Particle size distribution effects on gas-particle mass transfer within electrostatic precipitators

Varying degrees of mercury capture and transformation have been reported across electrostatic precipitators (ESPs). Previous analyses have shown that the dominant mass transfer mechanism responsible for mercury capture within ESPs is gas-particle mass transfer during particulate collection. Whereas previous analyses assumed dispersions of uniform size, the present analysis reveals the effects of polydispersity on both gas-particle mass transfer and particle collection within an ESP. The analysis reveals that the idealized monodisperse particle size distribution provides the highest gas-particle mass transfer but results in the lowest particle collection efficiency (% mass). As the particle size distribution broadens, gas-particle mass transfer decreases and particle collection efficiency increases. The results suggest that more than just reporting mean particle diameter provided by the sorbent manufacturer, pilot- and field-tests of sorbent injection for mercury emissions control need to experimentally measure the particle size distribution of the sorbent as it is injected in order to facilitate interpretation of their results.     

Estimates of increased black carbon emissions from electrostatic precipitators during powdered activated carbon injection for mercury emissions control

The behavior of mercury sorbents within electrostatic precipitators (ESPs) is not well-understood, despite a decade or more of full-scale testing. Recent laboratory results suggest that powdered activated carbon exhibits somewhat different collection behavior than fly ash in an ESP and particulate filters located at the outlet of ESPs have shown evidence of powdered activated carbon penetration during full-scale tests of sorbent injection for mercury emissions control. The present analysis considers a range of assumed differential ESP collection efficiencies for powdered activated carbon as compared to fly ash. Estimated emission rates of submicrometer powdered activated carbon are compared to estimated emission rates of particulate carbon on submicrometer fly ash, each corresponding to its respective collection efficiency. To the extent that any emitted powdered activated carbon exhibits size and optical characteristics similar to black carbon, such emissions could effectively constitute an increase in black carbon emissions from coal-based stationary power generation. The results reveal that even for the low injection rates associated with chemically impregnated carbons, submicrometer particulate carbon emissions can easily double if the submicrometer fraction of the native fly ash has a low carbon content. Increasing sorbent injection rates, larger collection efficiency differentials as compared to fly ash, and decreasing sorbent particle size all lead to increases in the estimated submicrometer particulate carbon emissions.     

Mass transfer in VOC adsorption on zeolite: experimental and theoretical breakthrough curves

From experimental results of adsorption of volatile organic compounds (VOCs) on zeolite, we propose simulations of the breakthrough curves based on the Linear Driving Force model. Experiments were run on fixed beds of hydrophobic commercial zeolites. Pollutants chosen are from several chemical classes with different polarities. A good agreement between experimental and numerical results is found when an adjustable value of the internal mass-transfer coefficient is used. A constant value of effective diffusivity is found independent of the nature and the amount of VOCs adsorbed. A relation linking intrapellet mass-transfer coefficient and equilibrium constant is proposed, including the average effective diffusivity, to make predictions of breakthrough curves for any kind of volatile organic pollutant in gaseous effluents.     

服装面料静电吸附抓取转移电极板优化设计

为提高服装定制化生产过程中机器人的使用效果,解决机器人末端执行器在加工过程中抓取转移面料吸附力不稳定问题,针对静电极板设计的关键因素,电极板的形状布置和结构参数进行了分析优化.通过构建针织纬编织物的模型,对当前4种电极分布形式进行仿真对比分析,得到最适合服装面料的电极板的形状布置:梳状电极.然后以单位面积吸附力最大为优...     

