Biodegradation of PCBs in two-phase partitioning bioreactors following solid extraction from soil

This article demonstrates the feasibility of a novel process concept for the remediation of PCB contaminated soil. The proposed process consists of PCB extraction from soil using solid polymer beads, followed by biodegradation of the extracted PCBs in a solid-liquid two-phase partitioning bioreactor (TPPB), where PCBs are delivered from the polymer beads to the degrading organisms. The commercially available thermoplastic polymer Hytrel was used to extract Aroclor 1242 from contaminated artificial soil in bench scale experiments. Initial PCB contamination levels of 100 and 1,000 mg kg(-1) could be reduced to 32% +/- 1 to 41% +/- 7 of the initial value after 48 h mixing in the presence of a mobilizing agent at polymer-to-soil ratios of 1% (w/w) and 10% (w/w). The decrease of detectable PCBs in the soil was consistent with an increase of PCBs in the polymer beads. It was further shown that Aroclor 1242 could be delivered to the PCB degrading organism Burkholderia xenovorans LB400 in a solid-liquid TPPB via Hytrel beads. A total of 70 mg Aroclor 1242 could be degraded in a 1 L solid-liquid TPPB within 80 h of operation.     

Coping with polychlorinated biphenyl (PCB) toxicity: Physiological and genome-wide responses of Burkholderia xenovorans LB400 to PCB-mediated stress

The biodegradation of polychlorinated biphenyls (PCBs) relies on the ability of aerobic microorganisms such as Burkholderia xenovorans sp. LB400 to tolerate two potential modes of toxicity presented by PCB degradation: passive toxicity, as hydrophobic PCBs potentially disrupt membrane and protein function, and degradation-dependent toxicity from intermediates of incomplete degradation. We monitored the physiological characteristics and genome-wide expression patterns of LB400 in response to the presence of Aroclor 1242 (500 ppm) under low expression of the structural biphenyl pathway (succinate and benzoate growth) and under induction by biphenyl. We found no inhibition of growth or change in fatty acid profile due to PCBs under nondegrading conditions. Moreover, we observed no differential gene expression due to PCBs themselves. However, PCBs did have a slight effect on the biosurface area of LB400 cells and caused slight membrane separation. Upon activation of the biphenyl pathway, we found growth inhibition from PCBs beginning after exponential-phase growth suggestive of the accumulation of toxic compounds. Genome-wide expression profiling revealed 47 differentially expressed genes (0.56% of all genes) under these conditions. The biphenyl and catechol pathways were induced as expected, but the quinoprotein methanol metabolic pathway and a putative chloroacetaldehyde dehydrogenase were also highly expressed. As the latter protein is essential to conversion of toxic metabolites in dichloroethane degradation, it may play a similar role in the degradation of chlorinated aliphatic compounds resulting from PCB degradation.     

Coping with Polychlorinated Biphenyl (PCB) Toxicity: Physiological and Genome-Wide Responses of Burkholderia xenovorans LB400 to PCB-Mediated Stress

The biodegradation of polychlorinated biphenyls (PCBs) relies on the ability of aerobic microorganisms such as Burkholderia xenovorans sp. LB400 to tolerate two potential modes of toxicity presented by PCB degradation: passive toxicity, as hydrophobic PCBs potentially disrupt membrane and protein function, and degradation-dependent toxicity from intermediates of incomplete degradation. We monitored the physiological characteristics and genome-wide expression patterns of LB400 in response to the presence of Aroclor 1242 (500 ppm) under low expression of the structural biphenyl pathway (succinate and benzoate growth) and under induction by biphenyl. We found no inhibition of growth or change in fatty acid profile due to PCBs under nondegrading conditions. Moreover, we observed no differential gene expression due to PCBs themselves. However, PCBs did have a slight effect on the biosurface area of LB400 cells and caused slight membrane separation. Upon activation of the biphenyl pathway, we found growth inhibition from PCBs beginning after exponential-phase growth suggestive of the accumulation of toxic compounds. Genome-wide expression profiling revealed 47 differentially expressed genes (0.56% of all genes) under these conditions. The biphenyl and catechol pathways were induced as expected, but the quinoprotein methanol metabolic pathway and a putative chloroacetaldehyde dehydrogenase were also highly expressed. As the latter protein is essential to conversion of toxic metabolites in dichloroethane degradation, it may play a similar role in the degradation of chlorinated aliphatic compounds resulting from PCB degradation.     

