Dechlorination Of Pentachlorophenol Research Articles

Compost-derived humic acid impacts on the biodechlorination of pentachlorophenol in high organic matter paddy soil

The long-term accumulation of pentachlorophenol (PCP) has adversely affected the paddy soil ecosystem. PCP reductive dechlorination under anaerobic conditions is an efficient pathway for PCP degradation. This process is affected by the content of organic matter and the iron mineral composition of the soil. Our previous study analyzed the effects of compost-derived Humic acids (HAs) on reductive dechlorination of PCP in a paddy soil system under Fe-reducing conditions. The effects and mechanisms of high organic matter and compost-derived HAs in promoting PCP dechlorination need further investigation. This study examined paddy soils with high organic matter content in Heilongjiang Province. PCP reductive dechlorination in this system was studied using HAs from three stages of municipal solid waste compost as soil supplements. The results showed that natural HA and microorganisms could promote the dechlorination and transformation of PCP in the paddy soil system. After removing humic acid, the detected concentrations of PCP in paddy soil and solid-liquid interface were 1.84 and 9.67 times of those in the original soil experiment, respectively. The concentration of low chlorine products decreased significantly in the sterilized group. Compost-derived HAs from different stage were also presented various effect on PCP reductive dichlorination. Furthermore, the synergistic effect between natural HA and compost-derived HAs would limit the electron donating capacity of compost-derived HAs in the paddy soil with high organic matter. Organic matter in soil has an important influence on pollutant fate. Late-stage HA were more effective in promoting PCP degradation than early-and middle-stage HAs. The research provided a comprehensive and meticulous analyses of the effects of compost-derived HAs on PCP bio-dechlorination in paddy soil with high organic matter.

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.

Mechanisms of aerobic dechlorination of hexachlorobenzene and pentachlorophenol by Nocardioides sp. PD653.

We sought to elucidate the mechanisms underlying the aerobic dechlorination of the persistent organic pollutants hexachlorobenzene (HCB) and pentachlorophenol (PCP). We performed genomic and heterologous expression analyses of dehalogenase genes in Nocardioides sp. PD653, the first bacterium found to be capable of mineralizing HCB via PCP under aerobic conditions. The hcbA1A2A3 and hcbB1B2B3 genes, which were involved in catalysing the aerobic dechlorination of HCB and PCP, respectively, were identified and characterized; they were classified as members of the two-component flavin-diffusible monooxygenase family. This was subsequently verified by biochemical analysis; aerobic dechlorination activity was successfully reconstituted in vitro in the presence of flavin, NADH, the flavin reductase HcbA3, and the HCB monooxygenase HcbA1. These findings will contribute to the implementation of in situ bioremediation of HCB- or PCP-contaminated sites, as well as to a better understanding of bacterial evolution apropos their ability to degrade heavily chlorinated anthropogenic compounds under aerobic conditions.

Sulfur in humin as a redox-active element for extracellular electron transfer

Humin (HM), an insoluble humic substance that occurs as an organo-mineral complex, mediates extracellular electron transfer (EET) among microorganisms in the geosphere. Although sulfur (S)-containing functional groups have been posited as possible redox-active groups in HM, there has been no direct evidence in this regard. Here, we characterized the redox-active S in HM from different natural sources using synchrotron radiation-based X-ray absorption spectroscopy in partial fluorescence yield mode. The S content in HM is less than 0.9%, with the oxidation states ranged widely from −2 to +6. About 9% to 19% of total S in HM was redox variable, corresponding to 1.2 × 10−5 to 17.1 × 10−5 Eq/g-HM redox capacity. The redox capacity of HM driven by S is comparable to or larger than the electron donating capacity of HM observed in anaerobic microbial dechlorination of pentachlorophenol, suggesting that S is one of the significant redox-active elements in HM. These findings provide new insights into the role of S cycling in biogeochemical processes and microbial energy networks.

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.

