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Long-Term Performance of an in Situ “Iron Wall” for Remediation of VOCs
Abstract
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.
... several other authors made similar conclusion which finally led to the "broad concensus" (O'Hannesin and Gillham 1998) that Fe 0 oxidative dissolution is the anodic reaction occurring simultaneously to the cathodic reduction of the contaminant of interest (e.g., an electrochemical reaction). It should be pointed out that this reasoning is limited to reducible contaminants, while several other non-reducible species, including pathogens, have been quantitatively eliminated from the aqueous phase in the presence of Fe 0 (You et al. 2005, Henderson and Demond 2007, Noubactep 2007. ...
... Fe 0 /sand mixtures were also used as pre-treatment systems to free inflowing water from dissolved O2 such that the pure Fe 0 main treatment system could be fully anoxic (O2 free) (Westerhoff and James 2003). Ironically, these efforts co-existed in the literature with the demonstration of the efficiency of Fe 0 PRBs using a Fe 0 /sand mixture comprising 22 % Fe 0 (w/w) (O'Hannesin and Gillham 1998). ...
... A last fundamental design aspect to consider is how the expected decrease of the permeability will influence the long-term efficiency of Fe 0 PRBs. In fact, Fe 0 PRBs are designed to be more permeable than the surrounding aquifer material (O'Hannesin and Gillham 1998, Zhang et al. 2022, Plessl et al. 2023. However, despite mixing Fe 0 with non-expansive materials, the permeability of the reactive zone (Fe 0 PRB) will still decrease. ...
Permeable reactive barriers (PRBs) containing metallic iron (Fe0) as reactive materials are currently considered as an established technology for groundwater remediation. Fe0 PRBs have been introduced by a field demonstration based on the fortuitous observation that aqueous trichloroethylenes are eliminated in Fe0-based sampling vessels. Since then, Fe0 has been tested and used for treating various biological (e.g., bacteria, viruses) and chemical (organic and inorganic) contaminants from polluted waters. There is a broad consensus on the view that "reactivity loss" and "permeability loss" are the two main problems hampering the design of sustainable systems. However, the view that Fe0 is a reducing agent (electron donor) under environmental conditions should be regarded as a distortion of Corrosion Science. This is because it has been long established that aqueous iron corrosion is a spontaneous process and results in the Fe0 surface being shielded by an oxide scale. The multi-layered oxide scale acts as a conduction barrier for electrons from Fe0. Accordingly, "reactivity loss", defined as reduced electron transfer to contaminants must be revisited. On the other hand, because "stoichiometric" ratios were considered while designing the first generation of Fe0 PRBs (Fe0 as reductant), "permeability loss" should also be revisited. The aim of this communication is to clarify this issue and reconcile a proven efficient technology with its scientific roots (i.e., corrosion science).
... Around 1990, technologies said to be based on redox properties of metallic iron (Fe(0)) were introduced as highly promising for groundwater remediation (Gillham and O'Hannesin, 1994;Matheson and Tratnyek, 1994). During the past three decades, the remediation Fe(0)/H2O system was investigated in detail (O'Hannesin and Gillham, 1998;Henderson and Demond, 2007;Gheju, 2011;Ghauch, 2015;Guan et al., 2015;Noubactep, 2015;Antia, 2020;He et al, 2020;Thakur et al., 2020). The contaminant removal capability of Fe(0)/H2O systems is largely associated with the ability of Fe(0) to "donate" electrons while being oxidized to Fe II species (O'Hannesin and Gillham, 1998;Henderson and Demond, 2007;Guan et al., 2015;He et al, 2020;Thakur et al., 2020). ...
... During the past three decades, the remediation Fe(0)/H2O system was investigated in detail (O'Hannesin and Gillham, 1998;Henderson and Demond, 2007;Gheju, 2011;Ghauch, 2015;Guan et al., 2015;Noubactep, 2015;Antia, 2020;He et al, 2020;Thakur et al., 2020). The contaminant removal capability of Fe(0)/H2O systems is largely associated with the ability of Fe(0) to "donate" electrons while being oxidized to Fe II species (O'Hannesin and Gillham, 1998;Henderson and Demond, 2007;Guan et al., 2015;He et al, 2020;Thakur et al., 2020). Relevant electron acceptors are supposedly a wide range of pollutants undergoing parallel reduction (e.g. ...
... Khudenko demonstrated the feasibility of using Cu 2+ cementation as a novel tool to generate Fe 2+ and H + for the reductive transformation of organics (Khudenko 1991). Khudenko (1991) was not considered while discussing the mechanism of RCl reduction from the middle of the 1990s onwards (Matheson and Tratnyek 1994, Warren et al. 1995, Weber 1996, O'Hannesin and Gillham 1998). ...
The global effort to mitigate the impact of environmental pollution has led to the use of various types of metallic iron (Fe(0)) in the remediation of soil and groundwater as well as in the treatment of industrial and municipal effluents. During the past three decades, hundreds of scientific publications have controversially discussed the mechanism of contaminant removal in Fe(0)/H2O systems, with the large majority considering Fe(0) to be oxidized by contaminants of concern. This view assumes that contaminant reduction is the cathodic reaction occurring simultaneously with Fe 0 oxidative dissolution (anodic reaction). This view contradicts the century old theory of the electrochemical nature of aqueous iron corrosion and hinders progress in designing efficient and sustainable remediation Fe(0)/H2O systems. The aim of the present communication is to demonstrate the fallacy of the current prevailing view based on articles published before 1910. It is shown that properly reviewing the literature would have avoided the mistake. Going back to the roots is recommended as the way forward and should be considered first while designing laboratory experiments.
... The efficiency of biotic and abiotic natural attenuation processes removing chlorinated organic compounds from the water phase under natural conditions is limited. Consequently, several remediation methods based on reductive dechlorination, using zero-valent iron (ZVI) [22][23][24][25], noble metal catalysts such as palladium (Pd) and rhodium (Rh) [26][27][28][29], or a combination of both [30][31][32][33][34][35][36], have been developed. In addition to the direct electron transfer on the ZVI surface for dechlorination, all methods use molecular hydrogen as the electron donor to convert the chlorinated organic compounds into non-chlorinated products. ...
... These techniques have been applied in in-situ remediation of contaminated aquifers. Examples comprise the application of ZVI in permeable reactive barriers (PRBs) [22,23,48,49], the direct injection of nano-scale ZVI, or nano-scale Fe/Pd bimetallic particles, both with or without support materials, into aquifers [24,25,48,[50][51][52][53][54][55][56]. Noble metal catalysts have also been implemented in in-borehole treatment techniques [30,31,57]. ...
... These issues have arisen from the awareness that although PRBs generally perform well after over a decade of operation [28,29], their long-term performance is still not well understood, especially in terms of hydraulic conductivity, (this statement has remained unchanged from 2007 until now [23]). For this reason, this review aimed to investigate the hydraulic behavior of PRBs composed of ZVI in light of the most recent findings. ...
... Good PRB performance was observed after 5 years of operation by O'Hannesin and Gillham [28] and after 15 years by Wilkin et al. [29], which demonstrated that the presence of mineral precipitates, such as calcium carbonate or iron oxides and sulfides, observed near the upstream PRB-aquifer interface did not significantly influence the hydraulic behavior of the PRB. However, in other cases, reductions in the hydraulic conductivity of the PRB [13,70,71] or the inefficient capture of contaminated groundwater [72] influenced PRB efficiency. ...
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.
... The interaction between contaminants and reactive materials is the main objective of the entire PRB system (Henderson and Demond, 2007). Remediation of a variety of contaminants was performed using several reactive materials during field applications of PRB around the world, such as ZVI, GAC, limestone, zeolite, and various organic materials (Faisal et al., 2018;O'Hannesin and Gillham, 1998;Obiri-Nyarko et al., 2014;Thiruvenkatachari et al., 2008;Wang et al., 2016). Therefore, it is essential to comprehensively describe some reactive materials predominantly employed in PRBs. ...
... PRB study (references) PRB site/study scenario Performance evaluation, remarks ZVI and/or ZVI/composite as reactive material O'Hannesin, 1992, 1994;Henderson and Demond, 2007;O'Hannesin and Gillham, 1998 Canadian Forces Base, Borden, Ontario, Canada -Pilot-scale study ...
