Method and system for treating organic matters in high-salt and high-organic matter gas field produced water

Abstract

The invention belongs to the technical field of water treatment, relates to an organic matter treatment method and system for high-salt and high-organic matter gas field produced water, and aims to improve the degradation efficiency of organic matters in the gas field produced water, reduce the treatment cost and improve the quality of discharged water. The method comprises the steps of oil separation precipitation, iron-carbon micro-electrolysis, primary flocculation precipitation, halotolerant bacteria primary biochemical treatment, persulfate advanced oxidation, halotolerant bacteria secondary biochemical treatment, secondary flocculation precipitation and desalination. The system comprises a corresponding treatment unit, resource utilization of the gas field produced water is achieved, environmental pollution is reduced, and social and economic values are achieved. The effluent treated by the method disclosed by the invention meets the COD (Chemical Oxygen Demand) and TDS (Total Discharge Solids) standard requirements of dry farming and water farming crops in Standard for Water Quality of Farmland Irrigation GB5084-2005, and the COD standard requirements of the primary standard of Integrated Wastewater Discharge Standard GB16297-1996.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and relates to a method and system for treating organic matter in produced water of a high-salt and high-organic-matter gas field. Background Art

[0002] During the oil and gas production process, the groundwater brought out of the ground along with the natural gas is called gas field produced water. This water usually contains a large amount of petroleum substances, soluble salts, insoluble suspended solids, etc., and has the water quality characteristics of "high mineralization, high chloride ions, high hydrogen sulfide, high organic matter, and low pH". With the changes in the oil field production area, production conditions, oil layer characteristics and production methods, the water quality of gas field produced water also shows variability. If it is directly reinjected or discharged without treatment, it will seriously pollute the soil and damage the ecological environment.

[0003] In the process of realizing the present invention, the inventors found that the existing treatment technology of gas field produced water has at least one of the following technical problems:

[0004] a) High salinity and high organic content limit the direct resource utilization of gas field produced water, such as agricultural irrigation and industrial water. When treating this type of produced water, traditional RO membrane filtration and evaporation crystallization technology face the problem that high concentration of organic matter easily blocks the RO membrane or reduces the heat transfer coefficient of the evaporator.

[0005] b) Existing oil separation and flocculation sedimentation pretreatment methods are mainly aimed at removing floating oil organic matter and colloidal organic matter. However, since the suspended colloids adsorb a large amount of organic matter, a spatial stable state or a vacancy stable state is formed, resulting in poor agent reaction kinetics and poor flocculation sedimentation effect.

[0006] c) High concentrations of chloride ions (20,000 to 50,000 mg / L) in gas field produced water will quench free radicals, which limits the efficiency of conventional advanced oxidation technology in the degradation of organic matter in high-salinity wastewater, resulting in low efficiency in the degradation of organic matter in high-salinity wastewater.

[0007] d) High salinity inhibits the activity of conventional microorganisms, which affects the efficiency of degradation of organic matter in produced water through microbial metabolism, resulting in low efficiency of organic matter removal by conventional biochemical treatment.

[0008] e) In the later stage of gas production, the foam drainage gas production method used due to the reduction of gas content will add surfactants and other organic matter into the water. These surfactants will cause a large amount of foam to be generated during the treatment of gas field produced water, increasing the instability of the treatment system.

[0009] f) Existing treatment technologies often require evaporation of the entire water volume, which results in high energy consumption and high operating costs. Especially when treating produced water from gas fields with large water volumes, the treatment costs are too high and are not suitable for cost-sensitive application scenarios. Summary of the invention

[0010] In view of this, the present invention aims to provide a method for treating organic matter in high-salt and high-organic gas field produced water, effectively improve the degradation efficiency of organic matter in gas field produced water, reduce the treatment cost of gas field produced water, improve the quality of discharged water, ensure the stable operation of the treatment system, and provide favorable conditions for the resource utilization of gas field produced water.

[0011] The inventor has continuously innovated and reformed through long-term exploration and attempts, as well as multiple experiments and efforts, to solve the above technical problems. The technical solution provided by the present invention is to provide a method for treating organic matter in produced water of a high-salinity and high-organic gas field, comprising the following steps:

[0012] S1, oil separation and sedimentation, remove most of the petroleum organic matter through gravity oil separation;

[0013] S2, iron-carbon micro-electrolysis, using the iron-carbon micro-electrolysis galvanic cell reaction to degrade macromolecular petroleum organic matter and precipitate sulfur ions;

[0014] S3, primary flocculation and sedimentation, adding sodium hydroxide and PAM for flocculation and sedimentation to remove colloidal organic matter;

[0015] S4, primary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to degrade small molecular organic matter;

[0016] S5, persulfate advanced oxidation, using granular activated carbon to activate persulfate to produce free radicals to oxidize refractory organic matter;

[0017] S6, secondary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to further degrade organic matter;

[0018] S7, secondary flocculation sedimentation, adding PAC and PAM for flocculation sedimentation to remove suspended matter and microbial flocs;

[0019] S8. Desalination: select evaporative desalination or RO membrane concentration followed by evaporative desalination according to the TDS value of the produced water.

[0020] Preferably, the persulfate is sodium persulfate.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The method for treating produced water from a high-salt and high-organic gas field of the present invention significantly improves the efficiency of organic matter removal and reduces operating costs through the coupling of a series of innovative steps. First, the oil separation and precipitation step effectively removes most of the petroleum organic matter, followed by the iron-carbon micro-electrolysis technology to degrade the macromolecular organic matter, improve the biodegradability, and achieve desulfurization at the same time, eliminating the influence of sulfur ions on advanced oxidation and biochemical systems. The primary flocculation precipitation further removes colloidal organic matter and precipitates iron ions by accurately adding sodium hydroxide and PAM. Salt-tolerant bacteria are particularly suitable for high-salt environments. Through the primary biochemical treatment of salt-tolerant bacteria, small-molecule organic matter produced by iron-carbon micro-electrolysis is degraded. The persulfate advanced oxidation step uses granular activated carbon to activate sodium persulfate to produce free radicals, and performs advanced oxidation on organic matter that is difficult to degrade in the primary biochemical process. The secondary biochemical treatment of salt-tolerant bacteria further degrades small-molecule organic matter, prevents small-molecule organic matter from passing through the RO membrane or entering the evaporation condensate, and improves the water quality of the effluent. The secondary flocculation precipitation ensures further purification of the water quality through the addition of PAC and PAM. Finally, the desalination step selected according to the TDS value, whether it is evaporation desalination or RO membrane concentration desalination, can ensure that the effluent water quality meets the standards for farmland irrigation or industrial water use. Overall, the method of the present invention not only improves the removal efficiency of organic matter in gas field produced water, reduces the use of chemical agents, and reduces energy consumption, but also has excellent effluent water quality, is environmentally friendly, and has significant social and economic value.

