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Permeable Reactive Barrier for Groundwater Remediation
Abstract
This article aims to provide an overview of the upcoming technology of permeable reactive barriers for groundwater remediation. A comprehensive list of references and web-links are also provided for further in-depth understanding. A brief discussion on the Australian perspective on this emerging technology is also included.
... Remediating these contaminated natural resources within permissible limits can be a significant challenge. Groundwater pollution is a serious concern since 2.5 billion people worldwide rely on it (Thiruvenkatachari et al., 2008). ...
... Funnel and Gate (F&G) systems are recommended for the expensive reactive materials (i.e., oxides, activated carbon, etc.) since the reactive zone requires less material than the continuous barrier system. Moreover, funnel and gate systems have been efficiently used in multi-PRBs systems where two or more contaminants are targeted (Thiruvenkatachari et al., 2008). ...
... Zeolites have three-dimensional aluminosilicate structures with high ion-exchange rates and surface area, which attributes to their sorption mechanism for PRBs (Thiruvenkatachari et al., 2008). Natural (i.e. ...
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.
... The two most-commonly used configurations in PRB designs are the continuous trench/slurry-type (Fig. 295 1a) and the funnel-and-gate (Fig. 1b) configurations. In the former configuration, a single and sufficiently 296 permeable reactive zone is installed across a contaminant plume that allows water to pass through the 297 barrier under its natural hydraulic gradient (Striegel et al., 2001;Thiruvenkatachari et al., 2008). The 298 continuous trench is preferable in most types of soils at depths of 5-30 m (Thakur et al., 2020), owing to 299 its simple design and high cost-effectiveness, compared with the funnel-and-gate configuration. ...
... Thus, it primarily comprises 307 of an impermeable funnel, a highly permeable gate, and an active material to hinder the pollutant and 308 capture the remediated water exiting from the downstream side. The impermeable funnel acts as a cut-309 off barrier that directs the groundwater flow into the reactor gate where treatment occurs through the 310 reactive medium (He et al., 2019;Thiruvenkatachari et al., 2008). Notably, to achieve remediation at the 311 least cost, the ratio of the funnel area to the gate area must be balanced. ...
... Compared with continuous barriers, funnel-and-gate systems are always preferable when more expensive 338 reactive materials are used to restrict the relatively high construction costs (Thiruvenkatachari et al., 2008). ...
... transformation, extraction and sequestration are frequently used to eliminate contaminants including radionuclides and heavy metals. Hydrocarbon and chlorinated organic pollutants are mostly eliminated through rhizoremediation, volatilization, degradation, and stabilization, with the likelihood of mineralization when certain plants, like Willow and Lucerne, are utilized [26,27]. ...
... In order to house the biotechnology & bioremediation part of the approach, the following alternative wording has been proposed: Biological PRB, biological enhanced PRB and Passive bio reactive barrier. Most talking PRB is in-situ strategy to remove heavy metals & chlorinated compounds from toxicated groundwater [27,28]. ...
Biotechnology is one of the emerging fields that can add new and better application in a wide range of sectors like health care, service sector, agriculture, and processing industry to name some. This book will provide an excellent opportunity to focus on recent developments in the frontier areas of Biotechnology and establish new collaborations in these areas. The book will highlight multidisciplinary perspectives to interested biotechnologists, microbiologists, pharmaceutical experts, bioprocess engineers, agronomists, medical professionals, sustainability researchers and academicians. This technical publication will provide a platform for potential knowledge exhibition on recent trends, theories and practices in the field of Biotechnology
... The reactive materials used in PRBs can be permanent, semi-permanent, or replaceable, and groundwater naturally flows through them (Maitra 2019). Chemically stable materials such as activated carbon can be utilized in both on-site and off-site PRB applications due to their impressive adsorption capacity against both organic and inorganic pollutants (Thiruvenkatachari et al. 2008). As the cost and availability also play a significant role in selecting a reactive material for PRB applications, ongoing research has been focused on investigating the potential of using waste materials as reactive media. ...
... Due to organic decay, the lifespan of the barrier could be limited. Hydrated lime (Ca(OH) 2 ) or calcium carbonate (CaCO 3 ) are cost-effective reagents for groundwater remediation, but they experience reduced system efficiency due to the coating of limestone flecks with iron precipitates (Thiruvenkatachari et al. 2008). In the same literature, ZVI is deemed ineffective as a reactive material for all types of organic contaminants, such as dichloroethane and dichloromethane. ...
Landfill leachate contributes to groundwater pollution. The Permeable Reactive Barrier (PRB) is a sustainable in-situ method to remediate groundwater. Finding cost-effective and efficient reactive materials is a key problem with PRBs. Hence, the present study aimed to assess the applicability of two composite reactive media beds derived from several waste materials (building waste, sludge, sea sand, iron particles, bagasse, saw dust, bio char, fly ash and coconut coir pith) for PRBs to treat groundwater contaminated by landfill leachate. The study comprised two identical laboratory-scale PRB reactors: an experimental reactor and a control reactor. Each reactor included two reactive media beds in series. In the experimental reactor, one of the two beds was filled with a composite reactive media derived from waste materials with high particle densities, while the other was filled with waste materials of low particle densities. In contrast, both the beds of the control reactor were filled with Granular Activated Carbon (GAC). The experimental PRB demonstrated removal rates of 97.08 ± 0.11% (Pb), 65.01 ± 2.14% (Mn), 55.03 ± 1.06% (Fe) and 78.34 ± 1.58% (COD). The control reactor achieved removal rates of 99.26 ± 0.08% (Pb), 94.46 ± 1.13% (Mn), 80.23 ± 0.93%(Mn) and 98.83 ± 0.14% (COD). The shear strength reductions were 19%, 27%, and 11% for the high-density, low-density, and GAC beds, respectively. The associated reductions in hydraulic conductivity were 24%, 12%, and 35%. The waste-derived reactive media possess multiple properties sourced from different materials and can address the removal of multiple contaminants simultaneously, comparable to GAC.
... Motivated by a wide range of engineering applications involving flow in multi-layer porous-fluid channels, several studies have demonstrated the possibility of improving heat transfer in modified equipment parts and thus have kindled great interest in further research on flows through such configurations. In particular, a three-layer channel with a centred or sandwiched porous layer has a significant role in environmental engineering studies such as (i) groundwater remediation through permeable reactive barriers inside aquifer [25,26], (ii) the development of advanced microfluidic devices with specific thermal and transport properties [27][28][29], and (iii) soil erosion and sediment transport. The universality of this model highlights its adaptability and relevance across a broader spectrum of technological and scientific domains. ...
... . Substituting (30) into the energy budget equation (25) and simplifying the resulting equation, we finally get the following energy equation in terms of disturbance amplitude corresponding to the mode with eigenvalue ω = αc ...
A linear stability analysis is performed to investigate the stability of a plane Poiseuille flow of a fluid-porous-fluid three-layer system in a channel with smooth rigid walls. It is widely recognized that a channel with an isotropic porous layer exhibits more stability than those bounded by two porous walls. We investigate the specific role of anisotropy in this context by assuming an anisotropic porous layer saturated with the same fluid. The porous layer is modeled using the volume-averaged Navier–Stokes equation, and fluid layers using the Navier–Stokes equation. The flows are coupled through a stress-jump condition at the porous-fluid interface, allowing for a continuous velocity profile across the entire flow domain. The Orr–Sommerfeld type boundary value problem is developed to provide a framework for performing linear stability analysis. The spectral collocation method is used to solve the eigenvalue problem for the amplitude of arbitrary wavenumber disturbances. The instability characteristics originating from two-dimensional infinitesimal perturbations of the most unstable modes are investigated intensively. Three types of instability are identified in long-wave, moderate-wave, and short-wave regimes. The instability modes of the short-wave regime are specified as the fluid modes, and the modes in the other two regimes are recognized as the porous modes. Due to the presence of different modes, the neutral stability boundaries display uni-modal, bi-modal, and tri-modal structure that depends on the mean permeability and anisotropy. It is revealed that either an increase in mean permeability, a decrease in the anisotropy parameter, or a decrease in the depth ratio decreases the critical Reynolds number of each unstable mode, destabilizing the flow. At low wall normal permeability of the porous medium with large depth ratios (such as in the ground structure of geothermal systems), the porous mode is the dominant mode, triggering long-wave instability. Moreover, an energy budget analysis decodes the instability mechanism due to physical parameters. An equation for the rate of change of the kinetic energy of the two-dimensional infinitesimal disturbances is derived. Through the Reynolds stress, the energy production term transfers energy from the base flow to the disturbance, increasing the kinetic energies in all the layers and enhancing the growth rate of the least stable mode. The study paves the way for a stability analysis of a hydro-dynamically and thermally fully developed laminar flow in a multi-layer fluid-porous-fluid system that would facilitate the prediction of parameter regime where the overall performance of the systems can be optimized depending on the relevant applications.
... It provides water for drinking as well as other domestic, agricultural, and industrial uses [9,10]. Groundwater is used by about 2.5 billion people in all over the world in their daily lives [11]. Groundwater is used to meet the demands of diverse industries when fresh surface water resources are scarce. ...
... PRB is a revolutionary groundwater cleanup technology that is employed all over the world. To facilitate waste disposal, this method combines adsorption, chemical precipitation, and degradation processes to induce physical, chemical, or biological reactions between contaminants and reactive compounds included in barriers [11,49]. Because of the cheap operation cost, longevity of media, and hydraulic performance, the in-situ application of PRB has sparked a lot of attention [50][51][52]. ...
... Permeable Reactive Barrier (PRB) approach for the containment of contaminants was introduced as an alternative to conventional remediation techniques, such as pump-and-treat, which were found to be either impractical or costly in the long-term restoration of contaminated groundwater [182][183][184]. High efficiency, low maintenance, low operation costs, and low ongoing energy requirements are some of the advantages of PRBs over conventional remediation techniques [185,186]. ...
... As can be seen from Table 5, the focus of the studies on the PRBs was mostly on the permeable adsorbing barrier (PAB), using an adsorbent as the reactive material for contaminants' remediation. Several researchers have reviewed this technique for the remediation of groundwater [183,190,191,184]. ...
... Permeable Reactive Barrier (PRB) approach for the containment of contaminants was introduced as an alternative to conventional remediation techniques, such as pump-and-treat, which were found to be either impractical or costly in the long-term restoration of contaminated groundwater [182][183][184]. High efficiency, low maintenance, low operation costs, and low ongoing energy requirements are some of the advantages of PRBs over conventional remediation techniques [185,186]. ...
... As can be seen from Table 5, the focus of the studies on the PRBs was mostly on the permeable adsorbing barrier (PAB), using an adsorbent as the reactive material for contaminants' remediation. Several researchers have reviewed this technique for the remediation of groundwater [183,190,191,184]. ...
Contaminant containment measures are often necessary to prevent or minimize offsite movement of contaminated materials for disposal or other purposes when they can be buried or left in place due to extensive subsurface contamination. These measures can include physical, chemical, and biological technologies such as impermeable and permeable barriers, stabilization and solidification, and phytostabilization. Contaminant containment is advantageous because it can stop contaminant plumes from migrating further and allow for pollutant reduction at sites where the source is inaccessible or cannot be removed. Moreover, unlike other options, contaminant containment measures do not require the excavation of contaminated substrates. However, contaminant containment measures require regular inspections to monitor for contaminant mobilization and migration. This review critically evaluates the sources of persistent contaminants, the different approaches to contaminant remediation, and the various physical-chemical-biological processes of contaminant containment. Additionally, the review provides case studies of contaminant containment operations under real or simulated field conditions. In summary, contaminant containment measures are essential for preventing further contamination and reducing risks to public health and the environment. While periodic monitoring is necessary, the benefits of contaminant containment make it a valuable remediation option when other methods are not feasible.
... Permeable reactive barrier (PRB) technology could be an alternative to traditional pumping and treatment systems to treat contaminated groundwater (Henderson & Demond 2007). Since 1990, many PRBs have been designed and implemented in different forms, including funnel and gat (Thiruvenkatachari et al. 2008). The reactants are inserted in front of the subsurface contaminated flow path to convert contaminants into environmentally acceptable by-products and reduce the contaminant concentration downstream. ...
... Accordingly, extensive studies and additional efforts are required to select new materials, determine their properties, increase absorbent longevity, and thus identify their suitability for use in PRB. On the other hand, predicting the longevity of PRBs and several other issues have yet to be conclusively answered, so the main focus for additional research should be on innovative technologies to increase a system's longevity (Thiruvenkatachari et al. 2008). Two-barrier PRB was examined in this study to determine whether it was effective in removing contaminants simultaneously, increasing the longevity of nZVIs, and its performance over time. ...
