Enhancement of oxygen transfer by pressure pulsation in aqueous glycerol fermentation

Aeration plays an important role in the production of glycerol by fermentation with yeast. Effective aeration depends on a number of factors, such as amount of air, fineness of air dispersion, rate of agitation, and time of gasliquid contact. This investigation dealt with the effect of periodic variation in gas pressure on oxygen transfer measured by sulfite oxidation and glycerol fermentation in stirred tanks. The oxygen transfer rate measured with the sulfite oxidation method was improved by 20–30% under the condition of pressure pulsation (PP) at 30°C. The yield and productivity of glycerol were increased by about 26 and 6.8%, respectively, in 48 h by employing a glucose concentration of 250 g/L with PP at 30°C.     

Effects of Oxygen Limitation on Xylose Fermentation, Intracellular Metabolites, and Key Enzymes of Neurospora crassa AS3.1602

The effects of oxygen limitation on xylose fermentation of Neurospora crassa AS3.1602 were studied using batch cultures. The maximum yield of ethanol was 0.34 g/g at oxygen transfer rate (OTR) of 8.4 mmol/L·h. The maximum yield of xylitol was 0.33 g/g at OTR of 5.1 mmol/L·h. Oxygen limitation greatly affected mycelia growth and xylitol and ethanol productions. The specific growth rate (μ) decreased 82% from 0.045 to 0.008 h⁻¹ when OTR changed from 12.6 to 8.4 mmol/L·h. Intracellular metabolites of the pentose phosphate pathway, glycolysis, and tricarboxylic acid cycle were determined at various OTRs. Concentrations of most intracellular metabolites decreased with the increase in oxygen limitation. Intracellular enzyme activities of xylose reductase, xylitol dehydrogenase, and xylulokinase, the first three enzymes in xylose metabolic pathway, decreased with the increase in oxygen limitation, resulting in the decreased xylose uptake rate. Under all tested conditions, transaldolase and transketolase activities always maintained at low levels, indicating a great control on xylose metabolism. The enzyme of glucose-6-phosphate dehydrogenase played a major role in NADPH regeneration, and its activity decreased remarkably with the increase in oxygen limitation.     

A quantum chemical approach to the mechanism of the biochemical action of nicotinamide

The reaction of protonated nicotinamide with hydride ion, which models the transfer of hydrogen from a substrate to the nicotinamideadeninedinucleotide (NAD⁺) molecule, i.e., the principal biological function of vitamin PP, was investigated by optimization of the geometry in terms of the self-consistent field (SCF) method with allowance for configuration interaction (CI) in the PM-3 approximation. It was shown that the initial event of the reaction is electron transfer, followed by the addition of a hydrogen atom to the NAD radical. The addition product is relatively stable and has a heat of formation of −68.25 kJ/mol. The geometric structure and the distribution of charges of the reagent and also the behavior of the singlet and triplet terms in the course of the reaction were analyzed. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, pp. 277–283, September–October, 1999.     

Virus rejection with two model human enteric viruses in membrane bioreactor system

A membrane bioreactor (MBR) with gravity drain was tested for virus rejection with two coliphages, T4 and f2, which were used as surrogates for human enteric viruses. Virus rejection was investigated by PVDF and PP membrane modules, with the pore sizes of 0.22 and 0.1 μm, respectively. In tap water system, 2.1 lg rejection of coliphage T4 could be achieved by PVDF membrane compared with complete rejection by PP membrane, while for coliphage f2 with smaller diameter, 0.3―0.5 lg rejection of the influent virus was removed by the two membranes. In domestic wastewater system, cake layer and gel layer on the membrane surface changed the cut-off size of the membrane so that there was no significant difference between PP and PVDF for each coliphage. The removal ratios of coliphage T4 and f2 in the MBR were more than 5.5 and 3.0 lg, respectively. Compared with 5.5 lg removal for virus T4 in the MBR system, only 2.1 lg (96.8%―99.9%) removal rate was observed in the conventional activated sludge system with the influent virus concentration fluctuating from 1830 to 57000 PFU/mL. Only 0.8%―22% virus removal was the effect of adsorption to activated sludge, which showed a decreasing tendency with the retention time, while 75%―98% was the effect of virus inactivation by microbial activity. It indicated that the major mechanism of virus removal was not the transfer of viruses from the water phase to the sludge phase but inactivation in the biological treatment process.     

