Pure Oxygen Supply Research Articles

Getting prepared for the fresh COVID19 wave:

Regular supply of pure oxygen is the need of the hour to be prepared for the fresh waves of COVID-19. The cost of such oxygen supplies should be economical to reach out to the masses & avoid unwelcome burden on the national economy. A requirement has always been felt to identify an alternate source of oxygen generation with readily available raw materials which can ensure its cost effectiveness and last mile oxygen availability through independent generation capabilities.Chemical generation of oxygen has been the go-to technology for portable oxygen generation. However, the cost of production and controlling the reaction has generally been uneconomical for commercial applications. The authors undertook a task to build up a prototype of chemical oxygen generator which did not require compressed gas. It on the principle of dissociation of Sodium per carbonate (SPC) into sodium carbonate and hydrogen peroxide. Hydrogen peroxide so produced interacts with catalyst MnO which further decomposes to produce oxygen. A cast iron tank with a reaction chamber at the bottom is fabricated where upper tank consists of water and space for storing gases. The flow of the water is regulated to control the speed of the reaction.The chemical mixture of sodium percarbonate and manganese dioxide is tightly packed in a cloth bag.Oxygen release valve is kept at the top of the tank which is connected via a pipe to the standard to check the quantity of oxygen as well as the oxygen mask for the patient.This equipment, has a to be the in the fight against COVID especially in remote and difficult to access areas as well as areas without electricity.

Comparing the Electrochemical Performance of Organic and Ionic Liquid-Based Electrolytes in Lithium-Oxygen Battery

Lithium-oxygen batteries (LOB) have been considered promising electrochemical energy storage devices to supersede current rechargeable batteries for next generation electric vehicles. Despite having tremendously high theoretical energy density (5200 Wh/kg), the practically achievable energy density (1700 Wh/kg) is far from commercial application till date. There are several challenges associated with Li anode, porous cathode and electrolyte that need to be resolved to achieve better results. The choice of suitable electrolyte for LOB is one of the biggest obstacles in its development. The various electrolytes that have been developed and studied come with limitations which includes thermal and chemical stability at higher voltages, volatility, viscosity, flammability, capability to dissolve incoming oxygen etc. Therefore, in order to improve current performance of battery, these parameters need to be optimized.This study focuses on the influence of organic and ionic liquid (IL)-based electrolytes on electrochemical performance of Li-O2 battery. [Pyr14][TFSI] and two commercially available organic solvents TEGDME and DMSO were investigated in this study. A series of tests were performed at various operating temperatures with the IL. Vulcan XC 72R coated carbon cloth with 30wt% PTFE is used as cathode. 1 mg/cm2 (+/-0.3mg/ cm2) is used as carbon loading. All experiments were conducted with pure oxygen supply at room temperature (unless stated otherwise). Li|Li Symmetric tests were also performed to measure the stability of electrolyte.The IL was tested at three different operating temperatures including room temperature (22°C), 35°C and 75°C. The results indicate that increase in temperature helps improve discharge capacity of battery. The discharge capacity obtained at three operating temperatures were 0.04 mAh/mg, 0.06 mAh/mg and 0.3 mAh/mg respectively. The improvement is in accordance with the fact that increase in temperature reduces IL viscosity and increases oxygen diffusivity. At discharge cut-off voltage of 2V, the discharge cycles did not show mass transfer limitation therefore, the subsequent tests were conducted with cut-off voltage set at 0V. This significantly improved the discharge capacity from 0.3 mAh/mg to 1.1 mAh/mg with discharge cycles limited by mass transfer effect.Two organic electrolytes TEGDME and DMSO were also tested at room temperature (22°C). The discharge capacities obtained were 4.65 mAh/mg and 5.43 mAh/mg. The higher discharge capacity of DMSO could be associated with its unique properties which includes donor number (DN), conductivity and viscosity. The DN for DMSO and TEGDME are 29.8 kcal/mol and 16.6 kcal/mol respectively. Higher DN improves discharge capacity by promoting growth of Li2O2 as bigger toroidal precipitates on cathode surface as opposed to its counterpart which produces Li2O2 insulating film. Similarly, DMSO has higher conductivity (2.11 mS/cm) and lower viscosity (1.94 cP) than TEGDME (0.3 mS/cm,4.05 cP) which improves species mobility.Finally, Li|Li symmetric tests were conducted at room temperature to measure stability of electrolytes. The results indicate, DMSO could cycle 60 cycles without significant surge in overpotential followed by TEGDME (40 cycles) and IL (20 cycles).

