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... The potential of dry solid potassium permanganate granules for oxidizing various VOCs has been reported in the literature (Mahmoodlu et al., 2013(Mahmoodlu et al., , 2014b. The oxidation of TCE, toluene, and ethanol is described by the following overall reaction equations: C 2 HCl 3ðgÞ þ 2KMnO 4ðsÞ /2K þ þ 2MnO 2ðsÞ þ 3Cl À þ 2CO 2ðgÞ þ H þ (1) C 6 H 5 CH 3ðgÞ þ 12KMnO 4ðsÞ þ 2H 2 O/12K þ þ 12OH À þ 12MnO 2ðsÞ þ 7CO 2ðgÞ (2) C 2 H 5 OH ðgÞ þ 4KMnO 4ðsÞ /4K þ þ 4OH À þ 4MnO 2ðsÞ þ 2CO 2ðgÞ ...
... Our recent study of VOC vapor diffusion through a partiallysaturated permeable reactive barrier showed that water saturation has a considerable effect on the removal capacity of a HPRB (Mahmoodlu et al., 2014b). The study also found that changes in pH values generated during the VOC oxidations according to their stoichiometric reactions (Eqs. ...
... This is reflected by a very slow rise of VOC concentrations in the headspace of the reactive columns (Fig. 2). The experimental results also show that the HPRB in the sand column was far more effective than that in our earlier setup (Mahmoodlu et al., 2014b) which involved the diffusion of VOC vapors only through a HPRB. This is due to the fact that VOC concentrations in the gas phase reaching the HPRB are now much lower as compared to those in our earlier studies. ...
... An alternative VI mitigation system involves the use of solid potassium permanganate to create a horizontal permeable reactive barrier (HPRB) aimed at oxidizing upward VOCs. In a series of batch and labscale column tests, Mahmoodlu et al. (2014aMahmoodlu et al. ( , b, 2015 have demonstrated the potential of HPRB in oxidizing TCE, toluene, and ethanol vapors migrating upward from a contaminated saturated zone. To scale-up these results and to evaluate the feasibility of this alternative mitigation system in real-scale applications, this study introduces a 1-D analytical solution that describes the attenuation of vapors through the reactive barrier. ...
... Namely, the higher values of L R in Table 1 correspond to the lower bound values of the k″ literature values, while the lower L R to the higher k″ values reported in the table. For the estimation of L R values, the concentration of the oxidant in the barrier was assumed equal to the solubility of potassium permanganate at 20°C, i.e. 64 g/l (Mahmoodlu et al., 2014a). Furthermore, a relative water saturation, S w (S w = θ w,HPRB / θ e,HPRB ), of 0.2 and a diffusion coefficient, D HPRB , equal to the diffusion coefficient in air were assumed. ...
... At lower pH values, Mahmoodlu et al. (2015) observed a reduction in HPRB reactivity in their lab-scale tests. The effects of pH on the oxidation rate constant can be described with the following equation (Mahmoodlu et al., 2014a): ...
Article
In this work we introduce a 1-D analytical solution that can be used for the design of horizontal permeable reactive barriers (HPRBs) as a vapor mitigation system at sites contaminated by chlorinated solvents. The developed model incorporates a transient diffusion-dominated transport with a second-order reaction rate constant. Furthermore, the model accounts for the HPRB lifetime as a function of the oxidant consumption by reaction with upward vapors and its progressive dissolution and leaching by infiltrating water. Simulation results by this new model closely replicate previous lab-scale tests carried out on trichloroethylene (TCE) using a HPRB containing a mixture of potassium permanganate, water and sand. In view of field applications, design criteria, in terms of the minimum HPRB thickness required to attenuate vapors at acceptable risk-based levels and the expected HPRB lifetime, are determined from site-specific conditions such as vapor source concentration, water infiltration rate and HPRB mixture. The results clearly show the field-scale feasibility of this alternative vapor mitigation system for the treatment of chlorinated solvents. Depending on the oxidation kinetic of the target contaminant, a 1 m thick HPRB can ensure an attenuation of vapor concentrations of orders of magnitude up to 20 years, even for vapor source concentrations up to 10 g/m³. A demonstrative application for representative contaminated site conditions also shows the feasibility of this mitigation system from an economical point of view with capital costs potentially somewhat lower than those of other remediation options, such as soil vapor extraction systems. Overall, based on the experimental and theoretical evaluation thus far, field-scale tests are warranted to verify the potential and cost-effectiveness of HPRBs for vapor mitigation control under various conditions of application.
... The potential of dry solid potassium permanganate granules for oxidizing various VOCs has been reported in the literature (Mahmoodlu et al., 2013(Mahmoodlu et al., , 2014b. The oxidation of TCE, toluene, and ethanol is described by the following overall reaction equations: C 2 HCl 3ðgÞ þ 2KMnO 4ðsÞ /2K þ þ 2MnO 2ðsÞ þ 3Cl À þ 2CO 2ðgÞ þ H þ (1) C 6 H 5 CH 3ðgÞ þ 12KMnO 4ðsÞ þ 2H 2 O/12K þ þ 12OH À þ 12MnO 2ðsÞ þ 7CO 2ðgÞ (2) C 2 H 5 OH ðgÞ þ 4KMnO 4ðsÞ /4K þ þ 4OH À þ 4MnO 2ðsÞ þ 2CO 2ðgÞ ...
... Our recent study of VOC vapor diffusion through a partiallysaturated permeable reactive barrier showed that water saturation has a considerable effect on the removal capacity of a HPRB (Mahmoodlu et al., 2014b). The study also found that changes in pH values generated during the VOC oxidations according to their stoichiometric reactions (Eqs. ...
... This is reflected by a very slow rise of VOC concentrations in the headspace of the reactive columns (Fig. 2). The experimental results also show that the HPRB in the sand column was far more effective than that in our earlier setup (Mahmoodlu et al., 2014b) which involved the diffusion of VOC vapors only through a HPRB. This is due to the fact that VOC concentrations in the gas phase reaching the HPRB are now much lower as compared to those in our earlier studies. ...
