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Mineral Precipitation Upgradient from a Zero‐Valent Iron Permeable Reactive Barrier
Abstract
Core samples taken from a zero-valent iron permeable reactive barrier (ZVI PRB) at Cornhusker Army Ammunition Plant, Nebraska, were analyzed for physical and chemical characteristics. Precipitates containing iron and sulfide were present at much higher concentrations in native aquifer materials just upgradient of the PRB than in the PRB itself. Sulfur mass balance on core solids coupled with trends in ground water sulfate concentrations indicates that the average ground water flow after 20 months of PRB operation was approximately twenty fold less than the regional ground water velocity. Transport and reaction modeling of the aquifer PRB interface suggests that, at the calculated velocity, both iron and hydrogen could diffuse upgradient against ground water flow and thereby contribute to precipitation in the native aquifer materials. The initial hydraulic conductivity (K) of the native materials is less than that of the PRB and, given the observed precipitation in the upgradient native materials, it is likely that K reduction occurred upgradient to rather than within the PRB. Although not directly implicated, guar gum used during installation of the PRB is believed to have played a role in the precipitation and flow reduction processes by enhancing microbial activity.
... 29−34 ZVI may stabilize SRB by maintaining favorable redox and pH conditions and producing molecular hydrogen as the electron donor for sulfate reduction. 31,35 The presence of sulfate reducers in the vicinity of ZVI is also supported by the detection of iron sulfides in iron corrosion rinds in coring samples collected at remediation sites. 29,30,32 However, microbial growth and mineral precipitation may reduce matrix permeability and create preferential flow patterns, 30,35 which makes it difficult to evaluate the intrinsic effect of SRB on ZVI reactivity using field observations. ...
... 31,35 The presence of sulfate reducers in the vicinity of ZVI is also supported by the detection of iron sulfides in iron corrosion rinds in coring samples collected at remediation sites. 29,30,32 However, microbial growth and mineral precipitation may reduce matrix permeability and create preferential flow patterns, 30,35 which makes it difficult to evaluate the intrinsic effect of SRB on ZVI reactivity using field observations. Among a limited number of laboratory investigations, Nooten et al. observed that iron materials recovered from a column operating under sulfatereducing conditions for 3 years were more reactive with PCE and TCE than the original iron particles. ...
... The creation of preferential flow paths is recognized as a critical factor leading to unsatisfactory or ineffective long-term treatment outcomes. 30,32,35 Data obtained so far seem to concur on the point that optimal sulfidation of ZVI requires relatively low levels of sulfur only 1,3,4,63,64 ; thus, biological conditioning of ZVI may be best achieved using a low but consistent delivery of biogenic forms of reduced sulfur. This suggests the need for well-controlled sulfate reduction using moderate levels of electron donor in order to maintain desired flow conditions. ...
Sulfur amendment of zerovalent iron (ZVI) materials has been shown to improve the reactivity and selectivity of ZVI toward a select group of organohalide contaminants in groundwater, most notably trichloroethene (TCE). In previous studies, chemical or mechanochemical sulfidation methods were used; however, the potential of using sulfate-reducing bacteria (SRB) to enable sulfur amendment has not been closely examined. In this study, lab-synthesized nanoscale ZVI (nZVI) and Peerless iron particles (ZVIPLS) were treated in a sulfate-reducing monoculture (D. desulfuricans) and an enrichment culture derived from freshwater sediments (AMR-1) prior to reactivity assessments with TCE as the model contaminant. ZVI conditioned in both cultures exhibited higher dechlorination efficiencies compared to unamended ZVIs. Remarkably, nZVI and ZVIPLS exposed to AMR-1 attained similar TCE dechlorination rates as their counterparts receiving chemical sulfidation (i.e., S-nZVI) using previously reported method. Product distribution data show that, in the SRB-ZVI system, abiotic dechlorination is the dominant TCE reduction pathway. In addition to dissolved sulfide, biogenic or synthesized FeS particles can enhance nZVI reactivity even as nZVI and FeS were not in direct contact, implying that SRB may influence the reactivity of ZVI via multiple mechanisms in different remediation situations. A shift in Archaea abundance in AMR-1 with nZVI amendment was observed but not with ZVIPLS. Overall, the synergy exhibited in the SRB-ZVI system may offer a valuable remediation strategy to overcome limitations of standalone biological or abiotic dechlorination approaches for chlorinated solvent abatement.
... However, in spite of the abundance of laboratory work on reduction of explosives by ZVI (recent examples include Bandstra et al., 2005;Monteil-Rivera et al., 2005;Oh et al., 2002), there have been few well-documented field trials of this approach to remediating explosives contaminated sites (one exception being Comfort et al., 2003). Recently, we have reported results from a field demonstration of a full-scale ZVI PRB for removal of explosives from groundwater at the Cornhusker Army Ammunition Plant (CAAP) near Grand Island, Nebraska Johnson et al., 2008a;Johnson et al., 2008b). ...
... Details of the core sampling and analysis are given in (Johnson et al., 2008a;Johnson et al., 2008b). Prior to core sample collection the overlying soils were removed down to near the water table. ...
... The coloration could be due to a variety of authigenic precipitates, including iron oxides, carbonates, and sulfides. In this case, we know that sulfate concentrations in the groundwater decrease significantly along the flow path and analysis of the solids (e.g., by X-ray photoelectron spectroscopy, XPS) showed that sulfur concentration on the surface of the particles was high for the up-gradient impacted and PRB particles, whereas it was below detection limits in the original Peerless iron/sand mixture and in the up-gradient unimpacted samples (Johnson et al., 2008b). In the most impacted zone, XPS gave a strong signal for pyrite (FeS 2 ). ...
We recently completed a pilot-scale permeable reactive barrier (PRB) with zero-valent iron (ZVI) to treat groundwater contaminated with explosives (TNT and RDX) at the Cornhusker Army Ammunition Plant (CAAP) near Grand Island, Nebraska. While the PRB at CAAP continues to be effective at removing explosives from the groundwater, the hydraulic performance is significantly reduced. This may be due to the accumulation of authigenic precipitates slightly up-gradient from the iron-containing zone. It is likely that the accumulation of new solid phases on the matrix materials in and around the treatment zone would also cause the system to be less effective at reducing contaminants. This, however, does not seem to be the case at CAAP. We report here that iron removed from the PRB is still quite reactive—with TNT and with RDX—when re- suspended and tested in laboratory batch experiments. Surprisingly, the up-gradient impacted samples showed reduction of TNT and RDX even though they did not contain ZVI. Also of note is that the core samples gave slower reduction of TNT than the dry ZVI/sand mixture, but the reverse was true for RDX. In all cases, however, the rates of TNT/RDX reduction by materials containing ZVI were within the range given by the de- sign guidelines.
... The presence of mineral precipitates, such as calcium and iron carbonates, was mostly observed at the barrier inlet and, in some cases [73,74], cemented areas. Finally, the hydraulic performance of a PRB could also depend on the construction method, as in the case of the PRB installed in Nebraska [13,75]. According to that study, a possible reason for the early loss of PRB hydraulic conductivity was the uneven degradation of guar gum slurry, which could have penetrated the upgradient aquifer during construction, thereby promoting excessive microbial activity and sulfide precipitation. ...
... Guar gum is a biopolymer slurry that allows trenches to remain open during filling with reactive media. Reduction in permeability at the entrance of the barrier one year after installation, which was linked to an excess of biological activity or the incomplete degradation of the guaro rubber used during installation; the presence of sulfides and iron carbonates [13,75] Note: w.r., weight ratio; CT, continuous trench; FG, funnel and gate; PTZ, pretreatment zone; CS, chlorinated solvents; TCE, trichloroethylene. ...
Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences “failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors.
... It is generally believed that metal removal by Fe 0 from groundwater is primarily due to surface adsorption and reductive mineral precipitation and co-precipitation [27,5,35]. Evolution of microbial communities in these reducing environments has often been reported [9,14]. Sulfate reducing bacteria (SRB) in particular are already well known for heavy metal precipitation as relatively stable metal sulfides (reaction 2-4) [3]. ...
... Fe 0 oxidation creates strongly reducing and oxygen depleted environment required by SRBs for optimum growth and also SRBs can utilize the H 2 produced by iron oxidation as an efficient electron donor [11,36,15]. H 2 consumption by SRBs can help in avoiding the fouling and over pressure within the PRBs, which further adds to the longevity of the treatment process [9,34]. Integration of SRB-Fe 0 systems can be synergistically beneficial for heavy metal removal as Fe 0 can remove metals efficiently, and eventually SRBs can form relatively stable metal sulfides. ...
We conducted a series of flow-through column experiments using aquifer sediment treated with zero valent iron (Fe0) with or without active microbial sulfate reduction. The aim of this study was to investigate the stability of Zn removed by Fe0 and impact of sulfate reducing bacteria (SRB). The leaching of Zn was assessed by flushing the aquifer in vertical glass columns with groundwater that was pre-treated with mixture of gases to simulate natural changes (pH and ORP) in subsurface environment (N2 + CO2 for pH and N2 + O2 for ORP) along with a control (N2 flushed). Zinc removed synergistically by Fe0 and SRBs was found to be more stable and did not leach from the aquifer sediment with pH or redox changes. We also observed that the Zn leaching in the aquifer treated only with Fe0 was more influenced by change in redox than by pH changes. These results were also confirmed by sequential metal extractions and scanning electron microscopy observations in the aquifer sediments. Mineral phases were predicted using geochemical modeling tool CHESS confirming that the metal removed in Fe0 + SRB conditions formed more stable precipitates and did not show any signs of leaching back to groundwater upon change in pH and redox conditions.
... Two simple methods for material selection were recently introduced[70][71][72].Finally, it should be explicitly said that the approach considering remediation Fe 0 /H 2 O systems as primary filtration systems is not negating the complex chemical and physical processes (adsorption, co-precipitation, desorption, oxidation, reduction) occurring in it. On the contrary, this approach takes into account the fundamental fact that volumetric expansive iron corrosion needs free space to occur optimally and explains why so many species have been successfully removed in systems designed for individual compounds[1,13,50,73,74]. For example, Johnson et al.[74] reported decrease in sulfate, carbonate, and calcium concentration in a barrier designed to remove explosives from contaminated groundwater. ...
... On the contrary, this approach takes into account the fundamental fact that volumetric expansive iron corrosion needs free space to occur optimally and explains why so many species have been successfully removed in systems designed for individual compounds[1,13,50,73,74]. For example, Johnson et al.[74] reported decrease in sulfate, carbonate, and calcium concentration in a barrier designed to remove explosives from contaminated groundwater. Constructing efficient Fe 0 /sand filters is an engineering Environ. ...
The use of metallic iron filters (Fe0 filters) has been discussed as a promising low-cost option for safe drinking water production at household level. Filter clogging due to the volumetric expansive nature of iron corrosion has been identified as the major problem of Fe0 filters. Mixing Fe0 and sand (yielding Fe0/sand filters) has been proposed as a tool to extent filter service life. However, no systematic discussion rationalizing Fe0:sand mixtures is yet available. This communication theoretically discussed suitable Fe0:sand proportions for efficient filters. Results suggested that Fe0/sand filters should not contain more that 50 vol-% Fe0 (25 wt-% when Fe0 is mixed with quartz). The actual Fe0 percentage in a filter will depend on its intrinsic reactivity.
... A PRB transforms the contaminations into less harmful substances or immobilizes them while allowing groundwater to pass through. The contaminant is either biologically or chemically transformed and/or physically removed [4] [5] [8] [9] [10]. Several reactive materials have been used including activated carbon, compost, clays, Fe II -bearing minerals, metallic iron, wood chip or zeolites. ...
