Electrochemical reactors are the most important elements of the "Izumrud" devices. They provide the fulfillment of the following basic conditions of the electrochemical treatment of water.

  The electrochemical reactors of the "Izumrud" devices consist of flow module electrolytic elements [8,9]. The element (Fig.6) is a miniature diaphragm electrolyzer with vertically mounted cylindrical electrodes: outer 1 and inner 2, with a thin-walled tubular porous ceramic diaphragm 3 between them dividing interelectrode space into two electrode chambers - anodic and cathodic. Electrodes 1, 2 and diaphragm 3 are mutually fixedly, hermetically and strictly co-axially fastened with the help of bushings made of dielectric material, and elastic sealing rings. Each bushing is supplied with a union for hydraulic communication with the appropriate electrode chamber: with the help of the unions on the outer bushings the flow of water through the inner electrode chamber is provided, and the flow of water through the outer electrode chamber is performed with the help of the unions on the inner bushings. The inlet unions of the electrode chambers are in the lower part of a vertically mounted element, and the outlet ones - in its upper part. Interelectrode space (IES) of the element is 3 mm, the permissible range being from 2.8 to 3.3 mm. With this IES value, the anodic and cathodic zones of intensive convection, diffusion and electromigration mixing of water under the action of current, flowing between the electrodes, come into contact (provided there is no diaphragm). This leads to a considerable reduction of the electrochemical system ohmic resistance in case of increased current density.

  Fig.6. Flow electrochemical module element

1 - cathode; 2 - anode; 3 - diaphragm; 4 - bushing; 5 - head; 6, 7 - seals; 8 - nut; 9 - washer

  The diameter D of the inner electrode's working part is determined by the ratio: 2 IES < D < 4 IES. Numerous experimental studies have proved that the optimum diameter of the inner electrode working part of the element is 8 mm. Consequently, the optimum diameter of the inner (working) part of the outer electrode is 14 mm. The optimum diameters of the element's inner and outer electrodes have been determined in order to ensure the contact of each microvolume of flowing water with the electrode's surface. This becomes possible when self-organization regimen of the interelectrode medium is achieved in the element's electrode chambers in the process of electrochemical treatment. An essential role in establishing the regimen of the electrochemical process self-organization belongs to the diaphragm.

  The diaphragm of the element is made of ceramics based on zirconium, aluminum and yttrium oxides. It may contain additives of lanthanum, niobium, tantalum, titanium, gadolinium, hafnium and other oxides. The diaphragm is highly resistant to the action of concentrated and diluted aqueous solutions of acids, alkali, oxidants, reductants, and corrosive gases (chlorine, chlorine dioxide, oxygen and ozone). It is insensitive to heavy metal ions, organic substances and has a practically unlimited service-life which by far exceeds the service-life of the element (40-60 thousand hours). In case it is soiled by oil products and metal hydroxides, the diaphragm can be repeatedly cleansed with detergent solutions, concentrated or diluted hydrochloric acid, and after cleaning its qualities are completely restored. The thin-walled ceramic diaphragm undergoes no size or shape alterations under pressure differential, it is hydrophilic, has a low electric and a high filtration resistance due to a large number of tiny open pores. Besides, the diaphragm's surface is able to absorb highly charged metastable particles coming from the electrodes. They hardly penetrate inside because the energy of interaction with the hydrophilic diaphragm material surface is higher than the energy of electromigration transport activation, and thus they do not undergo mutual neutralization. In the course of the element's work, two oppositely charged ion layers are formed on the inner and outer diaphragm surfaces. Their difference of potentials can reach 2.5 V. Because of charged surface ion layers the voltage of the diaphragm's electric field increases by 30-40 V/cm thus contributing to better ion mobility in the pores and lowering the element's electric resistance.

  Depending on the water purification technology used, the diaphragm for the element can be made as an ultra-, micro- or nanofiltration one. In the circular vertical smooth-walled electrode chambers of the element there are no conditions for the formation of stagnant or slow-flow zones.

  The length of the outer electrode of the element is 187 mm. The volume of the electrode chamber of the outer electrode is about 10 ml, and the volume of the electrode chamber of the inner electrode is 7 ml.

  The outer electrode of the element is a cathode, and is made of titanium, zirconium, tantalum or carbon glass. Dependant on the element's employment, the working surface of the outer electrode-cathode undergoes special treatment which helps reduce cathodic deposit formation, adds catalyst's properties to it, regulates the composition of electrochemical reaction products and provides the formation of gas bubbles of needed (optimum) diameter in a concrete technological process. For cathode surface coating, usually platinum or pyrocarbon are used.

  The anodes for the element are made of titanium covered with noble metals (platinum, iridium). Controlling the catalytic ability of the anode coating, selectivity of electrochemical synthesis processes and ability to form gas microbubbles of optimum size is provided by technological operations during coating. Each element is an individual electrochemical reactor and can be used both separately and together with other elements combined into the flow electrochemical reactor RFE or RFE-M [10,11].

  In all cases, mounting elements in a reactor of greater productivity is fulfilled by their hydraulic parallel connection with the help of collectors. In RFE reactors, the collectors for connecting elements are plates of dielectric material with inner channels for liquid flow, or parts of thick-walled pipes of dielectric material with sockets or unions for connection with elements (linear connection of elements). In the RFE-M reactors, the collectors secure radial connection of elements, water or solutions being fed or removed from the common center. The RFE-M reactors provide even distribution of liquid among elements with no special technical gadgets used, that is why they are more commonly applied than the RFE-type reactors. Electric connection of elements in RFE or RFE-M reactors can be consecutive, parallel or consecutive-parallel (mixed), depending on the concrete technological scheme of using the device for electrochemical activation of water or solutions.