Complete reductive dechlorination and mineralization of pentachlorophenol by anaerobic microorganisms

Core taxa, co-occurrence pattern, diversity, and metabolic pathways contributing to robust anaerobic biodegradation of chlorophenol

It is hard to achieve robustness in anaerobic biodegradation of trichlorophenol (TCP). We hypothesized that specific combinations of environmental factors determine phylogenetic diversity and play important roles in the decomposition and stability of TCP-biodegrading bacteria. The anaerobic bioreactor was operated at 35 °C (H condition) or 30 °C (L condition) and mainly fed with TCP (from 28 μM to 180 μM) and organic material. Metagenome sequencing was combined with 16S rRNA gene amplicon sequencing for the microbial community analysis. The results exhibited that the property of robustness occurred in specific conditions. The corresponding co-occurrence and diversity patterns suggest high collectivization, degree and evenness for robust communities. Two types of core functional taxa were recognized: dechlorinators (unclassified Anaerolineae, Thermanaerothrix and Desulfovibrio) and ring-opening members (unclassified Proteobacteria, Methanosarcina, Methanoperedens, and Rubrobacter). The deterministic process of the expansion of niche of syntrophic bacteria at higher temperatures was confirmed. The reductive and hydrolytic dechlorination mechanisms jointly lead to C-Cl bond cleavage. H ultimately adapted to the stress of high TCP loading, with more abundant ring-opening enzyme (EC 3.1.1.45, ∼55%) and hydrolytic dechlorinase (EC 3.8.1.5, 26.5%) genes than L (∼47%, 10.5%). The functional structure (based on KEGG) in H was highly stable despite the high loading of TCP (up to 60 μM), but not in L. Furthermore, an unknown taxon with multiple functions (dechlorinating and ring-opening) was found based on genetic sequencing; its functional contribution of EC 3.8.1.5 in H (26.5%) was higher than that in L (10.5%), and it possessed a new metabolic pathway for biodegradation of halogenated aromatic compounds. This new finding is supplementary to the robust mechanisms underlying organic chlorine biodegradation, which can be used to support the engineering, regulation, and design of synthetic microbiomes.

Anaerobic Microbial Dechlorination of 6:2 Chlorinated Polyfluorooctane Ether Sulfonate and the Underlying Mechanisms

The microbial transformation potential of 6:2 chlorinated polyfluorooctane ether sulfonate (6:2 Cl-PFESA) was explored in anaerobic microbial systems. Microbial communities from anaerobic wastewater sludge, an anaerobic digester, and anaerobic dechlorinating cultures enriched from aquifer materials reductively dechlorinated 6:2 Cl-PFESA to 6:2 hydrogen-substituted polyfluorooctane ether sulfonate (6:2 H-PFESA), which was identified as the sole metabolite by non-target analysis. Rapid and complete reductive dechlorination of 6:2 Cl-PFESA was achieved by the anaerobic dechlorinating cultures. The microbial community of the anaerobic dechlorinating cultures was impacted by 6:2 Cl-PFESA exposure. Organohalide-respiring bacteria originally present in the anaerobic dechlorinating cultures, including Geobacter, Dehalobacter, and Dehalococcoides, decreased in relative abundance over time. As the relative abundance of organohalide-respiring bacteria decreased, the rates of 6:2 Cl-PFESA dechlorination decreased, suggesting that the most likely mechanism for reductive dechlorination of 6:2 Cl-PFESA was co-metabolism rather than organohalide respiration. Reductive defluorination of 6:2 Cl-PFESA was not observed. Furthermore, 6:2 H-PFESA exhibited 5.5 times lower sorption affinity to the suspended biosolids than 6:2 Cl-PFESA, with the prospect of increased mobility in the environment. These results show the susceptibility of 6:2 Cl-PFESA to microbially mediated reductive dechlorination and the likely persistence of the product, 6:2 H-PFESA, in anaerobic environments.

Bioremediation of chlorophenol-contaminated sawmill soil using pilot-scale bioreactors under consecutive anaerobic-aerobic conditions

Chlorophenols (CPs), including pentachlorophenol (PCP), are chemicals of concern due to their toxicity and persistence. Here we describe a successful reactor-based remediation of CP-contaminated soil and assess changes in the toxicity patterns and bacterial communities during the remediation. The remediation consisted of separating half of the contaminated soil to be ground (samples M) in order to test whether the grinding expedited the remediation, the other half was left unground (samples P). Both soils were mixed with wastewater treatment sludge to increase their bacterial diversity and facilitate the degradation of CPs, and the resultant mixtures were placed in 2 bioreactors, M and P, operated for 16 months under anaerobic conditions to favor dehalogenation and for an additional 16 months under aerobic conditions to achieve complete mineralization. Samples were taken every 4 months for toxicity and microbial analyses. The results showed a 64% removal of total CPs (ΣCPs) in reactor P after just 18 months of remediation, whereas similar depletion in reactor M occurred after ∼25 months, indicating that the grinding decelerated the remediation. By the end of the experiment, both reactors achieved 93.5-95% removal. The toxicity tests showed a decrease in toxicity as the remediation progressed. The succession of bacterial communities over time was significantly associated with pH, anaerobic/aerobic phase and the concentration of the majority of CP congeners. Our data indicate that the supplementation of contaminated soil with sludge and further incubation in pilot-scale bioreactors under consecutive anaerobic-aerobic conditions proved to be effective at the remediation of CP-contaminated soil.