EXPERIMENTAL RESEARCH TO DETERMINE THE AFFECT OF AGENT TO THE QUALITY OF SYNGAS ON UPDRAFT GASIFIER MODEL

The thermal performance of the gasification process depends on many factors, in which gasification agent is one of the major factors affecting the quality and heat value of syngas. This research uses the empirical method to determine the effect of the gasification agent on the quality and heat value of the syngas when changing the composition of oxygen and steam. Experimental model of gasification using rice husk and coal materials with type of Top Lift UpDraft gasifier (TLUD). The results show that when using the air as an agent, at the equivalent ratio (ER) of about 0.25, the gas product produces the highest calorific value (3835 kJ/Nm3). As the oxygen concentration increases by 70% in the agent, the heat value increases considerably (8646 kJ/Nm3), but requires a pure oxygen supply. The addition of steam increased the calorific value of the gas product, but was negligible (an increase of 0.28% as the S/A ratio went from 0 to 7). The experiment also showed that with the ratio of S/A = 0.5, the quality of gas products is the best.

Cultivo en lote alimentado y condiciones de operación para la producción de una vacuna recombinante anti-amebiana con el sistema Pichia pastoris

It was developed a fed-batch bioprocess to produce a recombinant vaccine against Entamoeba histolytica under operational conditions attainable to large scale bioprocesses. We have produced this recombinant protein in shake flask and stirred tank bioreactor. Initial results in shake flask cultures under different methanol concentration of 0.5, 1.5 and 3% (v/v) produced extracellular protein at quantities of 10, 22 and 33 μg/mL, respectively. Then a scale-up process was performed from shake flask to fermenter by keeping similar volumetric power supply (P/V). The operational conditions were set up in fermenter as those used at commercial scale and supply of pure oxygen was avoided to keep the scalability of the bioprocess. After the scale-up process, the production of the recombinant protein reached 0.43 mg/mL, an improvement in production of 12 times, although the methanol and oxygen limited conditions observed. Maximum volumetric productivity of 3.75 mg/L h was achieved in fermenter cultures against 263.75 µg/L h reached in shake flask. Besides the limited conditions in methanol and oxygen, the yields obtained from the bioprocess were comparable to those observed in Mut+ strains previously reported, then saturated methanol conditions are not necessary to compensate limited oxygen conditions.

Cost-practical of glycolic acid bioproduction by immobilized whole-cell catalysis accompanied with compressed oxygen supplied to enhance mass transfer

Bioprocess for Glycolic acid (GA) production from ethylene glycol by whole-cell catalysis of Gluconobacter oxydans is restrained by various biological impediments and high production costs. In this study, these limitations were subsided through the implementation of immobilized whole-cell bio-catalysis combined with increased oxygen supply. Results indicated that this strategy noticeably enhanced mass transfer efficiency, and prolonged cell life that significantly reduced the cost of biomass. Ultimately, with immobilized whole-cell catalysis in air-open and oxygen-open bioreactor, 41.3 and 66.9 g/L of GA was obtained within 48 h, with an increment of 62.0%. Additionally, in oxygen-compressed bioreactor, 63.3 g/L of GA was accumulated with the yield of 97.2%. Subsequently, 605.7 g of GA was produced after 10 rounds of recovery experiments. Although there was a slight decrease in GA production compared with pure-oxygen supply, production cost was reduced with limited oxygen supply. This strategy commendably demonstrated cost-practical bioprocess for GA production.

