A method and device for treating black and odorous high-salinity wastewater

Abstract

The application discloses a black and odorous high-salinity wastewater treatment method and device, which comprises the following steps: pre-oxidizing black and odorous high-salinity wastewater after mixing reagents through aeration, scraping off upper-layer pollutants in the wastewater during the pre-oxidation, sequentially softening, adsorbing and depositing the wastewater after the upper-layer pollutants are removed, ozone-oxidizing supernatant after the deposition treatment, and recycling residual ozone during the ozone-oxidation, so that the black and odorous problems of long-stored high-salinity, high-suspended substance, high-organic substance and high-color wastewater are solved completely, and the resource utilization of the wastewater is realized successfully. In addition, part of sludge formed during the softening, adsorption and deposition treatment is reused in the subsequent black and odorous high-salinity wastewater treatment process, so that the sludge discharge amount during the wastewater treatment process is greatly reduced. The technical scheme provided by the application is economic and environment-friendly, the water quality indexes after the treatment are stable and up to the standard, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method and apparatus for treating black, odorous, and high-salt wastewater. Background Technology

[0002] Shale gas is primarily extracted using hydraulic fracturing, which generates a large amount of fracturing flowback fluid wastewater. This wastewater is characterized by high salinity, high suspended solids, high organic matter content, and high color. During long-term storage on-site, fracturing flowback fluid easily turns black and develops a foul odor, forming black and smelly water. This is because the flowback fluid is typically stored statically in flowback ponds, and a layer of floating oil often hinders oxygen exchange between the air and the water, creating an anaerobic environment at a certain depth. Simultaneously, the aerobic decomposition of organic matter in the flowback fluid causes the oxygen consumption rate to exceed the reoxygenation rate, resulting in oxygen deficiency. This leads to incomplete and slowed degradation of organic matter, and the anaerobic biodegradation process generates foul-smelling substances such as hydrogen sulfide, ammonia, and mercaptans. Furthermore, sulfate-reducing bacteria in the flowback fluid generate sulfur under anaerobic conditions. 2- , with Fe in water 2+ The reaction produces black FeS, which disperses in the water to form black water.

[0003] Conventional black and odorous wastewater typically occurs in urban or rural rivers. This type of water is characterized by low salinity and high biodegradability. Existing methods for treating black and odorous wastewater are mostly biological treatment methods. For example, invention patent CN 110885773 A develops a novel microbial agent (Stenotrophomonas sp.) sp3 for treating black and odorous river water, and patent CN 112978909 A uses an SRB reactor to treat nitrogen and phosphorus in black and odorous water. There are also methods that treat phosphorus in black and odorous wastewater through coagulation, such as patent CN112978909 A. However, because black and odorous shale gas fracturing flowback fluids often have characteristics such as high salinity, high hardness, high color, and high organic matter, the biodegradability of this type of wastewater is poor. Conventional black and odorous wastewater treatment methods are difficult to effectively reduce the organic matter content, color, and bacteria in this type of wastewater. When the treated water is reused internally to prepare fracturing fluid, there are strict requirements for indicators such as total iron and hardness in the water. Therefore, how to properly handle black and odorous fracturing flowback fluid is a key issue that needs to be addressed in the process of achieving clean shale gas production. Thus, there is an urgent need to invent an effective treatment solution for wastewater such as black and odorous shale gas fracturing flowback fluid that has been stored for a long time. This solution would address the environmental pollution problem caused by the black and odorous high-salt wastewater turning black and smelly during on-site storage, while also enabling the treated water to be rationally and effectively utilized as a resource, thereby greatly reducing on-site construction costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies for treating black, odorous, and high-salt wastewater. It provides a method and apparatus for effectively deodorizing and removing blackness from wastewater with characteristics of high salinity, high suspended solids, high hardness, high color, and high organic matter. This not only effectively solves the black and odor problems of shale gas fracturing flowback fluid that has been stored on-site for a long time, but also significantly improves the effluent quality of existing black and odorous water treatment, successfully realizing its resource utilization.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for treating black, odorous, and high-salinity wastewater, the method comprising the following steps:

[0007] Add the reagent to the black, smelly, and high-salt wastewater and mix thoroughly;

[0008] The black, odorous, and high-salt wastewater after mixing the reagents is aerated and pre-oxidized, and the upper layer of dirt in the black, odorous, and high-salt wastewater is scraped off during the aeration and pre-oxidation process.

[0009] The black, odorous, and high-salt wastewater, after the removal of the upper layer of pollutants, is subjected to softening, adsorption, and sedimentation treatment in sequence.

[0010] The supernatant after sedimentation is oxidized with ozone to obtain odorless and transparent water, thus completing the treatment of black, odorous, and high-salt wastewater.

[0011] As a further improvement of the present invention, the processing method further includes:

[0012] Part of the sludge generated during the softening, adsorption, and sedimentation processes is reused.

[0013] The reuse method includes: reusing a portion of the sludge formed for subsequent softening, adsorption, and sedimentation treatment of black, odorous, and high-salt wastewater after the removal of the upper layer of pollutants.

[0014] As a further improvement of the present invention, the processing method further includes:

[0015] Adjust the odorless, transparent water to neutral and use it to prepare new fracturing fluid.

[0016] As a further improvement of the present invention, the black, odorous, and high-salt wastewater includes, but is not limited to, shale gas fracturing reverse discharge fluid.

