Mineralization Of Pentachlorophenol Research Articles

Nghiên cứu phân hủy pentaclophenol trong nước bằng hệ oxy hóa percarbonic acid

In this work, the degradation of a persistent organic pollutant, pentachlorophenol (PCP) by a green oxydation system based on peroxymonocarbonate (HCO4-) was studied. Different factors including pH, HCO3- concentration, metal ion catalyst, temperature, and UV irradiation were investigated for their effects on PCP degradation. The results showed that among five tested metal ions (Co2+, Ni2+, Fe2+, Cu2+, Mn2+), Co2+ gave the best catalytic activity. The optimum degradation of PCP was obtained at the concentration of HCO3- and H2O2 of 10 mM and 25 mM, respectively, catalyzed by the presence of 0.1 mg/L Co2+ ion at the intrinsic pH value of the system (8÷10). Moreover, UV irradiation remarkably enhanced the radical formation in the oxydation system, which led to higher degradation efficiencies. The results of COD and TOC removal and LC/MS/LS analysis clearly revealed the potential of complete mineralization of PCP by the oxydation system H2O2/HCO3-/Co2+/UV.

Complete pentachlorophenol biodegradation in a dual-working electrode bioelectrochemical system: Performance and functional microorganism identification

Bioelectrochemical system (BES) can effectively promote the reductive dechlorination of chlorophenols (CPs). However, the complete degradation of CPs with sequential dechlorination and mineralization processes has rarely achieved from the BES. Here, a dual-working electrode BES was constructed and applied for the complete degradation of pentachlorophenol (PCP). Combined with DNA-stable isotope probing (DNA-SIP), the biofilms attached on the anodic and cathodic electrode in the BES were analyzed to explore the dechlorinating and mineralizing microorganisms. Results showed that PCP removal efficiency in the dual-working BES (84% for 21 days) was 4.1 and 4.7 times higher than those of conventional BESs with a single anodic or cathodic working electrode, respectively. Based on DNA-SIP and high-throughput sequencing analysis, the cathodic working electrode harbored the potential dechlorinators (Comamonas, Pseudomonas, Methylobacillus, and Dechlorosoma), and the anodic working enriched the potential intermediate mineralizing bacteria (Comamonas, Stenotrophomonas, and Geobacter), indicating that PCP could be completely degraded under the synergetic effect of these functional microorganisms. Besides, the potential autotrophic functional bacteria that might be involved in the PCP dechlorination were also identified by SIP labeled with 13C-NaHCO3. Our results proved that the dual-working BES could accelerate the complete degradation of PCP and enrich separately the functional microbial consortium for the PCP dechlorination and mineralization, which has broad potential for bioelectrochemical techniques in the treatment of wastewater contaminated with CPs or other halogenated organic compounds.

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.

Performance of photocatalytic ozonation process for pentachlorophenol (PCP) removal in aqueous solution using graphene-TiO2 nanocomposite (UV/G-TiO2/O3).

The aim of this study was to evaluate the efficiency of photocatalytic ozonation process using graphene-dioxide titanium nanocomposite in removing Pentachlorophenol (PCP) from aqueous solutions. In this study, nanocomposites with graphene to TiO2(G/T) ratios of 1:10 and 1:20 were synthesized by hydrothermal method, and its characteristics were assessed using various analyses, SEM, XRD, FTIR, TEM, BET and TGA. In this process, the effects of parameters including O3 concentration (0.25-1.25mg/L), nanocomposite concentration (50-500mg/L), initial PCP concentration (10-100mg/L), and time (10-60min), were studied. The results showed that PCP removal efficiency was increased by decreasing solute concentration. Increasing nanocomposite dose to 100mg/L was led to an increase in efficiency (99.1%), but then a decreasing trend was observed. Increasing the concentration of ozone, up to specific value, also enhanced the efficiency but then had a negative effect on process efficiency. Furthermore, the optimum ratio of the catalyst was determined to be 1:20. The highest efficiency of the process for initial pentachlorophenol concentration of 100mg/L was obtained 98.82% in optimum conditions (catalyst dose of 100mg/L and 60min). It is concluded that the photocatalytic ozonation process using graphene-dioxide titanium nanocomposite had the highest efficiency in removal and mineralization of PCP.

