Efficient and sustainable electrochemical wastewater treatment method and system

Abstract

A system for efficient and sustainable electrochemical treatment of wastewater includes a reactor tank, a first electrolytic cell having a stack of electrolytic cells each containing an anode of a first composition, a second electrolytic cell having a stack of electrolytic cells each containing an anode of a second composition, and a pollutant concentration measurement device for monitoring the contaminant concentration from the reactor tank to either the first electrolytic cell or the second electrolytic cell. Wastewater to be treated is fed from the reactor tank to the first electrolytic cell until a pollutant removal rate of about 0 mg / h is measured, thereby indicating a substantially constant contaminant concentration and an accumulation of by-products produced in the first electrolytic cell. Thereafter, the wastewater is fed from the reactor tank to the second electrolytic cell having anodes capable of efficiently treating the by-products of the reaction in the first electrolytic cell.

Description

[Technical field]

[0001] The present invention relates to a system and method for electrochemically treating wastewater while extending the useful life of electrodes to provide an efficient and sustainable pollutant removal process. [Background technology]

[0002] The demand for wastewater treatment systems is increasing due to tightening wastewater treatment regulations requiring industrial facilities to remove persistent water pollutants before discharge, and the current global shortage of clean water. This has led to an increased demand for cost-effective, sustainable wastewater treatment systems that use minimal chemical additions, do not generate secondary pollution, and have minimal operation and maintenance requirements.

[0003] The preferred approach for treating recalcitrant wastewater is by electrochemical oxidation, which is a sustainable, safe and highly efficient treatment solution capable of removing a wide variety of contaminants, such as persistent organic pollutants, dioxins, nitrogen species (e.g., ammonia), pharmaceuticals, pathogens, and microorganisms. One approach for wastewater treatment is by direct electrochemical oxidation of organic and / or inorganic contaminants, where such contaminants are oxidized directly at the anode surface. Another method is the indirect electrochemical oxidation of organic and / or inorganic contaminants by in situ generation of chemical oxidizing species (hydroxyl, chlorine, oxygen, perchlorate radicals, or compounds such as ozone, hydrogen peroxide, etc.). Those chemical oxidizing species are generated directly at the anode surface, which then oxidize the contaminants in the wastewater solution.

[0004] Wastewater treatment by electrochemical oxidation can produce certain by-products that, in some cases, cannot be treated with the same types of electrodes used to treat the contaminants in the wastewater, and in other cases, can be damaging to the electrodes even when present in low concentrations.

[0005] The prior art has failed to address the impact of by-products formed during wastewater treatment by electrochemical oxidation on the electrodes used (selected based on the original composition of the wastewater to be treated, i.e., based on the composition and pollutant concentration of the wastewater stream generated at the industrial site that needs to be disposed of, respectively). Several prior art documents describe the use of different electrodes to treat different wastewater compositions, the composition of the electrodes being selected based on the pollutants contained in the wastewater to be treated. US Pat. No. 10,144,659 describes the use of an electrolytic cell with a first type of anode for oxygen generation, e.g., an electrode coated with tin and antimony oxide, connected in parallel to a second electrolytic cell with a second type of anode for oxygen generation, e.g., a boron-doped diamond electrode, having a higher overvoltage for oxygen generation than the first type of anode, and the two electrolytic cells are configured for simultaneous use in the COD treatment of wastewater by anodic oxidation. In this prior art document, the electrodes are selected based solely on the original composition of the wastewater to be treated and are used simultaneously in parallel to treat the wastewater fed to the device. As described in this prior art document, the rationale behind this arrangement is to make maximum use of the more convenient and inexpensive elements, namely tin and antimony oxide based anodes and, to a lesser extent, BDD electrodes installed in their own appropriate electrolytic cells.

[0006] Such prior art arrangements achieve parallel treatment of wastewater streams having the same pollutants while achieving different levels of performance for each of the electrolyzers, e.g., a higher level of performance for the electrolyzer having a higher overpotential electrode for oxygen generation (BDD electrode). There is no discussion of reducing and addressing the impact of by-products generated during the treatment of the wastewater in either of the two electrolyzers.

