JPS637118B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention relates to environmental engineering technology, more specifically:
The present invention relates to a method and apparatus for electrochemical treatment of sewage (or wastewater) containing seawater and having various salt contents. PRIOR ART The problem of biosphere pollution is one of the first to be raised around the world today, and water pollution by sewage effluents occupies a special position in biosphere pollution. Seafaring has developed significantly, and as a result, the proportion of ship sewage in the total amount of sewage discharged into the ocean has increased significantly. As a result, most countries have taken steps to prevent ships without sewage treatment systems from sailing within their territorial waters. When designing a ship's sewage treatment system, special attention must be paid to treatment reliability. This is because electrochemical methods of sewage treatment, which involve treating sewage with coagulants produced during electrochemical dissolution of metals, are now very widespread. However, the practical use of such coagulants presents some difficulties for a number of reasons. One such difficulty is the formation of salt deposits on the electrodes. Such salt deposits increase the electrode resistance, thereby reducing the current flowing through the electrode (passivation), and also reduce the concentration of coagulant that forms in the interelectrode space and is introduced into the treated seawater. decrease and ultimately affect processing efficiency. Additionally, salt deposits can block the interelectrode space to such an extent that treatment fluid cannot flow between the electrodes, resulting in interruption of the seawater treatment process. When seawater containing sea salt, whose concentration varies widely depending on the location of the ship, is used for cleaning sanitary equipment on board the ship, such salt deposits are particularly characterized by sea conditions. Therefore, one of the problems in improving the reliability of marine sewage treatment is the problem of eliminating salt deposits on the electrodes. Thus, the known prior art sewage treatment method and device are covered by the inventor's USSR Inventor's Certificate No. 739004.
Cl. ² CO2F 1/46, the method comprises treating seawater-containing sewage in the cathode compartment of a diaphragm electrolyzer, then separating the magnesium-containing sediment, and processing in the anode compartment of the electrolytic cell and directing the magnesium-containing fluid from the cathode compartment to the anode compartment. Although this method prevents excessive salt deposition on the electrodes, a number of factors prevent it from treating sewage containing seawater with sufficient efficiency. These factors are as follows. 1. repeated treatment of the sediment in the anode compartment with further supply of magnesium-containing fluid to the cathode compartment increases the concentration of magnesium ions in the treated sewage;
As the solution becomes saturated, magnesium salts precipitate and these salts contaminate the purified sewage water. This definitely affects processing efficiency. 2 When sewage is treated only in the cathode compartment of the electrolyser, the electricity consumption is Somewhat expensive. 3. When the sediment is processed in the anode compartment of the electrolyzer, the anode compartment should have a large volume to prevent the anode area from being blocked by the sediment, so that the distance between the anode and the cathode is reduced. becomes somewhat larger and the voltage across the diaphragm electrolyzer takes on a higher value due to ohmic losses of the electrolyte, which in turn leads to an increase in the power consumption of the sewage treatment. 4. Separation of the magnesium-containing sediment requires a separate sump, which considerably increases the size of the sewage treatment plant, and under conditions of pitching, rolling and ship vibration the efficiency of the process is substantially reduced. Decrease. A more advanced method and apparatus for treating sewage is disclosed in US Pat. No. 4,188,278, Int.Cl. ² CO2B 1/82. This method of fluid treatment consists of flowing the fluid into the electrolytic cell through regions exhibiting different potentials, and the induction of these different potentials changes the accelerating and decelerating forces acting on the fluid along its path, causing the fluid to flow through regions exhibiting different potentials. causing severe turbulence between the individual layers of the The method is carried out in a device consisting of a pair of main electrodes and a plurality of auxiliary electrodes arranged between the main electrodes. Each of the main electrodes comprises a plurality of electrically connected rods arranged in a plane, and each of the auxiliary electrodes comprises an electrically insulating rod. The main electrodes also create regions exhibiting different potentials between the main electrodes, fluid flows through the regions exhibiting different potentials, and air bubbles are removed from the electrodes by an ultrasound source. The power consumption of the equipment implementing this method is also very high due to the ultrasonic vibrator, which serves to prevent salts from depositing on the cathode surface of the electrode. Furthermore, when placing electrodes across a fluid stream, fibrous contaminants stick to the electrodes and it is not possible to remove them by sonication. This is because the specific gravity of the fibrous contaminants is equal to the specific gravity of the fluid to be treated, and due to the highly turbulent region at the rear of the electrode,
