Gas field wastewater treatment process

Abstract

The invention discloses a gas field wastewater treatment process, belongs to the technical field of wastewater treatment, and solves the technical problems of poor treatment effect and high cost of fracturing flowback fluid in the prior art. The treatment process comprises regulating homogenization, flotation reaction, advanced oxidation, biochemical treatment, boron removal treatment and membrane treatment. The flotation reaction comprises adding 10-300 ppm of an organic breaker, 50-1100 ppm of a hard water softener, 1-200 ppm of a heavy metal scavenger, 1‰-2‰ of a flocculant, and 10-100 ppm of a coagulant aid to the wastewater, and pneumatically stirring the wastewater to obtain a supernatant. The advanced oxidation comprises performing ozone oxidation, iron-carbon micro-electrolysis and electrocatalytic oxidation on the supernatant obtained by the flotation reaction. The biochemical treatment comprises performing anaerobic denitrification and aerobic treatment on the wastewater after the advanced oxidation. The invention has the advantages of low dosage of reagents, simple and stable process, high treatment efficiency and no secondary pollution.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, in particular to a gas field wastewater treatment process. Background Art

[0002] Fracturing flowback fluid is a mixed liquid returned to the surface after hydraulic fracturing is used to increase oil and gas well production. It contains not only the fracturing fluid originally injected into the formation but also carries various contaminants from the formation. After years of development, hydraulic fracturing has become a key productivity enhancement measure for increasing oil and gas well productivity and reservoir recovery. Fracturing fluids possess high viscosity, low fluid loss, and excellent rheological properties, enabling them to transmit pressure and purify fractures. To meet these performance requirements, fracturing fluids require the addition of various additives, including thickeners, crosslinkers, biocides, clay stabilizers, high-temperature stabilizers, drainage aids, pH stabilizers, breakers, and fluid loss control agents. The flowback fluid returned to the surface primarily consists of suspended solids, crude oil, microorganisms, inorganic salts, inorganic acids, and organic matter, primarily polycyclic aromatic hydrocarbons. It is a complex multiphase dispersion system characterized by high COD, high stability, high viscosity, high toxicity, and resistance to degradation.

[0003] Therefore, the technical difficulties in treating fracturing flowback fluid lie in demulsification and gel breaking. To reduce COD, there are mainly biological bacterial treatment, chemical treatment and oxidative electrolysis methods. However, in actual projects, the treatment effect of fracturing flowback fluid is not good and the treatment cost is high. Summary of the Invention

[0004] The present invention aims to solve the technical problems of poor treatment effect and high cost of fracturing return fluid in the existing technology. It aims to provide a gas field wastewater treatment process that effectively degrades organic matter, removes heavy metals, and reduces COD. The process setting is reasonable, the amount of reagent added is small, the process is simple and stable, the treatment efficiency is high, there is no secondary pollution, and the effective separation of mineral oil, impurities and water is achieved.

[0005] The present invention is achieved through the following technical solutions:

[0006] A gas field wastewater treatment process, comprising regulating homogenization, and also comprising sequentially performing flotation reaction, advanced oxidation, biochemical treatment, boron removal treatment and membrane treatment;

[0007] The flotation reaction is to add 10-300 ppm of organic breaker, 50-1100 ppm of hard water softener, 1-200 ppm of heavy metal scavenger, 1‰-2‰ of flocculant, and 10-100 ppm of coagulant aid to the wastewater, and obtain a supernatant after pneumatic stirring;

[0008] The advanced oxidation comprises ozone oxidation, iron-carbon micro-electrolysis and electrocatalytic oxidation of the supernatant obtained from the flotation reaction;

[0009] The biochemical treatment includes anaerobic denitrification and aerobic treatment of the sewage after advanced oxidation, and the anaerobic denitrification reflow ratio is 80%-200%.

