Shale gas high-salinity wastewater electrochemical catalysis coupling membrane separation low-carbon treatment method

Abstract

The invention belongs to the field of oil and gas field high-salinity wastewater treatment, and particularly relates to a shale gas high-salinity wastewater electrochemical catalysis coupling membrane separation low-carbon treatment method which comprises the treatment steps of pretreatment, electrocatalytic oxidation, membrane separation, salt recycling and product recovery, intelligent management and control, energy coupling and the like. The dissolved air flotation unit generates micro-nano bubbles through a venturi-rotational flow coupling device and cooperates with PAC / PAM to realize efficient flotation; softening agents are added into the multi-stage sedimentation tank by stages, closed-loop control is carried out, and soluble barium, boron, fluoride and hardness are removed; the electrochemical oxidation unit strengthens mass transfer through ultrasonic waves and degrades organic matters difficult to treat; the membrane treatment realizes up-to-standard discharge of wastewater through a hollow fiber membrane bioreactor-roll type ultrafiltration membrane-anti-pollution type reverse osmosis membrane integrated system; the magnetic control evaporation crystallizer utilizes the magnetic field gradient and the temperature gradient to cooperatively regulate and control the crystallization process, the membrane separation strong brine is subjected to quality separation treatment, and high-purity salt products are produced. The method provided by the invention can effectively realize up-to-standard discharge treatment of shale gas fracturing flowback wastewater and resource utilization of evaporative crystallization salt, is also suitable for treating shale gas recovery wastewater with similar water quality characteristics, and has good popularization and application prospects.

Description

Technical Field

[0001] The present invention relates to the field of high-salt wastewater treatment in oil and gas fields, and particularly to a low-carbon treatment method for shale gas high-salt wastewater by electrochemically catalytic coupling membrane separation. Background Art

[0002] The fracturing flowback wastewater and gas production wastewater generated during shale gas extraction belong to high-salt wastewater, which has the characteristics of complex components (COD can reach more than 10,000 mg / L), high chloride content (can reach more than 50,000 mg / L), high TDS content (can reach more than 50,000 mg / L), poor biodegradability, high treatment difficulty, and high cost. Existing electrocatalytic oxidation mostly uses a direct current electric field (such as CN112573617A). Although it can degrade organic matter, the electrode surface is prone to fouling (fouling rate > 0.1 mm / h), and the anodic chlorine evolution reaction (Cl - →ClO - ) in a high-salt environment leads to electrode corrosion (weight loss rate > 5 mg / cm²·h). Some studies have tried to introduce magnetic field assistance (such as CN114314694A), but the magnetic field direction is parallel to the water flow (the included angle < 30°), and the Lorentz force has limited effect on mass transfer enhancement (the mass transfer coefficient is increased by < 20%). Ceramic membranes (such as Al 2 O 3 -based membranes) are used for high-salt wastewater treatment due to their good corrosion resistance (such as US20180244563A1), but the absolute value of the ζ potential on the membrane surface < 20 mV, and it is easy to adsorb charged colloids (membrane flux attenuation rate > 30%). The titanium dioxide modified membrane (such as CN113877377A) has photocatalytic function, but the nanocrystalline structure is unstable (lattice distortion rate > 15%), and it is easy to be blocked during long-term operation. Traditional evaporation crystallization (such as multi-effect evaporation) has high energy consumption, and the crystal size distribution is wide (10 - 500 μm), resulting in low salt purity. The magnetization crystallization technology (such as CN110482713A) promotes nucleation by applying an external magnetic field, but does not combine with pretreatment water quality softening (when the hardness > 100 mg / L, the crystallization efficiency decreases by 40%), and the proportion of seed addition lacks dynamic regulation. In terms of energy and intelligent control, existing systems mostly rely on grid power supply (such as CN113233554A), the photovoltaic coupling ratio < 30%, the MPPT efficiency is only 85% - 90%, and intelligent control mostly uses the PID algorithm (such as CN112850888A), but does not combine with the pretreatment effluent water quality parameters (such as COD, TDS) to dynamically optimize the electric field parameters, resulting in an energy consumption fluctuation > 15%. Therefore, it is urgent to develop a low-carbon treatment technology for shale gas high-salt wastewater that integrates efficient mass transfer enhancement, anti-pollution membrane separation, precise crystallization control, and intelligent energy coupling. Summary of the Invention

[0003] To address the above key technical problems, the present invention provides a low-carbon treatment method for shale gas high-salt wastewater through electrochemical catalysis coupled with membrane separation. Through mass transfer enhancement, anti-pollution design, and intelligent optimization, low-carbon, economical, and efficient treatment of shale gas high-salt wastewater can be achieved.

