Treatment method and device for up-to-standard discharge of fracturing flow-back fluid

Abstract

The invention relates to the technical field of fracturing flow-back fluid treatment, in particular to a treatment method and device for standard discharge of fracturing flow-back fluid, and the treatment method comprises the following steps: carrying out electric flocculation reaction treatment on the fracturing flow-back fluid to obtain electric flocculation effluent, then carrying out electrochemical oxidation reaction treatment to obtain electrochemical reaction effluent, and then carrying out aeration air flotation treatment to obtain the electrochemical reaction effluent. And finally, carrying out MBR (Membrane Bioreactor) biological treatment to obtain the fracturing flow-back fluid which can be discharged up to the standard. The device comprises an electric flocculation reactor, an electrochemical oxidation reactor, an aeration air floatation device, an MBR biological treatment device and an air compressor. According to the present invention, the electric flocculation-electrochemical oxidation-aeration air flotation-MBR biological treatment method is adopted, and no chemical agent is added, such that various harmful pollutants such as COD, SS, oil and the like in the fracturing flow-back fluid can be effectively removed, the secondary pollutants during the treatment process can be reduced, the biodegradability of the fracturing flow-back fluid can be improved, and the treatment cost can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing flowback fluid treatment, in particular to a method and a device for treating fracturing flowback fluid to discharge it in a standard manner. Background Art

[0002] Tight oil development usually adopts a batch drilling and batch fracturing mining model. With the continuous development of fracturing construction technology, the fracturing fluid system has gradually improved from the guar gum system to the slick water system. The types of fracturing fluid thickeners are constantly changing, and there are more and more synthetic polymer fracturing fluids. The synthetic polymer fracturing fluid is mainly polyacrylamide. Since polyacrylamide is a high molecular polymer, its main chain mainly exists in CC chain, which is not easy to break, resulting in the characteristics of complex fracturing fluid flowback, stable system, and high COD value. At the same time, chemical oxidation-coagulation sedimentation has the characteristics of large dosage (1000mg / L to 3000mg / L) and high treatment cost (about 20 yuan / m 3 Up to 40 yuan / m 3 ), large amounts of sludge (accounting for about 20% to 40% of the treated water), and other problems make the treatment of fracturing return fluid extremely difficult.

[0003] At present, the conventional treatment method for fracturing flowback fluid is "chemical oxidation-coagulation and sedimentation / flotation-adsorption / membrane treatment / biological". This process first uses chemical strong oxidants to break the gel, and then removes oil and suspended solids through coagulation and sedimentation or flotation. However, there are problems such as large dosage, high treatment cost, large amount of sludge, and easy fouling and clogging of membrane materials. After the treatment of fracturing flowback fluid, the purified water is used for reinjection into the oil field or compounding of fracturing fluid. During the fracturing operation, due to the large amount of water used in fracturing fluid preparation, it can be reused; when no fracturing operation is carried out (or in winter), the treated flowback fluid can only be reinjected into the nearby oil field, but the nearby oil field is often in a state of injection-production balance, and the water injection demand is often limited, resulting in the inability to absorb the surplus water in the oil field, resulting in water imbalance. Therefore, it is necessary to consider the standard discharge technology of fracturing flowback fluid to completely solve the water imbalance problem caused by fracturing development. Summary of the invention

[0004] The present invention provides a method and device for treating fracturing flowback fluid to meet the discharge standards, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the existing problems in the treatment of fracturing flowback fluid, such as complex composition, high COD value, large amount of sludge, large amount of added chemicals and high treatment cost.

[0005] One of the technical solutions of the present invention is achieved through the following measures: a method for treating fracturing return fluid to meet the discharge standards, which is carried out according to the following steps: the first step is to subject the fracturing return fluid to an electrocoagulation reaction treatment to obtain electrocoagulation effluent; the second step is to subject the electrocoagulation effluent to an electrochemical oxidation reaction treatment to obtain electrochemical reaction effluent; the third step is to subject the electrochemical reaction effluent to an aeration flotation treatment to obtain flotation effluent; the fourth step is to subject the flotation effluent to an MBR biological treatment to obtain a fracturing return fluid that meets the discharge standards.