The quality of groundwater resources is at catastrophic risk. The proper performance of iron nanoparticles has made a permeable reactive barrier (PRB) an alternative to conventional filtration methods. The performance of nanozerovalent iron (nZVI) PRBs is limited by particle aggregation, instability, and phase separation, even at low iron concentrations. Therefore, the precipitation of reactive materials and a decrease in the longevity of PRB are fundamental challenges. A laboratory setup is used to compare the performance of bare nZVI and xanthan gum (XG)-nZVI + Mulch PRB to simultaneously remove nitrate, sulfide, and arsenic in groundwater. nZVI (average diameter of 35–55 nm) particles are used as reactive media. The objectives are (1) to develop a method for treating nitrate, sulfide, and arsenic simultaneously in groundwater using organic mulch and XG-nZVI; and (2) to evaluate the longevity performance of the XG-nZVI + Mulch and bare nanoparticles treatment system over 10 days. The results showed that the XG-nZVI + Mulch barrier's performance for eliminating NO3-, As, and S2− was generally improved compared to the bare nZVI barriers by 5.7, 19.2, and 10.9%, respectively. Finally, despite the need for long-term sustainability assessment, XG-nZVI PRB performance is impressive, and this stability promises to improve the longevity of nanoparticles while used in PRBs.
HIGHLIGHTS
Permeable reactive barriers (PRBs) based on XG-nZVI + Mulch can lead to adequate remediation of NO3, As(V), S2− compared to the bare nZVI barriers by 5.7, 19.2, and 10.9%, respectively.;
The stability and longevity of the XG-nZVI + Mulch barrier are outstandingly better than the bare nanoparticles barrier.;
XG-nZVI + Mulch PRB's footprint is green and sustainable because of using recycled materials.;
... A very significant natural resource is groundwater to both terrestrial and aquatic ecosystems. One third of the world's population drinks groundwater as their primary potable source and uses it for domestic, production of food, industry [1], and irrigation of 40% of the food worldwide [2], despite its limited ecological resources consisting of a small portion of the total water distribution [3,4]. While the standards and needs of living on our natural environment are expanding, rising populations, ongoing urbanization, and industry increase the risk of groundwater contamination [5]. ...
... Beside the human medicine use, amoxicillin treats and prevents animal infections for increasing growth in a variety of domestic and food animals for broiler chickens, dogs, cats, horses, pigeons, pigs, sheep, goats, preruminating calves, cattle, and fish [15]. Usually, amoxicillin environmental degradation by a number of processes, such as (1) sorption, (2) transformation in biotics, and (3) transformation in abiotics, can influence the destiny and transit of organic compounds in the environment [16]. Over the years, the developments of treatment technologies and approaches for contaminated groundwater have become available allowing flexibility in how clean-up goals can be achieved. ...
This work uses a new nanoadsorbent after chemically synthesis from chicken eggshell wastes for removing amoxicillin (AMX) from aqueous solution. This removal was examined as a time function, initial concentration of AMX, pH, agitation speed, and adsorbent dosage. The study achieved the optimum time for equilibration in (90) min, at pH = 7 with an adsorbent dosage of 1.2 g. We applied many kinetic models to the sorption kinetic data where the pseudo-second-order model ( R 2 = 0.9924 ) was used to interpret the gained data at a rate constant K2 of (0.0077) g/(mg. min) at 200 rpm. Moreover, the adsorption calculated amount reached the experimentally required value and isotherm data best fitted the Langmuir model with R 2 (≥0.9486) than the Freundlich model. The intraparticle diffusion model revealed a diffusion dependent process. The different functional sets on the calcium/iron-surface as a layered double hydroxide (Ca/Fe)-LDH were important in sorpting the selected antibiotic. Forming (Ca/Fe)-LDH nanoparticles in the manufactured beads interacted with polluted water confirming that the nanoparticles own the prospective for acting as a latent sorbent to remove contaminants from aquatic media.
... 1,2 Among others, contaminants such as petroleum hydrocarbons (i.e., benzene, toluene, ethylene, and p-xylene, named BTEX) and chlorinated hydrocarbons are often detected in groundwater at various concentrations ranging from a few μg L −1 to several mg L −1 , 2−6 thereby posing a large risk to the environment and its ecological resources. 4 In situ chemical oxidation (ISCO) processes are considered efficient treatments for the removal of a wide range of organic contaminants from groundwater. 2,7,8 These processes involve underground injection of oxidative compounds, such as persulfates, peroxides, or gaseous ozone. 2 Ozone has a high oxidation potential (2.08 eV), 9 which reacts selectively with electron-rich moieties, often resulting in biodegradable transformation products. ...
... 10 Alternatively, ozone can react with surrounding constituents�including naturally occurring catalysts and intentionally added oxidants (e.g., hydrogen peroxide)�to form hydroxyl radicals that may also degrade ozone-resistant pollutants. 4,10,11 The practical use of in situ chemical ozonation (ISCO 3 ) processes, however, suffers from high energy consumption and inefficient distribution of the active ozone throughout the groundwater. 12 The ozone delivery method for ISCO 3 processes is a key factor for effective operation. ...
... Groundwater is the main source of drinking water worldwide [1,2]. However, there are numerous sites all over the world characterised by groundwater contaminated with organic and/or inorganic compounds, including toxic metals. ...
... • Mg(OH) 2 is much less soluble than Ca(OH) 2 in aqueous solutions (K S,Mg(OH)2 = 1 × 10 −11 ; K S,Ca(OH)2 = 4 × 10 −6 ); it is, therefore, an attractive alternative reagent for passive remediation systems [18]. • Upon contact with water, MgO hydrates to form Mg(OH) 2 , which buffers aqueous solutions' pH between 8.0-10.5 [18,32,33,35]. In this pH range, the solubility of most metal hydroxides is very low, so divalent metals cations, such as Zn 2+ , Cd 2+ , Ni 2+ , or Co 2+ , can be removed by precipitation [18,33,35,36]. ...
A laboratory method was designed and verified that allows for the testing of alkaline, magnesite-based reactive materials for permeable reactive barriers (PRBs) to remove heavy metals from contaminated groundwater. It was found that caustic calcined magnesia (CCM) with high reactivity and low solubility to remove Cu2+, Zn2+, Ni2+, and Mn2+ cations from mixed aqueous solutions can be prepared by calcination at a suitable temperature and residence time. Regarding the solubility of both the reactive material itself and the precipitates formed, the CCM should contain just a limited content of lime. One way is the calcination of a ferroan magnesite at temperatures above 1000 °C. However, the decrease in pH is accompanied by lower efficiency, attributed to the solid-phase reactions of free lime. A different way is the calcination of magnesite under the conditions when CaCO3 is not thermally decomposed. The virtually complete removal of the heavy metals from the model solution was achieved using the CCM characterised by the fraction of carbonates decomposed of approximately 80% and with the highest specific surface area. CCM calcined at higher temperatures could also be used, but this would be associated with higher consumption of crude magnesite. Under the conditions considered in the present work, the product obtained by the calcination at 750 °C for 3 h appeared to be optimal. The full heavy metal removal was observed in this case using less magnesite, and, moreover, at a lower temperature (resulting, therefore, in a lower consumption of energy for the calcination and material handling).
... Bioremediation and biotechnology can be used with bio-enhanced PRB, biological PRB, and passive bioreactive barrier. It can remediate chlorinated compounds and heavy metals in groundwater [19,20]. ...
Biotechnology is one of the emerging fields that can add new and better application in a wide range of sectors like health care, service sector, agriculture, and processing industry to name some. This book will provide an excellent opportunity to focus on recent developments in the frontier areas of Biotechnology and establish new collaborations in these areas. The book will highlight multidisciplinary perspectives to interested biotechnologists, microbiologists, pharmaceutical experts, bioprocess engineers, agronomists, medical professionals, sustainability researchers and academicians. This technical publication will provide a platform for potential knowledge exhibition on recent trends, theories and practices in the field of Biotechnology.
... The permeable reactive barrier (PRB) is a passive treatment technology for the decontamination of polluted groundwater. It was defined as an emplacement of reactive media in the subsurface designed to intercept a contaminant plume and provide a flow path through the reactive media, to transform the contaminants to less toxic forms and reduce their concentrations (Thiruvenkatachari et al, 2008). The schematic diagram of biochar-based materials as fillers for the remediation of groundwater in the PRB system is shown in Figure 27.3. ...
... For in situ applications, nano zerovalent iron (nZVI) can be directly injected into contaminated sites either in the form of sludge/suspension or integrated into the structure of permeable reactive barriers (PRBs). In the design of a PRB, groundwater flows passively through an engineered nZVI wall, causing contaminants to precipitate, adsorb, or transform into nonpolluting compounds [9]. Alternatively, nZVI can be utilized in ex situ applications following its integration into a support material, i.e., either a solid support material or a hybrid. ...
The objective of this study was to explore the removal of nitrate ions from groundwater by employing dynamic permeable reactive barriers (PRBs) with A400-nZVI. This research aimed to determine the parameters of the barrier and evaluate its overall capacity to retain nitrate ions during percolation with a potassium nitrate solution. The process involves obtaining zerovalent iron (nZVI) nanoparticles, which were synthesized and incorporated onto an anionic resin support material (A400) through the reduction reaction of ferrous ions with sodium borohydride (NaBH4). This is achieved by preparing a ferrous sulfate solution, contacting it with the ion exchange resin at various solid–liquid mass ratios and gradually adding sodium borohydride under continuous stirring in an oxygen-free environment to create the A400-nZVI barrier. The results of the study, focusing on the development of permeable reactive barriers composed of nano zero-valent iron and ion exchangers, highlight the significant potential of water treatment processes when appropriately sized. The research specifically assesses the effectiveness of NO3− removal by using the A400-nZVI permeable reactive barrier, conducting laboratory tests that simulate a naturally stratified aquifer with high nitrate contamination.
... These systems can be used individually or to supplement the other in situ remediation techniques. Advanced systems for permeable reactive barriers also have been developed, such as injection well systems, hydraulic fracturing, and passive groundwater capture and treatment by reactor cells, and nonpumping reactive wells for the in situ treatment of contaminants (Hosseini et al. 2018;Thiruvenkatachari et al. 2008;Wang et al. 2017). Studies have developed innovative PRB configurations and methods for the in situ remediation of arsenic and other contaminants. ...
A pumice-maghemite (P-maghemite) composite was developed using the chemical coprecipitation method with a 20% iron loading ratio by weight. The characterization of the composite using SEM and XRD indicated the effective loading and dispersion of nano-particles on the surface of the developed base materials. Thereafter, in situ sequestration experiments were conducted in the laboratory for an arsenic-polluted aquifer system using two well-integrated permeable reactive barrier (PRB) modules filled with the developed composite. A vertical fixed-bed column setup was used for the columnar PRB, whereas a sand tank experimental setup was employed for the well-screen-integrated PRB; both PRB systems were fed by a synthetic solution representing the arsenic-contaminated groundwater. More than 99% arsenic removal was observed in the columnar PRB, with an average effluent concentration of 4 μg/L at the end of the experiment, which is well below the acceptable limit of drinking water for arsenic (<10 μg/L). Removal of arsenic by the 4 cm wide well-screen-integrated PRB from 652 μg/L to less than 20 μg/L shows a great potential of the developed composite for arsenic remediation at slower groundwater flow rates. A maximum arsenic removal of 99% was attained at the start of the experiment, which decreased to 97% after 1 month of PRB operation. The effluent concentration of all other major ions also was reduced considerably in the PRB modules. The hydraulic conductivity of the developed media was reduced by 35% in the columnar PRB and by approximately 20% in the well-screen-integrated PRB. The high arsenic removal efficiency in continuous flow-through remediation systems indicates the applicability of the developed PRB system in in-situ remediation of arsenic-contaminated groundwater.
... AC-PRBs are an in-situ groundwater treatment option that involves the creation of a long narrow trench positioned downgradient of a contaminant plume and filling the trench with a wall of AC permeable reactive materials allowing the sequestering or reducing contaminants to less harmful forms (Guerin et al., 2002;Thiruvenkatachari et al., 2008). They are particularly useful in the Niger Delta case not only because they represent the most effective means of treating petroleum hydrocarbons but because they also offer cost-effective means of remediating groundwater. ...
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.
... In situ processing methods, such as the permeable reactive barrier (PRB), extend water cleanup times but significantly reduce operational costs by requiring only monitoring of the barrier's upgradient and downgradient water quality. For areas with trapped pollutants, on-site injection of reactive agents is preferable for destroying pollutants both at the contamination source and in groundwater [46,47]. ...
This study offers an updated overview of the soil and water remediation strategies employed to address the widespread environmental and public health risks associated with explosive compounds, particularly TNT and RDX. Recognizing soil contamination originating from military activities, industrial accidents, and historical land use, this review delves into physical, chemical, and biological approaches to mitigating ecological and human health concerns. While physical methods like excavation and disposal are effective, their applicability is constrained by cost and logistical challenges for large contaminated areas. Chemical methods, such as oxidation and reduction, focus on transforming explosives into less toxic byproducts. Biological remediation utilizing plants and microorganisms emerges as a cost-effective and sustainable alternative. This review highlights challenges, including the persistence of explosive compounds, potential groundwater leaching, and the necessity for long-term monitoring. Emphasizing the need for site-specific strategies, considering the contaminant type, concentration, soil properties, and regulatory requirements, this study advocates for integrated and sustainable remediation approaches in pilot-scale applications. It concludes by evaluating the appropriate solution based on the advantages and disadvantages of the categories of soil and groundwater remediation methods. The duration, the effectiveness, and the cost of available technologies were estimated.