[0017] As a further improvement of the present invention, the amount of sludge used for partial reuse includes 2 / 3 of the total amount of sludge discharged during the softening, adsorption and sedimentation treatment process.

[0018] As a further improvement of the present invention, the step of adding the reagent to the black, odorous, and high-salinity wastewater and mixing it evenly includes:

[0019] Add 50-1000 mg / L of coagulant to the black, odorous, and high-salt wastewater and mix thoroughly. Then add 0.1-10 mg / L of flocculant and mix thoroughly again.

[0020] As a further improvement of the present invention, the steps of sequentially softening, adsorbing, and settling the black, odorous, and high-salt wastewater after the removal of the upper layer of pollutants include:

[0021] After adding the first softener to the black, odorous, and high-salt wastewater that has had its upper layer of sludge removed and stirring until homogeneous, add the second softener and continue stirring until homogeneous. Then add the adsorbent and stir until homogeneous again. Next, add the coagulant and stir until homogeneous. Finally, add the flocculant and stir until homogeneous before allowing the wastewater to settle.

[0022] As a further improvement of the present invention, the first softening agent is added by adding sodium hydroxide to the black, odorous, and high-salt wastewater, adjusting the pH value to 10-11, and mechanically stirring at a speed gradient of 100-400 r / min, with a hydraulic retention time of 5-10 min.

[0023] As a further improvement of the present invention, the second softening agent is one or more of sodium carbonate, sodium bicarbonate, and sodium sulfate.

[0024] As a further improvement of the present invention, the adsorbent comprises powdered activated carbon, and the amount of the adsorbent added is set to 500-4000 mg / L, the mechanical stirring speed gradient is 100-400 r / min, and the hydraulic retention time is 6-12 min.

[0025] As a further improvement of the present invention, the step of ozone oxidation of the supernatant after sedimentation treatment includes:

[0026] A pH adjuster is added to the supernatant after sedimentation treatment to adjust the pH value of the supernatant to 8.5-9.5. Then, ozone is introduced into the supernatant with adjusted pH value to further oxidize and sterilize the supernatant.

[0027] As a further improvement of the present invention, the step of ozone oxidation of the supernatant after sedimentation treatment further includes:

[0028] The residual ozone during the treatment of the supernatant is recovered and reused in the aeration pre-oxidation process, and the residual ozone in the aeration pre-oxidation process is adsorbed and decomposed.

[0029] As a further improvement of the present invention, when recovering the residual ozone during the treatment of the supernatant and reusing it in the aeration pre-oxidation process,

[0030] The gas capacity in the aeration pre-oxidation process is set to 2%-10% of the total influent volume, and the hydraulic retention time is set to 5-20 minutes.

[0031] A black, odorous, high-salinity wastewater treatment device, the treatment device comprising:

[0032] The coagulation system is used to add chemicals to black, odorous, and high-salt wastewater and mix them evenly.

[0033] An air aeration pre-oxidation system is used to aerate and pre-oxidize black, odorous, and high-salt wastewater after mixing with chemicals, and to scrape off the upper layer of dirt in the black, odorous, and high-salt wastewater during the aeration and pre-oxidation process.

[0034] The softening coupled enhanced coagulation system is used to sequentially soften, adsorb, and settle black, odorous, and high-salt wastewater after the removal of the supernatant.

[0035] The ozone oxidation system is used to oxidize the supernatant obtained after treatment by the softening coupled enhanced coagulation system with ozone to obtain odorless and transparent water.

[0036] As a further improvement of the present invention, the softening coupled enhanced coagulation system is also used to reuse part of the sludge formed after the softening, adsorption and sedimentation treatment in the softening treatment, the adsorption treatment and the sedimentation treatment process.

[0037] As a further improvement of the present invention, the air aeration pre-oxidation system specifically includes an aeration tank with a scraping unit at the top, an aeration generating unit connected to the bottom of the aeration tank, and a sealed cover disposed on the outer periphery of the aeration tank.

[0038] The sealed enclosure has several ventilation openings on its periphery, and the ventilation openings are filled with adsorbent and ozone decomposition agent in sequence from the air inlet end to the air outlet end.

[0039] As a further improvement of the present invention, the ozone oxidation system includes an ozone reactor and an ozone generator connected to the bottom of the ozone reactor.

[0040] As a further improvement of the present invention, the ozone oxidation system further includes connecting the top of the ozone reactor to the bottom of the aeration tank in the air aeration pre-oxidation system, so as to recover the residual ozone during the treatment of the supernatant and reuse it in the aeration pre-oxidation process.

[0041] As a further improvement of the present invention, the softening coupled enhanced coagulation system includes a first softening reaction tank connected to the effluent end of the air aeration pre-oxidation system, a second softening reaction tank connected to the effluent end of the first softening reaction tank, an adsorption reaction tank connected to the effluent end of the second softening reaction tank, a coagulation reaction tank connected to the effluent end of the adsorption reaction tank, a flocculation reaction tank connected to the effluent end of the coagulation reaction tank, and an inclined tube sedimentation tank connected to the effluent end of the flocculation reaction tank; the supernatant discharge end of the inclined tube sedimentation tank is connected to the ozone oxidation system, and the sludge discharge ends of the inclined tube sedimentation tank, the first softening reaction tank, the second softening reaction tank, the adsorption reaction tank, the coagulation reaction tank, and the flocculation reaction tank are connected to a filter press system.

