Coalescence-selective filtration-deep bed filtration efficient oil-water separation system and method for separating oil and water

Abstract

The application provides a coalescence-selective filtration-deep bed filtration efficient oil-water separation system, which comprises a coalescence system, a selective filtration system and a deep bed filtration system, oil-containing wastewater enters a coalescer, and small oil beads are coalesced into larger oil beads through wetting coalescence and collision coalescence; the coalesced wastewater enters a selective filter, and oil beads and water flow out through oil channels and water channels respectively, so that preliminary separation is realized; the water after preliminary separation enters a deep bed filter, so that deep separation is realized; through the combined process of coalescence, selective filtration and deep bed filtration, efficient separation of oil and water and up-to-standard discharge or reuse of water are realized; and the system has the advantages of high treatment efficiency, low energy consumption, low carbon emission, recycling of oil and water, or up-to-standard discharge of water.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of special wetting oil-water separation device, and particularly relates to a high-efficiency oil-water separation system based on coalescence-selective filtration-deep bed filtration and a method for separating oil and water. BACKGROUND

[0002] Oil-containing wastewater is widely sourced from industries such as petroleum and chemical industry and mechanical manufacturing. Discharging untreated oil-containing wastewater not only causes serious harm to the environment, but also wastes oil and water resources. Traditional oil-containing wastewater treatment processes mainly include gravity sedimentation, air flotation, membrane separation, adsorption, biochemical method, chemical coagulation method, etc. These separation methods have certain shortcomings, such as high difficulty in resource recycling, large land occupation, low separation efficiency, high energy consumption, large amount of reagent, and easy membrane pollution. In addition, it is difficult to effectively separate emulsified oil-containing wastewater by using conventional physical or chemical methods due to small oil droplet size and high stability. The traditional separation method is gravity sedimentation, which needs to wait for oil droplets to float on the water surface, and oil is pumped away from the top of the gravity separation zone, and water is discharged from the bottom of the gravity separation zone. Therefore, the efficiency is low, and high-efficiency continuous oil-water separation cannot be achieved. In addition, the treatment effect of the mixed liquid with large oil droplet size is limited. For example, patent CN202410941573.8 discloses an oil-containing wastewater treatment system, which comprises a pre-filtering module for removing solid particles; a coalescence separation module for realizing water-oil separation; a conveying module for feeding materials; a base for supporting and installing the pre-filtering module and the coalescence separation module; the conveying module is connected with the pre-filtering module at the feeding end; and the pre-filtering module is connected with the coalescence separation module at the discharging end. After the oil-containing wastewater is treated by the coalescence separation module, the oil is separated by gravity sedimentation, and the oil droplets need to float on the water surface. The oil is pumped away from the top of the gravity separation zone, and the water is discharged from the bottom of the gravity separation zone. Therefore, high-efficiency continuous oil-water separation cannot be achieved.

[0003] For example, patent CN202322230909.3 discloses an oily wastewater treatment device, which comprises a pre-filtering pool, a slag collecting box is arranged on the left side of the pre-filtering pool, a water pump is fixed in the pre-filtering pool, an oil-water separation pool is fixed on the right side of the pre-filtering pool, a water tank and an oil tank are arranged below the oil-water separation pool, and a backwashing device is connected to the water tank and the pre-filtering pool. The pre-filtering pool is composed of a coarse grid, a fine grid, an ultrasonic transducer and a sand filter layer. The oily wastewater treatment device adopts a double filtration mechanism, can filter and separate impurities in the oily wastewater, avoids pipeline blockage caused by impurities, cooperates with a circulating backwashing mechanism, can use separated water to flush the filtration mechanism, avoids blockage of the filtration mechanism, ensures normal operation of the device, and ensures oil-water separation effect through a double oil-water separation mechanism. However, the separated water still contains low-concentration oil, and the oil concentration of the effluent cannot meet the requirements of the Discharge Standard of Pollutants for Petroleum Refining Industry (GB31570-2015), and cannot be applied to actual projects.

