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PubMed2006

Identification of the microbiological community in biogas systems and evaluation of microbial risks from gas usage.

The plans for introducing biogas produced from organic waste to the pipe system for natural gas has raised concerns about the risk of transmitting disease via the gas. To assess this risk, condensate water from gas pipes and gas from different parts of a biogas upgrading system were sampled and cultured for microbial content. On average, 10(5) cfu ml-1 were found in the condensate water throughout the system, while in the gas between 10 and 100 cfu m-3 were found. The microorganisms were subjected to further identification and found to represent a wide variety, e.g. fungi and spore-forming and non-spore-forming bacteria, including species such as Enterobacteriaceae. The number of microorganisms found in the biogas corresponded to the densities in sampled natural gas, which also held 10-100 cfu m-3. Since no pathogens were identified and since the exposure to gas from e.g. cookers and refuelling of cars may only result in the inhalation of small volumes of gas, the risk of spreading disease via biogas was judged to be very low.

Bacteria↗
PubMed2006

Passive landfill gas emission - Influence of atmospheric pressure and implications for the operation of methane-oxidising biofilters.

A passively vented landfill site in Northern Germany was monitored for gas emission dynamics through high resolution measurements of landfill gas pressure, flow rate and composition as well as atmospheric pressure and temperature. Landfill gas emission could be directly related to atmospheric pressure changes on all scales as induced by the autooscillation of air, diurnal variations and the passage of pressure highs and lows. Gas flux reversed every 20 h on average, with 50% of emission phases lasting only 10h or less. During gas emission phases, methane loads fed to a connected methane oxidising biofiltration unit varied between near zero and 247 g CH4 h(-1)m(-3) filter material. Emission dynamics not only influenced the amount of methane fed to the biofilter but also the establishment of gas composition profiles within the biofilter, thus being of high relevance for biofilter operation. The duration of the gas emission phase emerged as most significant variable for the distribution of landfill gas components within the biofilter.

Air Movements↗
PubMed2000

Treatment of persistent corneal epithelial defect with extended wear of a fluid-ventilated gas-permeable scleral contact lens.

PURPOSE: To report treatment of persistent corneal epithelial defects unresponsive to other therapies by extended wear of a fluid-ventilated gas-permeable scleral contact lens. METHODS: In this retrospective study, 14 eyes of 13 consecutive patients referred for the treatment of persistent corneal epithelial defects that failed to heal with conventional therapies or developed epithelial defects after penetrating keratoplasty for persistent corneal epithelial defects were fitted with an extended-wear gas-permeable scleral lens. These included seven eyes of six patients with Stevens-Johnson syndrome and seven eyes of seven patients who did not have Stevens-Johnson syndrome. Twelve eyes had undergone recent penetrating keratoplasty. All 14 eyes were fitted with a gas-permeable scleral contact lens designed to avoid the intrusion of air bubbles under its optic. An antibiotic and corticosteroid were added to the lens fluid reservoir or instilled before each lens insertion in 12 of 14 eyes. The lenses were worn continuously except for brief periods of removal for purposes of cleaning, replacement of the lens fluid reservoir, and examination and photography of the cornea. RESULTS: Five of the seven persistent corneal epithelial defects associated with Stevens-Johnson syndrome healed. The persistent corneal epithelial defects of four of these eyes re-epithelialized within 7 days, and a fifth healed in 27 days of gas-permeable scleral lens extended wear. A sixth persistent corneal epithelial defect that failed to heal initially re-epithelialized after a subsequent penetrating keratoplasty and gas-permeable scleral lens extended wear. The seventh eye healed after 3 days of gas-permeable scleral lens extended wear, but the persistent corneal epithelial defect subsequently recurred. Three of seven non-Stevens-Johnson syndrome persistent corneal epithelial defects re-epithelialized within 36 hours, 6 days, and 36 days, respectively. Of the six (six of 14) persistent corneal epithelial defects that failed to heal with a gas-permeable scleral lens extended wear, one subsequently healed after multiple amniotic membrane grafts. Microbial keratitis occurred in four eyes (four of 14) and graft failure in one eye, all of which required repeat penetrating keratoplasty. CONCLUSION: Extended wear of an appropriately designed gas-permeable scleral contact lens was effective in promoting the healing of persistent corneal epithelial defects in some eyes that failed to heal after other therapeutic measures. Re-epithelialization appears to be aided by a combination of oxygenation, moisture, and protection of the fragile epithelium afforded by the scleral lens. However, microbial keratitis represents a significant risk.