Electrodialytic bioproduction of xylonic acid in a bioreactor of supplied-oxygen intensification by using immobilized whole-cell Gluconobacter oxydans as biocatalyst

Immobilized whole-cell fermentation has been proven to be an effective method to improve the performance and cost-effectiveness of Gluconobacter oxydans ATCC 621. In the bio-oxidation of xylose to xylonic acid, the oxygen supply through the immobilized beads is a well-known factor that limits the biocatalytic performance of Gluconobacter oxydans as obligate aerobic bacteria. The activity of immobilized cells could be efficiently improved by execution of pressurized pure oxygen supply strategy. Subsequently, in order to further enhance the production efficiency of xylonic acid and reduce end-product inhibition, online-electrodialysis was employed. Finally, a design of pressurized oxygen supply bioreactor combining with online-electrodialysis was put forward for implementing successive production of xylonic acid. The central features of this a highly integrated design are feasible and thus might enable cost-competitive bacterial xylonic acid production.

Toward True Lithium-Air Batteries

Lithium-oxygen batteries with high energy densities are limited by pure oxygen feeding and side reactions that hinder their practical applications. In a recent Nature paper, Asadi et al. proposed powerful designs in a lithium-oxygen battery that offers an excellent cycle life in air-like atmosphere, a step closer to true lithium-air batteries.

Development Study of an Air Independent Fuel Cell System for an Autonomous Underwater Vehicle (AUV)

In this work a design process for the development of an air independent fuel cell system operating a commercial fuel cell stack as a range extender in an AUV is presented. The development follows an optimization strategy which has been derived from the universal fuel cell development plan proposed by Ang et al.[1] The first step is defining the constraints and the objectives in the design process. While constraints set the boundary conditions of the system the identified objectives are used as optimization parameters. The design plan follows the schematic in figure1: Figure 1: design concept for an optimized system used in an AUV The development of fuel cell systems used in a submarine environment will need to consider different boundary conditions than the development of a fuel cell system for automobiles. These constraints result from the sea water environment which can’t be used as an oxygen source and additionally hinders mass exchange with the fuel cell system because of pressure differences. As a result a closed fuel cell system relying on a pure oxygen supply has to be developed. The fuel cell is powering the AUV with a stationary output while a battery is buffering the power differential between the output und the consumption of the AUV. The AUV is used as a testing platform by the German navy and thereby sets very unique constraints on the system development. Additionally the commercial fuel cell stack is setting boundary conditions for the system development, which has to meet the stacks individual operating conditions. After identifying the boundary conditions the system size was identified as the optimization parameter. To optimize the system size different setups for the cooling system as well as the gas supply system found in the literature are evaluated. Setups meeting the boundary conditions are validated in a test bench with hardware-in-the-loop tests. Based on these measurements a volume-optimized system can be found. Challenges which deviate from this setup are identified and can be tackled in the subsequent design step. The next step is a discussion of the different concepts and an evaluation of their impact on the system operation. While the discussed solutions are still meeting the maximum system size, an evaluation of their influence on other design parameters can be made. From this different system designs are derived and the resulting operation strategies are compared to further improve the volume-optimized system. Also solutions targeting specific challenges like standby mode and system shutdown are evaluated and presented. In a last step the qualitative connections between the found system designs and the boundary conditions in this system are discussed leading to a more general approach for the development of air independent fuel cell systems for AUVs. [1] S. M. C. Ang, E. S. Fraga, N. P. Brandon, N. J. Samsatli, and D. J. L. Brett, “Fuel cell systems optimisation – Methods and strategies,” Int. J. Hydrogen Energy, vol. 36, no. 22, pp. 14678–14703, Nov. 2011. Figure 1

Recombinant protein production by engineered Escherichia coli in a pressurized airlift bioreactor: A techno-economic analysis

