Vapor Extraction Research Articles

The Mechanism for Remediation of Low-Permeable Soil Contaminated with Petroleum Hydrocarbons by Thermally-Enhanced Soil Vapor Extraction Combined with Sand Mixing

The Mechanism for Remediation of Low-Permeable Soil Contaminated with Petroleum Hydrocarbons by Thermally-Enhanced Soil Vapor Extraction Combined with Sand Mixing

Vapor-phase transport of per and polyfluoroalkyl substances: Processes, modeling, and implications

An increasing number of studies have demonstrated the presence of per and polyfluoroalkyl substances (PFAS) in the vapor phase. It is therefore important to consider the potential for vapor-phase transport of PFAS in soil and the vadose zone and to investigate the processes impacting the retention and transport of volatile PFAS in soil. It is also critically important to evaluate existing models and develop new models as needed for their application to PFAS vapor-phase transport. The objectives of the present work were to provide an overview of vapor-phase transport processes and modeling, with a specific focus on their relevance for PFAS, and to discuss implications for mass discharge to groundwater, vapor intrusion, and soil vapor extraction. Decades of research have been devoted to the retention and transport of legacy volatile organic contaminants in the vadose zone. This work provides an abundant source of information concerning the many factors and processes of relevance, and insights into the development and application of mathematical modeling. However, given the unique properties of PFAS, there is a need to conduct research to investigate vapor-phase transport of PFAS and to develop PFAS-specific models. We highlight with illustrative examples that vapor-phase transport can be significantly more rapid than aqueous-phase advective transport, which can result in enhanced mass discharge to groundwater.

The impact of years of training and possible technical, procedural, and individual risk factors for the development of atopic symptoms among bakery and confectionery trainees.

Occupational asthma is commonly observed in bakers and confectioners. Endogenous and exogenous risk factors contribute to bakers' asthma. A heightened awareness of this and early diagnosis can be helpful in terms of prevention. The aim of the study was to identify a temporal relationship between the years of training, as well as possible technical, procedural, and individual risk factors for the development of flour-exposure related atopic symptoms such as rhinitis, cough, and rash in young professionals. 127 bakers and confectioner trainees were observed over a one-year period. Two questionnaires served as test instruments. It was investigated whether the rates of atopic symptoms change over the course of a school year and which conditions in the workplace could be responsible for this. Descriptive statistics were used to answer the research questions concerning flour exposure and symptom rates. The Pearson-Chi-Square test was used for testing statistical differences between different groups (e.g. year of training, working conditions). An increase in rates of self-reported rhinitis, coughing, and rashes throughout the duration of traineeship was shown (e.g. rhinitis of bakers at work: 0% in the first year of training, 20% in the second and 33% in the third year of training). The installation of vapour extraction systems and low-dust transfer of baking agents led to fewer symptoms in the workplace (30% of participants with rhinitis symptoms worked with no installed vapour extraction systems). A medical history of atopy was positively correlated with the occurrence of symptoms. To prevent the development of asthma in bakers, methods to improve occupational health and safety should be developed. Creating low dust working conditions e.g., due to the use of vapour extraction systems should be considered.

Sustainable lindane waste remediation: Surfactant-driven residual DNAPL extraction and oxidation in a real landfill (LIFE SURFING)