[0042] As a further improvement of the present invention, the softening coupled enhanced coagulation system further includes connecting the sludge discharge end of the inclined tube sedimentation tank, the first softening reaction tank, the second softening reaction tank, the adsorption reaction tank, the coagulation reaction tank and the flocculation reaction tank to the water inlet end of the first softening reaction tank.

[0043] The beneficial effects of this invention are:

[0044] The method for treating black, odorous, and high-salt wastewater provided by this invention first involves aeration and pre-oxidation of the mixed reagents to remove the upper layer of pollutants, followed by softening, adsorption, and sedimentation treatments. The supernatant obtained after sedimentation is then subjected to ozone oxidation, thereby completely solving the black and odorous problems of long-standing high-salt, high-suspended solids, high-organic-matter, and high-color wastewater.

[0045] The black, odorous, and high-salinity wastewater treatment method provided by this invention reuses some of the sludge formed during the softening, adsorption, and sedimentation processes in the softening, adsorption, and sedimentation processes of the black, odorous, and high-salinity wastewater after the removal of the upper layer of contaminants. As a result, the black, odorous, and high-salinity wastewater treatment technology provided by this invention significantly reduces the amount of sludge discharged when treating the same volume of black, odorous, and high-salinity wastewater, to less than 80% of that of traditional methods.

[0046] The method for treating black, odorous, and high-salt wastewater provided by this invention recovers and reuses residual ozone during the treatment of the supernatant in the aeration pre-oxidation process. This not only realizes the resource utilization of residual ozone and further enhances the aeration pre-oxidation effect, but also effectively avoids atmospheric pollution by residual ozone without the need for ozone decomposition agents, significantly reducing treatment costs.

[0047] The black, odorous, and high-salt wastewater treatment method provided by this invention produces water with stable quality indicators that meet the water quality standards for shale gas fracturing flowback fluid reuse. When reused to prepare fracturing fluid, the performance indicators of the prepared fracturing fluid are significantly better than those of fracturing fluid prepared by existing methods, enabling it to meet the performance standards of slickwater and thus greatly reducing the economic cost of oil and gas field development.

[0048] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0049] Figure 1 This is a flow chart of the black, odorous, and high-salt wastewater treatment method of the present invention. Detailed Implementation

[0050] 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.

[0051] The method for treating black, odorous, and high-salinity wastewater provided by this invention includes the following steps:

[0052] Add the reagent to the black, smelly, and high-salt wastewater and mix thoroughly;

[0053] The black, odorous, and high-salt wastewater after mixing the reagents is aerated and pre-oxidized, and the upper layer of dirt in the black, odorous, and high-salt wastewater is scraped off during the aeration and pre-oxidation process.

[0054] The black, odorous, and high-salt wastewater, after the removal of the upper layer of pollutants, is subjected to softening, adsorption, and sedimentation treatment in sequence.

[0055] The supernatant after sedimentation is oxidized with ozone to obtain odorless and transparent water, thus completing the treatment of black, odorous, and high-salt wastewater.

[0056] Among them, black and odorous high-salt wastewater can be black and odorous shale gas fracturing flowback fluid (hereinafter referred to as flowback fluid), or other black and odorous high-salt wastewater with similar characteristics of high salt, high hardness, high color and high organic matter as black and odorous shale gas fracturing flowback fluid, such as black and odorous high-salt landfill leachate, black and odorous high-salt aquaculture waste liquid, etc.

[0057] The specific steps for aeration pre-oxidation treatment of black, odorous, and high-salt wastewater after mixing agents, taking black and odorous shale gas fracturing flowback fluid as an example, include: Figure 1 As shown, the black and odorous shale gas fracturing flowback fluid that has been stored in the raw water tank for a long time is first introduced into the coagulation system. The coagulation system includes a reaction tank 1 and a reaction tank 2 connected in sequence. First, a coagulant with a mass concentration of 50 to 1000 mg / L is added to the black and odorous shale gas fracturing flowback fluid. Then, mechanical stirring is carried out in the reaction tank 1 at a velocity gradient of 100 to 400 r / min, and the hydraulic retention time is set to 1 to 5 min. Polyaluminum chloride (PAC) is preferred as the type of coagulant. Next, a flocculant with a mass concentration of 0.1–10 mg / L is added. The preferred type of flocculant is polyacrylamide (PAM) with a cationicity of 50 and a molecular weight of 5 million. Mechanical stirring is carried out at a speed gradient of 20–80 r / min, and the hydraulic retention time is set to 2–8 min. This allows the suspended solids, colloids, and particles in the fracturing flowback fluid to be coagulated together. This makes it easier for the subsequent air aeration pre-oxidation system to remove suspended solids, colloids, and particles from the flowback fluid during wastewater treatment, thus completing the pre-coagulation process of the flowback fluid.

[0058] Next, the pre-coagulated return liquid is transported to an air aeration pre-oxidation system. This system includes an aeration tank equipped with a scraping unit at the top and an aeration generating unit connected to the bottom of the tank. The aeration generating unit specifically includes an air compressor and a porous diffuser. This configuration allows compressed air from the bottom of the aeration tank to enter and pass through the porous diffuser, forming uniform, high-density, micron-sized bubbles for aeration pre-oxidation. This effectively carries oil, lighter suspended solids, particulate matter, colloids, etc., from the wastewater to the surface of the aeration tank, forming scum. A scraper at this point scrapes this upper layer of sludge (typically 0-4 cm below the surface) into a wastewater collection tank, which then returns it to the raw water tank for black, odorous, and high-salt wastewater. The remaining water enters a softening coupled with enhanced coagulation system. The sludge deposited at the bottom during the aeration pre-oxidation process is then transported to a filter press for filtration.