This is because the cotton waste coagulation contaminants are destroyed, thereby interfering with the coagulation process of the colloidal contaminants. These facts ultimately affect the quality of sewage treatment. The turbulence of the water and wastewater flows causes intense mixing of the fluid electrode boundary layers, which lowers the PH of these layers and results in the formation of salt deposits on the electrode surfaces. Screens placed in the streamlines of the fluid stream complicate the equipment for implementing this method and affect the reliability of the equipment due to screen clogging. Also, in order to attach the electrodes to the walls of the housing and insulate them from the walls, it is necessary to provide an insulating space or to make the walls of the housing from an insulating material, thus making the construction of the electrolytic cell considerably more complex. . USSR Inventor's Certificate No. 912664, Int.Cl. ³ CO2F
The fluid treatment method implemented by the apparatus disclosed in No. 1/46 is much more effective than those described above. This method is
The sewage water is supplied to the anode and cathode compartments of a diaphragm cell with insoluble electrodes. In the cathodic compartment the sewage water is electrochemically alkalinized and in the anodic compartment it is acidified. The acid anolyte is then led to an electrocoagulator, where the chromium is reduced by divalent iron ions, which are formed during the dissolution of the soluble iron anode of the electrocoagulator. The anolyte from the electrocoagulator is directed to a flotation cell, to which is also supplied an alkaline catholyte. The catholyte is discharged from the cathode compartment of the diaphragm cell, and then separation of liquid and solid phases takes place in flotation cells and filters. Even though this method is somewhat effective, it is imperfect because it is not reliable enough.
This is because as the undissolved sewage salinity changes due to sea conditions, the current flowing through the electrodes of the diaphragm electrolyzer also changes, which in turn causes changes in the pH of the electrolyzer effluent and the dissolution rate of the electrolyzer electrodes. It is. As a result, the coagulant concentration in the sewage being treated changes and due to the presence of magnesium ions in the sewage, magnesium hydroxide, which blocks the electrodes, precipitates in the cathode area of the diaphragm electrolyser, thus ensuring sufficient effectiveness. This would make it impossible to treat sea sewage due to natural disasters. Moreover, in such systems of marine sewage treatment it is virtually impossible to remove magnesium hydroxide from the surface of the insoluble electrode by reversing the polarity. This is because, in the case of polarity reversal, the electric coagulator is supplied with alkaline-reacting sewage water and a passivating soluble iron electrode, and mechanical cleaning of the electrodes requires the use of complex equipment or the use of iron electrodes. The equipment must be either shut down periodically to clean or replace the equipment. USSR Inventor Certificate No. 874653, Int.Cl. ³ CO2F
The fluid treatment method and apparatus disclosed in 1/46 are also known in the art. The method, carried out in a coagulation device, involves supplying the fluid to be treated to the anode area of the insoluble electrode, from where it flows down by gravity to the anode area of the soluble electrode. The fluid to be treated flows from the anode area of the soluble electrode to the cathode area of the soluble electrode and then to the cathode area of the insoluble electrode. Purified water is drained from the cathode area of the insoluble electrode. When operating this device, sewage is treated by passing electrical current through both the insoluble and soluble electrodes. In this case, the concentration of the coagulant that forms in the interelectrode space depends on the salinity of the water and changes in accordance with the salinity change due to changes in the conductivity of the solution and thereby changes in the current flowing through the electrodes. Due to the fact that the current flows directly from the power source to the soluble electrode and the coagulant concentration is variable in the interelectrode space, the consumption of soluble electrode material is very high when treating sewage with high sea salt concentration. Furthermore, due to the fact that the fluid flow is directed from the anode area to the cathode area, deposits form on the soluble cathode surface. This is because the hydrogen ions generated on the anode dissolve the metal hydroxide on the soluble electrode,
A soluble electrode is then used to dissolve the metal hydroxide that forms on the soluble electrode due to the chemical reaction of the metal (e.g. aluminum (with water) which does not form a protective oxide film on the cathode during cathodic polarization). This is because the concentration of hydrogen ions supplied from the anode area is insufficient. Moreover, the hydroxyl ions that form on the insoluble cathode are transported by the generated hydrogen bubbles to the surface of the soluble cathode, and therefore the PH of the cathode surface is insufficient to form soluble metal compounds such as aluminum compounds. By directing the treated sewage stream from the anode area to the cathode area, magnesium hydroxide, which is also a good coagulant, is prevented from forming in the cathode area. This is because the sewage, which has a neutral reaction at the entrance to the device, is acidified at the anode and then alkalinized at the cathode area, down to the initial PH of the fluid, while magnesium hydroxide has a PH above 8.9.
