Treatment process of oilfield fracturing flow-back fluid wastewater

Abstract

The invention relates to a process for treating fracturing flow-back fluid wastewater of an oil field. The process comprises the following steps: performing rotational flow oil-water separation, super-atomization dissolved air flotation, primary biochemical treatment, secondary biochemical treatment, tertiary biochemical treatment, activated carbon biological filter treatment and the like on the fracturing flow-back fluid wastewater. According to the process, multiple treatment technologies such as physical, chemical and biological enhancement are combined, the biological treatment process is enhanced by introducing the specific biological enhancement fungicide and the activated carbon carrier, the removal efficiency of refractory organics in the wastewater is remarkably improved, and meanwhile, the stability and economical efficiency of the treatment process are ensured.

Description

Technical Field

[0001] The invention relates to a treatment process for oilfield fracturing flowback wastewater, in particular to a treatment method combined with bio-augmentation technology, and belongs to the technical field of wastewater deep treatment. Background Art

[0002] The fracturing flowback fluid of the oil field contains oil, salt, hardness, heavy metal ions and high molecular polymers. These pollutants are stable in structure and have high concentrations, which brings great challenges to the treatment of wastewater. Traditional treatment methods such as the "old three-stage" process have problems such as long sedimentation time, low treatment capacity, large floor space, and large amount of purification agent addition, resulting in high treatment costs; the activated sludge in the biochemical treatment method is often threatened by phenols, cyanide, sulfur, benzene series, polycyclic aromatic hydrocarbons and other toxic substances in the system, resulting in a sharp decrease in the number of functional microbial flora, affecting the chemical oxygen demand COD Cr Removal of other indicators.

[0003] In the process of industrial wastewater treatment, microbial degradation technology has the advantages of being green, low-carbon and low-cost compared to physical and chemical methods. Microbial degradation technology mainly works through the following mechanisms: (1) Adsorption: Microorganisms adsorb harmful substances in wastewater to the cell surface through adsorption sites on the cell wall or cell surface, providing a material basis for subsequent degradation processes; (2) Enzymatic hydrolysis: The enzymes secreted by microorganisms can catalyze chemical reactions of organic matter in wastewater and decompose it into small molecules, such as carbon dioxide and water; (3) Co-metabolism: Some microorganisms can use harmful substances in wastewater as carbon sources or energy sources for growth and reproduction, while achieving degradation of harmful substances.

[0004] In the treatment process of oilfield fracturing flowback fluid wastewater, it is an urgent need of the industry to combine bio-enhanced degradation technology with physical and chemical technologies to achieve the synergistic degradation of multiple harmful substances in the wastewater, improve the wastewater treatment efficiency and reduce the wastewater treatment cost. Summary of the invention

[0005] The present invention proposes a treatment process for oilfield fracturing flowback fluid wastewater, which strengthens the biological treatment process by introducing specific bio-enhanced bacterial agents and activated carbon carriers, significantly improves the removal efficiency of refractory organic matter in the wastewater, and ensures the stability and economy of the treatment process.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A process for treating oilfield fracturing flowback wastewater comprises the following steps:

[0008] 1) Cyclone oil-water separation: The oilfield fracturing flowback wastewater is introduced into the cyclone oil-water separator. Under the action of centrifugal force, the oil and water are separated, the oil phase is reused, and the water phase is demulsified and flocculated;

[0009] 2) Super atomized dissolved air flotation: The wastewater after demulsification, flocculation and sedimentation enters the super atomized dissolved air flotation machine, and the suspended matter in the wastewater floats with the atomized bubbles and is then scraped off;

[0010] 3) Primary biochemical treatment: The wastewater after flotation treatment is introduced into the hydrolysis and acidification reaction tank to hydrolyze and acidify some pollutants to improve the biodegradability of the wastewater;

