Steady-state analytical model for vapour-phase volatile organic compound (VOC) diffusion in layered landfill composite cover systems

2017 ◽  
Vol 54 (11) ◽  
pp. 1567-1579 ◽  
Author(s):  
Haijian Xie ◽  
Qiao Wang ◽  
Huaxiang Yan ◽  
Yunmin Chen
Keyword(s):  
Analytical Model ◽  
Water Saturation ◽  
Soil Layer ◽  
Surface Flux ◽  
Vapour Phase ◽  
Retardation Factor ◽  
Protective Layers ◽  
Cover System ◽  
Volatile Organic ◽  
Benzene Concentration

An analytical model for the diffusion of one-dimensional vapour-phase volatile organic compounds (VOCs) through a four-layer landfill composite cover system consisting of a protective layer, drainage layer, geomembrane (GMB), and compacted clay liner (CCL) is developed. Effects of degree of water saturation (Sr), adsorption, and degradation on vapour-phase VOC diffusion in a cover system are then analyzed. The vapour-phase benzene concentration profile increases with increase of Sr in the drainage and protective layers. When Sr1 = Sr2 = 0.5 (where Sr1 and Sr2 are degree of water saturation of the protective and drainage layers, respectively), surface flux for the case with the degree of water saturation of the CCL layer Sr4 = 0.3 is 1.3 and 1560 times larger than that with Sr4 = 0.7 and = 0.9, respectively. The effect of adsorption of the VOCs in the CCL on performance of the cover system is more important than that in the drainage and protective layers. Surface flux and concentration of benzene tends to be zero when CCL is amended with 0.5% biochar due to an increase of the retardation factor. The effect of degradation rate on benzene concentration increases with increase of degree of water saturation. The influence of half-life of VOCs in the soil layer, t1/2, on vapour-phase VOC concentration can be neglected when Sr ≤ 0.3.

scholarly journals Exposure Studies of Different Kinds of Volatile Organic Compounds in Vapour Phase with a Narrow-gap Cell Containing CuxS Modified Carbon Microdisc Electrode

2018 ◽  
Vol 63 (1) ◽  
pp. 170-178 ◽  
Author(s):  
László Kiss
Keyword(s):  
Acetic Acid ◽  
Volatile Organic Compounds ◽  
Ethyl Acetate ◽  
Organic Compounds ◽  
Modified Electrode ◽  
Vapour Phase ◽  
Narrow Gap ◽  
Current Increase ◽  
Interelectrode Gap ◽  
Volatile Organic

In this article, the feasibility of the CuxS modified carbon microdisc electrode was examined by exposure to four different volatile organic compounds (2-propanol, acetic acid, ethyl acetate and n-butylamine) directly in their vapour phase using cyclic voltammetry and amperometry. The performance of the modified microdisc was compared with the bare carbon microdisc (30 μm in diameter) which was involved in a narrow-gap cell. By using both methods high current increase was observed for 2-propanol with the modified electrode and its sensitivity was sufficiently higher than with the bare electrode. The modified electrode showed lower current signals in case of acetic acid and n-butylamine. The latter formed a condensation layer at the interelectrode gap. Neither the bare nor the modified electrode was sensitive to ethyl acetate.

scholarly journals Calculation of the Height of Capillary Rise of Water in Soils

2020 ◽  
Vol 8 (6) ◽  
pp. 4832-4835
Keyword(s):  
Water Saturation ◽  
Underground Structure ◽  
Capillary Rise ◽  
Soil Layer ◽  
Underground Water ◽  
Wall Material ◽  
Capillary Water ◽  
Temporary Streams ◽  
Filter Water ◽  
Soil Pores

