Treatment process of oily wastewater

Abstract

The invention relates to an oily wastewater treatment process which comprises the following steps: carrying out air flotation treatment on oily wastewater in an air flotation reactor in the presence of a composite efficient air flotation agent, the composite efficient air flotation agent contains an air flotation agent, a flotation auxiliary agent and an air flotation collecting agent; the air flotation agent contains an inorganic metal salt and / or an inorganic polymeric flocculant; the flotation auxiliary agent contains an organic polymer coagulant aid; the air flotation collecting agent contains a compound with the structural formula of R-O-(CH2CH2O) n-[CH2CH (CH3) O] mPO3M2, R is H or C6-C20 alkyl, n is selected from an integer of 0-50, m is selected from an integer of 0-50, m and n are not 0 at the same time, and M is H or a monovalent metal cation. According to the treatment process disclosed by the invention, the oil removal and suspended matter removal effects of the air flotation treatment unit can be improved.

Description

Technical Field

[0001] The present application relates to a process for treating oily wastewater. Background Art

[0002] With the rapid development of the petrochemical industry, a large amount of petrochemical wastewater is discharged and increasing day by day. Oil in the wastewater of petrochemical enterprises is one of the main pollutants. The oil content in the incoming water of refinery wastewater treatment plants is often high due to the processing of inferior crude oil or the start-up of upstream devices. If it is not properly handled, it will affect the stable operation of the secondary biochemical unit and the entire sewage treatment plant.

[0003] The oil removal pretreatment process mainly includes adjustment, oil separation and flotation. According to the source of oily wastewater and the form of oil in water, the oil in wastewater can be divided into four categories: floating oil, dispersed oil, emulsified oil and dissolved oil. The oil separation unit mainly removes floating oil and some dispersed oil with larger particles in wastewater, and the flotation unit removes dispersed oil with smaller particles and some emulsified oil in wastewater.

[0004] The principle of flotation is to utilize the physical and chemical principle that oil droplets easily adhere to the surface of air bubbles. Microbubbles are directly injected into sewage to allow the sewage and microbubbles to be fully mixed. Under the joint action of flotation agents, the hydrophilicity and stability of dispersed oil, emulsified oil, suspended matter and colloidal particles in sewage are destroyed, and their aggregation ability is increased, thereby causing physical and chemical flocculation. Emulsified oil and tiny suspended matter adhere to the surface of air bubbles and float to the surface of the water with the bubbles to be separated and removed.

[0005] The flotation process is mature and low-cost, and is widely used in wastewater treatment in oil fields, petrochemicals and other fields. However, there are also problems such as high energy consumption and low removal efficiency of dispersed oil and emulsified oil. At present, the research hotspots of flotation technology are more focused on equipment development and coupling with other processes. For example, patent CN1260149C proposes a microwave-ultraviolet flotation synergistic wastewater treatment method. This method is that ultraviolet light reacts with the blown air under the action of microwaves to produce ozone, and the flotation effect of the blown air is used to synergistically treat wastewater; patent CN214829601U discloses a flotation-activated carbon adsorption-ozone flotation oil removal and COD removal device. These new methods are combined with other processes, using microwaves or ozone generators to generate micron-level ozone bubbles, so that ozone and solution are fully mixed, and organic matter in wastewater is removed by oxidation of ozone or hydroxyl radicals while improving the flotation effect. However, the processes of these devices are relatively complex and have high requirements for the quality of the incoming water. The chromaticity and oil content of the incoming water affect the working efficiency of the microwave. Excessive oil content clogs the activated carbon adsorption column and affects the oil removal effect. The oxidation reaction requires a long residence time. Too long a residence time results in large space occupation or low processing capacity.

