Fracturing fluid treatment method based on MABR

Abstract

The present application relates to the technical field of sewage treatment, and is a fracturing flowback fluid treatment method based on MABR, which is performed according to the following steps: in the first step, the fracturing flowback fluid is sequentially introduced into a first-stage MABR tank, a second-stage MABR tank and a third-stage MABR tank for treatment, and the sludge reflux ratio of each stage of MABR tank is controlled to be 100% to 300% during the treatment process; in the second step, after the treatment is completed, part of the effluent of the third-stage MABR tank is refluxed to the first-stage MABR tank to improve the biodegradation rate of the fracturing flowback fluid. The fracturing flowback fluid treatment method based on MABR can effectively remove COD, NH4 + -N and total nitrogen in the fracturing flowback fluid and improve the comprehensive removal efficiency of pollutants in the fracturing flowback fluid, according to the characteristics of high chemical oxygen demand, high salinity, high viscosity and refractory of the fracturing flowback fluid, by using MABR to culture and domesticate specific microorganisms and performing multi-stage treatment.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a fracturing flowback fluid treatment method based on MABR. Background Technology

[0002] Shale formations have extremely low porosity and permeability, necessitating fracturing during extraction. Horizontal wells and hydraulic fracturing are key technologies in shale gas development. Hydraulic fracturing utilizes natural or artificial fractures, injecting a fracturing system containing various additives into the formation under high pressure to expand the reservoir fracture network. After fracturing, the fracturing fluid is drained, while the proppant remains in the fractures to improve the reservoir network structure, thereby increasing oil and gas production. In addition, fracturing technology is also commonly used in conventional oil and gas reservoirs to increase production and extend the lifespan of older reservoirs. The large-scale application of hydraulic fracturing technology is accompanied by the generation of significant amounts of flowback fluid. In conventional fracturing operations in my country, the flowback fluid volume per well is approximately 100 m³. 3 Up to 200m 3 In the development of shale gas, due to the application of fracturing technologies such as horizontal well staged fracturing, volumetric fracturing, and simultaneous fracturing, the flowback fluid of each well can reach 3000m³. 3 up to 6000m 3 Depending on the geological conditions, 10% to 70% of the fracturing fluid will be returned to the surface after the fracturing operation. Fracturing fluids typically contain a variety of additives, mainly including gelling and foaming components, friction reducers, crosslinking agents, fracturing agents, pH adjusters, bactericides, corrosion inhibitors, scale inhibitors, clay stabilizers, and surfactants.

[0003] Fracturing flowback fluid mainly comes from well washing wastewater before and after fracturing operations and fracturing flowback water after fracturing operations. By comparing the composition of various fracturing flowback fluids, it was found that most fracturing flowback fluids contain guar gum, petroleum residues, polymers, chloride ions, iron ions and other heavy metal ions. In general, fracturing flowback fluid has the following characteristics: (1) It has many types of pollutants, complex composition and high content, mainly including high concentrations of guar gum, oil, polymers and sulfate-reducing bacteria; (2) It has high viscosity, high degree of emulsification, high content of suspended solids and difficulty in settling and effluent; Fracturing flowback fluid that has not been effectively treated will cause major pollution to the regional environment and soil, whether it is discharged or injected into the formation. Therefore, how to effectively treat fracturing flowback fluid is of great significance to the sustainable development of oil and gas extraction. At present, the treatment of fracturing flowback fluid discharge mainly adopts the traditional oilfield wastewater treatment process, and specialized targeted processes are still in the exploratory stage, mainly including physical methods, chemical methods and biological methods.

[0004] Reverse osmosis works by applying a pressure greater than the osmotic pressure to the brine side of the membrane, causing water on the brine side to flow to the pure water side. Reverse osmosis technology is widely used in seawater desalination, industrial wastewater treatment, and food processing concentration. However, when the total dissolved solids in the feed water are too high, scaling can occur on the membrane surface. Furthermore, the process generates a large amount of reverse osmosis concentrate, with contaminant concentrations several times higher than the feed water, making it less feasible to treat the return wastewater using reverse osmosis technology.

[0005] Flocculation sedimentation involves adding flocculants (mainly inorganic, organic, complex, and microbial substances) and coagulants to fracturing flowback fluid. Utilizing various mechanisms such as adsorption bridging, sedimentation netting, double-layer compression, and adsorption neutralization, suspended particles in the water destabilize, collide, and aggregate to form larger flocs. Gravity then causes the suspended particles to settle, achieving solid-liquid separation. Flocculation sedimentation is one of the most commonly used methods for treating fracturing flowback fluid due to its advantages of low investment, small equipment footprint, and large processing capacity. This method effectively reduces the COD content in the flowback fluid, simplifying subsequent treatment. However, flocculation sedimentation also has drawbacks, including excessive chemical dosage, excessive sludge production, and poor removal of water-soluble organic matter.