[0004] Therefore, it is a technical problem to be solved to develop a treatment device for emulsified oily wastewater with small oil droplet size, high stability and difficult to be effectively treated by direct gravity separation. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a coalescence-selective filtration-deep bed filtration efficient oil-water separation system, which can efficiently and continuously separate oil and water, realize recycling of oil resources and discharge or reuse of water resources. The oily wastewater treatment system of the present application increases the oil droplet size through coalescence process, realizes physical separation of oil and water through double-channel selective filtration, further purifies water quality through deep bed filtration, realizes recycling of backwashing water, finally obtains water quality meeting the discharge standard or reuse, and reduces energy consumption and carbon emissions. The coalescer is used to coalesce small oil droplets in the oily wastewater into larger oil droplets, improving the subsequent filtration efficiency. The double-channel selective filter comprises a water channel of underwater super-hydrophilic super-oleophobic medium and an oil channel of super-hydrophobic super-oleophilic medium, which is used to realize physical separation of oil and water, and the oil resources can be recycled. The deep bed filter is used to further remove low-concentration oil in water, ensure that the water quality meets the standard, and the oil concentration of the effluent meets the requirement of less than 5 mg / L in the Discharge Standard of Pollutants for Petroleum Refining Industry (GB31570-2015). The recycling system returns the backwashing water of the deep bed filter to the coalescer, realizing recycling treatment.

[0006] Specifically, the coalescence-selective filtration-deep bed filtration efficient oil-water separation system provided by the present application comprises a coalescence system, a selective filtration system and a deep bed filtration system.

[0007] Further, the coalescence system comprises a coalescer, and the coalescer is internally filled with a mixture of super-hydrophobic super-oleophilic medium and underwater super-hydrophilic super-oleophobic medium.

[0008] Further, the mass ratio of the super-hydrophobic super-oleophilic medium and the super-hydrophilic underwater super-oleophobic medium is 0.9-1.1:0.9-1.1, a wetting gradient from super-oleophilic to super-oleophobic is constructed, and wetting coalescence and collision coalescence are formed.

[0009] The wetting gradient forms an unbalanced force on the oil droplets, which not only enhances the demulsification capacity of the coalescer, but also reduces the head loss to facilitate the gradual coalescence and separation of the oil droplets, thereby realizing the effective increase of the particle size of the emulsified oil in the wastewater. The super-oleophilic medium attracts and coalesces the tiny oil droplets through hydrophobic force, realizing demulsification; the super-oleophobic medium prevents the coalesced oil droplets from being dispersed again by using its surface properties, reducing oil loss during the treatment process.

[0010] Wetting coalescence is that the oil droplets in the liquid phase continuously adhere, coalesce and spread on the surface of the super-hydrophobic super-oleophilic medium, so that an oil film is formed on the surface of the medium, and finally the oil droplets are separated from the medium under the action of fluid drag force and buoyancy. Collision coalescence is that the super-hydrophobic super-oleophilic medium and the super-hydrophilic underwater super-oleophobic medium are mixed to form a wetting gradient from super-oleophilic to super-oleophobic, which forms an unbalanced force on the oil droplets and a tortuous channel, improves the flow field, increases the probability of collision between oil droplets, and promotes the gradual coalescence and separation of oil droplets.

[0011] Further, the preparation steps of the super-hydrophilic underwater super-oleophobic medium are as follows:

[0012] S1: 190-210g of quartz sand (QS) and 450-550ml of NaOH solution are mixed and stirred at 600-700r / min at 20-30℃ for 22-26h to obtain a sand sample; impurities are removed and the sand surface is etched to produce more micron and nanometer structures.

[0013] S2: The treated sand sample is washed with 160-220ml of anhydrous ethanol for 3 times to remove residual NaOH and dried at 65-70℃ for 11-13h.

