Cleavage Of Benzene Ring Research Articles

Efficiency of CaZn₂(OH)₆·2H₂O and ZnO nanoparticles in photocatalytic degradation of amoxicillin after multiple cycles

The widespread use of antibiotics has increased their presence in wastewater, largely due to inadequate removal by conventional treatment methods. This highlights a critical need for effective degradation strategies to mitigate environmental and public health risks. This study reports the photocatalytic degradation of amoxicillin (AMX) using calcium zinc hydroxide dihydrate [CaZn2(OH)6·2H2O] (CZ) and zinc oxide (ZnO) nanoparticles (NPs) synthesized by different routes. X-ray diffraction results confirmed the formation of CZ NPs with an 81–95% crystalline phase, while ZnO NPs present a single crystalline phase. The photolysis of AMX under UV-A light (365 nm) was strongly pH-dependent, with degradation rates of 34.7, 5.7, and 4.2% observed at pH 3, 5, and 13, respectively. Maximum adsorption occurred at pH 3, with ZnO achieving 63–83.2% AMX removal and 23.5–47.1% in the case of CZ. The highest overall AMX removal was observed at pH 3, where adsorption dominated the photocatalytic process for both CZ and ZnO. At pH 5 and 13, degradation was primarily driven by photocatalysis in CZ materials, particularly CZ-HT and CZ-SG, while adsorption remained predominant in ZnO. Proton nuclear magnetic resonance analysis indicates benzene ring cleavage in AMX photodegraded by CZ materials. Furthermore, the residues of photodegraded AMX by CZ materials lost antimicrobial activity against Gram-positive and Gram-negative bacteria. Additionally, the reuse of NPs over four cycles maintained consistent degradation performance, highlighting their potential for repeated applications. The comparative analysis of CZ and ZnO NPs superior photocatalytic efficiency of CZ in degrading AMX. This efficiency, along with its potential for repeated use, establish CZ as a promising material for environmental applications aimed at reducing antibiotic contamination and the associated risks of resistance development.

Efficient and sustainable removal of linear alkylbenzene sulfonate in a membrane biofilm: Oxygen supply dosage impacts mineralization pathway

Linear alkylbenzene sulfonate (LAS) can be thoroughly mineralized within sufficient oxygen (O2), but which is energy intensive and may causes serious foaming problem. Although cometabolism can achieve efficient LAS removal within a wide range of O2 dosages, how O2 dosage systematically affects LAS metabolic pathway is still unclear. Here, membrane aerated biofilm reactor (MABR) enabled accurate O2 delivery and bulk dissolved oxygen (DO) control. MABR achieved efficient removal of LAS (>96.4 %), nitrate (>97.8 %) and total nitrogen (>96.2 %) at the three target DO conditions. At high DO condition (0.6 mg/L), LAS was efficiently removed by aerobic mineralization (predominant) coupled with aerobic denitrification biodegradation with the related functional enzymes. Pseudomonas, Flavobacterium, Hydrogenophaga, and Pseudoxanthomonas were dominant genus contributing to four possible LAS aerobic metabolic pathways. As O2 dosage reduced to only 29.7 % of the demand for LAS mineralization, O2 facilitated LAS activation, benzene-ring cleavage and a portion of respiration. NO3--N respiration-induced anaerobic denitrification also contributed to ring-opening and organics mineralization. Desulfomicrobium and Desulfonema related two possible anaerobic metabolic pathways also contributed to LAS removal. The findings provide a promising strategy for achieving low-cost high LAS-containing greywater treatment.

Two-way role of iron-carbon in biochemical reactions: microelectrolysis and enhanced activity of aerobic granular sludge for efficient refractory wastewater treatment