[0010] When treating wastewater, the present invention first adjusts the wastewater to a suitable pH by homogenizing, removes most of the sludge and recovers floating oil, then performs flotation reaction and drug addition treatment, discharges the sludge, obtains a supernatant, and then decomposes part of the organic matter through ozone oxidation to achieve the purpose of decolorization, converts refractory organic matter into more biodegradable organic matter through iron-carbon micro-electrolysis, converts part of the toxic organic matter into low-toxic or non-toxic organic matter, removes part of the COD, and decomposes refractory and toxic substances in the wastewater into low-molecular and low-toxic or non-toxic substances through electrocatalytic oxidation, providing favorable conditions for subsequent biochemical treatment.

[0011] Afterwards, in anaerobic denitrification, the hydrolysis effect of domesticated facultative anaerobic microorganisms is used to convert large molecular organic matter into small molecular organic matter that is conducive to the degradation of aerobic microorganisms. The denitrification effect of denitrifying bacteria is used to remove nitrate or denitrify in the wastewater to achieve the purpose of denitrification. Then, contact oxidation is carried out. Under aeration conditions, the directed domestication of salt-tolerant microorganisms is used to completely decompose the soluble and colloidal organic matter under high salt conditions. Finally, boron removal treatment is carried out to reduce the boron content in the wastewater, and membrane treatment is used to achieve the purpose of desalination, removal of heavy metals and radioactive ions, and obtain clean water that meets the requirements.

[0012] The present invention combines physical, electrochemical and biological methods to treat gas field wastewater, adopts the order of chemical degradation first and regeneration treatment, and prevents the adverse effects of toxic, harmful or difficult-to-degrade substances in the wastewater on biochemical microorganisms. The treatment agent of the present invention is low in price, widely available, low in dosage, and simple and easy to use. The solid phase, water phase and oil phase separation speeds of the entire process are fast, and indicators such as CODr, ammonia nitrogen and total phosphorus can be quickly reduced to standard requirements. The amount of agent added is small, which saves treatment costs, and recovers crude oil in the fracturing return fluid. After harmless treatment, the sewage enters the urban pipe network, which not only saves clean water resources but also avoids the problem of gas field wastewater being discharged and polluting the environment.

[0013] Furthermore, the conditioning and homogenization process specifically involves adjusting the wastewater pH to 6-9 and allowing it to settle by gravity for 16-24 hours to remove most of the sludge and recover floating oil. Specifically, conditioning and homogenization are performed in a regulating tank. Hydrochloric acid and caustic soda solutions (20%-40% concentration) are added to adjust the wastewater pH to 6-9, providing a suitable acid-base environment for subsequent treatment. A floating oil collection drum collects the oil-water mixture on the surface of the wastewater in the regulating tank and transfers it to an oil-water separator to ensure there is no floating oil in the regulating tank. The mixed liquid entering the oil-water separator undergoes oil-water separation (gravity separation), with the separated mineral oil outsourced for disposal and the aqueous phase returned to the regulating tank.

[0014] Furthermore, the organic breaker is HJP-103 (Kaifeng Hengju Biotechnology Co., Ltd.), the hard water softener is a mixture of any one or more of calcium carbonate, anhydrous sodium sulfate, calcium oxide, sodium phosphate, disodium EDTA, and tetrasodium EDTA, the heavy metal scavenger is a mixture of any one or more of sodium sulfide, water glass, sodium carbonate, sodium phosphate, magnesium aluminum silicate, polyaluminum chloride, organic sulfur polymer TMT, HMC-M1 heavy capture agent, xanthate, and dithiocarbamate, the flocculant is PAC or polyferric sulfate, and the coagulant aid is cationic PAM.

[0015] Furthermore, during the iron-carbon micro-electrolysis, a flocculant is added, using KW3820 or cationic PAM. The redox action of the Fe / C primary cell generates a series of reactions, including redox reactions, primary cell reactions, electrochemical enrichment, physical adsorption, and coagulation and precipitation. This causes organic matter in the water to undergo chain scission, ring opening, and carbonization, converting difficult-to-degrade organic matter into more biodegradable organic matter, and converting some toxic organic matter into low-toxic or non-toxic organic matter, removing some COD. Simultaneously, the flocculant is used to remove iron / ferrous ions, some organic pollutants, and suspended solids from the wastewater through flocculation and precipitation. The iron-carbon micro-electrolysis system uses an integrated sintered filler, avoiding the problems of traditional equipment such as easy passivation and the generation of large amounts of iron sludge.