... Similarly, any monitoring or observation network should be based on the anticipated behavior of the system. There are two main strategies: (i) to hinder, modify or remove the migration of the contaminant from the source to the environment [1,15,61,65]; or (ii) to protect the recipients from contamination by filters, barriers or pumping [13,14,72]. New techniques are continuously being developed to manipulate the contaminant source, but the latter strategy may be necessary for non-point sources as well as for contaminant plumes that have migrated long distances in the subsurface. ...
Water is one of the essential interactive environmental and vital components for sustaining life on Earth. The increasing awareness about our environment and the recognition of the need for its protection support rational and efficient use of water resources planning qualitatively and quantitatively. In this context, using numerical models as a tool for diagnosing, managing, and predicting groundwater behavior has been gaining considerable importance in recent years. The study of solute transport related to groundwater contamination has become the focus of numerous researchers from many viewpoints, and the resulting achievements are so scattered and extensive. Therefore, this work documents various literature to systematically study the available theoretical and experimental works on groundwater contaminant transport modelling. Here, a simplified systematic and integrative picture of the present status of groundwater contamination is provided to emphasize the new trends and challenges to facilitate future research directions for more comprehensive analyses of the solute transport phenomena, with some recommendations toward solving these challenges.
... V vseh znanih primerih (sicer vedno podkritičnega) dokazanega onesnaženja je bil krivec neustrezen beton, ki ni zadoščal zahtevam naročnika 5 in v vseh takih primerih je izvajalec vrtino saniral. Poleg tega so se v zadnjem času pojavile nove tehnologije, ki že sedaj zelo nizko verjetnost onesnaženja podtalnice še bistveno znižajo 6 . ...
Pridobivanje ogljikovodikov z metodo tako imenovanega hidravličnega frakcioniranja (hidravličnega lomljenja oz. s tujko: frackinga) je znana že približno 70 let. Šele v zadnjem desetletju pa je postala ekonomsko zanimiva. Medtem, ko ZDA postajajo zaradi uporabe te tehnologije energetsko samozadostne, cene električne energije tam padajo, cena nafte na svetovnih trgih pa je padla pod polovico tiste izpred masovne uporabe frakcioniranja, v Evropi zaradi okoljskih pomislekov naftnih skrilavcev oz. bituminoznih peskov ne izkoriščamo. Potenciale imamo tudi v Sloveniji. V medijih je bila v preteklosti izkoriščanje skrilavcev in bituminoznih peskov pogosta tema in laiku je težko ločiti zrnje od plev. V Prekmurju, ki ima potencial za pridobivanje ogljikovodikov s pomočjo omenjene tehnologije, so civilne iniciative (karkoli že to pomeni) izrazile ostro nestrinjanje z uporabo te tehnologije. Glede na izjave udeležencev shodov bi naj šlo za okoljsko nevarnost bibličnih razsežnosti. Tudi poročanje medijev je v večini primerov precej enostransko. Zato bomo v prispevku na poljuden način skušali pojasniti fizikalne postopke, uporabo kemičnih snovi pri omenjeni tehnologiji in njene posledice za okolje na podlagi dosedanjih izkušenj. Pri tem se bomo omejili zgolj na znanstveno-tehnično podprta in preverljiva dejstva.
... Additionally, around two billion individuals rely on this water for drinking purposes. [2][3][4][5] In addition to natural sources of contamination, various human activities contribute to the release of diverse quantities and types of contaminants, including the use of pesticides, disposal of waste in sanitary landll sites, storage of chemicals in underground tanks, application of contaminated soil, and transportation of chemical liquids. [6][7][8][9][10] It is very important to note that the inltration of contaminants into the aquifer results in the formation of a distinctive plume, the migration of which is determined by the characteristics of the soil and the velocity of groundwater. ...
This study investigates the effectiveness of using Iraqi clay as a low-permeability layer to prevent the migration of lead and nickel ions in groundwater-aquifers. Tests of batch operation have been conducted to determine the optimal conditions for removing Pb 2+ ions, which were found to be 120 minutes of contact time, a pH of 5, 0.12 g of clay per 100 mL of solution, and an agitation of 250 rpm. These conditions resulted in a 90% removal efficiency for a 50 mg L −1 initial concentration of lead ions. To remove nickel ions with an efficiency of 80%, the optimal conditions were 60 minutes of contact time, a pH of 6, 12 g of clay per 100 mL of solution, and an agitation of 250 rpm. Several sorption models were evaluated, and the Langmuir formula was found to be the most effective. The highest sorption capacities were 1.75 and 137 mg g −1 for nickel and lead ions, respectively. The spread of metal ions was simulated using finite element analysis in the COMSOL multiphysics simulation software, taking into account the presence of a clay barrier. The results showed that the barrier creates low-discharge zones along the down-gradient of the barrier, reducing the rate of pollutant migration to protect the water sources.
... The continuous permeable reactive barrier (C-PRB) is a common PRB configuration that involves the placement of reactive materials in a continuous trench perpendicular to the groundwater flow (Higgins and Olson, 2009). This configuration has several advantages, including simple structure, convenient construction, and minimal interference with the natural groundwater flow (Thiruvenkatachari et al., 2008). However, C-PRBs are expensive to construct and use materials that can be costly, limiting their application to sites with large contaminant plumes or deep groundwater (Bortone et al., 2013). ...
The passive convergence-permeable reactive barrier (PC-PRB) was proposed to address the limitations of traditional PRB configurations. To evaluate the hydraulic and pollutant removal performance of the PC-PRB system, we developed a simulation code named PRB-Trans. This code uses the two-dimensional (2D) finite element method to simulate groundwater flow and solute transport. Case studies demonstrate that PC-PRB technology is more efficient and cost-effective than continuous permeable reactive barrier (C-PRB) in treating the same contaminated plume. Implementation of PC-PRB technology results in a 33.3% and 72.7% reduction in PRB length (LPRB) and height (HPRB), respectively, while increasing 2D horizontal and 2D vertical pollutant treatment efficiencies of PRB by 87.8% and 266.8%, respectively. In addition, the PC-PRB technology has the ability to homogenize the pollutant concentration and pollutant flux through the PRB system, which can mitigate the problems arising from uneven distribution of pollutants in the C-PRB to some extent. The LPRB required for PC-PRB decreases as the water pipe length (Lp) increases, while the HPRB required initially decreases and then increases with increasing Lp. The effect of passive well height (Hw) on HPRB is not as significant as that of Lp on HPRB. Overall, PC-PRB presents a promising and advantageous PRB configuration in the effective treatment of various types of contaminated plumes.
... Additionally, around two billion individuals rely on this water for drinking purposes. [2][3][4][5] In addition to natural sources of contamination, various human activities contribute to the release of diverse quantities and types of contaminants, including the use of pesticides, disposal of waste in sanitary landll sites, storage of chemicals in underground tanks, application of contaminated soil, and transportation of chemical liquids. [6][7][8][9][10] It is very important to note that the inltration of contaminants into the aquifer results in the formation of a distinctive plume, the migration of which is determined by the characteristics of the soil and the velocity of groundwater. ...
This study investigates the effectiveness of using Iraqi clay as a low-permeability layer to prevent the migration of lead and nickel ions in groundwater-aquifers. Tests of batch operation have been conducted to determine the optimal conditions for removing Pb 2+ ions, which were found to be 120 minutes of contact time, a pH of 5, 0.12 g of clay per 100 mL of solution, and an agitation of 250 rpm. These conditions resulted in a 90% removal efficiency for a 50 mg L −1 initial concentration of lead ions. To remove nickel ions with an efficiency of 80%, the optimal conditions were 60 minutes of contact time, a pH of 6, 12 g of clay per 100 mL of solution, and an agitation of 250 rpm. Several sorption models were evaluated, and the Langmuir formula was found to be the most effective. The highest sorption capacities were 1.75 and 137 mg g −1 for nickel and lead ions, respectively. The spread of metal ions was simulated using finite element analysis in the COMSOL multiphysics simulation software, taking into account the presence of a clay barrier. The results showed that the barrier creates low-discharge zones along the down-gradient of the barrier, reducing the rate of pollutant migration to protect the water sources.
... Natural zeolite (ZE), which deposits naturally can treat heavy metals due to its structure. Granular activated carbon (GAC) and ZE are efficient and high-cost commonly applied reactive materials (Thiruvenkatachari et al. 2008;Halim et al. 2010;Kumar et al. 2013). ...
Total iron is one of the problematic contaminants existing in the landfill leachate, which may lead to both ground and surface water pollution. This study was conducted to find out the potential of a low-cost composite adsorbent (COM) to treat total iron in landfill leachate using batch sorption experiments. The COM was composed mainly of brick-and-mortar waste and biochar with small amounts of granular activated carbon (GAC) and natural zeolite. Both kinetic and adsorption isotherm experiments were conducted for the COM as well as for its ingredients individually, to optimize the contact time and mass of the adsorbent, respectively. The removal efficiency of the COM was 95.0%, whereas that of high-cost zeolite and GAC were 89.7% and 93.0%, respectively. The initial total iron concentration, stirring speed, temperature, and initial pH were optimized for the COM. The total iron removal efficiency increased with the increment of the initial total iron concentration, stirring speed and temperature, and the reduction of the initial pH of the influent. Finally, a verification test was conducted with the COM at the optimum conditions. Four replicates were tested. All the replicates gave an average removal efficiency of 99.2 %. The average adsorption capacity was 1.3 mg/g, and the measurements were fitted the best with a Langmuir isotherm model with R² equal to 1. Hence, the COM has the potential to be applied as a reactive/packing medium in any treatment process of landfill leachate or wastewater of the similar characteristics as landfill leachate.
... • the life span of ZVI [2,4,[16][17][18][19][20][21][22]; • the necessity for and relevance of an in-depth knowledge of hydrogeology and the nature of contaminated plumes [13,16,17]; • the necessity for detailed and comprehensive field monitoring to evaluate the effectiveness of the PRBs [2,23]; • the necessity for a better understanding of the removal mechanisms activated by ZVI-based aqueous systems [22,[24][25][26][27]. ...
Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences “failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors.
... Permeable barriers are considered to be a better long-term solution, as they do not disrupt groundwater movement and do not induce blockages in the geologic horizon [5][6][7]. A variety of natural materials, including zeolites [8][9][10], limestone [6,11], apatite [12], artificially created materials such as cement-based filter media (CBFM) [13], waste products (e.g., fly ash [14]), as well as numerous organic materials and their compositions with minerals [15], can be used to create these barriers. ...
Groundwater samples contaminated with potentially toxic elements (PTE), including metals and nitrate ions, were collected at a depth of 8-10 m from the Siberian Chemical Plant multicomponent waste storage. The possibility of developing a permeable biogeochemical barrier with zeolite and lightweight expanded clay aggregate (LECA) was investigated. The mass fraction and properties of several metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb) were determined to investigate their fixation on the chosen materials at the given experimental conditions. It was established that metals in sulfide or phosphate forms can be effectively immobilized via biomineralization on LECA, whereas metals from the non-chalcogen group are primarily retained in the form of phosphates. The formation of biogenic deposits of iron sulfide, which serve as a sorption-precipitation phase during the immobilization of the majority of metals, is an important aspect of the LECA loading process. The use of LECA and zeolite in the form of a two-component barrier is feasible based on the data obtained. It is assumed that metal immobilization processes occur due to sorption mechanisms in the zone of zeolite loading. Microbial nitrate removal and the formation of iron sulfide phases under reducing conditions, which form a geochemical barrier for metals, are expected in the LECA zone.
... The effectiveness of PRB depends largely on the reactive factor used. For many years, the following were used as reactive factors in PRBs: zero-valent iron [10,11], waste products, and natural materials, e.g., chitin, fly ash, clay soil, zeolites [12,13], humic acids [14], polymers, and carbon materials [15][16][17][18][19]. From an economic standpoint, the main problem with PRBs is the need to remove and recover the spent reactive material after the cleaning process [20]. ...
This paper aims to propose an alternative to the known permeable reactive barriers (PRBs). PRB is one of the methods, which is a reactive barrier placed below the ground, to clean up contaminated groundwater. New polymer active substrates (ASs) were used to prevent soil contamination by toxic heavy metals. The active substrates consisted of a mixture of poly(vinyl chloride), Aliquat 336, and bis(2-ethylhexyl)adipate, which was applied to the skeleton material (fiberglass or textile). Aliquat 336 was used as a binding agent for metal ions (Cr(VI), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II)). In contrast with the PRBs, the ASs (from AS-1 to AS-5) were obtained in a simple way using the pouring method. The obtained ASs could be recycled and reused. The active substrates were used for the binding of various metal ions from aqueous solutions and the examined soil. It was found that the active substrate AS-1 decreased the concentrations of nickel, cadmium, and lead by more than 50% and that of chromium by more than 90% in the aqueous solution. High sorption efficiency for chromium and zinc metals (81% and 66%) with the use of AS-2 was also found, owing to which the migration of metals from soil to water can be limited. In the soil environment, active substrate AS-5 with the addition of a plasticizer showed the greatest effectiveness. This solution resulted in a reduction in each tested metal ion of at least 50%, and reductions in cadmium, lead, and copper of over 70%.
