CN114906978A - System and method for combined treatment of shale gas fracturing flow-back fluid and domestic sewage - Google Patents

Abstract

The invention discloses a system for combined treatment of shale gas fracturing flowback fluid and domestic sewage, which comprises a preprocessor, an advanced oxidation generator, a mixing pool and a bioreactor which are sequentially connected through pipelines; the advanced oxidation generator is connected with a pipeline for introducing ozone, the mixing tank is connected with a pipeline for introducing urban domestic sewage, the bioreactor is also connected with a pipeline for introducing air, and the bioreactor discharges a water outlet for purified water. The process for treating the shale gas fracturing flow-back fluid comprises the following steps: 1) adding a preprocessor for preprocessing to obtain a supernatant; 2) then the supernatant enters an advanced oxidation generator for oxidation to obtain advanced oxidized sewage; 3) then mixing with urban domestic sewage, conveying to a bioreactor, and carrying out microbial treatment to enable the water sample to reach the purified water of discharge standard. The invention combines oxidation and biological methods, leads the fracturing flow-back fluid to reach the discharge requirement after oxidation treatment, and utilizes domestic sewage to supplement nitrogen and phosphorus to realize the combined treatment with the domestic sewage.

Description

System and method for combined treatment of shale gas fracturing flow-back fluid and domestic sewage

Technical Field

The invention relates to the technical field of fracturing flow-back fluid treatment, in particular to a system and a method for combined treatment of shale gas fracturing flow-back fluid and domestic sewage.

Background

Fracturing is a main measure for yield increase and transformation of oil and gas wells, and a series of environmental protection problems are brought by fracturing flowback fluid while the fracturing scale of the oil and gas wells is continuously increased. According to analysis of water quality detection data of a large amount of flow-back liquid, the flow-back liquid contains a large amount of solid suspension; the phenomenon of blackening and smelling occurs after long-time storage; the turbidity is high (200-500 NTU); the Chemical Oxygen Demand (COD) is high (200-2000 mg/L); and Ca ²⁺ 、 Mg ²⁺ 、Fe ²⁺ 、Fe ³⁺ The content of metal ions with divalent or higher is high. The direct reuse can cause the further deterioration of water quality, and not only can cause damage and shadow to the reservoirEnvironmental risks are also increased depending on the performance specifications of the fracturing fluid. Therefore, the flow-back liquid must be treated before the liquid is used repeatedly.

The existing treatment methods mainly comprise a Fenton oxidation method, an electrochemical catalytic oxidation method and a biological method. However, in the three methods, certain technical difficulties exist in the treatment process of the shale gas fracturing flow-back fluid, and the three methods are as follows:

the first stage of the Fenton oxidation process is Fe ²⁺ H is to be ₂ O ₂ Rapidly decomposed into a large amount of hydroxyl free radicals, and the hydroxyl free radicals oxidize target organic pollutants, thereby achieving the effect of degrading COD in the wastewater, and simultaneously Fe ²⁺ Will be converted into Fe ³⁺ And exists in the system in the form of iron mud. The Fenton oxidation method has an acidic reaction system, a large amount of iron mud is generated after the reaction, secondary pollution is easily caused, and H is contained in the iron mud ₂ O ₂ As a main oxidant, the oxidant is not easy to transport, so the application is limited, the treatment cost of the process is high, and the treatment effect cannot meet the expected requirement.

The electrochemical catalytic oxidation method degrades organic matters in the wastewater through generated hydroxyl free radicals OH, and OH has extremely strong oxidation activity and almost no selectivity to the action substances. The electrochemical catalytic oxidation method needs a large amount of electric power, has high use cost and has high requirement on water quality.

The biological method is that microorganisms utilize substances in the fracturing flow-back fluid or externally added nutrient substances, carbon sources and the like to carry out metabolism, growth and reproduction, and simultaneously degrade organic matters in the fracturing flow-back fluid to generate stable inorganic matters. The biological method has high requirement on the quality of the inlet water and long period, and the fracturing flow-back fluid has poor biodegradability and higher salinity and is not beneficial to the growth of microorganisms. If the fracturing flowback fluid is directly treated by a biological method, a stable microbial community is difficult to form in the system, and the final treatment effect is difficult to achieve the expected target.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a system for the combined treatment of shale gas fracturing flowback fluid and domestic sewage, which has stable COD value of effluent and lower cost and can provide sufficient nutrient elements such as nitrogen, phosphorus and the like for microorganisms.

The invention also aims to provide a method for jointly treating shale gas fracturing flowback fluid and domestic sewage based on the system.

In order to achieve the purpose, the invention is realized by the following technical scheme: a system for combined treatment of shale gas fracturing flowback fluid and domestic sewage is characterized by comprising a preprocessor, an advanced oxidation generator, a mixing pool and a bioreactor which are sequentially connected through pipelines; the advanced oxidation generator is also connected with a pipeline for introducing ozone from the outside, the mixing tank is also connected with a pipeline for introducing urban domestic sewage, a pipeline for introducing external air is also connected from the outside in the bioreactor, and a water outlet for discharging purified water is arranged at the bottom of the bioreactor.

The working principle of the technical scheme is that the fracturing flow-back fluid subjected to catalytic ozonation and urban domestic sewage are subjected to cooperative treatment, wherein the addition of the urban domestic sewage can reduce the biotoxicity of a biological reaction system, and partial nutrients (carbon, nitrogen and phosphorus) required by the growth of microorganisms are supplemented for the biological reaction system, so that a good environment is provided for the growth of the microorganisms of the system, and the combined treatment of the domestic sewage and the fracturing flow-back fluid is realized.

In order to better realize the invention, the device further comprises an ozone input device, wherein the ozone input device comprises an oxygen cylinder and an ozone generator, an output pipe of the oxygen cylinder is communicated with an input pipe of the ozone generator, and an output pipe of the ozone generator extends into the advanced oxidation generator.

In order to better realize the invention, the bioreactor further comprises an air pump, a pipeline for outputting high-pressure air of the air pump extends into the bioreactor, and a rotor flow meter is further arranged on the pipeline for outputting high-pressure air.

In order to better realize the invention, further, the advanced oxidation generator and the mixing tank are both provided with a mixing and stirring device, and the bioreactor is a sequencing batch biofilm reactor.

The method for jointly treating the shale gas fracturing flow-back fluid and the domestic sewage according to the system comprises the following steps:

(1) adding the shale gas fracturing flow-back fluid into a preprocessor, carrying out coagulation treatment on the shale gas fracturing flow-back fluid by using a coagulant and a coagulant aid, and removing suspended matters and partial organic matters in the shale gas fracturing flow-back fluid to obtain a supernatant;

(2) the supernatant in the preprocessor enters an advanced oxidation generator, and hydroxylamine and Fe-Al pass through the advanced oxidation generator ₂ O ₃ The supernatant is oxidized by the concerted catalysis ozone process, partial organic matters and macromolecular organic matters which are difficult to biodegrade in the supernatant are removed, the biodegradability of the supernatant is greatly improved, and advanced oxidized sewage is obtained;

(3) conveying the obtained advanced oxidized sewage to a mixing tank to be mixed with urban domestic sewage according to the ratio of 1:1, then conveying the mixed sewage to a bioreactor, and degrading organic matters in the mixed solution into stable inorganic matters by utilizing a microbial community domesticated in the bioreactor and introducing air for aeration so as to enable a water sample to reach a discharge standard.

The key step of the technical scheme is the step (2), namely hydroxylamine and Fe-Al are passed through in an advanced oxidation generator ₂ O ₃ The process of oxidizing the supernatant by the concerted catalysis ozone process has the following specific oxidation mechanism:

①Fe-Al ₂ O ₃ and O ₃ Function of between

With O alone ₃ Oxidation phase, Fe-Al ₂ O ₃ /O ₃ Process pair COD _Cr And DOC are removed to a certain extent, which shows that Fe-Al ₂ O ₃ Can well catalyze O ₃ . This can be attributed to the following 3 points: 1) Fe-Al ₂ O ₃ The surface Fe oxide can catalyze the ozone decomposition, and in addition, under the acidic or neutral condition, the surface of the Fe oxide can generate hydroxyl which is O ₃ OH is generated after absorption, and pollutants are further oxidized; 2) o in solution ₃ Will be in gamma-Al ₂ O ₃ Generates OH under the action of (1), and is adsorbed on Fe-Al ₂ O ₃ The pollutants can be oxidized and degraded under the action of OH generated on the surfaces of the solution and the catalyst; 3) in acid stripsIn one piece, H in solution ⁺ Will erode the load Al ₂ O ₃ Fe oxide of the surface to produce Fe ²⁺ /Fe ³⁺ ，Fe ²⁺ /Fe ³⁺ Will promote O ₃ Generation of OH ^[22,81,82] The oxidation of the system to pollutants is enhanced, and the specific reaction formula is as follows:

FeO+2H ⁺ →Fe ²⁺ +H ₂ O

Fe ₂ O ₃ +6H ⁺ →2Fe ³⁺ +3H ₂ O

Fe ²⁺ +O ₃ →O ₂ +FeO ²⁺

H ₂ O+FeO ²⁺ →·OH+Fe ³⁺ +OH ^—

Fe ²⁺ +FeO ²⁺ +2H ⁺ →H ₂ O+2Fe ³⁺

Fe ³⁺ +O ₃ →FeO ²⁺ +·OH+O ₂ +H ⁺

② HA and O ₃ Function of between

HA and O ₃ The reaction between them is mainly influenced by pH. When the pH is higher<5.96 HA is predominantly NH in solution ₃ OH ⁺ Form exists when 5.96<pH<13.74 HA is predominantly NH in solution ₂ OH form, when at pH>13.74 HA is predominantly NH in solution ₂ O ^- The form exists. Under the conditions of acidity, neutrality and alkalescence, HA can promote O ₃ The decomposition of (A), i.e. both protonation and non-protonation, promotes O ₃ Decomposition of (3). It was further found that HA and O are in different forms ₃ Has a different reaction rate from that of O, and is not protonated ₃ The reaction rate of (A) is far faster than that of protonation and O ₃ The reaction rate of (c). Under acidic conditions, HA and O ₃ The main reactions are as follows:

⁺ NH ₃ O ^— +O ₃ →NH ₃ O ^·+ +O ₃ ^·—

O ₃ ^·— +H ⁺ →HO ₃ ·

HO ₃ ·→·OH+O ₂

herein, HA/O ₃ Under the process, COD _Cr And DOC, but the effect of HA concentration on DOC removal indicates that HA still promotes O ₃ In this context HA and O ₃ The reaction of (a) follows the above reaction scheme.

