Method and system for wastewater treatment using in-situ cleaning of electrodes

Abstract

A system for wastewater treatment employing in-situ cleaning of electrodes, comprising: at least one reactor for treating wastewater, said wastewater comprising chloride salts (sodium chloride, potassium chloride, calcium chloride, etc.) with a chloride concentration between 500 mg / L to 5,000 mg / L; and a controller for controlling the current supplied to the reactor by controlling the electrode active area and / or current density, such that the total amount of aqueous free chlorine produced during the wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally to produce a treated wastewater with a concentration of hydrochloric acid between 500 mg / L and 5,000 mg / L and a pH less than or equal to 4. After the addition of sodium bisulfite in the treated wastewater, the wastewater is recirculated back into the reactor. This ensures in-situ cleaning of the electrodes within the electrochemical reactor without the need for any additional equipment.

Description

Technical Field

[0001] The present invention relates to a method and system for wastewater treatment employing in-situ cleaning with electrodes, and more specifically, to a method and system for treating wastewater containing chlorides.

[0002] background

[0003] Due to increasingly stringent wastewater treatment regulations requiring industrial facilities to eliminate recalcitrant water pollutants before discharge, and the current global shortage of clean water, the demand for wastewater treatment systems is high. Therefore, there is an increasing need for cost-effective, sustainable wastewater treatment systems that minimize chemical additions, do not generate secondary pollution, and have minimal operation and maintenance requirements.

[0004] A preferred method for treating recalcitrant wastewater is electrochemical oxidation, a sustainable, safe, and efficient treatment solution for eliminating a wide range of pollutants such as persistent organic pollutants, dioxins, nitrogenous substances (e.g., ammonia), pharmaceuticals, pathogens, microorganisms, and other contaminants. One method for treating wastewater involves the electrochemical oxidation of organic and / or inorganic pollutants, whereby such pollutants are oxidized on the anode surface.

[0005] In wastewater treatment systems employing electrochemical oxidation, the anode catalyst is selected from the group consisting of platinum, tin oxide, antimony-tin oxide, ruthenium oxide, iridium oxide, niobium-doped antimony-tin oxide, graphite, manganese oxide, diamond, or boron-doped diamond. The electrodes used in wastewater treatment can increase the overall system cost, especially for applications requiring the removal of large quantities of organic materials.

[0006] Furthermore, due to the deposition of contaminants on the electrode surface, the electrodes undergo scaling and subsequent degradation, making them less effective for wastewater treatment. To clean the electrodes, such deposits need to be removed. In the past, this typically required shutting down the system and, depending on the damage caused by the mineral deposits, manually cleaning or replacing the electrodes.

[0007] In the past, manual cleaning or replacement of electrodes has been addressed by reversing the polarity of the charge applied to the electrolytic cell in the stack. However, such methods require both the anode and cathode in the stack to be coated with a catalyst to allow the cell to operate in reverse polarity. This can be very expensive.

[0008] Another method for cleaning electrodes involves adding a solution of low concentrations of organic acids, such as lactic acid / gluconic acid or citric acid, to the wastewater during the treatment process. This method requires the safe supply and discharge of the cleaning solution into the system, increasing system complexity. Furthermore, the addition of organic acid solutions may not be permitted at some sites with strict restrictions on the introduction of chemicals not needed for wastewater treatment.

[0009] Such a method is presented, for example, in U.S. Patent No. 7,722,746, which describes a self-cleaning chlorine generator that uses a predetermined volume of a pH-lowering agent, such as hydrochloric acid, introduced into an electrolysis chamber to dissolve mineral deposits according to a predetermined cycle schedule during periods when the system is not in operation.

[0010] U.S. Patent No. 7,922,890 describes a similar method using acid generated in an acid generation cell, separate from the electrolytic cell used to treat brine solutions. When the electrolytic cell stops, the acid is supplied to it during a cleaning cycle. The system operates in this acid-cleaning mode until a carbonate detector signals that the system is clean and the acid used to clean the electrolytic cell is discharged into a separate wastewater drain. The cleaned electrolytic cell can then be used to treat brine solutions again.