Rain and melt water will form temporary accumulations of surface water on the surface. When they seep into the ground, temporary streams of leaky filter water are formed. If a limited section of water-resistant soil layer or the roof of an underground structure is encountered in the path of these waters, a temporary aquifer-the upper layer of ground water-may form above them. In temporary and permanent aquifers, the soil pores are completely filled with gravitational water, the degree of water saturation is equal to one, and there is pressure under the surface of underground water. Above this surface is a zone of capillary moisture, while the level of capillary rise is determined by the granulometric composition of the soil and ranges from tens of centimeters in sand to several meters in dusty and clay soils. Capillary water rises in the ground on free canals formed by mutually communicating pores, or is kept in them in limbo.The lifting of the liquid in the capillary continues until the gravity acting on the column of the liquid in the capillary becomes equal to the resulting force. Capillary water penetrates from the ground into the walls and rises to a height of up to 2 meters. The normal moisture content of the brick walls is 0.02...0,03, and in the case of unprotected contact with moist soil is increased to 0.15...0.25. On the inside of the walls there is a damp, mildew. Evaporating water increases humidity in the room, and the salts released when it evaporates from salt solutions lead to peeling paint, destruction of plaster and wall material.

scholarly journals A Theory of Water Percolation in Snow

1972 ◽  
Vol 11 (63) ◽  
pp. 369-385 ◽  
Author(s):  
S. C. Colbeck
Keyword(s):  
Water Saturation ◽  
Water Flux ◽  
Surface Flux ◽  
Gravity Drainage ◽  
Water Fluxes ◽  
Periodic Surface ◽  
Water Percolation ◽  
Wave Forms ◽  
Particular Solution ◽  
Measured Water

Abstract A theory is developed to describe the vertical percolation of water in isothermal snow. The general theory of Darcian flow is reviewed to establish a reasonable physical basis for the construction of a model. It is shown that in simple gravity drainage, capillarity is negligible compared with gravity since values of water saturation are generally in the “mid-range”. It is postulated that the permeability to the water phase increases as a certain function of the water saturation, and porosity is assumed to decrease linearly with depth. Ice layers and other inhomogeneities are treated in the theory by considering the permeability of the snow with the inhomogeneities included. A method by which this value of permeability can be calculated is presented using the method of characteristics. The theory is applied to the Seward Glacier firn where Sharp measured water fluxes at various depths. A periodic surface flux is assumed and the particular solution for water flux at any depth is given. From this solution the wave forms passing each depth are constructed and compared with the measured ones. Although the experimental data are affected by the presence of ice layers, the comparison between theory and experiment is favorable and the theory is thought to be essentially correct.

Solving a direct problem as a new method of seismic microzonation

2021 ◽  
pp. 38-53
Author(s):  
Alexander S. Aleshin ◽  
Vladimir V. Pogrebchenko ◽  
Sergey N. Nikitin
Keyword(s):  
Direct Problem ◽  
Water Saturation ◽  
Soil Layer ◽  
Seismic Intensity ◽  
Seismic Microzonation ◽  
Acceleration Pulse ◽  
Territorial Planning ◽  
New Type ◽  
Seismic Impact ◽  
Seismic Impacts

The article describes a new type of seismic microzonation, called the method of solving a direct problem. The main methodological technique in this case is the formation of models of the soil layer on the basis of complex engineering-geological and geophysical studies. An original computer simulation technique based on the use of a short acceleration pulse as the initial seismic impact is proposed. In the calculations of the increment of seismic intensity, a new formula is used that takes into account all the factors of the influence of soil properties on the parameters of seismic impacts – seismic rigidity, water saturation, resonant effects and the nonlinearity of the reaction of soils to strong seismic impacts. Based on the obtained data, the models of ground layers at the construction site are mapped and the parameters of seismic impacts that correspond to the properties of each model of ground massif are determined. The proposals presented in the article are reflected in the regulatory documents devoted to the SMZ of objects of increased responsibility and territorial planning.

Analytical Model of Water Flow in Coal with Active Matrix

2014 ◽  
Vol 59 (4) ◽  
pp. 1077-1086
Author(s):  
Jakub Siemek ◽  
Jerzy Stopa
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Analytical Model ◽  
Water Flow ◽  
Water Saturation ◽  
Exact Analytical Solution ◽  
Capillary Forces ◽  
Coal Matrix ◽  
Macro Scale

