Degradation Of Pentachlorophenol Research Articles

Degradation of pentachlorophenol in peroxymonosulfate/heat system: Kinetics, mechanism, and theoretical calculations

In this work, we systematically investigated the transformation of pentachlorophenol (PCP) in the heat-activated peroxymonosulfate (PMS) system. The degradation efficiency of PCP increased with initial PMS concentration, temperature and pH. The calculated % reaction stoichiometric efficiency (RSE) reached up to 92.2%. SO42− was found to promote the degradation of PCP, because it significantly enhanced the generation of HO• and SO4•− as confirmed by EPR experiments. According to the radical quenching tests, SO4•− was the dominant reactive radical for PCP degradation. A total of 10 intermediates were identified, and hydroxylation, sulfate addition, dechlorination and oligomerization were speculated as main reaction pathways. Then, possible reactions between reactive radicals and substrate were calculated at the m062x/land2dz level to interpret the mechanisms of different reactions. It was found that ionic PCP had lower activation energy than molecular PCP, and hence showed higher reactivity towards SO4•− and HO• in the course of radical addition reaction. As for the coupling reaction, SO4•− more likely to react with ionic PCP to generate phenoxy radicals than HO•, due to the negative Gibbs free energy change. Meanwhile, the abstraction of an Cl atom by HO• was confirmed to be the first step for the formation of dechlorination products. In addition, toxicity evaluation by ECOSAR and TEST programs illustrated that the toxicity of reaction products was all lower than that of PCP. Findings of this work demonstrated the feasibility of this PMS/heat method for effective removal of PCP in contaminated waters.

Effects of compost-derived humic acid on the bio-dechlorination of pentachlorophenol in high iron content paddy soil

Pentachlorophenol (PCP) is a common residual organic pollutant in paddy soil, and its harmful effects on soil ecosystems have been confirmed. Humic acid (HA) could act as an electron shuttle to promote the reductive dechlorination of PCP under anaerobic conditions. Humic-like substances produced by composting of kitchen waste were able to facilitate the reductive dechlorination of PCP during Fe(III) oxide reduction by iron-reducing bacteria. However, the effects of compost-derived HAs on reductive dechlorination of PCP in a paddy soil system with a high iron content have not been fully confirmed. The characteristics of HAs from different stages of composting during bio-dechlorination of PCP were still unclear. The functional components of compost-derived HAs, which are responsible for reductive dechlorination of PCP in different stages of composting, also need further investigation. In this study, we conducted a series of experiments on the Guangdong paddy soil system with high iron content (17.5 mg kg−1) to investigate the reductive dechlorination of PCP by HA in the early, middle, and later stages of food waste composting. The results showed that the middle- and late-stages of compost-derived HAs all promoted reductive dechlorination of PCP in the paddy system, but it was opposite in the early-stage. Significant differences were also presented in the components of HAs from different stages of composting. The early-stage compost-derived HAs contain numerous easy degradable components, it would inhibit the dechlorination of PCP by the changes of microbial metabolism in paddy soil. Compost-derived HAs in the middle composting stage showed the best reductive dechlorination effects on PCP. The reason might be that the compost-derived HAs in the middle composting stage could act both as electron donors and transfers. The electron transfer capacities (ETC) of middle-stage compost-derived HAs were significantly higher than those in the early and later composting stages. Compared with the natural HAs in the soil system, compost-derived HAs contained more chlorinated products with lower toxicities after the PCP degradation. This result mainly contributed to the detoxification and mineralization of PCP in the soil. These findings clarified the effects of compost-derived HAs on PCP bio-dechlorination in paddy soil with high iron content, identifying the optimal phase of compost-derived HA and providing a theoretical basis for the utilization of kitchen waste composting as a resource of HA.