[0023] On the basis of the above technical solution, the present invention can also be improved as follows:

[0024] Further:

[0025] In the step S1, the removal efficiency of petroleum organic matter is adjusted by controlling the oil separation sedimentation time and the oil layer height.

[0026] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0027] In step S1, the effective separation of the oil layer and water is ensured by precisely controlling the time of oil separation and sedimentation, while reducing the cross-sectional area of ​​the oil layer and increasing the height of the oil layer, thereby optimizing the removal efficiency of petroleum-based organic matter. This not only improves the operational flexibility of the treatment unit, but also makes the treatment process more refined to adapt to different water quality conditions. Compared with the prior art, this further technical solution can more effectively reduce the content of petroleum-based organic matter and reduce the load of subsequent treatment steps, thereby improving the efficiency and stability of the treatment system as a whole, while reducing the use of chemical agents and energy consumption, and achieving a more economical and environmentally friendly water treatment process.

[0028] On the basis of the above technical solution, the present invention can also be improved as follows:

[0029] Further:

[0030] In step S2, the removal efficiency of petroleum organic matter is adjusted by controlling the pH value of the gas field produced water and the reaction time; the filler of the iron-carbon micro-electrolysis reactor has an iron content of 75%, a carbon content of 10% to 15%, and a catalyst content of 10% to 15%.

[0031] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0032] By controlling the pH value and reaction time of the produced water from the gas field, the iron-carbon micro-electrolysis is ensured to be in the best reaction conditions, and the removal efficiency of petroleum organic matter is optimized. By optimizing the filler ratio of the iron-carbon micro-electrolysis reactor, the treatment efficiency of produced water from high-salt and high-organic gas fields can be significantly improved. Specifically, in step S2, the filler of the iron-carbon micro-electrolysis reactor is carefully designed with an iron content of 75%, a carbon content of 10% to 15%, and a catalyst content of 10% to 15%. Such a ratio can ensure the formation of an efficient micro-electrolysis environment inside the reactor. The high iron content provides sufficient anode material, which promotes Fe 2+ The production of carbon and catalyst in the microelectrolysis process is improved, while the appropriate amount of carbon and catalyst helps to improve the electron transfer efficiency and reaction rate, thereby enhancing the degradation ability of large molecular petroleum organic matter. Compared with the existing technology, this improvement not only improves the efficiency of the microelectrolysis process, but also helps to reduce the treatment cost, because the more efficient reaction reduces the energy and time required, while improving the treatment effect, making the subsequent treatment steps easier, and ultimately achieving better effluent water quality. In addition, this filler ratio also helps to improve the stability and durability of the system, reducing maintenance requirements and operating costs. At the same time, the Fe dissolved in the filler 2+ It reacts with sulfide ions to produce black precipitate, which avoids the influence of sulfide ions on subsequent sodium persulfate activation oxidation and biochemical reactions.

[0033] On the basis of the above technical solution, the present invention can also be improved as follows:

[0034] Further:

[0035] In step S3, the dosage of sodium hydroxide is adjusted according to the pH value of the produced water from the gas field to ensure the flocculation and precipitation effect; and the dosage of PAM is further optimized by monitoring the turbidity of the supernatant after flocculation and precipitation.

[0036] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0037] According to the pH value of the gas field produced water, the dosage of sodium hydroxide is accurately adjusted to ensure the best flocculation and sedimentation effect. It is ensured that under alkaline conditions, flocculants such as iron salts can be fully hydrolyzed to form effective flocs, thereby improving the removal efficiency of suspended matter and some colloidal organic matter. In addition, by monitoring the turbidity of the supernatant after flocculation and sedimentation, real-time feedback and further optimization of the dosage of polyacrylamide (PAM) can be provided to ensure the stability and sedimentation effect of the flocs. Compared with the prior art, this further technical solution can more accurately control the flocculation and sedimentation process, reduce the waste of chemical agents, reduce treatment costs, and improve the efficiency of water purification and the clarity of the effluent. This optimization of the flocculation and sedimentation process not only improves the economy and environmental friendliness of the entire water treatment system, but also provides strong support for the efficient treatment and resource utilization of gas field produced water.

[0038] On the basis of the above technical solution, the present invention can also be improved as follows:

[0039] Further:

[0040] In the step S4 and / or S6, the salt-tolerant bacteria is a yeast fungus, and the deposit number is CCTCC M 20241391.

[0041] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0042] The present invention achieves significant improvement in the treatment technology of organic matter in produced water from high-salinity and high-organic matter gas fields by applying a specific yeast fungus, Barnettozyma hawaiiensis, which is salt- and acid-resistant, in step S4 and / or S6. This yeast fungus has excellent salt and acid resistance, enabling it to effectively degrade difficult-to-degrade organic matter such as benzene series in a high-salinity and acidic environment. Compared with the prior art, the beneficial effects of using this yeast fungus include:

[0043] Improved degradation efficiency: Barnettozyma hawaiiensis is able to directly degrade BTEX, reducing the need for traditional advanced oxidation pretreatment, thereby reducing treatment cost and complexity.

[0044] Enhanced environmental adaptability: The yeast fungus can remain active in a wide range of pH 3 to 10 and sodium chloride concentration of 0% to 12%, which enables it to adapt to wastewater treatment needs under different water quality conditions.

[0045] Reduced operating costs: Because the yeast fungus can work effectively in high-salt environments, it reduces dependence on expensive physical and chemical treatment methods, thereby reducing long-term operating costs.

[0046] Improved treatment stability: The salt and acid resistance of Barnettozyma hawaiiensis improves the stability of the treatment system and reduces the decline in treatment efficiency due to water quality fluctuations.

[0047] Environmentally friendly: The biological treatment method does not produce secondary pollution and meets environmental protection requirements. The cultivation and preservation of the yeast fungus are relatively simple, which helps to achieve sustainable development.

[0048] On the basis of the above technical solution, the present invention can also be improved as follows:

[0049] Further:

[0050] In step S5, the ratio of the persulfate addition concentration to the wastewater TOC concentration is 4-6, the filling rate of the granular activated carbon in the reactor is 50%, and the removal efficiency of the difficult-to-degrade organic matter is adjusted by controlling the pH value and the reaction time.

