Oily wastewater treatment system and process

Abstract

The present invention discloses an oily wastewater treatment system and process, which relates to the technical field of wastewater treatment, including: S1, pretreatment: removing large solid impurities by filtering; S2, subjecting the pretreated oily wastewater to gravity sedimentation and adjusting the pH value; for emulsified oily wastewater, a demulsifier needs to be added after gravity sedimentation; S3, treating the oily wastewater with modified PAN fiber: filling 3 to 4 layers of modified PAN fiber in an adsorption tower, with a layer spacing of 5 to 10 cm, and a thickness of each layer of 50 to 60 cm. During the filling process, the void ratio is controlled between 75 and 85%, and the temperature in the tower is controlled between 20 and 30°C; S4, post-treatment process. The present invention provides a new, efficient and low-consumption treatment technology, which uses modified fiber adsorbents to treat oily wastewater, combines modified fibers with existing processes, and can effectively reduce the oil content in wastewater while reducing costs, so that the oil content of wastewater meets the discharge standard.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to an oily wastewater treatment system and process. Background Art

[0002] A large amount of oily wastewater is generated during industrial production, such as oil extraction, oil refining, chemical industry, metal processing and other industries. These oily wastewaters are directly discharged into the nature, which will cause serious pollution to the environment. The oil substances contained in oily wastewater are usually divided into four categories: floating oil, dispersed oil, emulsified oil and dissolved oil. Among them, emulsified oil is difficult to handle due to its strong stability, which is the focus and difficulty of wastewater treatment.

[0003] At present, the main processes for treating oily wastewater are: ① Gravity and mechanical separation method: Based on the difference in oil and water density, oil and water are separated through equipment such as oil separators; this method is suitable for removing floating oil, but it is not effective for emulsified oil and dispersed oil. ② Air flotation method: By generating microbubbles to adhere to oil droplets, they float and separate; this method is suitable for treating dispersed oil and emulsified oil, with high efficiency, but it usually requires the addition of flocculants, and the equipment maintenance and operation costs are high. ③ Flocculation method: By adding flocculants, oil droplets are promoted to aggregate, and then removed by sedimentation or air flotation. It is suitable for treating emulsified oil, but the amount of reagents used is large, which may cause secondary pollution. ④ Adsorption method: Adsorbents such as activated carbon are used to adsorb dissolved oil and other organic matter. This method is suitable for deep treatment, but the adsorbent cost is high and there is a problem of regeneration. ⑤ Biochemical method: Degrade organic matter by microbial metabolism. It is suitable for treating dissolved oil, but it has limited effect on high-concentration emulsified oil and dispersed oil, and is easily affected by changes in water quality. ⑥Membrane separation method: uses semipermeable membrane to intercept oil droplets and surfactants, which is suitable for wastewater treatment with high emission standards, but membrane pollution and high cost are the main problems. ⑦Electrolysis method: removes emulsified oil and dissolved oil through electrolysis, but there are problems such as large metal consumption and high operating costs.

[0004] Even though there are currently a variety of methods for treating oily wastewater, the following problems still exist: it is difficult to completely remove emulsified oil and dissolved oil in wastewater; the equipment cost is relatively high when using membrane separation and adsorption methods to treat wastewater; the equipment maintenance cost of flotation and electrolysis methods is relatively high; when flocculants or other additives are added, secondary pollution may occur, and the sludge needs to be treated, making the treatment process more complicated; the biochemical method is sensitive to changes in water quality and is easily affected by load changes, which affects the treatment effect. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a system and process for treating oily wastewater, which can effectively reduce the oil content in the wastewater so that the oil content of the wastewater meets the discharge standard.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A process for treating oily wastewater, comprising:

[0008] S1, pretreatment: remove large solid impurities by filtration;

[0009] S2, subjecting the pretreated oily wastewater to gravity sedimentation and adjusting the pH value; for emulsified oily wastewater, a demulsifier needs to be added after gravity sedimentation;

[0010] S3, Treatment of oily wastewater using modified PAN fiber:

[0011] Filling 3-4 layers of modified PAN fiber in an adsorption tower, with a layer spacing of 5-10 cm and a thickness of 50-60 cm for each layer. During the filling process, the void ratio is controlled between 75% and 85%, and the temperature in the tower is controlled between 20 and 30°C.

