Fermentation and oxygen transfer characteristics in serine alkaline protease production by recombinant Bacillus subtilis in molasses‐based complex medium

Serine alkaline protease (SAP) production in a complex medium based on physically pretreated molasses by recombinant Bacillus subtilis carrying pHV1431::subC gene is described. The effects of oxygen transfer were investigated in 3.5 dm³ bioreactor systems with controls for agitation rate, dissolved oxygen, pH, temperature, and foam formation under two different agitation rates, ie N = 500 and 750 min^?1, and four different air flow rates, ie Q/V_R = 0.2, 0.5, 0.7, and 1.0 vvm, at a molasses concentration equivalent to initial sucrose concentration (C_So) of 20 kg m^?3. The yield values (Y_X/S, Y_X/O, Y_S/O) and maintenance coefficient of oxygen (m_O), were calculated. m_O decreased with the increase in the air‐inlet rate. Increase in oxygen transfer rate increased the rate of growth and SAP activity, and affected the cultivation time to achieve maximum expression of SAP activity. At Q/V_R = 0.5 vvm and N = 750 min^?1, SAP activity reached 2250 U cm^?3 at t = 36 h. The oxygen transfer coefficient (K_La) and oxygen uptake rate (?r_O) were measured throughout the fermentations and their variation with the oxygen transfer conditions determined. New correlations for the calculation of K_La and ?r_O are proposed. Copyright © 2004 Society of Chemical Industry     

Reactivities of Guaiacyl and Syringyl Lignin Model Phenols Towards Oxidation with Oxygen-Alkali

A range of guaiacyl and syringyl lignin model phenols was treated with oxygen in 1M potassium hydroxide solution at 70°C. The reactions were monitored by high performance liquid chromatography and gas chromatography-mass spectrometry. The reactions of the phenols, which followed pseudo-first-order kinetics, were faster for syringyl than for guaiacyl phenols. For the various 4-substituted syringols the reactivities were in decreasing order CH₂-syringyl > CHOH[sbnd]CH₃ π C₃H₇ ⁿ > CH₂OH > COOH > CHO > CO[sbnd]CH₃. Reaction of 1-guaiacylpropane in 1M potassium hydroxide with oxygen gave products of oxidative scission of the aromatic ring and no dehydrodimer, whereas at pH 11.5 some dehydrodimer was among the reaction products. Vanillyl alcohol and syringyl alcohol yielded vanillin and syringaldehyde, respectively, as minor oxidation products. However, the reaction sites for the series of phenols were generally the aromatic rings rather than the side-chains. Oxidation of alkaline solutions of the phenols with oxygen at 1.0 MPa pressure and 110 and 150°C gave similar mixtures of acids and hydroxyacids.     

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. II. The Effect of Temperature,pH, Alkalinity,and DOM Properties

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O₃) decomposition, O₃-exposure, ?OH-exposure and the ratio R_ct of the concentrations of ?OH and O₃ has been studied. For a standardized single ozone dose of 1 mg/L in all experiments, considerable variations in O₃-exposure and ?OH-exposure were found. This has important implications for water treatment plants regarding the efficiency of oxidation and disinfection by O₃. In oligotrophic surface waters and groundwaters, minimal calibration experiments are needed to model and control the ozonation process, whereas in eutrophic surface waters more frequent measurements of O₃ kinetics and R_ct values are required to evaluate seasonal variations.     

Mechanisms responsible for enhancing low-temperature oxidation resistance of nonstoichiometric (Zr,Ti)C

A series of (Zr,Ti)C_x (x = 0.7–1.0) samples were fabricated by a modified spark plasma sintering apparatus to investigate the effects of carbon concentration and Ti substitutions on the oxidation behavior. Crushed powders of (Zr,Ti)C_x were oxidized in lab air (N₂–20-vol.% O₂) from room temperature to 900°C. The results indicated that Zr_0.8Ti_0.2C_0.8, with a nominal carbon concentration x = 0.8, displayed good oxidation resistance, which was attributed to the formation of dense t-(Zr,Ti)O₂ oxide solid solution. During the oxidation of (Zr,Ti)C_x, Ti substitutions for Zr enhanced the outward diffusion of carbon, enabling a uniform carbon layer and a Zr–Ti–C–O layer on the surface of carbides. The formed carbon layer improved the oxidation resistance of (Zr,Ti)C_x below 550°C, where carbon is relatively oxidation resistant. Increasing the Ti concentration was found to enhance the oxidation resistance of (Zr,Ti)C_x with an increased oxidation onset temperature (672 ± 2°C for Zr_0.8Ti_0.2C_0.8).     

