Biodegradation Of Benzene Research Articles

Highly efficient synthetic bacterial consortium for biodegradation of aromatic volatile organic compounds: Behavior and mechanism

Aromatic volatile organic compounds (VOCs) are prevalent pollutants in chemically contaminated sites, posing threats to ecological safety and human health. To address the challenge of achieving low-carbon, low-cost, green, and sustainable in-situ remediation at these sites, a highly efficient synthetic bacterial consortium was constructed for biodegradation of selected pollutants (i.e., benzene, toluene, ethyl benzene, m-xylene, chlorobenzene, p-chlorotoluene, and p-chlorotrifluorotoluene). Under optimized conditions, the consortium achieved a total degradation efficiency of 77%. Biodegradation of benzene, toluene, ethyl benzene, and m-xylene followed first-order kinetics, while p-chlorotoluene and p-chlorotrifluorotoluene followed zero-order kinetics. The mechanisms were analyzed using microbiome technology at genetic, protein, and metabolic levels, identifying key enzymes and differences in protein expression and related metabolites. Carbon dioxide measurements and fluorescence spectrum analysis elucidated the transformation pathways. These findings underscore the consortium’s significant potential for achieving effective, eco-friendly, and sustainable bioremediation of aromatic VOCs in chemically contaminated environments.

A column study: Impact of redox, substrate composition and exposure order on toluene and benzene biodegradation and microbial communities

Aromatic compounds persist as hazardous contaminants in both aquatic and terrestrial environments, needing rapid and effective remediation strategies. This study evaluated toluene and benzene biodegradation under sulfate and nitrate-reducing conditions in column experiments, utilizing aquifer sediments from a contaminated site. Over a period of 36 weeks, four glass columns were operated simultaneously in an alternating flow-batch regime. Each column received either nitrate or sulfate as an electron acceptor while being exposed to different substrate compositions in varied exposure orders. A redox dependent contaminant removal efficiency was observed, with toluene removal efficiency at 81% under sulfate and 55% under nitrate-reducing conditions, and benzene removal efficiency approximately at 44% and 59%, respectively, within 4–6 weeks. The rapid removal under anaerobic conditions was attributed to the alternating flow-batch regime, allowing biomass growth in batch mode, and applying selection pressure to non-specific biodegraders during flow regime. Toluene removal remained unaffected by benzene's presence but exhibited slight inhibition in the presence of an aromatic mixture composed of BTEX, indene, indane, and naphthalene. Benzene removal efficiency dropped to 8% in the presence of toluene but remained unaffected by the mixture. Pre-exposure to a single compound enhanced breakdown efficiency when further faced with a more complex mixture. Additionally, beta-diversity analysis conducted on the four columns revealed distinct microbial community clustering between sulfate and nitrate-reducing conditions, emphasizing the determining role of redox conditions. Findings of this study can be used to develop more effective pollution cleanup strategies, specifically targeting parameters like redox conditions, substrate interactions, and pollution history, thus improving our ability to mitigate contamination across diverse environments.

Shift in Bacterial Community Structure in the Biodegradation of Benzene and Toluene under Sulfate-Reducing Condition.

Groundwater contaminated by benzene and toluene is a common issue, posing a threat to the ecosystems and human health. The removal of benzene and toluene under sulfate-reducing condition is well known, but how the bacterial community shifts during this process remains unclear. This study aims to evaluate the shift in bacterial community structure during the biodegradation of benzene and toluene under sulfate-reducing condition. In this study, groundwater contaminated with benzene and toluene were collected from the field and used to construct three artificial samples: Control (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L, and HgCl2 250 mg/L), S1 (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L), and S2 (benzene 100 mg/L, toluene 2.5 mg/L, sulfate 940 mg/L). The contaminants (benzene and toluene), geochemical parameters (sulfate, ORP, and pH), and bacterial community structure in the artificial samples were monitored over time. By the end of this study (day 90), approximately 99% of benzene and 96% of toluene could be eliminated in both S1 and S2 artificial samples, while in the Control artificial sample the contaminant levels remained unchanged due to microbial inactivation. The richness of bacterial communities initially decreased but subsequently increased over time in both S1 and S2 artificial samples. Under sulfate-reducing condition, key players in benzene and toluene degradation were identified as Pseudomonas, Janthinobacterium, Novosphingobium, Staphylococcus, and Bradyrhizobium. The results could provide scientific basis for remediation and risk management strategies at the benzene and toluene contaminated sites.

