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Groundwater contamination with chlorinated solvents, such as trichloroethylene or TCE, is a major environmental challenge. The development of innovative, efficient, and sustainable remediation technologies is needed. In this study, iron electrolysis is assessed as a potential technology for the remediation of TCE contaminated groundwater. A three-stage experimental program is conducted in this study: (i) the evaluation of chemical changes in the electrolyte due to iron electrolysis in batch reactors, as well as the investigation of TCE degradation rates; (ii) the optimization of electrochemical operating variables using a multivariable statistical approach; and (iii) the assessment of a proposed electrochemical system under flow conditions for the remediation of groundwater contaminated with TCE. The first phase of this study focuses on the temporal chemical changes in the electrolyte due to iron electrolysis and TCE degradation kinetics with various electrode materials. Unlike an inert anode, an iron anode releases Fe (II) into the system and generates a highly reducing electrolyte condition (lower oxidation-reduction potential). This reducing electrolyte condition facilitates the reductive dechlorination of TCE. The TCE dechlorination rate of various anode materials is investigated. The iron anode coupled with a copper foam cathode provides the best TCE dechlorination performance. In the second stage, the significance of changes in operating variables on final TCE elimination efficiency (FEE) and specific energy consumption (SEC) is investigated using an iron anode-copper cathode couple. Under the same total charge conditions, changes in applied current impact FEE the most. For SEC, the ionic conductivity of the electrolyte is the most influential parameter. In the final stage, a three-electrode (the sequence of an iron anode, a copper foam cathode, and an MMO anode) electrochemical system is implemented for the remediation of TCE in groundwater under flow conditions. Higher TCE removal efficiencies are reached at a lower flow rate, supporting the conclusion that a longer residence time of the electrolyte improves TCE removal efficiency. Conversely, the treating capacity of TCE is higher for a higher flow rate.
Groundwater is susceptible to pollution due to improper waste disposal. Groundwater contamination continues to be a problem in areas where population relies on groundwater as a major source of drinking water. Development of technologies, such as in situ electrochemical transformation to clean contaminated groundwater is of great importance. Electrochemical systems, which mainly consist of two or more arranged electrodes that are immersed in wells in groundwater, are of interest because of their ability to manipulate redox conditions to transform contaminants into non-toxic forms. Aquifers in karst regions are very susceptible to contamination and present a significant exposure routes due to presence of fissures and channels that facilitate contaminant transport under high flow rate. Trichloroethylene (TCE), a toxic chlorinated solvent that causes major health problems, is present in many contaminated aquifers including many that reside in karst regions. Treatment of aquifers contaminated with TCE is difficult in the presence of other contaminants, such as chromate, selenate, and nitrate, which interfere with TCE transformation and degradation mechanisms. Moreover, presence of natural organic matter (NOM) in the groundwater can influence transformation of TCE and other contaminants. Therefore, it is important to evaluate transformation of TCE in the presence of contaminant mixtures in groundwater. In this study, a series of experiments are conducted to (1) evaluate of the effect of co-existing organic and inorganic compounds on the electrochemical dechlorination of trichloroethylene (TCE) in simulated karst media; and (2) assessment of the impacts of high groundwater flow rates in the presence of palladium (Pd) catalyst on TCE transformation rate and the accumulation of precipitates. A small-scale flow-through limestone column is used to simulate a karst aquifer media to evaluate dechlorination of TCE in the presence of organic and inorganic compounds. Iron anode was used to produce ferrous ions and promote reducing conditions in the column. Various current intensities (30, 60, and 90 mA) were applied under the flow rate of 1 mL min−1 and initial TCE concentration of 1 mg L−1. Under the same testing conditions, presence of chromate has the highest influence on TCE removal followed by selenate and then nitrate. The reduction of TCE under 90 mA current, 1 mL min−1 flow rate, and 1 mg L−1 initial TCE concentration, was inhibited in the presence of humic acids due to competition for direct electron transfer and/or reaction with atomic hydrogen produced at the cathode surface by water electrolysis. The use of iron anode creates favorable conditions for TCE reduction but produces aggregates in combination with ferrous ions, which may impact the long-term performance of the remedial system. A vertical acrylic column, with Pd pellets placed on the cathode surface, was used to investigate the impacts of Pd-based catalysis for the removal of TCE under high flow rate (1 L min−1). The effects of electrode materials and current intensities on precipitation, pH and ORP are assessed. The following electrode materials and arrangements were tested: (a) two MMO electrodes as an anode and a cathode, (b) a cast-iron anode and a MMO cathode, and (c) a cast-iron anode and a copper foam cathode. Current intensities of 500, 250, 125, and 62 mA were tested under the flow rate of 1 L min−1 and 5 mg L−1 of initial concentration of TCE. Under the conditions of 1 L min−1 flow, 500 mA current, and 5 mg L−1 initial concentration of TCE, removal efficacy using iron anodes (96%) is significantly higher than that of mixed metal oxide (MMO) anodes (66%) because the iron anode supports reduction conditions by electrolysis. Two types of cathodes (MMO and copper foam) in the presence of Pd/Al2O3 catalyst under various currents (250, 125, and 62 mA) were used to evaluate the effect of cathode materials on TCE removal efficacy. The similar removal efficiencies were achieved for both cathodes, but more precipitation generated with copper foam cathode. Palladium improved TCE degradation by 120% for 250 mA, 100% for 125 mA, 100% for 62 mA, under the conditions of using an iron anode followed by a copper foam cathode with 1 L min−1 flow rate. The high velocities of groundwater flow can have important implications since the groundwater flow rate can significantly fluctuate, especially in karst aquifers. The optimization of the electrochemical systems for successful operation under high flow rates allows the robustness and great flexibility for the application. It is assumed that the high flow rate would favor the transformation of contaminants since it would flush out precipitates and prevent clogging.
