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Chemistry and Microbiology of Permeable Reactive Barriers for in Situ Groundwater Clean-Up
Critical Reviews In Environmental Science and Technology
Abstract
Permeable reactive barriers (PRBs) are receiving a great deal of attention as an innovative, cost-effective technology for in situ clean up of groundwater contamination. A wide variety of materials are being proposed for use in PRBs, including zero-valent metals (e.g., iron metal), humic materials, oxides, surfactant-modified zeolites (SMZs), and oxygen- and nitrate- releasing compounds. PRB materials remove dissolved groundwater contaminants by immobilization within the barrier or transformation to less harmful products. The primary removal processes include: (1) sorption and precipitation, (2) chemical reaction, and (3) biologically mediated reactions. This article presents an overview of the mechanisms and factors controlling these individual processes and discusses the implications for the feasibility and long-term effectiveness of PRB technologies.
... Certain heavy metals such as arsenic (As), cadmium (Cd), hexavalent chromium (Cr(VI)), lead (Pb), nickel (Ni), uranium (U), zinc (Zn) etc., have also been treated using ZVI that reduces these elements to a lower oxidation state while additionally forming barely soluble compounds, thus precipitating them inside the ZVI wall Pérez et al., 2018;Simon et al., 2004Simon et al., , 2003Wilkin et al., 2014Wilkin et al., , 2005. However, a lower reactivity of various ZVI brands at certain contaminated sites prompted the use of GAC or a permeable pea gravel wall promoting microbiological degradation, especially in Europe, for treating polycyclic aromatic hydrocarbons (PAHs) and/or benzene, toluene, ethylbenzene and xylene (BTEX) Gholami et al., 2019;Gibert et al., 2019;Scherer et al., 2000;Torregrosa et al., 2019). GAC proved to be a promising and effective adsorptive material for the removal of PAHs and special other organic contaminants (Birke et al., 2003). ...
... Several reviews on PRBs have been published in the last few years, however, most of these papers focus on specific issues of ZVI without providing extensive field performance information on various sites around the world (Henderson and Demond, 2007;Korte, 2001;Scherer et al., 2000). However, Birke et al. (2003) provided comprehensive insights into European field-scale PRB applications and their performances after certain years of operations. ...
... However, several heavy metals, even radionuclear elements, have also been remediated at sites such as Elizabeth City, North Carolina and Y-12 Plant, Oak Ridge, respectively, using ZVI through various reductive reactions, but also including precipitation and adsorption (Matheson et al., 2002). Besides cVOCs and certain radioactive heavy metals, ZVI has been applied relatively in very small numbers to some other common heavy metals due to the lack of affordable and sustainable alternative reactive materials at the initial phases of PRB installations (Birke et al., 2003;Scherer et al., 2000;Wilkin and Puls, 2003). Certain research works have addressed the gradual decrease in the long-term performance of ZVI-based PRBs due to reactivity differences of applied different ZVI brands Henderson and Demond, 2007;Li et al., 2019Li et al., , 2016Noubactep et al., 2005;VanStone et al., 2004;Xiao et al., 2022), and uncertain precipitation of secondary contaminants (especially covering carbonates, hydroxides, oxide-hydroxides), which may lead to a decrease in groundwater flow through the barrier due to lower permeability, that is, clogging (Bortone et al., 2013;Canzano et al., 2014;Fang et al., 2021;Flury et al., 2009b;Mittal et al., 2021Mittal et al., , 2020Noubactep, 2008Noubactep, , 2007Pérez et al., 2018;Richards, 2008;Santonastaso et al., 2018b;Wang et al., 2016;Wanner et al., 2013). ...
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.
... In early 1990, Fe 0 was introduced as reducing agent for groundwater remediation in permeable reactive barriers (iron walls). Fe 0 has been proven particularly efficient for the decontamination of halogenated organic compounds (O´Hannesin & Gillham 1998, Scherer et al. 2000, Henderson & Demond 2007, Gillham 2010. Subsequent studies have confirmed the efficiency of Fe 0 for quantitative removal of several substances (and substance classes) including nitrate, bromate, chlorate, nitro aromatics compounds, pathogens, pesticides, arsenic, chromium, copper, lead, triazoles, uranium, and zinc (Bigg & Judd 2000, Scherer et al. 2000, Henderson & Demond 2007, You et al. 2005, Diao & Yao 2009, Pradeep & Anshup 2009, Tellen et al. 2010. ...
... Fe 0 has been proven particularly efficient for the decontamination of halogenated organic compounds (O´Hannesin & Gillham 1998, Scherer et al. 2000, Henderson & Demond 2007, Gillham 2010. Subsequent studies have confirmed the efficiency of Fe 0 for quantitative removal of several substances (and substance classes) including nitrate, bromate, chlorate, nitro aromatics compounds, pathogens, pesticides, arsenic, chromium, copper, lead, triazoles, uranium, and zinc (Bigg & Judd 2000, Scherer et al. 2000, Henderson & Demond 2007, You et al. 2005, Diao & Yao 2009, Pradeep & Anshup 2009, Tellen et al. 2010. Although successful removal of reducible (e.g. ...
... As regarding inorganic contaminants, reductive precipitation (Gu et al. 1998, Puls et al. 1999), co-precipitation (Lackovic et al. 2000, Komnitsas et al. 2006, Noubactep et al. 2006) and adsorption onto iron oxides and oxyhydroxides are considered as major reaction paths. Whether a contaminant is adsorbed, co-precipitated or reduced, it should not be remobilized under field conditions (Scherer et al. 2000). This prerequisite makes co-precipitation the most suitable removal mechanism as slowly precipitated iron oxides are not likely to be dissolved under natural conditions (Heron et al. 1994). ...
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.
... PRBs are defined as an in situ remediation zone in which contaminants are passively captured, removed or broken down while it allows uncontaminated water to pass through. The primary removal method is either physical (sorption, precipitation), chemical (ion exchange) or biological [49][50][51][52]. ...
... When physical or chemical remediation of groundwater shows little or no degradation of contaminants, then degrading pollutants with a biological oxidation process may be helpful. Many pollutants such as chlorinated solvents tend to be easily reduced if oxidized; here, microorganisms will perform a reduction process by exploiting contaminants as their main source for energy and the required materials to synthesize their cells [49]. The bioremediation technique is a very effective remediation process based upon the degradation of contaminants by microorganisms; remediation efficiency in this process depends on the working environment, such as the temperature, pH, electron acceptors and the concentration of nutrients [68]. ...
... In the groundwater, the presence of oxygen is usually little; in this case, the anaerobic microbes electron acceptors is utilized. However, it is effective to remediate groundwater contaminated by monoaromatic hydrocarbons by using oxygen-releasing compounds in the PRBs [49,56,69]. ...
The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people’s lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier’s use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants’ uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.
... W. Blowes et al., 2000;D. Blowes et al., 1995;Henderson & Demond, 2007;Liu et al., 2013;Savard et al., 2010;Scherer et al., 2000;Wilson & Mackay, 1995). According to USEPA 2002USEPA & 2005, it also serves as a water resource conservation method as no water is removed from the aquifer and all water that passes through the PRB is returned to the native aquifer in a cleaner form. ...
... According to USEPA 2002USEPA & 2005, it also serves as a water resource conservation method as no water is removed from the aquifer and all water that passes through the PRB is returned to the native aquifer in a cleaner form. (USEPA, 2009;Henderson & Demond, 2007;Liu et al., 2013;Savard et al., 2010;Scherer et al., 2000;Wilson & Mackay, 1995) Once installed, PRB does not require above ground facilities or energy inputs, and it can take advantage of the in situ groundwater flow to bring the contaminants in contact with the reactive materials Savard et al., 2010). Therefore, PRB's present a promising fluoride remediation option as they are designed to operate in situ for years with little or no maintenance (Gillham & O'Hannesin, 1994;Gu et al., 1999;Kresic, 2008;Roehl et al., 2005). ...
... Most of the PRB's installed during 1996-2006 used iron based adsorbents. In 2004, out of 200 PRBs worldwide, 120 were iron based (90 in the United States) (Scherer et al., 2000). Zero valent iron, ZVI (Fe 0 ) has been found to be a strong chemical reductant as its reaction can proceed in situ under normal groundwater conditions and is able to convert many mobile oxidized oxyanions and oxy cations into immobile forms, breaks down chlorinated organic compounds (Hashim et al., 2011;Matheson et al., 1994;Roberts et al., 1996) reduces many halogenated methane's, ethane, ethene and other halogenated compounds at ambient temperatures, remediate groundwater contaminated by COCs (Baric et al., 2012;Wilkin et al., 2014) nitrate (Baric et al., 2012;Suthar et al., 2009;Tarkalson et al., 2006;Wick et al., 2012), arsenic (R. C. Liu et al., 2013), and heavy metals (Lu et al., 2012). ...
A wide variety of pump and treat methods like chemical precipitation, adsorption, ion exchange and reverse osmosis have been trialled for many decades for fluoride removal from groundwater, but the problem of fluoride contaminated water remains in many parts of the world largely because these processes require constant monitoring, are expensive to implement and maintain at decentralised scale due to lack of reticulation infrastructure, and possess sludge disposal problem. This paper presents an overview of various fluoride removal processes and the limitations associated with each process and the application of in-situ permeable reactive barrier for remediating fluoride contaminated groundwater is explored, which displays the potential to be a cost effective, low maintenance and energy intensive technology.
