Longer Contact Time Research Articles

Cost effective activated carbon treatment process for removing free chlorine from water

AbstractExperiments of batch treatment and column breakthrough were conducted to compare the dechlorination effectiveness of five activated carbons: three made from coal (of different activation) and one each from coconut shell and fruit nut/shell. The removal of free chlorine was accomplished by physical adsorption and chemical reaction; adsorption was the main removal mechanism initially while chemical reaction by catalytic reduction was responsible for continued removal of free chlorine. Removal of free chlorine was enhanced by a longer contact time, a lower pH, and a higher initial/influent free chlorine concentration. Using < 180 mesh particles of activated carbon in mixed batch reactors, the carbon's adsorptive capacity for free chlorine was established in 2 h; the carbons' adsorptive capacities for free chlorine were in the same order as their phenol numbers, the indicator of small micropores. The coconut carbon had the highest adsorptive capacity but was much less reactive relative to the commercial coal and fruit shell carbons. Much more free chlorine was removed in the lab carbon columns than the carbons' adsorptive capacities due to catalytic reduction of the adsorbed free chlorine on carbon surface. The free chlorine removal capacities of the two spent carbons were similar to the respective new carbons. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

The feeding process of Cimex lectularius (Linnaeus 1758) and Cimex hemipterus (Fabricius 1803) on different bloodmeal sources

The bedbugs Cimex lectularius and Cimex hemipterus are obligate hematophages in all their nymphal instars as well as in the adult stage. The efficiency with which the insects obtain blood from their hosts is directly related to their population dynamics. In the present study we compared the feeding process and salivary content in individuals of these two species when fed on different blood sources or host sites, using a cibarial pump electromyogram. Females ingested more blood than males but needed longer contact time with the host to complete the meal. The bedbug C. lectularius was more efficient than C. hemipterus in obtaining blood from mice and pigeons. With regard to the feeding site on mice, it was easier for the insects to obtain blood from the skin of the belly than that of the back. Individuals of C. hemipterus were able to maintain the cibarial pump functioning at higher frequencies for longer periods when fed on pigeons treated with anticoagulant. Although saliva from C. lectularius contained more hemeproteins and showed more anti-clotting activity its total protein content was similar to that of C. hemipterus. Overall, C. lectularius obtains a bloodmeal more efficiently from its hosts, which may have enabled this species to reach higher levels of infestation than C. hemipterus.

Selective separation of copper and nickel by solvent extraction using LIX 984N

Selective separation of copper and nickel from ammoniacal/ammonium carbonate medium was carried out by using LIX 984N diluted with deodourised kerosene. The study of the influence of equilibration time, equilibrium pH, extractant concentration and selective stripping of copper and nickel has been optimized. It was found that both the metal extractions were unaffected by the changes in pH. Nickel extraction equilibrium was reached at a longer contact time than that for copper and nickel extraction depends greatly on the extractant concentration in the organic phase. Co-extraction, ammonia scrubbing and selective stripping of copper and nickel were performed for a solution containing 3 g dm − 3 each of copper and nickel and 60 g dm − 3 ammonium carbonate. The extraction and the percentage of stripping for nickel and copper were almost quantitative.

Changes in Heavy Metal Concentrations in Acid Soils Under Pine Stands Subjected to Repeated Applications of Biosolids

The distribution of metals in biosolid-amended soils (as measured by acid extraction) to a depth of 53 cm was examined for evidence of translocation and possible redeposition and to determine whether downward-moving heavy metals interacted with the subsoil. The soil is a sandy acid forest soil (Dystric Cambisol) located in a high-leaching environment. The biosolid was applied twice (in 2001 and 2002) at three different loading rates, and soils were sampled in the 3 years following the first application (2002, 2003, and 2004). Zinc, chromium, nickel, and copper accumulated in the uppermost horizon (0- to 4-cm depth), and the highest concentrations corresponded to the highest doses of biosolids. The lack of cadmium accumulation in this horizon was attributed to the high mobility of this element. Between 4 and 9 cm to the 48-cm depth, and with few exceptions, there were no significant differences (P < 0.05) between the different doses of biosolids and control. The existence of both subsurface lateral flow and preferential flow may explain the lack of differences. Cadmium mainly accumulated at 48 to 53 cm, which was the depth of the water table. At this depth, an overall increase in the concentrations of the other heavy metals was also observed. This pattern was attributed to the longer time of contact between the soil-reactive surface and soil solution.

