Electrochemical waste removal

BDD electrodes are commonly used for electrochemical (waste) water treatment because of their efficient ability for total organic carbon (TOC) removal. The aim to carry out selective electrochemical processes seems therefore to be self-contradictorily. 

Juttner K, Kreysa G, Kleifges KH, Rottmann R (1994) Electrochemical waste cleanup process for simultaneous removal of SO2 and NO. Chem Ing Tech 66 82-85. doi 10.1002/dte.330660115... 

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

A bone is classified according to shape as flat, long, short, or irregular. A living bone consists of three layers the periosteum, the hard cortical bone, and the bone marrow or cancellous bone. The periosteum is a thin coUagenous layer, filled with nerves and blood vessels, that suppHes nutrients and removes cell wastes. Because of the extensive nerve supply, normal periosteum is very sensitive. When a bone is broken, the injured nerves send electrochemical neural messages relaying pain to the brain. 

The first equation is an example of hydrolysis and is commonly referred to as chemical precipitation. The separation is effective because of the differences in solubiUty products of the copper(II) and iron(III) hydroxides. The second equation is known as reductive precipitation and is an example of an electrochemical reaction. The use of more electropositive metals to effect reductive precipitation is known as cementation. Precipitation is used to separate impurities from a metal in solution such as iron from copper (eq. 1), or it can be used to remove the primary metal, copper, from solution (eq. 2). Precipitation is commonly practiced for the separation of small quantities of metals from large volumes of water, such as from industrial waste processes. 

Universal waste battery Battery means a device consisting of one or more electrically connected electrochemical cells, which is designed to receive, store, and deliver electric energy. An electrochemical cell is a system consisting of an anode, a cathode, and an electrolyte, plus such connections (electrical and mechanical) as may be needed to allow the cell to deliver or receive electrical energy. The term battery also includes an intact, unbroken battery from which the electrolyte has been removed. 

The limiting-current method has been used widely for studies in packed and fluidized beds (see Table VII, Part H). Limiting current measurements in these systems overlap in part with the design and analysis of packed-bed and fluidized-bed electrochemical reactors in particular the potential distribution in, and the effectiveness of, such reactors (for example, for metal removal from waste streams) is an extensive area of research, which cannot be covered in this review. For a complete discussion of porous flow-through electrodes the reader is referred to Newman and Tiedemann (N8d). 

Andco Environmental Processes, Inc., has developed an electrochemical iron generation process to remove hexavalent chromium and other metals from gronndwater and aqneons wastes. As contaminated water flows through a treatment cell, electrical cnrrent passes between electrodes, releasing ferrons and hydroxyl ions. The small gap between electrodes allows almost instantaneons rednction of chromium ions. Depending on the pH, varions solids may form. 

Electrochemical iron generation is a site-specific technology that is pH dependent. Process pH should be from 6 to 9. Optimal removal efficiencies require electrochemical treatment in combination with an ideal precipitation pH for the metals being removed. Nearly all fuU-scale systems include a pH control system. Andco performs lab and pilot-scale testing to evaluate the ability of the process to treat a particular waste stream. If flow rates or contaminant loads fluctuate, control equipment is required to compensate for changes in influent. 

Liquid wastes containing hexavalent chromium require reduction of chromium to the trivalent state prior to metal removal. Commonly used reducing agents are sodium metabisulfite, sulfur dioxide, ferrous sulfide, and other ferrous ions (ferrous sulfate, ferrous chloride, or electrochemically generated ferrous ion). All of these reagents create some form of chromium sludge, which must be separated and dewatered before disposal. 

Mercury represents a serious environmental risk, and the study of removal of mercury from wastewater has received considerable attention in recent years. Mercury concentration was usually reduced by deposition on a cathode with high surface area. Removal of mercury is studied using extended surface electrolysis which reduces the level of mercury to below acceptable concentrations of 0.01 ppm in wastes by employing a Swiss roll cell with a cadmium-coated, stainless-steel cathode. An industrial cell with a fluidized bed electrode has also been studied. Graphite, as an efficient porous electrode, has been used to remove traces of mercuric ions form aqueous electrolyte solutions. In order to apply the electrochemical method for some effluents, it is necessary to use sodium hypochlorite to convert elemental mercury and less soluble mercury compounds to water-soluble mercuric-chloride complex ions. 

Finally, soil remediation processes are farther along than the remediation of low-level waste because some practical tests have been made in the field. In some systems, the results are those desired. The costs of the thermal process for removing metal from soils are so high that funding of the development of the electrochemical approach would seem to offer good returns. 

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 ... 

When the waste contains more complex molecules such as compounds refractory to oxidation with OH radicals, as well as in the presence of inorganic ions which can be precursor of long-life oxidants, the Faradic yield cannot be calculated by (8.3) and different alternatives have been proposed. Faouzi and co-worker (Faouzi et al. 2006) proposed a comparison between electrochemical oxidation at BDD anodes and Fenton and Ozone treatments for the removal of dyes a specific parameter OCC (oxygen-equivalent chemical-oxidation capacity) was proposed which is defined as the kg of 02 equivalent to the quantity of oxidant used in each AOP to treat 1 m3 of wastewater. As highlighted by the authors, the parameter OCC may only give information on the chemical efficiency of the oxidants, but it does not give any information related to the real cost of the treatment, as the oxidants can... 

Shen, F., Chen, X.M., Gao, P. and Chen, G. (2003) Electrochemical removal of fluoride ions from industrial waste water. Chem. Eng. Sci. 58, 987-993. 

ERIX [Electrochemically Regenerated Ion exchange system] A process for removing hydrofluoric acid from aqueous wastes from the electronics industry. The fluoride ion is trapped in an ion-exchange resin, which is continuously regenerated electrochemically. Developed by BOC Edwards and first installed in the University at Albany, State University of New York, in 2006. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

Fig. 10. Electrochemical reactor used for the simultaneous treatment and removal of cyanide and cadmium from a metal-finishing waste stream. (Adapted from [44]).

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