In-situ treatment of gaseous benzene in fixed-bed biofilter with polyurethane foam: Functional population response and benzene transformation pathway

Volatile organic compounds emitted from landfills posed adverse effect on health. In this study, gaseous benzene was biologically treated using an in-situ biofilter without air pump. Its performance was investigated and the removal efficiency of benzene reached over 90 %. The decrease in the average benzene concentration was consistent with first-order reaction kinetics. Mycolicibacterium dominated the bacterial consortium (41–57 %) throughout the degradation. Annotation of genes by metagenomic analysis helped to deduce the degradation pathways (benzene degradation, catechol ortho-cleavage and meta-cleavage) and to reveal the contribution of different species to the degradation process. In total, 21 kinds of key genes and 13 enzymes were involved in the three modules of benzene transformation. Mycolicibacter icosiumassiliensis and Sphingobium sp. SCG-1 carried multiple functional genes critically involved in benzene biodegradation. These findings provide technical and theoretical support for the in-situ bioremediation of benzene-contaminated soil and waste gas reduction in landfills.

Synchronous removal of gaseous toluene and benzene and degradation process shifts in microbial fuel cell-biotrickling filter system

Illustrating the biodegradation processes of multi-component volatile organic compounds (VOCs) will expedite the implication of biotechnology in purifying industrial exhaust. Here, performance shifts of microbial fuel cell and biotrickling filter combined system (MFC-BTF) are investigated for removing single and dual components of toluene and benzene. Synchronous removal of toluene (95 %) and benzene (97 %) are achieved by MFC-BTF accompanied with the output current of 0.41 mA. Elevated content of extracellular polymeric substance facilitates the mass transfer of benzene with the presence of toluene. Strains of Bacteroidota, Proteobacteria and Chloroflexi contribute to the removal of dual components VOCs. Empty bed reaction time and the VOCs concentration are the important factors influencing their dissolution in the system. The biodegradation of toluene and benzene proceeds with 2-hydroxymuconic semialdehyde and o-hydroxybenzoic acid as the main intermediates. These results provide a comprehensive understanding of multi-component VOCs removal by MFC-BTF and guide the system design, optimization, and scale-up.

Long‐term evaluation of hydrocarbon degradation rates within the source zone under natural and enhanced attenuation for site closure purposes

AbstractDespite addressing the cleanup of petroleum hydrocarbon contamination plumes in groundwater, challenges with site closure persist due to the ongoing long‐term contaminant release from source zones. Thus, source zone monitoring even in the presence of residual light nonaqueous‐phase liquid (LNAPL) is mandated by many countries' regulatory agencies before site closure. In this study, four independent controlled‐release sites, each containing a particular fraction of ethanol in gasoline, that is, 10%, 24%, 25%, and 85% (v/v), were subjected to monitored natural attenuation (MNA) alone (E24 and E85), and with nitrate (E25) and sulfate (E10) biostimulation at the vicinity of the source zone. To the best of the authors' knowledge, this is the longest controlled gasohol release monitoring study performed to date at the source zone for site closure (nearly 18 years of monitoring). Both natural source zone depletion and biostimulation were found to reduce benzene concentrations to acceptable remediation target levels according to environmental regulatory councils. Benzene biodegradation rates (λs) were one order of magnitude higher than those reported in the literature for diluted concentrations in groundwater plumes. The decay rate of benzene varied between 0.45 and 1.75/year and was strongly influenced by the mass of ethanol. Compared to biostimulation with nitrate (half‐life of 1.52 years), MNA alone resulted in faster benzene removal rates (half‐life of 0.96 years). Anaerobic biostimulation with sulfate had negligible effects on benzene, toluene, ethylbenzene, and xylene (o‐, m‐, and p‐xylene [BTEX]) biodegradation compared to natural attenuation alone. The highest ethanol concentration (E85) led to faster benzene removal (with a half‐life of 0.40 years), which was even higher than MNA under lower ethanol concentrations (E24). Benzene half‐life was 2.2‐fold slower in the site with the lowest ethanol (E10) compared to E85, indicating that the negative effects of ethanol on BTEX biodegradation appeared to be short‐lived and may need to be re‐evaluated over the long term. Benzene decay rates were approximately six times slower in the source zone than the rates obtained for groundwater plumes, emphasizing the importance of targeting the LNAPL after plume retreat. The study's findings can assist practitioners in better predicting the lines of evidence for BTEX bioremediation and remediation cleanup times at a lower cost in the presence of ethanol, as well as providing guidance for determining whether biostimulation is necessary to expedite source zone remediation for site closure.