[0016] Furthermore, the electrocatalytic oxidation is carried out within an electrocatalytic oxidation cell, which is equipped with at least two sets of electrocatalytic oxidation devices. The electrocatalytic oxidation devices utilize bifunctional electrodes, i.e., titanium-based electrodes doped with metal oxides. The electrocatalytic oxidation cell utilizes the bifunctional electrodes, with the potential difference generated between the anode and cathode surfaces, to oxidize and decompose organic matter and reduce and precipitate metal ions, respectively. Specifically, one side comprises a multinary metal oxide electrocatalytic anode surface doped with rare earth metals, which exhibits high electrocatalytic oxidation activity, enabling the degradation and mineralization of relatively stable organic matter. The other side comprises an electrocatalytic cathode surface, which exhibits electrochemical reduction activity, enabling the electrodeposition and removal of heavy metal ions.

[0017] Furthermore, the boron removal treatment reduces the boron content in the sewage to below 0.5 mg / L.

[0018] Furthermore, the boron removal process utilizes KL+CC filter media. During KL treatment of boron-containing wastewater, 30% of the KL effluent is recycled to produce a boron concentrate. The higher the boron content in the concentrate, the more likely it is for aggregated particles to exist as B5O6(OH)4, allowing boron to be easily and efficiently adsorbed while simultaneously removing its hydroxide. CC has a high boron removal capacity. Compared to ion exchange resins, reverse osmosis, or other traditional technologies, this technology consumes very few chemicals when cleaning the adsorbent. This unique method can effectively treat large volumes of water.

[0019] Furthermore, the membrane treatment includes microfiltration membrane, ultrafiltration membrane and reverse osmosis membrane treatment units.

[0020] Furthermore, the microfiltration membrane and ultrafiltration membrane intercept colloids and fine particles larger than 0.1-1 microns and larger than 0.001-0.01 microns, respectively. The reverse osmosis membrane utilizes a single-stage, two-stage ultrahigh-pressure reverse osmosis membrane. The microfiltration and ultrafiltration membranes provide a protective barrier for the reverse osmosis membrane assembly, ensuring its stable operation.

[0021] Furthermore, the residence time of the flotation reaction stage is 2-16 hours, the residence time of the advanced oxidation stage is 5-10 hours, the residence time of the biochemical treatment stage is 20-50 hours, the residence time of the boron removal treatment stage is 2-8 hours, and the residence time of the membrane treatment stage is 0.5-4 hours.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1. The present invention combines physical, electrochemical and biological methods to treat gas field wastewater, adopts the order of chemical degradation first and then regeneration treatment, prevents the adverse effects of toxic, harmful or difficult-to-degrade substances in the wastewater on biochemical microorganisms, and effectively degrades organic matter and reduces COD through a combined process of ozone oxidation, iron-carbon micro-electrolysis and electrocatalytic oxidation, and sets a suitable reflux ratio, providing favorable conditions for subsequent biochemical treatment. At the same time, the treatment agent is inexpensive, widely available, and requires low dosage. The process is simple and easy, and the solid phase, aqueous phase and oil phase separation speed of the entire process are fast. Indicators such as CODr, ammonia nitrogen, and total phosphorus can be quickly reduced to standard requirements.

[0024] 2. The present invention uses a bifunctional electrode of "metal oxide-doped titanium-based electrode" in the electrocatalytic oxidation process section, which not only has a high-level electrocatalytic oxidation activity function, which can degrade and mineralize organic matter with a relatively stable structure, but also has an electrochemical reduction activity function, which can remove heavy metal ions by electrodeposition. At the same time, the bifunctional electrode of "metal oxide-doped titanium-based electrode" has a long life, can reduce costs, and avoids the problems of high requirements for the number of power pulses, frequent replacement of cathode plates, and short life of ordinary electrocatalytic oxidation.

