Porous Ceramic Disc Research Articles

Removal of Escherichia Coli from water using functionalized porous ceramic disk filter coated with Fe/TiO2 nano-composites

The availability of safe drinking water is an important issue in developing countries and remote areas where clean drinking water cannot be fully accessed. In this study, a low cost porous ceramic disk filter (PCDF) functionalized with Fe/TiO2 nano-composites was used to remove E. coli from water. The production of PCDFs coated with Fe/TiO2 nano-composites was optimized in terms of mass ratio of iron to titanium dioxide in Fe/TiO2 nano-composites, coated weight and rice-husk ratio using response surface methodology. The rice-husk ratio had a great influence on the filtration rate. PCDFs had micro pores that could trap most E. coli. Fe/TiO2 nano-composites could take advantage of the dual roles of nano-TiO2 and Fe to play a synergistic bactericidal effect on the removal of E. coli. During the operation of modified PCDFs, the concentration of E. coli and the light conditions were very important. This study provided a theoretical support for exploring the ceramic disk filter modification and bacteria reduction using PCDFs impregnated with Fe/TiO2 nano-composites. The results can help find a cost-effective and safe solution for solving drinking water problems in rural and remote areas.

Novel Method Reveals a Narrow Phylogenetic Distribution of Bacterial Dispersers in Environmental Communities Exposed to Low-Hydration Conditions.

In this study, we developed a method that provides profiles of community-level surface dispersal from environmental samples under controlled hydration conditions and enables us to isolate and uncover the diversity of the fastest bacterial dispersers. The method expands on the porous surface model (PSM), previously used to monitor the dispersal of individual bacterial strains in liquid films at the surface of a porous ceramic disc. The novel procedure targets complex communities and captures the dispersed bacteria on a solid medium for growth and detection. The method was first validated by distinguishing motile Pseudomonas putida and Flavobacterium johnsoniae strains from their nonmotile mutants. Applying the method to soil and lake water bacterial communities showed that community-scale dispersal declined as conditions became drier. However, for both communities, dispersal was detected even under low-hydration conditions (matric potential, -3.1 kPa) previously proven too dry for P. putida strain KT2440 motility. We were then able to specifically recover and characterize the fastest dispersers from the inoculated communities. For both soil and lake samples, 16S rRNA gene amplicon sequencing revealed that the fastest dispersers were substantially less diverse than the total communities. The dispersing fraction of the soil microbial community was dominated by Pseudomonas species cells, which increased in abundance under low-hydration conditions, while the dispersing fraction of the lake community was dominated by Aeromonas species cells and, under wet conditions (-0.5 kPa), also by Exiguobacterium species cells. The results gained in this study bring us a step closer to assessing the dispersal ability within complex communities under environmentally relevant conditions.IMPORTANCE Dispersal is a key process of bacterial community assembly, and yet, very few attempts have been made to assess bacterial dispersal at the community level, as the focus has previously been on pure-culture studies. A crucial factor for dispersal in habitats where hydration conditions vary, such as soils, is the thickness of the liquid films surrounding solid surfaces, but little is known about how the ability to disperse in such films varies within bacterial communities. Therefore, we developed a method to profile community dispersal and identify fast dispersers on a rough surface resembling soil surfaces. Our results suggest that within the motile fraction of a bacterial community, only a minority of the bacterial types are able to disperse in the thinnest liquid films. During dry periods, these efficient dispersers can gain a significant fitness advantage through their ability to colonize new habitats ahead of the rest of the community.

Low pH, high salinity: Too much for microbial fuel cells?

Twelve single chambered, air-cathode Tubular Microbial Fuel Cells (TMFCs) have been filled up with fruit and vegetable residues. The anodes were realized by means of a carbon fiber brush, while the cathodes were realized through a graphite-based porous ceramic disk with Nafion membranes (117 Dupont). The performances in terms of polarization curves and power production were assessed according to different operating conditions: percentage of solid substrate water dilution, adoption of freshwater and a 35mg/L NaCl water solution and, finally, the effect of an initial potentiostatic growth.All TMFCs operated at low pH (pH=3.0±0.5), as no pH amendment was carried out. Despite the harsh environmental conditions, our TMFCs showed a Power Density (PD) ranging from 20 to 55mW/m2kgwaste and a maximum CD of 20mA/m2kgwaste, referred to the cathodic surface.COD removal after a 28-day period was about 45%.The remarkably low pH values as well as the fouling of Nafion membrane very likely limited TMFC performances. However, a scale-up estimation of our reactors provides interesting values in terms of power production, compared to actual anaerobic digestion plants. These results encourage further studies to characterize the graphite-based porous ceramic cathodes and to optimize the global TMFC performances, as they may provide a valid and sustainable alternative to anaerobic digestion technologies.

