Benzene, Toluene, Ethylbenzene And Xylene Removal Research Articles

Fly ash-based zeolitic materials of different surface chemistry and texture: Insight into adsorption performance and mechanisms of aqueous BTEX removal

Water contamination caused by anthropogenic, and unforecasted release of BTEX (benzene, toluene, ethylbenzene and xylene) compounds threatens the quality and integrity of aquatic ecosystems. BTEX sorption with novel materials characterized by increased hydrophobicity and stability has been proposed to overcome such contamination. This study aimed to investigate the whole array of hydrothermally synthesized zeolitic materials exhibiting different properties, as well as zeolite/carbon and zeolite/vermiculite composites, to analyse their potential in removing aqueous BTEX. Various parameters and experimental conditions, including the type of volatile organic compounds (VOCs), initial concentration, BTEX coexistence, and increased solution salinity, were studied to verify the applicability of the derived materials. The adsorption capacity of the materials and their governing removal mechanisms were additionally elucidated. The primary removal mechanism involved partitioning on unburned carbon residues, which was observed in zeolite/carbon composites showing the highest BTEX removal efficiency. NaA-zeolite/carbon composite was the most effective in removal of BTEX, with the removal capacity of 15.36 mg/g towards p-xylene. Moreover, the increased salinity of the BTEX solution affects adsorption performance for polar adsorbates, irrespectively of the applied zeolite/carbon composite. Fly-ash (FA) and high-carbon fly-ash (HCFA) were successfully valorised into products with better textural features. These products may effectively tackle organic water pollution caused by VOCs under near-real-life conditions.

Removal of BTEX (Benzene, Toluene, Ethyl benzene and Xylene) from aqueous solutions using surface-modified zeolite

<p>BTEX, also known as benzene, toluene, ethyl benzene, and xylene, is a common gasoline oxygenate. The contamination of groundwater and surface water with BTEX and its primary breakdown product has drawn a lot of attention. However, surface-modified zeolite's sorption mechanisms and affinity for BTEX can be employed to potentially remove these toxins from water. Tert-butyl alcohol (TBA) was utilized to alter the morphology of the adsorbent. Based on the findings, it can be concluded that zeolites have a greater capability for removing emerging chemicals. Some of the emerging compounds' relatively large dimensions limit their natural ability to lower values. Gas chromatography was used to determine the BTEX concentration decrease range. The Yoon-Nelson and Adams-Bohart model's use of mathematical modelling to determine the efficacy of the column's adsorption. The model with the highest R2 values for characterizing equilibrium isotherm data describes equilibrium adsorption data. To gain an understanding of the shape, pore structure, and active sites, the characterisation is concentrated on quantitative analysis using XRD, qualitative analysis using FTIR, and optical study using SEM.</p>

Assessment of the improved performance of magnetite-modified vermiculite in the reduction of BTEX and metals, as well as toxicity in petroleum-produced water

Petroleum-produced water has raised considerable environmental concerns due to the large amount of contaminants-containing wastewater, generated during petrol and gas extraction. The present work proposes for the first time the use of vermiculite modified by magnetite (Fe3O4) nanoparticles (VMT-mag) as adsorbent for the extraction of metals and BTEX (benzene, toluene, ethylbenzene, and xylene) pollutants and toxicity reduction. Thermally-treated vermiculite was modified by Fe3O4 nanoparticles of 20 nm, which were strongly adhered to the surface, contributing to the magnetization of the material and adsorption of the metals. A 5 min exposure of wastewater to VMT-mag at 15 mg mL−1 led to the removal of 93 % of dissolved organic carbon, 85 % of BTEX compounds, and a reduction of 30–87% of metals (Ba, Al, Ag, Hg and Pb) at low concentration. An investigation was also conducted regarding the efficiency of VMT-mag in reducing toxicity via toxicity assays using the water flea Daphnia similis (ABTN NBR 12713 protocol); the results showed a reduction of Lethal Concentration at 50 % death (LC50) from 5.80 (v/v) to 13.3 % (v/v), respectively, for the samples before and after treatment. The findings show that the application of the proposed VMT-mag can lead to a significant reduction of toxicity and the removal of BTEX and metals in petroleum-produced water.

