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INVENTION
Patent of the Russian Federation RU2286949

METHOD AND DEVICE FOR UNDERGROUND DECOMPOSITION OF ORGANIC CONTAINING ELECTRODUCTIVE WATER SOLUTIONS OF WASTE

The name of the inventor: SHREMMER Ishtvan (HU); TYLKI Peter (HU)
The name of the patent holder: GI Ts. CFT (HU)
Address for correspondence: 129010, Moscow, ul. B. Spasskaya, 25, p. 3, LLC "Law firm Gorodissky & Partners", Pat. G.B. Yegorova, registration number 513
The effective date of the patent: 2002.07.16

The invention relates to the decomposition of organic contents of aqueous solutions of waste. The method involves immersing the electrodes in a solution, creating and maintaining an electric arc discharge between the electrodes and the electrically conductive solution. The arc discharge is generated by an electric current with a current density of at least 0.5 A / cm ² , at a voltage of at least 70 V and a symmetrical alternating current of at least 10 Hz, whereby the organic content of the solution is decomposed into water, carbon dioxide and nitrogen. During the process, the optimum pH and / or conductivity of the solution is maintained. The device comprises a feed container for starting materials, at least one decomposition circuit and a storage tank. The technical effect is to increase the economy and ecological compatibility of the method.

DESCRIPTION OF THE INVENTION

The present invention relates to a method and apparatus for underwater decomposition of organic contents of electrically conductive aqueous solutions of waste. The method and apparatus can be used to decompose various organic materials contained in electrically conductive waste solutions, for example for decomposition of EDTA or iron-EDTA (Fe-EDTA) complex. The method and apparatus can be used to decompose the organic contents of radioactive waste solutions, for example for processing radioactive waste produced during decontamination of the second-cycle steam generator in nuclear power plants.

The treatment of waste solutions containing organic materials, in particular the treatment of radioactive waste solutions, is a problem for the protection of the environment. Elimination of EDTA and Fe-EDTA from the waste solution is particularly difficult. Treatment of wastes using both known systems and newly introduced new methods is seriously complicated by EDTA content in liquid radioactive waste, and EDTA seriously worsens the stability of radioactive waste already conditioned for final disposal. By decomposing EDTA in solution, the volume of the waste solution can be significantly reduced, which significantly reduces the cost of post-treatment and storage.

Non-radioactive solutions containing EDTA, and require special treatment before their release into the environment. This makes the storage of waste solutions expensive, and at the same time represents a great burden on the environment.

To reduce the content of organic substances in aqueous solutions of waste, various solutions are known.

Known treatments include converting waste solutions into solid material by thermal drying as disclosed, for example, in German patent DE 1639299. The drawback of this method is the very high cost associated with the large amount of energy necessary to vaporize the water contained in the solution. Storage of the material obtained with this method, environmentally friendly, is expensive and involves additional complications.

Another known method is the decomposition of organic material using ozone. According to US Pat. No. 4,761,208, the process comprises introducing hydrogen peroxide into a waste solution containing organic materials. However, the effectiveness of this method is very low, since residual organic radicals can not be obtained in free form. Even when the effectiveness of ozone decomposition is improved by means of a catalyst, the decomposition is incomplete. An additional disadvantage of the method is that it is difficult to control.

Another solution for reducing the content of organic substances in aqueous solutions is biodegradation. However, using this method, the content of EDTA in the solution can not be removed and, in addition, the bactericidal action of the solution can not be lowered.

US Pat. No. 5,630,915 discloses a method and apparatus for decontaminating water. In accordance with this method, an electric arc discharge is created between the electrodes partially submerged in the liquid. To intensify the oxidation, hydrogen peroxide in the pretreatment tank is added to the waste solution. The electrodes are connected to a capacitor, which is charged when an alternating current of 60 Hz is flowing. Thus, a pulsed electric arc discharge is created between the anode and the cathode in the form of needles. Because of the conical shape of the electrodes, the reaction proceeds along a very small interface, and the cathode rapidly loses its mass. In addition, because of the impulsive nature of electric arc discharges, the method has low throughput. For this reason, it can be economically used only for processing small quantities of waste solutions or only to reduce the level of contamination to lower values.