... The PRB technology using metallic iron (Fe 0 ) has gained acceptance as an effective passive remediation strategy for the treatment of a variety of organic and inorganic contaminants in groundwater [5] [8] [9] [10] [11] [12] [13] [14]. Even pathogens are efficiently removed in Fe 0 /H 2 O systems [15] [16]. ...
The interpretation of processes yielding aqueous contaminant removal in the presence of elemental iron (e.g., in Fe0/H2O systems) is subject to numerous complications. Reductive transformations by Fe0 and its primary corrosion products (FeII and H/H2) as well as adsorption onto and co-precipitation with secondary and tertiary iron corrosion products (iron hydroxides, oxyhydroxides, and mixed valence FeII/FeIII green rusts) are considered the main removal mechanisms on a case-to-case basis. Recent progress involving adsorption and co-precipitation as fundamental contaminant removal mechanisms have faced a certain scepticism. This work shows that results from electrocoagulation (EC), using iron as sacrificial electrode, support the adsorption/co-precipitation concept. It is reiterated that despite a century of commercial use of EC, the scientific understanding of the complex chemical and physical processes involved is still incomplete.
... Two simple methods for material selection were recently introduced[70][71][72].Finally, it should be explicitly said that the approach considering remediation Fe 0 /H 2 O systems as primary filtration systems is not negating the complex chemical and physical processes (adsorption, co-precipitation, desorption, oxidation, reduction) occurring in it. On the contrary, this approach takes into account the fundamental fact that volumetric expansive iron corrosion needs free space to occur optimally and explains why so many species have been successfully removed in systems designed for individual compounds[1,13,50,73,74]. For example, Johnson et al.[74] reported decrease in sulfate, carbonate, and calcium concentration in a barrier designed to remove explosives from contaminated groundwater. ...
... On the contrary, this approach takes into account the fundamental fact that volumetric expansive iron corrosion needs free space to occur optimally and explains why so many species have been successfully removed in systems designed for individual compounds[1,13,50,73,74]. For example, Johnson et al.[74] reported decrease in sulfate, carbonate, and calcium concentration in a barrier designed to remove explosives from contaminated groundwater. Constructing efficient Fe 0 /sand filters is an engineering Environ. ...
The use of metallic iron filters (Fe0 filters) has been discussed as a promising low-cost option for safe drinking water production at household level. Filter clogging due to the volumetric expansive nature of iron corrosion has been identified as the major problem of Fe0 filters. Mixing Fe0 and sand (yielding Fe0/sand filters) has been proposed as a tool to extent filter service life. However, no systematic discussion rationalizing Fe0/sand mixtures is yet available. This communication theoretically discussed suitable Fe0/sand proportions for efficient filters. Results suggested that Fe0/sand filters should not contain more that 50 vol% Fe0 (25 wt% when Fe0 is mixed with quartz). The actual Fe0 percentage in a filter will depend on its intrinsic reactivity.
... The application of zero-valent iron (Fe 0 ) in the dechlorination degradation of chlorinated organic compounds had been extensively explored in recent years due to its low cost, high activity and non-toxicity [6,7]. Compared to micron-sized particles, Fe 0 with particle size at nanoscale (nFe) exhibited more reactive activity due to its larger surface area [8][9][10][11]. However, nFe had some disadvantages in the application of water pollution control and in situ remediation, such as rapid agglomeration and easy oxidation passivation, which can affect subsequent dechlorination degradation [12][13][14]. ...
Attapulgite (ATP) disaggregated by a ball milling–freezing process was used to support Fe/Ni bimetallic nanoparticles (nFe/Ni) to obtain a composite material of D-ATP-nFe/Ni for the dechlorination degradation of 2,4-dichlorophenol (2,4-DCP), thus improving the problem of agglomeration and oxidation passivation of nanoscale zero-valent iron (nFe) in the dechlorination degradation of chlorinated organic compounds. The results show that Fe/Ni nanoparticle clusters were dispersed into single spherical particles by the ball milling–freezing-disaggregated attapulgite, in which the average particle size decreased from 423.94 nm to 54.51 nm, and the specific surface area of D-ATP-nFe /Ni (97.10 m2/g) was 6.9 times greater than that of nFe/Ni (14.15 m2/g). Therefore, the degradation rate of 2,4-DCP increased from 81.9% during ATP-nFe/Ni application to 96.8% during D-ATP-nFe/Ni application within 120 min, and the yield of phenol increased from 57.2% to 86.1%. Meanwhile, the reaction rate Kobs of the degradation of 2,4-DCP by D-ATP-nFe/Ni was 0.0277 min−1, which was higher than that of ATP-nFe/Ni (0.0135 min−1). In the dechlorination process of 2,4-DCP by D-ATP-nFe/Ni, the reaction rate for the direct dechlorination of 2,4-DCP of phenol (k5 = 0.0156 min−1) was much higher than that of 4-chlorophenol (4-CP, k2 = 0.0052 min−1) and 2-chlorophenol (2-CP, k1 = 0.0070 min−1), which suggests that the main dechlorination degradation pathway for the removal of 2,4-DCP by D-ATP-nFe/Ni was directly reduced to phenol by the removal of two chlorine atoms. In the secondary pathway, the removal of one chlorine atom from 2,4-DCP to generate 2-CP or 4-CP as intermediate was the rate controlling step. The final dechlorination product (phenol) was obtained when the dechlorination rate accelerated with the progress of the reaction. This study contributes to the broad topic of organic pollutant treatment by the application of clay minerals.
... This is attributed to a reduction in aqueous permeability caused by the presence of trapped gas, consistent with reductions resulting from hydrogen gas exsolution and trapping from the reaction of NaBH 4 and water observed previously (Mohammed et al., 2019). The presence of nZVI and precipitation of iron hydroxides may also have contributed to this reduction (Johnson et al., 2008;Jeen et al., 2012;Fronczyk and Pawluk, 2014;Tosco et al., 2014), but because the volume of gas generated was sufficient to overcome the trapping capacity of the sand, and even small amounts of trapped gas can significantly reduce the aqueous permeability, gas production alone is sufficient to explain the difference in tracer transport. ...
The injection of nanoscale zero-valent iron (nZVI) can be an effective technique for the treatment of groundwater contaminants, including chlorinated solvents. However, its effectiveness can be limited by natural reductant demand (NRD) reactions, including the reduction of water resulting in the production of hydrogen gas. This study presents results from a series of laboratory experiments to investigate gas production and mobilization following the injection of nZVI solutions, along with sodium borohydride (NaBH4) that is used for nZVI synthesis. Experiments were performed in a thin, two-dimensional flow cell (22 × 34 × 1 cm³) to measure hydrogen gas volumes and local gas saturations, and to investigate the distribution of gas within and above the injection zone. An additional experiment was conducted in a larger flow cell (150 × 150 × 2 cm³) containing dissolved trichloroethene (TCE) to assess changes in aqueous flow pathways and enhanced vertical transport of TCE by mobilized gas. The results showed substantial gas production (60% to 740% of the injected solution volume) resulting in gas mobilization as a network of gas channels above the injection zone, with more gas produced from greater excess NaBH4 used during nZVI synthesis. Trapped gas saturations were sufficient to cause the diversion of aqueous flow around the nZVI injection zone. In addition, gas production and mobilization resulted in the bubble-facilitated transport of TCE, and detectable concentrations of TCE and reaction products (ethane and ethene) above the target treatment zone.
... Fouling, or reduced permeability below local flowrates, is unlikely to occur as the precipitates maintain a low-density structure similar to lime-softening residuals. Secondary settling, as related to water treatment, is prevented by the CBFM macrostructure and demonstrates the benefit of precipitation within the large, cemented, pores as opposed to an upgradient or upstream precipitation system (Johnson et al. 2008). The uncompacted calcite is then still chemically and hydrodynamically available to replenish sorption sites. ...
Lime softening produces an estimated 10,000 metric tons of dry drinking water treatment wastes (DWTW) per year, costing an estimated one billion dollars annually for disposal worldwide. Lime softening wastes have been investigated for reuse as internal curing agents or supplementary cementitious materials in concrete as well as a high‐capacity sorbent for heavy metal removal. Lead, cadmium, and zinc are common heavy metals in groundwater contaminated by mine tailings. Cement‐based filter media (CBFM) are a novel material‐class for heavy metal remediation in groundwater. This study investigated the incorporation of DWTW as a recycled, low‐cost additive to CBFM for the removal of lead, cadmium, and zinc. Jar testing at three different metal concentrations and breakthrough column testing using synthetic groundwater were performed to measure removal capacity and reaction kinetics. Jar testing results show as DWTW content increases at low concentrations, removal approaches 100% but at high metal concentrations removal decreases due to saturation or exhaustion of the removal mechanisms. Removal occurs through the formation of metal carbonate precipitates, surface sorption, and ion exchange with calcium according to the preferential series Pb+2 > Zn+2 > Cd2+. Removal kinetics were also measured through column testing and exceeded estimated calculations derived from batch jar testing isotherms due to the large formation of oolitic metal carbonates. Lead, cadmium, and zinc was concentrated in the column precipitates from 0.29, 0.23, and 20.0 ug/g in the influent solution to approximately 200, 130, 14,000 ug/g in the reacted DWTW‐CBFM. The control and DWTW‐CBFM columns had statically similar removal for zinc and lead. In the DWTW‐CBFM, cadmium had decreased removal of approximately 25% due to proportionately decreased hydroxide content from cement replacement with 25% DWTW. This study shows the potential for DWTW as an enhancement to CBFM, thereby valorizing an otherwise waste material. Furthermore, the concentrative abilities of CBFM through precipitate and oolitic mineral formation could provide a minable waste product and close the waste‐product cycle for DWTW. This article is protected by copyright. All rights reserved.
... Therefore, the strongly reducing and alkalescent condition created by Fe 0 corrosion would be suitable for the growth of SRB, and the hydrogen and/or ferrous iron can serve as electron donor for the reduction of sulfate by SRB (Kumar et al., 2015). Furthermore, the SRB could utilize H 2 and alleviate its pressure in the permeable reactive barrier (PRB), and this is benefit for the long-term remediation efficiency of PRB technique (Johnson et al., 2010;Kumar et al., 2015). Besides, the ferrous iron ions could play key roles in the synthesis of hydrogenase, which are involved in the mass transport and electron transfer process of the SRB metabolism (Bryant et al., 1993;Guo et al., 2017). ...
The technology of integrating nanoscale zero-valent iron (nZVI) and functional anaerobic bacteria has broad prospects for groundwater remediation. This review focuses on the interactions between nZVI and three kinds of functional anaerobic bacteria: organohalide-respiring bacteria (OHRB), sulfate reducing bacteria (SRB) and iron reducing bacteria (IRB), which are commonly used in the anaerobic bioremediation. The coupling effects of nZVI and the functional bacteria on the contaminant removal in the integrated system are summarized. Generally, nZVI could create a suitable living condition for the growth and activity of anaerobic bacteria. OHRB and SRB could synergistically degrade organic halides and remove heavy metals with nZVI, and IRB could reactive the passivated nZVI by reducing the iron (hydr)oxides on the surface of nZVI. Moreover, the roles of these anaerobic bacteria in contaminant removal coupling with nZVI and the degradation mechanisms are illustrated. In addition, this review also discusses the main factors influencing the removal efficiency of contaminants in the integrated treatment system, including nZVI species and dosage, inorganic ions, organic matters, pH, type of pollutants, temperature, and carbon/energy sources, etc. Among these factors, the nZVI species and dosage play a fundamental role due to the potential cytotoxicity of nZVI, which might exert a negative impact on the performance of this integrated system. Lastly, the future research needs are proposed to better understand this integrated technology and effectively apply it in groundwater remediation.