Industrial wastewater contained a large amount of refractory organics, and single treatment processes had limitations. This study investigated the mechanism of refractory organics removal using iron-carbon built-in coupled activated sludge (ICAS) and explored the role and function of iron-carbon (IC) within the ICAS system. The aerobic granular sludge (AGS) cultivated with IC exhibited a loose surface and a tight interior structure. Iron in the AGS concentrated near the outer layer to form a crust, which protected the inner microorganisms. IC promoted EPS secretion and regulated the abundance of positive and negative signaling molecules to maintain AGS stability. Experiments using quinoline as a model refractory organic showed that both physical adsorption by IC and biological adsorption by sludge rapidly fixed a large amount of pollutants, providing a buffer capacity for the system. The iron mineral crust on the AGS surface enhanced quinoline adsorption. Hydroxylation was the first step in quinoline degradation, with IC upregulating the genes iorA/B, qorB, and wrbA involved in this process, and the relative abundances of quinoline-degrading bacteria. Both pyridine ring opening and benzene ring cleavage occurred in the single IC system, and the microelectrolysis process produced •OH and [H], which made degradation pathway for quinoline through IC more complex than microbial degradation. Although the IC-mediated pathway accounted for only a small part of overall quinoline removal in the ICAS system, the ICAS system not only preserved the microelectrolysis process but also enhanced microbial metabolic activity. This work provided insights into the synergistic removal of pollutants and maintenance of AGS stability by the ICAS process, ensuring efficient treatment of refractory organic wastewater.

Phenanthrene metabolism in Panicum miliaceum: anatomical adaptations, degradation pathway, and computational analysis of a dioxygenase enzyme.

Polycyclic aromatic compounds (PAHs) are persistent organic pollutants of environmental concern due to their potential impacts on food chain, with plants being particularly vulnerable. While plants can uptake, transport, and transform PAHs, the precise mechanisms underlying their localization and degradation are not fully understood. Here, a cultivation experiment conducted with Panicum miliaceum exposed different concentrations of phenanthrene (PHE). Intermediate PHE degradation compounds were identified via GC-MS analysis, leading to the proposal of a phytodegradation pathway featuring three significant benzene ring cleavage steps. Our results showed that P. miliaceum exhibited the ability to effectively degrade high levels of PHE, resulting in the production of various intermediate products through several chemical changes. Examination of the localization and anatomical characteristics revealed structural alterations linked to PHE stress, with an observed enhancement in PHE accumulation density in both roots and shoots as treatment levels increased. Following a 2-week aging period, a decrease in the amount of PHE accumulation was observed, along with a change in its localization. Bioinformatics analysis of the P. miliaceum 2-oxoglutarate-dependent dioxygenase (2-ODD) DAO-like protein revealed a 299 amino acid structure with two highly conserved domains, namely 2OG-FeII_Oxy and DIOX_N. Molecular docking analysis aligned with experimental results, strongly affirming the potential link and direct action of 2-ODD DAO-like protein with PHE. Our study highlights P. miliaceum capacity for PAHs degradation and elucidates the mechanisms behind enhanced degradation efficiency. By integrating experimental evidence with bioinformatics analysis, we offer valuable insights into the potential applications of plant-based remediation strategies for PAHs-contaminated environments.

Sulfadiazine chlorination disinfection by-products in constructed wetlands: Identification of biodegradation products and inference of transformation pathways

Disinfection by-products (DBPs) formed from chlorination of antibiotics have greater toxicity than their parent compounds. Herein, this study investigated the biotransformation process of sulfadiazine Cl-DBPs in constructed wetlands (CWs). Results showed that, S atom on sulfonyl group, and N atoms on primary and secondary amine groups were the most reactive sites of sulfadiazine molecule. S1–N4 and S1–C8 of sulfadiazine are the most vulnerable bonds to cleave, followed by C14–N4 and C11–N5 bonds. In the chlorination process, sulfadiazine went through C–N bond cleavage, N-reductive alkylation, halogenation, and desulfonation to produce two aromatic Cl-DBPs. In the biodegradation process in CWs, sulfadiazine Cl-DBPs went through processes mainly including dechlorination, S–N bond cleavage, aniline-NH2 oxidation, desulfonation, phenol-OH oxidation, benzene ring cleavage, C–N bond cleavage, and β-oxidation of fatty acids under the action of a variety of oxidoreductases and hydrolases, during which a total of ten biodegradation products was identified. Moreover, sulfadiazine affected the biodegradation rather than the adsorption process in CWs. The two aromatic sulfadiazine Cl-DBPs had much higher bioaccumulation potentials than their parent sulfadiazine, but for the ten biodegradation products of sulfadiazine Cl-DBPs in CWs, 70% and almost 100% of them had lower bioaccumulation potentials than sulfadiazine and their parent sulfadiazine Cl-DBPs, respectively. The CWs were effective in reducing the environmental risk of sulfadiazine Cl-DBPs.

