Degradation Of Pentachlorophenol Research Articles

α-Fe2O3 modified ZnO flower-like microstructures with enhanced photocatalytic performance for pentachlorophenol degradation

Novel α-Fe2O3 modified ZnO flower-like microstructures were successfully prepared via a simple and rapid solution route with different α-Fe2O3 contents. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–vis diffuse reflectance spectra (UV–vis DRS) and N2 adsorption/desorption. Photocatalytic activity of the as-prepared α-Fe2O3/ZnO composites was evaluated by degradation of pentachlorophenol (PCP) under simulated solar light. The results indicated that α-Fe2O3/ZnO composites showed higher photocatalytic activity than pure ZnO. The optimum photocatalytic activity of α-Fe2O3/ZnO composite with molar ratio of 1:7 was nearly 2 times as high as that of pure ZnO. The remarkably increased performance of α-Fe2O3/ZnO was mainly attributed to the synergistic effect between α-Fe2O3 and ZnO. In addition, the α-Fe2O3/ZnO composites also showed excellent circulation stability.

Photocatalytic degradation of pentachlorophenol by N-F-TiO2: identification of intermediates, mechanism involved, genotoxicity and ecotoxicity evaluation.

In the present study the photocatalytic degradation of a toxic priority pollutant, PCP, in the presence of N-F codoped TiO2 was explicitly investigated. The efficiency of the process to remove PCP was monitored for the first time through combined evaluation of several aspects: the kinetic study of the PCP degradation, identification of transformation products by a combination of mass spectrometric techniques (HR-LC-MS and GC-MS), assessment of total mineralization during the process, and evaluation of the genotoxicity and ecotoxicity of the initial and treated solutions applying the cytokinesis block micronucleus (CBMN) assay and Microtox assay, respectively. On the basis of identified products, a proposed degradation pathway is presented, involving mainly oxidative dechlorination reactions. Genotoxicity and ecotoxicity studies clearly demonstrated the efficiency of the photocatalytic process in the detoxification as well as in the elimination of genotoxicity and cytotoxicity of the irradiated solutions.

Photocatalytic degradation of pentachlorophenol by visible light Ν-F-TiO₂ in the presence of oxalate ions: optimization, modeling, and scavenging studies.

The efficiency of heterogeneous photocatalysis using N-F-TiO2 as photocatalyst to degrade a priority pollutant, pentachlorophenol (PCP), in the presence of oxalates (OA) was investigated in detail. Response surface methodology was used to optimize the effect of three variables (catalyst concentration, OA/PCP ratio, and pH) on the photocatalytic degradation of pentachlorophenol. A quadratic model was established as a functional relationship between three independent variables and the degradation efficiency of PCP. The results of model fitting and statistical analysis demonstrated that the pH played a key role in the degradation of PCP. Within the studied experimental ranges, the optimum conditions for maximum PCP degradation efficiency (97.5 %) were: catalyst concentration 600 mg L(-1), OA/PCP ratio 2, and pH 10. The contribution of HO(·), O2 (·-), and e(-) produced during the photocatalytic treatment was investigated with the addition of scavengers. The photocatalytic degradation was essentially proceeded through an oxidative mechanism at both acid and alkaline pH values by HO(.) and O2 (·-) radicals attack. It was found that O2 (·-) were the major reactive species involved in PCP degradation in pH 4 and HO(·) in pH 10.

Biodegradation of hexachlorobenzene by a constructed microbial consortium.

A consortium comprised of an engineered Escherichia coli DH5α and a natural pentachlorophenol (PCP) degrader, Sphingobium chlorophenolicum ATCC 39723, was assembled for degradation of hexachlorobenzene (HCB), a persistent organic pollutant. The engineered E. coli strain, harbouring a gene cassette (camA (+) camB (+) camC) that encodes the F87W/Y96F/L244A/V247L mutant of cytochrome P-450cam (CYP101), oxidised HCB to PCP. The resulting PCP was then further completely degraded by ATCC 39723. The results showed that almost 40 % of 4 μM HCB was degraded by the consortium at a rate of 0.033 nmol/mg (dry weight)/h over 24 h, accompanied by transient accumulation and immediate consumption of the intermediate PCP, detected by gas chromatography. In contrast, in the consortium comprised of Pseudomonas putida PaW340 harbouring camA (+) camB (+) camC and ATCC 39723, PCP accumulated in PaW340 cells but could not be further degraded, which may be due to a permeability barrier of Pseudomonas PaW340 for PCP transportation. The strategy of bacterial co-culture may provide an alternative approach for the bioremediation of HCB contamination.