... The potential of dry solid potassium permanganate granules for oxidizing various VOCs has been reported in the literature (Mahmoodlu et al., 2013(Mahmoodlu et al., , 2014b. The oxidation of TCE, toluene, and ethanol is described by the following overall reaction equations: C 2 HCl 3ðgÞ þ 2KMnO 4ðsÞ /2K þ þ 2MnO 2ðsÞ þ 3Cl À þ 2CO 2ðgÞ þ H þ (1) C 6 H 5 CH 3ðgÞ þ 12KMnO 4ðsÞ þ 2H 2 O/12K þ þ 12OH À þ 12MnO 2ðsÞ þ 7CO 2ðgÞ (2) C 2 H 5 OH ðgÞ þ 4KMnO 4ðsÞ /4K þ þ 4OH À þ 4MnO 2ðsÞ þ 2CO 2ðgÞ ...
... Our recent study of VOC vapor diffusion through a partiallysaturated permeable reactive barrier showed that water saturation has a considerable effect on the removal capacity of a HPRB (Mahmoodlu et al., 2014b). The study also found that changes in pH values generated during the VOC oxidations according to their stoichiometric reactions (Eqs. ...
... This is reflected by a very slow rise of VOC concentrations in the headspace of the reactive columns (Fig. 2). The experimental results also show that the HPRB in the sand column was far more effective than that in our earlier setup (Mahmoodlu et al., 2014b) which involved the diffusion of VOC vapors only through a HPRB. This is due to the fact that VOC concentrations in the gas phase reaching the HPRB are now much lower as compared to those in our earlier studies. ...
Article
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Permeable reactive barriers are commonly used to treat contaminant plumes in the saturated zone. However, no known applications of horizontal permeable reactive barriers (HPRBs) exist for oxidizing volatile organic compounds (VOCs) in the unsaturated zone. In this study, laboratory column experiments were carried out to investigate the ability of a HPRB containing solid potassium permanganate, to oxidize the vapors of trichloroethylene (TCE), toluene, and ethanol migrating upward from a contaminated saturated zone. Results revealed that an increase in initial water saturation and HPRB thickness strongly affected the removal efficiency of the HPRB. Installing the HPRB relatively close to the water table was more effective due to the high background water content and enhanced diffusion of protons and/or hydroxides away from the HPRB. Inserting the HPRB far above the water table caused rapid changes in pH within the HPRB, leading to lower oxidation rates. The pH effects were included in a reactive transport model, which successfully simulated the TCE and toluene experimental observations. Simulations for ethanol were not affected by pH due to condensation of water during ethanol oxidation, which caused some dilution in the HRPB.
... where the diffusion coefficient of TCE in water, given by Mahmoodlu, Hassanizadeh, Hartog, and Raoof (2014) is: (4) where the diffusion coefficient of TCE in air, given by Mahmoodlu et al. (2014) is: ...
... where the diffusion coefficient of TCE in water, given by Mahmoodlu, Hassanizadeh, Hartog, and Raoof (2014) is: (4) where the diffusion coefficient of TCE in air, given by Mahmoodlu et al. (2014) is: ...
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In this paper, we analyse and model the mass transfer of trichloroethylene in the surface layer of soil. Our study essentially focuses on arid soils taking into account the phase change liquid–vapour. We have then examined the validity of the assumption of local equilibrium by comparing the values of instantaneous pressure of the trichloroethylene during transfer process and the equilibrium vapour pressure. It appears that the assumption of local equilibrium during the transfer of trichloroethylene cannot be admitted.
... The governing equations for the VOC concentrations in the headspace and the water reservoir (Mahmoodlu et al., 2014(Mahmoodlu et al., , 2015Schwarzenbach et al., 2003;Yoshii et al., 2012) can be written as: ...
... was reached within the water reservoir. One can take advantage of this by decoupling Eq. (2) from Eq. (1) to produce a separate independent equation for C w of the form (Mahmoodlu et al., 2014(Mahmoodlu et al., , 2015Schwarzenbach et al., 2003;Yoshii et al., 2012) ...
Article
In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using completely coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling while decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.
... Transport parameters determine flow and solute transport through the soil column (Mahmoodlu et al., 2014(Mahmoodlu et al., , 2015. Soil compaction and fine sediment infiltration tend to reduce the porosity, hydraulic conductivity, and soil water retention. ...
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The hydraulic properties of unsaturated porous media very much depend on their pore structure as defined by the size, arrangement, and connectivity of pores. Several empirical and quasi-empirical approaches have been used over the years to derive pore structure information from the particle size distribution. In this study, we used the discrete element method to simulate the pore structure of various sands as affected by compaction and particle mixing processes. We used five sands with different mean grain sizes to investigate the effects of different sand mixing ratios and degrees of compaction on pore structure as well as on the intrinsic permeability and the soil water retention curve. Average pore body and pore throat sizes were found to be determined mostly by the smaller particles as represented by the effective diameter D10. The effects of compaction on the average pore body and pore throat radii were used to simulate expected decreases in the permeability. We obtained mostly linear relationships between permeability and the average pore body and throat radii when mixing different unimodal sands. The intrinsic permeability of the coarser sands was found to be far more sensitive to porosity than the finer sands. Simulations of unsaturated conditions showed that the van Genuchten hydraulic parameter α increased nonlinearly with increasing grain size and mean pore body size of the sand mixtures. Compaction caused a linear decrease in α with decreasing porosity and pore body size. However, no clear correlation between the van Genuchten parameter n and porosity or D10 was found for the different compaction and mixing simulations.
... where c w O2 and c a O2 are oxygen concentrations in water and air, respectively, t is time, s is local volume fraction of water, D w O2 and D a O2 are the diffusion coefficients of oxygen in water and air, respectively, and J O2 provides a sink term due to oxygen consumption in the electrochemical reactions. The concentration field is continuous and Henry's law may be applied to couple oxygen concentration at the air-water interfaces as [49,50]: ...