... The permeable reactive barrier (PRB)is an alternative solution that exerts less influence on groundwater flow but also performs in-situ remediation. (Scherer et al., 2000);It is also one of the economical methods to contain the contaminants in a complicated geological and hydrogeological conditions (Fronczyk and Garbulewski, 2013). The PRBs are in situ treatment zones capturing a plume of contaminants, confining the movement of contaminants and releasing the treated water (Gillham, 2010). ...
... Zero-valentiron (ZVI) was the first and mainly used in PRB as the reactive material for converting contaminants to nontoxic or immobile species, dehalogenating hydrocarbon sand precipitating anions and oxyanions for grounder water remediation, (United States Environmental Protection Agency, 1998;Scherer et al, 2000;Tratnyek et al, 2003;Gillham et al, 2010); Microorganisms or the material which stimulates the growth of microbes, such as humic materials and oxides, were commonly proposed as biological materials for PRB to remediate the nitrate and sulfate species (United States Environmental Protection Agency, 1998;Scherer et al, 2000);Zeolite was another ideal alternative material for PRB based on its adsorption capacity and high ion exchange capacities (Jorgensen and Weatherley, 2003;Altare et al, 2007;Fronczyk, 2008;Belbase et al, 2013;Joanna et al, 2013). ...
... Zero-valentiron (ZVI) was the first and mainly used in PRB as the reactive material for converting contaminants to nontoxic or immobile species, dehalogenating hydrocarbon sand precipitating anions and oxyanions for grounder water remediation, (United States Environmental Protection Agency, 1998;Scherer et al, 2000;Tratnyek et al, 2003;Gillham et al, 2010); Microorganisms or the material which stimulates the growth of microbes, such as humic materials and oxides, were commonly proposed as biological materials for PRB to remediate the nitrate and sulfate species (United States Environmental Protection Agency, 1998;Scherer et al, 2000);Zeolite was another ideal alternative material for PRB based on its adsorption capacity and high ion exchange capacities (Jorgensen and Weatherley, 2003;Altare et al, 2007;Fronczyk, 2008;Belbase et al, 2013;Joanna et al, 2013). ...
Zeolite and sand mixture is an ideal reactive filling material for the Permeable Reactive barrier (PRB) due to its higher hydraulic conductivity and sorption capacity. This study applied three ASTM standard tests to examine the geotechnical engineering properties of ASTM 20-30 sand and zeolite (clinoptilolite) mixtures with varying zeolite mass percentages (25%, 50% and 75%). Conducted lab tests including: Proctor compaction, hydraulic conductivity in rigid wall permeameter and onedimensional consolidation. The goals of this study were to quantify the impact of zeolite content and compactive effort on the density, conduction and compressibility of the sand-zeolite mixtures.
... The widest implementation of the PRB technology is on remediation of groundwater polluted with oxidized carbon-contaminants (OCC), serving as electron acceptors under reducing conditions, such as chlorinated solvents, which in turn hinders the potential precipitation of natural background elements, such as iron or manganese, clogging the media and reducing efficiency. Nevertheless, reduced carbon-contaminants (RCC), which are common groundwater contaminants such as petroleum hydrocarbons, are more efficiently removed under aerobic biodegradation [7][8][9], imposing a special challenge for the application of PRBBs. Phenolic compounds, which are widely used in the manufacturing of pharmaceuticals, dyes, perfumes, pesticides, lubrication oils, and solvents are common RCCs discharged into the environment. ...
... Whereas most if not all PRBBs reported have been based on bioaugmentation through adsorbed microorganisms [8,9,[11][12][13], we focused on entrapment of bacteria in a confined polymeric matrix in the tents of millimetre range, i.e. macro-encapsulation, thus preventing the biomass from being washed-out. The encapsulation approach implemented in the study was the 'small bioreactor platform' (SBP) using a cellulose-acetate envelope which enables the introduction and maintenance of the augmenting bacterial cultures at high concentration under conditions preserving their long-term activity [14,15]. ...
The present study explored bacterial aerobic biodegradation of reduced carbon-contaminants (RCC) in a pilot system mimicking remediation of a saturated aquifer in a permeable reactive biobarrier (PRBB). Bioaugmentation was performed with a pure culture of Pseudomonas putida macro-encapsulated in a cellulose-acetate porous envelope and integrated transversely to the flow trajectory of the fluid in the biobarrier and compared with controls without capsules. The macro-encapsulation technique applied allowed the incorporation of a built-in nutrient core for the slow release of macronutrients, i.e., N,P, instead of exogenous nutrients supply. 3-Chlorophenol (3CP) at a concentration range of 350-500 mg/L was chosen as an RCC model compound. The findings indicate efficient 3CP biodegradation during the PRBB operation with similar degree of transformation (76±2% and 72±2%) and mineralization (55±4% vs. 49±3%) for exogenous and built-in nutrients supply, respectively. The extent of dechlorination in both cases (54±10% vs. 40±2%, respectively) followed mineralization rather than transformation suggesting that Cl- release took place in late transformation stages. Negligible decontamination was observed in the control system without bioaugmentation. Concluding, tailored PRBB with macro-capsules incorporating a built-in nutrient core to support bacterial growth presents a significant environmental advantage controlling excess nutrients release required in bioremediation of oligotrophic systems.
... This is because if autotrophic denitrification were taken place, the concentration of Fe would remain high (Rysgaard et al. 2001). More so, the top soil is rich in oxygen, which is preferentially utilised over anaerobic electron acceptors like Fe (Scherer et al. 2000). This is because if autotrophic denitrification were taken place, the concentration of Fe would remain high (Rysgaard et al. 2001). ...
... This is because if autotrophic denitrification were taken place, the concentration of Fe would remain high (Rysgaard et al. 2001). More so, the topsoil is rich in oxygen, which is preferentially utilised over anaerobic electron acceptors like Fe (Scherer et al. 2000). The nitrogen transformation process from NO 3 − to either NO 2 − , N 2 or NH 4 + -through denitrification, fixation ammonification and nitrification-is another factor of consideration (Westermann and Ahring 1987). ...
In an effort to determine the reason behind excellent nitrate remediation capacity at Kelantan region, a multivariate approach is employed to evaluate extent to which the influence of sea on soil geochemical composition affect variation pattern of groundwater quality. The results obtained from geochemical analysis of paleo-beach soil in coastal site at Bachok revealed multiple redox activity at different soil strata, involving both heterotrophic and autotrophic denitrification. In soil and water analysis, eight of the fourteen hydro-geochemical parameters (conductivity, temperature, soil texture, oxidation reduction potential, pH, total organic carbon, Fe, Cu, Mn, Cl−, SO42−, NO2−, NO3− and PO43−) measured using standard procedures were subjected to multivariate analysis. Evaluation of general variation pattern across the area reveals that the principal component analysis (PCA), hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA) are in consonance with one another on apportioning three parameters (SO42−, Cl− and conductivity) to the coastal sites and two parameters (Fe and NH4+ or NO3−) to inland sites. The step forward analysis of LDA reveals four parameters in order of decreasing significance as Cl−, Fe and SO42−, while the two-way HCA identifies three clusters on location basis, respectively. In addition to the significant data reduction obtained, the results indicate that proximity to sea and location/geological-based influence are more significant than temporal-based influence in denitrification. By extension, the research reveals that influence of labile portion of natural resources is explorable for broader application in other remediation strategies.
... A number of past reviews can be found on various PRB reactive materials (Blowes et al., 2000, Scherer et al., 2008, Obiri-Nyarko et al., 2014. Reactive materials usually act as chemical and /or biological reagents or catalysts to support the chemical reactions associated to the removal of the target contaminants. ...
... In majority of the PRBs up to date, granular iron media (i.e. Zero Valent Iron (ZVI or Fe 0 )) has been used (Gu et al., 1999, Liang et al., 2000, Scherer et al., 2008, Statham et al., 2016, to treat chlorinated organic contaminants and inorganic contaminants (radionuclides, Ni, Cr, As ,U, Cu, Zn, Pb,Cd,Fe,SO4 2 ). In the case of treating acidic ground water, reactive materials used in most of the past studies were limestone, mixtures of limestone and organic carbon rich materials such as wood chips , municipal compost, paper mill pulp (Obiri-Nyarko et al., 2014). ...
... A number of past reviews can be found on various PRB reactive materials (Blowes et al., 2000, Scherer et al., 2008, Obiri-Nyarko et al., 2014. Reactive materials usually act as chemical and /or biological reagents or catalysts to support the chemical reactions associated to the removal of the target contaminants. ...
... In majority of the PRBs up to date, granular iron media (i.e. Zero Valent Iron (ZVI or Fe 0 )) has been used (Gu et al., 1999, Liang et al., 2000, Scherer et al., 2008, Statham et al., 2016, to treat chlorinated organic contaminants and inorganic contaminants (radionuclides, Ni, Cr, As ,U, Cu, Zn, Pb,Cd,Fe,SO4 2 ). In the case of treating acidic ground water, reactive materials used in most of the past studies were limestone, mixtures of limestone and organic carbon rich materials such as wood chips , municipal compost, paper mill pulp (Obiri-Nyarko et al., 2014). ...
... A number of past reviews can be found on various PRB reactive materials (Blowes et al., 2000, Scherer et al., 2008, Obiri-Nyarko et al., 2014. Reactive materials usually act as chemical and /or biological reagents or catalysts to support the chemical reactions associated to the removal of the target contaminants. ...