Effects of landfill refuse on the reductive dechlorination of pentachlorophenol and speciation transformation of heavy metals

Landfill refuse is a mixture of inorganic minerals and organic matter that is capable of undergoing complexation and redox reactions due to its active functional groups. Organic matter often combines with minerals in landfill refuse and it remains unclear whether this combination involves electron transfer. Therefore, the effects of landfill refuse composition on reductive dechlorination and speciation transformation of heavy metals were investigated in this study. Results show that landfill refuse comprises protein- and humic-like substances, aliphatic structures, and a large number of hydroxyl, carboxyl, quinoid and other active functional group. The electron donating capacity (0.09–0.26 μmol/g(C)) of landfill refuse was found to be higher than its electron accepting capacity (0.03–0.23 μmol/g(C)), indicating that electron donating groups (hydroxyl) were the main redox-active moieties, facilitating the reductive dechlorination of pentachlorophenol (PCP) by microorganism. Fe2O3, FeO and SiO2 were the main inorganic minerals affecting PCP dechlorination. The speciation distribution of heavy metals in landfill refuse was determined by the BCR sequential extraction method. Results showed that Zn and Ni have high potential migration capacity, poor stability and the highest bioavailability, while Cr, Cu and Pb are relatively stable and have weak migration potential. The oxygen- and nitrogen-containing functional groups, aliphatic structures and aromatic carbon in landfill refuse can promote the transformation of Ni and Cr from an unstable to stable state. Protein-like substances exhibit a strong Cu binding ability, allowing Cu to combine with organic matter more easily than other assessed heavy metals. Both Fe2O3 and FeO affected the stability of Cu. FeO promoted the stabilization of Zn, whereas Fe2O3 and SiO2 promoted Cu instability. These results could provide some references for the treatment of organic chlorides and the stabilization of heavy metals in landfill refuse in China.

Electrocatalytic hydrodechlorination of pentachlorophenol on Pd-supported magnetic biochar particle electrodes

To enhance the catalytic activity of Pd and to facilitate rapid recovery, a novel Pd/CuFe2O4/peanut shell-derived biochar (Pd/M−PSBC) particle electrode was developed and applied toward the electrocatalytic hydrodechlorination of pentachlorophenol (PCP) in a three-dimensional reactor. The physicochemical properties and the electrochemical performance of the particle electrode were systematically characterized through a series of characterizations, such as scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and linear sweep voltammetry. The results demonstrate a uniform Pd distribution across the M−PSBC surface having an average particle size of 5 nm. Furthermore, the Pd/M−PSBC electrode exhibited outstanding hydrogen adsorption activity. Under optimal experimental conditions, voltage of 0.8 V, particle electrode dosage of 20 mg (2.2 wt% Pd loading), the PCP (50 mg/L) removal efficiency and the dechlorination efficiency reached 99.0% and 93.1%, respectively. By undertaking consecutive cycling experiments the stability of the Pd/M−PSBC electrode toward PCP dechlorination was observed to be excellent. Finally, a toxicity assessment confirmed the reduction of PCP and PCP intermediate toxicities.

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.

Maize straw biochar addition inhibited pentachlorophenol dechlorination by strengthening the predominant soil reduction processes in flooded soil

Biochar has received increasing attention for its multifunctional applications as a soil amendment. The dual effect of biochar on reductive organic pollutants and soil biogeochemical processes under anaerobic environments in parallel has yet to be fully explored. In this study, anaerobic batch experiments were conducted to examine the effect of biochar on both reductive transformation of pentachlorophenol (PCP) and soil redox processes in flooded soil. Compared to biochar-free controls, the reductive dechlorination of PCP was significantly inhibited following biochar addition, with the inhibition degree increased with increasing amount of biochar. Dissimilatory iron and sulfate reduction, as well as the production of methane, were significantly enhanced following biochar addition. The bacterial and archaeal communities showed a functional selection responded to the addition of biochar and PCP, with the core functional groups at the genus level including Dethiobacter, Clostridium, Geosporobacter, Desulfuromonas, Desulfatitalea, and Methanosarcina. These findings indicated that biochar could affect soil microbial redox processes and may act as an electron mediator altering electron distribution from PCP dechlorination to the predominant soil reduction processes, and increase understanding regarding biochar’s comprehensive effects on the remediation of natural flooded soil polluted by chlorinated organic pollutants that can be degraded reductively.