[0059] After entering the softening coupled enhanced coagulation system, the softening coupled enhanced coagulation system specifically includes a first softening reaction tank connected to the effluent end of the air aeration pre-oxidation system. Figure 1The softening coupled enhanced coagulation system includes a reaction tank 3, a second softening reaction tank (reaction tank 4) connected to the effluent end of the first softening reaction tank, an adsorption reaction tank (reaction tank 5) connected to the effluent end of the second softening reaction tank, a coagulation reaction tank (reaction tank 6) connected to the effluent end of the adsorption reaction tank, a flocculation reaction tank (reaction tank 7) connected to the effluent end of the coagulation reaction tank, and an inclined tube sedimentation tank (reaction tank 8) connected to the effluent end of the flocculation reaction tank. The supernatant discharge end of the inclined tube sedimentation tank is connected to the ozone oxidation system, while the sludge discharge end of the inclined tube sedimentation tank is connected to the filter press system and the inlet end of the first softening reaction tank. In addition, it should be noted that the inlet and outlet of the same reaction tank should not be set at the same horizontal level to effectively avoid short circuits in the water path, thereby ensuring that the added agents can fully act on the waste liquid in the tank. Furthermore, it is necessary to ensure that the effluent from the flocculation reaction tank enters from the lower part of the inclined tube in the inclined tube sedimentation tank, so that the effluent flowing from the inclined tube sedimentation tank to the ozone oxidation system does not contain sludge.

[0060] With this setup, the black, odorous, and high-salt wastewater, after the removal of the upper layer of sludge, will undergo softening, adsorption, and sedimentation treatment sequentially in this system. Before flowing into the first softening reaction tank, the first softening agent, corresponding to softening agent a (NaOH) in the diagram, should be added to the flowback liquid, and mechanical stirring should be performed at a speed gradient of 100–400 r / min, with a hydraulic retention time of 5–10 min, to adjust the pH value of the fracturing flowback liquid to 10–11, so that magnesium ions in the flowback liquid form Mg(OH)2 precipitate and HCO3- in the flowback liquid are precipitated. 3- Converted into CO3 2- and with some non-scaling cations (Ca 2+ Ba 2+ (etc.) to form carbonate precipitate; after the reaction is complete, a second softening agent is added, corresponding to softening agent b in the figure, specifically one or more of sodium carbonate, sodium bicarbonate, and sodium sulfate. When sodium carbonate is selected as the second softening agent, the dosage is 1000–5000 mg / L, and it is introduced into the second softening reaction tank for mechanical stirring. The mechanical stirring speed gradient is 100–400 r / min, and the hydraulic retention time is 5–10 min, so that a large amount of residual non-scaling cations (Ca) in the return liquid are removed. 2+ Ba 2+ (etc.) forms carbonate precipitates. It is worth mentioning that the type of softener used in this invention avoids the drawback of traditional wastewater softening agents like lime (Ca(OH)2), where the dosage is difficult to control. Specifically, if the lime dosage is too low, the removal rate of inorganic scale ions is low; while if the dosage is too high, the Ca in the lime... 2+Instead, it increases the concentration of residual inorganic scale ions. The softened wastewater then flows into the adsorption reaction tank. Before flowing into the adsorption reaction tank, 500-4000 mg / L of adsorbent should be added and stirred evenly. Powdered activated carbon can be used as the adsorbent. The mechanical stirring speed gradient should be set to 100-400 r / min, and the hydraulic retention time should be 6-12 min. The purpose is to adsorb organic matter, colloids, etc. in the black and odorous water, remove color and odor. Moreover, the adsorption process carried out in this way can make the adsorbent and wastewater mix more evenly and extend the action time, making the water treatment process more complete. The effect is significantly better than the existing adsorbent-filled adsorption process.

[0061] After adsorption treatment, the wastewater will continue to flow into the coagulation reaction tank and flocculation reaction tank, where it will be stirred evenly. Before flowing into the coagulation reaction tank, 50–1000 mg / L of coagulant PAC will be added and mechanically stirred at a speed gradient of 100–400 r / min, with a hydraulic retention time of 5–10 min. This aims to form small flocs from particles and colloids in the water, facilitating sedimentation. Before flowing into the flocculation reaction tank, 0.1–10 mg / L of flocculant (PAM with a cationicity of 50 and a molecular weight of 5 million) will be added and mechanically stirred at a speed gradient of 20–80 r / min, with a hydraulic retention time of 5–10 min. This aims to further form large flocs from the small flocs. Finally, the wastewater will enter the inclined tube sedimentation tank for settling for 20–40 min. The sludge deposited at the bottom of the inclined tube sedimentation tank will be combined with the small amount of sludge deposited in reaction tanks 1–5. One-third of the total sludge is pumped into a plate and frame filter press through the bottom sludge discharge pipe for dewatering, forming residue. The residue filtrate is returned to the raw water tank, while two-thirds of the total sludge is returned to the first softening reaction tank. Because the returned sludge contains alkaline substances, it can adjust the pH value of the water, which is conducive to the formation of inorganic scale and reduces the amount of softening agent added. The sludge also contains inorganic scale crystals, which can serve as nuclei for dissolved inorganic scale in the first softening reaction tank, making it easier for dissolved inorganic scale to be adsorbed onto the inorganic scale nuclei and gradually grow, which is conducive to the removal of inorganic scale ions. The sludge also contains some unsaturated powdered activated carbon, which can further adsorb organic matter, colloids, etc. in the sewage, removing blackness, odor, and organic matter. The sludge also contains unreacted coagulant flocculant, which can further capture small particles and suspended solids in the water. Therefore, the return treatment can improve water quality while reducing sludge production and the amount of treatment agents added, reducing the cost of chemical treatment and sludge treatment, thereby significantly improving economic benefits.