Catalytic Oxidation of CO Over Synthesized Nickel Ferrite Nanoparticles from Fly Ash

Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe₂O₄, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 ≤ T ≤ 800 °C, impure low crystalline NiFe₂O₄ phase formed. The main impurities are FeO (OH) and Fe₂O₃ · H₂O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 °C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe₂O₄ powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe₂O₄ powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2–8.5 nm), the higher surface area (25–55 m²/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.     

Promotional effect of hydroxyl on the aqueous phase oxidation of carbon monoxide and glycerol over supported Au catalysts

Gold particles supported on carbon and titania were explored as catalysts for oxidation of CO or glycerol by O₂ at room temperature in liquid-phase water. Although Au/carbon catalysts were not active for vapor phase CO oxidation at room temperature, a turnover frequency of 5 s⁻¹ could be achieved with comparable CO concentration in aqueous solution containing 1 M NaOH. The turnover frequency on Au/carbon was a strong function of pH, decreasing by about a factor of 50 when the pH decreased from 14 to 0.3. Evidently, a catalytic oxidation route that was not available in the vapor phase is enabled by operation in the liquid water at high pH. Since Au/titania is active for vapor phase CO oxidation, the role of water, and therefore hydroxyl concentration, is not as significant as that for Au/carbon. Hydrogen peroxide is also produced during CO oxidation over Au in liquid water and increasing the hydroxyl concentration enhances its formation rate. For glycerol oxidation to glyceric acid (C₃) and glycolic acid (C₂) with O₂ (1–10 atm) at 308–333 K over supported Au particles, high pH is required for catalysis to occur. Similar to CO oxidation in liquid water, H₂O₂ is also produced during glycerol oxidation at high pH. The formation of the C-C cleavage product glycolic acid is attributed to peroxide in the reaction.     

Basic rules of NO oxidation by Fe2+/H2O2/AA directional decomposition system

Basic rules of NO oxidation by a Fe²⁺/H₂O₂/AA directional decomposition system were researched based on the technical background of flue gas NO_x removal. Effects of gas‐liquid interfacial area, main gas, and solution parameters on NO oxidation efficiency (η) were analyzed. The results showed that adequate contact area was the precondition for high η by a Fe²⁺/H₂O₂/AA system. η decreased with the increase in NO concentration, which illustrated that this method would be efficient in oxidizing NO at a low concentration. η tended to decrease linearly with the growth in gas flow, however, the NO oxidation rate (v) rose with the increase in NO concentration and gas flow. η increased with the initial concentrations of H₂O₂ and Fe²⁺, but the amplitude decreased. Controlling the initial concentrations of H₂O₂ and Fe²⁺ to achieve reasonable synergies between generation rate and consumption rate of ·OH could weaken the invalid consumption of reactants. η increased with the increase in temperature in the range 30–60 °C, but it nearly did not change with temperature after 60 °C. This oxidation technology and the traditional wet flue gas desulphurization technology exhibited temperature synergy. Under typical pH of wet desulphurization, η and H₂O₂ consumption rate did not change obviously.     

