120 t转炉底吹CO2工艺研究及应用

介绍了某钢厂采用底吹CO2工艺,转炉冶炼CSP中低碳钢过程的变化,探究底吹CO2的工艺优势,为后续工艺优化提供借鉴.通过在120 t顶底复吹转炉进行底吹CO2工艺试验研究,分析了底吹CO2对钢水成分、炉渣成分、氧气消耗、钢中氮氧含量的影响.试验结果表明:底吹CO2工艺替代常规工艺切实可行,且有明显的工艺优势.底吹0.9...     

Influence of modified atmosphere and preservatives on the growth of Zygosaccharomyces rouxii isolated from dried fruits

The influence of water activity (alpha w), preservatives, modified atmosphere and their combinations on the growth of Z. rouxii was determined by cultivating two strains isolated from raisins and prunes in culture media under different conditions and by counting the colony forming units. Yeast extract glucose broths or agars were adjusted to the desired alpha w by means of glucose. Preservatives added to the media (0-600 ppm) were either K-sorbate, Na-benzoate or their mixture. Modified atmospheres were carried out by packing culture plates or flasks in plastic bags under different CO2-N2 gas mixture. Response surface design was carried out to optimize the growth inhibition of Z. rouxii by the mentioned factors. Although Z. rouxii is osmotolerant, the strains studied could not grow at alpha w 0.79. They also showed a high tolerance to CO2; even 80% CO2 seems to not inhibit growth. However, CO2 atmosphere at high pHs and low preservative concentrations stimulated yeast growth. At pH 4.0 and under modified atmosphere (80% CO2-20% N2), no growth was observed at any alpha w in the range of 0.80-0.90 when using a preservative concentration of 220 ppm Ksorbate or 280 ppm Na-benzoate.     

Kinetics of decreased LPS-stimulated cytokine release by macrophages exposed to CO2

The mechanisms responsible for the lack of inflammation after laparoscopic surgery remain unknown. Peritoneal macrophages (M phi) incubated in carbon dioxide (CO2) but not air or helium (He), had significant, reversible inhibition of lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF) and interleukin-1 (IL-1) release. In these experiments the kinetics of these C02-induced alterations in cytokine secretion were examined. Murine peritoneal Mphi were stimulated with LPS for 4 hr and incubated in different test gases (95% air/5% CO2,80%CO2/20%O2,80% He/20% O2) for intervals between 0.25 and 4 hr. Time between gas incubation and LPS stimulation was varied to determine the persistence of CO2 inhibition. Parallel M phi groups received LPS stimulation 24 hr later. Supernatant TNF and IL-1 were measured by bioassay and polymerase chain reaction was used to examine cytokine mRNA. Significant reversible inhibition of TNF and IL-1 was seen with CO2, but not He or air. Inhibition of IL-1 occurred 15 min after CO2 exposure, was associated with decreased IL-1 mRNA, and was rapidly lost following incubation in the control atmosphere. TNF inhibition was seen despite normal levels of TNF message, required more than 30 min of CO2 exposure, and persisted after CO2 removal. CO2 produced profound, reversible, inhibition of LPS-stimulated cytokine release by peritoneal Mphi. The transient inability to secrete inflammatory cytokines after CO2 exposure may explain the lack of systemic inflammation after laparoscopic surgery with CO2.     

Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 2. Interaction of flame with metal and slag in converter bath

