Graphene-supported micron zero-valent iron cooperates with immobilized microorganisms for long-term efficient chlorinated organics remediation.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Permeable Reactive Barriers: Cost-Effective and Sustainable Remediation of Groundwater Ravi Naidu, Dawit N. Bekele, and Volker Birke Two Decades of Application of Permeable Reactive Barriers to Groundwater Remediation Scott D. Warner Choosing the Best Design and Construction Technologies for Permeable Reactive Barriers Dawit N. Bekele, Ravi Naidu, Volker Birke, and Sreenivasulu Chadalavada Groundwater Modeling Involving PRBs: General Aspects, Case Study Sreenivasulu Chadalavada, Martin Wegner, and Ravi Naidu Impact of Trace Elements and Impurities in Technical Zero-Valent Iron Brands on Reductive Dechlorination of Chlorinated Ethenes in Groundwater Volker Birke, Christine Schuett, Harald Burmeier, and Hans-Jurgen Friedrich Fourteen-Year Assessment of a Permeable Reactive Barrier for Treatment of Hexavalent Chromium and Trichloroethylene Richard T. Wilkin, Tony R. Lee, Mary Sue McNeil, Chunming Su, and Cherri Adair Sequenced Permeable Reactive Barrier for the Pretreatment of Nitrate and Remediation of Trichloroethene Keely Mundle Organic-Based Permeable Reactive Barriers for the Treatment of Heavy Metals, Arsenic, and Acidity Ralph D. Ludwig, Richard T. Wilkin, Steven D. Acree, Randall R. Ross, and Tony R. Lee Effective Cleanup of Groundwater Contaminated with Radionuclides Using Permeable Reactive Barriers Franz-Georg Simon and Tamas Meggyes Reactive (Oxygen) Gas Barrier and Zone Technologies Ronald Giese, Frank Ingolf Engelmann, Dietrich Swaboda, Uli Uhlig, and Ludwig Luckner Remediation of PAHs, NSO-Heterocycles, and Related Aromatic Compounds in Permeable Reactive Barriers Using Activated Carbon Wolf-Ulrich Palm, Jan Sebastian Manz, and Wolfgang Ruck Case Study of PRB Application for the Remediation of Groundwater James Stening Permeable Reactive Barriers in Europe Volker Birke and Harald Burmeier

Combination of zeolite barrier and bio sparging techniques to enhance efficiency of organic hydrocarbon remediation in a model of shallow groundwater

Monitoring trichloroethene remediation at an iron permeable reactive barrier using stable carbon isotopic analysis

Fast dechlorination of trichloroethylene by a bimetallic Fe(OH)2/Ni composite

Remediation of lead (II)-contaminated soil using electrokinetics assisted by permeable reactive barrier with different filling materials

The application of Permeable Reactive Barriers (PRBs), an innovative clean-up technology for in-situ groundwater remediation, represents an effective alternative to traditional pump-and-treat systems and has raised strong interest during recent years. From recent statistics of the Italian Water Research Institute (IRSA), trichloroethylene (TCE) from industrial activities is the most widespread contaminant in groundwater. The goal of the research was to test the suitability and performance of a high purity granular iron reactive medium for TCE degradation by PRBs. The suitability was evaluated based on chemical and physical characteristics of the material and the performance of the granular iron, in terms of TCE removal efficiency, was evaluated by column tests.The experimental results showed that the characteristics of the granular iron are suitable for application as a reactive medium, since the hydraulic conductivity values were fully consistent with those reported in the literature, and the leaching tests indicated a reduced release of heavy metals. The overall removal efficiency of TCE was higher than 97% in all the tests performed at the flow rate of 0.25 cm3 min-1 (corresponding to a groundwater flow velocity of 0.37 m d-1) both for the 100% iron and the iron-sand columns. Moreover, TCE degradation around 60% was observed even in the first section of the columns fortypical groundwater flow velocity. The TCE reduction in the outlet stream was confirmed by the assessment of chlorine mass balance and by the absence of any reaction intermediate detected by GC-MS.Finally, the concentration profiles in the columns were not in agreement with those expected for a chemistry-controlled kinetic regime. This suggests that TCE degradation rate may have been limited by precipitation phenomena, hindering the contaminant transport to the iron surface.

This study provides a twenty-two-year record of in situ degradation of chlorinated organic compounds by a granular iron permeable reactive barrier (PRB). Groundwater concentrations of trichloroethene (TCE) entering the PRB were as high as 10670 μg/L. Treatment efficiency ranged from 81 to >99%, and TCE concentrations from <1 μg/L to 165 μg/L were detected within and hydraulically down-gradient of the PRB. After 18 years, effluent TCE concentrations were above the maximum contaminant level (MCL) along segments of the PRB exhibiting upward trending influent TCE. Degradation products included cis-dichloroethene ( cis-DCE), vinyl chloride (VC), ethene, ethane, >C4 compounds, and possibly CO2(aq) and methane. Abiotic patterns of TCE degradation were indicated by compound-specific stable isotope data and the distribution of degradation products. δ13C values of methane within and down-gradient of the PRB varied widely from -94‰ to -16‰; these values cover most of the isotopic range encountered in natural methanogenic systems. Methanogenesis is a sink for inorganic carbon in zerovalent iron PRBs that competes with carbonate mineralization, and this process is important for understanding pore-space clogging and longevity of iron-based PRBs. The carbon isotope signatures of methane and inorganic carbon were consistent with open-system behavior and 22% molar conversion of CO2(aq) to methane.