[0006] In fact, improving the flotation agent formula to improve the oil removal effect without adding new equipment is the most economical and feasible method. CN106140485A discloses a novel flotation agent composition, which includes: 1-30% alkyl tertiary amine monoquaternary ammonium salt, 1-30% propylene [(alkyl dimethyl / alkyl dimethyl) chloride / ammonium bromide], 1-10% nonylphenol polyoxyethylene polyoxypropylene ether, 1-10% N,N'-bislauroyl ethylenediamine diacetate sodium, 1-30% ethylene bis (alkyl polyoxyethylene ammonium chloride), and 0-15% pour point depressant. However, the main agent alkyl tertiary amine monoquaternary ammonium salt in the patent: dodecyl dimethyl benzyl ammonium chloride, tetradecyl trimethyl ammonium chloride, hexadecyl dimethyl benzyl ammonium chloride, octadecyl dimethyl benzyl ammonium chloride, octadecyl trimethyl ammonium bromide, etc. all have bactericidal functions, and dodecyl dimethyl benzyl ammonium chloride and tetradecyl trimethyl ammonium chloride are non-oxidizing bactericides commonly used in circulating cooling water systems. The current treatment process of the wastewater treatment plants of petrochemical enterprises adopts oil separation + flotation unit + biochemical treatment unit + deep treatment and reuse unit. The residual fungicide after using this patent to treat the wastewater will affect the treatment effect of the subsequent biochemical unit.

[0007] CN101376532A provides a method for treating low-temperature oily wastewater. During the transportation of oily wastewater after low-temperature demulsification to a wastewater treatment device, flotation agents are added to remove oil. The flotation agents can be selected from: cationic polyacrylamide, cationic polymers modified by polyacrylamide, and polyethers generated by the reaction of epichlorohydrin and fatty alcohol. The oil content in the water can be less than 5mg / L and the suspended matter content can be less than 5mg / L after wastewater treatment. However, this method has a good effect only on the treatment of upstream oily wastewater after crude oil pretreatment and demulsification, and has a poor flotation effect on downstream petrochemical wastewater containing other water treatment additives.

[0008] In addition to oily wastewater from atmospheric and vacuum treatment, catalytic cracking, and electric desalination, petrochemical oily wastewater is usually mixed with wastewater containing water treatment agents such as boiler and drum wastewater and circulating cooling water system wastewater. The water treatment agents in the wastewater will disperse tiny oil droplets, suspended matter and other pollutants in the water, prolonging the superstable equilibrium and supersaturation state of substances in the water, affecting the effect of flotation oil removal.

[0009] Therefore, it is necessary to develop composite high-efficiency flotation agents in a targeted manner according to the sewage quality conditions to improve the oil removal effect of the flotation unit. Summary of the invention

[0010] The purpose of the present disclosure is to provide a treatment process for oily wastewater, which can improve the oil removal and suspended matter removal effects of an air flotation treatment unit.

[0011] In order to achieve the above-mentioned object, the present invention provides a treatment process for oily wastewater, which comprises: in the presence of a composite high-efficiency flotation agent, subjecting the oily wastewater to flotation treatment in a flotation reactor; the composite high-efficiency flotation agent comprises a flotation agent, a flotation aid and a flotation collector; the flotation agent comprises an inorganic metal salt and / or an inorganic polymer flocculant; the flotation aid comprises an organic polymer flocculant; the flotation collector comprises a structural formula of RO-(CH2CH2O) n -[CH2CH(CH3)O] m A PO3M2 compound, wherein R is H or a C6-C20 alkyl group, n is selected from an integer of 0-50, m is selected from an integer of 0-50, and m and n are not 0 at the same time, and M is H or a monovalent metal cation.

[0012] Through the above technical solution, the treatment process disclosed in the present invention can significantly improve the oil removal and flocculation effects of the flotation unit and reduce the impact on the subsequent biochemical treatment system.

[0013] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0014] The following is a detailed description of the specific embodiments of the present disclosure. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0015] The present invention provides a treatment process for oily wastewater, which comprises: in the presence of a composite high-efficiency flotation agent, subjecting the oily wastewater to flotation treatment in a flotation reactor; the composite high-efficiency flotation agent contains a flotation agent, a flotation aid and a flotation collector; the flotation agent contains an inorganic metal salt and / or an inorganic polymer flocculant; the flotation aid contains an organic polymer coagulant; the flotation collector contains a structural formula of RO-(CH2CH2O) n -[CH2CH(CH3)O] m A PO3M2 compound, wherein R is H or a C6-C20 alkyl group, n is selected from an integer of 0-50, m is selected from an integer of 0-50, and m and n are not 0 at the same time, and M is H or a monovalent metal cation.