Two-phase partitioning bioreactors for treatment of volatile organic compounds

Two-phase partitioning bioreactors (TPPBs) allow the biological removal of volatile organic compounds (VOCs) from contaminated gas streams at unprecedented rates and concentrations. TPPBs are constructed by adding a non-aqueous phase (e.g. hexadecane, silicone oil) to an aqueous phase that contains the microorganisms responsible for degrading the VOCs. Presence of a water-immiscible phase improves the transfer of hydrophobic substrates (e.g. hexane, oxygen) or reduces the toxicity of inhibitory substances (e.g. benzene, toluene) to the microorganisms present in the aqueous phase. The non-aqueous phase is selected based on cost, safety, good partitioning properties towards the target pollutants, biocompatibility, and non-biodegradability. TPPBs have hitherto been designed as laboratory-scale well-mixed stirred-tank reactors or as biofilters that contain a non-aqueous phase. Scale-up and industrial use of TPPBs require elucidation and modeling of the mechanisms of substrate transfer and uptake; understanding of the mechanisms of microbial selection; identification or synthesis of new inexpensive and robust non-aqueous phases; and generation of suitable guidelines for process design and control.     

Bioremediation of Aroclor 1242 by a consortium culture in marine sediment microcosm

Plant terpenes have proven to be effective in stimulation of polychlorinated biphenyls (PCBs) biodegradation in soil systems. However, data on the application of plant terpenes in marine sediments contaminated with PCBs remains limited. The aim of this study was to ascertain the roles of a PCB degrading consortium and plant terpenes in stimulation of PCB biodegradation in marine sediments. The consortium culture 1-2Mix (strains 1-2M and 1-2T in commensalism), a utilizer of biphenyl and a natural substrate was enriched and isolated from marine sediments from the Busan coast, South Korea. PCB degradation by this culture was shown to be more effectively induced by tangerine peel extract than other known substrates (limonene, pinene, and cymene). Coastal sediment microcosms inoculated with 1-2Mix were set up to elucidate the effect of the consortium and plant terpenes on degradation of Aroclor 1242. After four weeks, the highest removal rates of PCBs, compared with the control (autoclaved sediment and no inoculation of 1-2Mix), were observed in order of the inducers tested; biphenyl (71.1%), tangerine peel extract (69.5%), surfactant (66.0%), and limonene (63.0%). Bioaugmentation effect was doubled in the presence of natural substrates such as tangerine peel extract and limonene, indicating effectiveness of these substrates in biostimulation. It was concluded that the tangerine peel extract could replace biphenyl as a feasible induction substrate for effective remediation of PCBs in the marine sediment.     

Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850

We have isolated and characterized a strain of Alcaligenes eurtrophus, designated H850, that rapidly degrades a broad and unusual spectrum of polychlorinated biphenyls (PCBs) including many tetra- and pentachlorobiphenyls and several hexachlorobiphenyls. This strain, which was isolated from PCB-containing dredge spoils by enrichment on biphenyl, grows well on biphenyl and 2-chlorobiphenyl but poorly on 3- and 4-chlorobiphenyl. Capillary gas-chromatographic analysis showed that biphenyl-grown resting cells of H850 degraded the components of 38 of the 41 largest peaks of Aroclor 1242 and 15 of the 44 largest peaks of Aroclor 1254, resulting in an overall reduction of PCBs by 81% for Aroclor 1242 (10 ppm) and 35% for Aroclor 1254 (10 ppm) in 2 days. Furthermore, H850 metabolized the predominantly ortho-substituted PCB congeners that resulted from the environmental transformation of the more highly chlorinated congeners of Aroclor 1242 by the upper Hudson River anaerobic meta-, para-dechlorination agent system C (J. F. Brown, R. E. Wagner, Jr., D. L. Bedard, M. J. Brennan, J. C. Carnahan, R. J. May, and J. J. Tofflemire, Northeast Environ. Sci. 3:167-179, 1984). The congener selectivity patterns indicate that a two-step process consisting of anaerobic dechlorination followed by oxidation by H850 can effectively degrade all of the congeners in Aroclor 1242 and possibly all those in Aroclor 1254.     

Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850.

We have isolated and characterized a strain of Alcaligenes eurtrophus, designated H850, that rapidly degrades a broad and unusual spectrum of polychlorinated biphenyls (PCBs) including many tetra- and pentachlorobiphenyls and several hexachlorobiphenyls. This strain, which was isolated from PCB-containing dredge spoils by enrichment on biphenyl, grows well on biphenyl and 2-chlorobiphenyl but poorly on 3- and 4-chlorobiphenyl. Capillary gas-chromatographic analysis showed that biphenyl-grown resting cells of H850 degraded the components of 38 of the 41 largest peaks of Aroclor 1242 and 15 of the 44 largest peaks of Aroclor 1254, resulting in an overall reduction of PCBs by 81% for Aroclor 1242 (10 ppm) and 35% for Aroclor 1254 (10 ppm) in 2 days. Furthermore, H850 metabolized the predominantly ortho-substituted PCB congeners that resulted from the environmental transformation of the more highly chlorinated congeners of Aroclor 1242 by the upper Hudson River anaerobic meta-, para-dechlorination agent system C (J. F. Brown, R. E. Wagner, Jr., D. L. Bedard, M. J. Brennan, J. C. Carnahan, R. J. May, and J. J. Tofflemire, Northeast Environ. Sci. 3:167-179, 1984). The congener selectivity patterns indicate that a two-step process consisting of anaerobic dechlorination followed by oxidation by H850 can effectively degrade all of the congeners in Aroclor 1242 and possibly all those in Aroclor 1254.     

Polymer selection for biphenyl degradation in a solid-liquid two-phase partitioning bioreactor

The commercially available thermoplastic polymer Hytrel was selected as the delivery phase for the hydrophobic model compound biphenyl in a solid-liquid two-phase partitioning bioreactor (TPPB), and 2.9 g biphenyl could successfully be degraded in 1-L TPPBs by a pure culture of the biphenyl-degrading bacterium Burkholderia xenovorans LB400 in 50 h and by a mixed microbial consortium isolated from contaminated soil in 45 h. TPPBs consist of an aqueous cell-containing phase and an immiscible second phase that partitions toxic and/or poorly soluble substrates (in this case biphenyl) on the basis of maintaining a thermodynamic equilibrium. This paper illustrates a rational strategy for selecting a suitable solid polymeric substance for the delivery of the poorly water-soluble model compound biphenyl. The partitioning of biphenyl between the selected polymers and water was analogous to partitioning of solutes between two immiscible liquid phases. The partitioning coefficients varied between 180 for Nylon 6.6 and 11,000 for Desmopan, where the later numerical value is comparable to biphenyl partitioning coefficients between water and organic solvents. Employing a solid delivery phase enabled the utilization of a surfactant-producing microbial mixed culture, which could not be cultivated in liquid-liquid TPPBs and thereby extended the range of biocatalysts that can be employed in TPPBs.     

Tuning biphenyl dioxygenase for extended substrate specificity.

Highly substituted polychlorinated biphenyls (PCBs) are known to be very resistant to aerobic biodegradation, particularly the initial attack by biphenyl dioxygenase. Functional evolution of the substrate specificity of biphenyl dioxygenase was demonstrated by DNA shuffling and staggered extension process (StEP) of the bphA gene coding for the large subunit of biphenyl dioxygenase. Several variants with an extended substrate range for PCBs were selected. In contrast to the parental biphenyl dioxygenases from Burkholderia cepacia LB400 and Pseudomonas pseudoalcaligenes KF707, which preferentially recognize either ortho- (LB400) or para- (KF707) substituted PCBs, several variants degraded both congeners to about the same extent. These variants also exhibited superior degradation capabilities toward several tetra- and pentachlorinated PCBs as well as commercial PCB mixtures, such as Aroclor 1242 or Aroclor 1254. Sequence analysis confirmed that most variants contained at least four to six template switches. All desired variants contained the Thr335Ala and Phe336Ile substitutions confirming the importance of this critical region in substrate specificity. These results suggest that the block-exchange nature of gene shuffling between a diverse class of dioxygenases may be the most useful approach for breeding novel dioxygenases for PCB degradation in the desired direction.     