Abstract This paper presents new analytical model of gas-water flow in coal seams in one dimension with emphasis on interactions between water flowing in cleats and coal matrix. Coal as a flowing system, can be viewed as a solid organic material consisting of two flow subsystems: a microporous matrix and a system of interconnected macropores and fractures. Most of gas is accumulated in the microporous matrix, where the primary flow mechanism is diffusion. Fractures and cleats existing in coal play an important role as a transportation system for macro scale flow of water and gas governed by Darcy’s law. The coal matrix can imbibe water under capillary forces leading to exchange of mass between fractures and coal matrix. In this paper new partial differential equation for water saturation in fractures has been formulated, respecting mass exchange between coal matrix and fractures. Exact analytical solution has been obtained using the method of characteristics. The final solution has very simple form that may be useful for practical engineering calculations. It was observed that the rate of exchange of mass between the fractures and the coal matrix is governed by an expression which is analogous to the Newton cooling law known from theory of heat exchange, but in present case the mass transfer coefficient depends not only on coal and fluid properties but also on time and position. The constant term of mass transfer coefficient depends on relation between micro porosity and macro porosity of coal, capillary forces, and microporous structure of coal matrix. This term can be expressed theoretically or obtained experimentally.

Effects of a semipervious lens on soil vapour extraction

1997 ◽  
Vol 341 ◽  
pp. 385-413 ◽  
Author(s):  
CHIU-ON NG ◽  
CHIANG C. MEI
Keyword(s):  
Soil Layer ◽  
Coarse Sand ◽  
Retardation Factor ◽  
Vapour Transport ◽  
Volatile Chemicals ◽  
Immobile Water ◽  
Volatile Organic Chemicals ◽  
Soil Vapour Extraction ◽  
Highly Porous ◽  
Vapour Extraction

We describe a theory for the removal of volatile organic chemicals from an unsaturated soil stratum consisting of highly porous coarse sand layers sandwiching a thin and semipervious lens. Each soil layer is modelled as a periodic array of spherical aggregates formed by solid grains and immobile water trapped by surface tension. Volatile chemicals are vaporized in the mobile air in pores between aggregates, dissolved in the intra-aggregate water, and adsorbed on the surface of soil grains. Using the effective transport equations derived for the aggregated soils, we consider shallow layers with sharp contrast in physical properties. An asymptotic analysis is developed for an axisymmetric geometry, yielding quasi-one-dimensional governing equations for individual layers. At the leading order the flow and the vapour transport are horizontal in the coarse layers but vertical in the semipervious lens. Numerical results are presented for a simple example to demonstrate the significance of the lens permeability, diffusivity and retardation factor, and the aggregate diffusivity in the coarse layers, on the vapour transport during the stages of contamination and air-venting.

scholarly journals An Analytical Model of Evaporation Efficiency for Unsaturated Soil Surfaces with an Arbitrary Thickness

2011 ◽  
Vol 50 (2) ◽  
pp. 457-471 ◽  
Author(s):  
Olivier Merlin ◽  
Ahmad Al Bitar ◽  
Vincent Rivalland ◽  
Pierre Béziat ◽  
Eric Ceschia ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Analytical Model ◽  
Land Surface ◽  
Soil Layer ◽  
Soil Evaporation ◽  
Atmospheric Conditions ◽  
Potential Evaporation ◽  
Evaporative Demand ◽  
Soil Layers ◽  
Arbitrary Thickness

Abstract Analytical expressions of evaporative efficiency over bare soil (defined as the ratio of actual to potential soil evaporation) have been limited to soil layers with a fixed depth and/or to specific atmospheric conditions. To fill the gap, a new analytical model is developed for arbitrary soil thicknesses and varying boundary layer conditions. The soil evaporative efficiency is written [0.5 − 0.5 cos(πθL/θmax)]P with θL being the water content in the soil layer of thickness L, θmax being the soil moisture at saturation, and P being a function of L and potential soil evaporation. This formulation predicts soil evaporative efficiency in both energy-driven and moisture-driven conditions, which correspond to P < 0.5 and P > 0.5, respectively. For P = 0.5, an equilibrium state is identified when retention forces in the soil compensate the evaporative demand above the soil surface. The approach is applied to in situ measurements of actual evaporation, potential evaporation, and soil moisture at five different depths (5, 10, 30, 60, and 100 cm) collected in summer at two sites in southwestern France. It is found that (i) soil evaporative efficiency cannot be considered as a function of soil moisture only because it also depends on potential evaporation, (ii) retention forces in the soil increase in reaction to an increase of potential evaporation, and (iii) the model is able to accurately predict the soil evaporation process for soil layers with an arbitrary thickness up to 100 cm. This new model representation is expected to facilitate the coupling of land surface models with multisensor (multisensing depth) remote sensing data.

