Polychlorinated Biphenyls Remediation Research Articles

PCB destruction in subcritical and supercritical water--evaluation of PCDF formation and initial steps of degradation mechanisms.

The reduction of polychlorinated biphenyl (PCB) emissions to the environment are contemporary issues of global efforts, and possible destruction technologies have to be selected and evaluated for PCB remediation. In this study PCB destruction in subcritical and supercritical water were assessed under oxidative conditions and nonoxidative, alkaline conditions. In both cases PCBs could be destroyed by more than 99%. The formation of polychlorinated dibenzofurans (PCDFs) during PCB destruction was evaluated. Under both oxidative and nonoxidative treatments of sub- and supercritical conditions, the formation of PCDFs was observed. The PCDFs formed in the early stages of PCB destruction resulted in up to 47-fold increase in terms of toxic equivalency (TEQ) compared to the initial PCB mixture. However, the PCDFs were destroyed together with the PCBs under more severe conditions i.e., at higher temperature or prolonged residence time. The mechanism of PCDF formation and the initial step of PCB degradation was evaluated. Our laboratory-scale investigation indicates that PCB destruction under supercritical water conditions is feasible, but because of the PCDF formation potential, in particular the high ratio of toxic 2,3,7,8-substituted congeners, conditions have to be carefully selected.

Remediation of PCBs in soil by surfactant washing and biodegradation in the wash by Pseudomonas sp. LB400

Solutions from the washing of polychlorinated biphenyl (PCB)-contaminated soil with a variety of commercial nonionic or anionic surfactants were incubated with Pseudomonas sp. LB400 in an attempt to remediate the soil and destroy the PCBs. Nonionic surfactants washed more PCBs from the soil (up to 89%) but inhibited their biodegradation. Anionic surfactants washed less PCBs from the soil but were more effective in biodegradation tests, removing up to 67% of total PCBs.

Construction and characterization of two recombinant bacteria that grow on ortho- and para-substituted chlorobiphenyls.

Cloning and expression of the aromatic ring dehalogenation genes in biphenyl-growing, polychlorinated biphenyl (PCB)-cometabolizing Comamonas testosteroni VP44 resulted in recombinant pathways allowing growth on ortho- and para-chlorobiphenyls (CBs) as a sole carbon source. The recombinant variants were constructed by transformation of strain VP44 with plasmids carrying specific genes for dehalogenation of chlorobenzoates (CBAs). Plasmid pE43 carries the Pseudomonas aeruginosa 142 ohb genes coding for the terminal oxygenase (ISPOHB) of the ortho-halobenzoate 1,2-dioxygenase, whereas plasmid pPC3 contains the Arthrobacter globiformis KZT1 fcb genes, which catalyze the hydrolytic para-dechlorination of 4-CBA. The parental strain, VP44, grew only on low concentrations of 2- and 4-CB by using the products from the fission of the nonchlorinated ring of the CBs (pentadiene) and accumulated stoichiometric amounts of the corresponding CBAs. The recombinant strains VP44(pPC3) and VP44(pE43) grew on, and completely dechlorinated high concentrations (up to 10 mM), of 4-CBA and 4-CB and 2-CBA and 2-CB, respectively. Cell protein yield corresponded to complete oxidation of both biphenyl rings, thus confirming mineralization of the CBs. Hence, the use of CBA dehalogenase genes appears to be an effective strategy for construction of organisms that will grow on at least some congeners important for remediation of PCBs.

An Integrated Surfactant Solubilization and PCB Bioremediation Process for Soils

Two decades after the manufacture and use of polychlorinated biphenyls (PCBs) were banned, PCB contamination remains widespread in the environment. Technologies available for PCB remediation are limited and often impractical for soils with dispersed PCB contamination. In this study, two remediation processes have been integrated for use on PCB-contaminated soils. This remediation strategy links in situ surfactant washing of PCBs from soil with aerobic biodegradation of the resulting surfactant-PCB solution by two field application vectors (F A Vs), Pseudomonas putida IFL5::TnPCB and Ralstonia eutropha B30F4::TnPCB, which utilize surfac-tants as growth substrates and cometabolize PCBs. A bench-scale demonstration of this process was performed using PCB-contaminated soils from an electric power substation site. In a 2-day recycling wash using a 1% (wt/vol) surfactant solution, greater than 70% of the PCBs were removed from the soil. In the biodegradation phase, greater than 90% of the surfactant and 35% of the PCBs were biodegraded in 12 days. The residual PCBs were partitioned onto a solid carrier resulting in greater than 90% removal of PCBs from the bioreactor effluent and a 50-fold reduction in the amount of PCB-contaminated material.

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.