[0006] The following is a further optimization and / or improvement of one of the above-mentioned technical solutions: In the first step, the electro-flocculation reaction treatment process is as follows: the fracturing flowback fluid is sent to the electro-flocculation reactor, and the suspended solids, oil and some organic matter in the fracturing flowback fluid are removed by the demulsification, coagulation and flotation of the electro-flocculation reactor to obtain electro-flocculation effluent.

[0007] In the above second step, the process of electrochemical oxidation reaction treatment is: the electrocoagulation effluent is sent to the electrochemical oxidation reactor for electrochemical oxidation reaction treatment, and the electrochemical reaction effluent is obtained after the COD, oil and suspended matter in the electrocoagulation effluent are removed by the electrochemical oxidation reactor.

[0008] In the third step, the aeration flotation treatment process is as follows: the effluent from the electrochemical reaction is sent to the aeration flotation device, and through a large amount of aeration, the oxygen content in the water is increased, the microbial activity in the water is increased, and a portion of small molecular organic matter is degraded. At the same time, small flocs, COD and suspended matter in the water are removed by flotation to obtain effluent after flotation.

[0009] In the fourth step, the effluent after flotation is sent to the MBR biological treatment device. After the organic pollutants in the water are degraded by the microorganisms in the MBR biological treatment device, the solid-liquid separation is carried out through the MBR membrane bioreactor to obtain the fracturing return fluid that can meet the discharge standards.

[0010] In the first step, during the electrocoagulation reaction treatment, the rated voltage of the electrocoagulation reactor is 2V to 7V, the treatment time is 20min to 30min, the distance between the plates is 1cm to 3cm, and the plate material is one of iron, aluminum, and graphite; or / and, in the second step, during the electrochemical oxidation reaction treatment, the rated voltage of the electrochemical oxidation reactor is 5V to 10V, the treatment time is 20min to 40min, the distance between the plates is 1cm to 3cm, and the plate material is graphite, titanium, ruthenium-iridium-titanium alloy, ruthenium-iridium alloy, iridium-tantalum alloy one of gold; or / and, in the third step, during aeration flotation treatment, the air-water ratio in the aeration volume is 2 to 8:1, and the aeration time is 2h to 4h; or / and, in the fourth step, during MBR biological treatment, the reactor type is one of an integrated membrane bioreactor and a composite membrane bioreactor, the membrane component is one of a hollow fiber membrane and a plate membrane, the membrane adopts one of a microfiltration membrane and an ultrafiltration membrane, the membrane pore size is 0.01 micron to 0.04 micron, the dissolved oxygen is 2mg / L to 4mg / L, and the residence time is 12h to 36h.

[0011] In the first step above, the rated voltage of the electric flocculation reactor is 5V, the processing time is 25min, the plate spacing is 2cm, and the plate material is iron; or / and, in the second step, the rated voltage of the electrochemical oxidation reactor is 7V, the processing time is 30min, the plate spacing is 2cm, and the plate material is ruthenium iridium titanium; or / and, in the third step, the gas-water ratio in the aeration volume is 4:1, and the aeration time is 3h; or / and, in the fourth step, the reactor type is a composite membrane bioreactor, the membrane component is a hollow fiber membrane, the membrane adopts a microfiltration membrane, the membrane pore size is 0.03 microns, the dissolved oxygen is 3mg / L, and the residence time is 24h.

[0012] The second technical solution of the present invention is achieved through the following measures: a device for implementing a treatment method for fracturing return fluid to meet the discharge standards, including an electric flocculation reactor, an electrochemical oxidation reactor, an aeration flotation device and an MBR biological treatment device, the lower inlet of the electric flocculation reactor is fixedly connected with a water pipeline, the lower outlet of the electric flocculation reactor and the lower inlet of the electrochemical oxidation reactor are fixedly connected with a first water outlet pipeline, the upper outlet of the electrochemical oxidation reactor and the lower inlet of the aeration flotation device are fixedly connected with a second water outlet pipeline, the lower outlet of the aeration flotation device and the upper inlet of the MBR biological treatment device are fixedly connected with a third water outlet pipeline, and the upper outlet of the MBR biological treatment device is fixedly connected with a fourth water outlet pipeline.

[0013] The following is a further optimization and / or improvement of the second technical solution of the above invention: The above also includes an air compressor, a first aeration pipeline is fixedly connected between the air outlet of the air compressor and the bottom air inlet of the aeration flotation device, a second aeration pipeline is fixedly connected between the first aeration pipeline and the bottom air inlet of the MBR biological treatment device, and a third aeration pipeline is fixedly connected between the second aeration pipeline and the upper air inlet of the MBR biological treatment device.