[0012] S4, post-treatment process: further treat the wastewater after modified fiber treatment to make the wastewater meet the discharge standard or reuse water standard.

[0013] Furthermore, the preparation method of the modified PAN fiber in step S3 is:

[0014] S31, washing and drying the PAN fiber;

[0015] S32, after acid washing and alkali washing of the PAN fiber, drying and storing in a dust-free environment;

[0016] S33, soaking the dried PAN fiber obtained in step S32 in an acrylic acid solution, adding an initiator of ammonium persulfate, and performing a grafting reaction at 65 to 75° C. for 3 to 4 hours to obtain a grafted fiber;

[0017] S34, nano-SiO2 is coated on the surface of the grafted fiber by the dip coating technology to obtain the modified PAN fiber; during the coating process, the nano-SiO2 in the dip coating solution 2 The concentration is 2-5% of the fiber mass, the impregnation liquid temperature is 40-60°C, the pH value is 7-8, and the time is controlled at 30-60 minutes.

[0018] Furthermore, in step S31, the PAN fibers are cleaned by spraying or ultrasonic cleaning, and dried by hot air blowing, with the temperature of the hot air being 80-120° C. and the wind speed being 1-2 m / s.

[0019] Furthermore, in step S32, the pickling solution during pickling is dilute hydrochloric acid or dilute sulfuric acid with a pH value of 3 to 5, and the pickling time is 0.5 to 1 hour; the alkaline washing solution during alkali washing is a sodium hydroxide solution with a pH value of 10 to 11, and the alkaline washing time is 0.5 to 1 hour; the drying temperature after pickling and alkali washing is 60 to 80°C, and the time is 1 to 2 hours.

[0020] Furthermore, in step S33, the concentration of the acrylic acid solution is 20-30%, and the amount of ammonium persulfate added is 0.5-1.0% of the mass of the acrylic acid.

[0021] Furthermore, in step S1, filtering is performed through a grid or a filter; in step S2, the pH value is adjusted to 3 to 9; and the amount of demulsifier used is 6 to 10 ppm of the volume of the oily wastewater.

[0022] Furthermore, when the oily wastewater is treated in step S3, the time the oily wastewater stays in the adsorption tower is 45 to 60 minutes.

[0023] Furthermore, step S3 also includes: discharging the adsorption saturated modified PAN fiber into a desorption tower for desorption treatment, selecting 40-60° C. water as the desorption liquid, the desorption time is 30-45 min, and the flow rate of the desorption liquid is 0.5-1 m / s; and then regenerating the desorbed modified PAN fiber with low-pressure steam.

[0024] The system for treating oily wastewater using the above treatment process comprises a wastewater storage tank, a filter tank and a sedimentation tank connected in sequence through pipelines; a modified fiber treatment unit is connected to the sedimentation tank through a pipeline, and a post-treatment unit is connected to the water outlet of the modified fiber treatment unit;

[0025] The modified fiber processing unit comprises 2 to 3 adsorption towers, the upper and lower ends of the adsorption towers are wastewater inlet and wastewater outlet, the adsorption towers are filled with 3 to 4 layers of modified PAN fibers, the interlayer spacing is 5 to 10 cm, the thickness of each layer is 50 to 60 cm, and the filling void ratio of the modified PAN fibers is 75 to 85%; the lower end of the adsorption tower is also provided with a filling port for filling the modified PAN fibers, the filling port is also connected to a desorption unit, and a regeneration system is provided in connection with the desorption unit.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a novel, efficient and low-consumption treatment technology, which utilizes modified fiber adsorbents to treat oily wastewater. The modified fiber is combined with existing processes to effectively reduce the oil content in the wastewater while reducing costs, so that the oil content of the wastewater meets the discharge standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a schematic diagram of the processing system provided by the present invention.

