A method and system for treating organic matter in produced water from a high-salt and high-organic gas field

Abstract

The present invention belongs to the field of water treatment technology and relates to a method and system for treating organic matter in high-salt and high-organic gas field produced water, which is intended to improve the degradation efficiency of organic matter in gas field produced water, reduce treatment costs, and improve the quality of discharged water. The method includes oil separation precipitation, iron-carbon micro-electrolysis, primary flocculation precipitation, primary biochemical treatment of salt-tolerant bacteria, advanced persulfate oxidation, secondary biochemical treatment of salt-tolerant bacteria, secondary flocculation precipitation and desalination steps. The system includes corresponding processing units to achieve resource utilization of gas field produced water, reduce environmental pollution, and have social and economic value. The effluent treated by the method of the present invention meets the COD and TDS standard requirements of the "Agricultural Irrigation Water Quality Standard" GB5084-2005 for dry and water-based dry (water) crops, as well as the COD requirements of the first-level standard of the "Comprehensive Sewage Discharge Standard" GB16297-1996.

Description

Technical Field

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

[0002] During oil and gas production, groundwater brought to the surface along with natural gas is called produced water. This water typically contains large amounts of petroleum-based substances, soluble salts, and insoluble suspended solids. Its water quality is characterized by high mineralization, high chloride ion concentrations, high hydrogen sulfide concentrations, high organic matter content, and a low pH. The quality of produced water varies with oilfield location, production conditions, reservoir characteristics, and production methods. Direct reinjection or discharge without treatment can severely contaminate the soil and damage the ecological environment.

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

[0004] a) High salinity and high organic matter content limit the direct resource utilization of gas field produced water, such as agricultural irrigation and industrial water. Conventional RO membrane filtration and evaporation crystallization technologies face the problem of high organic matter concentrations clogging the RO membrane or reducing the evaporator's heat transfer coefficient when treating this type of produced water.

[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 reagent reaction kinetics and poor flocculation sedimentation effect.

[0006] c) The high concentration of chloride ions (20,000-50,000 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 degrading 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 adopted due to the reduction of gas content will add surfactants and other organic substances to 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. This is especially true when treating produced water from large-volume gas fields. The treatment costs are too high, making it unsuitable for cost-sensitive applications. 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 improving the degradation efficiency of organic matter in gas field produced water, reducing the cost of gas field produced water treatment, improving the water quality of discharged water, ensuring the stable operation of the treatment system, and providing favorable conditions for the resource utilization of gas field produced water.

[0011] Through long-term exploration and attempts, as well as multiple experiments and efforts, and continuous reform and innovation, the inventors have solved the above technical problems. The technical solution provided by the present invention is to provide a method for treating organic matter in produced water from 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, uses 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 and sedimentation, adding PAC and PAM for flocculation and sedimentation to remove suspended matter and microbial flocs;