③ HA and Fe-Al ₂ O ₃ Function of between

HA/Fe-Al ₂ O ₃ /O ₃ Process pair COD _Cr And DOC removal is greater than HA/O ₃ And Fe-Al ₂ O ₃ /O ₃ And (5) processing. Especially in Fe-Al ₂ O ₃ /O ₃ After HA is introduced into the process, DOC removal rate is obviously increased, while in HA/O ₃ COD after treatment _Cr Both increased in DOC and increased in HA/Fe-Al ₂ O ₃ /O ₃ In the process by indirect catalysis of O ₃ In such a way as to enhance the oxidation performance of the system. The change in Fe element on the catalytic surface before and after oxidation indicates that HA converts ≡ Fe (III) on the catalyst surface to ≡ Fe (II), and thus Fe-Al in solution ₂ O ₃ The surface-formed hydroxyl ligand (≡ Fe (III) -OH) will react with N ₂ HOH reaction generates Fe (II) -OH, promotes Fe (III)/Fe (II) circulation, and further improves the oxidation performance of the system.

≡Fe(Ⅲ)-OH+N ₂ HOH→≡Fe(Ⅱ)-OH+NH ₂ O ^· +H ⁺

④O ₃ Direct oxidation

O ₃ As a strong oxidizing agent, it undergoes an addition reaction with an organic substance containing an unsaturated bond to degrade the organic substance. In this study, O alone ₃ After the treatment process is oxidized for 60min, COD is generated _Cr And DOC, indicating O ₃ The composite material can degrade part of macromolecular degradation-resistant organic matters in fracturing flowback fluid so as to improve the biodegradability of a water sample, but can not completely mineralize pollutants, and the composite material also has the same discovery in the text.

In order to better implement the method of the present invention, further, in the step (1), the coagulant is polyaluminium chloride, and the coagulant aid is polyacrylamide; the pretreatment process of adding the shale gas fracturing flow-back fluid into the preprocessor comprises the following steps: adjusting the pH value of the shale gas fracturing flow-back fluid to be neutral, adding polyaluminium chloride into the fracturing flow-back fluid with the dosage of not less than 400mg/L, stirring for 5min, adding polyacrylamide with the dosage of 20mg/L, slowly stirring for 1min, and standing for 30min to obtain a supernatant.

In order to better implement the method of the present invention, further, in the step (2), hydroxylamine and Fe-Al are added in the advanced oxidation generator ₂ O ₃ The specific process of oxidizing the supernatant by the concerted catalysis ozone process comprises the following steps:

(2.1) preparation of Fe-Al by immersion-calcination method ₂ O ₃ A catalyst;

(2.2) adjusting the pH value of the supernatant by using a pH regulator to ensure that the initial pH of the supernatant is 3.3-7.7;

(2.3) continuously stirring the supernatant liquid with the initial pH value adjusted, introducing ozone into the supernatant liquid, wherein the flow of the ozone is not less than 0.2L/min, and immediately adding Fe-Al ₂ O ₃ Catalyst and hydroxylamine solution, in which Fe-Al ₂ O ₃ The adding amount of the catalyst is not less than 5g/L, the adding amount of the hydroxylamine solution is not less than 0.01g/L, and the oxidation treatment process of the supernatant is completed after stirring reaction for 20-50 min.

In order to better realize the method of the invention, further, in the step (2.3), the initial pH value of the supernatant is 6.7, the flow rate of the ozone is 0.2L/min, and Fe-Al ₂ O ₃ The amount of the catalyst added was 5.26g/L, and the amount of the hydroxylamine solution added was 0.1 g/L.

In order to better realize the method of the invention, in the step (3), the water inlet and outlet amount of the bioreactor is 50-80% of the effective volume of the bioreactor, the reaction period is 24h, wherein the mixed sewage inlet time is 0.5h, the aeration time is 18-20 h, the aeration stop time is 3-5 h, and the water outlet time is 0.5 h.

In order to better implement the method of the present invention, in the step (3), the acclimation process of the microbial community comprises the following steps of taking the activated sludge of the effluent of the secondary sedimentation tank of the municipal sewage treatment plant as the substrate sludge, taking the municipal domestic sewage: and (3) acclimatizing the sewage in the ratio of 9:1, 4:1, 7:3 and 3:2 in sequence for 40-60 days after advanced oxidation, wherein each acclimatization ratio is 10-15 days.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) on one hand, the invention combines oxidation and biological methods, which can overcome the problem that indexes such as organic matters and the like are difficult to meet the emission requirement after the oxidation treatment of the fracturing flow-back fluid, on the other hand, the fracturing flow-back fluid and the municipal domestic sewage treatment are combined on a treated object, and the nitrogen and phosphorus in the domestic sewage are utilized to supplement the problem of insufficient nitrogen and phosphorus in the biological treatment of the fracturing flow-back fluid, so that the combined treatment of the domestic sewage is realized while the fracturing flow-back fluid is treated with high efficiency and low cost;

(2) the invention is based on HA/Fe-Al ₂ O ₃ /O ₃ The treatment method combines the preoxidized fracturing flow-back fluid with the treatment process of the municipal sewage treatment plant, so that the industrial operation of the treatment of the fracturing flow-back fluid is realized, the aim of economic and efficient treatment is fulfilled, and Fe-Al ₂ O ₃ As a catalyst, the catalyst has the characteristics of low cost, high catalytic efficiency, easy preparation, repeated utilization and no secondary pollution, and can effectively reduce the use of the catalyst;

(3) the microbial community in the biological method can be obtained by domesticating and culturing the microbial community in the urban domestic sewage, so the method has the advantages of wide source, low cost and high treatment efficiency;

(4) the invention has reasonable structure and perfect functions, solves the problems of unstable COD (chemical oxygen demand) of the effluent of the fracturing flow-back fluid treated by singly using advanced oxidation treatment and high cost, and insufficient contents of nutrient elements such as nitrogen, phosphorus and the like when the fracturing flow-back fluid is treated by singly using a biological method, has obvious effect and good development prospect, and is suitable for wide popularization and application.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a block diagram schematically illustrating the structure of the present invention;

FIG. 2 shows DOC removal rates at different dosages of polyaluminium chloride used as a coagulant in the present invention;

FIG. 3 shows DOC removal rates at different dosages for polyacrylamide as coagulant aid in the present invention;

FIG. 4 shows Fe-Al in the present invention ₂ O ₃ A flow chart for preparing the catalyst;

FIG. 5 shows the non-Fe-loaded gamma-Al of the present invention ₂ O ₃ SEM picture;

FIG. 6 shows Fe-loaded gamma-Al of the present invention ₂ O ₃ SEM picture;

FIG. 7 shows Fe-Al in the present invention ₂ O ₃ High resolution projection electron microscopy images of (a);

FIG. 8 is a mapping image of Al element in the present invention;

FIG. 9 is a mapping image of O elements in the present invention;

FIG. 10 is a mapping image of Fe element in the present invention;

FIG. 11 shows Fe-Al in the present invention ₂ O ₃ EDS map of (a);

FIG. 12 shows γ -Al in the present invention ₂ O ₃ 、Fe-Al ₂ O ₃ An XRD pattern of (a);

FIG. 13 shows Fe-Al in the present invention ₂ O ₃ The inert electrolyte titration curve of (a);

FIG. 14 is a graph of the effect of different O3 flow rates on DOC removal rate in accordance with the present invention;

FIG. 15 is a graph of different O3 flow vs. DOC removal, UV for the present invention ₂₅₄ And the influence of pH;

FIG. 16 is a graph of the effect of different catalyst additions on DOC removal in accordance with the present invention;

FIG. 17 shows DOC removal, UV, for different catalyst additions in the present invention ₂₅₄ And the influence of pH;

FIG. 18 is a graph of the effect of different HA concentrations on DOC removal rate in accordance with the present invention;

FIG. 19 is a graph of different HA concentrations versus DOC removal, UV, in accordance with the present invention ₂₅₄ And the influence of pH;

FIG. 20 is a graph of the effect of different initial pH on DOC removal rate in accordance with the present invention;

FIG. 21 is a graph of different initial pH vs. DOC removal, UV, for the present invention ₂₅₄ And the influence of pH;

FIG. 22 is a graph of the response curve of catalyst loading and HA concentration versus DOC removal in accordance with the present invention;

FIG. 23 is a line contour plot of catalyst loading and HA concentration versus DOC removal in accordance with the present invention;

FIG. 24 is a graph of the response curve of catalyst loading and initial pH to DOC removal rate in accordance with the present invention;

FIG. 25 is a line contour plot of catalyst loading versus initial pH versus DOC removal rate in accordance with the present invention;

FIG. 26 is a graph of the response curve of HA concentration and initial pH to DOC removal rate in accordance with the present invention;