[0011] In existing technical documents, additional chemical solutions must be added to the wastewater treatment system for electrode cleaning, even though these solutions are not necessary for wastewater treatment or for ensuring the safe discharge of treated wastewater. These chemical solutions are added from a supply tank or generated in a separate cell from the wastewater treatment electrochemical reactor and then supplied to the reactor for wastewater treatment. This complicates the entire wastewater treatment system and thus increases its cost.

[0012] Despite substantial advancements in the field, there remains a persistent need for a simplified system that allows for in-situ cleaning of electrodes without the addition of chemical solutions not yet used during wastewater treatment or during the discharge of treated water. This simplified system does not have any additional equipment for feeding or generating chemical solutions for cleaning the electrodes of the electrochemical reactor used for wastewater treatment. Invention Overview

[0014] This invention describes a wastewater treatment system for treating wastewater containing chloride salts with a chloride concentration between 500 mg / L and 5,000 mg / L, the system comprising:

[0015] - Reactor tank;

[0016] - At least one reactor, which includes at least one electrode for treating wastewater;

[0017] - A pump, which is used to supply wastewater from the reactor tank to the reactor;

[0018] - A controller, which controls the current supplied to the reactor by the power source; and

[0019] - A tank for storing sodium bisulfite, which is added to the reactor tank at the end of wastewater treatment when the reactor stops treating wastewater, to generate a certain amount of hydrochloric acid in the reactor tank.

[0020] The controller controls the current supplied to the reactor so that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, in order to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank for in-situ cleaning of the electrodes.

[0021] The controller controls the current supplied to the reactor by controlling the size of the active electrode area and / or the density of the current supplied to the reactor.

[0022] In some implementations, the size of the active electrode area is determined experimentally such that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0023] In other embodiments, the size of the electrode active area is controlled based on the amount of aqueous free chlorine detected in the reactor tank during system operation, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0024] In some embodiments, the current supplied to the reactor is controlled by controlling the current density, which is determined experimentally such that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0025] Alternatively, the current density can be controlled based on the amount of aqueous free chlorine detected in the reactor tank during system operation, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0026] In addition, in some other embodiments, both the size of the electrode active area and the current density are determined experimentally, such that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0027] However, in other embodiments, both the electrode active area and current density are controlled based on the detected amount of aqueous free chlorine, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0028] A wastewater treatment method is also disclosed, which includes the following steps:

[0029] a. A stream of wastewater containing chloride salts with a chloride concentration between 500 mg / L and 5,000 mg / L is supplied to a reactor tank and from the reactor tank to at least one reactor for treating the wastewater to remove chlorides and other contaminants contained in the wastewater;

[0030] b. Control the current supplied to the reactor used for wastewater treatment;

[0031] c. At the end of treatment, after the reactor stops treating wastewater and before the wastewater is discharged from the system, a certain amount of sodium bisulfite is supplied to the treated wastewater in the reactor tank to reduce the aqueous free chlorine level below a predetermined level that allows the wastewater to be discharged; and

[0032] d. The treated wastewater is recirculated from the reactor tank through the reactor and back to the reactor tank for a period of time determined experimentally, in order to clean the reactor electrodes.

[0033] The current supplied to the reactor for wastewater treatment is controlled such that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank for in-situ cleaning of the electrodes.

[0034] The current supplied to the reactor can be controlled by adjusting the size of the electrode active area and / or the current density of the reactor.

[0035] In some implementations, the size of the active electrode area is controlled to a value determined experimentally, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0036] In other embodiments, the size of the active electrode area is controlled based on the amount of aqueous free chlorine detected in the reactor tank during system operation, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0037] In some implementations, the current density is controlled to a value determined experimentally, such that the amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0038] In other embodiments, the current density is controlled based on the amount of aqueous free chlorine detected in the reactor tank during system operation, such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0039] In some implementations, the size of the electrode active area and the current density are both determined experimentally, such that the total amount of aqueous free chlorine produced until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0040] In other embodiments, both the size of the electrode active area and the current density are controlled based on the detected amount of aqueous free chlorine produced until the end of wastewater treatment, such that a certain amount of sodium bisulfite, determined experimentally, needs to be added to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank.

[0041] This invention relates to systems and methods for treating wastewater containing chloride salts (sodium chloride, potassium chloride, calcium chloride, etc.). Brief description of the attached diagram

[0043] The accompanying drawings illustrate specific preferred embodiments of the invention, but should not be construed as limiting the spirit or scope of the invention in any way.