FTIR-ATR Study of Water Uptake and Diffusion through Ion-Selective Membranes Based on Poly(acrylates) and Silicone Rubber

For the first time, FTIR-ATR spectroscopy was used to study the water uptake and its diffusion in ion-selective membranes (ISMs) based on poly(acrylates) (PAs) and silicone rubber (SR), which are emerging materials for the fabrication of ISMs for ultratrace analysis. Three different types of PA membranes were studied, consisting of copolymers of methyl methacrylate with n-butyl acrylate, decyl methacrylate, or isodecyl acrylate. Numerical simulations with the finite difference method showed that in most cases the water uptake of the PA and SR membranes could be described with a model consisting of two diffusion coefficients. The diffusion coefficients of the PA membranes were approximately 1 order of magnitude lower than those of plasticized poly(vinyl chloride) (PVC)-based ISMs and only slightly influenced by the membrane matrix composition. However, the simulations indicated that during longer contact times, the water uptake of PA membranes was considerably higher than that for plasticized PVC membranes. Although the diffusion coefficients of the SR and plasticized PVC membranes were similar, the SR membranes had the lowest water uptake of all membranes. This can be beneficial in preventing the formation of detrimental water layers in all-solid-state ion-selective electrodes. With FTIR-ATR, one can monitor the accumulation of different forms of water, i.e., monomeric, dimeric, clustered, and bulk water.

Construction of Bovine Serum Albumin Nanostructure by Scanning Probe Nanolithography

Abstract It is significant to develop methods of patterning materials and clipping molecules on nanometer scale according to people's needs. The development of scanning probe lithography provided a simple and useful method to construct nanostructures onto substrates. In this article, bovine serum albumin (BSA) nanostructures with controllable shapes and sizes were constructed by using scanning probe lithography. The influence of tip-substrate contact time and tip-substrate distance on nanostructure was investigated. Longer contact time of tip-substrate and shorter tip-substrate distance towards substrate can deposit more BSA molecules from atomic force microscopy (AFM) tip to surface. The oriented and controlled patterns of nanostructures on suitable substrate can provide the prospect of building functional nanodevices.

Numerical simulations on the influence of matrix diffusion to carbon sequestration in double porosity fissured aquifers

The double porosity model for fissured rocks, such as limestones and dolomites, has some features that may be relevant for carbon sequestration. Numerical simulations were conducted to study the influence of matrix diffusion on the trapping mechanisms relevant for the long-term fate of CO 2 injected in fissured rocks. The simulations show that, due to molecular diffusion of CO 2 into the rock matrix, dissolution trapping and hydrodynamic trapping are more effective in double porosity aquifers than in an equivalent porous media. Mineral trapping, although assessed indirectly, is also probably more relevant in double porosity aquifers due to the larger contact surface and longer contact time between dissolved CO 2 and rock minerals. However, stratigraphic/structural trapping is less efficient in double porosity media, because at short times CO 2 is stored only in the fissures, requiring large aquifer volumes and increasing the risk associated to the occurrence of imperfections in the cap-rock through which leakage can occur. This increased risk is also a reality when considering storage in aquifers with a regional flow gradient, since the CO 2 free-phase will move faster due to the higher flow velocities in fissured media and discharge zones may be reached sooner.

Use of Fenton's Reagent as a Disinfectant

AbstractSeveral compositions of Fenton's Reagent and hydrogen peroxide alone were used to disinfect combined sewage samples from a wastewater treatment facility. The presettled samples contained suspended solids (SS) and dissolved organic carbon (DOC) at concentrations of 28 and 290 mg/L, respectively. Disinfection with Fenton's Reagent was carried out at a pH between 5.90 and 6.0 and at a temperature of 25°C. All disinfected samples contained residual oxidants. Under all reaction conditions studied, complete inactivation of E. coli was achieved within one minute of the addition of Fenton's Reagent. Disinfection with hydrogen peroxide alone under similar conditions is incomplete even under much longer contact times. © 2009 Wiley Periodicals, Inc.