Thermodynamic analysis is applied to the physicochemical processes in the converter bath when intensifying bath heating by means of gas–oxygen burners. In the converter’s working space, when the combustion flames interact with the liquid bath, the oxygen and natural gas supplied through the burners and the oxygen supplied through the tuyere interact in a bubbling slag–metal emulsion. As a result, iron and the impurities are oxidized. The use of such burners changes the gas composition: not only O₂, CO, and CO₂ are present, but also H₂ and H₂O, which changes the oxidative capacity of the gas phase. The presence of solid carbon (for example, pulverized coal) in the burner flame may be used to control and intensify the combustion process. Combustion is most effective in the oxidation of carbon to CO when the oxygen excess is less than 1.0. The oxidation conditions of carbon in the melt change with variation in its activity as a function of its concentration and the temperature. The equilibrium in the M–O–C system may be described by the oxygen partial pressure \({P_{{O_2}}}\), which may be regarded as a universal characteristic. In addition, the equilibrium may be assessed on the basis of the associated ratios \({P_{CO}}/{P_{C{O_2}}}\) and \({P_{{H_2}}}/{P_{{H_2}O}}\) It is found that iron may be oxidized by oxygen and, to some extent, by carbon dioxide. At 1600–2000 K, there is practically no oxidation of iron by steam. The carbon dissolved in the steel is oxidized relatively effectively by oxygen and carbon dioxide until its concentration is less than 0.1% C. Steam oxidizes carbon very poorly and is not much more effective with manganese and silicon. With increase in temperature, the rate at which carbon dissolved in steel is oxidized by oxygen increases, while the oxidation rate of manganese and silicon falls. Above 1800 K, superoxidized slag with a high FeO content actively oxidizes silicon (to <2% Si), manganese (to <1% Mn), and carbon (to <1.5% C).     

Influences of morphine on the ventilatory response to isocapnic hypoxia

BACKGROUND: The ventilatory response to hypoxia is composed of the stimulatory activity from peripheral chemoreceptors and a depressant effect from within the central nervous system. Morphine induces respiratory depression by affecting the peripheral and central carbon dioxide chemoreflex loops. There are only few reports on its effect on the hypoxic response. Thus the authors assessed the effect of morphine on the isocapnic ventilatory response to hypoxia in eight cats anesthetized with alpha-chloralose-urethan and on the ventilatory carbon dioxide sensitivities of the central and peripheral chemoreflex loops. METHODS: The steady-state ventilatory responses to six levels of end-tidal oxygen tension (PO2) ranging from 375 to 45 mmHg were measured at constant end-tidal carbon dioxide tension (P[ET]CO2, 41 mmHg) before and after intravenous administration of morphine hydrochloride (0.15 mg/kg). Each oxygen response was fitted to an exponential function characterized by the hypoxic sensitivity and a shape parameter. The hypercapnic ventilatory responses, determined before and after administration of morphine hydrochloride, were separated into a slow central and a fast peripheral component characterized by a carbon dioxide sensitivity and a single offset B (apneic threshold). RESULTS: At constant P(ET)CO2, morphine decreased ventilation during hyperoxia from 1,260 +/- 140 ml/min to 530 +/- 110 ml/ min (P < 0.01). The hypoxic sensitivity and shape parameter did not differ from control. The ventilatory response to carbon dioxide was displaced to higher P(ET)CO2 levels, and the apneic threshold increased by 6 mmHg (P < 0.01). The central and peripheral carbon dioxide sensitivities decreased by about 30% (P < 0.01). Their ratio (peripheral carbon dioxide sensitivity:central carbon dioxide sensitivity) did not differ for the treatments (control = 0.165 +/- 0.105; morphine = 0.161 +/- 0.084). CONCLUSIONS: Morphine depresses ventilation at hyperoxia but does not depress the steady-state increase in ventilation due to hypoxia. The authors speculate that morphine reduces the central depressant effect of hypoxia and the peripheral carbon dioxide sensitivity at hyperoxia.     

