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Ocean Worlds biotic fingerprint: multispectral analysis of Micrococcus sp. impact on the reflectance of water vapour plumes
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Abstract
In this article, we present the results of an experiment carried out in a vacuum chamber during which we made multispectral images of Micrococcus sp. cells escaping an analog of the Enceladus’, the Saturnian satellite, ocean. We have added bacterial cells to the sample containing NaCl and NaHCO3, then we placed the sample in a vacuum chamber. We have imaged the evaporation process, bubble scrubbing, and then the process of bacteria emerge into the vacuum. We used a multispectral imaging technique in five optical channels: four visible and one NIR channel. By the analysis of the principal components of multispectral data and the ISO CLASS classification, we distinguished the phases of the experiment corresponding to the light scattering models (Mie solutions of Maxwell’s equations) on water vapor droplets and on the Micrococcus cells. We distinguished the blue and NIR channels as suitable for the detection of Micrococcus sp. in the water vapor.
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Total column water vapour has been retrieved from TROPOMI measurements in the visible blue spectral range and compared to a variety of different reference data sets for clear-sky conditions during boreal summer and winter. The retrieval consists of the common two-step DOAS approach: first the spectral analysis is performed within a linearized scheme and then the retrieved slant column densities are converted to vertical columns using an iterative scheme for the water vapour a priori profile shape, which is based on an empirical parameterization of the water vapour scale height. Moreover, a modified albedo map was used combining the OMI LER albedo and scaled MODIS albedo map. The use of the alternative albedo is especially important over regions with very low albedo and high probability of clouds like the Amazon region.
The errors of the total column water vapour (TCWV) retrieval have been theoretically estimated considering the contribution of a variety of different uncertainty sources. For observations during clear-sky conditions, over ocean surface, and at low solar zenith angles the error typically is around values of 10 %–20 %, and during cloudy-sky conditions, over land surface, and at high solar zenith angles it reaches values around 20 %–50 %.
In the framework of a validation study the retrieval demonstrates that it can well capture the global water vapour distribution: the retrieved H2O vertical column densities (VCDs) show very good agreement with the reference data sets over ocean for boreal summer and winter whereby the modified albedo map substantially improves the retrieval's consistency to the reference data sets, in particular over tropical land masses. However, over land the retrieval underestimates the VCD by about 10 %, particularly during summertime. Our investigations show that this underestimation is likely caused by uncertainties within the surface albedo and the cloud input data: low-level clouds cause an underestimation, but for mid- to high-level clouds good agreement is found. In addition, our investigations indicate that these biases can probably be further reduced by the use of improved cloud input data. For the general purpose we recommend only using VCDs with cloud fraction <20 % and AMF >0.1, which represents a good compromise between spatial coverage and retrieval accuracy.
The TCWV retrieval can be easily applied to further satellite sensors (e.g. GOME-2 or OMI) for creating uniform, long-term measurement data sets, which is particularly interesting for climate and trend studies of water vapour.
With the discovery of the persistent jets of water being ejected to space from Enceladus, an understanding of the effect of the space environment on potential organisms and biosignatures in them is necessary for planning life detection missions. We experimentally determine the survivability of microbial cells in liquid medium when ejected into vacuum. Epifluorescence microscopy, using a lipid stain, and SEM imaging were used to interrogate the cellular integrity of E. coli after ejected through a pressurized nozzle into a vacuum chamber. The experimental samples showed a 94% decrease in visible intact E. coli cells but showed a fluorescence residue in the shape of the sublimated droplets that indicated the presence of lipids. The differences in the experimental conditions versus those expected on Enceladus should not change the analog value because the process a sample would undergo when ejected into space was representative. E. coli was selected for testing although other cell types could vary physiologically which would affect their response to a vacuum environment. More testing is needed to determine the dynamic range in concentration of cells expected to survive the plume environment. However, these results suggest that lipids may be directly detectable evidence of life in icy world plumes.
Lipids and amino acids are regarded as important biomarkers for the search for extraterrestrial life in the Solar System. Such biomarkers may be used to trace methanogenic life on other planets or moons in the Solar System, such as Saturn’s icy moon Enceladus. However, little is known about the environmental conditions shaping the synthesis of lipids and amino acids. Here, we present the lipid production and amino acid excretion patterns of the methanogenic archaeon Methanothermococcus okinawensis after exposing it to different multivariate concentrations of the inhibitors ammonium, formaldehyde, and methanol present in the Enceladian plume. M. okinawensis shows different patterns of lipid and amino acids excretion, depending on the amount of these inhibitors in the growth medium. While methanol did not show a significant impact on growth, lipid or amino acid production rates, ammonium and formaldehyde strongly affected these parameters. These findings are important for understanding the eco-physiology of methanogens on Earth and have implications for the use of biomarkers as possible signs of extraterrestrial life for future space missions in the Solar System.