... In majority of the PRBs up to date, granular iron media (i.e. Zero Valent Iron (ZVI or Fe 0 )) has been used (Gu et al., 1999, Liang et al., 2000, Scherer et al., 2008, Statham et al., 2016, to treat chlorinated organic contaminants and inorganic contaminants (radionuclides, Ni, Cr, As ,U, Cu, Zn, Pb,Cd,Fe,SO4 2 ). In the case of treating acidic ground water, reactive materials used in most of the past studies were limestone, mixtures of limestone and organic carbon rich materials such as wood chips , municipal compost, paper mill pulp (Obiri-Nyarko et al., 2014). ...
... Different types of minerals and surface coatings have been observed to form under different geochemical conditions that would appear to be dictated by aquifer chemistry and the composition of the permeable reaction zone (Powell et al., 1995;Mackenzie et al., 1999;Puls et al., 1999b;Liang et al., 2000;Phillips et al., 2000;Bonin et al., 2000;Roh et al., 2000;Wilkin et al., 2002;Furukawa et al., 2002). Furthermore, microbiological impacts are also important to understand in order to better predict how long these systems will remain effective in the subsurface (Matheson, 1994;Weathers et al., 1997;Till et al., 1998;Gu et al., 1999Gu et al., , 2002Scherer et al., 2000;Gandhi et al., 2002). The presence of a large reservoir of iron coupled with plentiful substrate availability in the form of hydrogen supports the metabolic activity of iron-reducing, sulfate-reducing, and/or methanogenic bacteria. ...
... The possibility of exploiting microorganisms to enhance reductive treatment has been explored in laboratory studies (e.g., Till et al., 1998;Weathers et al., 1997;Gu et al., 1999;Oh et al., 2001;Gandhi et al., 2002). Scherer et al. (2000) provide a detailed review of laboratory investigations on combined microbial-Fe 0 systems. Bacterial improvements are possible, for example, by iron-reducing bacteria that could reductively dissolve Fe(III) oxide layers, participate in forming reactive mineral species such as green rust, or directly degrade contaminants. ...
This publication has been produced as part of EPA's strategic long-term research plan. It is published and made available by EPA’s Office of Research and Development (ORD) to assist the user community and to link researchers with their clients. The purpose of this document is to provide detailed performance monitoring data on full-scale Permeable Reactive Barriers (PRBs) installed to treat contaminated ground water at two different sites.
... Zero-valent iron (ZVI), a strong reductant (E h 0 = −0.44 V) [52], often has applications for the remediation of chlorinated organics owing to its relative abundance, ease of production, and maintenance [53]. Directional electron transfer from ZVI to the contaminant initiates two major reaction pathways: 1) dihaloelimination, or 2) hydrogenolysis of a halogenated contaminant [54]. ...
Advanced reduction processes (ARPs) have emerged as promising techniques for destruction of persistent per-and polyfluoroalkyl substances (PFAS) due to the formation of highly reductive hydrated electrons (e aq −). The present study provides a critical review of the progress and prospects of the field over the past three to five years categorizing topics into three main sections: i) state of the art of ARPs, comparing the promise and mechanisms of methods such as photochemical, ionizing irradiation, plasma, sonolysis, electroreduction, and zero-valent iron; ii) integration of ARPs with physical-separation methods, oxidation processes, and their role in regeneration/ management of PFAS-laden media; iii) challenges/innovations in real-world application of ARPs. Three primary future research directions are also proposed in alignment with the current and upcoming research focuses.
... Also, the surfactants have to be of relatively low toxicity, recovery, and reuse potential represents an additional area of consideration (Mulligan et al., 2001;Saenton et al., 2002). Comparatively, pump and treat systems have proven costly to meet applicable clean-up standards (Mackay and Cherry, 1989;Scherer et al., 2000;Vaux, 2011). The use of low-cost burden technologies would benefit the Niger Delta project, particularly considering Nigeria's currently weak and overstretched economy. ...
The Niger Delta, a region of immense ecological significance and rich biodiversity, has long faced the severe consequences of petroleum contamination resulting from intense oil exploration and various environmental stressors. In response to the pressing need for effective remediation and monitoring of contaminated matrices in the Niger Delta, this study delves into a comprehensive analysis. Through a systematic assessment considering certain criteria, advanced remediation technologies tailored to the specific environmental challenges in the region are identified. Organoclay-based reactive core materials (RCM), permeable reactive barriers (PRBs), and bioremediation have emerged as highly suitable solutions for remediating sediment, groundwater, and soil, respectively. These technologies span the spectrum from non-intrusive to less intrusive methods and have demonstrated exceptional efficacy in mitigating hydrocarbon contamination under the delta’s prevailing complex conditions. In addressing the critical need for monitoring the progress of remediation and post-remediation stages, a fully integrated approach is proposed. This strategy combines three essential components for tracking environmental quality improvements and understanding the recovery processes: traditional total chemical concentration (Ctotal) estimates, passive sampler-derived freely dissolved chemical concentration (Cfree) measurements, and ecological monitoring, specifically the recolonization test. Together, these components provide a more accurate description of risk and a comprehensive understanding of the recovery process. This study is concentrated on the systematic selection, supported by credible case study information, of tailored technical solutions for addressing the unique challenges of the Niger Delta. The novel outcomes lie in the identification of technology solutions carefully adapted for the region, representing a significant advancement in the field of environmental remediation in the Niger Delta. Science-based remediation and monitoring are key, and this study offers a decision-support tool for selecting optimal methods in the ongoing cleanup of the Niger Delta and similar areas. This supports a healthier, more resilient environment for both the region’s inhabitants and ecosystems.
... For the passive treatment of metals in groundwater, a permeable reactive barrier (PRB) is a good alternative (Ott, 2000). Challenges in PRB design include the little knowledge available on medium-and long-term performances of reactive material (Scherer et al., 2000;USEPA, 2014). ...
The performance of the phosphorylated lignocellulosic fiber (PLF) was assessed for metal removal in an acidic mine drainage (AMD) influent at pilot scale and at laboratory scale with synthetic water. Substrate showed strong potential for sorption with a cation exchange capacity (CEC) of 540 meq 100g⁻¹, a point of zero charge (PZC) of 7.3, and a limited amount of organic carbon released. Average concentrations (mg L⁻¹) of Ca, Mg, Fe, Mn, and Zn in the influent were 427, 289, 1,420, 18.3, and 19.2, respectively. Retention of 1635 mg g⁻¹ of Fe, 23.1 mg g⁻¹ of Mn, and 18.1 mg g⁻¹ of Zn was achieved by the PLFs at pilot scale. The pump and treat system was in function for a total of 852 h over a 9-week period and allowed the treatment of 4806 L of Fe-rich contaminated water from an abandoned mining site in Québec (Canada). This medium-term experiment allowed to assess some of the key uncertainties that limit biosorption applications at large scale, namely organic carbon release and longevity and degradation of biosorbents. The substrate was subject to degradation, but it was found that acidic water reaching the PLF was mainly responsible for its dissolution. Hence, the PLF is a good candidate for long-term treatment when the influent pH is higher than 6. Metal removal was about 10 times higher during the field experiments compared with laboratory-scale equilibrium experiment, suggesting that many sorption reactions took place in the field and not in the laboratory. Differences between the laboratory and pilot experiments are the scale (0.45 L vs 4806 L) and water characteristics (continuous feed of various metals in the field).
... This is the reason why Fe 0 is a long-term source of iron oxides for water remediation (James et al. 1992, Wakatsuki et al. 1993, Jia et al. 2007, Bradley et al. 2011, and not a long-term source of electrons for the reductive transformation of selected species (Lawrinenko et al. 2023a) (Figure 1). Figure 1 recalls that both concepts recognized the formation of the oxide scale on Fe 0 . On the one hand, the reductive transformation concept strives to explain why electron transfer from Fe 0 occurs despite the presence of the oxide scale (Scherer et al. 2000, Lawrinenko et al. 2023a). ...
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).
... Constructed wetlands utilize plants and microbial communities to remove heavy metals through mechanisms such as phytoextraction, rhizofiltration, as well as microbial-mediated processes like adsorption and precipitation (Pat-Espadas et al. 2018). PRBs are subsurface barriers composed of reactive materials that intercept the flow of contaminated groundwater, facilitating reactions for the immobilization or removal of heavy metals through processes such as adsorption, precipitation, and redox reactions (Scherer et al. 2010). Packed bed iron-oxidation bioreactors employ iron-oxidizing bacteria to convert ferrous iron into ferric iron, which then interacts with heavy metals through adsorption, precipitation, and co-precipitation mechanisms (Johnson et al. 2002). ...
The uncontrolled release of acid mine drainage (AMD) results in the ongoing deterioration of groundwater and surface water, along with harmful impacts on aquatic ecosystems and surrounding habitats. This study employed a bibliometric analysis to examine research activities and trends related to AMD from 1991 to 2021. The analysis demonstrated a consistent growth in AMD research over the years, with a notable surge in the number of publications starting from 2014. Applied Geochemistry and Science of the Total Environment emerged as the top two extensively published journals in the field of AMD research. The USA held a prominent position, achieving the highest h-index (96) and central value (0.36) among 111 countries/territories, with China and Spain following closely behind. The author keyword analysis provides an overview of the main focuses in AMD research. Furthermore, the co-citation reference analysis reveals four primary domains of AMD research. Moreover, the prevention and remediation of AMD, including source prevention and migration control, as well as the hazards posed by heavy metals/metalloids and the mechanisms and techniques employed for their removal, are discussed in detail.