Permeable reactive barriers (PRBs) are significant among all the promising remediation technologies for treating contaminated aquifers and groundwater. Since the first commercial full field-scale PRB emplacement in Sunnyvale, California, in 1994–1995, >200 PRB systems have been installed worldwide. The main working principle of PRB is to treat a variety of contaminants downstream from the contaminated source zone (“hot spot”). However, to accurately assess the longevity of PRB, it is essential to know the total contaminant mass in the source area and its approximate geometry. PRBs are regarded as both a safeguarding technique and an advanced decontamination technique, depending on the contamination scenario and its outcome during the operational life of the barrier. In the last three decades, many PRBs were performed very well and provided a likely designated performance for the contaminated sites. However, there is still the necessity of its potential implications for different PRBs worldwide. Therefore, this study presents a comprehensive overview of field-scale PRBs applications and their long-term performance after on-site emplacements. This paper provides in-depth insight into PRBs as a potential passive remedial measure, covering all significant dimensions, for eliminating the contaminated plume over a long time in the subsurface. The overview will help all the stakeholders worldwide to understand the implications of PRB's field-scale application and help them take all the required measures before its on-site application to avoid any potential failure.
... Given that under natural conditions, Fe 0 is corroded only by protons from water dissociation (Eq. 1) [29], Miyajima and Noubactep [30] argued that reactivity loss is a mirage. In fact, "reactivity loss" has also occurred in Fe 0 -based permeable reactive barriers successfully working for up to two decades [31][32][33][34]. On the other hand, Roh et al. [35] reported on Fe 0 specimens from World War I still corroding in soils. ...
... All these systems operated for more that one year without clogging. In the framework of subsurface permeable reactive barriers, O'Hannesin and Gillham [31] tested a reactive wall containing 22 % Fe 0 balanced with gravel and reported on good hydraulic properties in the long term. Other systems with 100 % Fe 0 have failed because of loss of porosity coupled with the early development of preferential ow paths in the Fe 0 permeable reactive barrier [86]. ...
Metallic iron (Fe ⁰ ) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe ⁰ /sand) and manganese oxide (Fe ⁰ /MnO x ). In this study, a ternary Fe ⁰ /MnO x /sand system is characterized for its discoloration efficiency of methylene blue (MB) in quiescent batch studies for 7, 18, 25 and 47 d. The objective was to understand the fundamental mechanisms of water treatment in Fe ⁰ /H 2 O systems using MB as an operational tracer of reactivity. The premise was that, in the short term, both MnO 2 and sand delay MB discoloration by avoiding the availability of free iron corrosion products (FeCPs). Results clearly demonstrate no monotonous increase in MB discoloration with increasing contact time. As a rule, the extent of MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the vessels (test-tubes). The presence of MnO x and sand enabled the long-term generation of iron hydroxides for MB discoloration by adsorption and co-precipitation. Results clearly reveal the complexity of the Fe ⁰ /MnO x /sand system, while establishing that both MnO x and sand improve the efficiency of Fe ⁰ /H 2 O systems in the long-term. This study establishes the mechanisms of the promotion of water decontamination by amending Fe ⁰ -based systems with reactive MnO x .
... In specific cases, PRB has employed a combination of 22% Fe 0 and 78% concrete as the active medium to remove groundwater trichloroethylene and tetrachlorethylene [20]. The world's first full-scale reducing PRB, used to treat acidic mine wastewater, removes pollutants and generates alkalinity through sulfate reduction, metal sulfide precipitation, trace element adsorption, and co-precipitation [21,22]. ...
This study investigates the adsorption of cadmium (Cd) by red mud–loess mixed materials and assesses the influence of quartz sand content on permeability. Shear tests are conducted using various pore solutions to analyze shear strength parameters. The research validates solidification methods for cadmium-contaminated soils and utilizes SEM-EDS, FTIR, and XRD analysis to elucidate remediation mechanisms. The findings suggest that the quartz sand content crucially affects the permeability of fine-grained red mud–loess mixtures. The optimal proportion of quartz sand is over 80%, significantly enhancing permeability, reaching a coefficient of 6.7 × 10−4 cm/s. Insufficient quartz sand content of less than 80% fails to meet the barrier permeability standards, leading to a reduced service life of the engineered barrier. Adsorption tests were conducted using various pore solutions, including distilled water, acidic solutions, and solutions containing Cd, to evaluate the adsorption capacity and shear characteristics of the red mud–loess mixture. Additionally, the study examines the behavior of Cd-loaded red mud–loess mixtures in various pore solutions, revealing strain-hardening trends and alterations in cohesiveness and internal friction angle with increasing Cd concentrations. The analysis of cement–red mud–loess-solidified soil demonstrates enhancements in soil structure and strength over time, attributed to the formation of crystalline structures and mineral formations induced by the curing agent. These findings provide valuable insights into the remediation of cadmium-contaminated soils.
... On the contrary, sand can be added to reduce the cost or increase the permeability of the barrier [11,12] in case the permeable reactive barrier (PRB) methodology requires a more permeable material used in the barrier than the aquifer soil [8,[13][14][15][16][17][18][19] to control and treat the contaminated groundwater while passing through, based on its reactivity against the heavy metals [20,21], chlorinated organics [22], radionuclides [23] etc in the soil. This alternative passive technology may involve one or more reactive materials in a barrier such as zero-valent iron (ZVI) [24][25][26][27], hydroxyapatite [28], and activated carbon [29] or natural rocks; limestone [30], attapulgite [31], sepiolite [32][33][34], zeolite [12,[33][34][35][36] which have been mechanically brought to a certain grain size or processed minerals such as organoclay [37][38] and organozeolite [38]. ...
Areas vulnerable to catastrophic disasters such as hurricane, landslide and earthquake require ready and sustainable solutions for the post-pollution scenarios. Clinoptilolite type zeolite resources of Türkiye can serve economical and sustainable solutions as a quick response. While the studies on application of zeolite-bentonite mixtures in the landfill liners or zeolite with sand in permeable reactive barrier (PRB)s are common, the slurry form of fine-grained zeolite in subsurface reactive barriers is not received an attention by the researchers. In this context, this laboratorial study presents the preliminary findings on one-dimensional consolidation and hydraulic conductivity tests on crushed zeolite samples S1 and S2 having 33 and 84% fine particle size fraction, respectively. S2 shows the higher compression index than S1, without a significant change in swelling index attributed to less than 4% clay contents. A self-designed rigid wall type permeameter was used to study on reconstituted slurry like materials under the benefit of back pressure saturation without the consolidation during testing that encountered in flexible wall permeameter. Falling head – rising tail water procedure was adopted under the back pressure in between 200 and 700 kPa. S2 samples reconstituted under 25, 50, 100 and 200 kPa show a gradual decrease in kv from 3×10-8 to 2×10-9 m/s. Previous observations on the sample of S1 revealed 8 times higher kv values under the same sv'. Since the fine content of zeolite limits kv, the proposed permeameter will be beneficial to determine the proper grain size distribution of fill materials considering the barrier height and in-situ stress conditions before the environmental studies with leachate.
... The permeable reactive barrier (PRB) technology has gained acceptance as an effective passive remediation strategy for the treatment of a variety of chlorinated organic and inorganic contaminants in ground water (e.g., O'Hannesin and Gillham, 1998;Blowes et al., 2000). The technology combines subsurface fluidflow management with contaminant treatment by combinations of chemical, physical and/or biological processes. ...
Contamination of ground-water resources by arsenic is a widespread environmental problem; consequently, there is an escalating need for developments and improvements of remedial technologies to effectively manage arsenic contamination in ground water and soils. In June 2005, a 9.1 m long, 14 m deep, and 1.8 to 2.4 m wide (in the direction of ground-water flow) pilot-scale permeable reactive barrier (PRB) was installed at a former metal smelting facility. The reactive barrier was designed to treat ground water contaminated with moderately high concentrations of both arsenite and arsenate. The reactive barrier was installed over a 3-day period using bio-polymer slurry methods and modified excavating equipment for deep trenching. The reactive medium was composed entirely of granular iron. A monitoring network of approximately 40 ground-water sampling points was installed in July 2005. Monitoring results indicate arsenic concentrations >25 mg L-1 in wells located hydraulically upgradient of the PRB. Within the PRB, arsenic concentrations are reduced to 2 to <0.01 mg L-1. After 2 years of operation, monitoring points located within 1 m of the downgradient edge of the PRB showed significant decreases in arsenic concentrations at depths intervals impacted by the emplaced zerovalent iron. Arsenic removal in the PRB results from several pathways involving adsorption to iron oxide and iron sulfide surfaces. These different uptake processes lead to multiple oxidation states and bonding environments for arsenic in the reactive medium as indicated using spectroscopic methods. This report covers aspects of site characterization, remedial design and implementation, and monitoring results for this pilot-scale PRB, including a flux-based analysis for arsenic.