[0016] The treatment process disclosed in the present invention adopts a compounded high-efficiency flotation agent. The flotation collector contained in the compound high-efficiency flotation agent can effectively promote the reaction between the cationic flotation agent and the water treatment agent in the oily wastewater, and make the generated tiny precipitates adsorbed on the surface of the bubbles, rise rapidly to achieve the purpose of solid-liquid separation, thereby further greatly improving the aggregation ability and electrostatic properties of oil and suspended matter in the oily wastewater; on the other hand, the flotation collector has good self-penetration, and its hydrophilic group can firmly adsorb on the surface of tiny oil droplets, while the hydrophobic group is thrown to the water side, which is conducive to making the tiny oil droplets rise to the liquid surface together with the bubbles, further promoting the removal of dispersed oil with tiny particle size and part of the emulsified oil, and significantly improving the flotation treatment effect. Therefore, the treatment process disclosed in the present invention can significantly improve the oil removal and flocculation effect of the water treatment unit and reduce the impact on the subsequent biochemical treatment system.

[0017] According to the present disclosure, the structural formula RO-(CH2CH2O) n -[CH2CH(CH3)O] m In PO3M2, M is H + or monovalent metal cations.

[0018] According to the present disclosure, the weight ratio of the oily wastewater to the amount of the flotation agent can vary within a wide range. In a specific embodiment of the present disclosure, the weight ratio of the oily wastewater to the amount of the flotation agent is 1:(0.02-10), and the oily wastewater is calculated based on the oil in the oily wastewater; preferably, the weight ratio of the oily wastewater to the amount of the flotation agent is 1:(0.5-5). The weight ratio of the oily wastewater to the amount of the flotation agent within the above-mentioned ratio can more effectively remove the oil and suspended matter in the oily wastewater and further improve the flocculation effect.

[0019] According to the present disclosure, the weight ratio of the amount of the flotation agent to the amount of the flotation aid can vary within a wide range, for example, it can be (1-1000): 1, preferably (5-500): 1, and more preferably (10-40): 1. When the amount ratio of the flotation agent to the flotation aid in the composite high-efficiency flotation agent is within the above range, the ratio is appropriate, and the oil in the oily wastewater can be removed more effectively, and the flocculation effect can be further improved.

[0020] According to the present disclosure, the weight ratio of the amount of the flotation collector to the amount of the flotation aid can vary within a wide range. In a specific embodiment of the present disclosure, the weight ratio of the flotation collector to the amount of the oily wastewater is (0.05-20):1, and the oily wastewater is calculated based on the oil in the oily wastewater; preferably, the weight ratio of the flotation collector to the amount of the oily wastewater is (0.1-5):1. The weight ratio of the flotation collector to the flotation aid within the above range is suitable, which can further improve the oil removal and flocculation effect of the flotation reaction unit and reduce the processing pressure of the subsequent water treatment process.

[0021] In a specific embodiment of the present disclosure, R is a C6-C20 alkyl group, more preferably a C8-C16 alkyl group.

[0022] In a specific embodiment of the present disclosure, n is selected from an integer of 5-22, and m is selected from an integer of 5-20.

[0023] In a specific embodiment of the present disclosure, the monovalent metal cation is selected from Na + and / or K + .

[0024] In a specific embodiment of the present disclosure, the metal in the inorganic metal salt is one or more of aluminum, iron, aluminum, potassium and sodium. According to the present disclosure, the metal in the inorganic metal salt is mainly aluminum and iron, or contains one or more of aluminum potassium, aluminum sodium, aluminum iron, iron sodium and iron potassium.