[0062] A pH adjuster (such as hydrochloric acid / sodium hydroxide) is added to the supernatant after sedimentation to adjust its pH to 8.5-9.5. The pH-adjusted supernatant is then transported to an ozone oxidation system. This system includes an ozone reactor and an ozone generator connected to the bottom of the reactor. The ozone flow rate is set to 0.05-0.2 m / s. 3 The system operates at a speed of / s, and the residence time of the return liquid in the ozone reactor is set to 20–40 minutes. With this setup, air is ionized in the ozone generator to form ozone. The ozone then enters the ozone reaction tank from the bottom of the ozone reactor, forming micron-sized bubbles through a porous diffuser. This oxidizes and sterilizes the wastewater, further reducing the organic matter, bacteria content, and ammonia nitrogen in the black and odorous water. Furthermore, it should be noted that the pH value of the wastewater needs to be adjusted to a certain range before entering the ozone oxidation system. This is because ozone primarily removes organic matter from wastewater through oxidation. Ozone oxidation of organic matter involves two main reactions: first, ozone itself oxidizes the organic matter; second, ozone generates highly oxidizing hydroxyl radicals, which rapidly react with the organic matter to achieve oxidation. Our experiments revealed that under low pH (acidic) conditions, there are fewer hydroxyl radicals in the water, resulting in less organic matter mineralization via hydroxyl radicals. Organic matter primarily undergoes ozone decomposition, where large organic molecules break down into smaller ones, leading to less organic matter removal (mineralization) and consequently, a lower TOC removal rate. As pH increases, the OH- ions in the water... - Increase, OH - This process induces ozone to generate hydroxyl radicals, which have extremely high oxidation potentials. These radicals can 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 generate a large amount of inorganic scale [CaCO3, Mg(OH)2], increasing the turbidity of the backflow solution. The generated inorganic scale will hinder the oxidation efficiency of ozone on organic matter, thereby reducing the TOC removal rate. Therefore, in this technical solution, it is preferable to adjust the pH value between 8.5 and 9.5.

[0063] Meanwhile, the top of the ozone reactor is connected to the bottom of the aeration tank in the air aeration pre-oxidation system. Residual ozone flows back into the aeration tank through the gas outlet at the top of the ozone reactor to re-participate in the aeration pre-oxidation process. This not only oxidizes reducing substances in the fracturing flowback fluid to form precipitates (e.g., ferrous ions are oxidized to ferric ions to form precipitates), but also degrades some large organic molecules, mineralizes some small organic molecules, and kills bacteria (sulfate-reducing bacteria, saprophytic bacteria, iron bacteria, etc.). It also promotes the rise of more bubbles, further improving the treatment efficiency of the aeration pre-oxidation process and increasing ozone utilization. Furthermore, to effectively prevent residual ozone from escaping, a sealed enclosure is installed around the aeration tank. Several ventilation openings are provided on the perimeter of this enclosure, and each opening is filled sequentially with adsorbent and ozone decomposition agent from the inlet to the outlet. Among them, rare earth nano ozone decomposition agents can be selected as ozone decomposition agents, and granular activated carbon can be selected as odor adsorbents, so as to effectively prevent ozone from escaping and polluting the surrounding air, and ensure that the gas discharged during the air aeration pre-oxidation treatment process is non-toxic, odorless and pollution-free.

[0064] Furthermore, after connecting the residual ozone to the aeration tank of the air pre-oxidation treatment process, it should be ensured that the gas volume in the tank reaches 2%-10% of the total volume of the fracturing flowback fluid influent, and the hydraulic retention time is set to 5-20 minutes.

[0065] The effluent from the ozone oxidation system is odorless and transparent. It is adjusted to neutral using a pH adjuster (hydrochloric acid can be used) before being transported to a clear water tank, where it can be used to prepare new fracturing fluid.

[0066] When the above-mentioned treatment method and apparatus were applied to the treatment of two types of long-term stored black and odorous fracturing flowback fluids, it was found that the black and odorous high-salt wastewater treatment method of the present invention has a significantly improved effect compared with the existing conventional fracturing flowback fluid treatment methods. The specific details are as follows:

[0067] Example 1: The fracturing flowback fluid that had turned black and smelled foul after being left in the centralized storage tank of a shale gas platform in southern Sichuan for a long time was treated. The water quality of the untreated raw water, the effluent treated by the conventional on-site treatment method (coagulation sedimentation method), and the effluent treated by the method of this invention (coagulation-aeration pre-oxidation-softening coupled enhanced coagulation-ozone oxidation) were compared. The comparison results are shown in Table 1.

[0068] Table 1 Comparison of raw water quality and effluent quality treated by the two technologies.