Adolescent↗
PubMed1991

B-scan ultrasonography of eyes containing intravitreal gas.

Contact B-scan ultrasonography was performed on postoperative eyes containing intravitreal gas. Correlation of the ultrasonograms with the ophthalmoscopic findings disclosed that intraocular gas had a characteristic appearance on B-scan ultrasonography. Gas-fluid and gas-tissue interfaces were so highly reflective that no structures within or behind a bubble could be visualized. Shadowing, reverberation, and reflection artifacts were prominent, and dominated ultrasonographic findings. If the ultrasonographic characteristics of gas are understood, it is possible to use B-scan ultrasonography to determine if intraocular gas is present, whether there are one or several bubbles, and what percentage of the vitreous cavity is filled by gas. Specular reflection from a gas-fluid interface may be used to examine portions of the eye that might not otherwise be easily seen with ultrasonography.

Eye↗
PubMed1990

Hazards of laser beam reflections in eyes containing gas.

Three patients suffered photic or thermal laser injuries at unintended sites because of reflection from gas-fluid interfaces in eyes containing gas. Fresnel's equations predict the amount of light transmitted or reflected at optical interfaces. Application of Fresnel's equations demonstrate that significant laser reflection occurs at gas-fluid or fluid-gas interfaces, especially at high angles of incidence. Photocoagulation across gas-fluid or fluid-gas interfaces should be avoided to reduce the risk of unintended damage from reflected light. If photocoagulation must be performed across an interface, the surgeon should minimize the angle of incidence of the treatment laser beam, use a divergent beam, and consider the location and intensity of the reflected beam. Because of the higher phototoxicity of blue light, photocoagulation with blue-green lasers across gas-fluid or fluid-gas interfaces is undesirable. Proper polarization of the treatment laser beam may significantly reduce laser reflectance.

Aged↗
PubMed2003

Determination of gas-oil miscibility conditions by interfacial tension measurements.

Processes that inject gases such as carbon dioxide and natural gas have long been and still continue to be used for recovering crude oil from petroleum reservoirs. It is well known that the interfacial tension between the injected gas and the crude oil has a major influence on the efficiency of displacement of oil by gas. When the injected gas becomes miscible with the crude oil, which means that there is no interface between the injected and displaced phases or the interfacial tension between them is zero, the oil is displaced with maximum efficiency, resulting in high recoveries. This paper presents experimental measurements of interfacial tension between crude oil and natural gases (using a computerized drop shape analysis technique) as a function of pressure and gas composition at the temperature of the reservoir from which the crude oil was obtained. The point of zero interfacial tension was then identified from these measurements by extrapolation of data to determine minimum miscibility pressure (MMP) and minimum miscibility composition (MMC). The gas-oil miscibility conditions thus obtained from interfacial tension measurements have been compared with the more conventional techniques using slim-tube tests and rising-bubble apparatus as well as predictive correlations and visual observations. The miscibility pressures obtained from the new VIT technique were 3-5% higher than those from visual observations and agreed well with the slim-tube results as well as with the correlations at enrichment levels greater than 30 mol% C2+ in the injected gas stream. The rising bubble apparatus yielded significantly higher MMPs. This study demonstrates that the VIT technique is rapid, reproducible, and quantitative, in addition to providing visual evidence of gas-oil miscibility.

Journal Article↗
PubMed2002

Ultrasonic measurement of gas flow using electrostatic transducers.