Article
The production of liquid water in cathode catalyst layer, CCL, is a significant barrier to increase the efficiency of proton exchange membrane fuel cell. Here we present, for the first time, a direct three-dimensional pore-scale modelling to look at the complex immiscible two-phase flow in CCL. After production of the liquid water at the surface of CCL agglomerates due to the electrochemical reactions, water spatial distribution affects transport of oxygen through the CCL as well as the rate of reaction at the agglomerate surfaces. To explore the wettability effects, we apply hydrophilic and hydrophobic properties using different surface contact angles. Effective diffusivity is calculated under several water saturation levels. Results indicate larger diffusive transport values for hydrophilic domain compared to the hydrophobic media where the liquid water preferentially floods the larger pores. However, hydrophobic domain showed more available surface area and higher oxygen consumption rate at the reaction sites under various saturation levels, which is explained by the effect of wettability on pore-scale distribution of water. Hydrophobic domain, with a contact angle of 150, reveals efficient water removal where only 28% of the pore space stays saturated. This condition contributes to the enhanced available reaction surface area and oxygen diffusivity.
... The accidental release of petroleum hydrocarbons into the subsurface may cause petroleum vapor intrusion (PVI), a process by which vapors of petroleum chemicals migrate from subsurface to overlying buildings [1]. The resulting indoor air quality problem from these vapors can pose potential threats to human health [2][3][4]. The difference between PVI and vapor intrusion (VI) involving other volatile contaminants (typically chlorinated compounds), is the potential of petroleum hydrocarbons to biodegrade in the presence of oxygen [5]. ...
... Though these 1-D analytical models are widely used since they can be easily included in Excel V R spreadsheets for users' convenience, they are incapable of comprehensively showing multidimensional subsurface soil gas concentration profiles, which are useful to understand PVI site conditions. Compared to the above 1-D analytical models, more complex numerical models [Hers et al., 2000[Hers et al., , 2014Abreu and Johnson, 2006;Abreu et al., 2009Abreu et al., , 2013Bozkurt et al., 2009;Zeng et al., 2010;Knight and Davis, 2013;Zhang et al., 2015;Mahmoodlu et al., 2014;Ma et al., 2014] were also developed to simulate PVI. For instance, Hers et al. [2000] used VADBIO, a two-dimensional (2-D) numerical model for multispecies transport in unsaturated zone, to evaluate of the relevance of biodegradation in PVI. ...
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In this study we present an analytical solution of a two-dimensional petroleum vapor intrusion model, which incorporates a steady-state diffusion-dominated vapor transport in a homogeneous soil and piecewise first-order aerobic biodegradation limited by oxygen availability. This new model can help practitioners to easily generate two-dimensional soil gas concentration profiles for both hydrocarbons and oxygen and estimate hydrocarbon indoor air concentrations as a function of site-specific conditions such as source strength and depth, reaction rate constant, soil characteristics and building features. The soil gas concentration profiles generated by this new model are shown in good agreement with three-dimensional numerical simulations and two-dimensional measured soil gas data from a field study. This implies that for cases involving diffusion dominated soil gas transport, steady state conditions and homogenous source and soil, this analytical model can be used as a fast and easy-to-use risk screening tool by replicating the results of 3-D numerical simulations but with much less computational effort. This article is protected by copyright. All rights reserved.
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Many environmental and agricultural applications involve the transport of water and dissolved constituents through aggregated soil profiles, or porous media that are structured, fractured or macroporous in other ways. During the past several decades, various process-based macroscopic models have been used to simulate contaminant transport in such media. Many of these models consider advective-dispersive transport through relatively large inter-aggregate pore domains, while exchange with the smaller intra-aggregate pores is assumed to be controlled by diffusion. Exchange of solute between the two domains is often represented using a first-order mass transfer coefficient, which is commonly obtained by fitting to observed data. This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore-scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation.
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The performance of a proton exchange membrane fuel cell, PEMFC, is significantly affected by the rate of oxygen diffusion through the cathode catalyst layer, CCL. Continuum-scale modelling of PEMFCs requires knowledge of the effective oxygen diffusivity as a function of CCL porosity and its water saturation. To provide this functionality, we used three-dimensional pore-scale modelling to simulate the diffusion of oxygen under different liquid water saturations in CCLs having different porosity values. Solving the governing equations for immiscible two-phase flow, fluid distributions at different saturation levels were obtained. We show that the presence of liquid water initiates a hindering effect by decreasing the diffusive transport of oxygen. Oxygen diffusion, including dissolution of oxygen into the liquid water phase, was taken into account to calculate effective diffusivity values of the entire domain. The resulting effective diffusivity values showed good agreement with values reported in the literature, which are often based on quasi-empirical relationships. Utilizing a large number of simulation results, a correlation equation was developed for the effective diffusivity of oxygen as a function of porosity and liquid water saturation, which is appropriate to be used for macroscopic modelling of flow and transport in CCLs.
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Chlorinated solvents are extensively used in many activities and hence in the past decades impacted a large number of sites. The presence of these contaminants in groundwater is challenging particularly for the management of the vapor intrusion pathway. In this work we examine the potential feasibility of using horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from groundwater. Zero-valent iron (ZVI) powders, partially saturated with water and characterized by different specific surface areas (SSA), were tested, alone or mixed with sand, in lab-scale batch reactors using TCE as model compound. Depending on the type of iron powder used, a reduction of TCE concentration in the vapor phase from approximately 35% up to 99% was observed after 3 weeks of treatment. The best performance in terms of TCE reduction was obtained using the ZVI characterized by the intermediated values of the specific surface area (SSA). This finding, which is in contrast with the results generally observed in in aqueous solutions, was tentatively attributed to a non-selective higher reactivity of the fine-grained iron samples with water and dissolved oxygen (with a consequent iron passivation) or to the occurrence of a diffusion-limited reaction kinetics. Based on the first-order kinetic degradation rate constants estimated from the experimental data, a horizontal barrier of 1 m containing ZVI or a mixture of ZVI and sand can potentially lead to an attenuation of TCE vapors over 99%.
