Search

Thermally-enhanced soil vapor extraction (T-SVE) combined with sand mixing is an alternative technology for remediating low-permeable soil polluted by organic contaminants. In this study, a T-SVE apparatus with a large heating cylinder was constructed for exploring removal mechanisms of typical petroleum hydrocarbons of n-C11 and C13−16 alkanes, and dynamics of heat propagation within soils during T-SVE operation was simulated by CMG-STARS software. After 6 days of T-SVE, most of the soil concentration-gradient curves of n-alkanes almost coincided with their isothermal contours, suggesting the crucial role of heat conductivity on T-SVE remediation efficiency. The instantaneous concentration of n-alkanes in extracted gas showed great fluctuations, and higher than 90% of spiked n-alkanes was removed from soils. n-alkanes were more easily eliminated from soil with lower organic matter due to the less retention ratio despite the trivial impact of organic matter on heat transfer. By contrast, the higher soil moisture adopted in the study retarded heat transfer in the initial 2 days due to thermal consumption induced by water evaporation. During the last 4 days, however, the average temperature of more humid soil was obviously elevated, especially in the zones receiving less energy input. It was attributed to the fact that soil temperature was mainly determined by heat conduction, and soil pores still occupied by water were more beneficial for heat conduction, leading to the promoted evaporation of n-alkane and therefore eventual remediation efficiency. Suitable original soil moisture is important for T-SVE remediating low-permeable soil combined with sand mixing.Highlights: A T-SVE apparatus with a large heating cylinder was constructed. Thermal conductivity was a crucial factor influencing remediation efficiency. Volatilization of n-alkanes from heated soils showed an irregular pulsed mode. Soil organic matter exhibited a trivial impact on heat transfer behavior in soils. Higher soil moisture firstly retarded and then accelerated the removal of n-alkanes. [ABSTRACT FROM AUTHOR]

The Three Gorges Reservoir (TGR) is totally manmade, strongly influenced by anthropogenic activity, and lies on the upper reaches of Yangtze River. The periodic storage and discharge of water from the Three Gorges Dam could have altered the original air-plant/soil interactions of contaminants in TGR. Herein, paired atmospheric gas–particle, air–plant, and air–soil samples were collected to investigate the air–plant interaction and air–soil exchange of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). The air–plant interaction based on McLachlan's framework to our datasets suggests that PAHs were absorbed via gaseous deposition that was restricted by the plant–gas dynamic equilibrium. The equilibrium indicates a dynamic balance between the gaseous phase and plant surface in PAH absorption. The main limiting factor influencing the PAH uptake was the plant species rather than the atmospheric PAH concentration. The air–soil exchange of PAHs exhibited a net volatilization flux of 16.71 ng/m2/d from the soil to the air based on annual average. There was more volatilization and less deposition in summer and more deposition and less volatilization in autumn and winter. The soil serves as a secondary source of atmospheric PAHs. As the first attempt on probing the multi-interface geochemical process of PAHs, this study highlights the influence of manual water level manipulation from the TGD and environmental factors (such as temperature, humidity, and soil properties) on the regional fate of PAHs in the TGR. [Display omitted] • The PAHs were absorbed via gaseous deposition from the atmosphere. • The main limiting factor influencing the PAH uptake was the plant species. • The soil serves as a secondary source of atmospheric PAHs. • The air–soil exchange exhibited net volatilization from the soil to air. [ABSTRACT FROM AUTHOR]