[0014] Further, the preparation steps of the super-hydrophobic super-oleophilic medium are as follows:

[0015] (1) 190-210g of super-hydrophilic underwater super-oleophobic quartz sand, 180-220ml of N,N-dimethylformamide (DMF), 3-6ml of dodecyltrimethoxysilane (DTMS), 3-6ml of hexadecyltrimethoxysilane (HDTMS) and 3-6ml of octadecyltrichlorosilane (OTS) are mixed in a beaker, and stirred at 550-750r / min at room temperature for 22-26h.

[0016] (2) The sample is washed with 190-210 ml of anhydrous ethanol for 3 times until the pH value is neutral, and is dried in an oven at 50-70 DEG C for 10-14 h to prepare the super-hydrophobic super-oleophilic quartz sand DTMS-HDTMS-OTS@QS.

[0017] The super-hydrophobic super-oleophilic quartz sand is prepared by grafting silane coupling agent on the surface of the previously prepared super-hydrophilic underwater super-oleophobic quartz sand through silanization reaction.

[0018] The super-hydrophobic super-oleophilic medium is modified by the hydrophobic medium combined with three different silane coupling agents, which not only has stronger hydrophobicity, but also has a long-chain and broken-chain surface structure due to the different chain lengths of the three silane coupling agents, so that the oil film formed on the surface of the super-hydrophobic super-oleophilic medium is more stable and is not easy to fall off under the action of water force, thereby forming more stable super-hydrophobic super-oleophilic property in oil-water separation.

[0019] After the surface is grafted with octadecyltrichlorosilane (OTS) silane coupling agent, the quartz sand surface is grafted with many long alkyl chains, which can adsorb and quickly pass through oil droplets, while effectively intercepting water molecules, realizing the permeation of oil and the interception of water.

[0020] Further, the selective filtration system is a double-channel filter, which includes a water channel and an oil channel, both of which are independently and parallelly arranged, the water channel is filled with super-hydrophilic underwater super-oleophobic medium, which has high affinity for water and high repulsion for oil; the oil channel is filled with super-hydrophobic super-oleophilic medium, which has high affinity for oil and high repulsion for water. The super-hydrophilic underwater super-oleophobic medium in the water channel preferentially adsorbs water molecules to form a continuous water flow channel, while repelling oil droplets to prevent them from passing through.

[0021] The super-hydrophobic super-oleophilic medium in the oil channel preferentially adsorbs oil droplets to form a continuous oil flow channel, while repelling water molecules to prevent them from passing through.

[0022] The super-hydrophilic underwater super-oleophobic medium filled in the water channel (the same as the super-hydrophilic underwater super-oleophobic medium in the coalescer): after the quartz sand is etched by NaOH, a micro-nano scale rough structure appears on the surface, and more hydrophilic groups of hydroxyl (-OH) are generated on the surface, which can adsorb and quickly pass through water molecules, while effectively intercepting oil droplets, realizing the permeation of water and the interception of oil.

[0023] The super-hydrophobic super-oleophilic medium filled in the oil channel (the same as the super-hydrophobic super-oleophilic medium in the coalescer): after the surface is grafted with octadecyltrichlorosilane (OTS) silane coupling agent, the quartz sand surface is grafted with many long alkyl chains, which can adsorb and quickly pass through oil droplets, while effectively intercepting water molecules, realizing the permeation of oil and the interception of water.

[0024] Further, the filter body in the deep bed filtration system is a deep bed structure, and is filled with a stimulus-responsive wetting medium inside, and the filter medium has the ability to convert between super-oleophilicity and super-oleophobicity.