Mechanisms of benzene and benzo[a]pyrene biodegradation in the individually and mixed contaminated soils

There is a lack of knowledge on the biodegradation mechanisms of benzene and benzo [a]pyrene (BaP), representative compounds of polycyclic aromatic hydrocarbons (PAHs), and benzene, toluene, ethylbenzene, and xylene (BTEX), under individually and mixed contaminated soils. Therefore, a set of microcosm experiments were conducted to explore the influence of benzene and BaP on biodegradation under individual and mixed contaminated condition, and their subsequent influence on native microbial consortium. The results revealed that the total mass loss of benzene was 56.0% under benzene and BaP mixed contamination, which was less than that of individual benzene contamination (78.3%). On the other hand, the mass loss of BaP was slightly boosted to 17.6% under the condition of benzene mixed contamination with BaP from that of individual BaP contamination (14.4%). The significant differences between the microbial and biocide treatments for both benzene and BaP removal demonstrated that microbial degradation played a crucial role in the mass loss for both contaminants. In addition, the microbial analyses revealed that the contamination of benzene played a major role in the fluctuations of microbial compositions under co-contaminated conditions. Rhodococcus, Nocardioides, Gailla, and norank_c_Gitt-GS-136 performed a major role in benzene biodegradation under individual and mixed contaminated conditions while Rhodococcus, Noviherbaspirillum, and Phenylobacterium were highly involved in BaP biodegradation. Moreover, binary benzene and BaP contamination highly reduced the Rhodococcus abundance, indicating the toxic influence of co-contamination on the functional key genus. Enzymatic activities revealed that catalase, lipase, and dehydrogenase activities proliferated while polyphenol oxidase was reduced with contamination compared to the control treatment. These results provided the fundamental information to facilitate the development of more efficient bioremediation strategies, which can be tailored to specific remediation of different contamination scenarios.

Effects of short and long-term thermal exposure on microbial compositions in soils contaminated with mixed benzene and benzo[a]pyrene: A short communication

Polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) are the most persistent and toxic organic contaminants often found co-contaminated in anthropogenic and petrochemical industrial sites. Therefore, an experiment was performed for the safe biodegradation of benzene and benzo[a]pyrene (BaP) through thermally-enhanced biodegradation, and to explore the influence of elevated thermal treatments on microbial diversity and composition. The results revealed that elevated thermal treatments (15 to 45 °C) significantly enhanced the diversity of both bacteria and fungi. The composition analysis revealed that short-term and long-term elevated temperature conditions can directly enhance the specificity of microorganisms that play a crucial role in the biodegradation of benzene and BaP co-contaminated soil. Moreover, the indirect role of elevated temperature conditions on microbial compositions was through the fluctuations of soil properties, especially soil pH, moisture, TOC, potassium, phosphorous, total Fe, Fe(II), and Fe(III). In addition, the correlation analyses revealed that thermal exposure enhances the synergistic association (fungal-fungal, fungal-bacterial, bacterial-bacterial) of microbes to degrade the toxic contaminants and to cope with harsh environmental conditions. These results concluded that the biodegradation of benzene and BaP co-contamination was efficiently enhanced under the thermally-enhanced biodegradation approach and the elevation of temperature can affect the microbial compositions directly via microbial specificity or indirectly by influencing the soil properties.