Fertilizer N losses from agricultural systems have economic and environmental implications. Soil amendment with high C materials, such as coal char, may mitigate N losses. Char, a coal combustion residue, obtained from a sugar factory in Scottsbluff, NE, contained 29% C by weight. A 30‐d laboratory study was conducted to evaluate the effects of char addition on N losses via nitrous oxide (N2O) emission, ammonia (NH3) volatilization, and nitrate (NO3–N) leaching from fertilized loam and sandy loam soils. Char was applied at five different rates (0, 6.7, 10.1, 13.4, and 26.8 Mg C ha−1; char measured in C equivalent) to soils fertilized with urea ammonium nitrate (UAN) at 200 kg N ha−1. In addition, there were two negative‐UAN control treatments: no char (no UAN) and char at 26.8 Mg C ha−1 (no UAN). Treatment applied at 6.7 and 10.1 Mg C ha−1 in fertilized sandy loam reduced NH3 volatilization by 26–37% and at 6.7, 10.1, and 13.4 Mg C ha−1 in fertilized loam soils by 24% compared with no char application. Nitrous oxide emissions and NO3–N leaching losses were greater in fertilized compared with unfertilized soil, but there was no effect of char amendment on these losses. Because NO3–N leaching loss was greater in sandy loam than in loam, soil residual N was twofold higher in loam than in sandy loam. This study suggests that adding coal char at optimal rates may reduce agricultural reactive N to the atmosphere by decreasing NH3 volatilization from fertilized soils. [ABSTRACT FROM AUTHOR]

Abstract Permeability of gases in porous media is a vital parameter for the design of landfill liners and buffers for nuclear waste repositories, gas extraction from petroleum reservoirs and hydrate bearing sediments, vapor extraction to decontaminate soils, carbon dioxide sequestration, etc. It is well understood that the gas-phase permeability in porous media is predominantly governed by the porosity, pore-characteristics (viz., diameter and distribution), properties of the gas (viz., density, molecular size and weight, sorption capacity, and viscosity) and their state of saturation (S r). However, the nature of the flow of gas (viz., molecular, viscous and Knudsen), is influenced by the mean free-path, its compressibility and mean diameter of the pores. All these factors and complexities pose a challenge in determining the intrinsic permeability, K , which otherwise is assumed to be a (i) constant and (ii) fingerprint of porous media. In this context, and to facilitate easier determination of the gas-phase permeability, K g , of porous media, a test setup: Gas Conductivity Measuring device, GasCoM , has been developed. Efforts have also been made to understand the influence of the characteristics of the gas (viz., active, inert, non-polar, monoatomic, diatomic and mixture of several gases) on K g of different porous media (viz., soils of entirely different physico-chemical-mineralogical characteristics compacted at different densities and saturation, and commercially available alumina discs, referred to as standard porous media, SPM). A critical synthesis of the experimental data reveals that the flow of gas in porous media gets significantly influenced by (a) the hygroscopic moisture content, which also highlights the importance of its mineralogy and (b) its tortuosity. Furthermore, a correlation that can be employed for estimation of the K g , for various gas-porous media systems, GPMSs, has been proposed and validated by using experimentally obtained results. Highlights • A novel experimental methodology for determination of gas permeability in porous media. • Establishment of the influence of gas and porous media characteristics on the gas permeability. • Determination of the role of mineralogy and tortuosity of the porous media on the gas flow. • Development of an empirical relationship for estimating gas permeability of the porous media. [ABSTRACT FROM AUTHOR]

A series of column experiments were conducted to study volatile contaminant (benzene) removal and process principles using soil vapor extraction (SVE) under different thermal conditions. Compared with the normal SVE method, two thermal methods-steam injection and electrical resistance heating effectively increased the benzene vapor diffusion and removal rates. The removal efficiency of benzene with the electrical resistance heating method was 96.5%, which was significantly higher than that with the steam injection method (90.5%, p=0.002) or with the normal SVE method (85.2%, p=0.001). In addition, SVE with electrical resistance heating showed a more stable heating effect than SVE with steam injection in homogeneous sandy soil. Based on existing equilibrium SVE models, we established a one-dimensional non-equilibrium mass transfer model for estimating volatile contaminant removal under thermal enhancement. The improved model can accurately reflect benzene content variations using SVE with electrical resistance heating and provides a theoretical basis for preliminary site remediation assessments using SVE under continuous thermal treatment. [ABSTRACT FROM AUTHOR]