[0014] A first circulation pipeline is fixedly connected between the middle outlet at the right end of the above-mentioned electroflocculation reactor and the middle inlet at the left end of the electroflocculation reactor, a second circulation pipeline is fixedly connected between the middle outlet at the right end of the electrochemical oxidation reactor and the middle inlet at the left end of the electrochemical oxidation reactor, circulation pumps are fixedly installed on the first circulation pipeline and the second circulation pipeline, and water delivery pumps are fixedly installed on the third water outlet pipeline and the fourth water outlet pipeline.

[0015] The present invention adopts the electro-flocculation-electrochemical oxidation-aeration flotation-MBR biological treatment method, without adding chemical agents. It can not only effectively remove various harmful pollutants such as COD, SS (suspended solids) and oil in the fracturing return fluid, but also reduce secondary pollutants in the treatment process, while improving the biodegradability of the fracturing return fluid and reducing the treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 This is a schematic diagram of the process flow of Example 8 of the present invention.

[0017] The codes in the accompanying drawings are: 1 is an electric flocculation reactor, 2 is an electrochemical oxidation reactor, 3 is an aeration flotation device, 4 is an MBR biological treatment device, 5 is an incoming water pipeline, 6 is a first outlet water pipeline, 7 is a second outlet water pipeline, 8 is a third outlet water pipeline, 9 is a fourth outlet water pipeline, 10 is an air compressor, 11 is a first aeration pipeline, 12 is a second aeration pipeline, 13 is a third aeration pipeline, 14 is a first circulation pipeline, 15 is a second circulation pipeline, 16 is a circulation pump, and 17 is a water delivery pump. DETAILED DESCRIPTION

[0018] The present invention is not limited by the following embodiments, and specific implementation methods can be determined according to the technical scheme of the present invention and actual conditions. Unless otherwise specified, the various chemical reagents and chemicals mentioned in the present invention are all known and commonly used chemical reagents and chemicals in the prior art.

[0019] The present invention will be further described below in conjunction with embodiments: Example 1: The method for treating the fracturing return fluid to meet the discharge standards is carried out according to the following steps: the first step is to subject the fracturing return fluid to an electrocoagulation reaction treatment to obtain electrocoagulation effluent; the second step is to subject the electrocoagulation effluent to an electrochemical oxidation reaction treatment to obtain electrochemical reaction effluent; the third step is to subject the electrochemical reaction effluent to an aeration flotation treatment to obtain flotation effluent; the fourth step is to subject the flotation effluent to an MBR biological treatment to obtain a fracturing return fluid that meets the discharge standards.

[0020] The present invention integrates the electrochemical method, flotation and biological treatment methods, and organically combines the three into an electro-flocculation-electrochemical oxidation-aeration flotation-MBR biological treatment method. In the treatment process, not only does it not need to add chemical agents, but also reduces the secondary damage caused by pollutants in the treatment process. At the same time, the electrolysis method is coupled with the biological treatment, and the B / C ratio is improved by electrochemical oxidation. It can also treat the flowback fluid generated by fracturing of a polyacrylamide-based slippery water fracturing fluid system, and has very good breadth and adaptability.

[0021] Embodiment 2: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, in the first step, the process of the electro-flocculation reaction treatment is: the fracturing return fluid is sent to the electro-flocculation reactor 1, and the suspended matter, oil and part of the organic matter in the fracturing return fluid are removed by the demulsification, coagulation and flotation effects of the electro-flocculation reactor 1 to obtain the electro-flocculation effluent.

[0022] In the present invention, electrocoagulation is to use a soluble anode (iron or aluminum) to generate a large amount of cations under the action of an external voltage, and to react with the OH generated by electrolysis. - It combines to generate highly active flocculating groups, which can absorb suspended matter, oil and other pollutants in the water by utilizing its adsorption bridging and net-catching and sweeping functions. At the same time, a large number of microbubbles are precipitated on the cathode, which adhere to the flocs and float up.