... Because PRBs are used to treat plumes that may per sist for years or decades, regulators in particular are interested in determin ing how long PRBs will continue to retain a desirable minimum level of hydraulic capture and reactivity without requiring major maintenance or replacement of the reactive media. Of the several hundred PRBs that have been installed since the first full-scale PRB application occurred in 1994, many are reported to be performing acceptably, although the literature does include examples of concerns related to PRB performance including, but not limited to: (1) permeability loss due to solids formation and gas buildup (e.g., Henderson and Demond, 2011); (2) insufficient hydraulic performance due to incomplete or inaccurate subsurface characterization (e.g., Henderson and Demond, 2007); (3) the negative impact of anion competition (e.g., nitrate and chloride) on the treatment mechanisms important to contaminant reduction by iron metal (e.g., Moore and Young, 2005); (4) flow reduction upgradient of a PRB potentially due to upgradient diffusion of hydrogen and/or guar-gum from the PRB installation (Johnson et al., 2008), and (5) biofouling. ...
The year 2011 marked the 20th year anniversary of the first pilot testing of the permeable reactive barrier (PRB) as an in situ groundwater remedy by University of Waterloo researchers at the Canadian Forces Base (CFB) Borden site in Ontario, Canada (Gillham and O’Hannesin, 1994). Over the ensuing 20 years, the PRB concept would evolve from its standing as an “innovative” remedy for chemically impacted groundwater first commercially applied at a former semiconductor manufacturing facility in northern California, USA, to a “developed” technology that has been installed at sites around the globe, as well as being identified as one of the most sustainable groundwater treatment remedies available. Furthermore, over the past two decades, this remediation concept has grown to be the subject of research at many academic institutions; it has become a common-place addition to feasibility studies and alternative analysis documents for remediation projects. As a consequence, PRBs have been the specific focus of technical short courses and conferences, spanning the 1995 special session on PRBs at the American Chemical Society’s annual meeting in California, USA, to Internet-based short-courses sponsored by the U.S. Environmental Protection Agency (USEPA), to international meetings in the United Kingdom, Germany, and Italy, and to the September 2011 Clean-Up conference in Adelaide, Australia. Considering that the first full-scale commercial PRB composed of zero-valent iron (ZVI) was installed in November 1994 (Yamane, 1995) and continues to function, is the proof that this remedial approach is truly one of the more sustainable and resource conservative treatment concepts for chemically affected groundwater.
... Most of these were ZVI-based PRBs constructed to treat heavy metal contamination in high-sulfate groundwater by sequestration of the contaminants as low solubility metal sulfides. 36,37,182,183 The sulfide at these sites was biogenic from natural sulfate reduction, and relatively little attention was given to how this sulfide altered the composition and reactivity of the ZVI. More recently, there has been field-scale testing of ways to stimulate in situ formation of FeS without involvement of Fe(0). ...
Iron-based materials used in water treatment and groundwater remediation—especially micro- and nano-sized zerovalent iron (nZVI)—can be more effective when modified with lower-valent forms of sulfur (i.e., “sulfidated”). Controlled sulfidation for this purpose (using sulfide, dithionite, etc.) is the main topic of this review, but insights are derived by comparison with related and comparatively well-characterized processes such as corrosion of iron in sulfidic waters and abiotic natural attenuation by iron sulfide minerals. Material characterization shows that varying sulfidation protocols (e.g., concerted or sequential) and key operational variables (e.g., S/Fe ratio and sulfidation duration) result in materials with structures and morphologies ranging from core-shell to multiphase. A meta-analysis of available kinetic data for dechlorination under anoxic conditions, shows that sulfidation usually increases dechlorination rates, and simultaneously hydrogen production is suppressed. Therefore, sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal. This benefit is most likely due to inhibited corrosion as a result of sulfidation. Sulfidation may also favor desirable pathways of contaminant removal, such as (i) dechlorination by reductive elimination rather than hydrogenolysis and (ii) sequestration of metals as sulfides that could be resistant to reoxidation. Under oxic conditions, sulfidation is shown to enhance heterogeneous catalytic oxidation of contaminants. These net effects of sulfidation on contaminant removal by iron-based materials may substantially improve its practical utility for water treatment and remediation of contaminated groundwater.
... Physical and chemical heterogeneities of the environmental settings (such as the oxidation-reduction potential, pH, dissolved oxygen, concentrations of SO 4 2− and NO 3 − ) within and down gradient of the nZVI injection sites have significant impacts on the fate, transport, solubility, aggregation, bioavailability and toxicity of nZVI within groundwater and soil (Johnson et al., 2008(Johnson et al., , 2013Kouznetsova et al., 2007). Physicochemical parameters such as natural organic matter, pH, and hardness may have significance in toxicity. ...
Toxicity studies considering both the bare and stabilized forms of zero valent iron nanoparticles (nZVI) could be timely, given that ecological risks identified are minimized through modification or with substitution of approaches in the synthesis, development and environmental application of the nanoparticles before succeeding to volume production. This review is focused on the fate, transport and toxicological implications of the bare nZVI and surface modified particles used for environmental applications.
... The hydraulic conductivity (permeability) of granular Fe 0 filters and its evolution over time is a key design parameter for water treatment [29,30]. Published studies suggest that the permeability of a Fe 0 filter is specific to (i) the nature of used granular media and initial porosity of the filter, (ii) size of the filter, (iii) the characteristics of inflowing water and (iv) the water flow velocity (flow through rate) [31][32][33][34][35][36][37][38][39][40]. In essence, these are four groups of interdependant influencing parameters. ...
The use of granular metallic iron (Fe0) as filter material is gaining acceptance in the field of water treatment. Few works have been directed at developing design guidance for efficient Fe0 filters. This note consolidates earlier works and provides the scientific basis for the design and evaluation of Fe0 filters for water treatment at any scale. The approach assumes uniform corrosion of individual Fe0 particles and utilises the radius loss (X = R0 - R) to asses the extent of porosity loss in the whole system. Results corroborate that, for R0 £ 1.0 mm, sustainable filters must content less than 53 % Fe0 (v/v). A universal equation of Fe0 filters is provided given X as a function of the initial radius R0, the initial volume of Fe0, the initial porosity of the filter and the coefficient of volumetric expansion (O2 availability). This equation should be routinely incorporated in simulations for modelling the hydraulic conductivity of Fe0 filters. The model improves the discussion of published data on porosity loss.
... This is the rule of thumb on which future research should be based in order to accelerate progress in knowledge. Moreover, available results from field Fe 0 filters[5,19,20,32,32,[108][109][110] have to be evaluated using Eq. 11 as well. ...
Filtration systems based on metallic iron (Fe0 filters) have been successfully used for water treatment over the past two decades. Relevant Fe0 filters expand from subsurface permeable reactive barriers (PRBs) to household filters. Fe0 filters systems are shown efficient for the remediation of biological and chemical contamination. Properly designing a Fe0 filter is finding a long-term balance between two major interdependent design parameters: (i) Fe0 reactivity, and (ii) filter permeability. Other relevant design parameters include (i) aqueous flow velocity, (ii) bed thickness, and (iii) water chemistry. Water chemistry includes nature and extent of contamination. To date, attempts to design more sustainable Fe0 filters have been mostly pragmatic as: (i) reactive Fe0 has failed to be considered as in-situ generator of contaminant collectors (and ‘secondary’ reducing agents), and (ii) the volumetric expansive nature of iron corrosion has been overlooked. On the other hand, valuable design criteria were available in the hydrometallurgical literature (cementation using elemental metals) prior to the advent of Fe0 filters. As a consequence the literature is full of seemingly controversial results which are easily conciliated by the physico-chemistry of the system. The present review is limited at identifying some misconceptions and demonstrating their proliferation. Tools for better analyses are recalled. Recent X-ray tomography data are used as illustration of how valuable data are insufficiently discussed. It is hoped that the present contribution will boost systematic research for the design of more sustainable Fe0 filters.
... These observations were made about three months after the PRB installation in the monitoring wells near the PRB and after seven months in monitoring wells located further away from the PRB (Fiorenza and Christie 2008). The use of guar gum biopolymers typically used in the installation of PRBs may result in elevated guar-derived Dissolved Organic Carbon (DOC) levels that have been shown to persist in groundwater systems for periods of many months (Vidumsky et al. 2002;Crane et al. 2004;Johnson et al. 2008). An increase of sulfate-reducer bacteria population in the vicinity of the studied PRB was suggested to occur either as a function of iron corrosion or guar-derived carbohydrates, which could be acting as potential electron donors. ...
AbstractA pilot‐scale zero valent iron (ZVI) Permeable Reactive Barrier (PRB) was installed using an azimuth‐controlled ‐vertical hydrofracturing at an industrial facility to treat a chlorinated Volatile Organic Compound (VOC) plume. Following ZVI injection, no significant reduction in concentration was observed to occur with the exception of some multilevel monitoring wells, which also showed high levels of total organic carbon (TOC). These patterns suggested that the zero valent iron was not well distributed in the PRB creating leaky conditions. The geochemical data indicated reducing conditions in these areas where VOC reduction was observed, suggesting that biotic processes, associated to the guar used in the injection of the iron, could be a major mechanism of VOC degradation. Compound‐Specific Isotope Analysis (CSIA) using both carbon and chlorine stable isotopes were used as a complementary tool for evaluating the contribution of abiotic and biotic processes to VOC trends in the vicinity of the PRB. The isotopic data showed enriched isotope values around the PRB compared to the isotope composition of the VOC source confirming that VOC degradation is occurring along the PRB. A batch experiment using site groundwater collected near the VOC source and the ZVI used in the PRB was performed to evaluate the site‐specific abiotic isotopic fractionation patterns. Field isotopic trends, typical of biodegradations were observed at the site and were different from those obtained during the batch abiotic experiment. These differences in isotopic trends combined with changes in VOC concentrations and redox parameters suggested that biotic processes are the predominant pathways involved in the degradation of VOCs in the vicinity of the PRB.
... In this case, the important zone adjacent to the barrier is not taken into consider ation. However, the closest zone to the barrier (within 2 m) cannot be considered as a control, because the geochemical barrier affects it by Fe diffusion directed against the groundwater flow [30]. ...
Chlorinated hydrocarbons are among the most hazardous organic pollutants. The traditional remediation technologies, i.e., pumping of contaminated soil- and groundwater and its purification appear to be costly and not very efficient as applied to these pollutants. In the last years, a cheaper method of destroying chlorine-replaced hydrocarbons has been used based on the construction of an artificial permeable barrier, where the process develops with the participation of in situ bacteria activated by zerovalent iron. The forced significant decrease in the redox potential (Eh) down to -750 mV provides the concentration of electrons necessary for the reduction of chlorinated hydrocarbons. A rise in the pH drastically accelerates the dechlorination process. In addition to chlorine-organic compounds, ground water is often contaminated with heavy metals. The influence of the latter on the effect of zerovalent iron may be different: both accelerating its degradation (Cu) and inhibiting it (Cr). Most of the products of zerovalent iron corrosion, i.e., green rust, magnetite, ferrihydrite, hematite, and goethite, weaken the efficiency of the Fe-0 barrier by mitigating the dechlorination and complicating the water filtration. However, pyrrhotite FeS, on the contrary, accelerates the dechlorination of chlorine hydrocarbons.
... These observations were made about three months after the PRB installation in the monitoring wells near the PRB and after seven months in monitoring wells located further away from the PRB (Fiorenza and Christie 2008). The use of guar gum biopolymers typically used in the installation of PRBs may result in elevated guar-derived Dissolved Organic Carbon (DOC) levels that have been shown to persist in groundwater systems for periods of many months (Vidumsky et al. 2002;Crane et al. 2004;Johnson et al. 2008). An increase of sulfate-reducer bacteria population in the vicinity of the studied PRB was suggested to occur either as a function of iron corrosion or guar-derived carbohydrates, which could be acting as potential electron donors. ...