[0051] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0052] By adjusting the dosing concentration of persulfate so that it is maintained within a ratio range of 4 to 6 with the total organic carbon (TOC) concentration of the wastewater, the present invention achieves a significant improvement in the treatment method of produced water from a high-salt and high-organic gas field. This dosing strategy ensures that persulfate can efficiently generate free radicals under the catalytic action of granular activated carbon (GAC), specifically targeting the degradation of organic matter in the wastewater. This method not only improves the efficiency of the oxidation process and ensures the rapid removal of organic matter, but also reduces the consumption and cost of chemical agents by reducing the excessive use of persulfate. In addition, it also helps to reduce the generation of by-products and avoid unnecessary oxidation reactions, thereby improving the stability and adaptability of the treatment process. By controlling the filling rate of granular activated carbon, it is ensured that sodium persulfate activation has sufficient active sites, and at the same time, an electronic conductor is provided for the electron transfer of the redox reaction. Under the condition of high chloride ions, more free radicals are generated, and the electron transfer rate is accelerated, thereby significantly improving the oxidation efficiency of organic matter under high salt conditions. By controlling the pH value and reaction time, it is ensured that the persulfate activation oxidation is under the optimal reaction conditions, and the removal efficiency of difficult-to-degrade organic matter is optimized.

[0053] On the basis of the above technical solution, the present invention can also be improved as follows:

[0054] Further:

[0055] In the step S4 and / or S6, the degradation efficiency of organic matter is improved by controlling the pH value, temperature and residence time of the biochemical treatment of salt-tolerant bacteria; the polyurethane filler is regularly replaced or regenerated to maintain the activity and treatment efficiency of the salt-tolerant bacteria.

[0056] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0057] By precisely controlling the pH value, temperature and residence time of the secondary biochemical treatment of salt-tolerant bacteria in step S4 and / or S6, the present invention can significantly improve the degradation efficiency of organic matter, thereby accelerating the removal rate of pollutants in wastewater. In addition, the measures of regularly replacing or regenerating polyurethane fillers help maintain the activity of salt-tolerant bacteria and ensure the long-term stable operation and high-efficiency performance of the treatment system. Compared with the prior art, these improvements can reduce maintenance costs and improve the overall treatment effect, making the wastewater treatment process more economical and environmentally friendly.

[0058] On the basis of the above technical solution, the present invention can also be improved as follows:

[0059] Further:

[0060] In step S7, the dosage of sodium hydroxide is adjusted according to the pH value of the produced water from the gas field to ensure the flocculation and precipitation effect; the dosage of PAC and PAM is further adjusted by monitoring the turbidity of the supernatant after flocculation and precipitation.

[0061] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0062] According to the pH value of the produced water from the gas field, the dosage of sodium hydroxide is accurately adjusted to ensure the best flocculation and sedimentation effect. It is ensured that under alkaline conditions, the polyaluminium chloride (PAC) flocculant can be fully hydrolyzed to form effective flocs, which can achieve a more optimized flocculation and sedimentation effect, thereby improving the removal efficiency of suspended matter and biological flocs. In addition, by monitoring the turbidity of the supernatant after flocculation and sedimentation, the dosage of PAC and PAM can be adjusted in real time to ensure the flexibility and adaptability of the treatment process, further improve the effluent water quality, and reduce treatment costs. It makes wastewater treatment more precise and economical, and helps to achieve more efficient resource management and environmental protection.

[0063] On the basis of the above technical solution, the present invention can also be improved as follows:

[0064] Further:

[0065] In step S8, according to the produced water volume and TDS of the gas field, evaporation desalination or RO membrane concentration followed by evaporation desalination is selected; when the produced water volume of the gas field is ≤200m 3 / d or TDS ≥ 50000mg / L, evaporation is used for desalination; when the TDS of gas field produced water is < 50000mg / L, RO membrane concentration followed by evaporation for desalination is used.

[0066] Compared with the prior art, the beneficial effects of adopting the above further technical solution are:

[0067] Flexible selection of evaporative desalination or RO membrane concentration technology + evaporative desalination according to the water volume and total dissolved solids (TDS) value of gas field produced water can more effectively treat wastewater with different salinities and ensure the adaptability and economy of the treatment process. This method optimizes energy consumption and operating costs. For high-salinity wastewater, evaporative desalination can efficiently remove dissolved salts, while for wastewater with lower salinity, evaporative desalination after RO membrane concentration is more energy-efficient and cost-effective. Such improvements make the wastewater treatment process more flexible and economical, and help achieve sustainable resource management and environmental protection.

[0068] The present invention also provides a system for treating organic matter in produced water of a high-salt and high-organic gas field for executing the above method, comprising:

[0069] An oil separation and sedimentation unit, used to perform step S1;

[0070] An iron-carbon micro-electrolysis unit, used to perform step S2;

[0071] A primary flocculation and sedimentation unit, used to perform step S3;

[0072] A salt-tolerant bacteria primary biochemical treatment unit, used to perform step S4;

[0073] a persulfate advanced oxidation unit, for performing step S5;

[0074] A secondary biochemical treatment unit for salt-tolerant bacteria, used to perform step S6;

[0075] A secondary flocculation and sedimentation unit, used to perform step S7;

[0076] The desalination unit is used to perform step S8.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] The high-salt and high-organic gas field produced water treatment system provided by the present invention realizes the efficient removal of organic matter and salt in the gas field produced water through integrated oil separation precipitation, iron-carbon micro-electrolysis, flocculation precipitation, salt-tolerant bacteria biochemical treatment, persulfate advanced oxidation and desalination units. The beneficial effect of this systematic method is that it can flexibly adjust the treatment parameters according to different water quality conditions, ensuring the high efficiency and low cost of the treatment process. At the same time, the biological treatment link of the system reduces the dependence on chemical agents, reduces the risk of secondary pollution, and meets environmental protection requirements. In addition, the design of the system is easy to operate and maintain, and improves the stability and reliability of the treatment process. Through this system, the resource utilization of gas field produced water can be realized, environmental pollution can be reduced, and significant economic and environmental benefits can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0080] Figure 1 This is a diagram of the oil separation and sedimentation state of produced water from a high-salinity and high-organic gas field.

[0081] Figure 2 The iron-carbon and H 2 S reaction produces a black precipitate state diagram.