[0025] In a specific embodiment of the present disclosure, the inorganic polymer flocculant is selected from polyaluminum salts and / or polyferric salts. In a preferred specific embodiment, the flotation agent is selected from one or more of aluminum sulfate, potassium aluminum sulfate, aluminum chloride, ferric sulfate, ferric chloride, aluminum ferric chloride, aluminum ferric sulfate, polyaluminum sulfate, polyaluminum chloride (PAC), polyferric chloride sulfate, polyaluminum silicate sulfate and polyferric chloride.

[0026] According to the present disclosure, organic polymer coagulant aids are well known to those skilled in the art. In a specific embodiment of the present disclosure, the organic polymer coagulant aid is selected from one or more of anionic polyacrylamide, cationic polyacrylamide and non-ionic polyacrylamide, and the number average molecular weight of the polymer flocculant is 1 million to 50 million, preferably 3 million to 40 million.

[0027] In a specific embodiment of the present disclosure, the flotation collector is selected from one or more of C6-C20 fatty alcohol polyoxyethylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene ether phosphate salt, C6-C20 alkylphenol polyoxyethylene ether phosphate, C6-C20 alkylphenol polyoxyethylene ether phosphate salt, C6-C20 fatty alcohol polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxypropylene ether phosphate salt, C6-C20 alkylphenol polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxypropylene ether phosphate salt, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxyethylene polyoxypropylene ether phosphate and C6-C20 alkylphenol polyoxyethylene polyoxypropylene ether phosphate salt.

[0028] In a preferred embodiment of the present disclosure, the flotation collector is isooctyl polyoxyethylene ether phosphate. The flotation collector is compounded with a flotation agent and a flotation aid to form a composite high-efficiency flotation agent with better performance, which can more effectively improve the flocculation effect of the water treatment unit and remove oil from the wastewater to be treated.

[0029] In a specific embodiment of the present disclosure, the conditions of the flotation reaction include: a mixing reaction time of 1-10 min, a total residence time of 1-100 min, and a gas pressure of 0.25 MPa-0.4 MPa; preferably, the mixing reaction time is 2-6 min, the total residence time is 10-40 min, and the gas pressure is 0.3 MPa-0.4 MPa. Under the above conditions, the composite high-efficiency flotation agent in the flotation reactor contacts and reacts with the oily wastewater more fully, which can further improve the oil removal and suspended solids removal effects of the water treatment unit treatment process.

[0030] According to the present disclosure, the flotation reactor is well known to those skilled in the art. In order to promote the distribution effect of gas in the flotation reactor to further improve the effect of flotation treatment, in a specific embodiment of the present disclosure, a dissolved gas releaser is provided at the bottom of the flotation reactor, and the bubbles of the dissolved gas releaser are evenly distributed when the gas dissolved in water is dispersed, and the diameter of the microbubbles released by the dissolved gas releaser is 10μm-60μm, preferably 20-50μm.

[0031] The treatment process disclosed in the present invention is suitable for treating oily wastewater in the fields of petrochemical industry, etc. In a specific embodiment of the present invention, the oily wastewater is selected from one or more of atmospheric and vacuum wastewater, catalytic cracking wastewater, electric desalination wastewater, boiler wastewater, drum wastewater and circulating cooling water system wastewater. The treatment process disclosed in the present invention has a good treatment effect on mixed wastewater containing one or more of atmospheric and vacuum wastewater, catalytic cracking wastewater and electric desalination wastewater, and one or more of boiler wastewater, drum wastewater and circulating cooling water system wastewater. According to the present invention, the oil content and suspended matter content of the oily wastewater can vary in a large range. In one embodiment, the oil content in the wastewater is 20-500 mg / L, and the suspended matter content is 20-500 mg / L. The present invention is further illustrated by examples below, but the present invention is not limited thereto.

[0032] The raw materials used in the following examples and comparative examples are commercially available unless otherwise specified. The oily wastewater treated in Examples 1-4 and 6 and Comparative Examples 1, 3-4 is from the effluent of the oil separator unit of a domestic petrochemical plant, with an oil content of 75.0 mg / L and a suspended matter content of 53.0 mg / L.