Heat fluxes to combustor walls during continuous spin detonation of fuel-air mixtures

Pioneering measurements of heat fluxes to the walls of flow-type combustors of different geometries were performed in regimes of continuous spin detonation of fuel-air mixtures under unsteady heating. These heat fluxes are compared with those observed in the regime of conventional turbulent combustion in the same combustor. Air is used as an oxidizer, and acetylene or hydrogen is used as a fuel. For identical flow rates of the fuel, the heat fluxes to the combustor walls in regimes of continuous spin detonation and conventional combustion are close to each other; their mean steady values are ≈1 MW/m2 (≈0.5% of the enthalpy flux of the products over the channel cross section). In both detonation and combustion regimes, the maximum heat fluxes penetrate into the walls in the mixing region (where the heat release occurs). In the case of detonation, regenerative cooling of the combustor walls by the flow of the fresh mixture occurs in the heat-release region (region of propagation of the detonation-wave front). The regeneration becomes less effective in the downstream direction because of the shorter time of contact between the walls and the cold mixture and a longer time of contact between the walls and the hot products. More intense heating persists downstream of the front, where the regeneration ceases, but the temperature of the products is high. The character of heating of the wall in the region of rotation of the front of spin detonation waves depends on the number of these waves: the zone of the maximum heat release becomes narrower with increasing number of waves.

Gas Phase Chemistry in Cellulose Fast Pyrolysis

We experimentally and theoretically studied cellulose pyrolysis at high temperature and short residence time. We investigated the gas phase chemistry with dedicated experiments and feeding intermediates. Results have been also compared with equilibrium calculations, both single (gas) phase and allowing for solid C formation. Our aim was to understand the cellulose degradation mechanism and particularly the role of gas phase chemistry. We provided evidence of a simplified mechanism, where CO formation is a first, fast step that can be related to levoglucosan ring opening, while H2 comes from a totally different route, based on hydrocarbon reforming reactions, which also provide further CO. In addition, butadiene was identified as a key intermediate in the decomposition sequence. The different paths and rates of CO formation and H2 formation explain why the ratio of CO to H2 is not constant, particularly at short residence time. A two-stage process or longer contact time is required, if aiming at syngas pro...

Morphological and Thermal Properties of Cellulose−Montmorillonite Nanocomposites

Cellulose-layered montmorillonite (MMT) nanocomposites were prepared by precipitation from N-methylmorpholine- N-oxide (NMMO)/water solutions. Two hybrid samples were obtained to investigate the influence of the reaction time on the extent of clay dispersion within the matrix. It was observed that longer contact times are needed to yield nanocomposites with a partially exfoliated morphology. The thermal and thermal oxidative properties of the hybrids, which might be of interest for fire-resistant final products, were investigated by thermogravimetry and chemiluminescence (CL). The nanocomposites exhibited increased degradation temperatures compared to plain cellulose, and the partially exfoliated sample showed the maximum stability. This result was explained in terms of hindered transfer of heat, oxygen, and degraded volatiles due to the homogeneously dispersed clay filler. Kinetic analysis of the decomposition process showed that the degradation of regenerated cellulose and cellulose-based hybrids occurred through a multistep mechanism. Moreover, the presence of nanoclay led to drastic changes in the dependence of the activation energy on the degree of degradation. CL analysis showed that longer permanence in NMMO/water solutions brought about the formation of carbonyl compounds on the polymer backbone. Moreover, MMT increased the rate of dehydration and oxidation of cellulose functional moieties. As a consequence, cellulose was found to be less stable at temperatures lower than 100 degrees C. Conversely, at higher temperatures, the hindering of oxygen transfer prevailed, determining an increase in thermo-oxidative stability.