[0007] None of the known prior art documents recognizes that some by-products generated during the treatment of wastewater by electrochemical oxidation cannot be efficiently treated, especially in large quantities, by a type of electrode selected based on the original pollutant composition of the wastewater. For example, acetone produced during the treatment of wastewater containing isopropyl alcohol (IPA), when present in high concentrations, cannot be efficiently treated by precious metal oxide (PMO) electrodes known to be used for the treatment of IPA. Also, when electrochemically treating wastewater containing IPA using, for example, boron-doped diamond (BDD) electrodes, certain by-products (e.g., acetic acid) corrode the electrodes, shortening their lifespan, making it economically disadvantageous considering the cost of the electrodes. For this reason, connecting two electrolytic cells in parallel, for example as described in the above-mentioned US Patent No. 10,144,659, is not efficient in addressing this problem.

[0008] In the prior art, electrodes used in wastewater treatment have been selected based on the contaminants contained in the original wastewater stream to be treated. For example, as mentioned above, PMO electrodes have been selected to treat wastewater containing IPA without considering that acetone is generated during treatment and that PMO electrodes are not efficient at treating such by-products when present in high concentrations, and BDD electrodes have been selected to treat wastewater containing IPA because they are efficient at treating IPA without considering the generation of by-products such as acetic acid that would damage the BDD electrodes.

[0009] Therefore, there remains a need to improve wastewater treatment efficiency to provide more efficient and sustainable wastewater treatment methods and systems, taking into account the by-products generated when treating wastewater with one type of electrode. Summary of the Invention

[0010] The present invention describes an electrochemical wastewater treatment method, comprising: a. providing a wastewater stream to be treated to a reactor tank; b. treating the wastewater from the reactor tank in a first electrolytic cell comprising a stack of electrolytic cells and returning an effluent stream from the first electrolytic cell to the reactor tank, each electrolytic cell comprising an anode of a first composition; c. monitoring the contaminant concentration in the wastewater from the reactor tank; d. repeating the steps of treating the wastewater in the first electrolytic cell and discharging the effluent stream from the first electrolytic cell into the reactor tank until the concentration of contaminants in the wastewater being treated is substantially constant; e. when the concentration in the wastewater to be treated becomes substantially constant, stopping the treatment of the wastewater in the first electrolytic cell and treating the wastewater from the reactor tank in a second electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a second composition different from the first composition of the anodes of the first electrolytic cell; f. treating the wastewater in a second electrolytic cell and returning the effluent stream from the second electrolytic cell to the reactor tank; g. monitoring the contaminant concentration in the wastewater from the reactor tank; h. returning the effluent stream from the second electrolytic cell to the reactor tank until the contaminant concentration in the wastewater from the reactor tank reaches a preset target value; i. discharging the wastewater from the reactor tank to a pre-determined location.

[0011] In this method, the contaminant concentration is monitored by measuring the chemical oxygen demand concentration in the wastewater or by measuring the total organic carbon concentration in the wastewater.

[0012] The first composition of the anode of the first electrolytic cell is selected from among materials capable of treating the major contaminants in the wastewater stream and preferably is not substantially damaged by the by-products produced in the first electrolytic cell. The second composition of the anode of the second electrolytic cell is selected from among materials capable of treating the by-products of the reaction in the first electrolytic cell, or alternatively can be selected to also treat the major contaminants in the wastewater.

[0013] In a preferred embodiment, treatment of the wastewater from the reactor tank in the first electrolytic cell is stopped and treatment of the wastewater from the reactor tank in the second electrolytic cell is initiated when the contaminant removal rate in the wastewater stream supplied from the reactor tank drops to about 0 mg / h, indicating that the contaminant concentration in the wastewater supplied from the reactor tank (contaminant concentration as indicated by chemical oxygen demand concentration or total organic carbon concentration) remains substantially constant.