[0006] The basic principle of electrocoagulation for pollutant removal is that during sacrificial anode oxidation, metal ions released into the aqueous phase neutralize the charge of pollutants in the wastewater, repel similar charges, and coagulate with them to form flocs, further removing the pollutants and achieving water purification. Unlike traditional chemical coagulation, electrocoagulation does not require chemical reagents, only electric current, including alternating current and direct current. Electrocoagulation has a wide range of applications, capable of removing suspended solids, microorganisms, metals / metalloids, oil, organic matter, and hardness. Due to its low operating cost, high treatment efficiency, and minimal environmental impact, electrocoagulation has become an alternative to conventional industrial wastewater treatment. However, it also has some drawbacks, such as electrode passivation and low dissolved salt removal efficiency.

[0007] Advanced oxidation processes (AEs) generate highly reactive hydroxyl radicals (·OH) through various oxidation methods. ·OH can non-selectively convert most organic matter into smaller, less toxic or non-toxic molecules, or directly oxidize them into CO2 and H2O. AEs can remove organic contaminants and some inorganic contaminants (such as ammonium, cyanide, thiosulfate, and sulfides) from fracturing flowback fluids. While AEs are a highly efficient wastewater treatment process with advantages such as good degradation efficiency and fast treatment speed, they also suffer from high costs, high energy consumption, and poor removal of dissolved salts.

[0008] The membrane aeration biofilm reactor (MABR) is a novel wastewater treatment technology that combines gas separation membrane technology with biofilm water treatment technology. The core components include an oxygen-permeable hollow fiber membrane and a biofilm. The biofilm grows on the outer surface of the hollow fiber membrane. Air passes through the hollow fiber membrane to supply oxygen to the biofilm, and the organic matter, nitrogen, and phosphorus contained in the wastewater are adsorbed, absorbed, and decomposed by the biofilm (achieving simultaneous nitrification and denitrification), thus purifying the wastewater. The formation of the biofilm in the MABR mainly involves the following processes: (1) Activated sludge or active bacteria are inoculated into the MABR tank, and the microorganisms are in a suspended and dispersed state in the water; (2) The hollow fiber membrane is aerated, and the oxygen content on the membrane fiber surface is high, and the microorganisms accumulate in the oxygen-rich area on the membrane fiber surface; (3) The microorganisms attached to the surface of the hollow fiber membrane grow and reproduce, and secrete extracellular polymeric substances (EPS) with a certain viscosity, making the connection between the microorganisms and the membrane surface more stable; (4) The microorganisms use the oxygen provided by the aeration membrane to degrade pollutants in the water, and form a layered biofilm under the action of anisotropic mass transfer. Summary of the Invention

[0009] This invention provides a fracturing flowback fluid treatment method based on MABR, which overcomes the shortcomings of the prior art and can effectively solve the problems of high treatment cost and poor effect of existing wastewater treatment processes in the treatment of fracturing flowback fluid.

[0010] One of the technical solutions of this invention is achieved through the following measures: a fracturing flowback fluid treatment method based on MABR, comprising the following steps:

[0011] The first step involves sequentially introducing the fracturing flowback fluid into the first-stage MABR tank, the second-stage MABR tank, and the third-stage MABR tank for treatment. During the treatment process, the sludge return ratio of each stage of the MABR tank is controlled to be between 100% and 300%.

[0012] The second step involves returning a portion of the effluent from the third-stage MABR tank to the first-stage MABR tank after treatment to improve the biodegradation rate of the fracturing flowback fluid. The biofilms in the first, second, and third-stage MABR tanks are all loaded with active composite bacterial communities, which are combinations of several phyla including Proteobacteria, Bacteroidetes, Acidobacteria, Chlorella, Patellae, and Bacillus.

[0013] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0014] The aforementioned fracturing flowback fluid refers to well-washing wastewater before and after fracturing operations, or / and fracturing flowback water after fracturing operations.

[0015] The sum of the abundance of each species in the active complex microbial community in the first-level MABR pool, the second-level MABR pool, and the third-level MABR pool is over 85%.

[0016] The first-stage MABR tank is an anaerobic environment. The active complex microbial community in the first-stage MABR tank includes Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria, with the abundance of Proteobacteria being 30% to 50%, Bacteroidetes being 35% to 50%, Acidobacteria being 3% to 10%, and Chlorobacteria being 1% to 5%.