... It must be noted here, however, that the Fe 0 -H 2 O system is an ion-selective system with the highest affinity towards negatively charged pollutants [4,19]. The aforementioned studies have dealt with neutral [17] or cationic contaminants [8,18] with low affinity for the positively-charged (at circumneutral pH) iron (hydr)oxides covering the surface of Fe 0 . Thus, the question that arises is: what could be the influence of Fe 0 "dilution" with sand on removal efficiency of anionic pollutants, and, particularly, of reducible anionic contaminants, in an Fe 0 -H 2 O system? ...
The aim of the present study was to provide new knowledge regarding the effect of non-expansive inert material addition on anionic pollutant removal efficiency in Fe0-H2O system. Non-disturbed batch experiments and continuous-flow-through column tests were conducted using CrVI as a redox–active contaminant in three different systems: “Fe0 + sand”, “Fe0 only” and ”sand only”. Both experimental procedures have the advantage that formation of (hydr)oxide layers on Fe0 is not altered, which makes them appropriate proxies for real Fe0-based filter technologies. Batch experiments carried out at pH 6.5 showed a slight improvement of CrVI removal in a 20% Fe0 system, compared to 50, 80 and 100% Fe0 systems. Column tests conducted at pH 6.5 supported results of batch experiments, revealing highest CrVI removal efficiencies for “Fe0 + sand” systems with lowest Fe0 ratio. However, the positive effect of sand co-presence decreases with increasing pH from 6.5 to 7.1. Scanning electron microscopy—energy dispersive angle X-ray spectrometry and X-ray diffraction spectroscopy employed for the characterization of Fe0 before and after experiments indicated that the higher the volumetric ratio of sand in “Fe0 + sand” system, the more intense the corrosion processes affecting the Fe0 grains. Results presented herein indicate the capacity of sand at sustaining the efficiency of CrVI removal in Fe0-H2O system. The outcomes of the present study suggest that a volumetric ratio Fe0:sand = 1:3 could assure not only the long-term permeability of Fe0-based filters, but also enhanced removal efficiency of CrVI from contaminated water.
... After 22 years of operation, the TCE removal rate was still up to 98% (Torres E et al., 2017). In a military base in Ontario, Canada, a mixture of 22% granulated iron and 78% sand was used to form a permeable wall, removing 90% of trichloroethylene and 86% of tetra vinyl chloride (O'Hannesin SFUO and Gillham RW, 1998). The iron-modified manganese ore, which has been found to be the most effective in removing arsenic, was applied to the PRB technique at the As-contaminated site in Suxian District, Chenzhou City (Huang YB, 2018). ...
... The large mass percentage in nZVI indicates that oxidation has occurred which continues at the corrosion stage. This iron corrosion reaction will be used for water remediation from various kinds of contaminants, both organic and inorganic [20]. In addition, there are also S atoms derived from FeSO4 residue which may come from filter paper made of cellulose or carbon tape used during SEM analysis. ...
Zero-valent iron nanoparticles (nZVI) were successfully synthesized by metal salt reduction method using cinnamon as a reductor agent. Particle size analysis showed that the most optimum composition of FeSO4 and polyphenols was at a ratio of 4:1, resulting in Dv(10), Dv(50), and Dv(90) values of 23.7 nm, 44.6 nm, and 178 nm, respectively. Scanning electron microscopy showed that nZVI was spherical and agglomerated. X-ray diffraction pattern showed a peak at 45.03˚ that corresponds to nZVI. The batch test showed that nZVI has Ni(II) and Cr(VI) adsorption activity of 95.58% Ni and 64.29%, respectively.
... Over the past decades, metallic iron (Fe(0)), referred to as zero-valent iron (ZVI), has attracted significant attention for the remediation and treatment of water polluted with a wide range of contaminants [12]. ZVI has proven to be an effective material for removing multiple contaminants, including arsenic species [13][14][15], NO 3 − [16][17], NO 2 − , hexavalent chromium [18], heavy metals [19,20], as well as halogenated and nitrated organic compounds [21]. ...
Multivariate statistical techniques and artificial neural networks (ANNs) were used for the analysis, interpretation, and modeling of the results obtained in the study of zero-valent iron (ZVI) reactive beds designed for contaminant removal. A wide range of operating conditions was evaluated through more than 120 rapid small-scale column tests (RSSCT). The production of Fe(II) and Fe(III) species, dissolved oxygen consumption, and pH variation along the reactive bed were used as response variables for evaluating the process performance. Due to the complexity of the system, and the difficulty in defining and fitting kinetic parameters, ANN models were used to simulate the system without the need for kinetic expressions. Therefore the latter were used for assessing the system behavior within the investigated experimental domain and for evaluating the relative importance of the operating factors. In addition, the application of the multivariate techniques cluster analysis (CA) and principal component analysis (PCA) revealed underlying relationships among the response variables. Moreover, although multiple physicochemical processes are involved, the results obtained through PCA indicate that the main trends can be rationalized by considering a few key reactions only. The strategy of analyzing RSSCT results with different numerical techniques provides valuable knowledge for designing real-scale ZVI-based treatments aimed at the efficient elimination of a wide range of contaminants in the aqueous phase.
... The first pilot-scale PRB was installed in 1991 at the Canadian Forces Base, Borden, 123 Ontario, to treat a plume of chlorinated solvents (O'Hannesin and Gillham, 1998). ...
Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation.
... Actually, the Fe°-based filters removal process seems to be clarified despite the confusion and flaws that have long marred the understanding and interpretation of its remediation mechanisms [12][13][14]. Fe° filters are an efficient technology for environmental sanitation [15][16][17][18][19][20][21], the production of drinking water [3, 5-6, 8, 22-25], and the treatment of wastewater [16, 26 -28]. Fe° cannot coexist with water; it undergoes oxidation, corrosion of Fe° [11,30] into Fe 2+ ions, thus implying the couple Fe 2+ /Fe° (a). ...
... Clearly, only hybrid Fe 0 /aggregate systems are sustainable (Figure 2) [90]. This evidence is still not clear to many active researchers mainly because the Fe 0 PRB technology was demonstrated with a hybrid system (22 % Fe 0 w/w) [91], but the majority of the first generation Fe 0 PRBs was built with 100 % Fe 0 . Even today, hybrid Fe 0 /aggregate systems are still designed without rationalizing their choice [84]. ...
Scientific collaboration among various geographically scattered research groups on the broad topic of "metallic iron (Fe0) for water remediation" has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners including researchers from the same organization, domestic researchers also from non-academic organizations as well as international partners. The present analysis of recent publications of some few leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging, and reducing species (e.g. FeII , H2 , Fe3O4) but reductive transformation is not a relevant contaminant removal mechanism. The problem encountered in assessing the validity of the views of both schools arises from the quantitative dominance of the supporters of the first school who mostly ignore the second school in their presentations. The net result is that the various derivations of the original Fe0 remediation technology may be collectively flawed by the same thinking mistake. While recognizing that the whole research community strives for the success of a very promising, but yet to established technology, annual review articles are suggested as an ingredient for successful collaboration.
... Moreover, pre-treatment zones with up to 50 % Fe 0 (w/w) were tested as oxygen scavengers [34][35][36]. This occurred despite the fact that, under field conditions, quantitative contaminant removal in a field Fe 0 reactive permeable reactive barrier containing only 22 % Fe 0 (w/w) was reported [23,37,38]. This confusion motivated the first efforts to systematically test hybrid Fe 0 /aggregate systems [39]. ...
Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water treatment for the past 170 years. Fe0 generates solid iron corrosion products (FeCPs) which are known to in-situ coat the surface of aggregates, including granular activated carbon (GAC), gravel, lapillus, manganese oxide (MnO2), pyrite (FeS2), and sand. While admixing Fe0 and reactive aggregates to build hybrid systems (e.g. Fe0/FeS2, Fe0/MnO2, Fe0/sand) for water treatment, it has been largely overlooked that those materials would experience reactivity loss upon coating. This communication clarifies the relationships between aggregate addition and the sustainability of Fe0/H2O filtration systems. It is shown that any enhanced contaminant removal efficiency in a Fe0/aggregate/H2O system relative to the Fe0/H2O system is related to the avoidance/delay of particle cementation by virtue of the non-expansive nature of the aggregates. The argument that aggregate addition sustains any reductive transformation of contaminants mediated by electrons from Fe0 is disproved by the evidence that Fe0/sand systems are equally more efficient than pure Fe0 systems. This demonstration corroborates the concept that aqueous contaminant removal in iron/water systems is not a process mediated by electrons from Fe0. This communication reiterates that only hybrid Fe0/H2O filtration systems are sustainable.