[0014] In some embodiments, treatment of the wastewater in the first electrolytic cell is stopped and treatment of the wastewater in the second electrolytic cell is initiated at a time experimentally determined to correspond to when the contaminant concentration in the wastewater from the reactor tank becomes substantially constant or when the contaminant removal rate is approximately a preset value, in a preferred embodiment, such preset value is about 0 mg / h.

[0015] In one example, the wastewater to be treated is alcohol , or isopropyl alcohol and acetone, a first composition at the anode of the first electrolytic cell comprises a precious metal oxide, and a second composition at the anode of the second electrolytic cell comprises diamond or boron doped diamond.

[0016] Further disclosed is an electrochemical wastewater treatment system, the system comprising: a. a reactor tank for holding the wastewater to be treated; b. a first electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a first composition; c. a second electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a second composition; d. A contaminant concentration measuring device for monitoring the contaminant concentration in the wastewater from the reactor tank; e. A control unit for controlling the treatment of wastewater in the first electrolytic cell and the second electrolytic cell, wherein at the start of operation of the system, when wastewater is treated in the first electrolytic cell and the concentration of pollutants in the wastewater to be treated becomes substantially constant, the control unit commands the treatment of wastewater to be stopped in the first electrolytic cell and the treatment of wastewater to be started in the second electrolytic cell.

[0017] The contaminant concentration measuring device measures the chemical oxygen demand concentration in the wastewater from the reactor tank, and in some embodiments may measure the total organic carbon concentration in the wastewater from the reactor tank.

[0018] In the system, the first composition of the anode of the first electrolytic cell is preferably selected from among materials capable of treating the major contaminants in the wastewater stream fed to the first electrolytic cell and that are not substantially damaged by the by-products produced in the first electrolytic cell.

[0019] The second composition of the anode of the second electrolytic cell can be selected from among materials capable of treating the by-products of the reaction in the first electrolytic cell or can also be selected from among materials capable of treating the main pollutants in the wastewater.

[0020] When the contaminant removal rate falls to a preset value, e.g., about 0 mg / h, indicating that the contaminant concentration in the wastewater remains substantially constant, treatment of the wastewater in the first electrolytic cell is stopped and the wastewater is treated in the second electrolytic cell.

[0021] In another embodiment, wastewater is fed from the reactor tank to the first electrolytic cell until a preset time that is experimentally determined to correspond to when the contaminant removal rate reaches about 0%.

[0022] In one example, the wastewater is alcohol or isopropyl alcohol and acetone, a first composition at the anode of the first electrolytic cell comprises a precious metal oxide, and a second composition at the anode of the second electrolytic cell comprises diamond or boron doped diamond. [Brief description of the drawings]

[0023] The drawings illustrate certain preferred embodiments of the invention, but are not to be construed as limiting the spirit or scope of the invention in any way. [Figure 1] FIG. 1 shows a schematic diagram of a wastewater treatment system including two electrolytic cells with different types of electrodes according to the present invention. [Diagram 2] FIG. 2 shows a graph of the reduction in chemical oxygen demand (COD) concentration achieved while treating wastewater containing IPA according to the method of the present invention. [Diagram 3] FIG. 3 shows a graph of the COD concentration reduction shown in FIG. 2 along with the efficiency achieved by the method according to the present invention. [Figure 4] FIG. 4 shows the reduction in concentrations of two major pollutants in a wastewater stream treated according to the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Certain terms are used herein, but they are intended to be construed in accordance with the definitions given below. Also, terms such as "a" and "comprises" are to be considered open ended.

[0025] Herein, in a quantitative context, the terms "about" and "approximately" should be interpreted as within a range of up to plus or minus 10%. Similarly, the term "substantially constant" should be interpreted as varying within a range of plus or minus 10% of a median value over a period of time.

[0026] FIG. 1 shows a wastewater treatment system according to a preferred embodiment of the present invention.

[0027] The electrochemical wastewater treatment system 100 comprises a reactor tank 102, a first electrolytic cell 104 containing a stack of electrolytic cells, each containing an anode of a first composition, and a second electrolytic cell 106 containing a stack of electrolytic cells, each containing an anode of a second composition.