Degradation of nonionic surfactants and polychlorinated biphenyls by recombinant field application vectors

Degradation of polychlorinated biphenyls (PCBs) in the environment is limited by their aqueous solubility and the degradative competence of indigenous populations. Field application vectors (FAVs) have been developed in which surfactants are used to both increase the solubility of the PCBs and support the growth of surfactant-degrading strains engineered for PCB degradation. Surfactant and PCB degradation by two recombinant strains were investigated. Pseudomonas putida IPL5 utilizes both alkylethoxylate [polyoxyethylene 10 lauryl ether (POL)] and alkylphenolethoxylate [Igepal CO-720 (IGP)] surfactants as growth substrates, but only degrades the ethoxylate moiety. The resulting degradation products from the alkyl- and alkylphenolethoxylate surfactants were 2-(dodecyloxy)ethanol and nonylphenoldiethoxylates, respectively. Ralstonia eutropha B30P4 grows on alkylethoxylate surfactants without the appearance of solvent-extractable degradation products. It also degrades the 2-(dodecyloxy)ethanol produced by strain IPL5 from the alkylethoxylate surfactants. The extent of degradation of the alkylethoxylate surfactant (POL) was greater for strain IPL5 (90%) than for B30P4 (60%) as determined by the cobaltothiocyanate active substances method (CTAS). The recombinant strain B30P4::TnPCB grew on biphenyl. In contrast, the recombinant strain IPL5::TnPCB could not grow on biphenyl, and PCB degradation was inhibited in the presence of biphenyl. The most extensive surfactant and PCB degradation was achieved by the use of both recombinant strains together in the absence of biphenyl. PCB (Aroclor 1242) and surfactant (POL) concentrations were reduced from 25 ppm and 2000 ppm, respectively, to 6.5 ppm and 225 ppm, without the accumulation of surfactant degradation products. Given the inherent complexity of commercial surfactant preparations, the use of recombinant consortia to achieve extensive surfactant and PCB degradation appears to be an environmentally acceptable and effective PCB remediation option. Received 04 October 1996/ Accepted in revised form 04 August 1997     

Enhanced mineralization of polychlorinated biphenyls in soil inoculated with chlorobenzoate-degrading bacteria.

An Altamont soil containing no measurable population of chlorobenzoate utilizers was examined for the potential to enhance polychlorinated biphenyl (PCB) mineralization by inoculation with chlorobenzoate utilizers, a biphenyl utilizer, combinations of the two physiological types, and chlorobiphenyl-mineralizing transconjugants. Biphenyl was added to all soils, and biodegradation of 14C-Aroclor 1242 was assessed by disappearance of that substance and by production of 14CO2. Mineralization of PCBs was consistently greatest (up to 25.5%) in soils inoculated with chlorobenzoate degraders alone. Mineralization was significantly lower in soils receiving all other treatments: PCB cometabolizer (10.7%); chlorobiphenyl mineralizers (8.7 and 14.9%); and mixed inocula of PCB cometabolizers and chlorobenzoate utilizers (11.4 and 18.0%). However, all inoculated soils had higher mineralization than did the uninoculated control (3.1%). PCB disappearance followed trends similar to that observed with the mineralization data, with the greatest degradation occurring in soils inoculated with the chlorobenzoate-degrading strains Pseudomonas aeruginosa JB2 and Pseudomonas putida P111 alone. While the mechanism by which the introduction of chlorobenzoate degraders alone enhanced biodegradation of PCBs could not be elucidated, the possibility that chlorobenzoate inoculants acquired the ability to metabolize biphenyl and possibly PCBs was explored. When strain JB2, which does not utilize biphenyl, was inoculated into soil containing biphenyl and Aroclor 1242, the frequency of isolates able to utilize biphenyl and 2,5-dichlorobenzoate increased progressively with time from 3.3 to 44.4% between 15 and 48 days, respectively. Since this soil contained no measurable level of chlorobenzoate utilizers yet did contain a population of biphenyl utilizers, the possibility of genetic transfer between the latter group and strain JB2 cannot be excluded.     