Mineralization, kinetics, and degradation pathway of pentachlorophenol degradation from aqueous media via persulfate/dithionite process

The applicability of the dithionite/persulfate (DTN/PS) process for the degradation of pentachlorophenol (PCP) as an organic contaminant from aqueous solutions was investigated. Effective operational parameters, including the initial PCP concentration (25, 50, 100, and 150 mg/L), PS concentration (5, 10, 15, and 20 mg/L), DTN concentration (2.5, 5, 7, and 10 mg/L), solution pH (5, 7, 9, and 11), and reaction time (3, 5, 7, and 10 min) were investigated. To identify the influences of experimental factors involved in PCP degradation, an experimental design based on an orthogonal array was proposed using the Taguchi method. Based on the results, 97.28% of the PCP was removed at the optimal conditions (initial concentration of 25 mg/L, Na-PS (sodium persulfate) concentration of 20 mg/L, Na-DTN (sodium dithionite) concentration of 10 mg/L, pH of 11, and reaction time of 10 min) in the DTN/PS process. Moreover, COD and TOC removal rates were 75.2% and 41% in the DTN/PS process, respectively. An analysis of variance (ANOVA) indicated that PS is the most effective agent in removing PCP in the DTN/PS process. The compounds of phenol, 3,4-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, oxalic acid, propionic acid, tetrachloro-o-benzoquinone, and butanedioic acid were identified as intermediates.

Detecting and Quantifying Polyhaloaromatic Environmental Pollutants by Chemiluminescence-Based Analytical Method.

Polyhaloaromatic compounds (XAr) are ubiquitous and recalcitrant in the environment. They are potentially carcinogenic to organisms and may induce serious risks to the ecosystem, raising increasing public concern. Therefore, it is important to detect and quantify these ubiquitous XAr in the environment, and to monitor their degradation kinetics during the treatment of these recalcitrant pollutants. We have previously found that unprecedented intrinsic chemiluminescence (CL) can be produced by a haloquinones/H2O2 system, a newly-found ●OH-generating system different from the classic Fenton system. Recently, we found that the degradation of priority pollutant pentachlorophenol by the classic Fe(II)-Fenton system could produce intrinsic CL, which was mainly dependent on the generation of chloroquinone intermediates. Analogous effects were observed for all nineteen chlorophenols, other halophenols and several classes of XAr, and a novel, rapid and sensitive CL-based analytical method was developed to detect these XAr and monitor their degradation kinetics. Interestingly, for those XAr with halohydroxyl quinoid structure, a Co(II)-mediated Fenton-like system could induce a stronger CL emission and higher degradation, probably due to site-specific generation of highly-effective ●OH. These findings may have broad chemical and environmental implications for future studies, which would be helpful for developing new analytical methods and technologies to investigate those ubiquitous XAr.

Reaction of activated carbon zerovalent iron with pentachlorophenol under anaerobic conditions

Pentachlorophenol (PCP) is a toxic pollutant and often treated with zero-valent iron (ZVI) in groundwater. In order to improve the reaction rate and selectivity, activated carbon modified zero-valent iron to degrade PCP. This study investigated the effects of carbon loading on the structure, specific surface, and hydrophobicity of AC-ZVI. The results showed that water contact angle and specific surface, which determined hydrophobicity and adsorption capacity, account for the reactivity and selectivity of AC-ZVI during the reduction degradation of the contaminant PCP. The pseudo-first-order kinetic degradation rate of AC-ZVI is 7.44ⅹ10−2 h−1, and two times higher than for ZVI (3.21ⅹ10−2 h−1). Besides, as the [C/Fe]measured weight ratio increased, the ratio of KPCP/KH2 increased from a minimum of 0.218% to a maximum of 0.533%. Based on the pathway of AC-ZVI and PCP, the reduction degradation mechanism of PCP was discussed. These findings can contribute to the rational design of AC-ZVI with properties tailored to a variety of halogenated organics in groundwater remediation.

Whole-genome sequencing, genome mining, metabolic reconstruction and evolution of pentachlorophenol and other xenobiotic degradation pathways in Bacillus tropicus strain AOA-CPS1.