Regions with long-term animal manure applications based on nitrogen (N) requirements have concerns regarding elevated nutrient levels. Most attention has focused on phosphorus (P), but heavy metal accumulation has received attention due to perceived environmental concerns. Composting is a potential management practice that can reduce total manure mass and volume while creating a stabilized product that has less odor and fewer pathogens. However, composting animal manures can lead to high N loss via ammonia volatilization and increased concentrations of nonvolatile nutrients. The objective of this study was to measure copper (Cu) and zinc (Zn) concentrations in runoff water from plots fertilized with composted and fresh poultry litter. Seven treatments were evaluated in the first year: (i) unfertilized control, (ii) fresh poultry litter, (iii) normal compost (no amendment), (iv) composted litter with alum, (v) composted litter with phosphoric acid, (vi) composted litter with a microbial mixture, and (vii) composted litter with alum + microbial mixture. Six of these treatments were evaluated in Year 2 (alum + microbial mixture was not evaluated in Year 2). Rainfall simulators were used to produce a 5 cm h-1 storm event sufficient in length to cause 30 min of continuous runoff. Concentrations of Cu and Zn were elevated in compost compared with fresh poultry litter. However, metal concentrations in compost did not correlate well with metal concentrations in runoff water and may have been affected by compost maturity and amendment. Total Cu and Zn concentrations in runoff water did not differ between alum-amended compost and fresh poultry litter in each year. [ABSTRACT FROM AUTHOR]

The article looks at a study which is conducted to investigate vapor extraction (VAPEX) process to recover bitumen from vuggy porous media with n-pentane as hydrocarbon solvent. Topics discussed include fabrication of sintered glass-bead model with different vuggy-to total-pore-volume, increase in the vug porosity of the porous space significantly increased the live and dead oil production and flow communication of matrix were found to enhance live oil drainage towards the production well.

Abstract: In vapor intrusion screening models, a most widely employed assumption in simulating the entry of contaminant into a building is that of a crack in the building foundation slab. Some modelers employed a perimeter crack hypothesis while others chose not to identify the crack type. However, few studies have systematically investigated the influence on vapor intrusion predictions of slab crack features, such as the shape and distribution of slab cracks and related to this overall building foundation footprint size. In this paper, predictions from a three-dimensional model of vapor intrusion are used to compare the contaminant mass flow rates into buildings with different foundation slab crack features. The simulations show that the contaminant mass flow rate into the building does not change much for different assumed slab crack shapes and locations, and the foundation footprint size does not play a significant role in determining contaminant mass flow rate through a unit area of crack. Moreover, the simulation helped reveal the distribution of subslab contaminant soil vapor concentration beneath the foundation, and the results suggest that in most cases involving no biodegradation, the variation in subslab concentration should not exceed an order of magnitude, and is often significantly less than this. [Copyright &y& Elsevier]

The article presents a study to determine the effect of application and soil factors of fumigants in soil under commercial application that incorporate good agricultural practices (GAPs) in the U.S. Objectives of the study include quantifying vapor and non-vapor soil concentrations of methyl isothiocyanate (MITC), chloropicrin (CP) and dimethyl disulfide (DMDS) under commercial application scenarios which represents raised bed, plastic mulched vegetable production systems. Results of the study demonstrate an improved soil retention of agricultural fumigants.

The most common approach for remediation of unsaturated soils contaminated with volatile organic compounds (VOCs) is soil vapor extraction. Contamination in low-permeability fine-grained soils poses a significant technical challenge to in situ remediation efforts. The main objective of this paper is to evaluate prefabricated vertical drains (PVDs) as a method of increasing the effectiveness of the soil vapor extraction (SVE) process. The equivalent diameter for PVDs used for SVE applications was determined, and the radius of influence for PVDs were determined so as to measure the gas permeability for fine grained soil under differing conditions including densities, water content, and flow rates. This paper presents the discussions with regarding on the experiments using PVDs for contaminant recovery in the pilot-scale testing. The toluene tracer solution which is one of the oil contaminant BTEX (benzene, toluene, ethylbenzene, xylene) was used to evaluate contaminant remediation efficiency. The concentration of toluene from the extracted samples was measured in a sampling port with the elapsed time and flow rates after operating a PVDs system. [ABSTRACT FROM AUTHOR]

The article presents the results of a study which examined the effects of extraction pH, aging time, phosphate (P) source and P dose on phosphate-based (Pb) bioaccessibility in 10 contaminated soils from the U.S. Department of Defense (DoD) facilities. In this study, an in vitro extraction protocol that has been widely used to estimate changes in Pb bioaccessibility induced by soil amendments was used as a surrogate for oral bioavailability. Findings indicate that measurements differed significantly over 365 days and overall, soluble triple-super-phosphate was arguably the most effective amendment in time, dosage, and extraction pH.

