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  • 1
    Language: Japanese
    In: 混相流, 2018, Vol.32(1), pp.19-25
    Description: 〈p〉Transport of fine bubbles (FBs) in porous media has drawn increasing attention, as a promising technology for soil and groundwater remediation. Understanding the transport characteristics of FBs in soils is essential to optimize FB-based remediation techniques. FB transport is highly influenced by flow rate, gas species, chemical properties of FB water such as pH and ionic strength. Transport models for colloidal particles including colloid filtration theory are applicable for characterizing FB transport in the porous media. In addition, DLVO theory representing interaction energy between colloidal particles and collector was helpful for understanding attachment mechanism of FBs in the porous media.〈/p〉
    Keywords: Transport characteristics ; Transport model ; Porous media ; Attachment ; Colloid ; Interaction energy ; Transport Characteristics ; Transport Model ; Porous Media ; Attachment ; Colloid ; Interaction Energy
    ISSN: 0914-2843
    E-ISSN: 18815790
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  • 2
    Language: English
    In: Journal of Hazardous Materials, 2009, Vol.166(1), pp.207-212
    Description: The understanding of the gaseous adsorption process and the parameters of volatile organic compounds such as organic solvents or fuels onto soils is very important in the analysis of the transport or fate of these chemicals in soils. Batch adsorption experiments with six different treatments were conducted to determine the adsorption of isohexane, a gaseous aliphatic, onto volcanic ash soil (Tachikawa loam). The measured gas adsorption coefficient for samples of Tachikawa loam used in the first three treatments, Control, AD (aggregate destroyed), and AD-OMR (aggregate destroyed and organic matter removed), implied that the aggregate structure of volcanic ash soil as well as organic matter strongly enhanced gas adsorption under the dry condition, whereas under the wet condition, the aggregate structure played an important role in gas adsorption regardless of the insolubility of isohexane. In the gas adsorption experiments for the last three treatments, soils were sieved in different sizes of mesh and were separated into three different aggregate or particle size fractions (2.0–1.0 mm, 1.0–0.5 mm, and less than 0.5 mm). Tachikawa loam with a larger size fraction showed higher gas adsorption coefficient, suggesting the higher contributions of macroaggregates to isohexane gas adsorption under dry and wet conditions.
    Keywords: Volatile Organic Compound ; Adsorption ; Gas ; Aggregated Soil ; Organic Matter ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 3
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(3), pp.795-806
    Description: The air permeability (ka) and soil gas diffusion coefficients (Dp) are controlling factors for gas transport and fate in variably saturated soils. We developed a unified model for ka and Dp based on the classical Archie's law, extended by: (i) allowing for two-region gas transport behavior for structured soils, with the natural field moisture condition (set at −100 cm H2O matric potential [pF 2]) as the reference (spliced) point between the large-pore (drained pore diameter ≥30 μm at pF ≤ 2) and the small-pore (subsequently drained pores 2) regions, and (ii) including a percolation threshold, set as 10% of the total porosity for structureless porous media or 10% of the porosity in the large-pore region for structured soils. The resulting extended Archie's law with reference point (EXAR) models for ka and Dp were fitted to the measured data. For both structureless and structured porous media, Archie's saturation exponent (n) was higher for Dp than for ka, indicating higher water blockage effects on gas diffusion. For structured soils, the saturation exponent for the large-pore region (n1) was lower than for the small-pore region (n2). Generally, n1 values of∼1 for ka and 2 for Dp and n2 values of 4/3 for ka and 7/3 for Dp described the data well. Two reference-point expressions for ka at pF 2 were also developed and tested together with existing models for Dp at pF 2 against independent data across soil types. The best-performing reference-point models were a ka model based on the classical Kozeny equation and the Moldrup Dp model. ; p. 795-806.