A pentachlorophenol degrading bacterium was isolated from effluent of a wastewater treatment plant in Durban, South Africa, and identified as Bacillus tropicus strain AOA-CPS1 (BtAOA). The isolate degraded 29% of pentachlorophenol (PCP) within 9 days at an initial PCP concentration of 100 mg L-1 and 62% of PCP when the initial concentration was set at 350 mg L-1. The whole-genome of BtAOA was sequenced using Pacific Biosciences RS II sequencer with the Single Molecule, Real-Time (SMRT) Link (version 7.0.1.66975) and analysed using the HGAP4-de-novo assembly application. The contigs were annotated at NCBI, RASTtk and PROKKA prokaryotic genome annotation pipelines. The BtAOA genome is comprised of a 5,246,860-bp chromosome and a 58,449-bp plasmid with a GC content of 35.4%. The metabolic reconstruction for BtAOA showed that the organism has been naturally exposed to various chlorophenolic compounds including PCP and other xenobiotics. The chromosome encodes genes for core processes, stress response and PCP catabolic genes. Analogues of PCP catabolic gene (cpsBDCAE, and p450) sequences were identified from the NCBI annotation data, PCR-amplified from the whole genome of BtAOA, cloned into pET15b expression vector, overexpressed in E. coli BL21 (DE3) expression host, purified and characterized. Sequence mining and comparative analysis of the metabolic reconstruction of the BtAOA genome with closely related strains suggests that the operon encoding the first two enzymes in the PCP degradation pathway were acquired from a pre-existing pterin-carbinolamine dehydratase subsystem. The other two enzymes were recruited via horizontal gene transfer (HGT) from the pool of hypothetical proteins with no previous specific function, while the last enzyme was recruited from pre-existing enzymes from the TCA or serine-glyoxalase cycle via HGT events. This study provides a comprehensive understanding of the role of BtAOA in PCP degradation and its potential exploitation for bioremediation of other xenobiotic compounds.

A new strategy using nanoscale zero-valent iron to simultaneously promote remediation and safe crop production in contaminated soil.

Novel versatile nanomaterials may facilitate strategies for simultaneous soil remediation and agricultural production, but a thorough and mechanistic assessment of efficacy and safety is needed. We have established a new soil remediation strategy using nanoscale zero-valent iron (nZVI) coupled with safe rice production in paddy soil contaminated with pentachlorophenol (PCP). In comparison with rice cultivation in contaminated soil with 100 mg PCP per kg soil but without nZVI, the addition of 100 mg nZVI per kg soil increased grain yield by 47.1-55.0%, decreased grain PCP content by 83.6-86.2% and increased the soil PCP removal rate from 49.9 to 83.9-89.0%. The specific role of nZVI-derived root iron plaque formation in the safe production of rice has been elucidated, and the synergistic effect of nZVI treatment and rice cultivation identified in the nZVI-facilitated rhizosphere microbial degradation of PCP. This work opens a new strategy for the application of nanomaterials in soil remediation that could simultaneously enable safe crop production in contaminated lands.

Bi/SnO2/TiO2-graphene nanocomposite photocatalyst for solar visible light-induced photodegradation of pentachlorophenol.

In this study, for the first time, a TiO2/graphene (G) heterostructure was synthesized and doped by Bi and SnO2 nanoparticles through a hydrothermal treatment. The as-synthesized nanocomposite was employed for photocatalytic degradation of pentachlorophenol (PCP) under visible light irradiation. Structural characterizations such as X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD) proved the valence band alignment at Bi/SnO2/TiO2-G interfaces and crystallinity of the nanocomposite, respectively. The as-developed nanocomposite photocatalyst was able to decompose 84% PCP, thanks to the generation of a large number of active OH•- and O2•- radicals. To achieve this optimum photodegradation efficiency, various parameters such as pH, catalyst dosage, and PCP concentration were optimized. The results showed that the PCP photodegradation process followed the first-order kinetic model and the reaction rate constant rose from 0.007min-1 (Bi) to 0.0149min-1 (Bi/SnO2/TiO2-G). The PCP photodegradation efficiency did not decrease significantly after 5cycles, and the nanocomposite photocatalyst still showed a high efficiency of 68% in the last cycle. The excellent photocatalytic activity of Bi/SnO2/TiO2-G is ascribed as well as the heterostructure of the nanocomposite photocatalyst.

Adsorption-photocatalytic processes for removal of pentachlorophenol contaminant using FeNi3/SiO2/ZnO magnetic nanocomposite under simulated solar light irradiation.