The microbial community responsible for dechlorination and benzene ring opening during anaerobic degradation of 2,4,6‑trichlorophenol

This study describes the dechlorination ability of acclimated biomass, the high-throughput sequencing of the 16S ribosomal RNA (rRNA) gene of such microorganisms, and the analysis of their community structure in relation to special functions. Two types of acclimated biomass (AB-1 and AB-2) were obtained via different acclimated treatment processes and were used to degrade 2,4,6‑trichlorophenol. The degradation pathway and characteristics of trichlorophenol degradation were different between the two groups. AB-1 degraded trichlorophenol only to 4-chlorophenol. AB-2 completely dechlorinated trichlorophenol and opened the benzene ring. The 16S rRNA high-throughput sequencing method was employed to examine the microbial diversity. It was found that the microbial richness and diversity of AB-1 were higher than those of AB-2. Firmicutes and Bacteroidetes were 2.7-fold and 4.3-fold more abundant, respectively, in AB-1 than in AB-2. Dechlorination bacteria in AB-1 mainly included Desulfobulbus, Desulfovibrio, Dechloromonas, and Geobacter. The above-mentioned bacteria were less abundant in AB-2, but the abundance of Desulfomicrobium was twofold higher in AB-2 than in AB-1. The two types of acclimated biomass contained different hydrogen (H₂)-producing bacteria. AB-2 showed higher abundance and diversity of hydrogen-producing bacteria. There was no Ignavibacteriae in AB-1, whereas its abundance in AB-2 was 8.4%. In this biomass, Ignavibacteriae was responsible for opening of the benzene ring. This study indicates that the abundance and diversity of microorganisms are not necessarily beneficial to the formation of a functional dechlorinating community. The H₂-producing bacteria (which showed greater abundance and diversity) and Ignavibacterium were assumed to be core functional populations that gave AB-2 stronger dechlorination and phenol-degradation abilities. Control of lower oxidation reduction potential (E_h) and higher temperatures by means of fresh aerobic activated sludge as the starting microbial group, caused rapid complete dechlorination of 2,4,6‑trichlorophenol and benzene ring opening.

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 SO₄^2- 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.

A three-act play: pentachlorophenol threats to the cork oak forest soils mycobiome

Atmospheric release of persistent organic pollutants (POPs) constitutes a silent threat through chronic contamination of soils at global scale; yet fundamental understanding of their occurrence, sources and fate is still largely lacking. Similar to a three act play, this review comprises Setup, Confrontation and Resolution. The first emphasises the eighty years of the history of pentachlorophenol (PCP) usage, only recently classified as POP. The second focus on active sources of PCP pollution, including inside cork oak forests in N.W. Tunisia; a threat partially neutralised by the soil microbial diversity, especially fungi. As Resolution, the need for improved knowledge on the global distribution and impacts of PCP in soil microbial diversity as means to preserve the multi-functionality of terrestrial ecosystem is emphasised.

Bacterial Biotransformation of Pentachlorophenol and Micropollutants Formed during Its Production Process

Pentachlorophenol (PCP) is a toxic and persistent wood and cellulose preservative extensively used in the past decades. The production process of PCP generates polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) as micropollutants. PCDD/Fs are also known to be very persistent and dangerous for human health and ecosystem functioning. Several physico-chemical and biological technologies have been used to remove PCP and PCDD/Fs from the environment. Bacterial degradation appears to be a cost-effective way of removing these contaminants from soil while causing little impact on the environment. Several bacteria that cometabolize or use these pollutants as their sole source of carbon have been isolated and characterized. This review summarizes current knowledge on the metabolic pathways of bacterial degradation of PCP and PCDD/Fs. PCP can be successfully degraded aerobically or anaerobically by bacteria. Highly chlorinated PCDD/Fs are more likely to be reductively dechlorinated, while less chlorinated PCDD/Fs are more prone to aerobic degradation. The biochemical and genetic basis of these pollutants’ degradation is also described. There are several documented studies of effective applications of bioremediation techniques for the removal of PCP and PCDD/Fs from soil and sediments. These findings suggest that biodegradation can occur and be applied to treat these contaminants.

Dechlorination of chlorinated phenols by subnanoscale Pd 0 /Fe 0 intercalated in smectite: pathway, reactivity, and selectivity

Smectite clay was employed as templated matrix to prepare subnanoscale Pd(0)/Fe(0) particles, and their components as well as intercalated architectures were well characterized by X-ray energy dispersive spectroscopy (X-EDS) and X-ray diffraction (XRD). Furthermore, as-prepared Pd(0)/Fe(0) subnanoscale nanoparticles were evaluated for their dechlorination effect using chlorinated phenols as model molecules. As a result, pentachlorophenol (PCP) is selectively transformed to phenol in a stepwise dechlorination pathway within 6h, and the dechlorination rate constants show linearly relationship with contents of Pd as its loadings <0.065%. Comparing with PCP, other chlorinated phenols display similar degradation pattern but within much shorter time frame. The dechlorination rate of chlorinated phenols increases with decreasing in number of -Cl attached to aromatic ring, which can be predicted by the total charge of the aromatic ring, exhibiting an inversely linear relationship with the dechlorination rates. While the selectivity of dechlorination depends on the charges associated with the individual aromatic carbon. Chloro-functional groups at the ortho-position are easier to be dechlorinated than that at meta- and para- positions yielding primarily 3,4,5-TCP as intermediate from PCP, further to phenol. The effective dechlorination warrants their potential utilizations in development of in-situ remediation technologies for organic pollutants in contaminated water.

Controlling a toxic shock of pentachlorophenol (PCP) to anaerobic digestion using activated carbon addition

Several powdered and granular activated carbons (PACs and GACs) were tested for adsorption of pentachlorophenol (PCP) in bench-scale anaerobic digestion reactors to control the toxicity of PCP to acetoclastic methanogenesis. Results showed that the adsorption capacities of PAC were reduced by 21-54%, depending on the PAC addition time, in the presence of the methanogenic sludge compared to the controls without sludge. As a preventive measure, PAC at a low dose of 20% (mass ratio to the VSS) added 24 h prior to, or simultaneously with, the addition of PCP could completely eliminate the toxic effects of PCP. At the same dose, PAC also enabled methanogenesis to recover immediately after the sludge had been exposed to PCP for 24h. GAC was not effective in enabling the recovery of methanogenesis due to its slow adsorption kinetics; however, at a dose of 80% it could partially ameliorate the toxic shock of PCP.

