A method for treating oily wastewater

Abstract

The present invention relates to a method for treating oily wastewater, belonging to the technical field of oily wastewater treatment. The present invention provides a method for treating oily wastewater. By using a ceramic membrane capable of switching surface properties, the produced water and flushing water in the coarsened oily wastewater can be treated simultaneously, and oil droplets therein can be deeply removed. The main technical concept is as follows: in the produced water after coarsening treatment, the oil droplet particles increase. By using a hydrophilic and oleophobic ceramic membrane for treatment, water can pass through quickly, and the oil phase can be intercepted; when its working mode is switched to hydrophobic and oleophilic, since the coarsened flushing water contains more oil droplets, the oil-water separation can be effectively carried out, enabling the oil droplets to permeate through the membrane layer, thus realizing the re-treatment of the flushing water.

Description

Technical Field

[0001] The present invention relates to a method for treating oily wastewater, belonging to the technical field of oily wastewater treatment. Background Art

[0002] Researchers have developed many methods for treating oil-water mixtures, such as air flotation, oil-absorbing materials, and electrocoalescence. However, since it is difficult for air flotation and oil-absorbing materials to treat oil-in-water emulsions and electrocoalescence requires a large amount of electric energy, the separation and recovery of oil-in-water emulsions face great challenges.

[0003] In the prior art, a method for treating oily wastewater by coalescence has been disclosed. This method utilizes the characteristic that the affinities of oil and water phases for the coalescence material are very different. When oily sewage passes through the oilophilic coalescence material, fine oil particles in the water are intercepted and attached to the surface or pores of the material. The intercepted oil droplets wet and spread on the material surface, and further collide and coalesce with surrounding oil particles, and the oil droplets gradually coarsen. When the buoyancy of the oil droplets is greater than the adhesion ability between oil and solid, the oil particles peel off from the solid surface and float for separation. However, during the conventional coalescence treatment process, the filler needs to be regenerated and rinsed, and thus, a rinsing liquid with a high oil content will be produced during rinsing, and there is still a problem of secondary pollution. At the same time, the wastewater after coalescence still needs to be separated by a suitable oil-water separation method to separate larger oil droplets therein.

[0004] On the other hand, in the prior art, a technology for treating wastewater by using a ceramic membrane has also been disclosed. Adjusting the wettability and pore size of the membrane is the key to preparing an oil-water separation membrane. However, in some special cases, oil-in-water and water-in-oil emulsions will transform or coexist with each other. When the initial oil-water ratio is 1:9, the feed is a water-in-oil emulsion. Since most of the water is filtered by the membrane, the feed gradually becomes an oil-in-water emulsion. In this case, a membrane with a single wettability is no longer applicable. Summary of the Invention

[0005] The technical problem solved by the present invention is that the existing coalescence oil-water separation method has a problem of secondary pollution of oil-containing rinsing water during the regeneration process. The present invention provides a method for treating oily wastewater. By using a ceramic membrane capable of switching surface properties, the produced water and rinsing water in the coalesced oily wastewater can be treated simultaneously, and oil droplets therein can be deeply removed. The main technical concept is as follows: in the produced water after coalescence treatment, the oil droplet particles increase. By using a hydrophilic and oleophobic ceramic membrane for treatment, water can pass through quickly, and the oil phase can be intercepted. When its working mode is switched to hydrophobic and oleophilic, since the coalesced rinsing water contains more oil droplets, oil-water separation can be effectively carried out on it, and the oil droplets can permeate through the membrane layer, realizing the re-treatment of the rinsing water.

[0006] The technical solution is:

[0007] A method for treating oily wastewater, comprising the following steps:

[0008] Perform flocculation treatment on the oily wastewater to remove large particle suspended solids;

[0009] Treat the supernatant after flocculation treatment through a coalescence column filled with packing to increase the oil droplets;

[0010] Perform oil-water separation treatment on the effluent of the coalescence column using a ceramic membrane treated with a first regulator, so that water permeates through the membrane layer;

[0011] Use a flushing liquid to flush the used coalescence column to obtain flushing wastewater, and perform oil-water separation treatment on the flushing wastewater using a ceramic membrane treated with a second regulator, so that oil permeates through the membrane layer.