高炉处理烧结烟气脱硫脱硝理论分析

对利用高炉处理烧结烟气同时脱硫脱硝脱二噁英技术的可行性进行了理论探讨,分析高炉内部还原二氧化硫和氮氧化物,以及分解二噁英的热力学条件,探讨烧结烟气代替空气鼓风对理论燃烧温度、风量、炉缸煤气、炉顶煤气和铁水硫含量的影响.结果表明:二氧化硫、一氧化氮和二氧化氮的最低平衡体积分数分别为1.84×10^-13%、3.08×10^-11%和3.72×10^-21%,高炉内部还原二氧化硫和氮氧化物是可行的;高炉具有分解二噁英的有利热力学条件;烟气中二氧化硫和一氧化碳对理论燃烧温度的影响可忽略,氮氧化物能略微提高理论燃烧温度,二氧化碳体积分数增加1%,理论燃烧温度降低大约40.5℃,但通过降低鼓风湿度和提高富氧率等措施,能达到高炉正常生产时的炉缸热状态水平;随着烟气中二氧化碳含量的增加,风量、炉缸和炉顶煤气量都逐渐降低,炉缸煤气一氧化碳和氢气含量增加,炉顶煤气中一氧化碳、氢气、二氧化碳和水含量都增加,氮气含量显著降低;铁水硫含量与烟气二氧化硫含量成正比,但当二氧化硫质量浓度达到2000 mg·m^-3,铁水中硫质量分数仅为0.025%,铁水质量仍合格.通过综合调节高炉操作参数,也可以实现烧结烟气代替空气鼓风进行高炉炼铁生产,达到脱硫脱硝脱二恶英的目的.     

Oxygen Solubility in Fe–Co Melts Containing Carbon

In thermodynamic analysis of solutions of oxygen in Fe–Co melts containing carbon, the equilibrium constants of reactions between carbon and oxygen are determined, as well as the activity coefficients at infinite dilution and the interaction parameters in melts of different composition at 1873 K. The dependence of oxygen solubility in such melts on the cobalt and carbon content is calculated. In iron–cobalt melts, carbon has high oxygen affinity. The deoxidizing ability of carbon increase significantly with increase in cobalt content in the melt. In pure cobalt, it is more than an order of magnitude greater than in pure iron. Deoxidation by carbon produces gaseous oxides: carbon monoxide (CO) and dioxide (CO₂). The reaction of carbon and oxygen dissolved in the melt and hence the deoxidizing ability of carbon depend on the total gas pressure above the melt. Decrease in gas pressure significantly improves the reducing properties of carbon. The minimum oxygen concentration for alloys of the same composition is reduced by practically an order of magnitude with tenfold decrease in the total gas pressure. The gas composition above Fe–Co melts and the equilibrium carbon and oxygen concentrations in the melt are calculated with total gas pressures of 1.0, 0.1, and 0.01 atm. The optimal oxygen concentration (1–10 ppm) in Fe–Co melts is reached at carbon concentrations between 0.01 and 1% depending on the total gas pressure (0.01–1 atm). The solubility of oxygen in iron–cobalt melts containing carbon passes through a minimum, which is shifted to lower carbon content with increase in the melt’s cobalt content. Further additions of carbon increase the oxygen concentrations in the melt. With increase in cobalt content, this increase will be sharper.     

Flue Gas Carbon Dioxide Sequestration during Water Softening with Ion-Exchange Fibers

This study examines the use of ion-exchange fibers (IX fibers) to permanently sequester carbon dioxide present in flue gas into an aqueous phase as calcium or magnesium alkalinity while concurrently softening hard water. The only process inputs besides carbon dioxide (or flue gas) are snowmelt (or rainwater); no other chemicals are required for the regeneration of the IX fibers. Importantly, the process is not energy intensive and carbon dioxide does not need to be compressed to excessive pressures (>150?psi) for efficient use. Sources of carbon dioxide do not require concentration and, therefore, the use of raw flue gas ( ～ 17% CO2) is feasible with the rate of sequestration governed only by the partial pressure of carbon dioxide. While valid for flue gas obtained from any combustion process (e.g., coal, oil, natural gas, etc.), emissions from oil or gas combustion may be more appropriate for use in the described process due to the absence of mercury and particulates. It should also be noted that the presence of sulfur dioxide in flue gas would not adversely affect the process and may even enhance regeneration efficiency. The only product of the proposed process is an environmentally benign regenerant stream containing calcium and/or magnesium alkalinity. The unique property of IX fibers that makes the proposed process both environmentally sustainable and economically feasible is amenability to efficient regeneration with carbon dioxide and harvested snowmelt. Low intraparticle diffusional resistance is the underlying reason why IX fibers are amenable to efficient regeneration using snowmelt sparged with carbon dioxide; 95% calcium recovery was attained at a CO2 partial pressure of 6.8?atm. On the contrary, commercial weak-acid ion-exchange resins in spherical bead forms are ineffective for regeneration with carbon-dioxide-sparged snowmelt due to extremely slow ion-exchange kinetics involving counter-transport of Ca2+ (or Mg2+) and H+. The energy balance for a typical electric utility shows that up to 1% of carbon dioxide emitted during combustion would be sequestered in the softening process.     

