A method and system for treating black and smelly shale gas flow-back fluid

Abstract

The present application relates to wastewater treatment technical field discloses a kind of black and odorous shale gas flow-back fluid processing method and system, the processing method is into aeration tank into black and odorous flow-back fluid, bubble is formed by air aeration and residual ozone, oxidize and form deposit to reducing material, while residual ozone sterilization and degradation organic matter to flow-back fluid;The flow-back fluid after air aeration pre-oxidation system processing is into softening coupling enhanced coagulation system, and the treatment agent is added in multistage reaction tank, and the flow-back fluid is softened, coagulated and precipitated, and scale ions are removed;The supernatant after multistage reaction tank processing enters advanced oxidation system and is carried out depth oxidation treatment;Again into membrane system and carries out safe filtration.The processing method of the present application can effectively solve black and odorous problem, reduce the content of total hardness, total iron, suspended solids and bacteria in black and odorous water, and the like, and the dross and odorous gas can be effectively removed, and the water after treatment can reach the reuse water quality standard, and can be used as fracturing fluid preparation water.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a method and system for treating black and odorous shale gas backflow liquid. Background Technology

[0002] Hydraulic fracturing remains a commonly used method in shale gas development and production enhancement. Its main principle is to inject fracturing fluid and proppant into the well under pressure, disrupting the tight structure of the rock strata to create fractures, allowing shale gas to be released from the fractures. After fracturing, the fracturing fluid and water from the shale are returned to the surface as flowback fluid. Flowback fluids often have complex compositions, high color, high organic content, and high mineralization. In shale gas development, flowback fluids are typically stored in reservoirs ranging from several hundred to tens of thousands of cubic meters.

[0003] During long-term on-site storage, the backflow liquid easily turns black and smells foul, forming black and smelly water. This is because the backflow liquid is generally stored statically in the backflow tank, and a layer of floating oil often hinders the exchange of oxygen between the air and the water, creating an anaerobic environment at a certain depth. Simultaneously, the aerobic decomposition of organic matter in the backflow liquid causes the oxygen consumption rate to exceed the reoxygenation rate, resulting in oxygen deficiency. This leads to incomplete degradation of organic matter and a slower degradation rate. The anaerobic biodegradation process generates foul-smelling substances such as hydrogen sulfide, ammonia, and mercaptans. Furthermore, sulfate-reducing bacteria in the backflow liquid generate sulfur under anaerobic conditions. 2- , with Fe in water 2+ The reaction produces black FeS, which disperses in the water, forming black water. This type of wastewater has an unpleasant odor and easily pollutes the atmosphere; furthermore, the excessive concentration of pollutants in the water prevents its resource utilization.

[0004] Black and odorous wastewater typically occurs in urban or rural rivers. This type of water is characterized by low salinity and high biodegradability. Existing treatment methods for black and odorous wastewater include biological treatment, SRB reactor treatment, and coagulation treatment. However, black and odorous shale gas flowback fluid often exhibits high salinity, high hardness, high color, high organic matter, and poor biodegradability. Conventional treatment methods are insufficient to effectively reduce the organic matter content, color, and bacteria levels in this type of wastewater. Furthermore, the internal reuse of treated flowback fluid in fracturing fluid production requires specific limits on total iron and hardness. Therefore, black and odorous flowback fluid is a key issue that needs to be addressed in the clean production of shale gas. There is an urgent need to develop a treatment method and system for black and odorous shale gas flowback fluid to solve the problem of flowback fluid turning black and odorous during on-site storage. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for treating black and odorous shale gas runoff liquid, solving the aforementioned problems of black and odorous runoff liquid and failure to meet recycling standards; this treatment method can effectively solve the black and odor problems, reduce the content of total hardness, total iron, suspended solids and bacteria in black and odorous water, and effectively prevent odor from escaping.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for treating black and odorous shale gas flowback fluid, the method comprising:

[0008] The black and odorous backflow liquid is introduced into the aeration tank of the air aeration pre-oxidation system. Through air aeration and the formation of bubbles by residual ozone, the reducing substances in the backflow liquid are oxidized to form precipitates. At the same time, the residual ozone sterilizes and degrades organic matter in the backflow liquid. The bubbles carry suspended impurities to the surface of the liquid to form scum, which is then scraped off by a scraper.