... Thereby, the weaker of two forces attracts a charged compound to an oppositely Hence, direct contact with surface is dominant and adsorption becomes specific. Interestingly, the presence of charged oxide surfaces can sorb ions by both electrostatic attraction and surface complexation, which means both nonspecific and specific adsorption [43]. For cations, mono or binocular surface complexes are formed with a deprotonated hydroxyl group, which is accompanied by the acidification of the environment. ...
... groundwater, municipal solid waste landfill leachate, mine water, highways and urban runoff) and there are many parallels with the continuing development of such "passive" technologies. These include permeable reactive barriers (PRBs), constructed wetlands, sustainable drainage systems (SuDS), swales and bioswales (for examples see Scherer et al., 2000;Pat-Espadas et al., 2018;Woods-Ballard et al., 2007 andEkka et al., 2021 respectively). The mechanisms of trapping variously involve biogeochemical process within the matrix that induce metal sequestration from solution. ...
Many countries face serious strategic challenges with the future supply of both aggregates and critical elements. Yet, at the same time, they must sustainably manage continued multimillion tonne annual arisings of mineral-dominated wastes from mining and industry. In an antithesis of Circular Economy principles, these wastes continue to be landfilled despite often comprising valuable components, such as critical metals, soil macronutrients and mineral components which sequester atmospheric CO 2 . In this paper, the authors aim to introduce a new concept for value recovery from mineral-rich wastes where materials are temporarily stored and cleaned in landfill-like repositories designed to be mined later. The time in storage is utilised for remediating contaminated materials and separating and concentrating valuable components. It is proposed that this could be achieved through engineering the repository to accelerate “lithomimetic” processes, i.e. those mimicking natural supergene processes responsible for the formation of secondary ores. This paper summarises the concept and justifications and outlines fundamental aspects of how this new concept might be applied to the design of future repositories. The proposed concept aims to end the current “linear” landfilling of mineral-rich wastes in favour of reuse as aggregates and ores.
... Adsorption could contribute to the removal at the very beginning of the experimental run. Besides, hydrophobic expulsion is also a dominant mechanism for removal of the most nonpolar organic compounds [22]. For that, reactive media surfaces consisting of exchangeable molecules are important. ...
... In situ treatment is usually more economical, efficient, energy-saving, and environmentally friendly than ex situ treatment (Kuppusamy et al. 2016). Among numerous in situ treatment methods, permeable reactive barrier (PRB) has some good features, such as low cost, no external power, sustainable in situ treatment of a variety of pollutants, small interference to the ecological environment (Della Rocca et al. 2007;Powell et al. 1998;Scherer et al. 2000). Therefore, PRB remediation has become an important in situ treatment technology for groundwater contamination. ...
Permeable reactive barrier (PRB) is one of the most promising in situ treatment methods for shallow groundwater pollution. However, optimal design of PRB is very difficult due to a lack of comprehensive understanding of various complex influencing factors of PRB remediation. In this study, eight of the main factors of PRB, including hydraulic gradient I, permeability coefficient KPRB of PRB material, PRB length L, PRB width W, PRB distance from pollution source Dist., the ratio of the maximum adsorption capacity to Langmuir constant of PRB material Qmax/KL, the discharge rate of pollution source DR, and recharge concentration RC were investigated, to carry out the sensitivity analysis of PRB removal efficiency. The simulation experiments for Morris analysis were designed, and pollutant removal efficiency was numerically simulated by coupling MODFLOW and MT3DMS under two scenarios of high and low permeability and dispersivity. For a typical low permeability with low dispersity medium, the sensitivity ranking of factors from high to low is DR, RC, I, W, L, Dist., Qmax/KL, and KPRB, and for a typical high permeability with a high dispersity medium, the sensitivity ranking of factors from high to low is I, W, DR, Qmax/KL, L, RC, Dist., and KPRB. When considering multiple factors in PRB design, the greater the KPRB, L, W, Qmax/KL is, the higher the removal efficiency is; the greater the RC, I is, the lower the removal efficiency is. The rest factors remain ambiguous enhancement to removal efficiency.
... Passive treatment systems, such as permeable reactive barriers (PRBs), have the potential to reduce costs and eliminate the need to extract groundwater or continuously add substrates, electron acceptors, and nutrients for biological treatment. Scherer et al. 21 provide a review of PRBs for groundwater treatment using chemical and biological methods. Upadhyay and Sinha 22 reviewed permeable reactive biobarriers (PRBBs) for environmental clean-up. ...
... PRB systems utilize chemical, biological, and physical processes that occur naturally in the environment to remove contaminants in groundwater. They do not require maintenance after installation and thus have advantages over other technologies (Scherer et al., 2000;Obiri-Nyarko et al., 2014). ...
When not properly treated, nitrate and phosphate present in groundwater can damage human health and environments. In this study, laboratory column experiments were performed for sequential treatment of nitrate and phosphate in groundwater. Two columns were set up and connected: one to treat nitrate with organic carbon materials (i.e., woodchips) and the other to treat phosphate with basic oxygen furnace (BOF) slag. The columns were operated for a total of 1.6 years. The results showed that nitrate was removed through denitrification and phosphate was removed by precipitation of the phosphate minerals (e.g., hydroxyapatite). BOF slag was effective at removing phosphate, though the high pH (11–12) of the system's effluent water raised a concern for the downgradient areas. Of the three subsequent experiments performed, pH was near neutral when the effluent of the BOF slag column was passed through local soil. Sparging with CO2 and air, in contrast, resulted in pH levels that were either too low (5 in the case of CO2) or too high (9.5 in the case of air). The study shows that sequential permeable reactive barrier (PRB) systems consisting of woodchips and BOF slag can be effective for removal of nitrate and phosphate in groundwater and they can be a long-term remedial solution for groundwater contaminated with both nitrate and phosphate.
... According to previous studies, the estimated life-time of iron granular particles ranged from several years to several decades 51,52 . Some studies assumed that iron particles will be completely consumed in the reaction of groundwater and estimated the lifetime of Fe 0 -based PRB by the iron mass and iron corrosion rate [53][54][55][56] . This approach to estimate the PRB service life is only valid, if the initial PRB pore volume and the used Fe 0 /aggregate ratio enable complete Fe 0 depletion 35,57 . ...
Solid iron corrosion products (FeCPs), continuously generated from iron corrosion in Fe ⁰ -based permeable reactive barriers (PRB) at pH > 4.5, can lead to significant porosity loss and possibility of system’s failure. To avoid such failure and to estimate the long-term performance of PRBs, reliable models are required. In this study, a mathematical model is presented to describe the porosity change of a hypothetical Fe ⁰ -based PRB through-flowed by deionized water. The porosity loss is solely caused by iron corrosion process. The new model is based on Faraday’s Law and considers the iron surface passivation. Experimental results from literature were used to calibrate the parameters of the model. The derived iron corrosion rates (2.60 mmol/(kg day), 2.07 mmol/(kg day) and 1.77 mmol/(kg day)) are significantly larger than the corrosion rate used in previous modeling studies (0.4 mmol/(kg day)). This suggests that the previous models have underestimated the impact of in-situ generated FeCPs on the porosity loss. The model results show that the assumptions for the iron corrosion rates on basis of a first-order dependency on iron surface area are only valid when no iron surface passivation is considered. The simulations demonstrate that volume-expansion by Fe ⁰ corrosion products alone can cause a great extent of porosity loss and suggests careful evaluation of the iron corrosion process in individual Fe ⁰ -based PRB.
... In Fig. 2 Similar structures were previously observed on X65 carbon steel samples during its corrosion in H 2 S/CO 2 environments for various periods of time [37]. The crystals that appear in Fig. 2 [3,38,39]. Zhao et al. [40] reported that in an environment containing SRB, the original corrosion products are mainly iron (oxyhydr)oxide. In the presence of SO 2-4 , (oxyhydr)oxide transforms to sulfide with the reaction of biogenic hydrogen sulfide, extracellular polymer substances, and organic acid. ...
... Los materiales de las BRP eliminan los contaminantes disueltos del agua subterránea, mediante la inmovilización dentro de la barrera o la transformación a productos menos nocivos, a través de mecanismos que incluyen la adsorción y precipitación, la reacción química y las reacciones biológicas (Scherer et al., 2000). Entre los materiales que han sido probados, el desarrollo de las barreras reactivas permeables se encuentran, la zeolita natural, zeolita modificada con hierro, apatita, apatita concentrada, caolín y bentonita cruda han (Vukojević et al., 2017), ceniza de carbón, caolinita, cáscara de coco (Asokbunyarat y Annachhatre 2017), pirita, hierro granular (Maitra, 2019), arcillas (Segura et al., 2015), y de algún modo la arena sílica, que se ha utilizado como parte de una mezcla con escoria y alúmina activada (McRae, 1999). ...
En este artículo se caracteriza la arena sílica de las costas del municipio de Alvarado, Veracruz, México, y se compara sus propiedades con los materiales usados en las barreras reactivas permeables, para permitir su uso, como una solución de remediación de acuíferos contaminados con lixiviados de basureros no controlados. Esto se logra mediante análisis granulométrico, determinación de humedad y concentración de sílice y fierro, con lo cual se obtienen partículas con tamaño de 0.707 mm, humedad relativa de 0.52 % y concentración de SiO2 y de Fe2O3 87.38 % y 2.72 % respectivamente, lo que, al comparar con materiales reactivos en uso, cumple con los criterios para ser usado como barrera para la remediación de acuíferos con lixiviados.
... There are numerous papers regarding permeable reactive barriers that have focused on removing pollutants with reactive media containing iron nanoparticles (Scherer et al., 2000;Henderson and Demond, 2007;Noubactep, 2010). Van-Nooten used a mixture of reactive substances to successfully eliminate organic and inorganic contaminants, such as ammonium (AOX) . ...