[0011] 4) Secondary biochemical treatment: the effluent from the hydrolysis and acidification reaction tank is introduced into the aerobic tank, and a bio-enhanced bacterial agent is added to the aerobic tank and cultured. The bio-enhanced bacterial agent cooperates with the activated sludge to degrade and remove the remaining pollutants in the wastewater; the bio-enhanced bacterial agent is composed of the following bacterial species: Methylobacterium phyllosphaerae, Pseudomonas denitrificans, Rhodococcus ruber and Ochrobactrum tritici, wherein Methylobacterium and Pseudomonas denitrificans are both deposited in the General Microbiological Center of the China Microbiological Culture Collection Administration, and the deposit number of Methylobacterium is: CGMCC No.3660; the deposit number of Pseudomonas denitrificans is: CGMCC No.10845; other bacterial species can be selected from any bacterial species purchased from any purchase channel on the market, and the viable bacterial count of each of the above bacterial species is not less than 10 8 CFU / g;

[0012] 5) Tertiary biochemical treatment: The effluent from the aerobic pool is introduced into the tertiary biochemical pool. The tertiary biochemical treatment adopts activated carbon-microorganism combined treatment. Powdered activated carbon is added to the tertiary biochemical pool to form a dedicated environment of activated carbon-microorganisms to adsorb and biochemically remove the remaining pollutants in the wastewater.

[0013] 6) Activated carbon biofiltration: The effluent from the tertiary biochemical pool is introduced into the activated carbon biofiltration reactor to filter the wastewater while further reducing the content of residual organic matter in the wastewater. The ammonia nitrogen, total nitrogen and COD in the effluent can meet the emission standards.

[0014] Furthermore, in step 4), the ratio of the amount of live bacteria of each species in the biological enhancement agent is 1:(2-3):(2-3):1, and the dosage is more than 100 ppm, preferably 200-500 ppm.

[0015] Furthermore, in step 4), the temperature of the aerobic tank is controlled at 15-25° C., the pH is controlled at 6-8, the organic COD removal load is 0.1-0.2 kg COD / (mlss*d), and the residence time is 16-24 h.

[0016] Furthermore, in step 4), a carbon source is added to the aerobic pool while adding the bio-enhancing agent. The carbon source is a combination of one or more of methanol, acetic acid, sodium acetate, flour or glucose. Preferably, the amount of the carbon source added is 50-200 ppm.

[0017] Furthermore, the residence time of step 3) is 12-24 hours.

[0018] Further, the specific surface area of ​​the powdered activated carbon in step 5) is 800-1500m 2 / g, pore size is 1-5nm, and dosage is 100-400ppm.

[0019] Furthermore, the residence time in step 5) is 4-8h.

[0020] The mechanism of action of each strain in the biological enhancement agent provided by the present invention is as follows:

[0021] 1) Methylobacterium is a Gram-negative bacterium and an efficient bacterium for degrading high molecular weight polycyclic aromatic hydrocarbons. It has a very good biological denitrification effect while efficiently degrading polycyclic aromatic hydrocarbons in water.

[0022] 2) Denitrifying Pseudomonas: Belonging to the genus Pseudomonas, it is a highly efficient bacterium that opens the ring structure of benzene derivatives. It can effectively degrade benzene derivatives in water while reducing the content of ammonia nitrogen and COD in the water. It has strong resistance and adaptability to volatile phenols and can effectively degrade them to produce harmless carbon dioxide and water.

[0023] 3) Rhodococcus: Belongs to the genus Rhodococcus, it is a ring-opening bacterium for benzene derivatives and aromatic hydrocarbons such as naphthalene and anthracene. Under aerobic conditions, it can use benzene derivatives and aromatic hydrocarbons as nutrients such as carbon and nitrogen sources. The functional enzymes secreted by the microorganism act on specific sites on the benzene ring and aromatic hydrocarbon structure, causing them to open the ring to form small molecule organic acids for its own use.

[0024] 4) Ochrobacterium tritici: Under aerobic conditions, it can efficiently utilize inorganic poisons such as cyanide and thiocyanate, converting them into other non-toxic small molecules, reducing the toxicity of the system. It has a certain degradation effect on sodium linear alkylbenzene sulfonate.