[0025] Further, the stimulus-responsive wetting medium is a pH-responsive switchable wetting medium, and the preparation steps are as follows:

[0026] Step one: 180-220 g of quartz sand is cleaned with 180-220 ml of ethanol and 180-220 ml of deionized water for 3 times, 13-16 min each time, and is dried in a 70-90°C oven for 11-13 h to obtain pretreated quartz sand;

[0027] Step two: 5-7 mL of 3-(aminopropyl)triethoxysilane (APTES) and 1-3 mL of 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS) are dissolved in 180-220 mL of n-heptane, and the mixture is stirred at 50-70°C for 2.5-3.5 h to obtain a mixed solution;

[0028] Step three: 180-220 g of pretreated quartz sand is added to the mixed solution prepared in step two, and is stirred and mixed at 550-750 r / min for 25-35 min to obtain modified quartz sand;

[0029] Step four: the modified quartz sand is dried at 70-90°C for 11-13 h to obtain a pH-responsive switchable wetting medium APTES-FOTS@QS.

[0030] APTES provides the hydrophilic characteristics of the material, and FOTS provides the hydrophobic characteristics of the material.

[0031] Wetting conversion mechanism: during the filtration stage, when filtering oil in low-concentration oil-containing wastewater, an alkaline solution with pH≈10 can be used to convert the surface of the medium to super-hydrophobic super-oleophilic properties in advance. When pH≈10, the surface of the medium is super-hydrophobic super-oleophilic, a small amount of oil is adsorbed on the surface of the medium, water is discharged through the deep bed filter to meet the discharge standard, and the purpose of meeting the discharge standard of oil-containing wastewater is achieved. During the backwashing stage, an acid solution with pH≈2 can be used to convert the surface of the medium to super-hydrophilic underwater super-oleophobic properties. When pH≈2, the surface of the medium is super-hydrophilic underwater super-oleophilic, and the oil adsorbed on the surface of the medium is desorbed through backwashing. The backwashing water of the deep bed filter returns to the coalescer through the circulation system, realizing cyclic treatment and reducing water resource waste.

[0032] The application also provides a method for separating oil and water by using the coalescence-selective filtration-deep bed filtration high-efficiency oil-water separation system as described above.

[0033] The coalesced wastewater enters the double-channel selective filter, and the oil droplets and water flow out through the oil channel and the water channel respectively, realizing preliminary separation, and the selective separation efficiency reaches 99.99%, and the separated oil can be recycled.

[0034] The preliminarily separated water enters the deep bed filter, further removes low-concentration oil, realizes deep separation, and ensures that the water quality meets the discharge standard. The oil concentration of the deep bed filter effluent meets the requirement of less than 5 mg / L in the "Petroleum Refining Industrial Pollutant Discharge Standard" (GB31570-2015). The backwashing water of the deep bed filter returns to the coalescer through the circulation system, realizing cyclic treatment and reducing water resource waste.

[0035] Compared with the prior art, the application has the following advantages and positive effects:

[0036] 1. The application is suitable for emulsified oil-containing wastewater with colloidal stability, and the oil droplets are small in size, stable and cannot be directly separated by gravity. In the coalescer, two coalescence media, super oil-wet and super oil-repellent, are filled to form a wettability gradient, and a coalescence separator with a wettability gradient is constructed to realize demulsification and increase the size of oil droplets. For oil-water mixture with larger oil droplets, a double-channel filter with selective filtration for oil and water is constructed, so that the water phase flows out from the water channel and the oil flows out from the oil channel, realizing efficient and continuous separation of oil and water. The water channel is filled with super hydrophilic and super oleophobic underwater medium, and the oil channel is filled with super hydrophobic and super oleophilic medium. For low-concentration oil-containing wastewater, a deep bed filter with wettability conversion is constructed to solve the problems of low backwashing efficiency and easy clogging in the deep bed filtration process, realizing the dual efficiency of filtration and backwashing. The filter medium filled in the filter can be converted between super oil-wet and super oil-repellent through stimulus response, and the medium surface is converted to super oil-wet in the filtration stage to realize strong oil absorption performance, and the medium surface is converted to super oil-repellent in the backwashing stage to make the oil adhered to the medium surface easy to fall off.