Degradation and transformation of linear alkyl-benzene sulfonates (LAS) in integrated constructed wetland–microbial fuel cell systems

Linear alkylbenzene sulfonates (LAS) are the most commonly-used anionic surfactants in cleaning agents and detergents. Taking sodium dodecyl benzene sulfonate (SDBS) as the target LAS, this study investigated the degradation and transformation of LAS in integrated constructed wetland–microbial fuel cell (CW–MFC) systems. Results showed that, SDBS was able to improve the power output and reduce the internal resistance of CW–MFCs by reducing transmembrane transfer resistance of organics and electrons because of the amphiphilicity and solubilization, however, SDBS with relatively high concentration had a great potential to inhibit electricity generation and organics biodegradation of CW–MFCs because of the toxic effects on microorganisms. C atoms on alkyl group and O atoms on sulfonic acid group of SDBS had greater electronegativity and were prone to oxidation reaction. The biodegradation of SDBS in CW–MFCs was a process of alkyl chain degradation, desulfonation and benzene ring cleavage in sequence via ω, β and/or α-oxidations and radical attacks under the action of coenzymes and oxygen, in which 19 intermediates were produced, including four anaerobic degradation products (toluene, phenol, cyclohexanone and acetic acid). Especially, for the first time cyclohexanone was detected during the biodegradation of LAS. The bioaccumulation potential of SDBS was greatly reduced through the degradation by CW–MFCs, and thus the environmental risk of SDBS was effectively reduced.

Sodium tetraborate simultaneously enhances the degradation of acetaminophen and reduces the formation potential of chlorinated by-products with heat-activated peroxymonosulfate oxidation

In this study, sodium tetraborate (Na2B4O7) was introduced to enhance the degradation of acetaminophen (ACT) in heat-activated peroxymonosulfate (PMS) process. The elimination of ACT in Na2B4O7/heat/PMS process followed the pseudo-first order kinetics. The corresponding kobs value with 10 mM Na2B4O7 was 33.1 times higher than that in heat/PMS process. 1O2 and HO· were identified as primary reactive species via quenching experiments and electron paramagnetic resonance technology. B(OH)4−, the hydrolysis product of Na2B4O7, reacted with PMS to generate HOOB(OH)3−. 1O2 was generated by the self-decomposition of PMS using B(OH)4− as catalyst, while HO· was produced via the breakage of peroxide bond of PMS and HOOB(OH)3−under high temperature. ACT was degraded by reactive species via the pathways of -NH- bond breakage, -OH replacement, -NH2 oxidation and benzene ring cleavage. Nine transformation intermediates were detected by LC/Q-TOF/MS, and the toxicity of reaction solution decreased significantly with the elimination of ACT. Increasing Na2B4O7 dosage, PMS concentration, initial pH and reaction temperature were conducive to ACT elimination. Humic acid, Cl− and CO32− inhibited the degradation of ACT heavily, while SO42− and NO3− had the negligible effects. Moreover, B(OH)4− could react with free chlorine to the inert B(OH)3OCl− and further significantly suppress the formation of chlorinated by-products for the treatment of Cl−-containing water in Na2B4O7/heat/PMS process. This study provided an effective way to enhance the oxidation capacity of heat/PMS process and suppress the formation of chlorinated by-products in chloride-containing water, and the findings had important implications for using borate buffer in the studies of PMS-based advanced oxidation processes.

Efficient H2O2 generation and bisphenol A degradation in electro-Fenton of O-doped porous biochar cathode derived from spirit-based Distiller’s grains