Dehalococcoides mccartyi strain JNA dechlorinates multiple chlorinated phenols including pentachlorophenol and harbors at least 19 reductive dehalogenase homologous genes

Pentachlorophenol and other chlorinated phenols are highly toxic ubiquitous environmental pollutants. Using gas chromatographic analysis we determined that Dehalococcoides mccartyi strain JNA in pure culture dechlorinated pentachlorophenol to 3,5-dichlorophenol (DCP) via removal of the ortho and para chlorines in all of the three possible pathways. In addition, JNA dechlorinated 2,3,4,6-tetrachlorophenol via 2,4,6-trichlorophenol (TCP) and 2,4,5-TCP to 2,4-DCP and 3,4-DCP, respectively, and dechlorinated 2,3,6-TCP to 3-chlorophenol (CP) via 2,5-DCP. JNA converted 2,3,4-TCP to 3,4-DCP and 2,4-DCP by ortho and meta dechlorination, respectively. 2,3-DCP was dechlorinated to 3-CP, and, because cultures using it could be transferred with a low inoculum (0.5 to 1.5% vol/vol), it may act as an electron acceptor to support growth. Using PCR amplification with targeted and degenerate primers followed by cloning and sequencing, we determined that JNA harbors at least 19 reductive dehalogenase homologous (rdh) genes including orthologs of pcbA4 and pcbA5, pceA, and mbrA, but not tceA or vcrA. Many of these genes are shared with D. mccartyi strains CBDB1, DCMB5, GT, and CG5. Strain JNA has previously been shown to extensively dechlorinate the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1260. Collectively the data suggest that strain JNA may be well adapted to survive in sites contaminated with chlorinated aromatics and may be useful for in situ bioremediation.

Bacterial degradation of chlorophenols and their derivatives

Chlorophenols (CPs) and their derivatives are persistent environmental pollutants which are used in the manufacture of dyes, drugs, pesticides and other industrial products. CPs, which include monochlorophenols, polychlorophenols, chloronitrophenols, chloroaminophenols and chloromethylphenols, are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Several physico-chemical and biological methods have been used for removal of CPs from the environment. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing CPs from the environment. Several bacteria that use CPs as their sole carbon and energy sources have been isolated and characterized. Additionally, the metabolic pathways for degradation of CPs have been studied in bacteria and the genes and enzymes involved in the degradation of various CPs have been identified and characterized. This review describes the biochemical and genetic basis of the degradation of CPs and their derivatives.

Nocardioides daeguensis sp. nov., a nitrate-reducing bacterium isolated from activated sludge of an industrial wastewater treatment plant

A Gram-reaction-positive, rod-shaped, non-spore-forming bacterium (strain 2C1-5(T)) was isolated from activated sludge of an industrial wastewater treatment plant in Daegu, South Korea. Its taxonomic position was investigated by using a polyphasic approach. On the basis of 16S rRNA gene sequence similarity, the closest phylogenetic relatives were the type strains of Nocardioides nitrophenolicus (98.6 % similarity), N. kongjuensis (98.5 %), N. caeni (98.4 %), N. simplex (98.3 %), N. aromaticivorans (98.1 %) and N. ginsengisoli (97.5 %); the phylogenetic distance from other species with validly published names within the genus Nocardioides was greater than 3 %. Strain 2C1-5(T) was characterized chemotaxonomically as having ll-2,6-diaminopimelic acid in the cell-wall peptidoglycan, MK-8(H4) as the predominant menaquinone and iso-C16 : 0, C16 : 0 and C17 : 1ω6c as the major fatty acids. The G+C content of the genomic DNA was 74.9 mol%. These chemotaxonomic properties and phenotypic characteristics supported the affiliation of strain 2C1-5(T) to the genus Nocardioides. The results of physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 2C1-5(T) from existing species with validly published names. Therefore, strain 2C1-5(T) represents a novel species of the genus Nocardioides, for which the name Nocardioides daeguensis sp. nov. is proposed, with the type strain 2C1-5(T) ( = JCM 17460(T) = KCTC 19799(T)).

Long-term anaerobic mineralization of pentachlorophenol in a continuous-flow system using only lactate as an external nutrient

A simple anaerobic upflow column system (15 cm long, 5 cm inner diameter) for complete pentachlorophenol (PCP) mineralization has been established using a microbial consortium requiring only lactate as the external nutrient. With lactate as an electron donor, PCP was dechlorinated to 3-chlorophenol (3-CP) and phenol. The degradation of 3-CP and phenol proceeded without an external electron acceptor, indicating fermentative or syntrophic characteristics. A tracer experiment using (14)C-U-ring-labeled PCP confirmed the conversion of PCP into CO(2) (54.1%), CH(4) (48.1%), and biomass (0.6%). The nitrogen required for degradation was supplied by N(2)-fixation, evidenced from the nitrogen balance and an acetylene reduction assay. A 16S rRNA gene library analysis showed that bottom of the upflow column harbored the potential dechlorinators, Dehalobacter and Desulfitobacterium, and the phenol/3-CP fermentative or syntrophic degraders, Cryptanaerobacter and Syntrophus. The nitrogen-fixing facultative anaerobes, Rhizobiales, were detected in the top of the upflow column, with other possible nitrogen-fixers at both bottom and top of the upflow column. The mineralization rate reached 1.96 μmoles L(-1) d(-1) for 50 μM of the initial PCP concentration: one of the highest efficiencies reported. This compact anaerobic mineralization system requiring no external supply of an electron acceptor would be useful for the remediation of chlorinated aromatic compounds under anaerobic conditions.

Brevibacterium daeguense sp. nov., a nitrate-reducing bacterium isolated from a 4-chlorophenol enrichment culture

A Gram-reaction-positive, non-spore-forming, aerobic actinobacterial strain (2C6-41T) was isolated from the activated sludge from an industrial wastewater treatment plant in Daegu, South Korea. Its taxonomic position was investigated by using a polyphasic approach. On the basis of 16S rRNA gene sequence similarity, closest phylogenetic relatives to strain 2C6-41T were Brevibacterium pityocampae DSM 21720T (97.2 %), Brevibacterium salitolerans KCTC 19616T (96.7 %), Brevibacterium album KCTC 19173T (96.2 %) and Brevibacterium samyangense KCCM 42316T (96.2 %). The DNA G+C content of strain 2C6-41T was 66.4 mol%. Chemotaxonomic data, which included MK-8(H2) as the major menaquinone; meso-diaminopimelic acid, glutamic acid and alanine as cell-wall amino acids; ribose, mannose and glucose as major cell-wall sugars; and anteiso-C15 : 0, anteiso-C17 : 0, C16 : 0 and iso-C15 : 0 as major fatty acids, supported the affiliation of strain 2C6-41T to the genus Brevibacterium . The aromatic ring cleavage enzyme catechol 1,2-dioxygenase was not detected in strain 2C6-41T, but catechol 2,3-dioxygenase was detected. The results of physiological and biochemical tests, and the low level of DNA–DNA relatedness to the closest phylogenetic relative enabled strain 2C6-41T to be differentiated genotypically and phenotypically from recognized species of the genus Brevibacterium . The isolate is therefore considered to represent a novel species in the genus Brevibacterium , for which the name Brevibacterium daeguense sp. nov. is proposed. The type strain is 2C6-41T ( = KCTC 19800T = JCM 17458T).