Remediation of BTEX plume in a continuous flow model using zeolite-PRB

Adsorption is a well-known phenomenon that causes the remediation of BTEX (Benzene, Toluene, Ethylbenzene, and Xylene). Zeolite is typically useful for the removal of BTEX from groundwater. In this study, the migration of the BTEX plume was investigated in a bench-scale tank model as a shallow aquifer. The objective of this research was to analyze the performance of a natural zeolite in-situ PRB remediation technique. Natural zeolite was applied as a physical permeable reactive barrier. In the first part of the experiment, 40 ml of BTEX as a contaminant was injected at the injection point (BI) into the sand tank. Samples were taken periodically via 14 boreholes for BTEX test for 23 days and analyzed using a GC-FID instrument. The results indicated high removal rates of BTEX by passing through the zeolite barrier. Zeolite barrier reduced the BTEX concentration up to 90% of the initial value. However, the barrier efficiency started to decrease after 132 h since pollution injection reached a minimum amount (%53 of the initial value) due to occupying the free space and grain pore where BTEX was adsorbed onto the surface of zeolite, thereby decreasing the barrier efficiency.

Toxicity removal by Daphinia similis assay in BTEX contaminated groundwater using nanometric TiO2/ZrO2 film and black light

In this work, a photocatalytic tubular reactor, with a nanometric TiO2/ZrO2 film, immobilized on glass substrate, was developed in order to investigate the degradation of volatile organic compounds, such as, benzene, toluene, ethylbenzene and xylene (BTEX ) in groundwater sample, under black light irradiation (365nm). The BTEX compound were determined by solid phase microextraction (SPME) technique and analyzed by Gas Chromatography - Ionization Flame Detection (CG-FID). The efficiency of photocatalytic process was evaluated by determination of BTEX removal and toxicity, using Daphnia similis as organism-test. The influence of the initial concentration of BTEX in the degradation process was investigated. The degradation process of sample groundwater contaminated with BTEX (145μg/L) from gasoline, resulted in 90% of efficiency after 120 minutes of treatment. The toxicity (EC50-48 h) of the groundwater sample to Daphnia similis was 14.1% (10.5-19.0) for untreated samples. After 30 min of treatment, the EC50-48 h was of 84.3 (71-100%). The benzene efficiency removal was reduced in function of the increase of its initial concentrations that observation was not found for the other compounds studied.

Investigation of BTEX Adsorption on Carbon Nanotubes Cartridges from Air Samples

The volatile organic compounds (VOCs) contribute to serious air pollution problems in Viet Nam. Many studies have investigated in air quality monitoring and treatment, in order to determine the average concentrations of Benzene, Toluene, Ethylbenzene and Xylene (BTEX). Carbon nanotubes (CNTs) have been widely used as adsorbent in environmental treatment, especially for VOCs. This paper aims to determine the adsorption capacity of multiwalled carbon nanotubes for removal of BTEX from air samples. In preliminary study, the effects of various parameters during adsorption experiments were monitored such as flow rate, temperature and BTEX concentrations in air samples. The equipment for BTEX removal was developed by our research team consisting of filter columns, air sample bags, adsorption cartridge. The air samples containing BTEX were conducted directly through a cartridge packed with adsorbent. The adsorption experiments were carried out under various operating conditions such as temperature (30 - 40°C), gas concentration (0,57 - 4,77 mg/L) and the gas flow rate (10 - 90 mL/min). In addition, isotherm studies of CNTs for BTEX removal were achieved by using Langmuir and Freundlich models. The results showed that the experimental parameters were optimized at a flow rate of 30 mL/min and an ambient temperature at 30°C. The adsorption capacity of CNTs increased proportionally with BTEX concentrations. The specific affinity of CNTs for BTEX from air samples was in order of X > E > T > B. The experimental isotherm data were well-fit with the Langmuir model for Benzene and Xylene removal, and the Freundlich model for Toluene and Ethylbenzene adsorption. The CNTs presented highly potential application for BTEX adsorption thanks to their microporous structure and high surface area.