Development of radon sources with a high stability and a wide range

A solid (222)Rn (radon) source using a fibrous and porous SiC ceramic disk was developed. The emission rate of radon emanated from the disk depended on the content of (226)Ra and the sintering temperature. A (226)Ra sulfate ((226)RaSO4) solution was dropped on a fibrous SiC ceramic disk (33 mmφ) of 1 mm in thickness, and sintered at 400 °C. The radon concentration from a disk containing (226)Ra of 1.85 MBq was measured to be 38 kBq m(-3) at a carrier airflow rate of 0.5 L min(-1). By adjusting the (226)Ra content or the sweep airflow rate, the radon concentrations were easily controlled over a wide range of over three orders of magnitude. The concentration was very stable for a long term. The compactness of the source disk made is easy for handling the source container and the shielding of gamma radiation from (226)Ra and its decay products. Such advantages in a radon generation system are desirable for experiments of high-level, large-scale radon exposure.

Influence of support structure on the permeation behavior of polyetherimide-derived carbon molecular sieve composite membrane

Abstract Polyetherimide (PEI) was used as polymeric precursor to prepare selective carbon molecular sieve (CMS) layer supported by a porous Al2O3 ceramic disk. The effects of the porous structure and surface roughness of the ceramic support on the interfacial adhesion and texture of the PEI/Al2O3-derived composite CMS membrane were investigated by modulating the sintering temperature and holding time. When the surface roughness of the ceramic support increased, the pore size and its distribution of the selective CMS layer were found to have shifted to the larger one and its roughness increased from the top to the bottom surface. This structure resulted in high permeability and low selectivity. Our results indicate that the porous structure of the ceramic support also played an important role in dominating the pore size and its distribution of the selective CMS layer, which influences the gas separation performance.

TDR pressure cell for monitoring water content retention and bulk electrical conductivity curves in undisturbed soil samples

AbstractThe water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR‐pressure cell (TDR‐Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR‐Cell consists of a 50‐mm‐long and 50‐mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49‐mm‐long and 3‐mm‐diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR‐Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2‐mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σa, as a function of the water content, σa(θ), of the undisturbed soil samples were also performed. An excellent correlation (R2 = 0·988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR‐Cell and those obtained from the 2‐mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σa(θ) relationship was well described by a simple power expression (R2 > 0·95), in which the power factor, defined as tortuosity, ranged between 1·18 and 3·75. Copyright © 2011 John Wiley & Sons, Ltd.

The effect of loading icariin on biocompatibility and bioactivity of porous β-TCP ceramic

In order to enhance the ability of calcium phosphate-based biomaterials for bone defect repair, icariin (Ica), one natural product with ability of promoting osteoblasts differentiation in vitro and enhancing bone formation in vivo, was loaded into porous β-tricalcium phosphate ceramic (β-TCP) disks. The obtained Ica-loaded porous β-TCP ceramic (Ica/β-TCP) disks were characterized by SEM. The SEM photos indicated that the disks had porous structure and the surface morphology of the porous β-TCP ceramic (β-PTCP) disks had no obvious difference from the Ica/β-TCP disks. The Ica release curve of Ica/β-TCP disks showed a burst release during the first 1day and the concentration of released Ica during the first 3days had low cytotoxicity. The loading Ica in Ica/β-TCP disks hardly affected the attachment and morphology of Ros17/28 cells, however, the Ica/β-TCP disks were favorable to supporting the proliferation and differentiation of Ros17/28 cells better compared with the β-PTCP disks. There was plenty of bone-like apatite formed on the surface of Ica/β-TCP disks soaked in SBF solution for three days. After back intramuscular implantation of rats for three months, no obvious osteogenic evidence was detected in β-PTCP disks, but new bone formation was observed in Ica/β-TCP disks. Fibrous tissues and slight inflammatory reaction was also found in the Ica/β-TCP disks and β-TCP disks. Therefore, the loading Ica did not change the biocompatibility of β-TCP ceramic, but enhanced the bioactivity of β-TCP ceramic in vivo. The Ica/β-TCP ceramic had potential to be used for bone defect repair.