[0069]

[0070]

[0071] The comparison results of water quality indicators for reclaimed water show that the total hardness, total iron, bacteria (SRB, FB), scaling tendency, and compatibility of the raw water all exceed the recommended water quality indicators for reclaimed water. Conventional methods are effective in removing total iron and suspended solids, but less effective in treating total hardness, bacteria, scaling tendency, and compatibility. The four indicators of the treated water still exceed the reclaimed water quality standards (NB / T14002.3-2015). In contrast, the water quality treated by the method of this invention is significantly better than that treated by conventional methods and fully meets the reclaimed water quality standards. Furthermore, the comparison results of conventional water quality indicators for black and odorous water show that the color, total organic matter (TOC), sulfides, petroleum hydrocarbons, and ammonia nitrogen content of the raw water are all high. Conventional methods are effective in removing color, but less effective in removing TOC, sulfides, petroleum hydrocarbons, and ammonia nitrogen. The method of this invention shows good removal effects for all four of these indicators, effectively solving the problem of "black and odorous" water.

[0072] Untreated raw water, effluent treated by conventional methods (coagulation sedimentation), and effluent treated by the method of this invention (coagulation-aeration pre-oxidation-softening coupled enhanced coagulation-ozone oxidation) were reused for the preparation of fracturing fluid. Table 2 shows the performance index comparison results of the slickwater prepared by each method.

[0073] Table 2 Performance Evaluation of Raw Water and Effluent from Two Treatment Technologies for Slippery Water

[0074]

[0075] The performance evaluation results of the fracturing fluid above show that the slickwater prepared from raw water exceeds the slickwater performance standard (NBT14003.1-2015) in terms of surface tension, scaling tendency, bacteria (SRB, FB), compatibility, and drag reduction. Conventional methods improve the surface tension of slickwater prepared from treated effluent, but the scaling tendency, bacteria, compatibility, and drag reduction still exceed the slickwater performance indicators. However, the slickwater prepared from effluent treated using the method of this invention shows significantly improved performance, fully meeting the slickwater performance indicators.

[0076] Furthermore, after treating 1000 cubic meters of black and odorous backflow liquid using the method of this invention, it was found that the amount of sludge discharged was significantly less than that of conventional methods, only about 74% of the amount of sludge discharged by conventional methods.

[0077] Example 2: The fracturing flowback fluid from a shale gas well No. 18 in Sichuan Province, which had turned black and smelled foul, was treated. The water quality of the untreated raw water, the effluent treated by conventional on-site treatment methods (coagulation sedimentation), and the effluent treated by the method of this invention (coagulation-aeration pre-oxidation-softening coupled enhanced coagulation-ozone oxidation) were compared. The comparison results are shown in Table 3.

[0078] Table 3 Comparison of raw water quality and effluent quality treated by the two technologies.

[0079]

[0080]

[0081] The water quality comparison results from the recommended water quality indicators for reclaimed water show that the total hardness, bacteria (SRB, TGB, FB), scaling tendency, and compatibility of the raw water all exceed the recommended water quality indicators for reclaimed water. Conventional methods are effective in removing suspended solids and total iron, but the total hardness, bacteria, scaling tendency, and compatibility of the treated water still exceed the reclaimed water quality standards (NB / T14002.3-2015). The method of this invention can significantly 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 reclaimed water quality standards. Furthermore, the comparison results of conventional water quality indicators for black and odorous water show that conventional methods are effective in removing color, but less effective in removing TOC, sulfides, petroleum hydrocarbons, and ammonia nitrogen. The method of this invention, however, is effective in removing all five of these indicators, effectively solving the problem of "black and odorous" water.

[0082] Untreated raw water, effluent treated by conventional methods (coagulation sedimentation), and effluent treated by the method of this invention (coagulation-aeration pre-oxidation-softening coupled enhanced coagulation-ozone oxidation) were reused for the preparation of fracturing fluid. Table 4 shows the performance index comparison results of the slickwater prepared by each method.

[0083] Table 4 Performance Evaluation of Raw Water and Effluent from Two Treatment Technologies for Slippery Water

[0084]

[0085] Table 4 shows that the slickwater prepared from the raw water exceeds the slickwater performance standards (NBT14003.1-2015) in terms of surface tension, scaling tendency, bacteria (SRB, TGB, FB), compatibility, and drag reduction. Conventional methods improve the surface tension of the effluent used to prepare the slickwater, but the scaling tendency, bacteria, compatibility, and drag reduction still exceed the slickwater performance indicators. However, the method of this invention significantly improves the performance of the effluent used to prepare the slickwater, fully meeting all the slickwater performance indicators.

[0086] Furthermore, after treating 500 cubic meters of black and odorous backflow liquid using the method of this invention, it was found that the amount of sludge discharged was significantly less than that of conventional methods, less than 80% of the amount of sludge discharged by conventional methods.

