Aromatic hydrocarbons like benzene, toluene, xylene, and ethylbenzene (BTEX) can escape into the environment from oil and gas operations and manufacturing industries posing significant health risks ...to humans and wildlife. Unlike conventional clean-up methods used, biological approaches such as bioremediation can provide a more energy and labour-efficient and environmentally friendly option for sensitive areas such as nature reserves and cities, protecting biodiversity and public health. BTEX contamination is often concentrated in the subsurface of these locations where oxygen is rapidly depleted, and biodegradation relies on anaerobic processes. Thus, it is critical to understand the anaerobic biodegradation characteristics as it has not been explored to a major extent. This review presents novel insights into the degradation mechanisms under anaerobic conditions and presents a detailed description and interconnection between them. BTEX degradation can follow four activation mechanisms: hydroxylation, carboxylation, methylation, and fumarate addition. Hydroxylation is one of the mechanisms that explains the transformation of benzene into phenol, toluene into benzyl alcohol or p-cresol, and ethylbenzene into 1-phenylethanol. Carboxylation to benzoate is thought to be the primary mechanism of degradation for benzene. Despite being poorly understood, benzene methylation has been also reported. Moreover, fumarate addition is the most widely reported mechanism, present in toluene, ethylbenzene, and xylene degradation. Further research efforts are required to better elucidate new and current alternative catabolic pathways. Likewise, a comprehensive analysis of the enzymes involved as well as the development of advance tools such as omic tools can reveal bottlenecks degradation steps and create more effective on-site strategies to address BTEX pollution.
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•Fumarate addition is an alternative activation step in Ethylbenzene biodegradation.•Benzyl alcohol and cresol are two alternative intermediates in Toluene's pathway.•Omics tools can help to identifty bottleneck steps and unknown compounds.•Benzene methylation and hydroxylation are simultaneously activated mechanism.
BTEX (benzene, toluene, ethylbenzene, xylene) are common pollutants often found in former gasworks sites together with some other contaminants like indene, indane and naphthalene (Ie, Ia, N). This ...study aimed to evaluate the inhibitory or stimulative substrate interactions between BTEX, and Ie, Ia, N during aerobic biodegradation. For this, batch bottles, containing originally anaerobic subsurface sediments, groundwater and indigenous microorganisms from a contaminated former gasworks site, were spiked with various substrate combinations (BTEX, BTEXIe, BTEXIa, BTEXN, BTEXIeIa, BTEXIeN, BTEXIaN, BTEXIeIaN). Subsequently concentrations were monitored over time. For the BTEXIeIaN mixture, initial concentrations were between 1 and 5 mg L-1, and all compounds were completely degraded by the microbial consortia within 39 days of incubation. The experimental data were fitted to a first order kinetic degradation model for interpretation of inhibition/stimulation between the compounds. Results showed that indene, indane, and naphthalene inhibited the degradation of benzene, toluene, ethylbenzene, o-xylene, with benzene being the most affected. M/p-xylene is the only compound whose biodegradation is stimulated by the presence of indene and indane (individually or mixed) but inhibited by the presence of naphthalene. 16S rRNA amplicon sequencing revealed differentiation in the microbial communities within the batches with different substrate mixtures, especially within the two microbial groups Micrococcaceae and Commamonaceae. Indene had more effect on the BTEX microbial community than indane or naphthalene and the presence of indene increased the relative abundance of Micrococcaceae family. In conclusion, co-presence of various pollutants leads to differentiation in degradation processes as well as in microbial community development. This sheds some light on the underlying reasons for that organic compounds present in mixtures in the subsurface of former gasworks sites are either recalcitrant or subjective towards biodegradation, and this understanding helps to further improve the bioremediation of such sites.
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•Microorganisms from an anaerobic subsurface fully degraded BTEXIeIaN aerobically.•Without N, Ie and Ia, individually or mixed, stimulate m/p-xylene degradation.•Benzene biodegradation is most strongly inhibited by the addition of Ie, Ia and N.•Different mixtures lead to different biodegradation and microbial patterns.•The relative abundance of Micrococcaceae increased in the presence of indene.
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•The cutting-edge pretreatment and analytical methods of BTEX in the environment are extensively discussed.•Different removal techniques of BTEX were reviewed, and their pros and cons ...were compared.•Reviewed the sources, fates and distribution of BTEX in the environment.