... The processes occurring at the interface Fe 0 /H 2 O are of great interest for the use of metallic iron in environmental remediation (e.g. in Fe 0 /H 2 O systems). A great deal of work has been reported in this area during the past 20 years [1][2][3][4][5][6][7][8][9][10]. Since the seminal work of Matheson and Tratnyek [1], a substantial amount of literature concerning the removal mechanism of various contaminants in Fe 0 /H 2 O systems has been published. ...
The term mixing (shaking, stirring, agitating) is confusing because it is used to describe mass transfer in systems involving species dissolution, species dispersion and particle suspension. Each of these mechanisms requires different flow characteristics in order to take place with maximum efficiency. This work was performed to characterize the effects of shaking intensity on the process of aqueous discoloration of methylene blue (MB) by metallic iron (Fe0). The extent of MB discoloration by three different materials in five different systems and under shaking intensities varying from 0 to 300 min-1 was directly compared. Investigated materials were scrap iron (Fe0), granular activated carbon (GAC), and deep sea manganese nodules (MnO2). The experiments were performed in essay tubes containing 22 mL of the MB solution (12 mg/L or 0.037 mM). The essay tubes contained either: (i) no reactive material (blank), (ii) 0 to 9.0 g/L of each reactive material (systems I, II and III), or (iii) 5 g/L Fe0 and 0 to 9.0 g/L GAC or MnO2 (systems IV and V). The essay tubes were immobilized on a support frame and shaken for 0.8 to 5 days. Non-shaken experiments lasted for duration up to 50 days. Results show increased MB discoloration with increasing shaking intensities below 50 min-1, a plateau between 50 and 150 min-1, and a sharp increase of MB discoloration at shaking intensities ≥ 200 min-1. At 300 min-1, increased MB discoloration was visibly accompanied by suspension of dissolution products of Fe0/MnO2 and suspension of GAC fines. The results suggest that, shaking intensities aiming at facilitating contaminant mass transfer to the Fe0 surface should not exceed 50 min-1.
... Iron-based alloys (metallic iron, elemental iron or Fe 0 materials) have been used as an abiotic contaminant reducing reagent for organic and inorganic groundwater contaminants for over 15 years [1][2][3][4][5][6][7][8][9][10][11][12][13]. In this context, Fe 0 materials are widely termed as zerovalent iron (ZVI) materials, contaminants have been denoted as reductates [14], and the bare surface of Fe 0 as reductant. ...
Despite two decades of intensive laboratory investigations, several aspects of contaminant removal from aqueous solutions by elemental iron materials (e.g., in Fe0/H2O systems) are not really understood. One of the main reasons for this is the lack of a unified procedure for conducting batch removal experiments. This study gives a qualitative and semi-quantitative characterization of the effect of the mixing intensity on the oxidative dissolution of iron from two Fe0-materials (material A and B) in a diluted aqueous ethylenediaminetetraacetic solution (2 mM EDTA). Material A (fillings) was a scrap iron and material B (spherical) a commercial material. The Fe0/H2O/EDTA systems were shaken on a rotational shaker at shaking intensities between 0 and 250 min-1 and the time dependence evolution of the iron concentration was recorded. The systems were characterized by the initial iron dissolution rate (kEDTA). The results showed an increased rate of iron dissolution with increasing shaking intensity for both materials. The increased corrosion through shaking was also evidenced through the characterization of the effects of pre-shaking time on kEDTA from material A. Altogether, the results disprove the popular assumption that mixing batch experiments is a tool to limit or eliminate diffusion as dominant transport process of contaminant to the Fe0 surface.
... Permeable reactive barriers of elemental iron (Fe 0 walls or remediation Fe 0 /H 2 O systems) are a valuable technological application that has been shown to be both environmentally friendly and cost-effective in the removal of various substances from contaminated waters [1][2][3][4][5][6][7]. Since its development in 1990 by Canadian hydrogeologists numerous papers have been written on the topic and approximately 120 iron walls installed worldwide [4]. ...
Metallic iron (Fe0) is a moderately reducing agent that has been reported to be capable of reducing many environmental contaminants. Reduction by Fe0 used for environmental remediation is a well-known process to organic chemists, corrosion scientists and hydrometallurgists. However, considering Fe0 as a reducing agent for contaminants has faced considerable scepticism because of the universal role of oxide layers on Fe0 in the process of electron transfer at the Fe0/oxide/water interface. This communication shows how progress achieved in developing the Becher process in hydrometallurgy could accelerate the comprehension of processes in Fe0/H2O systems for environmental remediation. The Becher process is an industrial process for the manufacture of synthetic rutile (TiO2) by selectively removing metallic iron (Fe0) from reduced ilmenite (RI). This process involves an aqueous oxygen leaching step at near neutral pH. Oxygen leaching suffers from serious limitations imposed by limited mass transport rates of dissolved oxygen across the matrix of iron oxides from initial Fe0 oxidation. In a Fe0/H2O system pre-formed oxide layers similarly act as physical barrier limiting the transport of dissolved species (including contaminants and O2) to the Fe0/H2O interface. Instead of this universal role of oxide layers on Fe0, improper conceptual models have been developed to rationalize electron transfer mechanisms at the Fe0/oxide/water interface.
... At present it is suggested that the mechanism of permeability loss in Fe 0 PRBs is due to the accumulation of insoluble minerals within the PRB pore network [10,13]. [10,13,[20][21][22][23][24][25][26]. Another mechanism reported attributes the permeability loss to the build-up of H 2 gas, formed due to the hydrolysis of water during Fe 0 corrosion [11,27,28]. ...
Over the past 30 years the literature has burgeoned with in-situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modelled. The results suggest that: (i) for the pH range of natural waters (> 4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non-expansive material; (ii) naturally-occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolising bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size-exclusion) water filter device.
... Research show that iron nano-particles may travel only a few centimeters in porous media from the injection position under typical groundwater conditions [11]. Johnson et al. [12] discussed that transport of significant mass loading of bare NZVI in porous media without varying large pore velocity through packed medium, mechanical increasing of NZVI, and/ or use of amendments to the NZVI, is confronted by serious difficulty. ...
In this work the application of a modified surface nano zero valent iron (NZVI) as bimetallic Fe/Cu particles to
remove high concentration of NO3
−-N through packed sand column has been studied. Dispersed nano-Fe/Cu
particles has been synthesized in water mixed ethanol solvent system (1:4 v/v) and described by XRD pattern,
TEM and SEM images and BET analyze. Batch experiments have been conducted to investigate the effect of
percentage coating of Fe0 by Cu on the nitrate removal. Research on packed sand column (120 cm length,
6.5 cm inner diameter) has been done under conditions of Nano-Fe/Cu concentration (2, 5, and 8 g l−1 of
solution), high initial NO3
−-N concentration (100, 200, and 300 mg l−1) and pore water velocity through sand
(0.125, 0.250, and 0.375 mm s−1) in seven sets. Results of batch experiments indicated the efficient coating
percentage of Fe0 by Cu in NO3
−-N reduction was 2.5% (w/w). In addition, increase of pore velocity of water
through packed sand has negative effect on the nitrate reduction rate. In contrast, increasing the injected mass
of nano particles and the influent NO3
−-N concentration would increase the rate of NO3
−-N reduction. The best
condition to reduce NO3
−-N has been observed at end of sand column as 75% of influent concentration when
nano-Fe/Cu concentration=8 g l−1, high initial NO3
−-N concentration=100 mg l−1 and pore water velocity
through sand=0.125 mm s−1.
... At present it is suggested that the mechanism of permeability loss in Fe 0 PRBs is due to the accumulation of insoluble minerals within the PRB pore network [10,13]. Relevant minerals include siderite (FeCO 3 ), aragonite (CaCO 3 ), and iron (hydr)oxides (e.g., Fe(OH) 2 , Fe(OH) 3 , FeOOH, Fe 2 O 3 , and Fe 3 O 4 ) [10,13,[20][21][22][23][24][25][26]. Another mechanism reported attributes the permeability loss to the build-up of H 2 gas, formed due to the hydrolysis of water during Fe 0 corrosion [11,27,28]. ...
Over the past 30 years the literature has burgeoned with in-situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modelled. The results suggest that: (i) for the pH range of natural waters (> 4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non-expansive material; (ii) naturally-occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolising bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size-exclusion) water filter device.
... In addition, they reported that mineral precipitations on the ZVI surface prevent further corrosion and significantly reduces the reactivity of ZVI. Johnson et al. (2008) studied a field-scale PRB-based ZVI in Nebraska to reduce the TNT and RDX of groundwater. They reported that installed PRB is effective in removing target contaminants; moreover, mineral precipitates affect hydraulic properties of PRB. ...
There are many fundamental problems with the injection of nano-zero-valent iron (NZVI) particles to create permeable reactive barrier (PRB) treatment zone. Among them the loss of medium porosity or pore blocking over time can be considered which leads to reduction of permeability and bypass of the flow and contaminant plume up-gradient of the PRB. Present study provides a solution for such problems by confining the target zone for injection to the gate in a funnel-and-gate configuration. A laboratory-scale experimental setup is used in this work. In the designed PRB gate, no additional material from porous media exists. NZVI (d50 = 52 ± 5 nm) particles are synthesized in water mixed with ethanol solvent system. A steady-state condition is considered for the design of PRB size based on the concept of required contact time to obtain optimum width of PRB gate. Batch experiment is carried out and the results are used in the design of PRB gate width (~50 mm). Effect of high initial NO3–-N concentration, NZVI concentration, and pore velocity of water in the range of laminar groundwater flow through porous media are evaluated on nitrate-N reduction in PRB system. Results of PRB indicate that increasing the initial NO3–-N concentration and pore velocity has inhibitor effect—against the effect of NZVI concentration—on the process of NO3–-N removal. Settlement velocity (S.V.) of injected NZVI with different concentrations in the PRB is also investigated. Results indicate that the proposed PRB can solve the low permeability of medium in down-gradient but increasing of the S.V. especially at higher concentration is one of the problems with this system that needs further investigations.
A permeable reactive barrier (PRB) can be deployed to remediate acid mine drainage. The performance of a PRB material under different boundary conditions (pH, flow velocity, and sulfate concentration) was investigated in a series of column experiments applying in‐situ optical sensing methods for pH and oxygen detection. The reactive material consisted of organic components (compost, wood, and coconut shell) mixed with calcium carbonate and fine gravel. The input concentrations were around 1000 mg/L for iron and 3000 mg/L for sulfate, and the pH value was 6.2. The remediation efficiency of iron was 14.6% and of sulfate 15.2%, but was expected to scale up when moving to a field‐site PRB with greater thickness. The iron and sulfate removal was influenced by decreasing the flow velocity and increasing the sulfate input concentration and the pH value. In an experiment with low pH boundary conditions (pH = 2.2), acidity was neutralized in the PRB by calcium carbonate during an experiment duration of 47 days. The modeling program MIN3P was used to create a simulation of the laboratory experiments. This helps to design parameters, for example, the residence time in the PRB, which is necessary for close to 100% remediation efficiency. This study shows the application of optical oxygen and pH monitoring in PRBs. In this context, they can be used to monitor the stability of a PRB for the remediation of acid mine drainage (AMD).
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.
As a technology for in situ treatment and remediation of groundwater contamination, permeable reaction barriers (PRBs) have the advantages of operational efficiency and low infrastructure footprint. In order to clarify previous research results and provide references for future research on remediation of contamination by dissolved oil contaminants in groundwater, the focus of this article is to review and compare the application of PRBs for the removal of dissolved oil contaminants and highlights the research gaps. We concentrate on the relationship between structure design, media types and service life of PRBs, along with groundwater flow velocity, temperature, pH and other hydrochemical conditions. These influencing factors are used to make a detailed explanation and analysis of remediation of oil contamination in groundwater. The current application of PRBs is mainly limited to heavy metals and inorganics, rather than persistent organics such as components in oil. The application of new PRB materials and combination of multiple remediation technologies in oil-contaminated sites will be the focus of future research.
Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.
In quest of meeting the requirements of sustainable development, coupling zero valent iron (ZVI) with microorganisms has attracted extensive attentions for enhancing biological wastewater and sludge treatment in terms of microbial growth, nutrients removal, and resources recovery. Given to the significant role of ZVI playing in biological wastewater and sludge treatment, a thorough evaluation of the associated interactions among ZVI and microorganisms is necessary to further scale-up the application of ZVI-based biotechnologies. To this end, this review comprehensively summarizes the mechanisms of ZVI for enhancing nutrients removal (i.e., C, N, S and P) in several typical biological wastewater treatment processes, discusses the role of ZVI in improving the excess sludge reduction by dewatering or anaerobic digestion for methane production, and analyzes the feasibility of recovering phosphorus from anaerobic sludge digestion system in the form of vivianite through using ZVI. Knowledge gaps regarding the application of ZVI in sludge or wastewater treatment are also identified in this review to facilitate the further development of the ZVI-based biological technology.
As an environmentally friendly material, biochar has been widely used to remediate soil/water contaminants such as heavy metals and organic pollutants. The addition of biochar or modified biochar to porous media might affect the retention of plastic particles and thus influence their fate in natural environment. In this study, both biochar and magnetic biochar (Fe3O4-biochar) were synthesized via a facile precipitation method at room temperature. To determine the significance of biochar and Fe3O4-biochar amendment on the transport and deposition behaviors of plastic particles, the breakthrough curves and retained profiles of three different sized plastic particles (0.02 μm nano-plastic particles, and 0.2 μm and 2 μm micro-plastic particles) in quartz sand were compared with those obtained in quartz sand either with biochar or Fe3O4-biochar amendment in both 5 mM and 25 mM NaCl solutions. The results show that for all three different sized plastic particles under both examined solution conditions, the addition of biochar and Fe3O4-biochar in quartz sand decreases the transport and increases the retention of plastic particles in porous media. Fe3O4-biochar more effectively inhibits the transport of plastic particles than biochar. We found that the addition of biochar/Fe3O4-biochar could change the suspension property and increase the adsorption capacity of porous media (due to the increase of porous media surface roughness and negatively decrease the zeta potentials of porous media), contributing to the enhanced deposition of plastic particles. Moreover, we found that negligible amount of biochar and Fe3O4-biochar (<1%) were released from the columns following the plastic particle transport when the columns were eluted with very low ionic strength solution at high flow rate (to simulate a sudden rainstorm). Similarly, small amount of plastic particles were detached from the porous media under this extreme condition (16.5% for quartz sand, 14.6% for quartz sand with biochar amendment, and 7.5% for quartz sand with Fe3O4-biochar amendment). We found that over 74% of the Fe3O4-biochar can be recovered from the porous media after the retention of plastic particles by using a magnet and 87% plastic particles could be desorbed from Fe3O4-biochar by dispersing the Fe3O4-biochar into 10 mM NaOH solution. In addition, we found that the amendment of unsaturated porous media with biochar/Fe3O4-biochar also decreased the transport of plastic particles. When biochar/Fe3O4-biochar were added into porous media as one layer of permeable barrier near to column inlet, the decreased transport of plastic particles could be also obtained. The results of this study indicate that magnetic biochar can be potentially applied to immobilize plastic particles in terrestrial ecosystems such as in soil or groundwater.
Groundwater pH is one of the most important geochemical parameters in controlling the interfacial reactions of zero-valent iron (ZVI)with water and contaminants. Ball milled, microscale ZVI (mZVI bm )efficiently dechlorinated TCE at initial stage (<24 h)at pH 6–7 but got passivated at later stage due to pH rise caused by iron corrosion. At pH > 9, mZVI bm almost completely lost its reactivity. In contrast, ball milled, sulfidated microscale ZVI (S-mZVI bm )didn't experience any reactivity loss during the whole reaction stage across pH 6–10 and could efficiently dechlorinate TCE at pH 10 with a reaction rate of 0.03 h ⁻¹ . Increasing pH from 6 to 9 also enhanced electron utilization efficiency from 0.95% to 5.3%, and from 3.2% to 22%, for mZVI bm and S-mZVI bm , respectively. SEM images of the reacted particles showed that the corrosion product layer on S-mZVI bm had a puffy/porous structure while that on mZVI bm was dense, which may account for the mitigated passivation of S-mZVI bm under alkaline pHs. Density functional theory calculations show that covered S atoms on the Fe(100)surface weaken the interactions of H 2 O molecules with Fe surfaces, which renders the sulfidated Fe surface inefficient for H 2 O dissociation and resistant to surface passivation. The observation from this study provides important implication that natural sulfidation of ZVI may largely contribute to the long-term (>10 years)efficiency of TCE decontamination by permeable reactive barriers with pore water pH above 9.
Permeable reactive barrier (PRB) filled with zero valent iron (ZVI, Fe⁰) can be an effective option to remove nitrate from contaminated groundwater. The long-term performance of such PRBs, however, might be compromised by the problem of declining reactivity and permeability, which could cause a decrease in the nitrate removal efficiency. In this study we explored suitable model formulations that allow for a process-based quantification of the passivation effect on denitrification rates and tested the model for a 40 years long operation scenario. The conceptual model underlying our selected formulation assumes the declining reactivity of the ZVI material through the progressing passivation caused by the precipitation of secondary minerals and the successive depletion of the ZVI material. Two model scenarios, i.e., the base model scenario which neglects the explicit consideration of the passivation effect and one performed with the model in which the impact of the passivation effect on denitrification was considered, were compared. The modeling results illustrate that nitrate removal in the model of considered passivation started to be incomplete after 10 years, and the effluent nitrate concentration of PRB rose up to 86% of the injected water concentration after 40 years, in contrast to the base scenario, corresponding well with the field observations of successively declining nitrate removal efficiencies. The model results also showed that the porosity of the PRB increased in both models. In order to improve and recover the reactivity of ZVI, pyrite was added to the PRB, resulting in completely nitrate removal and lower consumption of ZVI. © 2017, China University of Geosciences and Springer-Verlag GmbH Germany.
A permeable reactive barrier (PRB) has been defined as “an in situ permeable treatment zone designed to intercept and remediate a contaminant plume” (ITRC, 2005). The PRB concept is illustrated schematically in Figure 7.1, which shows a contaminant plume moving, under natural hydraulic gradients, through a permeable “wall” of reactive material and exiting on the downgradient side with the contaminants removed. Remediation within the PRB can proceed through removal, as in the case of sorption or precipitation reactions, or by degradation as in the case of a range of biological or abiotic reactions for treatment of organic contaminants.
A field trial was conducted at Casey Station, Antarctica to assess the suitability of a permeable reactive barrier (PRB) media sequence for the remediation of sites containing both hydrocarbon and heavy metal contamination. An existing PRB was modified to assess a sequence consisting of three sections: (i) Nutrient release/hydrocarbon sorption using ZeoPro™ and granular activated carbon; (ii) Phosphorus and heavy metal capture by granular iron and sand; (iii) Nutrient and excess iron capture by zeolite.
The media sequence achieved a greater phosphorus removal capacity than previous Antarctic PRB configurations installed on site. Phosphorus concentrations were reduced during flow through the iron/sand section and iron concentrations were reduced within the zeolite section. However, non-ideal flow was detected during a tracer test and supported by analysis of media and liquid samples from the second summer of operation. Results indicate that the PRB media sequence trialled might be appropriate for other locations, especially less environmentally challenging contaminated sites.
An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, from the products of a chemical reaction involving explosive materials, or from a nuclear reaction that is uncontrolled. In order for an explosion to occur, there must be a local accumulation of energy at the site of the explosion, which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. Modern explosives or energetic materials are nitrogen-containing organic compounds with the potential for self-oxidation to small gaseous molecules (N
In the present study, controlled laboratory column experiments were conducted to understand the biogeochemical changes during the microbial sulfate reduction. Sulfur and oxygen isotopes of sulfate were followed during sulfate reduction in zero valent iron incubated flow through columns at a constant temperature of 20 ± 1 °C for 90 d. Sulfur isotope signatures show considerable variation during biological sulfate reduction in our columns in comparison to abiotic columns where no changes were observed. The magnitude of the enrichment in δ34S values ranged from 9.4‰ to 10.3‰ compared to initial value of 2.3‰, having total fractionation δS between biotic and abiotic columns as much as 6.1‰. Sulfur isotope fractionation was directly proportional to the sulfate reduction rates in the columns. Oxygen isotopes in this experiment seem less sensitive to microbial activities and more likely to be influenced by isotopic exchange with ambient water. A linear relationship is observed between δ34S and δ18O in biotic conditions and we also highlight a good relationship between δ34S and sulfate reduction rate in biotic columns.
Available data on the iron-containing nanomaterials are reviewed. Main attention is paid to the following themes: synthetic methods, structures, composition and properties of the nano zerovalent iron (NZVI), and polymorphic forms of iron oxides and FeOOH. Synthetic methods summarized here include a series of physico-chemical methods such as microwave heating, electrodeposition, laser ablation, radiolytical techniques, arc discharge, metal-membrane incorporation, pyrolysis, combustion, reverse micelle and co-deposition routes. We have also included a few “greener” methods. Coated, doped, supported with polymers or inert inorganic materials, core–shell nanostructures, in particular those of iron and its oxides with gold, are discussed. Studies of remediation involving iron-containing nanomaterials are discussed and special attention is paid to the processes of remediation of organic contaminants (chlorine-containing pollutants, benzoic and formic acids, dyes) and inorganic cations (Zn(II), Cu(II), Cd(II) and Pb(II)) and anions (nitrates, bromates, arsenates). Water disinfection (against viruses and bacteria), toxicity and risks of iron nanomaterials application are also examined.
This study investigated multiple electron transfer pathways for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biodegradation in the presence of bioavailable Fe(III) and electron shuttling compounds. In order to identify the dominant electron transfer pathway for RDX biodegradation, three sets of experiments were performed including aquifer material incubations, kinetics experiments, and cell suspensions. Incubations with aquifer sediment reduced RDX most rapidly in the presence of electron shuttling compounds such as anthraquinone-2,6-disulfonate (AQDS) and purified humic substances. In addition, RDX was reduced before the onset of significant accumulation of Fe(II), suggesting that reduced shuttles transferred electrons to Fe(III) rapidly, with the resulting Fe(II) reducing RDX. This hypothesis was also supported by the kinetic experiments; the rate of electron transfer from anthrahydroquinone-2,6-disulfonate (AH(2)QDS) to Fe(III) was approximately 10 5 times faster than the rate of AH(2)QDS electron transfer to RDX. However, an alternate hypothesis considered was direct reduction of RDX by the hydroquinone prior to the onset of Fe(III) reduction. Pure culture studies with a model Fe(III)/electron shuttle reducer (G. metallireducens) were performed to determine which pathway was most dominant. The resting cell suspension experiments demonstrated that there are four possible electron transfer pathways for RDX biodegradation; however, the rates of the electron shuttle-mediated pathways were consistently the fastest. When the Fe(II)-mediated electron transfer pathway was inhibited with the Fe(II) ligand Ferrozine, the rate and extent of RDX degradation decreased, but reduction continued. This suggests that multiple electron transfer pathways [reduction by hydroquinones and Fe(II)] overlapped in the presence of Fe(III), but inhibiting the iron pathway did not limit degradation. This demonstrates that RDX is concurrently reduced by electron shuttles and Fe(II) during electron-shuttle mediated biodegradation.