Structure Property Relationship in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO X8R System

A novel BaTiO₃–Na_0.5Bi_0.5TiO₃–Nb₂O₅–NiO (BT‐NBT‐Nb‐Ni) system that meets the X8R specification (?55°C–150°C, ΔC/C≤±15%) of multilayer ceramic capacitors (MLCCs) was fabricated, with a maximum dielectric constant of 2350 at room temperature (25°C). Core–shell microstructure was observed by transmission electron microscopy (TEM), accounting for the good dielectric temperature stability. The role of Ni on the formation of core–shell structure and phase structure, and the subsequent relationship between structure and dielectric/ionic conduction properties were investigated. It was observed that the addition of Ni could adjust the ratio of core/shell, and significantly reduces the dielectric loss over the studied temperature range. A new Ba₁₁(Ni, Ti)₂₈O_66+x phase with a 10‐layer close‐packed structure was identified by X‐ray diffraction (XRD), serving as a source of oxygen vacancies for ionic conduction in addition to Ba(Ni,Ti)O₃. Furthermore, the impedance spectroscopy measurements demonstrated the remarkable impact of these Ni‐induced oxygen vacancies on both the grain and grain‐boundary conductivities.     

Thermal oxidation kinetics for a poly(bismaleimide)

The thermal oxidation of poly(bismaleimide) of the F655‐2 type, supplied by Hexcel‐Genin, was studied by isothermal gravimetry at 180, 210, and 240°C and various oxygen pressures ranging from 0 to 1.2 bar. Comparison of various sample thicknesses and visible microscopy observations on bulk aged samples shows that the whole oxidized layer has a depth of about 75 μm at 240°C, 138 μm at 210°C, and 229 μm at 180°C. An attempt was made to build a kinetic model to predict this depth. It is based on a differential equation in which O₂ diffusion and its consumption rate, r(C), are coupled, C being the O₂ concentration. Its resolution needs two sets of experiments: the first one to determine the O₂ diffusivity and solubility in the polymer, and the second one to determine r(C). The mathematical form of r(C) is derived from a mechanistic scheme of radical chain oxidation in which initiation is mainly due to POOH decomposition. This expression contains two kinetic parameters, α and β, the values of which are determined from the experimental curves of mass loss rate against O₂ pressure (in the stationary state). The theoretical predictions, at each temperature under consideration, are in excellent agreement with experimental results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3418–3430, 2001     

The oxidation of Fe(II) with Cu(II) in acidic sulfate solutions with air at elevated pressures

The oxidation of ferrous ions in acidic sulfate solutions in the presence of cupric ions at elevated air pressures was investigated in a high-intensity gas–liquid contactor. The study was required for the design of the regeneration steps of the novel Vitrisol^® desulphurization process. The effects of the Fe²⁺ concentration, Cu²⁺ concentration, Fe³⁺ concentration, initial H₂SO₄ concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, i.e., T?=?50?°C, 70?°C, and 90?°C. Most of the experiments were determined to be affected by the mass transfer of oxygen, and therefore true intrinsic kinetics could not be fully determined. An increase in Fe²⁺ and Cu²⁺ concentrations, as well as the partial pressure of oxygen and temperature, increased the Fe²⁺ oxidation rate. H₂SO₄ did not influence the Fe²⁺ oxidation rate. An increase in Fe³⁺ concentration decreased the Fe²⁺ oxidation rate. Although determined from experiments partially affected by mass transfer, a first order of reaction in Fe²⁺ was observed, fractional orders in both Cu²⁺ and O₂ were measured, a zero order in H₂SO₄ was determined, and a negative, fractional order in Fe³⁺ was obtained. The activation energy was estimated to be 31.3?kJ/mol.     

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV‐C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H₂O₂ /UV − C oxidation and (3) sequential application of ozonation followed by H₂O₂ /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, f_B. The successive treatment combination, where a preliminary ozonation step was carried out prior to H₂O₂ /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H₂O₂ /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H₂O₂ /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (f_B) was more pronounced for the biologically pretreated wastewater with an almost two‐fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H₂O₂ /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (k_app), and the second order OH· formation rates (r_i) have been calculated. © 2001 Society of Chemical Industry     

Effect of char gasification reaction order on bounding solutions for char combustion

The rate of oxidation and surface temperature of a char particle during combustion is determined by the combined action of reactions of carbon with oxygen and CO₂ at the surface and carbon monoxide with O₂ in the gas phase. Limiting values for the rates and temperature were determined by Amundson et al. assuming that the CO₂ and CCO₂ reactions were first order with respect to the gas reactant concentration. Results are presented here for the cases in which the CO₂ reaction is zeroth order and the CCO₂ reaction is both first and zero order to bound the reaction orders found in practice. Allowance for zeroth order kinetics is found to have a profound effect on the shape of the bounding solutions for burning rates and temperatures, most notably by showing that diffusion-limited combustion can occur at much lower temperatur than would be predicted using first order kinetics.     