FIG. 27 is a line contour plot of HA concentration versus initial pH versus DOC removal rate in accordance with the present invention;

FIG. 28 is a graph showing the results of a catalyst recycling experiment in accordance with the present invention;

FIG. 29 is an SEM image of a recycled catalyst in accordance with the present invention;

FIG. 30 shows DOC and UV for different processes in the present invention ₂₅₄ Removing the effect graph;

FIG. 31 shows the COD of different processes of the present invention _Cr 、BOD ₅ The removal effect and the B/C value change graph;

FIG. 32 is HA/Fe-Al of the present invention ₂ O ₃ /O ₃ Identifying ESR spectrogram by using process active free radicals;

FIG. 33 shows Fe-Al unused in the present invention ₂ O ₃ XPS spectra of elements Al, C, O and Fe;

FIG. 34 shows Fe-Al unused in the present invention ₂ O ₃ XPS spectra of elemental Fe;

FIG. 35 shows Fe-Al used in the present invention ₂ O ₃ XPS spectra of elements Al, C, O and Fe;

FIG. 36 shows Fe-Al unused in the present invention ₂ O ₃ XPS spectra of elemental Fe;

FIG. 37 is a drawing of HA/Fe-Al in the present invention ₂ O ₃ /O ₃ A process oxidation mechanism diagram.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Example 1:

the main structure of this embodiment, as shown in fig. 1, includes a preprocessor, an advanced oxidation generator, a mixing tank, and a bioreactor connected in sequence by pipes; the advanced oxidation generator is also connected with a pipeline for introducing ozone from the outside, the mixing tank is also connected with a pipeline for introducing urban domestic sewage, a pipeline for introducing external air is also connected from the outside in the bioreactor, and a water outlet for discharging purified water is arranged at the bottom of the bioreactor.

The method for jointly treating the shale gas fracturing flow-back fluid and domestic sewage by using the system comprises the following steps:

(1) adding the shale gas fracturing flow-back fluid into a preprocessor, carrying out coagulation treatment on the shale gas fracturing flow-back fluid by using a coagulant and a coagulant aid, and removing suspended matters and partial organic matters in the shale gas fracturing flow-back fluid to obtain a supernatant;

(2) the supernatant in the preprocessor enters an advanced oxidation generator, and hydroxylamine and Fe-Al are passed through in the advanced oxidation generator ₂ O ₃ The supernatant is oxidized by the concerted catalysis ozone process, partial organic matters and macromolecular organic matters which are difficult to biodegrade in the supernatant are removed, the biodegradability of the supernatant is greatly improved, and advanced oxidized sewage is obtained;

(3) conveying the obtained advanced oxidized sewage to a mixing tank to be mixed with urban domestic sewage according to the ratio of 1:1, then conveying the mixed sewage to a bioreactor, and degrading organic matters in the mixed solution into stable inorganic matters by utilizing a microbial community domesticated in the bioreactor and introducing air for aeration so as to enable a water sample to reach a discharge standard.

Wherein in the step (1), the coagulant is polyaluminium chloride, and the coagulant aid is polyacrylamide; the pretreatment process of adding the shale gas fracturing flow-back fluid into the preprocessor comprises the following steps: adjusting the pH value of the shale gas fracturing flow-back fluid to be neutral, adding polyaluminium chloride into the fracturing flow-back fluid with the dosage of not less than 400mg/L, stirring for 5min, adding polyacrylamide with the dosage of 20mg/L, slowly stirring for 1min, and standing for 30min to obtain a supernatant.

In the step (2), the specific process of oxidizing the supernatant by the ozone process catalyzed by the hydroxylamine and the Fe-Al2O3 in the advanced oxidation generator is as follows:

(2.1) preparation of Fe-Al by immersion-calcination method ₂ O ₃ A catalyst;

(2.2) adjusting the pH of the supernatant with a pH adjusting agent such that the initial pH of the supernatant is 6.7;

(2.3) continuously stirring the supernatant liquid with the initial pH value adjusted, and introducing ozone into the supernatant liquid, wherein the flow rate of the ozone is0.2L/min, and immediately adding Fe-Al ₂ O ₃ Catalyst and hydroxylamine solution, in which Fe-Al ₂ O ₃ The adding amount of the catalyst is 5.26g/L, the adding amount of the hydroxylamine solution is 0.1g/L, and the oxidation treatment process of the supernatant is completed after stirring reaction for 20-50 min.

In the specific process of the step (3), the water inlet and outlet amount of the bioreactor is 50-80% of the effective volume of the bioreactor, the reaction period is 24 hours, the mixed sewage inlet time is 0.5 hour, the aeration time is 18-20 hours, the aeration stopping time is 3-5 hours, and the water discharging time is 0.5 hour.

The domestication process of the microbial community specifically comprises the steps of taking the activated sludge of the effluent of a secondary sedimentation tank of an urban sewage treatment plant as substrate sludge, taking the urban domestic sewage: and (3) acclimatizing the sewage in the ratio of 9:1, 4:1, 7:3 and 3:2 in sequence for 40-60 days after advanced oxidation, wherein each acclimatization ratio is 10-15 days. The microbial community of the biological reaction system is obtained by domesticating the sludge of the secondary sedimentation tank of the urban domestic sewage treatment plant, so that the microbial community has specificity, good salt resistance, good adaptability to the fracturing flow-back fluid and high-efficiency treatment capability.

Example 2:

in this embodiment, an ozone input unit is further added on the basis of the above embodiment, as shown in fig. 1, the ozone input unit further includes an ozone cylinder, the ozone input unit includes an oxygen cylinder and an ozone generator, an output pipe of the oxygen cylinder is communicated with an input pipe of the ozone generator, and an output pipe of the ozone generator extends into the advanced oxidation generator. The ozone generator is used for producing ozone gas (O) ₃ ) The ozone generator is of a high-voltage discharge type, oxygen conveyed by the oxygen cylinder is decomposed and polymerized into ozone by using high-voltage power, and the ozone is conveyed into the advanced oxidation generator. Wherein, the ozone generator and the oxygen cylinder are common and can be obtained by the technical personnel in the field. In addition, since the oxygen cylinder mainly functions to supply oxygen for the ozone generator, it is in practical use andin consideration of comprehensive cost, an air pump can be used for replacing an oxygen cylinder, air is compressed in the air pump and then is conveyed to the ozone generator, oxygen is contained in the air, the requirement of the ozone generator for the oxygen can be met after a large amount of air is input by the air pump, and the air pump is used for replacing the oxygen cylinder, so that the ozone generator is safer in storage and transportation and relatively lower in cost. Other parts of this embodiment are the same as those of the above embodiment, and are not described again.

Example 3:

in this embodiment, on the basis of the above embodiment, an air pump is further added, a pipeline for outputting high-pressure air by the air pump extends into the bioreactor, and a rotameter is further installed on the pipeline for outputting high-pressure air. The air pump mainly inputs high-pressure air into the bioreactor to aerate the bioreactor. The rotameter is arranged to control the flow rate of the pumped high-pressure air, so that the bioreactor can be aerated better. Other parts of this embodiment are the same as those of the above embodiment, and are not described again.

Example 4:

in this embodiment, on the basis of the above embodiments, the advanced oxidation generator and the bioreactor are further defined, and the advanced oxidation generator and the mixing tank are both provided with a mixing and stirring device. The advanced oxidation generator needs to fully mix the catalyst, the persulfate solution and the introduced ozone, so that a mixing and stirring device is specially arranged to enable the catalyst to catalyze the ozone/persulfate coupling system to oxidize the supernatant. The mixing tank is used for mixing the sewage after advanced oxidation and the urban domestic sewage, so that the mixing and stirring device is particularly arranged, the sewage and the urban domestic sewage can be repeatedly mixed, and the sewage which is uniformly mixed can be conveniently input into the bioreactor. In addition, the bioreactor is further limited to be a sequencing batch biofilm reactor. Compared with SBR, the sequencing batch biofilm reactor is developed by adding filler on the basis of SBR, and microorganisms can be attached to the biofilm filler, so that the sequencing batch biofilm reactor has the characteristics of an activated sludge method and a biofilm method, and the pollutant treatment capacity of the sequencing batch biofilm reactor can be improved. The sequencing batch biofilm reactor is preferably used as a bioreactor, and other reactors which can be the same as or similar to the sequencing batch biofilm reactor can be selected. Other parts of this embodiment are the same as those of the above embodiment, and are not described again.

Example 5:

in the embodiment, aiming at the method for the combined treatment of the shale gas fracturing flow-back fluid and the domestic sewage, experimental materials are selected and analyzed to obtain the main characteristics of the general fracturing flow-back fluid, so that an experimental basis is provided for subsequent experiments.

1. Selection of Experimental materials

The fracturing flowback fluid from a certain well of Yibin Changning is used as an experimental material, and the fracturing flowback fluid is light yellow in color, slightly fishy in smell and provided with suspended particles.

2. Analytical method in experimental process

(1) COD is determined by a rapid digestion spectrophotometry for determining chemical oxygen demand of water (HJ/T399-2007).

(2) TP is determined by ammonium molybdate spectrophotometry (GB/T11893-1989) for determining total phosphorus in water.

(3) TN is measured by alkaline potassium persulfate digestion ultraviolet spectrophotometry (HJ636-2012) for determination of total nitrogen in water.

(4)Cl ^- The determination is carried out by silver nitrate titration method (GB11896-89) for determining chloride in water.

(5) Suspended matter (SS) is measured by the gravimetric method for measuring suspended matter in water (GB/T11901-1989).

(6)O ₃ The gas phase concentration was measured by iodometry (CJ/T-2010).

(7) And (3) DOC measurement: the water sample passes through a 0.45 mu m fiber filter membrane and then enters a TOC-L instrument for analysis.