Simultaneous removal of benzene, toluene, ethylbenzene and xylene (BTEX) by CaO2 based Fenton system: Enhanced degradation by chelating agents

Most of the calcium peroxide (CaO2) based Fenton oxidation studies focus on the individual pollutant degradation. In this study, the simultaneous oxidation of benzene, toluene, ethylbenzene, and xylene (denoted as BTEX) by CaO2 based Fenton system was demonstrated. It was observed that BTEX removal increased with increasing molar ratios of CaO2/Fe(II)/BTEX. In the case of CaO2/Fe(II)/BTEX molar ratio of 5/5/1, BTEX removal were 35% in the ultrapure water and 15% in the actual groundwater. In the case of CaO2/Fe(II)/BTEX molar ratio of 40/40/1, BTEX removal were elevated to 98% in the ultrapure water and 88% in the actual groundwater. Chelating Fe(II) agents, such as citric acid (CA), oxalic acid (OA), and glutamic acid (GA), significantly enhanced the destruction of BTEX. When the molar ratio of Fe(II)/CA, Fe(II)/GA, and Fe(II)/OA was 10/20 while fixing CaO2/Fe(II)/BTEX molar ratio of 10/10/1, the enhancements in BTEX removal were 60%, 32%, and 72%, respectively. In terms of BTEX removal, OA chelated Fe(II) was demonstrated to be most effective in the CaO2/Fe(II)/BTEX system. Based on TOC analysis, the transformation effect was confirmed. The transformation products of BTEX were determined and oxidation pathways were proposed, in which HO was mostly responsible to the parent compounds mineralization.

BTEX removal by fungi in continuous flow aerobic reactor

ABSTRACT The removal of benzene, toluene, ethylbenzene and xylene (BTEX) compounds by Aspergillus niger AN 400 was studied in a continuous flow reactor which was operated at hydraulic retention time (HRT) of 12 hours evaluate the efficiency of the system in the bioremediation of water polluted with gasoline in the presence (Step 1) and absence (Step 2) of 0.5 g.L-1 glucose. In the first step it was also studied the influence of the addition of nutrients in the influent on the efficiency of the process. The addition of nutrients was beneficial to the process and, with the removal of glucose, the efficiency was maintained due to the use of ethanol - which is a Brazilian gasoline constituent (25%) - and was used as co-substrate. Both ethanol and glucose are more easily assimilated carbon and energy sources for fungi and were used as co-substrate in the degradation of BTEX. Thus, in Step 2, when only ethanol was in the biomedia, averages percentage of 88% for benzene, 90% in toluene, 90% ethylbenzene and 91% for meta, para and ortho-xylene (m, p and o-xylene) were reached, with the formation of phenolic by-products in between. The fungal population in the middle prevailed throughout the operation of the reactor.

Efficient removal of BTEX from aqueous solution by β-cyclodextrin modified poly(butyl methacrylate) resin

Abstract Efficient removal of benzene, toluene, ethylbenzene and xylene (BTEX) from aqueous solution has been studied with a β-cyclodextrin (β-CD) modified poly(butyl methacrylate) resin (poly(BMA-Co-CD). The effects of the amount of β-CD in poly(BMA-Co-CD), pH, ionic strength, contact time, and temperature of the solution on the adsorption of BTEX were investigated in details. Adsorption data were fitted very well to Freundlich model. The results showed that the β-CD groups on the resin played a significant role for adsorption of BTEX, and quantum chemical calculation confirmed the experimental results. The resin exhibits good performance e.g. high adsorption capacity, high separation efficiency, and easy regeneration.

Experimental treatment of a refinery waste air stream, for BTEX removal, by water scrubbing and biotrickling on a bed of Mitilus edulis shells

The paper presents the results of a two-stage pilot plant for the removal of benzene, toluene, ethylbenzene and xylene (BTEX) from a waste air stream of a refinery wastewater treatment plant (WWTP). The pilot plant consisted of a water scrubber followed by a biotrickling filter (BTF). The exhausted air was drawn from the main works of the WWTP in order to prevent the free migration to the atmosphere of these volatile hazardous contaminants. Concentrations were detected at average values of 12.4 mg Nm−3 for benzene, 11.1 mg Nm−3 for toluene, 2.7 mg Nm−3 for ethylbenzene and 9.5 mg Nm−3 for xylene, with considerable fluctuation mainly for benzene and toluene (peak concentrations of 56.8 and 55.0 mg Nm−3, respectively). The two treatment stages proved to play an effective complementary task: the water scrubber demonstrated the ability to remove the concentration peaks, whereas the BTF was effective as a polishing stage. The overall average removal efficiency achieved was 94.8% while the scrubber and BTF elimination capacity were 37.8 and 15.6 g BTEX d−1 m−3, respectively. This result has led to outlet average concentrations of 1.02, 0.25, 0.32 and 0.26 mg Nm−3 for benzene, toluene, ethylbenzene and xylene, respectively. The paper also compares these final concentrations with toxic and odour threshold concentrations.