BTEX are highly toxic environmental compounds that have carcinogenic and mutagenic effects in humans. These components are ubiquitous in environmental samples like water, air, and soil, which increase the risk of human exposure. Therefore, it is necessary to develop rapid, inexpensive, accurate, sensitive, and efficient sample-preparation and analytical methods to detect BTEX, thus reducing the harmful effect of BTEX on the environment and human health. This research reviewed the sources, fate, and distribution of BTEX in the general environment. In addition, a comprehensive summary and comparison of the current determination methods and different removal techniques in various environmental samples is discussed in detail. Also, the analytical and removal challenges and the futuristic development strategies established for BTEX are provided. In conclusion, the current review presents comprehensive evaluation on cutting-edge technologies in the field of BTEX determination and removal.
Microplastics are increasingly entering marine, limnic and terrestrial ecosystems worldwide, where they sorb hydrophobic organic contaminants. Here, the sorption behavior of the fuel-related water ...contaminants benzene, toluene, ethyl benzene and xylene (BTEX) and four tertiary butyl ethers to virgin and via UV radiation aged polypropylene (PP) and polystyrene (PS) pellets was investigated. Changes in material properties due to aging were recorded using appropriate polymer characterization methods, such as differential scanning calorimetry, Fourier transform infrared spectroscopy, gel permeation chromatography, X-ray photoelectron spectroscopy, and microscopy.
Pellets were exposed to water containing BTEX and the ethers at 130–190 μg L−1 for up to two weeks. Aqueous sorbate concentrations were determined by headspace gas chromatography. Sorption to the polymers was correlated with the sorbate's Kow and was significant for BTEX and marginal for the ethers. Due to substantially lower glass transition temperatures, PP showed higher sorption than PS. Aging had no effect on the sorption behavior of PP. PS sorbed less BTEX after aging due to an oxidized surface layer.
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•PP showed a higher sorption capacity for BTEX than PS.•Weathering did not affect the sorption capacity of PP, but decreased the sorption capacity of PS.•Glass transition temperature was mainly influencing the sorption behavior of PP and PS.•Absorption was the main sorption mechanism for PP.•Adsorption was the main sorption mechanism for PS.
The sorption of the present pollutants is not increased by aging of the polypropylene and polystyrene particles.
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•Hydrodynamic cavitation is effective in PS and PMS activation.•SO4•− and HO• radicals were predominant reactive species for BTEX degradation.•The inhibitory effect of inorganic ...anions on BTEX degradation ranked Cl− < SO42− < CO32–.•Surprising synergism of PMS and Cl− increased the degradation by formation of Cl-based radical species.•Degradation pathways of BTEX were proposed by intermediates identified by HPLC-DAD.
Hydrodynamic cavitation (HC) is an emerging technology gaining interest in water treatment for use in elimination of a wide range of organic pollutants. The energy released during cavitation phenomenon has number of applications and, particularly, it can be utilized for activation of persulfate (PS) and peroxymonosulfate (PMS). In the present study, hybrid techniques: HC combined with persulfates – HC-PS and HC-PMS were tested for the degradation of BTEX in water. Studies on the effect of initial PS and PMS concentration showed that a molar ratio of the oxidant to BTEX equal to 5 is favorable for both cases. Thus, in 240 min HC-PS-5 process allowed to degrade 91.51%, 95.50%, 94.65%, 94.95% of benzene, toluene, ethylbenzene and o-xylene, respectively, while 90.85%, 94.50%, 94.36%, 93.07% of those compounds were degraded by HC-PMS-5. BTEX degradation pathway was proposed for HC-PS-5 and HC-PMS-5 processes relying on the identification of the main reaction intermediates using liquid chromatography coupled with UV diode array detector (HPLC-UV-DAD). Benzyl alcohol, phenol, benzoic acid, benzaldehyde and o-cresol were the main intermediates of BTEX degradation, which multistep pathway involved H-abstraction, OH addition and dealkylation in route to mineralization. At final time of treatment primary and secondary pollutants were effectively degraded. In terms of kinetics, BTEX degradation followed the pseudo-first-order reaction model and the degradation kinetics were faster in HC-PMS-5 system than in HC-PS-5. Surprisingly, the presence of chloride ions (Cl−) in HC-PMS-5 improved the degradation efficiency of alkylated benzene derivatives indicating a synergistic effect of Cl− with SO4•− radicals.