Biodegradation of Benzene Under Microaerobic Conditions: a Groundwater Microcosm Experiment Combined with a Multiomics Approach and DNA Stable Isotope Probing

Monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX) are the most common contaminants of the groundwater and can easily contaminate drinking water sources due to their relatively high water solubility. Among these compounds, benzene is known to have carcinogenic properties and is considered to be persistent under anoxic conditions. Although deep knowledge was acquired both on the aerobic and anaerobic degradation of benzene in the past three decades, the diversity of those bacteria which are able to degrade it under microaerobic conditions, is still unknown. To come over this limitation aerobic and microaerobic benzene-degrading microcosms were established using groundwater sediment of a BTEX-contaminated site and the evolved bacterial communities were investigated through a polyphasic approach including multiomics analysis and DNA stable isotope probing. The obtained results shed light on the fact that the aerobic and microaerobic benzene-degrading bacterial communities were distinctly different. In the aerobic microcosms members of the genus Pseudomonas overwhelmingly dominated the bacterial communities by showing even 40-50% abundance. In contrast, under microaerobic conditions members of the genera Azovibrio and Malikia dominated the communities, while the abundance of Pseudomonas drastically decreased compared to that of was observable in the aerobic microcosms. Results obtained by the analysis of microcosms spiked with 13C6-benzene confirmed these observations. In heavy DNA fractions obtained from the aerobic microcosms the enrichment of Pseudomonas and Rhizobiaceae-related 16S rRNA gene fragments was observable. At the same time, labelled DNA from the microaerobic microcosms contained mostly Azovibrio and Malikia-related sequences, while the abundance of Pseudomonas 16S rRNA gene sequences was below 2%. Besides, by using metagenomic dataset of a previous microaerobic experiment we managed to reconstruct an Azovibrio genome, in which a complete meta-cleavage pathway for the aerobic degradation of aromatic hydrocarbons was identified. Overall, it can be concluded that under microaerobic conditions members of Comamonadaceae and Rhodocyclaceae can be the key benzene degraders in contaminated subsurface environments.

Anaerobic and microaerobic biodegradation of benzene: Effect of important intermediates

The effect of important intermediates on the anaerobic and microaerobic benzene biodegradation was investigated. An up-flow anaerobic/microaerobic sludge blanket reactor was operated at a hydraulic retention time (HRT) of 24 h and fed with water contaminated with benzene (∼4.2 mg L−1) and ethanol (1 g COD L−1). Initially, reactor operating parameters such as variation of applied flow rates, microaeration application points, and effluent recirculation were studied to optimize microaeration. Secondly, the interference of benzene degradation intermediates (phenol, benzoate, and toluene) was investigated. The addition of low concentrations of oxygen (0.5–2 mL air min−1) ensured high benzene removals (∼76–86 %), with the best obtained for a flow rate of 1 mL of air min−1, for which there was a d% removal increase compared to the anaerobic stage. Although the contact time between the air bubbles was short, the best application point was close to the feed. Effluent recirculation was necessary to maintain good mass transfer and high benzene removal efficiencies. The loss by stripping was considered negligible, even at the microaerobic stages, proving the biological removal of this compound. Finally, the intermediates added to the contaminated water reduced benzene removal, with benzoate being the compound that most negatively influenced the benzene removal process, even under microaerobic conditions. Therefore, it is a key intermediate in the benzene anaerobic and microaerobic biodegradation process.

Thermally enhanced biodegradation of benzo[a]pyrene and benzene co-contaminated soil: Bioavailability and generation of ROS

In this study, a set of comprehensive experiments were conducted to explore the effects of temperature on the biodegradation, bioavailability, and generation of reactive oxygen species (ROS) by thermally enhanced biodegradation (TEB) under benzene and BaP co-contaminated conditions. The biodegradation rates of benzene increased from 57.4% to 88.7% and 84.9%, and the biodegradation efficiency of BaP was enhanced from 15.8% to 34.6% and 28.6%, when the temperature was raised from the ambient temperature of 15 °C to 45 °C and 30 °C, respectively. In addition, the bioavailability analysis results demonstrated that the water- and butanol-extractable BaP increased with elevated temperatures. High enzymatic activities and PAH-RHDα gene in gram-positive bacteria favored the long-term elevated temperatures (30 and 45 °C) compared to gram-negative bacteria. Moreover, ROS species (O2•− and •OH) generation was detected which were scavenged by the increased superoxide dismutase and catalase activities at elevated temperatures. Soil properties (pH, TOC, moisture, total iron, Fe3+, and Fe2+) were affected by the temperature treatments, revealing that metal-organic-associated reactions occurred during the TEB of benzene–BaP co-contamination. The results concluded that biodegradation of benzene–BaP co-contamination was greatly improved at 45 °C and that microbial activities enhanced the biodegradation under TEB via the increased bioavailability and generation and degradation of ROS.