ABSTRACT Standard cultivation protocols for high cell-density cultures of recombinant E. coli rely on air enrichment with oxygen to prevent oxygen limitation. This way of increasing oxygen supply impacts on process economics due to the high cost of pure oxygen. Reactor pressurization is an alternative approach to improve oxygen mass transfer. In the present study, the performance of pressurized airlift bioreactor in growing r E. coli cells was evaluated. Experiments were performed in a pressurized internal-loop airlift bioreactor (ALB) and in a non-pressurized stirred tank reactor (STR), both with 5 L working volume, equipped with a system for automatic control and monitoring of pressure, temperature, pH, and dissolved oxygen. Pressurization showed to be crucial to improve ALB performance in biomass formation (29 g DCW L −1 ) and protein production (201 mg protein g DCW −1 ), resulting in protein productivity (240 mg protein −1 h −1 ) and energy efficiency (11 g protein kWh −1 ) similar to the achieved in STR (200 mg protein L −1 h −1 and 13 g protein kWh −1 , respectively). Due to the high cost of pure oxygen, air enrichment revealed to be economically unfeasible for ALB. By pressurizing the bioreactor up to 0.41 MPa, without pure oxygen supply, an 8.7-fold increase in economic efficiency is estimated, what shows the potential of this innovative strategy for aerobic cultures.

Laccase mediated oxidation of industrial lignins: Is oxygen limiting?

The effect of external oxygen supply on laccase mediated oxidation of different types of lignins [Organosolv, Indulin AT, sodium (Na) lignosulfonates and magnesium (Mg) lignosulfonates] was investigated. This study demonstrates for the first time that oxygen as an essential electron acceptor is limiting in laccase mediated oxidation of lignin processes. Oxygen levels decreased to undetectable levels and remained undetectable for a long period in shaking samples without external oxygen supply. The decrease in fluorescence intensity attributed to the modification in conjugated carbonyl, biphenyl, phenylcoumarins and stilbene groups during laccase oxidationwas 40 times faster in sample mixtures supplied with pure oxygen than shaking samples without external oxygen supply and has direct implications on saving time. However, despite a general increase in molecular weight in all laccase treated lignins, pure oxygen supply does not always lead to the highest Mw. For example Mg-lignosulfonates treated with Trametes villosa laccase under shaking conditions without external oxygen supply had the highest Mw 85,777kDa as compared to 68,842kDa in the presence of pure oxygen. This study therefore shows demonstrates the importance of supplying oxygen to laccase mediated reactions in order to shorten the incubation time and ensure complete oxidation.

Microbial desalination cell for concurrent hydrogen peroxide production and desalination

Microbial desalination cells (MDCs) are novel desalination approaches because of using biocatalyst, with the ability to convert organic waste to bioenergy in various forms, to desalinate salty water. If MDCs were applied to the production of hydrogen peroxide, which is an important green oxidant, less energy-intensive and eco-friendly hydrogen peroxide production can be achieved during desalination. Here, we examined MDCs for concurrent hydrogen peroxide and desalination by varying an applied voltage, initial sodium chloride concentration, electrode materials, oxygen concentration, catholyte pH and catholyte concentration. The hydrogen peroxide production rate and salt removal rate (SR) increased by 0·033 kg (H2O2/m3)/h and 197·5 mg/(L·h) with increasing applied voltage. Carbon felt showed the highest hydrogen peroxide production (0·197 kg H2O2/m3) but the lowest SR (119·0 mg/(L·h)). Compared with air supply, pure oxygen supply dramatically improved hydrogen peroxide production (100%), but the SR only slightly improved (10%). With increasing sodium chloride concentration from 5 to 30 g/L, the hydrogen peroxide production and the SR increased, reaching 0·261 kg H2O2/m3 at 30 g/L and 236 mg/(L·h) at 20 g/L, respectively. The highest hydrogen peroxide production was achieved at catholyte pH 4, but the highest SR was achieved at pH 7. With increasing catholyte concentration from 5 to 100 mM, the hydrogen peroxide production and the SR increased.

High cell density cultivation of Pseudomonas putida KT2440 using glucose without the need for oxygen enriched air supply.