[0017] The aforementioned second-stage MABR tank is an aerobic environment. The active complex microbial community in the second-stage MABR tank includes Bacteroidetes, Proteobacteria, Patellar Bacteria, and Bacillus, with the abundance of Bacteroidetes being 35% to 45%, Proteobacteria being 35% to 45%, Patellar Bacteria being 5% to 10%, and Bacillus being 1% to 6%.

[0018] The active complex microbial community in the aforementioned third-stage MABR pool includes Proteobacteria, Bacteroidetes, and Acidobacteria, with the abundance of Proteobacteria ranging from 30% to 50%, Bacteroidetes from 40% to 45%, and Acidobacteria from 3% to 10%.

[0019] In the second step mentioned above, the sludge return ratio of a portion of the effluent from the third-stage MABR tank to the first-stage MABR tank is 100% to 300%.

[0020] The treatment conditions for the first-stage, second-stage, and third-stage MABR tanks are as follows: treatment temperature 15℃ to 26℃, pH value 6.5 to 8.5, hydraulic retention time 16 hours to 30 hours, aeration pressure of 0 MPa to 0.015 MPa for the first-stage MABR tank, 0.02 MPa to 0.05 MPa for the second-stage MABR tank, and 0.015 MPa to 0.03 MPa for the third-stage MABR tank.

[0021] The biofilm-loaded active composite microbial communities in the above-mentioned MABR tanks at all levels were obtained by circulating biofilm formation, preliminary acclimatization, and fracturing flowback acclimatization in the MABR tank using compound microbial agents and activated sludge. The preliminary acclimatization was carried out using simulated wastewater, with an acclimatization period of 3 to 10 days. The fracturing flowback acclimatization was carried out using fracturing flowback liquid, with an acclimatization period of 7 to 15 days. The compound microbial agents consisted of Proteobacteria and Bacteroidetes, with an effective viable bacteria ratio of Proteobacteria:Bacteroidetes of 30 to 50: 50 to 70.

[0022] The MABR-based fracturing flowback fluid treatment method of this invention addresses the characteristics of fracturing flowback fluid, such as high chemical oxygen demand, high salinity, high viscosity, and recalcitrant degradation. It utilizes MABR to cultivate and acclimate specific microorganisms for multi-stage treatment, effectively removing COD and NH4 from the fracturing flowback fluid. +-N and total nitrogen, improving the overall removal efficiency of contaminants in fracturing flowback fluid. Attached Figure Description

[0023] Appendix Figure 1 This is a schematic diagram of the process flow of the present invention.

[0024] The codes in the attached diagram are as follows: 1 is the storage tank, 2 is the air compressor, 3 is the first-stage MABR tank, 4 is the second-stage MABR tank, 5 is the third-stage MABR tank, 6 is the sewage pipeline, 7 is the effluent pipeline, 8 is the tank circulation pipeline, 9 is the tank circulation pump, 10 is the air inlet pipeline, 11 is the air outlet pipeline, 12 is the main circulation pipeline, 13 is the return pump, 14 is the hollow fiber membrane module, and 15 is the feed pump. Detailed Implementation

[0025] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, percentages in this invention refer to mass percentages; unless otherwise specified, solutions in this invention refer to aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C. Unless otherwise specified, all equipment and apparatus used in this invention are known and commonly used equipment and apparatus in the art.

[0026] The present invention will be further described below with reference to embodiments:

[0027] Example 1: The MABR-based fracturing flowback fluid treatment method is carried out according to the following steps:

[0028] The MABR-based fracturing flowback fluid treatment method is carried out according to the following steps:

[0029] The first step involves sequentially introducing the fracturing flowback fluid into the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 for treatment. During the treatment process, the sludge return ratio of each MABR tank is controlled to be between 100% and 300%.

[0030] In the second step, after treatment, a portion of the effluent from the third-stage MABR tank 5 is returned to the first-stage MABR tank 3 to improve the biodegradation rate of the fracturing flowback fluid. The biofilms in the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 are all loaded with active composite bacterial communities, which are Proteobacteria ( ). Proteobacteria Bacteroidetes ( Bacteroidetes ), Acidobacteria ( Acidobacteria ), Green Curvature ( ChloroflexiPatellar Bacteria ( Patescibacteria ) and Bacillus phylum ( Gemmatimonadetes A combination of several of them.

[0031] Example 2: As an optimization of the above example, the fracturing flowback fluid is the well washing wastewater before and after fracturing operation and the fracturing flowback water after fracturing operation.

