Remediation Of Organic Contaminants Research Articles

Mo0 and Mo4+ bimetallic reactive sites accelerating Fe2+/Fe3+ cycling for the activation of peroxymonosulfate with significantly improved remediation of aromatic pollutants.

In Fe2+/peroxymonosulfate (PMS) activation system, the slow cycle rate of Fe3+/Fe2+ has been considered to be the limiting step in the remediation of organic contaminants. In this paper, commercial molybdenum (Mo) powder is employed as the cocatalyst in Fe2+/PMS system, which can significantly accelerate the Fe3+/Fe2+ cycling efficiency by the exposed bimetallic active sites of Mo4+ and Mo0, and the process is accelerated as the amount of Mo powder increased. The Mo cocatalytic Fe2+/PMS system exhibits an enhanced performance for the activation of PMS and the removal of different aromatic pollutants including dyes, phenolic pollutants and antibiotics, in a wide pH range of 4.0-9.0. Importantly, Mo powder exhibits excellent cycle performance in the PMS activation system, and rhodamine B (RhB) can be removed within 10min even after 5 cycles. Electron paramagnetic resonance (EPR) prove that the sulfate radicals (SO4-) is the major reactive oxides species in the PMS activation, the increase of Fe2+ content induced by the cocatalytic effect of Mo powder can effectively promote the production of SO4- and increase the utilization of PMS. In addition, to observe the process of pollutant removal more intuitively, HPLC-MS is used to analyze the decomposing pathway of RhB and sulfadiazine in Mo+FeSO4+PMS system. It is believed that this research provides a new idea for the efficient activation of PMS by iron ions in a wide initial pH range, which is expected to be applied to the treatment of large-scale industrial wastewater.

Activation of peroxymonosulfate by Fe doped g-C3N4 /graphene under visible light irradiation for Trimethoprim degradation

Fe-doped g-C3N4 / graphene (rGO) composites were investigated as catalysts for the activation of peroxymonosulfate (PMS) to degrade Trimethoprim (TMP) under visible light irradiation. The rapid recombination of photogenerated electron-hole pairs in g-C3N4 may be suppressed by doping with Fe and incorporating rGO. The TMP degradation efficiency using 0.2% Fe-g-C3N4/2 wt% rGO/PMS was 3.8 times than that of g-C3N4/PMS. The degradation efficiency of TMP increased with higher catalyst dosages and PMS concentrations. Acidic condition (pH = 3) was observed to significantly enhance the TMP degradation efficiency from 61.4% at pH = 6 to nearly 100%. By quenching experiments and electron spin resonance (ESR), O2− was found to play an important role for the activation of PMS to accelerate the generation of reactive radicals for the TMP degradation. A total of 8 intermediates derived from hydroxylation, demethoxylation and carbonylation were identified through theoretical calculations and the HRAM/LC–MS-MS technique, and transformation pathways of TMP oxidation were proposed. TOC removal rate of TMP increased as reaction time was prolonged. Acute toxicity estimation by quantitative structure-active relationship analysis indicated that most of the less toxic intermediates were generated. The aim of this study was to elucidate and validate the functionality of a promising polymeric catalyst for the environmental remediation of organic contaminants.

Catalytic oxidation of clofibric acid by peroxydisulfate activated with wood-based biochar: Effect of biochar pyrolysis temperature, performance and mechanism

Wood-based biochars were fabricated at different pyrolysis temperatures of 400–700 °C and used to activate peroxydisulfate (PDS) for the degradation of clofibric acid (CA). Biochar pyrolyzed at 700 °C (BC700) showed more excellent catalytic performance toward CA removal (97.8% in a 60 min reaction) than other BCs. The BC700/PDS process performed efficiently at initial pH range of 4.0–9.0. The effects of PDS concentration and BC700 dosage on CA removal were also examined. Radical quenching experiments and electron paramagnetic resonance (EPR) spectra were applied to identify the reactive radicals generated in the BC700/PDS system. The role of persistent free radicals (PFRs), oxygen functional groups and π-π* transitions in aromatic rings of BC700 for the PDS activation was explored. The reaction intermediates of CA were identified by liquid chromatography–mass spectrometry (LC–MS) and the corresponding degradation pathway was proposed. This study contributes to the development of green materials for sustainable remediation of organic contaminants in water and provides support for further studies.

Reduced graphene oxide-metal nanoparticle composite membranes for environmental separation and chloro-organic remediation.