Degradation of benzene in anaerobic groundwater in the typical cold industrial region: Identification, interactions, and optimization of nitrate-/sulfate-reducing assemblages

Nitrate (NO3−) and sulfate (SO42−) are the electron acceptors (EAs) for benzene biodegradation in anaerobic groundwater. The efficiency of benzene biodegradation depends on the strength of the interaction between benzene degradation and EA reduction combinations. However, the interactions are less studied. Hence, the present study focuses on the effect of groundwater EA coexistence on the anaerobic degradation of benzene under cold climate conditions. Herein, response surface methodology (RSM) and artificial neural network (ANN) are used to predict and optimize the EAs (NO3− and SO42−) for the anaerobic degradation of benzene. The root mean square error and correlation coefficient of RSM and ANN fitting models fulfill the accuracy requirements. Experimental results show that NO3− stimulation degrades benzene more significantly than SO42− stimulation. Thus, the coexistence of NO3− and SO42− has a favorable effect on benzene degradation. Besides, the degradation efficiency of benzene is not affected by a single EA, and there is a higher degradation efficiency under the coexistence of two EAs. Furthermore, the optimization model predicts that for 29.93 mg/L benzene concentration in groundwater, the NO3− and SO42− concentrations with high microbial degradation efficiencies are 0.87 mmol/L and 1.12 mmol/L, respectively. In addition, the best degradation efficiencies predicted by the RSM and ANN models are 75.42% and 73.65%, respectively. The RSM model had greater predictive ability than ANN model. Hence, this study provides an idea for the sustainable bioremediation of an aromatic hydrocarbon-contaminated environment where multiple EAs coexist.

Mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX mixed contaminants in soil by native microbial consortium

Despite the co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) in the field, to date, knowledge on the bioremediation of benzene and benzo[a]pyrene (BaP) mixed contaminants is limited. In this study, the mechanisms underlying the biodegradation of benzene and BaP under individual and co-contaminated conditions followed by the enhanced biodegradation using methanol, ethanol, and vegetable oil as biostimulants were investigated. The results demonstrated that the benzene biodegradation was highly reduced under the co-contaminated condition compared to the individual benzene contamination, whereas the BaP biodegradation was slightly enhanced with the co-contamination of benzene. Moreover, biostimulation significantly improved the biodegradation of both contaminants under co-contaminated conditions. A trend of significant reduction in the bioavailable BaP contents was observed in all biostimulant-enhanced groups, implying that the bioavailable BaP was the preferred biodegradable BaP fraction. Furthermore, the enzymatic activity analysis revealed a significant increase in lipase and dehydrogenase (DHA) activities, as well as a reduction in the catalase and polyphenol oxidase, suggesting that the increased hydrolysis of fats and proton transfer, as well as the reduced oxidative stress, contributed to the enhanced benzene and BaP biodegradation in the vegetable oil treatment. In addition, the microbial composition analysis results demonstrated that the enriched functional genera contributed to the increased biodegradation efficiency, and the functional genera in the microbial consortium responded differently to different biostimulants, and competitive growth was observed in the biostimulant-enhanced treatments. In addition, the enrichment of Pseudomonas and Rhodococcus species was noticed during the biostimulation of benzene and BaP co-contamination soil, and was positively correlated with the DHA enzyme activities, indicating that these species encode DHA genes which contributed to the higher biodegradation. In conclusion, multiple lines of evidence were provided to shed light on the mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX co-contamination with native microbial consortiums.

Isotherm Coefficient for Benzene and Toluene Adsorption on Granular Activated Carbon for Preparation of Biobarrier

Biobarrier combines the adsorption and biodegradation processes which are carried out simultaneously. This method can increase the rate of contaminant reduction, reduce contaminant toxicity and extend the life of activated carbon. This study aims to evaluate the characteristics of benzene and toluene adsorption on granular activated carbon (GAC). The ratio of adsorption in the expanded bed to the fixed bed determines the operating conditions in the benzene biodegradation process experiment. The results showed that the GAC was distributed in the micropore and mesopore regions with a pore diameter of 15 Å to 23 Å. The molecular diameters for benzene and toluene are 5.285 Å and 5.72 Å, respectively, which fit the pores. The adsorption capacity of activated carbon can be represented well using the Freundlich equation. Freundlich’s constants for benzene and toluene are Kf = 17.87 (1/n = 0.46) and Kf = 25.88 (1/n = 0.45).