This is because it can only be generated in .
Moreover, when such a flow system is used with a large number of electrode pairs, the construction of the device becomes even more complex since the fluid stream to be treated must be guided in a zigzag pattern. Moreover, due to the fact that the distance between the insoluble and soluble electrodes is large, the influence of the field of the insoluble electrode on the soluble electrode is not significant when the seawater concentration of the treated sewage is low, and the field The influence does not affect the content of coagulant obtained in the interelectrode space of the insoluble electrode. Object and Arrangement of the Invention The main object of the invention is to provide the treatment of sewage containing seawater of varying salinity by an electrochemical method in which the potential of a soluble electrode is shifted into the active range. With this main objective in mind, an electrochemical sewage treatment method is provided which comprises the steps of producing a coagulant in the interelectrode area of insoluble and soluble electrodes and subsequently discharging purified sewage. The method according to the invention supplies sewage in separate streams to the anode and cathode interelectrode areas of an electrolytic cell, and passes a current through the insoluble electrodes to apply a coagulant to the interelectrode areas of both the insoluble and soluble electrodes. generate. The soluble electrode is electrically insulated from the insoluble electrode, and the ratio of current to sewage flow rate is greater than or equal to 0.01 A.hr/. Outline of the invention and explanation of effects The inventor of the present invention discovered the following fact through experiments. That is, because of this design, when current flows only from the soluble electrode to the electrically insulated insoluble electrode, the current becomes dielectric and leaks in the direction of fluid flow from the insoluble electrode to the soluble electrode, thereby increasing the The potential is shifted to its active dissolution range, so that the soluble electrode, especially the aluminum electrode, dissolves. Such a method makes it possible to treat sewage containing seawater with various salinities. When sewage containing a negligible amount of sea salt is passed through a diaphragm electrolyzer, the conductivity of the sewage being treated is low. In this case, as current flows through the insoluble electrode, the dissipative capacity of the sewage water increases, and as a result, the influence of the insoluble electrode field on the soluble power also increases. As the potential of the soluble electrode is shifted significantly into the range of active electrode dissolution, rapid dissolution of the soluble electrode is achieved and the concentration of soluble metal ions in the fluid being treated is increased. The soluble metals coagulate colloidal contaminants in the sewage water. Due to the low salinity of the sewage, the magnesium ion content is also low, and therefore a relatively small amount of magnesium hydroxide forms in the interelectrode space of the insoluble electrode. When passing sewage with high sea salt concentrations, the dielectric properties of the fluid being treated are reduced and the effect of the current-carrying insoluble electrode field on the soluble electrodes is weakened. The shift in potential of the insoluble electrode is reduced and the soluble electrode hardly dissolves. The coagulant in this case is magnesium hydroxide, which is produced during electrolysis as the sewage water is made alkaline in the cathode area of the insoluble electrode. Experiments have also found a relationship between electric current and the flow rate of treated sewage (i.e. volume
quantity of electricity)). The above relationship is 0.01
A.hr/ or more, which is sufficient to shift the potential of the soluble electrodes into the range of their active dissolution, so that a constant total coagulant concentration can be maintained in the interelectrode space. When the salinity of the treated sewage takes on various values, the amount of aluminum dissolved depends on the salinity of the sewage. That is, the amount of aluminum dissolved increases when the salinity of the sewage is low and decreases as the salinity increases. The total coagulant concentration is constant and therefore provides self-control of the sewage treatment process, and the consumption of aluminum electrodes can be reduced by 1/2 to 1/4. Moreover, since the sewage to be treated first flows between the insoluble electrodes and then between the soluble electrodes, the sewage is first acidified and then alkalinized near the insoluble electrodes, thus making the soluble products, namely aluminum ions and aluminate, thereby eliminating the formation of salt deposits on the soluble electrode. It is advisable to supply an unstabilized direct current to the insoluble electrode. By using an unstabilized direct current, the potential of soluble electrodes can be shifted more effectively into the range of their active dissolution compared to a stabilized current of the same strength. Maintain the pH of the anode area within the range of 2 to 3.5,