(8) BOD is "Water quality five days Biochemical Oxygen Demand (BOD) ₅ ) The measurement dilution and inoculation method (HJ505-2009) of (1).

(9) Characterization of materials

And (3) shooting the surface morphology of the catalyst by adopting a ZEISSGemini300 scanning electron microscope. EDS energy spectrum testing is carried out on the catalyst by adopting a Smartedx type energy spectrometer. The crystal structure of the catalyst was analyzed by a pannaceae X' pertro diffractometer. A Bruker EMXnano type electron paramagnetic resonance (ESR) is used to detect free radicals in the system. The organic components of the fracturing fluid were analyzed by a gas chromatograph-mass spectrometer (7890A chromatograph +5975C Mass spectrometer, Agilent).

(10) Test method of zero potential

Determination of the zero charge point (pH) of the catalyst by means of inert electrolyte titration _pzc ). The specific method comprises the following steps:

taking a plurality of 50mL centrifuge tubes, adding 2.0g of ground catalyst, adding a proper amount of distilled water and HNO ₃ Or NaOH solution to a final volume of 20mL and to allow pH to be distributed over a range. After equilibration for 4 days at 25. + -. 0.2 ℃ with shaking for 1h each day, the pH was measured and recorded as pH. Then adding KNO of 2mol/L into each centrifuge tube ₃ 0.5mL, shake for 3h, determine pH, and record pH ₀ . At Δ pH (i.e., pH) ₀ -pH) is plotted against pH to obtain an inert electrolyte titration curve.

3. Performing water quality analysis on the selected experimental material

Aiming at the fracturing flowback fluid from a certain well of Yibin Changning, the analysis method is adopted to obtain the water quality condition of the column of the fracturing flowback fluid, and the following concrete steps are as follows:

table-fracturing flow-back liquid water quality analysis meter for experiment

The main characteristics of the fracturing flow-back fluid can be obtained according to the table I:

(1) the CODCr value of the fracturing flow-back fluid is higher and reaches 780.69mg/L, which is far higher than the first-level emission standard limit (60 mg/L) of the petrochemical industry in the Integrated wastewater discharge Standard (GB 780.69-.

(2) The fracturing flow-back fluid has high salinity, the TDS and Cl-concentration respectively reach 27000mg/L and 21507.13mg/L, and microorganisms are difficult to survive and cannot be directly treated by a biochemical method.

Example 6:

in this embodiment, on the basis of the fracturing flow-back fluid selected in the above embodiment, a concrete pretreatment process is performed to obtain an optimal coagulant and coagulant aid dosage, and the specific experimental process is as follows:

polyaluminium chloride (PAC) is used as a coagulant and Polyacrylamide (PAM) is used as a coagulant aid, and the polyaluminium chloride and the polyacrylamide are combined to pretreat the fracturing flow-back fluid so as to remove suspended particles. And (4) screening the concentrations of PAC and PAM by taking DOC removal rate and turbidity as investigation indexes. Preparing 5% PAC solution and 1% PAM solution, and storing at normal temperature.

PAC concentration screening: the fracturing flowback fluid with the appropriate volume is measured in a 100mL beaker, the PAC solution with the appropriate volume is added to make the concentration of the PAC solution be 0, 50, 100, 200, 300, 400, 500, 600 and 700mg/L, the mixture is rapidly stirred for 5min, and PAM with the concentration of 40mg/L is added. Slowly stirring for 1min, standing for 30min, collecting supernatant, and measuring DOC and turbidity.

And (4) PAM concentration screening: measuring a fracturing flow-back fluid with a proper volume in a 100mL beaker, adding a PAC solution with an optimal concentration volume, quickly stirring for 5min, adding a proper amount of PAM to make the concentration of the PAM to be 0, 10, 20, 30, 40, 50 and 60mg/L, slowly stirring for 1min, standing for 30min, taking a supernatant, and measuring DOC and turbidity.

The specific experimental results are as follows:

as can be seen from fig. 2, the DOC removal rate gradually increased and the turbidity gradually decreased as the PAC concentration increased. Part of organic matters in the fracturing flow-back fluid can be settled and removed along with the suspended particles, so that the DOC removal rate is gradually increased. But when the PAC content is more than 400mg/L, suspended matters in the fracturing flow-back fluid are greatly reduced, and the DOC removal rate is gradually gentle and tends to be stable.

As can be seen from fig. 3, the DOC removal rate gradually decreases after gradually increasing with the increase of the PAM concentration, and the DOC removal rate sharply decreases when the PAM concentration reaches 60mg/L, because PAM is an organic polymer, and when the concentration is too high, the DOC removal rate decreases due to the contribution of residual PAM in the frac flowback fluid. Therefore, the optimal PAM concentration is 20 mg/L.

The analysis of the water quality of the fracturing flow-back fluid after the coagulation pretreatment is shown in the table II;

water quality analysis meter for secondary coagulation pretreatment fracturing return drainage

According to the contents in the table II, the turbidity and the SS of the fracturing flow-back fluid are greatly reduced after the coagulation pretreatment, the values are respectively 0.8 and 39.44mg/L, and the removal rates respectively reach 99.84 percent and 95.17 percent. In addition, coagulation pretreatment is performed on COD _Cr DOC, TN and TP also have a certain removing effect, and the removing rate is 18.94%, 37.22%, 4.58% and 39.46% in sequence.

Example 7:

this example is based on the above examples and uses SEM and EDS to prepare Fe-Al ₂ O ₃ The catalyst is subjected to morphological characteristics, surface distribution and composition analysis, and specifically comprises the following steps:

Fe-Al ₂ O ₃ the catalyst is prepared by adopting an impregnation-calcination method, and the specific preparation process is shown in figure 4 and specifically comprises the following steps:

weighing a certain amount of clean active gamma-Al ₂ O ₃ The resultant was immersed in pure water at normal temperature with stirring for 12 hours, followed by drying at 100 ℃ for 12 hours and baking at 500 ℃ for 4 hours in a muffle furnace under an air atmosphere. The roasted carrier is stirred and dipped and activated for 1h in a certain volume of 30 percent nitric acid solution at the constant temperature of 70 ℃. Activated gamma-Al ₂ O ₃ Mixing with 0.75mol/L ferric nitrate, continuously stirring for 1h in a water bath kettle at 50 ℃, taking out, filtering and standing for 1 h. Drying the impregnated catalyst at 120 ℃ for 12h, finally roasting the catalyst in a muffle furnace at 550 ℃ for 4h under the air atmosphere, and cooling the catalyst to room temperature to obtain Fe-Al ₂ O ₃ A catalyst.

The obtained Fe-Al ₂ O ₃ Catalyst, shown in FIGS. 5 and 6, Fe-Al ₂ O ₃ And gamma-Al ₂ O ₃ The surface topography is clearly distinguished, according to FIG. 5It is known that gamma-Al is not supported by Fe ₂ O ₃ The surface of the material is smooth and has compact pores; as can be seen from FIG. 6, the Fe-loaded γ -Al ₂ O ₃ It was found that the surface was rough and uneven with a large number of irregular particles adhered thereto because the metal active oxide component of Fe was in γ -Al after the immersion firing ₂ O ₃ Surface build-up and curing.

As can be seen from FIGS. 7 to 10, these metal active oxide components of Fe were uniformly attached to the surface of the carrier.

As can be seen from FIG. 11, Fe-Al ₂ O ₃ Contains Al, O and Fe elements, wherein Al and O are gamma-Al ₂ O ₃ The main constituent elements of the carrier have the largest content ratio, and the mass fractions of Al, O and Fe are 47.41%, 47.81% and 4.78% in sequence. From the above, Fe was successfully supported on the active γ -Al ₂ O ₃ The above.

Example 8:

this example is based on the above examples and is for gamma-Al ₂ O ₃ And Fe-Al ₂ O ₃ XRD characterization is carried out, and an XRD pattern and gamma-Al are combined ₂ O ₃ (JCPDS #04-0800) and Fe ₂ O ₃ (JCPDS #85-0599) PDF standard card comparison, the results are shown in FIG. 12:

the diffraction peaks of the catalyst are all broad, indicating that the crystallinity of the catalyst is low, which is a common feature of alumina. gamma-Al ₂ O ₃ Diffraction peaks appearing at 2 θ ═ 37.4 °, 45.8 °, and 67.3 ° in the XRD spectrum, at Fe — Al ₂ O ₃ None of them is changed; fe ₂ O ₃ Diffraction peaks appearing at 24.2 °, 33.2 °, 35.8 °, 49.6 °, and 54.1 ° of 2 θ, at Fe — Al ₂ O ₃ Obvious diffraction peaks appear; in addition, diffraction peaks with smaller intensity appear at 2 θ of 35.9 °, 60.5 °, 72.4 ° and 76.2 °, which is consistent with the diffraction peaks of FeO (JCPDS #89-0687) on the XRD spectrum. The data show that Fe is successfully loaded on gamma-Al after the excessive impregnation-calcination method ₂ O ₃ Surface, and mainly Fe ₂ O ₃ In the form of FeO, and a small proportion thereof.

Example 9:

this example is based on the above examples and uses inert electrolyte titration to titrate the catalyst Fe-Al ₂ O ₃ The results are shown in fig. 13, and when Δ pH is 0, pH is 7.38, indicating Fe — Al ₂ O ₃ The zero potential of the catalyst was 7.38, i.e. when the pH was adjusted<7.38，Fe-Al ₂ O ₃ Carrying out positive charge; when the pH is higher>7.38 of, Fe-Al ₂ O ₃ Is negatively charged.