[0044] Figure 1 The illustration shows a schematic diagram of a wastewater treatment system employing in-situ cleaning with electrodes according to the present invention.

[0045] Detailed description

[0046] Certain terms are used in this description and are intended to be interpreted according to the definitions provided below. Additionally, terms such as “a” and “comprise” should be considered open-ended.

[0047] The wastewater treatment system according to the present invention Figure 1 As shown in the image.

[0048] The electrochemical wastewater treatment system 100 includes an equalization tank 102, a reactor tank 110, and at least one reactor 112 comprising a stack of electrolytic cells. Wastewater stream 101 is fed into the equalization tank 102 via a filter 103, and wastewater stream 105 exiting the equalization tank is fed into the reactor tank 110 via a pump 106. Wastewater stream 107 is fed from the reactor tank 110 into the reactor 112 via a pump 108 and a filter 109. Treated wastewater stream 114 exiting the reactor is recycled back to the reactor tank, and the cycle of recycling wastewater through reactor 112 and back to reactor tank 110 is repeated for up to the time required to remove the desired level of contaminants from the wastewater. The time required to remove contaminants from the wastewater can be determined through experimental testing of the system or by continuously monitoring the contaminant levels in the reactor tank. When it is determined that the contaminant level reached in the reactor tank is at or below the level that allows water to be discharged into the environment, a sodium bisulfite solution (SBS) is supplied from tank 118 to reactor tank 110 to reduce the level of aqueous free chlorine in the treated wastewater and to lower the pH of the wastewater to be discharged, as explained further below. When it is determined that the level of aqueous free chlorine in the tank and the pH of the wastewater have reached the required limits, valve 122 is opened and the treated wastewater stream 120 is discharged from the system.

[0049] The system of the present invention is also provided with means for adjusting the conductivity of the wastewater being treated. A sodium hydroxide solution is fed from tank 116 into the treated wastewater stream 114 via a pump, which is then recycled back to reactor tank 110. In a preferred embodiment, the temperature of the wastewater in reactor tank 110 is maintained within predetermined limits by circulating at least a portion of the wastewater from reactor tank 110 through radiator 113.

[0050] The system also includes a controller 130 that receives information from the operational data collector device 132 and controls the power supply 134 that provides current to the reactor 112. The operational data collector device 132 collects information about the concentration of contaminants in the reactor tank, the amount of aqueous free chlorine in the reactor tank, and other parameters. The amount of aqueous free chlorine in the reactor tank is provided to the data collector device by a sensor that monitors the oxidation-reduction potential of the wastewater.

[0051] This invention relates to systems and methods for treating wastewater containing chloride salts (sodium, potassium, calcium, etc.). In the examples described herein, the wastewater to be treated contains sodium chloride; however, those skilled in the art will understand that similar chemical reactions occur during the electrochemical treatment of wastewater containing potassium chloride, calcium chloride, etc., and the systems and methods described herein refer to wastewater containing any type of chloride. During the electrochemical oxidation treatment process of the wastewater to be treated, chloride ions from the wastewater are oxidized into aqueous free chlorine. Because it is required to ensure that the aqueous free chlorine generated during wastewater treatment does not evolve into chlorine gas, the pH of the wastewater is controlled to be above about 9 during treatment. This ensures that all aqueous free chlorine generated during the treatment process remains in the aqueous phase as hypochlorite according to the following reaction:

[0052] NaCl + H₂O → NaClO + H₂

[0053] Due to restrictions on the level of chlorine that can be discharged from wastewater treatment systems, sodium bisulfite (SBS) is added to the treated wastewater after treatment is stopped and before the treated wastewater is discharged into the environment to neutralize hypochlorite into hydrochloric acid and sulfuric acid, as shown in the reaction below:

[0054] NaClO + Na₂HO₃S → HCl + H₂SO₄

[0055] Depending on the amount of free chlorine in the water, the addition of sodium bisulfite leads to a decrease in the pH of the treated water. It was found that for systems previously used to treat wastewater containing sodium chloride, the pH of the wastewater decreased to approximately 6 to 8 after the addition of sodium bisulfite to neutralize the free chlorine in the water.