Isolation of a BTEX-degrading bacterium, Janibacter sp. SB2, from a sea-tidal flat and optimization of biodegradation conditions

An enrichment culture was established using seawater containing BTEX (benzene, toluene, ethylbenzene and xylene) compounds to isolate a BTEX-degrading bacterium from contaminated sea-tidal flat. The enriched microbial communities were characterized by 16S rRNA-based DGGE profiling, which indicated that a Janibacter species was dominant during the enrichment. Strain SB2, corresponding to the major band and able to degrade all BTEX compounds, was isolated and characterized. NH4Cl, NaH2PO4, cell mass and BTEX concentrations were used as independent variables to optimize the degradation of BTEX by strain SB2 in a tidal flat and a statistically significant (R(2)=0.8933, p<0.0001) quadratic polynomial mathematical model was suggested. For the initial concentration of 240 mg/L BTEX in a slurry system containing 3.0×10(7) cells/L, 45.5% BTEX removal was observed under the optimum condition of NH4Cl and NaH2PO4, while 32.2% BTEX removal was observed under the untreated condition of NH4Cl and NaH2PO4.

Assessment of ability of three chemical oxidants to remove hydrocarbons from soils polluted by Bonny Light crude oil.

Three prominent hydrocarbon groups found in crude oil- Polycyclic Aromatic Hydrocarbon (PAH);Benzene,Toluene,Ethylbenzene and Xylene(BTEX) and Total Petroleum hydrocarbon(TPH) were used to study the ability of three chemical oxidants-Fenton’s reagent, Potassium permanganate, and Potassium persulfate to degrade hydrocarbons in crude oil inundated soils. This was done by spiking soil samples with Bonny light crude oil and subsequently treating the mixture with the different chemical oxidants at acidic, neutral and basic pH media for each of the oxidants. Oil extracts from the treated and untreated soil samples were later analyzed for the three hydrocarbon groups using a gas chromatograph (GC). Treatment with Fenton’s reagent proved very efficient in the removal of the hydrocarbons especially at the acidic pH with some components of TPH experiencing complete disappearance. Also the four ringed-PAHs were depleted more than the three ringed- ones at the indicated pHs. For the treatment with potassium persulfate, while the oxidant was good in the removal of BTEX at the different pHs, it was found to be very inefficient for the removal of PAHs. Generally, Four and five ringed–PAHs were degraded more than the three and two ringed-PAHs, an indication that degradation of PAHs by oxidants may be a function of hydrocarbon structure. Treatment with potassium permanganate was found to be pH dependent with most of the depletions occurring at acidic pH. Even though potassium permanganate was not as good as the other oxidants in the removal of aliphatic hydrocarbons(TPH), it was found to be effective in the removal of aromatic hydrocarbon(BTEX and PAH). Also the four ringed-PAHs such as pyrene, benzoanthracene, and chrysene were seriously attacked at all pHs. BTEX was also attacked more at acidic pH with above 90% removal at the acidic pH.

Comparison of the efficiencies of modified clay with polyethylene glycol and tetradecyl trimethyl ammonium bromide for BTEX removal

Aims: In this study, the effectiveness of modified clay [montmorillonite (Mt)] with polyethylene glycol (PWG) and tetradecyl trimethyl ammonium bromide (TTAB) on the benzene, toluene, ethylbenzene and xylene (BTEX) removal from aqueous solution was investigated.Materials and Methods: The batch adsorption experiments including surfactant loading rates (0.2-4 cation exchange capacity [CEC] of the clay), contact time (0-24 h), pH (4-12) and adsorbate concentration (10-200 mg/L) were conducted at room temperature (25°C) with 100 mL of BTEX solution into a 200-mL conical flask and mixed by an orbital shaker (250 rpm for 24 h). Results: It was found that the optimum adsorption condition obtains for the surfactant loading rate of 200% clay CEC for both the adsorbents at the contact time of 24 h. The sorption capacity of BTEX by both the adsorbents was in order of benzene toluene ethylbenzene xylene. The results of both the adsorbents also showed that the pseudo-second-order kinetic model and Freundlich isotherm model fitted the experimental data better than of other kinetic and isotherm models, respectively.Conclusion: The adsorption capacity of TTAB-Mt (22.11 mg/g) was slightly higher than PEG-Mt (18.77 mg/g). With regard to lower toxic effects and lower cost of nonionic surfactants than the cationic type, using the nonionic modified Mt is preferred than cationic modified Mt for the removal of BTEX from aqueous solution.