[0009] The backflow liquid treated by the air aeration pre-oxidation system is fed into the multi-stage reaction tank of the softening coupled enhanced coagulation system. Treatment agents are added to the multi-stage reaction tank to soften, coagulate and precipitate the backflow liquid, removing scale ions and reducing suspended solids and turbidity.

[0010] The supernatant after treatment in the multi-stage reaction tank enters the ozone reactor of the advanced oxidation system for deep oxidation treatment. A pH adjuster is first added to the inlet of the ozone reactor to adjust the pH to 8.5-9.5, and then hydrogen peroxide is added to accelerate the removal of organic matter.

[0011] The wastewater treated by the ozone reactor is safely filtered through the ultrafiltration membrane of the membrane system.

[0012] Preferably, the aeration tank is sealed by a sealing device and exhausts air through the vent of the sealing device.

[0013] Preferably, the vent is filled with activated carbon adsorbent and ozone decomposition agent.

[0014] Preferably, the gas emitted from the aeration tank is first treated with activated carbon adsorbent and then with ozone decomposition agent.

[0015] Preferably, the air flow rate in the aeration tank is 2%-10% of the backflow liquid influent, and the hydraulic retention time is 5-20 minutes.

[0016] Preferably, the scraper is driven by a drive source to reciprocate on the upper surface of the return liquid.

[0017] Preferably, the multi-stage reaction tank includes at least five reaction tanks, and the inlet and outlet of each of the individual reaction tanks are not located on the same horizontal plane.

[0018] Preferably, the treatment agent is added at the same location as the corresponding inlet of the reaction tank.

[0019] Preferably, the treatment agent includes softener a, softener b, coagulant and flocculant.

[0020] The softener selected is NaOH, which is used to adjust the pH and participate in the precipitation reaction of non-scaling cations.

[0021] Preferably, the multi-stage reaction tank stores internal sludge through a sludge hopper and discharges the sludge through a sludge discharge pipe connected to the sludge hopper. The return liquid has a residence time of 20 to 40 minutes in the final reaction tank.

[0022] Preferably, 2 / 3 of the sludge discharged from the sludge discharge pipe is pumped back to the first reaction tank, so that the inorganic scale in the sludge precipitates as crystal nuclei, which is used to accelerate the precipitation of inorganic scale ions in the return liquid in the first reaction tank. Furthermore, the unreacted coagulant and flocculant in the sludge will further capture and sweep up suspended solids and particles in the return liquid, softening and coupling to enhance coagulation while reducing the amount of sludge generated.

[0023] The remaining 1 / 3 of the sludge discharged through the sludge discharge pipe is transported to the screw press for dewatering.

[0024] Preferably, the hydrogen peroxide concentration is 5–30 mM.

[0025] Preferably, the ozone reactor is equipped with an ultraviolet lamp with a wavelength of 180-400 nm, and the residence time of the backflow liquid in the ozone reactor is 20-40 min.

[0026] Preferably, the residual ozone source is the recycling of ozone that did not participate in the reaction in the ozone reactor.

[0027] A black and odorous shale gas backflow liquid treatment system includes an air aeration pre-oxidation system, a softening coupled enhanced coagulation system, an advanced oxidation system, and a membrane system.

[0028] The air aeration pre-oxidation system is used to pre-oxidize, sterilize, and remove impurities from the return liquid.

[0029] The softening coupled enhanced coagulation system is used to soften, coagulate and precipitate the return liquid after treatment by the air aeration pre-oxidation system, remove scale ions from the return liquid and reduce the suspended solids and turbidity of the return liquid.