[0029] Among them, the names corresponding to the figure numbers are: 1-filtration tank, 2-sedimentation tank, 3-adsorption tower, 31-wastewater inlet, 32-wastewater outlet, 33-filling port, 4-post-treatment unit, 5-desorption unit, 6-regeneration system, 7-wastewater storage tank. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0031] Example 1

[0032] This embodiment provides a process for treating oily wastewater, comprising:

[0033] S1, wastewater pretreatment: remove large solid impurities through screens or filters.

[0034] S2, the pretreated wastewater is transported to a sedimentation tank for gravity sedimentation and the pH value is adjusted to 3 to remove heavier oil droplets and suspended solids; a demulsifier is added to destroy the stability of oil droplets in the oily wastewater, and the amount of the demulsifier is 6ppm of the volume of the oily wastewater.

[0035] S3, the oily wastewater obtained in step S2 is transported to a modified fiber processing unit through a water pump; the following three steps are mainly performed in the modified fiber processing unit:

[0036] S31: Adsorption: Select modified PAN fiber to treat the wastewater, fill the modified PAN fiber into an adsorption tower, the adsorption tower can be a common adsorption tower in the field of wastewater treatment, fill 3 layers of modified PAN fiber in the adsorption tower, the layer spacing is 5 cm, the thickness of each layer is 50 cm, in order to facilitate the flow of wastewater and the adsorption process, the modified PAN fiber is controlled to have a void ratio of 75% during the filling process, the temperature in the tower is controlled at 20°C, the hydraulic retention time is 45 minutes, and a downflow adsorption tower design is adopted;

[0037] S32: Desorption: The saturated modified PAN fiber is discharged into a desorption tower, water with a temperature of 40-60°C is selected as the desorption liquid, the desorption time is controlled at 30 minutes, and the flow rate of the desorption liquid is 0.5 m / s, so as to reduce the adsorption force between the oil droplets and the fiber, and make the desorbed oil droplets aggregate into large particles, which is convenient for subsequent oil-water separation and recovery; in this step, the wastewater flowing out of the adsorption tower can be monitored in real time, and the oil content in the wastewater can be used to judge whether the modified PAN fiber is saturated with adsorption;

[0038] S33: Modified fiber regeneration: The desorbed modified PAN fiber was regenerated using low-pressure steam (0.3 MPa) at a temperature of 80° C. for 20 min.

[0039] S4: Post-treatment process: Use biological treatment and advanced oxidation processes to further treat the wastewater treated by the modified fiber treatment unit to reduce COD and BOD in the wastewater so that the wastewater meets the discharge standard or reuse water standard.

[0040] The preparation method of modified polyacrylonitrile (PAN) fiber in the above method is:

[0041] (1) Pretreatment: PAN fibers were cleaned to remove grease and impurities on the surface, and spray-cleaned. The fibers were dried by hot air blowing to ensure the reaction activity during the modification process. The hot air blowing temperature was 80 °C and the wind speed was 1 m / s.

[0042] (2) Acid washing and alkali washing: Use dilute hydrochloric acid to acid wash the PAN fiber to remove residual metal ions. The pH value of the acid washing solution is controlled at 3 and the acid washing time is 0.5 h. Then use sodium hydroxide solution to alkaline wash the fiber to increase the carboxyl and hydroxyl functional groups on the fiber surface to provide active sites for subsequent modification. The pH value of the alkaline washing solution is controlled at 10 and the alkaline washing time is 0.5 h. After the acid washing and alkaline washing are completed, it needs to be dried again at a drying temperature of 60 ° C for 1 h. After drying, it is stored in a dust-free environment to avoid re-absorption of dust and moisture.

[0043] (3) Chemical grafting: The dried PAN fiber obtained in step (2) is immersed in a 20% by weight acrylic acid (AA) solution, and an initiator ammonium persulfate (APS) is added, the amount of ammonium persulfate added is 0.5% by weight of the acrylic acid, and the grafting reaction is carried out at 65° C. for 3 hours, so that the acrylic acid is polymerized on the surface of the PAN fiber to form a graft chain, thereby obtaining a grafted fiber, which exhibits significantly increased hydrophilicity and adsorption capacity;

[0044] (4) Physical coating: Nano-silicon dioxide (SiO2) is coated on the surface of the grafted fiber by dip coating technology. 2 ), the modified PAN fiber can be obtained. During the coating process, the nano-SiO 2 The concentration of nano-SiO2 is 2% of the fiber mass, the impregnation temperature is 40℃, the pH value is 7, and the time is controlled at 30min to ensure that the nano-SiO2 2 Evenly distributed on the fiber surface. Nano-SiO 2 The addition of can not only increase the specific surface area of ​​the fiber, but also form a three-dimensional network structure to enhance the mechanical strength of the fiber, which can further improve the adsorption capacity and thermal stability of the fiber.