Novel maltotriose esters enhance biodegradation of Aroclor 1242 by Burkholderia cepacia LB400

The objective of this research was to evaluate the effect of enzymatically synthesized maltotriose fatty acid monoesters (Ferrer, M., et al. 2000 Tetrahedron 56, 4053–4061) on Aroclor 1242 solubilization and biodegradation. Three forms of the surfactant, laurate, palmitate and stearate monoester, were tested. Potential enhancement of solubilization of hydrophobic substances mediated by these non-ionic surfactants was exploited in this study. A polychlorinated biphenyl (PCB) degrading organism, Burkholderia cepacia LB400, was also selected. It was found that all surfactants were effective in solubilizing Aroclor 1242 but the rate of Aroclor 1242 biodegradation proceeded rapidly only in the presence of 6-O-palmitoylmaltotriose. For example, the addition of 48 mg 6-O-palmitoylmaltotriose/l increased the apparent solubility from 140 to 305 g/l. As a result, only 8% of the Aroclor remained at the end of 24 h incubation. In contrast, 49.2% of the Aroclor 1242 remained in the absence of surfactant. It appears that maltotriose fatty acid monoesters can significantly increase the bioavailability, and thereby accelerate the biodegradation of highly chlorinated PCBs, particularly Aroclor 1242, by Burkholderia cepacia LB400. The possibility of obtaining these biodegradable surfactants with high yield, easy recovery and high purity by using a new enzymatic methodology, makes maltotriose esters available for bioremediation purposes.     

Enhanced Degradation of a Mixture of Polycyclic Aromatic Hydrocarbons by a Defined Microbial Consortium in a Two-Phase Partitioning Bioreactor

Biological treatment methods are effective at destroying polycyclic aromatic hydrocarbons (PAHs), and some of the highest rates of PAH degradation have been achieved using two-phase-partitioning bioreactors (TPPBs). TPPBs consist of a cell-containing aqueous phase and a biocompatible and immiscible organic phase that partitions toxic and/or recalcitrant substrates to the cells based on their metabolic demand and on maintaining the thermodynamic equilibrium of the system. In this study, the degradation of a 5-component mixture of high and low molecular weight PAHs by a defined microbial consortium of Sphingomonas aromaticivorans B0695 and Sphingomonas paucimobilis EPA505 in a TPPB was examined. The extremely low aqueous solubilities of the high molecular weight (HMW) PAHs significantly reduce their bioavailability to cells, not only in the environment, but in TPPBs as well. That is, in the two-phase system, the originally selected solvent, dodecane, was found to sequester the HMW PAHs from the cells in the aqueous phase due to the inherent high solubility of the hydrophobic compounds in this solvent. To circumvent this limitation, the initial PAH concentrations in dodecane were increased to sufficient levels in the aqueous phase to support degradation: LMW PAHs (naphthalene, phenanthrene) and fluoranthene were degraded completely in 8 h, while the HMW PAHs, pyrene and benzo[a]pyrene, were degraded by 64% and 11%, at rates of 42.9 mg l⁻¹ d⁻¹ and 7.5 mg l⁻¹ d⁻¹, respectively. Silicone oil has superior PAH partitioning abilities compared to dodecane for the HMW PAHs, and was used to improve the extent of degradation for the PAH mixture. Although silicone oil increased the bioavailability of the HMW PAHs and greater extents of biodegradation were observed, the rates of degradation were lower than that obtained in the TPPB employing dodecane.     

Terpene-utilizing isolates and their relevance to enhanced biotransformation of polychlorinated biphenyls in soil

Orange peels, eucalyptus leaves, pine needles and ivy leaves were addedseparately to soil spiked with Aroclor 1242 (100 mgkg^-1.Polychorinated biphenyls (PCBs) disappeared after six months in all theamended soils, but not in unamended soils. Although biphenyl was not addedto any of the soils, all four amended soils had much higher levels(10⁸/g) of biphenyl-utilizing bacteria than the unamendedcontrol (10³/g). Ten random isolates obtained from these soilswere identified as coryneform bacteria. Five isolates, that were distinctlydifferent, were studied further with respect to growth on pure terpenes andmetabolism of PCBs. The most effective strains were Cellulomonas sp. T109and R. rhodochrous T100, which metabolized 83% and 80% ofAroclor 1242, respectively, during a six day period of growth on cymene andlimonene, respectively. The bphA gene, cloned as a 2.8 Kb Sa/I fragment ofpAW6194 from cbpA (Walia et al. 1990) hybridized to total DNA of allcoryneform isolates, and to the well-established PCB degrader Rhodococcusgloberulus. In contrast, a 5 Kb XhoI-SmaI fragment of the bphA gene(Furukawa & Miyazaki 1986) did not show any homology to the genomic DNAof any of the isolates or to R. globerulus, but did hybridize to two otherwell-known PCB degraders Pseudomonas sp. LB400, and Alcaligenes eutrophusH850. The data presented herein indicate that terpenes may be naturalsubstrates for biphenyl-degrading bacteria and may enhance substantialtransformation of Aroclor 1242.     

