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New approach toin-situ treatment of contaminated groundwaters
Abstract
The focus of the ongoing research described in this paper is the in situ treatment of contaminated groundwater. The goal is to establish a technology and methodology capable of removing hazardous constituents from the groundwater without the liabilities of resource depletion, treated water disposal, expensive and energy-intensive withdrawal well fields, or expensive surface treatment facilities. Among the possible subsurface treatment processes are sorption, ion exchange, precipitation, and nutrient and/or oxygen-enhanced microbiological degradation.
... Permeable reactive barriers were initially reported by [53]. The idea underlying a PRB is very simple. ...
... Starr & Cherry (1994) proposed the term "funnel and gate", which was initially discussed by [53]. A funnel and gate system is a passive remediation technique that changes flow patterns so that groundwater mostly flows via high conductivity gaps (the gates) by using cutoff barriers (the funnel). ...
... In the simplest situation, a trench of the required width can be excavated and backfilled with reactive material to intercept the contaminated layer. Normally, this approach would be limited to modest depths in geologic materials that are stable [53]. ...
... Since the 1990s, many in situ treatment methods for pollutant remediation ha studied, and research using PRB is still being actively pursued and developed. T method was first reported by Mcmurthy and Elton [47], and a permeable barrie with a reactant is installed in the path that groundwater containing pollutant through. It is a method to remove pollutants by inducing a chemical reaction b reactants and pollutants when polluted groundwater passes through a wall. ...
... Since the 1990s, many in situ treatment methods for pollutant remediation have been studied, and research using PRB is still being actively pursued and developed. The PRB method was first reported by Mcmurthy and Elton [47], and a permeable barrier filled with a reactant is installed in the path that groundwater containing pollutants flows through. It is a method to remove pollutants by inducing a chemical reaction between reactants and pollutants when polluted groundwater passes through a wall. ...
... Since the 1990s, many in situ treatment methods for pollutant remediation h studied, and research using PRB is still being actively pursued and developed. method was first reported by Mcmurthy and Elton [47], and a permeable barr with a reactant is installed in the path that groundwater containing pollutan through. It is a method to remove pollutants by inducing a chemical reaction reactants and pollutants when polluted groundwater passes through a wall. ...
Most food waste is incinerated and reclaimed in Korea. Due to the development of industry, soil and groundwater pollution are serious. The purpose of this study was to study recycled materials and eco-friendly remediation methods to prevent secondary pollution after remediation. In this study, recycled food waste ash was filled in a permeable reactive barrier (PRB) and used as a heavy metal adsorption material. In situ remediation electrokinetic techniques (EK) and acetic acid were used. Electrokinetic remediation is a technology that can remove various polluted soils and pollutants, and is an economical and highly useful remediation technique. Thereafter, the current density increased constantly over time, and it was confirmed that it increased after electrode exchange and then decreased. Based on this result, the acetic acid was constantly injected and it was reconfirmed through the water content after the end of the experiment. In the case of both heavy metals, the removal efficiency was good after 10 days of operation and 8 days after electrode exchange, but, in the case of lead, it was confirmed that experiments are needed by increasing the operation date before electrode exchange. It was confirmed that the copper removal rate was about 74% to 87%, and the lead removal rate was about 11% to 43%. After the end of the experiment, a low pH was confirmed at x/L = 0.9, and it was also confirmed that there was no precipitation of heavy metals and there was a smooth movement by the enhancer and electrolysis after electrode exchange.
... In the present study, an attempt has been made to remove the excess amount of Zn from groundwater using advanced numerical modelling. A review of literature shows that heavy metals from the subsurface domain have been removed through various mechanisms that include adsorption (Morrison and Spangler [1]), precipitation (McMurtry and Elton [2]) and biological treatment (Kurniawan et al. [3]). Similarly, Babel and Kurniawan [4] found that zero valent iron is a very popular adsorbent that could help remove Zn from the groundwater if placed within the permeable reactive barriers (PRBs). ...
... In the above equations, represents the head (m); is the concentration of solute (M/L 3 ); is effective porosity of the aquifer; is the flow velocity in the x direction (L/T); and are the coefficients of hydrodynamic dispersion (L 2 /T) in x and y directions respectively; and t is time (T); is the concentration of solute in the source (M/L 3 ); T is the saturated thickness (L); * is the volume flux per unit area (L/T) and is the retardation factor. An alternating direction implicit (ADI) technique is used to discretize eqn (2). Further, a numerical 2D code was developed using MATLAB programming and named MAT2D. ...
The study provides a methodology of obtaining optimal design parameters of Permeable Reactive Barriers (PRB) through a multi-objective optimization problem involving the cost and time of remediation. A PRB is an in-situ eco-friendly remediation technology that comprises reactive material that helps remove heavy metals and petroleum hydrocarbons from groundwater. A numerical model is developed in the study to solve the contaminant transport equation that is validated and thereafter used to simulate cases of contamination due to heavy metals. Subsequently, the required length and width of the continuous reactive barrier are determined from the plot of maximum relative concentrations. The impact of various hydraulic parameters on the design parameters as well as the cost of PRB is then studied following which the maximum length and width of the barrier as well as the total cost to clean up is determined. A similar exercise is further conducted for BTEX contaminated site after validating the developed model. A PRB is placed at varying distances from the source of pollution and the corresponding length, width and time for remediation computed. Following this, a multi-objective algorithm is developed to minimize the two objectives namely: The cost and time for remediation. Two different Hybrid algorithms are developed combining various algorithms and a set of Paretos of cost and time of remediation for different population sizes is computed using Artificial Neural Networks (ANN). The performance of the algorithms is then analysed using two performance analysers. A set of optimal solutions for the length, width, distance of barrier from the source and the corresponding cost and time of remediation are subsequently computed.
... Groundwater contamination is an environmental concern of worldwide relevance [1][2][3][4]. The conventional method to treat contaminated aquifers involves pumping groundwater up from the aquifer, treating it above-ground, and either re-injecting it back into the aquifer or discharging it elsewhere (pump-and-treat method) [2]. ...
... Therefore, the pump-andtreat method is cost-intensive and ineffective as a rule. As an alternative, permeable reactive barriers (PRB) were introduced to treat contaminated groundwater below ground [1,3] and the PRB technology is currently under development [5][6][7]. A PRB transforms the contaminations into less harmful substances or immobilizes them while allowing groundwater to pass through. ...
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.