[0045] The modified PAN fiber obtained by the above method has high efficiency and reusable performance. The above modification method is a low-cost and environmentally friendly modification method, and has the potential for industrial-scale application. Through the characterization of the modified PAN fiber prepared above, its surface presents a porous structure with a pore size distribution between 20 and 50 nm, which increases the specific surface area of ​​the fiber by modification, up to 45 m 2 / g (the specific surface area of ​​unmodified PAN fiber is 12m 2 / g), thereby increasing the adsorption capacity and thus the adsorption performance of the fiber; carboxyl (-COOH) and hydroxyl (-OH) functional groups were successfully introduced on the surface of the modified PAN fiber, which can enhance the chemical affinity of the fiber to oil droplets and provide more adsorption sites for oil substances. Thermogravimetric analysis showed that the modified PAN fiber had good thermal stability and began to decompose at 350°C, while the initial decomposition temperature of the unmodified PAN fiber was only 280°C, which was much lower than that of the modified PAN fiber; the reason for the enhanced thermal stability was that the nano-SiO 2 Through testing, the modified PAN fiber has an adsorption capacity of 78 mg / g for oil, which is 3 times higher than that of the original PAN fiber. The modified PAN fiber has a better adsorption capacity for floating oil, dispersed oil, emulsified oil and dissolved oil.

[0046] After five cycles of adsorption-desorption, the adsorption capacity of the modified PAN fiber decreased by only 10%, indicating that the material has good regeneration performance and long-term application potential. The desorption process uses a simple low-pressure steam treatment, which is low-cost and easy to operate, making it suitable for industrial applications.

[0047] like Figure 1 As shown, this embodiment also provides an oily wastewater treatment system, including a wastewater storage tank 7, a filter tank 1 and a sedimentation tank 2 which are connected in sequence through pipelines; a modified fiber processing unit is connected to the sedimentation tank 2 through a pipeline, and a post-processing unit 4 is connected to the outlet of the modified fiber processing unit. The post-processing unit 4 is used to further process the wastewater to reduce COD and BOD in the wastewater, so that the wastewater meets the discharge standard or the reuse water standard.

[0048] The modified fiber processing unit includes two adsorption towers 3, the upper and lower ends of the adsorption towers 3 are wastewater inlet 31 and wastewater outlet 32, the adsorption towers 3 are filled with 3 layers of modified PAN fibers, the interlayer spacing is 5 cm, the thickness of each layer is 50 cm, and the filling void ratio of the modified PAN fibers is 75%; the lower end of the adsorption tower 3 is also provided with a filling port 33 for filling the modified PAN fibers, and the filling port 33 is also connected to a desorption unit 5, and the adsorption saturated modified PAN fibers can be transported to the desorption unit 5 for desorption, and a regeneration system 6 connected to the desorption unit 5 is also provided to achieve the regeneration of the modified PAN fibers and achieve the purpose of reuse. In addition, valves are provided on each pipeline, and a pump for transporting oily wastewater is also provided. The purpose of setting up two adsorption towers in this embodiment is to achieve continuous treatment of oily wastewater. In actual use, the first adsorption tower is selected to treat the oily wastewater, and the rest is reserved. When the modified PAN fiber in the first adsorption tower is saturated with adsorption, the second adsorption tower is used to adsorb the oily wastewater by adjusting the valve. At this time, the modified PAN fiber in the first adsorption tower can be discharged into the desorption unit and the regeneration system, and the modified PAN fiber can be refilled into the first adsorption tower to achieve continuous treatment of the wastewater.