The detection of silica-rich dust particles, as an indication for ongoing hydrothermal activity, and the presence of water and organic molecules in the plume of Enceladus, have made Saturn's icy moon a hot spot in the search for potential extraterrestrial life. Methanogenic archaea are among the organisms that could potentially thrive under the predicted conditions on Enceladus, considering that both molecular hydrogen (H2) and methane (CH4) have been detected in the plume. Here we show that a methanogenic archaeon, Methanothermococcus okinawensis, can produce CH4under physicochemical conditions extrapolated for Enceladus. Up to 72% carbon dioxide to CH4conversion is reached at 50 bar in the presence of potential inhibitors. Furthermore, kinetic and thermodynamic computations of low-temperature serpentinization indicate that there may be sufficient H2gas production to serve as a substrate for CH4production on Enceladus. We conclude that some of the CH4detected in the plume of Enceladus might, in principle, be produced by methanogens.
There is an increasing interest in the icy moons of the Solar System due to their potential habitability and as targets for future exploratory missions, which include astrobiological goals. Several studies have reported new results describing the details of these moons' geological settings; however, there is still a lack of information regarding the deep subsurface environment of the moons. The purpose of this article is to evaluate the microbial habitability of Europa constrained by terrestrial analogue environments and sustained by radioactive energy provided by natural unstable isotopes. The geological scenarios are based on known deep environments on Earth, and the bacterial ecosystem is based on a sulfate-reducing bacterial ecosystem found 2.8 km below the surface in a basin in South Africa. The results show the possibility of maintaining the modeled ecosystem based on the proposed scenarios and provides directions for future models and exploration missions for a more complete evaluation of the habitability of Europa and of icy moons in general.
We analyzed Cassini Imaging Science Subsystem (ISS) images of the plume of Enceladus to derive particle number densities for the purpose of comparing our results with those obtained from other Cassini instrument investigations. Initial discrepancies in the results from different instruments, as large as factors of 10-20, can be reduced to ∼2 to 3 by accounting for the different times and geometries at which measurements were taken. We estimate the average daily ice production rate, between 2006 and 2010, to be 29 ± 7 kg/s, and a solid-to-vapor ratio, S/V > 0.06. At 50 km altitude, the plume's peak optical depth during the same time period was τ ∼ 10(-3); by 2015, it was ∼10(-4). Our inferred differential size distribution at 50 km altitude has an exponent q = 3. We estimate the average geothermal flux into the sea beneath Enceladus' south polar terrain to be comparable to that of the average Atlantic, of order 0.1 W/m(2). Should microbes be present on Enceladus, concentrations at hydrothermal vents on Enceladus could be comparable to those on Earth, ∼10(5) cells/mL. We suggest the well-known process of bubble scrubbing as a means by which oceanic organic matter and microbes may be found in the plume in significantly enhanced concentrations: for the latter, as high as 10(7) cells/mL, yielding as many as 10(3) cells on a 0.04 m(2) collector in a single 50 km altitude transect of the plume. Mission design can increase these numbers considerably. A lander mission, for example, catching falling plume particles on the same collector, could net, over 100 Enceladus days without bubble scrubbing, at least 10(5) cells; and, if bubble scrubbing is at work, up to 10(8) cells. Key Words: Enceladus-Microbe-Organic matter-Life detection. Astrobiology 17, xxx-xxx.