[0023] Embodiment 3: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, in the second step, the process of electrochemical oxidation reaction treatment is: the electroflocculation effluent is sent to the electrochemical oxidation reactor 2 for electrochemical oxidation reaction treatment, and the COD, oil content and suspended matter in the electroflocculation effluent are removed by the electrochemical oxidation reactor 2 to obtain electrochemical reaction effluent.

[0024] In the present invention, electrochemical oxidation is direct oxidation of organic matter on the electrode surface to convert pollutants directly into small molecular organic matter or generate ·OH oxidation under the action of an electric field, thereby breaking the CC main chain of polyacrylamide polymers and improving the biodegradability of fracturing flowback fluids.

[0025] Embodiment 4: As an optimization of the above embodiment, as shown in the attached Figure 1As shown, in the third step, the process of aeration flotation treatment is as follows: the effluent from the electrochemical reaction is sent to the aeration flotation device 3, and through a large amount of aeration, the oxygen content in the water is increased, the microbial activity in the water is increased, and a part of the small molecular organic matter is degraded. At the same time, small flocs, COD and suspended matter in the water are removed by flotation to obtain effluent after flotation.

[0026] In the present invention, aeration flotation is to increase the oxygen injection amount through a large amount of aeration, thereby increasing the degradation of easily degradable organic small molecules in the fracturing flowback fluid, and further removing the tiny flocs generated in the electrochemical oxidation process through flotation.

[0027] Embodiment 5: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, in the fourth step, the effluent after flotation is sent to the MBR biological treatment device 4, and the organic pollutants in the water are degraded by the microorganisms in the MBR biological treatment device 4, and then the solid-liquid separation is carried out through the MBR membrane bioreactor to obtain the fracturing return fluid that can meet the discharge standards.

[0028] In the present invention, MBR biological treatment (Membrane Bio-Reactor, MBR) is a sewage treatment system that organically combines membrane separation technology with biological treatment technology. The membrane module replaces the secondary sedimentation tank of the traditional biological treatment technology, maintains a high concentration of activated sludge in the bioreactor, increases the organic load of biological treatment, and can effectively treat fracturing return fluid with complex components and many difficult-to-degrade substances, achieving good removal effects on COD, NH3-N, SS, etc.

[0029] Embodiment 6: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, in the first step, during the electrocoagulation reaction treatment, the rated voltage of the electrocoagulation reactor 1 is 2V to 7V, the treatment time is 20min to 30min, the distance between the plates is 1cm to 3cm, and the plate material is one of iron, aluminum, and graphite; or / and, in the second step, during the electrochemical oxidation reaction treatment, the rated voltage of the electrochemical oxidation reactor 2 is 5V to 10V, the treatment time is 20min to 40min, the distance between the plates is 1cm to 3cm, and the plate material is graphite, titanium, ruthenium-iridium-titanium alloy, ruthenium-iridium alloy, iridium-tantalum alloy; or / and, in the third step, during aeration flotation treatment, the air-water ratio in the aeration volume is 2 to 8:1, and the aeration time is 2h to 4h; or / and, in the fourth step, during MBR biological treatment, the reactor type is one of an integrated membrane bioreactor and a composite membrane bioreactor, the membrane component is one of a hollow fiber membrane and a plate membrane, the membrane adopts one of a microfiltration membrane and an ultrafiltration membrane, the membrane pore size is 0.01 micron to 0.04 micron, the dissolved oxygen is 2mg / L to 4mg / L, and the residence time is 12h to 36h.

[0030] Embodiment 7: As an optimization of the above embodiment, as shown in the attached Figure 1As shown, in the first step, the rated voltage of the electric flocculation reactor 1 is 5V, the processing time is 25min, the electrode spacing is 2cm, and the electrode material is iron (+) and iron (-); or / and, in the second step, the rated voltage of the electrochemical oxidation reactor 2 is 7V, the processing time is 30min, the electrode spacing is 2cm, and the electrode material is ruthenium iridium titanium (+) and ruthenium iridium titanium (-); or / and, in the third step, the gas-water ratio in the aeration volume is 4:1, and the aeration time is 3h; or / and, in the fourth step, the reactor type is a composite membrane bioreactor, the membrane component is a hollow fiber membrane, the membrane adopts a microfiltration membrane, the membrane pore size is 0.03 microns, the dissolved oxygen is 3mg / L, and the residence time is 24h.