The LIFE SURFING Project was carried out at the Bailin Landfill in Sabiñánigo, Spain (2020-2022), applying Surfactant Enhanced Aquifer Remediation (SEAR) and In Situ Chemical Oxidation (S-ISCO) in a 60-meter test cell beneath the old landfill, to remediate a contaminated aquifer with dense non-aqueous phase liquid (DNAPL) from nearby lindane production. The project overcame traditional extraction limitations, successfully preventing groundwater pollution from reaching the river.In spring 2022, two SEAR interventions involved the injection of 9.3 m3 (SEAR-1) and 6 m3 (SEAR-2) of aqueous solutions containing 20 g/L of the non-ionic surfactant E-Mulse 3®, with bromide (around 150 mg/L) serving as a conservative tracer. 7.1 and 6.0 m3 were extracted in SEAR-1 and SEAR-2, respectively, recovered 60–70 % of the injected bromide and 30–40 % of the surfactant, confirming surfactant adsorption by the soil. Approximately 130 kg of DNAPL were removed, with over 90 % mobilized and 10 % solubilized. A surfactant-to-DNAPL recovery mass ratio of 2.6 was obtained, a successful value for a fractured aquifer. In September 2022, the S-ISCO phase entailed injecting 22 m3 of a solution containing persulfate (40 g/L), E-Mulse 3® (4 g/L), and NaOH (8.75 g/L) in pulses over 48 h, oxidizing around 20 kg of DNAPL and ensuring low toxicity levels after that.Preceding the SEAR and S-ISCO trials, 2020 and 2021 were dedicated to detailed groundwater flow characterizations, including hydrological and tracer studies. These preliminary investigations allowed the design of a barrier zone between 317 and 557 m from the test cell and the river, situated 900 m away. This zone, integrating alkali dosing, aeration, vapor extraction, and oxidant injection, effectively prevented the escape of fluids to the river. Neither surfactants nor contaminants were detected in river waters post-treatment. The absence of residual phase in test cell wells and reduction of chlorinated compound levels in groundwater were noticed till one year after S-ISCO.

Optimizing CO2 sequestration in Vapor Extraction Process: A Meso-Scale analysis of oil Viscosity, Permeability, and mobile oil orientation effects

Carbon dioxide (CO2) use in Vapor Extraction (VAPEX) has attracted attention for its potential to enhance oil recovery by altering oil density and viscosity, leading to convective-mixing flow in the VAPEX boundary layer. This study explores CO2 sequestration via dissolution into this layer, with a focus on the impact of oil viscosity, permeability, and mobile oil orientation. An isothermal lattice Boltzmann model, which accounts for the variable oil properties like viscosity and diffusion coefficient dependent on dissolved CO2 concentration, was developed for the analysis. Results show that reduced oil viscosity leads to accelerated growth of density fingers and an expanded area swept by CO2 dissolution. Similarly, heightened permeability and mobile oil angle contribute to these effects. This research provides novel insights into optimizing CO2 sequestration within the VAPEX process.

Influence of extraction and injection conditions on the performance of thermal-enhanced soil vapor extraction

Thermal-enhanced soil vapor extraction (T-SVE) is an in-situ remedial technique that can address the limitations of contaminant mass transfer and soil permeability. The relative humidity of the injected air, heating temperature of the thermal well, extraction pressure, and extraction mode are important design parameters of a T-SVE system that determine the temporal and spatial distributions of soil temperature and removal rate. Using a thermal–hydraulic–chemical coupled model with the interphase mass transfer of contaminants and water evaporation/condensation, this study investigated the effects of relative humidity, heating temperature, extraction pressure, and extraction mode on T-SVE performance. The results showed that with an increase in relative humidity, the heating temperature of the contaminated soil significantly improved; however, the removal rate of contaminants decreased, particularly in the late stage of remediation. Considering the heating temperature of the thermal well, a critical air relative humidity value that significantly affects the removal rate of contaminants was observed. The heating temperature of the thermal well must be considered in engineering design; however, the evaluation of the relative humidity of the air cannot be ignored.

Predicting removal efficiency of organic pollutants by soil vapor extraction based on an optimized machine learning method