[0012] The COD content in the described oily wastewater is 100 - 5000 mg / L, and the oil content is 10 - 2000 mg / L.

[0013] The ceramic membrane treated with the first regulator has superhydrophilic and underwater superoleophobic properties.

[0014] The ceramic membrane treated with the second regulator has superhydrophobic and superoleophilic properties.

[0015] The described first regulator is an acidic solution.

[0016] The described second regulator is an alcohol solvent.

[0017] The described packing is selected from one or a mixture of several of polypropylene fiber, expanded polytetrafluoroethylene material, and surface-hydrophobic-treated inorganic oxide particles.

[0018] The flocculant used in the described flocculation treatment is ferric chloride, polyaluminum chloride, aluminum chloride, aluminum sulfate, or anionic polyacrylamide.

[0019] The dosage of the described flocculant is 100 - 500 mg / L.

[0020] The preparation method of the described ceramic membrane comprises the following steps: prepare a tris(hydroxymethyl)aminomethane solution, add dopamine, copper sulfate, and hydrogen peroxide and mix evenly, then immerse the ceramic membrane in the mixed solution for reaction, take it out and immerse it in a silver nitrate solution, and then immerse it in a mixed solution containing methylvinyl dimethoxysilane, tridecyl 2-methyl-2-propenoate, and dimethylaminoethyl methacrylate, add an initiator for reaction, and take it out and dry after the reaction.

[0021] The concentration of the tris(hydroxymethyl)aminomethane solution is 20 - 500 mM, and dopamine, copper sulfate, and hydrogen peroxide are added so that their concentrations are 1 - 5 mg / mL, 1 - 50 mM, and 5 - 50 mM respectively; the concentration of the silver nitrate solution is 0.05 - 0.2 M;

[0022] The concentrations of methylvinyldimethoxysilane, tridecyl 2-methyl-2-propenoate, and dimethylaminoethyl methacrylate in the mixed solution are 0.001 - 0.1 M, 0.001 - 0.4 M, and 0.002 - 0.6 M respectively. The initiator is azobisisobutyronitrile. The reaction temperature is 40 - 90 °C, and the reaction time is 0.5 h - 10 h.

[0023] A method for regulating the hydrophilicity and hydrophobicity of a ceramic membrane. After treating the membrane with an acid solution, the surface turns into superhydrophilicity. After treating the membrane with ethanol, the surface turns into superhydrophobicity.

[0024] Beneficial effects

[0025] In the oil-containing wastewater treatment method of the present invention, through the treatment of coalescence, the oil droplets in the oil-containing wastewater can continuously collide and contact with the filler when contacting with the filler, thereby increasing, so that the oil droplets can be better removed in subsequent other treatment processes. At the same time, during the treatment process, the secondary sewage generated can be removed by deeply treating the filler washing water.

[0026] During the treatment process, the oil-containing wastewater and the washing water are separately treated by using a ceramic membrane with adjustable surface properties; in the produced water after the coalescence treatment, the oil droplet particles increase, and using a hydrophilic and oleophobic ceramic membrane for treatment can make the water pass through quickly and intercept the oil phase; when its working mode is switched to hydrophobic and oleophilic, since the washing water after coalescence contains more oil droplets, the oil-water separation can be effectively carried out, and the oil droplets can pass through the membrane layer, realizing the re-treatment of the washing water.