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.

Iodine-doping-assisted tunable introduction of oxygen vacancies on bismuth tungstate photocatalysts for highly efficient molecular oxygen activation and pentachlorophenol mineralization

In this work, the tunable introduction of oxygen vacancies in bismuth tungstate was realized via a simple solvothermal method with the assistance of iodine doping. With the predictions afforded by theoretical calculations, the as-prepared bismuth tungstate was characterized using various techniques, such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The different concentrations of the oxygen vacancies on bismuth tungstate were found to be intensely correlated with iodine doping, which weakened the lattice oxygen bonds. Owing to the sufficient oxygen vacancies introduced in bismuth tungstate as a result of iodine doping, the molecular oxygen activation was remarkably enhanced, thus endowing bismuth tungstate with high activity for the photocatalytic degradation of sodium pentachlorophenate. More encouraging is the total organic carbon removal rate of sodium pentachlorophenate over iodine-doped bismuth tungstate that exceeded 90% in only 2 h and was 10.6 times higher than that of the pristine bismuth tungstate under visible light irradiation. Moreover, the mechanism, through which the degradation of sodium pentachlorophenate over iodine-doped bismuth tungstate is enhanced, was speculated based on the results of radical detection and capture experiments. This work provides a new perspective for the enhanced photocatalytic degradation of organochlorine pesticides from the oxygen vacancy-induced molecular oxygen activation over iodine-doped bismuth tungstate.

Mineralization of pentachlorophenol by ferrioxalate-assisted solar photo-Fenton process at mild pH

This work reports the use of ferrioxalate complexes to assist solar photo-Fenton treatment of pentachlorophenol (PCP) in aqueous medium at mild pH, which inhibits the precipitation of iron hydroxides and allows working at a low iron dosage. The experimental parameters were optimized by assessing the effect of initial concentrations of H2O2 (0–2.5 mM) and Fe(II) (2–10 mg/L), pH (3.0–9.0) and iron/oxalic acid molar ratios (1:0–1:13.5) on total organic carbon (TOC) removal. Ferrioxalate-assisted solar photo-Fenton achieved 97.5% mineralization in 120 min, clearly outperforming conventional Fenton and solar photo-Fenton. The presence of photosensitive ferrioxalate complexes accounted for the enhancement, as a result of Fe(II) regeneration that accelerated the hydroxyl radical (OH) production. The time course of H2O2 and Fe(II) concentrations was evaluated under different iron/oxalic acid ratios. The five carboxylic acids determined by ion-exclusion HPLC and the eight aromatic by-products identified by GC-MS allowed the proposal of a degradation pathway that included hydroxylation, dechlorination and dimerization steps. Complete chloride ion release was achieved after 90 min of treatment.

Complete dechlorination and mineralization of pentachlorophenol (PCP) in a hydrogen-based membrane biofilm reactor (MBfR)

Complete biodegradation and mineralization of pentachlorophenol (PCP), a priority pollutant in water, is challenging for water treatment. In this study, a hydrogen (H2)-based membrane biofilm reactor (MBfR) was applied to treat PCP, along with nitrate and sulfate, which often coexist in contaminated groundwater. Throughout 120-days of continuous operation, almost 100% of up to 10 mg/L PCP was removed with minimal intermediate accumulation and in parallel with complete denitrification of 20 mg-N/L nitrate. PCP initially was reductively dechlorinated to phenol, which was then mineralized to CO2 through pathways that began with aerobic activation via monooxygenation by Xanthobacter and anaerobic activation via carboxylation by Azospira and Thauera. Sulfur cycling induced by SO42− reduction affected the microbial community: The dominant bacteria became sulfate-reducers Desulfomicrobium, sulfur-oxidizers Sulfuritalea and Flavobacterium. This study provides insights and a promising technology for bioremediation of water contaminated with PCP, nitrate, and sulfate.