The adsorption followed by photocatalytic degradation process was examined for the pentachlorophenol (PCP) removal from aqueous solution. These processes were accomplished by using FeNi3/SiO2/ZnO magnetic nanocomposite as an adsorbent-photocatalytic agent and under the irradiation of solar light. The magnetic nanocomposite used was first synthesized and then was characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating-sample magnetometer (VSM), and X-ray diffraction (XRD) spectroscopy. The PCP removal efficiency was tested for various factors, including pH, PCP concentration, and nanocomposite dose at different contact times. The characterization results of TEM, FE-SEM, and VSM analysis showed that the synthesized nanoparticles are amorphous and tend to agglomerate due to their high super-paramagnetic property. In addition, the EDX technique showed that the Zn and O elements had the highest weight percent in the synthesized nanocomposite, respectively. On the other hand, XRD analysis revealed that the crystalline size of the nanoparticles was about 42 nm. The kinetic of PCP degradation followed the pseudo-first-order model with R2 = 0.978. According to the results of the isotherm study, the adsorption of PCP onto the nanoparticles followed the Freundlich model. The results of adsorption-photocatalytic degradation experiments showed that 100% removal of PCP was obtained at optimum conditions of pH = 3, nanocomposite dose = 0.5 g/L, contact time = 180 min, and initial PCP concentration of 10 mg/L. Through the results obtained from this study, the adsorption process followed by solar light photocatalytic degradation process using FeNi3/SiO2/ZnO magnetic nanocomposite is found to be an efficacious treatment method for the removal of PCP contaminant from water and wastewater.

Microbial community response to the toxic effect of pentachlorophenol in paddy soil amended with an electron donor and shuttle

Understanding the degradation of pentachlorophenol (PCP) by indigenous microorganisms stimulated by an electron donor and shuttle in paddy soil, and the influences of PCP/electron donor/shuttle on the native microbial community are important for biodegradation and ecological and environmental safety. Previous studies focused on the kinetics and the microbial actions of PCP degradation, however, the effects of toxic and antimicrobial PCP and electron donor/shuttle on the microbial community diversity and composition in paddy soil are poorly understood. In this study, the effects of PCP, an electron donor (lactate), and the electron shuttle (anthraquinone-2, 6-disulfonate, AQDS) on the microbial community in paddy soil were investigated. The results showed that the presence of PCP reduced the microbial diversity compared to the control during PCP degradation, while increased the microbial diversity was observed in response to lactate and AQDS. The addition of PCP stimulated the microorganisms involved in PCP dechlorination, including Clostridium, Desulfitobacterium, Pandoraea, and unclassified Veillonellaceae, which were dormant in raw soil without PCP stress. In all of the treatments with PCP, the addition of lactate or AQDS enhanced PCP dechlorination by stimulating the growth of functional groups involved in PCP dechlorination and by changing the microbial community during dechlorination process. The microbial community tended to be uniform after complete PCP degradation (28 days). However, when lactate and AQDS were present simultaneously in PCP-contaminated soil, lactate acted as a carbon source or electron donor to promote the activities of microbial community, and AQDS changed the redox potential because of the production of reduced AQDS. These findings enhance our understanding of the effect of PCP and a biostimulation method for PCP biodegradation in soil ecosystems at the microbial community level, and suggest the appropriate selection of an electron donor/shuttle for accelerating the bioremediation of PCP-contaminated soils.

Application of the UV/sulfoxylate/phenol process in the simultaneous removal of nitrate and pentachlorophenol from the aqueous solution