Groundwater, one of the most important freshwater resources on Earth, is currently experiencing degradation in both quality and quantity. This has prompted scientists to seek solutions to this problem, one of which is permeable reactive barriers. While many researchers have studied PRBs, few have conducted comprehensive literature reviews. In this article bibliometric analysis has been done on permeable reactive barriers publications from 1995 to 2023. This study systematically analyzed various aspects of permeable reactive barriers research, including countries and sponsors, authors, journals, and keywords. This bibliometric analysis of permeable reactive barriers research revealed that China has become the leading country in publication output, due to its strong performance in recent years. The top journal in this field is Environmental Science and Technology, with 60 publications and 5726 citations. The author with the most publications is Faisal A.H., with 24 publications primarily published recently. Keyword analysis and clustering were performed to identify the leading and most popular topics in permeable reactive barriers research. Six clusters were identified, with heavy metals being the most popular topic. Nowadays, researchers are also showing a growing interest in sustainable and biological remediation. In the end, an in-depth comparison that compares different permeable reactive barrier methods with the conventional Pump and Treat approach has been carried out, with a particular emphasis on long-term sustainability and life-cycle cost considerations. Researchers can use the findings in this study as a helpful reference and comprehensive overview for their works.
The aim of this research involves investigating the elimination of nitrogen ions from groundwater through the application of dynamic permeable reactive barriers (PRB) utilizing A400-nZVI. The aim also implyies determining barrier parameters, as well as assessing the overall retention capacity of nitrogen ions through percolation with a potassium nitrate solution. The research involves obtaining zero valent iron nanoparticles (nZVI), which were synthesized and doped onto an anionic resin support material (A400) through the reduction reaction of ferrous ions with sodium borohydride (NaBH4). This was achieved by preparing a ferrous sulfate solution, contacting it with the ion exchange resin at various solid-liquid mass ratios, and gradually adding sodium borohydride under continuous stirring in an oxygen-free environment to create the A400-nZVI barrier. The outcomes of this study, focusing on the development of permeable reactive barriers composed of nanovalent iron and ion exchangers, demonstrate significant potential in purification processes when appropriately dimensioned. The research specifically evaluated the efficacy of NO3- removal using the A400-nZVI permeable reactive barrier, conducting laboratory tests that simulated a naturally stratified aquifer with high nitrate contamination.
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.
The degradation of environmental quality has become an escalating concern in contemporary society that precipitates
multifaceted issues. In response to this challenge and the imperative to restore natural environmental
equilibrium, researchers are intensifying their investigations into the utilization of carbon nanotubes (CNTs) for
environmental sustainability. CNTs manifest a notable adsorption capacity and superior reactivity, rendering
them highly sensitive and selectively responsive to environmental pollutants. The functionalization of CNTs has
yielded significant advancements in a diverse array of CNT-based sensors and adsorbents tailored for environmental
protection. This review comprehensively explores the varied advantages offered by CNTs across various
environmental applications. In addition to presenting the CNT use in air, water, and soil remediation, a particular
emphasis is placed on the regeneration of spent CNTs. Drawing insights from the reviewed literature, it is evident
that CNTs have been effectively regenerated and employed multiple times, underscoring their considerable
potential as a promising material for environmental detoxification. The challenges, perspectives, and future
considerations were presented at last to show the current situation and next potentials. This article assumes
paramount importance for scientists and technologists seeking robust solutions for air, soil, and water purification
challenges.
Mercury (Hg) contamination in groundwater poses significant environmental and health risks, necessitating effective remediation strategies. Recently, molybdenum disulfide (MoS2) nanosheets have emerged as a promising nanomaterial for the remediation of...
Groundwater pollution poses a significant threat globally, particularly in developing countries where inadequate sanitation facilities contribute to growing concerns about contamination from sewer leaks. Hence, the objective of this study is to present a comprehensive review, offering insights into diverse aspects of sewer leaks and their impacts on the urban groundwater system. This includes an exploration of leak sources, methods for leak detection, quantification approaches, analysis of contaminants in sewage along with their health effects, and strategies for mitigating both sewer leaks and groundwater contamination. This review addresses various factors leading to sewer infrastructure damage, emphasizing its importance in effective maintenance strategies. In this review, a range of contaminants released from sewer leaks were outlined, ranges from emerging contaminants to heavy metals that poses risk to the human health and environment. Further it evaluates various methods for detecting sewer leaks, emphasizing advancements in water quality analysis, visual, electromagnetic, and acoustics techniques. This research assesses diverse techniques for quantifying sewage leaks, including mass balance and wastewater balance and concludes pinpointing specific leak hotspots remains challenging. Furthermore, an appraisal of mitigation measures was also conducted, determining that rehabilitation serves as a more effective approach to stop leaks at their source. This paper delves into groundwater treatment methods, highlighting the difficulties in achieving optimal water quality and reveals that technologies such as Permeable Reactive Barrier and advanced oxidation processes exhibit potential in effectively removing trace-level pollutants. Overall, the review underscores the importance of understanding, detecting, and mitigating sewer leakage for the health and sustainability of groundwater systems.
This paper aims to compare and analyze different locally sourced kaolin samples for the synthesis of zeolite catalysts. Zeolite catalysts have gained significant attention due to their unique properties and applications in various industries. The synthesis of zeolite catalysts from kaolin, a locally available material, offers a cost-effective and sustainable alternative to chemical feedstocks. This study focuses on the characterization of kaolin samples, including their morphology, elemental composition and particle size, to determine their suitability for zeolite synthesis. The catalytic activity of the prepared zeolite catalysts will also be evaluated in the further research using plastic cracking as a model reaction. The findings of this research will contribute to the development of efficient and environmentally friendly zeolite catalysts for industrial applications.
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.
Non-pumping reactive wells (NPRWs) are subsurface structures used for the passive treatment of contaminated groundwater using wells containing reactive media. In the vicinity of NPRWs, a combination of hydrogeological and chemical processes makes it difficult to predict their longevity. In this study, we evaluated the longevity of NPRWs using the upscaling methods. A horizontal two-dimensional sandbox was constructed to mimic the hydrogeological and chemical processes in a single unit of NPRW (unit NPRW). The groundwater flow and solute transport were simulated numerically to validate the processes of contaminant spreading prevention in the sandbox. Dye tracing and arsenic transport tests showed different performance of NPRW due to induced flow and uneven consumption of reactivity, which is dependent on the pathway length and residence time of the coal waste. Through numerical modeling of the experiments, the fate-related processes of contamination around NPRW were described in detail in both spatial and temporal terms. The stepwise approach of the upscaling methods was used to predict the contamination-blocking performance of the entire facility based on the reactivity of the materials and the contamination removal of the unit NPRW.
Leachate produced by various landfill dump site causes serious problem to humans as well other living organisms. In 1990s, permeable reactive barrier has been introduced as it is placed at the side of the landfill dump site which reduces the contamination in the plume. Permeable reactive barrier has several reactive materials like zero valent iron, activated carbon, zeolite, limestone, and others. On the basis of several criteria among the various reactive material rubber (waste tire), fiber is selected as reactive material in this study. The performance of rubber in PRB is analyzed by preparing model setup in laboratory by studying the characteristics of leachate water and treated (using rubber fiber as reactive material) water. The rubber is selected based on the environmental aspect as nowadays it is a challenging task to dispose the tire wastes. Along with rubber, red soil and M-sand are used to improve its efficiency.KeywordsPRBRubberLeachateZero valent ironActivated carbon
Volumetric shrinkage behavior of clays due to drying is important for various engineering applications. Structures built on the plastic soils experience unwanted settlements or often experienced an increase in flow rates through fractured (cracked) clay soils used in dams and landfill cover system due to reduction in water content. The decrease in moisture content causes reduction in the soil volume due to the decrease in diffuse double layer thickness. The study of shrinkage characteristics of plastic clays requires variation of void ratio over a wide range of water contents. Laboratory estimation of entire volumetric shrinkage curve is often cumbersome due to practical problems in the accurate estimation of total volume or soil density. In this work, laboratory tests for the estimation of volumetric shrinkage curve are presented. The test results on low plastic clay and high plastic clay using the resin and standard mercury replacement techniques are presented. The residual red soil and two bentonite clays of different quality used in this work for developing the volumetric shrinkage curve from the slurry state to below shrinkage limit state. The mechanism behind the resin technique for the estimation of volume is given. The advantage of resin technique and limitation of standard shrinkage limit test method will be presented in detail in this paper.KeywordsShrinkageVoid ratioVolume changeWater contentDegree of saturation
This paper deals with the experimental studies carried out to explore the possibility of using naturally available bamboo to increase the bearing capacity of soft soil. There are many alternatives for stabilizing the soil, but this paper is solely focused on safety with economical solution which is the actual agenda of civil engineering. Also, where most of the construction focusing on creating something huge or new, this research is focusing on no harm to nature as bamboo is eco-friendly to the nature.Reinforcing with bamboo mat is an alternative solution to improve bearing capacity of clayey or marshy soil. As bamboo is biodegradable in nature, bitumen coating was used to improve the durability of bamboo. The research was conducted in the laboratory using an experimental test box of length 1000 mm, width 1000 mm, and height 1000 mm. Total eight experiments have been done on soil having no reinforcement and with reinforcement of bamboo mats with and without bitumen coating. Also, test has been conducted on weather bamboo mat which was placed under the soil for four months. Generally, the more reinforcement is used to increase the bearing capacity of clayey soil.KeywordsBambooClayBearing capacity
Industrialization has undoubtedly made our lives easier, but it has come at a price, the most serious of which is environmental degradation. Heavy metal accumulation is one of the most prime factors to the soil pollution globally. Heavy metal contamination that has led to the pollution of soil is becoming a global issue. A long-term solution to alleviate heavy metal contamination is extremely important. Among all the methods phytoremediation is a low cost, eco-friendly, and aesthetically pleasing. Phytoremediation is one of the most environmentally friendly methods for reclaiming, revegetating, remediating, and restoring heavy metal-contaminated landscapes. A number of researchers are now proposing the cultivation of aromatic plants such as lemongrass (Cymbopogon citratus) in such areas as it fulfills the purpose of phytoremediation while also providing financial benefits due to its variety of uses in medicinal and other purposes such as mosquito repellent. The phytoremedial capacity of lemongrass was investigated in a pot experiment using different industrial by-products such as fly ash. Factors such as metal tolerance index (MTI), growth toxicity index (GTI), bioaccumulation factor (BAF), translocation factor (TF) were studied. Lemongrass appears to be a possible phytoextractor for heavy metals like mercury, lead, copper, chromium, nickel, cadmium, and arsenic, according to our research. Because of its increased biomass and metal absorbing capability, lemongrass seemed to be the best plant species among all the types studied.KeywordsPhytoremediationLemongrassMetal tolerance indexIndustrial by-productsBio-accumulation factor
Soil is a natural resource which is sometimes used as a construction material. In few cases, soils show poor performance because of its inadequate engineering properties. Due to rapid growth in urbanization, the availability of component land is decreasing. It is forcing the construction work to be done on all types of soil including weak soils. But the poor physical and engineering properties of weak soil do not make it suitable for construction work, and as a result, it requires improvement. By using ground improvement techniques, these weak soils can be converted into competent soil. A planar or three-dimensional synthetic material has been used in this field to improve ground qualities is being termed as Geosynthetic. Geosynthetic ground reinforcement techniques are used to improve the physical and mechanical properties of weak soils and reduce the amount of immediate settlement and slope failure and also widely used for strengthening of in-situ soil, mechanical improvement of pavement layers from the sub-base up to the asphalt wearing course using different type of geosynthetics, from geotextile to geogrids and geocomposite. Geosynthetic clay liners (GCLs) are also used for landfills due to its low permeability and self-healing properties. Within this manuscript, a study has been done about the effects of geogrid, geocell, or geotextile on the bearing capacity of the soil. It is observed that there is fair amount of increment in the load carrying capacity of soil and reduced the amount of displacement in the footing. Geosynthetic reinforcement is also used for railway track construction and embankment construction.KeywordsBearing capacitySoil reinforcementGeogridGeotextileGeocellGeosynthetic clay liners
The thermal backfill is important for underground heavy crude oil storage tanks and oil pipelines to restrict the heat transfer through the source. The native soil might not be satisfactory as backfill material and, subsequently, require appropriate amendment. Biochar is a less thermally conductive material that can be amended to native soil to make it suitable for thermal backfill. A previous study found that adding different biochar fractions reduces the thermal characteristics of soil. However, in a previous study, soil-biochar composite (SBC) thermal characteristics were measured at maximum possible compaction states that are achieved at the maximum dry density and optimum water content. Consequently, the above results are the combination of the influence of maximum possible compaction states and biochar fractions. Therefore, to study the effect of different biochar fractions solitary on the thermal characteristics of SBC, the samples were compacted under two different conditions. In the first case, the sample was compacted at fixed load, while it was compacted at fixed density in the second case. The water content of SBC was kept the same for both cases. The soil was amended with three distinct biochar percentages (5, 10, and 15%) and three distinct biochar fractions [coarse (4.7–2 mm), medium (2–0.425 mm), and fine (0.425 mm-0.075 mm)], and their thermal characteristics were measured. The thermal characteristics of biochar admixed soil consistently reduced with a decrease in the size of biochar granules. Comparatively, the reverse trend was observed for the samples compacted at fixed density.KeywordsBiocharFixed loadBiochar fractionsFixed densityThermal characteristicsThermal backfill
Removal of hexavalent chromium, Cr(VI), from an artificial groundwater by two commercially available granular activated carbons (GACs) was investigated in batch and continuous-flow column studies. Experimental parameters examined included solution pH, presence of dissolved oxygen (DO),
and GAC pretreatment with reducing agents. As solution pH increased from 4 to 7.5, the amount of Cr(VI) removed by both GACs decreased significantly. Removal of DO from experimental systems enhanced GAC performance, but pretreatment of the GACs with reductants (ferrous iron or dithionite)
did not improve Cr(VI) removal. Equilibration with 0.01 M dibasic potassium phosphate [to extract adsorbed Cr(VI)] followed by a wash with 0.02 N sulfuric acid [to remove precipitated-sorbed Cr(III)] proved to be a viable method to regenerate carbons whose Cr(VI) removal capacities were exhausted.