[0004] The object of the present invention is achieved by the following technical solutions: A low-carbon treatment method for shale gas high-salt wastewater through electrochemical catalysis coupled with membrane separation, characterized by comprising the following steps: (1) Electro-catalytic oxidation: The pretreated shale gas high-salt wastewater is introduced into a three-dimensional multi-channel electrochemical catalytic reactor, and a corrosion-resistant and self-cleaning composite electrode is used. Electro-catalytic oxidation is carried out under the action of a pulsed electric field (frequency 100 - 500 Hz, duty cycle 20 - 50%), and an alternating magnetic field (0.5 - 2 T) is synchronously applied during the reaction. The mass transfer efficiency is enhanced in the magnetization separation zone through the Lorentz force, where the magnetic field direction is orthogonally arranged with the water flow direction at 90° ± 5°, and the magnetic induction intensity and the dosing ratio of crystallization crystal seeds (NaCl:CaCO 3 =1:0.1 - 0.5) are controlled in combination with the low hardness characteristics after pretreatment to achieve magnetization separation of salts (the crystal grain size is controlled within 50 - 200 μm); (2) Membrane separation: The mixed liquid after electro-catalytic oxidation is subjected to solid-liquid separation through a catalytic separation membrane module, where the separation membrane is a cobalt titanate composite silica fiber-based membrane or a titanium dioxide nanocrystal-loaded ceramic membrane, the membrane pore size is 0.1 - 5 μm, and the absolute value of the surface ζ potential ≥ 30 mV; (3) Salt resource utilization and product recovery: The separated high-purity salts (TOC < 50 ppm) are recovered through magnetization crystallization. In view of the residual PAC characteristics after pretreatment, Al 2 (SO 4 ) 3 crystal nucleus inducer (dosing amount 0.1 - 0.5 g / L) is added to control the crystal grain size within 50 - 200 μm, and the by-products of electro-catalytic oxidation are used to recover high-value organic substances through extraction or adsorption; (4) Intelligent control: The pH, conductivity, current density, and salt concentration are monitored in real time through an intelligent control system. A machine learning dynamic optimization module based on an LSTM neural network is trained based on the COD, TDS, and energy consumption data of the pretreated effluent, and the pulsed electric field parameters and magnetic field intensity are regulated in combination with a PID feedback algorithm, with an error range ≤ 5%; (5) Energy coupling: The reactor power supply system is jointly powered by solar photovoltaic panels and energy storage batteries. The tilt angle of the double-sided photovoltaic panels is 30 - 45°, and the orientation is within the range of ± 5° of the declination angle matching the local geographical latitude. The MPPT efficiency ≥ 95%. The capacity of the energy storage battery (lithium-ion battery or flow battery, cycle life ≥ 5000 times) matches the energy consumption fluctuation of the pretreatment unit by ± 10%, and the electric energy conversion efficiency ≥ 85%.

[0005] The pretreatment includes that the wastewater sequentially passes through a flotation unit (to remove suspended solids and oils), a chemical precipitation water softening unit (adding Ca(OH) 2 and Na 2 CO 3 , controlling the hardness of the effluent ≤ 50 mg / L, Ca 2+ ≤ 15 mg / L, Mg 2+ ≤ 5 mg / L) and a coagulation and precipitation unit (adding 50 - 300 mg / L of PAC and 2 - 10 mg / L of PAM, with the turbidity of the effluent ≤ 10 NTU), and adjusting the pH to 6 - 9.

[0006] The preparation method of the corrosion - resistant and self - cleaning composite electrode includes: (a) Using a Co@MIM catalyst doped with transition metals (M = Zn, Mn, Cu, Fe, Ni, doping amount is 5 - 20% of the molar amount of Co) as the active component, and obtaining a catalyst modified with transition metal oxides through annealing treatment (200 - 400 °C, heating rate 2 - 5 °C / min); (b) Mixing the catalyst with a polytetrafluoroethylene dispersion liquid and then coating it on the surface of a titanium - based or carbon - based electrode, and forming a self - cleaning coating through calcination (350 - 370 °C), the thickness of the coating is 10 - 50 μm, the contact angle of the coating ≥ 150°, and the surface roughness Ra ≤ 0.1 μm; (c) Further coating a single - layer graphene layer on the electrode surface, and the graphene layer forms a covalent bonding interface through plasma treatment to enhance the tolerance to residual PAC after pretreatment and the chloride ion corrosion resistance.