In situ groundwater remediation, which contains multiple contaminants simultaneously, is a fundamental challenge globally. One of the suitable technologies for the removal of several contaminants from groundwater is a permeable reactive barrier containing iron nanoparticles (NZVI-PRB). A laboratory-scale experimental setup is used as NZVI-PRB with a funnel-and-gate barrier. NZVI (average particle diameter (APS) = 35-70 nm) particles are used in PRB as a reactive media. NO 3-N, as a dominant element of required contact time, is considered for the design of the optimum width of PRB. Then, three contaminants of nitrate (NO 3), cadmium, and chromium (VI) were removed simultaneously from a shallow aquifer. With the development of Artificial Neural Network (ANN) in the context of Deep Neural Network (DNN) models and machine learning methods such as Support Vector Machine (SVM) and Linear Regression (LR), considerable progress has been made in various fields. In the final step, we assessed the performance of DNN, SVM, and LR models to estimate the residual contaminants based on preliminary experimental data. The average elimination of contaminants was stabilized at about 45% of the initial value. Our DNN model could estimate nitrate, cadmium, and chromium with a mean absolute percentage error (MAPE) of 7.05, 7.32, and 7.84, respectively. Our results showed that despite using a small dataset, utilizing a deep, fully connected network resulted in remarkably higher accuracy than the other methods. Notably, among the three contaminants, Nitrate estimation is performed more accurately and recommended for future large-scale modeling.
... To sum up, generation of less halogenated products with less affinity to dehalogenation and ZVI passivation as a result of solution pH increase (ca. pH ≥ 8) in higher column height serving as a physical barrier to inhibit electron transfer led to lower dechlorination rate [16,46]. ...
Chlorinated aliphatic hydrocarbons (CAHs) are amongst concerning contaminants with high detection in aquifers and soils. This work is focused on removal of tetrachloroethylene and its degradation products through a two-step process including a permeable ZVI column followed by UV/Fe/PDS process. The permeable ZVI column experiments were designed using response surface method with central composite design. Optimum condition of the permeable ZVI column was initial solution pH = 5, 2 mL/min flow and 26 cm column height which brought about 96% dechlorination efficiency. Total iron leach in the column effluent was 0.34 mg/L. The concentrations of CAHs in permeable ZVI column’s effluent were as follows: PCE ≤ 0.08 mg/L, TCE = 0.23 mg/L, cis-1,2-DCE = 0.36 mg/L, VC = 0.34 mg/L. Thus, further treatment step was required to comply with the corresponded standards. Regarding iron leach, a PDS-based advanced oxidation process was applied on the ZVI column’s effluent with focus on cumulative removal of CAHs. Complete removal of CAHs and 79.2% TOC removal were obtained at pH = 6 using 0.75 mM PDS, 6 W UV at 15 min reaction time. In UV/Fe/PDS process, synergy effect of 67% was observed.
... Zero valent iron Copper, arsenic compounds, molybdenum [54] Activated carbons Most heavy metals [55] Zeolites Lead, copper [56] Lime (alkaline minerals) Most heavy metals [34] Transformed red mud Iron, copper, zinc, nickel and lead [57] Oxides Arsenic compounds [58] Bio-barriers Aerobic degradation -Calcium peroxide, magnesium peroxide and hydrogen peroxide [59] Anaerobic degradation -Peat, sewage sludge, manure, sawdust, SRB [60] ...
Formation of acid mine drainage (AMD) is a widespread environmental issue that has not subsided throughout decades of continuing research. Highly acidic and highly concentrated metallic streams are indicative characteristics of such polluting streams. Humans, plants and surrounding ecosystems that are in proximity of AMD producing sites face immediate threat of their well-being. Remediation options include active and passive biological treatments which are markedly different in many aspects. On common grounds, sulfate reducing bacteria (SRB) instigates treatment systems where sulfate and heavy metals are removed to generate non-toxic streams. Passive systems are inexpensive to operate but entail fundamental drawbacks such as large land parcel and prolonged treatment period. Active bioreactors offer greater operational predictability and quicker treatment time. Yet, investment costs and lack of expertise negates wide scale usage. Advancement of technologies highlights the use of renewable raw materials for AMD clean up purposes, which will likely achieve much greener mitigation solutions.
... Permeable reactive barriers (PRBs) have been considered as a creative and economical technology for in situ treatment of polluted groundwater (Scherer et al. 2000;Thiruvenkatachari et al. 2008). The zone of reactive media in PRBs mainly plays a vital and indispensable part for pollutant removal (Obiri-Nyarko et al. 2014). ...
MIL-100(Fe), an environmental-friendly and water-stable metal–organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications.
Graphical abstract
... La considération du Fe 0 comme donneur d'électrons pour la dégradation des contaminants organiques ou pour leur conversion en formes moins ou non toxiques (exemple: la dégradation réductrice, la précipitation réductrice) s'est propagée (Laine et Cheng 2007, Thiruvenkatachari et al. 2008, Gillham 2010, Comba et al. 2011, Obiri-Nyarko et al.2014, Colombo et al. 2015) à la suite de la publication, par Matheson et Tratnyek (1994), d'un papier expliquant l'élimination du tétrachlorométhane (CCl4) dans le système Fe 0 /H2O par la réduction chimique. Cependant, pour les contaminants inorganiques, la précipitation réductrice (Gu et al. 1998, Puls et al. 1999), la co-précipitation (Lackovic et al. 2000, Komnitsas et al. 2006, Noubactep et al. 2006 En fait, qu'un contaminant soit adsorbé, co-précipité ou réduit, il ne devrait pas pouvoir se remobiliser dans les conditions naturelles (Scherer et al. 2000). Ce préalable fait de la coprécipitation le mécanisme d'élimination le plus adéquat dans la mesure où les oxydes de fer lentement précipités pourraient bien ne pas se dissoudre dans de telles conditions (Heron et al. 26 1994). ...
This thesis deals with metallic iron (Fe(0))for water treatment.
Steel wool was tested as Fe(0) source, and characterized for both its intrinsic reactivity (material screening) and efficiency (for water treatment) for the first time. Other achievements encompassed (I) testing the suitability of pozzolan as an alternative material to sand for the construction of metallic iron filters, and (II) testing the suitability of steel Fe(0)-based filters for water defluoridation. The work concludes that steel wool holds good promise as Fe(0)-bearing material for the construction of efficient, low-cost and reliable decentralized water treatment systems.
... Gillham and O'Hannesin [44] discovered that halogenated aliphatic compounds in groundwater can be reduced using bulk ZVI. This characteristic of iron led to the advanced Fe-PRB, in which vertical trenches were filled with granular ZVI, placed in the flow path of the underground contaminant plumes [45,46]. ...
In this study, we characterize the body of knowledge of groundwater remediation from 1950 to 2018 by employing scientometric techniques and CiteSpace software, based on the Science Citation Index Expanded (SCI-E) databases. The results indicate that the United States and China contributed 56.4% of the total publications and were the major powers in groundwater remediation research. In addition, the United States, Canada, and China have considerable capabilities and expertise in groundwater remediation research. Groundwater remediation research is a multidisciplinary field, covering water resources, environmental sciences and ecology, environmental sciences, and engineering, among other fields. Journals such as Environmental Science and Technology, Journal of Contaminant Hydrology, and Water Research were the major sources of cited works. The research fronts of groundwater remediation were transitioning from the pump-and-treat method to permeable reactive barriers and nanoscale zero‑valent iron particles. The combination of new persulfate ion‑activation technology and nanotechnology is receiving much attention. Based on the visualized networks, the intelligence base was verified using a variety of metrics. Through landscape portrayal and developmental trajectory identification of groundwater remediation research, this study provides insight into the characteristics of, and global trends in, groundwater remediation, which will facilitate the identification of future research directions.
... The PRB contains reactive materials and is placed underground in the path of the contaminated groundwater flow plume. Methods for removing heavy metals with a PRB include (1) sorption and precipitation, (2) chemical reaction, and (3) biologically mediated reactions (Scherer et al., 2000). ...
Permeable reactive barrier column tests were performed to investigate whether anaerobic bacteria in sheep manure could help remove As from groundwater. One column served as a control and was packed with zero-valent iron (ZVI), compost leaf, wood chips, glass beads, and gravel, after which it was sterilized. The other (‘inoculated column’) was packed with the same ingredients, with the addition of sheep manure as a source of anaerobic bacteria. Simulated As-contaminated groundwater was prepared based on groundwater samples from Sumbawa Island, Indonesia, but with the arsenic concentration adjusted to 50 mg/L. The inoculated column was found to remove As more effectively from the simulated groundwater than the sterilized one. A gradual decrease in sulfate concentration was observed in the inoculated column at the rate of 0.26 mmol of sulfate/L/day, suggesting that there was sulfate-reducing activity in the microbial population. In addition, the sulfur isotope ratio showed -4.3 (‰) and 0.2 (‰) in influent and effluent, respectively, indicating that sulfate-reducing bacteria (SRB) consumed δ32S preferentially. Using population size estimates from the most probable number (MPN) method, the population of SRB was found to increase with distance traveled in the column. Profiling the community composition of the bacteria in different fractions of the inoculated column using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) on 16S rRNA sequences suggested that a majority of bacteria were various Clostridium species and one species of Proteobacteria, Geobacter metallireducens GS-15. Some of them may contribute to the removal of arsenic.Keywords: Sheep manure, zero valence iron, arsenic, immobilization, sulfate-reducing bacteria
... The precipitation of secondary mineral phases leads to passivation of carbonate minerals and limited pH-buffering capacity in limestone drains for the treatment of acid rock drainage (Hammarstrom et al. 2003;Rötting et al. 2008). Groundwater treatment by permeable reactive barriers or by bioremediation (Hazen and Fliermans 1995;Ritter and Scarborough 1995) is frequently affected by the growth of biofilms, which can have detrimental effects on the efficacy of the remediation effort and modifies permeability and transport parameters (Scherer et al. 2000;Li et al. 2006;Wantanaphong et al. 2006). The precipitation of secondary oxide phases in case of groundwater remediation via in-situ chemical oxidation with permanganate also may result in less effective contaminant treatment or contaminant encapsulation (Nelson et al. 2001;Henderson et al. 2009). ...