Enhanced microbial degradation of pentachlorophenol from soil in the presence of earthworms: Evidence of functional bacteria using DNA-stable isotope probing

This study investigated the effect of two earthworm species (Amynthas robustus Perrier and Eisenia fetida Savigny) on the soil microbial degradation of pentachlorophenol (PCP). PCP-degrading microbes were identified using DNA-stable isotope probing (SIP). The results showed that adsorption and fixing to soil particles and organic fractions dominated the fate of PCP in soil without any amendments. The inoculation of both earthworm species significantly enhanced soil PCP disappearance and basal respiration. The DNA-SIP results revealed that Klebsiella, Cupriavidus, Aeromonas, and Burkholderia spp. were present at higher relative abundances in [13C]-labeled-PCP-amended soil microcosms than [12C]-PCP-amended soil in the presence of A. robustus, indicating that these bacterial species were responsible for PCP assimilation. Cupriavidus and Aeromonas sp. were also detected in the earthworm gut before inoculation, and their relative abundance was affected by earthworms. These results demonstrated that earthworms can introduce functional bacteria into soils and increase the population of PCP-degrading bacteria, thereby accelerating soil PCP degradation.

Dechlorination of pentachlorophenol by grinding at low rotation speed in short time

In order to apply grinding method for degradation of pentachlorophenol (PCP) to an industrial scale, the proportion of different materials [CaO, SiO2 and CO(NH2)2] and the size of grinding balls were examined. For saving energy and increasing dechlorination efficiency, the rotation speed and grinding time were maintained at relatively low values. At a mass ratio of grinding balls to materials (40:1), PCP was added into a big steel jar (300ml) with other materials to grind at 300r·min−1 for 5h. The results indicated that when PCP was mixed with CaO and SiO2 in a molar ratio of 1:60:60, the best dechlorination of 58.4% was achieved. CO(NH2)2 could not be used as hydrogen donor in the dehalogenation by mechanochemical reaction, since it restrained the dechlorination process. The size of grinding balls has significant effect on the reaction. The experiment with 5mm steel balls indicates that the weight is too light to provide appropriate energy for the reaction, while steel balls of 10 and 15mm could give better dechlorination reaction. It indicates that dechlorination depends on the mass of balls and fill rate.

Catalytic ozonation of pentachlorophenol in aqueous solutions using granular activated carbon

The efficiency of granular activated carbon (GAC) was investigated in this study as a catalyst for the elimination of pentachlorophenol (PCP) from contaminated streams in a laboratory-scale semi-batch reactor. The influence of important parameters including solution pH (2–10), radical scavenger (tert-butanol, 0.04 mol/L), catalyst dosage (0.416–8.33 g/L), initial PCP concentration (100–1000 mg/L) and ozone flow rate (2.3–12 mg/min) was examined on the efficiency of the catalytic ozonation process (COP) in degradation and mineralization of PCP in aqueous solution. The experimental results showed that catalytic ozonation with GAC was most effective at pH of 8 with ozone flow rate of 12 mg/min and a GAC dosage of 2 g. Compared to the sole ozonation process (SOP), the removal levels of PCP and COP were, 98, and 79 %, respectively. The degradation rate of kinetics was also investigated. The results showed that using a GAC catalyst in the ozonation of PCP produced an 8.33-fold increase in rate kinetic compared to the SOP under optimum conditions. Tert-butanol alcohol (TBA) was used as a radical scavenger. The results demonstrated that COP was affected less by TBA than by SOP. These findings suggested that GAC acts as a suitable catalyst in COP to remove refractory pollutants from aqueous solution.

Synthesis of α-Fe2O3/ZnO composites for photocatalytic degradation of pentachlorophenol under UV–vis light irradiation

A series of α-Fe2O3/ZnO composites with different α-Fe2O3 contents were successfully prepared by a simple and rapid method. The products were characterized by XRD, FESEM and UV–vis DRS. Photocatalytic activity of the as-prepared α-Fe2O3/ZnO composites was evaluated by degradation of persistent organic pollutant pentachlorophenol (PCP) in aqueous solution. Compared with pure ZnO, α-Fe2O3/ZnO composites show higher photocatalytic activity under UV–vis light irradiation. PCP is almost completely degraded by α-Fe2O3/ZnO composite with molar ratio 1:5 within 4h.

Degradation and dechlorination of pentachlorophenol by microwave-activated persulfate.