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The reduction of trichloroethylene (TCE) in gas phase by different types of granular zero-valent iron (Fe0) was examined in anaerobic batch vapor systems performed at room temperature. Concentrations of TCE and byproducts were determined at discrete time intervals by analysis of the headspace vapors. Depending on the type of iron used, reductions of TCE gas concentration from 35% up to 99% were observed for treatments of 6 weeks. In line with other experimental studies performed with aqueous solutions, the particle size was found to play a key role in the reactivity of the iron. Namely an increase of the TCE removal up to almost 3 times was observed using iron powders with particle size lower than 425 μm compared to iron powders with particle size lower than 850 μm. The manufacturing process of the iron powder was instead found to play only a limited role. Namely, no significant differences were observed in the TCE reduction by Fe0 obtained using an iron powder attained by water atomization and sieving compared to the removal achieved using an iron powder subjected to a further annealing processes to reduce the content of oxides. Conversely, the pretreatment of the iron powder with HCl was found to enhance the reactivity of the iron. In particular, by washing the iron powder of 425 μm with HCl acid 0.1 M the reduction of TCE after 6 weeks of treatment increase from approximately 80% for the as received material to >99% for the pretreated iron powder. We also performed tests at different humidity of the iron observing that not statistical differences were obtained using a water content of 10% or 50% by weight. In all the experiments, the only detectable byproducts of the reactions were C4-C6 alkenes and alkanes that can be attributed to a hydrogenation of the CCl bond.
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Background Potassium permanganate is a green and versatile industrial oxidizing agent. Due to its high oxidizing ability, it has received considerable attention and extensively used for many years in the synthesis, identification, and determination of inorganic and organic compounds. Objective Potassium permanganate is one of the most applicable oxidants, which has been applied in a number of processes in several industries. Furthermore, it has been widely used in analytical pharmacy to develop analytical methods for pharmaceutically active compounds using chemiluminescence and spectrophotometric techniques. Result This review covers the importance of potassium permanganate over other common oxidants used in pharmaceuticals and reported its extensive use and analytical applications using direct, indirect and kinetic spectrophotometric methods in different pharmaceutical formulations and biological samples. Chemiluminescent applications of potassium permanganate in the analyses of pharmaceuticals using flow and sequential injection techniques were also discussed. Conclusion This review summarizes the extensive use of potassium permanganate as a chromogenic and chemiluminescent reagent in the analyses of pharmaceutically active compounds to develop spectrophotometric and chemiluminescence methods since 2000.
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Volatile organic compounds (VOCs) and GHGs (CO2) movement in subsurface is topic of interest due to growing extraction and transportation of petroleum hydrocarbon products and CCS sites, respectively. The transport of raw and processed petroleum hydrocarbons through pipelines crossing urban setting and underground storage tanks cause these landscapes to be vulnerable to petroleum hydrocarbon spills. Fate and transport of these gases were studied in past too; however, very little attention was paid to the effects of hydrological variables on its movement of these contaminants in subsurface. Hydrological variables (e.g. soil moisture, infiltration, thickness of capillarity zone) controlled by direct (draining) and indirect (climate change) significantly affect the movement of VOCs in unsaturated zone. Increasing soil moisture content reduced the air-filled porosity of unsaturated zone, which directly decreases the gas diffusion, increases the gas-liquid partition and causes reduced risk of VOCs intrusion. Thus, a better understanding of influences of hydrological variables on VOCs movement will help environmental scientist and geochemist to accurately predict the vapour intrusion and its risk. This review manuscript is intended to narrow the gaps of understanding of role of hydrological variables on VOCs intrusion and its risk. A brief description is presented first to highlight the current knowledge on fate and transport of VOCs followed by the role of matrix setting on its movement in subsurface. Thereafter, a section is presented to elaborate the impact of VOCs and GHGs intrusion on the subsurface microbes.
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The use of permanganate solutions for in-situ chemical oxidation (ISCO) is a well-established groundwater remediation technology, particularly for targeting chlorinated ethenes. The kinetics of oxidation reactions is an important ISCO remediation design aspect that affects the efficiency and oxidant persistence. The overall rate of the ISCO reaction between oxidant and contaminant is typically described using a second-order kinetic model while the second-order rate constant is determined experimentally by means of a pseudo first order approach. However, earlier studies of chlorinated hydrocarbons have yielded a wide range of values for the second-order rate constants. Also, there is limited insight in the kinetics of permanganate reactions with fuel-derived groundwater contaminants such as toluene and ethanol. In this study, batch experiments were carried out to investigate and compare the oxidation kinetics of aqueous trichloroethylene (TCE), ethanol, and toluene in an aqueous potassium permanganate solution. The overall second-order rate constants were determined directly by fitting a second-order model to the data, instead of typically using the pseudo-first-order approach. The second-order reaction rate constants (M(-1)s(-1)) for TCE, toluene, and ethanol were 8.0×10(-1), 2.5×10(-4), and 6.5×10(-4), respectively. Results showed that the inappropriate use of the pseudo-first-order approach in several previous studies produced biased estimates of the second-order rate constants. In our study, this error was expressed as a function of the extent (P/N) in which the reactant concentrations deviated from the stoichiometric ratio of each oxidation reaction. The error associated with the inappropriate use of the pseudo-first-order approach is negatively correlated with the P/N ratio and reached up to 25% of the estimated second-order rate constant in some previous studies of TCE oxidation. Based on our results, a similar relation is valid for the other volatile organic compounds studied.
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It is known that in variably saturated porous media, dispersion coefficient depends on Darcy velocity and water saturation. In one-dimensional flow, it is commonly assumed that the dispersion coefficient is a linear function of velocity. The coefficient of proportionality, called the dispersivity, is considered to depend on saturation. However, there is not much known about its dependence on saturation. In this study, we investigate, using a pore network model, how the longitudinal dispersivity varies nonlinearly with saturation. We schematize the porous medium as a network of pore bodies and pore throats with finite volumes. The pore space is modeled using the multidirectional pore-network concept, which allows for a distribution of pore coordination numbers. This topological property together with the distribution of pore sizes are used to mimic the microstructure of real porous media. The dispersivity is calculated by solving the mass balance equations for solute concentration in all network elements and averaging the concentrations over a large number of pores. We have introduced a new formulation of solute transport within pore space, where we account for different compartments of residual water within drained pores. This formulation makes it possible to capture the effect of limited mixing due to partial filling of the pores under variably saturated conditions. We found that dispersivity increases with the decrease in saturation, it reaches a maximum value, and then decreases with further decrease in saturation. To show the capability of our formulation to properly capture the effect of saturation on solute dispersion, we applied it to model the results of a reported experimental study.
