Experimental Investigation of the Interaction of Soil Air Permeability and Soil Vapor Extraction

Soil vapor extraction column experiments were performed to investigate contaminant removal and its interaction with soil air permeability. Water, TCE, and PCE, and a mixture of TCE and PCE were used as contaminants. Three gradations of Ottawa sand were used at relative densities of 0.60 and 1.0:?medium, fine, and uniform. Soil air permeability was found to increase linearly with time by 25–150?% to a maximum value when the contaminant was completely removed. The largest increase in soil air permeability was found for fine and/or dense samples. The experimental data were used in a previously developed model by Farhan in 1998 and Farhan et al. in 2001 to predict column behavior. In general, the model predictions were in good agreement with the experimental results. They revealed that the assumption of local equilibrium between the pore air and contaminants is valid for a wide range of pore velocities (2.0–9.2 cm/s).     

Estimation of Operation Time for Soil Vapor Extraction Systems

Soil vapor extraction (SVE) has become an acceptable method of removing volatile organic compounds from soil. However, determining the length of time these systems should operate has been historically difficult. This paper presents a procedure for determining this length of operation. The procedure incorporates principles of uncertainty analysis, contaminant transport, and decision theory. An example is provided to illustrate the use of the procedure. Additional analysis of the results shows that a simple calculation can be made that will determine if a SVE system that has been operating for a period of time and is in the later stages of contaminant removal should continue to operate. This calculation consists of dividing the cost of treating the remaining contaminated soil with an alternative method (e.g., ex situ biological treatment) by the annual operation and maintenance cost and comparing this ratio to the inverse of the interest rate. If this ratio is less than the inverse of the interest rate the system should be shut off.     

Thermally Enhanced Vapor Extraction for Removing PAHs from Lampblack-Contaminated Soil

This work summarizes the results of a feasibility study in support of a soil venting-thermal desorption (SVTD) process for remediating lampblack-impacted soil. Lampblack is the solid residue resulting from the gasification of crude oil. The SVTD process couples soil vapor extraction with in situ heating. The objective of this study is to determine the required temperature for desorbing polycyclic aromatic hydrocarbons (PAHs), the compounds of regulatory concern, from lampblack. Bench-scale results are reported for the treatment of a soil-lampblack matrix containing 11 PAHs totaling about 4100 ppm (mg∕kg) total PAH (TPAH). Solids characterization analyses suggested that these PAHs constitute about 60% of the organic residue on a solid matrix dominated by fine-grained sand and carbon-based lampblack particles. Thin section imagery supports the conceptual model of hydrocarbons associated with the surface of sand grains. SVTD testing for the sand-lampblack solids indicates that temperatures in excess of about 250°C are sufficient to mobilize most of the PAHs. Specifically, at temperatures between 250°C and 300°C, the TPAH level in the soil-lampblack matrix was reduced to less than 100 ppm in 10 days. The dynamics of PAH removal were captured reasonably well by a mass balance accounting for the temperature dependent volatilization of an ideal PAH mixture. Both simulated and experimental results support the finding that the vast majority of the PAH removal from this sand-lampblack matrix was controlled by thermodynamic considerations (as opposed to mass transfer resistances). A small residual PAH fraction (roughly 40 ppm TPAH) was observed to persist in the solids even at temperatures in excess of 650°C. Although the specific state of these persistent PAHs is unknown, they may reside within an extremely nonvolatile residue or be otherwise strongly sequestered in the solid matrix.     

Measuring Aqueous-Air and Sorbed-Aqueous Mass Transfer Coefficients for Application in Soil Vapor Extraction

Soil vapor extraction (SVE) is a common remediation practice typically implemented without a rigorous design process because of insufficient or unspecific design data. Field observations have shown that the mass of contaminant removed by SVE often tails off over time. Significant time has been spent modeling SVE to gain a better understanding of the governing processes and the cause of tailing. Studies have shown that improper mass transfer coefficients affect modeling accuracy. As a result, considerable effort has been spent studying the mass transfer coefficients directly related to the non-aqueous-phase liquid (NAPL), with less emphasis on aqueous air and sorbed-aqueous mass transfer coefficients, despite affecting the observed tailing behavior. Accordingly, a laboratory and modeling study was undertaken with toluene to determine the appropriate aqueous air and sorbed-aqueous mass transfer coefficients. SVE column data generated in laboratory experiments were used to back-calculate the mass transfer coefficients by using FRACMAT, a numerical model. The developed experimental protocol allowed the placement of toluene contamination in the unsaturated soil environment without the development of a NAPL phase. The data generated by the SVE column with soils with organic matter and without organic matter, showed that the aqueous-air mass transfer coefficient was exponential, with the aqueous concentration the independent variable. For the zero to moderate organic matter content soils tested, the aqueous-air mass transfer coefficient varied from 1??s-1 to 0.001??s-1. Some sorbed contamination was also observed, requiring a sorbed-aqueous mass transfer coefficient. Numerical modeling with FRACMAT showed that the best sorbed-aqueous mass transfer coefficient was a constant value of 0.01??s-1. The aqueous-air mass transfer coefficient was observed to be the controlling rate limitation in SVE when no NAPL was present in the soil with the zero to moderate organic matter content soil. Studies with silty loam soil showed that additional mass transfer resistances occurred, which could be attributed to the increase in organic matter content and decrease in particle size.     