Abstract: The paper describes an experimental set-up designed to measure the volatilization of different pesticides after application under full-scale field conditions. The pesticides were sprayed around the circumference of a circle and measurements of meteorology and air concentrations of pesticides were taken in the centre of the circle. The paper describes how the dimensions like the radius of the circle and height of the mast in the experimental set-up are found from theoretical considerations. A method to increase the confidence of the flux calculations is described. It utilizes that several substances were applied simultaneously and that a certain parameter in the fitted concentration profiles depends on turbulence only and thus have the same value for all substances. The design was used during two campaigns, conducted on the same location, one during fall on bare soil and one in spring on a barley crop. [Copyright &y& Elsevier]

A new heavy-oil-recovery process, the steam alternating solvent (SAS) process, is proposed and studied using numerical simulation. The process is intended to combine the advantages of the steam-assisted gravity drainage (SAGD) and vapor-extraction (vapex) processes to minimize the energy input per unit oil recovered. The SAS process involves injecting steam and solvent alternately, and the basic well configurations are the same as those in the SAGD process. Field-scale simulations were conducted to assess the SAS process performance under typical Cold Lake, Alberta, reservoir conditions. These results suggested that the oil-production rate of an SAS process could be higher than that of a SAGD process, while the energy input was 18% less than that of a SAGD process. By varying the length of the steam- and solvent-injection periods in a cycle, a different set of steam/oil and solvent/oil ratios may be obtained because the temperature profiles and solvent-concentration distributions in the vapor chamber can be affected by the injection pattern. The process therefore can be\optimized for a specific reservoir under certain economic conditions. [ABSTRACT FROM AUTHOR]

Investigates the effect of moisture content, temperature and organic amendments on volatilization and degradation of soil-applied dimethylselenide (DMSe). Transport of DMSe in packed soil columns; Relationship between DMSe injection depth and emissions from packed soil columns; Comparison of various soil moisture levels on DMSe.

There is an important need to develop instrumentation that allows better understanding of atmospheric emission of toxic volatile compounds associated with soil management. For this purpose, chemical movement and distribution in the soil profile should be simultaneously monitored with its volatilization. A two‐dimensional rectangular soil column was constructed and a dynamic sequential volatilization flux chamber was attached to the top of the column. The flux chamber was connected through a manifold valve to a gas chromatograph (GC) for real‐time concentration measurement. Gas distribution in the soil profile was sampled with gas‐tight syringes at selected times and analyzed with a GC. A pressure transducer was connected to a scanivalve to automatically measure the pressure distribution in the gas phase of the soil profile. The system application was demonstrated by packing the column with a sandy loam in a symmetrical bed–furrow system. A 5‐h furrow irrigation was started 24 h after the injection of a soil fumigant, propargyl bromide (3‐bromo‐1‐propyne; 3BP). The experience showed the importance of measuring lateral volatilization variability, pressure distribution in the gas phase, chemical distribution between the different phases (liquid, gas, and sorbed), and the effect of irrigation on the volatilization. Gas movement, volatilization, water infiltration, and distribution of degradation product (Br−) were symmetric around the bed within 10%. The system saves labor cost and time. This versatile system can be modified and used to compare management practices, estimate concentration–time indexes for pest control, study chemical movement, degradation, and emissions, and test mathematical models. [ABSTRACT FROM AUTHOR]

