RU2203227C2 - Device for electrochemical cleaning of potable water - Google Patents

Abstract

FIELD: water treatment systems. SUBSTANCE: device includes electrochemical reactor, sludge receiver mounted in upper portion of reactor and inverted cone at positive buoyancy which closes upper hole of reactor. Located in lower portion of device is electrode unit including three groups of electrodes; two groups form stack of electrodes for electric coagulation and third group is used as anode for electric floatation. Said electrodes are connected with power supply source by means of switch gear. Accordingly, cathodes are connected with negative pole of power supply source during electric coagulation and anodes are connected with positive pole. During electric floatation, electric floatation anode is connected to positive pole of power supply source by means of switch gear; cathodes of electrode stack are disconnected from power supply source and anode polarity is reversed. Device may be provided with final filter. EFFECT: enhanced stability of cleaning process due to depassivation of anodes in electrode stack. 2 cl, 3 dwg

Description

 The proposed solution relates to the field of drinking water purification, to electrochemical water purifiers.

 The scope of the present invention can be the purification of tap water, as well as the purification of natural water for the supply of limited groups of people (group water purifier).

 Electrochemical water purification devices remove most of the contaminants, practically without changing the salt composition of the treated water. At the same time, as a rule, anthropogenic pollution is removed from the water: organic impurities, salts of heavy metals, radionuclides, synthetic surface-active substances (SAS), oil products. The water treated by the electrochemical treatment device has high organoleptic and physico-chemical properties. The water quality remains unchanged throughout the life of the installation, since, unlike sorption technologies, pollution does not accumulate in the device.

 Known designs of devices for electrochemical water treatment are described in the monographs of MG Granovsky, I.S. Lavrova, O.V. Smirnova "Electrical processing of liquids" (L., Chemistry, 1976); S.V. Yakovleva, I.G. Krasnoborodko, V.M. Rogova "Technology of electrochemical water treatment" (L., Stroyizdat, 1987).

 Known devices for electrochemical water treatment containing sequentially located electrolyzer, flotator and filter (SU 1761676 A1, SU 176I677 A1, SU 1761678 A1).

 Known devices for electrochemical water purification, containing sequentially located electrolyzer, electroflotator and filter, implementing the most promising method of water purification - electroflotocoagulation (MG Granovsky, V. S. Lavrov, O. V. Smirnov. "Electric processing of liquids", L., Chemistry, 1976, p. 190-191).

 It is known that "a significant drawback of electroflotocoagulation is the processes of passivation of the anodes to adsorption of foreign impurities on them" (SV Yakovlev et al. "Technology of electrochemical water treatment", L., Stroyizdat, 1987, p. 201).

 A device for electrochemical water treatment is also known, containing an electrolyzer, a flotator and a filter, in which these units are combined in one electrochemical reactor - an electroflotator (Application 98110953 dated June 17, 1998 for the invention "Method for the electrochemical treatment of drinking water and a device for its implementation") .

 Significant differences of this device are the presence of a sludge collector mounted on the upper part of the electrochemical reactor, mounted with the possibility of vertical movement on the upper opening of the reactor with positive buoyancy of the inverse cone, a package of soluble electrodes mounted directly above the electroflotation electrodes.

 The known device is the closest to the proposed technical solution in terms of technical nature, purpose and the maximum number of similar essential features and therefore it is selected for the prototype.

 The known prototype device contains (Fig. 1) an electrochemical reactor 1 with a sludge collector 2 fixed on its upper part, while a reverse cone having positive buoyancy 3 is mounted on the upper opening of the reactor 1 and has an electrode buoy 3 located in the lower part of the electrochemical reactor containing a package of electrocoagulation electrodes 5 and electroflotation electrodes 6, which is connected to a power source and control 7.

 The prototype device operates as follows.

 The electrochemical reactor 1 is filled with treated water. In the process of filling, the electrode block 4 is turned on. In this case, the electrocoagulation electrode package 5 (Fig. 2) produces during the anodic dissolution the anode material 8, which, as a rule, is aluminum. Aluminum ions, combined with hydroxide ions from the treated water, form aluminum hydroxide, which coagulates impurities from the water. At the same time, the cathode 9 of the packet of soluble electrodes 5 and the cathode 10 of the electroflotation electrodes 6 emit hydrogen bubbles, which migrate the formed coagulant flakes to the surface of the treated water. The filling of the reactor 1 ends when the water leaves its upper hole, raises the inverse cone 3 and fills the capacity of the sludge collector 2 above the upper edge of the neck of the reactor 1.