... This innovation was a part of collective efforts to realize of a concept for ground-water remediation in permeable reactive barriers (PRBs) introduced by McMurty and Elton [2]. The Fe 0 PRB technology was built on the fortuitous observation by Reynolds et al. [3] that Fe 0 eliminated trichloroethylene and other organic compounds from aqueous solutions [4] [5]. ...
... Initially used as filling materials for Fe 0 PRBs [2] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14], the use of Fe 0 has expanded to (i) soil mixing with granular Fe 0 and Fe 0 bimetallics (Fe 0 /Me) [8] [14], (ii) groundwater treatment with injected nano-scale Fe 0 (nano-Fe 0 and nano-Fe 0 /Me) [15] [16] [17] [18], (iii) drinking water and wastewater treatment with Fe 0 , Fe 0 /Me, and nano-Fe 0 [19] [20]. However, despite a great deal of research, the Fe 0 technology as a whole is still not really accepted [21] [22]. ...
The past two decades have witnessed a boom of sci-entific articles on relevant processes governing aqueous contaminant removal in the presence of metallic iron (Fe0). Nonetheless, transforming accumulated data into useful knowledge is difficult. The major limitation is that a the-ory of the system is yet to be established or accepted. Generally, the theory of the system is established during the period between a discovery and its market introduction (‘valley of death’). This communication argues that the too short ‘valley of death’ has harmed progresses in Fe0 technology. The introduction of this technology was cou-pled with the consensus that Fe0 is a reducing agent. However, the question as to whether the reductive trans-formation theory was worthy of pursuit remained inade-quately addressed. The aim of this paper is to offer an answer to this question. A critical evaluation of the reduc-tive transformation theory is presented. It is established that pursuing the reductive transformation theory was irrational. It is shown that it is worthy to base future work on the concept that contaminants are removed during the dynamic process of Fe0 oxidative dissolution and subse-quent hydroxide/oxide precipitation.
... Groundwater contamination is a serious problem of wolrwide concern. In the last twenty years new decontamination techniques for were developed, as the so called pump-and-treat systems requires continuous input of energy and constant monitoring (McMurty et al., 1985;Mackay et al., 1989;Starr et al., 1994). The contaminated groundwater is extracted for decontamination and reinjected after treatment (Mackay et al., 1989). ...
The reactivity of elemental iron, Fe0 is widely investigated for use in permeable
reactive barriers. Fe0 is known for its efficient removal of a wide range of contaminants, like organic and inorganic substances, heavy metals and viruses.
Beside its efficacy, Fe0 is unexpensive and available in quantities huge enough for
the use in permeable reactive barriers. Aqueous decontamination by Fe0 (e.g., in Fe0-H2O systems) may proceed by (i) contaminant adsorption onto Fe0, aged and nascentFe0 corrosion products, (ii) contaminant co-precipitation with nascent Fe0
corrosion products, (iii) contaminant reduction by Fe0 (direct reduction), and (iv) contaminant reduction by FeII and atomic or molecular hydrogen (indirect reduction). Investigations for the efficacy of Fe0 are abundantly performed under shaken conditions.
In this work the influence of shaking intensities on the decontamination in “Fe0-H2O” systems was investigated. Methylene blue (MB) was used as a model contaminant for the characterization of the removal efficiency of Fe0. MB is both
easy in handling and inexpensive and its adsorption behavior is comparable with
several organic contaminants. Besides, it is a contaminant of the textile industry
itself. MnO2 and GAC were added as comparable systems to the “Fe0-H2O” system
for a better understanding of proceeding processes in this system. Investigations were performed under non-shaken, mild and violent shaken conditions. Shaking duration was either one day, three or five days.
It could be shown, that shaking intensity as well as shaking duration has a significant influence on the discoloration of MB and thus decontamination. The generation of corrosion products was accelerated and the contaminant removal, which is mainly due to adsorption and co-precipitation on in-situ generated corrosion products, increased significantly. Furthermore, the pattern of discoloration, i.e. decontamination, under shaken conditions differed strongly from the pattern seen in the undisturbed experiments.
Data obtained by this work indicate, that experiments performed under shaken conditions might be difficult in transfer to reality and when compared with each other. Therefore, investigation of decontamination efficiency or removal mechanisms should be performed under undisturbed (non-shaken) conditions
... The use of PRBs as an alternative to the conventional pump and treat method has gained significant importance, because it is an economical technology and can remove a variety of heavy metals using different reactive materials (Ludwig et al. 2002;Bortone et al. 2013). Heavy metals, such as zinc (Zn), copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), and As from the subsurface domain have been removed through adsorption (Morrison and Spangler 1993;Järup 2003;Shashi andPratiksha 2017), precipitation (McMurty andElton 1985), and biological treatments (Kurniawan et al. 2006). A variety of low-cost adsorbents, such as chitosan, lignin, waste slurry, zeolites, and zero-valent iron (ZVI) (Babel and Kurniawan 2003;Geranio 2007;Han et al. 2016;Bilardi et al. 2021) have been adopted for the removal of heavy metals from groundwater. ...
This research presents a numerical investigation that employs a continuous adsorptive barrier (CAB) near heavily contaminated groundwater. The source is classified as a heavy metal finite point source that is found in landfills. A decision maker could benefit from the CAB design charts that are produced in this research in table and chart forms. Based on the results, the cost of the barrier installation (C CAB) and the estimated dimensions could be determined by a decision maker for a known finite source concentration at the site. To accomplish this, the problem is simplified and discretized using the finite-difference technique to solve a two-dimensional (2D) transport model, and the model's accuracy is then tested against a variety of real-world scenarios. The established model (PRBFD) was used to simulate heavy metal pollution that used adsorption as the natural attenuation. Later, the required aquifer length and width for a 4-year simulation were plotted. Then, it was discovered that natural remediation took longer to reach the remediation goal, and therefore, to meet the requirements, a reactive barrier was considered. Zero-valent iron (ZVI), which is a reactive material, is introduced next to the contaminant to absorb heavy metals in a CAB. Subsequently, a plot of the maximum relative concentrations in the longitudinal and transverse directions is generated from the data for peak concentrations that are obtained at various time (t) intervals, and the requisite CAB dimensions [e.g., length (L B) and width (W B)] are computed where the cost incurred in the system is calculated. Finally, a sensitivity analysis is performed to determine the impact of sensitive hydraulic parameters on the barrier dimensions and its design cost, and various design charts are generated for the most probable cases, which could allow a decision maker to identify the barrier dimensions for any known source concentration value. Practical Applications: A number of heavy metals, such as arsenic (As), lead (Pb), zinc (Zn), copper (Cu), and cadmium (Cd) adversely affect human health. Toxic metals could easily be transmitted to the human body by food or water, because heavy metals naturally transfer from the soil to crops and then into groundwater. This research was designed so that a decision maker could determine the size of the reactive barrier, along with the design cost, against known maximum concentrations of hazardous metals at the source; and permissible concentrations of the same metal contaminant at the barrier exit face without the use of mathematical modeling.