WO 99/01382 discloses a method and apparatus for treating flow-through contaminated water. In accordance with this method, an electrochemical reaction is used to treat water, and more particularly electrolysis. The device comprises an electrolytic cell containing inlet and outlet pipelines, a current source, a microprocessor-based monitoring unit, adjusting means and a supply pump. The adjustment means are connected to the supply pumps, which operate on signals from sensors continuously measuring the pH and electrical conductivity of the water being treated. The electrodes are immersed in the fluid in the electrolytic cell, while the electrodes are connected to a direct current source with a voltage of 25 V. The density of the applied current is 67 A / m ² . The disadvantages of this method include the inability to decompose all types of organic material.

It is an object of the present invention to provide a method and apparatus for underwater decomposition of organic contents of electrically conductive aqueous waste solutions that are capable of reducing, or under certain conditions, the removal of organic matter from aqueous waste solutions that is economical and environmentally friendly.

According to the invention, a plasma generated along the surface of the electrodes by the development of an electric arc discharge between the electrodes and the solution will perform thermal decomposition of organic materials, and the free radicals produced by the plasma will oxidize the organic materials in solution. Decomposition of organic materials can be enhanced by introducing an oxidizing material into the electrode region.

It is another object of the present invention to provide a method for underwater decomposition of organic contents of aqueous waste solutions which comprises measuring and, if necessary, determining the pH and / or electrical conductivity of the solution, maintaining an optimum pH and / or electrical conductivity during the process, and additionally partially or completely decomposing the organic Materials in solution. The method of the present invention is characterized by immersing the electrodes in a solution by obtaining and maintaining an electric arc discharge between the solution and the electrodes immersed in the solution by applying an electric current with a current density of at least 0.5 A / cm ² at a voltage of at least 70 V by Application of a symmetrical alternating current having a frequency of at least 10 Hz, and then decomposing the organic content of the solution into water, carbon dioxide and nitrogen. According to a preferred embodiment of the process, the pH and / or the electrical conductivity of the waste solution is set using a pretreatment solution. According to a preferred embodiment of the process, sodium hydroxide is added as a solution for pretreatment to determine the pH of the waste solution. According to yet another preferred embodiment, the pH of the waste solution containing EDTA is adjusted to a value in the range of from 8 to 13. It is also preferable that, as the pretreatment solution used to adjust the pH of the waste solution, Phosphoric acid is added. Preferably, sodium sulfate is added as the pretreatment solution to control the electrical conductivity of the waste solution. Preferably, sodium nitrate is added as the pretreatment solution, pH adjustment and electrical conductivity of the waste solution. To increase the efficiency of decomposition of organic content, it is useful to add hydrogen peroxide to the oxidant solution. As an oxidizer, it is useful to use ammonium peroxydisulphate or sodium nitrate.

It is another object of the present invention to provide an apparatus for underwater decomposition of organic contents of electrically conductive aqueous waste solutions. The device comprises a feed container for starting materials, at least one decomposition circuit and a storage tank. The apparatus according to the present invention comprises a decomposition circuit operating in a loading mode comprising a loading reactor for subsequent decomposition, a buffer tank and a circulation pump, wherein the feed container for the raw materials and the storage tank are connected to the decomposition circuit operating in the loading mode via a feed pump . The decomposition circuit operating in the loading mode is connected to the solution tank for pretreatment through a regulating unit and a feed pump, the irrigation condenser being connected to the charging reactor for subsequent decomposition. The irrigation condenser condenses and at least partially returns the vapors produced therein to the charging reactor. Electrodes are immersed in a solution of waste that is in the reactor for subsequent decomposition, operating in the loading mode. These electrodes are connected to a current source delivering an electric current with a current density of at least 0.5 A / cm ² , at a voltage of at least 70 V, which is capable of generating and maintaining an electric arc discharge between the waste solution and the immersed electrodes. A symmetrical alternating current of at least 10 Hz is applied from the current source. According to a preferred embodiment of the device, the oxidizer container is connected to the decomposition circuit operating in the loading mode via a feeder and a feed pump.