Mitigation of Damage to Solid Surfaces From the Collapse of Cavitation Bubble Clouds

The collapse of transient bubble clouds near a solid surface was investigated to test a scheme for mitigation of cavitation-induced damage. The target was a porous ceramic disk through which air could be forced. Transient cavitation bubbles were created using a shock-wave lithotripter focused on the surface of the disk. The dynamics of bubble clouds near the ceramic disks were studied for two boundary conditions: no back pressure resulting in surface free of bubbles and 10 psi (0.7 atm) of back pressure, resulting in a surface with a sparse (30% of area) bubble layer. Images of the cavitation near the surface were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5 MHz focused acoustic transducer) was aligned with the surface. Both the images and the acoustic measurements indicated that bubble clouds near a ceramic face without a bubble layer collapsed onto the boundary, subsequently leading to surface erosion. When a sparse bubble layer was introduced, bubble clouds collapsed away from the surface, thus mitigating cavitation damage. The erosion damage to the ceramic disks after 300 shock waves was quantified using micro-CT imaging. Pitting up to 1 mm deep was measured for the bubble-free surface, and the damage to the bubble surface was too small to be detected.

A TDR-pressure cell design for measuring the soil-water retention curve

This paper presents a new type of pressure cell associated with a zigzag-shaped time domain reflectometry (TDR) probe for determining the soil-water retention (θ(ψ)) curve of disturbed thin soil samples. The pressure cell, designed for pressures ranging between 0 and −500 kPa, consisted of a zigzag copper rod (150-mm long, 2 mm in diameter) vertically installed in a clear plastic cylinder (60-mm high, 50 mm in internal diameter) with six vertical copper rods (60-mm long, 2 mm in diameter) arranged around the inner wall of the plastic cylinder. The cylinder was closed at the base with a nylon cloth and placed on a porous ceramic disc. The inner rod and the six-rod grille of the cell were connected respectively to the inner and outer conductors of a coaxial cable. The results showed that the correlation between the apparent dielectric constant measured with a standard three-rod TDR probe and the zigzag-shaped TDR probe, both immersed in five different non-conductive fluids, was excellent (R2 = 0.99). On the other hand, the volumetric water content measured with the TDR probe of the pressure cell filled up with sand, 2-mm sieved loam and clay-loam soils was highly correlated to the corresponding values calculated from the gravimetric water content and the soil bulk density (R2 = 0.97; RMSE = 2.32 × 10−2). The parameters of the θ(ψ) curves measured for these three different soils with the TDR-pressure cell were within the range of values found in the literature. The cell was also used to study the θ(ψ) changes of a 2–4-mm sample of loam soil aggregates after a slow and a fast-wetting process. While negligible changes in both the soil structure and θ(ψ) were observed following slow wetting, fast wetting resulted in disintegration of aggregates and drastic changes in the shape of the θ(ψ) curve.

Introduction of a compliant gas-layer serves to mitigate damage to solid surfaces from the collapse of cavitation bubble clouds

The collapse of transient bubble clouds near a boundary was investigated. Transient cavitation bubbles were created using a shock-wave lithotripter. A porous ceramic disk (flow-pressure 7.5psi) was placed at the lithotripter focus. Air was forced through the disk to alter the boundary condition at the ceramic disk's proximal face. Gas pressure below 7.5psi resulted in a ceramic disk partially filled with fluid (rigid boundary); gas pressure over 7.5psi resulted in active bubbling at the proximal face (compliant boundary). Cavitation dynamics of bubble clouds near ceramic disks were studied for varying gas pressures (0-10psi). Images of the collapse were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5MHz focused transducer) was aligned with the lithotripter focus. Both the images and the acoustic measurements indicated that bubble clouds near a rigid boundary collapse onto the boundary, forming a re-entrant liquid jet whose impact leads to surface erosion. When a compliant boundary is introduced, bubble clouds collapse away from the surface, thus mitigating cavitation damage. The damage to the ceramic disks was quantified using micro-CT imaging. [Supported by the ORNL Spallation Neutron Source, which is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.]

Design and evaluation of photocatalytic micro-channel reactors using TiO 2-coated porous ceramics

Photocatalytic micro-channel reactor was designed by exploiting porous ceramic disks as a support for TiO 2 photocatalyst. Ethanol solution of titanyl(IV)acetylacetonate and a commercial titania sol were used as the starting materials for the synthesis of TiO 2 layer. A rougher surface of the TiO 2 channel was prepared from titanyl(IV)acetylacetonate solution by comparing with that from a titania sol. Photocatalytic activity of the micro-channel reactor at various circulation velocities was evaluated by measuring the decay of absrobance of methylene blue aqueous solution. Since the porous disks prepared with the titania sol showed a higher photocatalytic activity at medium flow rates, the surface roughness of the TiO 2 was found to decrease the activity. A stagnation region near the rough surface may expand at higher flow rates and then the mass transfer between the TiO 2 surface and the laminar flow was suppressed for the reactant molecules and decomposition intermediates.