[0037] 2.The coalescing separator with wettability gradient provided by the present application can effectively solve the treatment problem of colloidal stability emulsified oily wastewater, improve the oil-water separation efficiency, reduce energy consumption and environmental pollution, and has significant social, economic and environmental benefits. The oil-water efficient continuous separation device and method based on the double-channel filtration technology realizes the efficient continuous separation of oil and water through the selective filter medium and the optimized filter structure characteristics. The technology has the advantages of high separation efficiency, high treatment capacity and wide application range, and has wide application prospects in industrial production, environmental protection and daily life. The deep bed filter with wettability conversion function and the oil-water separation method provided by the present application realize the conversion of the filter medium between super oil-wet and super oil-repellent through the stimulus response mechanism, and solve the problems of low backwashing efficiency and easy blocking in the traditional deep bed filtration process. The technology has the advantages of high filtration efficiency, good backwashing effect and low operation cost, and has wide application prospects in the field of low-concentration oily wastewater treatment.

[0038] 3.The coalescence-filtration-deep bed filtration treatment system provided by the present application realizes the efficient separation of oil and water and the discharge or reuse of water quality up to standard through the combined process of coalescence, selective filtration and deep bed filtration, realizes the systematic treatment of actual oily wastewater from "cradle" to "tomb". The system has the advantages of high treatment efficiency, low energy consumption, low carbon emission, recycling of oil and water, or water up to standard discharge, realizes the circular economy benefit of "up to standard discharge and comprehensive utilization", and the research results will have very positive significance in promoting the resource utilization of wastewater, promoting the transformation and upgrading of industrial wastewater treatment technology, improving the efficiency of industrial wastewater treatment, and promoting the development of industrial wastewater treatment industry. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a schematic diagram of the coalescence-selective filtration-deep bed filtration efficient oil-water separation system of example 1;

[0040] Figure 2 is a front view of the coalescence system of example 1;

[0041] Figure 3 is a left view of the coalescence system of example 1;

[0042] Figure 4 is a schematic diagram of the double-channel selective filtration system of example 1;

[0043] Figure 5 is a schematic diagram of the deep bed filtration system of example 1;

[0044] In the figure: 1-coalescence system; 2-selective filtration system; 3-deep bed filtration system; 4-water inlet; 5-oil outlet; 6-water outlet; 7-backwash water inlet; 8-water inlet; 9-mixed filter material; 10-distribution plate; 11-water outlet; 12-support; 13-mixed filter material; 14-water inlet; 15-support; 16-oil outlet; 17-ultrahydrophobic and superoleophilic medium; 18-water inlet; 19-ultrahydrophilic and subaqueous superoleophobic medium; 20-water outlet; 21-support; 22-filtration column; 23-filter material layer; 24-supporting layer; 25-distribution layer; 26-pressure measuring tube; 27-filtration water inlet; 28-filtration overflow or backwash water outlet; 29-backwash water inlet; 30-rotameter; 31-filtered water. DETAILED DESCRIPTION

[0045] The present application can be better understood according to the following examples. However, it will be readily apparent to those skilled in the art that the examples described are merely illustrative of the present application and should not be considered as limiting the scope of the present application as described in the claims.

[0046] The technical solutions of the present application are further described below in combination with examples.