[0032] Fracturing flowback fluid contains a large amount of residual guar gum molecules, polyacrylamide, etc., and is a complex high-molecular-weight organic compound. Compared with domestic sewage, aquaculture wastewater, and industrial wastewater, it has the characteristics of high viscosity (5MPa•s to 10MPa•s, compared to 1MPa•s for clean water), severe emulsification (zeta potential 30V to 60V), good water quality stability, high mineralization (20000mg / L), and high oil content (300mg / L to 1000mg / L). The high chemical oxygen demand (COD), high salinity, high viscosity, and recalcitrant nature of fracturing flowback fluid make its treatment much more difficult than that of domestic sewage, aquaculture wastewater, and industrial wastewater.

[0033] Example 3: As an optimization of the above example, the sum of the relative abundance of each species in the active complex microbial community in the first-stage MABR pool 3, the second-stage MABR pool 4, and the third-stage MABR pool 5 is above 85%.

[0034] Example 4: As an optimization of Example 2 above, the first-stage MABR tank 3 is an anaerobic environment. The active complex microbial community loaded on the biofilm in the first-stage MABR tank 3 includes Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria, wherein the abundance of Proteobacteria is 30% to 50%, the abundance of Bacteroidetes is 35% to 50%, the abundance of Acidobacteria is 3% to 10%, and the abundance of Chlorobacteria is 1% to 5%.

[0035] Example 5: As an optimization of Example 2 above, the second-stage MABR tank 4 is an aerobic environment. The biofilm loaded in the second-stage MABR tank 4 contains active complex microbial communities including Bacteroidetes, Proteobacteria, Patellar Bacteria, and Bacillus, with the abundance of Bacteroidetes being 35% to 45%, the abundance of Proteobacteria being 35% to 45%, the abundance of Patellar Bacteria being 5% to 10%, and the abundance of Bacillus being 1% to 6%.

[0036] Example 6: As an optimization of Example 2 above, the biofilm-loaded active complex microbial community in the third-stage MABR tank 5 includes Proteobacteria, Bacteroidetes, and Acidobacteria, wherein the abundance of Proteobacteria is 30% to 50%, the abundance of Bacteroidetes is 40% to 45%, and the abundance of Acidobacteria is 3% to 10%.

[0037] Example 7: As an optimization of the above example, in the second step, the sludge return ratio of a portion of the effluent from the third-stage MABR tank 5 to the first-stage MABR tank 3 is 100% to 300%. Returning the effluent from the third-stage MABR tank 5 to the first-stage MABR tank 3 can further improve the biodegradability of the fracturing flowback fluid while completing the denitrification process.

[0038] Example 8: As an optimization of the above example, the treatment conditions for the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 are as follows: treatment temperature 15℃ to 26℃, pH value 6.5 to 8.5, hydraulic retention time 16 hours to 30 hours, aeration pressure of 0 MPa to 0.015 MPa for the first-stage MABR tank 3, 0.02 MPa to 0.05 MPa for the second-stage MABR tank 4, and 0.015 MPa to 0.03 MPa for the third-stage MABR tank 5.

[0039] In the first-stage MABR tank 3, a relatively low aeration pressure (0 to 0.015 MPa) is set to create an anaerobic environment within the reactor. This utilizes the hydrolysis and acidification process of microorganisms to degrade large molecular organic matter, improving the biodegradability of the fracturing flowback fluid. In the second-stage MABR tank 4, a wide-spaced aeration pressure (0.02 to 0.05 MPa) is set to create an aerobic environment within the reactor, removing most of the COD and achieving simultaneous nitrification and denitrification. In the third-stage MABR tank 5, the influent organic load is reduced, thus lowering the aeration pressure (0.015 to 0.03 MPa). This removes COD while simultaneously creating favorable conditions for denitrification, further reducing the total nitrogen in the effluent.

[0040] Proteobacteria, capable of using organic matter as a carbon source, are typical facultative heterotrophic bacteria. Most of the COD in fracturing flowback liquid is degraded by these microorganisms, and many denitrification-related bacterial communities belong to this phylum. An anaerobic environment was established in the first-stage MABR tank 3, which is conducive to the growth of denitrifying bacteria; therefore, Proteobacteria were abundant in the biofilm samples from the first-stage MABR tank 3. Bacteroidetes have the ability to degrade toxic substances and large carbohydrate molecules, are suitable for survival in high-salinity environments, and their relative abundance increases with increasing salinity. The fracturing flowback liquid had a high salinity (20000 mg / L), and after acclimation with the fracturing flowback liquid, the relative abundance of Bacteroidetes was high in all three reactors. Acidobacteria are widely present in wastewater treatment systems and MABR systems, and can reduce NO3--N and NO2--N to N2. Acidobacteria were abundant in MABR-1 and MABR-3.