Liquid-Impregnated Clay Solid Sorbents for CO2 Removal from Postcombustion Gas Streams

A novel liquid-impregnated clay sorbent [R. V. Siriwardane, U.S. Patent No. 6,908,497 B1 (2003)] was developed for carbon dioxide (CO2) removal in the temperature range of ambient to 60°C for both fixed-bed and fluidized-bed reactor applications. The sorbent is regenerable at 80–100°C. A 20-cycle test conducted in an atmospheric reactor with simulated flue gas with moisture demonstrated that the sorbent retains its CO2 sorption capacity with CO2 removal efficiency of about 99% during the cyclic tests. The sorbents suitable for fluidized-bed reactor operations showed required delta CO2 capacity requirements for sorption of CO2 at 40°C and regeneration at 100°C. The parameters such as rate of sorption, heat of sorption, minimum fluidization velocities, and attrition resistance data that are necessary for the design of a reactor suitable for capture and regeneration were also determined for the sorbent. A 20-cycle test conducted in the presence of flue-gas pollutant sulfur dioxide—SO2 (20 parts per million)—indicated that the sorbent performance was not affected by the presence of SO2.     

Application of the triad of blast furnace,oxygen converter,and electric arc furnace for reducing of carbon footprint

Carbon footprint is the mass of carbon formed in the full cycle of manufacturing one kind or another product. This carbon is included in greenhouse gases. During production of iron and steel are generated carbon monoxide and greenhouse gases: methane, and carbon dioxide. Methane and carbon monoxide burn to carbon dioxide by secondary energy resources. By this means, the carbon footprint by the production of iron and steel has determined by the weight of carbon dioxide formed in this production. As results of analysis of the processes of manufacture of iron and steel, it has revealed that the tandem of blast furnace with electric arc furnace is characterized by a lower value of integrated emissions of CO₂ than the tandem of blast furnace with an oxygen converter. It was proposed to process of the cast iron made by one blast furnace, then in the oxygen converter, and, at last, in one or more electric arc furnaces. Moreover, the electric arc furnace is loaded by 30% of iron produced in blast furnace, and the remaining 70% are complemented by metal scrap. In the oxygen converter is loaded, the part of cast iron (75–85%), that remained after processing in the arc furnace. The converter is applied the metal scrap for full loading. Calculations of total emission of carbon dioxide for different triads of these units are made. Simultaneous use of oxygen converter with electric arc furnaces for cast iron smelting (obtained from one blast furnace) helps to reduce reliably the emission of carbon dioxide to 20% as it is follows from these calculations. This suggests that such a triad of used units conforms to green technology. Example of the use of mentioned triad is for a full load of the converter applied to metal scrap. The calculations total emissions of carbon dioxide for different triads of these units were performed. From these calculations it follows that the simultaneous use of oxygen converters after electric arc furnaces for smelting iron (obtained from one blast furnace), it helps to reduce the emission of carbon dioxide to 20%. This suggests that this triad of used units conforms to green technology. An example of using this triad is in the Magnitogorsk Iron and Steel Works, where along with the oxygen converter, electric arc furnaces with the use of locally produced electricity at burning fuel of secondary energy resources from units, in which the fuel is burnt. This practice can be recommended for a number of other metallurgical enterprises.     