Soil vapor extraction (SVE) was a cost-effective technology for remediating volatile and semi-volatile organic contaminated soils. Many factors, including SVE parameters, soil properties, and contaminant characteristics, significantly influenced the remediation efficiency of SVE. The optimal conditions for organic pollutants removal efficiency were site-specific and varied among studies. Therefore, a generalized model was needed to predict the remediation efficiency of SVE in organic contaminated soils. This study employed machine learning to predict the removal efficiency of organic pollutants by SVE. The model's development was based on a trainset, and its predictive capabilities were evaluated using a testset. An XGBoost (XGB) model was derived from literature data (R2 = 0.9728). Time, pollutant type, and temperature were identified as the three most important features affecting SVE remediation efficiency. The accuracy (R2 = 0.9799) and universality of the model were enhanced through an optimization scheme. The developed XGB model demonstrated the ability to predict the removal efficiency of organic pollutants by considering all collected influential factors. The mechanism of multi-factor interaction on remediation efficiency was clarified. Overall, this study would contribute to evaluating the remediation potential of SVE for specific organic contaminated soils, aiding in maximizing the removal efficiency of organic pollutants under optimal conditions.

Enhancing water productivity and cost-effectiveness in hemispherical solar stills using sandy beds, reflectors, and a vapor extraction fan

The objective of this study was to enhance the performance of hemispherical solar stills (HSS) through experimental investigations utilizing various types of sand beds as thermal storage materials. The research examined the influence of sand type (yellow and black) and sand bed heights (1, 2, and 3 cm) on the efficacy of HSS. Additionally, the study explored the effects of external reflectors and a vapor extraction fan on the performance of sand-based HSS. The experimental results indicated that HSS using black sand demonstrated superior performance compared to other operating conditions in terms of both productivity and efficiency. Particularly, the most significant improvement in performance for the black sand hemispherical solar still (BSHSS) was observed when employing reflectors and a fan with a sand bed height of 1 cm, resulting in a substantial 154% increase in production, where the production for hemispherical SS and BSHSS + fan and reflectors was 4100 and 10400 mL/m2.day, respectively. Under these optimized conditions, the thermal efficiency of BSHSS + R + F reached 56%. In conclusion, an economic analysis was conducted, revealing that the cost for water treatment was $0.022 per liter for the conventional hemispherical solar still (HSS) and $0.012 per liter for the BSHSS equipped with reflectors and a condenser. These findings represent a significant advancement in enhancing the feasibility and efficiency of solar distillation systems, thereby addressing the global challenges of water scarcity and environmental sustainability.

NON-ISOTHERMAL MODELING OF SOIL VAPOR EXTRACTION SYSTEM INCLUDING SOIL TEMPERATURE EFFECT

Soil vapor extraction (SVE) is a proven effective in-situ technology for the removal of volatileorganic compounds (VOCs) from the subsurface. SVE process is highly sensitive to temperature.Studying annual soil temperature variation with depth declares that there is a considerable temperaturevariation in the upper few meters that may affect the overall efficiency of SVE process.A numerical model was developed to aid in investigation of field-scale soil vapor extractionprocess. The model is three-dimensional, time dependent that simulates nonisothermal vapor flow andtransport of multicomponent mixtures in soil and keeps track of the distribution of each compound inthe other three immobile phases (NAPL, aqueous, and sorbed). Rate limited interphase mass transferwith linear driving force expressions were used to model volatilization of oil into gas phase. A localequilibrium partitioning was assumed between gas, water, and solid phase. The model equations werediscretized using a standard Galerkin finite element method and solved using set iterative solutionalgorithm.Simulation of hypothetical field-scale problems was done. The physical domain described a threedimensionalsystem with flow to a single extraction well. A hypothetical soil temperature variationwith depth was incorporated with the model. The result of these simulations showed that thistemperature variation has a considerable effect on system efficiency and may play a role in optimumsystem configuration.

Study of factors affecting the remediation of contaminated soil through pneumatic fracturing and soil vapor extraction

