Utilization of cheese whey lactose by kluyveromyces fragilis for energy and growth under continuous fermentation

A heat balance was performed on a 25 L jacketed continuous stirred tank reactor used for the production of single cell protein from cheese whey usingKluyveromyces fragilis under three levels of retention time (12, 18, and 24 h), two levels of air flow rate (1 and 3 VVM), and three levels of mixing speed (200, 400, and 600 RPM) to determine the heat of reaction and the portions of lactose used for energy and growth as well as to assess the need for the cooling system. The yeast population size, oxygen concentration, and lactose concentration in the reactor as well as the portions of lactose used for energy and growth were all affected by the hydraulic retention time, mixing speed, and air flow rate. About 8-14% of lactose was utilized for energy and 86-92% was utilized for growth. The highest cell number was obtained at the 12 h retention time, 3 VVM air flow rate, and 600 RPM mixing speed. Under these conditions, the lactose removal efficiency was 95.6% and the yeast yield was 0.78 g cell/g lactose removed.     

Effect of the variation of the level of lactose conversion in an immobilized lactase reactor upon operating costs for the production of baker’s yeast from hydrolyzed cottage cheese whey permeate

Operating costs for the production of Baker’s yeast from hydrolyzed permeate from the ultrafiltration of cottage cheese whey were calculated as a function of the level of lactose conversion in the immobilized lactase reactor. These costs were calculated for the case of 90% conversion of lactose in the reactor and compared to those that result when running the reactor at lower conversions with recycle of unreacted lactose. Total operating costs were estimated by combining individual operating costs for the immobilized enzyme reactor, costs associated with processing a lactose recycle stream, and energy costs associated with cooling the reactor feed stream and sterilizing the hydrolysate stream. It was determined that operating costs are minimized at about 9.9 ￠/lb. of lactose when the reactor is run at approx. 72% conversion. This represents a savings of 2.4 ￠/lb. of lactose over the case of a once-through 90% conversion of lactose in the reactor.     

A mathematical model of ethanol fermentation from cheese whey

The cybernetic approach to modeling of microbial kinetics in a mixedsubstrate environment has been used in this work for the fermentative production of ethanol from cheese whey. In this system, the cells grow on multiple substrates and generate metabolic energy during product formation. This article deals with the development of a mathematical model in which the concept of cell maintenance was modified in light of the specific nature of product formation. Continuous culture data for anaerobic production of ethanol byKluyveromyces marxianus CBS 397 on glucose and lactose were used to estimate the kinetic parameters for subsequent use in predicting the behavior of microbial growth and product formation in new situations.     

Amorphization of Silicon during Mechanical Treatment of Its Powders: 2. Heats of Recrystallization

Exothermic effects arising during silicon powder heating after their mechanical treatment were measured by synchronous TG–DSC thermal analysis method. Silicon samples possessed semicrystalline structure. As temperature varied from room temperature to 1200°C at a rate of 10 and 50 deg/min, the heat was released in the range 550–800°C. The crystallization of amorphous phase was also observed in the same temperature range using the X-ray diffraction. As the amount of energy consumed during the mechanical treatment of powders increased, the value of the heat effect rose synchronously with the degree of amorphization. In this case, the ratio of the released heat to the content of X-ray amorphous phase was constant and equal to 6 ± 2 kJ/mol.     

Study of the Enzymatic Activity of Arthrobacter ureafaciens Neuraminidase by Isothermal Titration Calorimetry

Isothermal titration calorimetry was used to determine the enzymatic activity and thermodynamic activation parameters of Arthrobacter ureafaciens sialidase with the sialyl substrates α‐2,3‐, α‐2,6‐sialyllactoses and α‐2,8‐sialic acid dimer. By monitoring the heat released during hydrolysis, the Michaelis constant (K_m), catalytic rate constant (k_cat), activation energy, activation Gibbs energy, enthalpy, and entropy for different monovalent sialyl conjugates were calculated and found to be consistent with those derived by chromatographic or colorimetric assays. The observed decreases in the activation energy and transition entropy of sialyllactoses were larger than the Michaelis activation parameters of lactose‐free di‐sialic acid because of the specific enzyme activity of A. ureafaciens sialidase.     