Microbial dechlorination of chloroorganics and simultaneous decolorization of pulp-paper mill effluent by Pseudomonas putida MTCC 10510 augmentation

The physicochemical analyses of pulp-paper mill effluent revealed that it was dark brown with 1761 ± 2.3 color PtCo units having slightly alkaline pH, high biological oxygen demand and chemical oxygen demand values, and contained large quantities of organic and inorganic constituents, well above the prescribed standards. The bacterial growth, color reduction, and dechlorination were evident in all the four sets of experiments with different possible combinations of nutrient supplementation and Pseudomonas putida augmentation. A high degree of decolorization at 29.7% and 27.4% was observed by the effluent native microflora during 48 and 24 h, in unaugmented effluent supplemented with glucose + yeast extract and glucose + peptone, respectively. The extent of decolorization in glucose + yeast extract unaugmented effluent also corresponded with high degree of dechlorination (59.3%) during 60-h incubation (SET III). An appreciable level of growth, decolorization, and dechlorination was evident in nutrient unsupplemented P. putida augmented effluent as well as in the control natural effluent. However, a maximum level of growth response (OD 1.641-1.902) during 36-48 h, removal of color (39.72-48.2%) during 24-36 h, and chloride ions (80.1-83.5%) during 36 h was achieved in P. putida augmented effluent supplemented with glucose + yeast extract or peptone. Therefore, supplementation of effluent with glucose and yeast extract or peptone and concomitant augmentation with P. putida is required for efficient effluent decolorization and detoxification.

Chlorophenols and other related derivatives of environmental concern: properties, distribution and microbial degradation processes

Chlorophenols are chlorinated aromatic compound structures and are commonly found in pesticide preparations as well as industrial wastes. They are recalcitrant to biodegradation and consequently persistent in the environment. A variety of chlorophenols derivatives compounds are highly toxic, mutagenic and carcinogenic for living organisms. Biological transformation by microorganisms is one of the key remediation options that can be exploited to solve environmental pollution problems caused by these notorious compounds. The key enzymes in the microbial degradation of chlorophenols are the oxygenases and dioxygenases. These enzymes can be engineered for enhanced degradation of highly chlorinated aromatic compounds through directed evolution methods. This review underscores the mechanisms of chlorophenols biodegradation with the view to understanding how bioremediation processes can be optimized for cleaning up chloroaromatic contaminated environments.

Strategies for decolorization and detoxification of pulp and paper mill effluent

The potential hazards associated with industrial effluents, coupled with increasing awareness of environment problems, have prompted many countries to limit the indiscriminate discharge of untreated wastewaters. The pulp and paper industry has been among the most significant of industrial polluters of the waterways, and therefore has been one of the industries of concern. The pulp and paper industry produces large quantities of brown/black effluent that primarily result from pulping, bleaching, and paper-making production stages. The dark color and toxicity of pulp-paper mill effluent comes primarily from lignin and its chlorinated derivatives (e.g., lignosulphonic acid, resins, phenols, and hydrocarbons) that are released during various processing steps of lignocellulosic materials. The color originates from pulping and pulp bleaching stages, while adsorbable organic halides (AOX) originates exclusively from chlorine bleaching. Discharge of untreated effluent results in increased BOD/COD, slime growth, thermal problems, scum formation, discoloration, loss of aesthetic quality and toxicity to the aquatic life, in the receiving waterbodies. The dark brow color of pulp-paper effluent is not only responsible for aesthetic unacceptability, but also prevents the passage of sunlight through colored waterbodies. This reduces the photosynthetic activity of aquatic flora, ultimately causing depletion of dissolved oxygen. The pulp-paper organic waste, coupled with the presence of chlorine, results in the generation of highly chlorinated organic compounds. These toxic constituents of wastewater pose a human health risk through long term exposure. via drinking water and\or through consumption of fish that can bioaccumulate certain pollutants from the food chain. Therefore, considerable attention has been focused by many countries on decolorization of paper mill effluents , along with reduction in the contaminants that pose human health or other environmental hazards. Various physicochemical remediation treatments in the pulp-paper industry are now used, or have been suggested, but often are not implemented, because of the high cost involved. More recently, the paper and pulp industry has been investigating the use of biological remediation steps to replace or augment current treatment strategies. Certain biological treatments offer opportunities to reduce cost (both capital and operating), reduce energy consumption, and minimize environmental impact. Two primary approaches may be effective to curtail release of toxic effluents: first, development of pulping and bleaching processes that emphasize improved oxygen delignification or biopulping, plus partial or complete replacement of chlorine treatment with hydrogen peroxide or with biobleaching; second, implementation of biological processing that involves sequential two-step anaerobic-aerobic or three-step aerobic-anaerobic treatment technologies at end of pipe. The selection of the specific process will depend upon the type of pollutants/toxicants/mutagens present in the effluent. The use of environmental-friendly technologies in the pulp and paper industry is becoming more popular, partly because of increasing regulation, and partly because of the availability of new techniques that can be used to economically deal with pollutants in the effluents. Moreover, biotechnology research methods are offering promise for even greater improvements in the future. The obvious ultimate goal of the industry and the regulators should be zero emission through recycling of industrial wastewater, or discharge of the bare minimum amount of toxicants or color.

Effects of sulfuroxy anions on degradation of pentachlorophenol by a methanogenic enrichment culture

We studied the degradation of pentachlorophenol (PCP) under methanogenic and sulfate-reducing conditions with an anaerobic mixed culture derived from sewage sludge. The consortium degraded PCP via 2,3,4,5-tetrachlorophenol, 3,4,5-trichlorophenol, and 3,5-dichlorophenol and eventually accumulated 3-chlorophenol. Dechlorination of PCP and metabolites was inhibited in the presence of sulfate, thiosulfate, and sulfite. A decrease in the rate of PCP transformation was noted when the endogenous dissolved H(2) was depleted below 0.11 muM in sulfate-reducing cultures. The effect on dechlorination observed with sulfate could be relieved by addition of molybdate, a competitive inhibitor of sulfate reduction. Addition of H(2) reduced the inhibition observed with sulfuroxy anions. The inhibitory effect of sulfuroxy anions may be due to a competition for H(2) between sulfate reduction and dechlorination. When cultured under methanogenic conditions, the consortium degraded several chlorinated and brominated phenols.

