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PAH degradation and redox control in an electrode enhanced sediment cap.

ABSTRACT: Capping is typically used to control contaminant release from the underlying sediments. However, the presence of conventional sediment caps will often eliminate or slow natural degradation that might otherwise occur at the surface sediment. The objective of this study was to explore the potential of a novel reactive capping, an electrode enhanced cap for the remediation of PAH contaminated sediment. The study on electrode enhanced biodegradation of PAH in slurries showed that naphthalene concentration decreased from ~1000 ?g/L to ~50 ?g/L, and phenanthrene decreased from ~150 ?g/L to ~30 ?g/L in ElectroBioReactor within 4 days, and the copy numbers of PAH degrading genes increased by almost 2 orders of magnitude. In a cap microcosm, two carbon electrodes were emplaced within a sediment cap with an applied potential of 2 V. The anode was placed at the sediment-cap interface encouraging oxidizing conditions. Oxidation and Reduction Potential (ORP) profiles showed redox potential approximately 60-100 mV higher at the sediment-cap interface with the application of voltage than in controls. Vertical profiles of phenanthrene porewater concentration were obtained by PDMS-coated fiber, and results showed that phenanthrene at the depth of 0-0.5 cm below the anode was degraded to ~70% of the initial concentration within 10 weeks. PAH degrading genes showed an increase of approximately 1 order of magnitude at the same depth. The no power controls showed no degradation of PAH. These findings suggest that electrode enhanced capping can be used to control redox potential, provide microbial electron acceptor, and stimulate PAH degradation.

SUBMITTER: Yan F

PROVIDER: S-EPMC3544081 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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PAH degradation and redox control in an electrode enhanced sediment cap.

Yan Fei F Reible Danny D DD

Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986) 20120314 9

Capping is typically used to control contaminant release from the underlying sediments. However, the presence of conventional sediment caps will often eliminate or slow natural degradation that might otherwise occur at the surface sediment. The objective of this study was to explore the potential of a novel reactive capping, an electrode enhanced cap for the remediation of PAH contaminated sediment. The study on electrode enhanced biodegradation of PAH in slurries showed that naphthalene concent ...[more]

PMID: 23329859

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Project description:Bacteria play an important role in the removal of polycyclic aromatic hydrocarbons (PAHs) from polluted environments. In marine environments, Cycloclasticus is one of the most prevalent PAH-degrading bacterial genera. However, little is known regarding the degradation mechanisms for multiple PAHs by CycloclasticusCycloclasticus sp. strain P1 was isolated from deep-sea sediments and is known to degrade naphthalene, phenanthrene, pyrene, and other aromatic hydrocarbons. Here, six ring-hydroxylating dioxygenases (RHDs) were identified in the complete genome of Cycloclasticus sp. P1 and were confirmed to be involved in PAH degradation by enzymatic assays. Further, five gene clusters in its genome were identified to be responsible for PAH degradation. Degradation pathways for naphthalene, phenanthrene, and pyrene were elucidated in Cycloclasticus sp. P1 based on genomic and transcriptomic analysis and characterization of an interconnected metabolic network. The metabolic pathway overlaps in many steps in the degradation of pyrene, phenanthrene, and naphthalene, which were validated by the detection of metabolic intermediates in cultures. This study describes a pyrene degradation pathway for Cycloclasticus. Moreover, the study represents the integration of a PAH metabolic network that comprises pyrene, phenanthrene, and naphthalene degradation pathways. Taken together, these results provide a comprehensive investigation of PAH metabolism in CycloclasticusIMPORTANCE PAHs are ubiquitous in the environment and are carcinogenic compounds and tend to accumulate in food chains due to their low bioavailability and poor biodegradability. Cycloclasticus is an obligate marine PAH degrader and is widespread in marine environments, while the PAH degradation pathways remain unclear. In this report, the degradation pathways for naphthalene, phenanthrene, and pyrene were revealed, and an integrated PAH metabolic network covering pyrene, phenanthrene, and naphthalene was constructed in Cycloclasticus This overlapping network provides streamlined processing of PAHs to intermediates and ultimately to complete mineralization. Furthermore, these results provide an additional context for the prevalence of Cycloclasticus in oil-polluted marine environments and pelagic settings. In conclusion, these analyses provide a useful framework for understanding the cellular processes involved in PAH metabolism in an ecologically important marine bacterium.

Project description:UnlabelledSubseafloor sediment hosts a large, taxonomically rich, and metabolically diverse microbial ecosystem. However, the factors that control microbial diversity in subseafloor sediment have rarely been explored. Here, we show that bacterial richness varies with organic degradation rate and sediment age. At three open-ocean sites (in the Bering Sea and equatorial Pacific) and one continental margin site (Indian Ocean), richness decreases exponentially with increasing sediment depth. The rate of decrease in richness with increasing depth varies from site to site. The vertical succession of predominant terminal electron acceptors correlates with abundance-weighted community composition but does not drive the vertical decrease in richness. Vertical patterns of richness at the open-ocean sites closely match organic degradation rates; both properties are highest near the seafloor and decline together as sediment depth increases. This relationship suggests that (i) total catabolic activity and/or electron donor diversity exerts a primary influence on bacterial richness in marine sediment and (ii) many bacterial taxa that are poorly adapted for subseafloor sedimentary conditions are degraded in the geologically young sediment, where respiration rates are high. Richness consistently takes a few hundred thousand years to decline from near-seafloor values to much lower values in deep anoxic subseafloor sediment, regardless of sedimentation rate, predominant terminal electron acceptor, or oceanographic context.ImportanceSubseafloor sediment provides a wonderful opportunity to investigate the drivers of microbial diversity in communities that may have been isolated for millions of years. Our paper shows the impact of in situ conditions on bacterial community structure in subseafloor sediment. Specifically, it shows that bacterial richness in subseafloor sediment declines exponentially with sediment age, and in parallel with organic-fueled oxidation rate. This result suggests that subseafloor diversity ultimately depends on electron donor diversity and/or total community respiration. This work studied how and why biological richness changes over time in the extraordinary ecosystem of subseafloor sediment.

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PAH degradation and redox control in an electrode enhanced sediment cap.

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PAH degradation and redox control in an electrode enhanced sediment cap.

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