The degradation performance of pentachlorophenol (PCP) by the microwave-activated persulfate (MW/PS) process was investigated in this study. The results indicated that degradation efficiency of PCP in the MW/PS process followed pseudo-first-order kinetics, and compared with conventional heating, microwave heating has a special effect of increasing the reaction rate and reducing the process time. A higher persulfate concentration and reaction temperature accelerated the PCP degradation rate. Meanwhile, increasing the pH value and ionic strength of the phosphate buffer slowed down the degradation rate. The addition of ethanol and tert-butyl alcohol as hydroxyl radical and sulfate radical scavengers proved that the sulfate radicals were the dominant active species in the MW/PS process. Gas chromatography-mass spectrometry (GC-MS) was employed to identify the intermediate products, and then a plausible degradation pathway involving dechlorination, hydrolysis, and mineralization was proposed. The acute toxicity of PCP, as tested with Photobacterium phosphoreum, Vibrio fischeri, and Vibrio qinghaiensis, was negated quickly during the MW/PS process, which was in agreement with the nearly complete mineralization of PCP. These results showed that the MW/PS process could achieve a high mineralization level in a short time, which provided an efficient way for PCP elimination from wastewater.

A radical intermediate in the conversion of pentachlorophenol to tetrachlorohydroquinone by Sphingobium chlorophenolicum.

Pentachlorophenol (PCP) hydroxylase, the first enzyme in the pathway for degradation of PCP in Sphingobium chlorophenolicum, is an unusually slow flavin-dependent monooxygenase (kcat = 0.02 s–1) that converts PCP to a highly reactive product, tetrachlorobenzoquinone (TCBQ). Using stopped-flow spectroscopy, we have shown that the steps up to and including formation of TCBQ are rapid (5–30 s–1). Before products can be released from the active site, the strongly oxidizing TCBQ abstracts an electron from a donor at the active site, possibly a cysteine residue, resulting in an off-pathway diradical state that only slowly reverts to an intermediate capable of completing the catalytic cycle. TCBQ reductase, the second enzyme in the PCP degradation pathway, rescues this nonproductive complex via two fast sequential one-electron transfers. These studies demonstrate how adoption of an ancestral catalytic strategy for conversion of a substrate with different steric and electronic properties can lead to subtle yet (literally) radical changes in enzymatic reaction mechanisms.

Graphene TiO2 nanocomposites with high photocatalytic activity for the degradation of sodium pentachlorophenol

A series of graphene–TiO2 photocatalysts was synthesized by doping TiO2 with graphene oxide via hydrothermal treatment. The photocatalytic capability of the catalysts under ultraviolet irradiation was evaluated in terms of sodium pentachlorophenol (PCP-Na) decomposition and mineralization. The structural and physicochemical properties of these nanocomposites were characterized by X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy, scanning electron microscopy, Ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectra, and Fourier-transform infrared spectroscopy. The graphene–TiO2 nanocomposites exhibited higher photocatalytic efficiency than commercial P25 for the degradation of PCP-Na, and 63.4% to 82.9% of the total organic carbon was fully mineralized. The improved photocatalytic activity may be attributed to the accelerated interfacial electron-transfer process and the significantly prolonged lifetime of electron-hole pairs imparted by graphene sheets in the nanocomposites. However, excessive graphene and the inhomogeneous aggregation of TiO2 nanoparticles may decrease photodegradation efficiency.

Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2mgL−1) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34mMCH4/hg VSS) and aerobic activity (SOUR: 2.21mMO2/hg VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro-aerobic condition and PCP on microbial community. Furthermore, nucleotide sequencing indicated that the main microorganisms for PCP degradation might be related to Actinobacterium and Sphingomonas. These results provided insights into situ bioremediation of environments contaminated by PCP and had practical implications for the strategies of PCP degradation.

Physiological Characterization of Fungal Inoculum for Biotechnological Remediation of Soils

The aim of this work was to study the bioremediating potential of Lentinus crinitus CCIBt2611 according to the physiological condition of the inoculum. Inoculum was prepared using sugarcane ground husk (C:N 90), at several physiological ages and applied in soil contaminated with pentachlorophenol. The inoculum's potential was assessed by evaluating the mycelium's vigor at soil's colonization, determination of peroxidase and phenoloxidase activities, in vitro degradation of Remazol Brilliant Blue R and in vivo degradation of pentachlorophenol. The results showed that the assessed parameters were relevant to identify the quality of the inoculum. For L. crinitus, 10 day old inoculum showed good soil-colonization speed with significant enzymatic activities, indicating the role of Manganese-dependent peroxidase and laccase in degradation, and efficient degradation of pentachlorophenol.