Effects of humic acid on pentachlorophenol biodegrading microorganisms elucidated by stable isotope probing and high‐throughput sequencing approaches

Humic substances (HSs) are ubiquitous in soil and can be reversibly oxidized and reduced by acting as redox mediators. They participate in microbial metabolism and directly affect the biodegradation of organic pollutants. However, the effects of HSs on specific microbial taxa that are responsible for the degradation of organic pollutants remain unclear. In this research, the effects of humic acids (HAs), extracted from three types of soil, forest (CBHA), paddy (PSHA) and peat (YNHA) on the microbial community involved in anaerobic mineralization of pentachlorophenol (PCP) were investigated with high‐throughput sequencing and stable isotope probing (SIP) approaches. The results showed that all HA samples accelerated the biotransformation processes of PCP; the largest rate was obtained with YNHA. Illumina sequencing revealed that Desulfovibrio and Clostridium were the dominant functional bacteria for the dechlorination of PCP. During the subsequent PCP degradation and mineralization processes, HAs affected the diversity and abundance of microbial communities, and several taxa were enriched in the 13C‐heavy fractions compared with 12C‐heavy fractions. In the absence of HA, Methanobacterium and Spartobacteria showed a significant increase in 13C‐heavy fractions. Methanosarcina and OP11 were the dominant PCP degraders in microcosms when amended with CBHA, whereas Burkholderia and Methanobacterium were the key PCP degraders in PSHA‐ and YNHA‐amended experimental microcosms. These results improve our knowledge of the diversity and ubiquitous nature of HS‐utilizing microorganisms involved in PCP degradation, providing scientific support for the development of in situ bioremediation technologies for HS‐rich soil contaminated by PCP.Highlights All humic acids facilitated biodegradation of pentachlorophenol. The greater the carbon content of HA, the greater was the rate of dechlorination. Clostridium and Desulfovibrio dominated PCP dechlorination. SIP suggested that Methanobacterium, Methanosaricina, OP11, Spartobactria and Burholderia acquired PCP‐derived carbon.

GO Mediated TiO2 Nanotube Electrode for the Photoelectrocatalytic Degradation of Pentachlorophenol

GO/TiO2 nanotube array electrode was prepared on a titania plate by a simple in-situ anodization method. The physicochemical characteristics of synthesized TiO2 and GO/TiO2 electrodes were determined by Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman Spectroscopy, Ultraviolet-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier Transform Infrared spectra (FTIR), Photoluminescence (PL) spectroscopy and X-ray photoelectron spectroscopy (XPS). Synthesized GO/TiO2 nanotube electrodes were adjudged for its efficacy in the photoelectrocatalytic (PEC) degradation of Pentachlorophenol (PCP) aqueous solution. Box-Behnken design (BBD) was used to optimize the effect of graphene oxide (GO) loading (0.005–0.25 g/L), pH (3–8), applied current (20–60 mA) and degradation time (10–120 min) on the decomposition of PCP and energy consumption. At optimum conditions, 91% degradation and 85% mineralization of PCP was achieved after 90 min under UV-A illumination with 0.015 g/L of GO concentration, 20.68 mA applied current and at pH 3.14 by consuming 0.00068 kWh energy. Effect of reactive species scavengers on the degradation of PCP has been studied and hydroxyl radical was determined. Based on the LC-MS analysis results possible intermediates were identified and corresponding decomposition pathway of PCP was proposed.

Spatial Abundance and Distribution of Potential Microbes and Functional Genes Associated with Anaerobic Mineralization of Pentachlorophenol in a Cylindrical Reactor.