 Upon reaching this level, the filling of the reactor 1 with the treated water is stopped and the package of soluble electrodes 5 of the electrode block 4 is turned off, leaving the electroflotation electrodes 6 turned on. At the same time, hydrogen bubbles from the cathode 10 continue to exist. Since the anode of the II group of electroflotation electrodes 6 is an inert material (for example, graphite ), from it only atomic oxygen enters the treated water, which contributes to the disinfection of the treated water. At the end of the electroflotation process, the electroflotation electrodes 6 are turned off and the sludge collected on the surface of the water in the tank of the sump 2 is discharged into the sewer. At the same time, the return cone 3, which drops together with the water level, squeezes some purified water from the neck of the reactor 1 into the tank of the sump. water is sent to a final filter. After emptying the electrochemical reactor 1, the process is repeated with a new portion of the source water.

 The disadvantage of the prototype device is the process of passivation of the electrodes (anodes) of a package of soluble electrodes during operation of the device, which reduces the production of active coagulant, violates the stability of the physicochemical and organoleptic properties of the treated water during long-term operation of the installation, reduces the periods between replacements of the electrode block.

 It is known that when you turn on the package of soluble electrodes, the main load is carried by anodes. On them, during electrolysis, active metal ions of the anode (mainly aluminum) are formed, which in the interelectrode space form aluminum hydroxide molecules - the main coagulant during the electrochemical treatment of water. At the same time there is an electrolysis of the treated water. As a result of water electrolysis, atomic oxygen is released on the anode, which contributes to the oxidation of organic impurities in water, as well as a certain amount of hypochlorites, which, like atomic oxygen, contribute not only to the oxidation of impurities, but also to disinfection of water. At the cathode of the package of soluble electrodes hydrogen bubbles are formed, which in the prototype device at the first stage of water treatment act as a flotation reagent together with hydrogen bubbles released from the cathode of the electroflotation electrodes. At the second stage of processing — electroflotation — the packet of soluble electrodes is turned off, since along with the hydrogen bubbles (flotation reagent) necessary at this stage, the production of aluminum ion and the formation of its hydroxide would continue, which makes the electroflotation process ineffective.

 The anode of electroflotation electrodes is made of materials that emit only atomic oxygen into water. As a rule, the electroflotation anode is made of electrochemically inert materials: platinum, graphite, titanium coated with ruthenium or cobalt oxides (low-wear anodes).

 It is known that to combat passivation "a number of constructive measures have been developed that are used in practice: ultrasonic cleaning of the electrodes, vibration, shaking, high speed of water in the interelectrode space during pressure mode or due to recirculation, single-flow scheme of water movement, machining of electrodes with scrapers, blowing interelectrode space with a gas, a rotating soluble anode, etc. "(SV Yakovlev and others." Technology of electrochemical water purification ", p. 119).

 The proposed measures significantly complicate the device and, in addition, do not have a clearly confirmed theoretical basis substantiated by electrochemistry. Theoretical electrochemistry notes only the following activation factors: reduction with hydrogen during heating, reduction at the cathode with electrolytic hydrogen, storage of the active metal in full vacuum or in an atmosphere of hydrogen, activation by mechanical cleaning of the surface of a passive metal (N.A. Izgaryshev, S.V. Gorbachev. The course of theoretical electrochemistry. M.-L., GNT "chemical literature, 1951, p. 427).

 Of the measures used in practice, only the mechanical treatment with scrapers satisfies the requirements of theoretical electrochemistry. According to some authors, “polarity reversal, that is, cleaning the electrode with released hydrogen, is an equally effective way of activating the electrodes” (SV Yakovlev et al. “Technology of electrochemical water treatment” p. 65). Such a method for a limited time can be effective, however, since the polarity reversal is carried out in a package of soluble electrodes, both groups of the package (i.e., cathodes and anodes) must be made of one metal (in our case, an aluminum alloy). In this case, passivation of both groups of the packet is observed, accompanied by a significant decrease in the yield of active aluminum ion and, as a result, the need for a complete replacement of the packet of soluble electrodes. When performing the cathodes of a packet of soluble electrodes of iron alloys, and the anodes of aluminum alloys, any polarity reversal becomes undesirable.

 The aim of the invention is to ensure the stability of water purification processes by activating (depassuring) anodes in the electrocoagulation electrode package.