This annual report provides details on the research conducted at EMSL--the Environmental Molecular Sciences Laboratory in Fiscal Year 2008.
The efficacy and feasibility of using zerovalent zinc (ZVZ) to treat 1,2,3-trichloropropane (TCP)-contaminated groundwater was assessed in lab. and field expts. In the first portion of the study, the reactivity of com. available granular ZVZ toward TCP was measured in bench-scale batch-reactor and column expts. These results were used to design columns for on-site pilot-scale treatment of contaminated groundwater at a site in Southern California. Two of the ZVZ materials tested were found to produce relatively high rates of TCP degrdn. as well as predictable behavior when scaling from bench-scale to field testing. In addn., there was little decrease in the rates of TCP degrdn. over the duration of field testing. Finally, no secondary impacts to water quality were identified. The results suggest that ZVZ may be an effective and feasible material for use in engineered treatment systems, perhaps including permeable reactive barriers. [on SciFinder(R)]
Current knowledge of the basic principles underlying the design of Fe0 beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe0 beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe0 in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe0). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of CuII, NiII, and ZnII (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe0, (ii) additive admixture lengthened the service life of Fe0 beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe0/sand column was the most efficient for contaminant removal. The evolution of the permeability was well-fitted by the approach that the inflowing solution contained dissolved O2. The achieved results are regarded as starting point for a systematic research to optimize/support Fe0 filter design.
This final technical report documents the demonstration of a zero-valent iron (ZVI) in situ treatment well (ISTW) to remove explosives from groundwater. The general purpose of the demonstration was to evaluate the efficacy of ZVI ISTW for treating explosives-contaminated groundwater.
This final technical report documents the demonstration of a zero-valent iron (ZVI) permeable reactive barrier (PRB) for the removal of explosives from groundwater. The demonstration was conducted at the Cornhusker Army Ammunition Plant (CAAP) near Grand Island, Nebraska. The primary objective of this project was to evaluate the cost and performance of the ZVI PRB Performance of the PRB was evaluated by monitoring groundwater concentrations of explosives downgradient of the PRB. Data obtained during the demonstration were used to assess the costeffectiveness of this approach for long-term removal of explosives from groundwater. The primary advantages of ZVI PRBs for groundwater remediation are: 1. No aboveground remediation equipment is required 2. Rapid conversion of groundwater to reducing conditions 3. Low operation and maintenance costs 4. Long-lasting (>20 years) in situ treatment 5. Cost-effective. The cost-effective use of ZVI PRBs may be limited by the depth to groundwater and the ability to install the PRB in some geologic media. However, at sites without these physical constraints, the approach can be highly effective.
The fate of nano zero-valent iron (nZVI) during subsurface injection was examined using carboxymethylcellulose (CMC) stabilized nZVI in a very large three-dimensional physical model aquifer with detailed monitoring using multiple, complementary detection methods. A fluorescein tracer test in the aquifer plus laboratory column data suggested that the very-aggressive flow conditions necessary to achieve 2.5 m of nZVI transport could be obtained using a hydraulically constrained flow path between injection and extraction wells. However, total unoxidized nZVI was transported only about 1 m and <2% of the injected nZVI concentration reached that distance. The experimental data also indicated that groundwater flow changed during injection, likely due to hydrogen bubble formation, which diverted the nZVI away from the targeted flow path. The leading edge of the iron plume became fully oxidized during transport. However, within the plume, oxidation of nZVI decreased in a fashion consistent with progressive depletion of aquifer "reductant demand". To directly quantify the extent of nZVI transport, a spectrophotometric method was developed, and the results indicated that deployment of unoxidized nZVI for groundwater remediation will likely be difficult.
The derivation of atomistic potential parameters, based on electronic structure calculations, for modeling electron and hole polarons in titania polymorphs is presented. The potential model is a polarizable version of the Matsui and Akaogi model (Matsui, M.; Akaogi, M. Mol. Simul. 1991, 6, 239) that makes use of a shell model to account for the polarizability of oxygen ions. The −1 and +1 formal charges of the electron and hole polarons, respectively, are modeled by delocalizing the polaron’s charge over a titanium or oxygen ion, respectively, and its first nearest-neighbors. The charge distributions and the oxygen polarizability were fitted to the reorganization energies of a series of electron and hole polaron transfers in rutile and anatase obtained from electronic structure calculations at zero Kelvin and validated against lattice deformation due to both types of polaron. Good agreement was achieved for both properties. In addition, the potential model yields an accurate representation of a range of bulk properties of several TiO2 polymorphs as well as Ti2O3. The model thus derived enables us to consider systems large enough to investigate how the charge transfer properties at titania surfaces and interfaces differ from those in the bulk. For example, reorganization energies and free energies of charge transfer were computed as a function of depth below vacuum-terminated rutile (110) and anatase (001) surfaces using a mapping approach first introduced by Warshel (Warshel, A. J. Phys. Chem. 1982, 86, 2218). These calculations indicate that deviations from bulk values at the surface are substantial but limited to the first couple of surface atomic layers and that polarons are generally repelled from the surface. Moreover, attractive subsurface sites may be found as is predicted for hole polarons at the rutile (110) surface. Finally, several charge transfers from under-coordinated surface sites were found to be in the so-called Marcus inverted-region.
The working lifetime of permeable reactive barriers (PRBs) using Fe-0 as the reactive media is limited by precipitation of secondary minerals, due to reaction of groundwater with Fe-0. Since PRBs are emplaced at sites with widely differing groundwater chemistry, the suite of minerals that precipitate, as well as the rate of their formation, can vary widely. Using plausible phases obtained from field PRBs, the study shows that chemical equilibrium modeling can correctly predict the amounts of precipitates formed, based on the thermodynamic properties of Fe-0 and groundwater constituents. These predictions were compared to the results from the solid phase analysis from a field column experiment and from a field-installed PRB at Y-12 Plant, Oak Ridge, TN. Using the column chemical data molar distributions of the precipitates along the flow path were modeled. The maximum precipitation at the Fe-0-sand interface at the influent end was predicted, where pore water showed high saturation index (SI) with respect to calcite and iron (oxyhydr)oxide. In the absence of flow information, the field sampling data were used to construct an SI-pH diagram, from which the extent of reaction with Fe-0, the potential for precipitate buildup, and relative residence time for the pore water were identified. Kinetic and heterogeneous flow effects were also discussed. To illustrate the application of chemical equilibrium modeling to the design and planning phase of PRBs, groundwater data from four PRB sites were analyzed. The analysis shows that up to 0.63 cm(3)/L solid could form in pore water using an average Fe-0 dissolution rate, leading to severe clogging of Fe-0 medium over a 10-yr period of operation.
We recently completed a pilot-scale permeable reactive barrier (PRB) with zero-valent iron (ZVI) to treat groundwater contaminated with explosives (TNT and RDX) at the Cornhusker Army Ammunition Plant (CAAP) near Grand Island, Nebraska. While the PRB at CAAP continues to be effective at removing explosives from the groundwater, the hydraulic performance is significantly reduced. This may be due to the accumulation of authigenic precipitates slightly up-gradient from the iron-containing zone. It is likely that the accumulation of new solid phases on the matrix materials in and around the treatment zone would also cause the system to be less effective at reducing contaminants. This, however, does not seem to be the case at CAAP. We report here that iron removed from the PRB is still quite reactive—with TNT and with RDX—when re- suspended and tested in laboratory batch experiments. Surprisingly, the up-gradient impacted samples showed reduction of TNT and RDX even though they did not contain ZVI. Also of note is that the core samples gave slower reduction of TNT than the dry ZVI/sand mixture, but the reverse was true for RDX. In all cases, however, the rates of TNT/RDX reduction by materials containing ZVI were within the range given by the de- sign guidelines.
The primary objective of this report is to describe the results of the last round of monitoring conducted in July 2004, their relationship to the results of pervious rounds, and their implications for the longevity and hydraulic performance of the permeable reactive barrier (PRB).
This report discusses soil and ground-water sampling methods and procedures used to evaluate the long-term performance of permeable reactive barriers (PRBs) at two sites, Elizabeth City, NC, and the Denver Federal Center near Lakewood, CO. Both PRBs were installed in 1996 and have been monitored and studied since installation to determine their continued effectiveness for removing contaminants from ground water. An effective monitoring program requires appropriate soil and ground-water sampling techniques. For ground-water sampling, water quality indicator parameters must be monitored to determine when formation water has been accessed. Geochemical parameters include oxidation-reduction potential (ORP), pH, specific conductance, dissolved oxygen (DO), and turbidity. Field analytical methods are discussed along with interferences and issues which may arise when using certain electrodes or instruments in the field. Detailed field analytical procedures for hexavalent chromium, ferrous iron, alkalinity, hydrogen sulfide, and dissolved oxygen are described. Also included are laboratory methods for sample analyses for organics, cations, anions, and carbon. Sample collection methods, sample containers, preservation methods, and sample storage techniques are also discussed.
The U.S. Department of Defense (DOD) Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP) sponsored a project to assess performance and longevity issues at DOD permeable reactive barrier (PRIB) sites. The goal of this project was to evaluate short- and long-term performance issues associated with permeable reactive barriers (PRBs) installed at several United States Department of Defense (DoD) sites, A PRB is a passive, in situ technology, in which natural groundwater flow brings contaminants into contact with a reactive or adsorptive material that removes the dissolved contaminants and protects down gradient receptors. Therefore, PRBs have potentially lower life cycle costs compared to an equivalent pump-and-treat system. The key regulatory driver for the technology is the proven ability of common barrier materials, such as elemental iron, to meet groundwater cleanup standards for many common contaminants, including chlorinated solvents and certain heavy metals. Regulatory interest in this project was driven by the two challenges involved in implementing PRBs, namely, their longevity and hydraulic performance. The Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP) sponsored this project. The Naval Facilities Engineering Service Center (NFESC) was the lead agency for the DoD project. Eattelle, under contract to NFESC, planned and implemented the technical scope and has prepared this report to summarize the results.
The impact of microbiological and geochemical processes has been a major concern for the long-term performance of permeable reactive barriers containing zero-valent iron (Fe0). To evaluate potential biogeochemical impacts, laboratory studies were performed over a 5-month period using columns containing a diverse microbial community. The conditions chosen for these experiments were designed to simulate high concentrations of bicarbonate (17−33 mM HCO3-) and sulfate (7−20 mM SO42-) containing groundwater regimes. Groundwater chemistry was found to significantly affect corrosion rates of Fe0 filings and resulted in the formation of a suite of mineral precipitates. HCO3- ions in SO42--containing water were particularly corrosive to Fe0, resulting in the formation of ferrous carbonate and enhanced H2 gas generation that stimulated the growth of microbial populations and increased SO42- reduction. Major mineral precipitates identified included lepidocrocite, akaganeite, mackinawite, magnetite/maghemite, goethite, siderite, and amorphous ferrous sulfide. Sulfide was formed as a result of microbial reduction of SO42- that became significant after about 2 months of column operations. This study demonstrates that biogeochemical influences on the performance and reaction of Fe0 may be minimal in the short term (e.g., a few weeks or months), necessitating longer-term operations to observe the effects of biogeochemical reactions on the performance of Fe0 barriers. Although major failures of in-ground treatment barriers have not been problematic to date, the accumulation of iron oxyhydroxides, carbonates, and sulfides from biogeochemical processes could reduce the reactivity and permeability of Fe0 beds, thereby decreasing treatment efficiency.
Acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) are operationally defined methods for the analysis of sulfide and associated metals in aquatic sediments. The SEM-to-AVS ratio has been useful in explaining the results of bioassay tests of metal toxicants. This paper describes apparatus that can be used in the evolution of sulfide from sediments and a method for the analysis of the evolved sulfide and the liberated metal. The method was studied with respect to gas flow rate, digestion time, and acid concentration. Liberated and trapped sulfide was determined by a colorimetric method of analysis. Using the apparatus and conditions described in this paper, the colorimetric method of analysis is capable of detecting AVS at concentrations normally encountered with a recovery of sulfide of at least 90%. High precision is possible if this apparatus is used. The limit of detection of the method is approximately 0.01 m̈mol/g dry sediment. We added 6 M HC1 to produce a final concentration of approximately 1 M for the release of the AVS and SEM from unheated samples. We found that sulfide was not released from pyrite (FeS2) or copper sulfide (CuS) under these conditions. The liberation of copper from the two studied sediments indicates that copper was probably associated with another phase in these sediments. AVS is stable for several weeks in refrigerated or frozen samples.
Preface 1. Models for diffusion Part I. Fundamentals of Diffusion: 2. Diffusion in dilute solutions 3. Diffusion in concentrated solutions 4. Dispersion Part II. Diffusion Coefficients: 5. Values of diffusion coefficients 6. Diffusion of interacting species 7. Multicomponent diffusion Part III. Mass Transfer: 8. Fundamentals of mass transfer 9. Theories of mass transfer 10. Absorption 11. Absorption in biology and medicine 12. Differential distillation 13. Staged distillation 14. Extraction 15. Absorption Part IV. Diffusion Coupled with other Processes: 16. General questions and heterogeneous chemical reactions 17. Homogeneous chemical reactions 18. Membranes 19. Controlled release and related phenomena 20. Heat transfer 21. Simultaneous heat and mass transfer Problems Subject index Materials index.
RT3DV1 (Reactive Transport in 3-Dimensions) is computer code that solves the coupled partial differential equations that describe reactive-flow and transport of multiple mobile and/or immobile species in three-dimensional saturated groundwater systems. RT3D is a generalized multi-species version of the US Environmental Protection Agency (EPA) transport code, MT3D (Zheng, 1990). The current version of RT3D uses the advection and dispersion solvers from the DOD-1.5 (1997) version of MT3D. As with MT3D, RT3D also requires the groundwater flow code MODFLOW for computing spatial and temporal variations in groundwater head distribution. The RT3D code was originally developed to support the contaminant transport modeling efforts at natural attenuation demonstration sites. As a research tool, RT3D has also been used to model several laboratory and pilot-scale active bioremediation experiments. The performance of RT3D has been validated by comparing the code results against various numerical and analytical solutions. The code is currently being used to model field-scale natural attenuation at multiple sites. The RT3D code is unique in that it includes an implicit reaction solver that makes the code sufficiently flexible for simulating various types of chemical and microbial reaction kinetics. RT3D V1.0 supports seven pre-programmed reaction modules that can be used to simulate different types of reactive contaminants including benzene-toluene-xylene mixtures (BTEX), and chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE). In addition, RT3D has a user-defined reaction option that can be used to simulate any other types of user-specified reactive transport systems. This report describes the mathematical details of the RT3D computer code and its input/output data structure. It is assumed that the user is familiar with the basics of groundwater flow and contaminant transport mechanics. In addition, RT3D users are expected to have some experience in using the MODFLOW and MT3D computer codes and must be familiar with their input/output data structure.
The degradation of 2,4,6-trinitrotoluene (TNT) and other explosives by zero-valent iron (ZVI) is rapid and, as a result, potentially useful for both ex situ ground water “pump-and-treat” systems and in situ permeable reactive barriers. However, the usefulness of ZVI in either configuration may be limited by reaction-induced reduction in both hydraulic conductivity (K) and reactivity (as represented by the surface area–normalized rate constant, ksa). The impacts of dissolved oxygen and TNT on K and ksa are examined here using field and laboratory columns. The data suggest that K reduction in ZVI columns can be significant when dissolved oxygen is present. However, when TNT is present at approximately the same concentration (10 mg/L), it does not cause significant reduction in K. In contrast, TNT causes a significant reduction in ksa, while dissolved oxygen appears to have relatively little impact on the reactivity of the columns toward TNT.
The combination of detailed multilevel ground water geochemistry samples, a natural-gradient tracer test, minislug tests, and a numerical flow and transport model was used to examine flow through a zero-valent iron permeable reactive barrier (PRB) installed to remove explosives from ground water. After 20 months of operation, the PRB continued to completely remove explosives from the ground water flowing through it. However, the data indicate that a portion of ground water flow was being diverted beneath the PRB. Ground water geochemistry was significantly altered by the PRB, and concentrations of some ions, including sulfate, carbonate, and calcium, were substantially reduced due to precipitation. Field data and numerical model results indicate that, after 20 months of operation, flow through the PRB was reduced to approximately one-third of its expected value.
The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron-sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long-term, low-maintenance cost solution for many ground water contamination problems.
One of the newest and most promising remediation techniques for the treatment of contaminated groundwater and soil is the reactive barrier wall (commonly known as PRB for permeable reactive barrier or reactive barrier). Although a variety of treatment media and strategies are available, the most common technique is to bury granular iron in a trench so that contaminated groundwater passes through the reactive materials, the contaminants are removed and the water becomes `clean'. The principal advantages of the technique are the elimination of pumping, mass excavation, off-site disposal, and a very significant reduction in costs. The use of this technology is now becoming better known and implemented. Special construction considerations need to be made when planning the installation of reactive barriers or PRBs to ensure the design life of the installation and to be cost-effective. Geotechnical techniques such as slurry trenching, deep soil mixing, and grouting can be used to simplify and improve the installation of reactive materials relative to conventional trench and fill methods. These techniques make it possible to reduce the hazards to workers during installation, reduce waste and reduce costs for most installations. To date, most PRBs have been installed to shallow depths using construction methods such as open trenching and/or shored excavations. While these methods are usable, they are limited to shallow depths and more disruptive to the site's normal use. Geotechnical techniques are more quickly installed and less disruptive to site activities and thus more effective. Recently, laboratory studies and pilot projects have demonstrated that geotechnical techniques can be used successfully to install reactive barriers. This paper describes the factors that are important in designing a reactive barrier or PRB installation and discusses some of the potential problems and pitfalls that can be avoided with careful planning and the use of geotechnical techniques.
Factors controlling the concentration of dissolved hydrogen gas in anaerobic sedimentary environments were investigated. Results, presented here or previously, demonstrated that, in sediments, only microorganisms catalyze the oxidation of H2 coupled to the reduction of nitrate, Mn(IV), Fe(III), sulfate, or carbon dioxide. Theoretical considerations suggested that, at steady-state conditions, H2 concentrations are primarily dependent upon the physiological characteristics of the microorganism(s) consuming the H2 and that organisms catalyzing H2 oxidation, with the reduction of a more electrochemically positive electron acceptor, can maintain lower H2 concentrations than organisms using electron acceptors which yield less energy from H2 oxidation.The H2 concentrations associated with the specified predominant terminal electron-accepting reactions in bottom sediments of a variety of surface water environments were: methanogenesis, 7–10 nM; sulfate reduction, 1–1.5 nM; Fe(III) reduction, 0.2 nM; Mn(IV) or nitrate reduction, less than 0.05 nM. Sediments with the same terminal electron acceptor for organic matter oxidation had comparable H2 concentrations, despite variations in the rate of organic matter decomposition, pH, and salinity. Thus, each terminal electron-accepting reaction had a unique range of steady-state H2 concentrations associated with it.Preliminary studies in a coastal plain aquifer indicated that H2 concentrations also vary in response to changes in the predominant terminal electron-accepting process in deep subsurface environments. These studies suggest that H2 measurements may aid in determining which terminal electron-accepting reactions are taking place in surface and subsurface sedimentary environments.
Anaerobic corrosion of iron metal produces Fe2+, OH-, and H-2(g). Growing interest in the use of granular iron in groundwater remediation demands accurate corrosion rates to assess impacts on groundwater chemical composition. In this study, corrosion rates are measured by monitoring the hydrogen pressure increase in sealed cells containing iron granules and water. The principal interference is hydrogen entry and entrapment by the iron. The entry rate is described by Sievert's law (R = kP(H2)(0.5)), and the rate constant, k, is evaluated by reducing the cell pressure once during a test. For the 10-32 mesh iron used in this study, k initially was 0.015 but decreased to 0.009 mmol kg(-1) d(-1) kPa(-0.5) in 150 d. The corrosion rate in a saline groundwater was 0.7 +/- 0.05 mmol of Fe kg(-1) d(-1) at 25 degrees C-identical under water-saturated or fully-drained conditions. The rate decreased by 50% in 150 d due to alteration product buildup. The first 40-200 h of a corrosion test are characterized by progressively increasing rates of pressure increase. The time before steady-state rates develop depends on the solution composition. Data from this period should be discarded in calculating corrosion rates. Tests on pure sodium salt solutions at identical equivalent concentrations (0.02 equiv/L) show the following anion effect on corrosion rate: HCO3 > SO42- > Cl-. For NaCl solutions, corrosion rates decrease from 0.02 to 3.0 m.
A pilot-scale permeable reactive barrier (PRB) consisting of granular iron was installed in May 1995 at an industrial facility in New York to evaluate the use of this technology for remediation of chlorinated volatile organic compounds (VOCs) in groundwater. The performance of the barrier was monitored over a 2-year period. Groundwater velocity through the barrier was determined using water level measurements, tracer tests, and in situ velocity measurements. While uncertainty in the measured groundwater velocity hampered interpretation of results, the VOC concentration data from wells in the PRB indicated that VOC degradation rates were similar to those anticipated from laboratory results. Groundwater and core analyses indicated that formation of carbonate precipitates occurred in the upgradient section of the iron zone, however, these precipitates did not appear to adversely affect system performance. There was no indication of microbial fouling of the system over the monitoring period. Based on the observed performance of the pilot, a full-scale iron PRB was installed at the site in December 1997.
Data collected from a field study of in situ zero-valent iron treatment for TCE were analyzed in the context of coupled transport and reaction processes. The focus of this analysis was to understand the behavior of chemical components, including contaminants, in groundwater transported through the iron cell of a pilot-scale funnel and gate treatment system. A multicomponent reactive transport simulator was used to simultaneously model mobile and nonmobile components undergoing equilibrium and kinetic reactions including TCE degradation, parallel iron dissolution reactions, precipitation of secondary minerals, and complexation reactions. The resulting mechanistic model of coupled processes reproduced solution chemistry behavior observed in the iron cell with a minimum of calibration. These observations included the destruction of TCE and cis-1,2-DCE; increases in pH and hydrocarbons; and decreases in EH, alkalinity, dissolved O2 and CO2, and major ions (i.e., Ca, Mg, Cl, sulfate, nitrate). Mineral precipitation in the iron zone was critical to correctly predicting these behaviors. The dominant precipitation products were ferrous hydroxide, siderite, aragonite, brucite, and iron sulfide. In the first few centimeters of the reactive iron cell, these precipitation products are predicted to account for a 3% increase in mineral volume per year, which could have implications for the longevity of favorable barrier hydraulics and reactivity. The inclusion of transport was key to understanding the interplay between rates of transport and rates of reaction in the field.