Oxalate Ion Decomposition under UV Light from Low Pressure Mercury Vapor Lamps

Kinetics of oxalate ion decomposition under UV light from low pressure mercury vapor lamps (LPMVL) was studied in a batch reactor. The effects of UV light intensity (1.38×10^?6 to 5.27×10^?6 EL^?1s^?1, where E: Einstein or 1 mole of photons), temperature (15?35°C), initial oxalate concentration ((2.05?21.1)?×?10^?5 M), initial pH (5.45?8.94) and alkalinity (0–50 mg L^?1 as CaCO₃) on the photodecomposition kinetics of oxalate in de-ionized water were investigated. Oxalate decay followed split-rate pseudo-first-order kinetics. The decay rate constants decreased with increasing initial oxalate concentration, initial pH, alkalinity and temperature, but increased with UV light intensity. Solution pH increased during oxalate decomposition and reached a plateau as oxalate reached the analytical detection limit in de-ionized water. Addition of carbonate alkalinity virtually eliminated the pH profile. Time-dependent profiles for non-purgeable organic carbon (NPOC) and total carbon (TC) showed that the carbon not accounted for in NPOC is likely to have been converted to CO₂. The pH profile of oxalate decay was estimated using closed system carbonate equilibrium analysis. The dissolved oxygen (DO) utilization during oxalate decay ranged between 0.3–0.8 mol O₂ / mol oxalate. The effect of DO and the decay of natural dissolved organic carbon (DOC) were also explored. Natural DOC retarded oxalate photodecomposition. The decay rate constants were slightly lower in the absence of DO.     

Oxidation of a coal particle in flow of a supercritical aqueous fluid

A study was made of the conversion of single spherical coal particles of diameter 1–5 mm in a supercritical H₂O/O₂ fluid with an oxygen mass fraction of 0–6.6% in a semibatch reactor at a pressure of 30 MPa and a temperature of 673–1023 K. A decrease in the particle mass was observed in two parallel processes: gasification of coal with water and oxidation of coal with oxygen. An activation energy 19 ± 7 kJ/mole and a pre-exponential factor 10^−2±0.4 sec⁻¹ were obtained under the assumption of zero order for the concentration H₂O and an Arrhenius dependence for the rate of gasification with water. The oxidation with oxygen at a temperature above 780 K was found to be limited by the rate of O₂ diffusion to the coal organic matter. Below 780 K, the rate of heterogeneous oxidation with oxygen is described by a first-order reaction for the concentration of O₂ and a zero-order reaction for the concentration of H₂O with an activation energy of 150 ± 27 kJ/mole and a pre-exponential factor of 10^7.6±1.9 cm³/(g · sec). __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 23–31, March–April, 2008.     

Effect of composition on rheological behavior of iron oxides produced by hydrothermal method

The aim of the present work was to investigate the rheological properties of different iron oxides (Fe₃O₄, NiFe₂O₄, ZnFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄) aqueous suspensions. The oxides were produced through mixing the respective metallic sulfates within a closed isothermal reactor at 100 °C and at pH ≈12, in an oxidant environment (provided by H₂O₂ 0.63% w/v). The reactor was coupled with an adequate real-time data (RTD) acquisition system enabling measurement of temperature, pH and pressure. Obtained RTD data showed that once the isothermal conditions are reached, the pressure slowly decreases over time, which is a result of O₂ consumption through oxidation of Fe²⁺ to Fe³⁺. To characterize the suspensions as a function of temperature and shear rate, the steady rheology was used. The results revealed that the effect of temperature on viscosity of all suspensions was insignificant while steady rheology showed pseudoplastic behavior for all ferrites. The magnitude of viscosity and pseudoplasticity turned out to be in agreement with the hydrodynamic diameters of particles complying with the order: NiFe₂O₄>Fe₃O₄>Ni_0.5Zn_0.5Fe₂O₄>ZnFe₂O₄. Finally, the rheological behavior of suspensions was attributed to the concentration of OH groups on the surface of particles and this hypothesis was effectively supported by DRX, FTIR and TGA/DTA measurements.     