... The last two decades have witnessed the establishment of Fe 0 as powerful environmental remediation materials (Scherer et al. 2000, Henderson & Demond 2007, Cundy et al. 2008, Comba et al. 2011. Until recently, it has been commonplace to consider that the mechanism of metallic iron remediation varies depending on the contaminant of interest (O'Hannesin & Gillham 1998, Scherer et al. 2000, Henderson & Demond 2007, Cundy et al. 2008, Comba et al. 2011. Following this premise, research over the past decade has demonstrated the efficacy of Fe 0 for the remediation of a wide range of contaminants, including chlorinated organics, dyes, pharmaceutical products, selected inorganic ions, a wide range of heavy metals, and radionuclides (Cantrell et al. 1995, Blowes et al. 2000, Morrison et al. 2002, Morrison et al. 2006, Ghauch et al. 2010a, Ghauch et al. 2010b. ...
This thesis deals with the use of metallic iron (Fe0) for water treatment in general and the use of Fe0 for safe drinking water production in particular. The provision with safe drinking water is a real problem for 800 millions of people all over the world.Chapter 1 presents the concept of water treatment with Fe0 in a broader scientific context and
reveals research needs. Chapter 2 presents the 21 peer-reviewed journal articles on which the thesis is based in relation to their contribution to solve the problems from Chapter 1. Chapter 3 presents the same articles in the perspective of using Fe0 for safe drinking water production.Chapter 4 summarizes the major findings or the present work. An outlook is given in form of specific recommendations for future works. Chapter 5 gives an epilogue which is a sort of responses to the comments made by the referees on the submitted thesis. Chapter 6 lists cited references. The 21 papers on which this thesis is formulated are not appended to this version.
The experimental research was carried out at the Department of Applied Geology of the
University of Göttingen (Prof. Martin Sauter) between July 2005 and March 2009 and partly was financed by the German Research Foundation (DFG) under the Grant number DFG NO 626/2-1 and DFG NO 626/2-2.
I would like to thank Angelika Schöner, Paul Waofo and Sabine Caré for the scientific
collaboration during the study.
My acknowledgements also go to my colleagues of the Department of Applied Geology at the University of Göttingen, to my friends and collaborators for religious, cultural and sportive issues in Göttingen (and Krebeck), in Freiberg (Sachsen) and elsewhere. They provided the excellent atmosphere for this work.
Special thanks to: (i) my family for his endless support and (ii) Léonard Kwuida, Sabine Caré, and Ewa Lipczynska-Kochany for reading and re-reading the draft of this thesis.
... 1995; Lee et al., 2004). The adoption of the view that reducing electrons are from Fe 0 (electrochemical reaction) was based on a "broad consensus" (O'Hannesin and Gillham, 1998;Cao et al., 2021c;Hu et al., 2021a;Noubactep, 2022) with weak supporting evidence. Moreover, since 2007 the 'reductive transformation' theory has been systematically rejected in a series of papers, including reviews Gheju, 2011;Ghauch, 2015;Gheju, 2018). ...
An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contaminant removal has been in use for a decade: The methylene blue method (MB method). The approach considers the differential adsorptive affinity of methylene blue (MB) for sand and iron oxides. The MB method characterizes MB discoloration by sand as it is progressively coated by in-situ generated iron corrosion products (FeCPs) to deduce the extent of iron corrosion. The MB method is a semi-quantitative tool that has successfully clarified some contradicting reports on the Fe 0 /H2O system. Moreover, it has the potential to serve as a powerful tool for routine tests in the Fe 0 remediation industry, including quality assurance and quality control (QA/QC). However, MB is widely used as a 'molecular probe' to characterize the Fe 0 /H2O system, for instance for wastewater treatment. Thus, there is scope to avoid confusion created by the multiple uses of MB in Fe 0 /H2O systems. The present communication aims at filling this gap by presenting the science of the MB method, and its application and limitations. It is concluded that the MB method is very suitable for Fe 0 material screening and optimization of operational designs. However, the MB method only provides semi-quantitative information, but gives no data on the solid-phase characterization of solid Fe 0 and its reaction products. In other words, further comprehensive investigations with microscopic and spectroscopic surface and solid-state analyses are needed to complement results from the MB method.
... Among the available iron-based options, zero-valent iron (ZVI) is an effective reactive reagent for the removal of contaminants due to its high reduction potential of 440 mV [12,13]. The effectiveness of ZVI as a PRB media is defined by the rate of contaminant reduction generally, which relies upon the grain size and explicit surface region of the iron and the geochemical states of the aquifer [14,15]. ...
... As an intrinsic characteristic, reactivity loss can never be suppressed (Miyajima and Noubactep 2015). In other words, reactivity loss has occurred in reactive barriers satisfactorily operating for decades (O'Hannesin and Gillham 1998, Guan et al. 2015. These systems are still efficient because their designs (e.g. ...
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.
... The concern of this commentary is that the investigation of Fe(0) filters for the past 30 years has been biased by an insufficient system analysis (Noubactep 2011, Calabrò et al. 2021, Njaramba et al. 2021). Even results from systems working for decades (O'Hannesin and Gillham 1998, Phillips et al. 2010, Wilkin et al. 2014, Wilkin et al. 2019) cannot help to fill the gap in knowledge because existing systems were not monitored to enable a holistic discussion of the changes within them (Naseri et al. 2017, Yang et al. 2021. For subsurface Fe(0) PRBs in particular, one key design criterion has been that the permeability of the PRB shall be larger than that of the surrounding aquifer (Henderson andDemond 2007, ITRC 2011). ...
Over the past three decades, groundwater remediation using permeable reactive barriers (PRBs) has proven to be effective. The majority of installed PRBs uses metallic iron (Fe(0)) as a reactive material. However, the success of implemented Fe(0) PRBs is yet to be rationalized as Fe(0) is a generator of iron oxides (contaminant scavengers) and secondary reducing agents (e.g. Fe(II), Fe3O4, H2, green rust), This communication demonstrates that Fe(0) is not an environmental reducing agent. Therefore, more science-based investigations are needed to optimize the operation of Fe(0) PRBs. In particular, Fe(0) PRBs and Fe(0)-based water filters should be regarded as particular cases of "metal corrosion in porous media". A key feature of such systems is that the extent of Fe 0 corrosion temporally depends on the residual porosity (capillarity). Thus, the functionality of any Fe 0 PRB should be monitored in a way that the time-dependent variation of the kinetic of iron corrosion is discussed.
... The decontamination methods include: i) sorption and precipitation, ii) chemical 295 transformation and iii) biodegradation. In a first field-scale operation published in 1998, a mixture of granular iron and sand immobilized into sealable-joint sheet piling was used for the degradation of trichloroethene and tetrachloroethene in a Canadian sand aquifer (O'Hannesin and Gillham, 1998). Thereafter, most of the published documents on PRBs have focused on barriers filled with zero valent iron (ZVI) as a reactive material directed against chlorinated solvents, even if their application 300 was extended to other contaminants (halogenated aliphatic hydrocarbons, metals, metalloids, radionuclides, pesticides, petroleum hydrocarbons and nutrients) using microorganisms, activated carbon, zeolites, peat, saw dust and oxygen releasing compounds, amongst others. ...
Anthropogenic pollution coming from industrial processes, agricultural practices and consumer products, results in the release of toxic substances into rural and urban environments. Once released, these chemicals migrate through the atmosphere and water, and find their way into matrices such as sediments and groundwaters, thus making large areas potentially uninhabitable. Common pollutants, including heavy metal(loid)s, radionuclides, aliphatic hydrocarbons and halogenated organics, are known to adversely affect physiological systems in animal species. Pollution can be cleaned up using techniques such as coagulation, reverse osmosis, oxidation and biological methods, among others. The use of nanoparticles (NPs) extends the range of available technologies and offers particular benefits, not only by degrading, transforming and immobilizing contaminants, but also by reaching inaccessible areas and promoting biotic degradation. The development of NPs is understandably heralded as an environmentally beneficial technology; however, it is only now that the ecological risks associated with their use are being evaluated. This review presents recent developments in the use of engineered NPs for the in situ remediation of two paramount environmental matrices: soils and groundwaters. Emphasis will be placed on (i) the successful applications of nano-objects for environmental cleanup, (ii) the potential safety implications caused by the challenging requirements of [high reactivity toward pollutants] vs. [none reactivity toward biota], with a thorough view on their transport and evolution in the matrix, and (iii) the perspectives on scientific and regulatory challenges. To this end, the most promising nanomaterials will be considered, including nanoscale zerovalent iron, nano-oxides and carbonaceous materials. The purpose of the present review is to give an overview of the development of nanoremediators since they appeared in the 2000s, from their chemical modifications, mechanism of action and environmental behavior to an understanding of the problematics (technical limitations, economic constraints and institutional precautionary approaches) that will drive their future full-scale applications.