Ultrasonic gas flowmeters typically use narrowband piezoelectric transducer arrangements for interrogating the flow of gas in a pipe. In this work, the suitability of broadband electrostatic transducers operating at frequencies of up to 1 MHz for ultrasonic measurement of gas flow has been investigated. The transit time method of ultrasonic gas flow measurement was adopted and experiments were carried out using a laboratory test rig capable of producing a range of gas flowrates up to 17.5 m/s. The test rig also allowed easy interchange of different prototype flowmetering sections. Times of flight of ultrasonic waves interrogating the gas flow were measured using separate send/receive electrostatic transducer arrangements. Two flowmeter configurations were considered. The first interrogated the flow at 45 degrees in contra-propagating upstream and downstream directions. The second consisted of an up-stream interrogation at 45 degrees to the gas flow and an interrogation made normal to the flow direction. k factors correlating the fluid velocity along the ultrasonic path with the mean fluid velocity in the pipe were calculated using experimental ultrasonic data and anemometer measurements. All transducer configurations were numerically modelled using the computational fluid dynamics software package FLOTRAN (ANSYS Inc.). Theoretical gas flow velocities for both transducer arrangements were subsequently compared with experimental values and found to be in excellent agreement. A flow-dependent frequency shift of the received ultrasonic signals was also observed simultaneously with the transit time measurement.

Journal Article↗
PubMed2001

Flux enhancement with gas injection in crossflow ultrafiltration of oily wastewater.

The gas injection technique was introduced to achieve flux improvement in cross-flow ultrafiltration of oil emulsion. By the nitrogen gas injection, homogeneous liquid phase oil/water emulsion was changed to heterogeneous gas- liquid phase. The injected gas causes positive effect of promoting turbulence, but it also has negative effect of decreasing the effective membrane area due to the partial occupation of membrane pores by bubbles. The efficiency of the gas injection was found out to be dependent on bubble fractions in the mixture: at sufficient bubble fractions the higher flux was observed. but at lower bubble fractions the flux rather decreased compared with that without gas injection. An attempt was made to explain the mechanisms for the dual aspects of gas injection. Turbulence dampening effect was also observed when the dependence of mass transfer coefficient on cross-flow rate was investigated with gas injection.

Air Movements↗
PubMedDate not supplied

Hazardous air pollutant emissions from gas-fired combustion sources: emissions and the effects of design and fuel type.

Air emissions from gas-fired combustion devices such as boilers, process heaters, gas turbines and stationary reciprocating engines contain hazardous air pollutants (HAPs) subjected to consideration under the federal clean air act (CAA). This work presents a recently completed major research project to develop an understanding of HAP emissions from gas-fired boilers and process heaters and new HAP emission factors based on field emission tests of gas-fired external combustion devices used in the petroleum industry. The effect of combustion system design and operating parameters on HAP emissions determined by both field and research tests are discussed. Data from field tests of gas-fired petroleum industry boilers and heaters generally show very low emission levels of organic HAPs. A comparison of the emission data for boilers and process heaters, including units with and without various forms of NOx emission controls, showed no significant difference in organic HAP emission characteristics due to process or burner design. This conclusion is also supported by the results of research tests with different burner designs. Based on field tests of units fired with natural gas and various petroleum industry process gases and research tests in which gas composition was intentionally varied, organic HAP emissions were not determined to be significantly affected by the gas composition. Research data indicate that elevated organic HAP emission levels are found only under extreme operating conditions (starved air or high excess air combustion) associated with poor combustion.

Journal Article↗
PubMed1998

Mutagenic activities of exhaust gas and ash from sludge incineration plants.