Even allocation of benefits stabilizes microbial community engaged in metabolic division of labor.

Microbial communities execute metabolic pathways to drive global nutrient cycles. Within a community, functionally specialized strains can perform different yet complementary steps within a linear pathway, a phenomenon termed metabolic division of labor (MDOL). However, little is known about how such metabolic behaviors shape microbial communities. Here, we derive a theoretical framework to define the assembly of a community that degrades an organic compound through MDOL. The framework indicates that to ensure community stability, the strains performing the initial steps should hold a growth advantage (m) over the "private benefit" (n) of the strain performing the last step. The steady-state frequency of the last strain is then determined by the quotient of n and m. Our experiments show that the framework accurately predicts the assembly of our synthetic consortia that degrade naphthalene through MDOL. Our results provide insights for designing and managing stable microbial systems for metabolic pathway optimization.

Sulfate Land Application Enhances Biodegradation in a Petroleum Hydrocarbon Smear Zone

AbstractDelivery of sulfate to petroleum hydrocarbons (PHCs) source zones and groundwater plumes is desirable to enhance biodegradation rates when treatment has become limited due to depletion of sulfate. Sulfate land application involves spreading sulfate salts on ground surface and allowing their dissolution and infiltration of sulfate into subsurface. The objectives of this pilot‐scale investigation were to capture the vertical transport of sulfate beneath an application area, confirm that sulfate reduction was occurring, and explore how the added sulfate affected biodegradation of benzene and toluene. Approximately 4000 kg of gypsum was spread over a 30 m × 30 m study area above a smear zone located approximately 2 m below‐ground surface. Precipitation was augmented by two irrigation events. Groundwater samples, collected over 1058 days from multilevel wells and a conventional long‐screened monitoring well, were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), sulfate, bromide, dissolved inorganic carbon (DIC) and methane. Compound‐specific isotope analyses (CSIA) for benzene and toluene, and isotope analyses of13C‐DIC and34S‐SO42−were performed. Following application, an increase in sulfate concentration was noted in the smear zone.34S‐SO42−enrichment and13C‐DIC depletion indicated that sulfate reduction and mineralization of PHCs were enhanced. CSIA results provided unequivocal evidence of anaerobic biodegradation of benzene and toluene. After 1058 days when sulfate was depleted, methane concentrations were about three times greater than baseline conditions suggesting syntrophic benefit of the delivered sulfate. Observations from this investigation support the viability of sulfate land application to enhance biodegradation rates in shallow PHC smear zones.

Assessing the Biodegradation of BTEX and Stress Response in a Bio-Permeable Reactive Barrier Using Compound-Specific Isotope Analysis.

By using compound-specific isotope analysis (CSIA) in combination with high-throughput sequencing analysis (HTS), we successfully evaluated the benzene and toluene biodegradation in a bio-permeable reactive barrier (bio-PRB) and the stress response of the microbial community. Under stress conditions, a greater decline in the biodegradation rate of BTEX was observed compared with the apparent removal rate. Both an increase in the influent concentration and the addition of trichloroethylene (TCE) inhibited benzene biodegradation, while toluene biodegradation was inhibited by TCE. Regarding the stress response, the relative abundance of the dominant bacterial community responsible for the biodegradation of BTEX increased with the influent concentration. However, the dominant bacterial community did not change, and its relative abundance was restored after the influent concentration decreased. On the contrary, the addition of TCE significantly changed the bacterial community, with Aminicenantes becoming the dominant phyla for co-metabolizing TCE and BTEX. Thus, TCE had a more significant influence on the bio-PRB than an increasing influent concentration, although these two stress conditions showed a similar degree of influence on the apparent removal rate of benzene and toluene. The present work not only provides a new method for accurately evaluating the biodegradation performance and microbial community in a bio-PRB, but also expands the application of compound-specific isotope analysis in the biological treatment of wastewater.