[0033] Example 1

[0034] The dosage of the flotation agent polyaluminium chloride (PAC) is 60mg / L, the dosage of the flotation aid cationic polyacrylamide is 2mg / L, the dosage of the flotation collector isooctyl alcohol polyoxyethylene ether phosphate is 10mg / L, the mixing reaction time of the oily wastewater in the flotation reactor is 10min, the total residence time is 40min, and the gas pressure in the flotation reactor is 0.4MPa. The oil content and suspended matter content in the treated oily wastewater are shown in Table 1, the same below.

[0035] Example 2

[0036] The oily wastewater was treated in the same manner as in Example 1, except that the dosage of the flotation agent polyaluminium chloride (PAC) was 30 mg / L.

[0037] Example 3

[0038] The oily wastewater was treated in the same manner as in Example 1, except that the dosage of the flotation collector isooctyl alcohol polyoxyethylene ether phosphate was 5 mg / L.

[0039] Example 4

[0040] The oily wastewater was treated in the same manner as in Example 1, except that the total residence time of the oily wastewater in the flotation reactor was 25 min.

[0041] Example 5

[0042] The simulated oily wastewater was treated, the oil content in the wastewater was 75mg / L, and there was no water treatment agent in the wastewater. The dosage of the flotation agent PAC was 60mg / L, the dosage of the flotation aid cationic polyacrylamide was 2mg / L, the dosage concentration of the flotation collector isooctyl alcohol polyoxyethylene ether phosphate was 10mg / L, the total residence time of the wastewater in the flotation reactor was 40min, and the gas pressure in the flotation reactor was 0.4MPa.

[0043] Example 6

[0044] The oily wastewater was treated in the same manner as in Example 1, except that the dosage of the flotation collector isooctyl polyoxyethylene ether phosphate was 5 mg / L, the dosage of the flotation agent polyaluminum chloride (PAC) was 60 mg / L, and the dosage of the flotation aid cationic polyacrylamide was 3 mg / L.

[0045] Example 7

[0046] The oily wastewater was treated in the same manner as in Example 1, except that 10 mg / L lauryl alcohol polyoxyethylene ether phosphate was used instead of isooctyl alcohol polyoxyethylene ether phosphate as the flotation collector.

[0047] Example 8

[0048] The oily wastewater was treated in the same manner as in Example 1, except that 10 mg / L alkylphenol polyoxyethylene ether phosphate was used instead of isooctyl alcohol polyoxyethylene ether phosphate as the flotation collector.

[0049] Comparative Example 1

[0050] The oily wastewater was treated in the same manner as in Example 1, except that no flotation collector was added.

[0051] Comparative Example 2

[0052] The oily wastewater was treated in the same manner as in Example 5, except that no flotation collector was added.

[0053] Comparative Example 3

[0054] The oily wastewater was treated in the same manner as in Example 1, except that 10 mg / L nonylphenol polyoxyethylene ether was used instead of isooctyl alcohol polyoxyethylene ether phosphate as the flotation collector.

[0055] Comparative Example 4

[0056] The oily wastewater was treated in the same manner as in Example 1, except that 10 mg / L polyoxyethylene ether sulfonate was used instead of isooctyl polyoxyethylene ether phosphate as the flotation collector.

[0057] Table 1

[0058] Oil content, mg / L Suspended matter content, mg / L Example 1 11.8 5.9 Example 2 26.0 7.8 Example 3 23.9 9.2 Example 4 22.1 7.8 Example 5 10.4 6.1 Example 6 18.8 10.8 Example 7 12.6 10.8 Example 8 14.8 12.5 Comparative Example 1 29.1 15.0 Comparative Example 2 11.7 6.4 Comparative Example 3 31.9 19.1 Comparative Example 4 32.2 17.6

[0059] It can be seen from the above that the treatment process disclosed in the present invention can effectively remove oil and suspended matter in oily wastewater.