Performance of regenerated carbons exceeded that of virgin carbons, primarily because of the favorable adsorption of Cr(VI) at low pH values and the reduction of Cr(VI) to Cr(III) on acidic GAC surfaces. The presence of Cr(III) in acid wash solutions provides direct evidence that Cr(VI) is
reduced to Cr(III) in GAC systems under relatively acidic conditions. Granular activated carbon performance during five complete cycles was consistently high, which suggests that such a system will be able to function over many operation cycles without deleterious effects.
Research described in this research brief explores the geochemical and microbiological processes occurring within zero-valent iron treatment zones in permeable reactive barriers that may contribute to decreases in iron reactivity and decreases in reaction zone permeability that, in turn, may eventually lead to system plugging and failure. Using advanced surface analytical techniques together with detailed coring and water sampling programs at two geographically, hydrogeologically, and geochemically distinct iron barrier installation sites, specific objectives of this research project were to: 1) Characterize the type and nature of surface precipitates forming over time at the upgradient aquifer/iron interface, within the iron zone, and at the downgradient/iron interface. 2) Develop conceptual models that predict the type and rate of precipitate formation based on iron characteristics and water chemistry. 3) Identify type and extent of microbiological activity upgradient, within and downgradient in at least one of the chosen sites to evaluate microbiological response or effects from emplaced iron into an aquifer system. 4) Develop practical and cost-effective protocols for long-term performance assessments at permeable reactive barrier installations.
The removal of pollutants from the groundwater using permeable reactive barriers is a novel category of groundwater remediation technology. The first part of this work (Simon and Meggyes 2000) analysed the most relevant decontamination processes. This paper deals with engineering of permeable reactive barriers. Construction meth-ods of reactive barriers and cut-off walls exhibit similar features. In addition to conven-tional cut-off wall construction methods (single-and twin-phase diaphragm walls, composite cut-off walls, bored-pile walls, jet grouting, thin walls, sheet pile driven walls, injection and frozen walls) drilling, deep soil mixing, jet technology, arrays of wells, injected systems, hydraulic fracturing and biobarriers can be applied to construct per-meable reactive barriers. Permeable reactive barriers bear great future potential in remediation engineering.
The thorium and uranium uptake from their aqueous solutions by unpretreated and NaCl-pretreated zeolite-bearing volcanoclastic rock samples from Metaxades (Thrace, Greece) has been studied using a batch-type method. The concentration of the solutions varied between 50 and 20 000 mg/l. The NaCl pretreatment of the materials improved the thorium but not the uranium uptake. The absolute thorium uptake by the pretreated material, determined using neutron activation and X-ray fluorescence techniques, reached 12.41 mg/g, whereas the uranium uptake by the raw material was 8.70 mg/g. The uptake distribution coefficients (Kd) indicated that the relative thorium and uranium uptake is higher for initial concentrations below 250 mg/l. The zeolitic materials showed exceptional resistance to the initial low pH of the solutions used. The pHin was significantly increased due to the simultaneous hydrogen-ion uptake. The thorium and uranium uptake is a rather complicated phenomenon related to the aqueous chemistry of the elements, the nature of the constituent minerals and the properties of the zeoliferous rock specimens. The various metal species are bound through different uptake processes such as ion-exchange, adsorption and surface precipitation. Microporous minerals (zeolites, phyllosilicates) are mainly responsible for the considerable uptake ability of the rock samples studied.
The Australasia-Pacific Region supports approximately 50% of the world's population. The last half-century has witnessed a rapid increase in the regional population, agricultural productivity, industrial activities and trade within the region. Both the demand for increased food production and the desire to improve the economic conditions have affected regional environmental quality. This volume presents an overview of the fate of contaminants in the soil environment; current soil management factors used to control contaminant impacts, issues related to sludge and effluent disposals in the soil environment; legal, health and social impacts of contaminated land, remediation approaches and strategies to manage contaminated land, some of the problems associated with environmental degradation in the Australasia-Pacific Region and steps that we need to take to safeguard our environment.
Preface
Groundwater is one of mankind’s most important natural resources because it is the main source of drinking water. Contaminated sites resulting from industrial activity, mining, improper waste disposal or accidents involving hazardous substances pose a permanent threat to aquifers. Harmful chemicals can leach from polluted areas, for instance through rain water infiltrating the soil, and migrate downwards until they reach an underlying aquifer. The groundwater may become contaminated as a result and no longer usable as drinking water. It is, therefore, very important to develop and implement methods of preventing and reducing groundwater pollution. Pump-and-treat, the most frequently used conventional method for groundwater remediation, exhibits a number of shortcomings, while permeable reactive barriers (PRBs) represent a new and innovative technology with many advantageous features.
PRBs enable physical, chemical or biological in situ treatment of contaminated groundwater by bringing it into contact with reactive materials. The reactive material is inserted underground in a natural aquifer and intercepts the pollution plume as it is carried along within the aquifer, and thus the contaminants are treated without either wholesale soil excavation or water pumping. This cost-effective clean-up technology has much less impact on the environment than other methods, and since it requires hardly any energy input during operation, it is generally more economical over the long term than methods such as pump-and-treat that require continuous energy input.
While extensive research has been performed on many technological aspects of PRBs, and a number of contaminants have already been successfully treated by PRB systems, long-term performance has not been extensively considered and little is known about the processes influencing the long-term behaviour. This gap in our knowledge is all the more problematic because design life has a decisive influence on the economic viability of PRBs.
This book describes methods for the evaluation and enhancement of the long-term performance of PRB systems, especially of those targeting heavy metals such as uranium and organic contaminants, by sorption and/or precipitation mechanisms. The contents originate mainly from original research work performed within an international collaborative project funded by the European Commission. The project was called “Long-Term Performance of Permeable Reactive Barriers Used for the Remediation of Contaminated Groundwater” (acronym: “PEREBAR”) and was undertaken between the years 2000 and 2003. Processes that impair the barrier performance during PRB operation, and technologies to enhance the long-term efficacy of PRB systems were studied qualitatively and quantitatively. Two case study sites formed the central part of the project. The primary case study site was the former Hungarian uranium ore mining and processing area near the city of Pe´cs in Southern Hungary. The second site is located in Brunn am Gebirge, Austria, where an activated carbon PRB system is installed to treat a plume of organic contaminants at a former industrial site.
The first two chapters of this book introduce the field of PRBs as an innovative technology for passive groundwater remediation. Chapter 1 gives a brief introduction to the concept of PRBs. Potential reactive materials and the major biogeochemical mechanisms that can be utilised in PRBs are presented, and design considerations discussed. Particular attention is given to an up-to-date review on the application of PRBs, especially on the experiences and lessons learnt about the long-term performance of fullscale installations. Chapter 2 describes the practical aspects of PRB construction. In the first part of this chapter, cut-off wall construction methods are described, since PRB construction techniques are based firmly on experience gathered with these methods and because cut-off walls are integral parts of some PRB designs (e.g. funnel-and-gate systems). In the second part, PRB design considerations and construction techniques (including some innovative techniques) are explicitly discussed.
The next four chapters focus on the removal of uranium from contaminated groundwater by a selection of reactive materials including zeolites, hydroxyapatite (HAP) and elemental iron (Fe0, also widely referred to as “zero-valent iron” (ZVI)). The driving force behind the investigations described in these chapters was the case study site in Pe´cs, Hungary. Therefore the experimental conditions develop, chapter by chapter, towards the actual field conditions at that site. Chapter 3 describes the results of batch experiments conducted to evaluate the effectiveness of natural zeolitic tuff, hydroxyapatite, activated carbon, hydrated lime, elemental iron and iron oxides in removing uranium from aqueous solution. The experiments were conducted with simple solutions of uranyl nitrate dissolved in deionised water. It was found that elemental iron and hydroxyapatite are the most effective materials in removing uranium from water. Therefore, further experiments focused on these two materials.
Column experiments described in Chapter 4 showed that elemental iron and hydroxyapatite have strong uranium attenuation capabilities. The column experiments also showed the susceptibility of elemental iron to corrosion effects and the formation of secondary mineral precipitates due to the extreme geochemical conditions inside the iron matrix. A special feature of the column experiments was the development of a nondestructive method to measure the propagation of the uranium front during an experiment using a radiotracer. The column experiments were conducted with an artificial groundwater with a composition close to that of the case study site in Pe´cs. Chapter 5 describes the set-up and results of laboratory experiments conducted with groundwater taken from monitoring wells at the site in Pe´cs. These experiments focussed again on elemental iron and hydroxyapatite, and were conducted as column experiments and floor-scale box experiments (at cubic meter scale). The results of the experiments showed that the composition of the local groundwater, with its high concentrations of Ca, Mg, HCO3 and SO4, has a significant impact on the long-term functioning of PRB systems based on elemental iron.
Laboratory-based experiments are usually subject to rather artificial boundary conditions, and a number of crucial parameters and groundwater constituents may differ significantly from real field conditions. Therefore, with the experiments described in Chapter 6, the step from the laboratory to the field was taken. On-site column experiments with elemental iron and hydroxyapatite were designed and operated at a field test location on the former Hungarian uranium ore-processing site near the city of Pe´cs. The test site was located downstream of a large uranium-bearing waste rock pile where the shallow local groundwater showed significantly elevated concentrations of dissolved uranium. To simulate different flow conditions, small-scale columns were installed and operated within monitoring wells, and large-scale column experiments were located and operated very close to the monitoring wells used to supply their influent groundwater. The results of these on-site (and even partly in situ) column experiments showed that both elemental iron and hydroxyapatite effectively remove uranium from contaminated groundwater under field conditions. For elemental iron it could also be shown that the residence time of the contaminated groundwater in the reactive material controls, to some extent, the change of overall groundwater composition. It can be concluded that the volume of the reactive zone and the groundwater flow-velocity through the reactive zone are important design parameters for controlling adverse effects that occur within the elemental iron barriers (such as precipitation of secondary minerals) and are thus important to the long-term performance and operating life of iron-based PRBs.
The next two chapters address innovative ideas on improving the performance of PRBs, especially with respect to their long-term behaviour. Chapter 7 describes the development and testing of a new reactive material designed to sequester uranium (VI) from contaminated groundwater. This material, named PANSIL, consists of a polymeric resin coated onto the surface of quartz sand. The advantage of PANSIL is that it is selective towards the uranyl ion, available in a granular and durable form (important considerations for materials to be used in a PRB system), and does not have any side-effects on either the groundwater composition or the geochemical conditions in the barrier, and thus avoids secondary effects such as coating or clogging of the reactive matrix. Chapter 8 evaluates the feasibility of electrokinetic methods to positively affect the long-term efficiency of PRBs. The approach of coupling electrokinetic processes with PRB systems to reduce the advective transport of groundwater constituents that may impair the barrier function was studied in a series of laboratory experiments. The results described in this chapter suggest that the installation of an electrokinetic fence upstream of the barrier could indeed electrokinetically trap such groundwater constituents outside the barrier.