Nonequilibrium Nonaqueous Phase Liquid Mass Transfer Model for Soil Vapor Extraction Systems

Soil vapor extraction is a popular soil remediation technology that is hampered by less than optimal performance in the field due to mass transfer limitations. Therefore, laboratory column venting experiments were completed to quantify mass transfer limitations for the removal of multicomponent nonaqueous phase liquid (NAPL) contaminants from a silt loam soil at three water contents. The observed mass transfer limitations were quantified using a four phase multicomponent, nonequilibrium contaminant transport model based on first-order mass transfer kinetics. The overall mass transfer coefficient Kga was treated as a variable and modeled as a linear function of the NAPL volumetric fraction using two adjustable parameters (m, the slope parameter and Kgamin, the intercept). Both were back calculated from column venting data. The agreement between the calibrated model and experimental results were favorable for the removal of single and binary contaminants under conditions ranging from near equilibrium to severe mass transfer limitations and extended tailing. A strong dependency of Kga on water content was evident by the differences in Kgamin and to a lesser extent, m, at the three water contents investigated. A single expression Kga captured the performance of both components in the binary mixture. For the quaternary venting experiments a single expression for Kga captured the performance of all four components well under air dry conditions. However, the agreement between the hexane model versus the experimental result deteriorated significantly as the water content increased. This difference is attributed to hexane’s lower affinity for the water phase relative to the other three components in the mixture.     

Relating Damping to Soil Permeability

Published comparisons of complex moduli in dry and saturated soils have shown that viscous behavior is only evident when a sufficiently massive viscous fluid (like water) is present. That is, the loss tangent is frequency dependent for water saturated specimens, but nearly frequency independent for dry samples. While the Kelvin–Voigt (KV) representation of a soil captures the general viscous behavior using a dashpot, it fails to account for the possibly separate motions of the fluid and frame (there is only a single mass element). An alternative representation which separates the two masses, water and frame, is presented here. This Kelvin–Voigt–Maxwell–Biot (KVMB) model draws on elements of the long standing linear viscoelastic models in a way that connects the viscous damping to permeability and inertial mass coupling. A mathematical mapping between the KV and KVMB representations is derived and permits continued use of the KV model, while retaining an understanding of the separate mass motions.     

Vapor Adsorption Index for Expansive Soil Classification

A laboratory index defined as gravimetric water content at ambient relative humidity of 75% (w75) is proposed for qualitatively classifying the swelling potential of clays and clayey soils (e.g., low, moderate, high). The methodology is calibrated by comparison with existing plasticity-based and suction-based classification methodologies for a series of natural clays from Missouri and Colorado and clay mixtures prepared to represent a wide range of swelling potential. Procedures are described for obtaining w75 by placing samples in the headspace of an environmental chamber maintained under controlled humidity using a saturated NaCl solution. The proposed methodology has potential advantages over existing expansive soil classification methods because a large number of samples may be tested concurrently, no specialized testing equipment is required, and testing procedures may be readily automated. Measurements may be obtained in as little as 3–5?days with coefficients of variation ranging from 5 to 25%.     

Estimation of Soil Permeability Using an Acoustic Technique

A new method of estimating the permeability of soils using an acoustic technique is proposed in this technical note. Biot’s coupled theory of mixtures from the mid-1950s, which addresses the relationship between the permeability of saturated soils and the characteristic frequency of elastic waves, is used. The characteristic frequency is determined from the attenuation versus frequency curves obtained by acoustic sweep tests. This study presents the experimental technique for measuring the characteristic frequency of soils and calculation procedure for estimating the permeability of sandy soils. This technical note holds discussion for silty or clayey soils.     