Photofragmentation of a benzophenone derivative having benzylic C–O bond studied by laser flash photolysis in solution

Photochemical profiles of p-(4-phenylphenoxy)methylbenzophenone (PPMeBP) in solution were investigated by means of emission and transient absorption measurements. PPMeBP showed that fluorescence originating from the corresponding p-phenylphenoxy (PP) moiety at 295 K, and dual phosphorescence originating from the corresponding p-benzoylbenzyl (BB) and PP moieties at 77 K was observed. These observations indicated that the BB and PP moieties of PPMeBP have very little electronic conjugation. 266- and 308-nm laser flash photolyses of PPMeBP showed the formation of the p-phenylphenoxy radical, indicating that photoexcited PPMeBP undergoes C–O bond cleavage. Upon 355-nm laser photolysis of PPMeBP, the C–O bond did not dissociate, and formation of the triplet state of the PP moiety was observed. The apparent quantum yields of fragmentation of PPMeBP were found to depend on the excitation wavelength. Triplet sensitization of PPMeBP using benzophenone revealed that the C–O bond does not cleave in the triplet state of the PP moiety. Based on the schematic energy diagram for excited PPMeBP, the mechanism of the C–O bond was discussed.     

Magnetic field effects on microstructural variation of electrodeposited cobalt films

The electrodeposition process of Co films in a sulfuric acid solution was examined in a magnetic field (0–5 T). The surface morphology of Co films electrodeposited without a magnetic field was drastically modified with the variation of hydrogen gas evolution rate. Crystalline α-Co was formed in the range of pH = 1.5–6.0, while β-Co was not observed. When the magnetic field was superimposed perpendicular to the electric field in the acidic solution (pH = 1.5), the hydrogen evolution rate was promoted by MHD convection, which enhanced the ionic mass transfer (H⁺ and Co²⁺) near the electrode surface. Moreover, crystalline β-Co was formed simultaneously with the appearance of the elongated ridge-shape precipitates under a higher magnetic field (≥3 T). Contribution to special issue “Magnetic field effects in Electrochemistry”     

Transmission of N Atoms Through PP Membranes for Nitrogen Flowing Post Discharge Sterilisation Processes

This work reports on the results of investigations conducted with three layered polypropylene (PP) membranes which were exposed to a N₂ flowing microwave (100 W) post discharge, at several flow rates (0.03–1 Slm) and at gas pressure from 0.3 to 40 Torr. The N atoms transmission through the membrane was measured from the intensity variation of the N₂, 580 nm afterglow which is related to N atom density, before and after the membranes. The results obtained showed that N-atoms penetrate and cross the membranes with a transmission factor (T _N) varying from 20 to 70% during the exposure time (15 min), depending on flow rate and gas pressure. A maximum value T _N = 0.7 (±0.05) is found for sufficient low flow rate (less than 0.1 Slm), that is for low flow gas velocity (about 2 × 10² cm s⁻¹).     

Morphology, crystallization behavior and properties of impact-modified polypropylene copolymer with or without sodium benzoate as a nucleating agent

 The morphology, crystallization behavior, and properties of an impact-modified polypropylene (PP) copolymer with or without sodium benzoate were investigated. The contents of ethylene–propylene rubber (EPR) in the reactor-made PP copolymer is about 15 wt%. For comparison, blends of PP and EPR containing the same EPR composition were prepared by melt-mixing. Morphological studies by scanning probe microscopy indicated that the impact-modified copolymer consists of three different phases, i.e., polyethylene, PP, and EPR phases, which is considerably different from the morphology of the conventional PP/EPR blend of the corresponding composition. The impact-modified PP copolymer exhibited a higher crystallization rate in terms of the lower crystallization half-time and thus higher thermal and mechanical properties, such as impact strength and hardness, than the PP/EPR blend did. The addition of sodium benzoate as a nucleating agent to the copolymer increased the crystallization rate and the mechanical properties. Received: 4 June 2001 Accepted: 31 October 2001     

The Dependence of Gliding Arc Gas Discharge Characteristics on Reactor Geometrical Configuration

The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments.     

Electron Transfer Dissociation (ETD) of Peptides Containing Intrachain Disulfide Bonds

The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z + 33 Da, c + 32 Da, and z–32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N–Cα backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N–Cα bond was cleaved first, and radical-driven reactions caused cleavage at either an S–S bond or an S–C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%–100% of possible backbone fragmentation.     

