sulfate in all the studied systems.

Solid Suspension in a Boiling Stirred Tank with Radial Flow Turbines

This paper considers conditions in reactors in which solids must be maintained in suspension in a boiling liquid. The situation is analogous to, but differs from, the more commonly studied conditions when the liquid is well-below its boiling point in a gas-liquid-solid reactor. Impeller performance in both cases is usually controlled by the development of gas or vapor cavities behind the impeller blades. Power consumption, critical off-bottom suspension speed, and vapor holdup measurements are reported for impellers working in a three-phase model system of 0.1 mm glass beads at concentrations of 3, 6, 9, 15, and 21 vol %, suspended in deionized boiling water. The vessel was electrically heated, dished based, and of 0.48 m diameter. It was agitated by single 0.24 m diameter impellers. The three radial-flow disc turbines studied were a flat-blade Rushton turbine, RT-6, a hollow half-pipe blade turbine, Chemineer CD-6, and a hollow semi-elliptical blade turbine, HEDT. The modem CD-6 and HEDT impellers are highly efficient in handling high gas-phase loading and in maintaining high levels of power input throughout a range of impeller tip speeds. For all three impellers, the relative power demand (RPD, i.e., the ratio between the gassed and ungassed power at a given impeller speed) was only slightly affected by solids, even up to 21 vol %. In contrast to the effect of varying the gas sparge rate in a cold aerated system, the boil-off rate had only a limited effect on the RPD, the minimum impeller speed needed to maintain suspension, or the retained void fraction. When boiling, the void fraction was, as might have been expected, much lower than in cold systems at similar power input and off-gas rates. Correlations of vapor holdup and RPD for the three radial flow turbines are suggested as a reference for future industrial applications in which knowledge of both the power requirements and the actual liquid fraction retained in the reactor may be of commercial importance. The HEDT impeller is recommended for both vapor dispersion and solid suspension in ungassed boiling three-phase systems.

Shear profiles inside gas sparged submerged hollow fiber membrane modules

Gas sparging is a common strategy used to minimize and prevent fouling on membrane surfaces. Although there have been numerous studies on the hydrodynamic conditions and the mechanisms of fouling control in confined membrane systems such as tubular membranes, there is very limited literature available that describes the hydrodynamic conditions and mechanisms of fouling control in unconfined systems such as submerged hollow fiber membranes. The present study investigated bubble-induced shear profiles in submerged hollow fiber membrane modules using an electrochemical method for measuring shear forces. The effects of different operating conditions such as gas sparging rates, fiber packing densities, diffuser nozzle sizes, and module configurations (i.e. loosely versus tightly held) on shear profiles were studied. It was found that the hydrodynamic conditions in confined tubular membrane systems and unconfined submerged hollow fiber membranes are different, which implies that the mechanisms of fouling control in submerged hollow fiber membrane units may be different than those in confined systems such as the tubular membranes. Surface shear profiles during sparging were found to be substantially affected by the operating conditions (i.e. gas sparging rate, fiber packing density, diffuser nozzle size, and module configuration). The different shear profiles were due to the different bubble geometries and flow paths which resulted from the different operating conditions considered. For tightly held low and medium fiber packing density bundles the high number of shear events generated by small bubbles (i.e. small diffuser nozzle) resulted in more favorable hydrodynamic condition for fouling reduction and flux enhancement. The higher permeate fluxes that have been reported in loosely held submerged hollow fiber membrane systems likely result from the larger number of fibers (i.e. regions) that can be impacted by sparged bubbles in systems with loosely held fibers. The results from the present study provide a better understanding of the hydrodynamic conditions inside submerged hollow fiber membrane modules, and therefore a better understanding of possible mechanisms of fouling control via gas sparging.

Gas/Liquid Mass Transfer in Hot Sparged Systems

AbstractUnderstanding the effect of temperature on the volumetric mass transfer rate is of vital importance for the design of chemical reactors operated at elevated temperatures. The present study is motivated by a poor understanding of this effect due to previous limited investigations. Such an effect has been studied at the CSIRO Energy &amp; Thermofluids Engineering Laboratory in a mechanically agitated air‐water mixing tank with operating temperatures in the range of 20‐80d̀C at atmospheric pressure. The oxygen concentration of the liquid is measured by a dissolved oxygen probe. The volumetric mass transfer rate is estimated using a dynamic method. It has been found that the saturated oxygen concentration of the liquid does not change significantly with the gas sparging rate and impeller speed. The change of temperature affects the saturated oxygen concentration significantly. The volumetric mass transfer rate increases with the increase of liquid temperature in the range of 18‐60d̀C. Beyond 60d̀C, the transfer rate decreases. Such a decrease is mainly due to the dramatic drop in the gas void fraction.