 This goal is achieved by the fact that in the device for electrochemical water treatment, containing an electrochemical reactor, a sludge collector installed in the upper part of the reactor that closes the upper opening of the reactor with the possibility of vertical movement of the reverse cone with positive buoyancy, as well as the electrode block located in the lower part of the reactor, according to According to the invention, the electrode unit contains a package of electrodes made of alternating anodes and cathodes, while the anodes are made of electrochemically soluble about metal (aluminum or its alloys), and the electroflotation anode, connected through a switching device to a power supply and control, respectively, during electrocoagulation, the cathodes are connected to the negative pole of the power source, and the anodes of the electrode stack are connected to the positive, and when electroflotation is switched to positive the electroflotation anode is connected to the pole of the power source, the cathodes of the electrode package are disconnected from the power source, the polarity of the package anodes is reversed.

 The introduction of the above characteristics allows electrolytic coagulation and electroflotation processes necessary for the technology to be carried out and significantly passivation of the electrodes of the electrocoagulation electrode package anode is reduced, which allows stabilization of the physicochemical and organoleptic properties of the treated water at a high level for a period comparable to the dissolution time of the anode coagulation electrode package. Each stage of water treatment in the installation that implements the proposed technical solution has a number of factors that contribute to slowing down the processes of passivation of the anodes of the electrocoagulation electrode package or their activation. At the first stage - electrochemical coagulation - the passivation process to a certain extent depends on the ionic composition of the treated water. From theoretical chemistry it is known that in the presence of a sufficient amount of chlorine ions (chlorides) in water, the dissolution of the anodes proceeds practically according to the Faraday law. However, in most cases, this factor does not completely exclude the possibility of passivation of the anodes of the electrocoagulation electrode package. In addition, the replacement of the cathode material in the electrode stack with a more electropositive metal relative to the anode material, in accordance with the theory of electrochemical corrosion, contributes to the activation of the anodes. Since, as a rule, anodes are made of aluminum alloys, the manufacture of cathodes of a package of electrocoagulation electrodes from more electropositive materials than aluminum (for example, an alloy of iron, nickel, copper, etc.) promotes the activation of anodes in a package of electrocoagulation electrodes at the first stage of electrochemical water treatment. At the second stage of electric processing - electroflotation - according to the invention, the anodes of the package of electrodes are connected to the negative pole of the power source. As a result, they become the cathodes of the electroflotation electrode group. In accordance with the laws of electrochemistry, hydrogenation (hydrogenation) of the indicated electrodes occurs in this case, which, along with the factors described above, is the most powerful factor for activating the electrodes.

 The prior art does not reveal technical solutions having features that match the distinguishing features of the present invention, therefore, we can assume that the proposed solution meets the conditions of an inventive step.

 The essence of the invention is illustrated by graphic materials, where in FIG. 1 schematically shows a prototype device; figure 2 - electrode block of the device of the prototype; figure 3 schematically shows the proposed device.

 The proposed device (figure 3) as well as the prototype contains an electrochemical reactor 1 with a sludge collector 2 fixed on its upper part, while the inverse cone having positive buoyancy is mounted on the upper hole of the electrochemical reactor 1 with vertical buoyancy 3. In the lower part of the electrochemical Reactor 1 is an electrode unit 4 containing a package of electrocoagulation electrodes 5 with a cathode 9 and anode 8 and only an electroflotation anode 11 connected to a power supply and control 7.

 Unlike the prototype, the electrode block 4 contains three groups of electrodes, two of which, anodes 8 and cathodes 9, form a package of electrocoagulation electrodes, and the third group of electrodes is an electroflotation anode 11 connected through a switching device 12 to a power supply and control 7, respectively: during electrolytic coagulation, the cathodes 9 of the electrocoagulation electrode package are connected to the negative pole of the power supply 7, and the anodes 8 of the electrode package are connected to the positive pole, while electroflotation to the positive the electroflotation anode 11 is connected to the power supply 7, the cathodes of the electrode package are disconnected from the power source, and the polarity of the anodes of the electrode package is reversed.

 In the operation of the proposed device, three stages are clearly expressed: at the first stage, the electrochemical reactor 1 is filled with water that is being treated. At the same time, the package of electrocoagulation electrodes 5 is turned on, and the switching device 12 connects the cathode 9 to the negative pole of the power source, and the anodes 8 to the positive pole. Anodes 8 produce ions that form a coagulant (aluminum hydroxide). Cathodes 9 emit hydrogen bubbles, which act as a flotation reagent. Thus, at the first stage, the process of electroflotocoagulation in the flow mode is carried out. The filling of the electrochemical reactor 1 is completed when the water to be treated exits its mouth into the tank of the sludge collector 2 and raises the inverse cone 3 above the neck of the electrochemical reactor 1.