[0047] Example 1

[0048] This example provides a coalescence-selective filtration-deep bed filtration efficient oil-water separation system, as shown in Figure 1As shown, including coalescing system 1, double-channel selective filtration system 2 and deep bed filtration system 3, oil-containing wastewater from the water inlet 4 into the coalescing system 1, the coalescer of coalescing system 1 is filled with two kinds of coalescing medium of super oil-wet and super oil-repellent, forming a wettability gradient, building a coalescing separator with wettability gradient, realizing the purpose of demulsification and increasing oil bead size, in order to make the actual oil-containing wastewater to achieve discharge or reuse, need to build coalescing-selective filtration-deep bed filtration efficient oil-water separation system. First, the emulsified oil-containing wastewater with oil bead size less than 10 μm enters the coalescing system 1 filled with superhydrophobic superoleophilic and superhydrophilic underwater superoleophobic two kinds of coalescing medium, under the action of wettability gradient, small particle size oil beads gradually form large oil beads with particle size greater than 100 μm through wetting coalescence and collision coalescence, which is convenient for subsequent oil-water separation. Subsequently, the oil-containing wastewater flows out of the coalescing system 1 into the selective filtration system 2 to realize efficient continuous separation of oil and water, the oil flows out from the oil outlet 5 filled with superhydrophobic superoleophilic filter medium for recycling, and the wastewater containing a small amount of oil flows into the deep bed filtration system 3 from the water channel filled with superhydrophilic underwater superoleophobic medium on the other side. Finally, the low-concentration oil-containing wastewater from the double-channel selective filtration system 2 flows into the deep bed filtration system 3 for deep separation. In the filtration stage, an alkaline solution with pH≈10 can be used in advance to change the surface of the medium to superhydrophobic superoleophilic properties, adsorb a small amount of oil on the surface of the medium, and water flows out through the water outlet 6 to achieve the requirement of less than 5 mg / L in the “Petroleum Refining Industrial Pollutant Discharge Standard” (GB31570-2015). In the backwashing stage, an acid solution with pH≈2 can be used to change the surface of the medium to superhydrophilic underwater superoleophobic properties, and the oil adsorbed on the surface of the medium is desorbed by water inlet through backwashing inlet 7. The backwashing water of the deep bed filter returns to the coalescer through the circulation system, realizing cyclic treatment and reducing water resource waste.

[0049] The coalescing system 1 of the present application is as shown in Figure 2 and Figure 3 For emulsified oil-containing wastewater with colloidal stability, the oil bead size is small, the stability is high, and it cannot be directly separated by gravity. In the coalescer, superhydrophobic superoleophilic and superhydrophilic underwater superoleophobic two kinds of mixed filter material 9 are filled to build a coalescing separator with wettability gradient, realizing the purpose of demulsification and increasing oil bead size.

[0050] First, the emulsified oil-containing wastewater with oil bead size less than 10 μm enters the coalescing system from the water inlet 8, and the water distribution plate 10 is used to realize uniform water distribution of the coalescing system. Finally, under the action of the wettability gradient formed by the mixed filter material 9, small particle size oil beads gradually form large oil beads with particle size greater than 100 μm through wetting coalescence and collision coalescence, and then flow out of the coalescing system from the water outlet 11.

[0051] The double-channel selective filtration system 2 of the present application is as shown in Figure 4As shown, the oil-containing wastewater treated by the coalescing system flows into the selective filtration system from the water inlet 18 to achieve efficient and continuous separation from water. The oil in the oil-water mixture flows out of the oil outlet 16 through the oil channel filled with super-hydrophobic super-oleophilic medium 17 for recycling, and the wastewater containing a small amount of oil flows out of the water outlet 20 through the super-hydrophilic underwater super-oleophobic medium 19 in the double-channel selective filtration system.

[0052] The deep bed filtration system 3 of the present application is as shown Figure 5 As shown, in order to solve the problems of low backwashing efficiency and easy clogging of the deep bed filtration process, a deep bed filter with wettability conversion is constructed to achieve the purpose of high efficiency of filtration and backwashing. The filter medium filled in the filter can be converted between super-oleophilicity and super-oleophobicity through pH stimulus response, and the super-oleophilicity is converted to achieve strong oil absorption performance in the filtration stage, and the super-oleophobicity is converted to make the oil adhered to the surface of the medium easy to fall off in the backwashing stage.