scholarly journals Microbial reduction of iron and porewater biogeochemistry in acidic peatlands

2008 ◽  
Vol 5 (6) ◽  
pp. 1537-1549 ◽  
Author(s):  
K. Küsel ◽  
M. Blöthe ◽  
D. Schulz ◽  
M. Reiche ◽  
H. L. Drake
Keyword(s):  
Water Saturation ◽  
Global Climate ◽  
Soil Layer ◽  
Carbon Mineralization ◽  
Microbial Reduction ◽  
Electron Acceptors ◽  
Soil Conditions ◽  
Soil Layers ◽  
Reduction Of Iron ◽  
Pcr Products

Abstract. Temporal drying of upper soil layers of acidic methanogenic peatlands might divert the flow of reductants from CH4 formation to other electron-accepting processes due to a renewal of alternative electron acceptors. In this study, we evaluated the in situ relevance of Fe(III)-reducing microbial activities in peatlands of a forested catchment that differed in their hydrology. Intermittent seeps reduced sequentially nitrate, Fe(III), and sulfate during periods of water saturation. Due to the acidic soil conditions, released Fe(II) was transported with the groundwater flow and accumulated as Fe(III) in upper soil layers of a lowland fen apparently due to oxidation. Microbial Fe(III) reduction in the upper soil layer accounted for 26.7 and 71.6% of the anaerobic organic carbon mineralization in the intermittent seep and the lowland fen, respectively. In an upland fen not receiving exogenous Fe, Fe(III) reduction contributed only to 6.7%. Fe(II) and acetate accumulated in deeper porewater of the lowland fen with maximum concentrations of 7 and 3 mM, respectively. Both supplemental glucose and acetate stimulated the reduction of Fe(III) indicating that fermentative, incomplete, and complete oxidizers were involved in Fe(II) formation in the acidic fen. Amplification of DNA yielded PCR products specific for Acidiphilium-, Geobacter-, and Geothrix-, but not for Shewanella- or Anaeroromyxobacter-related sequences. Porewater biogeochemistry observed during a 3-year-period suggests that increased drought periods and subsequent intensive rainfalls due to global climate change will further favor Fe(III) and sulfate as alternative electron acceptors due to the storage and enhanced re-oxidation of their reduced compounds in the soil.

scholarly journals Analytical Model of Waterflood Sweep Efficiency in Vertical Heterogeneous Reservoirs under Constant Pressure

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Lisha Zhao ◽  
Li Li ◽  
Zhongbao Wu ◽  
Chenshuo Zhang
Keyword(s):  
Analytical Model ◽  
Oil Recovery ◽  
Constant Pressure ◽  
Water Saturation ◽  
Water Injection ◽  
Single Layer ◽  
Sweep Efficiency ◽  
Heterogeneous Reservoirs ◽  
Water Cut ◽  
Swept Volume

An analytical model has been developed for quantitative evaluation of vertical sweep efficiency based on heterogeneous multilayer reservoirs. By applying the Buckley-Leverett displacement mechanism, a theoretical relationship is deduced to describe dynamic changes of the front of water injection, water saturation of producing well, and swept volume during waterflooding under the condition of constant pressure, which substitutes for the condition of constant rate in the traditional way. Then, this method of calculating sweep efficiency is applied from single layer to multilayers, which can be used to accurately calculate the sweep efficiency of heterogeneous reservoirs and evaluate the degree of waterflooding in multilayer reservoirs. In the case study, the water frontal position, water cut, volumetric sweep efficiency, and oil recovery are compared between commingled injection and zonal injection by applying the derived equations. The results are verified by numerical simulators, respectively. It is shown that zonal injection works better than commingled injection in respect of sweep efficiency and oil recovery and has a longer period of water free production.

Sign in / Sign up

Export Citation Format

Share Document