[0007] The three - dimensional multi - channel electrochemical catalytic reactor includes: the anode area and the cathode area are arranged alternately, and the plate spacing is 5 - 20 mm; an ultrasonic assistance device with a frequency of 20 - 100 kHz is arranged in the reactor, and the distance between the ultrasonic probe and the electrode surface ≤ 5 mm, the sound intensity density ≥ 0.5 W / cm², and the ultrasonic frequency and the fundamental frequency of the pulsed electric field are in an integer - multiple relationship to inhibit the colloidal adsorption and scaling in the low - turbidity wastewater after pretreatment; a micro - bubble aeration system is integrated at the bottom, the gas - water ratio is 1:5 - 1:10, the bubble diameter ≤ 50 μm, and a surfactant (sodium dodecyl sulfate 0.1 - 1 mg / L) is added to reduce the probability of bubble coalescence.

[0008] The pulsed electric field parameters are optimized as follows: the initial current density is 20 - 100 mA / cm², which is dynamically adjusted to 5 - 50 mA / cm² according to the COD value of the effluent after pretreatment (50 - 500 mg / L), and the adjustment frequency is negatively correlated with the magnetic field strength; the pulse waveform is a square wave or a sawtooth wave, the peak voltage ≤ 5 V, and when COD > 300 mg / L, a gradient pulse mode with an increasing duty cycle is adopted, and an intermittent pulse mode (working cycle 30 - 60 s, interval 10 - 20 s) is adopted in the low COD range (< 100 mg / L) to reduce energy consumption.

[0009] The recovery of the high - value - added products includes: the percarbonamide produced by electro - catalytic oxidation is adsorbed and recovered by an anion - exchange resin (styrene - divinylbenzene copolymer modified with quaternary amine groups, exchange capacity ≥ 1.8 mmol / g); the organic acid by - products are selectively separated by a nanofiltration membrane (cut - off molecular weight 200 - 500 Da).

[0010] The device for the low - carbon treatment method of shale gas high - salt wastewater by electrochemical catalysis coupling membrane separation includes a pretreatment unit, an electrochemical catalytic reactor, a membrane separation module, a magnetization crystallizer, a product recovery module and an intelligent control terminal; the electrochemical catalytic reactor is internally provided with a self - cleaning electrode and a pulsed power supply, and externally integrated with a solar power supply interface.

[0011] A buffer tank is arranged between the pretreatment unit and the electrochemical catalytic reactor of the device, and the volume ratio is 1:3 - 1:5; the membrane separation module is connected in series with the electrochemical catalytic reactor through a micro - channel, the membrane flux ≥ 50 L / (m²·h), and the transmembrane pressure difference ≤ 0.1 MPa.

[0012] The beneficial effects of the present invention are: The present invention provides an electrochemically catalytic coupled membrane separation low-carbon treatment method for shale gas high-salt wastewater. Through the collaborative innovation of electrochemically catalytic coupled membrane separation technology and intelligent energy systems, the treatment efficiency and resource utilization level of shale gas high-salt wastewater can be significantly improved, and significant economic and environmental benefits can be obtained. Through the orthogonal arrangement design of alternating magnetic fields and pulsed electric fields and the design of self-cleaning electrodes and anti-pollution membranes, the present invention can achieve efficient mass transfer and enhanced anti-pollution ability of the treatment system, effectively reduce the membrane flux attenuation rate, inhibit colloid adsorption and scaling, and extend the electrode life. Based on the low hardness characteristics after pretreatment, combined with the dynamic matching of magnetic induction intensity and crystal seed dosing ratio, and the synchronous dosing of crystal nucleus inducing agents, the present invention can achieve precise control of crystal grain size and high-purity salt recovery. Through the LSTM-PID dual-mode dynamic regulation and efficient solar energy supply, the present invention can achieve intelligent optimization of the treatment system and significantly reduce energy consumption. Through anion exchange resins and nanofiltration membranes, the present invention can respectively achieve the efficient recovery and utilization of percarbonamide and organic acid by-products. The present invention adopts a modular integrated design of each treatment unit, which is suitable for distributed treatment of shale gas well sites and can solve problems such as the dispersion of mountain shale gas well development and the inconvenience of centralized collection and treatment of wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. is a process flow diagram of an electrochemically catalytic coupled membrane separation low-carbon treatment method for shale gas high-salt wastewater. DETAILED DESCRIPTION OF THE INVENTION