Pentachlorophenol (PCP) dechlorination in horizontal-flow anaerobic immobilized biomass (HAIB) reactors

This study verifies the potential applicability of horizontal-flow anaerobic immobilized biomass (HAIB) reactors to pentachlorophenol (PCP) dechlorination. Two bench-scale HAIB reactors (R1 and R2) were filled with cubic polyurethane foam matrices containing immobilized anaerobic sludge. The reactors were then continuously fed with synthetic wastewater consisting of PCP, glucose, acetic acid, and formic acid as co-substrates for PCP anaerobic degradation. Before being immobilized in polyurethane foam matrices, the biomass was exposed to wastewater containing PCP in reactors fed at a semi-continuous rate of 2.0 microg PCP g(-1) VS. The applied PCP loading rate was increased from 0.05 to 2.59 mg PCP l(-1)day(-1) for R1, and from 0.06 to 4.15 mg PCP l(-1)day(-1) for R2. The organic loading rates (OLR) were 1.1 and 1.7 kg COD m(-3)day(-1) at hydraulic retention times (HRT) of 24h for R1 and 18 h for R2. Under such conditions, chemical oxygen demand (COD) removal efficiencies of up to 98% were achieved in the HAIB reactors. Both reactors exhibited the ability to remove 97% of the loaded PCP. Dichlorophenol (DCP) was the primary chlorophenol detected in the effluent. The adsorption of PCP and metabolites formed during PCP degradation in the packed bed was negligible for PCP removal efficiency.

Studies on the toxic effects of pentachlorophenol on the biological activity of anaerobic granular sludge

In order to explore the pathway of the anaerobic biotreatment of the wastewater containing pentachlorophenol (PCP) and ensure the normal operation of Upflow Anaerobic Sludge Blanket (UASB) reactor, the anaerobic sludge under different acclimation conditions were selected to seed and start up UASB reactors. Anaerobic toxicity assays were employed to study the biological activity, the tolerance and the capacity to degrade PCP of different anaerobic granular sludge from UASB reactors. Results showed that the anaerobic granular sludge acclimated to chlorophenols (CPs) could degrade PCP more quickly (up to 9.50mg-PCP g(-1)TVS d(-1)). And the anaerobic granular sludge without acclimation to CPs had only a little activity of degrading PCP (less than 0.07 mg-PCP g(-1)TVS d(-1)). Different PCP concentrations (2, 4, 6, 8 mg L(-1)) had different inhibition effects on glucose utilization, volatile fatted acidity (VFA)-degrading and methanogens activity of PCP degradation anaerobic granular sludge, and the biological activity declined with the increase in PCP concentration. The methanogens activity suffered inhibition from PCP more easily. The different acclimation patterns of seeded sludge had distinctly different effects on biological activity of the degradation of PCP of anaerobic granular sludge from UASB reactors. The biological activity of the anaerobic granular sludge acclimated to PCP only was also inhibited. This inhibition was weak compared to that of anaerobic granular sludge acclimated to CPs, further, the activity could recover more quickly in this case. In the same reactor, the anaerobic granular sludge from the mid and base layers showed higher tolerance to PCP than that from super layer or if the sludge is unacclimated to CPs, and the corresponding recovery time of the biological activity in the mid and base layers were short. Acetate-utilizing methanogens and syntrophic propinate degraders were sensitive to PCP, compared to syntrophic butyrate degraders.

Effects of solvent, pH, salts and resin fatty acids on the dechlorination of pentachlorophenol using magnesium-silver and magnesium-palladium bimetallic systems

The effects of pH, organic co-solvent, salts such as sodium chloride, sodium sulfate, and co-pollutants, resin and fatty acids (RFAs) on the dechlorination of pentachlorophenol (PCP) by magnesium/silver (Mg/Ag) and magnesium/palladium (Mg/Pd) systems were examined in the present investigations. Such studies provide relevant information about the applicability of bimetallic systems for remediation of raw wastewaters (such as pulp bleaching effluents) or groundwater. Removal efficiencies of 10 mg L(-1) PCP by Mg/Pd and Mg/Ag systems at the end of 1 h reaction were 93% and 78%, respectively, in the presence of acetone (1% v/v). On the other hand, the removal efficiencies were 86% and 70% for reactions conducted in alcoholic solvents (1% v/v) using Mg/Pd and Mg/Ag systems, respectively. The efficiencies of PCP removal by the two bimetallic systems could be correlated to the dipole moments of co-solvents used. The second order reaction rate constant for PCP removal by Mg/Ag system was highest (0.03 L mg(-1) min(-1)) in the absence of any pH-control mechanism. Optimum pH for the dechlorination of PCP by Mg/Pd system was found to be approximately 5.5 and >92% of the compound was removed within 15 min of reaction. Presence of chlorinated and non-chlorinated resin fatty acids (RFAs) resulted in substantial reduction in the rate and extent of PCP removal by Mg/Ag system whereas dechlorination by Mg/Pd remained unaffected. Presence of sodium sulfate or sodium chloride in the reaction phase reduced the rate and extent of PCP removal by Mg/Ag system. PCP dechlorination by Mg/Pd system was adversely impacted by the addition of sodium chloride and unaffected by the presence of sodium sulfate.

Uptake, removal, accumulation, and phytotoxicity of 4-chlorophenol in willow trees

4-chlorophenol (4-CP) is a well-known hazardous chlorinated compound and a precursor for the synthesis of the herbicide 2,4-dichlorophenoxyacetate. The relation between uptake, accumulation, toxicity, and removal of 4-CP in willow trees (Salix viminalis) was determined. In addition, the feasibility of implementing phytoremediation as a treatment method for 4-CP contamination was investigated. Willows were exposed to 4-CP levels < or =79.9 mg/L in hydroponic solution. The transpiration of the trees was used to determine toxic effects. Almost no inhibition of transpiration was detected at concentrations > or =15 mg/L. For concentrations > or =37.3 mg/L, transpiration decreased to < or =50%, and the trees wilted. Trees exposed to 79.9 mg/L wilted and eventually died. For concentrations of 79.9 mg/L, a significantly higher amount of 4-CP remained at the end of experiments in the test system compared with the amount remaining at all other concentrations. The loss of chemical from the system in experiments with trees was high, < or =99.5%. In treeless experiments, the mass loss of 4-CP was only 6% to 10%. The results indicated that degradation in the root zone is the main reason for the removal of 4-CP from the media. Phytoremediation of 4-CP in willow trees seems to be a remediation option, especially at concentrations <37.3 mg/L, at which point degradation of 4-CP is rapid and efficient, and the toxic effects on trees are not lethal.