Bisphenol A (BPA) is an endocrine disrupting chemical with high detection frequency and content, which seriously harms the ecology and human health. Spirit-based distillers’ grains (DG) are solid residues produced during the brewing process, and their treatment has gotten the concern. It is an attractive effort to combine the comprehensive utilization of DG with the removal of BPA. Herein, O-doped porous biochar (OPB) was fabricated using DG as the precursor and used in an electro-Fenton (EF) system to degrade BPA. OPB exhibited a large surface area (i.e., 1432 m2/g) and doping of oxygen, which can facilitate dissolved O2 diffusion and enhance the yield of H2O2 (i.e., 3.0–15.5 mmol/L), and 20 mg/L BPA was rapidly removed by the EF system at the optimum condition (i.e., −0.5 V, pH 4, and 0.3 mM Fe2+) during 30 min with the apparent kinetic constant of 0.267/min. In addition, OPB demonstrated efficient stability in removing BPA after four cycles in the EF system. According to the results of density functional theory calculation and ultra-performance liquid chromatography–tandem mass spectrometry analysis, the three pathways were inferred to be hydroxylation, ketoneation, oxidation, and benzene ring cleavage, and then further decomposed into CO2 and H2O, and the toxicity to the environment gradually decreased with the occurrence of the reaction. This study provides a new idea for resource recovery from waste biomass to solve the problem of water pollution.

Screening of xylene degrading bacteria and optimization of their degradation characteristics in heavily polluted areas

ABSTRACT Aiming at the problems of high xylene concentration and difficult removal in heavily polluted areas, high-efficient degrading bacteria of volatile organic compounds (VOCs) xylene in heavily polluted areas were selected and screened from sewage sludge, and their degradation characteristics were studied. The response surface methodology (RSM) optimized the optimal degradation conditions. The results showed that the screened degrading strain was identified as Klebsiella by the 16SrDNA technology and named H-16. During the start-up phase of the reactor, the removal rate of xylene by strain H-16 fluctuated, and it was stable above 71.3% for 150 min. At 40°C, the degradation rate is the highest, reaching 63.25%. With an increasing inoculum amount of strain H-16, the degradation rate of xylene gradually increased, and the degradation rate could reach 86.1% when the inoculation amount was 25%. A neutral environment was more conducive to the degradation and removal of xylene. Through the analysis of the model and RSM, the optimal conditions for the degradation of xylene by H-16 were obtained: 38.89°C, pH 6.94 and 18.07%. GC-MS results showed that the possible degradation pathway of xylene began with demethylation, formation of pentene diacid by benzene ring cleavage, and finally oxidation to generate CO2 and H2O.

Visible-light-driven N and Fe co-doped carbon dots for peroxymonosulfate activation and highly efficient aminopyrine photodegradation

Low solar energy utilization, instability of Fe ions and Fe(III)/Fe(II) cycle difficulty are three main factors, limiting the photocatalytic activity of the Fe/peroxymonosulfate (PMS) system. Herein, based on the N and Fe co-doped carbon dots (N, Fe-CDs) synthesized by a facile one-pot hydrothermal method, a new Fe(III)/Fe(II) cycle system for PMS activation under visible light irradiation was proposed. The characterization experiments showed that Fe has been successfully doped to the sp2 graphitic structure and mainly existed as Fe-N and Fe-OH complexes, which played an important role in harvesting visible light, enhancing the stability of Fe ions and acting as active sites to accelerate electron transfer. Under visible light irradiation, the photogenerated electrons of N, Fe-CDs could be directly transferred to Fe (III) for Fe (II) formation via the ligand-to-mental charge transfer process, thus accelerating the Fe(III)/Fe(II) cycle. When N, Fe-CDs were used for activating PMS under visible light irradiation, aminopyrine could be efficiently degraded and mineralized to CO2 via the cleavage of pyrazole ring, demethylation, hydroxylation, decarbonylation and the cleavage of benzene ring. The produced O2− and 1O2 played the main roles in the whole photocatalytic reaction. The above results revealed that the novel N, Fe-CDs could effectively activate PMS under visible light irradiation for the degradation of pharmaceuticals in the polluted water.

Atomically dispersed Ag on δ-MnO2viacation vacancy trapping for toluene catalytic oxidation

Atomic dispersion of Ag on δ-MnO2was achievedviaH2O2-induced Mn vacancy trapping. Single-atom Ag could activate adjacent lattice oxygen, facilitating methyl oxidation and benzene ring cleavage to improve toluene oxidation activity.