Example 10:

in the present example, based on the above-described examples, O was considered by the controlled variable method ₃ Flow, catalyst addition, HA concentration, and initial pH effects on DOC removal. Meanwhile, in order to further clarify the change condition of the fracturing flow-back fluid after the reaction is finished, the pH and UV of the effluent are also considered ₂₅₄ (i.e., humus and aromatic compounds containing "C ═ C" and "C ═ O"), the experimental procedure was as follows:

1、O ₃ effect of flow on DOC removal

The reaction was carried out for 60min at a catalyst loading of 5g/L, HA concentration of 0.05g/L without adjusting the initial pH.

As can be seen from FIG. 14, after 60min of treatment, the time required for O treatment was determined ₃ When the flow rate was increased from 0.1L/min (135mg/h) to 0.2L/min (270mg/h), DOC removal increased from 9.46% to 14.36%, because of the increase with O ₃ Increase in flow, O ₃ The dissolution in water is increased, and HA and Fe-Al in the system ₂ O ₃ Catalyzing ozone to generate OH, so that the DOC removal rate is increased; when the ozone flow rate was further increased to 0.4L/min, the DOC removal rate was less changed due to O dissolved in water ₃ Close to saturation and maintain stability, continuously increasing O ₃ Flow rate of more O ₃ The molecules are transferred from the liquid phase to the gas phase to emerge without participating in the reaction, and can not continuously participate in the reaction, so the influence on the mineralization of the system is not obvious. Notably, in O ₃ When the flow rate is 0.1L/min, the DOC removal rate is-2.54% in the first 10min of the reaction, because suspended substances and original microorganisms in the fracturing flow-back fluid are oxidized by O ₃ And OH attack, making it smaller and smaller particles that could not pass through 0.45 μm and able to pass through 0.45 μm filter membrane, so that DOC is raised to some extent. But as the reaction time is prolonged, the part of small particles is replaced by O ₃ And OH is oxidized and decomposed, DOC continues to decrease, and DOC removal rate increases.

As can be seen from FIG. 15, following O ₃ Increase in flow, UV ₂₅₄ The pH value of the effluent is reduced and then becomes stable. This is because the organic acid generated by catalytic ozonolysis of the contaminants lowers the pH, but as the reaction time progresses, the rate of organic acid production decreases, while the acidic condition Fe-Al ₂ O ₃ Corrosion will consume H ⁺ Thus, the effluent pH was not further reduced.

2. Effect of catalyst addition on DOC removal

At O ₃ The reaction was carried out at a flow rate of 0.2L/min and an HA concentration of 0.05g/L for 60min without adjusting the initial pH.

As can be seen from fig. 16, the DOC removal rate gradually increases as the amount of catalyst addition increases. However, when the catalyst addition amount is more than 5g/L, the DOC removal rate tends to be flat. This can be explained from two aspects: with the increase of the dosage of the catalyst, TC adsorbed by the catalyst and degradation intermediate products increase; at the same time being O ₃ More active sites are provided, the effect between the active sites and HA is enhanced, more OH is generated in the system, and DOC removal is improved; when the catalyst is excessively added (more than 5g/L), the concentration of OH in the system is increased, the collision probability of OH and HA is improved, the consumption of OH is accelerated, and the DOC removal efficiency is not obviously increased. In addition, when the amount of the catalyst added is less than 2g/L, the DOC removal rate is less than 0 at the 10 th min of the reaction, and the DOC removal rate gradually increases as the reaction continues, because in the case of a small amount of the catalyst added, only ozone and a small amount of OH are present in the solution, and only a part of suspended particles are decomposed, and not completely oxidized, resulting in an increase in the DOC, which is similar to that in the case of O ₃ The flow rate was similar at 0.1L/min.

FIG. 17 shows DOC and UV after 60min of reaction ₂₅₄ And changes in the pH of the system. DOC and UV ₂₅₄ The change trend of (a) is substantially the same. The pH of the system increases with increasing catalyst addition, since the catalyst gradually consumes H under acidic conditions ⁺ But is corroded to gradually increase the pH.

3. Effect of HA concentration on DOC removal

At O ₃ The reaction was carried out for 60min at a flow rate of 0.2L/min and a catalyst dosage of 5g/L without adjusting the initial pH.

As can be seen from FIG. 18, the HA concentration is in the range of 0-0.10 g/L, and the DOC removal rate increases with the increase of the HA concentration, which is mainly due to the generation of more OH in the system, since HA can be reacted with O ₃ Simultaneously, the reaction can reduce the [ identical to ] Fe (III) on the surface of the catalyst into [ identical to ] Fe (II), and can also reduce the Fe in the solution ³⁺ Reduction to Fe ²⁺ Further catalyzing O ₃ OH is produced. However, if the HA concentration is higher than 0.10g/L, a large amount of HA in the system will compete with the organic matter for consumption OH as a strongly reducing substance, and eventually the DOC removal rate will be lowered.

As can be seen from fig. 19, the addition of HA significantly decreased the solution pH, so the final pH of the reaction gradually decreased as the HA concentration increased. HA concentration vs UV ₂₅₄ Is the same as its effect on DOC removal rate, primarily affected by HA as a catalyst and a reductant.

4. Effect of initial pH on DOC removal

The reaction was carried out for 60min under the conditions of O3 flow rate of 0.2L/min, catalyst addition of 5g/L and HA concentration of 0.10 g/L.

From fig. 20, fig. 21 shows that as the initial pH increases from 3 to 6, the DOC removal rate increases from high to low, and the final pH increases slowly; when the initial pH was further increased to 9, the DOC removal rate decreased. Fe-Al ₂ O ₃ pH of (1) _pzc At an initial pH of 3, the system pH is hardly changed, i.e. the catalyst is positively charged, while the HA is mostly NH ₃ OH ⁺ Since the HA is present in the system, the HA and the catalyst are charged, and the reaction between the HA and the catalyst is suppressed. While the initial pH was gradually increased to 6, the final pH of the system was also gradually increased, at which time the NH content of the system was increased ₂ Increasing OH graduallyThis favors HA and Fe-Al ₂ O ₃ Thereby resulting in an increase in DOC removal rate. NH (NH) ₂ OH and O ₃ And. OH, respectively, have a reaction rate constant of k ═ 2.1X 10 ⁴ M ^-1 s ^-1 And k is 9.5 × 10 ⁹ M ^-1 s ^-1 And NH ₃ OH ⁺ And O ₃ And. OH, respectively, have a reaction rate constant of k 2.0M ^-1 s ^-1 And k is 5.0 × 10 ⁸ M ^-1 s ^-1 . And NH ₃ OH ⁺ Compared with NH ₂ OH and O ₃ And OH has a higher reaction rate, while as the initial pH goes from 6 to 9, the final pH of the system also slowly increases to 7.5, at which point NH ₂ The number of OH in the system is rapidly increased, and a large amount of O ₃ And NH in OH quilt system ₂ OH consumption, resulting in a gradual decrease in DOC removal rate.

Example 11:

as can be seen from the results of the single factor experiments provided in the above examples, O ₃ The flow rate, the catalyst adding amount, the HA concentration and the initial pH all have certain influence on the DOC removal rate, but O is introduced ₃ After, O ₃ Solubility in the system is limited and therefore in O ₃ The DOC removal rate is not obviously influenced after the flow is more than 0.2L/min. Therefore, in this example, on the basis of the above examples, three factors, i.e., the catalyst addition amount, the HA concentration and the initial pH, were selected, and the DOC removal rate was used as a response value, and the response curve method was used to treat HA/Fe-Al ₂ O ₃ /O ₃ And (4) carrying out parameter optimization research on the oxidation fracturing flow-back fluid system. The simulation was performed using the Box-Behnken model in the software Design-Expert 10.0.8, and the selected experimental factors and parameter levels are shown in Table three below:

table three experiment influence factor coding and level table

The design and results of the experiments performed according to table three are shown in table four:

experimental design and results of surface method with four response surfaces

Utilizing a data analysis module in Design-Expert 10.0.8 to perform ANOVA analysis on the experimental result, detecting the significance of the model, performing multiple regression fitting, and establishing a quadratic polynomial response model, wherein the response surface model obtained by fitting is as follows:

Y＝18.64+1.51A+0.22B+2.07C+0.52AB+0.11AC-0.40BC-1.56A ² – 2.38B ² –2.86C ²

regression analysis of variance and significance testing of the model, the results are shown in table five:

table five regression equation analysis of variance and significance test table

Model confidence analysis, as shown in table six:

reliability analysis table for six models of table

From table five, F is 42.80 and P is 0.0001 in the model<0.05, which indicates that the model has high reliability. Mismatching term P-0.0558>0.05, the response effect is not obvious, and the model is reasonable. Theoretical calculation to obtain R _adj ² 0.9592, indicating that the model can account for 95.92% variability; r obtained in practice ² 0.9822, showing better agreement between model predictions and actual values, the model can be used for HA/Fe-Al ₂ O ₃ /O ₃ The system analyzes and predicts the oxidative degradation of the fracturing flow-back fluid. In this model, C, B ² 、C ² P value of less than 0.0001, an extremely significant variable; a and A ² Is less than 0.05, is a significant variable. The larger the F value is, sayObviously, the larger the influence of the factor on the experimental result is, the greater the F value of the independent variable is, the largest influence of the initial pH (F-34.27) on the DOC removal rate can be obtained by comparing the F values of the independent variables, and the other influencing factors are Fe-Al according to the significance ₂ O ₃ Addition amount and HA concentration.

As is clear from fig. 24 to 27, the initial pH significantly affects the DOC removal rate, and the optimal initial pH is about 6.7. When the initial pH is less than 6.0 or more than 8.0, the DOC removal rate is less than that of the initial pH at 6.7, and when the initial pH is near 6.7, the DOC removal rate is remarkably improved. This indicates that the proper initial pH contributes to HA/Fe-Al ₂ O ₃ /O ₃ And oxidizing and degrading organic matters in the fracturing flow-back fluid by the system.