... Given that under natural conditions Fe 0 is corroded only by protons from water dissociation (Eq. 1) 29 , Miyajima and Noubactep 30 argued that reactivity loss is a mirage. In fact, "reactivity loss" has also occurred in Fe 0 -based permeable reactive barriers successfully working for up to two decades [31][32][33][34] . On the other hand, Roh et al. 35 reported on Fe 0 specimens from World War I still corroding in soils. ...
Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx). In this study, a ternary Fe0/MnOx/sand system is characterized for its discoloration efficiency of methylene blue (MB) in quiescent batch studies for 7, 18, 25 and 47 days. The objective was to understand the fundamental mechanisms of water treatment in Fe0/H2O systems using MB as an operational tracer of reactivity. The premise was that, in the short term, both MnO2 and sand delay MB discoloration by avoiding the availability of free iron corrosion products (FeCPs). Results clearly demonstrate no monotonous increase in MB discoloration with increasing contact time. As a rule, the extent of MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the vessels (test-tubes). The presence of MnOx and sand enabled the long-term generation of iron hydroxides for MB discoloration by adsorption and co-precipitation. Results clearly reveal the complexity of the Fe0/MnOx/sand system, while establishing that both MnOx and sand improve the efficiency of Fe0/H2O systems in the long-term. This study establishes the mechanisms of the promotion of water decontamination by amending Fe0-based systems with reactive MnOx.
... Further mechanistic discussions have culminated in the erroneous recognition by O'Hannesin and Gillham[60] that the reductive transformation model was "a broad consensus". Nevertheless, the majority of active researchers are still considering the reductive transformation theory as scientifically established[61][62][63][64]. ...
Keeping up-to-date with the literature is a great challenge for all scientists because analyzing and sorting published data can be very laborious and time-consuming. With the use of metallic iron (Fe⁰) in environmental remediation, scientists are facing such a challenging situation. Without an appropriate background, it can be very difficult to discern which information is plausible and which one is not. This communication demonstrates how the chemistry of aqueous iron corrosion (Fe⁰/H2O system) facilitates a critical assessment of the literature on the decontamination of waters polluted with metals and metalloids. It is reiterated that the pH-dependent solubility of iron and the extent of the oxidation from FeII to FeIII species determine the extent of contaminant mitigation in Fe⁰/H2O systems. Future remediation Fe⁰/H2O systems should be designed based on the science of iron corrosion under aqueous conditions.
Water pollution is calling for a sustainable remediation method such as the use of metallic iron (Fe ⁰ ) to reduce and filter some pollutants, yet the reactivity and hydraulic conductivity of iron filters decline over time under field conditions. Here we review iron filters with focus on metallic corrosion in porous media, flaws in designing iron filters, next-generation filters and perspectives such as safe drinking water supply, iron for anaemia control and coping with a reactive material. We argue that assumptions sustaining the design of current Fe ⁰ filters are not valid because proposed solutions address the issues of declining iron reactivity and hydraulic conductivity separately. Alternatively, a recent approach suggest that each individual Fe ⁰ atom corroding within a filter contributes to both reactivity and permeability loss. This approach applies well to alternative iron materials such as bimetallics, composites, hybrid aggregates, e.g. Fe ⁰ /sand, and nano-Fe ⁰ . Characterizing the intrinsic reactivity of individual Fe ⁰ materials is a prerequisite to designing sustainable filters. Indeed, Fe ⁰ ratio, Fe ⁰ type, Fe ⁰ shape, initial porosity, e.g. pore size and pore size distribution, and nature and size of admixing aggregates, e.g. pumice, pyrite and sand, are interrelated parameters which all influence the generation and accumulation of iron corrosion products. Fe ⁰ should be characterized in long-term experiments, e.g. 12 months or longer, for Fe dissolution, H 2 generation and removal of contaminants in three media, i.e., tap water, spring water and saline water, to allow reactivity comparison and designing field-scale filters.
Quiescent batch experiments were conducted to evaluate the influences of Cl–, F–, HCO3–, HPO42–, and SO42– on the reactivity of metallic iron (Fe0) for water remediation using the methylene blue (MB) method. Strong discoloration of MB indicates high availability of solid iron corrosion products (FeCPs). Tap water was used as an operational reference. Experiments were carried out in graduated test tubes (22 mL) for up to 45 d, using 0.1 g of Fe0 and 0.5 g of sand. Operational parameters investigated were (i) equilibration time (0 to 45 d), (ii) 4 different types of Fe0, (iii) anion concentration (10 values), and (iv) use of MB and Orange II (O-II). The degree of dye discoloration, the pH, and the iron concentration were monitored in each system. Relative to the reference system, HCO3– enhanced the extent of MB discoloration, while Cl–, F–, HPO42–, and SO42– inhibited it. A different behavior was observed for O-II discoloration: in particular, HCO3– inhibited O-II discoloration. The increased MB discoloration in the HCO3– system was justified by considering the availability of FeCPs as contaminant scavengers, pH-increase, and contact time. The addition of any other anion initially delays the availability of FeCPs. Conflicting results in the literature can be attributed to the use of inappropriate experimental conditions. The results indicate that the application of Fe0–based systems for water remediation is a highly site-specific issue which has to include the anion chemistry of the water.
Metallic iron (Fe0) is readily available worldwide and it has shown promise for water treatment in filtration systems. Fe0 filters remove physical contamination (e.g. colloids, suspended particles), pathogens (e.g. bacteria, viruses), and micro-pollutants (e.g. arsenic, nitrate, pesticides, pharmaceuticals) from polluted waters. Accordingly, Fe0 filters can be used for water treatment applications where other materials (e.g. activated carbon, biochar, bone char) are economically or logistically infeasible. Therefore, Fe0 filters are a good candidate to help low-income communities in their efforts to achieve universal access to safe drinking water by 2030. The objective of this chapter is to summarize available knowledge on the design of Fe0 filters in order to booster their large scale application at household and small community levels. Optimal conditions for Fe0 filters include the rational choice of the used materials building the reactive zone (Fe0 and other aggregates), the Fe0 ratio in the reactive zone, the Fe0 mass (e.g. size of the filter or number of filters in series), and the contact time (flow velocity). The proper combination of these design parameters is discussed. Results show that: (i) all reactive Fe0 can be used for efficient water filters, (ii) only porous Fe0 materials are suitable for sustainable water filters, (iii) well-designed hybrid Fe0/aggregate systems are also sustainable, (iv) the major limitation of Fe0 filters is the lack of knowledge on the long-term corrosion rate. Future research efforts should last for months or years.
Advances in Drinking Water Purification
Small Systems and Emerging Issues
1st Edition - January 17, 2024
Editor: Sibdas Bandyopadhyay
Paperback ISBN: 9780323917339
9 7 8 - 0 - 3 2 3 - 9 1 7 3 3 - 9
eBook ISBN: 9780323972024
Description
Advances in Drinking Water Purification: Small Systems and Emerging Issues captures the knowledge and impact on the performance of various types of water purification technologies and identities the need for further development with a view to carry forward the SDG global targets of achieving safe and affordable drinking water. The book bridges the knowledge gap between various types of treatability options which is essential for selection of suitable treatment systems and augmentation in the desirable levels of specific contaminants. It focuses on providing the scope of selecting location specific technology options by presenting multiple approaches for treatment of most crucial toxic contaminants/pathogens.
In addition, it provides insights into the effect of nature of impurities and selection of treatment options on the global quality of drinking water, comprising its possible impacts on the efficiency of the techniques used and thus on the safety of drinking water. This information is indispensable in identifying the appropriate technology depending on the socioeconomic conditions to address the problem of decontamination in drinking water.
Permeable concrete is a class of materials that has long been tested and implemented to control water pollution. Its application in low-impact development practices has proved its efficiency in mitigating some of the impacts of urbanization on the environment, including urban heat islands, attenuation of flashfloods, and reduction of transportation-related noise. Additionally, several research efforts have been directed at the dissemination of these materials for controlling pollution via their use as permeable reactive barriers, as well as their use in the treatment of waste water and water purification. This work is focused on the potential use of these materials as permeable reactive barriers to remediate ground water and treat acid mine drainage. In this respect, advances in material selection and their proportions in the mix design of conventional and innovative permeable concrete are presented. An overview of the available characterization techniques to evaluate the rheology of the paste, hydraulic, mechanical, durability, and pollutant removal performances of the hardened material are presented and their features are summarized. An overview of permeable reactive barrier technology is provided, recent research on the application of permeable concrete technology is analyzed, and gaps and recommendations for future research directions in this field are identified. The optimization of the mix design of permeable reactive concrete barriers is recommended to be directed in a way that balances the performance measures and the durability of the barrier over its service life. As these materials are proposed to control water pollution, there is a need to ensure that this practice has minimal environmental impacts on the affected environment. This can be achieved by considering the analysis of the alkaline plume attenuation in the downstream environment.