[0041] Example 9: As an optimization of the above examples, the active composite microbial community loaded on the biofilm in each level of the MABR tank is obtained by circulating biofilm formation, preliminary acclimatization and fracturing flowback acclimatization in the MABR tank using compound microbial agents and activated sludge; the preliminary acclimatization is carried out using simulated wastewater, and the acclimatization period is 3 to 10 days; the fracturing flowback acclimatization is carried out using fracturing flowback liquid, and the acclimatization period is 7 to 15 days; the compound microbial agents are Proteobacteria and Bacteroidetes, and the effective viable bacteria ratio of Proteobacteria:Bacteroidetes is 30 to 50: 50 to 70.

[0042] The apparatus for implementing the MABR-based fracturing flowback fluid treatment method in this invention is shown in the attached figure. Figure 1 As shown, the device includes a storage tank 1, an air compressor 2, and a MABR tank group. The MABR tank group includes three MABR tanks connected in series: a first-stage MABR tank 3, a second-stage MABR tank 4, and a third-stage MABR tank 5. A wastewater pipeline 6 is fixedly connected between the discharge end of the storage tank 1 and the inlet end of the MABR tank group. A feed pump 15 is fixedly installed on the wastewater pipeline 6. An effluent pipeline 7 is fixedly connected to the discharge end of the MABR tank group. The circulating feed end on the upper left side of each MABR tank is connected to the circulating feed end on the lower right side of the MABR tank. Each of the three MABR tanks is fixedly connected to a pool circulation pipeline 8, and a pool circulation pump 9 is fixedly installed on each pool circulation pipeline 8. An air inlet pipeline 10 is fixedly connected between the air outlet of the air compressor 2 and the air inlet of each MABR tank. An air outlet pipeline 11 is fixedly connected to the air outlet of each MABR tank. A main circulation pipeline 12 is fixedly connected between the water outlet pipeline 7 and the feed inlet on the upper left side of the first-stage MABR tank 3. A return pump 13 is fixedly installed on the main circulation pipeline 12. Hollow fiber membrane modules 14 are installed in each of the three MABR tanks. As needed, valves that enable the normal operation of the device are fixedly installed on each pipeline.

[0043] The fracturing flowback fluid from storage tank 1 is sequentially introduced into the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 for treatment. A portion of the system effluent is returned to the first-stage MABR tank 3 for further removal of pollutants and improvement of effluent quality. Circulation pumps are installed in each MABR tank to provide flow rate and enhance the mass transfer process. Compressed air is supplied by air compressor 2 and enters the hollow fiber membrane module 14 through air inlet pipeline 10, providing oxygen for the growth and metabolism of microorganisms attached to the membrane fiber surface. Dissolved oxygen in each MABR tank can be controlled by adjusting the air pressure. The hydraulic retention time is controlled by adjusting the speed of the feed pump 15, and the reflux ratio is controlled by adjusting the speed of the return pump 13, achieving efficient removal of pollutants such as COD, ammonia nitrogen, and total nitrogen.

[0044] Example 10: The domestication process of the active complex microbial community was carried out according to the following steps:

[0045] Step 1, MABR membrane attachment

[0046] The microbial strains used in the biofilm formation experiment were activated sludge and compound bacterial agents from the secondary sedimentation tank of a municipal wastewater treatment plant. A multi-cycle biofilm formation method was employed. The specific steps of the biofilm formation operation are as follows: First, prepare 3L of nutrient solution with a COD concentration of approximately 300 mg / L and NH4+ concentration of... + The -N concentration was approximately 30 mg / L. 3 L of activated sludge and 3 L of nutrient solution were mixed thoroughly and added to each MABR tank. The aeration pressure was maintained at 0.02 MPa. The circulation pump was turned on and the flow rate was adjusted to 0.02 m / s for biofilm formation. After 24 hours of biofilm formation, excess sludge was discharged, and 0.5 L of activated sludge and an equivalent amount of nutrient solution were added back to the reactor to the original water level. This process was repeated every 24 hours. The same biofilm formation operation was performed on all three MABR tanks under identical conditions. After approximately 7 days of cultivation, a uniformly thick brown biofilm formed on the surface of the membrane fibers. Slight shaking resulted in only a small amount of sludge detaching, indicating successful biofilm formation within the MABR system.

[0047] The second step is initial domestication.