According to a preferred embodiment, the device comprises an additional continuous continuous decomposition contour which includes a main decomposition reactor, a buffer tank and a circulation pump, wherein the continuous decomposition contour is disposed between the decomposition circuit operating in the loading mode and the raw material container, such that the flow The contour of continuous decomposition is connected to the solution tank for pretreatment through the adjusting unit. In this case, the irrigation condenser is connected to the main decomposition reactor, wherein said irrigation condenser condenses and at least partially returns the vapors produced therein to the main decomposition reactor. The electrodes are immersed in the waste solution in said main decomposition reactor, the electrodes being connected to a current source supplying an electric current with a current density of at least 0.5 A / cm ² at a voltage of at least 70 V which forms and maintains an electric arc Discharge in the waste solution, between the solution and the immersed electrodes. The current source generates a symmetrical alternating current, preferably having a frequency of at least 10 Hz. Preferably, the oxidant container is connected to the continuous continuous decomposition loop through a feeder and a feed pump.

According to another preferred embodiment, the decomposition circuit operating in the loading mode and the continuous contour of the continuous decomposition contain filters incorporated therein. In this case, the electrodes are connected to a current source supplying a single-phase alternating current. A variant is possible when the electrodes are connected to a current source supplying three-phase alternating current.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The method of the present invention is based on the destruction of organic materials in conductive waste solutions by means of an electric arc discharge generated between the immersed electrodes and the solution. Process parameters are optimized experimentally. Experiments are carried out to decompose the organic content of an aqueous solution of waste containing EDTA, a radioactive aqueous waste solution containing EDTA, and to destroy the contents of the "citrox" waste solution. The following were investigated:

• Properties of electrodes: material, surface, geometry of cross-section, distance between electrodes;
• Properties of the waste solution: initial pH, the effect of pH change on the decomposition rate of EDTA;
• Other properties: the effect of the parameters of the current source on the process.

The experiments are carried out in a cooled glass vessel, with the waste solution having the following composition:

When choosing the appropriate metal for the electrodes, the following requirements were taken into account: the acceptable decomposition rate of organic substances in the waste solution, the relatively small loss of electrode material in the electric arc discharge, and that removing the metal obtained from the solution from the soluble electrodes was easy enough . During the experiments, electrodes made of tungsten, copper, titanium, nickel, stainless steel and unalloyed annealed iron were investigated. The experiments were carried out using electrodes with internal water cooling and without cooling. The cooling effect is not noticed when a single-phase alternating current is applied, but when a three-phase alternating current is used, cooling prevents overheating of the electrodes.

According to the experiments it was proved that the electrodes from W have the highest dissolution rate, the electrodes from Cu have an average dissolution rate and EDTA decomposition ability, but the precipitation of copper from the solution after the decomposition is completed is complicated. Electrodes from Ni demonstrate the best results both in dissolution rate and EDTA decomposition ability, but like copper, nickel can be removed from the solution only by adding an additional substance. Electrodes from Ti dissolve as slowly as Ni, but have a much lower degradation capacity of EDTA. The values ​​measured for stainless steel and for unalloyed annealed iron are almost identical. Compared to other electrodes, they have a satisfactory ability to decompose EDTA, while the dissolution rate of the electrode remains rather low. As a clear advantage of unalloyed annealed iron electrodes, it is noted that iron that dissolves during the procedure can be precipitated by alkalizing as easily as iron is initially contained in the waste solution. The iron hydroxide present in the solution, thanks to the decomposition of the iron complex and the dissolution of the electrodes, settles well and can be easily filtered out. Table 1 shows the results for the rate of decomposition of EDTA and the relative dissolution rate of the electrode (destroyed EDTA moles / dissolved grams of electrode) for each electrode metal.

Electrodes from Fe, as shown, are the best both in terms of decomposition of EDTA and in terms of post-treatment of the waste solution.