[0028] A wastewater stream 108 to be treated is fed to the reactor tank 102 via pump 110, and a wastewater stream 109 from the reactor tank is fed to the first electrolytic cell 104 via pump 112 and flow control valve 114 where it is treated to remove contaminants in the wastewater. After treatment, an effluent stream 116 from the first electrolytic cell 104 is returned to the reactor tank 102 and further recycled to the first electrolytic cell 104. This cycle is repeated and at the beginning of each cycle, the contaminant concentration in the wastewater stream fed to the first electrolytic cell 104 is measured by a contaminant concentration measuring device 118 as shown in FIG. 1. In other embodiments (not shown), the contaminant concentration in the wastewater can be measured at the outlet from the electrolytic cell 104, as the contaminant concentration in the effluent stream 116 returned to the reactor tank 102, or directly in the reactor tank. In any of the embodiments, the contaminant concentration is preferably measured at the same location in the system for consistency. During this process, the power supply 120 is controlled by the system's control unit 122 to supply power to the first electrolytic cell 104 while the second electrolytic cell 106 is not operating, and to keep the flow control valve 124 open to allow recirculation of wastewater from the first electrolytic cell 104 back to the reactor tank 102.

[0029] In one embodiment of the present invention, the wastewater to be treated contains contaminants, such as isopropyl alcohol (IPA) or isopropyl alcohol and small amounts of acetone, which need to be removed before the wastewater is discharged to a designated location. In this embodiment, the anode of the first electrolytic cell 104 is made of precious metal oxide (PMO), an anode known in the art to be used to treat wastewater containing IPA. It was observed that the electro-oxidation process carried out in the first electrolytic cell 104 produces acetone, and as the process continues, the contaminant concentration measured by the measuring device 118 becomes constant, indicating that the anode of the first electrolytic cell 104 is not able to further reduce the contaminants in the wastewater to be treated. This can be explained by the fact that the by-products produced during the electro-oxidation process, in this case acetone, can reach a total amount that exceeds the amount of acetone that can be treated by the PMO anode. The PMO anode is known to treat IPA in wastewater, but is not efficient at treating large amounts of acetone.

[0030] When the measuring device 118 indicates that the contaminant concentration in the wastewater in the reactor tank has become substantially constant, for example as indicated by a contaminant removal rate (mg / h) of approximately zero, good results are obtained by stopping the operation of the first electrolytic cell 104, disconnecting the power supply 120, closing the flow control valves 114, 124, supplying current from the power supply 126 to the second electrolytic cell 106, opening the flow control valve 128, and supplying the wastewater stream 109 from the reactor tank 102 to the second electrolytic cell 106 through the open flow control valve 128. The second electrolytic cell 106 has an anode made of diamond or boron-doped diamond. Diamond electrodes are also known to work well in the treatment of wastewater containing acetone and IPA. Experimentally, it has been found that diamond anodes are damaged by acetic acid, a by-product generated when treating wastewater containing IPA, and therefore do not last very long. They also found that when wastewater containing IPA was treated with a diamond anode, acetic acid was produced at a higher rate than when a PMO anode was used.

[0031] The system 100 continues to operate by feeding the wastewater from the reactor tank to the second electrolytic cell 106 and opening the flow control valve 125 to return the effluent stream 130 from the second electrolytic cell 106 to the reactor tank 102. The cycle of treatment in the second electrolytic cell 106 is repeated until the contaminant concentration measuring device 118 indicates that the wastewater in the reactor tank has been treated to an acceptable level of contaminants for disposal. As further shown in Figures 2, 3 and 4, overall very good results were obtained in terms of contaminant removal and process efficiency, and the life of the diamond electrodes was extended. This is because the second electrolytic cell is used to a greater extent to remove acetone formed during wastewater treatment via electro-oxidation on the PMO anode of the first electrolytic cell, and to a lesser extent to remove IPA, the main contaminant in the wastewater, resulting in less production of acetic acid.