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Volatile organic compounds (VOCs) may frequently contaminate groundwater and pose threat to human health when migrating into the unsaturated soil zone and upward to the indoor air. The kinetic of chemical oxidation has been investigated widely for dissolved VOCs in the saturated zone. But, so far there have been few studies on the use of in situ chemical oxidation (ISCO) of vapour phase contaminants. In this study, batch experiments were carried out to evaluate the oxidation of trichloroethylene (TCE), ethanol, and toluene vapours by solid potassium permanganate. Results revealed that solid potassium permanganate is able to transform the vapour of these compounds into harmless oxidation products. The degradation rates for TCE and ethanol were higher than for toluene. The degradation process was modelled using a kinetic model, linear in the gas concentration of VOC [ML(-3)] and relative surface area of potassium permanganate grains (surface area of potassium permanganate divided by gas volume) [L(-1)]. The second-order reaction rate constants for TCE, ethanol, and toluene were found to be equal to 2.0×10(-6)cms(-1), 1.7×10(-7)cms(-1), and 7.0×10(-8)cms(-1), respectively.
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A laboratory-scale study with a sand column was designed to simulate trichloroethylene (TCE) pollution in the aquifer environment with three-section controlled-release potassium permanganate (CRP) barriers. The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner. CRP particles with a 1:3 molar ratio of KMnO4 to stearic acid showed the best controlled-release properties in pure water, and the theoretical release time was 138.5 days. The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days. The molar ratio of KMnO4 to TCE in the three-section CRP barriers was 16:1, which was much lower than 82:1 as required when KMnO4 solution is used directly to achieve complete destruction of TCE. This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.
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The inhalation of volatile and semi-volatile organic compounds that intrude from a subsurface contaminant source into indoor air has become the subject of health and safety concerns over the last twenty years. Building subslab and soil gas contaminant vapor concentration sampling have become integral parts of vapor intrusion field investigations. While numerical models can be of use in analyzing field data and in helping understand the subslab and soil gas vapor concentrations, they are not widely used due to the perceived effort in setting them up. In this manuscript, we present a new closed-form analytical expression describing subsurface contaminant vapor concentrations, including subslab vapor concentrations. The expression was derived using Schwarz-Christoffel mapping. Results from this analytical model match well the numerical modeling results. This manuscript also explores the relationship between subslab and exterior soil gas vapor concentrations, and offers insights on what parameters need to receive greater focus in field studies.
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Persulfate is the newest oxidant that is being used for in situ chemical oxidation (ISCO) in the remediation of soil and groundwater. In this review, the fundamental reactions and governing factors of persulfate relevant to ISCO are discussed. The latest experiences for ISCO with persulfate are presented, with a focus on the different activation methods, the amenable contaminants, and the reactions of persulfate with porous media, based primarily on a critical review of the peer-reviewed scientific literature and to a lesser extent on non-reviewed professional journals and conference proceedings. The last sections are devoted to identifying the best practices based on current experience and suggesting the direction of future research.
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An expression has been derived to describe both saturated and unsaturated permeability of porous media in terms of the pore size distribution as obtained from mercury-injection data or water-desorption isotherms. An interaction model has been adopted wherein both pore radius and effective area available for flow have been considered. The permeability values obtained using this expression have been compared with water and gas permeabilities of a variety of porous media. Satisfactory agreement is found between experimental and calculated values over a wide range of permeability.
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The report is a comprehensive literature review that presents and assesses research results that pertain to the problems and inconsistencies observed in the sampling and analysis of soil volatile organic compounds (VOC) by SW-846 method 5030 (purge and trap) for sample preparation and extraction and methods 8240/8260 (gas chromatography/mass spectrometry) for sample analysis. Topics discussed include: interphase transfer mechanisms for VOCs in soil, soil VOC degradation processes, movement of VOCs in the vadose zone, models used for predicting the movement and fate of soil VOCs, soil sampling and preservation methods, analytical methodologies, field methods for determining soil gas and soil VOCs, as well as presenting the author's view of future research needs in the area of soil VOCs. The results and discussion presented in the report are intended to be used to evaluate problems with the current SW-846 methods and as guidance for research needed to formulate procedures that will increase the precision and accuracy of vadose zone VOC measurements.
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A complete vapor intrusion (VI) model, describing vapor entry of volatile organic chemicals (VOCs) into buildings located on contaminated sites, generally consists of two main parts- one describing vapor transport in the soil and the other its entry into the building. Modeling the soil vapor transport part involves either analytically or numerically solving the equations of vapor advection and diffusion in the subsurface. Contaminant biodegradation must often also be included in this simulation, and can increase the difficulty of obtaining a solution, especially when explicitly considering coupled oxygen transport and consumption. The models of contaminant building entry pathway are often coupled to calculations of indoor air contaminant concentration, and both are influenced by building construction and operational features. The description of entry pathway involves consideration of building foundation characteristics, while calculation of indoor air contaminant levels requires characterization of building enclosed space and air exchange within this. This review summarizes existing VI models, and discusses the limits of current screening tools commonly used in this field.
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There is evidence to suggest that the gas−water interface serves as an important retention domain for volatile organic compounds (VOCs) in vadose-zone soil. Moreover, vapor adsorption at the gas−water interface may represent the dominant retention mechanism under certain conditions. In general, vapor-phase interfacial adsorption is most significant for low organic matter soils at intermediate water contents. Among nonpolar compounds, those with low saturated vapor pressure have the greatest tendency for interfacial adsorption, as represented by higher interfacial sorption coefficients, KIA. Although polar compounds may have greater tendency to adsorb at the interface than nonpolar compounds, the high aqueous solubility of polar compounds may limit the relative importance of interfacial sorption to total contaminant retention. The magnitude of interfacial retention is controlled by the specific interfacial area, AIA, as well as by KIA. Validated methods for measuring AIA are currently lacking. However, three promising methods for measuring AIA in soils have been proposed. Preliminary results indicate that the three methods are complimentary in terms of the type of information derived, as well as their applicability for different water content ranges and varying scales (e.g., laboratory vs field).