Comparison of the efficiencies of modified clay with polyethylene glycol and tetradecyl trimethyl ammonium bromide for BTEX removal

Aims: In this study, the effectiveness of modified clay [montmorillonite (Mt)] with polyethylene glycol (PWG) and tetradecyl trimethyl ammonium bromide (TTAB) on the benzene, toluene, ethylbenzene and xylene (BTEX) removal from aqueous solution was investigated.Materials and Methods: The batch adsorption experiments including surfactant loading rates (0.2-4 cation exchange capacity [CEC] of the clay), contact time (0-24 h), pH (4-12) and adsorbate concentration (10-200 mg/L) were conducted at room temperature (25°C) with 100 mL of BTEX solution into a 200-mL conical flask and mixed by an orbital shaker (250 rpm for 24 h). Results: It was found that the optimum adsorption condition obtains for the surfactant loading rate of 200% clay CEC for both the adsorbents at the contact time of 24 h. The sorption capacity of BTEX by both the adsorbents was in order of benzene toluene ethylbenzene xylene. The results of both the adsorbents also showed that the pseudo-second-order kinetic model and Freundlich isotherm model fitted the experimental data better than of other kinetic and isotherm models, respectively.Conclusion: The adsorption capacity of TTAB-Mt (22.11 mg/g) was slightly higher than PEG-Mt (18.77 mg/g). With regard to lower toxic effects and lower cost of nonionic surfactants than the cationic type, using the nonionic modified Mt is preferred than cationic modified Mt for the removal of BTEX from aqueous solution.

Microbial communities and biodegradation in lab-scale BTEX-contaminated groundwater remediation using an oxygen-releasing reactive barrier

To remediate benzene, toluene, ethylbenzene and xylene (BTEX) -contaminated groundwater, a biotreatment process including biostimulation and bioaugmentation was simulated using oxygen-releasing reactive barriers (ORRB) and water with added BTEX in a lab-scale system. The results showed that the capability for BTEX removal decreases in the order of benzene, toluene, p-xylene, ethylbenzene for both added-nitrogen and no-added-nitrogen under BTEX concentrations at 30 mg l(-1). The removal efficiencies in ORRB systems were higher in the nitrogen-added condition for biostimulation compared with the no-nitrogen-added condition; moreover, an increased pattern for removal was observed during the bioaugmentation process. The oxygen content was found to be inversely proportional to the distance from the ORRB, as evidenced by observing that the average bacteria densities were two orders higher when located at 15 cm compared with 30 cm from the ORRB. The microbial community structure was similar in both cases of added-nitrogen and the no-added-nitrogen conditions.

An analysis of synergistic and antagonistic behavior during BTEX removal in batch system using response surface methodology

The removal of benzene, toluene, ethylbenzene and xylene (BTEX) as quaternary mixtures were studied in batch systems using a well-defined mixed microbial culture. The synergistic and antagonistic effects of total BTEX removal (BTEX T-RE) due to the presence of mixed substrate was evaluated through experiments designed by response surface methodology (RSM). The low and high concentrations of individual BTEX were 15 and 75 mg l −1, respectively. The results showed that, increasing the concentration of xylene increased the cumulative BTEX removal (BTEX T-RE), however the reverse occurred when benzene concentrations were increased from low to high levels. A mixed response of increasing and decreasing trend in the BTEX T-RE value was observed when either of toluene or ethylbenzene concentration was increased. When the concentrations of individual BTEX compounds were 30 mg l −1, the BTEX T-RE was about 58%. Complete BTEX T-RE was achieved at optimal BTEX concentrations of 48.1, 45.6, 49.3 and 56.6 mg l −1. The RSM approach was found efficient in explaining the main, squared and interaction effects among individual BTEX concentrations on the BTEX T-RE in a more statistically meaningful way.