Application of excess activated sludge ozonation in an SBR Plant. Effects on substrate fractioning and solids production

This paper provides new insights on the application of the ozonation process for the reduction of the activated sludge production in a sequencing batch reactor (SBR). The study was performed in two identical lab-scale SBRs plant, one for experimental activities (Exp SBR) and one used as control (Control SBR), both fed with domestic sewage. A fraction of the activated sludge collected from the Exp SBR at the end of the aerobic react phase was periodically subjected to ozonation for 30 minutes at three different specific dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and then recirculated before the beginning of the following cycle.Recirculation of the ozonated sludge to the Exp SBR did not appreciably affect the efficiency of the biological nitrogen and carbon removal processes. Nonetheless, an improvement of the denitrification kinetic was observed. Mixed liquor volatile and suspended solids (MLSS and MLVSS, respectively) concentrations in the reactor decreased significantly with time for long term application of the ozonation treatment. Kinetic batch tests on unstressed sludge taken from Control SBR indicated that the different oxidant dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and durations of the ozonation process (10, 20 and 30 minutes) used remarkably affected chemical oxygen demand (COD) and organic nitrogen fractioning. In particular, soluble and biodegradable fractions seemed to be higher at lower dosage and longer contact time.

Tillage Effects on Aggregate Turnover and Sequestration of Particulate and Humified Soil Organic Carbon

The seasonal dynamics of soil organic carbon (SOC) fractions and dry aggregates were investigated to determine whether aggregate turnover rates explain the variable influence of no‐till (NT) practices on SOC accrual in Illinois. Soils were collected (0–15 cm) of two 17‐yr‐old trials where NT and conventional tillage (CT) practices had variable effects on SOC sequestration in the 0‐ to 30‐cm depth. Soil was fractionated into loose particulate organic matter (LPOM), macroaggregate‐occluded particulate organic matter (OPOM), and humified fractions (HFs) associated with microaggregates and minerals. Dry aggregate mean weight diameter (DMWD) was used to evaluate structure expressed in the field. Within‐season changes in fraction concentrations indicate that C derived from LPOM and plant roots was transferred to OPOM at both sites. At DeKalb (silty clay loam), NT practices had less influence on SOC sequestration than at Monmouth (silt loam). DeKalb HF contents increased under NT while OPOM contents were unchanged. At Monmouth, NT practices increased SOC sequestration by increasing OPOM concentrations. Site‐based differences in SOC accrual were related to aggregate turnover rates, which were increased by NT practices at Monmouth but were unaffected by tillage at DeKalb. Trends in DMWD and aggregate turnover suggest that when aggregate turnover is slow, as at DeKalb, OPOM formation is limited. Slow turnover in the heavier soil permitted accumulation of HF because residues had longer contact times with particle surfaces. When aggregate turnover is faster, as in the Monmouth NT soil, there is greater chance for residue incorporation into aggregates and accumulation of OPOM. Rapid aggregate turnover limits opportunities for mineral affiliation and HF accrual. Aggregate dynamics predicted site‐based differences in the form and rate of SOC accrual caused by the use of NT practices.

Integrated simulation of drinking water treatment

Major emphasis must be laid on guaranteeing high standards in drinking water quality. This can only be achieved when the drinking water treatment plant operates optimally. In this paper a treatment plant, consisting of ozonation with low dosage of ozone, pellet softening, pH correction and activated carbon filtration, treating lake water with high content of natural organic matter is analysed. Models are developed to describe the processes under changing conditions. For integrated modelling interaction of the treatment steps is considered to take place through the water stream. Water quality parameters are influenced by preceding treatment steps and they determine the performance of the following treatment steps. Assuming that disinfection is sufficient in the treatment plant and suspended and colloidal solids are sufficiently removed in preceding steps, the main controlled parameters for a treatment plant are chemical stability (saturation index SI), biological stability (assimilable organic carbon AOC), disinfection by-products (bromate) and organic micro-pollutants (pesticides). It is concluded that with good use of the by-pass of a pellet softening reactor and with optimised operation of the fluidised bed, the dosage of chemicals can be minimised, resulting in reduction of costs, environmental emissions and maintenance. Ozonation has a key role in the bio-stability and the toxicity of the drinking water. When ozone is only applied for oxidation (low dosages) some organic micro-pollutants are reduced and the run-time of the activated carbon filters is prolonged. However, ozonation decreases the bio-stability of the drinking water and enhances bromate formation. Therefore, the quality benefits related to oxidation of organic micro-pollutants should be weighted against the formation of bromate and AOC. The increase of AOC concentrations should be compensated by longer contact times in the biological filters.