[0025] 3. The anaerobic and aerobic microorganisms used in the biochemical treatment of the present invention are all independently domesticated and cultured for a long time. They are put into use after being domesticated for 1-2 months, which avoids the problems of commercially available strains being unadaptable to high-salt water quality, having low survival rates, unclear biofilm formation, and poor or even no treatment effects.

[0026] 4. The boron removal treatment of the present invention adopts KL+CC filter material, which has a high boron removal ability and can effectively reduce the boron content to below 0.5 mg / L, with high treatment efficiency.

[0027] 5. The present invention adopts a combined process of microfiltration (MF) + ultrafiltration (UF) + reverse osmosis (RO), which can effectively remove colloids and fine particles, and achieve the purpose of desalination, removal of heavy metals and radioactive ions.

[0028] 6. The treatment process of the present invention can accept sewage that seriously exceeds the standard, and the maximum acceptable COD concentration of the influent is 20,000 mg / L. During actual operation, the process can be skipped according to the source water quality to reduce the treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0030] Figure 1 This is a process flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0032] Example 1

[0033] This embodiment provides a gas field wastewater treatment process, comprising the following steps:

[0034] 1. Monitor the gas field wastewater transported by tank trucks. Once it meets the water inlet standards, transfer the wastewater to the regulating tank through a lift pump. Add hydrochloric acid to adjust the pH to 7-8 and allow gravity sedimentation for 16-24 hours to remove most of the sludge and recover the floating oil.

[0035] 2. The wastewater from the regulating tank is pumped to the flotation machine. While stirring, 30 ppm of organic gel breaker HJP-103, 200 ppm of calcium carbonate, 40 ppm of anhydrous sodium sulfate, 2‰ of PAC, 20 ppm of cationic coagulant PAM (molecular weight 16 million, cationicity 70, the same below), and 40 ppm of heavy metal scavenger HMC-M1 are added in sequence. After pneumatic stirring, the wastewater flows to the rear end and remains there for 0.2-2 hours. A scraper removes the floating oil from the top into an oil tank, and the clear liquid is pumped to the ozone oxidation tank. The sludge at the bottom is pumped to the sludge tank for treatment.

[0036] 3. In the ozone oxidation tank, ozone generated by the ozone generator is mixed with wastewater through the ozone jet dosing device to form a gas-liquid mixture. This mixture is then transported to the ozone oxidation tank for a pressurized catalytic oxidation reaction, which decomposes some organic matter and achieves the purpose of decolorization. A gas collection hood is placed on the top of the ozone oxidation tank to collect and reuse unreacted ozone to avoid environmental pollution. The treated wastewater enters the iron-carbon micro-electrolysis cell through the overflow port.

[0037] 4. When the wastewater enters the iron-carbon micro-electrolysis cell, control the wastewater volume to be 1-5 cm higher than the iron-carbon filler, add hydrochloric acid to adjust the pH to 1-4, and react for 0.5-10 hours.

[0038] 5. After the iron-carbon micro-electrolysis treatment, the wastewater enters the sedimentation tank. A 20%-40% caustic soda solution is used to adjust the pH to 7-9. PAC 1‰ and cationic PAM 15ppm are added and slowly stirred until flocs form. The supernatant is pumped to the electrocatalytic oxidation tank, and the precipitated sludge is pumped to the sludge tank for treatment.

[0039] 6. The electrocatalytic oxidation tank utilizes a dual-function electrode, a "titanium-based electrode doped with metal oxides." The potential difference between its anode and cathode surfaces oxidizes and decomposes organic matter and reduces and precipitates metal ions, respectively. Two electrocatalytic oxidation devices are used. The hydraulic retention time is 4-6 hours. After sufficient chemical oxidation, the wastewater is pumped to an anaerobic tank for biochemical reactions, and the bottom sludge is pumped to a sludge tank for treatment.

[0040] The parameters and functions of each stage involved in advanced oxidation are shown in Table 1.