... This technology can be an alternative method for contaminated sites instead of conventional "pump and treat methods" (Vignola et al., 2011)- (Phillips, 2009). The PRBs firstly reported by (McMurtry and Elton, 1985) as hydraulically permeable, which react with groundwater and remove dissolved contaminants through sorption or biodegradation. The first pilot test of a PRB was conducted by the University of Waterloo in Ontario, Canada (Naidu and Birke, 2015). ...
... Some technologies for control of environmental pollution have been described by various authors and have been converted into products that are being marketed for control of pollution. These technologies vary considerably in their cost and efficiencies and include the pump and treat method (considered to be costeffective), in-situ soil vapor extraction, thermal enhancement systems, air stripping (Caetano et al., 2017), reactive barrier technology (Mcmurty and Elton, 1985;Guerin et al., 2002) and natural attenuation (Wiedemeier et al., 1996;U.S. EPA, 1999;Khan et al., 2004). ...
... During the 1980s a new concept emerged in the field of environmental remediation: the idea of using underground permeable reactive barriers (treatment walls) for in situ treatment of polluted groundwater [23,24]. A treatment wall (or a PRB) is a porous reactive or adsorptive medium that is placed in the path of a contaminated groundwater plume with the aim of either to capture the contaminants, or to transform them into less harmful substances, as the groundwater flows through the barrier under the natural hydraulic gradient, or both [25,26]. ...
Hexavalent chromium (CrVI) compounds are used in a variety of industrial applications and, as a result, large quantities of CrVI have been released into the environment due to inadequate precautionary measures or accidental releases. CrVI is highly toxic to most living organisms and a known human carcinogen by inhalation route of exposure. Another major issue of concern about CrVI compounds is their high mobility, which easily leads to contamination of surface waters, soil, and ground waters. In recent years, attention has been focused on the use of metallic iron (Fe0) for the abatement of CrVI polluted waters. Despite a great deal of research, the mechanisms behind the efficient aqueous CrVI removal in the presence of Fe0 (Fe0/H2O systems) remain deeply controversial. The introduction of the Fe0-based filtration technology, at the beginning of 1990s, was coupled with the broad consensus that direct reduction of CrVI by Fe0 was followed by co-precipitation of resulted cations (CrIII, FeIII). This view is still the dominant removal mechanism (reductive-precipitation mechanism) within the Fe0 remediation industry. An overview on the literature on the Cr geochemistry suggests that the reductive-precipitation theory should never have been adopted. Moreover, recent investigations recalling that a Fe0/H2O system is an ion-selective one in which electrostatic interactions are of primordial importance is generally overlooked. The present work critically reviews existing knowledge on the Fe0/CrVI/H2O and CrVI/H2O systems, and clearly demonstrates that direct reduction with Fe0 followed by precipitation is not acceptable, under environmental relevant conditions, as the sole/main mechanism of CrVI removal in the presence of Fe0.
... Remedial schemes operating with little energy have become popular in recent decades. For example, several field investigations showed the efficacy of trenches filled with reactive media (permeable reactive barriers) placed in the paths of migrating contaminant plumes (McMurtry and Elton 1985;Blowes et al. 2000;Guerin et al. 2002;Lai et al. 2006). Utilizing natural groundwater flow as a transport mechanism requires much less energy than drilling and pumping groundwater from wells. ...
A groundwater flow and mass transport model tested the capability of shallow excavations filled with coarse, reactive media to remediate a hypothetical unconfined aquifer with a maximum saturated thickness of 5 m. Modeled as contaminant sinks, the rectangular excavations were 10 m downgradient of an initial contaminant plume originating from a source at the top of the aquifer. The initial plume was approximately 259 m long, 23 m wide, and 5 m thick, with a downgradient tip located approximately 100 m upgradient of the site boundary. The smallest trench capable of preventing offsite migration was 11 m long (measured perpendicular to groundwater flow), 4 m wide (measured parallel to groundwater flow), and 3 m deep. Results of this study suggest that shallow trenches filled with coarse filter media that partially penetrate unconfined aquifers may be a viable alternative for remediating contaminated groundwater at some sites.
... In Situ Reactive Barriers The concept of using permeable in situ reactive barriers to treat a contaminant plume as it moves through an aquifer under natural hydraulic gradients (Figure 39c and 39d) was first suggested by McMurty and Elton (1985), but it has only recently begun to receive significant attention from the research community (Starr and Cherry, 1994). The funnel-and-gate concept, which combines impermeable barriers to contain and channel the flow of the contaminant plume toward the reactive barrier has received the most attention because numerous possible configurations can be developed to address different types of contaminant plumes and geologic settings ( Figure 40). ...
Though no author is listed for this publication, I wrote it.
... Furthermore, their effectiveness has been documented in the literature (Dwyer et al. 1996;Gavaskar 1999;Hocking and Well 2002;Mountjoy et al. 2003). Starr and Cherry (1994) introduced the term ''funnel and gate'' which its concept was first mentioned by McMurtry and Elton (1985) and sometime used interchangeably with PRBs; however, funnel and gate configuration consisted of impermeable walls that directed groundwater to the reactive middle gate or panel. ...
The pollution of groundwater by organic or inorganic pollutants, originating from either soil leaching or anthropogenic activities, is one of the major environmental issues. Remediation of this water source is of highest priority because many countries use it for drinking purpose. Pump-and-treat method is represented for many decades the major technique to treat groundwater infected with organic/inorganic pollutants. In last two decades, this technique becomes to be in lack with the sense of modern concepts of sustainability and renewable energy. Permeable reactive barriers (PRBs) technology was introduced as an alternative method for traditional pump-and-treat systems to remediate contaminated groundwater that was achieving these concepts. Within this issue, this technology has been proven to be a successful and most efficient promising method used by many researchers and in several projects due to its direct and simple techniques to remediate groundwater. A rapid progress from bench scale to field scale implementation in the PRB technique is recognized through the last few years. In addition, this technique was modeled theoretically for characterizing the migration of contaminants spatially and temporally through the barrier and, consequently, these models can be used for estimating the longevity of this barrier. An overview of this technique and the promising horizons for scientific research that integrates this method with sustainability and green technology practices are presented in the present study.