Livestock manure has been widely used in agriculture to improve soil productivity and quality. However, intensive application can significantly enhance soil nitrogen (N) availability and facilitate ammonia (NH 3) volatilization during rice cultivation. The effects of different rates of manure application on the NH 3 volatilization rate, its mechanism, and their relationships have not been comprehensively investigated. In this study, field trials were conducted to investigate NH 3 volatilization in rice paddy soils amended with different livestock manure, cattle manure (CM), and swine manure (SM), at a rate of 0 (NPK), 10, 20, and 40 Mg ha−1 during cultivation. Moreover, the soil physicochemical and biological properties and rice N uptake were investigated. Ultra-fine particulate matter (PM 2.5) was measured quantitatively and qualitatively. Manure application significantly increased NH 3 emissions compared to the control. Much higher volatilization rates were observed in the SM soils than in the CM soils, even when the same amount of N was applied. This is mainly related to the higher labile NH 4 + concentration and urease activity in SM soils. With increasing application levels, NH 3 emission rates proportionally increased in the SM, but there was no significant difference in the CM. Livestock manure application significantly increased NH 3 volatilization, particularly during the initial manure application and additional fertilization stages during rice cultivation. The results showed that the application of livestock manure significantly increased NH 3 volatilization. Moreover, the biochemical properties of manure composts, including labile N and urease activity, mainly affected NH 3 dynamics in rice paddies during cultivation rather than their type. Irrespective of manure application, PM 2.5 , did not show a significant difference at the initial stage of cultivation. NH 3 volatilization was not significantly correlated with the formation of PM 2.5. It is necessary to develop effective strategies for mitigating NH 3 volatilization and maintaining soil quality without decreasing rice productivity in paddy ecosystems. [Display omitted] • Swine manure caused higher NH 3 volatilization than cattle manure even at the same N amount. • Labile NH 4 + and urease activity mainly affect NH 3 volatilization in rice paddies during cultivation. • PM 2.5 did not show any significant difference in different manure amended fields. • NH 3 volatilizations were not significantly correlated with quantitative formation of PM 2.5. Manure compost applications significantly increased NH 3 volatilization. Much higher NH 3 volatilizations were observed in the SM applied soils than in the CM, even though the same amount of N was applied into the field. [ABSTRACT FROM AUTHOR]

The agricultural ecological system is an important part of the Yellow River Delta (YRD); however, soil reclamation may trigger environmental concerns about nitrate leaching and NH 3 volatilization in this area. To assess nitrogen losses during soil reclamation, a two-year field experiment was conducted with plastic film mulch, which is an effective way to alleviate water-salt stress. The Hydrus-2D software package was used to calculate nitrogen transport, transformation and losses. The results showed that nitrogen (N) retention in the soil varied during the two growing seasons, because soil water, salinity and climatic conditions acted together on nitrogen transport and transformation. Soil salinity promoted NH 3 volatilization, and the proportions of ammonia volatilization were 22.78 percent and 19.50 percent of the N input in 2018 and 2019, respectively, because urea hydrolysis, nitrification and soil N H 4 + - N adsorption capacity were limited by soil salt. N O 3 − - N leaching was controlled by soil water infiltration, climatic conditions and groundwater level. N O 3 − - N leaching was 43.84 percent and 32.89 percent of the nitrogen input in 2018 and 2019, respectively; the difference was mainly caused by the different distribution of rainfall during the growing season; thus, soil water infiltration increased under heavy rainfall because it broke the barrier formed by the plough pan. This study indicates that there is a risk of nitrogen pollution during soil reclamation. In addition, Hydrus-2D has considerable potential to calculate nitrogen losses under the effect of plastic film mulch in this area. [Display omitted] • Hydrus-2D was successfully used in the Yellow River Delta. • Soil salinity contributed to ammonia volatilization. • Heavy rainfall caused a high risk of NO 3 −-N leaching. • Nitrogen losses from farmland contributed to N pollution in this area. Hydrus-2D successfully calculated the risk of nitrogen pollution under the effect of plastic film mulch systems in the Yellow River Delta, China. [ABSTRACT FROM AUTHOR]