[0087] In summary, the black, odorous, and high-salinity wastewater treatment method provided by this invention first removes the upper layer of contaminants by aeration pre-oxidation of the mixed reagents, followed by softening, adsorption, and sedimentation treatments. The supernatant obtained after sedimentation is then subjected to ozone oxidation, thereby completely solving the black and odorous problems of long-standing high-salinity, high-suspended-solids, high-organic-content, and high-color wastewater. By reusing some of the sludge generated during the softening, adsorption, and sedimentation processes in the softening, adsorption, and sedimentation treatment of the already decontaminated black, odorous, and high-salinity wastewater, the sludge discharge of the black, odorous, and high-salinity wastewater treatment technology provided by this invention is significantly reduced compared to traditional shale gas fracturing flowback fluid treatment technology, reaching less than 80% of the amount required for treating the same volume of black, odorous, and high-salinity wastewater. By recovering and reusing residual ozone from the supernatant treatment process in the aeration pre-oxidation process, not only is the resource utilization of residual ozone achieved, further enhancing the aeration pre-oxidation effect, but also the pollution of the atmosphere by residual ozone can be effectively avoided without the need for ozone decomposition agents, significantly reducing treatment costs. Furthermore, the black, odorous, and high-salt wastewater treatment method provided by this invention produces water with stable quality indicators, meeting the water quality standards for shale gas fracturing flowback fluid reuse. When reused to prepare fracturing fluid, the performance indicators of the prepared fracturing fluid are significantly better than those prepared using existing methods, meeting the performance standards for slickwater and thus greatly reducing the economic costs of oil and gas field development.

[0088] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating black, odorous, and high-salinity wastewater, the method comprising the following steps: Add the reagent to the black, smelly, and high-salt wastewater and mix thoroughly; The black, odorous, and high-salt wastewater after mixing the reagents is aerated and pre-oxidized, and the upper layer of dirt in the black, odorous, and high-salt wastewater is scraped off during the aeration and pre-oxidation process. After the upper layer of sludge has been removed, the black, odorous, and high-salt wastewater enters the softening coupled enhanced coagulation system, where it undergoes softening, adsorption, and sedimentation treatment in sequence. The softening coupled enhanced coagulation system includes a first softening reaction tank connected to the effluent end of an air aeration pre-oxidation system, a second softening reaction tank connected to the effluent end of the first softening reaction tank, an adsorption reaction tank connected to the effluent end of the second softening reaction tank, a coagulation reaction tank connected to the effluent end of the adsorption reaction tank, a flocculation reaction tank connected to the effluent end of the coagulation reaction tank, and an inclined tube sedimentation tank connected to the effluent end of the flocculation reaction tank; the supernatant discharge end of the inclined tube sedimentation tank is connected to an ozone oxidation system. The inlet and outlet of the same reaction tank cannot be set at the same horizontal height. The effluent from the flocculation reaction tank enters from the lower part of the inclined tube set in the inclined tube sedimentation tank. The steps of sequentially softening, adsorbing, and settling the black, odorous, and high-salt wastewater after the removal of the upper layer of pollutants include: After adding the first softener to the black, smelly, and high-salt wastewater after removing the upper layer of dirt and stirring evenly, add the second softener and continue stirring evenly. Then add the adsorbent and stir evenly again. Next, add the coagulant and stir evenly. Finally, add the flocculant and stir evenly before settling. Before the adsorption-treated waste liquid flows into the coagulation reaction tank, 50–1000 mg / L of coagulant is added and mechanically stirred. The mechanical stirring speed is set at 100–400 r / min and the hydraulic retention time is 5–10 min. Before flowing into the flocculation reaction tank, 0.1–10 mg / L of flocculant is added and mechanically stirred. The mechanical stirring speed gradient is set at 20–80 r / min and the hydraulic retention time is 5–10 min. The first softening agent is added as follows: sodium hydroxide is added to the black, odorous, and high-salt wastewater to adjust the pH value to 10-11, and mechanical stirring is performed at a speed of 100-400 r / min, with a hydraulic retention time of 5-10 min. The second softening agent is one or more of sodium carbonate, sodium bicarbonate, and sodium sulfate; The supernatant after sedimentation is subjected to ozone oxidation to obtain odorless and transparent water, thereby completing the treatment of black, odorous, and high-salt wastewater; the step of ozone oxidation of the supernatant after sedimentation includes: A pH adjuster is added to the supernatant after sedimentation treatment to adjust the pH value of the supernatant to 8.5-9.

5. Then, ozone is introduced into the supernatant with adjusted pH value to further oxidize and sterilize the supernatant. The step of ozone oxidation of the supernatant after sedimentation treatment further includes: The residual ozone during the treatment of the supernatant is recovered and reused in the aeration pre-oxidation process, and the residual ozone in the aeration pre-oxidation process is adsorbed and decomposed.

2. The method for treating black, odorous, and high-salinity wastewater according to claim 1, wherein, The processing method further includes: The sludge formed during the softening, adsorption, and sedimentation processes is partially reused. The reuse method includes: reusing a portion of the sludge formed in the subsequent softening, adsorption, and sedimentation processes of black, odorous, and high-salt wastewater after the removal of the upper layer of pollutants.

3. The method for treating black, odorous, and high-salinity wastewater according to claim 1 or 2, wherein, The processing method further includes: Adjust the odorless, transparent water to neutral and use it to prepare new fracturing fluid.

4. The method for treating black, odorous, and high-salinity wastewater according to claim 3, wherein, The black, odorous, and highly saline wastewater is shale gas fracturing flowback fluid.

5. The method for treating black, odorous, and high-salinity wastewater according to claim 2, wherein, The amount of sludge used for partial reuse includes 2 / 3 of the total sludge discharged during the softening, adsorption and sedimentation treatment processes.

6. The method for treating black, odorous, and high-salinity wastewater according to claim 1, wherein, The adsorbent includes powdered activated carbon, and the amount of adsorbent added is set to 500-4000 mg / L, the mechanical stirring speed is 100-400 r / min, and the hydraulic retention time is 6-12 min.