Effects of Polychlorinated Biphenyls on Macromolecular Synthesis by a Heterotrophic Marine Bacterium

Growth rates and final cell yields of a polychlorinated biphenyl (PCB)-sensitive pseudomonad isolated from the open ocean were reduced in a dose-dependent manner by 10 to 100 μg of Aroclor 1254 per liter, a commercial mixture of PCB isomers added to its culture medium. Effects on growth rates were detected within 1 h (approximately one doubling time) of treatment. By 4 h posttreatment, the amounts of deoxyribonucleic acid and ribonucleic acid per cell in exponentially growing populations treated with sublethal doses of Aroclor were detectably lower than in appropriate controls. Corresponding cell protein values were slightly higher than in controls. Selective degradation of cell proteins or nucleic acids was not detected in cells whose growth was totally suppressed for 4 h by PCBs. Cells whose growth rate was inhibited 20 to 50% by Aroclor synthesized protein at normal rates for periods in excess of 5 h from the time the chlorinated hydrocarbons were added. In contrast, rates per cell of adenine uptake and adenine incorporation into deoxyribonucleic acid and total nucleic acids by the cells treated with PCBs were significantly lower than in control cells. Intracellular adenine pools of cells whose growth was inhibited to 20% of the control rate by PCBs were 30% smaller and appeared to require a longer interval to equilibrate than those of untreated cells. This may indicate impaired transport and/or efflux of this nucleic acid precursor through the membrane of affected cells. Inhibition of nucleic acid synthesis in this sensitive bacterium by PCBs could explain the observed inhibitory effects of the chlorinated hydrocarbons on its growth.     

Biodegradation of polychlorinated biphenyls in Aroclor 1232 and production of metabolites from 2,4,4'-trichlorobiphenyl at low temperature by psychrotolerant Hydrogenophaga sp. strain IA3-A

AIMS: To determine the extent and pattern of degradation of polychlorinated biphenyls (PCBs) in Aroclor 1232 at 5 degrees C by a psychrotolerant bacterium, and to confirm the formation of intermediates of PCB metabolism at low temperature using 2,4,4'-trichlorobiphenyl (2,4,4'-TCB). METHODS AND RESULTS: 10 ppm of Aroclor 1232 or 100 micromol l(-1) 2,4,4'-TCB was incubated with biphenyl-grown cells at 5 degrees C or 30 degrees C for 48 or 72 h. Degradation of PCBs and the products of metabolism of 2,4,4'-TCB were confirmed by gas chromatography and mass spectrometry. Extents of degradation of many of the PCBs were similar at 5 degrees C and 30 degrees C. The extent of biodegradation of PCBs in Aroclor 1232 at 5 degrees C was dependent on chlorination pattern. The 14 chlorine-containing intermediates of 2,4,4'-TCB metabolism, which were detected, include several isomers of dihydrodiols, dihydroxy compounds and meta-cleavage compounds. CONCLUSIONS: The bacterium will be useful for bioremediation of PCB-contaminated sites in cold climates; however, knowledge of the products of PCB metabolism is necessary, as they could be more toxic than the parent compounds. SIGNIFICANCE AND IMPACT OF THE STUDY: Substantial degradation of some PCBs in Aroclor 1232 was demonstrated at low temperature within 48 h. The detection of several isomeric intermediates suggests that multiple pathways are used to transform PCBs in this strain. For the first time, formation of metabolic products from 2,4,4'-TCB at low temperature is confirmed.     