[0049] The above method was used to treat the oily wastewater generated by a petrochemical enterprise. The oily wastewater generated by the petrochemical enterprise contained floating oil, dispersed oil and emulsified oil, with oil droplet sizes ranging from a few microns to hundreds of microns, a pH value of about 6.5, and a temperature of 28°C. After the above treatment, the oil content in the wastewater dropped from 800 mg / L after pretreatment to below 30 mg / L, meeting the discharge standard.

[0050] Example 2

[0051] Based on Example 1, the preparation method of modified polyacrylonitrile (PAN) fiber in this embodiment includes:

[0052] (1) Pretreatment: The PAN fibers were cleaned by ultrasonic cleaning to remove grease and impurities on the surface, and the fibers were dried by hot air blowing at a temperature of 120 °C and a wind speed of 2 m / s.

[0053] (2) Acid washing and alkali washing: Use dilute hydrochloric acid to acid wash PAN fiber, the pH value of the acid washing solution is controlled at 5, and the acid washing time is 1h; then use sodium hydroxide solution for alkali washing, the pH value of the alkali washing solution is controlled at 11, and the alkali washing time is 1h; after acid washing and alkali washing, dry at 80℃ for 2h, and store in a dust-free environment after drying to avoid re-absorption of dust and moisture.

[0054] (3) Chemical grafting: The dried PAN fiber obtained in step (2) is immersed in a 30% by mass acrylic acid (AA) solution, and an initiator ammonium persulfate (APS) is added, the amount of ammonium persulfate added is 1.0% by mass of acrylic acid, and the grafting reaction is carried out at 75°C for 4 hours to obtain a grafted fiber.

[0055] (4) Physical coating: Nano-silicon dioxide (SiO2) is coated on the surface of the grafted fiber by dip coating technology. 2 ), the modified PAN fiber can be obtained. During the coating process, the nano-SiO 2 The concentration is 5% of the fiber mass, the impregnation liquid temperature is 60°C, the pH value is 8, and the time is controlled at 60 minutes.

[0056] The modified PAN fiber prepared above was observed to have a porous structure on its surface, with pore sizes ranging from 20 to 50 nm and a specific surface area of ​​46 m 2 / g. Thermogravimetric analysis shows that the modified PAN fiber has good thermal stability and does not start to decompose until it reaches 350°C; through testing, the oil adsorption capacity of the modified PAN fiber in this embodiment reaches 80mg / g.

[0057] The modified PAN fiber prepared in this embodiment is used to treat the oily wastewater. The treatment process is the same as that in Example 1, and the wastewater comes from the same source as in Example 1. The collected oily wastewater contains floating oil, dispersed oil and emulsified oil. The oil droplet size ranges from a few microns to hundreds of microns. The pH value is 7.0, the temperature is 30°C, and the oil content is 800 mg / L. The wastewater is treated using the modified PAN fiber and process provided in this embodiment, and its oil content is reduced to below 30 mg / L, meeting the emission standards.

[0058] Example 3

[0059] Based on Example 1, the preparation method of modified polyacrylonitrile (PAN) fiber in this embodiment includes:

[0060] (1) Pretreatment: The PAN fibers were cleaned by ultrasonic cleaning to remove grease and impurities on the surface, and the fibers were dried by hot air blowing at a temperature of 100 °C and a wind speed of 1.5 m / s.

[0061] (2) Acid washing and alkali washing: Use dilute hydrochloric acid to acid wash the PAN fiber, the pH value of the acid washing solution is controlled at 4, and the acid washing time is 0.6h; then use sodium hydroxide solution for alkali washing, the pH value of the alkali washing solution is controlled at 10, and the alkali washing time is 0.8h; after the acid washing and alkali washing are completed, dry at 70℃ for 1.5h, and after drying, store in a dust-free environment to avoid re-absorption of dust and moisture.

[0062] (3) Chemical grafting: The dried PAN fiber obtained in step (2) is immersed in a 25% by mass acrylic acid (AA) solution, and an initiator ammonium persulfate (APS) is added. The amount of ammonium persulfate added is 0.8% of the mass of acrylic acid. The grafting reaction is carried out at 70°C for 3.5 hours to obtain a grafted fiber. (4) Physical coating: Nano-silicon dioxide (SiO2) is coated on the surface of the grafted fiber by dip coating technology. 2 ), the modified PAN fiber can be obtained. During the coating process, the nano-SiO 2 The concentration is 4% of the fiber mass, the impregnation liquid temperature is 50°C, the pH value is 7, and the time is controlled at 45 minutes.

