BTEX Degradation Research Articles

Biodegradation of catechol by Pseudomonas fluorescens isolated from petroleum‐impacted soil

AbstractBioremediation strategies have been applied to clean up petroleum hydrocarbon (PHC) impacted sites. Introducing PHC degrading microorganisms (bioaugmentation) and enhancing the in‐situ nutrients availability (biostimulation) are widely used strategies. These strategies can be combined to lead to a better bioremediation performance. In this work, Pseudomonas fluorescens was isolated from a PHC impacted site. Through a 23 factorial design plan, the effect of various combinations of nitrate, sulphate, and phosphate ions on the PHC bioremediation performance by P. fluorescens was investigated using catechol, an essential metabolic intermediate of BTEX degradation, as the sole carbon source. The maximum specific catechol degradation rate was chosen as the response to evaluate the catechol bioremediation performance. The ANOVA results indicated that the presence of nitrate ions alone lowered the maximum specific catechol degradation rate, which can be explained by the accumulation of nitrites and ammonia during the denitrification process by P. fluorescens. It was noted that dosing sulphate ions alone did not affect the bioremediation performance, which indicates P. fluorescens can grow in a sulphur‐limited environment. In contrast, the presence of sulphate and nitrate ions together can lead to a higher specific catechol degradation rate. This may be caused by the presence of sulphate that can suppress the production of nitrites. The importance of phosphate ions on catechol biodegradation was investigated. The absence of phosphate led to incomplete biodegradation. Introducing phosphate ions can accelerate catechol degradation, which can be explained by the secretion of organic acids.

Dynamics of hydrocarbon mineralization characterized by isotopic analysis at a jet-fuel-contaminated site in subtropical climate

Release of benzene, toluene, ethylbenzene, and xylene (BTEX) as components of the light non-aqueous phase liquids (LNAPL) contaminates soil and groundwater. Assessing the mechanisms of degradation and mineralization of BTEX in groundwater helps understand the migration of the dissolved plume, enabling the reduction of risks to humans. Here, we studied the fate of ethylbezene, m,p-xylenes and o-xylenes and the accompanying formation of methane in a Cenozoic lateritic aquifer in Brazil by compound-specific carbon stable isotope analysis (CSIA), to gain insights into the complex dynamics of release and biodegradation of BTEX in the LNAPL source zone. The enrichment of ∂13C in aromatic compounds dissolved in groundwater compared to the corresponding compounds in LNAPL indicate that CSIA can provide valuable information regarding biodegradation. The isotopic analysis of methane provides direct indication of oxidation mediated by aquifer oxygenation. The ∂13C-CO2 values indicate methanogenesis prevailing at the border and aerobic biodegradation in the center of the LNAPL source zone. Importantly, the isotopic results allowed major improvements in the previously developed conceptual model, supporting the existence of oxic and anoxic environments within the LNAPL source zone.

Application of S-doped TiO2 photocatalysts in degradation of BTEX from synthetic surfaces

S-doped anatase TiO2 (average grain size: 20 nm) was synthesized by a hydrothermal treatment, and the crystalline phase and morphology of the as-fabricated materials were characterized with XRD, TEM, and EDX. We investigated the catalytic reactions in a simulated environment (60 L environmental chambers) in tandem with TD-GC-MS determinations. Furthermore, the photocatalytic activity of S-doped TiO2 was evaluated by monitoring the degradation of BTEX from synthetic surfaces, and maximum of 85% degradation rate exhibited for the S-doped TiO2 under visible light after irradiation for 1 h.

Degradation of BTEX mixture by a new Pseudomonas putida strain: role of the quorum sensing in the modulation of the upper BTEX oxidative pathway.

A new Pseudomonas putida strain (AQ8) was isolated from a decommissioned oil refinery's soil in Italy and characterized for its ability to degrade BTEX. The draft genome of the new strain was sequenced and annotated for genes that encode enzymes putatively involved in BTEX degradation and quorum sensing. The strain was transformed with a plasmid expressing lactonase, which cleaves the autoinducer quorum sensing signal molecule, the acyl-homoserine lactone, to obtain a quorum sensing minus strain. P. putida AQ8 depleted the 40% on average of all the components of the initial BTEX concentration in 36h. The quorum sensing minus strain, in the same time interval, depleted only the 10% of the initial BTEX concentration. The role of quorum sensing in regulating the expression of the annotated benzene/toluene dioxygenase gene (benzA) and biphenyl/toluene/benzene dioxygenase (bphA) genes, which are involved in BTEX degradation, was studied by quantitative RT-real-time quantitative (q)PCR analysis. The qPCR data showed decreased levels of expression of the benzA and bphA genes in the quorum sensing minus strain. Our results showed, for the first time, quorum sensing modulation of the level of transcription of dioxygenase genes in the upper BTEX oxidation pathway.