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A pilot study was completed at a fractured crystalline bedrock site using a combination of soil vapor extraction (SVE) and in-situ chemical oxidation (ISCO) with Fenton's Reagent. This system was designed to destroy 1,1,1-trichloroethane (TCA) and its daughter products, 1,1-dichloroethene (DCE) and 1,1-dichloroethane (DCA). Approximately 150 pounds of volatile organic compounds (VOCs) were oxidized in-situ or removed from the aquifer as vapor during the pilot study. Largely as a result of chemical oxidation, TCA concentrations in groundwater located within a local groundwater mound decreased by 69 to 95 percent. No significant rebound in VOC concentration was observed in these wells. Wells located outside of the groundwater mound showed less dramatic decreases in VOC concentration, and the data show that vapor stripping and short-term groundwater migration following the oxidant injection were the key processes at these wells. Although the porosity of the aquifer at the site is on the order of 2 percent or less, the pilot study showed that SVE could be an effective remedial process in fractured crystalline rock. © 2002 Wiley Periodicals, Inc.
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Laboratory characterization studies, one-dimensional flow-through studies, and numerical model simulations were conducted to examine site conditions and system features that may have adversely affected in situ chemical oxidation (ISCO) performance at the Naval Training Center’s (NTC) Operable Unit 4 located in Orlando, Florida, and to identify potential ISCO system modifications to achieve the desired remediation performance. At the NTC site, ISCO was implemented using vertical injection wells to deliver potassium permanganate into a ground water zone for treatment of tetrachloroethylene and its breakdown products. However, oxidant distribution was much more limited than anticipated. Characterization studies revealed that the ground water zone being treated by ISCO was very fine sand with a small effective particle size and low uniformity coefficient, along with a high organic carbon content, high natural oxidant demand (NOD), and a high ground water dissolved solids concentration, all of which contributed to full-scale ISCO application difficulties. These site conditions contributed to injection well permeability loss and an inability to achieve the design oxidant injection flow rate, limiting the actual oxidant distribution at the site. Flow-through experiments demonstrated that more favorable oxidant delivery and distribution conditions are enabled by applying a lower oxidant concentration at a faster delivery rate for a greater number of pore volumes. Numerical simulations, run for a variety of conditions (injection/extraction well flow rates, injected oxidant concentration, amount of NOD present, and NOD oxidation rate), also revealed that low–oxidant concentration injection at a high flow rate is a more effective method to deliver the required mass of oxidant to the target treatment zone.
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In situ chemical oxidation (ISCO) with permanganate has been widely used for soil and groundwater treatment in the saturated zone. Due to the challenges associated with achieving effective distribution and retention in the unsaturated zone, there is a great interest in developing alternative injection technologies that increase the success of vadose-zone treatment. The subject site is an active dry cleaner located in Topeka, Kansas. A relatively small area of residual contamination adjacent to the active facility building has been identified as the source of a large sitewide groundwater contamination plume with off-site receptors. The Kansas Department of Health and Environment (KDHE) currently manages site remedial efforts and chose to pilot-test ISCO with permanganate for the reduction of perchloroethene (PCE) soil concentrations within the source area. KDHE subsequently contracted Burns & McDonnell to design and implement an ISCO pilot test. A treatability study was performed by Carus Corporation to determine permanganate-soil-oxidant-demand (PSOD) and the required oxidant dosing for the site. The pilot-test design included an ISCO injection approach that consisted of injecting aqueous sodium permanganate using direct-push technology with a sealed borehole. During the pilot test, approximately 12,500 pounds of sodium permanganate were injected at a concentration of approximately 3 percent (by weight) using the methods described above. Confirmation soil sampling conducted after the injection event indicated PCE reductions ranging from approximately 79 to more than 99 percent. A follow-up treatment, consisting of the injection of an additional 6,200 pounds of sodium permanganate, was implemented to address residual soil impacts remaining in the soil source zone. Confirmation soil sampling conducted after the treatment indicated a PCE reduction of greater than 90 percent at the most heavily impacted sample location and additional reductions in four of the six samples collected.
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The oxidation of ethanol by permanganate has been found to obey the rate law v=k[MeCHO][MnO 4 – ][H+]. The results are compared with those found for chromium (VI) oxidation of the same substrate. V=k[MeCHO][MnO 4 – ][H+]. , (VI).
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Soil vapour transport to indoor air is an important potential exposure pathway at many sites impacted by subsurface volatile organic compounds (VOCs). The inclusion of biodegradation in vadose zone transport models for benzene, toluene and xylene (BTX) and fuel hydrocarbons has been proposed; however, there is still significant uncertainty regarding biodegradation rates and the local effects of buildings or ground surface cover on fate and transport processes. The objective of this study was to evaluate biodegradation processes through comprehensive monitoring at a site contaminated with BTX and model simulation. Study methods included extensive vertical profiling of BTX vapour and light gas (oxygen and carbon dioxide) concentrations and moisture content, and semi-continuous monitoring of oxygen and pressure below a building floor slab. Significant vadose zone biodegradation over a relatively small depth interval was observed. Based on the observed soil vapour profile, first-order biodegradation rates were estimated by fitting an analytical solution for diffusion and biodecay to the data. Degradation rates were found to compare well to other reported laboratory and field data. A two-dimensional (2-D) numerical model incorporating vapour-phase diffusion, advection, sorption and biodegradation was used to simulate the effect of a building floor slab on transport processes. Model results demonstrate the sensitivity of vapour-phase BTX and oxygen transport to partial barriers to diffusion (e.g. building foundation) and highlight the importance of using a model that ties biodecay to oxygen availability. In addition, depressurization within a building and advective transport is shown to have a potentially significant effect on BTX fate, in soil below.
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Recent developments and trends in the use of headspace sampling with gas chromatography (GC) are reviewed and discussed. A brief overview of headspace analysis techniques and theory references is provided, followed by publication trend data on the various headspace-analysis techniques. The techniques described include static and dynamic headspace extraction, solid phase micro-extraction (SPME) and several additional techniques now receiving attention. Examples of applications in environmental, clinical, forensic, biological, food, flavor and pharmaceutical analysis are provided. Research in headspace-GC is very active and growing, with new applications being reported continually.