[0082] Figure 3 This is the GC-MS chromatogram of gas field produced water before and after the iron-carbon micro-electrolysis reaction in step S2. Figure 4 In the figure, a is after oil separation and sedimentation, before iron-carbon micro-electrolysis; b is after iron-carbon micro-electrolysis.

[0083] Figure 4 It is the flocculation and sedimentation effect of step S3.

[0084] Figure 5 It is a polyurethane filler inoculated with salt-tolerant bacteria.

[0085] Figure 6 This is a comparison chart of the TOC removal rate of different added ingredients in the advanced oxidation treatment step.

[0086] Figure 7 It is a three-dimensional fluorescence image of produced water from the gas field at each treatment stage. Figure 7 , (a) after processing in step S1, (b) after processing in step S2, (c) after processing in step S4, (d) after processing in step S5, (e) after processing in step S6, and (f) after processing in step S8.

[0087] Figure 8 This is the flow chart of the organic matter treatment system for produced water from a high-salt and high-organic gas field. DETAILED DESCRIPTION

[0088] The following describes the invention in conjunction with specific embodiments.

[0089] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0090] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0091] In this embodiment, the yeast fungus Barnettozyma hawaiiensis, the strain has a deposit number of CCTCC M20241391. The deposit date of the strain is June 27, 2024, the deposit unit is China Center for Type Culture Collection, and the deposit address is Wuhan University. The identification process and details of the strain are recorded in the patent application document CN202411752253.4.

[0092] Example 1

[0093] This embodiment simultaneously describes a method and system for treating organic matter in produced water from a high-salinity and high-organic-matter gas field.

[0094] The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field described in this embodiment comprises the following steps:

[0095] S1, oil separation and sedimentation, remove most of the petroleum organic matter through gravity oil separation;

[0096] S2, iron-carbon micro-electrolysis, using the iron-carbon micro-electrolysis galvanic cell reaction to degrade macromolecular petroleum organic matter and precipitate sulfur ions;

[0097] S3, primary flocculation and sedimentation, adding sodium hydroxide and PAM for flocculation and sedimentation to remove colloidal organic matter;

[0098] S4, primary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to degrade small molecular organic matter;

[0099] S5, persulfate advanced oxidation, using granular activated carbon to activate sodium persulfate to produce free radicals to oxidize refractory organic matter;

[0100] S6, secondary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to further degrade organic matter;

[0101] S7, secondary flocculation sedimentation, adding PAC and PAM for flocculation sedimentation to remove suspended matter and microbial flocs;

[0102] S8. Desalination: select evaporative desalination or RO membrane concentration followed by evaporative desalination according to the TDS value of the produced water.

[0103] See also Figure 8 , a system for treating organic matter in produced water from a high-salinity and high-organic gas field, comprising:

[0104] The oil separation and sedimentation unit 100 is used to perform step S1;

[0105] The iron-carbon micro-electrolysis unit 200 is used to perform step S2;

[0106] A primary flocculation and sedimentation unit 300, used to perform step S3;

[0107] The salt-tolerant bacteria primary biochemical treatment unit 400 is used to perform step S4;

[0108] A persulfate advanced oxidation unit 500, for performing step S5;

[0109] The salt-tolerant bacteria secondary biochemical treatment unit 600 is used to perform step S6;

[0110] A secondary flocculation and sedimentation unit 700, used to perform step S7;

[0111] The desalination unit 800 is used to execute step S8.

[0112] The detailed steps of the method for treating organic matter in produced water from a high-salt and high-organic gas field are as follows:

[0113] (1) Oil separation and precipitation:

[0114] This step procedure is performed by the oil separation and sedimentation unit 100 .

[0115] The produced water from the gas field contains a large amount of petroleum substances ( Figure 1 ), the organic matter concentration is very high (COD is 20000-31000mg / L), and most of the petroleum organic matter can be removed by gravity oil separation to reduce the processing load of organic matter in subsequent processes. After oil separation treatment, the COD concentration dropped to 7000-10000mg / L, and TOC was 755.12-1078.75mg / L. The produced water of the gas field contains a large amount of insoluble suspended matter. While gravity oil separation, the large particles of suspended matter are precipitated and removed. The oil separation retention time is 3-5h to ensure sufficient time for oil-water separation and suspended matter precipitation.

[0116] The produced water from the gas field is introduced into the oil separation and sedimentation unit, and the oil-like substances are floated to the water surface by gravity. The design of the oil separation and sedimentation unit should be conducive to oil-water separation. For example, inclined plates or inclined pipes can be used to increase the separation efficiency. In the oil separation and sedimentation unit, the floating oil-like substances enter the oil collecting pipe with a smaller cross-sectional area, increasing the height of the oil layer (the principle is the same as Figure 1 ), is collected and removed in the oil collecting pipe. While separating the oil, the insoluble suspended matter in the water settles at the bottom of the oil separation sedimentation unit to form a sludge layer. The precipitated sludge is regularly discharged from the bottom of the oil separation sedimentation unit through the sludge discharge system to maintain the effective volume of the sedimentation tank.

[0117] The configuration of an oil separation and sedimentation unit is as follows:

[0118] Grease trap: designed in a rectangular or circular shape to facilitate oil-water separation and sludge sedimentation.

[0119] Oil collecting pipe: installed on the upper part of the grease trap to collect and discharge the floating oil layer.

[0120] Sludge discharge system: located at the bottom of the grease trap, used to discharge settled sludge regularly.

[0121] Water inlet and outlet: located at the top and bottom of the grease trap, used to control the inlet and outlet of water.

[0122] The oil separation and sedimentation unit can effectively remove most of the petroleum organic matter and suspended solids in the produced water of the gas field, providing favorable conditions for the subsequent treatment steps. The expression "most" means that after the oil separation and sedimentation treatment, the concentration of these substances is significantly reduced, usually by more than 50%.

[0123] (2) Iron-carbon micro-electrolysis:

[0124] This step procedure is performed by the iron-carbon micro-electrolysis unit 200 .

[0125] Gas field produced water contains high concentrations of organic matter and colloidal suspended matter. The suspended matter colloids adsorb a large amount of COD organic matter, forming a spatial stable state or a vacancy stable state. Directly adding flocculants and coagulants will result in poor reagent reaction kinetics, poor flocculation effect, and high reagent consumption. Gas field water contains high hydrogen sulfide. If it is not removed in advance, a large amount of oxidants and toxic microorganisms will be consumed in the later stage, which is not conducive to the oxidative degradation and biochemical degradation of organic matter. After a large number of experimental studies and comparisons, combined with the water quality conditions of gas field produced water, iron-carbon micro-electrolysis is used for desulfurization and flocculation precipitation pretreatment.