This study explores the integration of separation performance of rGO membrane with heterogeneous oxidation reactions for remediation of organic contaminants from water. Herein, an approach was introduced based on layer-by-layer assembly for functionalizing rGO membranes with polyacrylic acid and then by in situ synthesis of Fe based reactive nanoparticles. TEM characterization of the cross-section lamella of the membranes showed a high density of nanoparticles (12% Fe) in the functionalized domain, signifying the importance of polyacrylic acid for in situ synthesis of nanoparticles. The membranes exhibited a pure water permeability of 1.9 LMH bar−1. The membranes had low to moderate salt retention, and more than 90% neutral red retention (organic probe molecule, size: 1.2 nm). The membranes also exhibited high retention of humic acids (80%), preventing these organics from entering the reactive domain, and thus potentially reducing the formation of undesired by-products. A persulfate mediated oxidative pathway was employed to demonstrate the reactive removal of organic contaminants. The membranes achieved >95% conversion by convectively passing 2 mM persulfate feed at a transmembrane pressure of 0.4 bar. Successful degradation of TCE (up to 61%) was achieved in a single pass by convective flowing of the feed solution through the membrane, generating up to 80% of the theoretical maximum chloride as one of the byproducts. Elevated temperatures significantly enhanced persulfate mediated TCE oxidation extent from 24% at 23 °C to 54% at 40 °C under batch operating conditions.

Electrokinetic remediation for the removal of organic contaminants in soils

Electrokinetic remediation is a technology developed in the late 80s of the XX century for the remediation of soils and other solid materials. This technology is still being investigated for developing new and effective applications in contaminated soils and sediments. The removal or elimination of organic contaminants in soil with electrokinetics has attracted much interest due to the lack of effective remediation technologies. Electrokinetics is able to remediate organics in soil when combined with facilitating agents such as surfactants, co-solvents, nanoparticles, and oxidizing chemicals that can help in the removal or degradation of the contaminants in situ. Electrokinetics have also combined with other remediating technologies: in situ chemical oxidation, bioremediation, and phytoremediation, with the objective of reaching a synergistic effect on the removal/elimination of organic contaminants in soil. This paper discusses the state-of-the-art of remediation of organic contaminants in soil with electrokinetic technology.

Carbon nanomaterials differentially impact mineralization kinetics of phenanthrene and indigenous microbial communities in a natural soil

Previous reports on how carbon nanomaterials (CNMs) affect the biodegradation and mineralization of organic contaminants are mainly limited to pure culture studies, but little is known about the mineralization process by more complex and environmentally-relevant microbial communities. This study investigated the impact of fullerenes C60 and two multi-walled carbon nanotubes (outer diameter < 8 nm: M8; >50 nm: M50) at 300 and 3000 mg/kg on the mineralization kinetics of 14C-phenanthrene (18.5 mg/kg) by indigenous microorganisms in a natural soil for 120 days. Phenanthrene mineralization kinetics fitted well with the logistic growth equation regardless of the CNMs present (R2 = 0.965–0.985). The maximum mineralization rates and the total mineralization fraction were positively correlated with the initial phenanthrene bioavailability, assessed via β-HPCD extraction. Phenanthrene exposure induced significant responses of the catabolic gene biomarker nidA, fungi and bacteria communities by 275, 30, and 5 times, respectively, indicating a non-neglectable role of the fungal communities in phenanthrene mineralization. CNMs exerted a sorption- and level-dependent suppression (7.4–47.2%) on the total phenanthrene mineralization fractions at 120 d. Carbon nanotubes (300, 3000 mg/kg) caused significant adverse effects on the biomass of bacterial (47.8–60.7%), fungal (31.4–71.6%) and nidA-carrying degraders (25.7–59.9%) in the absence or presence of phenanthrene, which contributed to the inhibition of the total mineralization fractions at 120 d. Bacterial community structure was not significantly impacted by CNMs alone or co-exposure of CNM-phenanthrene. However, the fungal community showed a significant shift upon exposure to carbon nanotubes, especially M8, with the relative abundance of potential PAH degraders repressed (8.5–40.3%) at both levels of M8 tested. This corroborates the higher sensitivity of fungal communities. The findings from this study are important to inform how the released CNMs affect soil microbial communities that play a key role in the fate and remediation of organic contaminants in soil.