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Laboratory experiments were conducted employing gas chromatographic techniques to evaluate the gaseous transport of volatile organic chemicals (VOCs) in water-unsaturated soil columns as influenced by interfacial (air-water) adsorption and water partitioning. VOCs [methylene chloride, tetrachloroethene (PCE), 1,1,1-trichloroethane (TCA), ethyl-benzene, p-xylene, chlorobenzene] with different water-partitioning and interfacial adsorption coefficients (air-water) were used to evaluate the theoretical basis of using these coefficients to predict the retardation factors (Rt) observed during gaseous transport. A loamy sand from Dover Air Force Base, DE, and a commercial sand were used as the column packing material to assess the effect of grain size on the air-water interfacial area (ai) and retardation at different water saturations (Sw). The ai were measured using n-alkanes. At low Sw, interfacial adsorption contributed most to the retardation for all VOCs during gaseous transport in the Dover soil which has little sorption capacity for the VOCs. As Sw increased, the fraction of Rt attributed to interfacial adsorption decreased, while that due to water partitioning increased for all of the VOCs used for this study. For the sand, with a more uniform grain-size distribution than the Dover soil, the contribution of air-water interfacial adsorption to the Rt of a VOC (p-xylene) was not as significant as that for the Dover soil due to small ai. The fractions of Rt attributed to interfacial adsorption and water partitioning were quantified. The observed Rt for the VOCs agreed well with those predicted based on the sorption coefficients and the quantities of sorption domains (Sw, ai).
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Headspace solvent microextraction (HSM) is a novel method of sample preparation for chromatographic analysis. It involves exposing a microdrop of high-boiling point organic solvent extruded from the needle tip of a gas chromatographic syringe to the headspace above a sample. Volatile organic compounds are extracted and concentrated in the microdrop. Next, the microdrop is retracted into the microsyringe and injected directly into the chromatograph. HSM has a number of advantages, including renewable drop (no sample carryover), low cost, simplicity and ease of use, short time of analysis, high sensitivity and low detection limits, good precision, minimal solvent use, and no need for instrument modification. This paper presents analytical characteristics of HSM as applied to the determination of benzene, toluene, ethylbenzene and xylenes in water.
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In situ chemical oxidation (ISCO) schemes using MnO4- have been effective in destroying chlorinated organic solvents dissolved in ground water. Laboratory experiments and field pilot tests reveal that the precipitation of Mn oxide, one of the reaction products, causes a reduction of permeability, which can lead to flow bypassing and inefficiency of the scheme. Without a solution to this problem of plugging, it is difficult to remove DNAPL from the subsurface completely. In a companion paper, we showed with batch experiments that Mn oxide can be dissolved rapidly with certain organic acids. This study utilizes 2-D flow-tank experiments to examine the possibility of nearly complete DNAPL removal by ISCO with MnO4-, when organic acids are used to remove Mn oxide. The experiments were conducted in a small 2-D glass flow tank containing a lenticular silica-sand medium. Blue-dyed trichloroethylene (TCE) provided residual, the perched and pooled DNAPL. KMnO4 at 200 mg/l was flushed through the DNAPL horizontally. Once plugging reduced permeability and prevented further delivery of the oxidant, citric or oxalic acids were pumped into the flow tank to dissolve the Mn oxide precipitates. Organic ligands removed the Mn oxide precipitates relatively quickly, and permitted another cycle of MnO4- flooding. Cycles of MnO4-/acid flooding continued until all of the visible DNAPL was removed. The experiments were monitored with chemical analysis and visualization. A mass-balance calculation indicated that by the end of the experiments, all the DNAPL was removed. The results show also how heterogeneity adds complexity to initial redistribution of DNAPL, and to the efficiency of the chemical flooding.
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A vital design parameter for any in situ chemical oxidation system using permanganate (MnO4-) is the natural oxidant demand (NOD), a concept that represents the consumption of MnO4- by the naturally present reduced species in the aquifer solids. The data suggest that the NOD of the aquifer material from Canadian Forces Base Borden used in our study is controlled by a fast or instantaneous reaction captured by the column experiments, and a slower reaction as demonstrated by both column and batch test data. These two reaction rates may be the result of the reaction of MnO4- with at least two different reduced species exhibiting widely different rates of permanganate consumption (fast rate >7 g of MnO4- as KMnO4/kg/day and slow rate of approximately 0.005 g/kg/day), or a physically/chemically rate-limited single species. The slow NOD reaction prevented fulfillment of the ultimate NOD during the days- to months-long batch experiments and allowed significant early MnO4- breakthrough (>98%) during transport in the column experiments. A large fraction of the organic carbon resisted oxidation over the 21-week duration of the batch experiments. This result demonstrates that NOD estimated from total organic carbon measurements can significantly overpredict the NOD value required in the design of an in situ chemical oxidation application.
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A simple method of solventless extraction of volatile organic compounds (benzene, toluene, ethylbenzene and xylenes) from aqueous samples was developed. This method allows direct injection of large volume of water sample into a gas chromatograph using the sorption capacity of the sorbent Chromosorb P NAW applied directly in the injection port of gas chromatograph. The system prevent water penetration into a column, keep it adsorbed on its surface until the analytes are stripped into a column, and the residual water is purging using split flow. The limit of detection ranging from 0.6 for benzene to 1.1 microg l(-1) for o-xylene and limit of quantification ranging 2.0-3.6 microg l(-1) are lower that those reached by gas chromatography with flame ionization detection and direct aqueous injection before.
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Bulk and intrinsic mass transfer processes across interfaces between nonaqueous phase liquids (NAPLs) and water were studied in water-saturated columns. Columns packed with different grain sizes of sand were used to create various NAPL-water interfacial areas along with different NAPL saturations. The intrinsic mass transfer coefficients were estimated from the bulk mass transfer coefficients, and the specific interfacial areas were measured using tracer studies. The bulk mass transfer coefficients increased with increasing NAPL-water specific interfacial area as well as NAPL saturation and pore velocity and with decreasing grain sizes. Moreover, the bulk mass transfer coefficients were correlated with NAPL-water specific interfacial area rather than NAPL saturation and were more sensitive at high NAPL-water interfacial areas than at low interfacial areas. In contrast, the intrinsic mass transfer coefficients were nearly independent of specific interfacial area and NAPL saturation but dependent on pore velocity. Reduction of NAPL saturation by dissolution caused a linear decrease in the bulk mass transfer coefficients.