[0030] The advanced oxidation system is used to perform deep oxidation treatment on the supernatant of the softening coupled enhanced coagulation system.

[0031] The membrane system uses an ultrafiltration membrane to safely filter the effluent from the advanced oxidation system.

[0032] Preferably, the air aeration pre-oxidation system includes an aeration tank, an air compressor, a scraper, a sealing device, and a vent. The scraper is used to scrape off the scum on the surface of the return liquid in the aeration tank.

[0033] Preferably, the softening coupling enhanced coagulation system is provided with multi-stage reaction tanks. The multi-stage reaction tanks recycle and reuse sludge and dewater it through a sludge discharge system. An inclined plate is provided in the last reaction tank to separate and settle suspended impurities in the return liquid and form a supernatant above the inclined plate.

[0034] Preferably, the advanced oxidation system includes an ozone reactor, an ozone generator, and an ultraviolet lamp.

[0035] The ozone generator is used to supply ozone to the backflow liquid in the ozone reactor, and the ozone flow rate in the ozone reactor is 0.05–0.2 m / s. 3 / s, the ultraviolet lamp is used for sterilization and to assist ozone and hydrogen peroxide in generating hydroxyl radicals.

[0036] Preferably, to ensure the water quality requirements of the ultrafiltration membrane feed water in the membrane system, hydrochloric acid is added at the ultrafiltration membrane inlet to adjust the pH to neutral.

[0037] The beneficial effects of this invention are:

[0038] 1. The treatment method of this invention can effectively solve the black and smelly problems, reduce the content of total hardness, total iron, suspended solids and bacteria in black and smelly water, scrape off the scum on the surface of the return fluid, and the activated carbon adsorbent and ozone decomposition agent set in the ventilation port, together with the sealed cover, effectively prevent the odor from escaping. The treated water fully meets the reuse water quality standards and can be used as water for the preparation of fracturing fluid.

[0039] 2. In this invention, 2 / 3 of the recovered sludge is returned to the first reaction tank, where inorganic scale in the sludge precipitates as crystal nuclei, accelerating the precipitation of inorganic scale ions in the return liquid from the first reaction tank. Furthermore, unreacted coagulants and flocculants in the sludge further trap and sweep away suspended solids and particles in the return liquid, softening and enhancing coagulation while reducing sludge production. The remaining 1 / 3 of the sludge is transported to a screw press for dewatering. The sludge output of this invention is more than 25% lower than that of conventional treatment methods.

[0040] 3. The water treated by this invention has a high standard membrane flux, which increases the service life of the ultrafiltration membrane and improves the fouling of the ultrafiltration membrane. Attached Figure Description

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] Figure 1This is a system diagram of the present invention for treating backflow liquid;

[0043] Figure 2 This is a comparison chart of the water quality of the raw water of this invention and the water treated by the two technologies;

[0044] Figure 3 This is a diagram showing the membrane fouling situation after filtering different return liquids using the ultrafiltration membrane of this invention;

[0045] Figure 4 This is a performance evaluation diagram of the raw water and the effluent from the two technologies used in this invention to prepare slippery water. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Figure 1 This is a system diagram for treating backflow liquid according to the present invention.

[0048] A method for treating black and odorous shale gas flowback fluid, the specific steps of which are as follows:

[0049] Step 1: The black and odorous backflow liquid enters the air aeration pre-oxidation system. The air aeration pre-oxidation system includes an aeration tank, an air compressor, scrapers, a sealing device, and vents. Air aeration pre-oxidation involves introducing air into the backflow liquid through the air compressor to form bubbles, while residual ozone from the advanced oxidation system enters the backflow liquid. This oxidizes the reducing substances in the backflow liquid to form precipitates (e.g., oxidizing ferrous ions to ferric ions to form precipitates), degrades some large molecular organic matter, mineralizes some small molecular organic matter, and sterilizes (sulfate-reducing bacteria, saprophytic bacteria, iron bacteria, etc.). The sediment and sludge in the aeration tank are discharged after being treated by a screw press.