[0014] The technical solution of the present invention is: an electrochemically catalytic coupled membrane separation low-carbon treatment method for shale gas high-salt wastewater, comprising the following steps: (1) Electro-catalytic oxidation: The pretreated shale gas high-salt wastewater is introduced into a three-dimensional multi-channel electrochemically catalytic reactor, and a corrosion-resistant and self-cleaning composite electrode is used. Under the action of a pulsed electric field (frequency 100 - 500 Hz, duty cycle 20 - 50%), electro-catalytic oxidation is carried out, and an alternating magnetic field (0.5 - 2 T) is synchronously applied during the reaction. In the magnetization separation zone where the mass transfer efficiency is enhanced by the Lorentz force, the magnetic field direction is orthogonally arranged at 90° ± 5° to the water flow direction, and combined with the low hardness characteristics after pretreatment, the magnetic induction intensity and the crystallization crystal seed dosing ratio (NaCl:CaCO 3 = 1:0.1 - 0.5) are controlled to achieve magnetization separation of salts (the crystal grain size is controlled within 50 - 200 μm); (2) Membrane separation: The mixed liquid after electro-catalytic oxidation is subjected to solid-liquid separation through a catalytic separation membrane module, wherein the separation membrane is a cobalt titanate composite silica fiber-based membrane or a titanium dioxide nanocrystal-loaded ceramic membrane, the membrane pore size is 0.1 - 5 μm, and the absolute value of the surface ζ potential is ≥ 30 mV; (3) Salt resource utilization and product recovery: The separated high-purity salt (TOC < 50 ppm) is recovered by magnetization crystallization. Considering the characteristics of residual PAC after pretreatment, Al 2 (SO 4 ) 3 crystal nucleus inducer (dosage 0.1 - 0.5 g / L) is added to control the crystal size to be 50 - 200 μm. The by-products of electrocatalytic oxidation are recovered by extraction or adsorption to obtain high-value-added organic substances; (4) Intelligent control: The pH, conductivity, current density, and salt concentration are monitored in real time through an intelligent control system. Based on the COD, TDS, and energy consumption data of the pretreated effluent, a machine learning dynamic optimization module based on an LSTM neural network is trained, and the pulse electric field parameters and magnetic field strength are regulated in combination with a PID feedback algorithm, with an error range ≤ 5%; (5) Energy coupling: The power supply system of the reactor is jointly powered by solar photovoltaic panels and energy storage batteries. The tilt angle of the double-sided photovoltaic panels is 30 - 45°, and the orientation is within the range of the declination angle ± 5° matching the local geographical latitude. The MPPT efficiency ≥ 95%. The capacity of the energy storage battery (lithium-ion battery or flow battery, cycle life ≥ 5000 times) matches the energy consumption fluctuation of the pretreatment unit ± 10%, and the electric energy conversion efficiency ≥ 85%.

[0015] The pretreatment includes the wastewater passing through a flotation unit (to remove suspended solids and oils), a chemical precipitation water softening unit (adding Ca(OH) 2 and Na 2 CO 3 , controlling the hardness of the effluent ≤ 50 mg / L, Ca 2+ ≤ 15 mg / L, Mg 2+ ≤ 5 mg / L) and a coagulation sedimentation unit (adding PAC 50 - 300 mg / L, PAM 2 - 10 mg / L, the turbidity of the effluent ≤ 10 NTU), and adjusting the pH to 6 - 9.

[0016] The preparation method of the corrosion-resistant and self-cleaning composite electrode includes: (a) Using a Co@MIM catalyst doped with transition metals (M = Zn, Mn, Cu, Fe, Ni, doping amount 5 - 20% of the Co molar amount) as the active component, a catalyst modified with transition metal oxides is obtained through annealing treatment (200 - 400 °C, heating rate 2 - 5 °C / min); (b) Mixing the catalyst with a polytetrafluoroethylene dispersion liquid and then coating it on the surface of a titanium-based or carbon-based electrode, and forming a self-cleaning coating through calcination (350 - 370 °C). The thickness of the coating is 10 - 50 μm, the contact angle of the coating ≥ 150°, and the surface roughness Ra ≤ 0.1 μm; (c) The electrode surface is further coated with a single-layer graphene layer, and the graphene layer forms a covalent bonding interface through plasma treatment to enhance the tolerance to residual PAC after pretreatment and the chloride ion corrosion resistance.

[0017] The three-dimensional multi-channel electrochemical catalytic reactor includes: an anode area and a cathode area arranged alternately, with a plate spacing of 5-20 mm; an ultrasonic assistance device with a frequency of 20-100 kHz is arranged in the reactor, and the distance between the ultrasonic probe and the electrode surface is ≤5 mm, the sound intensity density is ≥0.5 W / cm², and the ultrasonic frequency is an integer multiple of the fundamental frequency of the pulsed electric field to inhibit colloidal adsorption and scaling in the low-turbidity wastewater after pretreatment; a microbubble aeration system is integrated at the bottom, with an air-water ratio of 1:5-1:10, the bubble diameter is ≤50 μm, and a surfactant (sodium dodecyl sulfate 0.1-1 mg / L) is added to reduce the probability of bubble coalescence.