Detection of extant microbial life on Earth and elsewhere in the Solar System requires the ability to identify and enumerate micrometer-scale, essentially featureless cells. On Earth, bacteria are usually enumerated by culture plating or epifluorescence microscopy. Culture plates require long incubation times and can only count culturable strains, and epifluorescence microscopy requires extensive staining and concentration of the sample and instrumentation that is not readily miniaturized for space. Digital holographic microscopy (DHM) represents an alternative technique with no moving parts and higher throughput than traditional microscopy, making it potentially useful in space for detection of extant microorganisms provided that sufficient numbers of cells can be collected. Because sample collection is expected to be the limiting factor for space missions, especially to outer planets, it is important to quantify the limits of detection of any proposed technique for extant life detection. Here we use both laboratory and field samples to measure the limits of detection of an off-axis digital holographic microscope (DHM). A statistical model is used to estimate any instrument's probability of detection at various bacterial concentrations based on the optical performance characteristics of the instrument, as well as estimate the confidence interval of detection. This statistical model agrees well with the limit of detection of 10(3) cells/mL that was found experimentally with laboratory samples. In environmental samples, active cells were immediately evident at concentrations of 10(4) cells/mL. Published estimates of cell densities for Enceladus plumes yield up to 10(4) cells/mL, which are well within the off-axis DHM's limits of detection to confidence intervals greater than or equal to 95%, assuming sufficient sample volumes can be collected. The quantitative phase imaging provided by DHM allowed minerals to be distinguished from cells. Off-axis DHM's ability for rapid low-level bacterial detection and counting shows its viability as a technique for detection of extant microbial life provided that the cells can be captured intact and delivered to the sample chamber in a sufficient volume of liquid for imaging. Key Words: In situ life detection-Extant microorganisms-Holographic microscopy-Ocean Worlds-Enceladus-Imaging. Astrobiology 17, xxx-xxx.
Roth et al (2014a) reported evidence for plumes of water venting from a southern high latitude region on Europa - spectroscopic detection of off-limb line emission from the dissociation products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which plume activity could be implicated. Two show statistically significant features at latitudes similar to Roth et al, and the third, at a more equatorial location. We consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. If the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the Roth et al feature, however the apparent activity appears more frequently in our data.
We present a new algorithm for satellite retrievals of the atmospheric water vapour column in the blue spectral range. The water vapour absorption cross section in the blue spectral range is much weaker than in the red spectral range. Thus the detection limit and the uncertainty of individual observations are systematically larger than for retrievals at longer wavelengths. Nevertheless, water vapour retrievals in the blue spectral range have also several advantages: since the surface albedo in the blue spectral range is similar over land and ocean, water vapour retrievals are more consistent than for longer wavelengths. Compared to retrievals at longer wavelengths, the sensitivity for atmospheric layers close to the surface is higher due to the (typically 2 to 3 times) higher ocean albedo in the blue. Water vapour retrievals in the blue spectral range are also possible for satellite sensors, which do not measure at longer wavelengths of the visible spectral range like the Ozone Monitoring Instrument (OMI). We investigated details of the water vapour retrieval in the blue spectral range based on radiative transfer simulations and observations from the Global Ozone Monitoring Experiment 2 (GOME-2) and OMI. It is demonstrated that it is possible to retrieve the atmospheric water vapour column density in the blue spectral range over most parts of the globe. The findings of our study are of importance also for future satellite missions (e.g. Sentinel 4 and 5).
Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and relaxation dynamics at pico- to nanosecond timescales and at length scales relevant to cellular dimensions. Studies of high pressure dynamic effects in live organisms are needed to understand Earth’s deep biosphere and biotechnology applications. Here we applied QENS to study water transport in Shewanella oneidensis at ambient (0.1 MPa) and high (200 MPa) pressure using H/D isotopic contrast experiments for normal and perdeuterated bacteria and buffer solutions to distinguish intracellular and transmembrane processes. The results indicate that intracellular water dynamics are comparable with bulk diffusion rates in aqueous fluids at ambient conditions but a significant reduction occurs in high pressure mobility. We interpret this as due to enhanced interactions with macromolecules in the nanoconfined environment. Overall diffusion rates across the cell envelope also occur at similar rates but unexpected narrowing of the QENS signal appears between momentum transfer values Q = 0.7–1.1 Å−1 corresponding to real space dimensions of 6–9 Å. The relaxation time increase can be explained by correlated dynamics of molecules passing through Aquaporin water transport complexes located within the inner or outer membrane structures.
In recent updates of the HITRAN water vapour H2O spectroscopic compilation covering the blue spectral region (here: 394–480 nm) significant changes for the absorption bands at 416 and 426 nm were reported. In order to investigate the consistency of the different cross-sections calculated from these compilations, H2O vapour column density ratios for different spectral intervals were retrieved from long-path and multi-axis differential optical absorption spectroscopy (DOAS) measurements. We observed a significant improvement of the DOAS evaluation when using the updated HITRAN water vapour absorption cross-sections for the calculation of the reference spectra. In particular the magnitudes of the residual spectra as well as the fit errors were reduced.