[0050] The uniform, high-density, micron-sized bubbles formed by air aeration and residual ozone can bring substances with a density lower than the return liquid (such as petroleum hydrocarbons and suspended solids) to the surface, forming scum, which is then scraped off by a scraper. The scraper is equipped with a drive source that moves it reciprocating across the surface of the liquid in the aeration tank, scraping away and collecting the scum for later integrated treatment. The entire aeration tank is housed in a sealed enclosure, which can be a sealed cover with multiple ventilation openings on its surface. Figure 1 As shown, by filling the ventilation openings with activated carbon adsorbent and ozone decomposition agent, ozone and other odorous gases are prevented from escaping and polluting the surrounding air.

[0051] Furthermore, the air flow rate in the aeration tank is 2%-10% of the backflow liquid influent, and the hydraulic retention time is 5-20 minutes.

[0052] Step 2: The outlet of the air aeration pre-oxidation system is located slightly below the scum to prevent scum from flowing out and ensure that the supernatant enters the reaction tank 1 of the softening coupled enhanced coagulation system. Softener a (NaOH) is added to the inlet of reaction tank 1 and mechanically stirred. The stirring speed gradient is 100–400 r / min, and the hydraulic retention time is 5–10 min to adjust the pH of the return liquid to 10–11, causing magnesium ions in the return liquid to precipitate as Mg(OH)2 and HCO3- in the return liquid to precipitate. - Converted into CO3 2- CO3 2- With non-scaling cations (Ca 2+ Ba 2+ The reaction forms carbonate precipitates (in traditional methods, lime (Ca(OH)2) is added to the wastewater as a softening agent). Insufficient addition results in low removal rates of inorganic scale ions, while excessive addition leads to the formation of carbonate precipitates from the lime. 2+ Instead, it increases the concentration of residual inorganic scale ions. The completely reacted backflow liquid in reaction tank 1 enters reaction tank 2 from the bottom of reaction tank 1. At the inlet of reaction tank 2, a softening agent b (Na2CO3) with a concentration of 1 to 1.5 times the total hardness (calculated as CaCO3, mg / L) of the backflow liquid at the inlet of reaction tank 2 is added and mechanically stirred. The mechanical stirring speed gradient is 100 to 400 r / min, and the hydraulic retention time is 5 to 10 min, so that a large number of residual non-scaling cations (CaCO3, mg / L) in the backflow liquid are removed. 2+ Ba 2 + (etc.) to form carbonate precipitate; the completely reacted return liquid in reaction tank 2 enters reaction tank 3 from the upper part of reaction tank 2, and coagulant PAC is added at the inlet of reaction tank 3, the PAC dosage (mg / L) mPAC = 0.46TSS + 39 (TSS is the suspended solids content of the return liquid at the inlet of reaction tank 3, mg / L), and mechanical stirring is performed, the mechanical stirring speed gradient is 100-400 r / min, and the hydraulic retention time is 5-10 min; the completely reacted return liquid in reaction tank 3 enters reaction tank 4 from the lower part of reaction tank 3, and flocculant (PAM with a cationicity of 50 and a molecular weight of 5 million) is added at the inlet of reaction tank 4, the PAM dosage (mg / L) m PAM=0.0041TSS-0.9 (TSS is the suspended solids content of the return liquid at the inlet of reaction tank 4, mg / L), and mechanical stirring is performed. The mechanical stirring speed gradient is 20-80 r / min, and the hydraulic retention time is 5-10 min. The completely reacted return liquid in reaction tank 4 enters reaction tank 5. Reaction tank 5 is equipped with inclined plates to separate and precipitate suspended impurities in the water. A sludge hopper is set at the bottom of reaction tank 5. The inlet of reaction tank 5 is located in the middle and between the inclined plates and the sludge hopper. The residence time of the return liquid in reaction tank 5 is 20-40 min.