7. The method for treating black, odorous, and high-salinity wastewater according to claim 1, wherein, When the residual ozone from the treatment of the supernatant is recovered and reused in the aeration pre-oxidation process, The gas capacity in the aeration pre-oxidation process is set to 2%-10% of the total influent volume, and the hydraulic retention time is set to 5-20 minutes.

8. A device for treating black, odorous, and high-salinity wastewater, the device comprising: The coagulation system is used to add chemicals to black, odorous, and high-salt wastewater and mix them evenly. An air aeration pre-oxidation system is used to aerate and pre-oxidize black, odorous, and high-salt wastewater after mixing with chemicals, and to scrape off the upper layer of dirt in the black, odorous, and high-salt wastewater during the aeration and pre-oxidation process. A softening coupled enhanced coagulation system is used to sequentially soften, adsorb, and settle black, odorous, and high-salt wastewater after the removal of supernatants. The system includes a first softening reaction tank connected to the effluent end of an air aeration pre-oxidation system; a second softening reaction tank connected to the effluent end of the first softening reaction tank; an adsorption reaction tank connected to the effluent end of the second softening reaction tank; a coagulation reaction tank connected to the effluent end of the adsorption reaction tank; a flocculation reaction tank connected to the effluent end of the coagulation reaction tank; and an inclined tube sedimentation tank connected to the effluent end of the flocculation reaction tank. The supernatant discharge end of the inclined tube sedimentation tank is connected to an ozone oxidation system. The inlet and outlet of the same reaction tank should not be set at the same horizontal height. The effluent from the flocculation reaction tank should enter from the lower part of the inclined tube in the inclined tube sedimentation tank. The steps of sequentially softening, adsorbing, and settling the black, odorous, and high-salt wastewater after the removal of the upper layer of pollutants include: After adding the first softener to the black, smelly, and high-salt wastewater after removing the upper layer of dirt and stirring evenly, add the second softener and continue stirring evenly. Then add the adsorbent and stir evenly again. Next, add the coagulant and stir evenly. Finally, add the flocculant and stir evenly before settling. Before the adsorption-treated waste liquid flows into the coagulation reaction tank, 50–1000 mg / L of coagulant is added and mechanically stirred. The mechanical stirring speed is set at 100–400 r / min and the hydraulic retention time is 5–10 min. Before flowing into the flocculation reaction tank, 0.1–10 mg / L of flocculant is added and mechanically stirred. The mechanical stirring speed gradient is set at 20–80 r / min and the hydraulic retention time is 5–10 min. The first softening agent is added as follows: sodium hydroxide is added to the black, odorous, and high-salt wastewater to adjust the pH value to 10-11, and mechanical stirring is performed at a speed of 100-400 r / min, with a hydraulic retention time of 5-10 min. The second softening agent is one or more of sodium carbonate, sodium bicarbonate, and sodium sulfate; An ozone oxidation system is used to oxidize the supernatant obtained after treatment by a softening coupled enhanced coagulation system to obtain odorless and transparent water; the steps for ozone oxidation of the supernatant after sedimentation treatment include: A pH adjuster is added to the supernatant after sedimentation treatment to adjust the pH value of the supernatant to 8.5-9.

5. Then, ozone is introduced into the supernatant with adjusted pH value to further oxidize and sterilize the supernatant. The step of ozone oxidation of the supernatant after sedimentation treatment also includes: The residual ozone during the treatment of the supernatant is recovered and reused in the aeration pre-oxidation process, and the residual ozone in the aeration pre-oxidation process is adsorbed and decomposed.

9. The black, odorous, and high-salinity wastewater treatment device according to claim 8, wherein, The softening coupled enhanced coagulation system is also used to reuse part of the sludge formed after the softening, adsorption and sedimentation treatments in the softening treatment, the adsorption treatment and the sedimentation treatment processes.

10. The black, odorous, high-salinity wastewater treatment device according to claim 8 or 9, wherein, The air aeration pre-oxidation system specifically includes an aeration tank equipped with a scraping unit at the top, an aeration generating unit connected to the bottom of the aeration tank, and a sealed cover set on the outer periphery of the aeration tank. The sealed enclosure has several ventilation openings on its periphery, and the ventilation openings are filled with adsorbent and ozone decomposition agent in sequence from the air inlet end to the air outlet end.

11. The black, odorous, and high-salinity wastewater treatment device according to claim 8, wherein, The ozone oxidation system includes an ozone reactor and an ozone generator connected to the bottom of the ozone reactor.

12. The black, odorous, and high-salinity wastewater treatment device according to claim 11, wherein, The ozone oxidation system further includes connecting the top of the ozone reactor to the bottom of the aeration tank in the air aeration pre-oxidation system, so as to recover the residual ozone during the treatment of the supernatant and reuse it in the aeration pre-oxidation process.

13. The black, odorous, high-salinity wastewater treatment device according to claim 8, wherein, The sludge discharge ends of the inclined tube sedimentation tank, the first softening reaction tank, the second softening reaction tank, the adsorption reaction tank, the coagulation reaction tank, and the flocculation reaction tank are connected to a filter press system.

14. The black, odorous, high-salinity wastewater treatment device according to claim 13, wherein, The softening coupled enhanced coagulation system further includes connecting the sludge discharge end of the inclined tube sedimentation tank, the first softening reaction tank, the second softening reaction tank, the adsorption reaction tank, the coagulation reaction tank, and the flocculation reaction tank to the water inlet end of the first softening reaction tank.

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