A method incorporating laboratory analysis of constituents that formed as reaction products was developed and used to determine the flux of groundwater through a zerovalent iron-based permeable reactive barrier (PRB) installed to treat U-contaminated groundwater. Concentrations of three nonvolatile constituents (Ca, U, and V) that formed as reaction products in the PRB were analyzed in 279 samples. Areal distributions of the reaction products indicate that groundwater flowed through all portions of the PRB and that nearly the entire volume of reactive material is treating the groundwater. Almost 9 t of calcium carbonate precipitated in the PRB during the first 2.7 yr of operation, but only 24 kg of combined U- and V-bearing minerals precipitated during the same period. Concentration gradients of Ca, U, and V dissolved in the groundwater indicate that a hydraulically upgradient portion of the PRB lost some reactivity during the first 2.7 yr of operation. Calculations that partially couple porosity changes to ZVI reactivity suggest that loss of reactivity may be more limiting than porosity reduction for long-term performance of the PRB. Calculations using groundwater concentration gradients and solid-phase concentrations indicate that the mean groundwater flux ranged from 11 to 24 L/min, considerably less than the design flux of 185 L/min. Flux values calculated with all three constituents were in good agreement. This method provides a more accurate determination of groundwater flux than is possible with flow sensor measurements, dissolved tracers, or Darcy's law computations.
Long-term reactivity and permeability are critical factors in the performance of granular iron permeable reactive barriers (PRBs). Thus it is a topic of great practical importance, as well as scientific interest. In this study, four types of source solutions (distilled H2O, 10 mg/L TCE, 300 mg/L CaCO3, and 10 mg/L TCE + 300 mg/L CaCO3) were supplied to four columns containing a commercial granular iron material. In all four columns, gases accumulated to approximately 10% of the initial porosity and resulted in declines in permeability of approximately 50% to 80%. In the columns receiving CaCO3, carbonate precipitates accumulated to approximately 7% of the initial porosity, with no apparent decline in permeability. The data indicate that precipitates formed initially at the influent ends of the columns, reducing the reactivity of the iron in this region. As a consequence of the reduced reactivity, calcium and bicarbonate migrated further into the column, to precipitate in a region where the reactivity remained high. Thus precipitation occurred as a moving front through the columns. The results suggest improved methods for PRB design and rehabilitation, and also suggest improvements that are needed in the mathematical models developed for predicting long-term performance.
Apparent corrosion rates have been measured for several commercially available zerovalent irons by monitoring hydrogen evolution in closed cells. Sievert-type rate constants (ks) were determined to account for hydrogen entering the iron lattice. Thus corrected corrosion rates (Rcorr) are provided for all irons tested in this study. Because the rate of hydrogen entering the iron lattice increases with PH2(1/2), and the rate of hydrogen production from corrosion, far from equilibrium conditions, is independent of PH2, at some time under closed system conditions the two rates become equal and a steady-state PH2 is attained. A relation describing this condition has been derived: PH2SS = [Rcorr/ ks]2 For the granular irons considered in this study, PH2SS values vary from less than one to eight bars, in contrast to the calculated thermodynamic equilibrium PH2 values for anaerobic corrosion, which range from 138 to 631 bar depending on the assumed product of corrosion. Because groundwater flow at an iron permeable reactive barrier removes hydrogen gas in the dissolved state, PH2SS values will be less than calculated using the relation above. A method is presented to calculate PH2 values along the flow direction in a PRB, and thus the maximum PH2 value that can possibly develop, assuming no bacterial utilization of the produced hydrogen.
A 46 meter long, 7.3 meter deep and 0.6 meter wide reactive barrier was installed at the U.S. Coast Guard Support Center (USCG) in Elizabeth City, North Carolina, in June 1996. The reactive barrier was designed to remediate a hexavalent chromium [Cr(VI)] groundwater plume, in addition to treating portions of a larger and not yet fully characterized trichloroethylene (TCE) groundwater plume at the site. The barrier is composed of Peerless Metal and Abrasives of Detroit, Michigan (Peerless) granular iron and removes Cr(VI) and TCE from the groundwater via processes of reduction and precipitation, and reductive-dechlorination, respectively. In addition to nine large-screen compliance wells, a monitoring network of approximately 150 small-screen sampling points was installed in November 1996 to provide detailed information on changes in porewater geochemistry through the barrier. This network was sampled seven times between November 1996 and December 1998 at 3 to 6 month intervals: Novemb...
A 46 m long, 7.3 m deep, and 0.6 m wide permeable subsurface reactive wall was installed at the U.S. Coast Guard (USCG) Support Center, near Elizabeth City, North Carolina, in June 1996. The reactive wall was designed to remediate hexavalent chromium [Cr(VI)] contaminated ground water at the site, in addition to treating portions of a larger overlapping trichloroethylene (TCE) ground-water plume which has not yet been fully characterized. The wall was installed in approximately 6 hours using a continuous trenching technique, which simultaneously removed aquifer sediments and installed the porous reactive medium. The reactive medium was composed entirely of granular iron, with an average grain size (d 50 ) of 0.4 mm. The reactive medium was selected from various mixtures on the basis of reaction rates with Cr(VI), TCE and degradation products, hydraulic conductivity, porosity, and cost. The continuous wall configuration was chosen over a Funnel-and-Gate configuration, based on three-dim...
Changes in ground-water quality near two granular-iron permeable reactive barriers in a sand and gravel aquifer
- J G Savoie
- D B Kent
- R L Smith
- D R Leblanc
- D W Hubble
, J.G., D.B. Kent, R.L. Smith, D.R. LeBlanc, and D.W. Hubble. 2003. Changes in ground-water quality near two granular-iron permeable reactive barriers in a sand and gravel aquifer, Cape Cod, Massachusetts, 1997–2000. WRIR 03-4309.
Evaluation of permeable reactive barrier perfor-mance
- Reston
- Usgs U S Virginia
- Epa
Reston, Virginia: USGS. U.S. EPA. 2004. Evaluation of permeable reactive barrier perfor-mance. EPA 542 R-04 004. Washington, DC: U.S. EPA.
research scientist, Department of Environ-mental & Biomolecular Systems, Oregon Health & Science Uni-versity OR 97006; rthoms@ ebs.ogi
- Biographical Sketches
- R L Johnson
- D R Ph
- B S O 'brien Johnson
- Research
Biographical Sketches R.L. Johnson, Ph.D., corresponding author, professor, Depart-ment of Environmental & Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Rd., Beaverton, OR 97006; (503) 748-1193; rjohnson@ebs.ogi.edu. R.B. Thoms, M.S., research scientist, Department of Environ-mental & Biomolecular Systems, Oregon Health & Science Uni-versity, 20000 NW Walker Rd., Beaverton, OR 97006; rthoms@ ebs.ogi.edu. R. O'Brien Johnson, B.S., research assistant, Department of Environmental & Biomolecular Systems, Oregon Health & Sci-ence University, 20000 NW Walker Rd., Beaverton, OR 97006; johnsono@ebs.ogi.edu. J.T. Nurmi, Ph.D., senior research scientist, Department of En-vironmental & Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Rd., Beaverton, OR 97006; nurmi@ ebs.ogi.edu. P.G. Tratnyek, Ph.D., professor, Department of Environmental & Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Rd., Beaverton, OR 97006; (503) 748-1023;
Performance monitoring of a zero-valent iron permeable reac-tive barrier installed with biopolymer slurry, remediation of chlorinated and recalcitrant compound
- Washington Kelso
- C E Crane
- L A Morgan
- E Evans
- P Dacyk
- J Spies
Kelso, Washington: Columbia Analytical Services. Crane, C.E., L.A. Morgan, E. Evans, P. Dacyk, and J. Spies. 2004. Performance monitoring of a zero-valent iron permeable reac-tive barrier installed with biopolymer slurry, remediation of chlorinated and recalcitrant compound. In Proceedings of the International Conference on Remediation of Chlorinated and Recalcitrant Compounds, 4th, May 24–27, 2004, Monterey, California, A.R. Gavaskar and A.S.C. Chen, Chairs. 3A.06/01-03A.06/08. Columbus, Ohio: Battelle Press.
An in-situ permeable reactive barrier for the treatment of hexa-valent chromium and trichloroethylene in ground water RT3D a modular computer code for simulat-ing reactive multi-species transport in 3-dimensions. PNNL-SA-11720
- D W Blowes
- R W Puls
- R W Gillham
- C J Ptacek
- T A Bennett
- J G Bain
- C J Hanton-Fong
- C J Paul Chromatography
- Gen-Ics Sop
Blowes, D.W., R.W. Puls, R.W. Gillham, C.J. Ptacek, T.A. Bennett, J.G. Bain, C.J. Hanton-Fong, and C.J. Paul. 1999. An in-situ permeable reactive barrier for the treatment of hexa-valent chromium and trichloroethylene in ground water. Volume 2: Performance monitoring. EPA/600/R-99/095b. Washington, DC: U.S. EPA. Clement, T.P. 1997. RT3D a modular computer code for simulat-ing reactive multi-species transport in 3-dimensions. PNNL-SA-11720. Richland, Washington: Pacific Northwest National Laboratory. Columbia Analytical Services Inc. 2004. Standard operating pro-cedure: total sulfur for ion chromatography, SOP GEN-ICS.
Construction methods for the installation of permeable reactive barriers using the bio-polymer slurry method
- S Day
- R Schindler
Day, S., and R. Schindler. 2004. Construction methods for the installation of permeable reactive barriers using the bio-polymer slurry method. In Proceedings of the International Conference on Remediation of Chlorinated and Recalcitrant Compounds, 4th, May 24–27, 2004, Monterey, California, A.R. Gavaskar and A.S.C. Chen, Chairs. 3A.06/01-03A.06/08. Columbus, Ohio: Battelle Press.
senior research scientist
- J T Nurmi
- Ph D Nw Walker Rd
J.T. Nurmi, Ph.D., senior research scientist, Department of Environmental & Biomolecular Systems, Oregon Health & Science
University, 20000 NW Walker Rd., Beaverton, OR 97006; nurmi@
ebs.ogi.edu.
P.G. Tratnyek, Ph.D., professor, Department of Environmental
& Biomolecular Systems, Oregon Health & Science University,
20000 NW Walker Rd., Beaverton, OR 97006; (503) 748-1023;
corresponding author, professor 97006; (503) 748-1193; rjohnson@ebs.ogi 97006; rthoms@ ebs.ogi
- Biographical Sketches
- R L Johnson
- Ph D R O 'brien Johnson
Biographical Sketches
R.L. Johnson, Ph.D., corresponding author, professor, Department of Environmental & Biomolecular Systems, Oregon Health &
Science University, 20000 NW Walker Rd., Beaverton, OR 97006;
(503) 748-1193; rjohnson@ebs.ogi.edu.
R.B. Thoms, M.S., research scientist, Department of Environmental & Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Rd., Beaverton, OR 97006; rthoms@
ebs.ogi.edu.
R. O'Brien Johnson, B.S., research assistant, Department of
Environmental & Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Rd., Beaverton, OR 97006;
johnsono@ebs.ogi.edu.
Standard operating procedure: total sulfur for ion chromatography
- Columbia Analytical
- Services Inc
Columbia Analytical Services Inc. 2004. Standard operating procedure: total sulfur for ion chromatography, SOP GEN-ICS.
Evaluation of permeable reactive barrier performance
- U S Epa
Capstone report on the application monitoring and performance of permeable reactive barriers for ground-water remediation. Volume 1-Performance evaluations at two sites. EPA/600/R03/045a
- R T Wilken
- . W Puls
An in-situ permeable reactive barrier for the treatment of hexavalent chromium and trichloroethylene in ground water
- D W R W Blowes
- R W Puls
- C J Gillham
- T A Ptacek
- J G Bennett
- C J Bain
- . J Hanton-Fong Andc
- Paul
Evaluating the longevity and hydraulic performance of permeable reactive barriers at department of defense sites
- A B Gavaskar
- N Sass
- E Gupta
- J Drescher W-S.Yoon
- J Sminchak
- Hicks
- Condit
Changes in ground-water quality near two granular-iron permeable reactive barriers in a sand and gravel aquifer Cape Cod Massachusetts
- J G D B Savoie
- R L Kent
- D R Smith
- . W Leblanc
- Hubble