Enhanced biodegradation of hexachlorocyclohexane in upflow anaerobic sludge blanket reactor using methanol as an electron donor

Anaerobic dechlorination of technical grade hexachlorocyclohexane (THCH) was studied in a continuous upflow anaerobic sludge blanket (UASB) reactor with methanol as a supplementary substrate and electron donor. A reactor without methanol served as the experimental control. The inlet feed concentration of THCH in both the experimental and the control UASB reactor was 100 mg l(-1). After 60 days of continuous operation, the removal of THCH was >99% in the methanol-supplemented reactor as compared to 20-35% in the control reactor. THCH was completely dechlorinated in the methanol fed reactor at 48 h HRT after 2 months of continuous operation. This period was also accompanied by increase in biomass in the reactor, which was not observed in the experimental control. Batch studies using other supplementary substrates as well as electron donors namely acetate, butyrate, formate and ethanol showed lower % dechlorination (<85%) and dechlorination rates (<3 mg g(-1)d(-1)) as compared to methanol (98%, 5 mg g(-1)d(-1)). The optimum concentration of methanol required, for stable dechlorination of THCH (100 mg l(-1)) in the UASB reactor, was found to be 500 mg l(-1). Results indicate that addition of methanol as electron donor enhances dechlorination of THCH at high inlet concentration, and is also required for stable UASB reactor performance.

Dechlorination of chlorophenols by magnesium–silver bimetallic system

More than 85% of 10 mg L(-1) of pentachlorophenol (PCP) was removed by magnesium/silver (206/1.47 mM) bimetal system in the presence of acetic acid. Dechlorination was found to be sequential and phenol was identified as the ultimate hydrocarbon skeleton along with some accumulation of tetra-, tri-, and dichlorophenols. The dechlorination reaction was found to follow second-order kinetics. Lower PCP removal efficiency (35%) was observed when the reaction was carried out in the absence of acid using Mg(0)/Ag system. When the reaction was conducted using Mg(0) alone in the presence of acid, substantial sorption of PCP occurred with very low efficiency of PCP dechlorination. Dechlorination studies on 10 mg L(-1) initial concentrations of 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and 2,4,5-trichlorophenol (2,4,5-TCP), under identical conditions as to PCP, revealed that dechlorination efficiency and reaction rate constants decrease with decreasing number of chlorine atoms on the target compound. A correlation (R(2)>0.9) between the dechlorination rate constants and E(LUMO) for chlorophenols was obtained.

Assessment of pesticide residues in two arable soils from the semi-arid and subtropical regions of China

The residues of 31 chlorinated hydrocarbons (CHCs), 25 chlorophenols (CPs), 30 organophosphorus (OP) and pyrethroid (PRT) in two arable soils from the semi-arid and subtropical regions of China were assessed. Data obtained indicate that the main compounds of CHC pesticide residues in the semi-arid soil were 4,4'-DDE (25.3 ng/g) and beta-HCH (14.1 ng/g), which totally accounted to about 90% of total CHC residues detected. The total content of CHC residues detected in the subtropical soil was only 3.1 ng/g, of which approximately 50% was beta-HCH. However, the total content of CP residues in both of the soils was about 11 ng/g. In the semi-arid soil, only parathion-methyl amongst the 30 compounds of OP and PRT residues was detected (32.5 ng/g), whilst malathion and parathion-methyl (8.7 and 17.7 ng/g, respectively) detected in the subtropical soil. Based on these results, it was suggested the environmental risk of pesticide residues ranked in an order as CHCs (mainly as 4,4'-DDE, beta-HCH) > OP (parathion-methyl) > CPs for the semi-arid soil, and as OPs (parathion-methyl and malathion) > CPs > CHCs (beta-HCH) for the subtropical soil.

[14C]Pentachlorophenol mineralization in the rice rhizosphere with established oxidized and reduced soil layers

Flooded soils with rooted aquatic macrophytes have adjacent aerobic and anaerobic zones at the soil-water interface and rhizosphere where many common soil constituents undergo sequential oxidation and reduction reactions. To investigate whether pentachlorophenol (PCP) mineralization would also be enhanced under these conditions, a laboratory study was conducted to determine the conversion of [14C]PCP to 14CO2, 14CH4 and [14C]humic substances in soil microcosms with established aerobic-anaerobic zones at the soil-water interface and rice (Oryza sativa) rhizosphere. Contrary to what was expected, PCP was least rapidly degraded in rhizosphere-soil microcosms that contained the most extensive amounts of aerobic-anaerobic interfaces (63% PCP loss in 82 d) and was most rapidly degraded in soil microcosms that lacked redox interfaces in the soil profile (94% PCP loss in 82 d). Decreased PCP mineralization in the presence of aerobic-anaerobic interfaces was explained by (i) lack of sufficient O2 for aerobic PCP mineralization, due to the oxidation of other soil constituents in aerobic zones, and (ii) lack of an adequate supply of electron equivalents for reductive dechlorination of PCP, due to the reduction of other alternate electron acceptors in anaerobic zones. It was concluded that PCP mineralization is inhibited in flooded soils that contain extensive amounts of aerobic-anaerobic interfaces, due to redox cycling of other soil constituents that occur in these zones.