[0053] Each of reaction tanks 1 to 5 is equipped with a sludge hopper at the bottom. Once the sludge hopper reaches a certain volume, it is discharged through a sludge discharge pipe. Two-thirds of the sludge discharged through the sludge discharge pipe is returned to reaction tank 1. The inorganic scale precipitates in the sludge act as crystal nuclei, accelerating the precipitation of inorganic scale ions in the return liquid from reaction tank 1. Furthermore, unreacted coagulants and flocculants in the sludge further trap and sweep away suspended solids and particles in the return liquid, softening and enhancing coagulation while reducing sludge production. The remaining one-third of the sludge discharged through the sludge discharge pipe is transported to a screw press for dewatering. To avoid short-circuiting, the inlets and outlets of reaction tanks 1, 2, 3, 4, and 5 are located on different horizontal planes.

[0054] Step 3: The supernatant from sedimentation tank 5 in the softening coupled enhanced coagulation system enters the ozone reactor of the advanced oxidation system. Specifically, a pH adjuster (hydrochloric acid / sodium hydroxide) is added to the inlet of the ozone reactor to adjust the pH to 8.5-9.5. The purpose of adjusting the pH is as follows: Ozone is mainly used to remove organic matter from wastewater. Ozone oxidizes organic matter in two main ways: 1. Ozone itself oxidizes organic matter; 2. Ozone generates highly oxidizing hydroxyl radicals, which react rapidly with organic matter to achieve oxidation. Specifically, under low pH (acidic) conditions, there are fewer hydroxyl radicals (OH·) in the water, resulting in less organic matter mineralized by hydroxyl radicals. Organic matter mainly undergoes ozone decomposition, that is, large organic molecules decompose into small organic molecules, resulting in less removal (mineralization) of organic matter in the water. Therefore, the TOC removal rate in the water is low. As the pH increases, the OH· in the water... - Increase, OH - This will induce ozone to generate hydroxyl radicals, which have extremely high oxidation potentials. These radicals rapidly mineralize organic matter in the solution, ultimately producing CO2 and H2O, thus effectively removing the organic matter. However, when the pH of the backflow solution is too high (pH > 9.5), divalent ions in the backflow solution will form inorganic scale, such as CaCO3 and Mg(OH)2, increasing the turbidity of the backflow solution. The generated inorganic scale will hinder the oxidation efficiency of ozone on organic matter, leading to a decrease in TOC removal rate.

[0055] Hydrogen peroxide (5–30 mM) is added to the inlet of the ozone reactor. As a strong oxidant, the hydrogen peroxide accelerates the removal of organic matter. Ozone generated by the ozone generator enters the ozone reactor at a flow rate of 0.05–0.2 m / s. 3 / s, the ozone reactor is equipped with an immersion ultraviolet lamp with a wavelength of 180-400nm. The ultraviolet light helps ozone and hydrogen peroxide to generate hydroxyl radicals, which further removes organic matter. The residence time of the return liquid in the ozone reactor is 20-40min.

[0056] Step 4: The backflow liquid enters the membrane system through the middle and lower part of the ozone reactor. To ensure the water quality requirements of the ultrafiltration membrane feed water, hydrochloric acid is added at the ultrafiltration membrane inlet to adjust the pH to neutral. The ultrafiltration membrane effluent is clear water, which is used to prepare fracturing fluid.

[0057] For a specific example, the blackened and foul-smelling flowback fluid from a shale gas well (Well 18) in Sichuan was treated. The treatment effects of conventional methods (coagulation and sedimentation) and the method of this invention were compared. The results are as follows: Figure 2 As shown.

[0058] The water quality comparison analysis results show that the total hardness, bacteria (SRB), scaling tendency, and compatibility of the raw water exceed the recommended water quality indicators for reuse. Conventional treatment methods are effective in removing suspended solids and total iron, but less effective in removing total hardness and bacteria. Furthermore, the total hardness, bacteria, scaling tendency, and compatibility of the treated effluent still exceed the reuse water quality standards. The treatment method disclosed in this paper can effectively reduce the content of total hardness, total iron, suspended solids, and bacteria in black and odorous water, enabling the treated water to fully meet the reuse water quality standards.