[0063] The surface of the modified PAN fiber prepared above was observed to have a porous structure with a pore size distribution between 20 and 50 nm and a specific surface area of ​​45 m 2 / g. Thermogravimetric analysis shows that the modified PAN fiber has good thermal stability and does not start to decompose until the temperature reaches 350°C. Through testing, the oil adsorption capacity of the modified PAN fiber in this embodiment reaches 78 mg / g.

[0064] The modified PAN fiber prepared in this embodiment is used to treat the oily wastewater. The treatment process is the same as that in Example 1, and the wastewater comes from the same source as in Example 1. The collected oily wastewater contains floating oil, dispersed oil and emulsified oil. The oil droplet size ranges from a few microns to hundreds of microns. The pH value is 7.2, the temperature is 28°C, and the oil content is 780 mg / L. The wastewater is treated using the modified PAN fiber and process provided in this embodiment, and its oil content is reduced to below 30 mg / L, meeting the emission standards.

[0065] Example 4

[0066] The treatment process of oily wastewater provided in this embodiment includes:

[0067] S1, wastewater pretreatment: remove large solid impurities through screens or filters.

[0068] S2, the pretreated wastewater is transported to a sedimentation tank for gravity sedimentation and the pH value is adjusted to 8 to remove heavier oil droplets and suspended solids; a demulsifier is added at 6 ppm of the volume of the oily wastewater.

[0069] S3, the oily wastewater obtained in step S2 is transported to a modified fiber processing unit through a water pump; the following three steps are performed in the modified fiber processing unit:

[0070] S31: Adsorption: Select modified PAN fiber (prepared in the same manner as in Example 1) to treat wastewater, and fill the modified PAN fiber into an adsorption tower. The adsorption tower can be a commonly used adsorption tower in the field of wastewater treatment. Four layers of modified PAN fiber are filled in the adsorption tower, with a layer spacing of 10 cm and a thickness of each layer of 60 cm. During the filling process of the modified PAN fiber, the porosity is controlled between 85%, the temperature in the tower is controlled at 30° C., the hydraulic retention time is 60 min, and a downflow adsorption tower design is adopted;

[0071] S32: Desorption: The saturated modified PAN fiber is discharged into a desorption tower, water at a temperature of 60°C is selected as the desorption liquid, the desorption time is controlled at 45 minutes, and the flow rate of the desorption liquid is 1 m / s, so as to reduce the adsorption force between the oil droplets and the fiber, and make the desorbed oil droplets aggregate into large particles, which is convenient for subsequent oil-water separation and recovery; in this step, the wastewater flowing out of the adsorption tower is monitored in real time, and the oil content in the wastewater is used to judge whether the modified PAN fiber is adsorbed saturated;

[0072] S33: Modified fiber regeneration: The desorbed modified PAN fiber was regenerated with low-pressure steam (0.3 MPa) at a temperature of 120° C. for 40 min.

[0073] S4: Post-treatment process: Biological treatment and advanced oxidation processes can be used to further treat the wastewater treated by the modified fiber treatment unit to reduce COD and BOD in the wastewater so that the wastewater meets the discharge standard or reuse water standard.

[0074] The process provided in this embodiment is used to treat the oily wastewater. The source of the wastewater is the same as that in Example 1, except that the collection period is different. The collected oily wastewater contains floating oil, dispersed oil and emulsified oil. The oil droplet size ranges from a few microns to hundreds of microns. The pH value is 7.2, the temperature is 30°C, and the oil content is 790 mg / L. The wastewater is treated using the process provided in this embodiment, and its oil content is reduced to below 30 mg / L, meeting the emission standards.