Transformation of antimicrobial agent sulfamethazine by peroxymonosulfate: Radical vs. nonradical mechanisms

Peroxymonosulfate (PMS) is increasingly used as an oxidant for in situ remediation of organic contaminants in soil and groundwater. In this study we demonstrated that sulfamethazine (SMZ) could be transformed by PMS in the absence of any activators. Such transformation was ascribed to the oxidation by PMS per se, rather than free radicals (SO4− or HO), superoxide (O2−), or singlet oxygen (1O2). The aniline moiety of SMZ molecule was the reactive site for PMS oxidation, leading to the formation of nitrated products. This nitration pathway in fact played a significant role in the removal of SMZ in activated PMS oxidation processes. For instance, it contributed 26% of the total SMZ transformation, while SO4− contributed the other 74% during the removal of SMZ, in Co(II)/PMS oxidation process with initial PMS and Co(II) concentrations of 1.0 mM and 0.1 μM, respectively. Similar nitration reaction also occurred to other sulfonamide antibiotics bearing an aniline moiety upon the reaction with PMS. Since nitrated sulfonamide antibiotics appear more persistent than the parent compounds and may cause other environmental problems, such a pathway should not be desired. Therefore, PMS might not be an ideal oxidant for the treatment of sulfonamide antibiotics and other compounds having aniline moieties, especially in subsurface remediation practices where efficient activation of PMS represents a major challenge.

Identification and Regulation of Active Sites on Nanodiamonds: Establishing a Highly Efficient Catalytic System for Oxidation of Organic Contaminants

AbstractNanodiamonds exhibit great potential as green catalysts for remediation of organic contaminants. However, the specific active site and corresponding oxidative mechanism are unclear, which retard further developments of high‐performance catalysts. Here, an annealing strategy is developed to accurately regulate the content of ketonic carbonyl groups on nanodiamonds; meanwhile other structural characteristics of nanodiamonds remain almost unchanged. The well‐defined nanodiamonds with well‐controlled ketonic carbonyl groups exhibit excellent catalytic activity in activation of peroxymonosulfate for oxidation of organic pollutants. Based on the semi‐quantitative and quantitative correlations of ketonic carbonyl groups and the reaction rate constants, it is conclusively determined that ketonic carbonyl groups are the catalytically active sites. Different from conventional oxidative systems, reactive oxygen species in nanodiamonds@peroxymonosulfate system are revealed to be singlet oxygen with high selectivity, which can effectively oxidize and mineralize the target contaminants. Impressively, the singlet‐oxygen‐mediated oxidation system significantly outperforms the classical radicals‐based oxidation system in remediation of actual wastewater. This work not only provides a valuable insight for the design of new nanocarbon catalysts with abundant active sites but also establishes a very promising catalytic oxidation system for the green remediation of actual contaminated water.

Multi-walled Carbon Nanotubes Reduce Toxicity of Diphenhydramine to Ceriodaphnia dubia in Water and Sediment Exposures.

Multi-walled carbon nanotubes are adsorptive materials that have potential for remediation of organic contaminants in water. Sediment elutriate exposures were undertaken with Ceriodaphnia dubia to compare the toxic effects of diphenhydramine in the presence and absence of sediment and multi-walled carbon nanotubes. In both sediment and solution-only treatments, addition of 0.318mg/g of carbon nanotubes significantly decreased 48-h mortality relative to control, with a 78.7%-90.1% reduction in treatments with nanotube-amended sediment and 40.7%-53.3% reduction in nanotube-amended water exposures. The greatest degree of relative mortality reduction occurred in sediments containing higher levels of natural organic matter, indicating a potential additive effect.

Hydrothermal Carbon-Mediated Fenton-Like Reaction Mechanism in the Degradation of Alachlor: Direct Electron Transfer from Hydrothermal Carbon to Fe(III).