However, we also found that the best match between measurement and model is reached when the absorption cross-section of groups of lines are scaled by factors ranging from 0.5 to 1.9, suggesting that the HITRAN water vapour absorption compilation still needs significant corrections. For this spectral region we present correction factors for HITRAN 2009, HITRAN 2012, HITEMP and BT2 derived from field measurements. Additionally, upper limits for water vapour absorption in the UV-A range from 330 to 390 nm are given.
The jets of icy particles and water vapor issuing from the south pole of Enceladus are evidence for activity driven by some geophysical energy source. The vapor has also been shown to contain simple organic compounds, and the south polar terrain is bathed in excess heat coming from below. The source of the ice and vapor, and the mechanisms that accelerate the material into space, remain obscure. However, it is possible that a liquid water environment exists beneath the south polar cap, which may be conducive to life. Several theories for the origin of life on Earth would apply to Enceladus. These are (1) origin in an organic-rich mixture, (2) origin in the redox gradient of a submarine vent, and (3) panspermia. There are three microbial ecosystems on Earth that do not rely on sunlight, oxygen, or organics produced at the surface and, thus, provide analogues for possible ecologies on Enceladus. Two of these ecosystems are found deep in volcanic rock, and the primary productivity is based on the consumption by methanogens of hydrogen produced by rock reactions with water. The third ecosystem is found deep below the surface in South Africa and is based on sulfur-reducing bacteria consuming hydrogen and sulfate, both of which are ultimately produced by radioactive decay. Methane has been detected in the plume of Enceladus and may be biological in origin. An indicator of biological origin may be the ratio of non-methane hydrocarbons to methane, which is very low (0.001) for biological sources but is higher (0.1-0.01) for nonbiological sources. Thus, Cassini's instruments may detect plausible evidence for life by analysis of hydrocarbons in the plume during close encounters.
We observed physiological and metabolic activity ofShewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation
at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI
crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability
and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable
zone in the solar system.
The potential to scrub biogas in a high rate pond (HRP) was evaluated using apparatus designed to maximize gas-liquid contact. Experiments compared the removal of carbon dioxide from synthetic biogas by an "in-pond angled gutter" to that by a simulated "counter-current pit." Results showed that the counter current pit has potential for use in biogas scrubbing, with synthetic biogas carbon dioxide composition consistently reduced from 40% to < 5%. The in-pond angled gutter was less effective due to bubble coalescence which reduced the total bubble surface area available for gas transfer. Measurement of oxygen levels in the scrubbed biogas showed that despite supersaturation of oxygen in the HRP water, there was little transfer to the biogas, so that explosive methane/oxygen mixtures would not be formed. Theoretical calculations indicated that the amount of biogas likely to be formed during anaerobic treatment of municipal wastewater could be scrubbed in the HRP of the same advanced pond system with little influence on HRP pH, algal growth and treatment performance. These encouraging results justify further research on this method of biogas purification.
The Cassini spacecraft flew close to Saturn's small moon Enceladus three times in 2005. Cassini's UltraViolet Imaging Spectrograph
observed stellar occultations on two flybys and confirmed the existence, composition, and regionally confined nature of a
water vapor plume in the south polar region of Enceladus. This plume provides an adequate amount of water to resupply losses
from Saturn's E ring and to be the dominant source of the neutral OH and atomic oxygen that fill the Saturnian system.
The prolific activity and presence of a plume on Saturn's tiny moon Enceladus offers us a unique opportunity to sample the interior composition of an icy satellite, and to look for interesting chemistry and possible signs of life. Based on studies of the potential habitability of Jupiter's moon Europa, icy satellite oceans can be habitable if they are chemically mixed with the overlying ice shell on Myr time scales. We hypothesize that Enceladus' plume, tectonic processes, and possible liquid water ocean may create a complete and sustainable geochemical cycle that may allow it to support life. We discuss evidence for surface/ocean material exchange on Enceladus based on the amounts of silicate dust material present in the Enceladus' plume particles. Microphysical cloud modeling of Enceladus' plume shows that the particles originate from a region of Enceladus' near surface where the temperature exceeds 190 K. This could be consistent with a shear-heating origin of Enceladus' tiger stripes, which would indicate extremely high temperatures ( approximately 250-273 K) in the subsurface shear fault zone, leading to the generation of subsurface liquid water, chemical equilibration between surface and subsurface ices, and crustal recycling on a time scale of 1 to 5 Myr. Alternatively, if the tiger stripes form in a mid-ocean-ridge-type mechanism, a half-spreading rate of 1 m/year is consistent with the observed regional heat flux of 250 mW m(-2) and recycling of south polar terrain crust on a 1 to 5 Myr time scale as well.