We report on the potential of elevated groundwater temperatures and zero-valent iron permeable reactive barriers (ZVI PRBs), for example, through a combination with underground thermal energy storage (UTES), to achieve enhanced remediation of chlorinated hydrocarbon (CHC) contaminated groundwater. Building on earlier findings concerning deionized solutions, we created a database for mineralized groundwater based on temperature dependence of tetrachloroethylene (PCE) degradation using two popular ZVIs (i.e., Gotthart-Maier cast iron [GM] and ISPAT sponge iron [IS]) in column experiments at 25 °C-70 °C to establish a temperature-dependent ZVI PRB dimensioning approach. Scenario analysis revealed that a heated ZVI PRB system in a moderate temperature range up to 40 °C showed the greatest efficiency, with potential material savings of ~55% to 75%, compared to 10 °C, considering manageability and longevity. With a 25 °C-70 °C temperature increase, rate coefficients of PCE degradation increased from 0.4 ± 0.0 h-1 to 2.9 ± 2.2 h-1 (GM) and 0.1 ± 0.1 h-1 to 1.8 ± 0.0 h-1 (IS), while TCE rate coefficients increased from 0.6 ± 0.1 h-1 to 5.1 ± 3.9 h-1 at GM. Activation energies for PCE degradation yielded 32 kJ mol-1 (GM) and 56 kJ mol-1 (IS). Temperature-dependent anaerobic iron corrosion was key in regulating mineral precipitation and passivation of the iron surface as well as porosity reduction due to gas production.
Granular metallic iron (gFe0) materials have been widely used for eliminating a wide range of pollutants from aqueous solutions over the past three decades. However, the intrinsic reactivity of gFe0 is rarely evaluated and existing methods for such evaluations have not been standardized. The aim of the present study was to develop a simple spectrophotometric method to characterize the intrinsic reactivity of gFe0 based on the extent of iron dissolution in an ascorbic acid (AA-0.002 M or 2 mM) solution. A modification of the ethylenediaminetetraacetic acid method (EDTA method) is suggested for this purpose. Being an excellent chelating agent for FeII and a reducing agent for Fe III , AA induces the oxidative dissolution of Fe0 and the reductive dissolution of FeIII oxides from gFe0 specimens. In other words, Fe0 dissolution to FeII ions is promoted while the further oxidation to FeIII ions is blocked. Thus, unlike the EDTA method that promotes Fe0 oxidation to FeIII ions, the AA method promotes only the formation of FeII species, despite the presence of dissolved O2. The AA test is more accurate than the EDTA test and is considerably less expensive. Eight selected gFe0 specimens (ZVI1 through ZVI8) with established diversity in intrinsic reactivity were tested in parallel batch experiments (for 6 days) and three of these specimens (ZVI1, ZVI3, ZVI5) were further tested for iron leaching in column experiments (for 150 days). Results confirmed the better suitability (e.g. accuracy in assessing Fe0 dissolution) of the AA test relative to the EDTA test as a powerful screening tool to select materials for various field applications. Thus, the AA test should be routinely used to characterize and rationalize the selection of gFe0 in individual studies.
The concept that metallic iron (Fe0) is a reducing agent under environmental conditions has urged the large-scale application of Fe0 filters for environmental remediation and water treatment. During the past two decades, some 3,000 scientific articles have widely discussed the importance of processes yielding water treatment in Fe0/H2O systems. The current state-of-the-art knowledge is that Fe0 is the generator of (i) contaminant scavengers (iron hydroxides/oxides), and (ii) reducing agents (e.g. H/H2, FeII, green rusts, Fe3O4). In other words, contaminant reductive transformation in the presence of Fe0 is not mediated by electrons from the metal body (direct reduction).
The realization that Fe0 is not the reducing agent in Fe0/H2O systems has redirected fundamental researches on the operating mode of Fe0 filters. In this effort, a cationic azo dye (methylene blue, MB) has been presented as reactivity indicator to characterize changes in Fe0/H2O systems. The present study investigates the impact of contact time on the efficiency of Fe0/H2O systems. The research questions are "is there any direct relationship between experimental duration and system's efficiency?" If yes, how is the efficiency modified in the presence of natural additives such as manganese oxides (MnO2) and sand? Both research questions are justified by the evidence that the Fe0 surface is constantly shielded by an oxide scale which has been reported to mediate a 'reactivity loss' of Fe0 materials.
The methodology consists of (i) varying the experimental duration, and (ii) modifying the Fe0/H2O system by amending it with various amounts of MnO2 and sand. The efficiency of Fe0/sand/MnO2 systems for water treatment is characterized using methylene blue (MB) as reactivity indicator. Batch experiments using various weight ratios of Fe0 and the two additives were performed for up to six weeks (47 days). The impact of the intrinsic reactivity of MnO2 was characterized by using different types of MnO2. The MB discoloration process was investigated both under shaking and non-disturbed conditions.
The results clearly demonstrate the impact of increased contact time on the extent of MB discoloration in all tested systems (Fe0, Fe0/sand, Fe0/MnO2 and Fe0/sand/MnO2). As a rule, MB discoloration was improved by increased experimental duration. It was noted that the extent of MB discoloration is influenced by the diffusive (or advective) transport of MB from the solution to the reactive materials at the bottom of the test tubes. Without shaking, more time is needed for the transport of MB to the particles of tested materials. For experiments lasting for longer times, sand addition prevented Fe0 particles from compaction (cementation) at the bottom of the test-tubes. This enabled the long-term generation of iron hydroxides (new iron corrosion products) for the discoloration of MB by adsorption and co-precipitation. The same observation was made for Fe0/MnO2 systems. In other words, the addition of non-expansive materials (e.g. MnO2, sand) is necessary to sustain the efficiency of Fe0 filters. Shaking the test tubes increased the extent of MB discoloration by two different mechanisms: (i) speeding up the mass transport of MB solution towards the adsorptive materials, and (ii) speeding up the kinetics of Fe0 corrosion, creating new corrosion products. Discoloration processes occur due to MB diffusion and advection which are accelerated during the shaking operation. The results clearly delineate the complexity of the Fe0/MnO2/sand system and suggest that varying the experimental conditions will give more opportunities to discuss the efficiency of Fe0/H2O systems.
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 effects of rising groundwater temperatures on zerovalent iron (ZVI)-based remediation techniques will be critical in accelerating chlorinated hydrocarbon (CHC) degradation and side reactions. Therefore, tetrachloroethylene (PCE) degradation with three ZVIs widely used in permeable reactive barriers (Gotthart-Maier cast iron [GM], Peerless cast iron [PL], and ISPAT sponge iron [IS]) was evaluated at 10-70 °C in deionized water. From 10 to 70 °C, PCE degradation half-lives decreased from 25 ± 2 to 0.9 ± 0.1 h (PL), 24 ± 3 to 0.7 ± 0.1 h (GM), and 2.5 ± 0.01 to 0.3 ± 0.005 h (IS). Trichloroethylene (TCE) degradation half-lives at PL and GM decreased from 14.3 ± 3 to 0.2 ± 0.1 h (PL) and 7.6 ± 2 to 0.4 ± 0.1 h (GM). This acceleration of CHC degradation and the stronger shift toward reductive β-elimination reduced the concentration of potentially harmful metabolites with increasing temperatures. PCE and TCE degradation yields an activation energy of 28 (IS), 58 and 40 kJ mol-1 (GM), and 62 and 53 kJ mol-1 (PL). Hydrogen gas production by ZVI corrosion increased by 3 orders of magnitude from 10 to 70 °C, and an increased chance of gas clogging was observed at high temperatures.
Soil pollution is one of the main environmental issues worldwide. The intensive use of the soil for industrial and agricultural purposes increases the necessity of recovering brownfields and other polluted emplacements. There are many remediation technologies used until now for this aim, with nanoremediation and bioremediation being the most successful ones in terms of effectiveness and cost. On the one hand, zerovalent iron nanoparticles and their derivatives have been described as highly favorable remediation agents, being extensively used in soil and groundwater remediation. On the other hand, bioremediation, compared with nanoremediation that requires more time to reduce the same amount of pollutants, has many biological benefits, including making the soil ready for reuse. Considering the advantages and disadvantages of both technologies, a combined technology known as nanobioremediation has been developed, which acts as an extremely interesting alternative to merge the main advantages of nano- and bioremediation. In this chapter, the main aspects of nanoremediation and bioremediation are reviewed, and some examples of their use on full-scale applications are described. Finally, the application of a combined method, that is, nanobioremediation, is described.