[0018] The pulsed electric field parameters are optimized in the following way: the initial current density is 20-100 mA / cm², and it is dynamically adjusted to 5-50 mA / cm² according to the COD value (50-500 mg / L) of the effluent after pretreatment, and the adjustment frequency is negatively correlated with the magnetic field strength; the pulsed waveform is a square wave or a sawtooth wave, the peak voltage is ≤5 V, when COD>300 mg / L, a gradient pulse mode with an increasing duty cycle is adopted, and an intermittent pulse mode (working cycle 30-60 s, interval 10-20 s) is adopted in the low COD range (<100 mg / L) to reduce energy consumption.

[0019] The recovery of high-value products includes: the percarbonamide produced by electrocatalytic oxidation is adsorbed and recovered by an anion exchange resin (styrene-divinylbenzene copolymer modified with quaternary amine groups, exchange capacity ≥1.8 mmol / g); the organic acid by-products are selectively separated by a nanofiltration membrane (cut-off molecular weight 200-500 Da).

[0020] The device for the electrochemical catalytic coupling membrane separation low-carbon treatment method of shale gas high-salt wastewater includes a pretreatment unit, an electrochemical catalytic reactor, a membrane separation module, a magnetization crystallizer, a product recovery module and an intelligent control terminal; a self-cleaning electrode and a pulsed power supply are arranged in the electrochemical catalytic reactor, and a solar power supply interface is integrated externally.

[0021] A buffer tank is arranged between the pretreatment unit and the electrochemical catalytic reactor of the device, with a volume ratio of 1:3-1:5; the membrane separation module and the electrochemical catalytic reactor are connected in series through a microchannel, the membrane flux is ≥50 L / (m²·h), and the transmembrane pressure difference is ≤0.1 MPa.

[0022] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to these embodiments. Embodiment

[0023] Preparation of corrosion-resistant and self-cleaning composite electrode: Dissolve Co(NO 3 ) 2 ·6H 2 O and Fe(NO 3 ) 3 ·9H 2 O in deionized water according to the molar ratio of Co:Fe of 10:1, and add 2-methylimidazole (MIM) to make the molar ratio of metal ions to ligands 1:4; stir at room temperature for 24 h and then centrifuge. The obtained Co@Fe-MIM precursor is annealed in an N 2 atmosphere at a heating rate of 3 °C / min to 300 °C for 2 h to obtain the FeO / Co 3 O 4 composite oxide catalyst (BET specific surface area reaches 210 m² / g); then mix the catalyst with 60% polytetrafluoroethylene (PTFE) dispersion liquid according to the mass ratio of 7:3, and add isopropyl alcohol for ultrasonic dispersion to form a slurry; then use the doctor blade coating method to evenly coat the slurry on the surface of the pretreated titanium mesh (specification: 100 mesh, thickness 0.5 mm), and control the wet film thickness to 80 μm; then calcine in an air atmosphere at 360 °C for 30 min to obtain a micro-nano composite coating with a thickness of 35 ± 3 μm, measure the contact angle of 155° (ASTM D7334 standard), and the surface roughness Ra = 0.08 μm (measured by a white light interferometer); then grow monolayer graphene (number of layers < 3, defect density < 0.1%) on the copper foil by chemical vapor deposition, and transfer it to the coating surface by the electrochemical bubbling method; finally, perform Ar plasma treatment (power 200 W, treatment time 5 min) to form a C-O-Ti covalent bonding interface (531.5 eV characteristic peak detected by XPS) to prepare the corrosion-resistant and self-cleaning composite electrode. Through test verification, it is found that the comprehensive performance such as corrosion resistance, self-cleaning property, and PAC tolerance of the prepared corrosion-resistant and self-cleaning composite electrode is significantly improved. In 3.5% NaCl solution (25 °C), the corrosion current density of the composite electrode decreases from 1.2×10 -6 A / cm² before treatment to 3.8×10 -8 A / cm² (ASTM G59 standard); after 50 cycles of oil pollution (n-hexadecane) - cleaning, its contact angle still remains above 150°; when operating in wastewater containing 50 mg / L polyaluminum chloride (PAC) for 500 h, the electrode potential shift is less than 10 mV.