As Fenton systems suffer from the undesirable Fe(III)/Fe(II) cycle, great efforts were made to realize the effective reduction of Fe(III) to Fe(II). The effects of hydrothermal carbon (HTC) on the Fe(III)/H2O2 Fenton-like reaction and the subsequent degradation of alachlor in water was systematically investigated, and the results indicated that HTC could enhance alachlor degradation in Fe(III)/H2O2 by promoting the Fe(III)/Fe(II) cycle via electron transfer from HTC to Fe(III) ions. The apparent alachlor degradation rate constant in the HTC-G/Fe(III)/H2O2 system (7.02 × 10-2 min-1) was about 3 times higher than that in the Fe(III)/H2O2 system (2.25 × 10-2 min-1). The electron spin resonance spectra analysis revealed that HTC consists of abundant carbon-centered persistent free radicals to act as the electron donor. Meanwhile, the hydroxyl groups on the surface of HTC also played an important role in the enhanced alachlor degradation because the decrease in the surface hydroxyl groups on HTC significantly decreased the degradation of alachlor. On the basis of these results, an Fe(III) complex with surface hydroxyl groups on HTC was proposed to favor the electron transfer from the hydroxyl groups to Fe(III), and then, the simultaneously produced Fe(II) could accelerate the catalytic decomposition of H2O2 to facilitate alachlor degradation. These findings shed new light on the possible roles of carbon materials in a natural aquatic environment and provide a new pathway for environmental pollutant control and remediation of organic contaminants by HTC.

Bacterial community structure and functional potential in the northeastern Chukchi Sea

We performed a molecular microbial ecological analysis in the northeastern Chukchi Sea in order to characterize bacterial community structure and genetic potential for biogeochemical cycling and oil biodegradation in a region targeted for oil and gas exploration (Burger lease area). Samples were collected from the surface, middle (20m), and bottom (2–3m above seafloor) of the water column during the open-water season of August and September 2012 at 17 different locations. We determined bacterial community structure with 16S rRNA genes sequencing and detected functional genes, including an array of oil biodegradation and biogeochemical cycling (carbon, nitrogen and phosphorus cycling) genes, using the GeoChip 5.0 microarray, and then correlated molecular data to contextual physical and biogeochemical factors. Bacterial community structure differed significantly by depth (surface water vs. bottom water) and between sampling dates (August vs. September). While the relative abundance of major functional gene categories did not differ with depth, the abundance of individual functional genes for carbon cycling, nitrogen cycling, organic contaminant remediation, phosphorus cycling, sulfur cycling, virulence, and viruses differed between surface and bottom seawater samples. Aerobic oil degradation genes and taxa known to include oil-degrading bacteria were found at all three depths. These findings support previous observations that two different water masses contribute to a stratified water column in the summer open-water season of the Burger lease area, but indicate that potential function is fairly similar with depth despite differences in temperature, water chemistry, bacterial community structure, and individual functional gene alleles.

Variability in carbon isotope fractionation of trichloroethene during degradation by persulfate activated with zero-valent iron: Effects of inorganic anions

Stable carbon isotope analysis has the potential to be used for assessing the performance of in situ remediation of organic contaminants. Successful application of this isotope technique requires understanding the magnitude and variability in carbon isotope fractionation associated with the reactions under consideration. This study investigated the influence of inorganic anions (sulfate, bicarbonate, and chloride) on carbon isotope fractionation of trichloroethene (TCE) during its degradation by persulfate activated with zero-valent iron. The results demonstrated that the significant carbon isotope fractionation (enrichment factors ε ranging from −3.4±0.3 to −4.3±0.3‰) was independent on the zero-iron dosage, sulfate concentration, and bicarbonate concentration. However, the ε values (ranging from −7.0±0.4 to −13.6±1.2‰) were dependent on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during TCE degradation by persulfate activated with zero-valent iron. The dependence of ε values on chloride concentration, indicated that TCE degradation mechanisms may be different from the degradation mechanism caused by sulfate radical (SO4−). Ignoring the effect of chloride on ε value may cause numerous uncertainties in quantitative assessment of the performance of the in situ chemical oxidation (ISCO).

Sulfate radicals induced from peroxymonosulfate by cobalt manganese oxides (CoxMn3−xO4) for Fenton-Like reaction in water

A series of CoxMn3−xO4 particles as Fenton-like solid catalysts were synthesized, and their catalytic performance in oxidative degradation of organic dye compounds in water was investigated. The surface morphology and structure of the CoxMn3−xO4 catalysts were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that, as an oxide composite of Co and Mn elements, CoMn2O4 showed much stronger catalytic activity in peroxymonosulfate (PMS) oxidation than Co3O4, Mn2O3, and their physical mixture. Typically, the uses of 0.02g/dm3 CoMn2O4 and 0.2g/dm3 PMS yielded a nearly complete removal of Rhodamine B (0.03g/dm3) in 80min at 25°C. The efficiency of Rhodamine B decomposition increased with increasing temperature (15–55 °C), but decreased with the increase of fulvic acid concentration (0–0.08g/dm3). Furthermore, CoMn2O4 could maintain its catalytic activity in the repeated batch experiments. Moreover, HO and SO4− radicals participating in the process were evidenced using quenching experiments, and a rational mechanism was proposed. PMS oxidation with CoMn2O4 is an efficient technique for remediation of organic contaminants in wastewater.