High Cell Density (HCD) cultivation of bacteria is essential for the majority of industrial processes to achieve high volumetric productivity (g L(-1) h(-1) ) of a bioproduct of interest. This study developed a fed batch bioprocess using glucose as sole carbon and energy source for the HCD of the well described biocatalyst Pseudomonas putida KT2440 without the supply of oxygen enriched air. Growth kinetics data from batch fermentations were used for building a bioprocess model and designing feeding strategies. An exponential followed by linearly increasing feeding strategy of glucose was found to be effective in maintaining biomass productivity while also delaying the onset of dissolved oxygen (supplied via compressed air) limitation. A final cell dry weight (CDW) of 102 g L(-1) was achieved in 33 h with a biomass productivity of 3.1 g L(-1) h(-1) which are the highest ever reported values for P. putida strains using glucose without the supply of pure oxygen or oxygen enriched air. The usefulness of the biomass as a biocatalyst was demonstrated through the production of the biodegradable polymer polyhydroxyalkanoate (PHA). When nonanoic acid (NA) was supplied to the glucose grown cells of P. putida KT2440, it accumulated 32% of CDW as PHA in 11 h (2.85 g L(-1) h(-1) ) resulting in a total of 0.56 kg of PHA in 18 L with a yield of 0.56 g PHA g NA(-1) .

Laryngeal surgery using a CO2 laser: is a polyvinylchloride endotracheal tube safe?

ObjectiveWe performed retrospective clinical analysis and in vitro testing to analyze the risks involved in laryngeal surgery using a CO2 laser. Materials and methodsThe occurrence of adverse events during laryngeal surgeries using a CO2 laser, the reasons for these adverse events, and the risks of laryngeal laser surgery were analyzed in 704 patients. In vitro experiments were performed to observe the tolerance of the cuffs of polyvinylchloride (PVC) endotracheal tubes to the CO2 laser under conditions of filling water or air, different laser power levels, and different cutting patterns. The flammability of the PVC endotracheal tube under different oxygen concentrations, laser power levels, and laser cutting patterns were also studied. ResultsIn the 704 patients who underwent laryngeal laser surgery, the tracheal cuff broke in 92 cases; sparks were observed in 8 cases; and dense smoke, in 27 cases during surgery. No fires or explosions occurred. The in vitro results were as follows: (1) Under the intermittent stimulation mode, the water cuff did not break, but the air cuff broke during the first stimulation. (2) Under the continuous stimulation mode, the water and air cuffs broke easily, and the water and air cuffs broke immediately when the stimulation power was greater than 8 W. (3) Under the intermittent stimulation mode, the PVC endotracheal tube burned only under conditions of pure oxygen supply and 10 W of laser power. Under the continuous stimulation mode, the tube did not burn with 5 W of laser power, regardless of the oxygen concentration used. When the laser power level reached 8 W and the oxygen concentration was greater than 50%, the tube will easily burn. When the laser power level was 10 W, the tube burned at oxygen concentrations greater than 20%. ConclusionsBurning of the tube during laryngeal surgery using a CO2 laser could be effectively avoided when appropriate measures were taken, such as filling the endotracheal cuff with water, maintaining less than 40% oxygen concentration, using less than 8 W laser power, and using the intermittent stimulation mode.