As can be seen from fig. 22 to 25, the DOC removal rate gradually increases with the increase of the catalyst addition amount, but when the catalyst amount is greater than 6.0g/L, the increase of the DOC removal rate is not significant with the increase of the catalyst addition amount, which is similar to the results of fig. 3 to 8, indicating that the influence of the catalyst addition amount on the DOC removal rate is limited.

As can be seen from fig. 22, 23, 26, and 27, the effect of the HA concentration on the DOC removal rate is small for the same initial pH or catalyst addition amount.

The information reflected by the contour lines and the response curved surfaces is consistent with the data of the table, and the influence sequence on the DOC removal rate among the three experimental factors is initial pH > catalyst addition amount > HA concentration, but the interaction influence among the three factors is not obvious.

According to prediction, when the addition of the catalyst is 5.26g/L, the addition of HA is 0.1g/L, and the initial pH is 6.7, the DOC removal rate reaches the maximum value of 19.41%, the DOC removal rate is 19.16% under the condition through experiment, and only 0.25% of the DOC removal rate is different from the predicted value of the model, and further, the model is used for further explaining that the model is used for Fe-Al ₂ O ₃ /HA/O ₃ The system is feasible to analyze and predict the oxidative degradation of the fracturing flow-back fluid.

Example 12:

this example is based on the above examples and under optimal reaction conditions (i.e., O) ₃ The flow rate is 0.2L/min, Fe-Al ₂ O ₃ The adding amount is 5.26g/L, HA0.10g/L, initial pH 6.7) was subjected to a catalyst recycling experiment.

The results of the experiment are shown in FIG. 28, which is equivalent to the first (DOC: 20.36%, COD) _Cr 26.90%) the catalyst was compared in the second (DOC: 17.53%, COD) _Cr 23.26%), DOC and COD _Cr The removal rates were all reduced by about 3%, in the third time (DOC: 14.79%, COD) _Cr 22.31%) and the fourth time (DOC: 13.94%, COD) _Cr 21.04%) compared with the DOC and COD of the previous experiment _Cr The reduction value of each removal rate is less than 3 percent, which shows that the catalyst has better stability.

SEM and XRD characterization of the reacted material, as shown in FIG. 29 and FIG. 12, and Fe-Al before reaction ₂ O ₃ SEM, figure 6 compares, still many irregular small particles are attached to the surface, and the surface is rough and uneven; the diffraction peaks of the XRD map are not obviously changed, which shows that Fe-Al ₂ O ₃ The surface still has a large amount of Fe oxide distributed on the surface of the catalyst, so that the catalyst shows higher activity, therefore, DOC and COD _Cr The removal rate is still maintained at a certain level.

In addition, a small decrease in catalytic effect occurs with increasing cycle number, probably due to the ability of anions and organic acids in solution to replace Al ₂ O ₃ Surface hydroxyl groups, increased Al ₂ O ₃ And the adsorbed carboxylate has irreversible chemisorption, which results in a decrease in available Al — OH sites, and finally, a decrease in the catalytic performance of the catalyst upon reuse. In addition, Fe oxide on the surface portion of the catalyst is corroded, resulting in a decrease in Fe oxide concentration available in repeated experiments, and a decrease in catalytic performance, and thus DOC and COD _Cr The removal rate decreases.

Example 13:

this example is to further illustrate HA/Fe-Al ₂ O ₃ /O ₃ A control experiment is carried out on the oxidation mechanism of the fracturing flowback fluid by the system, and the control experiment specifically comprises the following steps:

1. control experiment

Under the same conditions, i.e. O ₃ The flow rate is 0.2L/min, the catalyst addition is 6g/L and the HA addition is 0.10g/L, the reaction time is 60min, and a control experiment is carried out on the capacity of 4 systems for treating the fracturing flow-back fluid.

The results are shown in FIG. 30 and FIG. 31, and the results are shown in 60min treatment by HA/Fe-Al ₂ O ₃ /O ₃ DOC and UV process ₂₅₄ And COD _Cr The removal of (a) was higher than that of the 3 control experiments. DOC (DOC) and UV (ultraviolet) of fracturing flowback fluid without oxidation treatment ₂₅₄ And COD _Cr 32.25mg/L, 0.3730 and 632.84mg/L, respectively. Through O ₃ And O ₃ DOC and COD of fracturing flowback fluid treated by HA technology _Cr All increased to different extents due to O ₃ And HA to O ₃ The free radicals generated by the catalysis attack the fine suspended particles in the fracturing flowback fluid and enable the fine suspended particles to release organic matters, but the released organic matters are not completely degraded. And through Fe-Al ₂ O ₃ /O ₃ DOC and COD of fracturing flowback fluid treated by process _Cr Respectively reduced to 32.09mg/L and 586.70mg/L, indicating that the introduction of the catalyst enhances the yield of system free radicals, thereby increasing the removal of organic matters. Through HA/Fe-Al ₂ O ₃ /O ₃ DOC and COD of fracturing flowback fluid treated by process _Cr Respectively reduced to 25.99mg/L and 459.50mg/L, and the removal of the organic matters in the fracturing flow-back fluid by the process is larger than that of Fe-Al ₂ O ₃ /O ₃ Process of passing through O ₃ DOC and COD of fracturing flowback fluid treated by HA technology _Cr All had increased, indicating HA/Fe-Al ₂ O ₃ /O ₃ In-process HA to indirectly catalyze O ₃ In such a way that the oxidizing power of the system is increased.

Several oxidation treatments all to UV ₂₅₄ Has the removing effect. Wherein HA/Fe-Al ₂ O ₃ /O ₃ The removal effect of the process is best, the removal rate reaches 46.49 percent, and the rest is Fe-Al in sequence from large to small according to the removal rate ₂ O ₃ /O ₃ 、 O ₃ 、HA/O ₃ The removal rate of the process is 32.65%, 22.63% and 18.53% in sequence. Notably, various processes are UV curable ₂₅₄ Although not like DOC and COD _Cr A negative increase occurs in the amount of time,but overall trend of change and DOC and COD _Cr Show uniformity and are all HA/O ₃ The process exhibits a maximum followed by O in order of magnitude ₃ 、Fe-Al ₂ O ₃ /O ₃ 、HA/Fe-Al ₂ O ₃ /O ₃ And (5) processing.

Biodegradability, i.e., BOD/COD value (B/C), is an index for evaluating biodegradability of wastewater, and the larger the value, the better biodegradability of wastewater. After oxidation by different oxidation processes, COD _Cr With different trends, but BOD ₅ The difficult biodegradable organic matters in the fracturing flow-back fluid are oxidized and degraded into easily biodegradable organic matters, and the B/C value is further increased. The B/C value is HA/Fe-Al from large to small ₂ O ₃ /O ₃ 、Fe-Al ₂ O ₃ /O ₃ 、HA/O ₃ 、O ₃ The process has the values of 0.149, 0.099, 0.062 and 0.057 in sequence.

The above results show that HA/Fe-Al ₂ O ₃ /O ₃ The process system has stronger degradation effect on the fracturing flow-back fluid and has higher biodegradability after degradation.

Example 14:

this example is to further illustrate HA/Fe-Al ₂ O ₃ /O ₃ The system carries out an active substance identification experiment on the oxidation mechanism of the fracturing flow-back fluid, and the method specifically comprises the following steps:

the experimental result is shown in fig. 32, which shows the ESR spectra of the system solution at 0min and 5min, and the solution does not have any strong signal peak when the system only has the catalyst at 0 min; when HA and Fe-Al are present ₂ O ₃ And O ₃ In the presence of the co-presence, a signal peak for. OH (intensity ratio of 1: 2: 1) appears in the solution, indicating that a large amount of. OH is present in the solution. In contrast, in the control experiment, only O was introduced ₃ And HA/O ₃ DOC and COD of the process _Cr All have a certain degree of increase, and Fe-Al ₂ O ₃ /O ₃ And HA/Fe-Al ₂ O ₃ /O ₃ Process Pair of DOC and COD _Cr All had been removed, indicating HA and Fe-Al ₂ O ₃ By addition of (2) promote O ₃ OH generated by decomposition, DOC and COD are increased _Cr And (4) removing.

Example 15:

this example is to further illustrate HA/Fe-Al ₂ O ₃ /O ₃ The system carries out a catalyst change experiment before and after oxidation on an oxidation mechanism of the fracturing flowback fluid, and the experiment is as follows:

in the control experiment, HA can catalyze ozone generation-OH in a mode of not directly catalyzing ozone, and the HA is supposed to be Fe-Al according to the prior literature ₂ O ₃ The [ ident ] Fe (III) on the surface of the catalyst is reduced into [ ident ] Fe (II), and then the [ ident ] Fe (II) catalyzes ozone to generate OH, and the [ ident ] Fe (II) HAs better catalytic ozone performance than the [ ident ] Fe (III), so the HA/Fe-Al ₂ O ₃ /O ₃ The process has higher removal effect on the fracturing flow-back fluid. To verify the speculation, XRD and XPS tests were performed on the catalyst after the reaction.

The results are shown in FIG. 12, FIGS. 33 to 36.