[0126] The gas field produced water that has been treated with oil separation and precipitation is introduced into the iron-carbon micro-electrolysis unit 200. At this time, the pH value of the water sample is 5 to 6, which is acidic. Hydrochloric acid is added to the gas field produced water to adjust the pH value to 3 to enhance the effect of iron-carbon micro-electrolysis.

[0127] The produced water from the gas field with adjusted pH value is introduced into the iron-carbon micro-electrolysis reactor, and the iron-carbon filler in the reactor is used for the galvanic cell reaction. The filler of the iron-carbon micro-electrolysis reactor is iron-carbon, which is melted from iron oxide, graphite powder and catalyst. Its iron content is 75%, carbon content is 10-15%, catalyst content is 10-15%, and the bulk density is 1.2-1.4 kg / m 3 The stacking porosity is 50-70%. During the reaction, the water level is guaranteed to be at least 5 cm above the top of the filler.

[0128] Fe is produced at the anode 2+ , [H] (hydrogen atom) and [O] (oxygen atom) are produced at the cathode level. These active substances easily undergo redox reactions with organic matter, reduce COD, and degrade large molecular petroleum organic matter into small molecular organic matter. Reducing the Zeta potential of colloids in produced water is conducive to the destabilization and sedimentation of colloidal suspended matter.

[0129] H in produced water 2 S and Fe in solution 3+ The reaction produces black Fe 2 S 3 Precipitation, experimental results such as Figure 2 As shown, H is eliminated 2 The influence of S on subsequent reactions.

[0130] The reaction time of iron-carbon micro-electrolysis is 2 to 3 hours to ensure sufficient reaction.

[0131] The iron-carbon micro-electrolysis is set up in 2 to 3 groups for easy maintenance, and a pump is used internally for internal reflux hydraulic stirring to ensure the uniformity of the reaction.

[0132] After the water sample was treated by iron-carbon micro-electrolysis, the COD was further reduced, the macromolecular organic matter was degraded, and the colloidal suspended matter was effectively treated, and then discharged as effluent and entered the subsequent treatment unit.

[0133] The configuration of an iron-carbon micro-electrolysis unit 200 is as follows:

[0134] Reactor: Designed as multiple groups in parallel to improve processing efficiency and facilitate maintenance.

[0135] Filler: Use special iron-carbon filler to ensure efficient reaction.

[0136] pH adjustment system: used to adjust the pH value of water samples before entering the reactor.

[0137] Stirring system: internal reflux hydraulic stirring is used to ensure the uniformity of the reaction.

[0138] Outlet system: collects treated water samples and transports them to the next treatment step.

[0139] (3) Primary flocculation sedimentation:

[0140] This step is performed by the primary flocculation and sedimentation unit 300. The gas field produced water treated by iron-carbon micro-electrolysis is introduced into the primary flocculation and sedimentation unit 300.

[0141] At this time, the pH value of the water sample has risen to 6 to 7. Sodium hydroxide is added to the produced water of the gas field to further adjust the pH value to 8 to 9 to promote the formation of iron salt flocs.

[0142] Under alkaline conditions, the iron-carbon reaction dissolves Fe and produces Fe 3+ and Fe 2+ ions, producing iron salt flocs, which help to adsorb and precipitate suspended matter and some colloidal organic matter in the water.

[0143] Polyacrylamide (PAM) is added to the produced water of the gas field with a pH value adjusted, and the dosage is controlled at 2-5 mg / L to enhance the flocculation effect. PAM works together with iron salt flocs to form larger flocs, which settle by gravity to separate the suspended matter and some colloidal organic matter in the water. During the sedimentation process, the sludge formed accumulates at the bottom of the sedimentation tank and is discharged regularly through the sludge discharge system.

[0144] After flocculation and sedimentation, the supernatant is discharged from the top of the sedimentation tank as treated effluent, with significantly reduced organic matter content and suspended solids concentration.

[0145] Control the surface load of the sedimentation tank to 1.5 to 2 m 3 / m 2 h to ensure the precipitation effect.

[0146] After the iron-carbon micro-electrolysis reaction, the organic matter is partially removed, and the macromolecular organic matter is degraded into small molecular organic matter ( Figure 3 It can be seen that before and after the iron-carbon reaction, the organic matter is reduced, the types are reduced, and the molecular weight becomes smaller), the Zeta potential of the colloid is reduced, and the flocculation effect is better ( Figure 4 ), H 2 S through Fe 2 S 3 Sedimentation removal provides better influent quality for subsequent biochemical treatment steps.

[0147] In some embodiments, the flocculation effect is evaluated by monitoring the COD and turbidity of the supernatant after flocculation precipitation, and the dosage of PAM is adjusted as needed.

[0148] (4) Primary biochemical analysis and precipitation of salt-tolerant bacteria:

[0149] This step is performed by the salt-tolerant bacteria primary biochemical treatment unit 400. The gas field produced water that has undergone primary flocculation and sedimentation treatment is introduced into the salt-tolerant bacteria primary biochemical treatment unit 400.

[0150] After the iron-carbon micro-electrolysis reaction, the organic macromolecules are degraded into small molecules, which can improve the biodegradability of organic matter. However, conventional microorganisms are inhibited by the high salt content in the gas field produced water, so special salt-tolerant bacteria are used for degradation. The special salt-tolerant bacteria are yeast fungi (Barnettozyma hawaiiensis), and the preservation number is CCTCC M 20241391. The bacteria have salt tolerance (sodium chloride mass percentage concentration 0-12%) and high efficiency in degrading organic matter.

[0151] Inoculate salt-tolerant bacteria into polyurethane fillers ( Figure 5 ), the concentration of salt-tolerant bacteria inoculated in polyurethane filler is 11.225 g / L, the specification of polyurethane filler is 2×2 cm, and the density is 1 g / cm 3 , add polyurethane filler to the first-level biochemical reactor of salt-tolerant bacteria (filling rate 75%). Under aerobic conditions, control the temperature to 30°C and the initial pH value to 5 to carry out the degradation reaction. The salt-tolerant bacteria degradation reaction lasts for 24 to 48 hours to ensure that the organic matter is effectively degraded.

[0152] After the biochemical reaction, the pH rises to 6-7.

[0153] The aged flocs in the effluent after biochemical treatment need to be precipitated to separate the suspended solids in the effluent. The surface load of the sedimentation tank should be controlled at 1.5 to 2 m 3 / m 2 h to ensure the precipitation effect.