Membrane fouling generated by small molecular-weight aromatic compounds with poor biodegradability is a major barrier to advanced petrochemical wastewater treatment using nanofiltration (NF) ...technology. In this study, the fouling behavior of ten BTEX with different substituent existing in petrochemical wastewater on the NF membrane was systematically investigated. By examining the effect of the number, position, and type of substituents on the permeability of NF membranes and membrane resistance analysis, combined with XDLVO theory and correlation analysis, we found that stronger dipole-dipole interactions of BTEX with higher polarity and hydrogen bonding effects between substituents and the membrane surface were verified to be the main forces driving the attachment to the surface of membranes. Furthermore, by analyzing the effect of common inorganic ions in petrochemical wastewater on membrane fouling, it was found that electron-donating substituents (-CH3, -C2H5, and -NH2) enhanced the electron cloud density of the benzene ring, a process that exacerbated membrane fouling by strengthening electrostatic interactions between the benzene ring and Ca2+ ions. The fouling potential of electron-withdrawing substituted (-NO2, -OH) BTEX exhibited the opposite trend. Overall, this study provides a theoretical basis for developing effective membrane fouling control strategies in NF advanced treatment of petrochemical wastewater.
Aromatic chemicals in petrochemical effluent are difficult to degrade, and their accumulation will cause significant harm to humans and ecological systems. Determine the composition of small molecule BTEX in petrochemical wastewater, gain an in-depth comprehension of the membrane fouling behavior of nanofiltration membrane filtration, identify the primary forces causing irreversible membrane surface fouling using experimental data and model fitting, and propose viable anti-fouling membrane modification strategies. Establish a technical foundation for membrane fouling management in the long-term operation of petrochemical wastewater membrane treatment.
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•Systematically evaluated the NP fouling behavior of ten BTEX present in petrochemical wastewater.•Type of substituents may emerge as a potentially critical determinant of membrane fouling.•XDLVO theory and correlation analysis identified polarity and H-bonding as key factors in NF treatment of BTEX.•Ca2+ exacerbated NP membrane fouling by BTEX with electron-donating substituents.
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•Asphaltenes as potential heterogeneous catalyst for activation of PS and PMS.•First attempt to activate of PS and PMS by asphaltenes.•Effectively degradation of BTEXs by PS and PMS ...activated using cavitation.•Degradation of BTEX was mediated by SO4•−, HO• and O2•− radicals.
This study investigated – for the first time – the simultaneous degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) by persulfate (PS) and peroxymonosulfate (PMS) activated by asphaltenes (Asph) under ultrasound (US) irradiation. Advantageous properties such as high thermal stability, low production cost and extensive availability make asphaltenes as an appealing carbonaceous material for heterogeneous catalysis. The application of asphaltenes in PS/US increased the degradation of BTEXs from 31%, 34%, 35%, 32%–78%, 94%, 98% and 98%, while the removal of these compounds in PMS/US system was improved from 26%, 27%, 24%, 20%–76%, 91%, 97%, 97%, respectively. PS and PMS activation followed a typical sulfate-radical based advanced oxidation processes. In terms of activation of PS and PMS, the particles of asphaltenes intensified formation of reactive radicals by creating additional centers of cavitational events. Moreover, owing to π–π stacking interaction between asphaltenes and sp2-hybridized systems of BTEX, the contaminants undergo adsorption on the surface of asphaltenes and subsequent oxidation by formed radicals. The radical route of BTEX degradation in both PS/US/Asph and PMS/US/Asph systems was mainly contributed by sulfate (SO4•−) and hydroxyl radicals (HO•) and coexisting superoxide radical anions (O2•−) played a minor role.
•A continuous two-stage pyrolysis of polystyrene was successfully conducted.•The styrene yield clearly decreased with increasing the auger reactor temperature.•The maximum BTEX and lowest styrene ...yields were almost the same at 26 wt%.•Oil obtained at high temperatures had an enhanced thermal-oxidative stability.•Oil obtained appeared to be used as a good source of BTEX aromatics.