Colostrogenesis: Mass transfer of immunoglobulin G1 into colostrum

Bovine IgG₁ is thought to be specifically transported by a process of transcytosis across the mammary epithelial cells during colostrogenesis. Mammary IgG₁ appearance in cow colostrum has typically been reported as a concentration and shows IgG₁ concentration to be extremely variable because of animal variation, colostrum milking time, and water dilution effects. To identify animal IgG₁ transfer capacity and separate it from the other effects, our objective was to determine first colostrum IgG₁ total mass. We collected 214 samples of totally milked first colostrum with recorded colostrum weights from 11 Pennsylvania dairy farms that participated in Pennsylvania Dairy Herd Improvement Association, analyzed colostrum for IgG₁ by ELISA, and calculated total IgG₁ mass. Median and mean concentrations of IgG₁ were 29.4 mg/mL and 37.5 ± 30.2 mg/mL, respectively, with a range of 9 to 166 mg/mL. However, total mass of IgG₁ had a median of 209.1 g, mean of 291.6 ± 315.8 g, and a range of 14 to 2,223 g. Colostrum IgG₁ concentration showed no relationship with colostrum volume, but IgG₁ mass had a positive relationship with volume. Colostrum IgG₁ mass was related to IgG₁ concentration (R² = 0.58). Using DHIA records for 196 animals, we established milk production for these animals to a 15-d equivalent. An established milk secretion relationship to mammary parenchyma tissue (secretory tissue) was calculated and showed no relationship of IgG₁ mass with mammary parenchyma tissue. In addition, we show that approximately 10% of the sampled animals had IgG₁ mass greater than 1 standard deviation above the mean (high mass transfer) and represented all parities tested (1-7). Whereas first-lactation animals showed less overall calculated parenchyma tissue when compared with other parities, approximately 10% of the first-lactation group animals were capable of high mass transfer, with one transporting 2,029 g into first colostrum. Concentration variance of IgG₁ can be attributed to water inclusion, whereas mass transfer provides a clear indication of animal IgG₁ transfer capacity. The specific mechanism of bovine mammary IgG₁ transfer is not clear, but secretory tissue mass does not explain the variation observed. We hypothesize that the animal variation is attributable to endocrine regulation or genetic variation of the transporter(s).     

Mass transfer during osmotic dehydration of pineapple: considering Fickian diffusion in cubical configuration

Osmotic dehydration kinetics of pineapple cubes (15×15×15 mm³) was studied over a range of concentration (40-70°B) and temperature (30-50°C) of osmotic solution. The effective diffusion coefficients for water and solute diffusion were determined, considering pineapple as cubical configuration, assuming osmotic dehydration to be governed by Fickian diffusion. The effective diffusion coefficients for water as well as solute were empirically correlated with concentration and temperature of osmotic solution. A high degree of correlation was observed between predicted and experimental values of the effective diffusion coefficients of water (R²=0.99) as well as solute (R²=0.96).     

Fish for human consumption: risk of contamination by mercury

Total mercury concentrations were measured in the muscle of different kinds of fish: megrim (Lepidorhombus boscii), common sole (Solea vulgaris), striped mullet (Mullus barbatus), anglerfish (Lophius piscatorius), and black-bellied angler (Lophius budegassa     

Modeling the Uptake of Semivolatile Organic Compounds by Passive Air Samplers: Importance of Mass Transfer Processes within the Porous Sampling Media

Air sampling based on diffusion of target molecules from the atmospheric gas phase to passive sampling media (PSMs) is currently modeled using the two-film approach. Originally developed to describe chemical exchange between air and water, it assumes a uniform chemical distribution in the bulk phases on either side of the interfacial films. Although such an assumption may be satisfied when modeling uptake in PSMs in which chemicals have high mobility, its validity is questionable for PSMs such as polyurethane foam disks and XAD-resin packed mesh cylinders. Mass transfer of chemicals through the PSMs may be subject to a large resistance because of the low mass fraction of gas-phase chemicals in the pores, where diffusion occurs. Here we present a model that does not assume that chemicals distribute uniformly in the PSMs. It describes the sequential diffusion of vapors through a stagnant air-side boundary layer and the PSM pores, and the reversible sorption onto the PSM. Sensitivity analyses reveal the potential influence of the latter two processes on passive sampling rates (PSRs) unless the air-side boundary layer is assumed to be extremely thick (i.e., representative of negligible wind speeds). The model also reveals that the temperature dependence of PSRs, differences in PSRs between different compounds, and a two-stage uptake, all observed in field calibrations, can be attributed to those mass transfer processes within the PSM. The kinetics of chemical sorption to the PSM from the gas phase in the macro-pores is a knowledge gap that needs to be addressed before the model can be applied to specific compounds.     