The influence of the surface of immersed electrodes as a function of the EDTA decomposition efficiency was studied. The measurements were carried out in a glass vessel with double walls of 250 cm ³ volume, which was equipped with a reflux condenser. During the measurement, two electrodes of annealed iron, 6 mm in diameter, at a distance of 1.5 cm from one another were gradually immersed in the solution in 0.5 cm steps. The measurement range was 0.5-5 cm. The current, temperature and voltage of the arc Discharge was measured during continuous operation. As the results show, the current increases in a linear proportion to the area of ​​the immersed electrode. At low values ​​of the immersed surface, the electric arc discharge develops only at the tips of the electrodes, which leads to low current values. At a current density of less than 0.5 A / cm ² , an electric arc discharge does not occur. The immersion of the larger electrode surface in the solution does not give a significant increase in the arc discharge, but the boiling becomes more intense, which causes more frequent interruptions of the arc discharge and an increase in the coolant consumption. The minimum ignition value at which the electric arc discharge develops is 70 V.

And the effect of the cross-sectional geometry of the electrode on the efficiency of EDTA decomposition was studied. Electrodes with circular and rectangular cross-sectional geometry with a distance between them equal to 1.5 cm were examined. The diameter of the electrode with a circular cross-section is 3 mm, 5 mm and 7 mm. The results of the experiments indicate that more thin, needle-shaped electrodes are more effective in the decomposition of EDTA. This is the result of a more intense and more stably maintained electric arc discharge that develops along the surface of the electrodes. The choice of the size of the electrode, however, is also determined by other factors, such as economic efficiency, which may make choosing a larger diameter electrode preferable. Experiments with rectangular cross-section electrodes give similar results, which confirm that the cross-section geometry should have a relatively small value when choosing the cross-section of the electrode.

And measurements were made to determine the optimum distance between the electrodes. The following distances were studied: 14 mm, 20 mm, 28 mm, 40 mm and 60 mm. When the distance between the electrodes is increased, the current decreases from 7 A to 5.5 A. In addition, as the distance between the electrodes is increased, the electric arc discharge region decreases, at 60 mm the arc discharge is formed only at the tips of the electrodes.

Further experiments were carried out using the optimum values ​​of the parameters established above. Then, the effect of the initial pH on the rate of EDTA degradation was studied. The initial pH was first set to 9. Since there was a decrease in the pH value of the solution during decomposition and, at the same time, a decrease in the rate of decomposition of EDTA, it was investigated how an increase in the initial pH value would affect the reaction rate. NaOH was used to increase the pH of the solution. The results are shown in Table 2.

As the results show, the efficiency of EDTA decomposition increases markedly with increasing initial pH, but in parallel with this, the dissolution of electrodes from iron also doubles. A somewhat more informative index is the ratio between the change in concentration and the rate of electrode mass loss (Åc / Åm). An increase in this ratio indicates that the system is approaching the optimal operating parameters. The maximum efficiency of the EDTA decomposition is achieved at pH 13, but to achieve this it is necessary to add too much NaOH and the electric arc discharge becomes so intense that the process becomes difficult to control. Taking into account these factors, it can be assumed that the efficiency of EDTA decomposition is optimal at an initial pH of 12.

During the experiments, it was determined that changes in the pH of the solution significantly affect the efficiency of EDTA degradation. Thus, an important goal of the subsequent experiments was to study how the pH of the solution varies with time. The measurements show that both the EDTA concentration and the pH vary exponentially with time and that the two curves are very similar in shape. The reaction rate increases significantly with increasing initial EDTA concentration and the initial pH value. From this it can be concluded that to control the process in an economical manner, the solution should be gradually concentrated in relation to EDTA and the pH of the solution should gradually increase. Due to the presence of nitrates in the solution, the rate of dissolution of the electrodes does not increase with time.