Some engineering parameters for Propionic acid fermentation coupled with Ultrafiltration

The effect of circulation rate on permeate flux, the energy requirements for heating or cooling, the reactor homogeneity, and cell activity are discussed for a continuous culture system with cell recycle. The fermentation system was a continuous stirred-tank reactor with an ultrafiltration membrane unit for cell recycle. The membranes have a tubular configuration and are composed of a carbon support coated with zirconium oxide. The permeate flux obtained for a long-run fermentation with Propionibacterium acidi-propionici was higher when the circulation rate was increased: 5.13 L/m²-h for a circulation rate of 0.810 m³/h and 7.09 L/m²-h for 1.104 m³/h. The temperature rise inside the fermenter for different circulation rates was studied, allowing determination of the need of input or output of energy for temperature control. Residence time distribution studies showed that, with a circulation rate of 0.606 m³/h, the dead volume was 9.2%, whereas at 1.104 m³/h the reactor behavior was almost ideal. The influence of the circulation rate on loss of cell activity is also discussed, and rheological studies are suggested as an indirect indicator of cell viability. We hereby express our recognition for the ongoing collaborations with James Gaddy (University of Arkansas) and Gerard Goma (INSA, Toulouse, France).     

Designing A Reactor to Generate Hydrogen Bubbles

Hydrogen is produced by the reaction between zinc and hydrochloric acid. This reaction is used to illustrate the importance of considering thermodynamics when designing a chemical reactor. The gas released is collected in soap bubbles that rise in the air, indicating that a lighter than air gas has been produced. The bubbles can be lit to add a dramatic effect to the demonstration. The reaction is highly exothermic, raising the temperature of the reaction materials and the reactor. Batch operation of this reactor would require short cooling periods between reactions. Alternatively, a modification of the design is suggested to allow for continuous cooling of the vessel, which would allow semicontinuous operation of the reactor. (Zinc would have to be periodically replenished as it is consumed in the reaction.) The consequences associated with the cooling of the vessel are discussed.     

Microbial conversion of 4-oxoisophorone by thermomonospora curvata using an air-bubbling hollow fiber reactor

Microbial conversion of 4-oxoisophorone (OIP) by thermophilic bacteriumThermomonospora curvata was attempted in a continuous process. The correlation between cell growth and microbial conversion was first examined in a batch culture. The results indicated that this microbial conversion was strongly dependent upon cell growth. In a continuous microbial conversion of OIP using a continuous stirred tank reactor, the cell density in the reactor seemed to be the limiting factor in the OIP conversion. Therefore, we developed an air-bubbling hollow fiber reactor to achieve a high density culture. By using this bioreactor, more than 3.3 times higher productivity was achieved. In addition, during the process, only a slight cell contamination to the product was observed. Therefore, this bioreactor is suitable for the continuous microbial conversion, considering further downstream processes and high productivity.     

Microcalorimetric study on the growth and metabolism of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Microcalorimetry is an experimental technique which allows us to precisely measure the energy released as a consequence of any transformation process. All organisms produce heat as a consequence of metabolism. The rate of heat production is an adequate measurement of metabolic activity of organisms and their constituent parts, cells and sub-cellular levels. Microorganisms produce small amounts of heat, in the order of 1–3 pW per cell. Despite the low quantity of heat produced by bacteria, their exponential replication in culture medium allows their detection using microcalorimetry. This study is a microcalorimetric study of the growth and metabolism of the bacterium Pseudomonas aeruginosa, using the heat liberated as a consequence of bacterial metabolism. With this aim, we used a Calvet microcalorimeter, inside which two Teflon screw-capped stainless steel cells were located (sample and reference). Experiments were carried out at final concentrations of 10⁶, 10⁵, 10³ and 10 CFU/mL, and a constant temperature of 309.65 K was maintained within the microcalorimeter. Recording the difference in calorific potential over time we obtained P. aeruginosa’s growth curves. The shape of these curves is characteristic and has a single phase. Thus, the heat flow curves were mathematically studied to calculate the growth constant and generation time of this bacterium.     