... (PRBs) is now 30 years old [1]. PRBs are a sustainable biological and/or chemical treatment approach, installed to passively remove or transform aqueous contaminants [2][3][4][5]. ...
The research community on using metallic iron (Fe0) for environmental remediation is virtually divided in two schools, characterized each by a different research tradition. The two are arbitrarily termed the ‘conventional’ and ‘critical’ schools. The conventional school has discovered Fe0 for environmental remediation and the critical school has conciliated the discovery with the mainstream corrosion science. It is very difficult to understand how both schools are suffering from a ‘dialogue of the deaf’. This communication clarifies the view of the critical school and demonstrates that there is no need for a third approach to conciliate both schools. All is needed is an holistic approach of the Fe0/H2O system, obeying to the laws of chemical thermodynamics.
Cite as:
Ebelle T.C., Makota S., Tepong-Tsindé R., Nassi A., Noubactep C. (2019): Metallic iron and the dialogue of the deaf. Fresenius Environmental Bulletin 28, 8331–8340.
... Contaminant removal can be effected in a variety of ways [185][186][187]. Treatment processes include adsorption [188,189], simple precipitation [190], adsorptive precipitation [183], reductive precipitation [169,176,179] and biologically mediated transformations [175,176,182]. ...
The purpose of this report is to provide an overview of remediation technologies that are particularly suited to the remediation of dispersed contamination. Dispersed low level contamination poses a particular challenge to those charged with its remediation. Many techniques are not efficient below certain concentration thresholds or entail more severe impacts on certain environmental compartments than the contamination itself. The technologies are outlined in brief and their advantages and limitations are discussed. The need for a holistic design of the remedial action is stressed.
... Contaminant removal can be achieved in a variety of ways [142][143][144]. Treatment processes include adsorption [145,146], simple precipitation [147], adsorptive precipitation [140], reductive precipitation [126,136] and biologically mediated aerobic or anaerobic transformations [132,133,139,148]. ...
... The controversy on the operating mode of Fe 0-based systems for water treatment originates from the approach used in their investigation. The technology was born at a time where groundwater remediation researchers were looking for suitable materials for PRBs after the concept presented by McMurty and Elton (1985). In fact, Reynolds et al. (1990) were investigating the potential for sampling bias caused by sorption of chlorinated organic contaminants to materials commonly used in groundwater sampling as they discovered 'halocarbons loss' due to reductive dechlorination (Gillham 2010). ...
This article critically evaluates recent review articles on using metallic iron (Fe(0)) for environmental remediation in order to provide insight for more efficient Fe(0)-based systems. The presentation is limited to peer-reviewed articles published during 2014 and 2015, excluding own contributions, dealing mostly with granular Fe(0). A literature search was conducted up to June 15th 2015 using Science Direct, SCOPUS, Springer and Web of Science databases. The search yielded eight articles that met the final inclusion criteria. The evaluation clearly shows that seven articles provide a narrative description of processes occurring in the Fe(0)/H20 system according to the concept that Fe(0) is a reducing agent. Only one article clearly follows a different path, presenting Fe(0) as a generator of adsorbing (hydroxides, oxides) and reducing (Fe(II), H/H2) agents. The apparent discrepancies between the two schools are identified and extensively discussed based on the chemistry of the Fe(0)/H20 system. The results of this evaluation indicate clearly that research on 'Fe(0) for environmental remediation' is in its infancy. Despite the current paucity of reliable data for the design of efficient Fe(0)-based systems, this review demonstrates that sensible progress could be achieved within a short period of time, specific recommendations to help guide future research are suggested.
Copyright © 2015 Elsevier Ltd. All rights reserved.
... Treatment walls, or permeable reactive barriers, first reported by McMurty and Elton (1985), involve construction of permanent, semi-permanent, or replaceable units across the flow path of a dissolved phase contaminant plume (Starr and Cherry 1993;Starr and Cherry 1994;Udell et al. 1995;Vidic and Pohland 1996;Jefferis et al. 1997;Sacre 1997). As the contaminated groundwater moves passively through the treatment wall, contaminants are removed by physical, chemical and/or biological processes, including precipitation, sorption, oxidation/reduction, fixation, or degradation. ...
A white spirit spill at a factory site located in a residential area of south eastern Australia, led to contamination of shallow groundwater feeding into a major river. The contaminated groundwater contained toluene, ethyl benzene, and xylene and n-alkanes in the C sub(6)-C sub(36) fraction range. A funnel and gate permeable reactive barrier was designed and built, based on preliminary pilot scale tests using peat as the medium for the gate. The removal efficiencies for the funnel and gate system varied from 63 to 96% for the monocyclic aromatic hydrocarbons. Average removal efficiencies for C sub(6)-C sub(9), C sub(10)-C sub(14), and C sub(15)-C sub(28) fraction ranges were 69.2, 77.6 and 79.5%, respectively. The lowest average removal efficiencies were for the C sub(29)-C sub(36) n-alkane fraction at 54%. The overall average removal efficiency for the funnel and gate system towards petroleum hydrocarbons present in the groundwater was 72% during the ten-month period over which data was collected, and has allowed relevant surface and groundwater quality objectives to be met. The downgradient monitoring wells reported concentrations of toluene, ethyl benzene, and xylene and C sub(6)-C sub(36) below the applicable surface water guidelines for these pollutants.
... Three main geometric configurations are available in the literature: (a) a continuous wall (CW) composed of reactive trenches or injection wells [1]; (b) a funnel-and-gate configuration (F&G) composed of two impermeable walls that direct the contaminated plume towards a filtering gate [2]; and (c) a caisson configuration (CC) similar to the previous one, but in which the flow in the filtering gate is in the upward direction [3]. ...
Permeable Reactive Barriers represent an innovative remediation technique of contaminated aquifers. Three geometric configurations are encountered in the literature: a continuous wall, a funnel-and-gate system, and a caisson configuration. The present paper is focused on the design of the second and third geometric configurations and presents an analytical solution of the flow in a Permeable Reactive Barrier based on the Schwarz-Christoffel transformation. This analytical solution is coupled to residence time calculations to define a methodology of design taking into account the most important parameters on the design of a PRB: cutoff width, slenderness of the reactive cell, and hydraulic conductivity. Finally, the study provides a guidance diagram for the design of funnel-and-gate or caisson configurations, as well as a case study.
... The concept of an in situ reactive wall for groundwater remediation was first proposed by McMurtry and Elton (1985). This remediation concept has been referred to more recently as permeable reactive walls, passive treatment systems, or in situ treatment zones or curtains (e.g., Blowes et al. 1995). ...