Continuous Consolidation of Polypropylene/Glass Fibre Commingled Fabric

Continuous consolidation of a polypropylene/glass fibre commingled fabric has been investigated using the roll forming process. For this manufacturing process, unconsolidated heated plies are progressively consolidated by passing through a series of rollers. First, compaction trials (performed to determine the most suitable processing parameters) have shown that the repeated application and release of pressure can significantly improve the level of consolidation by allowing trapped air to escape from the molten resin. The influence of the roller gaps, laminate temperature and processing speed has then been determined for the roll forming process. Quality of consolidation was assessed by observing polished micrographs of cross-sections and by determining the void content and flexural properties. Results showed that a roll gap sequence starting at 50% of the unconsolidated laminate thickness is satisfactory. For smaller roller gaps, results have shown that the fabric structure is altered by the squeezing flow of the resin. Results also showed that materials with high inlet temperatures and low process speeds have better levels of consolidation due to lower matrix viscosity and longer contact time with the rollers. Using optimum process parameters, continuous consolidation of 4 plies of 1485 g/m2 fabric at a rate of 0.5 m/min led to a satisfying quality of composite, with less than 4% void content.

Study on biosorption of humic acid by activated sludge

The biosorption performance of humic acid (HA) by activated sludge and the effects of inorganic metal ions as biosorption aid were investigated. It was confirmed that biosorption instead of biodegradation was responsible for HA removal. HA biosorption by activated sludge followed the Freundlich isotherm equation; however, biosorption of HA corresponded to the biosorption by a mixture of adsorbates. The removal efficiency improved when initial HA concentration was increased. While biosorption of HA can be suitably applied to treat high concentration HA wastewater because the HA concentration of blank sample was approximate to 1 mg/L. The total removal efficiency for HA improved when the quantity of adsorbent (activated sludge) was increased under constant contact time. The lower concentration of the adsorbent could realize the higher adsorptive capacity per gram activated sludge with a longer contact time, but the removal rate of pollutants was more important consideration in practice. Moreover, biosorption of HA was favored by addition of five metallic salts. The ionic strength increasing, cationic bridge, destabilization and precipitation are the main mechanisms to advance HA removal efficiency in solution after adding the salt (Na +), alkaline earth metallic (Ca 2+, Mg 2+) and hydrolyzing metallic (Al 3+, Fe 3+) ions, respectively.

Muscle activation characteristics of tumbling take-offs

In the floor exercise, a gymnast may receive a general composition score deduction associated with a lack of diverse tumbling sequences. Diversity in tumbling is defined as the ability to tumble both forward and backward, as well as twist and flip. A coach's ability to direct technical and physical training for these skill varieties is enhanced when thorough descriptions of the skills are available. The aim of this study was to describe and compare muscle activation of the lower extremity in various tumbling sequences characterized by differing body orientations. The stretch–shortening cycle actions during the take-off portion of four different tumbling sequences were analysed and the results compared across muscles and type of take-off (forward vs. backward, twisting vs. non-twisting). Thirteen female gymnasts performed three trials each of round-off flic-flac to backward layout and to backward layout with longitudinal axis twist, and front flic-flac to forward layout and to forward layout with longitudinal axis twist. Activation onset was assessed as an increase of the EMG of 200% above noise before initial floor contact. The EMG was normalized to peak values for each muscle bilaterally during each take-off. Results showed that muscle activation characteristics in the pre-activation and impact phase (contact to maximal floor depression) differed between tumbling series. Backward take-offs were characterized by longer contact times, greater relative activity of the gastrocnemius compared with the vastus lateralis during pre-activation, and greater biceps femoris activation during impact compared with forward take-offs. Twisting backward was associated with reduced muscle activity of the twisting limb, while twisting forward was associated with increased muscle activation on the twisting limb. These differential effects related to the specific nature of the take-off indicate that training to enhance the stretch–shortening cycle action in gymnasts must be specific to the orientation requirements of each specific skill.