The recycling rate of plastic waste needs to be improved worldwide. In that context, pyrolysis, through which petrochemical feedstock and alternative fuel can be obtained, has received significant attention. In this study, pyrolysis of polystyrene was conducted in a continuous two-stage process that has an auger reactor and a fluidized bed reactor connected in series. The main objective was to produce oils rich in benzene, toluene, ethylbenzene, and xylenes instead of typical polystyrene pyrolysis oils, which contain high amounts of styrene monomers with low thermal-oxidative stability. The effects of different reaction temperatures (in both reactors) and the type of fluidizing medium on the product distribution and composition were investigated. The maximum yield of benzene, toluene, ethylbenzene, and xylenes (26.3 wt%) was obtained at a temperature of 780 °C in the fluidized bed reactor. The oil and styrene yields at 780 °C were 86 and 26 wt%, respectively. To evaluate the fuel properties of the pyrolysis oil, its calorific value, API gravity, viscosity, density, ash content, pour point, flash point, and pH were examined. The results indicate that the pyrolysis oil can be both a good source of benzene, toluene, ethylbenzene, and xylenes and can potentially be used as a substitute source to gasoline or diesel fuels when it is mixed with oils with a low aromatic content.
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•A novel thiol-functionalized covalent organic framework was prepared.•High binding ability and fast uptake kinetics for BTEX and Hg(II) ion.•High binding selectivity for Hg(II) in ...the presence of other common metal ions.•Efficiently simultaneous removal of BTEX and Hg(II) ion in simulated sewage.
A novel thiol-functionalized covalent organic framework (COF-S-SH) was prepared as an adsorbent for the simultaneous removal of BTEX (benzene, toluene, ethyl benzene and xylenes) and Hg(II) ion from water. The COF-S-SH was obtained via a Schiff-base reaction between a new triamino-monomer (TABPB) and 2,5-divinylterephthalaldehyde, followed by the thiol-ene “click” reaction between 1,2-ethanedithiol and the vinyl groups. The COF-S-SH was characterized by FT-IR spectrum, energy-dispersive X-ray spectrum, 13C MAS NMR spectrum, nitrogen adsorption–desorption isotherms, thermo-gravimetric analysis, scanning electron microscope, X-ray diffraction, and zeta potential. The new adsorbent showed high binding ability with the maximum adsorption capacities (Qmax) of 150.2–255.8 mg/g for BTEX and 588.2 mg/g for Hg(II). The adsorbent also presented fast adsorption kinetics with rate constants of 0.01043–0.05002 g/mg/min for BTEX and 7.254 × 10−4 g/mg/min for Hg(II). Moreover, the adsorbent had good binding selectivity for Hg(II) against common metal ions in water. The adsorbent also showed good simultaneous uptake ability and good reusability for BTEX and Hg(II), and it has been applied to simultaneously removing BTEX and Hg(II) in the simulated sewage with the removal efficiencies of 63.6, 82.1, 94.6, 95.3 and 94.1% for benzene, toluene, ethyl benzene, m-xylene and Hg(II), respectively. Especially, it can reduce the low-concentration Hg(II) in the simulated sewage to a level lower than the drinking water limit. Therefore, COF-S-SH can be used as an excellent adsorbent material for simultaneously removing BTEX and Hg(II) in from the produced water and wastewater in petroleum chemistry industries.
•Forming the heterojunction is the most effective strategy to design the photocatalytic materials.•The process of photo-oxidizing BTEX overwhelmingly follows the Langmuir-Hinshelwood model.•The ...degradation pathways of BTEX are different owing to the differences of methyl and ethyl groups.•The combined technologies are mostly applied in practical application to photo-degrade BTEX.
BTEX with benzene ring and different groups (methyl and ethyl) have aroused enormous concern due to their wide sources and large contribution to photochemical reactions and ozone pollution. This paper systematically reviewed the photodegradation of BTEX including materials, operating parameters, and reaction mechanisms. The photocatalytic materials including monadic or binary metal oxides, hydroxides, and metal-free materials were broadened the optical absorption range and enhanced the absorption capacity by modifying, thus greatly improving the photocatalytic performance. The most effective strategy is forming the heterojunction with built-in fields, which enhances the light absorption capacity and leads lower recombination rate of photocarrier to generate more active oxygen species. The parameters of operating mode, initial concentration, flow rate, temperature, relative humidity and light play important roles in photocatalytic degradation of BTEX. Furthermore, this work highlights that the process of photo-oxidizing BTEX overwhelmingly follows the Langmuir-Hinshelwood model. The mechanisms including adsorption and surface reaction are described using the density functional theory calculations. The review reveals that BTEX are oxidized to the aldehyde and organic acids and opened the ring by active species, eventually mineralized to CO2 and H2O. Moreover, the different degradation pathways of BTEX are studied with the differences of position and number of methyl and ethyl groups. The technique combination is mostly used in the removal of BTEX due to complex working conditions in practical application. The challenge of catalyst inactivation can be regenerated by heating and UV cleaning.
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