Comparison and validation of methods for estimating heat generation rate of large-format lithium-ion batteries

The heat generation rate of a large-format 25 Ah lithium-ion battery is studied through estimating each term of the Bernardi model. The term for the reversible heat is estimated from the entropy coefficient and compared with the result from the calorimetric method. The term for the irreversible heat is estimated from the intermittent current method, the V–I characteristics method and a newly developed energy method. Using the obtained heat generation rates, the average cell temperature rise under 1C charge/discharge is calculated and validated against the results measured in an accelerating rate calorimeter (ARC). It is found that the intermittent current method with an appropriate interval and the V–I characteristics method using a pouch cell yield close agreement, while the energy method is less accurate. A number of techniques are found to be effective in circumventing the difficulties encountered in estimating the heat generation rate for large-format lithium-ion batteries. A pouch cell, using the same electrode as the 25 Ah cell but with much reduced capacity (288 mAh), is employed to avoid the significant temperature rise in the V–I characteristics method. The first-order inertial system is utilized to correct the delay in the surface temperature rise relative to the internal heat generation. Twelve thermocouples are used to account for the temperature distribution.     

硝酸镧引起Escherichia coli B代谢过程热爆发及其机理研究

采用微量热法研究了硝酸镧对Escherichia coli B生长代谢过程的影响, 发现高浓度硝酸镧引起E. coli B热谱图出现异常变化: 生长速率常数k值增大、产热峰显著升高和总发热量异常增加. 当硝酸镧浓度为300和500 mg/L时, 培养物在培养过程的总发热量分别是正常条件下的3.89和2.54倍. 用生物学方法对细胞存活率和生物量进行测定结果表明, 细胞在高浓度硝酸镧条件下增殖受到抑制、细胞生物量减少. 表明高浓度的硝酸镧存在时, E. coli B细胞生长受到抑制反而释放出比正常生长细胞多得多的热量, 将抑制状态细胞释放大量热量的现象称为热爆发. 分析热爆发的原因, 认为是La^3＋离子破坏细胞壁外膜而增加其透性, 导致细胞膜与外膜间的质子电化学势因质子外泄而降低或者不能形成, 氧化磷酸化过程中的能量不能有效地转化为ATP, 而以热能的方式释放出来. 细胞由于缺乏生物通用能量ATP, 因而其生长受到抑制.     

含氮合成气在三相淤浆床-固定床中直接合成二甲醚

在三相淤浆床－固定床反应装置中,研究含氮合成气直接合成二甲醚。使用双功能混合催化剂,粒度为0.15 mm～0.18 mm。在220 ℃～260 ℃、3.0 MPa～7.0 MPa、空速1 000 mL·g-1·h-1时考察了温度、压力及两种反应器中催化剂的装填比例对CO转化率及二甲醚选择性的影响。结果表明,一氧化碳转化率随反应压力的增加而提高,随着温度升高二甲醚的选择性变化不大,CO转化率的升高较明显,因此在催化剂活性适宜的温度范围内,该反应装置可以采用较高的反应温度。当260 ℃、7.0 MPa、三相床与固定床中催化剂比例为1∶1时,CO的转化率可达84.5％,二甲醚的选择性为78.7％。淤浆床－固定床反应装置具有操作稳定性好、CO转化率高的优点。催化剂在该装置中反应370 h活性没有明显下降。     

Use of the clark oxygen sensor with immobilized enzymes for determinations in flow systems

A small-volume cell has been constructed for amperometric flow measurements with a Clark oxygen sensor and its performance was tested. The Clark sensor can be combined with immobilized enzymes for determination of substances after enzymatic conversion during which oxygen is consumed or released. Two enzymes, glucose oxidase and tyrosinase, were used and two measuring techniques, employing the enzyme immobilized on the Clark sensor membrane and with the enzyme bound on a support in a preceding reactor, were tested and compared. It was found that, in the given system, measurement with the enzyme immobilized on the sensor membrane has better sensitivity, precision and response rate.     