Enhanced visible light photocatalysis with E‐waste‐based V2O5/zinc–ferrite: BTEX degradation and mechanism

AbstractBACKGROUNDBTEX removal is attracting increased attention owing to the detrimental impacts caused to human health, the foremost being neurological impairments. Thus, this study intended to assess the efficiency of zinc–ferrite/V2O5 (ZFV) nanocomposite for photocatalytic degradation of BTEX isomers in aqueous solution. Furthermore, the developed catalyst was magnetically separable, which may reduce the ecological impacts of the catalyst.RESULTSThe ZFV nanocomposite was prepared by a solvothermal process using V2O5 (extracted from treated E‐waste) and zinc–ferrite (synthesized through a chemical co‐precipitation method). The integration of elements in the ZFV nanocomposite was confirmed using powder X‐ray diffraction, Fourier transform infrared, Raman, diffuse reflectance and electrochemical impedance spectroscopies and scanning electron microscopy. Maximum BTEX degradation of 95% was achieved at 50 mg L−1 initial BTEX concentration, 0.50 g L−1 catalyst and pH 3. A minor decrease in the degradation efficiency (10%) of the catalyst was observed at the fifth cycle. The presence of H2O2 increased the degradation efficiency to 98% owing to the prevention of electron–hole recombination, while NaCl (60%), Na2CO3 (63%), NaNO3 (80%) and Na2SO4 (72%) decreased the degradation efficiency due to their hydroxyl scavenging properties. The degradation pathway was elucidated using gas chromatography with mass spectral studies.CONCLUSIONSThe findings of the present study relating to BTEX degradation using the magnetic ZFV nanocomposite and the degradation mechanism throw light on the environmental applications of the ZFV composite. The composite could be an alternative for the remediation of BTEX‐contaminated wastewaters. © 2020 Society of Chemical Industry

Enriching indigenous microbial consortia as a promising strategy for xenobiotics’ cleanup

Enrichment of indigenous microbial consortia from contaminated environments is very crucial for developing bioremediation strategies. In this study, xenobiotic degrading consortia from seven diverse contaminated soils or sediments were enriched under aerobic conditions for over a year using different xenobiotics, to develop robust consortia for xenobiotic bioremediation. The 16S rRNA gene amplicon sequencing revealed that enriched prokaryotic consortia were predominated by Proteobacteria (84.7%), whereas the xenobiotic degraders varied primarily dependent on contaminants, accounting for 91.1% and 79.4% of variance at the phylum and genus level, respectively, with Pseudomonas spp. (Gammaproteobacteria) and Paracoccus spp. (Alphaproteobacteria) dominating treatments in the presence and absence of BTEX, respectively. The origin of the microbial source also significantly affects degraders community composition but only explained a small proportion of the variance (4.7% phylum and 7.0% genus). Significant BTEX biodegradation occurred in 7 days of incubation with the enriched indigenous consortia, and the results suggest that Pseudomonas spp. are the major aerobic BTEX degraders. This conclusion is supported by the metabolic potential of BTEX for those isolated Pseudomonas strains in the literature. Taken together, these results provide evidence about the primary influence of contaminants on the selection of xenobiotic degrading prokaryotic communities and highlight a promising strategy through bioaugmentation for the cleanup of xenobiotic contaminated sites.

Efficient Photoelectrocatalytic Degradation of BTEX Using TiO2/CuO/Cu2O Nanorod-Array Film as the Photoanode and MWCNT/GO/Graphite Felt as the Photocathode