In low-permeability soils, the effectiveness of soil vapor extraction (SVE) is often constrained, resulting in increased time and operational expenses. In this study, pneumatic fracturing and the SVE were combined to remediate low-permeability clay contaminated with ammonia gas. The soil parameters, pneumatic fracturing parameters, extraction mode, and other influencing factors were investigated via laboratory testing. The results indicated that: (1) Pneumatically induced fracturing disrupts soil structure, forming cracks and providing new pathways for ammonium gas migration; (2) the soil crack area exhibits a quadratic function relationship with both the fracturing pressure and frequency, and the soil crack area increases with higher pneumatic frequencies, leading to a faster pneumatic pressure decline; (3) a denser network of pathways emerges within the soil due to the reduced distance between the two pneumatic fracturing points, consequently enhancing soil permeability and increasing pollutant elimination efficiency; (4) the ammonium gas removal efficiency gradually increases with an increase in the extracted vapor flow rate, but there is an optimal extraction flow rate (9 L/min); (5) continuous extraction combined with gas injection effectively ameliorates the issue of prolonged fluctuations in ammonium gas concentration during the later stages of extraction. (6) Fracturing and extraction reduce the moisture content of the surrounding soil. The results demonstrated the feasibility and superiority of pneumatic pre-fracturing extraction in low-permeability soils.

Choice of Remediation Technology for a Contaminated Soil by 1,2-Dichloroethane (DCA)

In Mexico, there are 635 sites contaminated by hazardous waste, due to the fact that a few years ago there was no legislation to support and guarantee environmental protection. This led to decades of contamination of soils and bodies of water. In the following case study, landfills were identified where 1,2-dichloroethane was stored, generating contaminated soil in this location, even affecting subway water bodies. The aim of this work is to identify the technologies for the remediation of contaminated soils, taking into account the affected site, the characteristics of the residue, costs and time, in order to determine the most effective and ideal technology. The Federal Remediation Technologies Roundtable (FRTR) will be considered as the counterpart for the selection of treatment technologies, published by the Remediation Bureau. The best technology for site remediation is "Soil Vapor Extraction", being the most ideal and efficient in terms of time and cost, and generating a high impact remediation outcome. The counterpart (FRTR) is considered to be a support tool that provides the most appropriate technologies for the remediation of a contaminated site.

Correction: Impact of Two-Phase Flow Pattern on Solvent Vapour Extraction

Correction: Impact of Two-Phase Flow Pattern on Solvent Vapour Extraction

Diffusion analysis of three kinds of species with two salts in two working fluids using Darcy's law using solar radiations

This specific research was carried out with the aim of investigating incompressible Casson fluid and Williamson liquid. Steady-state laminar boundary layer flow involving Brownian diffusion and thermophoretic diffusion is taken over a horizontal penetrating plate saturated with two distinct salts having distinct characteristics. Casson fluid motion was observed with the utilization of Darcy-Forchheimer technique. Whilst, Nanofluid motion and other salts motion induced by wall movement. Solar thermal collectors, Solar thermal systems, Solar cookers, Solar thermal energy, drying, generating electricity, chemical reactions, soil vapor extraction, medication and heat exchange medium. Physical quantities like density, temperature profile and concentration profile were addressed by aiding Bossiness approximation. Whereas the optimization of energy is carried out under the effects of cross-diffusion, regular diffusion and non-Fourier law for two different salt components. Formulation of acquired flow equations in terms of partial differential equations are further transformed into ordinary differential equations using similarity transformations. The numerical solution will be obtained by utilization of FE-method. It was found that the temperature field elevates on increasing solar thermal radiation number, modified Dufour numbers of salt 1 and salt 2. Thickness and width regarding momentum layers for Casson liquid rather than Williamson liquid while temperature field for Williamson liquid is higher than Casson liquid.

JEDAN PRIMER UPOTREBE AKTIVNOG GEOKOMPOZITA ZA SANACIJU DEPONIJE

The ''Chalk landfill Bruck I/II'', a former industrial landfill is located in Austria. The landfill was filled from 1926-1981 with calcium carbide, CHC and mercury contaminated wastes. The total amount of HCH is estimated to 100-1000 t. Since 1995 different remedial actions took place as well as continuous securing measures. In 2000 the site was put on the list of contaminated sites that need remediation and got codename K20. Additional tests in 2003 gave the site highest priority level one. In 2009 decision is made to remove all stored material and treat or safely store in state-of-the-art landfill. After observation of Hexachlorobenzene in food in the area around the thermal treatment plant works were stopped. The new course of action was to secure the waste on site. The new physical safeguard measures included an innovative, multifunctional surface sealing system consisting of calcium bentonite geosynthetic clay liner, an activated carbon mat, a LDPE membrane with integrated aluminium sheet and a drainage element. This system creates a strong barrier for volatile CHC. There are soil vapor extraction pipes below and above the sealing system to ensure a monitoring. Minimal interference with existing landfill body was requirement. To enable long term stability of the whole sealing system geogrids are used. The construction work was executed in 2016.