[0019] S8. Desalination: select evaporation desalination or RO membrane concentration followed by evaporation 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, 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 sedimentation step effectively removes most petroleum-based organic matter, followed by the iron-carbon micro-electrolysis technology to degrade large-molecule organic matter, improve biodegradability, and simultaneously achieve desulfurization, eliminating the effects of sulfur ions on advanced oxidation and biochemical systems. The first-level flocculation and precipitation further removes colloidal organic matter and precipitates iron ions through the precise addition of sodium hydroxide and PAM. Salt-tolerant bacteria are particularly suitable for high-salt environments. Through the first-level 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, which performs advanced oxidation on organic matter that is difficult to degrade through the first-level biochemical treatment. The second-level 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 second-level flocculation and precipitation ensures further purification of the water quality through the addition of PAC and PAM. Finally, the desalination step selected based on the TDS value, whether evaporative desalination or RO membrane concentration desalination, ensures that the effluent quality meets standards for agricultural irrigation or industrial 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 chemicals, and reduces energy consumption, but also provides excellent effluent 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 from the water is ensured by precisely controlling the oil separation and sedimentation time, while simultaneously reducing the cross-sectional area of ​​the oil layer and increasing its height, thereby optimizing the removal efficiency of petroleum-based organic matter. This not only increases the operational flexibility of the treatment unit but also allows for more refined treatment processes to accommodate varying water quality conditions. Compared to existing technologies, this advanced technical solution can more effectively reduce the content of petroleum-based organic matter and lower the load on subsequent treatment steps, thereby improving the overall efficiency and stability of the treatment system. It also reduces the use of chemicals and energy consumption, resulting in 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 the produced water from the high-salt and high-organic gas field is 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 the Fe 2+ The production of carbon and catalyst in appropriate amounts helps to improve the electron transfer efficiency and reaction rate, thereby enhancing the degradation ability of large molecular petroleum organic matter. Compared with existing technologies, this improvement not only improves the efficiency of the micro-electrolysis process, but also helps to reduce treatment costs, because more efficient reactions reduce the required energy and time, while improving treatment effects, making 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 gas field produced water 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 achieved to ensure the stability of the flocs and the sedimentation effect. Compared with the existing technology, this further technical solution can more accurately control the flocculation and sedimentation process, reduce the waste of chemical agents, reduce treatment costs, and at the same time improve the efficiency of water purification and the clarity of the effluent water. 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 steps 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 significantly improves organic matter treatment technology for produced water from high-salinity, high-organic-content gas fields by utilizing a specific yeast fungus—the salt- and acid-tolerant Barnettozyma hawaiiensis (CCTCC M 20241391)—in steps S4 and / or S6. This yeast fungus exhibits excellent salt and acid tolerance, enabling it to effectively degrade difficult-to-degrade organic matter, such as benzene series, in high-salinity and acidic environments. Compared to existing technologies, the beneficial effects of utilizing 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 the wastewater treatment needs of different water quality conditions.

[0045] Lower 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 tolerance of Barnettozyma hawaiiensis improves the stability of the treatment system and reduces the decline in treatment efficiency caused by 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 refractory organic matter is adjusted by controlling the pH value and reaction time.

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

[0052] By adjusting the persulfate concentration to maintain a ratio of 4 to 6 to the total organic carbon (TOC) concentration in the wastewater, the present invention achieves significant improvements in the treatment of produced water from high-salinity, high-organic gas fields. This dosing strategy ensures that persulfate, under the catalytic action of granular activated carbon (GAC), can efficiently generate free radicals, specifically targeting the degradation of organic matter in the wastewater. This method not only improves the efficiency of the oxidation process and ensures rapid removal of organic matter, but also reduces chemical consumption and costs by reducing excessive persulfate use. Furthermore, it helps reduce the formation of byproducts and avoid unnecessary oxidation reactions, thereby improving the stability and adaptability of the treatment process. By controlling the filling rate of the granular activated carbon, sufficient active sites are ensured for sodium persulfate activation, while providing an electron conductor for electron transfer in the redox reaction. Under conditions of high chloride ions, more free radicals are generated, accelerating the electron transfer rate, thereby significantly improving the oxidation efficiency of organic matter under high-salinity conditions. By controlling the pH value and reaction time, the persulfate activation oxidation is maintained under optimal reaction conditions, optimizing the removal efficiency of difficult-to-degrade organic matter.

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

[0054] Further:

[0055] In the steps 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; and 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, temperature, and residence time of the secondary biochemical treatment with salt-tolerant bacteria in steps S4 and / or S6, the present invention significantly improves the degradation efficiency of organic matter, thereby accelerating the removal of pollutants from wastewater. Furthermore, regularly replacing or regenerating the polyurethane filler helps maintain the activity of the salt-tolerant bacteria, ensuring the long-term stable operation and high performance of the treatment system. Compared to existing technologies, these improvements can reduce maintenance costs and improve overall treatment effectiveness, 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 gas field produced water to ensure the flocculation and precipitation effect; and 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] The dosage of sodium hydroxide is precisely adjusted based on the pH value of the gas field produced water to ensure optimal flocculation and sedimentation. This ensures that the polyaluminum chloride (PAC) flocculant is fully hydrolyzed under alkaline conditions to form effective flocs, enabling more optimized flocculation and sedimentation results, thereby improving the removal efficiency of suspended solids and biological flocs. Furthermore, by monitoring the turbidity of the supernatant after flocculation and sedimentation, the dosage of PAC and PAM can be adjusted in real time, ensuring the flexibility and adaptability of the treatment process, further improving effluent quality, and reducing treatment costs. This makes wastewater treatment more precise and economical, contributing to 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 water volume and TDS of the gas field produced water, evaporation desalination or RO membrane concentration followed by evaporation desalination is selected; when the water volume of the gas field produced water is ≤200m 3 / d or TDS≥50000mg / L, evaporation desalination is used; when the TDS of gas field produced water is <50000mg / L, RO membrane concentration followed by evaporation 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 combined with evaporative desalination, based on the volume and total dissolved solids (TDS) value of gas field produced water, allows for more effective treatment of wastewaters of varying salinities, ensuring the adaptability and cost-effectiveness of the treatment process. This approach optimizes energy consumption and operating costs. For high-salinity wastewater, evaporative desalination effectively removes dissolved salts, while for lower-salinity wastewater, RO membrane concentration followed by evaporative desalination is more energy-efficient and cost-effective. Such improvements make wastewater treatment more flexible and economical, contributing to sustainable resource management and environmental protection.

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

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

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

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

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

[0073] a persulfate advanced oxidation unit, configured to perform step S5;

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

[0075] A secondary flocculation and sedimentation unit, configured to execute 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 achieved, 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 following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

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

[0081] Figure 2 This is a diagram showing the state of a black precipitate produced by the reaction of iron-carbon with H2S in step S2.

[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 This 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 TOC removal rate of different added ingredients in the advanced oxidation treatment step.

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

[0087] Figure 8 This is a 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 details 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, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making 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 all conventional methods in the art.

[0091] In this example, the yeast fungus Barnettozyma hawaiiensis was deposited under the accession number CCTCC M20241391. The strain was deposited on June 27, 2024, with the China Center for Type Culture Collection and Wuhan University. The identification process and details of this strain are described in patent application 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 includes 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, uses 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 and sedimentation, adding PAC and PAM for flocculation and sedimentation to remove suspended matter and microbial flocs;

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

[0103] See also Figure 8 , a high-salt and high-organic gas field produced water organic matter treatment system, comprising:

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

[0105] Iron-carbon micro-electrolysis unit 200, used to perform step S2;

[0106] The first-stage flocculation and sedimentation unit 300 is 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] The secondary flocculation and sedimentation unit 700 is used to perform step S7;

[0111] The desalination unit 800 is configured 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 sedimentation:

[0114] This step 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 ), with very high organic matter concentrations (COD of 20,000 to 31,000 mg / L). Gravity oil separation can remove most of the petroleum-based organic matter, reducing the organic matter processing load in subsequent processes. Through oil separation, COD concentrations dropped to 7,000 to 10,000 mg / L, and TOC was 755.12 to 1,078.75 mg / L. Gas field produced water contains a large amount of insoluble suspended matter. Gravity oil separation is performed simultaneously with the removal of large suspended matter by sedimentation. The oil separation retention time is 3 to 5 hours, ensuring sufficient time for oil-water separation and suspended matter sedimentation.

[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 oil separation and sedimentation unit should be designed to facilitate oil-water separation. For example, inclined plates or inclined tubes 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, thereby increasing the oil layer height (the principle is the same as Figure 1 ) is collected and removed in the oil collection pipe. While separating the oil, insoluble suspended matter in the water settles at the bottom of the oil separation and sedimentation unit, forming a sludge layer. The settled sludge is regularly discharged from the bottom of the oil separation and sedimentation unit through a 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 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 regularly discharge settled sludge.