Anaerobic treatment of 2,4,6-trichlorophenol in an expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactor at 15 °C

Expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors were operated at 15 degrees C for the treatment of 2,4,6-trichlorophenol (TCP)-containing volatile fatty acid (VFA)-based wastewaters. The seed sludge used as inoculum for the control (no TCP) and test reactor was unexposed to chlorophenols (CPs) prior to the 425-day trial. TCP supplementation to the feed at 50 mg TCPl(-1) partially inhibited the anaerobic degradation of the VFA feed measured as COD removal efficiency. However, the withdrawal and subsequent application of stepwise increments to the TCP loading resulted in steady COD removal. Terminal restriction fragment length polymorphism analysis showed Methanosaeta-like Archaea in the control reactor over the experimental period. Different methanogenic populations were detected in the test reactor and responded to the changes in feed composition. Bacterial community analyses indicated changes in the community structure over time and suggested the presence of Campylobacter-like, Acidimicrobium-like and Heliophilum-like organisms in the samples. TCP mineralisation was by a reductive dechlorination pathway through 2,4-dichlorophenol (DCP) and 4-chlorophenol (4-CP) or 2-chlorophenol (2-CP). CP degradation rates in sludge granules from the lower chamber of the hybrid EGSB-AF reactor was in the order TCP > DCP > 4-CP > 2-CP. However, a biodegradability order of lower CPs > TCP was observed in fixed-film biomass taken from the upper reactor chamber, thus reflecting the role of this reactor section in the metabolism of residual lower CPs from the lower sludge-bed stage of operation.

Biodegradation of xenobiotics by anaerobic bacteria

Xenobiotic biodegradation under anaerobic conditions such as in groundwater, sediment, landfill, sludge digesters and bioreactors has gained increasing attention over the last two decades. This review gives a broad overview of our current understanding of and recent advances in anaerobic biodegradation of five selected groups of xenobiotic compounds (petroleum hydrocarbons and fuel additives, nitroaromatic compounds and explosives, chlorinated aliphatic and aromatic compounds, pesticides, and surfactants). Significant advances have been made toward the isolation of bacterial cultures, elucidation of biochemical mechanisms, and laboratory and field scale applications for xenobiotic removal. For certain highly chlorinated hydrocarbons (e.g., tetrachlorethylene), anaerobic processes cannot be easily substituted with current aerobic processes. For petroleum hydrocarbons, although aerobic processes are generally used, anaerobic biodegradation is significant under certain circumstances (e.g., O(2)-depleted aquifers, oil spilled in marshes). For persistent compounds including polychlorinated biphenyls, dioxins, and DDT, anaerobic processes are slow for remedial application, but can be a significant long-term avenue for natural attenuation. In some cases, a sequential anaerobic-aerobic strategy is needed for total destruction of xenobiotic compounds. Several points for future research are also presented in this review.

Successive rapid reductive dehalogenation and mineralization of pentachlorophenol by the indigenous microflora of farmyard manure compost

AIMS

To determine whether composting with animal manure can be used to effectively remediate soil from a pentachlorophenol (PCP)-contaminated site, and to establish the fate of the degraded xenobiotic.

METHODS AND RESULTS

Contaminated soil from a sawmill site was mixed with farm animal manure and composted in a 0.5 m3 silo under fully aerobic conditions. The disappearance and fate of PCP was monitored by gas chromatography (GC-ECD) and extensive mineralization confirmed in experiments with 14C-radiolabelled PCP. The disappearance of PCP was rapid and virtually complete within 6 days, prior to the onset of thermophilic conditions. Dechlorination of the PCP was found to be both reductive and sequential.

CONCLUSIONS

PCP removal from contaminated soil by aerobic composting with animal manure is efficient and proceeds via reductive dechlorination to virtually complete mineralization. This contrasts with other chlorophenol composting regimes in which mineralization is achieved but dechlorination intermediates do not accumulate to detectable levels.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study demonstrate that anaerobic reductive dechlorination can proceed in an aerobic composting environment and contribute to efficient pentachlorophenol removal. Farmyard manure composts may represent a rapid, low-cost, low-technology option for treatment of chlorophenol-contaminated soils.

Evidence for degradation of 2-chlorophenol by enrichment cultures under denitrifying conditions

Although chlorophenol (CP) degradation has been studied, no bacterium responsible for degradation of CP under denitrifying conditions has been isolated. Moreover, little substantial evidence for anaerobic degradation of CPs coupled with denitrification is available even for mixed cultures. Degradation of CP [2-CP, 3-CP, 4-CP, 2,4-dichlorophenol (DCP) or 2,6-DCP] under denitrifying conditions was examined in anaerobic batch culture inoculated with activated sludge. Although 3-CP, 4-CP, 2,4-DCP and 2,6-DCP were not stably degraded, 2-CP was degraded and its degradation capability was sustained in a subculture. However, the rate of 2-CP degradation was not significantly enhanced by subculturing. In 2-CP-degrading cultures, nitrate was consumed stoichiometrically and concomitantly during 2-CP degradation, and a dechlorination intermediate was not detected, suggesting that 2-CP degradation was coupled with nitrate reduction. A 2-CP-degrading enrichment culture degraded 2-CP in the presence of nitrate, but did not in the absence of nitrate or the presence of sulfate. This suggests that the enrichment culture strictly requires nitrate for degradation of 2-CP. The apparent specific growth rate of the 2-CP degrading species was 0.0139 d(-1). Thus the apparent doubling time of the 2-CP-degrading population in the enrichment culture was greater than 50 d, which may explain difficulty in enrichment and isolation of micro-organisms responsible for CP degradation under denitrifying conditions.

Naphthenic acids and surrogate naphthenic acids in methanogenic microcosms

Naphthenic acids (NAs) are a complex mixture of naturally occurring acyclic and cyclic aliphatic carboxylic acids in petroleum. In the Athabasca oil sands. NAs have been identified as the largest component of dissolved organic matter in the tailings waters from oils sands extraction processes. They are the major contributor to the acute toxicity of the fine tailings wastewaters at the oil sands extraction plants in northeastern Alberta, Canada. In this study, three sources of NAs were studied, including commercially available NAs, those extracted from oil sands process-affected waters, and individual naphthenic-like surrogate compounds. Analysis by gas chromatography-mass spectrometry demonstrated differences between the commercial and extracted NAs. The NAs derived from the process-affected waters showed a short-term inhibition of methanogenesis from H2 or acetate, but with time the populations resumed methane production. It has been postulated that microbial metabolism of the carboxylated side chains of NAs would lead to methane production. The two NA mixtures failed to stimulate methanogenesis in microcosms that contained either oil sands fine tailings or domestic sewage sludge. However, in microcosms with sewage sludge, methanogenesis was stimulated by some surrogate NAs including 3-cyclohexylpropanoic acid at 400-800 mg/L, 5-cyclohexylpentanoic acid at 200 mg/L or 6-phenylhexanoic acid at 200 and 400 mg/L. When added at 200 mg/L to methanogenic microcosms containing fine tailings, 3-cyclohexylpropanoic and 4-cyclohexylbutanoic acids produced methane yields that suggested mineralization of the side chain and the ring.