[0031] Embodiment 8: As attached Figure 1 As shown, the device for implementing the method for treating the fracturing return fluid that meets the standards and discharges it externally comprises an electric flocculation reactor 1, an electrochemical oxidation reactor 2, an aeration flotation device 3 and an MBR biological treatment device 4, the lower inlet of the electric flocculation reactor 1 is fixedly connected with a water supply pipeline 5, the lower outlet of the electric flocculation reactor 1 and the lower inlet of the electrochemical oxidation reactor 2 are fixedly connected with a first water outlet pipeline 6, the upper outlet of the electrochemical oxidation reactor 2 and the lower inlet of the aeration flotation device 3 are fixedly connected with a second water outlet pipeline 7, the lower outlet of the aeration flotation device 3 and the upper inlet of the MBR biological treatment device 4 are fixedly connected with a third water outlet pipeline 8, and the upper outlet of the MBR biological treatment device 4 is fixedly connected with a fourth water outlet pipeline 9.

[0032] In the present invention, unless otherwise specified, the equipment and devices used are all the equipment and devices known and used in the art.

[0033] Embodiment 9: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, it also includes an air compressor 10, a first aeration pipeline 11 is fixedly connected between the air outlet of the air compressor 10 and the bottom air inlet of the aeration flotation device 3, a second aeration pipeline 12 is fixedly connected between the first aeration pipeline 11 and the bottom air inlet of the MBR biological treatment device 4, and a third aeration pipeline 13 is fixedly connected between the second aeration pipeline 12 and the upper air inlet of the MBR biological treatment device 4.

[0034] Embodiment 10: As an optimization of the above embodiment, as shown in the attached Figure 1 As shown, a first circulation pipeline 14 is fixedly connected between the middle outlet at the right end of the electrocoagulation reactor 1 and the middle inlet at the left end of the electrocoagulation reactor 1, a second circulation pipeline 15 is fixedly connected between the middle outlet at the right end of the electrochemical oxidation reactor 2 and the middle inlet at the left end of the electrochemical oxidation reactor 2, a circulation pump 16 is fixedly installed on the first circulation pipeline 14 and the second circulation pipeline 15, and a water delivery pump 17 is fixedly installed on the third water outlet pipeline 8 and the fourth water outlet pipeline 9.

[0035] As required, conventional valves, thermometers and pressure gauges known in the art may be provided on the pipelines and equipment of the device for implementing the method for treating the fracturing flowback fluid to meet the discharge standards according to production needs.

[0036] Example 11: The fracturing flowback fluid of the slick water fracturing fluid system (oil content 96 mg / L, COD 1200 mg / L, suspended solids 186 mg / L) first enters the electro-flocculation reactor 1, the electro-flocculation electrodes are iron (+) and iron (-), the plate spacing is 2 cm, the rated voltage is 3V, and the electrolysis is 25 minutes to obtain the electro-flocculation effluent. The electro-flocculation effluent (oil content 19 mg / L, COD 712 mg / L, suspended solids 86 mg / L) enters the electrochemical oxidation reactor 2, the electrochemical oxidation electrodes are ruthenium iridium titanium (+) and titanium (-), the plate spacing is 2 cm, the rated voltage is 5V, and the electrolysis is 30 minutes. The electrochemical oxidation effluent (oil content 9 mg / L, COD 232 mg / L, suspended solids 56 mg / L) enters the aeration flotation device 3, the steam-water ratio is 2:1, the aeration time is 2 hours, and the effluent (oil content 5 mg / L, COD 212mg / L, suspended solids 26mg / L) enters MBR biological treatment device 4, and through aeration, the dissolved oxygen in the water is adjusted to 2mg / L. The residence time is 12h, and the effluent (oil content 0mg / L, COD 109mg / L, suspended solids 2mg / L) meets the standards and is discharged.