[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] Oil separation and sedimentation units effectively remove the majority of petroleum-based organic matter and suspended solids from produced water, facilitating subsequent treatment steps. The term "major" means that the concentration of these substances is significantly reduced after the oil separation and sedimentation process, typically 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 solids. These suspended colloids adsorb large amounts of COD organic matter, forming a spatially stable or vacant stable state. Directly adding flocculants and coagulants results in poor reaction kinetics, poor flocculation effectiveness, and high agent consumption. Gas field water also contains high levels of hydrogen sulfide. If not removed beforehand, it will consume significant amounts of oxidants and poison microorganisms, hindering the oxidative and biochemical degradation of organic matter. After extensive experimental research and comparisons, and taking into account the water quality conditions of gas field produced water, iron-carbon micro-electrolysis was used for desulfurization and flocculation sedimentation pretreatment.

[0126] The produced water from the gas field, which has undergone oil separation and sedimentation, is introduced into the iron-carbon micro-electrolysis unit 200. At this point, the water sample has an acidic pH of 5 to 6. Hydrochloric acid is added to the produced water to adjust the pH to 3, enhancing the effectiveness of the 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 galvanic cell reaction is carried out using the iron-carbon filler in the reactor. The filler of the iron-carbon micro-electrolysis reactor is iron-carbon, which is made by melting 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 should be at least 5 cm higher than the top of the packing.

[0128] Fe is produced at the anode 2+ At the cathode, [H] (hydrogen atoms) and [O] (oxygen atoms) are produced. These active substances readily undergo redox reactions with organic matter, reducing COD and degrading large-molecule petroleum organic matter into small molecules. This reduces the Zeta potential of colloids in produced water, facilitating the destabilization and sedimentation of suspended colloidal matter.

[0129] H2S in produced water and Fe in solution 3+ The reaction produces a black Fe2S3 precipitate. The experimental results are as follows Figure 2 As shown, the influence of H2S on subsequent reactions is eliminated.

[0130] The iron-carbon micro-electrolysis reaction time 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 is treated with iron-carbon micro-electrolysis, the COD is further reduced, the macromolecular organic matter is degraded, and the colloidal suspended matter is effectively treated, and then discharged as effluent and enters the subsequent treatment unit.

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

[0134] Reactor: designed to be connected in 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 the water sample before entering the reactor.

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

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

[0139] (3) Primary flocculation precipitation:

[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 point, the pH value of the water sample has risen to 6 to 7. Sodium hydroxide is added to the gas field produced water 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 pH-adjusted gas field produced water at a dosage of 2-5 mg / L to enhance flocculation. PAM interacts with the iron salt flocs to form larger flocs, which settle by gravity, separating suspended solids and some colloidal organic matter from the water. During the sedimentation process, the resulting sludge accumulates at the bottom of the sedimentation tank and is regularly discharged through the sludge discharge system.

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

[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, organic matter is partially removed and large molecular 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 decreased, the types decreased, and the molecular weight became smaller), the Zeta potential of the colloid decreased, and the flocculation effect was better ( Figure 4 ), H2S is removed by Fe2S3 precipitation, providing 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 the primary flocculation and sedimentation treatment is introduced into the salt-tolerant bacteria primary biochemical treatment unit 400.

[0150] After the iron-carbon microelectrolysis reaction, large organic molecules are degraded into smaller ones, improving their biodegradability. However, conventional microorganisms are inhibited by the high salt content in gas field produced water. Therefore, a special salt-tolerant bacteria, Barnettozyma hawaiiensis, with the deposit number CCTCC M 20241391, is used for degradation. This bacteria is salt-tolerant (sodium chloride concentration 0-12% by mass) and highly efficient in degrading organic matter.

[0151] Inoculate salt-tolerant bacteria into polyurethane filler ( Figure 5 ), the polyurethane filler was inoculated with salt-tolerant bacteria at a concentration of 11.225 g / L, the polyurethane filler specification was 2 × 2 cm, and the density was 1 g / cm 3 Polyurethane filler was added to the primary biochemical reactor for the halophilic bacteria (filling rate: 75%). Under aerobic conditions, the temperature was controlled at 30°C and the initial pH was 5, and the degradation reaction was carried out. The halophilic bacteria degradation reaction lasted for 24 to 48 hours to ensure effective degradation of the organic matter.

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

[0153] After biochemical treatment, the aged floccules in the effluent 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 first-level 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 second-level biochemical treatment.