Anaerobic transformation of chlorophenols in methanogenic sludge unexposed to chlorophenols

Transformation of all 19 chlorophenol (CP) isomers was investigated in a laboratory anaerobic methanogenic sludge that had not been exposed to synthetic chemicals. Concentration of CP was analyzed over time to calculate disappearance rate constants using first-order reaction kinetics and all possible CP degradation pathways were estimated. The rate constants ranged between 0.46 x 10(-3) and 0.161 day(-1). CPs were transformed via dechlorination. The chlorine atom at the ortho-position was the most easily dechlorinated, whereas dechlorination rate at the para-position was lowest. The overall pathways of CP transformation were much less diverse than that we previously found for contaminated sediment. The Dolfing hypothesis of microbial selection of the most thermodynamically favorable pathways was not applicable for CP transformation in this study as well as previous study performed by our group.

Biodegradation of pentachlorophenol in a continuous anaerobic reactor augmented with Desulfitobacterium frappieri PCP-1

In this work, a strain of anaerobic pentachlorophenol (PCP) degrader, Desulfitobacterium frappieri PCP-1, was used to augment a mixed bacterial community of an anaerobic upflow sludge bed reactor degrading PCP. To estimate the efficiency of augmentation, the population of PCP-1 in the reactor was enumerated by a competitive PCR technique. The PCP-1 strain appeared to compete well with other microorganisms of the mixed bacterial community, with its population increasing from 10(6) to 10(10) cells/g of volatile suspended solids within a period of 70 days. Proliferation of strain PCP-1 allowed for a substantial increase of the volumetric PCP load from 5 to 80 mg/liter of reaction volume/day. A PCP removal efficiency of 99% and a dechlorination efficiency of not less than 90.5% were observed throughout the experiment, with 3-Cl-phenol and phenol being observable dechlorination intermediates.

Biodegradation of low aqueous concentration pentachlorophenol (PCP) contaminated groundwater

Bioremedial treatment to remove low level organic contamination to regulatory standards has met with limited success. In this study source water from a contaminated surficial aquifer at a former wood treatment facility was used to evaluate the potential for indigenous microorganisms to degrade low level (< 1.0 mg) pentachlorophenol (PCP) to a regulatory drinking water standard of 0.001 mg/L. PCP degradation was evaluated in series of batch reactors in a two phase study to (a) determine the rate and extent of PCP removal and (b) evaluate the impact of nutrient amendment (N and P) on removal rate. All reactors with the exception of the abiotic control demonstrated PCP removal to a level < 0.002 mg/L within a maximum period of 32 d with and without nutrient amendment. A regression analysis of reactive phosphate (ortho-P) concentration versus removal rate produced an R2 of 0.94 (p = 0.006) indicating a significant correlation between the level of available phosphate and PCP degradation rate. Selective bacterial enumeration (for PCP degrading bacteria) revealed PCP-degrading bacteria increased in abundance prior to and in conjunction with the degradation phase to a density of between 10(3) to 10(4) CFU/ml. Isolates were also analyzed for total fatty acids using Fatty Acid Methyl Ester (FAME) methodology and the results indicated that PCP degrading bacteria were present in the aquifer and consisted of predominately fluorescent, oxidase positive Pseudomonas species. Overall, data indicate that autochthonous microbes are capable of removing low level PCP (< 1.0 mg/L) to approach if not reach the regulatory standard of 0.001 mg/L with the addition of oxygen, with or without nutrient amendment. Results of this research can be applied to full-scale implementation of in-situ or ex-situ bioremediation of groundwater at former wood treatment facilities.

Biodegradation of pentachlorophenol (PCP) by white rot fungal strains screened from local sources and its estimation by high-performance liquid chromatography

White rot fungal strains screened from local sources (wood trunks and from effluents of pulp and paper industry) were tested for their ability to biodegrade polymeric compounds, viz. polymeric dyes (crystal violet and brilliant green) and chlorinated phenol (pentachlorophenol). Two of the most promising strains showing maximum degradation of polymeric dyes were selected to study the biodegradation potential and pattern of biodegradation of pentachlorophenol (PCP), a commonly used leather preservative and a potential carcinogen. PCP was quantitatively estimated and analysed by high-performance liquid chromatography (HPLC). Conditions were optimized for the measurement of PCP on HPLC, which were: mobile phase, 60% acetonitrile and 40% water; flow rate, 1 mL/ min; column, mu Bondapack C18 RP and UV detector at 238 nm. One of the white rot fungal strains isolated from wood trunk showed a maximum 68% biodegradation of PCP in liquid-buffered medium in 16 days. The biodegradation pattern of PCP followed a pseudo-first-order kinetics. Studies on enhancement of biodegradation of polymeric dyes and PCP showed that the kinetics of biodegradation is greatly improved by the presence of manganese ions, H2O2 and glucose in the medium. This strongly suggests the involvement of peroxidase enzyme machinery of white rot fungus in the biodegradation process of PCP.

Microbial hexachlorobenzene dechlorination under three reducing conditions

The potential dechlorination of hexachlorobenzene (HCB) in medium by 1,2,3-trichlorobenzene (TCB)-adapted mixed culture under three reducing conditions was investigated. It was found that strongest to weakest HCB dechlorination occurred in the order of methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. Under denitrifying conditions, no dechlorination was observed during the first 20 days of incubation. Biotransformation occurred in this order: HCB-->pentachlorobenzene (PCB)-->1,2,3,5-tetrachlorobenzene (TeCB)-->1,3,5-TCB + 1,2,4-TCB-->1,3-dichlorobenzene (DCB), HCB dechlorination was delayed following treatment with ferric chloride and manganese dioxide, but enhanced by the addition of lactate and pyruvate under methanogenic or sulfate-reducing conditions, the addition of acetate had no significant effect on HCB dechlorination under any of the three reducing conditions. Sequential dechlorination was observed at concentrations of 2-50 mg/L, but at a significantly slower rate at the highest concentrations.