[0027] During the preparation of the ceramic membrane with adjustable surface properties, the modification treatment of dopamine uses the catechol group in the molecule to mineralize metal ions on the surface of the ceramic membrane, resulting in a rough surface; at the same time, due to the high adhesiveness of dopamine itself, a tight bond can be formed with the ceramic membrane; the acrylic compound in the preparation process is a key modification material. Since its ionizable tertiary amine group can be protonated and deprotonated, when it is applied to the ceramic membrane with switchable properties in this patent, the acrylic compound does not undergo protonation under the condition of ethanol treatment and maintains its folded conformation, cooperating with the long carbon chain to make the long-chain carbon extend out of the membrane surface, playing a hydrophobic role; at the same time, since the surface tension of the long carbon chain is greater than that of oil, the ceramic membrane has superhydrophobicity / superoleophilicity. On the other hand, after acid treatment, the tertiary amine group in the acrylic compound is protonated to form a positively charged ammonium group, and the molecular chain extension conformation also occurs. After the hydrogen bond combines with water molecules, the hydrophilic transformation of the ceramic membrane occurs, and the ceramic membrane also produces superhydrophilicity / underwater superoleophobicity. The addition of silane is because it contains methoxy groups on the silane, which can react with hydroxyl groups, making the cross-linked structure on the surface of the ceramic membrane more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Flow chart of the method of the present invention;

[0029] Figure 2 : Water contact angle images of the ceramic membrane with switchable properties, in an air environment. From top to bottom, the three rows are the contact angles after preparation, the contact angles after treatment with acidic solution, and the contact angles after continued ethanol treatment.

[0030] Figure 3 : Ceramic membrane with switchable properties, the left side is the water contact angle image under oil, and the right side is the oil contact angle image underwater.

[0031] Figure 4 : Changes in the contact angles of the ceramic membrane with switchable properties during the acid and alcohol cycle treatment.

[0032] Figure 5 : Process diagram of the ceramic membrane with switchable properties separating water / n - octane mixture. Among them, (a)-(c) are the process diagrams of separating water from the oil - water mixture, (d) is the device state diagram 1 h after complete water separation, and (e) is the water phase and oil phase diagram after complete water separation.

[0033] Figure 6 : Contact angles of the ceramic membrane in the comparative experiment after treatment with acidic solution and ethanol cycle. DETAILED DESCRIPTION OF THE INVENTION

[0034] Example 1

[0035] The water quality of the oily wastewater treated in this embodiment is shown in the following table:

[0036] CODcr BOD5 SS TOC Ammonia nitrogen Conductivity Petroleum Water quality 4530mg / L 559mg / L 329.1mg / L 1629mg / L 129mg / L 19.22mS / cm 43.7mg / L

[0037] Adopt the following treatment method: add 125 mg / L of flocculant ferric chloride to the wastewater, adjust the pH to about 8.0, after the flocculation reaction time of about 45 min, settle and remove the slag naturally; send the wastewater into a packed bed layer of polypropylene small ball fillers with an average particle size of 2 - 3 mm, make the feed flow rate 1 BV / h, and send the produced water into a ceramic membrane with superhydrophilic and underwater superoleophobic properties for filtration treatment, with the oil interception rate reaching 98%; after flushing the condensed oil on the surface of the fillers with backwash water, send the flushing water into a ceramic membrane with superhydrophobic and superoleophilic properties for filtration, with the water interception rate reaching 93%.

[0038] Among them, the ceramic membrane is prepared by the following method: soak the ZrO2 membrane with an average pore size of 200 nm in deionized water for pre-wetting for 3 h, then take it out and dry it. Then prepare a tris(hydroxymethyl)aminomethane solution with a concentration of 50 mM and a pH of 8.5 at room temperature, add 2 mg / mL of dopamine (DA), 5 mM of copper sulfate, and 19.6 mM of hydrogen peroxide to the tris(hydroxymethyl)aminomethane solution, and mix evenly. Immerse the pre-wetted ceramic membrane in the mixed solution, take it out, wash and dry it after oscillating and reacting for 2 h; then soak it in a 0.1 M silver nitrate solution at room temperature for 2 hours, take it out, wash and dry it; then soak it in a mixed solution of 0.01 M methylvinyl dimethoxysilane, 0.02 M tridecyl 2-methylacrylate, and 0.04 M dimethylaminoethyl methacrylate, add the initiator azobisisobutyronitrile, react at 70 °C for 8 h, take out the obtained membrane and dry it to obtain the ceramic composite membrane.