[0059] Conventional methods are effective at removing color from black and odorous water, but less effective at removing TOC, sulfides, petroleum hydrocarbons, and ammonia nitrogen. The treatment method disclosed in this paper is effective at removing all five of these indicators and can effectively solve the problem of "black and odorous" water.

[0060] By comparing the standard flux and membrane lifetime of raw water filtered by ultrafiltration membranes, effluent treated by conventional methods, and effluent treated according to this disclosure, the fouling of ultrafiltration membranes was further analyzed, and the results are as follows: Figure 3 As shown.

[0061] Figure 3 The vertical axis represents the membrane normalized flux (i.e., the flow rate of water passing through the ultrafiltration membrane), and the horizontal axis represents the membrane time (i.e., the time it takes for the ultrafiltration membrane to treat the wastewater).

[0062] Figure 3 The results showed that after filtering the wastewater through an ultrafiltration membrane for 400 minutes, the membrane standard flux decreased to 0.3, indicating that the ultrafiltration membrane suffered severe fouling, and the fitted membrane lifespan was 525 minutes.

[0063] After 400 minutes of water treated by conventional methods using ultrafiltration membrane filtration, the membrane standard flux decreased to 0.575, and the fitted membrane lifespan was 1040 minutes, which is longer than the lifespan of the ultrafiltration membrane used to filter raw water. This indicates that the ultrafiltration membrane has been contaminated to some extent, and conventional treatment can appropriately improve the quality of the return liquid.

[0064] After filtration of the water treated by this disclosure using an ultrafiltration membrane for 400 minutes, the membrane standard flux reached as high as 0.76, and the fitted membrane lifespan reached 1900 minutes, which is 3.6 times that of the raw water treated by ultrafiltration membrane filtration and 1.9 times that of water treated by conventional ultrafiltration membrane filtration methods. This indicates that ultrafiltration membrane fouling is greatly reduced, and the treatment method of this disclosure can effectively purify the backflow liquid. Therefore, the black and odorous backflow liquid treatment method proposed in this disclosure has good results, and the amount of sludge after treatment by this disclosure method is more than 25% less than that of conventional treatment methods.

[0065] Water resources of different qualities were used to prepare fracturing fluid (slickwater), and the performance evaluation results of slickwater are as follows: Figure 4 As shown.

[0066] Figure 4 The results showed that the slick water prepared from the raw water exceeded the performance standards for slick water in terms of surface tension, scaling tendency, bacteria (SRB), compatibility, and drag reduction. Conventional methods improved the surface tension of the water prepared from the raw water, but the scaling tendency, bacteria, compatibility, and drag reduction still exceeded the performance indicators of slick water. The performance of the water prepared from the raw water prepared by the method disclosed in this paper was significantly improved, and the performance indicators of slick water were fully met.

[0067] A black and odorous shale gas backflow liquid treatment system includes an air aeration pre-oxidation system, a softening coupled enhanced coagulation system, an advanced oxidation system, and a membrane system connected in sequence. The advanced oxidation system is connected to the air aeration pre-oxidation system and is used to involve residual ozone in the advanced oxidation system in the air aeration pre-oxidation system for oxidation.

[0068] Air aeration pre-oxidation system: used to remove substances with a density less than water, redox substances, and bacteria from the backflow liquid, such as petroleum, suspended solids, and organic matter, and remove reducing substances in the backflow liquid by pre-oxidation to form precipitates, such as oxidizing ferrous ions to ferric ions to form precipitates for removal.

[0069] Softening-coupled enhanced coagulation system: used to soften, coagulate and precipitate the return liquid after treatment by the air aeration pre-oxidation system, remove scale ions such as calcium, magnesium, barium and strontium from the return liquid, and effectively reduce the suspended solids and turbidity of the return liquid.