EVALUATION OF SILVER CARP FRY TRANSPORTATION METHODS ON WATER QUALITY AND SURVIVAL RATIO

The effect of stocking densities (30, 60, 90, and 120 g/l), durations of transportation (2, 4, and 6 hours), with two methods of aeration (pure oxygen and atmospheric air)in three different containers shapes (polyethylene bags, cylindrical and cuboids) on silver carp fry, and water quality parameters was tested. Water samples were taken at 2 h intervals after transport to determine oxygen concentration, pH, and total ammonia concentration. Oxygen concentration adjusted to 8 ppm for all treatments at transport start of silver carp fries. The results revealed that both water quality and survival ratio were affected by method of transportation. Oxygen concentration, pH values, ammonia concentration and survival ratio measured in pure oxygen supply were significantly (P<0.05) higher compared to those measured in atmospheric air supply under all treatments. The oxygen concentration of silver carp fry transportation was in the range of 0.67 to 7.11 mg/l, and the stocking densities from 30 to 120 g/l. Transportation durations significantly affected the oxygen concentration under closed system (polyethylene bags) and open system (cylindrical and cuboids containers). The pH values of the water during silver carp fry transportation were in the range of 6.35 to 7.2, and the lowest ph value of 6.35 was recorded at 30 g/l stocking density, 2 h duration of transportation, pure oxygen supply and polyethylene bags containers. The ammonia concentration values of silver carp fry transportation was in the range of 1.1 to 7.0 mg/l, and the lowest ammonia value of 1.1g/l was recorded at 30 g/l stocking density, 2 h duration of transportation, pure oxygen supply and polyethylene bags container. The lowest survival ratio of silver carp fry transportation value of 14.97% was recorded at 120 g/l stocking density, atmospheric air supply with 6 h duration of transportation, and the highest survival ratio value of 97.13% was recorded at 30 g/l stocking density, 2 h duration of transportation, pure oxygen supply and polyethylene bags containers. The lowest cost value of silver carp fry transportation of 0.09 L.E per 5g. for live fry was recorded at 120 g/l stocking density, 2 h duration of transportation, pure oxygen supply and polyethylene bags containers, but then, the highest cost value of silver carp fry transportation of 0.92 L.E. per 5g. for live fry was recorded at 30 g/l stocking density, 6 h duration of transportation, atmospheric air supply with polyethylene bags containers. From the obtained results, the best parameters of silver carp fry transportation methods could be transport with stocking density of (30 g/l), duration of transportation of (2 hours), methods of aeration of pure oxygen supply, and container shape of polyethylene bags to achieve the highest values of oxygen concentration and the survival ratio and the lowest values of the pH value, ammonia concentration and total cost.

Effect of aerosol carriers on ultrasonically prepared nanocrystalline ZnO powders

Nanocrystalline ZnO powders were synthesized using ultrasonic spraying and decomposition technique. The compressed air and pure oxygen were used as aerosol carriers. Effect of aerosol carriers on ultrasonically atomized nanocrystalline ZnO powders was studied. The powders were characterized using X-ray diffraction, transmission electron microscopy (TEM), electron diffraction, absorption spectroscopy and photoluminescence. The influence of air and oxygen on crystallite morphology was studied using TEM. It was confirmed from TEM analysis that the crystallites were nearly spherical in powder prepared in the presence of compressed air. In the presence of pure oxygen, the crystallites could acquire regular hexagonal shape. Complete hexagonal shapes may be due to sufficient (100%) supply of pure oxygen during the process of formation of ZnO nanocrystallite. The powder with regular shaped crystallites could be highly pure and also stoichiometric in nature. Pure oxygen could therefore be more advantageous as carrier than air for production of nanocrystalline ZnO powder. The effect of aerosol carriers (compressed air and pure oxygen) on crystallite morphology of nanocrystalline ZnO powders is reported in this article.

Impact of methanol concentration on secreted protein production in oxygen‐limited cultures of recombinant Pichia pastoris

The methylotrophic yeast Pichia pastoris is a powerful system for production of recombinant proteins, showing high ability to secrete properly folded proteins. A major plus is the strong AOX1 promoter highly induced by methanol. During growth on methanol, however, oxygen readily becomes limiting. In oxygen-limited cultivations of recombinant Pichia pastoris, the methanol concentration had a strong impact on the production of a single-chain antibody fragment (scFv). High methanol concentrations were required to compensate the lack of oxygen and fully induce recombinant protein production, at the same time reducing gratuitous biomass formation due to a lower biomass yield. Product concentrations of 60, 150, and 350 mg/L were obtained with methanol concentrations of 0.3, 1, and 3% (v/v). Moreover, accumulation of a putative product fragment that cannot be removed during affinity purification was prevented at high methanol concentrations. Cell vitality after 100 h was maintained above 98% and 96% of the culture with 0.3% and 3% methanol, respectively. In cultivations supplemented with oxygen, in contrast, methanol concentration between 0.3% and 3% did not influence the product yield of 300-400 mg/L. Thus, efficient recombinant protein production under oxygen-limitation seems to require high methanol concentrations, enabling product concentration as high as otherwise obtained only with expensive supply of pure oxygen.