[0041] Table 1. Parameters and effects of advanced oxidation

[0042]

[0043] 7. The sewage recirculation ratio in the anaerobic tank is set at 80%-160%, and it stays for 10-14 hours. The overflow enters the anoxic tank, and the bottom sludge is pumped to the sludge tank for treatment. In the anaerobic tank, the hydrolysis of domesticated facultative anaerobic microorganisms is used to convert large molecular organic matter into small molecular organic matter that is conducive to aerobic microbial degradation. Denitrification by denitrifying bacteria removes nitrates and denitrification in the wastewater, achieving the purpose of denitrification.

[0044] The bacteria added to the anaerobic tank are facultative anaerobic microorganisms, which are acclimated for 1-2 months before being added to the anaerobic tank. The initial addition amount is 100-200g / m 3 , at the same time press 0.1-10Kg / m 3 Flour, glucose, sodium acetate, glacial acetic acid, methanol or a mixture of the two is added as a carbon source to provide energy for the microorganisms. 30-50g of bacterial strains are added every day. The bacterial strains include methanogenic bacteria, pseudomonas, lactic acid bacteria, yeast, kidney-shaped worms, scale worms, and oblique tube worms. At the same time, the carbon source is added. After 10-30 days, sewage is added at a quarter of the tank volume every day, and the bacterial strain is continued to be added. The carbon source is halved every three days until the carbon source is no longer added after 12 days, and sewage is added at a normal flow rate.

[0045] 8. The anoxic tank denitrifies the sewage with a retention time of 2-10 hours. The wastewater overflows into the aerobic tank and the sludge at the bottom is pumped to the sludge tank for treatment.

[0046] 9. The aerobic tank is filled with honeycomb packing, which is submerged in the incoming wastewater. A Roots blower provides aeration and oxygenation at the bottom of the packing. Activated sludge is stabilized on the packing surface, and the biofilm is continuously renewed by the strong agitation of the updraft. Directly acclimated salt-tolerant microorganisms remove soluble and colloidal organic pollutants from the wastewater. The hydraulic retention time in the aerobic tank is 8-30 hours, and the air-to-water ratio is 8:1. After the aerobic reaction, the wastewater is pumped to the boron removal unit. The bottom sludge is pumped to a sludge tank for treatment.

[0047] The bacteria added to the aerobic pool are salt-tolerant microorganisms that have been domesticated for 1-2 months before being added to the aerobic pool. The initial addition amount is 100-200g / m 3 , at the same time press 0.1-10Kg / m 3 Flour, glucose, sodium acetate, glacial acetic acid, methanol, or a mixture of the two is supplemented as a carbon source to provide energy for the microorganisms. 30-50g of bacterial strains, including Bacillus, high-efficiency flocculants, proteases, Trichuris trichiura, Trichuris spp., and Acinetobacter calcoaceticus, are added daily, along with a carbon source, for 10-30 days. After this, sewage is introduced at a quarter of the tank volume daily, and bacterial strains are continuously added. The carbon source is halved every three days until, after 12 days, no more carbon source is added, and sewage is introduced at a normal flow rate.

[0048] 10. The wastewater passes through KL and CC filter media sequentially, reducing the boron content to below 0.5 mg / L. The wastewater is then pumped to the membrane treatment unit. The residence time in this stage is 2-8 hours. During the KL treatment of boron-containing wastewater, 30% of the KL effluent is recycled to produce a boron concentrate. The higher the boron content in the concentrate, the more likely it is to aggregate particles in the form of B5O6(OH)4, allowing the boron to be efficiently adsorbed and its hydroxide removed simultaneously. CC has a high boron removal capacity and consumes very little chemical reagents for adsorbent cleaning compared to ion exchange resins, reverse osmosis, or other traditional technologies. This unique method can effectively treat large volumes of water.

[0049] 11. The wastewater after boron removal is pumped into the membrane treatment system. Chloride salts, heavy metal ions, and radioactive ions are removed through microfiltration, ultrafiltration, and reverse osmosis membrane treatment units. Once the wastewater meets the discharge standards, it enters the clean water tank for monitoring and discharge. The residence time in this stage is 0.5-4 hours.