According to the present invention, both direct current and alternating current are used to decompose organic materials from aqueous waste solutions. To obtain an electric arc discharge at the electrodes, experiments were carried out using sinusoidal and rectangular pulsed single-phase and three-phase current sources. The model used was 300 ml of "citrox", commonly used for purification, which contained 50 g / l citric acid and 50 g / l oxalic acid. To establish the electrical conductivity and pH of the solution, 0.1 mol / l sodium nitrate was used. The pH of the solution was 1.6. The experiment was carried out at a current density of 1 A / cm ² . The experimental results are given in Table 3, which contains the decomposition efficiency values ​​as a function of time for a constant current of 50 Hz of sinusoidal alternating current and 1000 Hz of a square pulse alternating current.

Experiments show that, in addition to obtaining better efficiency of decomposition, the use of alternating current makes it possible to form an arc discharge, but also a more stable and reliable electric arc than is obtained by direct current.

Example 1

The method according to the present invention was used to decompose the contents of Fe-EDTA and other organic materials from the waste solutions obtained in the purification of the second-loop steam generator in nuclear power plants. The composition and pH of the solution were as follows:

The experiments were carried out in two thermostated glass vessels having a volume of 220 cm ³ and 1200 cm ³ . The applied voltage was 220 V / 50 Hz, the current range is 5-8 A, and the temperature range is 90-95 ° C. The electrodes from the annealed iron used for the experiment had a diameter of 7 mm with a depth of immersion of 2 cm. The distance between the electrodes was 2 cm in a smaller vessel and 4 cm in a larger vessel. The nominal voltage was gradually applied to the electrodes using a toroidal transformer. Changes in the EDTA content were detected by titration with zirconium oxychloride. The decomposition rate of EDTA was studied in the initial solution, and after the initial concentration of the solution tripled, and in the initial solution after the pH value increased. The results of the experiments are given in Table 4.

Comparing experiments 1 and 3, it can be clearly seen that in a more concentrated solution, the EDTA decomposition efficiency is greater. In a solution with a tripled concentration, the EDTA degradation rate more than doubled. By comparing the results obtained with Experiments 1 and 2, it can be assumed that a larger amount of EDTA corresponds to a greater efficiency of EDTA degradation. By increasing the volume of the solution five times, the rate of decomposition of EDTA increases by 1.7 from the initial value (with the pH remaining constant). Based on experiments 2 and 4, it can be argued that in an alkaline environment, the EDTA degradation is more effective. An increase in the pH of the solution from 9.1 to 12.3 leads to almost a doubling of the rate of decomposition of EDTA.

Measurements of the activity of the solution indicate that during the decomposition of the Fe-EDTA complex as a result of pH adjustment and the addition of hydrogen peroxide, some of the manganese content and probably the entire silver content of the solution is precipitated together with iron hydroxide. The concentration of highly active isotopes ( ¹³⁴ Cs, ¹³⁷ Cs, ⁵⁸ Co, ⁶⁰ Co) remains practically constant.

Example 2

After completion of the laboratory experiments, the EDTA degradation properties were studied using a larger device to obtain additional data for the construction of complex industrial scale devices intended for the decomposition of organic matter.

To increase the efficiency of EDTA decomposition, the number of electrodes was increased. This resulted in a more uniform electric field and allowed to increase the voltage applied to the electrodes. Increasing the current flow in the system makes it necessary to use a three-phase system to achieve a more uniform load of the power network. The system contains a buffer tank connected to a 2 dm ³ reactor. The solution is circulated from the buffer tank to the reactor and back through the pre-cooling unit using a centrifugal pump. Before entering the reactor, hydrogen peroxide was added to the circulating solution. The volume of the solution was kept constant by means of a reflux condenser attached to the reactor.

During the process, a square grid of 9 electrodes was used, while 3 electrodes were connected to each phase of the power network. The distance between the adjacent electrodes was 4 cm. Since adjacent electrodes are connected to different phases of the power circuit, the voltage between the electrodes is maximum. The composition of the test solution was identical to that used in Example 1. The initial pH value was 9.0. During steady-state operation, the temperature is 97 ° C, while the current at the electrode was 9-10 A, and the current per phase of the power network was 27-30 A. A hydrogen peroxide solution with a concentration of 30% was introduced at a rate of 20 cm ³ / h. The results of the experiment are shown in Table 5.