Promoting biodegradation of toluene and benzene in groundwater using microbial fuel cells with cathodic modification

A tubular microbial fuel cell (T-MFC) was used to remove benzene and toluene from groundwater with a great contaminant removal and power production efficiency. The main results were that T-MFC can completely degrade 200 mg/L toluene in 10 days under closed-circuit (CC) conditions, with a removal efficiency (RE) that is 38.2% greater than under open circuit (OC) conditions. When toluene and benzene were used as co-contaminants and a carbonized porous ceramic ring (CPCR) was added to the T-MFC cathode, the RE reached 100% within 6 days and the power density reached 15.6 W/m3. The radius of influence for 100% contaminant removal was 6 cm when the CPCR was added to the T-MFC cathode with a composite carbon source. The exoelectrogens Geobacter and Thermincola were the main species on the anodic surface, while the toluene-degrading bacteria Rhodocyclaceae dominated in the anode solution. This T-MFC is an innovative technology for the bioremediation of soil and groundwater that is contaminated by aromatic compounds, and has the potential to be used as a green energy device in the field.

Preferential removal of benzene, toluene, ethylbenzene, and xylene (BTEX) by persulfate in ethanol-containing aquifer materials.

The effective approaches to eliminate impacts of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) are concerned in the bioremediation of groundwater contaminated with ethanol-blended gasoline. In situ chemical oxidation (ISCO) is a common technique widely used for the remediation of contaminated groundwater. However, the selectivity of ISCO for BTEX and ethanol removal is poorly understood. Therefore, a batch experiment was performed with different aquifer materials, including calcareous soil, basalt soil, granite soil, dolomite, and sand. Gasoline was used to provide dissolved BTEX and ethanol reagent was used as additive to improve the quality of gasoline and to reduce the possibility of air pollution caused by gasoline. Persulfate (PS) was used as a chemical oxidant to oxidize organic contaminants. The target concentrations of BTEX and ethanol were 20mg/L and 1000mg/L, respectively. The results showed that ethanol could be preferentially degraded in the absence of PS and inhibit BTEX biodegradation. However, BTEX could be preferentially removed prior to ethanol in all aquifer materials used at ambient temperature, when PS was added at a PS/BTEX molar ratio of 150. Over 94% BTEX in sand, dolomite, and granite soil was preferentially removed with the first-order decay rate constants of 0.890-2.703day-1 within the first ~ 10days, followed by calcareous and basalt soil at the constants of 0.123-0.371day-1. Ethanol could compete with BTEX for sulfate radical at the first-order decay rate constants of 0.005-0.060day-1 for the first 25days, which was slower than that of BTEX. The pH quickly decreased to < 2.5 in dolomite, sand, and granite soil, but maintained > 6.2 in calcareous soil. Rich organic matter in calcareous and basalt soil had an inhibition effect on BTEX oxidation by PS. The pH buffer in calcareous soil may imply the potential of PS oxidation combined with bioremediation in carbonate rock regions.

Potential of Variovorax paradoxus isolate BFB1_13 for bioremediation of BTEX contaminated sites

Here, we report and discuss the applicability of Variovorax paradoxus strain BFB1_13 in the bioremediation of BTEX contaminated sites. Strain BFB1_13 was capable of degrading all the six BTEX-compounds under both aerobic (O2 conc. 8 mg l−1) and micro-aerobic/oxygen-limited (O2 conc. 0.5 mg l−1) conditions using either individual (8 mg‧l−1) or a mixture of compounds (~ 1.3 mg‧l−1 of each BTEX compound). The BTEX biodegradation capability of SBP-encapsulated cultures (SBP—Small Bioreactor Platform) was also assessed. The fastest degradation rate was observed in the case of aerobic benzene biodegradation (8 mg l−1 per 90 h). Complete biodegradation of other BTEX occurred after at least 168 h of incubation, irrespective of the oxygenation and encapsulation. No statistically significant difference was observed between aerobic and microaerobic BTEX biodegradation. Genes involved in BTEX biodegradation were annotated and degradation pathways were predicted based on whole-genome shotgun sequencing and metabolic analysis. We conclude that V. paradoxus strain BFB1_13 could be used for the development of reactive biobarriers for the containment and in situ decontamination of BTEX contaminated groundwater plumes. Our results suggest that V. paradoxus strain BFB1_13—alone or in co-culture with other BTEX degrading bacterial isolates—can be a new and efficient commercial bioremediation agent for BTEX contaminated sites.