[0050] Microfiltration (MF) + ultrafiltration (UF) can intercept colloids and fine particles larger than 0.1-1 microns and larger than 0.001-0.01 microns respectively, providing a protective barrier for the reverse osmosis (RO) membrane assembly to ensure its stable operation.

[0051] Among them, reverse osmosis (RO) adopts a one-stage two-stage ultra-high pressure reverse osmosis membrane treatment process:

[0052] The first stage SWRO system design parameters:

[0053] Influent TDS: 3%-4%

[0054] Operating pressure: 8MPa

[0055] Desalination rate: 90%

[0056] Recovery rate: 50% (concentrated water TDS 6%-8%)

[0057] Second stage UHPRO system design parameters:

[0058] Influent TDS: 6%-8%

[0059] Operating pressure: 12MPa

[0060] Salt rejection rate: 75%

[0061] Recovery rate: 50% (concentrated water TDS 12%-16%)

[0062] The comprehensive recovery rate is: 50% + (1-50%) 50% = 75%

[0063] The comprehensive desalination rate is 97.5%.

[0064] 12. The supernatant in the sludge pool overflows into the regulating tank. The bottom sludge is dehydrated and pressed into cakes using a plate and frame filter press every 10-120 days. The pressed water enters the regulating tank. After testing, the mud cake is sent to the brick factory for disposal as general waste.

[0065] The size of the tank and the processing capacity of the equipment involved in each stage of the present invention, such as homogenization adjustment, flotation reaction, advanced oxidation, biochemical treatment, boron removal treatment, and membrane treatment, are designed according to actual needs.

[0066] This environmentally friendly method combines physical, electrochemical, and biological methods to treat gas field wastewater. It employs a sequence of chemical degradation followed by regeneration to prevent the adverse effects of toxic, harmful, or difficult-to-degrade substances in the wastewater on biochemical microorganisms. Furthermore, the biochemical treatment utilizes targeted microbial domestication, reducing the dosage of reagents and treatment costs while achieving fully satisfactory treatment results. Crude oil is recovered from fracturing flowback fluid, and after harmless treatment, the wastewater enters the urban pipe network, conserving clean water resources while avoiding environmental pollution caused by the discharge of gas field wastewater, thereby ensuring the stable operation of the oilfield.

[0067] Example 2

[0068] The difference between this embodiment and embodiment 1 is that the flocculant PAC in step 2 is replaced by polyferric sulfate, and the addition amount is 2‰.

[0069] The other steps are the same as those in Example 1.

[0070] Example 3

[0071] The difference between this embodiment and embodiment 1 is that in steps 2 and 5, PAC and cationic PAM are replaced with an organic dehydrating agent KW3820 (Dongwan Kaiwell Environmental Protection Technology Co., Ltd.), the dosage in step 2 is 100-500 ppm, and the dosage in step 4 is 10-100 ppm.

[0072] The other steps are the same as those in Example 1.

[0073] Example 4

[0074] The difference between this embodiment and embodiment 1 is that the two groups of electrocatalytic oxidation devices in step 6 are replaced with three groups of electrocatalytic oxidation devices.

[0075] The other steps are the same as those in Example 1.

[0076] Example 5

[0077] The differences between this embodiment and embodiment 1 are: in step 6, the two groups of electrocatalytic oxidation devices are changed to three groups of electrocatalytic oxidation devices; and in step 7, the reflux ratio is 100%-200%.

[0078] The other steps are the same as those in Example 1.

[0079] Example 6

[0080] The difference between this embodiment and embodiment 1 is that step 7 is omitted, and the water output from step 6 directly enters step 8.

[0081] The other steps are the same as those in Example 1.

[0082] The treatment process of Examples 1-6 was used to treat the mixed wastewater generated during the drilling and production of 6 shale gas wells in Weiyuan and Luzhou, and the sewage treatment effect was good. The water inlet requirements before treatment in each process section of the present invention are shown in Table 2. The evaluation standard after treatment is: the third-level discharge standard of the "Comprehensive Sewage Discharge Standard" (GB / T 8978-1996). Among them, ammonia nitrogen, total phosphorus, petroleum, and chloride comply with the "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T 31962-2015) Class A, and barium ions reach the "Sichuan Province Water Pollutant Discharge Standard" (DB51190-93) Class W. By comparing the sewage treatment of Examples 1-6, the results are shown in Table 3.