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To provide a more complete understanding of the kinetics of in situ chemical oxidation (ISCO) with permanganate (MnO4-), we measured the kinetics of oxidation of 24 contaminants-many for which data were not previously available. The new data reported here were determined using an efficient method based on continuous measurement of the MnO4- concentration by absorbance spectrometry. Under these conditions, the kinetics were found to be first-order with respect to both contaminant and MnO4- concentrations, from which second-order rate constants (k") were readily obtained. Emerging contaminants forwhich k" was determined (at 25 degrees C and pH 7) include 1,4-dioxane (4.2 x 10(-5) M(-1) s(-1)), methyl t-butyl ether (MTBE) (1.0 x 10(-4) M(-1) s(-1)), and methyl ethyl ketone (MEK) (9.1 x 10(-5) M(-1) s(-1)). Contaminants such as 2,4,6-trinitrotoluene (TNT), the pesticides aldicarb and dichlorvos, and many substituted phenols are oxidized with rate constants comparable to tetrachloroethene (PCE) and trichloroethene (TCE) (i.e., 0.03-1 M(-1) s(-1)) and therefore are good candidates for remediation with MnO4- in the field. There are several--sometimes competing--mechanisms by which MnO4- oxidizes contaminants, including addition to double bonds, abstraction of hydrogen or hydride, and electron transfer.
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This paper presents a methodology for the evaluation of the intrinsic photocatalytic oxidation (PCO) kinetics of indoor air pollutants. It combines computational fluid dynamics (CFD) modeling of the fluid flow in the reactor with radiation field modeling and photocatalytic reaction kinetics to yield a rigorous model of a flat-plate, single-pass, flow-through photocatalytic reactor for indoor air purification. This method was applied to model the PCO of trichloroethylene (TCE) in humidified air and to derive kinetic parameters directly from kinetic data in an integral flow reactor. Steady-state PCO experiments of TCE over irradiated TiO2 (Degussa P25) thin films immobilized on glass supports were carried out at different radiation intensities, flow rates, and inlet substrate concentrations. The oxidation rate of TCE was found to be first-order on the incident photon flux and to follow a Langmuir-Hinshelwood type reaction kinetics rate law. Mass transfer resistances were observed at Reynolds numbers less than 46. Apparent quantum yields were found to be up to 0.97 mol Einstein(-1). A comparison of the model prediction with the experimental results in an integral reactor yielded pollutant-specific kinetic rate parameters which were independent of reactor geometry, radiation field, and fluid-dynamics. The kinetic parameters would,therefore, be more universally applicable to the design and scale-up of photocatalytic reactors for indoor air purification.
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The objectives of this bench-scale study were to (1) determine the optimal operational parameters and kinetics when potassium permanganate (KMnO4) was applied to in situ oxidize and remediate trichloroethylene (TCE)-contaminated groundwater and (2) evaluate the effects of manganese dioxide (MnO2) on the efficiency of TCE oxidation. The major controlling factors in the TCE oxidation experiments included molar ratios of KMnO4 to TCE (P value) and molar ratios of Na2HPO4 to Mn2+ (D value). Results show that the second-order decay model can be used to describe the oxidation when P value was less than 20, and the observed TCE decay rate was 0.8M(-1)s(-1). Results also reveal that (1) higher P value corresponded with higher TCE oxidation rate under the same initial TCE concentration condition and (2) higher TCE concentration corresponded with higher TCE oxidation rate under the same P value condition. Results reveal that significant MnO2 production and inhibition of TCE oxidation were not observed under acidic (pH 2.1) or slightly acidic conditions (pH 6.3). However, significant reduction of KMnO(4) to MnO2 would occur under alkaline condition (pH 12.5), and this caused the decrease in TCE oxidation rate. Results from the MnO2 production experiments show that MnO2 was produced from three major routes: (1) oxidation of TCE by KMnO4, (2) further oxidation of Mn2+, which was produced during the oxidation of TCE by KMnO4, and (3) reduction of MnO4(-1) to MnO2 under alkaline conditions. Up to 81.5% of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Moreover, the addition of Na2HPO4 would not decrease the TCE oxidation rate.
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The present study describes a method based on headspace-solid-phase dynamic extraction (HS-SPDE) followed by GC/MS for the qualitative and quantitative analysis of benzene, toluene, ethylbenzene, o-, m- and p-xylene (BTEX), and n-aldehydes (C(6)-C(10)) in water. To enhance the extraction capability of the HS-SPDE a new cooling device was tested that controls the temperature of the SPDE needle during extraction. Extraction and desorption parameters such as the number of extraction cycles, extraction temperature, desorption volume and desorption flow rate have been optimized. Detection limits for BTEX ranged from 19 ng/L (benzene) to 30 ng/L (m/p-xylene), while those for n-aldehydes ranged from 21 ng/L (n-heptanal) to 63 ng/L (n-hexanal). At a concentration level of 2 microg/L, the relative standard deviations (RSDs) for BTEX ranged from 3.9% (benzene) to 15.3% (ethylbenzene), while RSDs for n-aldehydes were between 6.1% (n-octanal) and 16.5% (n-hexanal) (n=7). Best results were obtained when the analyzed water samples were heated to 50 degrees C. At a water temperature of 70 degrees C GC responses decreased for all analyzed compounds. At a defined water temperature, a significant improvement of the GC response was achieved by cooling of the SPDE fiber during water extraction in comparison to an extraction keeping the fiber at room temperature. Evaluating the extraction cycles, for BTEX, the sensitivity was almost similar using 20, 40 and 60 extraction cycles. In contrast, the highest GC responses for n-aldehydes were achieved by the use of 60 extraction cycles. Optimizing the desorption parameters, best results were achieved using the smallest technical available desorption volume of 500 microL and the highest technical desorption flow rate of 50 microL/s. The method was applied to the analysis of melted snow samples taken from the Jungfraujoch, Switzerland (3580 m asl), revealing the presence of BTEX and aldehydes in snow.