Studies focusing on arsenic methylation and volatilization in paddy soil, aiming to limit bioaccumulation of arsenic (As) in rice grains, have attracted global attention. In this study, we explored three aspects of these topics. First, rainwater and trace H 2 O 2 were compared for their influence on the arsenic methylation and volatilization of paddy soil in different rice growth stages. Second, the arsenic accumulation in different parts of rice was affected by rainwater and trace H 2 O 2. Third, we determined whether rice fields were affected by rainwater and trace H 2 O 2. The result showed that the rainwater or trace H 2 O 2 irrigation caused As(III) to significantly decrease and As(V) to significantly increase in soil. A similar consequence occurred in the filling stage and mature stage of rice. The arsenic volatilization rates of the rainwater and trace H 2 O 2 irrigation were significantly higher than the control, and the arsenic volatilization of rainwater irrigation was the highest (51.0 μg m−2 d−1) in the filling stage. Compared to the control, the total arsenic and iAs of treatments decreased by 14–41% and 12–32% respectively. Finally, we found that rainwater and trace H 2 O 2 irrigation likely increased rice fields. • Rainwater and trace H 2 O 2 can decrease As(III) and increase As(V) in soil. • Rainwater and trace H 2 O 2 increased As volatilization in rice filling stage. • The iAs accumulation in rice grains was decreased by rainwater and trace H 2 O 2. • Rainwater and trace H 2 O 2 irrigation probably increased rice fields. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) volatilized from soils plays an important role in N cycle and air pollution, thus it is important to trace the emission source and predict source contributions to development strategies mitigating the environmental harmful of soil NH 3 volatilization. The measurements of 15N natural abundance (δ15N) could be used as a complementary tool for apportioning emissions sources to resolve the contribution of multiple NH 3 emission sources to air NH 3 pollution. However, information of the changes of δ15N–NH 3 values during the whole volatilization process under different N application rates are currently lacking. Hence, to fill this gap, we conducted a 15-day incubation experiment included different urea-N application rates to determine δ15N values of NH 3 during volatilization process. Results showed that volatilization process depleted 15N in NH 3. The average δ15N value of NH 3 volatilized from the 0, 20, 180, and 360 kg N ha−1 treatment was −16.2 ± 7.3‰, −26.0 ± 5.4‰, −34.8 ± 4.8‰, and −40.6 ± 5.7‰. Overall, δ15N–NH 3 values ranged from −46.0‰ to −4.7‰ during the whole volatilization process, with lower in higher urea-N application treatments than those in control. δ15N–NH 3 values during the NH 3 volatilization process were much lower than those of the primary sources, soil (−3.4 ± 0.1‰) and urea (−3.6 ± 0.1‰). Therefore, large isotopic fractionation may occur during soil volatilization process. Moreover, negative relationships between soil NH 4 +-N and NH 3 volatilization rate and δ15N–NH 3 values were observed in this study. Our results could be used as evidences of NH 3 source apportionments and N cycle. Image 1 • δ15N–NH 3 values of different N application rates were identified during the whole volatilization process. • The δ15N–NH 3 values decreased firstly and then increased during the incubation period. • Higher N application rates along with lower δ15N-NH 3 values. • Soil pH and NH 4 +-N concentration influenced the variations of δ15N-NH 3. [ABSTRACT FROM AUTHOR]

With the aim to improve the pollution removal efficiency, a layered extraction simulation device for the removal of benzene-contaminated soil via soil vapor extraction was constructed. The removal of benzene from soils by both layered extraction and unlayered extraction was explored based on the factors of extraction flow, extraction time, initial contaminant content, initial soil moisture content, and extraction method. Under the same conditions, layered extraction improved the repair efficiency, shortened the repair time, and decreased the cost of repair. Different factors exerted different influences on the extraction effect, but overall, compared with unlayered extraction, the removal rate of layered extraction can be increased by 2–20%. In particular, when the content of benzene was high, layered and intermittent extraction could remove more than 90% of benzene from the soil. When layered extraction was adopted, the pressure loss in the lower part of the soil layer was small and the air flow into the soil was large, which can promote the volatilization of benzene and thus improve its removal rate. Image 1 • The SVE layered extraction device was innovatively constructed to carry out layered remediation of contaminated soil. • The difference of benzene removal in soil by layered and unlayered extraction under different parameters was investigated. • The distribution of internal pressure of the layered and unlayered extraction tube was analyzed by numerical simulation. [ABSTRACT FROM AUTHOR]