Using algae bacteria consortia to effectively treat coking wastewater: Performance, microbial community, and mechanism

Coking wastewater is widely generated and poses a significant threat to the environment. Adopting algae bacteria consortia is promising and viable for coking wastewater treatment. In this study, the performance of activated sludge, non-aerated and aerated algae-bacteria consortia (ABC) for treating coking wastewater was investigated and compared. Aerated ABC showed maximum 87.16 ± 1.12% COD removal rates while non-aerated ABC could remove 78.62 ± 0.56% COD. TIN removal rates of aerated ABC and non-aerated ABC were 72.50 ± 0.78% and 80.99 ± 1.26%, respectively. Algae addition could increase the removal performance due to the material exchange between algae and bacteria. Aerated ABC had a larger particle size (119–225 μm) and good settling performance. Genus Comamonas, nitrogen removal bacteria, was predominant in two ABC reactors (average 62% and 60%, respectively) treating low coking wastewater. By comparison, genus Planococcus, denitrifying bacteria, became predominant in aerated algae-bacteria with a higher concentration of coking wastewater. Both genus Comamonas and Planococcus were detected with the benzene ring cleavage reaction function genes. The nitrogen removal pathway showed that nitrogen was removed by ammonia detoxification and nitrate dissimilation. The findings of this study would contribute to the application of ABC in coking wastewater treatment with reduce aeration energy input.

Effects of Constant Electric Field on Biodegradation of Phenol by Free and Immobilized Cells of Bradyrhizobium japonicum 273

It is shown that bacteria Bradyrhizobium japonicum 273 were capable of degrading phenol at moderate concentrations either in a free cell culture or by immobilized cells on granulated activated carbon particles. The amount of degraded phenol was greater in an immobilized cell preparation than in a free culture. The application of a constant electric field during cultivation led to enhanced phenol biodegradation in a free culture and in immobilized cells on granulated activated carbon. The highest phenol removal efficiency was observed for an anode potential of 1.0 V/S.H.E. The effect was better pronounced in a free culture. The enzyme activities of free cells for phenol oxidation and benzene ring cleavage were very sensitive to the anode potential in the first two steps of the metabolic pathway of phenol biodegradation catalyzed by phenol hydroxylase—catechol-1,2-dioxygenase and catechol-2,3-dioxygenase. It was observed that at an anode potential of 0.8 V/S.H.E., the meta-pathway of cleavage of the benzene ring catalyzed by catechol-2,3-dioxygenase became competitive with the ortho-pathway, catalyzed by catechol-1,2-dioxygenase. The obtained results showed that the positive effect of constant electric field on phenol biodegradation was rather due to electric stimulation of enzyme activity than electrochemical anode oxidation.

Influence of anions on ozonation of bisphenol AF: Kinetics, reaction pathways, and toxicity assessment

In this article, the degradation of 4, 4’-(hexafluoroisopropylidene) diphenol (bisphenol AF, BPAF) by ozone was studied and toxicity of the degradation products was evaluated. Kinetic studies showed that acidic conditions were more conducive to the ozone degradation of BPAF than alkaline conditions. In the presence of common anions, Br− and SO42− promoted the degradation of BPAF, whereas NO2−, NO3−, HSO3− inhibited the degradation, and the other anions and cations had no significant effect. The degradation products were analyzed by mass spectrometry, and were mainly manifested in hydroxylation, carboxylation and cleavage of benzene ring. The addition of NO2−, HSO3− and Br−produced the corresponding free radicals, resulting in the parent compound being attacked and affecting the degradation efficiency and pathways. The theoretical calculated results showed that the ortho-site of the BPAF phenolic hydroxyl group was more active than the meta-position, and it's more likely for free radicals to attack ortho-sites and initiate substitution reactions. Toxicity assessment of the products in the process of ozone degradation showed that toxicity of the products was reduced by benzene ring cleavage and a reduction in the F atomic number. However, the toxicity of nitro and brominated products of BPAF was increased. These findings provide some new insights into the role of common ions in ozonation process and product formation, and supplement the existing conclusions. The results of this study remind future researchers to concern that inorganic ions in real water may be converted into corresponding free radicals that affect the formation of ozone oxidation products.