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.
In this research, we scrutinize the distinctive factors precipitating groundwater
pollution within aquifers, aiming to unveil nuanced insights into the multifaceted origins of
contamination. Employing a robust methodology incorporating advanced analytical tools and
comprehensive data collection, our investigation dissects the intricate tapestry of pollutants
affecting aquifers. The study delves into the specific sources and mechanisms governing
groundwater pollution, identifying previously unexplored dimensions in extant literature. Our
results present a meticulous analysis, revealing the intricate interplay of diverse contaminants
within aquifer systems. The discourse in this article transcends the conventional
understanding of groundwater pollution causes, shedding light on unique and often
overlooked contributors to aquifer contamination. Through a systematic exploration of
distinctive factors, this research contributes to an enriched comprehension of the complexities
inherent in safeguarding groundwater quality. The findings bear significance for
policymakers, environmental scientists, and stakeholders vested in sustainable water resource
management, offering pragmatic insights for the mitigation of groundwater pollution at its
roots.
Metal contamination in water especially in groundwater sources is increasing due to changes in geochemistry in the aquifers. Overexploitation of water with increasing human population and development leads to overextraction of more water from groundwater sources which change the level of groundwater table and its geochemistry. Heavy metal contamination in groundwater has become a global health concern due to its harmful impact on human health and other living beings. Contamination of groundwater with metal leads to human health hazards through contaminated drinking water. More reports are there on arsenic contamination in groundwater and its effect on plants and animals including humans. Monitoring of metal contamination and estimation of its concentration in groundwater will be helpful in investigating contaminated sites and understanding its route and fate in the environment. Understanding metal contamination and its environmental concerns is important for assessing health hazards in developing mitigation strategies for health and environmental safety.
A bismuth oxyiodide photocatalyst having coexistent iodine deficient phases viz. Bi4O5I2 and Bi5O7I was prepared by using a solvothermal method followed by calcination process. This has been used for the degradation of model perfluoroalkyl acids such as perfluorooctanoic acid at low concentrations (1 ppm) under simulated solar light irradiation. 94% PFOA degradation with a rate constant of 1.7 h-1 and 65% defluorination of PFOA have been achieved following 2 h of photocatalysis. The degradation of PFOA happened by the parallel direct redox reactions with high energy photoexcited electrons at the conduction band, electrons in iodine vacancies and superoxide radicals. The degradation intermediates were analyzed by electrospray ionization-mass spectrometry in the negative mode. The catalyst was converted to a more iodine deficient Bi5O7I phase during photocatalysis following creation of iodine vacancies, some of which were compensated by the fluoride ions released from degraded PFOA.
Groundwater quality is deteriorating due to contamination from both natural and anthropogenic sources. Traditional "Pump and Treat" techniques of treating the groundwater suffer from the disadvantages of a small-scale and energy-intensive approach. Permeable reactive barriers (PRBs), owing to their passive operation, offer a more sustainable strategy for remediation. This promising technique focuses on eliminating heavy metal pollutants and hazardous aromatic compounds by physisorption, chemisorption, precipitation, denitrification, and/or biodegradation. Researchers have utilized ZVI, activated carbon, natural and manufactured zeolites, and other by-products as reactive media barriers. Environmental parameters, i.e., pH, initial pollutant concentration, organic substance, dissolved oxygen, and reactive media by-products, all influence a PRB's performance. Although their long-term impact and performance are uncertain, PRBs are still evolving as viable alternatives to pump-and-treat techniques. The use of PRBs to remove anionic contaminants (e.g., Fluoride, Nitrate, etc.) has received less attention since precipitates can clog the reactive barrier and hinder groundwater flow. In this paper, we present an insight into this approach and the tremendous implications for future scientific study that integrates this strategy using sustainability and explores the viability of PRBs for anionic pollutants.
This study examined the capability of segmented trenches with various placements to remediate groundwater contaminated by small holes in lined waste impoundments such as landfills. A groundwater flow and mass transport model simulated a small contaminant source above an unconfined alluvial aquifer. After the leachate plume evolved for 1,000 days, the source was shut off and clean-up trials commenced. Decoupled trench configurations, with one segment at the downgradient edge of a plume, and the other at high concentrations within the plume, expedited cleanup while limiting downgradient travel. At some sites, relatively efficient schemes documented here may be effective clean-up alternatives for contemporary landfills.
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.
Unprecedented high concentrations of heavy metals have been detected in the groundwater at a zinc smelter in Seokpo, South Korea. The outflow of the contaminated groundwater into the nearby Nakdong River must be prevented by some means such as permeable reactive barrier (PRB). As a reactive material for injection-type PRB, we have tested sulfidated nanoscale zerovalent iron (S-nZVI) to assess its efficacy in remediating the groundwater from the smelter. The S-nZVI efficiently removed Zn, Ni, and Al in the groundwater, and neutralized the groundwater to pH > 6. Sulfidation of nZVI greatly increased the removal of Cd (99.8%) compared to that by nZVI (7.2%). MINEQL+ modeling and particle characterization were performed to elucidate the forms of heavy metals in the solution and on the surface of S-nZVI. Raman and XPS results suggested that FeS on the surface of S-nZVI reacted with Cd(II) and Zn(II), forming more-stable CdS and ZnS. Sequential application of NaHCO3 after S-nZVI treatment in a column setup was suited for the removal of remaining Zn and Fe as well as the reduction of microbial toxicity. This study guides to use of S-nZVI for in-situ remediation of cadmium-contaminated groundwater with other coexisting heavy metals from a zinc smelter.
The use of Permeable Reactive Barriers as a material for the removal of heavy metals from the leachates of the Sanitary Landfills has been verified for various materials, the Silica Sand from the coasts of the municipality of Alvarado Veracruz in Mexico have the characteristics of size and composition Required to be used for this purpose, samples of leachate were collected from the Sanitary Landfill of the City of Veracruz and the concentrations of Ni, Cr+6 and Zn were determined were respectively 0.0818, 0.186 and 0.224 mg/l, three columns were built of acrylic and were filled with 20, 30 and 40 cm of washed and dried Silica Sand, treated and stabilized leachate was passed through the porous medium at a flow of 1.7 ml/s, taking samples at 40.75, 115 , 165 and 235 seconds for each column and the efficiency for the removal of these heavy metals was measured and a significant reduction of these pollutants was found, ranging from 76 to 93%. for Nickel, from 44 to 81 % in the case of hexavalent Chromium and from 65 to 92% for Zinc for a maximum time of 235 seconds, which indicates that this material can be used in the remediation of leachate.
A model of contaminant transport determined by infiltrating groundwater in geologic medium with adsorbing barrier is proposed, in which it is shown that requirements to the barrier permeability make a restriction on its adsorbing properties. Basing on the solution for contaminant concentration a restriction on minimal barrier’s length needed for treatment of contaminated region and characteristic time of the treatment as well are established. In the case when the material of the barrier has a double-porous structure the requirements to permeability do not influence its adsorbing capacity that can increase the barrier efficiency. It is stressed that at long times some additional action should be undertaken to avoid possible leaching of pollutants from the barrier into the environment.
Groundwater pollution remediation involves three remedial approaches: containment, i.e. preventing the contamination migration and exposure; active restoration, i.e. removal and treatment of the contamination; and natural attenuation through biological, naturally occurring chemical, or physical degradation processes so that contaminant is converted to harmless species. The chapter will be focusing on the various preventive as well as remedial techniques to combat groundwater pollution. Biological treatment techniques (bioaugmentation, bioventing, biosparging, bioslurping, and phytoremediation) will be discussed along with chemical (ozone and oxygen gas injection, chemical precipitation, membrane separation, ion exchange, carbon absorption, aqueous chemical oxidation, and surfactant enhanced recovery [SER]) and physical (pump and treat, air sparging, and dual phase extraction) techniques in detail. While nanotechnology is growing exponentially in playing an important role in environmental issues, it is slowly creeping into treatment of polluted groundwater. Carbon nanotubes (CNTs) and zero‐valent iron nanoparticles have been extensively studied in this context. The chapter will also focus on these nanomaterials and provide deep insight into them.
Groundwater contamination comes from natural and anthropogenic sources. Natural sources include weathering of minerals and anthropogenic sources include industrial effluent and leakage from service pipes, and agricultural activities. Heavy metals and pesticide pollution have become severe environmental problems and have received increasing attention in recent years. In this chapter, various remediation measures of different organic and inorganic contaminants in the groundwater are studied. Different treatment technologies used for the removal of various contaminants from aqueous system are introduced, evaluated, and compared. To improve and remove these contaminants’ pollution, full consideration should be taken to develop wastewater reuse. Multidisciplinary collaboration is required to develop innovative technologies for removal of heavy metals and pesticides residue from the aqueous system.