[0025] The preparation method of the biological enhancement agent of the present invention comprises the following steps:

[0026] (1) Primary seed culture: Under sterile conditions, Methylobacterium, Pseudomonas denitrificans, Rhodococcus erythrocytes, and Ochrobacterium tritici were selected and inoculated into LB medium, and cultured at 25-35° C. and 150-300 rpm for 24 h to obtain the primary seed culture solution of each strain;

[0027] (2) Secondary seed culture: Under sterile conditions, the primary seed culture solution of each strain was inoculated into LB medium at an inoculum amount of 1-10 vol%, and cultured at 25-35° C. and 150-300 rpm for 24-48 h to obtain the secondary seed culture solution of each strain;

[0028] (3) Fermentation: After the fermentation medium in the fermentation tank is disinfected, the secondary seed culture solution of each strain obtained in step (2) is inoculated into LB medium at an inoculum amount of 5-10 vol%, the temperature is controlled at 25-35° C., the rotation speed is 150-300 rpm, and the fermentation is carried out under the condition of aeration ratio of 1:(1-2). When the dissolved oxygen begins to rise, the fermentation is stopped to obtain the fermentation solution of each strain;

[0029] (4) Preparation of bio-enhanced bacterial agent: The fermentation broth of each strain obtained in step (3) is centrifuged and freeze-dried to obtain bacterial powder of each strain, and the bio-enhanced bacterial agent is prepared according to the proportion.

[0030] The beneficial effects of the process of the present invention are as follows:

[0031] (1) The various bacterial species in the bio-enhanced bacterial agent of the present invention cooperate with each other to effectively improve the ability of aerobic activated sludge to degrade COD, and can tolerate and degrade toxic inhibitory components such as oils, surfactants and high molecular polymers present in fracturing return fluid wastewater. The activated carbon has a strong adsorption capacity and can adsorb pollutants such as organic matter and heavy metals in the wastewater, providing space for the growth of microbial flora; maintaining the stability and diversity of the microbial community.

[0032] (2) Super atomized dissolved air flotation can quickly adsorb and remove most of the aggregate particles composed of suspended impurities, emulsified oil, surfactants, polymers, heavy metals, etc.

[0033] (3) The treatment process of the present invention has good effluent quality and high denitrification efficiency. The microbial sludge age attached to the system is long, and it has good denitrification and decarbonization effects. It can effectively degrade fracturing return fluid wastewater with a COD concentration of less than 3000 mg / L, and the COD degradation rate is more than 95%. This method has high degradation efficiency, short cycle, and stable operation, and can better meet market demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flow chart of the fracturing flowback fluid wastewater treatment process. DETAILED DESCRIPTION

[0035] In order to further explain the technical solution of the present invention, the principles and features of the present invention are described below through specific embodiments.

[0036] A treatment process for oilfield fracturing flowback wastewater, such as Figure 1 As shown, the method comprises the following steps: step 1, introducing the oilfield fracturing return fluid wastewater into a cyclone oil-water separator for oil-water separation; under the action of centrifugal force, oil and water are separated, the oil phase is reused, and the water phase is demulsified and flocculated; step 2, the effluent after demulsification, flocculation and precipitation flows into a super-atomized dissolved air flotation machine by gravity, and the suspended matter in the wastewater floats with the atomized bubbles and is then scraped off; step 3, the effluent of the super-atomized dissolved air flotation machine is lifted into a hydrolysis and acidification reaction tank for primary biochemical treatment. The hydrolysis and acidification process has a very good effect on the biochemical pretreatment of industrial wastewater. The retention time of the biochemical pool is 12h, and some pollutants are hydrolyzed and acidified to improve the biodegradability of the wastewater; Step 4, the effluent of the primary biochemical pool flows into the secondary biochemical pool by gravity. The secondary biochemical adopts an aerobic process and adds 100ppm of carbon source to the aerobic pool. The carbon source is a composite carbon source formed by a compound of methanol, acetic acid, sodium acetate and glucose in equal proportions. By adding the composite carbon source, the sludge concentration is increased. At the same time, a special biological enhancement agent is added and cultivated to greatly remove the remaining dissolved oil, high molecular polymers, petroleum hydrocarbons and other difficult-to-degrade components in the wastewater. The secondary biochemical pool is equipped with an independent sludge sedimentation and sludge return system to ensure an independent environment for the operation of aerobic sludge. Most of the COD in the sewage is removed in the secondary biochemical section. The bio-enhanced bacterial agent is composed of the following bacterial species: Methylobacterium phyllosphaerae, Pseudomonas denitrificans, Rhodococcus ruber, and Ochrobactrum tritici. Methylobacterium and Pseudomonas denitrificans are both deposited in the General Microbiological Center of the China Microbiological Culture Collection Administration. The deposit number of Methylobacterium is CGMCC No. 3660; the deposit number of Pseudomonas denitrificans is CGMCC No. 10845. Other bacterial species can be selected from any purchase channel on the market, and the viable bacterial count of each of the above bacterial species is not less than 10 8 CFU / g, the bio-enhanced bacteria and activated sludge work together, the temperature of the secondary biochemical tank is controlled at 15-25℃, the pH is controlled at 6-8, the organic COD removal load is 0.1-0.2kg COD / (mlss*d); the dosage of the bio-enhanced bacteria is 200ppm. The residence time of the secondary biochemical tank is 24h;