In this study, the author’s experience in the estimation of concrete strength by rebound hammer (RH) and ultrasonic pulse velocity (UPV) test is summarized and compared with destructive laboratory tests. In the destructive testing of concrete, only the impact resistance, ductility, yield strength can be obtained, whereas, through the non-destructive techniques (NDT) testing, discontinuities such as voids, cracks, and differences in material characteristics such as high strength materials or low strength materials can be more effectively attained and material under test can still be utilized after inspection. A various selection of NDT testing is available which can be used to provide information regarding the condition of the material and several other approaches can be used to derive the strength of material through NDT testing. To perform the test, samples of concrete blocks were prepared and kept under various curing conditions for assorted periods of time. Multiple tests were carried out under various conditions of various aged samples. Measurements and results from NDT are indicative of the properties of concrete such as porosity, the complexity of the pore network, water content, and strength. Samples that returned with the highest rebound number and peak compressive strength values using the RH test came from samples that were left for the first 14 days under adequate curing conditions with additional 14 days of dry conditions. Another condition that obtained peak results was the samples that were buried in the earth for 14 days as a means of curing. In the UPV testing, the strength depends on the aging of the concrete rather than the total curing days. In comparison with samples containing voids tested, it is found that as the voids are larger the UPV reading was more accurate which is indicative that NDTs have flaws that need to be taken into consideration.
Keywords:
Non-destructive testing Varied curing Buried moisture curing Hammer test Pulse velocity
The cement-based binder is mostly used in concrete. However, the production of CEM-I causes a significant amount of CO2 emission in the environment and requires a lot of energy. According to Portland Cement Association (PCA), on average 927 kg of CO2 is being emitted for every 1000 kg of CEM-I produced in the U.S. Geopolymer is an innovative and environment-friendly building material and an alternative to Portland cement. The use of a geopolymer can decrease CEM-I demand and make the construction industry more sustainable. Fly ash is an industrial by-product generally produced from a coal-based power plant. The geopolymerization reaction of fly ash with an alkaline solution of NaOH and Sodium Silicate can be used as a binder for the production of eco-friendly concrete. It is evident from the literature that geopolymer mortars achieve better strength with lower water content in the mix. However, lower water content also reduces workability. This study aimed to evaluate the influence of activator concentration and commercial superplasticizers’ dose on the workability and compressive strength of fly ash-based geopolymer paste and mortar specimens. PCE-based superplasticizer was used to assess its effect on fly ash-based geopolymer paste and mortars with lowered water content. The result demonstrates the effectiveness of up to 2% dose of PCE admixture in the geopolymer system. The best results were found in the samples containing 12 M activator concentration. Higher activator concentration not only influenced the workability, but also affected other properties of geopolymer mortar. Heat curing was found effective for improving the early strengths of both geopolymer pastes and mortars. However, high temperature may introduce adverse effects in geopolymer pastes by dry shrinkage and swelling.
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.
Groundwater is one of the prominent sources of usable water for human beings across the globe. The quality of groundwater is being compromised due to the advent of harmful pollutants from natural and anthropogenic activities sourced from rapid urbanization and industrialization. Many treatment techniques like oxidation, precipitation, coagulation, disinfection, adsorption, ion exchange, etc., using various chemicals like chlorine, ozone, aluminium sulphate, ferrous chloride, sodium aluminate, activated carbon, activated alumina, zeolites, iron, natural clay, etc., are in practice for groundwater remediation. One such prominent material, which imparts one or a combination of adsorption, reduction, oxidation, precipitation, and co‐precipitation principles for multi‐contaminant removal from groundwater is zero‐valent iron (ZVI). ZVI is widely used for removal of metalloids (As), heavy metals (Cr, Ni, Pb, Zn), nitrates, phosphates, chloro‐organic compounds, nitro amino compounds, dyes, phenol compounds, etc. This unique material, ZVI, possesses several advantages, including high reactivity, wide availability, multi‐component removal, no sludge, flexibility, low cost and technology ease, and few limitations of thick oxide formation, foreign particle hurdle, and narrow pH operation. This chapter showcases the usage of ZVI in groundwater remediation. More focus is laid to elucidate the synthesis and mechanism of ZVI, along with various research works reported. Recent advancements in ZVI research are inclined towards the synthesis of novel and modified ZVI and the future of ZVI technology is in its usage along with proper support of physical, chemical, or a combination of technologies, as well as its integration with other water treatment technologies to achieve superior contaminant removal from groundwater.
Increasing groundwater temperatures caused by global warming, subsurface infrastructure, or heat storage projects may interfere with groundwater remediation techniques using zero-valent iron (ZVI) technology by accelerating anaerobic corrosion. The corrosion behavior of three ZVIs widely used in permeable reactive barriers (PRBs), Peerless cast iron (PL), Gotthart-Maier cast iron (GM), and an ISPAT iron sponge (IS), was investigated at temperatures between 25 and 70 °C in half-open batch reactors by measuring the volume of hydrogen gas generated. Initially, the corrosion rates of all tested ZVIs increased with temperature; at temperatures ≤40 °C, a material-specific steady state is reached, and at temperatures >40 °C, passivation causes a decrease in long-term corrosion rates. The observed corrosion behavior was therefore assumed to be superimposed by accelerating and inhibiting effects, caused by surface precipitates where the fitting of measured corrosion rates by a modeling approach, using the corroded amount of Fe0 to account for passivating minerals, yields intrinsic activation energies (Ea, ZVI) of 81, 90, and 107 kJ mol-1 for IS, GM, and PL, respectively. An increase in H2 production might not be directly transferable to an increase in general ZVI reactivity; however, the results suggest that an increase in chlorinated hydrocarbon degradation rates can be expected for ZVI-PRBs in the immediate vicinity of low-temperature underground thermal energy storages (UTESs) or in the impact areas of high-temperature UTES with temperatures of ≤40 °C.
The evidence that metallic iron (Fe ⁰ ) is not an environmental reducing agent has been declared to be a claim. 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 Fe ⁰ remediation community is alien to graduate chemists, as it is a century old electrochemistry knowledge. Nevertheless, the peer review literature on "remediation using Fe ⁰ " seems to be aggressively controlled by self-appointed experts (e.g., journal editors) who are not tolerating any alternative thinking. This communication demonstrates the fallacy of the view that Fe ⁰ donates any electron to a dissolved species. The sole goal is to reconcile a proven efficient technology with his scientific roots, and enable the design of better Fe ⁰ remediation systems.
The degradation of refractory organics to harmless substances is one of the major concerns of some researchers. An emerging advanced oxidation process (AOP) is effective in generating sulfate radicals (SRs) capable of degrading organics. SRs have higher oxidation potentials and longer half-lives than hydroxyl radicals (HRs) appearing in traditional AOP. However, SRs can only be produced on-site by activating the oxidant. Persulfate (PS) is a strong oxidant which can be activated by nano-Fe⁰ to generate SRs due to high reactivity of nano-Fe⁰. At present, some researchers have used the nano-Fe⁰/PS process to treat refractory organics, and achieved more research results. This review in detail describes the characteristics of nano-Fe⁰ and PS, elaborates the mechanisms of activating PS by nano-Fe⁰ and nano-Fe⁰composites, discusses the reaction conditions in activating PS for refractory organics removal, and proposes some recommendations for future studies of nano-Fe⁰/PS system.
A large-scale field experiment on natural gradient transport of solutes in groundwater has been conducted at a site in Borden, Ontario. Well-defined initial conditions were achieved by the pulse injection of 12 m3 of a uniform solution containing known masses of two inorganic tracers (chloride and bromide) and five halogenated organic chemicals (bromoform, carbon tetrachloride, tetrachloroethylene, 1,2-dichlorobenzene, and hexachloroethane). A dense, three-dimensional array of over 5000 sampling points was installed throughout the zone traversed by the solutes. Over 19,900 samples have been collected over a 3-year period. The tracers followed a linear horizontal trajectory at an approximately constant velocity, both of which compare well with expectations based on water table contours and estimates of hydraulic head gradient, porosity, and hydraulic conductivity. The vertical displacement over the duration of the experiment was small. Spreading was much more pronounced in the horizontal longitudinal than in the horizontal transverse direction; vertical spreading was very small. The organic solutes were retarded in mobility, as expected.