From fig. 33, fig. 35 shows that the elements carbon (C1 s), aluminum (Al 2p), iron (Fe 2p), and oxygen (O1 s) are shown in the catalyst XPS spectrum. While for Fe element, as shown in FIGS. 34 and 36, Fe-Al is not used ₂ O ₃ And used Fe-Al ₂ O ₃ Fe 2p of _3/2 And Fe 2p _1/2 Peaks with binding energies at 711.3 and 724.9eV correspond to Fe (III), consistent with literature reports. However, used Fe-Al ₂ O ₃ Fe 2p of _3/2 And Fe 2p _1/2 The binding energy also shows peaks at 709.6 and 723.2eV, respectively, which correspond to Fe (II). Meanwhile, the peak areas of the fitting spectra are used for calculating that Fe (III) and Fe (II) respectively account for the total iron (Fe (III)/Fe _total And Fe (II)/Fe _total ) The ratio of (a) to (b). In HA/Fe-Al ₂ O ₃ /O ₃ In the process of treating fracturing flow-back fluid, in the presence of Fe-Al ₂ O ₃ The surface of the alloy is provided with a molar ratio (0.2847) of Fe (II)/total of Fe, and the unused Fe-Al ₂ O ₃ The surface was almost absent, indicating that Fe-Al ₂ O ₃ The reduction of Fe (III) to Fe (II) occurs on the surface.

In addition, after useFe-Al of ₂ O ₃ The XRD pattern of (1) shows diffraction peaks with smaller intensity at 2 theta (72.4 degrees) and 76.2 degrees, which is consistent with the diffraction peaks of FeO (JCPDS #89-0687) on the XRD pattern, while unused Fe-Al ₂ O ₃ There was no apparent diffraction peak, indicating that fe (ii) was produced during the catalytic oxidation, consistent with XPS results.

The above results show that in HA/Fe-Al ₂ O ₃ /O ₃ In the process of treating fracturing flow-back fluid, the presence of HA converts Fe-Al ₂ O ₃ Reduction of surface Fe (III) to Fe (II) to enhance catalytic O ₃ And (4) oxidizing.

Example 16:

this example is to further illustrate HA/Fe-Al ₂ O ₃ /O ₃ The experiment for comparing the oxidation mechanism of the system on the fracturing flow-back fluid and the water quality change before and after oxidation specifically comprises the following steps:

and (5) detecting and comparing the water quality indexes before and after oxidation, and specifically showing in a seventh table.

Water quality comparison table for front and rear parts of table heptaoxidation

As shown in the seventh Table, the HA/Fe-Al ₂ O ₃ /O ₃ After treatment, COD in the frac flowback fluid was determined by the presence of ozone and OH _Cr And DOC are removed to a certain extent, and the DOC is respectively reduced to 25.99mg/L and 459.50mg/L, and the removal rates can respectively reach 27.39 percent and 19.41 percent. And the BOD of the treated fracturing flow-back fluid ₅ The increase is 146.48% from 27.82mg/L to 68.57mg/L without decreasing or increasing, because the organic matters which are difficult to be biodegraded, such as macromolecules in the fracturing flow-back fluid, are oxidized and decomposed into organic matters which are easy to be biodegraded, such as micromolecules, by ozone and OH, so that BOD is generated ₅ And (4) rising. Without passing through oxygenThe B/C value of the treated coagulation fracturing flowback fluid is 0.044, and when the coagulation fracturing flowback fluid is subjected to HA/Fe-Al treatment ₂ O ₃ /O ₃ After treatment, the B/C value increased to 0.150. Although the B/C value of the oxidized fracturing flow-back fluid<0.25, the waste water is regarded as the waste water which is difficult to biodegrade, but compared with the fracturing flow-back fluid which is not subjected to oxidation treatment, the B/C value is increased by 240 percent, the biodegradability is greatly improved, and the foundation is laid for the subsequent biological treatment.

Some microorganisms and fine suspended matters exist in the coagulated fracturing flow-back fluid. While the strong active substance OH attacks the suspended substances, the SS of the water sample is reduced to 15.56mg/L due to oxidation, and the removal rate of the SS reaches 60.55%. Fe-Al ₂ O ₃ Has a porous structure and certain adsorption performance. HA/Fe-Al ₂ O ₃ The system has certain removal rate to TN and TP, and the removal rate can reach 32.15 percent and 24.06 percent respectively, which is probably caused by the adsorption effect of the catalyst.

Example 17:

this example was carried out on the basis of the above examples, with HA/Fe-Al ₂ O ₃ /O ₃ The oxidation mechanism of the fracturing flow-back fluid by the system is analyzed, and is specifically shown in fig. 37.

①Fe-Al ₂ O ₃ And O ₃ Function of between

As shown in FIG. 30 and FIG. 31, with O alone ₃ Oxidation phase, Fe-Al ₂ O ₃ /O ₃ Process pair COD _Cr And DOC are removed to a certain extent, which shows that Fe-Al ₂ O ₃ Can well catalyze O ₃ . This can be attributed to the following 3 points: 1) Fe-Al ₂ O ₃ The surface Fe oxide can catalyze the ozone decomposition, and in addition, under the acidic or neutral condition, the surface of the Fe oxide can generate hydroxyl which is O ₃ OH is generated after absorption, and pollutants are further oxidized; 2) o in solution ₃ Will be in gamma-Al ₂ O ₃ Generates OH under the action of (1), and is adsorbed on Fe-Al ₂ O ₃ The pollutants can be oxidized and degraded under the action of OH generated on the surfaces of the solution and the catalyst; 3) h in solution under acidic conditions ⁺ Will erode negativelyCarried on Al ₂ O ₃ Fe oxide of the surface to produce Fe ²⁺ /Fe ³⁺ ，Fe ²⁺ /Fe ³⁺ Will promote O ₃ OH is generated, the oxidation effect of the system on pollutants is enhanced, and the specific reaction formula is as follows:

FeO+2H ⁺ →Fe ²⁺ +H ₂ O

Fe ₂ O ₃ +6H ⁺ →2Fe ³⁺ +3H ₂ O

Fe ²⁺ +O ₃ →O ₂ +FeO ²⁺

H ₂ O+FeO ²⁺ →·OH+Fe ³⁺ +OH ^—

Fe ²⁺ +FeO ²⁺ +2H ⁺ →H ₂ O+2Fe ³⁺

Fe ³⁺ +O ₃ →FeO ²⁺ +·OH+O ₂ +H ⁺

② HA and O ₃ The function of (1).

Previous studies have shown that HA is associated with O ₃ The reaction between them is mainly influenced by pH. When the pH is higher<5.96 HA is predominantly NH in solution ₃ OH ⁺ Form exists when 5.96<pH<13.74 HA is predominantly NH in solution ₂ OH form, when at pH>13.74 HA is predominantly NH in solution ₂ O ^- The form exists. Under the conditions of acidity, neutrality and alkalescence, HA can promote O ₃ The decomposition of (A), i.e. both protonation and non-protonation, promotes O ₃ Decomposition of (3). It was further found that HA and O are in different forms ₃ Has a different reaction rate from that of O, and is not protonated ₃ The reaction rate of (A) is far faster than that of protonation and O ₃ The reaction rate of (2). HA and O ₃ The main reactions are as follows:

⁺ NH ₃ O ^— +O ₃ →NH ₃ O ^·+ +O ₃ ^·—

O ₃ ^·— +H ⁺ →HO ₃ ·

HO ₃ ·→·OH+O ₂

from FIG. 30, as shown in FIG. 31, HA/O ₃ Under the process, COD _Cr And DOC, but the effect of HA concentration on DOC removal indicates that HA still promotes O ₃ Decomposition of HA with O in the present application ₃ The reaction of (3) is as described above.

③ HA and Fe-Al ₂ O ₃ The function of (1).

In FIG. 30, FIG. 31, HA/Fe-Al ₂ O ₃ /O ₃ Process pair COD _Cr And DOC removal is greater than HA/O ₃ And Fe-Al ₂ O ₃ /O ₃ And (5) processing. Especially in Fe-Al ₂ O ₃ /O ₃ After HA is introduced into the process, DOC removal rate is obviously increased, while in HA/O ₃ COD after treatment _Cr And DOC increase, indicating HA in HA/Fe-Al ₂ O ₃ /O ₃ In the process by indirect catalysis of O ₃ In such a way as to enhance the oxidation performance of the system. The change in Fe element on the catalytic surface before and after oxidation indicates that HA converts ≡ Fe (III) on the catalyst surface to ≡ Fe (II), and thus Fe-Al in solution ₂ O ₃ The surface-formed hydroxyl ligand (≡ Fe (III) -OH) will react with N ₂ HOH reaction generates Fe (II) -OH, promotes the circulation of Fe (III)/Fe (II) ^[35] Thereby improving the oxidation performance of the system.

≡Fe(Ⅲ)-OH+N ₂ HOH→≡Fe(Ⅱ)-OH+NH ₂ O·+H ⁺

④O ₃ Direct oxidation

O ₃ As a strong oxidizing agent, it undergoes an addition reaction with an organic substance containing an unsaturated bond to degrade the organic substance. In this study, O alone ₃ After the treatment process is oxidized for 60min, COD is generated _Cr And DOC, indicating O ₃ The degradable organic matter of partial macromolecule among the flowing back is returned in the degradation fracturing to promote the biodegradability of water sample, but can not mineralize the pollutant totally.

Example 18:

the embodiment is directed at the analysis experiment of carrying the sewage after the advanced oxidation obtained to the mixing tank and mixing with urban domestic sewage, and specifically as follows:

according to the water quality index after oxidation, the activated sludge in the aeration tank of the golden sea sewage treatment plant in the new urban district is taken as the basis to carry out synchronous culture and domestication. The two stages of culture and acclimatization are combined, namely, a small amount of wastewater after catalytic oxidation is added at the beginning of culture, and the specific gravity is gradually increased in the culture process, so that the activated sludge is gradually adapted to the wastewater and has the capacity of treating the wastewater in the growth process.