[0070] Advanced oxidation system: Used for deep oxidation treatment of the supernatant in softening coupled enhanced coagulation system, further reducing organic matter, bacteria, color and other substances in the backflow liquid.

[0071] Membrane system: Used for safe filtration of effluent from advanced oxidation systems, further removing impurities from the backflow solution and reducing suspended solids, turbidity, organic matter, inorganic scale, etc. in the backflow solution.

[0072] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for treating black and odorous shale gas flowback fluid, characterized in that, The processing method includes: The black and odorous shale gas runoff liquid is introduced into the aeration tank of an air aeration pre-oxidation system. Through air aeration and the formation of bubbles by residual ozone, reducing substances in the runoff liquid are oxidized to form precipitates. Simultaneously, the residual ozone sterilizes and degrades organic matter in the runoff liquid. The bubbles carry suspended impurities to the surface, forming scum, which is then scraped off by a scraper. The aeration tank is sealed by a closed system, and exhaust is achieved through vents in the closed system. These vents are filled with activated carbon adsorbent and ozone decomposition agent. The gas emitted from the aeration tank is first treated by the activated carbon adsorbent and then by the ozone decomposition agent. The air in the aeration tank... The flow rate is 2% to 10% of the backflow influent, and the hydraulic retention time is 5 to 20 minutes. The backflow treated by the air aeration pre-oxidation system is introduced into the multi-stage reaction tank of the softening coupled enhanced coagulation system. Treatment agents are added to the multi-stage reaction tank to soften, coagulate, and settle the backflow, removing scale ions and reducing suspended solids and turbidity. The multi-stage reaction tank stores sludge in a sludge hopper and discharges and recycles the sludge through a sludge discharge pipe connected to the sludge hopper. The retention time of the backflow in the final reaction tank is 20 to 40 minutes. Two-thirds of the sludge discharged through the sludge discharge pipe is pumped back to the first reaction tank, where inorganic scale in the sludge precipitates as crystal nuclei, accelerating the precipitation of inorganic scale ions in the return liquid from the first reaction tank. Unreacted coagulants and flocculants in the sludge further trap and sweep away suspended solids and particles in the return liquid, softening and enhancing coagulation while reducing sludge production. The remaining one-third of the sludge discharged through the sludge discharge pipe is transported to a screw press for dewatering. The supernatant after treatment in the multi-stage reaction tank enters the ozone reactor of the advanced oxidation system for deep oxidation treatment. A pH adjuster is first added to the inlet of the ozone reactor to adjust the pH to 8.5-9.5, and then hydrogen peroxide is added to accelerate the removal of organic matter. The return liquid treated by the ozone reactor is safely filtered through the ultrafiltration membrane of the membrane system, and the residual ozone source is the recycling of ozone that did not participate in the reaction in the ozone reactor.

2. The method for treating black and odorous shale gas runoff fluid according to claim 1, characterized in that, The scraper is driven by a drive source to reciprocate on the upper surface of the return liquid.

3. The method for treating black and odorous shale gas runoff fluid according to claim 1, characterized in that, The multi-stage reaction tank includes at least five reaction tanks, and the inlet and outlet of each individual reaction tank are not located on the same horizontal plane.

4. The method for treating black and odorous shale gas runoff fluid according to claim 1, characterized in that, The treatment agent is added at the same location as the corresponding inlet of the reaction tank.

5. The method for treating black and odorous shale gas runoff fluid according to claim 1 or 4, characterized in that, The treatment agent includes softener a, softener b, coagulant and flocculant; The softener a is NaOH, which is used to adjust the pH and participate in the precipitation reaction of non-scaling cations.

6. The method for treating black and odorous shale gas runoff fluid according to claim 1, characterized in that, The concentration of the hydrogen peroxide is 5–30 mM.

7. The method for treating black and odorous shale gas runoff fluid according to claim 1, characterized in that, The ozone reactor is equipped with an ultraviolet lamp with a wavelength of 180–400 nm, and the residence time of the backflow liquid in the ozone reactor is 20–40 min.

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