β-Galactosidase from <Emphasis Type="Italic">Penicillium canescens</Emphasis>. Properties and immobilization

β-galactosidase from Penicillium canescens was immobilized on chitosan, sepharose-4B, foamable polyurethane and some other carriers. The highest yield of immobilization (up to 98%) was obtained by using chitosan as a carrier. The optimum pH and temperature were not significantly altered by immobilization. High stability of immobilized β-galactosidase during storage was demonstrated. Efficient lactose saccharification (over 90%) in whey was achieved by using immobilized β-galactosidase.     

Production of ethanol from starch by co-immobilizedZymomonas mobilis-glucoamylase in a fluidized-bed reactor

The production of ethanol from starch was studied in a fluidized-bed reactor (FBR) using co-immobilizedZymomonas mobilis and glucoamylase. The FBR was a glass column of 2.54 cm in diameter and 120 cm in length. TheZ. mobilis and glucoamylase were co-immobilized within small uniform beads (1.2-2.5 mm diameter) of κ-carrageenan. The substrate for ethanol production was a soluble starch. Light steep water was used as the complex nutrient source. The experiments were performed at 35κC and pH range of 4.0-5.5. The substrate concentrations ranged from 40 to 185 g/L, and the feed rates from 10 to 37 mL/min. Under relaxed sterility conditions, the FBR was successfully operated for a period of 22 d, during which no contamination or structural failure of the biocatalyst beads was observed. Volumetric productivity as high as 38 g ethanol/(Lh), which was 74% of the maximum expected value, was obtained. Typical ethanol volumetric productivity was in the range of 15-20 g/(Lh). The average yield was 0.49 g ethanol/g substrate consumed, which was 90% of the theoretical yield. Very low levels of glucose were observed in the reactor, indicating that starch hydrolysis was the rate-limiting step.     

Modeling liquid thermal explosion reactor containing <Emphasis Type="Italic">tert</Emphasis>-butyl peroxybenzoate

This study investigated the role played by green thermal analysis technology in promoting the use of resources, preventing pollution, reducing energy consumption and protecting the environment. The chemical tert-butyl peroxybenzoate (TBPB) has been widely employed in the petrifaction industries as an initiator of polymerization formation agent. This study established the thermokinetic parameters and thermal explosion hazard for a reactor containing TBPB via differential scanning calorimetry (DSC). To simulate thermokinetic parameters, a 5-ton barrel reactor of liquid thermal explosion model was created in this study. The approach was to develop a precise and effective procedure on thermal decomposition, runaway, and thermal hazard properties, such as activation energy (E _a), control temperature (CT), critical temperature (TCR), emergency temperature (ET), heat of decomposition (∆H _d), self-accelerating decomposition temperature (SADT), time to conversion limit (TCL), total energy release (TER), time to maximum rate under isothermal condition (TMR _iso), etc. for a reactor containing TBPB. Experimental results established the features of thermal decomposition and huge size explosion hazard of TBPB that could be executed as a reduction of energy potential and storage conditions in view of loss prevention.     

On-line Characterization of Physiological State in Poly(β-Hydroxybutyrate) Production by <Emphasis Type="Italic">Wautersia eutropha</Emphasis>