[0048] After successful biofilm formation, the biofilm exhibits high activity. A preliminary acclimatization experiment was conducted using simulated wastewater for 3 to 10 days. Under conditions of 0.02 MPa aeration pressure, 24-hour hydraulic retention time, and 100% reflux ratio, continuous influent was introduced into each stage of the MABR tank. The COD and NH4+ levels of the influent were gradually increased. + The removal efficiency of the biofilm for pollutants was evaluated by the concentration of NH4+-N. The average removal rates of COD and NH4+-N reached 93% and 98%, respectively, indicating that the reactor achieved the enrichment of functional bacteria in the biofilm and had a strong carbon removal and ammonia removal capacity.

[0049] The third step is to acclimatize the fracturing flowback fluid.

[0050] After acclimatization to simulated wastewater, the biofilm formed a relatively complete food chain, possessing stable carbon and nitrogen removal capabilities and a certain degree of adaptability to changes in influent water quality. Further acclimatization experiments were conducted using fracturing flowback fluid. The aeration pressures of the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 were controlled at 0.01 MPa, 0.03 MPa, and 0.02 MPa, respectively. Under conditions of a 24-hour hydraulic retention time (HRT) and a 100% reflux ratio, the proportion of fracturing flowback fluid in the influent nutrient solution was gradually increased using a continuous influent method. The fracturing flowback fluid acclimatization experiment lasted 7 to 15 days. During the acclimatization period, the proportion of fracturing flowback fluid in the influent was gradually increased. As the influent COD concentration increased, the effluent COD concentration also increased slowly. When the proportion of fracturing flowback fluid in the influent was gradually increased from 20% to 100%, the average COD removal first decreased from 62.71% to 48.25%, and then increased to 65.84%. As the influent TN concentration increases, the trend of effluent TN changes is similar to that of effluent COD. When the proportion of fracturing flowback fluid in the influent increases from 20% to 100%, the TN removal rate slowly decreases from 79.89% to 61.60%.

[0051] Example 11: The fracturing flowback fluid used in this example was provided by PetroChina (Xinjiang) Petroleum Engineering Co., Ltd., and was taken from a tight oil well in Karamay City, Xinjiang. The water quality indicators of the fracturing flowback fluid influent were as follows: COD 1100 mg / L, BOD 172 mg / L, ammonia nitrogen 22.4 mg / L, and total nitrogen 77 mg / L.

[0052] A compound bacterial agent with an effective viable count ratio of 50:50 (Proteobacteria:Bacteroidetes) was mixed with activated sludge. After acclimatization for a total of 20 days according to the acclimatization steps, the abundance of Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria in the first-stage MABR tank 3 was 33%, 44%, 9.2%, and 3.3%, respectively; the abundance of Bacteroidetes, Proteobacteria, Patellae, and Bacillus in the second-stage MABR tank 4 was 42%, 35%, 7.3%, and 5.9%, respectively; and the abundance of Proteobacteria, Bacteroidetes, and Acidobacteria in the third-stage MABR tank 5 was 34%, 41%, and 9.5%, respectively.

[0053] The operating parameters of the three-stage MABR tank are as follows: treatment temperature 21℃, pH value 7.64, hydraulic retention time 24 hours, recirculation ratio 200%, and aeration pressures of the first-stage MABR tank 3, the second-stage MABR tank 4, and the third-stage MABR tank 5 are 0.02MPa, 0.05MPa, and 0.02MPa, respectively. The recirculation ratio of the effluent from the third-stage MABR tank 5 back to the first-stage MABR tank 3 is 200%. After treatment, the effluent COD is 182 mg / L and NH4+ is... + -N was 0.4 mg / L and total nitrogen was 16.8 mg / L, with removal rates of 83.45%, 98.21% and 78.18%, respectively.

[0054] Example 12: The fracturing flowback fluid used in this example was provided by PetroChina (Xinjiang) Petroleum Engineering Co., Ltd., and was taken from a tight oil well in Karamay City, Xinjiang. The water quality indicators of the fracturing flowback fluid influent were as follows: COD 820 mg / L, BOD 172 mg / L, ammonia nitrogen 20.3 mg / L, and total nitrogen 65 mg / L.

[0055] A compound bacterial agent with an effective viable count ratio of Proteobacteria to Bacteroidetes (40:60) was mixed with activated sludge. After acclimatization for a total of 20 days according to the acclimatization steps: In the first-stage MABR tank 3, the abundance of Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria were 49%, 36%, 7.3%, and 1.3%, respectively; In the second-stage MABR tank 4, the effective viable count percentages of Bacteroidetes, Proteobacteria, Patellae, and Bacillus were 39%, 38%, 6.3%, and 4.9%, respectively; In the third-stage MABR tank 5, the effective viable count percentages of Proteobacteria, Bacteroidetes, and Acidobacteria were 44%, 42%, and 8.3%, respectively.