Verification of Heme Catalytic Cycle with 5-Aminosalicylic Acid and Its Application to Soil Remediation of Polycyclic Aromatic Hydrocarbons

Catalytic degradation of pentachlorophenol in soil by heme and hydrogen peroxide has been hypothesized to occur through nonspecific catalytic reactions similar to those involving ligninase. The present study examines the evidence for a heme catalytic mechanism for the oxidation of organic compounds. In the presence of hydrogen peroxide, heme is converted to the ferryl heme radical (Hm-Fe +4• ), which can oxidize organic compounds, such as 5-aminosalicylic acid (5-ASA). A second 5-ASA may later be oxidized by ferryl heme (Hm-Fe +4 ), which reverts to the ferric heme state (Hm-Fe +3 ) to complete the cycle. We believe that this catalytic cycle is involved in the degradation of hazardous pollutants, such as polycyclic aromatic hydrocarbons (PAHs). Remediation via heme catalytic reactions of PAHs in soil from a pole yard was evaluated, and about 96% of PAHs was found to disappear within 42 days after treatment with heme and hydrogen peroxide. In addition, benzo[a]pyrene and six other PAHs were undetectable among a total of 16 PAH compounds examined. Therefore, we propose heme catalysis as a novel technology for the remediation of hazardous compounds in contaminated soil.

A comprehensive overview of bacteria and fungi used for pentachlorophenol biodegradation

Pentachlorophenol (PCP) is an extremely dangerous worldwide pollutant due to its high toxicity towards all organisms. It has been introduced into the environment mainly as a wood preservative, biocides and from the bleaching of paper or tissues. The use of PCP indiscriminate has led to the contamination of water and soil systems. Many countries have specific regulations, guidelines or procedures for the management and disposal of PCP but the most common methods are: adsorption with activate carbons, incineration in an approved and secure area, closed in sealed containers and biological degradation. PCP depletion can occur either by abiotic processes such as: absorption, volatilization and photo degradation or by biotic degradation. One of the main studies focused on remediation using plants, animals and microbial communities. Aerobic and anaerobic microorganisms can degrade PCP under a variety of conditions and at different PCP concentrations. Bacterial strains such as Pseudomonas sp., Sphingomonas sp., Arthrobacter sp., Mycobacterium sp., Flavobacterium sp., Serratia sp. and Bacillus sp., and fungal cultures as Trametes sp., Phanerochaete sp., Anthracophyllum sp., Armillaria sp., Bjerkandera sp., Ganoderma sp., Lentinula sp., Penicillium sp, Trichoderma sp., Rhizopus sp. and Plerotus sp. showed various rates and extent of PCP degradation. This review focuses on PCP degradation by various aerobic and anaerobic microorganisms with emphases on the biological and chemical aspects. Furthermore we will analyze intermediate products, processes and enzymes involved in the degradation of PCP in different environmental conditions and at various PCP concentrations.

Degradation of pentachlorophenol by hydroxyl radicals and sulfate radicals using electrochemical activation of peroxomonosulfate, peroxodisulfate and hydrogen peroxide

The present study is to investigate the reactivity of free radicals (SO4− and HO) generated from common oxidants (peroxomonosulfate (PMS), peroxodisulfate (PDS) and hydrogen peroxide (HP)) activated by electrochemically generated Fe2+/Fe3+ ions which furthermore are evaluated to destroy pentachlorophenol (PCP) in aqueous solution. The effect of solution pH and amount of oxidants (PMS, PDS and HP) in electrocoagulation (EC) on PCP degradation is analyzed in detail. The experimental results reveal that, optimum initial solution pH is 4.5 and PMS is more efficient oxidant addition in EC. 75% PCP degradation is achieved at 60min electrolysis time from PMS assisted EC. According to the first order rate constant, faster PCP degradation rate is obtained by PMS assisted EC. The PCP degradation rate by oxidant assisted EC is observed in the following order: EC/PMS>EC/PDS>EC/HP>EC. Further to identify the influences of experimental factors involved in PCP degradation by oxidant assisted EC, an experimental design based on an orthogonal array (OA) L9 (33) is proposed using Taguchi method. The factors that most significantly affect the process robustness are identified as A (oxidant) and B (pH) which together account for nearly 86% of the variance.