Functional interplays of microbial activity, genetic diversity and contaminant transformation are poorly understood in reactors for mineralizing halogenated aromatics anaerobically. Here, we investigated abundance and distribution of potential microbes and functional genes associated with pentachlorophenol (PCP) anaerobic mineralization in a continuous-flow cylindrical reactor (15 cm in length). PCP dechlorination and the metabolite (phenol) were observed at segments 0–8 cm from inlet, where key microbes, including potential reductive dechlorinators (Dehalobacter, Sulfurospirillum, Desulfitobacterium and Desulfovibrio spp.) and phenol degraders (Cryptanaerobacter and Syntrophus spp.), as well as putative functional genes, including putative chlorophenol reductive dehalogenase (cprA) and benzoyl-CoA reductase (bamB), were highly enriched simultaneously. Five types of putative cprAs, three types of putative bamBs and seven types of putative nitrogenase reductase (nifHs) were determined, with their copy numbers decreased gradually from inlet to outlet. Distribution of chemicals, bacteria and putative genes confirmed PCP dechlorination and phenol degradation accomplished in segments 0–5 cm and 0–8 cm, respectively, contributing to a high PCP mineralization rate of 3.86 μM d−1. Through long-term incubation, dechlorination, phenol degradation and nitrogen fixation bacteria coexisted and functioned simultaneously near inlet (0–8 cm), verified the feasibility of anaerobic mineralization of halogenated aromatics in the compact reactor containing multiple functional microbes.

The key microorganisms for anaerobic degradation of pentachlorophenol in paddy soil as revealed by stable isotope probing

Pentachlorophenol (PCP) is a common residual persistent pesticide in paddy soil and has resulted in harmful effect on soil ecosystem. The anaerobic microbial transformation of PCP, therefore, has been received much attentions, especially the functional microbial communities for the reductive transformation. However, the key functional microorganisms for PCP mineralization in the paddy soil still remain unknown. In this work, DNA-based stable isotope probing (SIP) was applied to explore the key microorganisms responsible for PCP mineralization in paddy soil. The SIP results indicated that the dominant bacteria responsible for PCP biodegradation belonged to the genus Dechloromonas of the class β-Proteobacteria. In addition, the increased production of 13CH4 and 13CO2 indicated that the addition of lactate enhanced the rate of biodegradation and mineralization of PCP. Two archaea classified as the genera of Methanosaeta and Methanocella of class Methanobacteria were enriched in the heavy fraction when with lactate, whereas no archaea was detected in the absence of lactate. These findings provide direct evidence for the species of bacteria and archaea responsible for anaerobic PCP or its breakdown products mineralization and reveal a new insight into the microorganisms linked with PCP degradation in paddy soil.

Understanding fungal functional biodiversity during the mitigation of environmentally dispersed pentachlorophenol in cork oak forest soils.

Pentachlorophenol (PCP) is globally dispersed and contamination of soil with this biocide adversely affects its functional biodiversity, particularly of fungi - key colonizers. Their functional role as a community is poorly understood, although a few pathways have been already elucidated in pure cultures. This constitutes here our main challenge - elucidate how fungi influence the pollutant mitigation processes in forest soils. Circumstantial evidence exists that cork oak forests in N. W. Tunisia - economically critical managed forests are likely to be contaminated with PCP, but the scientific evidence has previously been lacking. Our data illustrate significant forest contamination through the detection of undefined active sources of PCP. By solving the taxonomic diversity and the PCP-derived metabolomes of both the cultivable fungi and the fungal community, we demonstrate here that most strains (predominantly penicillia) participate in the pollutant biotic degradation. They form an array of degradation intermediates and by-products, including several hydroquinone, resorcinol and catechol derivatives, either chlorinated or not. The degradation pathway of the fungal community includes uncharacterized derivatives, e.g. tetrachloroguaiacol isomers. Our study highlights fungi key role in the mineralization and short lifetime of PCP in forest soils and provide novel tools to monitor its degradation in other fungi dominated food webs.

