Redox Control and Hydrogen Production in Sediment Caps Using Carbon Cloth Electrodes

Sun, Mei; Yan, Fei; Zhang, Ruiling; Reible, Danny D.; Lowry, Gregory V.; Gregory, Kelvin B.

doi:10.1021/es101003j

Cited by 27 publications

(21 citation statements)

References 32 publications

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“…Data from this study will enable better design of reactive sediment caps, 6 electrode-based remedial approaches, 25 and energy generation from environmentally-deployed electrodes. 26–28 …”

Section: Introductionmentioning

confidence: 99%

Effect of Applied Voltage, Initial Concentration, and Natural Organic Matter on Sequential Reduction/Oxidation of Nitrobenzene by Graphite Electrodes

Sun¹,

Reible²,

Lowry³

et al. 2012

Environ. Sci. Technol.

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Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H2 at the cathode and oxidizing conditions and O2 at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (kNB) and NSB (kNSB) increased with applied voltage between 2V and 3.5 V (when the initial NB concentration was 100 µM, kNB=0.3 d−1 and kNSB=0.04 d−1at 2V; kNB=1.6 d−1 and kNSB=0.64 d−1at 3.5 V) but stopped increasing beyond the threshold of 3.5V. When initial NB concentration decreased from 100 to 5 µM, kNB and kNSB became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased kNB while slightly increased kNSB, but only to a limited extent (~factor of 3) for dissolved organic carbon content up to 100 mg/l. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation.

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Section: Introductionmentioning

confidence: 99%

Effect of Applied Voltage, Initial Concentration, and Natural Organic Matter on Sequential Reduction/Oxidation of Nitrobenzene by Graphite Electrodes

Sun¹,

Reible²,

Lowry³

et al. 2012

Environ. Sci. Technol.

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“…It was expected that siderite and calcite would provide long term pH buffering capacity while bicarbonate would provide short term pH buffering capacity. Studies had previously shown that an unbuffered system would exhibit pH excursions which would hinder microbial community development (Sun et al, 2010). The pH in the control cap system was stable without buffering.…”

Section: Methodsmentioning

confidence: 99%

“…A technology for a continuous introduction of electron acceptors and providing conditions conducive to hydrocarbon oxidation has limited bioremediation of PAH contaminated sediments. Using an electric current may be an alternative option for supplying more favorable electron acceptors and conditions, providing a potentially viable remedial approach (Strycharz et al, 2008; Aulenta et al, 2009; Sun et al, 2010; Zhang et al, 2010; Chun et al, 2013). …”

Section: Introductionmentioning

confidence: 99%

Electro-bioremediation of contaminated sediment by electrode enhanced capping

Yan

Reible

2015

Journal of Environmental Management

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In-situ capping often eliminates or slows natural degradation of hydrocarbon due to the reducing conditions in the sediments. The purpose of this research was to demonstrate a reactive capping technique, an electrode enhanced cap, to produce favorable conditions for hydrocarbon degradation and evaluate this reactive capping technique for contaminated sediment remediation. Two graphite electrodes were placed horizontally at different layers in a cap and connected to external power of 2 V. Redox potentials increased and pH decreased around the anode. Phenanthrene concentration decreased and PAH degradation genes increased in the vicinity of the anode. Phenanthrene concentrations at 0–1 cm sediment beneath the anode decreased to ~50% of initial concentration over ~70 days, while phenanthrene levels in control reactor kept unchanged. A degradation model of electrode enhanced capping was developed to simulate reaction-diffusion processes, and model results show that a reaction-dominated region was created in the vicinity of the anode. Although the degradation dominated region was thin, transport processes in a sediment cap environment are typically sufficiently slow to allow this layer to serve as a permeable reactive barrier for hydrocarbon decontamination.

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“…This conceptual model could be exploited to augment sand-based caps with organic carbon (i.e., electron donor) to promote and sustain microbial activity in the cap. A more aggressive approach has been proposed by Sun et al (2010) who investigated the use of electrodes within a bench-scale cap to supply both hydrogen (electron donor) and oxygen (electron acceptor). The idea is intriguing since the electrodes could supply a stable source of electron donor within the cap to support reductive biotransformations and also provide oxygen to artificially create a sequenced anaerobic to aerobic treatment approach, which would be advantageous for the treatment of PCBs and chlorinated solvents.…”

Section: In Situ Cappingmentioning

confidence: 99%