Highly organic natural media as permeable reactive barriers: TCE partitioning and anaerobic degradation profile in eucalyptus mulch and compost

A pilot scale permeable reactive barrier (PRB) demonstration project was initiated by the US Navy Engineering Field Activity (EFA) West at the former Naval Air Station (NAS) Moffett Field site in Mountain View, California in late 1995. Performance evaluations and cost-benefit analyses were performed by US Naval Facilities Engineering Service Center (NFESC) at the Moffett Field site, which were sponsored by the Department of Defense (DOD) Environmental Security Technology Certification Program (ESTCP). The Moffett Field PRB uses a funnel-andgate system design. The funnel is made of interlocking steel sheet piles and the gate consists of a reactive cell filled with zero-valent granular iron. Performance monitoring was conducted at the site to demonstrate the effectiveness of the PRB technology in capturing and remediating ground water that contained dissolved chlorinated hydrocarbon compounds. The primary contaminants of concern at Moffett Field in the vicinity of the PRB were trichloroethene (TCE), cis-1,2 dichloroethene (cDCE), and perchloroethene (PCE) at upgradient concentrations of about 2,900 micrograms per liter tug/L), 280 ug/L, and 26 ug/L, respectively. Monitoring events included measuring water levels, testing field parameters, and ground-water quality sampling at about 75 monitoring points. Tracer tests using bromide solutions and flow-velocity meter testing were also completed in April and August 1997. Iron cell coring samples were collected and analyzed in December 1997 for early indications of chemical precipitation. The iron cell coring analyses and geochemical modeling from Moffett Field indicated that changes in inorganic chemistry may be caused by precipitation of calcium carbonates, iron-sulfide, and hydroxide compounds. Chemical precipitates are of significant concern because of the potential loss of reactivity and permeability in the iron cell. Long-term performance and life-expectancies of PRBs are generally unknown. The DOD ESTCP, Environmental Protection Agency (EPA), and Department of Energy (DOE) are sponsoring additional performance evaluations at several PRB sites to help find answers to the longevity concerns. In the meantime, these agencies are also attempting to help gain widespread regulatory acceptance and user confidence in implementing the PRB technology.

The work reported here demonstrates that zero valent iron (ZVI), a material used in permeable reactive barriers, yields degradation rate constants for trichloroethylene (TCE) that are considerably different depending on whether they are determined in deionised water or in groundwater. Batch studies using ZVI and TCE-spiked deionised (DI) water and TCE-contaminated groundwater revealed that within 50 h, 80 % of the TCE present in groundwater was mineralised, compared to TCE-spiked deionised water in which only 50 % of TCE was demineralised by ZVI in 50 h. In both TCE-spiked groundwater and DI water, cis-dichloroethylene was the major by-product, and it was reduced together with TCE after 96 h of treatment. Along with changes in concentrations of TCE and its metabolites, increased levels of chloride confirmed TCE degradation. TCE-spiked groundwater gave a higher rate constant (k) under similar conditions. The elevated chloride (830 mg/l) concentrations of the groundwater could be a possible reason for this higher rate constant, in spite of the fact that groundwater also contains higher inorganic carbon (132 mg/l) and calcium (26 mg/l) and has a pH of 7.9. The rate constant (0.017–0.03223 h−1) and half-life of TCE (21.5 to 40 h) are within the reported ranges in the literature. The implications of the results for the performance of ZVI in permeable reactive barriers are that not only groundwater chemistry, but also groundwater flow conditions, plays a key role in TCE degradation.

Understanding the fate of complex electron-donor materials is important for developing efficient biostimulation strategies to treat ground water contamination by chlorinated ethenes (CEs). The fermentation product distributions and H2 production of common permeable reactive barrier (PRB) carbon substrates (dairy whey, sodium lactate syrup, and Hydrogen Release Compound [HRC]) were monitored as measures of substrate efficiency in aquifer microcosms spiked with trichloroethene (TCE). In long-term experiments, the fermentation of PRB substrates to slow-degrading organic acids maintained low H2 partial pressures (≤ 10−3.5) that, as previous studies suggest, may give competitive advantage to dechlorinators over hydrogenotrophic methanogens. Whey-amended and lactate-amended microcosms exhibited faster complete dechlorination and, according to organic acid carbon flow, higher rates of fermentation to acetate. In HRC-amended microcosms, propionate appeared to serve as a carbon sink that prolonged dechlorination. Upon complete dechlorination, whey microcosms contained the highest percentage of organic acid carbon. Native Dehalococcoides populations increased by 3 orders of magnitude (per g sediment) in whey-amended microcosms. Whey's efficiency improved in microcosms prepared with aquifer sediment and water from within a downgradient whey PRB. Results suggested whey loading values of 0.2 kg/m3 may be appropriate under sufficiently reducing conditions to efficiently stimulate hydrogenotrophic and potentially actetotrophic dechlorinating populations. Renewal of whey PRBs may, however, be required. Implications for further long-term study of cost-efficiencies are discussed.