[0032] When the pollutant concentration measuring device detects that the pollutant concentration in the wastewater reaches a preset value required by regulation, the control unit of the system 122 directs the opening of the flow control valve 132 and an effluent stream of treated wastewater 134 is discharged from the system to a designated location.

[0033] Variations of this concept may be possible in various embodiments. For example, in a preferred embodiment, the pollutant concentration measuring device 118 may measure the chemical oxygen demand (COD) concentration in the wastewater provided from the reactor tank, while in other embodiments, the pollutant measuring device 118 measures the total organic carbon (TOC) concentration in the wastewater, where the COD and TOC concentrations are indicative of the amount of pollutants in the wastewater. Also, in a preferred embodiment, the pollutant concentration and the respective COD and TOC concentrations are measured by the pollutant measuring device 118, which includes sensors for sensing such concentrations, while in alternative embodiments, samples are taken periodically from the wastewater to be treated and the pollutant concentrations are determined in a laboratory from the samples taken.

[0034] In the above example, the anode of the first electrolytic cell is formed from a precious metal oxide and the anode of the second electrolytic cell is formed from boron-doped diamond, but in other embodiments, the anode of the first electrolytic cell can be selected from other materials, such as platinum group metals (PGM), titanium suboxides (i.e., Magneli TiOx), and the anode of the second electrolytic cell can be selected from carbon-based materials (glassy carbon or diamond) and mixed metal oxides. In general, the material of the anode of the first electrolytic cell is selected based on the pollutant composition of the wastewater to be treated, and the material of the anode of the second electrolytic cell is selected from materials that can destroy by-products generated during the treatment of the first electrolytic cell. In some embodiments, the anode of the second electrolytic cell can also destroy at least one pollutant or the main pollutant in the wastewater to be treated, which is originally fed into the system from an external source, but may be damaged by by-products generated during such treatment.

[0035] For example, in another embodiment, a wastewater stream containing methanol (CHOH) and chlorides is first treated in a first electrolytic cell containing a PMO anode until a measurement device indicates a substantially constant contaminant concentration level or a contaminant removal rate near 0 mg / h. The substantially constant contaminant concentration level or a contaminant removal rate near 0 mg / h is determined to be caused by the production of a by-product of the reaction in the first electrolytic cell, identified as chloroform (CHCl), after which the wastewater stream from the reactor tank is treated in a second electrolytic cell containing a BDD electrode capable of efficiently treating the wastewater containing chloroform.

[0036] In a preferred embodiment, the control unit 122 of the system determines that a plateau in contaminant concentration has been reached when the contaminant removal rate, measured in milligrams of contaminant or COD per hour, falls to approximately zero, and applies power to the second electrolytic cell to begin wastewater treatment. In other embodiments, the timing of the switch between the first and second electrolytic cells for treating the wastewater stream can be determined experimentally in a laboratory based on when the contaminant concentration of the wastewater supplied from the reactor tank reaches a plateau for a particular volume of wastewater having the detected contaminant composition, i.e., when the contaminant concentration remains substantially constant, and the control unit switches operation between the two electrolytic cells in an industrial implementation of the system based on the timing recorded from the experiment.

[0037] In another embodiment, the total organic carbon (TOC) in the wastewater at a given moment is monitored by a pollutant concentration measuring device, and when the control unit determines that the total organic carbon concentration becomes substantially constant and fluctuates between a particular range (e.g., plus or minus 10%), or when the TOC removal rate (amount of TOC removed per hour) becomes approximately 0 mg / h, the second electrolytic cell is activated to begin wastewater treatment.

[0038] In some embodiments, two electrolysis stacks, each enclosed in a first electrolytic cell and a second electrolytic cell of the embodiment shown in Figure 1, can be placed directly in the reactor tank 102 and operated in the same manner by sequentially activating the power supplies of each of the electrolysis stacks to treat the wastewater as described above. In such embodiments, no valves are required to feed the wastewater to be treated to the first and second electrolytic cells, respectively.