A study of the electrochemical behavior of hematoxylin as an important bioactive flavonoid

The electrochemical oxidation of hematoxylin, as an important biological molecule, was studied using cyclic voltammetry. In this study, the effect of different parameters such as pH, hematoxylin concentration, and time window of the chosen electrochemical method has been used for understanding the oxidation mechanism of hematoxylin. The results show that the oxidation mechanism of hematoxylin is an E_rC_iE_r mechanism. Also, the experimental data indicate that, in acidic and basic pHs, the rate of the subsequent chemical reaction is less than neutral pH. It is supposed that the subsequent chemical reaction of dimerization is more likely for the oxidation form of hematoxylin and hydroxylation, and intramolecular reactions cannot be considered as coupled chemical reactions. Finally, it is concluded that, in the dimerization process, hematoxylin reacts as a nucleophile with the o-quinone ring formed through the electrooxidation of hematoxylin and produces a dimer compound.     

Response behaviour of oxygen sensing solid electrolytes

The response time (t _r) after a step change in oxygen partial pressure was investigated for some solid electrolytes used in Nernst type oxygen sensors. The electrolyte as well as the (porous) electrode material affect the value oft _r. Stabilized Bi₂O₃ materials exhibit slower response rates (largert _r values) than stabilized ZrO₂. Introduction of Bi₂O₃ in stabilized ZrO₂ increases the response time. Gold electrodes show a higher response rate than platinum in the oxygen partial pressure and temperature region used.     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

Development of a model for the anodic behavior of T60 titanium in chlorinated and oxygenated aqueous media. Application to the specific conditions of hydrothermal oxidation (1 MPa<pressure<30 MPa, 20 °C<temperature<400 °C)

This work evaluates the anodic electrochemical behavior of titanium metal in hydrothermal oxidation conditions (up to 400 °C and 28 MPa) in chlorinated media in order to estimate the supercritical water oxidation reactors reliability for the treatment of less than 10% organic-waste waters. The titanium room temperature dissolution mechanism in chlorinated acidic medium (pH<0) is not fundamentally modified by oxygen. Deduced from the ‘current-potential’ and ‘valence-potential’ curves, it is based on four crucial elementary steps leading to two branches: a so-called active branch corresponding to a trivalent dissolution (its effect is inversely proportional to the pH), and a passive branch (TiO₂ oxide formation with a very limited tetravalent dissolution). In hydrothermal oxidation (pH>1), only the second branch is effective. The titanium protection is directly related to the oxide stability in high pH systems. The mechanism model is expressed in terms of ‘current-potential’ laws, which provide kinetic parameters using optimization calculations. The different elementary steps reaction rates were estimated as well as the evolution of the reaction intermediates coverage ratios with the potential. The quantification of each elementary step was performed to understand and/or orient the materials behavior according to different factors (pH, chloride ions contents, potentials…).     

Oxygen transport through dense BaBi0.05Sc0.1Co0.85O3−δ ceramic membrane

Novel dense perovskite BaBi_0.05Sc_0.1Co_0.85O_3−δ (BBSC) membranes showed promising flux performance to separate oxygen from air. The oxygen transport through BBSC in discs and hollow fibres geometry were modelled as a function of oxygen partial pressure in the permeate side and temperature using simple correlations. The oxygen diffusion (D_O) and surface exchange (k_S) coefficients and also the characteristic thickness (L_C) were extracted from the series of flux data based on disc membranes. Employing the obtained oxygen diffusion coefficient, the surface exchange coefficients (k_f and k_r) for the hollow fibre geometry can then be obtained from another tubular correlation by fitting with flux data based on hollow fibre membranes. The physical importance of the parameters (i.e. D_O, k_S, L_C, k_f and k_r) was discussed. The effects of controllable variables, i.e. temperature and oxygen partial pressure, in the permeate side onto oxygen flux performance were also elaborated.