[0037] The preparation method of the bio-enhanced bacterial agent is as follows:

[0038] (1) Primary seed culture: Under sterile conditions, Methylobacterium, Pseudomonas denitrificans, Rhodococcus erythrocytes, and Ochrobacterium tritici were selected and inoculated into LB medium, and cultured at 30°C and 220 rpm for 24 h to obtain the primary seed culture solution of each strain;

[0039] (2) Secondary seed culture: Under sterile conditions, the primary seed culture solution of each strain was inoculated into LB medium at an inoculum rate of 2 vol%, and cultured at 30° C. and 220 rpm for 24 h to obtain the secondary seed culture solution of each strain;

[0040] (3) Fermentation: After the fermentation medium in the fermentation tank is disinfected, the secondary seed culture solution of each strain obtained in step (2) is inoculated into LB medium at an inoculum amount of 5 vol%, the temperature is controlled at 30° C., the rotation speed is 220 rpm, and the fermentation is carried out under the condition of aeration ratio of 1:2. When the dissolved oxygen begins to rise, the fermentation is stopped to obtain the fermentation solution of each strain;

[0041] (4) Preparation of bio-enhanced bacterial agent: The fermentation broth of each strain obtained in step (3) is centrifuged and freeze-dried to obtain bacterial powder of each strain, and the bio-enhanced bacterial agent is prepared according to the ratio of the live bacterial count of each strain of 1:3:2:1.

[0042] Step 5: The effluent from the secondary biochemical pool flows into the tertiary biochemical pool by gravity. The tertiary biochemical pool adopts an activated carbon-microorganism combined treatment process. In the tertiary biochemical pool, powdered activated carbon is continuously added. The total amount of activated carbon added is 300ppm to form a dedicated environment for activated carbon-microorganisms. The activated carbon system is equipped with independent sludge sedimentation and sludge return systems to ensure the independent environment for the operation of the activated carbon-microorganism system. The specific surface area of ​​the powdered activated carbon is 800m 2 / g, pore size is 2-4nm, and the residence time of the tertiary biochemical pool is 6h; step six, the effluent from the tertiary biochemical pool flows into the activated carbon biofilter, which adopts an upward flow activated carbon biofiltration reactor. While filtering the wastewater, the content of residual organic matter in the wastewater can be further reduced. The upward flow activated carbon biofiltration reactor has a higher biological concentration and a higher organic load. The porous spherical filter material provides a better growth environment for microorganisms, which is easy to form biofilms and operate stably. It can maintain more biomass on the surface of the filter material and between the filter materials. The amount of microorganisms per unit volume is much larger than the amount of microorganisms in the activated sludge method (up to 10-15g / L). The high concentration of microorganisms makes the filtration efficiency high, and the ammonia nitrogen, total nitrogen and COD of the effluent can meet the emission standards.

[0043] The COD, NH3-N and total nitrogen content in the wastewater before treatment and the effluent after treatment were detected by the above-mentioned method of microbial enhanced treatment of fracturing flowback fluid wastewater. In this embodiment, GB11914-89 "Determination of Chemical Oxygen Demand of Water Quality - Dichromate Method" was used to determine COD; distillation-titration method was used to determine NH3-N; GB 11894-89 "Determination of Total Nitrogen in Water Quality - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry" was used to determine total nitrogen, and the results are shown in Table 1.

[0044] Table 1 Treatment effect of fracturing flowback wastewater

[0045]

[0046] The results in Table 1 show that the application of this treatment process can improve the removal rates of ammonia nitrogen, total nitrogen and COD in oilfield fracturing flowback wastewater, with the COD removal rate reaching more than 95%, making the effluent indicators meet the national first-level emission standards.