[0039] For comparison, polyacrylic acid compounds are not added during the preparation of the ceramic membrane. A ZrO2 membrane with an average pore size of 200 nm is immersed in deionized water for pre-wetting for 3 h, and then taken out and dried. Then, a 50 mM tris(hydroxymethyl)aminomethane solution with a pH of 8.5 is prepared at room temperature. 2 mg / mL of dopamine (DA), 5 mM of copper sulfate, and 19.6 mM of hydrogen peroxide are added to the tris(hydroxymethyl)aminomethane solution and mixed evenly. The pre-wetted ceramic membrane is immersed in the mixed solution, shaken and reacted for 2 h, then taken out, washed and dried; then immersed in a 0.1 M silver nitrate solution at room temperature for 2 hours, taken out, washed and dried; then immersed in a mixed solution of 0.01 M methylvinyldimethoxysilane and 0.02 M tridecyl 2-methyl-2-propenoate, and an initiator azobisisobutyronitrile is added, and the reaction is carried out at 70 °C for 8 h. The obtained membrane is taken out and dried to obtain a ceramic composite membrane. In the above preparation process, the catechol groups in polydopamine can form coordination bonds with metal ions, thereby inducing the metallization of metal ions and depositing a dense micro / nano structure on the surface of the substrate membrane, and then cross-linking to construct a high-performance intelligent ceramic composite membrane. A one-pot reaction of the ceramic membrane with silane compounds, long carbon chain-containing compounds, and acrylic acid compounds is adopted, and in-situ cross-linking is carried out with the copolymer generated on the surface of the substrate membrane. On the one hand, it can cross-link the substrate membrane and the generated copolymer in the form of chemical bonds to enhance the stability of the composite membrane, and on the other hand, it can increase the loading amount of the copolymer and enhance the super-wettability of the membrane.

[0040] As Figure 6 shown, the contact angle of the composite ceramic membrane prepared in the comparative experiment during the same cyclic treatment as above can be seen that the contact angle does not change after being alternately treated with an aqueous solution of pH = 1 and alcohol, indicating that the composite membrane does not have the characteristic of adjustable properties.

[0041] Example 2

[0042] The quality of the oily wastewater treated in this example is shown in the following table:

[0043] CODcr BOD5 SS TOC Ammonia nitrogen Conductivity Petroleum Water quality 4870mg / L 612mg / L 343.2mg / L 1762mg / L 153mg / L 22.74mS / cm 46.1mg / L

[0044] Adopt the following treatment method. Add 150 mg / L of the flocculant ferric chloride to the wastewater, adjust the pH to about 8.5, and after about 60 min of flocculation reaction, naturally settle to remove the slag; send the wastewater into a hydrophobic modified alumina packing bed with an average particle size of 2 - 3 mm, make the feed flow rate 2 BV / h, and send the produced water into a ceramic membrane with super-hydrophilic and underwater super-oleophobic properties for filtration treatment, and the oil interception rate reaches 97%; after flushing the condensed oil on the surface of the packing with backwashing water, send the flushing water into a ceramic membrane with super-hydrophobic and super-oleophilic properties for filtration, and the water interception rate reaches 92%.

[0045] The preparation method steps of the ceramic membrane used are as follows: Immerse the Al2O3 membrane with an average pore size of 2.5 μm in deionized water for pre-wetting for 3 h, then take it out and dry it. Then, prepare a 50 mM tris(hydroxymethyl)aminomethane solution with a pH of 8.5 at room temperature, add 2 mg / mL dopamine (DA), 5 mM copper sulfate, and 19.6 mM hydrogen peroxide to the tris(hydroxymethyl)aminomethane solution, and mix evenly. Immerse the pre-wetted ceramic membrane in the mixed solution, take it out, wash and dry it after oscillating and reacting for 2 h; then immerse it in a 0.1 M silver nitrate solution at room temperature for 2 hours, take it out, wash and dry it; then immerse it in a mixed solution of 0.01 M methylvinyldimethoxysilane, 0.02 M tridecyl 2-methylacrylate, and 0.04 M dimethylaminoethyl methacrylate, add the initiator azobisisobutyronitrile, and react at 70 °C for 8 h. Take out the obtained membrane and dry it to obtain the ceramic composite membrane.