Chapters 9–11 report investigations and research work conducted at the two case study sites in Hungary and Austria. The characteristics of the former Hungarian uranium ore mining and processing site near the city of Pe´cs in Southern Hungary, including its pollution history, hydrogeology and ongoing remediation activities, are presented in Chapter 9. The chapter also describes the site investigations carried out to find and characterise a suitable location for an experimental PRB system to treat the uraniumcontaminated groundwater. In Chapter 10, the design, construction and operation of an experimental elemental iron barrier at the Pe´cs case study site are described. The aim of this pilot-scale barrier is the removal of dissolved uranium from the local groundwater. It consists of 38 tonnes of shredded cast iron placed in a shallow aquifer in a small valley downstream of a large, uranium-bearing waste rock pile. During the first year of operation uranium removal from the groundwater by the experimental barrier has been very successful. At the same time the change in overall groundwater composition of the barrier effluent indicated that strong geochemical processes were taking place inside the barrier material. These processes include the formation of significant amounts of precipitates, mainly carbonates, which in the long-term might lead to changes in the hydraulic properties of the system. Chapter 11 describes the geological, hydrogeological and environmental characteristics of a former industrial site in Brunn am Gebirge, Austria which is heavily contaminated with organic contaminants such as polycyclic aromatic hydrocarbons (PAH), hydrocarbons, BTEX, phenols and chlorinated hydrocarbons. A groundwater remediation scheme, called a “Adsorptive Reactor and Barrier (AR&B) System”, has been implemented at the site. This system is designed as a hydraulic barrier with four gates that funnel the groundwater through adsorptive reactors containing activated carbon. This chapter also describes the routine monitoring applied at the site to document the groundwater clean-up efficiency of the AR&B system and additional sampling and testing conducted at the activated carbon reactors to investigate those hydrogeochemical parameters that may allow an assessment of the long-term performance of the system.
In the final chapter, Chapter 12, some issues concerning the regulatory acceptance of PRBs and cost data currently available for PRBs are discussed. By addressing the issue of long-term performance of PRBs, an important aspect of this technology, we aim to advance PRB technology as an accepted, scientifically sound, costeffective and stable tool for passive groundwater remediation. Thus we hope to contribute, with this book, to an improvement in pollution management and a reduction in the exposure of groundwater resources to harmful pollutants, and thereby safeguard water resources for future generations.
Karl Ernst Roehl, Karlsruhe, Germany
Tamas Meggyes, Franz-Georg Simon, Berlin, Germany
D. I. Stewart, Leeds, United Kingdom
Contaminated land is an increasingly important environmental, health, economic and planning issue in Australia and a number of initiatives and approaches have been developed for dealing with these issues. As part of this process Government agencies are placing greater emphasis on the state of soils and the soil environment, recognising the soil’s role as a potential repository for pollutants, as a transmitter of undesirable materials to surface and groundwaters and as a potential source of contaminants in the food chain.
The application of ultrasonic energy to rejuvenate iron surfaces in a permeable treatment wells to enhance/restore the rate of trichloroethylene (TCE) degradation is studied. Iron taken from all depths showed an improvement after field application of ultrasound. Rate constants improved from 21 to 67% compared to samples taken before ultrasound treatment. Exposure time and power used are both important aspects of treatment. As corrosion products and precipitates build up on the surface, the reaction with TCE is diminished because the unoccupied surface area is decreased. Ultrasound was demonstrated to remove corrosion products, precipitates, and other debris from the iron surface. This served to increase the available iron surface and improve the rate of the dehalogenation reaction. This is an abstract of a paper presented at the 221st ACS National Meeting (San Diego, CA 4/1-5/2001).
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.
In Situ Remediation Engineering provides a comprehensive guide to the design and implementation of reactive zone methods for treatment of all major classes of groundwater contamination. It teaches the fundamentals that underlie development of cost-effective reactive zone strategies, guides the selection of cost-effective remedial strategies and provides environmental engineers and scientists with tools to achieve optimal deployment of source area, reactive barrier, and site-wide treatments. It offers extensive coverage of remedial system operation, discussing reagent injection strategies, interpretation of process monitoring results for biological and chemical reactive zone systems, and impacts of treatment processes on aquifer hydraulic characteristics.
This study investigated the use of vegetable oil to cleanse nitrate from groundwater. The hypothesis on which the study was based was that oil trapped in the soil matrix would form an immobile organic zone through which water flows; nitrate in the water would be removed as microbial denitrifiers utilized the oil as a carbon source. Laboratory studies show that the procedure has merit. Both corn and soybean oil rapidly stimulated native bacteria to remove nitrate from water in static anaerobic bioreactors. Soybean oil/water mixtures ranging from 0.8 to 12.5% oil in water were tested and all were effective at supporting denitrification. Also, denitrification occurred rapidly at nitrate concentrations up to 2000 ppm NO3-N. In addition to studies with static bioreactors, soil column studies were conducted. Soybean oil injected into 2.5 x 34 cm columns containing aquifer matrix or sand removed nitrate from flowing water. Flow rates of up to 600 mL/day were successful. Innocuous vegetable oil may provide the basis for a simple and inexpensive method of nitrate removal from contaminated groundwater.
Laboratory studies were conducted to identify the optimum sorbent material to use in the construction of a full-scale, in-situ sorbent barrier for intercepting a 90Sr plume within a surficial water-bearing sand and gravel layer. Evaluation of a set of materials for use as a passive sorbent wall was first approached through a series of batch sorption tests, using 85Sr tracer, on a set of natural zeolites and metal oxides to determine their effectiveness for sorbing 90Sr. Selected materials, based on their sorption capability in the screening experiments, were further tested in flow-through columns to assess hydraulic performance and sorptive characteristics under dynamic flow conditions. Test data were incorporated into a one-dimensional finite difference model and estimates were made of in-situ performance over extended time frames with respect to 90Sr breakthrough and loading on the barrier material. Several natural zeolites were found to remove 85Sr effectively from groundwater that contains 120 μg/ml of Ca, an element that can compete with Sr during sorption. A barrier wall of thickness 1.2 m was estimated to have a maximum life of about 10 years before replacement or regeneration of the sorbent bed is required.
A novel approach to emplacing chemically reactive barriers is the injection of zero-valent iron (Fe{sup 0}) colloids into the subsurface. A difficulty encountered in this approach is that the dense Fe{sup 0} colloids settle out of solution with time, decreasing the distance the colloids can be injected into the subsurface. Studies were conducted to evaluate if several viscous shear-thinning fluids could enhance Fe{sup 0} colloid emplacement in porous media. Aqueous solutions of three nontoxic polymers at different concentrations were investigated: a synthetic high molecular weight polymer [vinyl polymer, (VP)], a biopolymer (gum xanthan, GX), and a cellulose-type polymer (carboxymethyl cellulose, CMC). The use of shear-thinning fluids greatly increases the mobility of the colloidal Fe{sup 0} suspensions in porous media. VP was superior to GX and GMC because the VP suspensions produced the lowest back pressures, resulting in the highest hydraulic conductivities.
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 generation and release of acidic drainage containing high concentrations of dissolved metals from decommissioned mine wastes is an environmental problem of international scale. A potential solution to many acid drainage problems is the installation of permeable reactive walls into aquifers affected by drainage water derived from mine waste materials. A permeable reactive wall installed into an aquifer impacted by low-quality mine drainage waters was installed in August 1995 at the Nickel Rim mine site near Sudbury, Ontario. The reactive mixture, containing organic matter, was designed to promote bacterially mediated sulfate reduction and subsequent metal sulfide precipitation. The reactive wall is installed to an average depth of 12 feet (3.6 m) and is 49 feet (15 m) long perpendicular to ground water flow. The wall thickness (flow path length) is 13 feet (4 m). Initial results, collected nine months after installation, indicate that sulfate reduction and metal sulfide precipitation is occurring. The reactive wall has effectively removed the capacity of the ground water to generate acidity on discharge to the surface. Calculations based on comparison to previously run laboratory column experiments indicate that the reactive wall has potential to remain effective for at least 15 years.
Nitrate is now recognized as a widespread ground water contaminant, which has led to increased efforts to control and mitigate its impacts. This study reports on the long-term performance of four pilot-scale field trials in which reactive porous barriers were used to provide passive in situ treatment of nitrate in ground water. At two of the sites (Killarney and Borden), the reactive barriers were installed as horizontal layers underneath septic system infiltration beds; at a third site (Long Point), a barrier was installed as a vertical wall intercepting a horizontally migrating septic system plume; and at the fourth site (North Campus), a barrier was installed as a containerized subsurface reactor treating farm field drainage water. The reactive media consisted of 15% to 100% by volume of waste cellulose solids (wood mulch, sawdust, leaf compost), which provided a carbon source for heterotrophic denitrification. The field trials have been in semicontinuous operation for six to seven years at hydraulic loading rates ranging from six to 2000 L/day. Trials have been successful in attenuating influent NO3⁻ (or NO3⁻+ NH4⁺ at Borden) concentrations averaging from 4.8 mg/L N at North Campus to 57 mg/L N at Killarney, by amounts averaging 80% at Killarney, 74% at Borden, 91 % at Long Point, and 58% at North Campus. Nitrate consumption rates were temperature dependent and ranged from 0.7 to 32 mg L N/day, but did not deteriorate over the monitoring period. Furthermore, mass-balance calculations indicate that carbon consumption by heterotrophic denitrification has so far used only about 2% to 3% of the initial carbon mass in each case. Results suggest that such barriers should be capable of providing NO3⁻ treatment for at least a decade or longer without carbon replenishment.
There is a limited amount of information about the effects of mineral precipitates and corrosion on the lifespan and long-term performance of in situ Fe° reactive barriers. The objectives of this paper are (1) to investigate mineral precipitates through an in situ permeable Fe° reactive barrier and (2) to examine the cementation and corrosion of Fe° filings in order to estimate the lifespan of this barrier. This field scale barrier (225-ft long x 2-ft wide x 31-ft deep) has been installed in order to remove uranium from contaminated groundwater at the Y-12 plant site, Oak Ridge, TN. According to XRD and SEM-EDX analysis of core samples recovered from the Fe° portion of the barrier, iron oxyhydroxides were found throughout, while aragonite, siderite, and FeS occurred predominantly in the shallow portion. Additionally, aragonite and FeS were present in up-gradient deeper zone where groundwater first enters the Fe° section of the barrier. After 15 months in the barrier, most of the Fe° filings in the core samples were loose, and a little corrosion of Fe° filings was observed in most of the barrier. However, larger amounts of corrosion (10-150 m thick corrosion rinds) occurred on cemented iron particles where groundwater first enters the barrier. Bicarbonate/carbonate concentrations were high in this section of the barrier. Byproducts of this corrosion, iron oxyhydroxides, were the primary binding material in the cementation. Also, aragonite acted as a binding material to a lesser extent, while amorphous FeS occurred as coatings and infilings. Thin corrosion rinds (2-50 m thick) were also found on the uncemented individual Fe° filings in the same area of the cementation. If corrosion continues, the estimated lifespan of Fe° filings in the more corroded sections is 5 to 10 years, while the Fe° filings in the rest of the barrier perhaps would last longer than 15 years. The mineral precipitates on the Fe° filing surfaces may hinder this corrosion but they may also decrease reactive surfaces. This research shows that precipitation will vary across a single reactive barrier and that greater corrosion and subsequent cementation of the filings may occur where groundwater first enters the Fe° section of the barrier.
The oxidation and mineralization of hexadecane in silica sand slurries was investigated using aggressive Fenton-like reactions [high concentrations of hydrogen peroxide and an iron (II) catalyst]. When spiked with 0.1mmolkg−1 hexadecane, 56% of the hydrocarbon was sorbed to the silica sand and most of the remaining hexadecane was found as nonaqueous phase liquid (NAPL). Gas-purge methodology documented that hexadecane desorption from the silica sand slurries was negligible over 72h. Three process variables [hydrogen peroxide concentration, slurry volume and soluble iron (II) amendment] were studied to determine their effects on hexadecane oxidation. A central composite rotatable experimental design was used to determine the most effective oxidation conditions as well as possible interactions between variables. In addition to investigating the oxidation of the parent compound, parallel experiments were conducted using 14C-hexadecane to evaluate its mineralization. The recovery of 14C-CO2 confirmed that under the most effective conditions (high concentrations of hydrogen peroxide and low slurry volumes), 83% of the sorbed and NAPL-phase hexadecane was mineralized to CO2 and H2O. The iron (II) concentration had a negligible effect on parent compound degradation within the range investigated (5 to 25mM) but was a significant variable in promoting the mineralization of hexadecane. The results show that under aggressive Fenton-like conditions, even a highly hydrophobic compound that is sorbed and in a NAPL-phase can be oxidized to its thermodynamic endpoints.
A novel approach to emplacing chemically reactive barriers is the injection of zero-valent iron (Fe°) colloids into the subsurface. A difficulty encountered in this approach is that the dense Fe° colloids settle out of solution with time, decreasing the distance the colloids can be injected into the subsurface. Studies were conducted to evaluate if several viscous shear-thinning fluids could enhance Fe° colloid emplacement in porous media. Aqueous solutions of three nontoxic polymers at different concentrations were investigated: a synthetic high molecular weight polymer [vinyl polymer, (VP)], a biopolymer (gum xanthan, GX), and a cellulose-type polymer (carboxymethyl cellulose, CMC). The use of shear-thinning fluids greatly increases the mobility of the colloidal Fe° suspensions in porous media. VP was superior to GX and GMC because the VP suspensions produced the lowest back pressures, resulting in the highest hydraulic conductivities.