We have found that the exhaust gas from many incineration plants of municipal solid wastes (MSW) show significant mutagenic activities. The mutagenic activities of exhaust gas from incineration plants of the other wastes have not been studied in detail. Here, we analyzed the mutagenic activities and compounds in exhaust gas and ash from seven sludge incineration plants. Some samples of the exhaust gas from the sludge incineration plants showed high mutagenic activities; although, none of the ash residues showed mutagenic activities. There was no relationship between the mutagenic activities and furnace types, the plant size or the apparent residence time of the gas in the furnace. The mutagenic activities of the exhaust gas were produced during incomplete combustion at lower temperatures. Direct mutagenic activities without S9 mix were higher than indirect mutagenic activities with S9 mix which was made from rat liver homogenate and was used to test mutagenic activity after metabolism. These results are different to those of MSW incineration plants. We analyzed the mutagenic compounds in the exhaust gas by GC/MS after fractionation by HPLC, but they could not be identified. We found that the mutagenic compounds in the exhaust gas were different from the compounds that were produced from the MSW incineration plants. We believed that these mutagenic compounds might be non-volatile and more polar than the heterocyclic amines, Trp-P-2, Trp-P-1 and Glu-P-1, which are typical mutagenic compounds in sewage and sludge.

Animals↗
PubMed2003

Comparison of silicone oil versus gas tamponade in the treatment of idiopathic full-thickness macular hole.

PURPOSE: To compare anatomic and functional outcomes of macular hole surgery with either silicone oil or C(3)F(8) gas tamponade. DESIGN: Retrospective comparative interventional study. PARTICIPANTS: Fifty-four eyes of 51 patients underwent pars plana vitrectomy for macular holes. Thirty-one eyes were treated with silicone oil tamponade, and 23 eyes were treated with C(3)F(8) tamponade. METHODS: Demographics, preoperative and postoperative characteristics, and complications were analyzed. MAIN OUTCOME MEASURES: Preoperative and postoperative visual acuity, initial hole closure, number of persistent or recurrent holes, number of reoperations, and final hole closure. RESULTS: The silicone oil and gas tamponade groups were demographically similar. The rate of hole closure after one operation with oil tamponade was significantly lower than that with gas tamponade (65% vs. 91%; P = 0.022). The percentage of patients undergoing a second operation was significantly higher in the oil group (35% vs. 4%; P = 0.006). However, with reoperations, the final rate of hole closure was similar between the oil and gas groups (90% vs. 96%; P = 0.628). The final median visual acuity for the gas group was significantly better than for the oil group (20/50 vs. 20/70; P = 0.047). CONCLUSIONS: C(3)F(8) gas proved to be a more effective tamponade than silicone oil with respect to achieving initial closure of macular holes. Eyes receiving an oil tamponade required significantly more reoperations to achieve a similar rate of hole closure compared with eyes undergoing a gas tamponade. Final visual acuity was better for gas-operated eyes than for silicone-operated eyes.

Aged↗
PubMed1999

Noninvasive measurement of the hydrostatic pressure in a fluid-filled cavity based on the disappearance time of micrometer-sized free gas bubbles.

A new method for noninvasive pressure measurement, based on the disappearance time of micrometer-sized free gas bubbles, is described in this article. An ultrasound (US) contrast agent, consisting of encapsulated gas bubbles, is used as a vehicle to transport the free gas bubbles to the desired region where the pressure is to be measured. The small free gas bubbles are generated at the region of interest (e.g., heart chambers), from the encapsulated gas bubbles, which rupture when they are exposed to a single low-frequency (e.g., 0.5 MHz), high acoustic amplitude US burst. The released gas bubbles persist for only a few ms and dissolve in the liquid, depending on their size, the gas, the liquid characteristics and ambient parameters such as temperature, gas concentration and pressure. A pressure-disappearance time relationship is determined using a sequence of high-frequency (e.g., 10 MHz), low acoustic amplitude US pulses. From in vitro experiments, reproducible results show a significant difference between the disappearance time of the bubbles as function of the local pressure, resulting in a quicker disappearance of the bubble for higher values of the pressure. The sensitivity of the method to small pressure changes (50 mmHg) is demonstrated.

Contrast Media↗
PubMed2001

Application of ESP for gas cleaning in cement industry--with reference to India.