[0075] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A process for treating oily wastewater, characterized in that: include: S1, pretreatment: remove large solid impurities by filtration; S2, subjecting the pretreated oily wastewater to gravity sedimentation and adjusting the pH value; for emulsified oily wastewater, a demulsifier needs to be added after gravity sedimentation; S3, Treatment of oily wastewater using modified PAN fiber: Fill 3-4 layers of modified PAN fiber in the adsorption tower, with a layer spacing of 5-10 cm and a thickness of 50-60 cm for each layer. During the filling process, the void ratio is controlled between 75-85%, and the temperature in the tower is controlled between 20-30°C. The preparation method of modified PAN fiber is as follows: S31, washing and drying the PAN fiber; S32, after acid washing and alkali washing of the PAN fiber, drying and storing in a dust-free environment; S33, soaking the dried PAN fiber obtained in step S32 in an acrylic acid solution, adding an initiator of ammonium persulfate, and performing a grafting reaction at 65-75° C. for 3-4 hours to obtain a grafted fiber; S34, the modified PAN fiber is obtained by coating nano-silica on the surface of the grafted fiber through the dip coating technology; During the coating process, the concentration of nano-SiO2 in the impregnation solution is 2-5% of the fiber mass, the impregnation solution temperature is 40-60°C, the pH value is 7-8, and the time is controlled at 30-60 minutes; S4, post-treatment process: further treat the wastewater after modified fiber treatment to make the wastewater meet the discharge standard or reuse water standard.

2. A process for treating oily wastewater according to claim 1, characterized in that: In step S31, the PAN fiber is cleaned by spraying or ultrasonic cleaning, and dried by hot air blowing. The temperature of the hot air is 80-120° C. and the wind speed is 1-2 m / s.

3. A process for treating oily wastewater according to claim 2, characterized in that: In step S32, the pickling solution during pickling is dilute hydrochloric acid or dilute sulfuric acid with a pH value of 3-5, and the pickling time is 0.5-1h; the alkaline washing solution during alkali washing is a sodium hydroxide solution with a pH value of 10-11, and the alkaline washing time is 0.5-1h; the drying temperature after pickling and alkali washing is 60-80°C, and the time is 1-2h.

4. A process for treating oily wastewater according to claim 3, characterized in that: In step S33, the concentration of the acrylic acid solution is 20-30%, and the amount of ammonium persulfate added is 0.5-1.0% of the mass of the acrylic acid.

5. A process for treating oily wastewater according to claim 1 or 4, characterized in that: In step S1, filtering is performed through a grid or a filter; in step S2, the pH value is adjusted to 3-9; and the amount of demulsifier used is 6-10 ppm of the volume of the oily wastewater.

6. A process for treating oily wastewater according to claim 5, characterized in that: When the oily wastewater is treated in step S3, the oily wastewater stays in the adsorption tower for 45 to 60 minutes.

7. A process for treating oily wastewater according to claim 6, characterized in that: Step S3 also includes: discharging the adsorption saturated modified PAN fiber into a desorption tower for desorption treatment, selecting 40-60° C. water as the desorption liquid, the desorption time is 30-45 min, and the flow rate of the desorption liquid is 0.5-1 m / s; and then regenerating the desorbed modified PAN fiber with low-pressure steam.

8. A system for treating oily wastewater using the treatment process according to any one of claims 1 to 7, characterized in that: It comprises a wastewater storage tank (7), a filtering tank (1) and a sedimentation tank (2) which are connected in sequence via pipelines; a modified fiber processing unit is connected to the sedimentation tank (2) via a pipeline, and a water outlet of the modified fiber processing unit is connected to a post-processing unit (4); The modified fiber processing unit comprises 2 to 3 adsorption towers (3), wherein the upper and lower ends of the adsorption towers (3) are wastewater inlets (31) and wastewater outlets (32), and the adsorption towers (3) are filled with 3 to 4 layers of modified PAN fibers, wherein the interlayer spacing is 5 to 10 cm, the thickness of each layer is 50 to 60 cm, and the filling void ratio of the modified PAN fibers is 75 to 85%. The lower end of the adsorption tower (3) is also provided with a filling port (33) for filling the modified PAN fibers, and the filling port (33) is also connected to a desorption unit (5), and a regeneration system (6) is provided in connection with the desorption unit (5).

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