Recent advances in two-phase partitioning bioreactors for the treatment of volatile organic compounds

Biological processes are considered to be the most cost-effective technology for the off-gas treatment of volatile organic compounds (VOC) at low concentrations. Two-phase partitioning bioreactors (TPPBs) emerged in the early 1990s as innovative multiphase systems capable of overcoming some of the key limitations of traditional biological technologies such as the low mass transfer rates of hydrophobic VOCs and microbial inhibition at high VOC loading rates. Intensive research carried out in the last 5 years has helped to provide a better understanding of the mass transfer phenomena and VOC uptake mechanisms in TPPBs, which has significantly improved the VOC biodegradation processes utilizing this technology platform. This work presents an updated state-of-the-art review on the advances of TPPB technology for air pollution control. The most recent insights regarding non-aqueous phase (NAP) selection, microbiology, reactor design, mathematical modeling and case studies are critically reviewed and discussed. Finally, the key research issues required to move towards the development of efficient and stable full-scale VOC biodegradation processes in TPPBs are identified.     

Biotransformations of Aroclor 1242 in Hudson River test tube microcosms.

A microcosm system to physically model the fate of Aroclor 1242 in Hudson River sediment was developed. In the dark at 22 to 25 degrees C with no amendments (nutrients, organisms, or mixing) and with overlying water being the only source of oxygen, the microcosms developed visibly distinct aerobic and anaerobic compartments in 2 to 4 weeks. Extensive polychlorinated biphenyl (PCB) biodegradation was observed in 140 days. Autoclaved controls were unchanged throughout the experiments. In the surface sediments of these microcosms, the PCBs were biologically altered by both aerobic biodegrading and reductive dechlorinating microorganisms, decreasing the total concentration from 64.8 to 18.0 micromol/kg of sediment in 1140 days. This is the first laboratory demonstration of meta dechlorination plus aerobic biodegradation in stationary sediments. In contrast, the primary mechanism of microbiological attack on PCBs in aerobic subsurface sediments was reductive dechlorination. The concentration of PCBs remained constant at 64.8 micromol/kg of sediment, but the average number of chlorines per biphenyl decreased from 3.11 to 1.84 in 140 days. The selectivities of microorganisms in these sediments were characterized by meta and para dechlorination. Our results provide persuasive evidence that naturally occurring microorganisms in the Hudson River have the potential to attack the PCBs from Aroclor 1242 releases both aerobically and anaerobically at rapid rates. These unamended microcosms represent a unique method for determining the fate of released PCBs in river sediments.     

一株联苯降解菌的特性及鉴定*

从华北油田污染土壤中筛选出一株能够以联苯为唯一碳源和能源生长的菌株。该菌生长的最适联苯浓度为0．2％～0．4％,在联苯浓度为0．1％的培养基中培养36h后降解率达99．8%。该菌还可以降解苯甲酸钠、邻苯二酚、间苯二酚、对苯二酚和多氯联苯Aroclorl221、Aroclorl242等芳香族化合物。通过16S rDNA基因序列分析鉴定该菌为嗜吡啶红球菌(Rhodococcus pyridinovorans)。     

Degradation of polychlorinated biphenyl mixtures (Aroclors 1242, 1254, and 1260) by the white rot fungus Phanerochaete chrysosporium as evidenced by congener-specific analysis.

Evidence for substantial degradation of polychlorinated biphenyl mixtures Aroclor 1242, 1254, and 1260 by the white rot fungus Phanerochaete chrysosporium, based on congener-specific gas chromatographic analysis, is presented. Maximal degradation (percent by weight) of Aroclors 1242, 1254, and 1260 was 60.9, 30.5, and 17.6%, respectively. Most of the congeners in Aroclors 1242 and 1254 were degraded extensively both in low-N (ligninolytic) as well as high-N (nonligninolytic) defined media. Even more extensive degradation of the congeners was observed in malt extract medium. Congeners with varying numbers of ortho, meta, and para chlorines were extensively degraded, indicating relative nonspecificity for the position of chlorine substitutions on the biphenyl ring. Aroclor 1260, which has not been conclusively shown to undergo aerobic microbial degradation, was shown to undergo substantial net degradation by P. chrysosporium. Maximal degradation of Aroclor 1260 was observed in malt extract medium (18.4% on a molar basis), in which most of the individual congeners were degraded.