Wastewater treatment challenges by conventional methods have necessitated the need for alternative/complementary methods that are environmentally safe and efficient especially towards recalcitrant organic pollutants. In this regard, a novel highly active visible-light responsive photoanode with the ternary hybrid CuO/Cu2O/TiO2 nanorods array film is proposed to enhance electron transfer in the photoelectrocatalytic (PEC) degradation of BTEX (benzene, toluene, ethyl benzene, and xylenes) by combining with MWCNT/GO/GF cathode. Structural, morphological, optical, electrochemical, and elemental analysis of proposed electrodes is investigated in detail. Response surface methodology (RSM) comprising of full-factorial central composite design (CCD) with five factors and five levels has been used to examine the effects of different operating parameters such as electrode distance, current density, treatment time (t), solution pH, and conductivity in a PEC batch reactor. BTEX mineralization in aqueous solution was examined with multiple responses such as chemical oxygen demand (COD) and specific energy consumption. During multiple response optimization, the desirability function approach was employed to concurrently maximize COD removal and minimize energy consumption. At the optimum condition, 81.3% COD removal and 9.5 kWh/kg of COD removed were observed. The photoelectrocatalytic oxidization mechanism of BTEX with proposed anode and cathode was discussed, then the possible degradation pathway of BTEX identified using GC–MS.

Remediation of BTEX and Cr(VI) contamination in soil using bioelectrochemical system-an eco-friendly approach.

Soil contamination with benzene, toluene, ethylbenzene and xylene isomers (BTEX) has raised increasing concern because of its high solubility in water and toxicity to biotic communities. This study aims at investigating the process and prospects of deploying bioelectrochemical system (BES) for the removal of BTEX from artificially contaminated soil using Pseudomonas putida YNS1, alongside the reduction of hexavalent chromium (Cr(VI)). The BES was setup with desired operating conditions: initial concentration of BTEX (50-400mg/L in 100mL of sterilized water), pH (4-10) and applied potential voltage (0.6-1.2V) with 10μL log-phase culture along with the addition of Cr(VI) (10mg/L). Samples were collected at regular intervals and analysed for BTEX degradation using gas chromatography and Cr(VI) reduction using UV-Vis spectrophotometer. Under optimized conditions (initial BTEX concentration, 200mg/L; pH7; and applied voltage 0.8V with Cr(VI) of 10mg/L), 92% of BTEX was degraded and 90% Cr(VI) was reduced from the contaminated soil. The intermediates produced during degradation were analysed through gas chromatography-flame ionization detector (GC-FID), and the possible degradation pathway was elucidated. The results indicated that BES could be effective for simultaneous degradation of BTEX along with Cr(VI) reduction.

Heterogeneous Electro-Fenton Process by MWCNT-Ce/WO3 Nanocomposite Modified GF Cathode for Catalytic Degradation of BTEX: Process Optimization Using Response Surface Methodology

This study investigates the degradation and mineralization of BTEX by heterogeneous electro-Fenton process using GO/MWCNT/Fe3O4 as a catalyst and MWCNT-Ce/WO3/GF as an electrode. The nanoscale MWCNT-Ce/WO3 composite catalyst was distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. After optimization of pH and time variables, the Box–Behnken experimental design (BBD) and response surface methodology (RSM) were used to design and optimize the performance of proposed system and energy consumption. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.98) and adj-R2 (0.97). The significance levels of linear and interaction effects of the reaction parameters on process efficiency were obtained. Then, the optimization of the working conditions for the design of a sustainable treatment system with optimum efficiency was carried out using a response surface methodology. The experiment carried out in the calculated optimal conditions for the electro-Fenton degradation process (current intensity 300 mA, catalyst dosage of 0.6 g, initial BTEX concentration of 100 ppm, and electrode distance of 1 cm) showed a BTEX removal of 73.2% and energy consumption of 12.3 (kWh/m3) close to the theoretical value predicted by the model 73. 2% and 11.8 (kWh/m3), respectively. Furthermore, the reusability test of GO/MWCNT/Fe3O4 nanocomposite after several cycles confirmed the high catalytic activities of adsorbent. Comparing the proposed system with conventional GF electrode and Fe2+ catalyst showed that modification of cathode and catalyst led to increasing COD removal efficiency by around 36.6 and 31.6%, respectively. The findings of present study revealed that the proposed heterogeneous electro-Fenton process can be utilized as pre-treatment technology to improve the biodegradability and reduce the organic load of wastewater by combine oxidation and coagulation.