Mass balance of total mercury and monomethylmercury in coastal embayments of a volcanic island: significance of submarine groundwater discharge

To understand the contribution of submarine groundwater discharge (SGD) to the coastal mass budgets of Hg and monomethylmercury (MMHg), preliminary mass balance estimates were made for Hwasun and Bangdu Bays on Jeju Island, known to have large SGD due to the high permeability of the volcanic rocks. The mass balance results indicate that SGD is a main source of Hg in Hwasun Bay (23 ± 14 × 10(-2) mol yr(-1), 34%) and Bangdu Bay (23 ± 20 × 10(-2) mol yr(-1), 67%), although the contribution from atmospheric deposition was considerable (25% for Hwasun and 23% for Bangdu). MMHg was also discharged primarily from submarine groundwater at Hwasun (0.30 ± 0.17 × 10(-2) mol yr(-1), 55%) and Bangdu (0.65 ± 0.49 × 10(-2) mol yr(-1), 64%), which was higher than atmospheric deposition (6% for Hwasun and 2% for Bangdu) and sediment diffusion flux (5% for Hwasun and 3% for Bangdu). The overall mass balance results suggest that, although there are large spatial variations in SGD rates throughout the region, the coastal mass budgets of Hg and MMHg need to include SGD as well as atmospheric deposition and sediment diffusion as primary sources of Hg and MMHg.     

Formulation of a cured meat product by the dewatering-impregnation soaking (DIS) process: Mass transfer study and assessment of product quality

Venison muscle meats were simultaneously salted and dried by soaking in a mixed concentrated solution (salt/corn starch syrup) at a low temperature, a process known as dewatering and impregnation soaking (DIS). Cured products of suitable market quality (in terms of their salt and water content) were obtained with this process. The impregnation of standard curing additives (nitrites and polyphosphates) into the meat product was controlled by mixing these compounds in the concentrated solution. Also, beneficial effects of additives on the physicochemical, microbiological and organoleptic characteristics of the product are confirmed. The present study highlights the choice of DIS process and proposed optimal DIS conditions for formulating cured products.     

Memory effects on adsorption tubes for mercury vapor measurement in ambient air: elucidation, quantification, and strategies for mitigation of analytical bias

The short- and long-term memory effects associated with measurements of mercury vapor in air using gold-coated silica adsorption tubes have been described. Data are presented to quantify these effects and to determine their dependence on certain relevant measurement parameters, such as number of heating cycles used for each analysis, age of adsorption tube, mass of mercury on adsorption tube, and the length of time between analyses. The results suggest that the long-term memory effect is due to absorption of mercury within the bulk gold in the adsorption tube, which may only be fully liberated by allowing enough time for this mercury to diffuse to the gold surface. The implications of these effects for air quality networks making these measurements routinely has been discussed, and recommendations have been made to ensure any measurement bias is minimized.     

Oxidative refolding of lysozyme assisted by negatively charged liposomes: relationship with lysozyme-mediated fusion of liposomes

Oxidative refolding of denatured/reduced lysozyme was examined in the presence of charged liposomes composed of neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG). Surface charge density of liposomes had a marked effect on the interaction between liposomes and reduced lysozyme which is observed in the early stage of the refolding. It was found that there was a critical level of surface charge density of liposomes (-0.15 C/nm2) at which the interaction between liposomes and lysozyme drastically changed. At the surface charge density of liposomes ranging from -0.15 to -1.4 C/nm2, the interaction between liposomes and lysozyme resulted in aggregate formation. In contrast, at the surface charge density ranging from 0 to -0.15 C/nm2, no aggregate formation was observed if the lysozyme/liposome molar ratio was less than 600. On the basis of the experimental results, a model for the interaction between charged liposomes and lysozyme was proposed, focusing on the mechanism of protein-induced fusion of charged liposomes as well as protein refolding on liposomes. Then, the optimal condition for oxidative refolding of lysozyme was examined in the presence of charged liposomes by controlling the lysozyme-liposome interaction. The reactivation yield of lysozyme was improved up to 85% in the presence of liposomes with a surface charge density of -0.14 C/nm2.     