[0083] Table 1. Water requirements before treatment in each process section

[0084]

[0085] Table 3. Test results of treated effluent

[0086]

[0087]

[0088] Note: Category I pollutants were not detected and were not detected before and after treatment. The boron content in the effluent was below 0.5 mg / L, meeting WHO requirements.

[0089] Field experiments and online monitoring data show that all indicators of the effluent treated by the treatment process of the present invention meet the standard requirements. By comparison, Example 5 has the best effect. It can be seen that the installation of the electrocatalytic oxidation device and the appropriate reflux ratio can effectively improve the wastewater treatment effect.

[0090] In summary, the gas field wastewater treatment process of the present invention has the advantages of low dosage of reagents, simple and stable process, high treatment efficiency, and no secondary pollution. It realizes the effective separation of mineral oil, impurities and water, and solves the direct or potential impact of gas field wastewater on the environment.

[0091] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gas field wastewater treatment process, characterized in that: It includes sequential homogenization, flotation reaction, advanced oxidation, biochemical treatment, boron removal treatment and membrane treatment; The flotation reaction is to add 10-300 ppm of organic breaker, 50-1100 ppm of hard water softener, 1-200 ppm of heavy metal scavenger, 1‰-2‰ of flocculant and 10-100 ppm of coagulant aid to the wastewater, and obtain a supernatant after pneumatic stirring; The advanced oxidation comprises ozone oxidation, iron-carbon micro-electrolysis and electrocatalytic oxidation of the supernatant obtained from the flotation reaction; The biochemical treatment includes anaerobic denitrification and aerobic treatment of the wastewater after advanced oxidation, and the anaerobic denitrification reflow ratio is 80%-200%; The boron removal treatment reduces the boron content in the sewage to below 0.5 mg / L, and the boron removal treatment uses KL+CC filter material; The membrane treatment includes microfiltration membrane, ultrafiltration membrane and reverse osmosis membrane treatment units; The residence time of the flotation reaction stage is 2-16 hours, the residence time of the advanced oxidation stage is 5-10 hours, the residence time of the biochemical treatment stage is 20-50 hours, the residence time of the boron removal treatment stage is 2-8 hours, and the residence time of the membrane treatment stage is 0.5-4 hours.

2. A gas field wastewater treatment process according to claim 1, characterized in that: The regulating homogenization specifically includes: adjusting the pH of the wastewater to 6-9, gravity settling for 16-24 hours, removing most of the sludge and recovering the floating oil.

3. A gas field wastewater treatment process according to claim 1, characterized in that: The organic gel breaker is HJP-103, the hard water softener is a mixture of any one or more of calcium carbonate, anhydrous sodium sulfate, calcium oxide, sodium phosphate, disodium EDTA, and tetrasodium EDTA, the heavy metal scavenger is a mixture of any one or more of sodium sulfide, water glass, sodium carbonate, sodium phosphate, magnesium aluminum silicate, polyaluminum chloride, organic sulfur polymer TMT, HMC-M1 heavy capture agent, xanthate, and dithiocarbamate, the flocculant is PAC or polyferric sulfate, and the coagulant aid is cationic PAM.

4. A gas field wastewater treatment process according to claim 1, characterized in that: During the iron-carbon micro-electrolysis, a flocculant is also added, wherein the flocculant is a cationic PAM.

5. A gas field wastewater treatment process according to claim 1, characterized in that: The electrocatalytic oxidation is carried out in an electrocatalytic oxidation pool, in which at least two groups of electrocatalytic oxidation devices are arranged. The electrocatalytic oxidation devices use bifunctional electrodes of titanium-based electrodes doped with metal oxides.

6. A gas field wastewater treatment process according to claim 1, characterized in that: The reverse osmosis membrane adopts a one-stage two-stage ultra-high pressure reverse osmosis membrane.

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