Culture fluorescence measurement technique has the potential for on-line characterization of metabolic status of fermentation processes. Many fluorophores present inside the living cells such as NADH + H⁺, tryptophan, pyridoxine, and riboflavin fluoresce at specific excitation and emission wavelength combinations. Since these key intracellular metabolites are involved in cell growth and metabolism, their concentration change at any time inside the cell could reflect the changes in cell metabolic activity. NADH + H⁺ spectrofluorometry was used for on-line characterization of physiological state during batch cultivation of poly-β-hydroxybutyric acid (PHB) production by Wautersia eutropha. The culture fluorescence increased with an increase in the biomass concentration with time. A linear correlation between cell mass concentration and net NADH + H⁺ fluorescence was established during active growth phase (13 to 38 h) of batch cultivation. The rate of change of culture fluorescence (dF/dt) exhibited a gradual increase during the predominantly growth phase of batch cultivation (till 20 h). Thereafter, a sudden drop in the dF/dt rate and its leveling was recorded indicating major changes in culture metabolism status which synchronized with the start-up of accumulation of PHB. After 48 h, yet another decrease in the rate of change of fluorescence (dF/dt) was observed primarily due to severe substrate limitation in the reactor. On-line NADH + H⁺ fluorescence signal and its rate (dF/dt) could therefore be used to distinguish the growth, product formation, and nutrient depletion stage (the metabolic state marker) during the batch cultivation of W. eutropha.     

Kinetic Studies of Bulk Ge22Se78−xBix (x=0, 4 and 8) Semiconducting Glasses

Results of phase transformations, enthalpy released and specific heat of Ge₂₂Se_78–xBi_x(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T _g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T _g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T _g, at a heating rate of 5 K min^–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol^–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T _c–T _g and the enthalpy released during the crystallization process. Below T _g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date.     

A small sample-size automated adiabatic calorimeter from 70 to 580 K

An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580 K, equipped with a small sample cell of 7.4 cm³ in the internal volume has been developed. In order to obtain a good adiabatic condition of the calorimeter at high temperature, the calorimeter was surrounded in sequence by two adiabatic shields, three radiation shields and an auxiliary temperature-controlled sheath. The main body of the cell made of copper and the lid made of brass are silver-soldered and the cell is sealed with a copper screw cap. A sealing gasket made of Pb-Sn alloy is put between the cap and the lid to ensure a high vacuum sealing of the cell in the whole experimental temperature range. All the leads are insulated and fixed with W30-11 varnish, thus a good electric insulation is obtained at high temperature. All the experimental data, including those for energy and temperature are collected and automatically with a personal computer using a predetermined program. To verify the accuracy of the calorimeter, the heat capacities of α-Al₂O₃ of the calorimetric standard reference material is measured. The standard deviations of experimental heat capacity values from the smoothed values are within ± 0.28%, while the inaccuracy is within ±0.4% compared with those of the National Bureau of Standards over the entire working temperature range. Project supported by the National Natural Science Foundation of China (Grant No. 29573133).     

Inactivation of Botrytis cinerea during thermophilic composting of greenhouse tomato plant residues

The effectiveness of in-vessel thermophilic composting on the inactivation of Botrytis cinerea was evaluated. The bioreactor operated on an infected mixture of tomato plant residues, wood shavings, and municipal solid compost (1∶1.5∶0.28). Tap water and urea were added to adjust the moisture content and C∶N ratio to 60% and 30∶1, respectively. Used cooking oil was added as a bioavailable carbon source to compensate for heat losses from the system and extend the thermophilic compositing stage. The controlled thermophilic composting process was successful in inactivating B. cinerea. During all experiments, the average reactor temperature increased gradually, reaching its peak after 31 h of operation. Temperatures in the range of 62.6–63.9°C were maintained during the thermophilic stage by the intermittent addition of used cooking oil. The results of the enzyme-linked immunosorbent assay test indicated that the initial concentration of B. cinerea in the compost samples (14.6 μg of dried mycelium/g of compost) was reduced to 12.9, 8.8, and 2.4 μg/g after 24, 48, and 72 h of thermophilic composting, respectively. Plating assay indicated that the mold was completely inactivated in samples after 48 h of thermophilic composting. No significant reduction in B. cinerea was observed during the transient phase (first 30 h of rising temperature) because the temperature reached the lethal level of 55°C after 23 h, thus allowing only 7 h of exposure to temperatures higher than 55°C during this phase. The relatively short time required for complete inactivation of B. cinerea was achieved by maintaining a constant high temperature and a uniform distribution of temperature and extending the duration of the thermophilic stage by the addition of the proper amount of bioavailable carbon (used cooking oil).