The attention of environmental decision makers is increasingly being focused on the movement of pollutants into ground water. Of particular importance is the transport and speciation of metals. The MINTEQA2 model is a versatile, quantitative tool for predicting the equilibrium behavior of metals in a variety of chemical environments. MINTEQA2 is a geochemical speciation model capable of computing equilibria among the dissolved, adsorbed, solid, and gas phases in an environmental setting. MINTEQA2 includes an extensive database of reliable thermodynamic data that is also accessible to PRODEFA2, an interactive program designed to be executed prior to MINTEQA2 for the purpose of creating the required MINTEQA2 input file. The report describes how to use the MINTEQA2 model. The chemical and mathematical structure of MINTEQA2 and the structure of the database files also are described. The use of both PRODEFA2 and MINTEQA2 are illustrated through the presentation of an example PRODEFA2 dialogue reproduced from interactive sessions and the presentation of MINTEQA2 output files and error diagnostics. The content and format of database files also are explained.
Walls constructed of a new type of steel sheet piling with joints that can be sealed after driving serve to contain zones of contamination so that contaminants will not migrate offsite and to provide an isolated subsurface environment in which subsurface remediation technologies can be applied with excellent environmental safety. The sheet pile joints incorporate a cavity that can be filled with sealant after driving, and that provide access for quality control operations. Both the single and double cavity versions are well-suited to non-conventional configurations that provide a very high degree of containment.
In 1980, the United States Congress passed the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), requiring cleanup of abandoned hazardous waste sites, and in 1984, amended the Resource Conservation and Recovery Act (RCRA) to require cleanup of contamination at active sites. These legislative actions were prompted by several occurrences of groundwater contamination by hazardous materials; the most highly publicized being the Love Canal incident in Niagara Falls, New York. Thus, within a remarkably short period of time, groundwater remediation emerged as an activity of national priority. A recent and comprehensive report of the U.S. National Academy of Science (NAS, 1994) discusses the history, methods and performance of groundwater remediation efforts in the U.S. over the intervening fifteen years.
Flow-through column tests were conducted to investigate the products of degradation of aqueous trichloroethene (TCE) in contact with granular iron metal. The results indicated the degradation process to be pseudo-first-order and the rate constant to be relatively insensitive to the initial concentration of TCE over the range from about 1.3 to 61 mg/L. The principal degradation product was ethene, followed by ethane with substantially smaller amounts of other C1−C4 hydrocarbons. About 3.0−3.5% of the initial TCE appeared as chlorinated degradation products, including the three dichloroethene isomers and vinyl chloride. Although the chloride mass balance was generally between 98 and 102%, a maximum of 73% of the carbon could be accounted for in the identified products. Based on the low concentrations of chlorinated degradation products in the solution phase, it is proposed that most of the TCE remains sorbed to the iron surface until complete dechlorination is achieved.
A combination of new and previously reported data on the kinetics of dehalogenation by zero-valent iron (Fe0) has been subjected to an analysis of factors effecting contaminant degradation rates. First-order rate constants (kobs) from both batch and column studies vary widely and without meaningful correlation. However, normalization of these data to iron surface area concentration yields a specific rate constant (kSA) that varies by only 1 order of magnitude for individual halocarbons. Correlation analysis using kSA reveals that dechlorination is generally more rapid at saturated carbon centers than unsaturated carbons and that high degrees of halogenation favor rapid reduction. However, new data and additional analysis will be necessary to obtain reliable quantitative structure−activity relationships. Further generalization of our kinetic model has been obtained by accounting for the concentration and saturation of reactive surface sites, but kSA is still the most appropriate starting point for design calculations. Representative values of kSA have been provided for the common chlorinated solvents.
Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100-mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first-order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
The occurrence of groundwater contamination by chlorinated solvents is widespread throughout the industrialised world. Because these solvents have a density greater than water, the sources of contaminant groundwater plumes in many cases are expected to be pools and zones of residual solvent that are located below the water table. A tracer experiment designed to provide a simplified simulation of the above scenario has been conducted at the University of Waterloo Borden field site. A homogeneous block of sand containing residual solvent at 5% residual saturation of the pore space was emplaced 1 m below the water table. This source zone measured 1.5 × 1 × 0.5 m and contained a mixture of chloroform (TCM), trichloroethylene (TCE), perchloroethylene (PCE) and gypsum powder to provide sulfate as a conservative inorganic tracer. Subsequent groundwater flow through the source zone created a continuous plume of dissolved solutes down-gradient. The plume was monitored by a three-dimensional array of over 2300 sampling points and after 15 months extended 60 m from the source. This paper presents an overview of the experiment, with field results of source dissolution and dissolved-phase plume transport. The field results were selected to give an indication of the complexity of the observed field data. Some preliminary modeling of the data to estimate the approximate magnitude of dispersion parameters and comparison of these values with other tracer tests is presented.
Solute sorption in aquifer systems is significantly affected by processes which occur at the scale of individual solid particles, such that proper physical characterization of the solids is requisite to fully understanding solute transport. Methods for characterizing grains of sandy aquifer material with respect to physical properties relevant to sorption are described and assessed. The properties include particle density, porosity, pore size distribution, specific surface area, and carbon content. Because intraparticle porosity, specific surface area, and organic carbon are quite low for sandy materials, methods routinely used for characterizing solids must be carefully evaluated and adapted for use on aquifer solids. The methods considered here were applied to aquifer material acquired at a site in Borden, Ontario, where numerous transport studies have been conducted. Results with well-characterized model solids are also included, as appropriate, for method evaluation.Results with the Borden solids are reported for eight size fractions and for the homogenized bulk material. Mineralogical characterization of the fractions served as an indispensable complement to the physical characterization methods. Pulverization of samples in a shatterbox was shown to be useful for homogenizing samples and reducing variability. We found a modified dry combustion method to be superior to wet oxidation for determining organic carbon. Surface area measurements were indicative of significant internal porosity, and pore size distributions obtained by gas adsorption and mercury porosimetry were found to be consistent and complementary. For the Borden material—which has an immeasurably low clay mineral content—specific surface area, intraparticle porosity, and organic carbon content were all greatest in the larger size fractions.
Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.
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.
Ph.D. Environmental Science and Engineering Reductive dehalogenation is an important reaction that generally leads to detoxification of many halogenated methanes. Halogenated methanes are widely used in industrial and commercial applications and the inadvertent or deliberate release of these chemicals has caused contamination of the atmosphere, soil and groundwater. The research presented here details the study of several systems for reductive dehalogenation of chlorinated methanes. The first system described in this dissertation involves reductive dechlorination of chlorinated methanes by laboratory cultures of methanogens. A vessel was constructed that allowed maintenance of anaerobic conditions and minimized losses of the volatile chlorocarbons. Methylene chloride was not dechlorinated in the presence of pure cultures of methanogens. Similarly, dechlorination did not occur in enrichments made with samples from several different anaerobic digesters. Abiotic dehalogenation studies showed that cobalamins, cobalt-centered macrocyclic compounds, catalyzed the reductive dechlorination of several halomethanes in anaerobic, closed batch systems. These studies focused on immobilization of cobalamins to several types of supports for use in pollution remediation strategies. Cyanocobalamin bound to Epoxy-Activated Sepharose 6B and talc catalyzed the rapid reduction of carbon tetrachloride and methylene chloride to sequentially reduced products. Corroding iron metal was also studied as a reductant for halogenated methanes. Several chlorinated methanes were reductively dechlorinated in closed, anaerobic, laboratory-scale model systems containing granular iron. Carbon tetrachloride was sequentially dehalogenated, via chloroform, to methylene chloride. The initial rate of each reaction was pseudo-first order in substrate and declined substantially with each dehalogenation step. Trichloroethene was also dechlorinated by iron, although more slowly than carbon tetrachloride. The reaction of chlorinated methanes appears to involve a direct interaction between the substrate and the iron surface. When surface condition is constant, the rate of reaction is roughly first-order in iron surface area and the rate increases markedly with increasing iron surface area. Studies were also performed to determine the effects of microbial and geochemical processes that developed during a field demonstration in which iron metal had been buried in the path of a chlorinated-solvent contaminated plume. Two sets of cores were obtained and examined for microbial and geochemical developments one, and two, years after burial of the iron.
Cover title. Thesis (M.S.)--University of Waterloo, 1993. Includes bibliographical references (leaves 55-56). Photocopy. s
Reductive dechlorination of chlorinated ethenes by iron metal
- T M Sivavec
- . P Homey
A new type of steel sheet piling with sealed joints for ground water pollution control . Paper presented at the 45th Canadian Geotechnical Conference
- R C Starr
- J A Cherry
- E S Vales
Redox-active media selection for permeable reactive barriers
- T M P D Sivavec
- D P Mackenzie
- . S Horney
- Bagel