Design and operation of unbaffled aerated agitated vessels with unsteadily forward–reverse rotating impellers handling viscous Newtonian liquids

AbstractDesign and operation of unbaffled aerated agitated vessels with multiple unsteadily forward–reverse rotating impellers (AJITERs) for viscous Newtonian liquids were studied. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, geometrical conditions such as the diameters of vessel and impeller, and the physical properties of liquids on the drag and added moment of inertia coefficients, necessary to predict the average and maximum power consumptions of the impellers in AJITERs, were evaluated and the empirical relationships which estimate values of each of these coefficients are presented. The effects of operating conditions, geometrical conditions and liquid physical properties on the gas hold‐up, ϕgD, and volumetric oxygen transfer coefficient, kLaD, were evaluated in relation to the total power input which is the sum of the average power consumption of impellers, ie average agitation power input, and aeration power input. Empirical relationships, useful for design and operation of AJITERs, were obtained for each viscosity range, where the dependences of ϕgD and kLaD on the specific total power input and superficial gas velocity differed, to predict ϕgD and kLaD respectively as a function of the specific total power input, superficial gas velocity and liquid physical properties.© 2003 Society of Chemical Industry

Flow and mass transfer in aerated viscous Newtonian liquids in an unbaffled agitated vessel having alternating forward–reverse rotating impellers

Flow and mass transfer characteristics in aerated viscous Newtonian liquids were studied for an unbaffled aerated agitated vessel with alternating rotating impellers (AAVAI), ie with multiple forward–reverse rotating impellers having four delta blades. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, and the liquid physical properties (viscosity) on the gas hold-up, ϕgD, and volumetric oxygen transfer coefficient, kLaD were evaluated experimentally. The dependences of ϕgD and kLaD on the specific total power input and superficial gas velocity differed, depending on the ranges of liquid viscosity. Empirical relationships are presented for each viscosity range to predict ϕgD and kLaD as a function of the specific total power input, superficial gas velocity and viscosity of liquid. Based on a comparative investigation of the volumetric coefficient in terms of the specific total power input between the AAVAI and conventional aerated agitated vessels (CAAVs) having unidirectionally rotating impellers, the usefulness of AAVAI as a gas–liquid agitator treating viscous Newtonian liquids is also discussed. © 2001 Society of Chemical Industry

Flow and mass transfer in aerated viscous Newtonian liquids in an unbaffled agitated vessel having alternating forward–reverse rotating impellers

AbstractFlow and mass transfer characteristics in aerated viscous Newtonian liquids were studied for an unbaffled aerated agitated vessel with alternating rotating impellers (AAVAI), ie with multiple forward–reverse rotating impellers having four delta blades. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, and the liquid physical properties (viscosity) on the gas hold‐up, ϕgD, and volumetric oxygen transfer coefficient, kLaD were evaluated experimentally. The dependences of ϕgD and kLaD on the specific total power input and superficial gas velocity differed, depending on the ranges of liquid viscosity. Empirical relationships are presented for each viscosity range to predict ϕgD and kLaD as a function of the specific total power input, superficial gas velocity and viscosity of liquid. Based on a comparative investigation of the volumetric coefficient in terms of the specific total power input between the AAVAI and conventional aerated agitated vessels (CAAVs) having unidirectionally rotating impellers, the usefulness of AAVAI as a gas–liquid agitator treating viscous Newtonian liquids is also discussed.© 2001 Society of Chemical Industry

A study of the performance of a sparged packed bed electrode reactor for the direct electrochemical oxidation of propylene

A non-linear model for the direct electrochemical oxidation of propylene in a new type of reactor — a sparged packed bed electrode reactor (SPBER) is developed. The model consists of a set of second-order ordinary differential equations, which includes a one-dimensional Poisson equation, describing the effect of the electric field on this system, and material balance equations for reactants and products. The model accounts for gas–liquid mass transport, liquid–solid mass transport at the electrode, heterogeneous electrochemical reaction and homogeneous reaction in the bulk solution. The reactant, propylene, undergoes direct oxidation to the epoxide, which undergoes further chemical reaction (saponification), in solution, to the glycol. Numerical solution of this model is used to determine lateral distributions of overpotential, current density and concentrations of products in a SPBER, and to simulate the effects of important operating parameters, such as gas sparging rate and applied overpotential, on these distributions.

Improvements in titer, productivity, and yield using Solka-floc for cellulase production.

Researchers studying cellulase enzymes for the economical production of fuel ethanol envision cellulose as the carbon source. However, submerged Trichoderma reesei cultures grown on cellulose exhibit high run-to-run variability. Thus, an investigation of 30 batch cellulase production experiments was instrumental in determining fermentation conditions that improved enzyme titers, yields, and productivities. Eighteen of the 30 batch experiments experienced minimal process upsets and were classified into eight groups based on agitation rate, gas sparge rate, and the use of oxygen supplementation. Comparing corn steep liquor with yeast extract/peptone also tested the effect of different sources of nitrogen in the media. Average 7-d enzyme titers were doubled from 4 to 8 FPU/mL primarily by increasing aeration.