Application of a radial‐flow bioreactor in the production of β1,3‐N‐acetylglucosaminyltransferase‐2 fused with GFPuv using stably transformed insect cell lines

An RFB (radial-flow bioreactor) with a reactor volume of 5 ml was applied to produce human beta3GnT (beta1,3-N-acetylglucosaminyltransferase) using two stably transformed insect cell lines. When air was supplied to the RFB, cell growth stopped at 4 days of culture and beta3GnT was not detected. However, with a supply of pure oxygen, the cell concentration, assumed from glucose consumption, increased by 1.3x10(7) cells/ml. Insect cells attached to poly(vinyl alcohol) matrixes packed in the RFB and grew confluently; 5.6 m-units/ml beta3GnT was produced under the conditions of pure oxygen supply and addition of glucose and glutamine. This RFB was first applied in beta3GnT production using stably transformed insect cells. The amount of beta3GnT production in only a 5 ml-scale RFB was comparable with that of a 100 ml shaking flask culture.

A consideration of the economic efficiency of hydrogen production from biomass

A feasibility study of a hydrogen production system using woody biomass with a pyrolysis process was conducted as part of NEDO's WE-NET project. Using the pyrolysis process, various solid fuels and waste materials can be gasified, and synthesis gas suitable for hydrogen production can be obtained without the need for a pure oxygen supply. Using this system, it is expected that 7.4 billion m 3/ yr (NTP) of hydrogen from biomass stock will be produced for domestic supply in Japan. The capital cost of the plant used in this study is $3950/ kW H 2 out, and product supply cost is 0.108 $/ kWh H 2 out.

Optimization of Dissolved Oxygen Supply Method for Maximum Virginiamycin Production

To maximize the production of virginiamycin (VM and VS) which is commercially used as an antibiotic mixed in animal feed, an empirical approach was employed in the batch culture of Streptomyces virginiae. Here, effects of Dissolved Oxygen (DO) concentration and/or DO supplying condition such as pure oxygen supply and agitation speed changes on the maximum cell concentration at the production phase as well as production activity of virginiamycin were investigated. In order to keep DO concentration in the fermenter at a certain level, either agitation speed or inlet oxygen concentration of supplying gas can be manipulated. It was found that the increase of agitation speed gave positive effect on antibiotics productivity apart from the controlled DO concentration. Optimum DO concentration and agitation speed including VB-C addition was determined for maximize virginiamycin production.

Change in nitrite conversion direction from oxidation to reduction in heterotrophic bacteria depending on the aeration conditions

For investigation of the effects of aeration on nitrite- and nitrate-transforming activities of various heterotrophic bacteria, a series of coefficients of the oxygen absorption rate ( K d, 8–99 × 10 −7 mol/ml·min·atm) in 500-ml shaking flasks were determined by varying plug types and culture volumes. Bacillus badius I-73, which neither shows denitrification activity nor utilize nitrate as a nitrogen source, consumed nitrite and accumulated nitrate at all K d values at which experiments were conducted. In B. subtilis I-41, which dose show denitrification activity, the manner of nitrite and nitrate conversion was influenced by the culture time and K d, and the direction of conversion was changed from reduction to oxidation, as the K d of the culture increased. Pseudomonas pavonaceae, another denitrification-positive strain, metabolized both nitrite and nitrate to more reduced compounds at low K d, and the direction of conversion changed from reduction to oxidation at K d=20 × 10 −7 mol/ml·min·atm. Such switching behavior was also observed when P. pavonaceae was cultured continuously during variation of the aeration conditions with supply of pure oxygen. Many other denitrification-positive strains behaved similarly to P. pavonaceae, and showed their own critical K d, the point at which the direction of nitrite metabolism changed. The results of intact-cell reaction experiments indicate that this switching might be caused by inhibition and repression of nitrite-reducing activity, and by stimulation of nitrite-oxidizing activity by oxygen.