Biowaste-source-dependent synthetic pathways of redox functional groups within humic acids favoring pentachlorophenol dechlorination in composting process

Humic acids (HAs) can function as electron mediators for contaminants transformation in different environments. The humus respiration can facilitate pentachlorophenol (PCP) dechlorination during different biowastes composting. However, different characteristics of synthetic pathways of redox functional groups within HAs during different biowastes composting have never been characterized. Herein, we assessed the synthetic pathways of redox functional groups within HAs from protein-, lignocellulose-, and lignin-rich composts that facilitated the microbially reductive dechlorination of PCP, respectively. The results show that the aromatic systems are the major electron-accepting moieties of HAs and function as electron shuttles to facilitate the PCP dechlorination. Amino acid and reducing sugar are the major precursors for the synthesis of redox functional groups within HAs in protein-rich composts, and polyphenols and amino acids are discerned as the significant components to synthesize redox functional groups of HAs in lignocellulose- and lignin-rich composts. Seven groups of bacterial communities based on relationships among remarkable precursors, key bacterial communities, and redox functional groups within HAs are classified as participants in the precursors’ catabolism and aromatic system’ anabolism. Furthermore, the significant environmental factors on the synthetic pathways of redox functional groups within HAs in composting are confirmed by structural equation models. Conclusively, the regulating methods for promoting PCP dechlorination by HAs during different biowastes composting are proposed. Our results can help in understanding the distinct formative mechanisms of redox functional groups within HAs during different biowastes composting, providing insights into a classification-oriented approach for recycling utilization of different biowastes.

Bacterial networks mediate pentachlorophenol dechlorination across land-use types with citrate addition

Soil microorganisms play a crucial role in the bioremediation of pentachlorophenol (PCP)-contaminated soils. However, whether and how soil bacterial networks with keystone taxa affect PCP dechlorination is not well understood. The present study investigated the effects of citrate on soil bacterial networks mediating PCP dechlorination by direct and indirect transformation in iron-rich upland and paddy soils. The rates of PCP dechlorination and Fe(II) generation were accelerated by citrate addition, particularly in the paddy soils. Network analysis revealed that the topological properties of bacterial networks were changed by citrate addition; more modules and keystone taxa were significantly correlated with PCP dechlorination and Fe(II) generation in the networks. Random forest modeling indicated that Clostridiales was the most important bacterial order; it was significantly involved in both the direct and indirect pathways of PCP dechlorination. Citrate addition had less influence on the balance between the direct and indirect pathways of PCP dechlorination in the upland soils, whereas it enhanced biological PCP dechlorination more directly and efficiently in the paddy soils. Our results suggested that land-use type and citrate addition play a critical role in controlling the biogeochemical mechanisms of PCP dechlorination.

Anaerobic Dechlorination by a Humin-Dependent Pentachlorophenol-Dechlorinating Consortium under Autotrophic Conditions Induced by Homoacetogenesis.

Anoxic aquifers suffer from energy limitations due to the unavailability of organic substrates, as dictated by hydrogen (H2) for various electron-accepting processes. This deficiency often results in the accumulation of persistent organic pollutants, where bioremediation using organic compounds often leads to secondary contamination. This study involves the reductive dechlorination of pentachlorophenol (PCP) by dechlorinators that do not use H2 directly, but rather through a reduced state of humin—a solid-phase humic substance—as the extracellular electron donor, which requires an organic donor such as formate, lactate, etc. This shortcoming was addressed by the development of an anaerobic mixed culture that was capable of reductively dechlorinating PCP using humin under autotrophic conditions induced by homoacetogenesis. Here, H2 was used for carbon-dioxide fixation to acetate; the acetate produced was used for the reduction of humin; and consequently used for dechlorination through reduced humin. The 16SrRNA gene sequencing analysis showed Dehalobacter and Dehalobacterium as the possible dechlorinators, while Clostridium and Oxobacter were identified as the homoacetogens. Thus, this work contributes to the development of an anaerobic consortium that balanced H2 dependency, where efficiency of humin reduction extends the applicability of anaerobic microbial remediation in aquifers through autotrophy, syntrophy, and reductive dechlorination.