Anaerobic phenanthrene biodegradation by a newly isolated sulfate-reducer, strain PheS1, and exploration of the biotransformation pathway

Phenanthrene is a widespread and harmful polycyclic aromatic hydrocarbon that is difficult to anaerobically biodegrade. Current challenges in anaerobic phenanthrene bioremediation are a lack of degrading cultures and limited knowledge of biotransformation pathways. Under sulfate-reducing conditions, pure-cultures and biotransformation processes for anaerobic phenanthrene biodegradation are poorly understood. In this study, strain PheS1, which is phylogenetically closely related to Desulfotomaculum, was found to be a sulfate-reducing phenanthrene-degrading bacterium. Anaerobic phenanthrene biodegradation using PheS1 was proposed based on metabolite and genome analyses, and the initial step was identified as carboxylation based on the detection of 2-phenanthroic acid, [13C]-2-phenanthroic acid, and [D9]-2- phenanthroic acid when phenanthrene+HCO3−, phenanthrene+H13CO3−, and [D10]-phenanthrene+HCO3− were used as the substrate, respectively. PheS1 genome ubiD gene encoding of carboxylase putatively involved in the biodegradation was performed. Next, benzene ring reduction and cleavage that produced benzene compounds and cyclohexane derivative were reported to occur in the downstream biotransformation processes. Additionally, benzene, naphthalene, benz[a]anthracene, and anthracene can be utilised by PheS1, whereas pyrene and benz[a]pyrene cannot. We discovered a new phenanthrene-degrading sulfate-reducer and provided the anaerobic phenanthrene biotransformation pathway under sulfate-reducing conditions, which can act as a reference for practical applications in bioremediation and for studying the molecular mechanisms of phenanthrene in anaerobic zones.

Achieving toluene efficient mineralization over K/ɑ-MnO2via oxygen vacancy modulation

Oxygen vacancy plays an important role in adsorption and activation of oxygen species and therefore promotes the catalytic performance of materials in heterogeneous oxidation reactions. Here, a series of K-doped ɑ-MnO2 materials with different K loadings were synthesized by a reproducible post processing process. Results show that the presence of K+ enhances the reducibility and oxygen vacancy concentration of ɑ-MnO2 due to the break of charge balance and the formation of low valence Mn species. 4-K/MnO2 material exhibits the highest toluene oxidation activity and satisfied long-term stability and water resistance owing to its superior reducibility and abundant surface absorbed oxygen (Oads). In situ DRIFTS demonstrate that Oads greatly accelerates toluene dehydrogenation rate and promotes benzoate formation, enhancing the activation and decomposition of toluene molecules. Moreover, the CC cleavage of benzene ring (forming maleic anhydride) is the rate-determining step of toluene oxidation, which can be easily occurred over 4-K/MnO2.

Metagenomic analysis of aromatic ring-cleavage mechanism in nano-Fe3O4@activated coke enhanced bio-system for coal pyrolysis wastewater treatment

In current study, nano-Fe3O4@activated coke enhanced bio-system (FEBS) under limited-oxygen condition was applied for efficient treatment of aromatic organics in coal pyrolysis wastewater. Metagenomic analyses revealed functional microbiome linkages and mechanism involved in aromatic ring-cleavage. Based on biodegradation efficiency in different reactors, FEBS supplementation conferred the best organic removal (avg. 92.29%). It also showed a remarkable advantage in biodegradability maintenance (>40%) over control reactors. Metagenomics profiling revealed the degradation processes were driven by Fe3O4 redox reactions and microbial biofilm, while the suspended sludge was the principal force for aromatic mineralization. Based on the analysis of functional species and genes, most bacteria cleaved the benzene ring preferably through the aerobic pathways, mediated by catechol 1, 2-dioxygenase, catechol 2, 3-dioxygenase and protocatechuate 3, 4-dioxygenase (66−84%). Ecological network showed that Comamonas testosterone-centered microbiome and Azotobacter linked to the nitrogen (N)-heterocyclic ring-cleavage. Network linkage further demonstrated that Alicycliphilus and Acidovorax were the key tone taxa involved in benzene ring-cleavage. Finally, combined with analysis of degradation products, bacteria degraded N-heterocyclic ring containing organic aromatic compounds (quinoline) mainly through anaerobic processes, whereas cleavage of benzene ring preferred aerobic pathways. The enriched functional species were the primary reason for the enhanced biodegradation in FEBS.