This book provides a comprehensive overview of innovative remediation techniques and strategies for soils contaminated by heavy metals or organic compounds (e.g. petroleum hydrocarbons, NAPLs and chlorinated organic compounds). It discusses various novel chemical remediation approaches (in-situ and ex-situ) used alone and in combination with physical and/or thermal treatment. Further, it addresses the recovery of NAPLs, reuse of leaching solutions, and in-situ chemical reduction and oxidation, and explores the chemical enhancement of physical NAPLs recovery from both practical and theoretical perspectives. Also presenting the state-of-the-art in waste-assisted bioremediation to improve soil quality and the remediation of petroleum hydrocarbons, the book is a valuable resource for students, researchers and R&D professionals in industry engaged in the treatment of contaminated soils.
The purpose of this book is to help engineers and scientists better understand dense nonaqueous phase liquid (DNAPL) contamination of groundwater and the methods and technology used for characterization and remediation. Remediation of DNAPL source zones is very difficult and controversial and must be based on state-of-the-art knowledge of the behavior (transport and fate) of nonaqueous phase liquids in the subsurface and site specific geology, chemistry and hydrology. This volume is focused on the characterization and remediation of nonaqueous phase chlorinated solvents and it is hoped that mid-level engineers and scientists will find this book helpful in understanding the current state-of-practice of DNAPL source zone management and remediation.
We are proposing this comprehensive volume aimed at bridging and bonding of the theory and practical experiences for the elimination of a broad range of pollutants from various types of water and soil utilizing innovative nanotechnologies, biotechnologies and their possible combinations. Nowadays, a broad range of contaminants are emerging from the industry (and also representing old ecological burdens). Accidents and improper wastewater treatment requires a fast, efficient and cost-effective approach. Therefore, several innovative technologies of water and soil treatments have been invented and suggested in a number of published papers. Out of these, some nanotechnologies and biotechnologies (and possibly also their mutual combinations) turned out to be promising for practical utilization – i.e., based on both extensive laboratory testing and pilot-scale verification. With respect to the diverse character of targeted pollutants, the key technologies covered in this book will include oxidation, reduction, sorption and/or biological degradation. In relation to innovative technologies and new emerging pollutants mentioned in this proposed book, an important part will also cover the ecotoxicity of selected pollutants and novel nanomaterials used for remediation. Thus, this work will consist of 8 sections/chapters with a technical appendix as an important part of the book, where some technical details and standardized protocols will be clearly presented for their possible implementation at different contaminated sites. Although many previously published papers and books (or book chapters) are devoted to some aspects of nano-/biotechnologies, here we will bring a first complete and comprehensive treatise on the latest progress in innovative technologies with a clear demonstration of the applicability of particular methods based on results of the authors from pilot tests (i.e., based on the data collected within several applied projects, mainly national project “Environmentally friendly nanotechnologies and biotechnologies in water and soil treatment” of the Technology Agency of the Czech Republic, and 7FP project NANOREM: “Taking Nanotechnological Remediation Processes from Lab Scale to End User Applications for the Restoration of a Clean Environment”). This multidisciplinary book will be suitable for a broad audience including environmental scientists, practitioners, policymakers and toxicologists (and of course graduate students of diverse fields – material science, chemistry, biology, geology, hydrogeology, engineering etc.).
The suitability of Advanced Oxidation Processes (AOPs) for pollutant degradation was recognised in the early 1970s and much research and development work has been undertaken to commercialise some of these processes. AOPs have shown great potential in treating pollutants at both low and high concentrations and have found applications as diverse as ground water treatment, municipal wastewater sludge destruction and VOCs control. Advanced Oxidation Processes for Water and Wastewater Treatment is an overview of the advanced oxidation processes currently used or proposed for the remediation of water, wastewater, odours and sludge. The book contains two opening chapters which present introductions to advanced oxidation processes and a background to UV photolysis, seven chapters focusing on individual advanced oxidation processes and, finally, three chapters concentrating on selected applications of advanced oxidation processes. Advanced Oxidation Processes for Water and Wastewater Treatment will be invaluable to readers interested in water and wastewater treatment processes, including professionals and suppliers, as well as students and academics studying in this area. Dr Simon Parsons is a Senior Lecturer in Water Sciences at Cranfield University with ten years' experience of industrial and academic research and development.