[0154] The effluent after the primary biochemical treatment and sedimentation by salt-tolerant bacteria serves as the influent for the next step of treatment, and its organic matter content is further reduced, providing better water quality for subsequent advanced oxidation and secondary biochemical treatment.

[0155] The configuration of a salt-tolerant bacteria primary biochemical treatment unit 400 is as follows:

[0156] Bioreactor: A container designed for the growth and metabolism of microorganisms, either batch or continuous flow.

[0157] Polyurethane filler: acts as a carrier for microorganisms, providing a large surface area to support the growth of microorganisms.

[0158] Temperature control system: used to maintain the temperature inside the reactor at 30°C.

[0159] pH control system: used to adjust and control the pH value in the reactor.

[0160] Water inlet and outlet: located at the top and bottom of the reactor respectively, used to control the inlet and outlet of water.

[0161] Sedimentation tank: used to collect the effluent after biochemical reaction and carry out sedimentation treatment.

[0162] (5) Persulfate advanced oxidation:

[0163] This step is performed by the persulfate advanced oxidation unit 500. The supernatant of the gas field produced water that has undergone primary biochemical treatment and precipitation treatment with salt-tolerant bacteria is introduced into the persulfate advanced oxidation unit 500.

[0164] The salt-tolerant bacteria in step (4) degrade all easily degradable organic matter, leaving only the macromolecular organic matter that is difficult to degrade, thereby reducing the subsequent removal load of advanced oxidation organic matter.

[0165] Granular activated carbon (GAC) with a specification of Φ4×10mm and a filling rate of 50% is loaded in the persulfate advanced oxidation reactor as a persulfate activator. Sodium persulfate (PDS) is used as an oxidant. Under the synergistic effect of high concentration of chloride ions (20000-50000 mg / L), more hydroxyl radicals and sulfate radicals are produced, and the electron transfer rate is accelerated. Under the joint action of free radical and non-free radical electron transfer pathways, rapid degradation of organic matter under high salt conditions is achieved.

[0166] like Figure 6 As shown, the removal efficiency of TOC by GAC-activated PDS was greatly increased under the condition of adding sodium chloride.

[0167] Therefore, under high chloride ion conditions, granular activated carbon (GAC) activated sodium persulfate to carry out advanced oxidation treatment of organic matter in high-salt wastewater, avoiding the effect of chloride ion quenching on hydroxyl radicals and promoting the oxidation effect of organic matter.

[0168] The residence time of the oxidation reactor is 4 to 6 hours and is divided into 2 to 3 reaction sections to ensure sufficient reaction.

[0169] The ratio of persulfate addition concentration to wastewater TOC concentration is 4 to 6, and it is added evenly in each stage to improve oxidation efficiency. The pH value of the influent reaction in the last stage is controlled at 5 to optimize the oxidation effect.

[0170] 2 to 3 groups of reactors are set up to facilitate maintenance and replacement of fillers to ensure the continuity and stability of the treatment process.

[0171] After the water sample was treated with persulfate advanced oxidation, the difficult-to-degrade macromolecular organic matter was effectively degraded, and the effluent was used as the influent for the next step of treatment.

[0172] A persulfate advanced oxidation unit 500 configuration reference is as follows:

[0173] Reactors: Designed as continuous flow or batch reactors to suit different processing requirements.

[0174] Granular activated carbon (GAC): acts as an activator for persulfate to improve oxidation efficiency.

[0175] Sodium persulfate (PDS) dosing system: used to accurately control the dosage of oxidant.

[0176] pH control system: used to adjust and control the pH value in the reactor.

[0177] Water inlet and outlet: located at the top and bottom of the reactor respectively, used to control the inlet and outlet of water.

[0178] Multi-stage reaction section: By setting up multiple reaction sections, the processing efficiency and flexibility can be improved.

[0179] (6) Secondary biochemical analysis of salt-tolerant bacteria:

[0180] The produced water from the gas field that has undergone persulfate advanced oxidation treatment is introduced into the salt-tolerant bacteria secondary biochemical treatment unit 600.

[0181] After the persulfate advanced oxidation, the organic matter is effectively removed, and the macromolecular organic matter is oxidized again into small molecular organic matter. If the advanced oxidation is continued, the cost of the reagent is high, so the salt-tolerant bacteria secondary biochemical method is used to further degrade the organic matter. The salt-tolerant bacteria inoculated are yeast fungi (Barnettozyma hawaiiensis). The salt-tolerant bacteria are inoculated into the polyurethane filler ( Figure 5 ), the concentration of salt-tolerant bacteria inoculated in polyurethane filler is 11.225 g / L, the specification of polyurethane filler is 2×2 cm, and the density is 1 g / cm 3 , add polyurethane filler to the first-level biochemical reactor of salt-tolerant bacteria, with a filling rate of 75%. Under aerobic conditions, control the temperature to 30°C, the initial pH value to 5, and carry out the second-level biochemical degradation reaction. The degradation time is 24 to 48 hours to ensure that the small molecular organic matter is effectively degraded.

[0182] The effluent after the secondary biochemical treatment with salt-tolerant bacteria is used as the influent for the next step of treatment, and its organic matter content is further reduced.

[0183] During the secondary biochemical treatment process, the organic matter concentration and pH value of the effluent are monitored and adjusted when necessary to ensure the treatment effect.

[0184] (7) Secondary flocculation precipitation:

[0185] The gas field produced water that has undergone secondary biochemical treatment with salt-tolerant bacteria is introduced into the secondary flocculation sedimentation unit 700. Since the pH value of the water sample rises to 6-7 after the secondary biochemical treatment, sodium hydroxide needs to be added to adjust the pH value to 8-9 to optimize the flocculation conditions. Polyaluminium chloride (PAC) is added to the gas field produced water with adjusted pH value, and the dosage is controlled at 100-200 mg / L to form effective flocs. At the same time, polyacrylamide (PAM) is added, and the dosage is controlled at 3-5 mg / L to enhance the stability and sedimentation performance of the flocs. PAC and PAM work together to form larger flocs, which are precipitated by gravity to separate suspended matter and microbial flocs in the water.

[0186] During the sedimentation process, the sludge formed accumulates at the bottom of the sedimentation tank and is discharged regularly through the sludge discharge system. After flocculation and sedimentation, the supernatant is discharged from the top of the sedimentation tank as treated effluent, with significantly reduced organic matter content and suspended solids concentration.