[0037] Example 12: The fracturing flowback fluid of the slick water fracturing fluid system (oil content 85 mg / L, COD 1532 mg / L, suspended solids 198 mg / L) first enters the electro-flocculation reactor 1, the electro-flocculation electrodes are iron (+) and iron (-), the plate spacing is 2 cm, the rated voltage is 5V, and the electrolysis is performed for 30 minutes to obtain the electro-flocculation effluent. The electro-flocculation effluent (oil content 18 mg / L, COD 942 mg / L, suspended solids 74 mg / L) enters the electrochemical oxidation reactor 2, the electrochemical oxidation electrodes are ruthenium iridium titanium (+) and titanium (-), the plate spacing is 2 cm, the rated voltage is 7V, and the electrolysis is performed for 30 minutes. The electrochemical oxidation effluent (oil content 10 mg / L, COD 396 mg / L, suspended solids 55 mg / L) enters the aeration flotation device 3, the steam-water ratio is 4:1, the aeration time is 3 hours, and the effluent (oil content 5 mg / L, COD 321mg / L, suspended solids 22mg / L) enters MBR biological treatment device 4, and the dissolved oxygen in the water is adjusted to 3mg / L through aeration. The residence time is 24h, and the effluent (oil content 0mg / L, COD91mg / L, suspended solids 2mg / L) meets the standards and is discharged.

[0038] Example 13: Slippery water fracturing fluid system The fracturing flowback fluid (oil content 66 mg / L, COD 1541 mg / L, suspended solids 187 mg / L) first enters the electro-flocculation reactor, the electro-flocculation electrodes are iron (+) and iron (-), the plate spacing is 2 cm, the rated voltage is 6V, and the electrolysis is performed for 30 minutes to obtain electro-flocculation effluent. The electro-flocculation effluent (oil content 15 mg / L, COD 771 mg / L, suspended solids 55 mg / L) enters the electrochemical oxidation reactor, the electrochemical oxidation electrodes are ruthenium iridium titanium (+) and titanium (-), the plate spacing is 2 cm, the rated voltage is 7V, and the electrolysis is performed for 40 minutes. The electrochemical oxidation effluent (oil content 8 mg / L, COD 277 mg / L, suspended solids 35 mg / L) enters the aeration flotation device 3, the steam-water ratio is 6:1, the aeration time is 4 hours, and the effluent (oil content 5 mg / L, COD 221mg / L, suspended solids 18mg / L) enters MBR biological treatment device 4, and through aeration, the dissolved oxygen in the water is adjusted to 3mg / L. The residence time is 36h, and the effluent (oil content 0mg / L, COD 62mg / L, suspended solids 2mg / L) meets the standards and is discharged.

[0039] The fracturing flowback fluids treated by flocculation-electrochemical oxidation-aeration flotation-MBR biological treatment in Examples 11 to 13 of the present invention were tested for external discharge indicators, and the results are shown in Table 1. As shown in Table 1, the fracturing flowback fluids treated by the present invention meet the external discharge requirements.

[0040] In summary, the present invention adopts the electro-flocculation-electrochemical oxidation-aeration flotation-MBR biological treatment method without adding chemical agents. It can not only effectively remove various harmful pollutants such as COD, SS and oil in the fracturing return fluid, but also reduce secondary pollutants in the treatment process, while improving the biodegradability of the fracturing return fluid and reducing the treatment cost.

[0041] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations. .

Claims

1. A method for treating fracturing flowback fluid to discharge in compliance with standards, characterized in that The following steps are followed: first, subjecting the fracturing flowback fluid to an electrocoagulation reaction treatment to obtain electrocoagulation effluent; second, subjecting the electrocoagulation effluent to an electrochemical oxidation reaction treatment to obtain electrochemical reaction effluent; third, subjecting the electrochemical reaction effluent to an aeration flotation treatment to obtain flotation effluent; The fourth step is to subject the effluent after flotation to MBR biological treatment to obtain fracturing flowback fluid that meets discharge standards.

2. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 1, characterized in that In the first step, the electro-flocculation reaction treatment process is: the fracturing return fluid is sent to the electro-flocculation reactor, and the suspended matter, oil and some organic matter in the fracturing return fluid are removed by the demulsification, coagulation and flotation effects of the electro-flocculation reactor to obtain electro-flocculation effluent.

3. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 1 or 2, characterized in that In the second step, the process of electrochemical oxidation reaction treatment is as follows: the electrocoagulation effluent is sent to an electrochemical oxidation reactor for electrochemical oxidation reaction treatment, and the electrochemical reaction effluent is obtained after the COD, oil content and suspended solids in the electrocoagulation effluent are removed by the electrochemical oxidation reactor.

4. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 3, characterized in that In the third step, the aeration flotation treatment process is as follows: the effluent from the electrochemical reaction is sent to the aeration flotation device, and through a large amount of aeration, the oxygen content in the water is increased, the microbial activity in the water is increased, and a portion of small molecular organic matter is degraded. At the same time, small flocs, COD and suspended matter in the water are removed through flotation to obtain effluent after flotation.

5. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 4, characterized in that In the fourth step, the effluent after flotation is sent to the MBR biological treatment device. After the organic pollutants in the water are degraded by the microorganisms in the MBR biological treatment device, the solid-liquid separation is carried out through the MBR membrane bioreactor to obtain the fracturing return fluid that can meet the discharge standards.

6. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 5, characterized in that In the first step, during the electrocoagulation reaction treatment, the rated voltage of the electrocoagulation reactor is 2V to 7V, the treatment time is 20min to 30min, the plate spacing is 1cm to 3cm, and the plate material is one of iron, aluminum, and graphite; or / and, in the second step, during the electrochemical oxidation reaction treatment, the rated voltage of the electrochemical oxidation reactor is 5V to 10V, the treatment time is 20min to 40min, the plate spacing is 1cm to 3cm, and the plate material is graphite, titanium, ruthenium-iridium-titanium alloy, ruthenium-iridium alloy, iridium-tantalum alloy or / and, in the third step, during aeration flotation treatment, the air-water ratio in the aeration volume is 2 to 8:1, and the aeration time is 2h to 4h; or / and, in the fourth step, during MBR biological treatment, the reactor type is one of an integrated membrane bioreactor and a composite membrane bioreactor, the membrane component is one of a hollow fiber membrane and a plate membrane, the membrane adopts one of a microfiltration membrane and an ultrafiltration membrane, the membrane pore size is 0.01 micron to 0.04 micron, the dissolved oxygen is 2mg / L to 4mg / L, and the residence time is 12h to 36h.

7. The method for treating fracturing flowback fluid to meet the discharge standards according to claim 6, characterized in that In the first step, the rated voltage of the electrocoagulation reactor is 5V, the processing time is 25min, the plate spacing is 2cm, and the plate material is iron; or / and, in the second step, the rated voltage of the electrochemical oxidation reactor is 7V, the processing time is 30min, the plate spacing is 2cm, and the plate material is ruthenium iridium titanium; or / and, in the third step, the gas-water ratio in the aeration volume is 4:1, and the aeration time is 3h; or / and, in the fourth step, the reactor type is a composite membrane bioreactor, the membrane component is a hollow fiber membrane, the membrane uses a microfiltration membrane, the membrane pore size is 0.03 microns, the dissolved oxygen is 3mg / L, and the residence time is 24h.

8. A device for implementing the method for treating fracturing flowback fluid to meet the discharge standards according to any one of claims 1 to 7, characterized in that The invention comprises an electric flocculation reactor, an electrochemical oxidation reactor, an aeration flotation device and an MBR biological treatment device. The lower inlet of the electric flocculation reactor is fixedly connected with a water supply pipeline, the lower outlet of the electric flocculation reactor and the lower inlet of the electrochemical oxidation reactor are fixedly connected with a first water outlet pipeline, the upper outlet of the electrochemical oxidation reactor and the lower inlet of the aeration flotation device are fixedly connected with a second water outlet pipeline, the lower outlet of the aeration flotation device and the upper inlet of the MBR biological treatment device are fixedly connected with a third water outlet pipeline, and the upper outlet of the MBR biological treatment device is fixedly connected with a fourth water outlet pipeline.

9. The device according to claim 8, characterized in that It also includes an air compressor, a first aeration pipeline is fixedly connected between the air compressor outlet and the bottom air inlet of the aeration flotation device, a second aeration pipeline is fixedly connected between the first aeration pipeline and the bottom air inlet of the MBR biological treatment device, and a third aeration pipeline is fixedly connected between the second aeration pipeline and the upper air inlet of the MBR biological treatment device.

10. The device according to claim 8 or 9, characterized in that A first circulation pipeline is fixedly connected between the middle outlet at the right end of the electrocoagulation reactor and the middle inlet at the left end of the electrocoagulation reactor, a second circulation pipeline is fixedly connected between the middle outlet at the right end of the electrochemical oxidation reactor and the middle inlet at the left end of the electrochemical oxidation reactor, circulation pumps are fixedly installed on the first circulation pipeline and the second circulation pipeline, and water delivery pumps are fixedly installed on the third water outlet pipeline and the fourth water outlet pipeline.

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