A new approach to improve precipitable water vapour estimations of Sentinel-3A satellite data using LST, elevation and NDVI over Iran

ABSTRACT The total precipitable water vapour (TPW) extraction algorithm using the Sentinel-3A Ocean and Land Colour Instrument (OLCI) has the potential to be improved on a regional scale. The aim of this study was to improve the TPW extraction algorithm of OLCI for the first time using environmental variables, including the Normalized Difference Vegetation Index (NDVI), land surface temperature (LST), and elevation from mean sea level, on a regional scale over Iran. A previously developed TPW recovery algorithm was applied to the OLCI data during cloud-free days throughout a one-year period (1 January–29 December 2020). The artificial neural network (ANN) methodology was utilized in eight models. The evaluation results revealed the effectiveness of the models varied based on the topography and climate of each station. The assessment findings demonstrated that model 2, which integrated LST, elevation, and NDVI data in the ANN framework, outperformed other models across the study area.

Spatially resolved detection of small molecules from press-dried plant tissue using MALDI imaging.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a chemical imaging method that can visualize spatial distributions of particular molecules. Plant tissue imaging has so far mostly used cryosectioning, which can be impractical for the preparation of large-area imaging samples, such as full flower petals. Imaging unsectioned plant tissue presents its own difficulties in extracting metabolites to the surface due to the waxy cuticle. We address this by using established delipidation techniques combined with a solvent vapor extraction prior to applying the matrix with many low-concentration sprays. Using this procedure, we imaged tissue from three different plant species (two flowers and one carnivorous plant leaf). Material factorization analysis of the resulting data reveals a wide range of plant-specific small molecules with varying degrees of localization to specific portions of the tissue samples, while facilitating detection and removal of signal from background sources. This work demonstrates applicability of MALDI-MSI to press-dried plant samples without freezing or cryosectioning, setting the stage for spatially resolved molecule identification. Increased mass resolution and inclusion of tandem mass spectrometry are necessary next steps to allow more specific and reliable compound identification.

Numerical investigations of influence on thermal conductive heating in DNAPL-impacted soils by heterogeneity

The treatment of dense non-aqueous phase liquid (DNAPL) source zones is challenging, particularly in heterogeneous media. Thermal conductive heating (TCH) has the potential to treat DNAPL source zones for its ability to enhance mass transfer. This study uses numerical modeling combined with Monte Carlo simulation to examine the influence of heterogeneity of the permeability field on the DNAPL distribution and TCH remediation. It is found that the longer horizontal correlation length of high-permeable clay lens would contribute to accelerate multiphase convection and then heat conduction in horizontal direction. The presence of DNAPL (both in NAPL phase and dissolved), pressure, and permeability are all contributory factors to phase change. Realizations with shorter horizontal correlation lengths always have a larger vertical spreading of DNAPL. As a shallow vapor extraction well was applied in this study, higher TCE removal rate can be obtained in the realizations with a shorter horizontal correlation length when NAPL phase of TCE is existed in the domain.