Phytoremediation Efficiency of a PCP-Contaminated Soil using Four Plant Species as Mono- and Mixed Cultures

Bioremediation of soil polluted by pentachlorophenol (PCP) is of great importance due to the persistence and carcinogenic properties of PCP. Phytoremediation has long been recognized as a promising approach for removal of PCP from soil. The present study was conducted to investigate the capability of four plant species; white clover, ryegrass, alfalfa, and rapeseed grown alone and in combination to remediate pentachlorophenol contaminated soil. After 60 days cultivation, white clover, raygrass, alfalfa, and rapeseed all significantly enhanced the degradation of PCP in soils. Alfalfa showed highest efficiency for the removal of PCP in single cropping flowed by rapeseed and ryegrass. Mixed cropping significantly enhanced the remediation efficiencies as compared to single cropping; about 89.84% of PCP was removed by mixed cropping of rapeseed and alfalfa, and 72.01% of PCP by mixed cropping of rape and white clover. Mixed cropping of rapeseed with alfalfa was however far better for the remediation of soil PCP than single cropping. An evaluation of soil biological activities as a monitoring mechanism for the bioremediation process of a PCP-contaminated soil was made using measurements of microbial counts and dehydrogenase activity.

Pentachlorophenol remediation by Enterobacter sp. SG1 isolated from industrial dump site.

Chlorophenols contamination is serious concern to the environment due toxicity to all forms of life. Among all the chlorophenols, pentachlorophenol (PCP) is more detrimental to the environment. Pentachlorophenol used as pesticide, herbicide, antifungal agent and wood preservative which causes environmental pollution. In the present research a PCP degrading bacterium was isolated and characterized from industrial dump site. This isolate used PCP as its sole source of carbon and energy and was capable of degrading this compound, as indicated by stoichiometric release of chloride, ring cleavage activity and biomass formation. Based on morphological, biochemical and 16S rRNA gene sequence analysis this strain was identified as Enterobacter sp. SG1. Gas Chromatography (GC) analysis revealed that this strain was able to degrade PCP up to a concentration of 2 mM. This study showed that the removal efficiency of PCP by SG1 was found to be very effective and can be used in degradation of PCP contaminated site or waste in the environment.

Effect of Soya Lecithin on Solubilization and Biodegradation of Pentachlorophenol by <i>Anthracophyllum discolor</i>

The effect of soya lecithin (SL) on solubilization and biodegradation of pentachlorophenol (PCP) by Anthracophyllum discolor was evaluated. Besides, the PCP effect on critical micelle concentration (CMC) of SL and the effect of PCP and SL on the ligninolytic activity of A. discolor were evaluated. The PCP solubilization test was performed for 100, 200 and 400 mg·L-1 with SL solution varying concentrations of ranging from 0 to 0.9 g·L-1. The effect of PCP (5 to 20 mg·L-1) on CMC of SL by conductivity was evaluated. The effect of SL (0 to 0.9 g·L-1) on biodegradation of PCP (21.4 mg·L-1) in modified Kirk medium was studied. The results showed that SL addition enhanced PCP solubility in water. The solubilities of 100, 200 and 400 mg·L-1 of PCP were about 4.2, 5.0 and 2.5 times higher than their solubility in pure water when the system was added with 0.9 g·L-1 of SL. We found that the increase in PCP concentration caused a decrease in the CMC value. In the biodegradation assay, in liquid medium supplemented with 0.9 g·L-1 of SL, the 94.4% of PCP was biodegraded after 26 days of incubation. In contrast, in the control assay (without SL), the 76.5% of PCP was removed. The PCP degradation was confirmed by the presence of its metabolites. During biodegradation assay, A. discolor mainly produced manganese peroxidase reaching a maximum of 96.8 U·g-1 (dw) when the culture medium was added with 0.6 g·L-1 of SL. These results show that SL can be applied to increasing the bioavailability and biodegradation of PCP.

Synthesis and Characterization of Rhodium Doped on TiO2/HCP for Enhanced Photocatalytic Performance on Pentachlorophenol

Visible‐light‐responsive material based on Rhodium doped on titanium dispersed on dealuminated clinoptilolite (TiO2/HCP) was synthesized via a combination of the sol‐gel method and photoreductive deposition technique. The photocatalyst surface characterization, structural and optical properties were investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive X‐ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and UV‐visible spectra (UV‐VIS). Doping TiO2/HCP with Rh imparts a red shifting of the absorption band into the visible light region according to UV‐VIS. The prepared composite materials were evaluated for their photocatalytic activities on pentachlorophenol (PCP) degradation under sunlight irradiation. The Rhodium doped TiO2/HCP exhibited enhanced photocatalytic activity and can be considered as a potential photocatalyst in wastewater treatment.