Soil Water Retention and Conductivity When Vapor Flow Is Important

Models of soil water transport often calculate conductivity K from the water retention curve (WRC). Residual water content (θr) has been defined as θ where K = 0. When nonisothermal, coupled vapor and liquid water transport are considered, θr>0 fails because vapor transport often reduces θ to near zero. The author’s objective was to test a model that used unsaturated K(θ) with θ dependence typical of θr>0, while a WRC with θr = 0 was used elsewhere in the model. The system was a closed column of steady state, unsaturated, nonisothermal fine quartz sand with temperature (T) ranging from 5 to 40°C. Soil parameters were adjusted to simulate replicated experimental data from one initial θ condition. The model predicted θ and T within the range of the experimental data and reproduced the sharp drying front. It also satisfactorily modeled experiments with several different initial θ. Model heat flux predictions averaged 11% more than measured values. Experiments performed with two soil column lengths were not substantially different.     

关于改善烧结料层透气性途径的探讨

主要介绍葫芦岛锌厂铅锌冶炼厂烧结机烧结料层透气性的情况,以及通过控制混合料成分、粒度等途径改善料层透气性,最终优化焙烧条件.     

Air Permeability of Waste in a Municipal Solid Waste Landfill

The permeability of compacted municipal solid waste in a landfill with respect to air (or gas) flow was estimated using a short-term air injection test. Air was added to 134 vertical wells installed at three different depths at flow rates in the range of 0.14?–1.4?m3?min?1 and the corresponding steady state pressures were recorded. The permeability of the waste with respect to airflow (described here as the air permeability) was estimated for different anisotropy ratios (kr/kz = 1, 10, and 100) using a steady state, two-dimensional, axisymmetric analytical fluid flow model in conjunction with the measured flow and pressure data. The air permeability of landfilled municipal solid waste modeled as an isotropic medium was found to range from 1.6×10?13 to 3.2×10?11?m2. The estimated air permeability results were on the low end of values previously applied to model landfill gas flow. Estimated air permeability decreased significantly with increasing waste depth. The lower permeability encountered in the deeper layers was primarily attributed to the lower porosity of the waste caused by higher overburden pressures and higher moisture content of waste in deeper layers of the landfill than in shallow layers. The results suggest that multiple wells screened at different depths provide greater control of air distribution within the landfill. Leachate recirculation was documented to impact the ability to add air. In addition to limitations posed by standing water in many of the deeper wells, waste exposed to leachate recirculation was found to be significantly less permeable to air when compared to original conditions.     

Permeability Reduction of Soil Filters due to Physical Clogging

Soil filters, which are commonly used to provide stability to the base soils in subsurface infrastructure, are prone to long-term accumulation of fine micron-sized particles. This causes reduction in the permeability, which in turn may lead to intolerable decreases in their drainage capacity. In this paper, the extent of this reduction is addressed using results from both experimental and theoretical investigations. In the experimental phase, a sandy soil commonly used as a filter or drainage layer was subjected to pore fluids containing polystyrene or kaolinite particles, and their permeability reductions were determined in terms of the pore fluid suspension parameters. In the theoretical phase of the investigation, a representative elemental volume of the soil filter was modeled as an ensemble of capillary tubes and the permeability reduction due to physical clogging was simulated using basic principles of flow in cylindrical tubes. The results from the experimental and theoretical investigations were in good agreement. In general, the permeability reduced by more than one order of magnitude, even when the migrating particles were smaller than the majority of the soil filter pores. The concentration of particles in the pore stream affected the rate at which the permeability reduced. Self-filtration of particles, which is prominent at higher flow rates, may itself lead to a 20% reduction in the permeability for these sands.     

Transformation and Transport of Vinclozolin from Soil to Air

A laboratory chamber was designed and used to determine the headspace flux of the fungicide vinclozolin (3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-oxzoli-dine-2,4-dione) and its three degradation products from chamber surfaces, 20–30 mesh Ottawa sand, and sterilized and nonsterile North Carolina Piedmont aquic hapludult soils following fungicide spray applications. Results indicate that vinclozolin and its degradation products are influenced by the presence of soil particles, fluid-filled pore space, soil organic matter and clay content, and microbes. The formation of 2-[(3,5-dichlorophenyl)-carbamoyl]oxy-2-methyl-3-butenoic acid (“M1”), was highest in pore water with elevated pH levels, and the degradation is enhanced by the presence of microbes. M1 was also released from lower pH soil pore water, especially when the fungicide was incorporated into the soil. Unlike prior studies of vinclozolin degradation in solutions, this study found that, in soil, both M1 and 3′,5′-dichloro-2-hydroxy-2-methylbut-3-enanilide (“M2”) can be produced in the same soil column. These results indicate that engineering controls and agricultural practices following application can affect the amount and pathway of vinclozolin’s degradation.     