结合CCS的炉顶煤气循环—氧气鼓风高炉CO2减排分析

 介绍了炉顶煤气循环—氧气鼓风高炉炼铁技术的研发进展,阐述了碳捕捉及封存技术(CCS)的特点及其技术成熟度,重点分析了几种CO2分离方法的原理及其适用条件,最后应用IPCC2006方法计算分析了结合碳捕捉及封存技术的炉顶煤气循环氧气鼓风高炉的CO2减排效果。结果表明：新工艺的吨铁CO2排放量为582.40kg,较传统高炉CO2减排55%。结合碳捕捉及封存技术的炉顶煤气循环氧气鼓风高炉炼铁技术的开发,能够促进中国钢铁工业CO2减排,对钢铁工业的可持续发展具有十分重要的现实意义和深远影响。     

Aerobic and anaerobic metabolism of Listeria monocytogenes in defined glucose medium

A defined medium with glucose as the carbon source was used to quantitatively determine the metabolic end products produced by Listeria monocytogenes under aerobic and anaerobic conditions. Of 10 strains tested, all produced acetoin under aerobic conditions but not anaerobic conditions. Percent carbon recoveries of end products, typified by strain F5069, were as follows: lactate, 28%; acetate, 23%; and acetoin, 26% for aerobic growth and lactate, 79%; acetate, 2%; formate, 5.4%; ethanol, 7.8%; and carbon dioxide, 2.3% for anaerobic growth. No attempt to determine carbon dioxide under aerobic growth conditions was made. The possibility of using acetoin production to assay for growth of L. monocytogenes under defined conditions should be considered.     

基于废气分析的RH脱碳模型

为连续预测RH熔池内碳含量,实现对RH脱碳终点碳含量控制,以物质C平衡为基础,通过对某钢厂250 t RH废气分析系统分析的废气流量以及废气中CO、CO₂含量进行连续监控,建立了基于废气分析的RH脱碳数学模型.该模型计算表明:对于冶炼成品中碳质量分数≤ 30×10^-6的超低碳钢,模型计算RH脱碳终点碳质量分数误差都在±5×10^-6之间;在RH脱碳后期,废气中CO+CO₂质量分数低于5%时,熔池内脱碳速率低于10^-6 min^-1,此时可判定脱碳结束.同时结合现场工艺条件分析了压降平台以及吹氧操作对RH脱碳速率的影响.     

The oxidation of zinc vapor in CO-CO2-N2 gas mixtures

The kinetics of oxidation of zinc vapor in the Zn-CO-CO₂-N₂ system was investigated for zinc partial pressures of 0.01 to 0.09 atm, carbon monoxide partial pressures up to 0.5 atm, and carbon dioxide partial pressures up to 0.6 atm at 730 °C to 900 °C. The experimental apparatus consisted of a flow reactor and a multitemperature zone furnace. Known gas compositions were generated and the rate of oxidation of zinc vapor was determined from the mass of zinc oxide deposited under controlled conditions. The rate of oxidation of zinc was found to be a function of temperature and of the partial pressures of zinc, carbon monoxide, and carbon dioxide. It was autocatalytic with respect to carbon monoxide and independent of the total mass of zinc oxide deposited. The reactions occurring in parallel for this mechanism are

Effect of moisture and nitrogen levels on the decomposition of wheat straw in soil

Two per cent of wheat straw was mixed with samples of a slightly degraded chernozem soil, and its decomposition was studied at 10, 20, and 30 per cent moisture content of the soil with the addition of 160, 240, and 400 ppm of NH4 + -N. The overall decomposition, measured as CO2 production, and total carbon loss from the soil at 28 degrees C was enhanced by the added nitrogen at all levels of moisture in proportion to the quantity added. Maximum mineralization of the straw carbon was observed at 30 per cent moisture content but there was no significant difference between the amount of carbon mineralized at 20 and 30 per cent moisture levels. No stabilization of the substrate took place in the soil except at 240 and 400 ppm of applied nitrogen at 30 per cent moisture level towards the end of the incubation period. More straw carbon was mineralized when the soil samples were subjected to daily measurements of CO2 evolved than when CO2 measurements were made at intervals over the same period of incubation.     