[0056] The operating parameters of the three-stage MABR tank are as follows: treatment temperature 21℃, pH value 7.64, hydraulic retention time 24 hours, recirculation ratio 200%, and aeration pressures of MABR tank 3 (first stage), MABR tank 4 (second stage), and MABR tank 5 (third stage) 0.01 MPa, 0.04 MPa, and 0.025 MPa, respectively; the recirculation ratio of the effluent from MABR tank 5 back to MABR tank 3 (first stage) is 200%. After treatment, the effluent COD is 174 mg / L and NH4+ is... + -N was 0.5 mg / L and total nitrogen was 18.13 mg / L, with removal rates of 82.75%, 97.62% and 77.62%, respectively.

[0057] Example 13: The fracturing flowback fluid used in this example was provided by PetroChina (Xinjiang) Petroleum Engineering Co., Ltd., and was taken from a tight oil well in Karamay City, Xinjiang. The water quality indicators of the fracturing flowback fluid influent were as follows: COD 1200 mg / L, BOD 172 mg / L, ammonia nitrogen 25.4 mg / L, and total nitrogen 87 mg / L.

[0058] A compound bacterial agent with an effective viable count ratio of Proteobacteria to Bacteroidetes (30:70) was mixed with activated sludge. After acclimatization for a total of 20 days according to the acclimatization steps: In the first-stage MABR tank 3, the abundance of Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria were 45%, 46%, 4.4%, and 1.1%, respectively; in the second-stage MABR tank 4, the abundance of Bacteroidetes, Proteobacteria, Patellae, and Bacillus were 40%, 41%, 5.3%, and 2.6%, respectively; and in the third-stage MABR tank 5, the abundance of Proteobacteria, Bacteroidetes, and Acidobacteria were 46%, 44%, and 3.3%, respectively.

[0059] The operating parameters of the three-stage MABR tank are as follows: treatment temperature 21℃, pH value 7.64, hydraulic retention time 24 hours, recirculation ratio 200%, and aeration pressures of MABR tank 3 (first stage), MABR tank 4 (second stage), and MABR tank 5 (third stage) 0.015 MPa, 0.05 MPa, and 0.03 MPa, respectively; the recirculation ratio of the effluent from MABR tank 5 back to MABR tank 3 (first stage) is 200%. After treatment, the effluent COD is 154 mg / L and NH4+ is... + -N was 0.4 mg / L and total nitrogen was 16.1 mg / L, with removal rates of 87.16%, 98.42% and 81.49%, respectively.

[0060] Comparative Example: The fracturing flowback fluid used in the comparative example was provided by PetroChina (Xinjiang) Petroleum Engineering Co., Ltd., and was taken from a tight oil well in Karamay City, Xinjiang. The water quality indicators of the fracturing flowback fluid influent were as follows: COD 1123 mg / L, BOD 185 mg / L, ammonia nitrogen 25.4 mg / L, and total nitrogen 77.8 mg / L.

[0061] The comparative bacterial strains were activated sludge from the secondary sedimentation tank of a wastewater treatment plant. After 20 days of acclimatization: in the first-stage MABR tank 3, the abundances of Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorobacteria were 21%, 17%, 14.2%, and 9.1%, respectively; in the second-stage MABR tank 4, the abundances of Bacteroidetes, Proteobacteria, Patellar Bacteria, and Bacillus were 28%, 21%, 15.3%, and 12.6%, respectively; and in the third-stage MABR tank 5, the abundances of Proteobacteria, Bacteroidetes, and Acidobacteria were 26%, 25%, and 14.7%, respectively.

[0062] The operating parameters of the three-stage MABR tank are as follows: treatment temperature 21℃, pH value 7.64, hydraulic retention time 24 hours, recirculation ratio 200%, and aeration pressures of MABR tank 3 (first stage), MABR tank 4 (second stage), and MABR tank 5 (third stage) 0.015MPa, 0.05MPa, and 0.03MPa, respectively. The recirculation ratio of the effluent from MABR tank 5 to MABR tank 3 (first stage) is 200%. After treatment, the effluent COD is 486 mg / L and NH4+ is... + -N was 10.4 mg / L and total nitrogen was 30.4 mg / L, with removal rates of 56.72%, 59.05% and 60.92%, respectively.

