Pollutants electrochemical removal

Drogui, P., Asselin, M., Brar, S.K., Benmoussa, H., and Blais, J.F., Electrochemical removal of pollutants from agro-industry wastewaters, Separation and Purification Technology, 61, 301-310, 2008. 

Kiener LV, Uhrich KD (1987) Electrochemical removal of color from dye laden wastewater, Water and Pollution Control Assoc of South Carolina Fall Conf, Nov 24 cited in Ref [312]... 

The electrochemical removal of contaminants may not be always possible or practical. For instance, a site may be too polluted to be treated to the acceptable level by any of the technologies, but it is critical to reduce the risk posed by the site contamination. The common approach used for risk reduction is stabilization and solidification (or immobilization) technology. In this approach, contaminants are transformed into a form that does not allow them to be released into the environment. Electrochemical approach may be used to stabilize the contaminated soils at a low cost and it will serve as an interim or pretreatment process to permanent treatment technologies. 

For some combinations of heavy metals, it is also necessary to use enhancement solutions to ensure the simultaneous removal of all pollutants (Ottosen et ai, 2003). Especially, the presence of As in the soil necessitate alternative solutions to the acidic front since As generally has low mobility under acidic conditions, whereas As is more mobile under alkaline conditions, where most heavy metals are not mobile (Le Hecho, TelUer, and Astruc, 1998 Ottosen et aL, 2000). Le Hecho, Tellier, and Astruc (1998) conducted laboratory experiments with spiked soils, where the pollutants were As and Cr. Successful remediation was obtained in the developing alkaline front combined with the injection of sodium hypochlorite. As was mobile in the alkaline environment, and Cr(III) was oxidized to Cr(VI) by hypochlorite and mobilized in the alkaline environment. In loamy sand polluted with Cu and As from wood preservation. As and Cu were mobile simultaneously after the addition of NH3 to the soil (Ottosen et a/., 2000). As was mobile due to the alkaline environment and Cu formed charged tetra-ammine complexes. For the simultaneous mobilization and electrochemical removal of Cu, Cr, and As, ammonium citrate has shown to be successful (Ottosen et al, 2003). 

The second project considers electrochemistry in its relations with environmental problems. The two major topics are the development of electrochemical monitors specially adapted to pollution, and the electrochemical removal of environmental pollutants, these processes can be made economic and highly selective. Three successive workshops have already been devoted to these topics, with special emphasis on electrochemical sensors in water analysis. 

AOPs are valuable tertiary treatments allowing not only inactivation of a wide spectrum of pathogens but also the removal of a great number of the so-called emerging pollutants (pharmaceutical, personal care products). These are not totally removed during conventional treatment, but remain in the wastewater effluents [33]. Among different alternatives electrochemical oxidation with bom doped diamond electrodes (BDD) has been reported to be effective on eliminating... 

Numerous commercial dyes are metal chelate complexes. These metals form pollutants which must be eliminated. One of the strongest points in favour of electrochemical reduction/removal of metal ions and metal complexes - the metal ions and weakly complexed ions form the toxic species - and of the metals from the metal-complex dye is that they are eliminated from the solution into the most favorable form as pure metal, either as films or powders. Polyvalent metals and metalloids can be transferred by reduction or oxidation treatment to one valency, or regenerated to the state before use, e.g. Ti(III)/Ti(IV), Sn(II)/Sn(IV), Ce(III)/Ce(IV), Cr(III)/Cr(VI), and can be recycled to the chemical process. Finally, they can be changed to a valence state better suited for separation, for instance, for accumulation on ion exchangers, etc. Parallel to the... 

The processes controlling transfer and/or removal of pollutants at the aqueous-solid phase interface occur as a result of interactions between chemically reactive groups present in the principal pollutant constituents and other chemical, physical and biological interaction sites on solid surfaces [1]. Studies of these processes have been investigated by various groups (e.g., [6-14]). Several workers indicate that the interactions between the organic pollutants/ SWM leachates at the aqueous-solid phase surfaces involve chemical, electrochemical, and physico-chemical forces, and that these can be studied in detail using both chemical reaction kinetics and electrochemical models [15-28]. 

However, such a complex system would not be helpful to describe organic-removal wastewater-treatment processes because of its high degree of complexity and, therefore, in an attempt to achieve a useful model, some assumptions could be made in order to simplify the model. Hence the transformation of this distributed-parameter model in a simpler lumped-parameter model is very common in the modeling of wastewater-treatment processes, because it is not very important to obtain detailed information about what happens in every point of the cell but simply to know in a very simple way how the pollution of a influent waste decreases at the outlet of the electrochemical cell. In this context, there are three types of approaches typically used ... 

The second item that needs to be fixed is the number of species and the reactions, including the stoichiometric coefficients and also the kinetics of the processes. In this context, in electrochemical oxidation processes it is important to discern between two types of anodes those that behaves only as electrons sinks (named nonactive) and those that suffer changes during the electrochemical oxidation which influence on the treatment (named active electrodes). In both cases, the main processes related to removal of the pollutant that involves irreversible oxidative routes. Consequently, the reductive processes are less important and it can be presumed that in the cathodic zone only hydrogen evolution occurs. Nevertheless, if some organic compound can be reduced at the cathode, the mass-transfer and the reduction processes must be included in the model scheme. 

Costentin, C., Robert, M. and Savcant, J.-M. (2003) Successive removal of chloride ions from organic polychloride pollutants. Mechanisms of reductive electrochemical elimination in aliphatic gem-polychlorides, a, fi-polychloroalkcncs, and a, fi-polych loro alkanes in mildly pro-tic medium. J. Am. Chem. Soc. 125, 10729-10739. 

Electrochemical wastewater treatment — may involve (a) -> electrolysis with the purpose of heavy metal ion removal, (b) electrochemical transformation of anions, e.g., perchlorate, nitrate, (c) oxidation of organic pollutants, (d) - electrodialysis, or (e) - capacitive deionization. 

These treatments manipulate selected physicochemical properties of pollutants in such a way that they are either rendered less harmful (or even virtually harmless in some cases) or else removed from the target medium. They are based on redox, acid-base, complexation, electrochemical, solubility, and catalytic principles, as discussed below. 

Studies on the electrochemical treatment and removal of these gaseous pollutants have increased considerably since the 1970s. In many cases, the electrochemical routes may be cleaner than currently existing technologies, and/or more economically viable. Furthermore, reaction products from gas treatment may be salable by-products. A review on electrochemical separation of gases has been published in an earlier volume of this series [101]. 

Anodic oxidation was shown to be a useful method for the removal of organic pollutants from aqueous solutions [15]. Partial decomposition of hazardous organic compounds to biodegradable compounds or complete decomposition to H2O and CO2 can be achieved by the electrochemical treatment of waste [14]. Two different categories of electrochemical treatment of waste-water or waste can be distinguished ... 

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