[0060] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0061] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0062] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A process for treating oily wastewater, characterized in that: The treatment process comprises: in the presence of a composite high-efficiency flotation agent, flotation treatment is performed on the oily wastewater in a flotation reactor; The composite high-efficiency flotation agent contains a flotation agent, a flotation aid and a flotation collector; The flotation agent contains inorganic metal salts and / or inorganic polymer flocculants; the flotation aid contains organic polymer coagulants; the flotation collector contains a structural formula of RO-(CH2CH2O) n -[CH2CH(CH3)O] m A PO3M2 compound, wherein R is H or a C6-C20 alkyl group, n is selected from an integer of 0-50, m is selected from an integer of 0-50, and m and n are not 0 at the same time, and M is H or a monovalent metal cation.

2. The process according to claim 1, wherein: The weight ratio of the oily wastewater to the amount of the flotation agent is 1:(0.02-10), and the oily wastewater is calculated based on the oil in the oily wastewater; Preferably, the weight ratio of the oily wastewater to the amount of the flotation agent is 1:(0.5-5).

3. The process according to claim 1, wherein: The weight ratio of the flotation agent to the flotation aid is (1-1000):1, preferably (5-500):

1.

4. The process according to claim 1, wherein: The weight ratio of the flotation collector to the oily wastewater is (0.05-20):1, and the oily wastewater is calculated based on the oil in the oily wastewater; Preferably, the weight ratio of the flotation collector to the oily wastewater is (0.1-5):

1.

5. The process according to claim 1, wherein: The R is a C6-C20 alkyl group; preferably, the R is C8-C16; n is selected from an integer of 0-50, m is selected from an integer of 0-50, and m and n are not simultaneously 0; the monovalent metal cation is selected from Na + and / or K + .

6. The process according to claim 1, wherein: The metal in the inorganic metal salt is one or more of aluminum, iron, aluminum, potassium and sodium; the inorganic polymer flocculant is selected from polymerized aluminum salt and / or polymerized iron salt; The flotation agent is selected from one or more of aluminum sulfate, potassium aluminum sulfate, aluminum chloride, ferric sulfate, ferric chloride, aluminum ferric chloride, aluminum ferric sulfate, polyaluminum sulfate, polyaluminum chloride, polyferric sulfate, polyaluminum silicate sulfate and polyferric chloride; The organic polymer coagulant is selected from one or more of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide. The number average molecular weight of the polymer flocculant is 1 million to 50 million, preferably 3 million to 40 million.

7. The process according to claim 1, wherein: The flotation collector is selected from one or more of C6-C20 fatty alcohol polyoxyethylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene ether phosphate salt, C6-C20 alkylphenol polyoxyethylene ether phosphate, C6-C20 alkylphenol polyoxyethylene ether phosphate salt, C6-C20 fatty alcohol polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxypropylene ether phosphate salt, C6-C20 alkylphenol polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxypropylene ether phosphate salt, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 fatty alcohol polyoxyethylene polyoxypropylene ether phosphate, C6-C20 alkylphenol polyoxyethylene polyoxypropylene ether phosphate and C6-C20 alkylphenol polyoxyethylene polyoxypropylene ether phosphate.

8. The process according to claim 1, wherein: The conditions of the flotation reaction include: a mixing reaction time of 1-10 min, a total residence time of 1-100 min, and a gas pressure of 0.25 MPa-0.4 MPa; Preferably, the mixing reaction time is 2-6 min, the total residence time is 10-40 min, and the gas pressure is 0.3 MPa-0.4 MPa.

9. The process according to claim 1, wherein: A dissolved air releaser is arranged at the bottom of the air flotation reactor, and the diameter of microbubbles released by the dissolved air releaser is 10 μm-60 μm.

10. The process according to claim 1, wherein: The oily wastewater is selected from one or more of atmospheric and vacuum wastewater, catalytic cracking wastewater, electric desalination wastewater, boiler wastewater, drum wastewater and circulating cooling water system wastewater; The oil content in the wastewater is 20-500 mg / L, and the suspended matter content is 20-500 mg / L.