Comparing the results of the experiment with the results obtained in the laboratory scale experiment, it can be concluded that both the energy consumption of the decomposition and the final concentration of EDTA (C ^F_EDTA ) are significantly lower, in an experiment where three-phase current and hydrogen peroxide injection , Than in a laboratory scale experiment, with the same duration. The experiments show that the specific energy consumption of the EDTA decomposition decreases with an increase in the volume of the waste solution, which increases the amount of EDTA.

Example 3

Based on the results of laboratory experiments, decomposition of organic materials into 450 m ³ of waste solution was carried out in two stages using the device shown in the drawing. In the first stage, the solution was concentrated and the main EDTA decomposition was carried out. The restriction, which prevents further concentration of the solution, is due to the content of boric acid. Decomposition of EDTA was intensified by the addition of hydrogen peroxide. In the first stage, 70-75% of the original EDTA content was removed using a continuous decomposition reactor.

In the second stage, a loading reactor with a final degree of EDTA removal of 96.5% was used to decompose the EDTA. The rate of decomposition of EDTA in the second loop was increased by introducing NaOH into the buffer tank.

The suspension of iron hydroxide precipitated during the decomposition of EDTA was removed on a centrifuge. The parameters used during the EDTA decomposition:

An apparatus for performing a method for underwater decomposition of organic contents of conductive waste solutions in accordance with the present invention comprises a continuous decomposition flow path 16 and a decomposition circuit 17 operating in a loading mode. In the continuous decomposition flow path 16, the main decomposition reactor 6, the buffer tank 5, the filter 9, the feeder 12, and the circulation pump 10 are connected via conduits. The buffer tank 5 of the continuous decomposition flow loop 16 is connected to the feed container 1 for the raw materials by means of an adjusting unit 18 and a delivery pump 4. The pre-treatment tank 2 is connected to the adjusting unit 18 and through a feed pump. The feeder 12 of the continuous decomposition contour 16 is connected to the oxidizer vessel 3 via the feed pump 4. The electrodes are immersed in the main decomposition reactor 6 equipped with overflow 14. The internal space of the main decomposition reactor 6 is connected to the condenser 13. Water condensing in the condenser 13 can be Pumped, or alternatively returned to the buffer vessel 5. The electrodes of the main decomposition reactor 6 are connected to a current source supplying a symmetrical alternating current.

The configuration of the decomposition circuit 17 operating in the loading mode is identical to the configuration of the continuous contour flow 16. The decomposition circuit 17 operating in the loading mode comprises a charging reactor 7 for subsequent decomposition, a buffer tank 5, a filter 9 and a feeder 11 and is connected to the storage tank 8 via a conduit. The buffer tank 5 of the decomposition circuit 17 is connected to the buffer tank 5 of the continuous decomposition flow loop 16, while the feed 11 of the decomposition circuit 17 is connected to the oxidant tank 3 via the feed pump 4. The condenser 13 is connected to the charging reactor 7, the condensing water In it, is returned partially or completely to the charging reactor 7.

The work of the device is carried out as follows

The solution to be treated is introduced from the waste solution tank into the feed container 1 (drawing) for the raw materials by means of a feed pump operating in the loading mode. The feed pump is driven by a level detector that protects the supply container 1 for raw materials from overfilling or emptying. After the waste solution is introduced into the feed container 1 for the raw materials, the feed pump 4 feeds it to the regulating unit 18 where the pH and the electrical conductivity of the solution are set to the experimentally determined optimum values ​​by adding a pretreatment solution introduced from the pre-mix tank 2 Processing, by means of a pump 4. Sodium hydroxide, potassium hydroxide or lithium hydroxide can be used as a pretreatment solution. The pretreated solution is then introduced into the buffer tank 5 of the continuous contour flow 16. The volume of the fluid entering the buffer tank 5 is set using a measurement and control system known in the art. The solution is then introduced into the feeder 12 by means of the circulation pump 10 through the filter 9, while the valve 20 is closed and the valve 21 is open. The filter 9 removes a solid material that initially contained a solution or that is formed during the pH adjustment and / or the conductivity of the solution. In the feeder 12, the oxidant is introduced into the solution at a predetermined dosing rate, which is set in preliminary experiments. The oxidizer may be either organic or inorganic, and may be a combination thereof. As an oxidizing agent, an aqueous solution of hydrogen peroxide, ammonium peroxydisulphate, sodium hypochlorite, benzoyl peroxide or a mixture thereof can be used. Decomposition of organic content and can be carried out without an oxidizer.