Characterization of a novel carbendazim-degrading strain Rhodococcus sp. CX-1 revealed by genome and transcriptome analyses

The persistence and ecotoxicity of carbendazim residues pose a potential risk to environmental ecology and human health. Here, a novel and highly efficient carbendazim-degrading bacterium Rhodococcus sp. CX-1, capable of utilizing carbendazim as its sole source of carbon and energy, was isolated from contaminated soil. The biodegradation characteristics and metabolic pathways were studied by mass spectrometry, genomic annotation, and transcriptome analysis. The degradation rate of carbendazim by strain CX-1 was 3.98–9.90 mg/L/h under different conditions, and the optimum degradation conditions were 40 °C and pH 7.0. The addition of carbon sources (glucose, fructose, and sucrose, 100 mg/L) could accelerate carbendazim degradation. HPLC-MS/MS identification suggested that carbendazim is first hydrolyzed into 2-aminobenzimidazole and then to 2-hydroxybenzimidazole, and is ultimately mineralized to carbon dioxide. The genome of strain CX-1 contained 6,511,628 bp nucleotides, 2 linear plasmids, 2 circular plasmids, and 6437 protein coding genes. Genome annotation and transcriptome analysis indicated that carbendazim degradation may be regulated by the degradation genes harbored in the chromosome and in plasmid 2, and two different degradation pathways of carbendazim by imidazole ring cleavage or benzene ring cleavage were predicted. This study provided new insight to reveal the biodegradation mechanism of carbendazim; furthermore, strain CX-1 is a promising bioresource for carbendazim bioremediation.

Electrochemical degradation of three phthalate esters in synthetic wastewater by using a Ce-doped Ti/PbO2 electrode

A Ce-doped Ti/PbO2 electrode was prepared in a deposition solution containing Ce3+ and Pb2+ ions by electrodeposition, and the surface morphology, crystal structure and elemental states were characterized by SEM, XRD and XPS. The electrode was used to investigate the simultaneous degradation of three phthalate esters (PAEs), i.e., dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP) in synthetic wastewaters. The results showed that the electrode exhibited excellent electrocatalytic activity and good reusability and stability, and the removal efficiencies of 5 mg L−1 DBP, DMP and DEP in 0.05 M Na2SO4 (pH 7) reached 98.2%, 95.8% and 81.1% at current density of 25 mA cm−2 after 10 h degradation, respectively. The degradation processes followed pseudo first-order kinetic model very well, and the observed rate constants of DBP, DEP and DMP were 0.42, 0.40 and 0.29 h−1, respectively. The energy consumption in three PAEs degradation was also assessed. The main degradation products of the three PAEs were identified by using liquid chromatography-tandem mass spectrometry, and the possible degradation pathways mainly included dealkylation, hydroxyl addition, decarboxylation and benzene ring cleavage. This work is a promising candidate for efficient treatment of multiple PAEs in wastewater and protection of the aquatic ecological environment.

Decomposition of gas phase benzene under different conditions in atmospheric strong ionization non–thermal plasma

Atmospheric volatile organic compounds (VOCs) from industry and automobiles are posing a serious threat to the environment and human health, and hence efficient control methods are indispensable. This paper presents a laboratory-scale study on the decomposition mechanism for benzene using strong ionization dielectric barrier discharge (DBD) at atmospheric pressure. The specific input energy (SIE), current density, and concentration were studied. The results show that the removal efficiency of benzene increased from 12% to 69% with the increase of SIE from 0.5 to 3.8 kJ/L. The decline in current density by 66.48% and 43.7% for an initial benzene concentration of 300 ppm, was due to increased oxygen content (from 2.4% to 20.9%) and relative humidity (from 18.9% to 90%), respectively, thus electron concentration and consequentially enhancing the removal efficiency over 93%. Further, the beta parameter of the VOC decomposition law decreased from 3.1 kJ/L at 300 ppm to 1.6 kJ/L at 100 ppm. This shows that •O and •OH radicals are key species for the decomposition of benzene and electron dissociation reactions principally control the process. The highest ozone concentration was detected at 5.5 mg/L when no benzene is present, while the main NOx species (NO and NO2) increased with increasing SIE. The Maxwell–Boltzmann electron energy distribution function was solved using the strong ionization discharge reactor (~10 eV), showing that approximately 84.8 % of high-energy electrons possess enough energy to cause the benzene ring cleavage and free radical production. Finally, GCMS and FTIR test results suggested that the byproducts mainly consisted of phenol and substitutions of phenol. The study results show that the strong ionization DBD reactor efficiently removes benzene from polluted air.