And in the cathode area, it is wise to carry out the process while maintaining the pH within the range of 10.5 to 12.5. Carrying out the method under such conditions provides complete inactivation of the pathogenic formations contained in the sewage. _This is ^{because the} cathode area of _{the electrolytic} cell _and This is because pathogenic organisms in the anode area are killed. It is advisable to mix and combine the effluents from the cathode and anode areas. When the process effluents from the cathode and anode areas are mixed and combined, the sewage reacts as follows: 2H ₂ O+2e=H ₂ +2OH ^- (cathode) H ₂ O−2e=2H ⁺ +1/2O ₂ (anode) 3H It is neutralized according to ₂ O=H ₂ +1/2O ₂ +2H ₂ O. In view of the above main objects, there is also provided an apparatus for carrying out the method of the invention, which comprises a diaphragm cell comprising at least two pairs of electrodes. Each of said electrode pairs comprises an insoluble electrode and a soluble electrode arranged in a line, and the electrode pairs are arranged alternately in an anode area and a cathode area. According to the invention, the device is such that in each pair of electrodes the insoluble electrode is separated from the soluble electrode by a dielectric separator, the outer shape of the separator matching the end face of the insoluble electrode and facing the soluble electrode. The length ratio of the soluble electrode and the soluble electrode is 1:2 or less. Placing the electrodes in line because the sewage flow moving along the surface of the electrodes provides optimal conditions for the electric field created by the insoluble electrodes carrying current to affect the soluble electrodes carrying no current. provides the best conditions for electrode operation. A dielectric separator provided between the insoluble and soluble electrodes prevents electrical contact between said electrodes and further prevents the potential of the insoluble electrode from being imposed on the soluble electrode, which in turn Passivation can be prevented and excessive consumption of the soluble electrode can be reduced when the salt content of the treated sewage is high. The use of a dielectric separator whose contour matches the end face of the insoluble electrode and faces the soluble electrode provides maximum influence of the electric field of the insoluble electrode on the soluble electrode. Furthermore, when the dielectric separator is configured in this manner, the electrode boundary layer of the sewage being treated does not mix with the remainder of the fluid being treated. This prevents the formation of salt deposits on the surface of the soluble electrode. When current flows through an insoluble electrode, the largest PH change occurs near the electrode. And it is important that the fluid stream in the electrode boundary space must not have time to mix with the rest of the fluid being treated. This provides high alkalinity and acidity in the electrode boundary space of the soluble electrode, thus preventing the formation of insoluble salt deposits during soluble, particularly aluminum electrode dissolution. By placing in line a pair of electrodes, including an insoluble electrode and a soluble electrode, in the anode area, separated by a dielectric separator, and another pair of similar electrodes in the cathode area, the cathode area and the anode of the electrolytic cell are separated by a dielectric separator. The formation of soluble electrolytic products in both areas is prevented. The fluid to be treated flows in parallel flows. Reversal of the polarity of the upper and lower soluble electrodes prevents the formation of magnesium hydroxide on the surface and provides further activation of the soluble electrodes. A ratio of the lengths of the soluble and insoluble electrodes of 1:2 or less results in a shift of the potential of the soluble electrode to the range of active dissolution over the entire length of the soluble electrode. This is because at any other ratio the current flowing through the insoluble electrode will not