When the solution is discharged from the feeder 12, the circulation pump 10 enters it into the main decomposition reactor 6. In the main decomposition reactor 6, the electrodes are immersed in the solution, while the electrodes are connected to the current source 19. In the main decomposition reactor 6, the solution heated by the current reaches an optimum temperature and an electric arc discharge is formed between the electrodes and the solution. Of course, the solution can be pre-heated by other means. The electric arc discharge between the solution and the electrodes decomposes the organic content of the waste solution and causes the fluid to boil. The water vapor produced in the reactor is introduced into the condenser 13, where they are cooled. The condensed water is then partially or completely returned to the main decomposition reactor 6. The percentage of water to be returned can be controlled by selecting the degree of opening of the valves 22 and 23. By reducing the percentage of recycled water returned, even to zero, an optimal concentration of organic solution materials can be selected.

The waste solution is continuously circulated in the continuous decomposition flow loop 16 by the circulation pump 10 so that the solution is introduced through the overflow 14 of the main decomposition reactor 6 into the buffer vessel 5. The level of the solution in the vessel 5 is set by establishing the ratio of the injected and evacuated fluid or return of the condensate to reach a stationary Optimal concentration in the system. The solution has an optimum concentration if its mass flow is equal to the difference between the injected and pumped out streams.

When the optimum concentration is reached, the solution is introduced into the decomposition circuit 17 operating in the loading mode through the overflow pipe of the buffer tank 5 after opening the valve 24. In the decomposition circuit 17, the waste solution is introduced into the charging reactor 7 for subsequent decomposition through the filter 9 and the feeder 11 c By the circulation pump 10, while the valve 25 is closed and the valve 26 is open. The role of the filter 9 and feeder 11 is identical to the role of their analogs in the continuous contour flow. The waste solution flows back to the buffer vessel 5 from the charging reactor 7 through the overflow 15. The process starts in the decomposition circuit 17 operating in the loading mode immediately after the buffer tank 5 is filled through the overflow pipe 14 of the continuous contour flow 16.

The charging reactor 7 for subsequent decomposition, and its electrodes and current source are identical in structure to the analogs of the main decomposition reactor 6. The electric arc discharge generated in the charging reactor 7 between the immersed electrodes and the waste solution decomposes the residual organic matter content in the solution and causes the fluid to boil. The water vapor generated in the reactor is cooled in the condenser 13. Condensed water is partially returned through the valve 27 and its residue is pumped through the valve 28. In the charging reactor 7, the decomposition of organic materials takes place at the optimum concentration of organic substances. To maintain a constant concentration of organic substances, as the decomposition of organic materials and the quantity of organic materials is reduced, the amount of water is reduced by evacuating part of the condensed water from the system.

The circuit 17, operating in the loading mode, operates until the desired degree of decomposition of organic substances is achieved.

Experiments show that in the continuous decomposition flow loop 16, the degree of decomposition of organic substances of 70-75% can be achieved, while in the loop operating in the loading mode it increases to 96.5%. The effectiveness of this method can be further increased by continuous operation.

Alternatively, the method can be carried out by circulating the waste solution in only one decomposition circuit 17 operating in the loading mode. A single loop process can be used to decompose organic matter from a waste solution that does not contain EDTA. In this case, the efficiency of decomposition of organic materials will be lower.

List of symbols

CLAIM

1. A method for underwater decomposition of organic contents of aqueous solutions of waste, comprising: measuring and, if necessary, changing by adding a solution for pretreatment of the pH and electrical conductivity of the solution, maintaining the optimum pH and / or electrical conductivity during the process, and carrying out The complete or partial decomposition of the organic content of the solution, characterized in that electrodes are immersed in the solution, an electric arc discharge is formed and maintained between the electrodes and the electrically conductive solution by applying an electric current with a current density of at least 0.5 A / cm ² , At least 70 volts, and applying symmetrical alternating current at a frequency of at least 10 Hz, while decomposing the organic contents of the solution into water, carbon dioxide and nitrogen.