[0056] It was also determined that if hypochlorite production increases, more sodium bisulfite will be needed to neutralize the free chlorine in the water, causing the pH of the treated wastewater to drop further to about 4 or below. If the treated wastewater is recycled through the reactor, this facilitates the dissolution of scale deposited on the electrode surfaces. As found, the dissolution of hardness deposits is enhanced due to the exchange between chloride and carbonate ions in the scale, which leads to the dissolution of scale deposited on the electrode surfaces in the treated water.

[0057] The system and method of the present invention are designed for treating wastewater containing chloride salts with chloride concentrations between 500 mg / L and 5,000 mg / L, and address the problem of reducing the pH of the treated wastewater to be discharged to below about 4 for in-situ electrode cleaning by increasing the amount of chemical solution generated within the wastewater treatment reactor, instead of providing such a chemical solution for electrode cleaning from an external electrolytic cell, and without using any additional chemicals not already involved in the wastewater treatment process.

[0058] According to a preferred embodiment of the invention, the current supplied to the reactor is controlled by controller 130 such that the total amount of aqueous free chlorine generated during treatment requires the addition of a certain amount of sodium bisulfite to produce hydrochloric acid in the range of 500 mg / L to 5,000 mg / L, and such that the pH of the treated wastewater is less than or equal to 4. The current to be supplied to the reactor to meet these requirements can be determined experimentally through tests conducted in a laboratory on the water to be treated, or it can be actively controlled during operation by monitoring the amount of aqueous free chlorine generated during treatment. As mentioned above, the amount of aqueous free chlorine generated during wastewater treatment is monitored by a sensor that monitors the redox potential of the wastewater.

[0059] The current supplied to reactor 112 can be controlled by controlling the size of the electrode active area of ​​reactor 112 or by controlling the current density. The electrode active area is defined as the total area of ​​the active electrodes in reactor 112 that are supplied with current from power source 134 and are treating wastewater. Those skilled in the art will understand that the system can be configured with only one reactor 112, and in this case, the electrode active area is defined by the area of ​​the electrodes in the reactor that are supplied with current from the power source and operate to treat wastewater. Controller 130 controls the density of the current supplied to reactor 112 and / or the number of electrodes or reactors connected to the power source according to the conditions mentioned above to obtain the desired current supplied to the reactor.

[0060] Used to operate as described above and Figure 1 The method of the system of the present invention illustrated in the figure can be summarized as follows. Wastewater stream 101 is supplied to equalization tank 102 and further supplied to reactor tank 110 via pump 106. Wastewater 107 is supplied from reactor tank 110 to reactor 112, which is connected to a power source, and is treated within the reactor. The treated wastewater 114 is recycled back to reactor tank 110, and this cycle is repeated for an experimentally determined period of time to reduce the contaminant concentration in the wastewater to a limit that allows for the discharge of treated wastewater. The contaminant concentration in the wastewater in the reactor tank is monitored by an operational data collector device 132, and it is transmitted to a controller, which stops supplying power to reactor 112 when the contaminant concentration has reached the desired level.

[0061] During the treatment process, the operation data collector device 132 also collects information about the wastewater in reactor tank 110, such as the amount of aqueous free chlorine generated during the treatment process.

[0062] After the wastewater has been treated and before it is discharged from the system, reactor 112 is disconnected from the power supply. Sodium bisulfite solution is supplied from tank 118 to reactor tank 110. The pH of the wastewater in the reactor tank is monitored by data collector device 132. When the pH of the wastewater in the tank reaches 4 or lower, the wastewater is recycled through reactor 112 and returned to the tank for an experimentally determined amount of time to achieve in-situ cleaning of the electrodes. Subsequently, the treated wastewater stream 120 is discharged from the system.

[0063] During wastewater treatment, the current supplied to the reactor is controlled such that, after the addition of sodium bisulfite, the sodium hypochlorite produced during wastewater treatment will generate hydrochloric acid in the reactor tank at a concentration between 500 mg / L and 5,000 mg / L, and cause the pH of the treated wastewater to be less than or equal to 4. The amount of current to be supplied to the reactor is determined experimentally through tests conducted in a laboratory for the specific characteristics of the wastewater to be treated, or by continuously monitoring the amount of aqueous free chlorine in the reactor tank 110 during wastewater treatment by the data collector device 132.