[0024] This example treats shale gas high-salt wastewater with a COD of 2000 mg / L, a TDS of 15000 mg / L, a hardness (calculated as CaCO 3 ) of 450 mg / L, and an oil content of 200 mg / L. The wastewater enters the air flotation unit in the pretreatment for treatment, and the effluent (the removal rate of suspended solids and oil is 95%) enters the chemical precipitation softening treatment (Ca(OH)2 and Na 2 CO 3 Dosages are 1.2 g / L and 0.8 g / L respectively, and the effluent (Ca² + = 12 mg / L, Mg² + = 3 mg / L) enters the coagulation and sedimentation treatment (PAC and PAM dosages are 200 mg / L and 6 mg / L respectively); the effluent from the coagulation treatment (turbidity = 8 NTU, pH = 7.5) enters the electrocatalytic oxidation treatment unit. The plate spacing of the three-dimensional reactor is 10 mm, the pulse electric field frequency is 300 Hz (square wave), the duty cycle is 40%, the magnetic field strength is 1.5 T (orthogonal angle 90° ± 3°), the seeding ratio (NaCl:CaCO 3 ) is 1:0.3, a Co@MIM composite electrode doped with 15% Fe is used (coating contact angle 152°, roughness Ra = 0.08 μm), the ultrasonic frequency is 60 kHz (3 times the pulse fundamental frequency), the air-water ratio of microbubble aeration is 1:8, and the bubble diameter is 40 μm; the effluent from the electrocatalytic oxidation treatment enters the membrane separation treatment unit, and a cobalt titanate composite silica fiber membrane with a ζ potential of -35 mV (pore size 0.5 μm) is used; the training data set of the intelligent control LSTM neural network contains 200 groups of historical operation data, the current density is dynamically adjusted to 35 mA / cm² (when COD = 150 mg / L), the tilt angle of the double-sided photovoltaic panel of the energy system is 38° (matching the local latitude 35° ± 3°), and the capacity fluctuation of the lithium-ion energy storage battery is controlled within +9%. The COD removal rate of the final treated effluent reaches 97.5%, the TDS recovery rate reaches 94.7%, the purity of the crystalline salt TOC = 32 ppm, the particle size is 120 ± 20 μm, the recovery rate of urea peroxide reaches 89%, and the photovoltaic power supply ratio reaches 78%. Example

[0025] In this example (the parts not specified below are implemented according to Example 1), the shale gas fracturing flowback wastewater is treated. The initial COD of the wastewater is 3500 mg / L, the TDS is 25000 mg / L, the hardness (calculated as CaCO 3 ) is 600 mg / L, and the petroleum substances are 300 mg / L. The wastewater enters the flotation unit in the pretreatment, and the effluent (98% of suspended solids and oils removed) enters the chemical precipitation and softening treatment (the dosages of Ca(OH) 2 and Na 2 CO 3 are 1.5 g / L and 1.0 g / L respectively), and the effluent (Ca² + = 10 mg / L, Mg² += 2 mg / L) enters the coagulation and sedimentation treatment (the dosages of PAC and PAM are 250 mg / L and 8 mg / L respectively); the effluent from the coagulation treatment (turbidity = 6 NTU, pH = 8.2) enters the electrocatalytic oxidation treatment unit. The plate spacing of the three-dimensional reactor is 15 mm, the pulse electric field frequency is 400 Hz (sawtooth wave), the duty cycle is 35%, the magnetic field strength is 2 T (orthogonal angle 90° ± 2°), and the seeding addition ratio (NaCl:CaCO 3 ): 1:0.4. The electrode uses a Co@MIM composite electrode doped with 18% Ni (the contact angle of the coating is 155°, roughness Ra = 0.07 μm), the ultrasonic frequency is 80 kHz (2 times the pulse fundamental frequency), the gas-water ratio of microbubble aeration is 1:6, and the bubble diameter is 30 μm; the effluent from the electrocatalytic oxidation treatment enters the membrane separation treatment unit, and a titanium dioxide nanocrystalline ceramic membrane with ζ potential = +38 mV (pore size 0.2 μm) is used; the intelligent control LSTM neural network predicts the change of COD in real time, dynamically switches the gradient pulse mode (the duty cycle increases from 30% to 45% when COD = 380 mg / L), the tilt angle of the double-sided photovoltaic panel of the energy system is 42° (matching the local latitude 40° ± 2°), and the capacity fluctuation of the flow battery is +8%. The COD removal rate of the final treated effluent is 98.1%, the TDS recovery rate is 95.2%, the purity of the crystalline salt TOC = 28 ppm, the particle size is 180 ± 25 μm, the recovery rate of organic acids is 92% (the rejection rate of the nanofiltration membrane is ≥ 90%), and the proportion of photovoltaic power supply is 82%.