[0053] First, the low-concentration oil-containing wastewater treated by the double-channel selective filtration system enters the deep bed filtration system from the filtration water inlet 27. In the filtration stage, when filtering the oil in the low-concentration oil-containing wastewater, an alkaline solution with pH≈10 can be used in advance to convert the medium surface of the filter material layer 23 to super-hydrophobic super-oleophilic properties, the medium adsorbs a small amount of oil on the medium surface, and the water is filtered out through the filtered water 31 for discharge, achieving the purpose of discharging the oil-containing wastewater up to the standard. In the backwashing stage, an acid solution with pH≈2 can be used to convert the medium surface of the filter material layer 23 to super-hydrophilic underwater super-oleophobic properties, and the oil adsorbed on the medium surface of the filter material layer 23 is desorbed by the backwashing water inlet 29, and the backwashing water of the deep bed filter returns to the coalescing system through the filtration overflow or backwashing water outlet 28, achieving cyclic treatment and reducing water resource waste.

[0054] Example 2

[0055] The present embodiment provides a method for separating oil and water using the coalescing-selective filtration-deep bed filtration efficient oil-water separation system of Example 1.

[0056] First, the emulsified oil-containing wastewater with oil droplets smaller than 10 μm and a concentration of 200 g / L enters the coalescer, and under the action of the wettability gradient, the small oil droplets are coalesced into larger oil droplets with a particle size greater than 100 μm through wettability coalescence and collision coalescence. The coalescing separator with wettability gradient is constructed, and compared with the coalescer filled with only a single special wettability medium, the oil coalescing performance is improved by 60%;

[0057] Subsequently, the coalesced oily wastewater enters the double-channel selective filter, and the oil and water flow out through the oil channel and the water channel respectively, realizing preliminary separation with a separation efficiency as high as 99.99%, and the separated oil can be recycled. At this time, the oil concentration in the oily wastewater is 20 mg / L, which does not meet the requirement of less than 5 mg / L in the Discharge Standard of Pollutants for Petroleum Refining Industry (GB31570-2015). Therefore, a deep bed filtration system needs to be used for treatment to meet the discharge standard or for recycling.

[0058] Finally, the low-concentration oily wastewater separated by the double-channel selective filtration system enters the deep bed filtration system to further remove a small amount of oil in the oily wastewater, realize deep separation, and the oil concentration of the deep bed filtration effluent meets the requirement of less than 5 mg / L in the Discharge Standard of Pollutants for Petroleum Refining Industry (GB31570-2015), and the water can be discharged or recycled. The backwashing water of the deep bed filtration system can be returned to the coalescer for recycling, reducing water resource waste.

[0059] In summary, the present application is directed to the oily wastewater with small oil droplet size, high stability and unable to be directly separated by gravity, a coalescence separator with a wettability gradient is constructed to realize the purposes of demulsification and increasing the oil droplet size, a double-channel filter with selective filtration of oil and water is constructed to make the water phase flow out from the water channel and the oil flow out from the oil channel, realizing efficient and continuous separation of oil and water. In view of the problems of low backwashing efficiency and easy clogging of the deep bed filtration process, a deep bed filter with wettability conversion is constructed to realize the purposes of high efficiency of filtration and backwashing. The filter medium filled in the filter can be converted between super-oleophilicity and super-oleophobicity through stimulus response, and the super-oleophilicity is converted to realize strong oil absorption performance in the filtration stage, and the super-oleophobicity is converted to make the oil adhered to the surface of the medium easily fall off in the backwashing stage.

[0060] The technology has the advantages of high filtration efficiency, good backwashing effect and low operation cost, and has a wide application prospect in the field of actual oily wastewater treatment.