[0039] In this embodiment, the electrolyzers used in the experiments were flow-through reactors with a PMO plate anode / electrode for the first electrolyzer and a BDD plate anode / electrode for the second electrolyzer. Those skilled in the art will readily appreciate that other types of electrodes (e.g., bipolar electrodes, mesh electrodes) can be used to apply the method of the present invention.

[0040] Other auxiliary equipment shown in the drawings includes a filter 140, flow control valves 142, 144 for controlling the supply of wastewater to and from the reactor tank 102, and a reactor tank ventilation system 148 for removing gases formed during the electro-oxidation treatment of the wastewater. Such auxiliary equipment and their operation are known to those skilled in the art.

[0041] The method of operating the system shown in Figure 1 and described above can be summarized as follows: A wastewater stream to be treated is fed to a reactor tank 102 and then from the reactor tank to a first electrolytic cell 104, which contains a stack of electrolytic cells. Each electrolytic cell contains an anode made of a first composition, for example a precious metal oxide (PMO). The wastewater is treated in the first electrolytic cell 104 and an effluent stream 116 from the electrolytic cells is returned to the reactor tank 102. This process is repeated until the contaminant concentration in the wastewater stream 109 fed from the reactor tank is substantially constant as measured by a contaminant concentration measuring device 118 or until the contaminant removal rate calculated by the system's control unit 122 falls below approximately zero or a preset value. At this time, the supply of wastewater to the first electrolytic cell is stopped, the electrolytic cell is disconnected from its DC power supply 120, the second electrolytic cell 106 is supplied with current from its power supply 126, and the wastewater stream to be treated is fed from the reactor tank 102 to the second electrolytic cell 106, which contains a stack of electrolytic cells. Each electrolytic cell contains an anode of a second composition different from the composition of the anodes of the first electrolytic cell 104. The wastewater is treated in the second electrolytic cell 106 and an effluent stream 130 is returned from the second electrolytic cell to the reactor tank 102 while measurements of the contaminant concentrations are continued in the wastewater stream 109 fed from the reactor tank to the second electrolytic cell. The treatment process in the second electrolytic cell continues until the contaminant concentrations measured in the wastewater stream 109 from the reactor tank 102 reach a preset target value indicating that the wastewater complies with regulatory conditions, after which the wastewater is discharged.

[0042] The first composition of the anode in the first electrolytic cell is selected from among materials capable of treating the primary contaminants in the wastewater stream and that are not substantially damaged by by-products produced in the first electrolytic cell, and the second composition of the anode in the second electrolytic cell is selected from among materials capable of efficiently treating the by-products or at least the primary by-products of the wastewater treatment reactions in the first electrolytic cell, or materials capable of efficiently treating the by-products or at least the primary by-products of the treatment reactions and also efficiently treating the primary contaminants in the wastewater, but that may be damaged by the by-products during treatment of the primary contaminants in the wastewater over longer periods of use.

[0043] The wastewater is treated in the first electrolytic cell until the contaminant concentration in the wastewater stream fed from the reactor tank remains substantially constant and the contaminant concentration removal rate falls to approximately zero. The contaminant concentration can be measured as a COD concentration or a TOC concentration.

[0044] Other embodiments of the system include one or more electrolytic cells that can be operated in sequence as needed to destroy the by-products of the reaction in the electrolytic cell where the wastewater has already been treated.

[0045] Figures 2, 3 and 4 show the results obtained by treating wastewater containing isopropyl alcohol (IPA) and acetone in the system shown in Figure 1 with a first electrolytic cell having an anode made of a precious metal oxide (PMO) plate and a second electrolytic cell having an anode made of a boron doped diamond (BDD) plate.