Partial cardiopulmonary bypass in rats for evaluating ischemia-reperfusion injury

The authors developed a miniaturized partial cardiopulmonary bypass model in rats by using membrane oxygenators. Sprague-Dawley rats underwent general anesthesia and tracheostomy for ventilation. Partial cardiopulmonary bypass was carried out through the jugular cannula (18 gauge) for venous blood drainage and through the femoral arterial cannula (24 gauge) at a flow of 50 ml/kg/min. Membrane oxygenators used in this study maintained arterial oxygen tensions (PaO2) at 300-500 mmHg and carbon dioxide tensions (PaCO2) at 25-35 mmHg, with a gas mixture of 95% O2 + 5% CO2 (n = 7) for at least 2 hr of bypass circulation. To test the feasibility of this system for investigation of ischemia-reperfusion injury, hypoxic challenges with gas mixtures of different oxygen concentrations were examined. After equilibration of the bypass circulation for 1 hr, the following gases were tested for 15 min: Group I, 95% air + 5% CO2 (FiO2 = 0.21, n = 5); Group II, 10% O2 + 5% CO2 + 85% N2 (FiO2 = 0.1, n = 5); and Group III, 95% N2 + 5% CO2 (FiO2 = 0, n = 5). Equilibrated PaO2 values after challenge with these gases for 15 min were as follows: Group I: 89.6 +/- 3.7, Group II: 53.8 +/- 1.4, Group III: 25.6 +/- 2.0 mmHg (p < 0.01 between Groups I and II, I and III, II and III; p < 0.01 vs. prehypoxic PaO2 values in all groups). PaO2 values returned to the previous level within 15 min after return to the standard gas mixture (95% O2 + 5% CO2) supply. This system provided stable cardiopulmonary bypass in rats for at least 2 hr and may be useful for investigation of ischemia-reperfusion injury.     

Pulse oximetry in severe carbon monoxide poisoning

STUDY OBJECTIVES: To evaluate the accuracy and quantitate the error of pulse oximetry measurements of arterial oxygenation in patients with severe carbon monoxide (CO) poisoning. DESIGN: Retrospective review of patient clinical records. SETTING: Regional referral center for hyperbaric oxygen therapy. PATIENTS: Thirty patients referred for treatment of acute severe CO poisoning who demonstrated carboxyhemoglobin (COHb) levels >25%, with simultaneous determinations of arterial hemoglobin oxygen saturation by pulse oximetry (SpO2) and arterial blood gas (ABG) techniques. MEASUREMENTS AND RESULTS: COHb levels and measurements of arterial oxygenation from pulse oximetry, ABG analysis, and laboratory CO oximetry were compared. SpO2 did not correlate with COHb levels. SpO2 consistently overestimated the fractional arterial oxygen saturation. The difference between arterial hemoglobin oxygen saturation (SaO2) calculated from ABG analysis and SpO2 increased with increasing COHb level. CONCLUSIONS: Presently available pulse oximeters overestimate arterial oxygenation in patients with severe CO poisoning. An elevated COHb level falsely elevates the SaO2 measurements from pulse oximetry, usually by an amount less than the COHb level, confirming a prior observation in an animal model. Accurate assessment of arterial oxygen content in patients with CO poisoning can currently be performed only by analysis of arterial blood with a laboratory CO-oximetry.     

CO2顶吹比例对转炉终点控制的影响

结合CO₂的高温反应特性,针对性地制定了CO₂冶炼工艺,并对转炉顶吹CO₂比例对终点磷、氮和碳氧浓度积的影响进行了工业试验研究。结果表明:随着转炉冶炼前中期CO₂顶吹比例由4.84%逐渐提高到9.68%,转炉终点磷的质量分数先下降后基本不变,氮的质量分数逐渐下降,碳氧浓度积与渣中TFe变化趋势基本相同,均为先降低后增加,对于不同指标最佳顶吹CO₂比例不同。试验转炉终点磷、氮的质量分数、碳氧浓度积与渣中TFe均下降,下降比例最高分别为20.4%、34.3%、12.92%和8.89%。      