Effect of pH on mercury uptake by an aquatic bacterium: implications for Hg cycling

We studied the effect of increasing hydrogen ion (H+) concentration on the uptake of mercury (Hg(II)) by an aquatic bacterium. Even small changes in pH (7.3-6.3) resulted in large increases in Hg(II) uptake, in defined media. The increased rate of bioaccumulation was directly proportional to the concentration of H+ and could not be explained by assuming that the source of Hg to the bacteria was diffusion of neutrally charged species such as HgCl2. Thus, pH appeared to affect a facilitated mechanism by which Hg(II) is taken up by the cells. Lowering the pH of Hg solutions mixed together with natural dissolved organic carbon, or with whole lake water, also increased bacterial uptake of Hg(II). These findings have several potential implications for mercury cycling, including effects on elemental mercury production, mercury sedimentation, and microbial methylation of Hg(II), and could be part of the explanation for the observed positive correlation between lake acidity and methyl mercury levels in fish.     

Volatile Components of Raw Peanuts: Analysis by Gas-Liquid Chromatography and Mass Spectrometry

SUMMARY: The volatile components associated with the aroma and flavor of raw peanuts have been studied. These components were isolated using lowtemperature vacuum distillation and cryogenic trapping. Ten components were identified from the liquid N₂ trap using the combined technique of gas-liquid chromatography and mass spectrometry. The "backbone" compound of the raw peanut aroma appears to be hexanal, with other components adding the proper character.     

Impact of natural organic matter on monochloramine reduction by granular activated carbon: the role of porosity and electrostatic surface properties

Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters-one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity.     

Reduction of oxidized mercury species by dicarboxylic acids (C2-C4): kinetic and product studies

Mercury is an environmental contaminant of global concern. The reduction of oxidized mercury species (Hg(II)) by organic acids to elemental mercury (Hg0) is significant for understanding the cycling of mercury between the atmosphere and aqueous systems. This study focused on the reduction of Hg(II) by small, semivolatile dicarboxylic acids (C2-C4). The reaction kinetics was studied using cold vapor atomic fluorescence spectroscopy (CVAFS), and the products of the reaction were analyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and nuclear magnetic resonance (NMR) spectrometry. The effects of light, dissolved oxygen and chloride ion on reaction rates were also investigated. The highest reaction rates were observed in systems free of both oxygen and chloride ion with the second-order apparent rate constants of 1.2 x 10(4), 4.9 x 10(3), and 2.8 x 10(3) (L x mol(-1) x s(-1)) for oxalic, malonic, and succinic acids at pH 3.0 and T = 296 +/- 2 K, respectively. The photoreduction of Hg(II) was mediated by the complexes formed between Hg" and dicarboxylic acids, and the identified products were Hg0, hydroxycarboxylic acids and monocarboxylic acids. Our results also indicated that the presence of chloride ion significantly reduced the reduction rate by competing with the complexation of Hg" with dicarboxylic acids, while dissolved oxygen retarded the production of Hg0 by involving in the reoxidation of reduced Hg species to Hg(II). Based on our experimental results, a tentative mechanism is proposed and the potential environmental implications are discussed.     

Physical adsorption of aflatoxin B1 by lactic acid bacteria and Saccharomyces cerevisiae: a theoretical model

The ability of lactic acid bacteria (LAB) and Saccharomyces cerevisiae to remove aflatoxin B1 (AFB1) from liquid medium was tested. The experimental results indicated that (i) AFB1 binding to microorganisms was a rapid process (no more than 1 min); (ii) this binding involved the formation of a reversible complex between the toxin and microorganism surface, without chemical modification of the toxin; (iii) the amount of AFB1 removed was both toxin- and bacteria concentration-dependent; and (iv) quantitatively similar results were obtained with viable and nonviable (heat-treated) bacteria. According to these details, a physical adsorption model is proposed for the binding of AFB1 to LAB and S. cerevisiae, considering that the binding (adsorption) and release (desorption) of AFB1 to and from the site on the surface of the microorganism took place (AFB1 + S <--> S - AFB1). The model permits the estimation of two parameters: the number of binding sites per microorganism (M) and the reaction equilibrium constant (K(eq)) involved, both of which are useful for estimating the adsorption efficiency (M x K(eq)) of a particular microorganism. Application of the model to experimental data suggests that different microorganisms have similar K(eq) values and that the differences in toxin removal efficiency are mainly due to differences in M values. The most important application of the proposed model is the capacity to select the most efficient microorganism to remove AFB1. Furthermore, it allows us to know if a modification of the adsorption efficiency obtained by physical, chemical, or genetic treatments on the microorganism is a consequence of changes in M, K(eq), or both.