Photocatalytic microreactor study using TiO2-coated porous ceramics

Two kinds of porous ceramic disks, having through-holes with diameters of 0.1 and 0.05 mm, were coated with TiO2 using two different starting solutions: titanyl(IV)acetylacetonate and a commercial titania sol (STS-01). The morphology of these porous ceramics before and after TiO2 coating was observed by SEM. The TiO2-coated porous ceramics were examined as honeycomb photocatalytic microreactors. The photocatalytic activity was evaluated using the decomposition of methylene blue solution for radiation angles of 0° and 10° with respect to the pore axis. The highest photocatalytic activity was obtained for the porous ceramic having the pore diameter of 0.1 mm, coated with titanyl(IV)acetylacetonate and irradiated with a light angle of 0° with respect to the pore axis.

Lactic acid enantioseparation by means of porous ceramic disc and hollow fiber organic membrane

The d, l-lactic acid racemic mixture ( d, l-LA) was used as model mixture to study the separation of the enantiomers using the chiral selector N-3,5-dinitrobenzoyl- l-alanine-octylester ( l-SO). Two types of membrane separation were applied, namely supported liquid membrane and chiral solid membrane. In the first case the chiral selector dissolved in toluene was physically immobilised into the polypropylene hollow fiber membrane pores. In the case of the chiral solid membrane, the selector was introduced in a ceramic disc by means of its organic solution by ultrafiltration and than toluene solvent was evaporated from the pores. After its evaporation from the membrane, the l-SO selector should remain behind on the membrane internal phase by adsorptive bound or crystalline form. Both types of membrane processes could separate the enantiomers of lactic acid. The chiral solid membrane has better separation efficiency where fluxes of the d-lactic acid were changed between 4 × 10 −4 and 15 × 10 −4 mol/(m 2 h) while the average selectivity could reach about 15. For supported liquid membrane these values were changed between 3 × 10 −6 and 4 × 10 −6 mol/(m 2 h) as well as 1.2 and 2, respectively.

Membrane of PVA coated on porous catalytic ceramic disks supported H 3PW 12O 40

Catalytic disks of porous ceramic plates supported H 3PW 12O 40 were prepared. Cross-linked poly vinyl alcohol (PVA) composite membranes using the catalytic disks as the matrixes were obtained by spin coating. The dehydration reaction of butanediol (BD) to form tetrahydrofuran (THF) was taken as a model reaction to testify the catalytic activity of the disk, and which was found to be a good catalyst compared with the original H 3PW 12O 40. The separative properties of the membrane were also examined by pervaporation using the same reacting mixture, and the water content in the reactor was much less than THF during the reaction coupled pervaporation.

Membrane formation techniques for gas permeation measurements for side-chain crystalline polymers

Modifications of traditional membrane support assemblies are described that permit accurate measurement of gas permeability coefficients for side-chain crystalline poly( n-alkyl acrylate)s or poly( n-alkyl methacrylate)s above and below the melting point. These modifications address the problems associated with the very brittle nature of these materials below the melting point and their fluid-like nature above the melting point. An Anopore™ porous ceramic disc coated with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) masked with aluminum tape on the downstream surface was the support ultimately chosen to perform these measurements. The problems and concerns leading to the choice of this assembly are described. Crystallite orientation in solvent cast films of the side-chain crystalline polymers is demonstrated by wide-angle X-ray diffraction (WAXD). Melting the film and recrystallization on cooling effectively eliminates such orientation.

Smolder ignition of polyurethane foam: effect of oxygen concentration

Experiments have been conducted to study the ignition of both forward and opposed smolder of a high void fraction, flexible, polyurethane foam in a forced oxidizer flow. Tests are conducted in a small scale, vertically oriented, combustion chamber with supporting instrumentation. An electrically heated Nichrome wire heater placed between two porous ceramic disks, one of which is in complete contact with the foam surface, is used to supply the necessary power to ignite and sustain a smolder reaction. The gaseous oxidizer, metered via mass flow controllers, is forced through the foam and heater. A constant power is applied to the igniter for a given period of time and the resulting smolder is monitored to determine if smolder is sustained without the assistance of the heater, in which case smolder ignition is considered achieved. Reaction zone temperature and smolder propagation velocities are obtained from the temperature histories of thermocouples embedded at predetermined positions in the foam with junctions placed along the fuel centerline. Tests are conducted with oxygen mass fractions ranging from 0.109 to 1.0 at a velocity of 0.1 mm/s during the ignition period, and 0.7 or 3.0 mm/s during the self-sustained propagation period. The results show a well-defined smolder ignition regime primarily determined by two parameters: igniter heat flux, and the time the igniter is powered. These two parameters determine a minimum igniter/foam temperature, and a minimum depth of smolder propagation (char), which are conditions required for ignition to occur. The former is needed to establish a strong smolder reaction, and the latter to reduce heat losses from the incipient smolder reaction to the surrounding environment. The ignition regime is shifted to shorter times for a given igniter heat flux with increasing oxygen mass fraction. A model based on concepts similar to those developed to describe the ignition of solid fuels has been developed that describes well the experimental ignition results.