[0187] Control the surface load of the sedimentation tank at 0.8m 3 / m 2 h to ensure the precipitation effect.

[0188] The flocculation effect was evaluated by monitoring the turbidity and organic matter concentration of the supernatant after flocculation and sedimentation, and the dosage of PAC and PAM was adjusted as needed.

[0189] (8) Desalination:

[0190] The supernatant of the gas field produced water that has undergone secondary flocculation and sedimentation treatment is introduced into the desalination unit 800 .

[0191] The water volume and total dissolved solids (TDS) concentration of the supernatant are tested to determine the appropriate desalination method.

[0192] The supernatant after precipitation can be further desalted in two ways.

[0193] When the gas field produced water volume ≤ 200m 3 / L or TDS ≥ 50000mg / L, evaporation desalination technology can be used. Choose appropriate evaporation equipment, such as mechanical vapor recompression (MVR) or multiple-effect evaporation (MED). Use steam as a heat source to carry out the evaporation process to crystallize and separate the dissolved salts in the water. Through the early advanced oxidation and salt-tolerant bacteria biochemistry, the condensate after evaporation has less organic matter (TOC is 10-30mg / L, COD is 30-100mg / L). According to the water quality standards, the condensate is used for farmland irrigation or directly discharged to meet the first-level standard of the "Comprehensive Sewage Discharge Standard".

[0194] When the TDS of gas field produced water is less than 50000mg / L, reverse osmosis (RO) membrane technology is used for desalination. The RO membrane separates fresh water, which can be used for resource utilization or discharge in compliance with standards. The concentrated water is evaporated and crystallized to further reduce the salt content. Through RO membrane concentration pretreatment, the amount of evaporated water is reduced and energy consumption is reduced. It is expected that the amount of evaporated water can be reduced by more than 50%, significantly reducing operating costs.

[0195] The desalinated fresh water and condensate are collected separately and subsequently utilized or discharged according to water quality and demand.

[0196] Example 2

[0197] This embodiment is a specific case of organic matter treatment in produced water from a high-salinity and high-organic gas field.

[0198] The water quality of produced water from high-salinity and high-organic gas fields is shown in Table 1.

[0199] Table 1 Raw water quality

[0200]

[0201] Oil separation and sedimentation: The raw water is subjected to 4 hours of oil separation and sedimentation to remove a large amount of floating oil and large suspended solids; the COD and TOC of the effluent after oil separation are significantly reduced.

[0202] Iron-carbon micro-electrolysis: Add hydrochloric acid to the effluent water to adjust the pH value to 3. The water sample enters two sets of parallel iron-carbon micro-electrolysis reactors and reacts for 2 hours. 2+ The generation of [H] promotes the oxidative degradation of organic matter and removes H 2 S.

[0203] Primary flocculation sedimentation: Add sodium hydroxide to the water sample after micro-electrolysis treatment to adjust the pH value to 9. Add 3 mg / L PAM for flocculation sedimentation. The surface load of the sedimentation tank is 2m 3 / m 2 h. After precipitation, the suspended solids and colloidal organic matter in the supernatant are further reduced.

[0204] Primary biochemical treatment of salt-tolerant bacteria: The supernatant was adjusted to pH 5 and entered the primary biochemical pool of salt-tolerant bacteria. Polyurethane filler inoculated with salt-tolerant bacteria Barnettozyma hawaiiensis was added with a filling rate of 75%. Aerobic biochemical reaction was carried out at 30°C for 1 day.

[0205] Sedimentation and advanced oxidation: After the biochemical effluent is precipitated, the supernatant enters the GAC+PDS advanced oxidation reactor. The GAC filling rate is 50%, the mass concentration ρ(PDS) / TOC=5, and it is added in two stages. The pH value of the last stage of the reaction is controlled at about 5 to improve the oxidation efficiency.

[0206] Secondary biochemical treatment with salt-tolerant bacteria: After advanced oxidation, the wastewater enters the secondary biochemical pool with salt-tolerant bacteria. Polyurethane filler is added again with a filling rate of 75% for a 1-day biochemical reaction.

[0207] Secondary flocculation sedimentation: The pH value of the secondary biochemical effluent was adjusted to 8. 100 mg / L PAC and 3 mg / L PAM were added for flocculation sedimentation. The surface load of the sedimentation tank was 0.8 m 3 / m 2 ·h.

[0208] Evaporation and resource utilization: Due to the small amount of water, it is directly evaporated after biochemical treatment. The evaporated condensate is utilized as a resource or discharged in compliance with the standards.

[0209] The COD of the condensate outlet water is 90.97 mg / L, the pH value is 7.1, and the TDS is 43.5 mg / L.

[0210] Since the TDS is 34150mg / L, the water sample after secondary flocculation and sedimentation can also be concentrated by RO membrane. A matching filter device is required before entering the RO membrane to protect the RO membrane from damage by suspended matter and large particles. The RO membrane concentrated water enters the evaporator for evaporation and crystallization to recover salt. The evaporation condensate and RO membrane fresh water are discharged for farmland irrigation or standard discharge.

[0211] The COD of RO membrane effluent is 36.5 mg / L, pH value is 6.5, and TDS is 300 mg / L.

[0212] The effluent in both cases meets the COD and TDS standards for dry and wet land crops in the "Agricultural Irrigation Water Quality Standard" GB5084-2005, COD≤200(150)mg / L, TDS≤1000mg / L (non-saline-alkali land), and the first-level standard for COD in the "Integrated Sewage Discharge Standard" GB16297-1996 (COD≤100mg / L for other discharge units).

[0213] In this embodiment, after the raw water of the high-salt and high-organic gas field produced water has been processed through various treatment steps, as shown in Table 2, the TOC of the raw water of the high-salt and high-organic gas field produced water has been significantly reduced from 1693 mg / L of the raw water to 11.74 mg / L after RO membrane treatment, and the total removal rate is as high as 99.31%. At the same time, the conductivity has also dropped from 68.3 ms / cm to 0.59 ms / cm, showing the effective removal of salt. This series of treatment steps not only improves the water quality, but also provides the possibility for the recycling and reuse of water resources, which has important environmental and economic value.

[0214] Table 2 Processing results of each step

[0215]

[0216] Three-dimensional fluorescence imaging is a technique used to analyze the composition of organic matter in water bodies. It reveals the presence and relative content of different organic matter in water samples by measuring fluorescence intensity. In the treatment of gas field produced water, three-dimensional fluorescence imaging can show the effect of each treatment step on the removal of organic matter, such as Figure 7 shown.