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

[0156] Biochemical reactor: A container designed for the growth and metabolism of microorganisms, which can be 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] The persulfate advanced oxidation reactor is filled with granular activated carbon (GAC) measuring 4 x 10 mm in diameter and with a fill ratio of 50%, serving as a persulfate activator. Sodium persulfate (PDS) is used as an oxidant. The synergistic effect of high chloride ion concentrations (20,000 to 50,000 mg / L) generates more hydroxyl and sulfate radicals, while accelerating electron transfer. The combined effects of free radical and non-radical electron transfer pathways enable rapid degradation of organic matter under high salinity conditions.

[0166] like Figure 6 As shown in the figure, 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 perform advanced oxidation treatment on organic matter in high-salt wastewater, avoiding the effect of chloride ions on quenching 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 dosage to wastewater TOC concentration is 4 to 6, and it is evenly added 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, ensuring 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 inlet water for the next step of treatment.

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

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

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

[0175] Sodium persulfate (PDS) dosing system: used to precisely 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, processing efficiency and flexibility can be improved.

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

[0180] The gas field produced water 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, organic matter is effectively removed, and 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 species inoculated is yeast fungus (Barnettozyma hawaiiensis). The salt-tolerant bacteria are inoculated into the polyurethane filler ( Figure 5 ), the polyurethane filler was inoculated with salt-tolerant bacteria at a concentration of 11.225 g / L, the polyurethane filler specification was 2 × 2 cm, and the density was 1 g / cm 3 Polyurethane filler was added to the primary biochemical reactor of salt-tolerant bacteria, with a fill rate of 75%. Under aerobic conditions, the temperature was controlled at 30°C and the initial pH was 5, and the secondary biochemical degradation reaction was carried out. The degradation time was 24 to 48 hours to ensure the effective degradation of small molecular organic matter.

[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 and sedimentation:

[0185] Produced water from the gas field, which has undergone secondary biochemical treatment with salt-tolerant bacteria, is introduced into the secondary flocculation and sedimentation unit 700. Since the pH of the water sample rises to 6-7 after secondary biochemical treatment, sodium hydroxide is added to adjust the pH to 8-9 to optimize flocculation conditions. Polyaluminum chloride (PAC) is added to the pH-adjusted produced water at a dosage of 100-200 mg / L to form effective flocs. Polyacrylamide (PAM) is also added at a dosage of 3-5 mg / L to enhance the stability and settling performance of the flocs. The PAC and PAM work together to form larger flocs, which settle by gravity, separating suspended solids and microbial flocs from the water.

[0186] During the sedimentation process, the sludge formed accumulates at the bottom of the sedimentation tank and is regularly discharged 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 content and total dissolved solids (TDS) concentration of the supernatant were 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 ≥ 50000 mg / L, evaporation desalination technology can be used. Select 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 biochemical treatment, the condensate after evaporation has less organic matter (TOC is 10-30 mg / L, COD is 30-100 mg / 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 "Integrated Sewage Discharge Standard".

[0194] When the TDS of gas field produced water is less than 50,000 mg / L, reverse osmosis (RO) membrane technology is used for desalination. The RO membrane separates fresh water, which can be used for resource utilization or discharged in compliance with standards. The concentrated water fraction is evaporated and crystallized to further reduce the salt content. RO membrane concentration pretreatment reduces evaporative water volume and lowers energy consumption. It is expected to reduce evaporative water volume by over 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 treating organic matter in produced water from a high-salt 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 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 H2S at the same time.

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

[0204] Halophilic bacteria primary biochemical treatment: The supernatant is adjusted to pH 5 and then fed into the halophilic bacteria primary biochemical tank. Polyurethane filler inoculated with the halophilic bacteria Barnettozyma hawaiiensis is added to a 75% fill rate. Aerobic biochemical reaction is carried out at 30°C for one day.

[0205] Sedimentation and Advanced Oxidation: After sedimentation, the supernatant from the biochemical effluent enters the GAC+PDS advanced oxidation reactor. The GAC is filled at a 50% rate and has a mass concentration of ρ(PDS) / TOC of 5. The reactor is fed in two stages. The pH of the final stage is controlled at approximately 5 to improve 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%, and the biochemical reaction is carried out for one day.