[0026] This example treats the wastewater of Example 1. The pretreatment only uses simple filtration for treatment. The effluent (hardness 380 mg / L, turbidity = 25 NTU) enters the electrochemical unit for treatment. A conventional electrochemical reactor, ordinary titanium electrodes, a DC electric field (voltage 4 V), no magnetic field effect, no seeding addition, and the particle size is not controlled during the crystallization process are used; the effluent from the electrochemical treatment enters the membrane separation treatment unit, and an ordinary ceramic membrane (ζ potential = -15 mV, pore size 1 μm) is used for treatment; an ordinary control system is used, the fixed current density is 80 mA / cm², and the energy system is powered by the mains. The COD removal rate of the final treated effluent is 77.5%, the TDS recovery rate is 70%, the purity of the crystalline salt TOC = 210 ppm, the particle size is 10 - 500 μm, and the percarbamide is not recovered (the resin is severely blocked).

[0027] This embodiment treats the wastewater of Embodiment 2. Only multi-media filtration is used for pretreatment, and the effluent (hardness 420 mg / L, turbidity = 35 NTU) enters the electrochemical unit for treatment. Graphite electrodes are used, in constant current mode (100 mA / cm²), without magnetic field; the treated effluent is further treated by a reverse osmosis membrane (ζ potential = -10 mV, pore size 0.5 μm); a common control system is adopted, and the energy system is powered by the mains. The final treated effluent has a COD removal rate of 84.3%, a TDS recovery rate of 76%, the purity of the crystalline salt TOC = 180 ppm, uneven particle size (50 - 400 μm), and the organic acids are not separated (serious membrane fouling).

[0028] Through comparative analysis of the examples and comparative examples, it is found that the present invention is significantly superior to the traditional process in terms of deep COD removal, high-value salt recovery, system energy efficiency ratio, etc. through the coupling of electricity-magnetism-membrane multi-techniques, intelligent dynamic regulation and low-carbon energy supply design. The alternating magnetic field combines with the gradient pulse electric field to enhance mass transfer, the LSTM algorithm dynamically optimizes the current density, and the magnetization crystallization + Al 2 (SO 4 ) 3 inducer precisely controls crystal growth, the membrane with ζ potential ≥ 30 mV inhibits the attachment of organic substances, and realizes the high-value recovery of by-products such as urea peroxide and organic acids, as well as the intelligent dynamic optimization and control of the treatment system and the coupling of energy and treatment, with remarkable economic and environmental benefits, meeting the industrial requirements of "low-carbon, resource-based, and intelligent" for shale gas wastewater treatment, and having outstanding industrial application value.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention. The protection scope claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-carbon treatment method for shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation, characterized in that: The following steps are involved: (1) Electrocatalytic oxidation: The pretreated shale gas high-salinity wastewater is passed into a three-dimensional multi-channel electrochemical catalytic reactor, and electrocatalytic oxidation is carried out under the action of a pulsed electric field (frequency 100-500 Hz, duty cycle 20-50%) using a corrosion-resistant and self-cleaning composite electrode. During the reaction, an alternating magnetic field (0.5-2T) is applied simultaneously to enhance the mass transfer efficiency of the magnetic separation zone through the Lorentz force. The magnetic field direction is orthogonal to the water flow direction at 90°±5°, and the magnetic induction intensity and the crystal seed addition ratio (NaCl:CaCO3=1:0.1-0.5) are controlled in combination with the low hardness characteristics after pretreatment to achieve magnetic separation of salt (the particle size of the crystal particles is controlled at 50-200μm); (2) Membrane separation: The mixed liquid after electrocatalytic oxidation is separated into solid and liquid by passing through a catalytic separation membrane assembly, wherein the separation membrane is a cobalt titanate composite silica fiber-based membrane or a titanium dioxide nano-single crystal-loaded ceramic membrane, the membrane pore size is 0.1-5 μm and the absolute value of the surface zeta potential is ≥30 mV; (3) Salt resource utilization and product recovery: The separated high-purity salt (TOC < 50ppm) is recovered by magnetic crystallization. According to the characteristics of residual PAC after pretreatment, Al2(SO4)3 nucleus inducer (dosage 0.1-0.5g / L) is added simultaneously to control the crystal particle size to 50-200μm. The electrocatalytic oxidation by-products are extracted or adsorbed to recover high-value-added organic matter; (4) Intelligent control: The intelligent control system monitors pH, conductivity, current density and salt concentration in real time. The machine learning dynamic optimization module based on the LSTM neural network is trained based on the pre-treated effluent COD, TDS and energy consumption data. The pulse electric field parameters and magnetic field intensity are controlled in combination with the PID feedback algorithm, with an error range of ≤5%; (5) Energy coupling: The reactor power supply system is powered by solar photovoltaic panels and energy storage batteries. The bifacial photovoltaic panels are tilted at an angle of 30-45° and face a declination angle within the range of ±5° that matches the local geographical latitude. The MPPT efficiency is ≥95%. The capacity of the energy storage battery (lithium-ion battery or liquid flow battery, with a cycle life of ≥5000 times) matches the energy consumption fluctuation of the pretreatment unit by ±10%, and the power conversion efficiency is ≥85%.