2. A process according to claim 1, characterized in that sodium hydroxide is used as the pretreatment solution to change the pH of the waste solution.

3. A process according to claim 2, characterized in that the pH of the waste solution containing EDTA is set in the range of 8 to 13.

4. A process according to claim 1, characterized in that phosphoric acid is used as the pretreatment solution used to change the pH of the waste solution.

5. A process according to claim 1, characterized in that sodium sulfate is used as the pretreatment solution to adjust the electrical conductivity of the waste solution.

6. The process of claim 1, wherein sodium nitrate is used as a pretreatment solution for changing the pH and electrical conductivity of the waste solution.

7. A method according to any one of claims 1 to 6, characterized in that an oxidant is added to the waste solution to accelerate the decomposition of organic materials.

8. A process according to claim 7, characterized in that hydrogen peroxide is used as the oxidizing agent.

9. A process according to claim 7, characterized in that ammonium peroxydisulphate or sodium nitrate is used as the oxidizing agent.

10. An apparatus for underwater decomposition of organic contents of electrically conductive aqueous solutions of waste, comprising a feed container (1) for raw materials, at least one decomposition circuit (17) and a storage tank (8), the feed container (1) for raw materials And the storage tank (8) are connected to the decomposition circuit (17) through the supply pump (4), and the decomposition circuit (17) is connected to the pretreatment solution tank (2) through the adjusting unit (18) and the supply pump (4), Wherein the decomposition circuit (17) comprises electrodes immersed in the waste solution and connected to a current source (19), characterized in that it comprises a decomposition circuit (17) operating in a charging mode and containing a charging reactor (7) for subsequent decomposition, A buffer tank (5) and a circulating pump (10), an irrigation condenser (13) connected to a charging reactor (7) for condensing at least a partial return to the charging reactor (7) of the vapors that it forms, The electrodes are immersed in the waste solution in the charging reactor (7) and connected to a current source (19) supplying an electric current with a density of at least 0.5 A / cm ² at a voltage of at least 70 V, which is sufficient to create and Maintaining an electric arc discharge between the electrodes and the waste solution, the current source (19) being designed to create a symmetrical alternating current of at least 10 Hz.

11. Apparatus according to claim 10, characterized in that the oxidation tank (3) is connected to the decomposition circuit (17) operating in the loading mode through the feeder (11) and the feed pump (4).

12. A device as claimed in claim 11, characterized in that it comprises an additional continuous decomposition flow loop (16) which comprises a main decomposition reactor (6), a buffer tank (5) and a circulation pump (10) and is connected between the circuit (17) (1) for the raw materials such that the continuous decomposition flow loop (16) is connected to the pre-treatment solution tank (2) through the adjustment means (18), the irrigation condenser (13) connected to the main reactor (6) And decomposed and designed to condense and at least partially return to the main reactor (6) the decomposition of the vapors that it forms in, wherein the electrodes are immersed in the waste solution in the main decomposition reactor (6) and connected to a current source (19) Supplying an electric current with a density of at least 0.5 A / cm ² at a voltage of at least 70 V, which is sufficient to create and maintain an electric arc discharge between the electrodes and the waste solution, the current source (19) being designed to create Symmetrical alternating current, frequency of at least 10 Hz.

13. Apparatus according to claim 12, characterized in that the oxidizer tank (3) is connected to the continuous contour (16) through the feeder (12) and the feed pump (4).

14. Apparatus according to any one of claims 10 to 13, characterized in that the decomposition circuit (17) operating in the loading mode and / or the continuous contour (16) comprises a built-in filter (9).

15. The device of claim 14, wherein the electrodes are connected to a single-phase AC power source (19).

16. The device of claim 14, wherein the electrodes are connected to a three-phase alternating current source.

print version
Published on February 19, 2007

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