It is predicted that climate change will result in big changes to the global distribution of rainfall, causing drought and desertification in some regions and floods in others. Already there are signs of such changes occurring, with particularly serious consequences for poorer countries. The need for international cooperation in managing the effects of climate change, and other influences on the hydrological cycle, is becoming urgent. Future wars may well be fought over water. This book is part of a series focusing on key issues in environmental science and technology. Focusing on the sustainability of water supplies to the growing populations throughout the world, this volume consists of articles contributed by a group of experts drawn from around the globe. Issues covered include: policy making in the European Union; rural water supplies in Africa; chemical monitoring and analytical methods; water use in agriculture; social justice in supplying water; potable water recycling, and sustainable water treatment. The book will be useful to those working in the water industry, policy makers and planners, researchers and environmental consultants, and students in environmental science, technology, engineering, and management. There is also much here to interest all concerned with major environmental issues such as climate change and the many other factors which influence the sustainability of water supplies.
This chapter discusses applications of engineered nanoparticles (NPs) and nanotechnology in the agricultural production chain, and nano-selenium and its nanomedicine applications. Today, nanotechnology represents a promising approach to improve agricultural production and remediate polluted toxicity sites. These technologies can lead to an uncontrolled release of undesired NP substances into the environment, with the potential to contaminate soil and groundwater. There is also a need to direct research in such a way that better choices can be made and to promote less costly NP production and application procedures. Given this, it is necessary to study and understand the behavior of these new materials.
The fate of NPs once introduced in water and soil, and the advantages of their use and possible toxicity risks, is also discussed. The potential for the application of nanotechnologies is enormous and much is still to be discovered. With the increase in the world population and the demand for food, new agricultural practices have been developed to improve food production using more effective pesticides and fertilizers. Fertilizer particles can be coated with nanomembranes that facilitate slow and steady release of nutrients. Coating and cementing of nano- and subnanocomposites can regulate the release of nutrients from the fertilizer capsule.
Over the last thirty years, several techniques of groundwater (GW) remediation based on the principles of physical (air sparging), biological (bioventing), and chemical (e.g., ion exchange) processes have proven to be effective; however, only a handful of them could successfully be implemented at a community or regional scale due to issues like longevity, a requirement of significant investment and operation cost, skilled labors, and others. Therefore, considering the scope of Permeable Reactive Barriers (PRBs) to be implemented on a regional scale and its capability to be a significant replacement for several existing GW treatment methods, this review was prepared with the following objectives: (i) to compare the PRB method with the conventional methods of groundwater treatment along with the possibility and problems associated with the PRB installation in pilot-scale; (ii) to enlist all the probable sets of adsorbents (reactive materials) that can be used for different types of organic and inorganic contaminants; (iii) to understand the key mechanisms of degradation/removal of contaminants involved in PRB design; and (iv) to put forward the future research perspectives of this domain. Review augments that PRBs certainly has a low maintenance cost and a longer life span of ̃30 years that requires very ordinary skills. PRBs promose to be effective in developing countries like India, Bangladesh, and Sri Lanka for the removal of geogenic contaminants like arsenic and fluoride given the appropriate aquifer depth and hydrogeological settings like hydraulic gradient and transmissivity. Furthermore, reactive fillers required in PRBs are readily available, have longer expected life, and operate with no surrounding disturbances. With the advent of several green nanomaterials based adsorbents, PRB’s performance can achieve another height, but it needs the experiences from several pilot and larger scale projects. Indeed PRBs are the need of the hour, but a more programming-based investigation would be expected for its superior comprehension.
With the increase in the world population and the demand for food, new agricultural practices have been developed to improve food production using more effective pesticides and fertilizers. These technologies can lead to an uncontrolled release of undesired substances into the environment, with the potential to contaminate soil and groundwater. Today, nanotechnology represents a promising approach to improve agricultural production and remediate polluted sites. Fertilizer particles can be coated with nanomembranes that facilitate slow and steady release of nutrients. Coating and cementing of nano- and subnanocomposites can regulate the release of nutrients from the fertilizer capsule. This chapter discusses some applications of engineered NPs and nanotechnology in the agricultural production chain and nanoselenium and its nanomedicine applications. The fate of the advantages and possible toxicity risks of nanomaterials once introduced in water and soil are also discussed. The potential for the application of nanotechnologies is enormous, and much is still to be discovered. Given this, we need to study and understand the behavior of these new materials. We also need to direct research in such a way as to help us make better choices and to promote less costly nanomaterial production and application procedures.
In this paper we study cardinal invariants of Hattory space of real numbers. A Hattory space of real numbers contained a Sorgenfrey line.
Chemical reduction, using a catalyzed metal powder as the reductant, has been found to degrade many toxicants found in chemical plant waste streams to non-toxic forms. The process is particularly useful for the toxicants dissolved in water ( mu g/l to mg/l levels) which cannot be removed by physical means. Degradation to 1 mu g/l and less is commonly achieved. This allows reuse or safe discharge of the waters. The process appears to be simple, effective and economical. Reductants such as catalyzed iron, zinc or aluminum powders have been used in effecting treatment by such mechanisms as hydrogenolysis, hydroxylation, saturation of aromatic structure, condensation, ring opening and rearrangements to change the toxicants to an innocuous form. The toxicants are chemically changed, rather than remaining in a concentrated solution, transferred to a solvent phase, or transmitted to the air.
The current focus is the establishment of a replenishable bioactive zone (catalytic filter) along expanding plume boundaries by the injection of a representative methanotrophic bacterium, Methylosinus trichosporium OB3b. This microbial filter strategy has been successfully demonstrated using emplaced, attached resting cells (no methane additions) in a 1.1 m flow-through test bed loaded with water-saturated sand. Two separate 24 h pulses of TCE (109 ppb and 85 ppb), one week apart, were pumped through the system at a flow velocity of 15 mm h-1; no TCE (<0.5 ppb) was detected on the downstream side of the microbial filter. Subsequent excavation of the wet sand confirmed the existence of a TCE-bioactive zone 21 days after it had been created. Additional experiments with cells in sealed vials and emplaced in the 1.1 m test bed yielded a high resting-cell finite TCE biotransformation capacity of about 0.25 mg per mg of bacteria. -from Authors
Chemical reduction, using a catalytically-activated metal powder as the reductant, has been found to degrade many toxicants found in chemical plant waste streams to non-toxic forms. The toxicants are chemically changed to a form innocuous to the environment, rather than remaining in a concentrated solution or transmitted to the air. The chemistry of the process and the means for carrying out the reaction are described. Several applications of the process are described. The allegedly carcinogenic trihalomethanes (THM's) (chloroform, bromoform) and intermediates were degraded in a six-month pilot test from an average 242 mu g/l to well below the EPA control level, with 75% of the samples analyzing less than 5 mu g/l THM's. Reduction of trichloroethylene, tetrachloroethylene and trichloroethane from about 250 mu g/l to less than 5 mu g/l is also described. Chlorobenzene was shown to be effectively degraded, with identification of the principal products as the vastly less toxic cyclohexanol. Successful degradation of a PCB waste to detection limits was shown, as well as the pesticide chlordane.
Atrazine is the most widely used herbicide in the U.S. and has been detected in surface water and groundwater. Technologies are needed for onsite and in situ remediation of water and soil containing atrazine. We investigated the potential of using fine-grained, zero-valent iron (Fe) to remove atrazine and promote its degradation in contaminated water and soil. Atrazine loss from aqueous solution increased with increasing Fe0 concentration (w/v). Agitating 20 μg 14C-ring-labeled atrazine L-1 with 10% Fe0 (w/v) removed 92% of the 14C from solution within 48 h. Only about 4% of the 14C lost from solution was extractable from the iron with 3 mM CaCl2 (readily available pool), 81% was extractable with CH3CN (potentially available pool), and 11% was unextractable residues. A companion experiment indicated that most of the 14C extracted from the iron with 3 mM CaCl2 after the 48-h Fe0 treatment was unaltered atrazine, while the CH3CN extract contained approximately 33% atrazine and 48% was unidentified atrazine transformation products. Treating a highly contaminated solution (20 mg atrazine L-1) with 20% Fe0 (w/v) removed 88% of the 14C (added as 14C-ring-labeled atrazine) from solution within 48 h. Deethylatrazine was the main atrazine transformation product detected in solution after treatment, but small amounts of deisopropylatrazine, didealkylatrazine, and hydroxyatrazine were also found. Treating Sharpsburg surface soil containing 1 mg atrazine kg-1 with Fe0 (2%, w/w) increased atrazine mineralization from 4.1 to 11.2% after 120 d. Pyrite (4% FeS2, w/w) also increased atrazine mineralization in surface soil, but was less effective in the presence of NO3- or SO42- (100 mg kg-1 soil). Adding 2% Fe0 (w/w) and 100 mg NO3- kg-1 to contaminated subsurface soil increased atrazine mineralization from 0.4 to 8.2% within 120 d, and unextractable residues increased from 4.6 to 9.8%. These results indicate iron can sorb atrazine and promote its transformation in water and soil.
Denitrification studies were conducted in sand columns in order to differentiate between the effects of gas and biomass accumulation on the clogging of the interstitial spaces, and to optimize conditions for prolonged operation. Four biodegradable carbon sources were used: sucrose, acetate, formate and ethanol. The results suggest that it is the accumulation of biologically produced gas that causes clogging of the columns. Of the four carbon sources tested, formate brought the lowest accumulation of gas and the highest permeability levels in the column.