[0217] By analyzing the three-dimensional fluorescence images of gas field produced water at each treatment stage, we can intuitively evaluate the removal effect of organic matter.

[0218] After the oil separation and sedimentation step ( Figure 7 In a), there is still a certain amount of high molecular organic matter in the water sample, which is manifested by a high fluorescence intensity.

[0219] After iron-carbon micro-electrolysis treatment ( Figure 7 In b), the fluorescence intensity decreases, indicating that some organic matter is degraded or transformed.

[0220] After primary biochemical treatment with salt-tolerant bacteria ( Figure 7 In c), the fluorescence image shows that the organic matter is further reduced, indicating the effective degradation of organic matter by microorganisms.

[0221] GAC+PDS advanced oxidation step ( Figure 7 Middle (d) leads to a further decrease in fluorescence intensity, reflecting that advanced oxidation results in more organic matter being mineralized or converted into smaller molecules.

[0222] After secondary biochemical treatment ( Figure 7 In middle (e), the fluorescence graph shows fewer fluorescence peaks, indicating that most of the organic matter has been effectively removed.

[0223] Finally, after evaporation of condensate or RO membrane treatment ( Figure 7 In middle (f), the three-dimensional fluorescence image shows that the fluorescence intensity is extremely low, reflecting the significant reduction of organic matter in the water sample, which meets the standards for farmland irrigation or discharge.

[0224] The fluorescence images confirm that after the entire treatment process, the organic matter in the gas field produced water has been significantly purified, and the water quality has reached the expected treatment standard, suitable for resource utilization or discharge. Through these three-dimensional fluorescence images, we can intuitively see the effect of each treatment step on the removal of organic matter in the gas field produced water, thereby evaluating the efficiency and optimization space of the entire treatment process. This information is of great value for improving water treatment processes and improving water quality.

[0225] In the description of the present invention, it should be understood that "-" and "~" represent the range between two values, and the range includes the endpoints. For example: "AB" represents a range greater than or equal to A and less than or equal to B. "A~B" represents a range greater than or equal to A and less than or equal to B.

[0226] In the description of the present invention, the term "and / or" herein is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0227] In the description of the invention, the numerical values ​​of time, temperature, ratio, mass, etc. involved may be based on actual measurements, standard parameters of equipment, simplified rounding results, or within an acceptable error range, ensuring the practicability and repeatability of the invention.

[0228] In the description of the present invention, the term "about" or "approximately" is used to express the approximate value of a numerical value or range, allowing a certain error to ensure the flexibility and practicality of the description while remaining within an acceptable error range, with the maximum error range not exceeding 10% of the corresponding numerical value or numerical range.

[0229] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for treating organic matter in produced water from a high-salinity and high-organic gas field, characterized in that: The following steps are involved: S1, oil separation and sedimentation, remove most of the petroleum organic matter through gravity oil separation; S2, iron-carbon micro-electrolysis, using the iron-carbon micro-electrolysis galvanic cell reaction to degrade macromolecular petroleum organic matter and precipitate sulfur ions; S3, primary flocculation and sedimentation, adding sodium hydroxide and PAM for flocculation and sedimentation to remove colloidal organic matter; S4, primary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to degrade small molecular organic matter; S5, persulfate advanced oxidation, using granular activated carbon to activate persulfate to produce free radicals to oxidize refractory organic matter; S6, secondary biochemical treatment with salt-tolerant bacteria, using salt-tolerant bacteria to further degrade organic matter; S7, secondary flocculation sedimentation, adding PAC and PAM for flocculation sedimentation to remove suspended matter and microbial flocs; S8. Desalination: select evaporative desalination or RO membrane concentration followed by evaporative desalination according to the TDS value of the produced water.

2. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In the step S1, the removal efficiency of petroleum organic matter is adjusted by controlling the oil separation sedimentation time and the oil layer height.

3. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In step S2, the removal efficiency of petroleum organic matter is adjusted by controlling the pH value of the gas field produced water and the reaction time; the filler of the iron-carbon micro-electrolysis reactor has an iron content of 75%, a carbon content of 10% to 15%, and a catalyst content of 10% to 15%.

4. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In step S3, the dosage of sodium hydroxide is adjusted according to the pH value of the produced water from the gas field to ensure the flocculation and precipitation effect; the dosage of PAM is further adjusted by monitoring the turbidity of the supernatant after flocculation and precipitation.

5. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In the step S4 and / or S6, the salt-tolerant bacteria is a yeast fungus, and the deposit number is CCTCC M 20241391.

6. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In step S5, the ratio of the persulfate addition concentration to the wastewater TOC concentration is 4-6, the filling rate of the granular activated carbon in the reactor is 50%, and the removal efficiency of the difficult-to-degrade organic matter is adjusted by controlling the pH value and the reaction time.

7. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In the step S4 and / or S6, the degradation efficiency of organic matter is improved by controlling the pH value, temperature and residence time of the biochemical treatment of salt-tolerant bacteria; the polyurethane filler is regularly replaced or regenerated to maintain the activity and treatment efficiency of the salt-tolerant bacteria.

8. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In step S7, the dosage of sodium hydroxide is adjusted according to the pH value of the produced water from the gas field to ensure the flocculation and precipitation effect; the dosage of PAC and PAM is further adjusted by monitoring the turbidity of the supernatant after flocculation and precipitation.

9. The method for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to claim 1, characterized in that: In step S8, according to the gas field produced water volume and TDS, evaporation desalination or RO membrane concentration followed by evaporation desalination is selected; when the gas field produced water volume is ≤200m 3 / d or TDS ≥ 50000mg / L, use evaporation to remove salt; when the TDS of gas field produced water is When the concentration is less than 50000mg / L, RO membrane is used for concentration and then evaporation for desalination.

10. A system for treating organic matter in produced water from a high-salinity and high-organic-matter gas field according to any one of claims 1 to 9, characterized in that: include: An oil separation and sedimentation unit, used to perform step S1; An iron-carbon micro-electrolysis unit, used to perform step S2; A primary flocculation and sedimentation unit, used to perform step S3; A salt-tolerant bacteria primary biochemical treatment unit, used to perform step S4; a persulfate advanced oxidation unit, for performing step S5; A secondary biochemical treatment unit for salt-tolerant bacteria, used to perform step S6; A secondary flocculation and sedimentation unit, used to perform step S7; The desalination unit is used to perform step S8.

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