[0046] As shown in FIG. 2, the wastewater stream to be treated had a total pollutant concentration of 2022 mg / l COD (chemical oxygen demand) including 680 mg / l IPA and 115 mg / l acetone. After about 26 hours of treating the wastewater in the first electrolytic cell with the PMO anode, the COD concentration of the wastewater fed from the reactor tank to the first electrolytic cell, shown by curve 210, dropped to about 130 mg / l, after which the COD concentration reached a plateau whereby the pollutant (COD) concentration began to stabilize, initially increasing slightly to about 194 mg / l, and then fluctuating between about 180 and about 195 mg / l for about 7 hours. Also, the concentration of IPA remained constant at about 10 mg / l, and the concentration of acetone was also relatively constant (50-80 mg / l). At this point, the treatment of the wastewater in the first electrolytic cell was stopped, and treatment of the wastewater in the second electrolytic cell was started. The second electrolyzer was operated for about an additional 17 hours, reducing the COD concentration in the wastewater stream fed from the reactor tank to greater than 99% removal, as shown by curve 220 in Figure 2. In this example, the switch between the first and second electrolyzers was performed when the COD removal rate (COD concentration per hour) was close to zero.

[0047] The efficiency of treatment using the present system and method is shown in Figure 3. The results show that the current efficiency, which correlates the amount of pollutants (COD) removed with the applied current and treatment time, begins to decrease while the wastewater is being treated in the first electrolytic cell containing the PMO anode, as shown by curve 310, and then increases again when the wastewater to be treated is fed to the second electrolytic cell containing the BDD anode, as shown by curve 320.

[0048] FIG. 4 shows the results of another test in which the method was used to treat a wastewater stream containing 858 mg / l IPA and 65 mg / l acetone within a total of 2366 mg / l COD. In this test, it was found that while the IPA concentration decreased during treatment in the first electrolyzer containing the PMO anode, as shown in curve 410, the acetone concentration began to increase, as shown in curve 420, due to the fact that acetone was also produced as a by-product during IPA treatment in the first electrolyzer. In this example, wastewater treatment in the first electrolyzer containing the PMO anode was stopped after about 32 hours of operation when it was observed that no further COD reduction could be achieved as measured by COD removal rate, and the wastewater stream was fed to a second electrolyzer, thereby achieving reduction to non-detection (<10 mg / l COD) using a BDD electrode to remove acetone. In this case, at the time of switchover, no IPA remained in the wastewater stream to be treated, and only the by-product (acetone) from the reaction in the first electrolyzer was removed.

[0049] While particular elements, embodiments and applications of the present invention have been shown and described, it should be understood that the present invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the teachings set forth above, without departing from the spirit and scope of the present disclosure, and such modifications are to be considered as encompassed within the scope of the appended claims.

[0050] The various embodiments described above can be combined to provide further embodiments. All U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned herein and / or listed in the Application Data Sheet (if any), including U.S. Provisional Patent Application No. 62 / 847,158, filed May 13, 2019, are hereby incorporated by reference in their entirety. Aspects of the embodiments can be modified, if necessary, to provide further embodiments using concepts from various patents, applications, and publications. These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. That is, the claims are not limited by this disclosure.

Claims

1. 1. An electrochemical wastewater treatment method comprising the steps of: a. feeding a wastewater stream to be treated into a reactor tank; b. treating the wastewater from the reactor tank in a first electrolytic cell comprising a stack of electrolytic cells and discharging an effluent stream from the first electrolytic cell into the reactor tank, each electrolytic cell comprising an anode of a first composition; c. monitoring the concentration of contaminants in the wastewater from the reactor tank; d. repeating the steps of treating wastewater in the first electrolytic cell and discharging an effluent stream from the first electrolytic cell into the reactor tank until the pollutant removal rate in the wastewater stream provided from the reactor tank falls to about 0 mg / h; e) when the pollutant removal rate in the wastewater stream provided from the reactor tank drops to about 0 mg / h, stopping the treatment of the wastewater in the first electrolytic cell and treating the wastewater from the reactor tank in a second electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a second composition different from the first composition of the anode of the first electrolytic cell, the second composition of the anode of the second electrolytic cell being selected from among materials capable of treating the by-products of the reaction in the first electrolytic cell; f. treating the wastewater in the second electrolytic cell and returning an effluent stream from the second electrolytic cell to the reactor tank; g. monitoring the concentration of contaminants in the wastewater from the reactor tank; h. returning the effluent stream from said second electrolytic cell to said reactor tank until a contaminant concentration in the wastewater from said reactor tank reaches a preset target value; i. discharging wastewater from said reactor tank to a predetermined location.