This book devotes the first three chapters to a concise review of basic concepts of groundwater hydrology. The transition to contaminate transport is made through a broadly based discussion of cources of contamination and data collection - hydrology to transport to reactions to microbiological reactions. Chapters on reactive transport and bioremediation follow and the final chapter is a practical discussion of the legal aspects of ground water contamination.
Permeable reactive barriers designed to enhance bacterial sulfate reduction and metal sulfide precipitation have the potential to prevent acid mine drainage and the associated release of dissolved metals. Two column experiments were conducted using simulated mine-drainage water to assess the performance of organic carbon-based reactive mixtures under controlled groundwater flow conditions. The simulated mine drainage is typical of mine-drainage water that has undergone acid neutralization within aquifers. This water is near neutral in pH and contains elevated concentrations of Fe(II) and SO4. Minimum rates Of SO4 removal averaged between 500 and 800 mmol d(-1) M-3 over a 14-month period. Iron concentrations decreased from between 300 and 1200 mg/L in the influent to between <0.01 and 220 mg/L in the columns. Concentrations of Zn decreased from 0.6-1.2 mg/L in the input to between 0.01 and 0.15 mg/L in the effluent, and Ni concentrations decreased from between 0.8 and 12.8 mg/L to <0.01 mg/L. The pH increased slightly from typical input values of 5.5-6.0 to effluent values of 6.5-7.0. Alkalinity, generally <50 mg/L (as CaCO3) in the influent, increased to between 300 and 1300 mg/L (as CaCO3) in the effluent from the columns. As a result of decreased Fe(II) concentrations and increased alkalinity, the acid-generating potential of the simulated mine-drain age water was removed,and a net acid-consuming potential was observed in the effluent water.
This paper examines the potential of using laboratory-synthesized nanoscale iron particles to transform chlorinated methanes. The iron particles have diameters on the order of 1--100 nm. Palladized iron particles were prepared by depositing palladium on the surface of iron. Batch experiments were conducted to compare reactions of chlorinated methanes with palladized nanoscale iron, nanoscale iron, and commercial grade iron particles. Rapid transformations of tetrachloromethane (CT) and trichloromethane (CF) were achieved with the palladized nanoscale iron particles. Typically 0.1 mM CT or CF was reduced below detection limits within 1 h. Methane and dichloromethane (DCM) were the major end products. Yields of methane and DCM from CT were 52% and 23%, respectively. Little degradation of DCM was observed within 72 h. With the nanoscale iron and commercial-grade iron particles, much slower reactions of chlorinated methanes were observed. Kinetic analyses indicated that the surface area-normalized rate coefficients k{sub SA} of the nanoscale iron and commercial grade iron particles were one to two orders of magnitude lower than those of the palladized nanoscale iron.
This document addresses the factors that have been found to be relevant for successfully implementing PRBs for contaminant remediation. Additionally, it provides sufficient background in the science of PRB technology to allow a basic understanding of the chemical reactions proposed for the contaminant transformations that have been witnessed both in the laboratory and in field settings. It contains sections on PRB-treatable contaminants and the treatment reaction mechanisms, feasibility studies for PRB implementation, site characterization for PRBs, PRB design, PRB emplacement, monitoring for both compliance and performance, and summaries of several field installations. The appendices supplement this information with a detailed table of information available in the literature through 1997, summarizing the significant findings of PRB research and field studies (Appendix A), a further examination of the physical and chemical processes important to PRBs, such as corrosion, adsorption, and precipitation (Appendix B), and a set of scoping calculations that can be used to estimate the amount of reactive media required and facilitate choosing among te possible means of emplacing the required amount of media (Appendix C). Appendix D provides a list of acronyms and Appendix E a glossary of terms that are used within this document.
This book presents the results of the University of Waterloo's research to test permeable, reactive barriers with the goal of finding the best in situ method for groundwater remediation. The results of field demonstrations of permeable, reactive barriers are presented. Attention is focused on plumes containing mixtures of chlorinated and aromatic hydrocarbons. Abiotic and anaerobic and aerobic bioremediation methods were tested.
Because of the limitations of conventional pump-and-treat systems in treating groundwater contaminants, permeable barriers are potentially more cost-effective than pump-and-treat systems for treating dissolved chlorinated solvent plumes, which may persist in the saturated zone for several decades. Other contaminants, such as chromium or other soluble heavy metals, can also be treated with this technology. The authors discuss the types of permeable barriers, their design and construction, and how they can be monitored to evaluate compliance. It provides practical guidance on reactive media selection, treatability testing, hydrogeologic and geochemical modeling, and innovative installation techniques for the evaluation and application of this promising new technology. The types of permeable barriers discussed include: trench-type and caisson-based reactive cells; innovative emplacements, such as horizontal trenching and jetting; and continuous reactive barriers versus funnel-and-gate systems. The material is organized in an easy-to-read format, with topics and illustrations that will be useful to readers already familiar with barriers, and to those just being introduced to the technology.
Halogenated volatile organic compounds, including chlorinated solvents, are the most frequently-occurring type of soil and groundwater contaminant at Superfund and other hazardous waste sites in the United States. The U.S. Environmental Protection Agency (EPA) estimates that, over the next several decades, site owners will spend billions of dollars to clean up these sites. New technologies that are less costly and more effective are needed to accomplish hazardous waste site remediation. As these new and innovative technologies are being developed and used, site managers require information on how they work, their performance to date, and how to evaluate their application at a particular site. This report provides an overview of the fundamentals and field applications of in situ bioremediation to remediate chlorinated solvents in contaminated soil and groundwater. In situ treatment is increasingly being selected to remediate sites because it is usually less expensive, and does not require waste extraction or excavation. In addition, in situ bioremediation is more publicly acceptable than above-ground technologies because it relies on natural processes to treat contaminants. This document presents information at a level of detail intended to familiarize federal and state project managers, permit writers, technology users, and contractors with in situ bioremediation. The report describes how chlorinated solvents are degraded, how to enhance the process by the addition of various materials and chemicals, design configurations, and the typical steps taken to evaluate technology feasibility at a specific site. It also includes a list of technology vendors and nine case studies of field applications. It is important to note that this report cannot be used as the sole basis for determining this technology's applicability to a specific site.
We report on the encapsulation of enzyme (catalase) by the controlled polymer multilayer coating of biocrystals, achieved by the sequential adsorption of oppositely charged polyelectrolytes onto enzyme crystal templates. An extremely high enzyme loading in each polymer capsule is obtained, and the activity of the encapsulated enzyme is preserved. The polymer-encapsulated enzyme is stable against protease degradation: The polymer-coated enzyme retains 100% of its activity after incubation for 100 min with protease, whereas uncoated, solubilized catalase loses more than 90% of its initial activity within 100 min under the same conditions. This simple, general, and versatile approach can potentially be applied for the encapsulation of various crystallized substances for catalysis and drug delivery applications.
Benzo[a]pyrene of natural and anthropogenic sources is one of the toxic, mutagenic, polycyclic aromatic hydrocarbons (PAHs) listed as priority pollutants. This study focuses on an integrated treatment of benzo[a]pyrene involving sequential chemical oxidation and biological degradation. The objectives are to (1) provide mechanistic details in the ozone-mediated degradation of benzo[a]pyrene in the aqueous phase, (2) test the biodegradability of resultant intermediates, and (3) test the feasibility for the coupled chemical-biological treatment of the five-ring PAH. Batch and packed column reactors were used to examine the degradation pathways of benzo[a]pyrene subject to ozonation in the aqueous phase. After different ozonation times, samples containing reaction intermediates and byproducts from both reactors were collected, identified for organic contents, and further biologically inoculated to determine their biodegradability. The O3-pretreated samples were incubated for 5, 10, 15, and 20 days; afterward biochemical oxygen demand (BOD), chemical oxygen demand (COD), and E. coli toxicity tests were conducted along with qualitative and quantitative determinations of benzo[a]pyrene, intermediates, and reaction products by GC/FID and GC/MS methods. Prevalent intermediates identified at different stages included ring-opened aldehydes, phthalic derivatives, and aliphatics. The degradation of benzo[a]pyrene is primarily initiated via O3-mediated ring-opening, followed by O3 and hydroxyl radical fragmentation, and ultimately brought to complete mineralization primarily via hydroxyl radicals. Intermediates formed during chemical oxidation were biodegradable with a measured first-order rate constant (k0) of 0.18 day-1. The integrated chemical-biological system seems feasible for treating recalcitrant compounds, while pretreatment by chemical oxidation appears useful in promoting soluble intermediates from otherwise highly insoluble, biologically inaccessible benzo[a]pyrene.
This research investigated the long-term performance of zero-valent iron for mediating the reductive dechlorination of trichloroethylene (TCE). Over a 2-year period, rates of TCE dechlorination in columns packed with iron filings were measured in simulated groundwaters containing either 3 mM CaSO4, 5 mM CaCl2, or 5 mM Ca(NO3)2. At early elapsed times, TCE reaction rates were pseudo-first-order in TCE concentration and were independent of the solution pH. With increasing elapsed time, reaction rates deviated from pseudo-first-order behavior due to reactive site saturation and increased iron surface passivation toward the influent end of each column. The extent of passivation was dependent on both the TCE concentration and the background electrolyte solution. For most of the investigation, TCE reaction rates in 3 mM CaSO4 and 5 mM CaCl2 solutions were statistically identical at the 0.05 confidence level. However, TCE reaction rates in 5 mM Ca(NO3)2 were slower. In columns operated using chloride- and sulfate-containing waters, the effective half-life for TCE dechlorination increased from approximately 400 min after 10 days elapsed to approximately 2500 min after 667 days. The effective TCE half-life in the nitrate-containing water increased from approximately 1500 min after 10 days to approximately 3500 min after 667 days. Measurements of iron corrosion rates in nitrate and chloride solutions showed that nitrate contributed to increased iron surface passivation and decreased rates of iron corrosion. Corrosion current measurements indicated that halocarbon reduction on fresh iron surfaces was cathodically controlled, whereas on aged iron surfaces, iron corrosion was anodically controlled. Anodic control of iron corrosion contributed to the development of reactive site saturation with time and to similar reaction rates for TCE and perchloroethylene. Passivation of the iron surfaces was found to be dependent on the adhering tendency of the corrosion products and not on the overall mass of corrosion products in the columns. The decrease in TCE reaction rates over time can be attributed to anodic control of iron corrosion and not to increasing reactant mass transfer limitations associated with diffusion through porous corrosion products.
A permeable reactive barrier, designed to remove metals and generate alkalinity by promoting sulfate reduction and metal sulfide precipitation, was installed in August 1995 into an aquifer containing effluent from mine tailings. Passage of groundwater through the barrier results in striking improvement in water quality. Dramatic changes in concentrations of SO4 (decrease of 2000−3000 mg/L), Fe (decrease of 270−1300 mg/L), trace metals (e.g., Ni decreases 30 mg/L), and alkalinity (increase of 800−2700 mg/L) are observed. Populations of sulfate reducing bacteria are 10 000 times greater, and bacterial activity, as measured by dehydrogenase activity, is 10 times higher within the barrier compared to the up-gradient aquifer. Dissolved sulfide concentrations increase by 0.2−120 mg/L, and the isotope 34S is enriched relative to 32S in the dissolved phase SO42- within the barrier. Water chemistry, coupled with geochemical speciation modeling, indicates the pore water in the barrier becomes supersaturated with respect to amorphous Fe sulfide. Solid phase analysis of the reactive mixture indicates the accumulation of Fe monosulfide precipitates. Shifts in the saturation states of carbonate, sulfate, and sulfide minerals and most of the observed changes in water chemistry in the barrier and down-gradient aquifer can be attributed, either directly or indirectly, to bacterially mediated sulfate reduction.
Laboratory batch and column studies were conducted to develop permeable reactive mixtures to remove phosphorus from the effluent of onsite wastewater disposal systems. Mixtures can be placed in situ, as horizontal or vertical reactive barriers in sediments receiving wastewater discharge, or can be used in single pass, self-contained treatment modules in alternative treatment systems. Reactive mixtures composed of silica sand, high calcium crushed limestone, and readily available metal oxides were tested to evaluate phosphorus attenuation. Iron/calcium oxides, produced from steel manufacturing, and fine-grained activated aluminum oxide outperformed other oxides tested during batch experiments. These materials removed greater than 99% of PO4 from a 10 mg/L PO4−P solution within 1 h of contact. Long-term attenuation capacities of the mixtures were assessed by continually loading bench-scale columns with a 3.3 mg/L PO4−P solution, at representative groundwater flow rates. A column containing 50 wt % silica sand, 45 wt % limestone, and 5 wt % iron/calcium oxide averaged >90% reduction in phosphate over 4 years (≈1450 pore volumes). X-ray and SEM microprobe analyses of the reacted solids showed phosphorus ac cumulations on the surfaces of iron oxide phases and discrete precipitates of microcrystalline hydroxyapatite [Ca5(PO4)3OH]. A second column containing 50 wt % silica sand, 40 wt % limestone, and 10 wt % activated aluminum oxide achieved >99% reduction in PO4 over a period of 2 years (≈413 pore volumes). The treatment performance in this system can be attributed to the high adsorption capacity of the aluminum oxide.