[0061] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A coalescence - selective filtration - deep bed filtration high efficiency oil water separation system characterized in that, The system comprises a coalescing system, a selective filtration system and a deep bed filtration system; The coalescing system comprises a coalescer filled with a mixture of super-hydrophobic super-oleophilic medium and super-hydrophilic sub-aqueous super-oleophobic medium; The mass ratio of the super-hydrophobic super-oleophilic medium and the super-hydrophilic sub-aqueous super-oleophobic medium is 0.9-1.1:0.9-1.1, a wetting gradient from super-oleophilic to super-oleophobic is formed, and wetting coalescence and collision coalescence are formed; The selective filtration system is a double-channel filter comprising a water channel and an oil channel, which are independent and parallel to each other, the water channel is filled with super-hydrophilic sub-aqueous super-oleophobic medium, and the oil channel is filled with super-hydrophobic super-oleophilic medium; The filter body of the deep bed filtration system is in a deep bed structure and filled with a stimulus-responsive wetting medium, the stimulus-responsive wetting medium is a pH-responsive switchable wetting medium, and the filter medium has the ability to switch between super-oleophilic and super-oleophobic.

2. The coalescence-selective filtration-deep bed filtration efficient oil-water separation system according to claim 1, characterized in that, The preparation steps of the super-hydrophilic sub-aqueous super-oleophobic medium are as follows: S1: 190-210g of quartz sand and 450-550ml of NaOH solution are mixed at 20-30℃ with stirring at 600-700r / min for 22-26h to obtain a sand sample; S2: the treated sand sample is washed with 160-220ml of anhydrous ethanol for 3 times to remove residual NaOH and dried at 65-70℃ for 11-13h.

3. The coalescence-selective filtration-deep bed filtration efficient oil-water separation system according to claim 2, characterized in that, The preparation steps of the super-hydrophobic super-oleophilic medium are as follows: (1) 190-210g of super-hydrophilic sub-aqueous super-oleophobic quartz sand, 180-220ml of N,N-dimethylformamide, 3-6ml of dodecyltrimethoxysilane, 3-6ml of hexadecyltrimethoxysilane and 3-6ml of octadecyltrichlorosilane are mixed in a beaker, stirred at 550-750r / min at room temperature for 22-26h; (2) the sample is washed with 190-210ml of anhydrous ethanol for 3 times until the pH value is neutral, and dried in an oven at 50-70℃ for 10-14h to prepare super-hydrophobic super-oleophilic quartz sand DTMS-HDTMS-OTS@QS.

4. The coalescence-selective filtration-deep bed filtration efficient oil-water separation system according to claim 1, characterized in that, The stimulus-responsive wetting medium is a pH-responsive switchable wetting medium, and the preparation steps are as follows: Step one: 180-220g of quartz sand is ultrasonically cleaned with 180-220ml of ethanol and 180-220ml of deionized water for 3 times, 13-16min each time, and dried in a 70-90℃ oven for 11-13h to obtain pretreated quartz sand; Step two: 5-7mL of 3-(aminopropyl)triethoxysilane and 1-3mL of 1H,1H,2H,2H-perfluorooctyltrichlorosilane are dissolved in 180-220mL of n-heptane, stirred at 50-70℃ for 2.5-3.5h to obtain a mixed solution; Step three: 180-220g of pretreated quartz sand is added to the mixed solution prepared in step two, and stirred and mixed at 550-750r / min for 25-35min to obtain modified quartz sand; Step four: the modified quartz sand is dried at 70-90℃ for 11-13h to obtain a pH-responsive switchable wetting medium APTES-FOTS@QS.

5. The method for separating oil and water by the coalescence-selective filtration-deep bed filtration high efficiency oil-water separation system according to any one of claims 1-4, characterized in that, the oil-containing wastewater enters the coalescer, and the tiny oil droplets are coalesced into larger oil droplets through wetting coalescence and collision coalescence; the coalesced wastewater enters the double-channel filter, and the oil droplets and water flow out through the oil channel and the water channel respectively, realizing preliminary separation; the water after preliminary separation enters the deep bed filter, realizing deep separation.

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