An overview of geoenvironmental engineering for in situ remediation of contaminated land is presented. After a brief introduction, an historical perspective of remediation in the United States and the United Kingdom is presented as background for the remainder of the presentation, that includes descriptions of the remediation process, including assessment, some technological considerations for remediation, and the existing or potential technologies that may be used for remediation of contaminated land. Emphasis is placed on in situ technologies that are separated into four categories: (1) passive containment, (2) active containment, (3) passive treatment, and (4) active treatment. The costs associated with the technologies also are discussed briefly. Finally, the role of geotechnical engineering in geoenvironmental engineering for in situ remediation of contaminated land is discussed.
... der Immobilisierung zu erreichen oder aber mehrere Schadstoffgruppen gemeinsam zu behandeln.Eine Spezialform der permablen Reaktionswände ist das Prinzip des sogenannten funnel-and-gate. Bei diesem System, das erstmals vonMCMURTHY & ELTON (1985) vorgestellt wurde, wird die kontaminierte Grundwasserabstromfahne mit z. B. in den Untergrund eingebrachten Absperrwänden oder mittels horizontaler Zementbohrlochinjektion gefasst und durch die reaktive Wand geleitet. ...
... The treatment of such contaminated materials by conventional techniques is often expensive. A recent development to remediate such a contamination is the implementation of permeable reactive barriers [5][6][7][8][9][10]. Most of the current full-scale reactive barriers use metallic iron (Fe 0 -based alloys widely termed as zerovalent iron) as treatment medium. ...
The solubilization of arsenic (As) from an ore material (native Arsenic [As, trig.] with Lollingite [FeAs2, rh.]) was characterized in leaching tests lasting for ≤ 99 days. The experiments were performed with materials of different particle sizes (≤ 2 mm), in different waters and under test conditions relevant to As mobilization at near surface contaminated sites. The impact of dolomite [CaMg(CO3)2], metallic iron (Fe0), and pyrite (FeS2) on As release was accessed. Two different types of batch experiments were conducted with a constant amount of the base material and different types of water (deionised, mineral, spring, and tap water). For comparison parallel experiments were conducted with 0.1M EDTA, 0.1M Na2CO3 and 0.1M H2SO4. The results indicated no significant effect of carbonate addition on As solubilization. Fe0 and FeS2 addition essentially slowed the initial As solubilization. H2SO4 was the sole leaching agent significantly influencing As solubilization from the base material. The general trend assuming that “the smaller the particle size the quicker the As release” was not strictly verified because in samples of smaller particle sizes (d < 0.063) As was partly oxidized to more stable species.
... 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. This is not surprising given that: (i) the concept of permeable reactive barrier (PRB) is regarded as a significant advance in remediation technology [11,12], and (ii) iron PRBs have been demonstrated very efficient to mitigate contaminants in surface and ground waters [3][4][5]. Moreover, Fe 0 /H 2 O systems have been shown to effectively removed aqueous species of various nature. ...
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.
... Widespread groundwater contamination has prompted intensive efforts to find efficient and affordable remediation technologies. Recently, the introduction of in situ permeable reactive barriers for groundwater remediation [1,2] which contains a removing agent. The groundwater passing through a reactive barrier is ideally completely freed from contaminants [3][4][5]. ...
Aqueous contaminant removal in the presence of metallic iron (e.g. in Fe0/H2O systems) is characterized by the large diversity of removing agents. This paper analyses the synergistic effect of adsorption, co-precipitation and reduction on the process contaminant removal in Fe0/H2O systems on the basis of simple theoretical calculations. The system evolution is characterized by the percent Fe0 consumption. The results showed that contaminant reduction by Fe0 is likely to significantly contribute to the removal process only in the earliest stage of Fe0 immersion. With increasing reaction time, contaminant removal is a complex interplay of adsorption onto iron corrosion products, co-precipitation or sequestration in the matrix of iron corrosion products and reduction by Fe0, FeII or H2/H. The results also suggested that in real world Fe0/H2O systems, any inflowing contaminant can be regarded as foreign species in a domain of precipitating iron hydroxides. Therefore, current experimental protocols with high contaminant to Fe0 ratios should be revisited. Possible optimising of experimental conditions is suggested.
... The Fe 0 reactive wall technology is one aspect of the materialization of the original idea of McMurty and Elton [18] that a passive design " using natural groundwater flow and a treatment media " can " capture or treat the contaminants without the need for regeneration or replacement " . With the publication of this innovative concept in August 1985, an ongoing effort for efficient reactive materials for permeable reactive barriers started. ...
Remediation of contaminated groundwater is an expensive and lengthy process. Permeable reactive barrier
of metallic iron (Fe0 PRB) is one of the leading technologies for groundwater remediation. One of
the primary challenges for the Fe0 PRB technology is to appropriately size the reactive barrier (length,
width, Fe0 proportion and nature of additive materials) to enable sufficient residence time for effective
remediation. The size of a given Fe0 PRB depends mostly on accurate characterization of: (i) reaction
mechanisms and (ii) site-specific hydrogeologic parameters. Accordingly, the recent revision of the fundamental
mechanisms of contaminant removal in Fe0/H2O systems requires the revision of the Fe0 PRB
dimensioning strategy. Contaminants are basically removed by adsorption, co-precipitation and size
exclusion in the entire Fe0 bed and not by chemical reduction at a moving reaction front. Principle calculations
and analysis of data from all fields using water filtration on Fe0 bed demonstrated that: (i)
mixing Fe0 and inert additives is a prerequisite for sustainability, (ii) used Fe0 amounts must represent
30–60 vol.% of the mixture, and (iii) Fe0 beds are deep-bed filtration systems. The major output of this
study is that thicker barriers are needed for long service life. Fe0 filters for save drinking water production
should use several filters in series to achieve the treatment goal. In all cases proper material selection is
an essential issue.
... Accordingly, reducing chlorinated organic compounds is an ideal way to make them less toxic and more biodegradable. The discovery of Gillham et al. [12] coincided with the active search of appropriate materials for reactive walls after the concept for groundwater remediation presented by McMurty and Elton [16]. From 1990 on, Fe 0 has been tested at several scales and is now an established technology for water treatment (groundwater remediation, wastewater treatment, safe drinking water production) [4, 5,789 11]. ...