Inelastic Analysis of Pile–Soil Interaction

In this paper, inelastic pile–soil interaction is analyzed by using a hybrid type of numerical method. Piles are modeled as linear finite elements and the soil half-space is modeled using boundary elements. Inelastic modeling of the soil media is introduced by a rational approximation to a continuum with nonlinear interface springs along the piles. For this purpose, a modified ?zdemir’s nonlinear model is implemented and systems of equations are coupled for piles and pile groups at interacting nodes. To verify the proposed algorithm, three experimental results from previously conducted tests on piles under static axial and lateral loads are compared with those obtained from the present analysis.     

Experimental and Numerical Analysis of Soil–Pipe Interaction

Cases of pipeline damage caused by landslides are common in coastal or mountainous regions, where a continuous monitoring/repair activity is planned in order to maintain their serviceability. The analysis of the soil–structure interaction phenomenon can be invoked to improve the planning and design of buried pipelines, to guide monitoring, and to reduce the risk of damage or failure. Two different approaches are considered in this paper: small scale laboratory tests and numerical simulations using the distinct element method (DEM). The experimental setup consists of a box filled with sand and water. Several experiments were performed, in which the diameter and the depth of the tube varied. The numerical simulations are divided in two separate series: in the first, the numerical model is calibrated and its reliability in reproducing the experimental tests is checked; in the second series, the direction of the relative displacement between the tube and the surrounding “numerical soil” varies over the range ±90° with respect to the horizontal. In the latter, both vertical and horizontal components of the drag force are measured and the corresponding interaction diagrams are constructed. The DEM simulations provide useful information about the shape of the failure mechanisms and the force transfer within the soil.     

Fe液中Bi蒸气溶解平衡及第三组元的影响

用密封反应室气液平衡法,测定了Bi蒸气在Fe液中的溶解平衡及第三组元Cr,Cu,C,Al和Si对Bi溶解量的影响,得到Fe液中Bi蒸气溶解反应标准溶解吉布氏自由能与温度的关系式,以及1873K温度下Fe液中第三组元与Bi的活度相互作用系数.     

Ni-Cr-Co基高温合金在含有水蒸汽的空气中的高温腐蚀行为

利用热重分析法、SEM(EDX)和X射线衍射研究了一种Ni-Cr-Co基高温合金在两种不同水蒸汽含量的空气中的高温腐蚀行为.结果表明:合金在750℃含有10%H₂O的空气中的腐蚀动力学规律为先遵从抛物线后遵从直线规律,试样表面形成Cr₂O₃层,并且有内氧化物生成.合金在775℃含有5%H₂O的空气中腐蚀时,试样表面致密的氧化层由Cr₂O₃,TiO₂和CoCr₂O₄组成,同时也发生了内氧化现象.水蒸汽加速了合金的腐蚀速度.整个腐蚀过程由元素通过氧化膜的传输控制.     

Estimating Air Vapor Pressure in a Semiarid Region Using FAO-56 Methodology

This paper presents three models for the estimation of vapor pressure from temperature and humidity data as suggested by Food and Agriculture Organization (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) that have been compared for their performance using daily data from 2002 through 2007 for a semiarid climatic region of Udaipur in Rajasthan, India. Vapor pressure data obtained from dew-point temperature has been used as actual vapor pressure. Model?1 performed better than the remaining two models. Lower values of vapor pressure are better modeled by the three models than higher values. The average absolute error of Model?1 varied from 5.09 to 15.59%, of Model?2 from 5.59 to 19.73%, and that of Model?3 from 5.62 to 37.21%. Estimates of vapor pressure obtained from the three models were also used to estimate open-water evaporation determined by the modified Penman method; the results were compared. Errors in vapor pressure data did not significantly affect estimates of evaporation, indicating that other factors such as energy budget played a much more significant role than mass transfer influence for this arid basin. Errors in evaporation estimation were <4% for Model?1, <9% for Model?2, and <14% for Model?3. Even for Models?2 and 3 they were <6% for most months. In general, Model?1 was found to be the best model of vapor pressure estimation and also caused the fewest errors in estimation of evaporation.     

大气环境质量与旅游的交互影响效应分析

从大气环境质量标准入题,阐释了大气质量对旅游者、旅游资源和旅游交通的影响,同时分析了旅游交通的发展及各种能源的使用,部分旅游活动的开展和旅游产品的开发对大气质量产生的影响.提出应该利用科技手段、行政手段、经济手段、法律手段和宣传教育手段保护大气环境,使旅游与大气环境能可持续发展.     

提高制氧机氧气提取率的研究与应用

主要通过优化工艺操作控制,依靠数学模型修正工艺控制,科学匹配工艺运行参数,通过购置在线氮中氧分析仪,对工艺控制效果进行跟踪,分析和验证工艺运行参数匹配实效,最终实现制氧机在一定的单位空气量下产氧量最大的目标。