Nitrification in Pure Oxygen Activated Sludge Systems

Mixed liquor pH and temperature are two parameters that affect the growth rate of nitrifying bacteria and therefore the minimum solids retention time required to achieve nitrification. The objective of this study was to determine the consequence of low mixed liquor pH, and to determine if pH depression could be alleviated by recovering alkalinity through denitrification in a pure oxygen activated sludge system. The study was conducted at the University of Manitoba using laboratory scale, pure oxygen activated sludge reactors, fed with primary effluent. The results indicated that when denitrification was not included in the process, the concentration of CO2 in the headspace of the pure oxygen reactors increased to as high as 15% due to carbon oxidation and endogenous respiration. The high CO2 concentration in the headspace combined with low alkalinity caused by nitrification resulted in bulk mixed liquor pHs below 5.5. In order to maintain complete nitrification at a temperature of 24°C and a mixed liquor pH of 5.5, a solids retention time (SRT) of 12 days was required. In comparison, when denitrification was included in the process the pH of the mixed liquor was increased to 6.4 allowing for full nitrification at an SRT of 5.6 days at a temperature of 24°C. The increase in pH in the denitrification trains was attributed to three factors: recovery of alkalinity through the denitrification process, the conversion of influent carbon to CO2 in the anoxic reactor allowing the CO2 to escape to the atmosphere, and the recycle of mixed liquor super saturated with CO2 from the pure oxygen reactor to the anoxic reactor allowing the CO2 to escape to the open atmosphere. It was determined that the nitrifier growth rate at 12°C was approximately 50% of the rate measured at 24°C. At mixed liquor pHs between 6.0 and 6.3 at a temperature of 12°C, the specific nitrifier growth rate was between 0.12 and 0.15?d?1, while at 24°C, the specific nitrifier growth rate was between 0.25 and 0.30?d?1 at pHs ranging from 5.0 to 6.1     

Hemodynamic rounds series II: Coronary hemodynamics for angioplasty and stenting after myocardial infarction: use of absolute, relative coronary velocity and fractional flow reserve

To assess the effects and site of action of a sub-anaesthetic concentration of isoflurane, desflurane and sevoflurane (0.1 minimum alveolar concentration (MAC)) on respiratory control, we measured the ventilatory response to square wave changes in PE1CO2 against a background of normoxia. Using the computer steered "end-tidal forcing system", 2 min of steady state ventilation were followed by a step increase in PE1CO2 (1-1.5 kPa). This level was maintained for 8 min, followed by a step decrease to the original value for another 8 min. Each hypercapnic response was separated into a fast, peripheral component and a slow, central component, characterized by a time constant, carbon dioxide sensitivity, time delay and off-set. We studied 25 healthy volunteers; they performed 2-3 studies without and 2-3 studies during inhalation of the anaesthetic agent. Level of sedation was scored using a subjective seven-point scale from 0 (= alert and awake) to 6 (unrousable). In the isoflurane (16 subjects, 33 control, 37 drug studies) and sevoflurane (15 subjects, 40 control, 41 drug studies) studies, peripheral carbon dioxide sensitivity was reduced by approximately 45% and approximately 27% (ANOVA, P < 0.05 vs control), respectively, without affecting central carbon dioxide sensitivity or apnoeic threshold. In the desflurane study (16 subjects, 36 control, 37 drug studies), no significant effect was observed for any of the variables measured. A significant relation was observed between sedation score and change from control in central carbon dioxide sensitivities in the isoflurane and desflurane studies and in the change in the ratio peripheral carbon dioxide sensitivity over total carbon dioxide sensitivity in the sevoflurane studies. At the highest level of sedation observed (score 3-arousal state comparable with "light sleep"--in three subjects) these latter variables differed significantly from those in the other observed sedation levels (scores 1 and 2-a state of drowsiness). We conclude that 0.1 MAC of isoflurane and sevoflurane depressed the peripheral chemoreflex loop, without affecting the central chemoreflex loop. Desflurane at the same MAC showed no effect on peripheral and central carbon dioxide sensitivity. When the level of sedation was considered, our data suggested that at levels of sedation comparable with sleep, a depressive effect of all three anaesthetics was observed on the central chemoreflex loop.