Effect of O2, Ni0 coatings, and iron oxide phases on pentachlorophenol dechlorination by zero-valent iron.

This study explores the zero-valent iron (ZVI) dechlorination of pentachlorophenol (PCP) and its dependence on the dissolved oxygen (O2), presence/formation of iron oxides, and presence of nickel metal on the ZVI surface. Compared to the anoxic system, PCP dechlorination was slower in the presence of O2, which is a potential competitive electron acceptor. Despite O2 presence, Ni0 deposited on the ZVI surfaces catalyzed the hydrogenation reactions and enhanced the PCP dechlorination by Ni-coated ZVI bimetal (Nic/Fe). The presence of O2 led to the formation of passivating oxides (maghemite, hematite, lepidocrocite, ferrihydrite) on the ZVI and Nic/Fe bimetallic surfaces. These passive oxides resulted in greater PCP incorporation (sorption, co-precipitation, and/or physical entrapment with the oxides) and decreased PCP dechlorination in the oxic systems compared to the anoxic systems. As received ZVI comprised of a wustite film, and in the presence of O2, only ≈ 17% PCP dechlorination observed after 25days of exposure with tetrachlorophenol being detected as the end product. Wustite remained as the predominant oxide on as received ZVI during the 25days of reaction with PCP under oxic and anoxic conditions. ZVI acid-pretreatment resulted in the replacement of wustite with magnetite and enhanced PCP degradation (e.g. ≈ 52% of the initial PCP dechlorinated after 25days under oxic condition) with accumulation of mixtures of tetra-, tri-, and dichlorophenols. When the acid-washed ZVI was rinsed in NiSO4/H2SO4 solution, Ni0 deposited on the ZVI surface and all the wustite were replaced with magnetite. After 25days of exposure to the Nic/Fe, ≈ 78% and 97% PCP dechlorination occurred under oxic and anoxic conditions, respectively, producing predominantly phenol. Wustite and magnetite are respectively electrically insulating and conducting oxides and influenced the dechlorination and H2 production. In conclusion, this study clearly demonstrates that the dissolved oxygen present in the aqueous solution decreases the PCP dechlorination and increases the PCP incorporation when using ZVI and Nic/Fe bimetallic systems. The findings provide novel insights towards deciphering and optimizing the performance of complex ZVI and bimetallic systems for PCP dechlorination in the presence of O2.

Redox properties and dechlorination capacities of landfill-derived humic-like acids

Electron transfer capacities (ETC) of humic-like acids (HLA) and their effects on dechlorination are dependent on their redox-active properties. Aging and minerals can affect the chemical compositions and structures of HLA. However, the underlying mechanism and the impacts on the dechlorination capacities of HLA are poorly understood. We investigated how redox properties change in association with the intrinsic chemical natures and exterior minerals of the HLA extracted from landfilled solid wastes. Furthermore, the ETC of the landfill-derived HLA could be strengthened by increasing landfill age and demineralization, thereby facilitating the dechlorination of pentachlorophenol (PCP). The HLA molecules started to polymerize aromatic macromolecules during landfilling, leading to an increase in ETC and dechlorination capacities. Macromolecular HLA were dissociated to smaller molecules and exposed more aromatic and carboxyl groups when separated from minerals, which enhanced the ETC and the dechlorination abilities of the HLA. Microbial-mediated dechlorination was an effective way to degrade PCP, and almost 80% of the PCP was transformed after 40 days of demineralized HLA and Shewanella oneidensis MR-1 incubation. The demineralization and aging further facilitated the microbial-mediated PCP dechlorination. The findings provide a scientific base for improving in-situ bioremediation of chlorinated compound-contaminated soils using freshly synthesized HLA.