2. 10. The method of claim 1 , a first composition of the anode of said first electrolytic cell is selected from among materials capable of treating the primary contaminants in a wastewater stream and which are not substantially damaged by by-products produced in said first electrolytic cell.

3. 10. The method of claim 1 , The method according to claim 1, wherein the second composition of the anode of said second electrolytic cell is selected so as to be capable of treating also the major pollutants in the wastewater.

4. 10. The method of claim 1 , wherein the ceasing of treatment of wastewater from said reactor tank in said first electrolytic cell and the beginning of treatment of wastewater from said reactor tank in said second electrolytic cell are scheduled at times empirically determined to correspond to when a pollutant removal rate in the wastewater stream supplied from said reactor tank drops to about 0 mg / h.

5. 10. The method of claim 1 , 1. A method according to claim 1, wherein the wastewater comprises isopropyl alcohol or isopropyl alcohol and acetone, a first composition of the anode of the first electrolytic cell comprises a precious metal oxide, and a second composition of the anode of the second electrolytic cell comprises diamond or boron doped diamond.

6. 1. An electrochemical wastewater treatment system comprising: a. a reactor tank for holding the wastewater to be treated; b. a first electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a first composition; c) a second electrolytic cell comprising a stack of electrolytic cells, each electrolytic cell comprising an anode of a second composition, the second composition of one or more anodes of the second electrolytic cell being selected from among materials capable of treating by-products of the wastewater treatment reactions in the first electrolytic cell; d. a contaminant concentration measuring device for monitoring the contaminant concentration in the wastewater from the reactor tank; and a control unit for controlling the treatment of wastewater in the first electrolytic cell and the second electrolytic cell, wherein at start-up of the system, when wastewater from the reactor tank is treated in the first electrolytic cell and a pollutant removal rate in the wastewater stream provided from the reactor tank drops to about 0 mg / h, the control unit commands the first electrolytic cell to stop treating the wastewater from the reactor tank and the second electrolytic cell to start treating the wastewater from the reactor tank.

7. The electrochemical wastewater treatment system according to claim 6, A wastewater treatment system, characterized in that a first composition of one or more anodes of said first electrolytic cell is selected from among materials capable of treating the main pollutants in the wastewater to be treated and that are not substantially damaged by by-products produced during treatment in said first electrolytic cell.

8. The electrochemical wastewater treatment system according to claim 6, A wastewater treatment system, characterized in that the second composition of the anode of the second electrolytic cell is selected from among materials capable of treating the major pollutants in the wastewater.

9. The electrochemical wastewater treatment system according to claim 6, 11. A wastewater treatment system comprising: a reactor tank configured to supply wastewater to said first electrolytic cell for a predetermined period of time that is experimentally determined to correspond to when a contaminant removal rate in the wastewater supplied from said reactor tank drops to approximately 0 mg / h.

10. The electrochemical wastewater treatment system according to claim 6, 1. A wastewater treatment system comprising: a wastewater treatment system comprising: isopropyl alcohol or isopropyl alcohol and acetone; a first composition of an anode of said first electrolytic cell comprising a precious metal oxide; and a second composition of an anode of said second electrolytic cell comprising diamond or boron doped diamond.

11. The electrochemical wastewater treatment system according to claim 6, A wastewater treatment system, characterized in that the first electrolytic cell and the second electrolytic cell are disposed outside the reactor tank, and wastewater to be treated is supplied from the reactor tank to each electrolytic cell and returned from each electrolytic cell to the reactor tank via a flow control valve.

12. 7. The electrochemical wastewater treatment system according to claim 6, The first electrolytic cell and the second electrolytic cell are disposed within the reactor tank, and the wastewater to be treated is supplied directly from the reactor tank to each electrolytic cell and returned directly from each electrolytic cell to the reactor tank.

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