A knowledge system (KS) is a knowledge that is unique to a given group of persons. This form of knowledge may have a local or natural origin and is linked to the community that has produced it. On the contrary, the core of mainstream science (MS) is the desire to profoundly understand processes, through sequential studies such as hypothesis formulation, experiment and prediction. Thus, KS is communitarian and MS is universal. KS can be understood and rendered universal through MS. In general, a process discovery (know-how) may be intuitive, accidental, conjectural or inspirational but outcomes should be predictable and repeatable as soon as the know-why is achieved by MS. This paper argues that the technology of using metallic iron for water treatment has all the characteristics of a KS and that promoters of this technology have deliberately rejected scientific arguments leading to the know-why of the fortuitous discovery. Consequently, the technology has developed into an impasse where controversial discoveries are reported on all relevant aspects. It is concluded that the integrity of science in endangered by this communitarian behaviour.
... Ground water remediation using permeable reactive barriers (PRB) also is an innovative technology developed in the early 1990s (Simon and Meggyes, 2000). Treatment walls-so called PRB, first reported by Mc Murthy and Elton (1985) , involve construction of permanent, semipermanent or replaceable units across the flow path of a dissolved phase contaminant plume (Turlough et al., 2002). The material used in the barrier may vary depending on the type of contaminants being treated. ...
There have been increasing interests m finding new and innovative solution tor removal of contaminants from soils recently. In the present investigation, electro kinetic (EK) process coupled wim activated carbon barrier to remove Nickel from kaolinite clayey soil is investigated. Laboratory tests were performed by applying a constant voltage to nominal electric field strength of 1 and 1.25 V/cm with initial Ni concentration (500 mg/kg) for 3 and 7 days. Results revealed that, the coupled technology of EK with barrier when filled with activated carbon could effectively prevent the reverse electro osmotic flow which has adverse effect on the Ni removal from soil. In addition, 20-50% of Nickel migration towards the cathode during the tests was achieved.
Science denial relates to rejecting well-established views that are no longer questioned by scientists within a given community. This expression is frequently connected with climate change, and evolution. In such cases, prevailing views are built on historical facts and consensus. For water remediation using metallic iron (Fe0), the remediation Fe0/H2O system, a consensus on electrochemical contaminant reduction was established during the 1990s and is still prevailing. Arguments against the reductive transformation concept has been regarded for more than a decade as 'science denial'. However, is it the prevailing concept that had denied the science of aqueous iron corrosion? This communication retraces the path used by our research group to question the reductive transformation concept. It is shown that the validity of the following has been questioned: (i) analytical applications of arsenazo III method for the determination of uranium, (ii) molecular diffusion as sole relevant mass transport process in the vicinity of the Fe0 surface in filtration systems, and (iii) volumetric expansive nature of iron corrosion at pH > 4.5. Item (i) questions the capability of Fe0 to serve as electron donor for UVI reduction under environmental conditions. Items (ii) and (iii) are interrelated as the Fe0 surface is permanently shielded by an oxide scale acting as diffusion barrier to dissolved species and conductive barrier to electrons from Fe0. The net result is that no electron transfer from Fe0 to contaminants is possible under environmental conditions. This conclusion refutes the validity of the reductive transformation concept and call for alternatives.
Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argumentation has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old-knowledge. Nevertheless, the peer reviewed literature on "remediation using Fe0" seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots, and enable the design of better Fe0 remediation systems.
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.
Solid iron corrosion products (FeCPs), continuously generated from iron corrosion in Fe ⁰ -based permeable reactive barriers (PRB) at pH > 4.5, can lead to significant porosity loss and possibility of system’s failure. To avoid such failure and to estimate the long-term performance of PRBs, reliable models are required. In this study, a mathematical model is presented to describe the porosity change of a hypothetical Fe ⁰ -based PRB through-flowed by deionized water. The porosity loss is solely caused by iron corrosion process. The new model is based on Faraday’s Law and considers the iron surface passivation. Experimental results from literature were used to calibrate the parameters of the model. The derived iron corrosion rates (2.60 mmol/(kg day), 2.07 mmol/(kg day) and 1.77 mmol/(kg day)) are significantly larger than the corrosion rate used in previous modeling studies (0.4 mmol/(kg day)). This suggests that the previous models have underestimated the impact of in-situ generated FeCPs on the porosity loss. The model results show that the assumptions for the iron corrosion rates on basis of a first-order dependency on iron surface area are only valid when no iron surface passivation is considered. The simulations demonstrate that volume-expansion by Fe ⁰ corrosion products alone can cause a great extent of porosity loss and suggests careful evaluation of the iron corrosion process in individual Fe ⁰ -based PRB.
In recent years, different suitable technologies have been developed for the remediation of environmental contaminations. The current chapter presents an overview of the permeable reactive barrier (PRB) technologies, which includes the state of the art, the merits and limitations, the reactive media used, and the mechanisms employed to transform or immobilize contaminants. Moreover, coupling PRB with electrokinetic remediation that present a greater remove and degradation percentage of organic, inorganic compounds. Finally, we present some cases of the PRB-EK that have been developed to describe the process of soil remediation.
The technology of using metallic iron (Fe 0) for in-situ generation of iron oxides for water treatment is a very old one. The Fe 0 remediation technology has been rediscovered in the framework of groundwater remediation using permeable reactive barriers (PRBs). Despite its simplicity, the improvement of Fe 0 PRBs is fraught with difficulties regarding their operating modes. The literature dealing with Fe 0 remediation contains ambiguities regarding its invention and its development. The present paper examines the sequence of contributions prior to the advent of Fe 0 PRBs in order to clarify the seemingly complex picture. To achieve this, the current paper addresses the following questions: (i) What were the motivations of various authors in developing their respective innovations over the years?, (ii) What are the ancient achievements which can accelerate progress in knowledge for the development of Fe 0 PRBs?, and (iii) Was Fe 0 really used for the removal of organic species for the first time in the 1970s? A careful examination of ancient works reveals that: (i) the wrong questions were asked during the past three decades, as Fe 0 was premised as a reducing agent, (ii) credit for using Fe 0 for water treatment belongs to no individual scientist, (iii) credit for the use of Fe 0 in filtration systems for safe drinking water provision belongs to scientists from the 1850s, while credit for the use of Fe 0 for the removal of aqueous organic species does not belong to the pioneers of the Fe 0 PRB technology. However, it was these pioneers who exploited Fe 0 for groundwater remediation, thereby extending its Processes 2020, 8, x; doi: FOR PEER REVIEW, x FOR PEER REVIEW 2 of 17 potential. Complementing recent achievements with the chemistry of the Fe 0 /H 2 O system would facilitate the design of more sustainable Fe 0-remediation systems.