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.

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.

Mineralization of pentachlorophenol with enhanced degradation and power generation from air cathode microbial fuel cells

The combined anaerobic-aerobic conditions in air-cathode single-chamber MFCs were used to completely mineralize pentachlorophenol (PCP; 5 mg/L), in the presence of acetate or glucose. Degradation rates of 0.140 ± 0.011 mg/L-h (acetate) and 0.117 ± 0.009 mg/L-h (glucose) were obtained with maximum power densities of 7.7 ± 1.1 W/m(3) (264 ± 39 W/m(2), acetate) and 5.1 ± 0.1 W/m(3) (175 ± 5 W/m(2), glucose). At a higher PCP concentration of 15 mg/L, PCP degradation rates increased to 0.171 ± 0.01 mg/L-h (acetate) and 0.159 ± 0.011 mg/L-h (glucose). However, power was inversely proportional to initial PCP concentration, with decreases of 0.255 W/mg PCP (acetate) and 0.184 W/mg PCP (glucose). High pH (9.0, acetate; 8.0, glucose) was beneficial to exoelectrogenic activities and power generation, whereas an acidic pH = 5.0 decreased power but increased PCP degradation rates (0.195 ± 0.002 mg/L-h, acetate; 0.173 ± 0.005 mg/L-h, glucose). Increasing temperature from 22 to 35°C enhanced power production by 37% (glucose) to 70% (acetate), and PCP degradation rates (0.188 ± 0.01 mg/L-h, acetate; 0.172 ± 0.009 mg/L-h, glucose). Dominant exoelectrogens of Pseudomonas (acetate) and Klebsiella (glucose) were identified in the biofilms. These results demonstrate that PCP degradation using air-cathode single-chamber MFCs may be a promising process for remediation of water contaminated with PCP as well as for power generation.

Reductive dechlorination and mineralization of pentachlorophenol in biocathode microbial fuel cells

Simultaneous anaerobic and aerobic degradation pathways in two-chamber, tubular microbial fuel cells (MFCs) facilitated pentachlorophenol (PCP) mineralization by a mediator-less biocathode. PCP was degraded at a rate of 0.263±0.05mg/L-h (51.5mg/gVSS-h) along with power generation of 2.5±0.03W/m3. Operating the biocathode MFC at 50°C improved the PCP degradation rate to 0.523±0.08mg/L-h (103mg/gVSS-h) and power production to 5.2±0.03W/m3. A pH of 6.0 increased the PCP degradation rate to 0.365±0.02mg/L-h (71.5mg/gVSS-h), but reduced power. While mediators were not needed, adding anthraquinone-2,6-disulfonate increased power and PCP degradation rates. Dominant bacteria most similar to the anaerobic Desulfobacterium aniline, Actinomycetes and Streptacidiphilus, and aerobic Rhodococcus erythropolis, Amycolatopsis and Gordonia were found on the biocathode. These results demonstrate efficient degradation of PCP in biocathode MFCs and the effects of temperature, pH and mediators.

Interactions of synthetic Fe(II)–Fe(III) green rusts with pentachlorophenol under various experimental conditions

Sorption of pentachlorophenol (PCP) to three different green rusts (GRs) was studied versus time and initial PCP concentration at neutral pH. A competitive adsorption occurred when salicylate or silicate was present in the reaction medium. The monitoring of chloride formation and PCP byproducts indicated the absence of any possible reductive pathway in the PCP removal. All solid characterization showed that the PCP sorption in the presence or absence of foreign ligands did not alter the GR structure. Addition of nitrate (weak oxidant) involved a gradual release of PCP in solution from the sorbent solid. This is probably due to the oxidative transformation of GR into magnetite that sorbs less PCP. However, reaction with a strong oxidant (H 2O 2) involved both dechlorination and mineralization of PCP via oxidation reaction. HPLC and ion chromatography analysis, TOC and dissolved iron measurements showed that PCP had been degraded by heterogeneous Fenton-like reaction. Both X-ray diffraction analysis and Raman spectroscopy showed that the oxidation of GR may lead to magnetite (Fe 3O 4) or goethite (α-FeOOH), depending on the oxidant type. As green rusts have considerable potential in environmental applications, the influence of naturally occurring ligands and/or oxidants on the reactivity of green rusts should be considered.