Electrostatic precipitators (ESP) are used for gas cleaning in almost every section of cement manufacture. Application of ESP is studied, keeping in view Indian conditions. The characterisation of dust emissions has been done for different units, such as rotary kiln and raw mill, alkali by-pass, clinker cooler, cement and coal mill, in terms of exit gas quantity, temperature, dew point, dust content and particle size. It is seen that all these characteristics have a wide range of variance. The ESP system must effectively deal with these variations. The fundamental analytical expression governing the performance of ESP, i.e. the Deutsch equation, and that for particle migration velocity, were analysed to predict the effect of major operating parameters, namely particle size, temperature and applied voltage. Whereas the migration velocity (and the efficiency) varies directly with the particle size, it is proportional to the square and square root of applied voltage and absolute temperature of the gas, respectively. The increase in efficiency due to temperature is not seen in dc based ESP, perhaps due to more pronounced negative effect on the applied voltage due to the increase in dust resistivity at higher temperatures. The effect of gas and dust characteristics on the collection efficiency of ESP, as seen in the industrial practice, is summarised. Some main process and design improvements effectively dealing with the problem of gas and dust characteristics have been discussed. These are gas conditioning, pulse energization, ESP-fabric filter (FF) combination, improved horizontal flow as well as open top ESP.Generally, gas conditioning entails higher operating and maintenance costs. Pulse energization allows the use of hot gas, besides reducing the dust emission and power consumption. The improved horizontal flow ESP has been successfully used in coal dust cleaning. The open top or vertical flow ESP has a limitation on collection efficiency as it provides for only one electric field.

Air Pollutants↗
PubMed2006

Characterization of gas-phase molecular interactions on differential mobility ion behavior utilizing an electrospray ionization-differential mobility-mass spectrometer system.

Differential mobility spectrometry (DMS) is a rapidly advancing technology for gas-phase ion separation. The interfacing of DMS with mass spectrometry (MS) offers potential advantages over the use of mass spectrometry alone. Such advantages include improvements to mass spectral signal/noise ratios, orthogonal/complementary ion separation to mass spectrometry, enhanced ion and complexation structural analysis, and potential for rapid analyte quantitation. The introduction of a new ESI-DMS-MS system and its utilization to aid in the understanding of DMS separation theory is described. A current contribution to DMS separation theory is one of an association/dissociation process between ions/molecules in the gas phase during the differential mobility separation. A model study was designed to investigate the molecular dynamics and chemical factors influencing the theorized association/dissociation process, and the mechanisms by which these gas-phase interactions affect an ion's DM behavior. Five piperidine analogues were selected as model analytes, and three alcohol drift gas dopants/modifiers were used to interrogate the analyte ions in the gas phase. Two proposed DMS separation mechanisms, introduced as Core and Façade, corresponding to strong and weak attractions between ions/molecules in the gas phase, are detailed. The proposed mechanisms provide explanation for the observed changes in analyte separation by the various drift gas modifiers. Molecular modeling of the proposed mechanisms provides supportive data and demonstrates the potential for predictive optimization of analyte separation based on drift gas modifier effects.

Journal Article↗
PubMedDate not supplied

On-line measurement of gas production rates.

Gas evolution rates represent an important variable to track in biological and certain electrochemical processes. Accurate gas flow rate sensors exist for gas streams possessing a pressure head, such as when pressurized air or oxygen is delivered to a fermentation process. However, these devices impose pressure heads that can inhibit gas production and, therefore, yield false measurements. Examples of effected processes would include electrochemical production of a gas at the electrode (e.g., electrolysis) or anaerobic fermentation (e.g., anaerobic production of methane). In this work, we present an on-line gas measurement technique that measures on-line gas production from an anaerobic microbial process that is continuously fed simulated food waste over a 6-month period. Commentary is given on the sensor's accuracy and ease of use within the context of long-term operation, ability to measure both low and high gas production rates, as well as its potential for process control and system-health monitoring.

Algorithms↗
PubMed2003

As, Hg, and Se flue gas sampling in a coal-fired power plant and their fate during coal combustion.