More than two-third of the world population depends on groundwater for drinking purpose. Several countries are on the verge of water crisis due to the overexploitation of groundwater for irrigational and industrial purposes. The available sources of water are currently affected by a large number of geogenic (As, F, NO3, etc.) and anthropogenic contaminants (Pb, Cd, Hg, etc.). These contaminants cause severe health effects both carcinogenic and mutagenic. There are several remediation technologies employed for the groundwater as well as soil remediation including pump and treat, air sparging, natural attenuation and containment. For the second and third world countries, permeable reactive barrier (PRB) can prove to be a major replacement for the already existing methods like the pump and treat. The topics which are discussed in the chapters following PRBs are its design, mechanisms, softwares, reactive materials, case studies in developed countries and its economic viability. The important aspects of using PRBs are easily available adsorbent material like compost, limestone, etc.; the time scale for which it can be used is decades, and the operational and maintenance cost are low. The chapter also includes favorable hydrogeological conditions for the installation of PRBs. It also brings the different set of adsorbents (reactive materials) that can be used for a different type of contaminants organic and inorganic. We have also looked out for the mechanism of degradation being a reduction, sorption, etc. This chapter also includes the possibility and problems which we can face during the installation of PRB in pilot-scale before implementing it at a larger scale. At last, we have compared different case studies, the filler material used, the type of construction used, the date of operational setup and cost analysis of PRBs. The chapter has been concluded in a good note depicting all the pros and cons of PRBs.
Over the last thirty years, several techniques of groundwater (GW) remediation based on the principles of physical (air sparging), biological (bioventing), and chemical (e.g., ion exchange) processes have proven to be effective; however, only a handful of them could successfully be implemented at a community or regional scale due to issues like longevity, a requirement of significant investment and operation cost, skilled labors, and others. Therefore, considering the scope of Permeable Reactive Barriers (PRBs) to be implemented on a regional scale and its capability to be a significant replacement for several existing GW treatment methods, this review was prepared with the following objectives: (i) to compare the PRB method with the conventional methods of groundwater treatment along with the possibility and problems associated with the PRB installation in pilot-scale; (ii) to enlist all the probable sets of adsorbents (reactive materials) that can be used for different types of organic and inorganic contaminants; (iii) to understand the key mechanisms of degradation/removal of contaminants involved in PRB design; and (iv) to put forward the future research perspectives of this domain. Review augments that PRBs certainly has a low maintenance cost and a longer life span of ̃30 years that requires very ordinary skills. PRBs promose to be effective in developing countries like India, Bangladesh, and Sri Lanka for the removal of geogenic contaminants like arsenic and fluoride given the appropriate aquifer depth and hydrogeological settings like hydraulic gradient and transmissivity. Furthermore, reactive fillers required in PRBs are readily available, have longer expected life, and operate with no surrounding disturbances. With the advent of several green nanomaterials based adsorbents, PRB’s performance can achieve another height, but it needs the experiences from several pilot and larger scale projects. Indeed PRBs are the need of the hour, but a more programming-based investigation would be expected for its superior comprehension.
The efficacy of passive treatment systems for remediating acid rock drainage can be limited by the seasonal flux of discharge and metal concentrations that may not have been considered during treatment design. A review of passive treatment options for acid rock drainage indicates reduced efficacy due to seasonal periods of increased drainage and metal concentrations that lead to mineral precipitation, surface passivation, and flow bypass. In select cases, passive treatment systems prematurely failed due to seasonal flux or experienced substantially reduced treatment efficacy and life of the system. Complimentary systems are needed to minimise impacts from seasonal flux of drainage and metal concentrations to improve treatment efficacy and preserve the life of a multi-component system or a downstream primary system. Multi-component systems are possible with integration of existing treatment systems and design of new treatment options to tailor treatment to site specifications.
Chromium (Cr) is an important metal used in a variety of industrial applications, which significantly contribute to pollution of air, soil, and waters. In natural environments, chromium can exist mainly in two of its most stable oxidation states, (+III) and (+VI). Among them, Cr(VI) is the most hazardous due to its high mobility in the environment and severe harmful effects exerted on all living matters. Therefore, it should be removed from all contaminated waters. During the last 25 years, there has been great interest in using metallic iron (Fe0) for the abatement of Cr(VI) pollution. The first mechanism, known as the reductive-precipitation mechanism, was proposed at the beginning of the nineties, and attributed the efficiency of Fe0 in removing Cr(VI) mainly to the direct electron transfer from the Fe0 surface to Cr(VI), followed by precipitation of the resulted cations as simple hydroxides and/or mixed Fe(III)-Cr(III) (oxi)hydroxides. Recently, new perspectives were added to this early mechanism. A new concept, known as the adsorption-coprecipitation mechanism, suggests that direct reduction with Fe0, if applicable, is less important than had previously been assumed by the reductive-precipitation mechanism; accordingly, contaminants are quantitatively removed in Fe0/H2O systems principally by adsorption, coprecipitation, and size exclusion, while reduction, when possible, is mainly the result of indirect reducing agents
produced by Fe0 corrosion. In spite of the substantial research work that has proven the capability of metallic iron as a reactive material to remove Cr(VI), there is no consensus at this time in what regards the mechanism of this process. Therefore, after providing an overview of chromium occurrence, chemistry, and toxicity, this work will critically review the existing knowledge on this subject, clearly demonstrating that mechanism of Cr(VI) removal with Fe0 is more complex than the simple reductive precipitation.
This chapter provides two case studies of permeable reactive barriers (PRBs) installed to intercept and treat groundwater affected by acid drainage and heavy metals. The Nickel Rim permeable barrier was designed to treat effluent containing potential acidity (as dissolved ferrous iron) from decommissioned mine wastes, and the Vancouver barrier was designed to treat groundwater impacted by elevated concentrations of heavy metals, including cadmium, copper, nickel, and zinc. Both reactive barriers treated the impacted groundwater to acceptable concentration levels while decreasing the net acidity within the groundwater. Sulfate reduction rates within both barriers decreased with time, however, rates were sufficient to attenuate heavy metals below regulatory guidelines. In order to design and install an effective PRB, the geology, hydrogeology, and geochemistry of the aquifer system must be well characterized and understood. Design specifications should account for heterogeneities within the aquifer and barrier as well as the effects of fluctuating water tables and the possibility of reductive dissolution of ferric iron (oxy)hydroxide phases within the aquifer downgradient of the reactive barrier. Permeable reactive barriers provide a cost-effective strategy for the long-term treatment of acid mine drainage and heavy metals in both urban and remote settings.