Predicting soil concentrations and remediation target values of BTEX by an off-gas based mass transfer model

Soil vapor extraction (SVE) is a widely used technology for the remediation of volatile organic compounds (VOCs) contaminated soils. Residual concentrations of VOCs are crucial for assessing the SVE process and planning when to stop this process, however, the measurement of their residual concentrations in the soil is complicated. Herein, a pseudo-first-order sequential reaction model was established to predict the mass transfer of the BTEX (benzene, toluene, ethylbenzene, xylene) between the soil and off-gas during the SVE process. Based on this mass transfer model, the residual concentrations of BTEX in the soil during the trailing stage could be accurately estimated (R2 > 0.89) by their off-gas concentrations that were directly monitored in real time. Considering the removal efficiency and operating costs, a concept of the remediation target values (RTV) was proposed for the SVE technology, and its relevant model (R2 > 0.92, NRMSE = 6.4–16.8 %) was established based on the experimental data. The remediation endpoint can be further estimated based on the RTV with an overall accuracy of 84–100 %. These findings provide a simple and fast way to predict VOC concentrations in soil with easy-to-know factors and online monitoring of off-gas concentrations and will guide and optimize the SVE process toward more economical and efficient techniques for soil remediation.

Modeling BTEX Multiphase Partitioning with Soil Vapor Extraction under Groundwater Table Fluctuation Using the TMVOC Model

The effects of groundwater table fluctuation (GTF) on the remediation of a petrochemically polluted riverside using soil vapor extraction (SVE) were investigated. The migration and transformation of benzene, toluene, ethylbenzene, and o-xylene (BTEX) in cases of natural attenuation, SVE without GTF, and SVE with GTF were simulated using the TMVOC model. The results showed that the optimized extraction well pressure and influencing radius of the target site were 0.90 atm and 8 m, respectively. The removal rates of BTEX in cases of natural attenuation, SVE without GTF, and SVE with GTF were 11.49%, 85.16%, and 97.33%, respectively. The removal rate of BTEX was maximized in the case of SVE with a GTF amplitude of 0.5 m to 1 m. The removal rates of benzene (99.99%), toluene (99.74%), ethylbenzene (96.37%), and o-xylene (94.72%) were maximized in the case of SVE with GTF. For the cases of SVE without GTF and SVE with GTF, mass losses of BTEX in gaseous (0.05 kg, 0.05 kg, respectively) and aqueous phases (5.46 kg, 5.87 kg, respectively) were consistent. However, the mass loss of BTEX in the non-aqueous phase liquid (NAPL) phase in the case of SVE with GTF (155.13 kg) exceeded that in the case of SVE without GTF (135.41 kg). This is because GTF positively affected both the solubility and volatility of BTEX in the NAPL phase. With the groundwater table decreasing, flows of gas and gaseous pollutants increased by 25% along the vertical section. At this stage, the removal rates of volatile organic compounds can be further improved by increasing the flow of the extraction well.

A numerical simulation of thermally-enhanced soil vapor extraction with a validation of an actual contaminated site

Thermally-enhanced soil vapor extraction (T-SVE) remediation technology is widely used in organic-contaminated sites due to its high efficiency, short remediation period and controllable secondary contamination. However, the remediation efficiency is affected by the complex site factors, which leads to the uncertainty of the remediation process and energy waste. Thus, it is necessary to optimize T-SVE systems to accurately remediate the sites. In this work, a pilot site of reagent factory in Tianjin was taken as the research object to validate the model, and the T-SVE process parameters of a VOCs-contaminated sites were predicted by this simulation method. The simulation results showed that the Nash efficiency coefficient E of the measured and simulated temperature rise data in the study area was 0.885, and the linear correlation coefficient R of the measured and simulated concentrations of cis-1,2-dichloroethylene after remediation was 0.877, indicating that this simulation method is highly reliable. Based on this numerical simulation method, some parameters of the T-SVE process at the VOCs-contaminated site of an insulation plant in Harbin were simulated and optimized. Included a heating well spacing of 3.0 m, extraction pressure of 40 Kpa, extraction well influence radius of 4.35 m, extraction flow rate of 2.97 × 10-4 m3/s, and a theoretical number of 25 extraction wells (adjusted to 29 wells in practice), and the corresponding extraction well layout has been designed. The results can provide a technical reference for the future application of T-SVE in the remediation of organic-contaminated sites.