 Simultaneously with the completion of filling the reactor 1 and the capacity of the sludge collector 2, the electrocoagulation electrode package 5 is disconnected, and the switching device 12 disconnects the cathodes 9 of the electrode package, changes the polarity of the anode 8 of the electrode package, and electroflotation anode 11 connects to the positive pole of the power source.

 The second stage of electric water treatment - electroflotation - proceeds in a non-flow mode. In this case, hydrogenation of the electrodes 8 of the electrocoagulation electrode package occurs and hydrogen bubbles are emitted from them, which is the main flotation reagent. The hydrogenation of the electrodes 8 over the period of the process (stage) of electroflotation activates these electrodes, almost completely eliminating the phenomena of passivity of the metal. In the process of electroflotation, coagulant flakes migrate into the capacity of the sludge collector 2 to the surface of the water. After the exposition of electroflotation, the electrode unit 4 is completely turned off. When the power supply to the electrode unit 4 is turned off, the last processing stage proceeds: the treated water is drained from the electrochemical reactor 1. The treated water is drained by dumping the sludge from the sludge collector 2. In this case, the return cone 3, lowering with the level water, squeezes out part of the purified water from the neck of the electrochemical reactor I into the capacity of the sludge collector 2, helping to reduce the influx of suspensions onto the filter during the final filtration. Since steel electrodes 9 and aluminum electrodes 8 are in contact through an electrolyte (water), reactions occur that also contribute to the activation of the aluminum electrode.

 At the end of draining the treated water, the treatment cycle is repeated with a new portion of water.

 Thus, the proposed technical solution allows you to keep the electrodes that perform electrolytic coagulation in an activated state, delaying the development of passivation, thereby achieving the goal - improving the stability of water purification processes by activating the anodes in the electrocoagulation electrode package.

 To verify the effectiveness of the proposed technical solution, an experimental device was manufactured containing an electrochemical reactor with a top of the sludge collector and an inverse cone with positive buoyancy mounted on the neck of the reactor, the electrode block of which contains a package of electrocoagulation electrodes, the cathodes of which are made of an iron alloy (Article 3) and the anodes are made of aluminum alloy (AMG), as well as the electroflotation anode made of titanium coated with cobalt oxide (cobalt oxide tovy titanium anode - OCTA). The specified electrode unit, in accordance with the invention, is connected to a power source and control a switching device that allows you to connect the electrode groups in pairs.

The initial electrical parameters of the electrode unit: the voltage on the electrocoagulation electrode package is 20 V, the current strength is 4 A, the electroflotation voltage is 20 V, the current strength is 2 A (corresponds to the optimum value of 6 ÷ 7 mA / cm ² ). More than 900 cycles of electrical processing have been carried out. The current was monitored continuously during electrocoagulation and electroflotation. After almost three months of testing, the current strength on the package of coagulation electrodes and in the electroflotation circuit remained virtually unchanged.

 In another experiment, a passivated electrocoagulation electrode package was used. The initial current strength was 2.5 A. During water treatment, the current strength on the electrocoagulation electrode package gradually increased and after three cycles increased to 4 A. During subsequent operation (more than 20 cycles), there was a pronounced tendency to maintain the maximum possible current strength in the electrode package electrocoagulation.

 Thus, the lengthy experiments confirmed the high efficiency of the proposed technical solution.

Claims (2)

 1. A device for the electrochemical purification of drinking water, containing an electrochemical reactor, a sludge collector installed in the upper part of the reactor, closing the upper hole of the electrochemical reactor with the possibility of vertical movement of the reverse cone with positive buoyancy, and also located in the lower part of the electrochemical reactor electrode unit, characterized in that the electrode unit is formed by a package of electrocoagulation electrodes and an electroflotation anode connected through a switching device with a power source, in the case of operation of the device in the electrocoagulation mode, the cathodes of the packet are connected to the negative pole of the power source, and the anodes to the positive pole of the power source, and when the device is in electroflotation by means of a switching device, the electroflotation anode is connected to the positive pole of the power source, the cathodes of the package of electrodes are disconnected from the power source, and the polarity of the anodes of the package is reversed.  2. The device according to claim 1, characterized in that the anodes of the electrocoagulation electrode package are made of aluminum alloys, the cathodes are made of more electropositive materials with respect to aluminum, such as iron, nickel or copper, and the electroflotation anode is made of low-wear material, such like platinum, graphite, titanium coated with ruthenium or cobalt oxides.

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