Insights into the role of humic acid on Pd-catalytic electro-Fenton transformation of toluene in groundwater.

A recently developed Pd-based electro-Fenton (E-Fenton) process enables efficient in situ remediation of organic contaminants in groundwater. In the process, H2O2, Fe(II), and acidic conditions (~pH 3) are produced in situ to facilitate the decontamination, but the role of ubiquitous natural organic matters (NOM) remain unclear. This study investigated the effect of Aldrich humic acid (HA) on the transformation of toluene by the Pd-based E-Fenton process. At pH 3 with 50 mA current, the presence of HA promoted the efficiency of toluene transformation, with pseudo-first-order rate constants increase from 0.01 to 0.016 as the HA concentration increases from 0 to 20 mg/L. The HA-enhanced toluene transformation was attributed to the accelerated thermal reduction of Fe(III) to Fe(II), which led to production of more hydroxyl radicals. The correlation of the rate constants of toluene transformation and HA decomposition validated hydroxyl radical (·OH) as the predominant reactive species for HA decomposition. The finding of this study highlighted that application of the novel Pd-based E-Fenton process in groundwater remediation may not be concerned by the fouling from humic substances.

Spirodela polyrhiza stimulates the growth of its endophytes but differentially increases their fenpropathrin-degradation capabilities

In situ remediation of organic contaminants via physical, chemical, and biological approaches is a practical technique for cleansing contaminated water and soil. In the present study, we showed that the three bacterial strains Pseudomonas sp. E1, Klebsiella terrigena E42, and Pseudomonas sp. E46, which can infect and colonize the aquatic plant Spirodela polyrhiza, utilize fenpropathrin as the sole carbon source for growth. S. polyrhiza helped enhance fenpropathrin degradation by E46 by 17.5%, only slightly improved fenpropathrin degradation by E42, and had no effect on strain E1. The application of plant exudates and extracts from fenpropathrin-unexposed/induced plants stimulated bacterial growth of the three strains, but resulted in differential fenpropathrin degradation, suggesting that not all plants and their endophytic bacteria are suitable for coupling phytoremediation and microbial-remediation. Moreover, addition of soil sediments to a microcosm not only stimulated the growth of strain E46 but also increased the rate of fenpropathrin degradation.

Fotocatálise do azul de metileno na presença de óxido de bismuto sob irradiação de luz UV e solar

Bismuth oxide (Bi 2 O 3 ), an n-type semiconductor has been satisfactorily investigated for photocatalytic organic contaminant remediation . The Bi 2 O 3 w as prepared by solution combustion synthesis (SCS) using as the oxidizing bismuth nitrate in acidic medium and urea as fuel. The influence of the type of synthesis on the photocatalytic properties of the oxide formed was investigated by XRD. From the diffractograms was verified that the materials obtained are predominantly of Bi 2 O 3 crystals, it is possible to identify a sample with two crystalline phases, mono clinic ( ? - Bi 2 O 3 ) and tetragonal ( ? - Bi 2 O 3 ), and the other with only the monoclinic ( ? - Bi 2 O 3 ). The two-phase oxide showed higher photocatalytic activity for discoloration of methylene blue under UV irradiation (60.59%) and under sunlight (61.64%) in 664 nm, followed kinetic law of pseudo-first order.

Permanganate diffusion and reaction in sedimentary rocks

In situ chemical oxidation using permanganate has frequently been used to treat chlorinated solvents in fractured bedrock aquifers. However, in systems where matrix back-diffusion is an important process, the ability of the oxidant to migrate and treat target contaminants within the rock matrix will likely determine the overall effectiveness of this remedial approach. In this study, a series of diffusion experiments were performed to measure the permanganate diffusion and reaction in four different types of sedimentary rocks (dark gray mudstone, light gray mudstone, red sandstone, and tan sandstone). Results showed that, within the experimental time frame (~2 months), oxidant migration into the rock was limited to distances less than 500 μm. The observed diffusivities for permanganate into the rock matrices ranged from 5.3 × 10(-13) to 1.3 × 10(-11) cm(2)/s. These values were reasonably predicted by accounting for both the rock oxidant demand and the effective diffusivity of the rock. Various Mn minerals formed as surface coatings from reduction of permanganate coupled with oxidation of total organic carbon (TOC), and the nature of the formed Mn minerals was dependent upon the rock type. Post-treatment tracer testing showed that these Mn mineral coatings had a negligible impact on diffusion through the rock. Overall, our results showed that the extent of permanganate diffusion and reaction depended on rock properties, including porosity, mineralogy, and organic carbon. These results have important implications for our understanding of long-term organic contaminant remediation in sedimentary rocks using permanganate.