Proof of concept was obtained that Fe(0) can stoichio metrically reduce nitrate to ammonium and that cathodic hydrogen [produced during anaerobic Fe(0) corrosion by water] can sustain microbial denitrification to reduce nitrate to more innocuous products (i.e., N2O and N2). Autotrophic, denitrifying growth on Fe(0) was proven through the use of a dual-flask apparatus. Cathodic H2 from a flask containing Fe(0) was allowed to diffuse to another (anoxic) flask containing a pure culture of Paracoccus denitrificans, where denitrification and microbial growth were observed. Nitrate reduction and end product distribution were studied in batch reactors amended with either steel wool or Fe(0) powder. Steel wool, with a smaller specific surface area, was less reactive, and its corrosion did not significantly increase the pH of the solution. This allowed for a greater participation of denitrifiers in the nitrate removal process, which increased nitrate removal rates and transformed a greater portion of the added nitrate to innocuous gases rather than to ammonium. Combining denitrifiers with the more reactive Fe(0) powder did not increase removal rates or decrease the proportion of nitrate reduced to ammonium. This was attributed to a corrosion-induced increase in pH above the tolerance range of the bacteria (pH > 10). Nitrate removal was sustained over 4 months in flow-through columns packed with steel wool and seeded with autotrophic denitrifiers. Increasing the hydraulic retention time from 0.67 to 2.33 days increased the nitrate removal efficiency and decreased the fraction of nitrate reduced to ammonium. The finding that Fe(0) can sustain autotrophic denitrification may have practical applications to treat nitrate-contaminated waters in ex-situ or in-situ reactive filters.
Transformation of halogenated organic compounds (HOCs) by zero-valent iron represents one of the latest innovative technologies for environmental remediation. For example, iron can be used to construct a reactive wall in the path of a contaminated groundwater plume to degrade HOCs. In this paper, an efficient method of synthesizing nanoscale (1−100 nm) iron and palladized iron particles is presented. Nanoscale particles are characterized by high surface area to volume ratios and high reactivities. BET specific surface area of the synthesized metal particles is 33.5 m2/g. In comparison, a commercially available Fe powder (<10 μm) has a specific surface area of just 0.9 m2/g. Batch studies demonstrated that these nanoscale particles can quickly and completely dechlorinate several chlorinated aliphatic compounds and a mixture of PCBs at relatively low metal to solution ratio (2−5 g/100 mL). Surface-area-normalized rate constants (KSA) are calculated to be 10−100 times higher than those of commercially available iron particles. The approach presented offers unique opportunities for both fundamental research and technological applications of zero-valent metals. For example, a potential application of the nanoscale particles is to inject the metal particles directly into contaminated aquifers instead of building iron walls.
A combination of new and previously reported data on the kinetics of dehalogenation by zero-valent iron (Fe0) has been subjected to an analysis of factors effecting contaminant degradation rates. First-order rate constants (kobs) from both batch and column studies vary widely and without meaningful correlation. However, normalization of these data to iron surface area concentration yields a specific rate constant (kSA) that varies by only 1 order of magnitude for individual halocarbons. Correlation analysis using kSA reveals that dechlorination is generally more rapid at saturated carbon centers than unsaturated carbons and that high degrees of halogenation favor rapid reduction. However, new data and additional analysis will be necessary to obtain reliable quantitative structure−activity relationships. Further generalization of our kinetic model has been obtained by accounting for the concentration and saturation of reactive surface sites, but kSA is still the most appropriate starting point for design calculations. Representative values of kSA have been provided for the common chlorinated solvents.
The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product. Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 × 10-2, 3.4 × 10-2, and 8.8 × 10-3 min-1, respectively, in the presence of 33 g/L acid-washed, 18−20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ± 0.2 × 10-2 min-1 m-2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing rate (rpm), suggest that the observed reaction rates were controlled by mass transfer of the NAC to the metal surface. The decrease in reduction rate for nitrobenzene with increased concentration of dissolved carbonate and with extended exposure of the metal to a particular carbonate buffer indicate that the precipitation of siderite on the metal inhibits nitro reduction.
This paper reports on the first phase of a project designed to determine the potential of peats in extracting hydrocarbons from groundwater. Peat samples with markedly different compositions were slurried under controlled conditions in either saturated solutions or emulsions of benzene, toluene, or m-xylene. All peats were characterized in order to determine the possible correlation between various parameters and extraction capacities. All peats were found to be capable of extracting substantial amounts of either free-phase or dissolved hydrocarbons from water. Free-phase extraction ranged from 30 to 50% of the starting wet volume of the peats. Solution extraction produced reductions in concentrations of between 53 and 97%, depending on the peat type. In solution, toluene was found to be more slowly adsorbed than either benzene or m-xylene. In general, the best hydrocarbon adsorption from solution can be achieved by using peats that are low in fiber and birefringent organics and high in ash and guaiacyl lignin pyrolysis products.
Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100-mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first-order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
A new alternative septic-system design is presented utilizing reactive porous media barriers for passive in situ attenuation of NO3−. The reactive material consists of solid organic carbon (sawdust) which promotes NO3- attenuation by heterotrophic denitrification. Four field trials are discussed demonstrating two barrier configurations: as a horizontal layer positioned in the vadose zone below a conventional septic-system infiltration bed and as a vertical wall intercepting a horizontally flowing downgradient plume. During one year of operation both barrier configurations have been successful in substantial attenuation (60 to 100%) of input NO3- levels of up to 125 mg/1 as N. The horizontal layer configuration can be readily installed during the construction of new infiltration beds, whereas the vertical wall configuration may be more appropriate for retrofitting existing septic systems where NO3- contamination has already occurred. The layer configuration allows the flexibility of constructing the barrier in the vadose zone by using coarse silt or fine sand matrix material that has the ability to remain tension-saturated, and thus anaerobic, even when positioned above the water table.
Advantages of the barrier system are that it is simple to construct, no surface structures or additional plumbing are necessary, and treatment is passive requiring no energy consumption and little or no maintenance. Mass balance calculations and preliminary results suggest that conveniently sized barriers have the potential to last for decades without replenishment of the reactive material.
This study evaluates the potential of using granular iron metal for the abiotic removal of the organic ground water pollutant trichloroethene (TCE) in the presence of the common inorganic co-contaminants chromate and nitrate, respectively. Our long-term column experiments indicate a competitive process between TCE dechlorination and reductive transformation of chromate and nitrate, which is reflected in a significantly delayed onset of TCE dechlorination. Delay times and therefore the ranges of the nonreactive flowpaths increased with increasing experimental duration, resulting in a migration of the contaminants through the iron metal treatment zone. The present investigation also indicates that the calculated migration rates of TCE and the added cocontaminants chromate and nitrate are linearly related to the initial content of the cocontaminants. With an average pore water velocity of 0.6 m/d and a surface area concentration of 0.55 m2/mL in the column, the calculated migration rates varled between 0.10 cm/d and 5.86 cm/d. The particular similarity between the values of TCE migration and the migration of the strong oxidants chromate and nitrate and the long-term steady state of the TCE dechlorination in the absence of the chromate and nitrate indicates that these competitive transformations are the driving force for the gradual passivation of the granular iron due to the buildup of an electrically insulating Fe(III)-oxyhydroxide. Based on these passivation processes, general formulae were developed that allow a simplified approximation of breakthrough times for the contaminants TCE, chromate, and nitrate.
The potential of the Fenton’s reagent for oxidation of p-aminophenols, which are the main developers used in white and black processes, was assessed. Metol [N-methyl-p-aminophenol] was chosen as a model. Degradation of this compound by Fenton’s reagent was examined under dark conditions as a function of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H2O2, 9.0×10−4 M Fe2+, pH 3–5 and room temperature, the initial COD of a 5×10−3 M metol solution was reduced by about 50% within 2 h. After this time, additional COD reduction was very slow (about 20% in five days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavage products. Metol conversion behaved as a first-order reaction with respect to metol and Fe2+. Complete destruction of residual organic matter could be achieved at high temperatures (about 60°C) or by using the photo-Fenton reaction, which thus opens up prospects for an effective treatment of p-aminophenols in effluents from photographic processes.
The surface properties of activated carbon are characterized by their surface acidity, surface ash content and elemental composition. The surface acidity of activated carbon can be readily determined by alkalimetric titration and calculated by the Gouy-Chapman theory of electrical double layer. Electrophoretic mobility measurement provides little information on the nature of the acidity of the activated carbons. No correlation can be deduced between the surface chemical composition and the acidity.
The selectivity of three different natural zeolites for lead has been investigated at two different solution concentrations. The three zeolites examined (clinoptilolite, mordenite and ferrierite) were prepared in both the sodium and ammonium forms before exchange with lead was attempted. The selectivity of these materials for lead was measured in terms of experimental ion-exchange isotherms at a temperature of 298 K. The systems were checked carefully for precipitation and, in contrast to recent work on synthetic X and Y samples1, little evidence for non-stoichiometry of exchange was found. With three exceptions all systems were found to be reversible. For those systems which were not reversible, it is argued evidentially that the irreversibility is due primarily to the exchanges being ternary in nature rather than binary. Different selectivity trends for the sodium and ammonium forms of the zeolites are discussed, and thermodynamic data are derived for those systems shown to be reversible. It is concluded that in addition to clinoptilolite, both natural ferrierite and mordenite show promise as means of extracting lead from effluent solutions.
Data from long-term groundwater sampling, limited coring, and associated studies are synthesised to assess the variability and intrinsic remediation/natural attenuation of a dissolved hydrocarbon plume in sulphate-rich anaerobic groundwater. Fine vertical scale (0.25- and 0.5-m depth intervals) and horizontal plume-scale (>400 m) characteristics of the plume were mapped over a 5-year period from 1991 to 1996. The plume of dissolved BTEX (benzene, toluene, ethylbenzene, xylene) and other organic compounds originated from leakage of gasoline from a subsurface fuel storage tank. The plume was up to 420 m long, less than 50 m wide and 3 m thick. In the first few years of monitoring, BTEX concentrations near the point of leakage were in approximate equilibrium with non-aqueous phase liquid (NAPL) gasoline. NAPL composition of core material and long-term trends in ratios of BTEX concentrations in groundwater indicated significant depletion (water washing, volatilisation and possibly biodegradation) of benzene from residual NAPL after 1992. Large fluctuations in BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations. A combination of temporal and spatial groundwater quality data was required to adequately assess the stationarity of plumes, so as to allow inference of intrinsic remediation. Contoured concentration data for the period 1991 to 1996 indicated that plumes of toluene and o-xylene were, at best, only partially steady state (pseudo-steady state) due to seasonal groundwater flow changes. From this analysis, it was inferred that significant remediation by natural biodegradation was occurring for BTEX component plumes such as toluene and o-xylene, but provided no conclusive evidence of benzene biodegradation. Issues associated with field quantification of intrinsic remediation from groundwater sampling are highlighted. Preferential intrinsic biodegradation of selected organic compounds within the BTEX plume was shown to be occurring, in parallel with sulphate reduction and bicarbonate production. Ratios of average hydrocarbon concentrations to benzene for the period 1991 to 1992 were used to estimate degradation rates (half-lives) at various distances along the plume. The estimates varied with distance, the narrowest range being, for toluene, 110 to 260 days. These estimates were comparable to rates determined previously from an in situ tracer test and from plume-scale modelling.
The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II) + H2O2] for liquid waste treatments was assessed. The insoluble products yielded were amenable to oxidation to ring-cleavage products and ultimately to carbon dioxide. Mineralization was confirmed by mass spectrometry. The kinetics of precipitation was determined from scattering measurements, at 500 nm, of the insoluble substance produced as a function of time. The influence of experimental variables on the removal of aromatic amines from aqueous solutions by formation of insoluble products and ring-cleavage products was established. Complete removal took about 1 and 3 h of treatment overall for the formation of insoluble products and ring-cleavage products, respectively. Residual hydrogen peroxide, iron(II) concentration, chemical oxygen demand and chromatographic techniques were used to determine when the reaction was finished. The iron(II) concentration was found to be crucial to the nature of the end products obtained (insoluble products, ring-cleavage products, CO2).
Permeable reactive barriers are an emerging alternative to traditional pump and treat systems for groundwater remediation. This technique has progressed rapidly over the past decade from laboratory bench-scale studies to full-scale implementation. Laboratory studies indicate the potential for treatment of a large number of inorganic contaminants, including As, Cd, Cr, Cu, Hg, Fe, Mn, Mo, Ni, Pb, Se, Tc, U, V, NO3, PO4 and SO4. Small-scale field studies have demonstrated treatment of Cd, Cr, Cu, Fe, Ni, Pb, NO3, PO4 and SO4. Permeable reactive barriers composed of zero-valent iron have been used in full-scale installations for the treatment of Cr, U, and Tc. Solid-phase organic carbon in the form of municipal compost has been used to remove dissolved constituents associated with acid-mine drainage, including SO4, Fe, Ni, Co and Zn. Dissolved nutrients, including NO3 and PO4, have been removed from domestic septic-system effluent and agricultural drainage.