[0207] Secondary flocculation and 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 and 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, evaporation treatment is carried out directly after biochemical treatment. The evaporated condensate is utilized as a resource or discharged in compliance with standards.

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

[0210] Since the TDS is 34150 mg / L, the water sample after secondary flocculation and sedimentation can also be concentrated using RO membranes. A filtration device is required before entering the RO membrane to protect the membrane from suspended solids and large particulate matter. The RO membrane concentrate enters the evaporator for evaporation and crystallization to recover salt. The evaporation condensate and RO membrane fresh water are discharged for agricultural irrigation or to meet discharge standards.

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

[0212] The effluent in both cases meets the COD and TDS standard requirements for dryland and wetland 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 example, after undergoing various treatment steps, the TOC content of high-salinity, high-organic gas field produced water from this high-salinity, high-organic gas field was significantly reduced, as shown in Table 2, from 1693 mg / L in the raw water to 11.74 mg / L after RO membrane treatment, achieving a total removal rate of 99.31%. Simultaneously, the conductivity also decreased from 68.3 mS / cm to 0.59 mS / cm, demonstrating effective salt removal. This series of treatment steps not only improves water quality but also enables water recycling and reuse, providing significant environmental and economic benefits.

[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 weight 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 decreased, indicating that some organic matter was degraded or transformed.

[0220] After primary biochemical treatment with salt-tolerant bacteria ( Figure 7 In middle 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 extremely low fluorescence intensity, reflecting a significant reduction in organic matter in the water sample, which meets the standards for farmland irrigation or discharge.

[0224] Fluorescence images confirm that the organic matter in the gas field produced water has been significantly reduced throughout the entire treatment process, meeting the expected treatment standards and making it suitable for resource utilization or discharge. These 3D fluorescence images provide a visual representation of the effect of each treatment step on the removal of organic matter from the gas field produced water, allowing us to assess the efficiency of the entire treatment process and potential for optimization. This information is valuable for improving water treatment processes and enhancing water quality.

[0225] In the description of the present invention, it should be understood that "-" and "~" represent a 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" 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 and mass involved may be based on actual measurements, standard parameters of equipment, simplified rounding results, or within an acceptable error range, ensuring the practicality 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 merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating organic matter in produced water from a high-salt 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, uses 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 and sedimentation, adding PAC and PAM for flocculation and sedimentation to remove suspended matter and microbial flocs; S8, desalination, select evaporation desalination or RO membrane concentration followed by evaporation desalination according to the TDS value of the produced water; In the steps S4 and / or S6, the salt-tolerant bacteria are yeast fungi. Barnettozyma hawaiiensis , the deposit number is CCTCC M 20241391, and the yeast fungus also has the characteristics of acid resistance and degradation of benzene series.

2. The method for treating organic matter in produced water from a high-salt and high-organic 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-salt and high-organic 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-salt and high-organic 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 gas field produced water to ensure the flocculation and precipitation effect; and 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-salt and high-organic 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 refractory organic matter is adjusted by controlling the pH value and the reaction time.

6. The method for treating organic matter in produced water from a high-salt and high-organic gas field according to claim 1, characterized in that: In the steps 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; and the polyurethane filler is regularly replaced or regenerated to maintain the activity and treatment efficiency of the salt-tolerant bacteria.

7. The method for treating organic matter in produced water from a high-salt and high-organic 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 gas field produced water to ensure the flocculation and precipitation effect; and the dosage of PAC and PAM is further adjusted by monitoring the turbidity of the supernatant after flocculation and precipitation.

8. The method for treating organic matter in produced water from a high-salt and high-organic 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 ≤200m³ / d or TDS is ≥50000mg / L, evaporation desalination is adopted; when the gas field produced water TDS is ≥50000mg / L, evaporation desalination is adopted. When the concentration is less than 50000 mg / L, RO membrane is used for concentration and then evaporation for desalination.

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