Capping is typically used to control contaminant release from the underlying sediments. While conventional capping doesn’t necessarily provide the removal of contaminants, incorporating a “funnel and gate” reactive barrier with capping has the potential to treat contaminants or limit contaminant migration. The purpose of this study was to develop a model of funnel and gate systems for remediation of contaminated sediment. Numerical modeling of vertical two dimensional water flow and solute transport was built in COMSOL MULTIPHYSICS 3.4. The model was employed to evaluate the performance of the funnel and gate system, i.e. residence time, removal efficiency, and breakthrough curve. Two types of gate, reactive and adsorptive gates, were evaluated for the remediation of phenanthrene contaminated sediment. The simulated results showed that the performance of the reactive gates depended on Damkohler number at the gate, and adsorptive gate could effectively slow contaminate migration into water body, and decrease the maximum concentration at the gate. This model could potentially serve as a design tool of funnel and gate systems for a range of typical sediment capping conditions.
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.
The permeable reactive barrier (PRB) has been an innovative in situ ground-water remediation concept for more than 15 years, though it has been only over the last 10 years that the PRB has been considered a practical alternative for groundwater treatment. Although close to 50 full-scale and tens more pilot tests have been installed since the first commercial application in 1994, and there have been close to one thousand technical papers and presentations since the early 1990s, the technology is still not considered a developed technology due to a perceived lack of cost and performance data. Over the past ten years, the number of full-scale PRBs installed may have been limited first by the uncertainty in applying a new remedial technology, and second, by the need for the designer and user to collect and understand the comprensive characterization, engineering, and logistical information required for each site specific consideration. However, the use of the PRB will become more commonplace as alternative materials and installation options continue to develop, and more information on successes, failures, and cost information become available.
Analytical and numerical three-dimensional (3-D) simulations have been conducted and compared to data obtained from a large-scale (50 m), natural gradient field injection experiment. Eighteen different xenobiotic compounds (i.e. benzene, toluene, o-xylene, naphthalene, 1,1,1-TCA, PCE, and TCE) and bromide as a conservative tracer, were injected for 195 days in the anaerobic part of the leachate plume downgradient of the Grindsted Landfill, Denmark. The injection area is an unconfined sandy aquifer with heterogeneities of clay and silt layers. Simulations with homogeneous and heterogeneous hydraulic conductivity compared well to the observed breakthrough curves and snapshots of the injection plumes.
This study evaluated the effect of heterogeneity in hydraulic conductivity on the tendency for contaminant plumes to attenuate via dilution, hydrodynamic dispersion, and molecular diffusion in simulated aquifers. Simulations included one homogeneous and four increasingly heterogeneous hydraulic conductivity fields. A numerical mass transport model generated an initial contaminant plume for each case; all initial plumes had the same mass. Next, the model simulated plume migrations through the simulated aquifers. Results suggest that highly heterogeneous settings are potentially effective at plume attenuation. Low-velocity zones in heterogeneous settings delay plume travel, enabling more time for natural processes to lower contaminant concentrations in groundwater. © 2012 Wiley Periodicals, Inc.
This chapter provides a concise review of the waste compounds originating from nuclear power generation and other radioisotope-releasing activities, and how these could be treated for beneficial use. Recent developments in the bioremediation of radionuclides such as uranium(VI) and technicium(VII) and related biochemical pathways in bacteria are evaluated. Biochemical processes that have yielded positive results are presented as part of the review and their impact on the future of power generation is evaluated.
Numerical models were used to simulate alternative funnel-and-gate groundwater remediation structures near property corners in hypothetical homogeneous and heterogeneous unconfined aquifers. Each structure comprised a highly permeable central gate (hydraulic conductivity = 25 m/d) and soil-bentonite slurry walls (hydraulic conductivity = 0.00009 m/d). Gates were perpendicular to regional groundwater flow and approximately 5 m from a contaminant plume's leading tip. Funnel segments collinear to the central gate reached property boundaries; additional funnel segments followed property boundaries in the most hydraulically upgradient direction. Structures were 1 m thick and anchored into the base of the aquifer. Two structures were simulated for each aquifer: one with a 3.0-m-long central gate and funnels on either side; and a second with a 1.5-m-long central gate, funnels on either side, and 0.75-m-long end gates. Funnels were lengthened in successive simulations, until a structure contained a contaminant plume. Results suggest that, for the same total gate length, one-gate structures may facilitate more rapid remediation, up to 44 percent less time in trials conducted in this study, than multiple-gate structures constructed near property corners. However, in order to effectively contain a plume, one-gate structures were up to 46 percent larger than multiple-gate structures. © 2011 Wiley Periodicals, Inc.
Long-term performance of a permeable reactive barrier (PRB) filled with
zero-valent iron (ZVI) and crushed stone as reactive media was evaluated
by about ten years groundwater monitoring from its installation. After
2619 days (about 7.2 years), increase of chlorinated volatile organic
carbons (CVOCs) concentrations in groundwater was observed at
down-gradient wells. Reactive media was sampled from the center of PRB
at 3158 days (about 8.7 years) to conduct a series of laboratory tests,
which examines the dechlorination coefficient and the conditions of iron
powder. Test results showed the iron powder from PRB still maintains
sufficient dechlorination ability of CVOCs, and the thickness of
corrosion material ranges less than 5μm and the most of the metal
portion remains. Therefore, it was considered that the PRB preserves its
function to reduce CVOCs concentration in groundwater met the
Environmental Quality Standards for Groundwater (EQSG) of Japan.
The application of a surface, permeable reactive barrier has been implemented at a remote site in the Canadian Arctic for the remediation of soils and water contaminated with polychlorinated biphenyls (PCBs). The initial barrier system was installed in July 2003. Preliminary work in both the field and the laboratory suggested that geotextiles alone may not be adequate for this particular Arctic barrier system, owing to issues related to survivability (specifically the effects of high UV and freeze-thaw) and clogging. Subsequent field and laboratory work demonstrated that granular materials trapped the majority of PCB-contaminated soil without impeding hydraulic performance; however, fines were escaping. Extensive column testing in the laboratory has shown that a nonwoven geotextile filter can be applied with success with a granular permeable reactive barrier system. This paper presents the results of laboratory experiments and field research used in the design of this barrier system.
Remediation of petroleum contaminated groundwater has become one of hotspots in environment research in recent years. PRB is a cost-effective and environmental benign technology. Based on the PRB technology abroad and domestically, this paper puts forward reactive media should be screened based on the ingredients, types and properties of the pollutants. Design and construction of PRB should be rely on the hydrogeological conditions of contaminated site. Immobilizing microorganism is an effective way to improve remediation efficiency and prolong using life of adsorption PRB. PRB has broad application prospects in remediation of petroleum contaminated groundwater.
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