This study was aimed to evaluate the performance of hydrated electron (eaq−) and SO2− generated from reaction between UV/sulfoxylate/phenol ring (USP) for the simultaneous removal of nitrate and pentachlorophenol (PCP) from aqueous solutions. The results indicated, with adding PCP (50 mg L−1) in the photoreactor, 94% of NO3− reduction (50 mg L−1) (with N2, NO2− and NH4+ selectivity of 98.9%, 0.21% and 0.85%, respectively) was achieved; while in the backbite of PCP in solution, 91.6% of NO3− was reduced (with N2, NO2− and NH4+ selectivity of 80.15%, 19.6% and 0.19%, respectively). Therefore, it turned out that the hydrated electrons generated in UV/phenol process, has a significant role in the reduction of nitrate and resulted in the higher N2 selectivity and the lower nitrite selectivity. This point can be the great importance from the public health point of view. Also 96% of PCP degradation and 87% of PCP mineralization were obtained by SO2− generated from UV/sulfoxylate. The optimum conditions (the maximum degradation and mineralization of PCP and also the maximum nitrate reduction (with the higher N2 selectivity and the lower nitrite selectivity)), were obtained at sulfoxylate dosage, 100 mg L−1; reaction time, 180 min and pH, 7.0. The USP process indicated the higher performance of USP than the UV alone and sulfoxylate alone, as nitrate and PCP reduction rates by UV alone, sulfoxylate alone and USP processes were obtained (24% and 66%), (18% and 17%) and (94% and 96%), respectively. Also kinetic studies were proved the results mentioned above, as values of robs for USP in the nitrate reduction and degradation of PCP were (17 and 31 times) and (1.4 and 4.25 times) than that of the sulfoxylate alone and UV alone, respectively. Values of energy consumption for the removal of nitrate and PCP were 26 kWh m−3 and 22 kWh m−3, respectively. The several intermediate products including acetic acid, ethane-1,2-diol, acetic acid dihydroxyethene isomers, benzoquinone, 2-chlorobenzene-1,4-diol, adipic acid were identified by the LC/MS analysis. Therefore, it was found the USP process due to smaller total cost and energy consumption and also the higher robs, might be an efficient method for the simultaneous removal of nitrate and pentachlorophenol (PCP) form aqueous solution.

Role of tetrachloro-1,4-benzoquinone reductase in phenylalanine hydroxylation system and pentachlorophenol degradation in Bacillus cereus AOA-CPS1

This study reports a ≅12.5 kDa protein tetrachloro-1,4-benzoquinone reductase (CpsD) from Bacillus cereus strain AOA-CPS1 (BcAOA). CpsD is purified to homogeneity with a total yield of 35% and specific activity of 160 U·mg−1 of protein. CpsD showed optimal activity at pH 7.5 and 40 °C. The enzyme was found to be functionally stable between pH 7.0–7.5 and temperature between 30 °C and 35 °C. CpsD activity was enhanced by Fe2+ and inhibited by sodium azide and SDS. CpsD followed Michaelis-Menten kinetic exhibiting an apparent vmax, Km, kcat and kcat/Km values of 0.071 μmol·s−1, 94 μmol, 0.029 s−1 and 3.13 × 10−4 s−1·μmol−1, respectively, for substrate tetrachloro-1,4-benzoquinone. The bioinformatics analysis indicated that CpsD belongs to the PCD/DCoH superfamily, with specific conserved protein domains of pterin-4α-carbinolamine dehydratase (PCD). This study proposed that CpsD catalysed the reduction of tetrachloro-1,4-benzoquinone to tetrachloro-p-hydroquinone and released the products found in phenylalanine hydroxylation system (PheOHS) via a Ping-Pong or atypical ternary mechanism; and regulate expression of phenylalanine 4-monooxygenase by blocking reverse flux in BcAOA PheOHS using a probable Yin-Yang mechanism. The study also concluded that CpsD may play a catalytic and regulatory role in BcAOA PheOHS and pentachlorophenol degradation pathway.

Cloning, overexpression, purification, characterization and structural modelling of a metabolically active Fe2+ dependent 2,6-dichloro-p-hydroquinone 1,2-dioxygenase (CpsA) from Bacillus cereus strain AOA-CPS_1

2,6-Dichloro-p-hydroquinone (DiCHQ) aromatic-ring cleavage by DiCHQ 1,2-dioxygenase (CpsA) is very crucial for complete transformation of pentachlorophenol (PCP) to 2-chloromaleylacetate in Bacillus cereus AOA-CPS_1 (BcAOA). The 978 bp gene (cpsA) was detected and amplified in the genome of BcAOA; cloned, overexpressed and purified to homogeneity. CpsA showed a single ≅36.9 kDa protein band on SDS-PAGE and exhibited optimum activity at 30 °C and pH 9.0. CpsA was stable between 20 °C and 40 °C, and also retained about 90% of its activity at 60 °C for 120 min. The enzyme retained about 90% activity between pH 9.0 and 11.5 and 60% activity at pH 13.0. CpsA was found to be Fe2+ dependent as about 90% increased activity was observed in the presence of FeSO4. CpsA showed apparent vmax, Km, kcat and kcat/Km of 27.77 ± 0.9 μMs−1, 0.990 ± 0.03 mM, 4.20 ± 0.04 s−1 and 4.24 ± 0.03 s−1 mM−1, respectively at pH 9.0. Analysis of the reaction products via GC–MS confirmed 2-chloromaleylacetate as the ring-cleavage product. CpsA 3D structure revealed a conserved 2-His-1-carboxylate facial triad motif (His 9, His 244 and Thr 11), with Fe3+ at the centre. Findings from this study provide new insights into the involvement of this enzyme in PCP degradation and suggests alternate possible mechanism of ring-cleavage by dioxygenases.