Biodegradation of BTEX by indigenous microorganisms isolated from UCG project area, South Sumatra

Recently Indonesia is conducting Underground Coal Gasification (UCG) project in South Sumatra for power generation.The potential of negative impacts from UCG on groundwater and the broader environment can not be ignored since past similar projects were often confronted with pollution isues of BTEX and PAHs due to condensation of tar-loaded gas. This study focuses on finding indigenous microorganisms capable of BTEX degradation and evaluate their biodegradability. Several microorganisms were successfully isolated and screened. Pseudomonas putida and Bacillus cereus were chosen for this bioremediation study since the bacteria were predominant and highly viable on the screening test. The BTEX degradation has been studied in single component using single and mixed bacterial cultures in the concentration range of 250-500 ppm. The experimental results show that biodegradation of BTEX by P. putida ranged from 61.4-70.2% and by B.cereus ranging 63.9-74.7 % at initial BTEX concentration of 500 ppm.Meanwhile, consortium of both isolates has the highest percentage of BTEX biodegradation (67.8-79,8%) during 14 days of retention time.The findings reveal that indigenous bacteria of P. putida dan B. cereus exhibit the potential to be used for decontamination of BTEX as an anticipated mitigation for potential pollution coming from the UCG project.

Genomic Diversity of Two Hydrocarbon-Degrading and Plant Growth-Promoting Pseudomonas Species Isolated from the Oil Field of Bóbrka (Poland).

Hydrocarbon-degrading bacteria are important resources for use in phytoremediation applications. Yet, for many hydrocarbonoclastic strains the genetic information regarding pollutant degradation and detoxification has not been thoroughly revealed. In this study, hydrocarbon-degrading bacteria were isolated from a long-term oil-polluted soil in Bóbrka, Poland. Pseudomonas spp. was the most dominant species. Of all 69 isolated strains tested in the laboratory using qualitative biochemical assays, 61% showed the capability to use diesel as sole carbon source, 33% could produce indole, 19% produced siderophores, 36% produced organic acids, and 54% were capable of producing 1-aminocyclopropane-1-carboxylate (ACC)-deaminase. From all morphologically and genetically different strains, two representative Pseudomonas spp., strain VI4.1 and VI4T1, were selected for genome sequencing. Genomic analyses indicated the presence of the full naphthalene dioxygenase operon (plasmid and chromosomal), of genes involved in the degradation of BTEX compounds (Benzene, Toluene, Ethylbenzene, Xylene) and alkanes (alkB gene) as well as the anthranilate degradation pathway (strain VI4T1) and terephthalate dioxygenase protein (strain VI4.1). Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) analyses confirmed naphthalene and BTEX degradation within seven days. Motility, resistance to abiotic stresses, high and low temperatures, low pH, and salinity were confirmed at the genetic level and experimentally verified. The presence of multiple degradative and plant growth promotion genes, together with the in vitro experimental evidence, indicates the high value of these two strains and their potential use for sustainable site clean-up.

Lab-Scale Biodegradation Study of BTEX under the Unsaturated Condition and Its Effect on Soil Matric Potential

ABSTRACTBenzene, toluene, ethylbenzene, and xylene are collectively known as BTEX which contributes to volatile environmental contaminants. This present study investigates the microbial degradation of BTEX in batch and continuous soil column experiments and its effects on soil matric potential. Batch degradation experiments were performed with different initial concentrations of BTEX using the BTEX tolerant culture isolated from petroleum-contaminated soil. In batch study, the degradation pattern for single substrate showed that xylene was degraded much faster than other compounds followed by ethylbenzene, toluene, and benzene with the highest μmax = 0.140 h−1 during initial substrate concentration of 100 mg L−1. Continuous degradation experiments were performed in a soil column with an inlet concentration of BTEX of about 2000 mg L−1 under unsaturated flow in anaerobic condition. BTEX degradation pattern was studied with time and the matric potential of the soil at different parts along the length of the column were determined at the end of the experiment. In continuous degradation study, BTEX compounds were degraded with different degradation pattern and an increase in soil matric potential was observed with an increase in depth from top to bottom in the column with applied suction head. It was found that column biodegradation contributed to 69.5% of BTEX reduction and the bacterial growth increased the soil matric potential of about 34% on an average along the column height. Therefore, this study proves that it is significant to consider soil matric potential in modeling fate and transport of BTEX in unsaturated soils.

Geochemical conceptual model of BTEX biodegradation in an iron-rich aquifer

A geochemical conceptual model was developed to interpret long-term field monitoring data of the chemical speciation related to BTEX biodegradation in a tropical iron-rich aquifer that was contaminated by a large volume of jet fuel. Biodegradation under dissimilatory iron reduction is widely favored due to the abundance of iron oxides in the sediment. Concomitantly with iron-reduction, the methanogenesis pathway plays an important role in the microbial degradation of BTEX. The conceptual model was proposed to link the geochemical zonation with BTEX mineralization and secondary reactions. The representativeness of the chemical speciation of the studied hydrocarbon-contaminated aquifer is best supported when PCO2 is fixed and dissolved oxygen, potentially present due to mass transfer from entrapped air, is considered in the model. These findings emphasize the need of both constraints to properly interpret BTEX biodegradation in a tropical iron-rich aquifer.