Evaluation of <Superscript>137</Superscript>Cs soil-to-plant transfer: Natural and model experiments

Soil and meadow grass were sampled in the whole territory of Lithuania in 1992–2000. For the laboratory experiment, spring wheat Triticum aestivum L. “Nandu” was used because its root system type is similar to that of perennial meadow grass. The ¹³⁷Cs soil-to-plant transfer factor of spring wheat was determined and the results were compared with the predicted values using a compartment model of soil-to-plant transfer and with the results of the field experiment. The results of comparing the measured and calculated transfer factor using the model show rather good coincidence, however, the calculated values were overestimated. The reason for overestimation can be that the uptake rate is not influenced only by the soil-to-plant transfer. The results of the model experiment (from 0.005 m²·kg⁻¹ to 0.053 m²·kg⁻¹) are close to those of the field measurements for grass (from 0.013 m²·kg⁻¹ in 1992–1995 to 0.10 m²·kg⁻¹ in 1999–2000).     

Steam reforming of dimethyl ether to hydrogen-rich gas

The steam reforming of dimethyl ether (DME) (SR) to a hydrogen-rich gas over a mechanical mixture of WO_x/ZrO₂ (the DME hydration catalyst) and CuZnAlO_x (the methanol SR catalyst) was studied. The mechanically mixed catalyst was shown to provide almost complete conversion of DME to the hydrogen-rich gas containing <0.5 vol.% of CO at 300°C, atmospheric pressure, gas hourly space velocity (GHSV) of 10000 h⁻¹ and molar ratio H₂O/DME = 3. The hydrogen production rate in DME SR was found to reach 180–250 mmol H₂/(g_cat·h) at 250–300°C.     

Multi-component analysis of tetracyclines, sulfonamides and tylosin in swine manure by liquid chromatography–tandem mass spectrometry

A multi-component method focussing on thorough sample preparation has been developed for simultaneous analysis of swine manure for three classes of antibiotic—tetracyclines, sulfonamides, and tylosin. Liquid manure was initially freeze-dried and homogenised by pulverization before extraction by pressurised liquid extraction. The extraction was performed at 75°C and 2,500 psig in three steps using two cycles with 0.2 mol L⁻¹ citric acid buffer (pH 4.7) and one cycle with a mixture of 80% methanol with 0.2 mol L⁻¹ citric acid (pH 3). After liquid–liquid extraction with heptane to remove lipids, the pH of the manure was adjusted to 3 with formic acid and the sample was vacuum-filtered through 0.6 μm glass-fibre filters. Finally the samples were pre-concentrated by tandem SPE (SAX-HLB). Recoveries were determined for manure samples spiked at three concentrations (50–5,000 μg kg⁻¹ dry matter); quantification was achieved by matrix-matched calibration. Recoveries were >70% except for oxytetracycline (42–54%), sulfadiazine (59–73%), and tylosin (9–35%) and did not vary with concentration or from day-to-day. Limits of quantification (LOQ) for all compounds, determined as a signal-to-noise ratio of 10, were in the range 10–100 μg kg⁻¹ dry matter. The suitability of the method was assessed by analysis of swine manure samples from six different pig-production sites, e.g. finishing pigs, sows, or mixed production. Residues of antibiotics were detected in all samples. The largest amounts were found for tetracyclines (up to 30 mg kg⁻¹ dry matter for the sum of CTC and ECTC). Sulfonamides were detected at concentrations up to 2 mg kg⁻¹ dry matter (SDZ); tylosin was not detected in any samples.      

Continuous dynamic-gravimetric preparation of calibration gas mixtures for air pollution measurements

 The preparation of calibration gas mixtures for air pollution measurements by the dynamic-gravimetric method was investigated using sulphur dioxide in nitrogen as a model. The target mole fraction was 200×10^–9 mol/mol, with the option of also getting smaller mole fractions. Thermal mass flow meters calibrated with reference mass flows were used to measure the dilution gas flow (nitrogen). The relative standard uncertainty of the dilution gas flows between 10 mg/s (approx. 500 ml/min) and 40 mg/s (approx. 2000 ml/min) was 0.15%. The mass flow of the target component measured as the permeation rate was determined via the quasi-continuous observation of the loss in the permeation tube mass during the measuring time. A magnetic coupling system and an adapted microbalance were used for this purpose. The results presented show permeation rates measured over the lifetime of a tubular permeation source. The measurement cycles took between 3 days and 7 h at least. The relative standard uncertainty of the mixture composition did not exceed 2%. First comparisons with gas mixtures prepared by the static-gravimetric method show compatibility. The applicability of the system is not restricted to the SO₂/N₂ mixture. It can also be used for preparing other gas mixtures in this field of application. Received: 26 April 2000 / Accepted: 12 September 2000     