reach the remote portion of the soluble electrode with its field lines. It is advisable to make the thickness of the soluble electrode greater than the thickness of the insoluble electrode. Such a configuration of the soluble electrode can improve the effect of the electric field of the insoluble electrode carrying current on the soluble electrode not carrying current, thus increasing the shift of the potential of the soluble electrode into the active dissolution range, and The thicker the soluble electrode, the greater the influence of the aforementioned electric field of the insoluble electrode on the soluble electrode. It is expedient to make the insoluble electrode so that the end of the insoluble electrode facing the soluble electrode has a small cross-sectional area symmetrical about the electrode axis. In this case, from any point, even the field line from the inclined plane of the upper surface of the insoluble electrode is perpendicular to the surface of the soluble electrode and valid up to a substantial height, so that current flows with the insoluble electrode in such a configuration. The effect of the electric field on soluble electrodes can be improved. It is advisable for the diaphragm of the electrolytic cell to protrude at least 5 mm from the end surface of the insoluble electrode. A distinctive feature of such a configuration of the diaphragm is that when the device is used for the treatment of sewage with a low seawater salt content, soluble salts, in particular produced during the dissolution of the aluminum electrode, with a pH value of 8 or more and a PH value of 4 or less The idea is that the aluminum is dissolved in the sewage being treated and forms a hydroxide gel only when the anolyte and catholyte are mixed together. This configuration of the diaphragm prevents hydroxide formation on the upper end of the soluble electrode and promotes hydroxide formation in the fluid volume remote from the soluble electrode, thereby reducing deposits on the soluble electrode. It is possible to treat sewage containing seawater with different salinities. It made sense to create a separate plate dielectric separator. The required effect can be achieved by creating a separate plate dielectric separator. That is, it is possible to insulate the insoluble electrode and the soluble electrode from each other, improve the effect of the electric field on the soluble electrode, and save on insulating material. The precise nature and characteristics of the invention will become more apparent from the following embodiments of the invention with reference to the accompanying drawings. The method of the invention is carried out as follows. The sewage to be treated is conducted into the interelectrode space between an insoluble, in particular a graphite electrode, and an adjacent soluble, in particular an aluminum electrode. At the same time, a stabilized or unstabilized (when the wave is not stretched after rectification) direct current is passed through the graphite electrode. As the current passes through, the cathode area and the anode area change according to the following reaction: 2H ₂ O+2e=H ₇ +2OH ^- (cathode) (1) H ₂ O−2e=2H ⁺ +1/2O ₂ (anode) ( 2) Becomes the seat of ongoing water electrolysis. Under the influence of the alkali and acid produced according to reactions (1) and (2), pathogenic organisms in the anode and cathode areas of the electrolytic cell are killed and the sewage water is disinfected. The sewage water is neutralized when the effluent from the cathode and anode areas mix with each other. The reaction is as follows. 2H ₂ O+2e=H ₂ +2OH ^- H ₂ O−2e=2H ⁺ +1/2O ₂ (Anode) 3H ₂ O=H ₂ +1/2O ₂ +2H ₂ O As the salinity changes, the gap between the insoluble and soluble electrodes Adjust the volume electricity according to the salinity of the sewage to be treated so that the total concentration of coagulant in the space (i.e. magnesium and aluminum hydroxide does not change). The concentration of seawater in the supplied sewage varies depending on the location of the ship, from 0.1 g/1 river water to 35 g/1 ocean water. When treating low salinity sewage, the field created by the insoluble electrode is The potential of the soluble electrode is shifted to the range of its active dissolution.The potential of the soluble electrode placed in the anodic area is shifted negatively and the potential of the soluble electrode placed in the cathodic area is shifted positive. Table 1 shows the relationship between the potential of the soluble electrode and the amount of dissolved electricity flowing through the insoluble electrode when the sea salt concentration in sewage is 0.2 g/.