Effects of Freezing on the Survival of Escherichia coli and Bacillus and Response to UV and Chlorine After Freezing

Escherichia coli (E. coli) and Bacillus megaterium bacteria were frozen at -15 degrees C using a freezer and a spray freezing method. The frozen Bacillus spores were also exposed to UV and free chlorine. An average of 4.7-log inactivation was obtained from the spray ice with 2-day storage time, while the freezer freezing only caused 0.84-log reduction with the same storage time. Significantly higher inactivation levels were observed for the E. coli cells with 2-day storage compared with those without storage. The spray freezing was found more effective in killing the E. coli cells, while more cells were sublethally injured by the freezer freezing. Freezing did not kill the Bacillus megaterium spores, but affected their response to UV and chlorine. Greater inactivation levels were observed at higher free chlorine doses or longer contact time, and the UV fluence-response curve showed initial rapid kill followed by tailing for the frozen spores.

Factors affecting the formation of zeolite seed layers and the effects of seed layers on the growth of zeolite silicalite-1 membranes

The present study investigates the formation of silicalite-1 seed layers on a porous carbon support of 0.5 μm pore size and α-A12O3 supports with different pore sizes (0.1 μm and 4 μm) via the slip-casting technique. The effects of support property, seed size and solvent on the formation of seed layers were investigated in detail. The growth of silicalite-1 membranes on different seeded supports by hydrothermal synthesis was also evaluated. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterizations indicate that a continuous seed layer can be obtained on the smooth support of 0.1 μm pore size by using any seed of 100 nm, 600 nm or 2.2 μm in size, whereas, on the coarse supports with either 0.5 μm or 4 μm pore size, a continuous seed layer cannot be formed using the above seed sizes and the same seeding time. At a longer contact time, a seed layer can also be formed using 100 nm seed on the supports with larger pore size. However, the layer is not uniform and smooth. For a hydrophobic porous carbon support, seeding ethanol suspension, which has weak polarity, favors the formation of a continuous seed layer. The seed layers and membranes grown from the smaller seed are more uniform and continuous and possess smoother surfaces than those from the larger seed. The seed layer and respective grown membrane formed from nanosized seed (100 nm) are the most uniform and compact. With this method of seeded secondary synthesis of zeolite membranes, the quality of a membrane mainly depends on the quality of the seed layer.

Bacterial responses in activity and community composition to photo-oxidation of dissolved organic matter from soil and surface waters

To better understand how photo-oxidation of dissolved organic matter (DOM) affects microbial activity and DOM processing along hydrological flow paths in an arctic catchment, we conducted experiments measuring responses in bacterial production (BP) to sunlight-exposed DOM from up-slope sources, including soil, stream, and lake water. Overall, sunlight exposure significantly reduced specific ultra-violet absorbance and dissolved organic carbon concentrations and increased phenolic concentrations; these changes were more pronounced in soil than in surface waters. Sunlight-exposed DOM reduced BP in common inoculum bioassay experiments at short time scales (hours), but the magnitude of the effect differed among DOM sources and was related to phenolic content; effects were more negative on DOM sources with high phenolic contents. In contrast, longer contact times (weeks) between bacteria and photo-oxidized soil, stream, and lake water DOM enhanced, did not change, and reduced BP, respectively. In these longer-term experiments, sunlight-exposed DOM had a greater positive effect on lake than stream BP, and caused shifts in bacterial community composition (based on denaturing gradient gel electrophoresis of bacterial-specific 16S rDNA). Changes in bacterial community composition were greater in response to sunlight-exposed DOM from soils than from the stream. Our findings suggest that overall impacts of DOM photo-oxidation in aquatic environments depends on DOM source, and that contrasting effects of photo-oxidized DOM at varying time scales may be partly due to shifts in the bacterial community composition to groups better able to consume photoproducts or tolerate harmful radicals.