Efficient decomposition of pentachlorophenol by a high photon flux UV/sodium hydrosulfite: Kinetics, intermediates and associated transformation pathway

This study was conducted to investigate the performance of sodium hydrosulfite-mediated photoreduction (SMP) process for the reduction of the pentachlorophenol (PCP). The influence of various parameters, quenchers and anions in water, were investigated on the performance of the SMP. The PCP degradation rates by SMP, UV alone and sodium hydrosulfite alone were achieved 100 %, 65 % and 16 %, respectively (under optimum conditions: sodium hydrosulfite dosage, 100 mg L−1; pH, 7.0 and reaction time, 80 min). Also, the kinetic studies confirmed the superiority of SMP than the other process (robs values for SMP were 69 and 9.8 times of the sodium hydrosulfite alone and UV alone, respectively).Under the selected conditions 56 % of total organic carbon (TOC) was mineralized. The amounts of energy consumed for SMP, UV alone and sodium hydrosulfite alone were estimated 16, 35 and 19 and kWh m-3, respectively. The results indicated adding quenchers in the solution, significantly was declined degradation performance. Therefore, it was found the SMP process due to smaller total cost and energy consumption and also the higher robs, might be an efficient method for the removal of pentachlorophenol form aqueous solution.

Prediction and Optimization of Pentachlorophenol Degradation and Mineralization in Heterogeneous Catalytic Ozonation Using Artificial Neural Network

In this study, artificial neural network was used to predict pentachlorophenol (PCP) degradation in aqueous solution by catalytic ozonation process in a laboratory-scale semi-batch reactor. The catalyst used in this process was the alumina (γ-Al2O3). Results indicated that after 60 min optimal condition: 0.5 g/L of (γ-Al2O3), 0.5 L/min the flow rate of ozone, pH 8 and 100 mg/L PCP initial concentration, 96% of target pollutant was degraded in catalytic ozonation process. In artificial neural network evaluation, a comparison between the model data and laboratory results revealed a high degree of correlation that indicated the model was capable of defining the PCP elimination efficiency with high accuracy. Artificial neural network predicted results are very close to the experimental results with correlation coefficient (R2) of 0.989 and mean square error of 0.000421. The sensitivity analysis indicated that all studied variables (pH, dosage of catalyst and initial concentration of PCP) have strong influence on PCP degradation.

Proteomic analysis of the response of Rhizopus oryzae ENHE to pentachlorophenol: Understanding the mechanisms for tolerance and degradation of this toxic compound

Pentachlorophenol (PCP) is a toxic compound widely distributed in the environment. Rhizopus oryzae ENHE has been shown to possess PCP degradation capacities, peroxidases and phenoloxidases are expected to be involved in the degradation process but no studies have been performed that confirm this hypothesis. We have carried out a proteomic study aiming to understand the mechanisms by which R. oryze tolerates and degrades PCP. After culturing the fungus in media with and without PCP, the secretome and the intracellular proteome were analyzed by shotgun proteomics and 2D-Gel Electrophoresis, respectively. Proteins were identified by LC–MS/MS. In the intracellular proteome, 37 proteins were identified from the spots showing higher intensity or exclusive presence in cultures with PCP. Some redundant identifications of proteins appearing in more than one spot, like proteins belonging to energy metabolism, stress response and cell signaling. Proteins putatively involved in PCP degradation, like peroxidases and a methyltransferase, were also identified. In the secretome, 14 proteins were detected that showed at least 2-fold higher abundance in the broths from cultures with PCP. This work provides new information on the response of R. oryzae to the presence of PCP and allowed the identification of some proteins putatively involved in the degradation of the compound.