[0063] As can be seen from the treatment effects of Examples 11 to 13 and the comparative examples, the ratio of each type of bacteria in the active composite microbial community used in this invention can effectively remove COD and NH4 from the fracturing flowback fluid. + -N and total nitrogen were removed at a rate of over 77%, including NH4+. + The removal rate of -N can reach over 97%, effectively improving the overall removal efficiency of contaminants in fracturing flowback fluid. Furthermore, using MABR to cultivate and domesticate specific microorganisms for fracturing flowback fluid treatment eliminates the need for chemical additives, reducing treatment costs.

[0064] In summary, the MABR-based fracturing flowback fluid treatment method of the present invention addresses the characteristics of fracturing flowback fluid, such as high chemical oxygen demand, high salinity, high viscosity, and recalcitrant degradation. By utilizing MABR to cultivate and domesticate specific microorganisms and performing multi-stage treatment, the overall removal efficiency of pollutants in fracturing flowback fluid is improved.

[0065] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for treating fracturing flowback fluid based on MABR, characterized in that... Follow these steps: The first step involves sequentially introducing the fracturing flowback fluid into the first-stage MABR tank, the second-stage MABR tank, and the third-stage MABR tank for treatment. During the treatment process, the sludge return ratio of each stage of the MABR tank is controlled to be between 100% and 300%. The second step involves returning a portion of the effluent from the third-stage MABR tank to the first-stage MABR tank after treatment to improve the biodegradation rate of the fracturing flowback fluid. Among them, the biofilms in the first-stage MABR tank, the second-stage MABR tank, and the third-stage MABR tank are all loaded with active composite bacterial communities; The fracturing flowback fluid is well-washing wastewater before and after fracturing operation and / or fracturing flowback water after fracturing operation; The first-stage MABR tank is an anaerobic environment. The active complex microbial community in the first-stage MABR tank includes Proteobacteria, Bacteroidetes, Acidobacteria, and Chlorophylloides, with the abundance of Proteobacteria being 30% to 50%, Bacteroidetes being 35% to 50%, Acidobacteria being 3% to 10%, and Chlorophylloides being 1% to 5%. The second-stage MABR tank is an aerobic environment. The active complex microbial community in the second-stage MABR tank includes Bacteroidetes, Proteobacteria, Patellar Bacteria, and Bacillus, with the abundance of Bacteroidetes being 35% to 45%, Proteobacteria 35% to 45%, Patellar Bacteria 5% to 10%, and Bacillus 1% to 6%. The active complex microbial community in the third-stage MABR tank includes Proteobacteria, Bacteroidetes, and Acidobacteria, with the abundance of Proteobacteria being 30% to 50%, Bacteroidetes being 40% to 45%, and Acidobacteria being 3% to 10%. The biofilm-loaded active composite microbial community in each level of MABR tank was obtained by circulating biofilm formation, preliminary acclimatization, and fracturing flowback acclimatization in the MABR tank using compound microbial agents and activated sludge. The preliminary acclimatization was carried out using simulated wastewater, with an acclimatization period of 3 to 10 days. The fracturing flowback acclimatization was carried out using fracturing flowback liquid, with an acclimatization period of 7 to 15 days. The compound microbial agents consisted of Proteobacteria and Bacteroidetes, with an effective viable bacteria ratio of Proteobacteria:Bacteroidetes of 30 to 50: 50 to 70.

2. The fracturing flowback fluid treatment method based on MABR according to claim 1, characterized in that... The sum of the abundance of each species in the active complex microbial community in the first-level MABR pool, the second-level MABR pool, and the third-level MABR pool is above 85%.

3. The fracturing flowback fluid treatment method based on MABR according to claim 1 or 2, characterized in that... In the second step, a portion of the effluent from the third-stage MABR tank is returned to the first-stage MABR tank, with a sludge return ratio of 100% to 300%.

4. The fracturing flowback fluid treatment method based on MABR according to claim 1 or 2, characterized in that... The treatment conditions for the first, second, and third stage MABR tanks are as follows: treatment temperature 15℃ to 26℃, pH value 6.5 to 8.5, hydraulic retention time 16 hours to 30 hours, aeration pressure of 0 MPa to 0.015 MPa for the first stage MABR tank, 0.02 MPa to 0.05 MPa for the second stage MABR tank, and 0.015 MPa to 0.03 MPa for the third stage MABR tank.

5. The fracturing flowback fluid treatment method based on MABR according to claim 3, characterized in that... The treatment conditions for the first, second, and third stage MABR tanks are as follows: treatment temperature 15℃ to 26℃, pH value 6.5 to 8.5, hydraulic retention time 16 hours to 30 hours, aeration pressure of 0 MPa to 0.015 MPa for the first stage MABR tank, 0.02 MPa to 0.05 MPa for the second stage MABR tank, and 0.015 MPa to 0.03 MPa for the third stage MABR tank.

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