Aerobic Bacterial Degraders With Their Relative Pathways for Efficient Removal of Individual BTEX Compounds

Benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are of great environmental concern due to their toxicity and carcinogenicity. Bacterial removal of BTEX has proven to be highly efficient, cost‐effective, and non‐disruptive, provided that, efficient bacterial degraders are available. The objective of this study, therefore, is to discover aerobic bacterial degraders with their relative pathways that could be employed for the efficient removal of individual BTEX compounds. A total of 22 petroleum hydrocarbon degrading aerobic bacteria from the river water in close vicinity to a petrol refinery were isolated and identified previously. These bacteria were further screened for their potential to degrade individual BTEX compounds. Primary selection of BTEX degraders was carried out by using conventional enrichment culture technique and gas chromatography/mass spectrophotometry (GC/MS) analyses. Out of the 22 isolates, five were found to degrade BTEX efficiently and further characterized through PCR analyses for their initial attack and cleavage genes as well as GC/MS analyses of the intermediate metabolites to decipher the degradation pathways used. The study elucidates new efficient bacterial strains of Acinetobacter calcoaceticus Fe10, Serratia nematodiphila Mn11, Raoultella planticola Ag11, Pseudomonas koreensis Hg11, and Micrococcus luteus Sr11 with their relative pathways for aerobic removal of the individual BTEX compounds.

Study on the Effect of Sulfate on the Degradation of BTEX in Leakage Area of Gasoline by Using Numerical Simulation

In order to explore the migration of sulfate electron acceptors injected into aqueous media, and study the specific attenuation of BTEX with sulfate injecting. In this study, the laboratory sand tank was used for the injecting and natural attenuation monitoring experiments. The combination of MODFLOW and RT3D was used to simulate the attenuation process of sulfate and natural degradation of BTEX. The results showed that the concentration of sulfate in the source area was significantly lower than that of the surrounding area at the 600th day after injected on the 416th day and BTEX concentration also gradually tends to zero. The injection experiments were conducted for a total of 46 days with the injected sulfate quality of 1488.24 g, and the calculated sulfate output of 1320.52 g. It can be seen that the input was significantly higher than the output and the sulfate loss could be judged as acting on Redox reactions .Sulfate promoted the degradation of BTEX. The numerical simulation was carried out for the water flow model and water quality model calibration, the normalized RMS of water flow model and water quality model are 9.8% and 8% respectively, which are less than 10% of the conventional limit. The model can accurately simulate the migration of sulfate and BTEX attenuation and predict the further pollution of BTEX. And can be applied to the actual site contaminated by BTEX that has important practical significance.

Process bioengineering applied to BTEX degradation in microaerobic treatment systems

The effect of different microaeration flow rates and dosing points, and of effluent recirculation, on microaerobic BTEX degradation in an anaerobic bioreactor was assessed. Additionally, a sensitivity and recovery analysis for this system was performed during microaeration failure simulations. Under anaerobic conditions, BTEX removal efficiencies between 55 and 82% were achieved depending on the compound, being benzene the most recalcitrant one. Microaeration (0.5–2.0 mL air min−1) ensured high removal efficiencies (>83%) for all compounds, and the best results were obtained for the flow rate of 1.0 mL air min−1, particularly for benzene, with a 30% increase in its removal efficiency. Effluent recirculation showed to be an important factor to improve mass transfer and, consequently, BTEX removal. Volatilization was negligible even under microaerobic conditions, suggesting that microbial activity was the main removal mechanism. Finally, after microaeration shutdown periods, the bioreactor could recover its prior performance within up to 2 days.

Investigation of photocatalytic degradation of BTEX in produced water using γ-Fe2O3 nanoparticle

Among different methods for produced water treatment, photocatalytic process is an alternative and innovative technology that is more used in water treatment. In this work BTEX was used as an indicator of produced water. γ-Fe2O3 nanoparticles have been synthesized via co-precipitation methods. XRD, DRS, FTIR and SEM techniques have been employed for detecting the particle size, morphology, different functional groups, the optical absorption characteristics and the crystal structure of the synthesized nanoparticle. Experimental tests were designed by the OFAT method. The effective ranges of the main factors on the photocatalytic degradation of BTEX including pH (3–7), catalyst concentration (0–250 mg L−1), UV light intensity (0–100 W) and visible light intensity (0–225 W) were obtained. When maghemite nanoparticles are under visible light and UV light, the best removal efficiency achieved 95% in 5 days and 97% in 90 min, respectively. In addition the photocatalytic process, adsorption and photolysis process of maghemite nanoparticles were studied.