Ambient O2 is a switch between [1-electron/1-radical] vs. [2–electron] oxidative catalytic path in Fe-Phthalocyanines

The catalytic redox-intermediates of a Fe-Phthalocyanine (FePc) catalyst have been mapped using Dual-Mode EPR i.e. parallel-EPR to detect integer-spin and perpendicular-EPR to detect half-integer spin states. Molecular O2 can switch the catalytic oxidative path of FePc catalyst between either a [two-electron, 2e] or an [1 electron+1 radical] path. In absence of O2 the key reaction-intermediate is a Low-Spin [FeIV(S = 1)-PCradical(S = 1/2)] state i.e. formed via a [2–electron path] vs. a High-Spin FeIVO(S = 2) state, formed in the presence of O2via an [1-electron+1-radical] path, respectively resulting in distinct kinetic catalytic profiles at pentachlorophenol (PCP) degradation.

Biochar enhances bioelectrochemical remediation of pentachlorophenol-contaminated soils via long-distance electron transfer

The soil bioelectrochemical system (SBES) is a promising biotechnology for the remediation of contaminated soils. However, the effective distance of pollutant removal in the SBES was usually limited in a few centimeters near the electrode surface. In this study, we used biochar as the model conductor to construct a conductive network with microbes in the soil matrix to extend the effective distance of pollutant removal in the SBES. Pentachlorophenol (PCP) was used as the representative contaminant to probe long-distance electron transfer facilitated by the networks. The removal of PCP and microbial community analyses at different distances toward the electrode were monitored. The results showed that PCP transformation in the SBES without biochar amendment mainly occurred within 4 cm around the electrode. However, the effective distance of ∼ 16 cm toward the electrode could be achieved for efficient PCP degradation in the SBES amended with highly conductive biochar. Microbial community analysis confirmed the establishment of bacteria-biochar networks, where Desulfitobacterium and Geobacter were enriched and spatially distributed in the biochar-amended SBES. The results demonstrate that long-distance electron transfer can be achieved in the biochar-amended soil matrix, and shed light on the development of bioelectrochemical strategy for efficient organic pollutant degradation in soils.

Biodegradation and biotransformation of pentachlorophenol by wood-decaying white rot fungus Phlebia acanthocystis TMIC34875

Pentachlorophenol (PCP) has been introduced into the environment mainly as a wood preservative and biocide. The degradation and transformation of PCP in liquid culture by wood-decaying fungus capable of degrading organochlorine pesticides was investigated in this study. The results of tolerance test showed that the tolerance level of Phlebia acanthocystis to PCP in potato dextrose agar medium was higher than that of other Phlebia species. At the end of 10 days of incubation, P. acanthocystis was able to remove 100% and 76% of PCP (25 μM) in low-nitrogen and potato dextrose broth media, respectively. The decrease of PCP in P. acanthocystis culture is accompanied by the formation of pentachloroanisole and p-tetrachlorohydroquinone via methylation and oxidation reactions. Moreover, the p-tetrachlorohydroquinone formed is rapidly converted to methylated products including tetrachloro-4-methoxyphenol and tetrachloro-1,4-dimethoxybenzene. The activities of lignin peroxidase and manganese peroxidase were found to increase in extracellular fluid from fungal culture treated with high-concentration PCP, with maximum values of 169.6 U/L and 73.4 U/L, respectively. The in vitro degradation of PCP and p-tetrachlorohydroquinone was confirmed using extracellular fluid of P. acanthocystis, suggested that the methylation of both compounds is related to extracellular enzymes. Degradation of PCP was efficiently inhibited by piperonyl butoxide or 1-aminobenzotriazole, demonstrating that cytochrome P450 monooxygenase is involved in fungal transformation of PCP, particularly in the oxidation of PCP to p-tetrachlorohydroquinone. Additionally, P. acanthocystis mineralized 9.3% of the PCP to 14CO2 in low-nitrogen culture during 42 days. Results obtained in the present study are in favor of the use of P. acanthocystis as a microbial tool of remediation of PCP-contaminated sites.

Photocatalytic degradation of pentachlorophenol by activated carbon-supported ZnO

Photocatalytic degradation of pentachlorophenol by activated carbon-supported ZnO