[Table] As shown in Table 1, the value of the potential generated at the soluble electrode when different amounts of accumulated electricity are passed through the insoluble electrode, and the first
By comparing with the anodic polarity curve in the figure, −
A potential range of 1.2V to −0.5V is compatible with the passive state of aluminum, and more negative than −1.2V −
Potentials more positive than 0.5V are shown to be compatible with the range of active aluminum dissolution. To provide a potential matching the range of active aluminum dissolution, the current applied to the insoluble electrode was varied from 20 to
Either adjusting to 60 A or varying the flow rate of the fluid being treated in the range 120-1200/hour at constant current is required. When treated with insoluble graphite electrodes, the sewage flows with little mixing into the interelectrode space along the insoluble and soluble aluminum electrodes. The aluminum electrode melts under the influence of the electric field created by the graphite electrode. During dissolution, ions of the dissolved metal that solidify the colloidal contaminants enter the sewage water. Aluminum (or iron when iron electrodes are used) is the main coagulant in the sewage solution being treated, and this indicates that the concentration of Mg(OH) ₂ and Al ³⁺ at a salt concentration of 0.2 g/ This is clear from Table 2, which shows the relationship between the volume of electricity flowing in

[Table] Total concentration with umium ion

Claims (1)

[Claims] 1. An electrochemical treatment method for sewage containing seawater, comprising the steps of generating a coagulant in the interelectrode area of an insoluble electrode and a soluble electrode of a diaphragm electrolytic cell, and subsequently discharging purified sewage. , the sewage is supplied in separate streams to the anode and cathode areas of the electrolytic cell, and a current is applied to the insoluble electrode to apply a coagulant to the interelectrode space of both the insoluble electrode and the soluble electrode, which is electrically insulated from the insoluble electrode. 1. A method for electrochemical treatment of sewage, characterized in that the ratio between the electric current and the flow rate of the sewage is 0.01 A.hr/or more. 2. The method according to claim 1, characterized in that an unstabilized direct current is supplied to the insoluble electrode. 3. During the process, keep the pH of the anode area within the range of 2 to 3.6.
The method according to claim 1, wherein the method is carried out while maintaining the pH of the cathode area within the range of 10.5 to 12.5. 4. A method according to claim 3, characterized in that the sewage effluents from the anode area and the cathode area are mixed together. 5. forming a coagulant in the interelectrode area of the insoluble and soluble electrodes of the diaphragm cell and subsequently discharging purified sewage, supplying the sewage in separate streams to the anode and cathode areas of the cell; , a current is passed through the insoluble electrode to produce a coagulant in the interelectrode space of both the insoluble electrode and the soluble electrode, which is electrically insulated from the insoluble electrode, and the ratio between the current and the sewage flow rate is 0.01A. An implementation apparatus for electrochemically treating sewage containing seawater at a temperature of at least 1 hr/hr, the apparatus comprising a diaphragm electrolytic cell containing at least two pairs of electrodes, each pair of electrodes being arranged in a line with an insoluble electrode; soluble electrodes, the insoluble electrode 2 of each electrode pair is separated from the soluble electrode 3 by a dielectric separator 4, the outer shape of the separator 4 corresponds to the end surface of the insoluble electrode 2, and the soluble electrode 3 , the electrode pairs are arranged alternately in the anode area and the cathode area 6, 7, respectively, and the length ratio of the soluble electrode 3 and the insoluble electrode 2 is 1:2 or less. processing equipment. 6. Device according to claim 5, characterized in that the end of the insoluble electrode 2 facing the soluble electrode 3 is made to have a reduced cross-sectional area. 7. The device according to claim 6, characterized in that the thickness of the soluble electrode 3 is greater than the thickness of the insoluble electrode 2. 8. The device according to claim 5, characterized in that the partition wall 5 of the electrolytic cell is made to protrude at least 5 mm from the end face of the soluble electrode 3 in order to prevent deposition on the end face of the soluble electrode 3. 9. Device according to claim 5, characterized in that the dielectric separator 4 between the insoluble electrode 2 and the soluble electrode 3 is made from a separate plate.