Influence of the transport direction on gas permeation in two-layer ceramic membranes

Experimental and theoretical results of studying gas permeation through porous membranes are presented. In order to mimic an asymmetric membrane two porous ceramic disks with different pore radii were arranged in series. Besides the possibility to perform conventional permeation measurements, the applied experimental setup permits the determination of the pressure at the interface between the two discs. To predict the performance of the asymmetric structure, in preliminary experiments structure parameters were determined for both membranes separately. For the same total pressure difference across the two-disk arrangement, different interlayer pressures and fluxes were predicted and detected experimentally depending on the flow direction.

A new soil metric potential sensor based on time domain reflectometry

We developed and tested a new sensor based on time domain reflectometry (TDR) to measure soil matric potential (h). The TDR‐matric (TM) sensor is constructed of porous disks having different known maximum pore sizes and stacked within a coaxial cage. The constant relationship between water content (θ) and h of the TM porous matrix is initially calibrated and subsequently used to infer matric potential of the surrounding soil, similar to existing porous heat dissipation and electrical resistance sensors. The θ of the sensor's porous matrix in hydraulic equilibrium with the surrounding soil is measured by TDR travel time analysis. Prototype sensors were constructed using porous ceramic and plastic disks having maximum pore diameters between 120 μm(2.5 kPa) and about 0.6 μm (0.5 MPa). Calibration tests to evaluate sensor θ‐h relationships were completed in a pressure chamber apparatus using four soils. These results and those from sensors installed in soil lysimeters in the presence of growing plants showed consistent θ‐h relationships and synchronized responses of soils and TM sensors to changing water status. Pairing standard TDR probes with the new TM sensors facilitates in situ determination of soil θ(h) relationships, using conventional TDR instrumentation. The sensor design accommodates construction of media‐ or application‐specific sensors using combinations of disks having different pore sizes. There is a trade‐off between the TM sensor's matric potential range and its sensitivity to changes in the surrounding soil. Additionally, a mismatch between the pore size distributions of the TM sensor and the soil (mostly relevant to coarse‐textured soils) can lead to hydraulic decoupling of these and other porous sensors.

Oxygen transfer in a bubble column with porous ceramic gas distributor

Gas and liquid mass transfer in a bubble column with porous ceramic gas distributor was investigated. The porous ceramic disc of our self‐made was used as a gas distributor to compare with commercial products made of sintered glasses. The volumetric gas‐liquid mass transfer coefficient was determined by the dynamic method. We found that the volumetric mass transfer coefficient ( kLa ) measured from our discs is higher than that of commercial product, especially in the low gas flux region ( Ug < 1 cm/sec ). Experimental results showed that the volumetric mass transfer coefficient was significantly effective in pore size of the gas distributor. The kLa value decreased with increasing pore size of a distributor.

A study of forward smolder ignition of polyurethane foam

Experiments have been conducted to study ignition of forward smolder of a high void fraction, flexible, polyurethane foam in a forced airflow. Tests are conducted in a small-scale, vertically oriented, cylindrical test section with supporting instrumentation. A Nichrome wire heater placed between two porous ceramic disks, one of which is in contact with the foam surface, is used to supply the necessary power to ignite and sustain a smolder reaction. A constantpower is applied to the heater for a given time, and the resulting smolder is monitored. Reaction zone temperature and smolder propagation velocity are obtained from the temperature histories of thermocouples embedded at predetermined positions in the foam with junctions placed along the fuel centerline. Air is forced through the heater and foam and controlled via mass flow controllers. Forced flow air velocities of 0 to 10 mm/s during smolder ignition and 1 to 10 mm/s during smolder propagation were used. the results show a well-defined smolder ignition regime primarily determined by two parameters, igniter power flux, and the time the igniter is powered. They also show that a requirement for ignition is that the fuel-igniter interface must attain a minimum temperature. An energy balance model has been developed that describes the observed ignition results. The model is based on the assumption that for ignition to occur the heater must provide a heat flux equivalent to a propagating smolder front at a given distance from the igniter.