[0047] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A process for treating oilfield fracturing flowback wastewater, characterized in that: The steps include: 1) Cyclone oil-water separation: The oilfield fracturing flowback wastewater is introduced into the cyclone oil-water separator. Under the action of centrifugal force, the oil and water are separated, the oil phase is reused, and the water phase is demulsified and flocculated; 2) Super atomized dissolved air flotation: The wastewater after demulsification, flocculation and sedimentation enters the super atomized dissolved air flotation machine, and the suspended matter in the wastewater floats with the atomized bubbles and is then scraped off; 3) Primary biochemical treatment: The wastewater after flotation treatment is introduced into the hydrolysis and acidification reaction tank to hydrolyze and acidify some pollutants to improve the biodegradability of the wastewater; 4) Secondary biochemical treatment: the effluent from the hydrolysis and acidification reaction tank is introduced into the aerobic tank, and a bio-enhanced bacterial agent is added to the aerobic tank and cultured. The bio-enhanced bacterial agent cooperates with the activated sludge to degrade and remove the remaining pollutants in the wastewater; the bio-enhanced bacterial agent is composed of the following bacterial species: Methylobacterium phyllosphaerae, Pseudomonas denitrificans, Rhodococcus ruber and Ochrobactrum tritici, wherein Methylobacterium and Pseudomonas denitrificans are both deposited in the General Microbiological Center of the China Microbiological Culture Collection Administration, and the deposit number of Methylobacterium is: CGMCC No.3660; the deposit number of Pseudomonas denitrificans is: CGMCC No.10845; other bacterial species can be selected from any bacterial species purchased from any purchase channel on the market, and the viable bacterial count of each of the above bacterial species is not less than 10 8 CFU / g; 5) Tertiary biochemical treatment: The effluent from the aerobic pool is introduced into the tertiary biochemical pool. The tertiary biochemical treatment adopts activated carbon-microorganism combined treatment. Powdered activated carbon is added to the tertiary biochemical pool to form a dedicated environment of activated carbon-microorganisms to adsorb and biochemically remove the remaining pollutants in the wastewater. 6) Activated carbon biofiltration: The effluent from the tertiary biochemical pool is introduced into the activated carbon biofiltration reactor to filter the wastewater while further reducing the content of residual organic matter in the wastewater. The ammonia nitrogen, total nitrogen and COD in the effluent can meet the emission standards.

2. The process according to claim 1, characterized in that Step 4) The ratio of the amount of live bacteria of each species in the biological enhancement agent is 1:(2-3):(2-3):

1.

3. The process according to claim 1 or 2, characterized in that Step 4) The dosage of the bio-enhancing agent is above 100 ppm.

4. The process according to claim 3, characterized in that The dosage of the biological enhancement agent is 200-500ppm.

5. The process according to claim 1, 2 or 4, characterized in that In step 4), the temperature of the aerobic pool is controlled at 15-25° C., the pH is controlled at 6-8, the organic COD removal load is 0.1-0.2 kgCOD / (mlss*d), and the residence time is 16-24 h.

6. The process according to claim 3, characterized in that In step 4), the temperature of the aerobic pool is controlled at 15-25° C., the pH is controlled at 6-8, the organic COD removal load is 0.1-0.2 kg COD / (mlss*d), and the residence time is 16-24 h.

7. The process according to claim 1 or 2, characterized in that In step 4), a carbon source is added to the aerobic pool while adding the bio-enhancing agent. The carbon source is a combination of one or more of methanol, acetic acid, sodium acetate, flour or glucose. Preferably, the amount of the carbon source added is 50-200 ppm.

8. The process according to claim 5, characterized in that In step 4), a carbon source is added to the aerobic pool while adding the bio-enhancing agent. The carbon source is a combination of one or more of methanol, acetic acid, sodium acetate, flour or glucose. Preferably, the amount of the carbon source added is 50-200 ppm.

9. The process according to claim 1 or 2, characterized in that The residence time of step 3) is 12-24h.

10. The process according to claim 1 or 2, characterized in that The specific surface area of ​​the powdered activated carbon in step 5) is 800-1500m 2 / g, pore size is 1-5nm, dosage is 100-400ppm, and residence time of step 5) is 4-8h.

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