Nanoparticle for degradation of BTEX in produced water; an experimental procedure

BTEX are the most aromatic hydrocarbons in produced water. Due to hazardous effects of BTEX on environment and to human health, different methods were applied for produced water treatment. One of these methods is nanophotocatalytic process. In this paper for the first time, maghemite nanoparticles were used to remove the pollutants. Maghmite was synthesized by wet chemical method as semiconductor photocatalysis. The synthesized nanoparticles were characterized by Diffuse Reflectance Spectroscopy (DRS), X-ray diffraction analysis technique and scanning electron microscope (SEM). The impact of the main factors including pH (3–7), catalyst concentration (0–250 mg/l) and UV light intensity (0–100 W) were studied. Response surface methodology was utilized to apply and optimize the experiments and results. From the analysis of the results the equation of quadratic polynomial model was obtained. R2 and R2adj for the model were 0.94 and 0.88 respectively, which indicate the model matches the experimental data. Outputs reveal that the best removal efficiency of BTEX (82%) was observed in 90 min at pH = 3, nanoparticle concentration = 170 mg/l, and UV light intensity = 100 W.

BTEX degradation by a newly isolated bacterium: Performance, kinetics, and mechanism

A new isolate identified as Rhodococcus sp. ZJUT312 via taxonomic and 16S rRNA analysis was used for the efficient degradation of benzene, toluene, ethylbenzene, and xylene (BTEX). The strain ZJUT312 was able to degrade all the BTEX. Their average biodegradation rates followed the order o-xylene > ethylbenzene > toluene > benzene > m-xylene > p-xylene. The degradation rate of o-xylene reached as high as 0.117 mmol L−1 h−1, which was one to two orders of magnitude higher than that of all other reported o-xylene degrading bacteria. GC-MS analysis revealed that o-xylene degradation pathway mainly proceeded with 2-methylbenzylalcohol as an intermediate and CO2 as a final product. Mass balance analysis of the carbon element indicated that approximately 59% the o-xylene carbons were transferred to cell biomass and about 20% were mineralized into CO2. Furthermore, the o-xylene degradation kinetics fitted well with Haldane's model. The maximum specific degradation rate (0.953 h−1) was approximately 2.25 times higher than the reported data in the literature.

Microbial community of a gasworks aquifer and identification of nitrate-reducing Azoarcus and Georgfuchsia as key players in BTEX degradation

We analyzed a coal tar polluted aquifer of a former gasworks site in Thuringia (Germany) for the presence and function of aromatic compound-degrading bacteria (ACDB) by 16S rRNA Illumina sequencing, bamA clone library sequencing and cultivation attempts. The relative abundance of ACDB was highest close to the source of contamination. Up to 44% of total 16S rRNA sequences were affiliated to ACDB including genera such as Azoarcus, Georgfuchsia, Rhodoferax, Sulfuritalea (all Betaproteobacteria) and Pelotomaculum (Firmicutes). Sequencing of bamA, a functional gene marker for the anaerobic benzoyl-CoA pathway, allowed further insights into electron-accepting processes in the aquifer: bamA sequences of mainly nitrate-reducing Betaproteobacteria were abundant in all groundwater samples, whereas an additional sulfate-reducing and/or fermenting microbial community (Deltaproteobacteria, Firmicutes) was restricted to a highly contaminated, sulfate-depleted groundwater sampling well. By conducting growth experiments with groundwater as inoculum and nitrate as electron acceptor, organisms related to Azoarcus spp. were identified as key players in the degradation of toluene and ethylbenzene. An organism highly related to Georgfuchsia toluolica G5G6 was enriched with p-xylene, a particularly recalcitrant compound. The anaerobic degradation of p-xylene requires a metabolic trait that was not described for members of the genus Georgfuchsia before. In line with this, we were able to identify a putative 4-methylbenzoyl-CoA reductase gene cluster in the respective enrichment culture, which is possibly involved in the anaerobic degradation of p-xylene.