[0064] The requirements described above are achieved by controlling the size of the electrode active area of ​​the reactor used for wastewater treatment or by controlling the density of the current supplied to the reactor. In some embodiments, both the size of the electrode active area and the current density are controlled based on the requirements described above.

[0065] Therefore, in some embodiments, the size of the electrode active area is controlled such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a certain amount of sodium bisulfite, determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank after a metered supply of the sodium bisulfite solution, and to bring the pH of the treated wastewater to less than or equal to 4. The required size of the electrode active area can be determined experimentally by testing in a laboratory for the specific characteristics of the wastewater to be treated, or by continuously monitoring the level of aqueous free chlorine in the reactor tank 110 during wastewater treatment by the data collector device 132. Typically, if the required size of the electrode active area is determined by laboratory testing, the electrode active area will remain constant during wastewater treatment; however, if the determination of the size of the electrode active area is based on monitoring the level of aqueous free chlorine, the size of the electrode active area can be varied during wastewater treatment operation depending on the detected level of aqueous free chlorine by increasing or decreasing the number of reactors in operation, or, if only one electrochemical reactor is used, by increasing or decreasing the number of active electrodes connected to the power source.

[0066] In other embodiments, the density of the current supplied to reactor 112 by power source 134 is controlled such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a predetermined amount of sodium bisulfite, determined experimentally, to generate hydrochloric acid in the reactor tank at a concentration between 500 mg / L and 5,000 mg / L after the metered supply of sodium bisulfite, and to bring the pH of the treated wastewater to less than or equal to 4. The current density can be determined experimentally by testing in a laboratory setting for the specific characteristics of the wastewater to be treated, or by continuously monitoring the level of aqueous free chlorine in reactor tank 110 via data collector device 132 during wastewater treatment. Similar to the electrode active area, if the current density is determined experimentally, it will generally remain constant during wastewater treatment operation; however, if the current density is determined based on continuous monitoring of the level of aqueous free chlorine in reactor tank during wastewater treatment, it can be varied during wastewater treatment operation according to the detected level of aqueous free chlorine.

[0067] In an alternative embodiment, both the size of the active electrode area and the current density supplied to the reactor are simultaneously controlled such that the total amount of aqueous free chlorine generated until the end of wastewater treatment requires the addition of a predetermined amount of sodium bisulfite, determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank after the metered supply of sodium bisulfite, and to bring the pH of the treated wastewater to less than or equal to 4. The values ​​of the active electrode area and current density can be determined experimentally by testing in a laboratory setting for the specific characteristics of the wastewater to be treated, or by continuously monitoring the level of aqueous free chlorine in the reactor tank 110 via data collector device 132 during wastewater treatment. Similar to the previous embodiments, if determined experimentally, the size of the electrode active area and the value of the current density can be constant, or if they are based on the monitored level of aqueous free chlorine generated during treatment, the values ​​can be varied during wastewater treatment operation.

[0068] In all embodiments, the active electrode area and / or current density required to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L and / or to bring the pH of the treated wastewater to less than or equal to 4 in the reactor tank after a quantitative supply of sodium bisulfite, according to the present invention, are higher than the active electrode area and / or current density required to treat wastewater only to reduce the concentration of pollutants to meet wastewater discharge requirements.

[0069] Compared to existing technologies, the system and method of the present invention have the advantage of not adding additional chemical solutions to the wastewater treatment system for cleaning electrodes, which are unnecessary for wastewater treatment or for ensuring the safe discharge of treated wastewater. It is known that sodium bisulfite is added to treated wastewater in wastewater systems, but in amounts different from those described in this invention, to neutralize hypochlorite into hydrochloric acid and sulfuric acid to meet wastewater discharge requirements.

[0070] While specific elements, embodiments, and applications of the invention have been shown and described, it will be understood that the invention is not limited thereto, as modifications can be made by those skilled in the art without departing from the spirit and scope of this disclosure, particularly in accordance with the foregoing teachings. Such modifications will be considered to be within the scope and rights of the appended claims.