[0046] As Figure 2 shown, the wettability of the prepared composite membrane, after being treated with an aqueous solution with pH = 1 and after being treated with alcohol. Among them, the prepared composite membrane initially shows superhydrophobicity, shows superhydrophilicity after being treated with an aqueous solution with pH = 1, and switches to superhydrophobicity after being further treated with alcohol, indicating that the prepared composite membrane has switchable superwetting properties. Figure 3 Shows the wettability of the prepared composite membrane to oil droplets and water droplets under water and under oil. Among them, the left figure is the underwater oil contact angle image of the composite membrane in the superhydrophobic state, and the right figure is the underwater oil contact angle image of the composite membrane in the superhydrophilic state, indicating that the prepared composite membrane has superhydrophobic / superoleophilic properties and has superhydrophilic / underwater superoleophobic properties after being treated with an aqueous solution with pH = 1. Figure 4 Shows the contact angle of the prepared composite membrane after being alternately treated with an aqueous solution with pH = 1 and alcohol. It can be seen from the figure that after multiple cycles, the composite membrane can still maintain superwetting properties, indicating that the composite membrane has a certain stability to this switching behavior.

[0047] The separation process of the water-in-oil and oil-in-water emulsions by the prepared composite membrane through a self-made separation device under gravity conditions is as Figure 5 shown. It can be seen from the figure that the permeate of the originally turbid milky white dichloromethane-in-water and n-octane-in-water emulsions becomes clear and transparent after being separated by the composite membrane, indicating that the prepared composite membrane can effectively separate oil-water emulsions.

Claims

1. A method for treating oily wastewater, characterized in that, It includes the following steps: Perform flocculation treatment on the oily wastewater to remove large particulate suspended matters; Treat the supernatant after flocculation treatment through a coalescence column filled with packing materials to increase the oil droplets; Perform oil-water separation treatment on the effluent of the coalescence column by using a ceramic composite membrane treated with a first regulator to allow water to pass through the membrane layer; the ceramic composite membrane after being treated with the first regulator is further treated with a second regulator; Use a rinsing liquid to rinse the used coalescence column to obtain rinsing wastewater, and perform oil-water separation treatment on the rinsing wastewater by using the above-mentioned ceramic composite membrane treated with the second regulator to allow oil to pass through the membrane layer; The ceramic composite membrane treated with the first regulator has superhydrophilic and underwater superoleophobic properties; the ceramic composite membrane treated with the second regulator has superhydrophobic and superoleophilic properties; The said first regulator is an acidic solution; the said second regulator is an alcohol solvent; The preparation method of the said ceramic composite membrane includes the following steps: Prepare a tris(hydroxymethyl)aminomethane solution, add dopamine, copper sulfate, and hydrogen peroxide and mix evenly to obtain a mixed solution, then immerse the ceramic membrane in the mixed solution for reaction, take it out and immerse it in a silver nitrate solution to obtain a ceramic membrane treated with the silver nitrate solution, and then immerse it in a mixed solution containing methylvinyl dimethoxysilane, tridecyl 2-methyl-2-propenoate, and dimethylaminoethyl methacrylate, add an initiator for reaction, take it out and dry it after the reaction to obtain the ceramic composite membrane.

2. The method for treating oily wastewater according to claim 1, wherein, The COD content in the said oily wastewater is 100 - 5000 mg / L, and the oil content is 10 - 2000 mg / L.

3. The treatment method of oily wastewater according to claim 1, wherein The said packing materials are selected from one or a mixture of several of polypropylene fibers, expanded polytetrafluoroethylene materials, and surface-hydrophobic-treated inorganic oxide particles.

4. The method for treating oily wastewater according to claim 1, characterized in that, The flocculant used in the said flocculation treatment is ferric chloride, polyaluminum chloride, aluminum chloride, aluminum sulfate, or anionic polyacrylamide; the addition amount of the flocculant is 100 - 500 mg / L.

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