As, Hg, and Se are the most volatile elements in the flue gas from a coal-fired power plant. Significant amounts of these elements cause an undesired direct gaseous emission, which leads to a serious environmental health risk. The main focus of this study is to evaluate the possibility of simultaneous sampling of these volatile elements using an accurate official method for Hg (the most volatile element). A study of As, Hg, and Se emissions from a 1400 MW coal-fired power plant equipped with electrostatic precipitators (ESPs) was carried out for the combustion of a mixture of two types of coal. Simultaneous sampling of coal, bottom ash, fly ash, flue gas, and particles associated with the gas phase has been performed. Flue gas has been sampled by the Ontario Hydro Method Sampling Train, an ASTM method for Hg speciation. This sampling method was tested for As and Se sampling. As and Se determinations have been performed by HG-AAS, and Hg has been determined by CV-AAS. The results were used to examine the following: overall mass balances, relative distribution of these elements in the coal-fired power plant; As, Hg, and Se concentrations in coal and combustion residues; and predominant oxidation state for Hg in flue gas. The mass balances obtained for As, Hg, and Se were satisfactory in all cases; nevertheless, relative enrichment values in fly ash for As and Se were low; therefore, we concluded that As sampling in flue gas can be conducted by application of the Ontario Hydro Method; nevertheless Se released in the gas phase is not completely collected by this sampling train. Application of this sampling method allowed for performance of Hg speciation. The results indicated that Hg(II) was the predominant species in flue gas. It has also been proved that 24%, more than 99.8%, and 90% for As, Hg, and Se in the stack emissions, respectively, were in the gaseous phase.

Air Pollutants↗
PubMed2000

Gas phase oxidants of cigarette smoke increase nitric oxide synthase and xanthine oxidase activities of rabbit brain synaptosomes.

In the present study we demonstrated that NO synthase and xanthine oxidase of synaptosomes isolated from rabbit brain cortex can be activated by the gas phase of cigarette smoke to produce nitric oxide and superoxide which react together to form peroxynitrite. Expose of synaptosomes, up to 3 hours, in the gas phase of cigarette smoke, a gradual increase in both nitric oxide and superoxide release that were inhibited by N-monomethyl-L-arginine (100 microM) and oxypurinol (1 mM), respectively, was observed. NO synthase and xanthine oxidase activities were increased approximately three fold after treatment of synaptosomes with the gas phase of cigarette smoke as compared with the gas phase deprived of oxidants. Synaptosomes treated with the gas phase of cigarette smoke dramatically increased 3-nitrotyrosine production (used as an index of peroxynitrite formation). Synaptosomes treated with the gas phase of cigarette smoke, promptly increased malondialdehyde production with subsequent decrease of synaptosomal plasma membrane fluidity estimated by fluorescence anisotropy of 1,4-(trimethyl-amino-phenyl)-6-phenyl-hexa-1,3,5-triene. Gas phase deprived of oxidants showed a small but not statistically significant (p > 0.05) effect on both malondialdehyde and membrane fluidity. In summary, the present results indicate that activation of NO synthase and xanthine oxidase of brain cells by oxidants contained in the gas phase of cigarette smoke lead to the formation of peroxynitrite a causative factor in neurotoxicity.

Animals↗
PubMed2006

Stabilization of the disk around beta Pictoris by extremely carbon-rich gas.

The edge-on disk surrounding the nearby young star beta Pictoris is the archetype of 'debris disks', which are composed of dust and gas produced by collisions between--and evaporation of--planetesimals, analogues of Solar System comets and asteroids. These disks may provide insight into the formation and early evolution of terrestrial planets. Previous work on beta Pic concluded that the disk gas has roughly solar abundances of elements, but this poses a problem because such gas should rapidly be blown away from the star, contrary to observations showing a stable gas disk in keplerian rotation. Here we report the detection of singly and doubly ionized carbon (C II, C III) and neutral atomic oxygen (O I) gas in the beta Pic disk. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, because the carbon overabundance should keep the gas disk in keplerian rotation. The overabundance may indicate that the gas is produced from material more carbon-rich than expected of Solar System analogues.

Journal Article↗