Capillary electrophoresis-atmospheric pressure chemical ionization-mass spectrometry using an orthogonal interface: Set-up and system parameters

The feasibility of atmospheric pressure chemical ionization (APCI) as an alternative ionization technique for capillary electrophoresis-mass spectrometry (CE-MS) was investigated using a grounded sheath-flow CE-MS sprayer and an orthogonal APCI source. Infusion experiments indicated that highest analyte signals were achieved when the sprayer tip was in close vicinity of the vaporizer entrance. The APCI-MS set-up enabled detection of basic, neutral, and acidic compounds, whereas apolar and ionic compounds could not be detected. In the positive ion mode, analytes could be detected in the entire transfer voltage range (0–5 kV), whereas highest signal intensities were observed when the corona discharge current was between 1000 and 2000 nA. In the negative ion mode, the transfer voltage typically was 500 V and the optimum corona discharge current was 6000 nA. Analyte signals were raised with increasing nebulizing gas pressure, but the pressure was limited to 25 psi to avoid siphoning and current drops. Signal intensities appeared to be optimal and constant over a wide range of sheath liquid flow rate (5–25 μL/min) and vaporizer temperature (200–350 °C). APCI-MS signals were unaffected by the composition of the background electrolyte (BGE), even when it contained sodium phosphate and sodium dodecyl sulfate (SDS). Consequently, BGE composition, sheath-liquid flow rate, and vaporizer temperature can be optimized with respect to the CE separation without affecting the APCI-MS response. The analysis of a mixture of basic compounds and a steroid using volatile and nonvolatile BGEs further demonstrates the feasibility of CE-APCI-MS. Detection limits (S/N = 3) were 1. 6–10 μM injected concentrations.     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols at Ni(II)–quercetin complex modified multi-wall carbon nanotube paste electrode

A modified electrode Ni(II)–Qu–MWCNT-PE has been fabricated by electrodepositing nickel(II)–quercetin [Ni(II)–Qu] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. Ni(II)–Qu–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–MWCNT-PE and Ni(II)–Qu-carbon paste electrode. It also shows electrocatalytic activity toward the oxidation of methanol and other short chain aliphatic alcohols, such as ethanol, 1-propanol, and 1-butanol. The catalytic peak current and peak potential decrease in exponential form with the increase of carbon number of the chains. Kinetic parameters such as the electron transfer coefficient, α, rate constant, k _s, of the electrode reaction, and the catalytic rate constant, k _cat, for oxidation of methanol are determined. The stability and reproducibility of the Ni(II)–Qu–MWCNT-PE are good for practical applications.     

Extraction studies of plutonium from acidic solution using γ-ray induced PC-88A/TBP modified polymers

2-Ethylhexyl-2-ethylhexyl phosphonic acid (PC-88A) and Tributylphosphate (TBP) extractants have been attached to polypropylene (PP) in granular, film and non-woven fabric forms, by a simultaneous γ-ray irradiation method. The extraction of plutonium from the acidic radioactive liquid waste by modified polymers was studied by varying the γ-ray dose. The uptake of plutonium was also studied by polyethylene (PE) in film form. This modified polymer also showed extraction capability for plutonium from nitric acid medium. The uptake of plutonium depends upon the γ-ray dose as well as the nature and source of the polymer. Liquid–solid extraction studies showed that the equivalent amount of uptake of plutonium on TBP–polyethylene film requires twice the γ-ray dose as compare to TBP–polypropylene film. It was observed that at given γ-ray dose polypropylene fabric is not sturdy, compare to the granules and films, and material leach out in aqueous phase. The presence of other solvents like di-methyl formamide (DMF) and cyclohexane during γ-ray irradiation were able to enhance the extraction capabilities. The optimum conditions established during this study was successfully applied for the separation of plutonium, uranium and thorium from the fission products in acidic waste solution.     