2. The method for treating shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation and low-carbon treatment according to claim 1 is characterized in that: The pretreatment includes the wastewater passing through the flotation unit (removing suspended matter and oil), the chemical precipitation water softening unit (adding Ca(OH)2 and Na2CO3 to control the effluent hardness ≤50mg / L, Ca 2+ ≤15mg / L, Mg 2+ ≤5mg / L) and coagulation sedimentation unit (adding PAC 50-300mg / L, PAM 2-10mg / L, effluent turbidity ≤10NTU), adjust the pH to 6-9.

3. The method for treating shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation and low-carbon treatment according to claim 1, characterized in that: The preparation method of the corrosion-resistant-self-cleaning composite electrode comprises: (a) Using Co@MIM catalyst doped with transition metal (M = Zn, Mn, Cu, Fe, Ni, with a doping amount of 5-20% of the molar amount of Co) as the active component, a transition metal oxide-modified catalyst was obtained by annealing (200-400°C, heating rate 2-5°C / min); (b) The catalyst is mixed with a polytetrafluoroethylene dispersion and then coated on the surface of a titanium-based or carbon-based electrode, and calcined (350-370°C) to form a self-cleaning coating with a coating thickness of 10-50 μm, a coating contact angle of ≥150°, and a surface roughness Ra of ≤0.1 μm; (c) The electrode surface is further coated with a single-layer graphene layer, and the graphene layer is plasma treated to form a covalently bonded interface to enhance the tolerance to residual PAC after pretreatment and the resistance to chloride ion corrosion.

4. The method for treating shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation and low-carbon treatment according to claim 1, characterized in that: The three-dimensional multi-channel electrochemical catalytic reactor comprises: the anode area and the cathode area are arranged alternately, and the distance between the plates is 5-20mm; an ultrasonic auxiliary device with a frequency of 20-100kHz is arranged in the reactor, and the distance between the ultrasonic probe and the electrode surface is ≤5mm, the sound intensity density is ≥0.5W / cm², and the ultrasonic frequency is an integer multiple of the fundamental frequency of the pulsed electric field, so as to inhibit the colloid adsorption and scaling in the low turbidity wastewater after pretreatment; a microbubble aeration system is integrated at the bottom, the air-water ratio is 1:5-1:10, the bubble diameter is ≤50μm, and a surfactant (sodium dodecyl sulfate 0.1-1mg / L) is added to reduce the probability of bubble merging.

5. The method for treating shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation and low-carbon treatment according to claim 1, characterized in that: The pulse electric field parameters are optimized in the following ways: the initial current density is 20-100mA / cm², which is dynamically adjusted to 5-50mA / cm² according to the COD value of the effluent after pretreatment (50-500mg / L), and the adjustment frequency is negatively correlated with the magnetic field strength; the pulse waveform is a square wave or a sawtooth wave, and the peak voltage is ≤5V. When COD>300mg / L, a gradient pulse mode with increasing duty cycle is adopted, and an intermittent pulse mode (working cycle 30-60s, interval 10-20s) is adopted in the low COD range (<100mg / L) to reduce energy consumption.

6. The method for treating shale gas high-salinity wastewater by electrochemical catalysis coupled membrane separation and low-carbon treatment according to claim 1, characterized in that: The high value-added product recovery includes: the percarbamide produced by electrocatalytic oxidation is adsorbed and recovered by anion exchange resin (quaternary amine-modified styrene-divinylbenzene copolymer, exchange capacity ≥1.8mmol / g); the organic acid by-products are selectively separated by a nanofiltration membrane (molecular weight cutoff 200-500Da).

7. A device for implementing the method according to any one of claims 1 to 6, characterized in that: It includes a pretreatment unit, an electrochemical catalytic reactor, a membrane separation component, a magnetized crystallizer, a product recovery module and an intelligent control terminal; the electrochemical catalytic reactor is equipped with a self-cleaning electrode and a pulse power supply, and an external integrated solar power supply interface.

8. The device according to claim 7, characterized in that A buffer tank is provided between the pretreatment unit and the electrochemical catalytic reactor, with a volume ratio of 1:3-1:5; the membrane separation component and the electrochemical catalytic reactor are connected in series through a microchannel, the membrane flux is ≥50L / (m²·h), and the transmembrane pressure difference is ≤0.1MPa.

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