[0071] The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned in this specification and / or listed in the application data sheet, if any, including U.S. Provisional Patent Application No. 63 / 177,274, filed April 20, 2021, are incorporated herein by reference in their entirety. If necessary, aspects of the embodiments may be modified to incorporate concepts from multiple patents, applications, and publications to provide yet another set of embodiments. These and other changes to the embodiments may be made based on the detailed description above. Generally, the terminology used in the appended claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be construed as encompassing all possible embodiments and the full scope of equivalents to which such claims are granted. Therefore, the claims are not limited by this disclosure.

Claims

1. A method for wastewater treatment, comprising the following steps: a. A stream of wastewater containing chloride salts with a chloride concentration between 500 mg / L and 5,000 mg / L is supplied to a reactor tank of a wastewater treatment system, and from the reactor tank is supplied to at least one reactor of the wastewater treatment system for treating the wastewater, the at least one reactor comprising at least one electrode to remove chlorides contained in the wastewater; b. Control the current supplied to the reactor used to treat the wastewater; c. At the end of the treatment, after the reactor stops treating the wastewater and before the wastewater is discharged from the wastewater treatment system, a certain amount of sodium bisulfite is supplied to the treated wastewater in the reactor tank to reduce the aqueous free chlorine level to below a predetermined level that allows the wastewater to be discharged. as well as d. The treated wastewater is recirculated from the reactor tank through the reactor and back to the reactor tank for an experimentally determined period of time to clean the electrodes of the reactor. The current supplied to the reactor for treating the wastewater is controlled such that the total amount of aqueous free chlorine produced until the end of the wastewater treatment requires the addition of a certain amount of sodium bisulfite, determined experimentally, to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce treated wastewater with a pH less than or equal to 4 in the reactor tank for in-situ cleaning of the electrodes.

2. The method of claim 1, wherein the current supplied to the reactor is controlled by controlling the size of the electrode active area and / or the current density of the reactor.

3. The method according to claim 2, wherein the size of the electrode active area is controlled to a value determined experimentally, such that the total amount of aqueous free chlorine generated until the end of the wastewater treatment requires the addition of a certain amount of sodium bisulfite determined experimentally, to generate hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to generate the treated wastewater with a pH less than or equal to 4 in the reactor tank.

4. The method of claim 2, wherein the size of the electrode active area is controlled based on the amount of aqueous free chlorine detected in the reactor tank during operation of the wastewater treatment system, such that the total amount of aqueous free chlorine generated until the end of the wastewater treatment requires the addition of an experimentally determined amount of sodium bisulfite to generate hydrochloric acid in the reactor tank at a concentration between 500 mg / L and 5,000 mg / L and to generate the treated wastewater in the reactor tank with a pH less than or equal to 4.

5. The method of claim 2, wherein the current density is controlled to an experimentally determined value such that the total amount of aqueous free chlorine produced until the end of the wastewater treatment requires the addition of an experimentally determined amount of sodium bisulfite to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce the treated wastewater with a pH less than or equal to 4 in the reactor tank.

6. The method of claim 2, wherein the current density is controlled based on the amount of aqueous free chlorine detected in the reactor tank during operation of the wastewater treatment system, such that the total amount of aqueous free chlorine generated until the end of the wastewater treatment requires the addition of an experimentally determined amount of sodium bisulfite to generate hydrochloric acid in the reactor tank at a concentration between 500 mg / L and 5,000 mg / L and to generate the treated wastewater in the reactor tank with a pH less than or equal to 4.

7. The method according to claim 2, wherein the size of the electrode active area and the current density are both determined experimentally, such that the total amount of aqueous free chlorine produced until the end of the wastewater treatment requires the addition of an experimentally determined amount of sodium bisulfite to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce the treated wastewater with a pH less than or equal to 4 in the reactor tank.

8. The method of claim 2, wherein both the size of the electrode active area and the current density are controlled based on the detected amount of aqueous free chlorine produced until the end of the wastewater treatment, such that the total amount of aqueous free chlorine produced until the end of the wastewater treatment requires the addition of an experimentally determined amount of sodium bisulfite to produce hydrochloric acid at a concentration between 500 mg / L and 5,000 mg / L in the reactor tank and to produce the treated wastewater with a pH less than or equal to 4 in the reactor tank.

9. The method according to claim 1, wherein the chloride salt is sodium chloride.

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