We numerically model the dynamics of the Enceladus plume ice grains and define our nominal plume model as having a particle size distribution n ( R ) ~ R−q with q = 4 and a total particulate mass rate of 16 kg s ⁻¹ . This mass rate is based on average plume brightness observed by Cassini across a range of orbital positions. The model predicts sample volumes of ~1600 µg for a 1 m ² collector on a spacecraft making flybys at 20–60 km altitudes above the Enceladus surface. We develop two scenarios to predict the concentration of amino acids in the plume based on these assumed sample volumes. We specifically consider Glycine, Serine, α-Alanine, α-Aminoisobutyric acid and Isovaline. The first ‘abiotic’ model assumes that Enceladus has the composition of a comet and finds abundances between 2 × 10 ⁻⁶ to 0.003 µg for dissolved free amino acids and 2 × 10 ⁻⁵ to 0.3 µg for particulate amino acids. The second ‘biotic’ model assumes that the water of Enceladus's ocean has the same amino acid composition as the deep ocean water on Earth. We compute the expected captured mass of amino acids such as Glycine, Serine, and α-Alanine in the ‘biotic’ model to be between 1 × 10 ⁻⁵ to 2 × 10 ⁻⁵ µg for dissolved free amino acids and dissolved combined amino acids and about 0.0002 µg for particulate amino acids. Both models consider enhancements due to bubble bursting. Expected captured mass of amino acids is calculated for a 1 m ² collector on a spacecraft making flybys with a closest approach of 20 km during mean plume activity for the given nominal particle size distribution.
Enceladus, a satellite of Saturn, with its radius of 250 km is the smallest geologically active celestial body in the Solar System. Our model of core origin and evolution indicates that for hundreds of My there were conditions preferable an origin of life. We continue consideration of hypotheses that Enceladus was a cradle of the life in the Solar System. We found that simple organisms could be ejected in icy grains into space by volcanic jets or by meteoroid impacts. Several mechanisms could be responsible for later transport of the grains to the early Earth and other terrestrial planets. We suggest that Enceladus is the most appropriate body for a cradle of life in the Solar System.
Recognizing that descriptions of the physical mechanisms whereby sea-salt particles are introduced into the atmosphere have been treated in some detail by Blanchard (1983) in an earlier publication in this series (Liss and Slinn, 1983), it seems appropriate in this contribution to critique several explicit models for the estimation of the number of sea-salt aerosols per size interval, per unit area of the sea surface, per unit time, produced by these mechanisms under specified meteorological conditions, and in so doing illustrate the state of knowledge of the various processes that link the flux of sea-salt aerosol up from the sea surface to the wind speed measured at an elevation of 10 meters.
We examine Cassini Imaging Science Subsystem images of the E ring taken over a period of almost 7 yr, from 2006 September to 2013 July, in which long, sinuous structures dubbed tendrils are present. We model these structures by numerically integrating the trajectories of particles launched from the sources of the most active geysers recently located along the four main fractures crossing the south polar terrain of the moon, and producing from these integrations synthetic images that we then compare to the real ones. We include the effects of charging and the electromagnetic forces on the particles in addition to the gravity of Saturn and Enceladus. We demonstrate that these structures are produced by the highest velocity particles erupting from the most active geysers and entering Saturn's orbit, and not perturbations of E ring particles by Enceladus. The detailed structures of the tendrils change with the orbital position of Enceladus, a finding likely to be the result of the diurnal variability in the source activity. © 2015. The American Astronomical Society. All rights reserved..