BTEX and ethanol removal in horizontal-flow anaerobic immobilized biomass reactor, under denitrifying condition

A denitrifying consortium was used as inoculum to form a biofilm in horizontal-flow anaerobic immobilized biomass reactor. The reactor was fed with hydrocarbons, separately (benzene at 13.8, 15.4 and 26.5 mg/L; toluene 30.8 mg/L; ethylbenzene 33.3 mg/L; xylene 32.1 mg/L), and also with a benzene, toluene, ethylbenzene and xylene (BTEX) mix solution of approximately 5.0 mg/L of each hydrocarbon. The hydrocarbons were dissolved in a solution containing ethanol. Organic matter removal efficiencies were of 95% with benzene and toluene amendments and about 76% with ethylbenzene, m-xylene and the BTEX-mix amendments. Hydrocarbons removal efficiencies were of 99% at an initial concentration of benzene 26.5 mg/L, toluene 30.8 mg/L, m-xylene 32.1 mg/L, ethylbenzene 33.3 mg/L and BTEX 26.5 mg/L. Microbial diversity assessed by a small portion of 16S DNA suggested the predominance of species related to the phylotypes Pseudomonas, Paracoccus and Bacteroides. This system showed to be an alternative to treating wastewater contaminated with nitrate, ethanol and hydrocarbons.

Field investigation of the natural attenuation and intrinsic biodegradation rates at an underground storage tank site

Contamination of groundwater by petroleum-hydrocarbons is a widespread environmental problem. Natural attenuation is a passive remedial approach to degrade and dissipate contaminants in soil and groundwater. In this study, a mass flux approach was used to calculate the contaminant mass reduction and field-scale decay rate at a gasoline spill site. The mass flux technique is accomplished using the differences in total contaminant mass flux across two cross sections of the contaminant plume. The mass flux calculation shows that up to 88% of the dissolved BTEX (benzene, toluene, ethylbenzene, and xylene isomers) removal was observed by natural attenuation processes. The efficiency of intrinsic biodegradation was evaluated by the in situ tracer method. A first-order decay model was applied for the natural attenuation and intrinsic biodegradation rate calculation. Results reveal that intrinsic biodegradation process was the major cause of the BTEX reduction among the natural attenuation mechanisms, and iron reduction was the dominant biodegradation pattern within the plume. Approximately 87% of the BTEX removal was caused by intrinsic biodegradation processes. The calculated BTEX natural attenuation and intrinsic biodegradation rates were 0.24 and 0.16% l/day, respectively. Results suggest that natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the efficiency of the natural attenuation.

Control of BTEX migration by intrinsic bioremediation at a gasoline spill site

A full-scale and detailed intrinsic bioremediation investigation was conducted at a gasoline spill site in Dublin, North Carolina, USA. Due to the appearance of nonaqueous phase liquid (NAPL) hydrocarbons beneath the former spill location, dissolved BTEX (benzene, toluene, ethylbenzene, and xylene isomers) are being continuously released from NAPL into the groundwater with a total BTEX concentration of 60 mg/l. At this spill site, a cropland extends from the mid-plume area to the downgradient edge of the plume. Approximately 15 mg/l of nitrate as nitrogen was detected in groundwater beneath the cropland due to the usage of fertilizer. During the three-year study, the following tasks were conducted: (1) groundwater analysis; (2) microbial enumeration; and (3) mass flux and decay rate calculations. Results show that BTEX concentrations dropped to below detection limit (BDL) before they reached the downgradient monitor, well located 110 m from the spill location. Groundwater and microbial analyses indicate that iron reduction was the dominant biodegradation process between the source and mid-plume area. However, nitrate spill in the cropland area switched the degradation pattern to denitrification, and also changed the preferential removal of certain BTEX components. Under iron-reducing conditions, toluene and o-xylene declined most rapidly followed by m+p-xylene, benzene, and ethylbenzene. Within the denitrifying zone, toluene and m+p-xylene had very rapid degradation, followed by ethylbenzene, o-xylene, and benzene. The mass flux calculations show that up to 93.1% of the BTEX was removed within the iron-reducing zone, and 5.6% of the BTEX was degraded within the nitrate spill zone. The remaining 1.3% was removed within the oxidized zone at the downgradient edge of the plume. Toluene had the highest first-order decay rate (0.16%) detected in the iron-reducing zone and benzene had the lowest rate (0.07%) within the denitrification area. Results reveal that the mixed intrinsic bioremediation processes (iron reduction, denitrification, methanogenesis, aerobic biodegradation) have effectively contained the plume, and iron reduction played an important role on the BTEX removal.