: Significant laboratory and field research has demonstrated that zero-valent metals will reductively dechlorinate dissolved chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) to ethene in groundwater. Permeable reactive barriers (PRBs) containing zero-valent iron (ZVI) as the reactive material have been shown to be effective in treating plumes of dissolved chlorinated solvents. PRB technology is passive; however, it relies on dense non-aqueous phase liquid (DNAPL) dissolution and transport of dissolved chlorinated solvents to the PRB for treatment, and therefore PRBs do not reduce the cleanup time for sites where DNAPL is present. Nano-scale ZVI particles (nZVI), either in a water slurry or as particles contained within an oil emulsion droplet (EZVI), have advantages over the conventional PRB applications since they may be injected deeper in the subsurface than is practical for conventional PRBs, and can be injected directly into DNAPL source areas. Laboratory and field tests have demonstrated that treatment of chlorinated ethenes such as TCE with nZVI particles is more rapid than with conventional forms of granular iron (Wang and Zhang, 1997; Lien and Zhang, 2001; Elliott and Zhang, 2001; Lowry et al. 2004). Nano-scale ZVI is significantly more reactive than micro-scale ZVI or iron powders because the smaller particle size gives the nZVI a larger surface area per unit mass. The degradation of chlorinated solvents by ZVI regardless of particle size is believed to occur via both reductive dechlorination and -elimination (Arnold and Roberts, 2000). The dechlorination reactions occur at the iron surface and require excess electrons produced from the corrosion of the ZVI in water. Through this process, the target chemicals undergo sequential dechlorination steps, resulting in the formation of non-chlorinated hydrocarbon products (e.g., ethene and ethane).

In June and July 2001, the Massachusetts Department of Environmental Protection (MassDEP) installed a permeable reactive barrier (PRB) to treat a groundwater plume of chlorinated solvents migrating from an electronics manufacturer in Needham, Massachusetts, toward the Town of Wellesley's Rosemary Valley wellfield. The primary contaminant of concern at the site is trichloroethene (TCE), which at the time had a maximum average concentration of approximately 300 micrograms per liter directly upgradient of the PRB. The PRB is composed of a mix of granular zero‐valent iron (ZVI) filings and sand with a pure‐iron thickness design along its length between 0.5 and 1.7 feet. The PRB was designed to intercept the entire overburden plume; a previous study had indicated that the contaminant flux in the bedrock was negligible. Groundwater samples have been collected from monitoring wells upgradient and downgradient of the PRB on a quarterly basis since installation of the PRB. Inorganic parameters, such as oxidation/reduction potential, dissolved oxygen, and pH, are also measured to determine stabilization during the sampling process. Review of the analytical data indicates that the PRB is significantly reducing TCE concentrations along its length. However, in two discrete locations, TCE concentrations show little decrease in the downgradient monitoring wells, particularly in the deep overburden. Data available for review include the organic and inorganic analytical data, slug test results from nearby bedrock and overburden wells, and upgradient and downgradient groundwater‐level information. These data aid in refining the conceptual site model for the PRB, evaluating its performance, and provide clues as to the reasons for the PRB's underperformance in certain locations. © 2008 Wiley Periodicals, Inc.

Permeable reactive barrier (PRB) is one of the most promising in situ treatment methods for shallow groundwater pollution. However, optimal design of PRB is very difficult due to a lack of comprehensive understanding of various complex influencing factors of PRB remediation. In this study, eight of the main factors of PRB, including hydraulic gradient I, permeability coefficient KPRB of PRB material, PRB length L, PRB width W, PRB distance from pollution source Dist., the ratio of the maximum adsorption capacity to Langmuir constant of PRB material Qmax/KL, the discharge rate of pollution source DR, and recharge concentration RC were investigated, to carry out the sensitivity analysis of PRB removal efficiency. The simulation experiments for Morris analysis were designed, and pollutant removal efficiency was numerically simulated by coupling MODFLOW and MT3DMS under two scenarios of high and low permeability and dispersivity. For a typical low permeability with low dispersity medium, the sensitivity ranking of factors from high to low is DR, RC, I, W, L, Dist., Qmax/KL, and KPRB, and for a typical high permeability with a high dispersity medium, the sensitivity ranking of factors from high to low is I, W, DR, Qmax/KL, L, RC, Dist., and KPRB. When considering multiple factors in PRB design, the greater the KPRB, L, W, Qmax/KL is, the higher the removal efficiency is; the greater the RC, I is, the lower the removal efficiency is. The rest factors remain ambiguous enhancement to removal efficiency.