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Evaluates the effects of external cathodic current on the trichloroethylene (TCE) degradation rate by zero-value iron (ZVI). Sets up a bench scale test and a reactor where electrolytic reduction can take place.
Electrochemical Water Treatment Methods provides the fundamentals and applications of electrochemical water treatment methods to treat industrial effluents. Sections provide an overview of the technology, its current state of development, and how it is making its way into industry applications. Other sections deal with historical developments and the fundamentals of 18 methods, including coupled methods, such as Electrocoagulation, Peroxi-Coagulation and Electro-Fenton treatments. In addition, users will find discussions that relate to industries such as Pulp and Paper, Pharmaceuticals, Textiles, and Urban/Domestic wastewater, amongst others. Final sections present advantages, disadvantages and ways to combine renewable energy sources and electrochemical methods to design sustainable facilities. Environmental and Chemical Engineers will benefit from the extensive collection of methods and industry focused application cases, but researchers in environmental chemistry will also find interesting examples on how methods can be transitioned from lab environments to practical applications. Offers an excellent overview of the research advances and current applications of electrochemical technologies for water treatment Explains, in a comprehensive way, the fundamentals of different electrochemical uses and applications of different technologies Provides a large number of examples as evidence of practical applications of electrochemistry to environmental protection Explores the combination possibilities with other treatment technologies or emerging technologies for destroying water pollutants
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.
Permeable reactive barriers (PRB) containing zero-valent iron (ZVI) have been used for the in situ remediation of groundwater contaminated with trichloroethylene (TCE) for almost two decades; however, ZVI is susceptible to passivation over time, which greatly reduces its treatment efficiency. Several recent studies have suggested that electrically-induced reduction (EIR), the application of low-level direct current, may restore the reactivity of passivated ZVI in situ. In this study, a continuous-flow column reactor was fabricated to treat TCE-contaminated groundwater and assess the effects of low-voltage direct current (0-12 V) on abiotic TCE reduction. In experiments with partially passivated ZVI, application of current increased the rate and the extent of abiotic TCE reduction; both were correlated with voltage. Based on calculated reaction rate coefficients, TCE reduction in passivated ZVI is a first-order reaction. While several mechanisms contribute to the abiotic reduction of TCE in passivated ZVI, they are difficult to isolate experimentally.
This research investigated the mechanism, kinetics and feasibility of nitrate, arsenate, and trichloroethylene inactivation on zerovalent iron (ZVI), mixed-valent iron oxides, and boron doped diamond film electrode surfaces, respectively. Nitrate () is a common co-contaminant at sites remediated using permeable reactive barriers (PRBs). Therefore, understanding nitrate reactions with ZVI is important for understanding the performance of PRBs. This study investigated the reaction mechanisms of with ZVI under conditions relevant to groundwater treatment. Tafel analysis and electrochemical impedance spectroscopy were used to probe the surface reactions. Batch experiments were used to study the reaction rate of with freely corroding and cathodically protected iron wires. The removal kinetics for the air formed oxide (AFO) were 2.5 times slower than that of water formed oxide (WFO). This research also investigated the use of slowly corroding magnetite (Fe3O4) and wustite (FeO) as reactive adsorbent media for removing As(V) from potable water. Observed corrosion rates for mixed valent iron oxides were found to be 15 times slower than that of zerovalent iron under similar conditions. Electrochemical and batch and column experiments were performed to study the corrosion behavior and gain a deeper understanding on the effects of water chemistry and operating parameters, such as, empty bed contact times, influent arsenic concentrations, dissolved oxygen levels and solution pH values and other competing ions. Reaction products were analyzed by X-Ray diffraction and XPS to determine the fate of the arsenic. This research also investigated use of boron doped diamond film electrodes for reductive dechlorination of trichloroethylene (TCE). TCE reduction resulted in nearly stoichiometric production of acetate. Rates of TCE reduction were found to be independent of the electrode potential at potentials below -1 V with respect to the standard hydrogen electrode (SHE). However, at smaller overpotentials, rates of TCE reduction were dependent on the electrode potential. Short lived species analysis and density functional simulations indicate that TCE reduction may occur by formation of a surface complex between TCE and carbonyl groups present on the surface.
Trichloroethylene (TCE) is a volatile, chlorinated aliphatic organic compound. It has been used ubiquitously as an ingredient in industrial cleaning agents and as a degreasing agent, which has resulted in widespread contamination of groundwater. Since TCE is a highly oxidized compound, reduction reactions are considered a promising way to treat it. Permeable reactive barriers (PRB) containing highly-reducing reactive media [e.g., zero-valent iron (Fe° or ZVI)] have been successfully used in situ to remediate TCE in groundwater. There have been more than 200 ZVI PRBs installed worldwide since the mid-1990s. Despite their promise, ZVI PRBs are susceptible to passivation over time, largely due to oxidation of the Fe° by dissolved oxygen or nitrate. Several recent studies have suggested that electrically-induced reduction (EIR) is a promising approach to restore reductive activity in passivated ZVI PRBs. The overall objectives of this study were to simulate in the laboratory a ZVI PRB to remediate TCE-contaminated groundwater and systematically evaluate the effect of applying direct current. Results suggest that: (1) any enhancements in the rate or extent of TCE removal in `fresh' ZVI that may be the result of application of direct current are indistinguishable from those due to TCE reduction by ZVI alone; (2) upon application of direct current (6V and 12V) to partially passivated ZVI, a significant improvement in TCE reduction was observed; (3) the longevity of ZVI de-passivated by EIR was not determined, but preliminary results suggest the observed effect may be short-lived and be due to direct reduction of TCE by electrons; and (4) experiments in a partially passivated ZVI-sand column suggest that observed enhancements in TCE removal are correlated with voltage, with higher current densities resulting in faster rates of TCE reduction.