Laboratory denitrifcation studies were conducted in a sand column using sucrose as a biodegradable carbon source. The denitrification capacity of the system was followed for more than one year. Column efficiency was dependent on the flow rate and on the carbon to nitrogen ratio in the treated water. After a few months of operation, visible accumulation of gas in the active zone was accompanied by a marked decrease in column permeability. Vacuum treatment restored permeability to its original level; only partial recovery was achieved by simply allowing the slow natural release of gas. We suggest that under the conditions tested, clogging resulted from the accumulation of microbiologically produced gas.
The early development of ideas on cation exchange from 1850 to 1900 is described. From 1900 to the present, the coverage has been divided as the work has concentrated on soil acidity, alkali soils, and classical cation exchange studies. The discovery of crystallinity in soil clays and the rediscovery of the importance of noncrystalline oxides adsorbed on crystalline clay minerals as sources of pH‐dependent acidity and anion exchange are reviewed. Some of the more important contributions made in understanding ion exchange in soils are covered in some detail. Other contributions are mentioned. It is concluded that despite the progress made, our understanding is still far from complete.
Chemical barriers are an emerging technology used for the in situ remediation of groundwater. They are placed in the subsurface environment perpendicular to groundwater flow where they selectively remove targeted groundwater contaminants while permitting water and other nontargeted constituents to pass through freely. A novel approach to emplacing chemical barriers is by the injection of zerovalent iron (Fe0) colloids into the subsurface. The objective of this study was to determine the effect of influent Fe0 colloid concentration and injection rate on colloid retention by columns of sand. Suspensions of Fe0 colloids (2 ± 1 μm) were injected into coarse-grain sand that simulated a simplified aquifer matrix. Influent colloid injection rate (P ≤ 0.01) and concentration (P ≤ 0.05) had a significant effect on colloid retention by the sand. Efficiency of the column to retain colloids decreased as the concentration of retained colloids increased. Colloids were uniformly distributed throughout 1-m long columns at concentrations >3 g kg-1. Based on filtration theory, gravitational settling was clearly the primary mechanism controlling colloid retention; diffusion, electrostatic attraction, and interception were less important mechanisms. These results were rationalized as follows: the high density of the colloids (7.6 g cm-3) enhanced gravitational settling, the fast experimental flow rates minimized diffusion, the weak surface charge of the colloids and sediments minimized electrostatic attraction, and the small size of the colloids relative to the sand particles (640 μm) minimized interception.
The leaching of chromium-copper-arsenic salts from old wood preservation sites is a threat to ground water at many places in Sweden. The installation of in situ reactive barriers is an attractive passive technique to prevent the further spreading of contaminants. Contaminated soil was taken from an old preservation site and leached under conditions designed to imitate the field conditions. The arsenic load during the three-month duration of the test corresponded to a load at the field site during three years. The B horizon material proved to be efficient for retention of arsenic, despite the observation that As(III) dominated the As speciation. The As(III) concentration was reduced from 1 to 3 mg dmâ»Â³ to < 0.02 mg dmâ»Â³. Pure peat was, as expected, not suited as a reactive barrier for As, and a mixed B horizon/peat reactive barrier also proved unsatisfactory for the removal of As. It is therefore important to separate the B horizon material from any peat that is used to sorb heavy metals. Before applying the B horizon reactive barrier technique in the field, the effect of the naturally occurring variability of the reactive compounds should be tested. The inclusion of oxidizing agents in the barrier could possibly improve the lifetime considerably. Furthermore, the influence of the flow rate should be evaluated since the kinetics of the arsenic adsorption is relatively slow.
The project began in an attempt to develop technology to ameliorate acid mine drainage (AMD) problems occurring at the Sherman Iron Ore Mine of Temagami, Ontario, Canada. A series of laboratory experiments were conducted to evaluate the effectiveness of an electrochemical approach to ameliorate AMD. An electrochemical cell was constructed using a block of massive sulphide-graphite rock from the mine site as the cathode, scrap iron as the sacrificial anode, and acidic leachate collected from the mine site as the electrolyte. The cell was effective at raising the pH of ≈ 41.0 L of leachate from 3.0 to a maintenance value of ≈ 5.6. This result was accompanied by a significant decrease in redox potential from > 650 to
This laboratory investigation evaluated candidate permeable-barrier media designed to remove benzene from in-situ ground water. There are many obvious potential permeable-barrier media, such as granular-activated carbon or ion-exchange resins; however, these are prohibitively expensive for most potential barrier applications. Therefore, developing low cost, yet effective, barrier materials would expand the breadth of potential applications. This investigation considered the effectiveness of several common materials including coal, powder-activated carbon (PAC), peat, sawdust, and zeolite. These materials were mixed with silica sand, then used in a bottle point isotherm procedure. The PAC and sand mixture was selected as the media for a column investigation, based on the results of batch sample investigations. The evaluation of this mixture in the column investigation showed that batch study efficiency projections were exceeded by 37%. Possible reasons for that finding are proposed. Eventually, these data will be used to design field barriers.
Solid peroxides and peroxyhydrates degrade into a basic salt, water, and molecular oxygen when in contact with biologically active soils. Column reactors were used to quantify the extent to which three solid peroxides would stimulate growth of aerobic, heterotrophic bacteria and fungi in contaminated tundra soil. Soils in contact with a peroxide compound were incubated in column reactors at field moisture conditions at either 12 or 25°C with no mixing. After 1200-h incubations, localized concentrations of bacteria and fungi were at least 2 orders of magnitude greater in soil amended with sodium carbonate peroxyhydrate than in soil containing either calcium peroxide or magnesium peroxide. Only in soil containing sodium carbonate peroxyhydrate did microbes grow to an appreciably higher concentration than in control soil, which contained no peroxide. Stimulation of both bacterial and fungal growth occurred primarily at distances of less than 5 cm from the peroxide, suggesting that under static moisture conditions, only localized microbial growth can be expected in acidic tundra soils.
A chemical barrier is a permeable zone of reactive materials emplaced in the subsurface to remove ground‐water contaminants while allowing clean ground water to pass through. Because dissolved ferric chloride hydrolyzes to amorphous ferric oxyhydroxide when it contacts calcite (CaCO 3 ), it may be viable to emplace a zone of amorphous ferric oxyhydroxide (an absorbent for U, Mo, and other inorganic contaminants) into calcite‐bearing geologic units by injecting ferric chloride through wells. For a chemical barrier to be successful, it must remain permeable and must be immobile.
This investigation monitored chemical compositions, hydraulic conductivity, and iron mobility in laboratory columns and in a two‐dimensional tank to determine the viability of injecting ferric chloride to form an amorphous ferric oxyhydroxide chemical barrier. We introduced a ferric chloride solution (1,345 mg/l [0.024 m] Fe) to calcite‐bearing alluvial gravel to form a chemical barrier of amorphous ferric oxyhydroxide, followed by solutions contaminated with U and Mo. The simulated chemical barriers decreased U and Mo concentrations to less than 0.05 mg/1 (2.1×10 ‐7 m) and 0.01 (1.0×10 ‐7 m), respectively; however, the breakthrough front is spread out with concentrations increasing to more than regulatory guideline values sooner than predicted. The hydraulic conductivity of calcite‐bearing alluvial gravel decreased substantially during ferric chloride introduction because of the formation of carbon dioxide but increased to within factors of 1 to 5 of the original value as synthetic ground water flowed through the system. Amorphous ferric oxyhydroxide that formed in these experiments remained immobile at flow rates exceeding those typical of ground water. These laboratory results, in conjunction with site‐specific characterization data, can be used to design chemical barriers emplaced by injection of ferric chloride.
A field lest to evaluate the applicability of an oxygon‐releasing compound (ORC) to the rernediation of ground water contaminated with benzone and toluene was conducted in the Borden Aquifer in Ontario. Canada. Benzene and toluene were injected as organic substrates to represent BTEX compounds, bromide was used as a tracer, and nitrate was added to avoid nitrate‐limited conditions.
The fate of the solutes was monitored along four lines of monitoring points and wells. Two lines studied the behavior of the solutes upgradient and downgradient of two large‐diameter well screens filled with briquets containing ORC and briquets without ORC. One line was used to study the solute behavior upgradient and downgradient of columns of ORC powder placed directly in the saturated zone. The remaining line was a control.
The results indicate that ORC in both briquet and powder form can release significant amounts of oxygen to conlaminated ground water passing by it. In the formulation used in this work, oxygen release persisted for at least 10 weeks. Furthemiore, the study indicates that the enhancement of the available dissolved oxygen content of at least 4 mg/L each of the ground water by ORC can support biodegradation of benzene and toluene dissolved in ground water. Such concentrations are typical of those encountered at sites contaminated with petroleum hydrocarbons; therefore, these results suggest that there is promise for ORC to enhance in situ biodegradation of BTKX contaminants at such sites using passive (nonpumping) systems to contact the contaminated ground water with the oxygen source.
The degradation of methyl parathion in soil with various amounts of acidified powdered zinc under field conditions was studied. Treatment was progressively more effective with increasing amounts of zinc. Disappearance of parent compound was followed for 2 1/2 years. The expected conversion product aminomethyl parathion and its N-methyl derivative were formed. In addition, N,N-dimethylamino, and the azo and azoxy condensation products were characterized by high resolution mass spectrometry. Aminomethyl parathion was shown to be identical to an authentic standard. The other specific positional isomers were considered likely, but were not proven by mass spectrometry. Structure elucidation was made with high resolution mass spectrometry, using the direct insertion probe, and with gas chromatography/low resolution mass spectrometry.