    Keywords: Models ; Water ; Soil Air ; Soil Types ; Porous Media ; Air ; Equations ; Permeability ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 4
    Language: English
    In: Journal of Geotechnical and Geoenvironmental Engineering, July, 2011, Vol.137(7), p.653(10)
    Description: Landfill sites have been implicated in greenhouse warming scenarios as a significant source of atmospheric methane. In this study, the effects of extreme compaction on the two main soil-gas transport parameters, the gas diffusion coefficient ([D.sub.p]) and the intrinsic air permeability ([k.sub.a]), and the cumulative methane oxidation rate in a landfill cover soil were investigated. Extremely compacted landfill cover soil exhibited negligible inactive soil-air contents for both [D.sub.p] and ka. In addition, greater [D.sub.p] and [k.sub.a] were observed as compared with normal compacted soils at the same soil-air content ([epsilon]), likely because of reduced water-blockage effects under extreme compaction. These phenomena are not included in existing predictive models for [D.sub.p]([epsilon]) and ka([epsilon]). On the basis of the measured data, new predictive models for [D.sub.p]([epsilon]) and ka([epsilon]) were developed with model parameters (representing air-filled pore connectivity and water-blockage effects) expressed as functions of dry density ([[rho].sub.b]). The developed [D.sub.p] ([epsilon]) and [k.sub.a] (e) models together with soil-water retention data for soils at normal and extreme compaction ([[rho].sub.b] = 1.44 and 1.85 g [cm.sup.-3]) implied that extremely compacted soils will exhibit lower [D.sub.p] and [k.sub.a] at natural field-water content (-100 cm [H.sub.2]O of soil-water matric potential) because of much lower soil-air content. Numerical simulations of methane gas transport, including a first-order methane oxidation rate, were performed for differently compacted soils by using the new predictive [D.sub.p]([epsilon]) model. Model results showed that compaction-induced difference in soil-air content at a given soil-water matric potential condition is likely the most important parameter governing methane oxidation rates in extremely compacted landfill cover soil. DOI: 10.1061/(ASCE)GT.1943-5606.0000459. CE Database subject headings: Landfills; Coverings; Gas; Parameters; Methane. Author keywords: Landfill final cover soil; Gas transport parameters; Compaction.
    Keywords: Atmospheric Carbon Dioxide -- Analysis ; Waste Management -- Analysis ; Methane -- Analysis ; Permeability -- Analysis ; Natural Gas Transmission -- Analysis
    ISSN: 1090-0241
    E-ISSN: 19435606
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  • 5
    Language: English
    In: Water Research, 01 May 2016, Vol.94, pp.120-127
    Description: Global warming and urbanization together with development of subsurface infrastructures (e.g. subways, shopping complexes, sewage systems, and Ground Source Heat Pump (GSHP) systems) will likely cause a rapid increase in the temperature of relatively shallow groundwater reservoirs (subsurface thermal pollution). However, potential effects of a subsurface temperature change on groundwater quality due to changed physical, chemical, and microbial processes have received little attention. We therefore investigated changes in 34 groundwater quality parameters during a 13-month enhanced-heating period, followed by 14 months of natural or enhanced cooling in a confined marine aquifer at around 17 m depth on the Saitama University campus, Japan. A full-scale GSHP test facility consisting of a 50 m deep U-tube for circulating the heat-carrying fluid and four monitoring wells at 1, 2, 5, and 10 m from the U-tube were installed, and groundwater quality was monitored every 1–2 weeks. Rapid changes in the groundwater level in the area, especially during the summer, prevented accurate analyses of temperature effects using a single-well time series. Instead, Dual-Well Analysis (DWA) was applied, comparing variations in subsurface temperature and groundwater chemical concentrations between the thermally-disturbed well and a non-affected reference well. Using the 1 m distant well (temperature increase up to 7 °C) and the 10 m distant well (non-temperature-affected), the DWA showed an approximately linear relationships for eight components (B, Si, Li, dissolved organic carbon (DOC), Mg , NH , Na , and K ) during the combined 27 months of heating and cooling, suggesting changes in concentration between 4% and 31% for a temperature change of 7 °C.
    Keywords: Subsurface Thermal Pollution ; Ground Source Heat Pump (Gshp) Systems ; Long-Term Heating and Cooling ; Confined Marine Aquifer ; Dual-Well Analysis (Dwa) ; Groundwater Quality ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 6
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(5), pp.1509-1517
    Description: The gas diffusion coefficient (Ds,g) and solute diffusion coefficient (D(s,l)) and their dependencies on fluid content (κ) (equal to soil–air content θ for D(s,g) and soil–water content ɛ for D(s,l)) are controlling factors for gas and solute transport in variably saturated soils. In this study, we propose unified, predictive models for D(s,g)(ɛ) and D(s,l)(θ) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid-induced reduction term including a percolation threshold (ɛ(th) for D(s,g) and θ(th) for D(s,l)). Different percolation threshold terms adopted from recent studies for gas (D(s,g)) and solute (D(s,l)) diffusion were applied. For gas diffusion, ɛth was a function of bulk density (total porosity), while for solute diffusion θ(th) was best described by volumetric content of finer soil particles (clay and organic matter), FINES(vol). The resulting LIquid and GAs diffusivity and tortuosity (LIGA) models were tested against D(s,g) and D(s,l) data for differently-textured soils and performed well against the measured data across soil types. A sensitivity analysis using the new Maxwell’s Law based LIGA models implied that the liquid phase but not the gaseous-phase tortuosity was controlled by soil type. The analyses also suggested very different pathways and fluid-phase connectivity for gas and solute diffusion in unsaturated soil. In conclusion, the commonly applied strategy of using the same, soil-type-independent model for gas and solute diffusivity in analytical and numerical models for chemical transport and fate in variably-saturated soils appears invalid, except for highly sandy soils. The unified LIGA model with differing percolation thresholds for diffusion in the liquid and gaseous phases solves this problem. ; p. 1509-1517.