Complete anaerobic mineralization of pentachlorophenol (PCP) under continuous flow conditions by sequential combination of PCP‐dechlorinating and phenol‐degrading consortia

Complete mineralization of 50 µM of pentachlorophenol (PCP) was achieved anaerobically under continuous flow conditions using two columns connected in series with a hydraulic retention time of 14.2 days, showing the highest reported mineralization rate yet of 3.5 µM day(-1). The first column, when injected with a reductive PCP dechlorinating consortium, dechlorinated PCP to mainly phenol and traces of 3-chlorophenol (3-CP) using lactate supplied continuously as an electron donor. The second column, with an anaerobic phenol degrading consortium, decomposed phenol and 3-CP under iron-reducing conditions with substantial fermentative degradation of organic compounds. When 20 mM of lactate was introduced into the first column, the phenol degradation activity of the second column was lost in a short period of time, because the amorphous Fe(III) oxide (FeOOH) that had been packed in the column before use was depleted by lactate metabolites, such as acetate and propionate, flowing into the second column from the first column. The complete mineralization of PCP was maintained for a long period by reducing the lactate concentration to 4 mM, effectively extending the longevity of second-column activity with no depletion of FeOOH for more than 200 pore volumes (corresponding to 3,000 days). The carbon balance showed that 50 µM PCP and 4 mM lactate in the influent had transformed to CO(2) (81%) and CH(4) (3%) and had contributed to biomass growth (8%). A comparison of the microbial consortia introduced into the columns and those flowing out from the columns suggested that the introduced population did not flow out during the experiments, although the microbial composition of the phenol column was considered to be affected by the inflow of microbes from the PCP dechlorination column. These results suggest that a sequential combination of reductive dechlorinating and anaerobic oxidizing consortia is useful for anaerobic remediation of chlorinated aromatic compounds in a microbial permeable reactive barrier.

Effect of oxygen availability on the removal efficiency and sludge characteristics during pentachlorophenol (PCP) biodegradation in a coupled granular sludge system

This study systematically investigated the metabolism of pentachlorophenol (PCP) in batch experiments using coupled sludge granules under various dissolved oxygen concentrations. Results indicated that the oxygen condition in serum bottles has a significant effect on the microorganism metabolism. A greater degree of mineralization of PCP was achieved under oxygen-limited conditions (e.g., 40 and 60 initial headspace oxygen percentage (IHOP)), producing trichlorophenol (TCP), dichlorophenol (DCP) and monochlorophenol (MCP) as intermediates and chloride as one of the final products. Reductive dechlorination was identified as the primary pathway for the PCP degradation. Under strictly anaerobic or slightly oxidative conditions (0 and 20 IHOP), the reductive dechlorination of PCP led to an accumulation of TCP. Under aerobic conditions (80 and 100 IHOP), PCP degradation was less significant due to the hindered reductive chlorination in the presence of oxygen. It is also observed that cell hydrophobicity, protein (PN) concentration, settling velocity and specific gravity of the sludge granules decreased with IHOP from 0 to 60, and then increased with IHOP from 60 to 100. Specific methanogenic activity (SMA) and specific oxygen uptake rate (SOUR) confirmed that degradation of PCP was achieved by methanogenic and methanotrophic populations coexisting in a single granule. Because of a combination of reductive and oxidative degradation mechanisms, aerobic or facultative bacteria were found to oxidize the intermediates of PCP degradation products produced by methanogens and strict anaerobes during fermentation.