Secondary plant metabolites and root exudates: guiding tools for polychlorinated biphenyl biodegradation

Synthetic organic compounds are hallmark of modern society. They are ubiquitous ranging from home, workplace to agriculture industry, which leads to their non-judicious dispensing into environment. Unfortunately most of them, especially polychlorinated biphenyls (PCBs), are deemed as persistent organic pollutants posing serious health risks to human. Hence, there is an alarming need of phasing out these chemicals and remediating contaminated sites in eco-friendly manner. Phytoremediation has emerged as a highly promising approach which capitalizes on plants and their associated microorganisms for removal of pollutants from targeted sites. Plant root exudations and secondary metabolites efficiently orchestrate selective recruitment of potential PCB-degrading microbial consortia within the rhizosphere and inside plant tissues. Structural analogy between organic contaminants and secondary plant metabolites (SPMEs) renders possible uptake and subsequent degradation of pollutants by microorganisms. Present review is focused on potential role of plant root exudates and SPMEs in structuring and orchestrating remediation of PCBs within rhizosphere and inside plant tissues. Also, recent developments in tools and techniques to study remediation of organic contaminants with special reference to PCBs are addressed.

Treatment of a Trichloroethylene Source Zone using Persulfate Activated by an Emplaced Nano-Pd–Fe0 Zone

Recently, metal nanoparticles have attracted attention as promising peroxygen activators for the rapid and effective remediation of organic contaminants. In this work, a one-dimensional physical model experiment was designed to investigate the mobility of the metal nanoparticles in porous media and the potential use of metal nanoparticles as peroxygen activators for in situ treatment of source zones. We found that our synthesized nano-Pd–Fe0 particles were mobile in a non-geological porous medium and relatively immobile in a geological porous medium. In addition, we observed that iron-based bimetallic nanoparticles were able to remain in suspension in an ideal aqueous system much longer (>6 weeks) than iron-based monometallic nanoparticles (<1 h). To overcome the nano-Pd–Fe0 particle delivery issue in geological porous media, an activation zone approach was adopted. Nano-Pd–Fe0 particles were injected in order to create a zone to activate persulfate for the treatment of a trichloroethylene source zone. Trichloroethylene mass destruction was only 9 % higher in the nano-Pd–Fe0 activated persulfate system compared to the non-activated persulfate system as revealed by a short-duration chloride concentration spike in the effluent. In addition, the nano-Pd–Fe0 activation zone was rapidly deactivated after being exposed to persulfate as visually observed by a color change, indicating that the longevity of the activation zone is limited.

Steam and air co-injection in removing residual TCE in unsaturated layered sandy porous media

Steam and air co-injection is a promising technique for volatile and semi-volatile organic contaminant remediation in heterogeneous porous media. In this study, removal of trichloroethene (TCE) with steam-air co-injection was investigated through a series of 2D sandbox experiments with different layered sand structures, and through numerical simulations. The results show that a layered structure with coarse sand, in which steam and air convection are relatively rapid, resulted in a higher removal rate and a larger removal ratio than those observed in an experiment using finer sand; however, the difference was not significant, and the removal ratios from three experiments ranged from 85% to 94%. Slight downward movement of TCE was observed for Experiment 1 (TCE initially in a fine sand zone encased in a coarse sand), while no such movement was observed for Experiment 2 (TCE initially in two fine sand layers encased in a coarse sand) or 3 (TCE initially in a silty sand zone encased in a coarse sand). Simulations show accumulation of TCE at the interface of the layered sands, which indicates a capillary barrier effect in restraining the downward movement of TCE. This effect is illustrated further by a numerical experiment with homogeneous coarse sand, in which continuous downward TCE movement to the bottom of the sandbox was simulated. Another numerical experiment with higher water saturation was also conducted. The results illustrate a complicated influence of water saturation on TCE removal in a layered sand structure.