Insights into interactions between vanadium (V) bio-reduction and pentachlorophenol dechlorination in synthetic groundwater

Aquifer co-contamination by vanadium (V) and pentachlorophenol (PCP) involves complicated biogeochemical processes that remain poorly understood, particularly from the perspective of microbial metabolism. Batch experiment results demonstrated that V(V) and PCP could be competitively bio-reduced, with 96.0 ± 1.8% of V(V) and 43.4 ± 4.6% of PCP removed during 7 d operation. V(V) was bio-transformed to vanadium (IV), which could precipitate naturally under circumneutral conditions, facilitating the removal of up to 78.2 ± 3.1% dissolved total V. The PCP reductive dechlorination products were mainly 2,4,6-trichlorophenol and 4-monochlorophenol with lower toxicity. High-throughput 16S rRNA gene sequencing indicated that Pseudomonas, Soehngenia, and Anaerolinea might be responsible for the two bio-transformations, with detected functional genes of nirS and cprA. Extracellular reduction by cytochrome c and intracellular conversion by nicotinamide adenine dinucleotide (NADH) occurred for both V(V) and PCP. Extracellular proteins in microbial-secreted extracellular polymeric substances (EPS) might also be involved in these enzymatic bioprocesses. EPS could protect microbial cells through V(V) binding by the chemically reactive carboxyl (COO−), and hydroxyl (–OH) groups. These findings elucidate the metabolic processes during anaerobic V(V) and PCP biotransformation, advance understanding of their biogeochemical fates, and provide a foundation on which to develop novel strategies for remediation of co-contaminated aquifers.

Oxidative Mineralization and Dechlorination Effects of Micron/Nanosize Birnessite on Pentachlorophenol in Contaminated Soil

Chlorinated aromatic organic compounds are extremely toxic to the environment and cause cancer to the human body. Pentachlorophenol (PCP) is a hydrophobic and ionic organic compound that is employed as a production material in various industries. Although the Taiwanese government has banned the use of PCP for years, large PCP-contaminated areas remain in Southern Taiwan. Chemical oxidation, which has been proposed as a viable method for restoring PCP-contaminated areas, involves the use of micronanosize birnessite (δ-MnO2), which is a type of manganese oxide and a natural mineral in soil environments. The goal of this study was to simulate the decontamination of the underlying soil of the PCP-contaminated areas, which is situated in anaerobic and lightless environment. Through the use of a self-developed gas release and absorption reaction flask, the oxidative mineral decarboxylation and dechlorination effects of δ-MnO2 on PCP in aerobic and anaerobic (with oxygen removed through the use of nitrogen) environments without light were investigated. Results indicated that adding δ-MnO2 facilitated the oxidative decarboxylation and dechlorination of PCP and the release of Cl− in an aerobic, lightless environment without microbial activity. In the anaerobic environment, the oxidative decarboxylation effect of δ-MnO2 on PCP decreased significantly, and the dechlorination effect was the primary reaction. Accordingly, adding δ-MnO2 inorganically destroys aromatic benzene and releases CO2 and Cl−. The molar ratio between CO2 and Cl− was calculated to assess the mechanisms of the distinct reaction systems. The parameters and data acquired from the experiment, which involved simulating the conditions of the contaminated areas, can be used in planning the on-site management of the PCP contamination; in particular, these parameters and data provide a reference for eliminating PCP from underlying soil—including groundwater-saturated layers.

Biochar mediates activation of aged nanoscale ZVI by Shewanella putrefaciens CN32 to enhance the degradation of Pentachlorophenol

The bioreduction of aged nanoscale zero valent iron (NZVI) by Shewanella putrefaciens CN32 (CN32) in the presence of different biochar materials was conducted to understand how biochars mediated the activation of aged NZVI to enhance the removal efficiency of contaminants. The results indicated that the prepared biochars contained different oxygen-containing functional groups (such as OCO, COOH, CO, CO, CC, CH and CC). The biochars significantly enhance electron transfer from CN32 to aged NZVI, thus accelerating reductive dechlorination of Pentachlorophenol (PCP). The maximum PCP degradation rate (kmax) was 2.45 mg·L−1·d−1, which was 2.6 times greater than that of the biochar-free control (0.94 mg·L−1·d−1). The intermediates of phenol were detected after 30 days, likely indicating that reductive dechlorination was the dechlorination pathway of PCP. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis showed that vivianite, as a secondary mineral, was formed during the bioreduction aged NZVI-BC600 (Biochar prepared at 600 °C with NZVI activation) by CN32. Vivianite was formed mainly through the reaction of Fe(II) and PO43−. The combined electrochemical and electron paramagnetic resonance analysis might suggest that biochar associated semiquinone radical (CO) were likely involved in the bioreduction of aged NZVI. This study provided some theoretical support for further research on biochar mediated bioreduction activation of aged NZVI to enhance the degradation of contaminants.