    Keywords: Clay ; Sandy Soils ; Bulk Density ; Solutes ; Mathematical Models ; Organic Matter ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 7
    Language: English
    In: Waste Management, 2011, Vol.31(12), pp.2464-2472
    Description: ► The effects of soil physical properties on gas transport parameters were investigated. ► Higher values of and exhibited in the ‘+gravel’ than the ‘−gravel’ fraction at same soil–air content ( ). ► Recent power law models for (WLR) and (RPL) were modified. ► Model parameters were linearly related to easily measurable dry bulk density ( ). Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, , and particle size fraction on the main soil–gas transport parameters – soil–gas diffusivity ( / , ratio of gas diffusion coefficients in soil and free air) and air permeability ( ) – under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting values ranging from 1.40 to 2.10 g cm . Results showed that and values for the ‘+gravel’ fraction (〈35 mm) became larger than for the ‘−gravel’ fraction (〈2 mm) under variably-saturated conditions for a given soil–air content ( ), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on and was most pronounced for the ‘+gravel’ fraction. Normalized ratios were introduced for all soil–gas parameters: (i) for gas diffusivity / , the ratio of measured to in total porosity ( ), (ii) for air permeability / , the ratio of measured to at 1235 kPa matric potential (=pF 4.1), and (iii) for soil–air content, the ratio of soil–air content ( ) to total porosity ( ) (air saturation). Based on the normalized parameters, predictive power-law models for ( / ) and ( / ) models were developed based on a single parameter (water blockage factor for and for ). The water blockage factors, and , were found to be linearly correlated to values, and the effects of dry bulk density on and for both ‘+gravel’ and ‘−gravel’ fractions were well accounted for by the new models.
    Keywords: Air Permeability ; Gas Diffusivity ; Dry Bulk Density ; Landfill Final Cover ; Engineering ; Chemistry
    ISSN: 0956-053X
    E-ISSN: 1879-2456
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  • 8
    In: Water Resources Research, February 2012, Vol.48(2), pp.n/a-n/a
    Description: Diffusivity was measured for 12 rock and construction material samples using a diffusion chamber method with oxygen as the tracer gas. Several steps were implemented to minimize leakage between the sample and the core holder, and rigorous tests were performed to evaluate and correct the overall leakage of the diffusion apparatus. This method was proven capable of rapidly measuring the diffusion coefficient for consolidated samples having dimensionless diffusivity values greater than 4.7 × 10 in a relative short duration (hours to 1 day). Gas diffusion measurements were also conducted for 11 repacked sediments and sands. Our results are consistent with literature data from liquid tracer through‐diffusion methods; the diffusivity versus porosity relationship for our data can be described by Archie's law. The value in Archie's law was found to be correlated to pore size: the finer the pore size is, the larger the value is. A linear regression equation can describe the change of with ln (the volumetric mean pore diameter) for most rocks with 〈 1.3 μm, while the outliers can be correlated to narrower pore size distribution. Gas diffusivity measured for consolidated rocks and construction materials Archie's law describes diffusivity‐porosity relation with different m values Relations between diffusivity and pore‐size distribution proposed
    Keywords: Diffusion ; Pore Size Distribution ; Porosity
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 9
    Language: English
    In: Journal of Porous Media, 2018, Vol.21(7), pp.607-622
    ISSN: 1091-028X
    E-ISSN: 19340508
    Source: Begell House, Inc. (via CrossRef)
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  • 10
    Language: English
    In: Journal of Contaminant Hydrology, January 2018, Vol.208, pp.61-67
    Description: An understanding of nano-scale bubble (NB) transport in porous media is important for potential application of NBs in soil/groundwater remediation. It is expected that the solution chemistry of NB water highly influences the surface characteristics of NBs and porous media and the interaction between them, thus affecting the stability and transport characteristics of NB. In this study, in addition to stability experiments, one-dimensional column transport experiments using glass beads were conducted to investigate the effects of pH on the NB transport behavior. The results showed that the NBs were more stable under higher pH. Column transport experiments revealed that entrapment of NBs, especially larger ones, was enhanced in lower-pH water, likely suggesting pH-dependent NB attachment and physical straining, both of which are also probably influenced by bubble size. Although relatively smaller NBs were released after switching the eluting fluid to one with lower ionic strength, most of the NBs in lower-pH water were still retained in the porous media even altering the chemical condition.
    Keywords: Nano Bubble (Nb) ; Solution Chemistry ; Transport ; Porous Media ; Engineering ; Environmental Sciences ; Geography
    ISSN: 0169-7722
    E-ISSN: 1873-6009
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