We have supplemented Voyager imaging data from Enceladus (limited to phase angles of 13°-43°) with recent Earth-based CCD observations to obtain an improved determination of the Bond albedo, to construct an albedo map of the satellite, and to constrain parameters in Hapke's (1986, Icarus 67, 264-280) photometric equation. A major result is evidence of regional variations in the physical properties of Enceladus' surface. The average global photometric properties are described by single scattering albedo ω̄o = 0.998 ± 0.001, macroscopic roughness parameter θ̄ = 6 ± 1°, and Henyey-Greenstein asymmetry parameter g = -0.399 ± 0.005. The value of θ̄ is smaller than the 14° found by fitting whole-disk data, which include all terrains on Enceladus. The opposition surge amplitude Bo = 0.21 ± 0.07 and regolith compaction parameter h = 0.014 ± 0.02 are loosely constrained by the scarcity of and uncertainty in near-opposition observations. From the solar phase curve we determine the geometric albedo of Enceladus pv = 0.99 ± 0.06 and phase integral q = 0.92 ± 0.05, which correspond to a spherical albedo A = p vq = 0.91 ± 0.1. Since the spectrum of Enceladus is fairly flat (D. P. Cruikshank, 1980, Icarus 41, 246-258; B. J. Buratti, 1984, Icarus 59, 392-405), we can approximate the Bond albedo AB with the spherical albedo. Our photometric analysis is summarized in terms of an albedo map which generally reproduces the satellite's observed lightcurve and indicates that normal reflectances range from 0.9 on the leading hemisphere to 1.4 on the trailing one. The albedo map also reveals an albedo variation of 15% from longitudes 170° to 200°, corresponding to the boundary between the leading and trailing hemispheres.
Thermal history of Enceladus is investigated from the beginning of accretion to formation of its core (∼400 My). We consider model with solid state convection (in a solid layer) as well as liquid state convection (in molten parts of the satellite). The numerical model of convection uses full conservative finite difference method. The roles of two modes of convection are considered using the parameterized theory of convection. The following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. Heat transfer processes are: conduction, solid state convection, and liquid state convection. It is found that core formation was completed only when liquid state convection had slowed down. Eventually, the porous core with pores filled with water was formed. We investigated also thermal history for different values of the following parameters: time of beginning of accretion tini, duration of accretion tacr, viscosity of ice close to the melting point ηm, activation energy in formula for viscosity E, thermal conductivity of silicate component ksil, ammonia content XNH3, and energy of serpentinization cserp. All these parameters are important for evolution, but not dramatic differences are found for realistic values. Moreover, the hypothesis of proto-Enceladus (stating that initially Enceladus was substantially larger) is considered and thermal history of such body is calculated. The last subject is the Mimas-Enceladus paradox. Comparison of thermal models of Mimas and Enceladus indicates that period favorable for ‘excited path of evolution’ was significantly shorter for Mimas than for Enceladus.
In this paper, the influences of air bubbling mode, air flow rate, air bubble size and feed water quality on the membrane fouling of immersed hollow-fiber (HF) membrane for ultrafiltration of river water were investigated. The membrane was operated in the intermittent suction mode of 9min on/1min off. The results showed that continuous air bubbling was more effective for mitigating membrane fouling than intermittent bubbling (1min on/9min off in the study) at the same air flow rates of 1.0, 2.5, 5.0, and 7.5m3/m2h, respectively. Furthermore, an optimum air flow rate was observed for immersed HF membrane system when considering the alleviating effect on membrane fouling and energy consumption simultaneously, with the optimum value determined as 5.0m3/m2h in this investigation. It was also found that the smaller the air bubble was (4dia of 3.5, 5.0, 6.5, and 8.0mm were investigated), the more effective the air bubbling would be for mitigating the membrane fouling of immersed HF membrane. However, even if air bubbling was performed, eliminating membrane foulants from the feed water before ultrafiltration was still necessary for the reduction of membrane fouling.
$erratia marcescens has been used to demonstrate that bacterial concentrations in jet drops from bursting bubbles can be much higher than the concentration in the water in which the bubbles burst. The ratio of the concentrations is the concentration factor C. A rotating tank was used to study the stripping of bacteria. from the bulk air-water interface. Values for C range from 1 to about 100, increasing with drop size up to about 80 m in diameter. For a given drop size, C varies inversely with the bacterial concentration in the bulk suspension. A bubble 'aging tube' has been developed in which bubbles can be aged (while suspended in a downward moving stream of water) for any given time before they rise to the surface to break. Drops from these bubbles show an increase of C with bubble age, indicating a time rate of change of the adsorption of bacteria to the surface of the bubble. C reaches a steady-state value as high as 10 in 10-20' sec. Surface-active organic material is also adsorbed onto a rising bubble. This process lowers the surface-free energy and, in turn, results in a decrease of the jet-drop size and ejection height. / The concentration of bacteria in jet drops from bursting bubbles can be many times higher
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
A radiation-driven ecosystem on Jupiter's moon is not beyond the
bounds of possibility.
How much dust does Enceladus eject
- S Kempf
- M Horanyi
- J Schmidt
- B Southworth
Kempf, S., Horanyi, M., Schmidt, J., & Southworth, B. (2015). How much
dust does Enceladus eject?. EGUGA, 10528.