Pentachlorophenol alters the acetate-assimilating microbial community and redox cycling in anoxic soils

Acetate is a common electron donor that can drive microbial reductive processes in anaerobic environments. Apart from acting as a terminal electron acceptor, chlorinated organic pollutant of pentachlorophenol (PCP) has antimicrobial properties but little is known about its effect on anaerobic microbial populations during bioremediation. To elucidate the effect of PCP on the anaerobic microbial community, DNA-based stable isotope probing was performed using 13C-acetate as a substrate in two depths (0–20 cm and 80–100 cm) of mangrove soils. The addition of PCP had little influence on Fe(III) reduction, but dramatically inhibited the SO42− reduction, resulting in a high emission of CH4 under anoxic conditions. Correspondingly, PCP significantly affected the composition of prokaryotic 13C-labeled OTUs (Operational Taxonomic Units) at both soil depths. Members of Clostridiales (Firmicutes) and Burkholderiales (Betaproteobacteria) were dominant 13C-acetate utilizers and potential PCP degraders. The PCP addition decreased sulfate reduction process through inhibition of classical sulfate- and sulfur-reducing bacteria belonging to families of Desulfarculaceae, Desulfobulbaceae and Desulfobacteraceae. Our study showed that indigenous microbial communities associated with terminal electron-accepting pathways (e.g. Fe3+ and SO42− reduction) changed differently during PCP dechlorination. These findings suggest a great impact of chlorinated pollutants on the soil biogeochemical processes.

Commercial steel wool used for Zero Valent Iron and as a source of dissolved iron in a combined red-ox process for pentachlorophenol degradation in tap water

Pentachlorophenol solutions in tap water were treated with a combined process of zero valent iron (ZVI) reduction followed by a photo-Fenton oxidation. Commercial steel wool was used as ZVI source, demonstrating its effectivity for pentachlorophenol de-chlorination at acidic pH values. The reductive pathway was monitored by the use of excitation emission matrices, showing the transformation of the initial compound into the fluorescent species 4-chlorophenol and phenol.While the use of tap water represented a drawback in photo-Fenton oxidative reactions (at least half kinetic constants values) an improvement was achieved when the reductive stage was applied in the studied pH range. The transformation of pentachlorophenol into phenol produced an increase in oxidative stage rate of about 8 times. This fact could be related to the treatment time and hydrogen peroxide consumption of the photo-Fenton process, enhancing the economic viability. Furthermore, the de-chlorination of the pentachlorophenol minimized the possibility of releasing toxic by-products in the photo-Fenton process.

Characterization of biochars derived from different materials and their effects on microbial dechlorination of pentachlorophenol in a consortium.

The properties of biochars derived from different raw materials (rice husk, bamboo, caragana, and garbage) and their effects on the microbial reductive dechlorination of pentachlorophenol (PCP) were investigated to understand how biochars influence the biotransformation of environmental pollutants. The results indicated that only caragana-derived biochar showed stable electron transfer activity for PCP dechlorination. Electro(chemical) analyses revealed that caragana biochar had the highest electrical conductivity (EC) (2.22 × 106 μS cm−1), while those of the other biochars were <1500 μS cm−1. The electron transfer capacities were within the ranges of 61.63–155.83 μmol e− g−1. Cyclic voltammetry analysis suggested that there were no obvious redox peaks for the biochars, while the Fourier transform infrared analysis showed similar transmission spectra with variable absorption intensity; this suggested that all biochars possessed similar structures and functional group classes and the enhancement of PCP dechlorination was not attributable to the redox reaction. Overall, the beneficial effects of caragana biochar on PCP dechlorination depended on the EC rather than the redox functional groups, possibly because high EC values enabled the highest electron transfer, and thus resulted in the greatest promotion of reductive dechlorination activity.