Mesophilic Digestion Kinetics of Manure Slurry

Anaerobic digestion kinetics study of cow manure was performed at 35°C in bench-scale gas-lift digesters (3.78 l working volume) at eight different volatile solids (VS) loading rates in the range of 1.11–5.87 g l⁻¹ day⁻¹. The digesters produced methane at the rates of 0.44–1.18 l l⁻¹ day⁻¹, and the methane content of the biogas was found to increase with longer hydraulic retention time (HRT). Based on the experimental observations, the ultimate methane yield and the specific methane productivity were estimated to be 0.42 l CH₄ (g VS loaded)^–1 and 0.45 l CH₄ (g VS consumed)^–1, respectively. Total and dissolved chemical oxygen demand (COD) consumptions were calculated to be 59–17% and 78–43% at 24.4–4.6 days HRTs, respectively. Maximum concentration of volatile fatty acids in the effluent was observed as 0.7 g l^–1 at 4.6 days HRT, while it was below detection limit at HRTs longer than 11 days. The observed methane production rate did not compare well with the predictions of Chen and Hashimoto’s [1] and Hill’s [2] models using their recommended kinetic parameters. However, under the studied experimental conditions, the predictions of Chen and Hashimoto’s [1] model compared better to the observed data than that of Hill’s [2] model. The nonlinear regression analysis of the experimental data was performed using a derived methane production rate model, for a completely mixed anaerobic digester, involving Contois kinetics [3] with endogenous decay. The best fit values for the maximum specific growth rate (μ _m) and dimensionless kinetic parameter (K) were estimated as 0.43 day^–1 and 0.89, respectively. The experimental data were found to be within 95% confidence interval of the prediction of the derived methane production rate model with the sum of residual squared error as 0.02.     

Artificial neural network for the evaluation of CO2 corrosion in a pipeline steel

This paper presents a predictive model for the determination of different types of corrosion by using electrochemical impedance spectroscopy curves and artificial neural network. This proposed model obtains predictions for three different types of corrosion by using Nyquist impedance curves from four input variables: inhibitor concentration, time of exposure, and the real and imaginary experimental component of these curves. The model takes into account the variations of inhibitor concentration over steel to decrease the corrosion rate. For the network, the Levenberg–Marquardt learning algorithm, the hyperbolic tangent sigmoid transfer function and the linear transfer function were used. The best fitting training data set was obtained with five neurons in the hidden layer, which made possible to predict satisfactory efficiency (R > 0.99). On the validation of the data set, simulations and theoretical data tests were in good agreement (R > 0.9905). The developed model can be used for the determination of the type of curves related to the nature phenomena and rate of corrosion at the metal surface.     

Evaluation and application of argon and helium microstrip plasma for the determination of mercury by the cold vapor technique and optical emission spectrometry

The suitability of a 2.45-GHz atmospheric pressure, low-power microwave microstrip plasma (MSP) operated with Ar and He for the determination of Hg by continuous-flow cold vapor (CV) generation, using SnCl₂/HCl as the reducing agent, and optical emission spectrometry (OES) using a small CCD spectrometer was studied. The areas of stability for a discharge in the Ar and in the He MSP enclosed in a cylindrical channel in a quartz wafer were investigated. The excitation temperatures as measured for discharge gas atoms (Ar I, He I), and the electron number densities at 35–40 W and 15–400 mL min⁻¹ were found to be at the order of 3,200–5,500 K and 0.8 × 10¹⁴–1.6 × 10¹⁴ cm⁻³, respectively. The relative intensity of the Hg I 253.6-nm line and the signal-to-background ratio as a function of the forward power (35–40 W) as well as of the flow rate of the working gas (15–400 mL min⁻¹) were evaluated and discussed. For the selected measurement conditions, the Ar MSP was established to have the lower detection limit for Hg (0.6 ng mL⁻¹) compared with the He MSP. The linearity range is up to 300 ng mL⁻¹ and the precision is on the order of 1–3%. With the optimized CV Ar MSP-OES method a determination of Hg in spiked domestic and natural waters at concentration levels of 20–100 μg L⁻¹ and an accuracy of 1–4% could be performed. In an NIST domestic sludge standard reference material, Hg (3.64 μg g⁻¹) could be determined with a relative standard deviation of 4% and an agreement better than 4%.