Simulating urban domestic sewage and passing through HA/Fe-Al according to a certain proportion ₂ O ₃ /O ₃ The oxidized fracturing flowback fluid is mixed and used with NaHCO ₃ The pH is adjusted to neutral and introduced into the reactor. And (3) taking the water sample after advanced oxidation accounting for the same proportion as the same stage, and adjusting the acclimation time of each stage according to the water outlet condition of each stage for approximately 8-14 days, wherein the group is a catalytic oxidation-SBBR group. Additionally setting coagulation-SBBR, O ₃ SBBR and blank control (no pressurized flowback). The A/O/A/O mode is adopted, the period is 24 hours, wherein the oxygen deficiency (4 hours), the oxygen deficiency (13 hours), the oxygen deficiency (2.5 hours), the oxygen deficiency (4 hours) and the water inlet and outlet are respectively 15 minutes. Sampling and measuring every two days, and stably taking mud for freezing and storing the discharged water at each stage. The percentage of the fracturing flow-back fluid is 10%, 20%, 30%, 40% and 50% in sequence, the percentage of the fracturing flow-back fluid corresponds to stages I, II, III, IV and V respectively, in addition, in order to verify the stability of the treatment groups in treating the fracturing flow-back fluid, when the percentage of the fracturing flow-back fluid is 50% and the stage V is finished, the culture is continued for 4-8 days, and the water condition is observed, namely the stage VI.

The experiment adopts a 1L beaker with the diameter of 11cm and the height of 16cm, and the biomembrane material is a fiber composite material.

Activated sludge is taken from an aeration tank of a golden sea sewage treatment plant in a new urban district of the adult city, is subjected to aeration for 2 days, is precipitated for 3 hours, is discharged, is poured into simulated urban domestic sewage, is put into a fiber composite material, and is subjected to aeration and biofilm formation for 2 days.

The formula of the simulated urban domestic sewage is shown in the table eight:

table eight simulated urban domestic sewage formulation table

The formula of the trace elements is shown in the table nine:

formula table of trace elements

And (4) experimental conclusion:

1. the water quality of the inlet water at each stage in the bioreactor

The proportion of inflow and fracturing flowback liquid, DOC and COD in each stage of the bioreactor _Cr TN, TP and Cl ^- The values are shown in Table ten:

TABLE Ten different stages HA/Fe-Al ₂ O ₃ /O ₃ -SBBR influent water quality status gauge

As can be seen from the Table ten, DOC and TN decrease with increasing frac flowback fluid fraction, TP and Cl ^- Increases with increasing frac flowback fluid fraction.

2. Evaluation of treatment Effect

In the stabilization phase, through HA/Fe-Al ₂ O ₃ /O ₃ Mixing the treated fracturing flow-back fluid and simulated domestic sewage in a ratio of 1:1, feeding the mixture into an SBBR reactor, and treating at about 20 ℃ for 24 hours, wherein the DOC of effluent is lower than 10mg/L, the removal rate reaches 92%, and the COD of the effluent is _Cr Less than 60mg/L, the removal rate reaches 88 percent, and the first-level standard of the integrated wastewater discharge standard is met.

For HA/Fe-Al ₂ O ₃ /O ₃ The water quality of the SBBR effluent is analyzed, and the water outlet limit values of the integrated wastewater discharge standard (GB 8978-:

TABLE eleven HA/Fe-Al ₂ O ₃ /O ₃ SBBR effluent quality and partial standard comparison table

Note: "/" indicates no requirement or stipulation.

As can be seen from the eleventh Table, HA/Fe-Al ₂ O ₃ /O ₃ The main indexes of the detection in the effluent of SBBR can reach the secondary indexes of the integrated wastewater discharge standard (GB 8978- _Cr 、BOD ₅ DOC can reach the first-level standard of 'Integrated wastewater discharge Standard', pH, SS, and COD _Cr And TN can reach the first grade B standard of discharge standard of urban sewage treatment plants.

It is understood that the working principle and working process of the system structure for the combined treatment of shale gas fracturing flowback fluid and domestic sewage, such as the components of the pre-processor, the advanced oxidation generator, the mixing tank, the bioreactor and the like, according to one embodiment of the present invention are well known in the art and will not be described in detail herein.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims (10)

1. A system for combined treatment of shale gas fracturing flowback fluid and domestic sewage is characterized by comprising a preprocessor, an advanced oxidation generator, a mixing pool and a bioreactor which are sequentially connected through pipelines; the advanced oxidation generator is also connected with a pipeline for introducing ozone from the outside, the mixing tank is also connected with a pipeline for introducing urban domestic sewage, a pipeline for introducing external air is also connected from the outside in the bioreactor, and a water outlet for discharging purified water is arranged at the bottom of the bioreactor.

2. The system of claim 1, further comprising an ozone input unit, wherein the ozone input unit comprises an oxygen cylinder and an ozone generator, an output pipe of the oxygen cylinder is communicated with an input pipe of the ozone generator, and an output pipe of the ozone generator extends into the advanced oxidation generator.

3. The system for the combined treatment of shale gas fracturing flow-back fluid and domestic sewage according to claim 1 or 2, further comprising an air pump, wherein a pipeline for outputting high-pressure air of the air pump extends into the bioreactor, and a rotameter is further mounted on the pipeline for outputting high-pressure air.

4. The system for the combined treatment of the shale gas fracturing flow-back fluid and the domestic sewage as claimed in claim 1 or 2, wherein the advanced oxidation generator and the mixing tank are both provided with a mixing and stirring device, and the bioreactor is a sequencing batch biofilm reactor.

5. The method for jointly treating the shale gas fracturing flow-back fluid and the domestic sewage by using the system as claimed in claims 1-4, is characterized by comprising the following steps:

(1) adding the shale gas fracturing flow-back fluid into a preprocessor, carrying out coagulation treatment on the shale gas fracturing flow-back fluid by using a coagulant and a coagulant aid, and removing suspended matters and partial organic matters in the shale gas fracturing flow-back fluid to obtain a supernatant;

(2) the supernatant in the pre-processor enters an advanced oxidation generator, and hydroxylamine and water are passed through the advanced oxidation generatorFe-Al ₂ O ₃ The supernatant is oxidized by the concerted catalysis ozone process, partial organic matters and macromolecular organic matters which are difficult to biodegrade in the supernatant are removed, the biodegradability of the supernatant is greatly improved, and advanced oxidized sewage is obtained;

(3) conveying the obtained advanced oxidized sewage to a mixing tank to be mixed with urban domestic sewage according to the ratio of 1:1, then conveying the mixed sewage to a bioreactor, and degrading organic matters in the mixed solution into stable inorganic matters by utilizing a microbial community domesticated in the bioreactor and introducing air for aeration so as to enable a water sample to reach a discharge standard.

6. The method for the combined treatment of the shale gas fracturing flow-back fluid and the domestic sewage as claimed in claim 5, wherein in the step (1), the coagulant is polyaluminium chloride, and the coagulant aid is polyacrylamide; the pretreatment process of adding the shale gas fracturing flow-back fluid into the preprocessor comprises the following steps: adjusting the pH value of the shale gas fracturing flow-back fluid to be neutral, adding polyaluminium chloride into the fracturing flow-back fluid with the dosage of not less than 400mg/L, stirring for 5min, adding polyacrylamide with the dosage of 20mg/L, slowly stirring for 1min, and standing for 30min to obtain a supernatant.

7. The method for combined treatment of shale gas fracturing flow-back fluid and domestic sewage as claimed in claim 6 or 5, wherein in step (2), hydroxylamine and Fe-Al in advanced oxidation generator ₂ O ₃ The specific process of oxidizing the supernatant by the concerted catalysis ozone process comprises the following steps:

(2.1) preparation of Fe-Al by immersion-calcination method ₂ O ₃ A catalyst;

(2.2) adjusting the pH value of the supernatant by using a pH regulator to ensure that the initial pH of the supernatant is 3.3-7.7;

(2.3) continuously stirring the supernatant liquid with the initial pH value adjusted, introducing ozone into the supernatant liquid, wherein the flow of the ozone is not less than 0.2L/min, and immediately adding Fe-Al ₂ O ₃ Catalyst and hydroxylamine solution, in which Fe-Al ₂ O ₃ The addition amount of the catalyst is not less than5g/L of hydroxylamine solution, the addition amount of the hydroxylamine solution is not less than 0.01g/L, and the oxidation treatment process of the supernatant is completed after stirring reaction for 20-50 min.

8. The method for combined treatment of shale gas fracturing flow-back fluid and domestic sewage as claimed in claim 7, wherein in step (2.3), the initial pH value of the supernatant is 6.7, the flow rate of ozone is 0.2L/min, and Fe-Al is adopted ₂ O ₃ The amount of the catalyst added was 5.26g/L, and the amount of the hydroxylamine solution added was 0.1 g/L.

9. The method for combined treatment of the shale gas fracturing flow-back fluid and the domestic sewage as claimed in claim 6 or 5, wherein in the step (3), the water inlet and outlet amount of the bioreactor is 50-80% of the effective volume of the bioreactor, the reaction period is 24h, wherein the mixed sewage inlet time is 0.5h, the aeration time is 18-20 h, the aeration stop time is 3-5 h, and the water outlet time is 0.5 h.

10. The method for the combined treatment of the shale gas fracturing flow-back fluid and the domestic sewage as claimed in claim 6 or 5, wherein in the step (3), the acclimation process of the microbial community is that the activated sludge of the effluent of the secondary sedimentation tank of the municipal sewage treatment plant is used as the bottom sludge, and the municipal sewage: and (3) acclimatizing the sewage in the ratio of 9:1, 4:1, 7:3 and 3:2 in sequence for 40-60 days after advanced oxidation, wherein each acclimatization ratio is 10-15 days.

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