A process for treating wastewater and recovering waste mineral oil

Abstract

The present application discloses a process for treating wastewater to recover waste mineral oil, which comprises the following steps: Step 1: Add acid to the wastewater to adjust the pH to 4.8 - 5.2, add a demulsifier and mix. After standing for 2 - 3 h, extract the upper oil layer to obtain the first treated wastewater; Step 2: Perform air flotation treatment on the first treated wastewater for 30 - 60 min, then add a demulsifier and mix for 20 - 40 min, then add an oil-absorbing resin. After standing for 2 - 3 h, take out the oil-absorbing resin to obtain the second treated wastewater; Step 3: Add acid to the second treated wastewater to adjust the pH to 2 - 4, and then perform a Fenton reaction to obtain the third treated wastewater; Step 4: Add alkali to the third treated wastewater to adjust the pH to 7 - 9, add an adsorbent. After standing for 4 - 6 h, recover the adsorbent and discharge it externally. The process of the present application can fully recover waste mineral oil during the process of treating wastewater into dischargeable water resources.

Description

Technical Field

[0001] The present application relates to the field of wastewater treatment, and in particular to a process for treating wastewater to recover waste mineral oil. Background Art

[0002] China is a large automobile country. Every year, a large number of used oil cans are discarded due to the filling of engine oil. The used oil cans are made of various recyclable materials such as metal and plastic, and can be reused after recycling and regeneration. However, due to years of use, there is a lot of waste mineral oil inside the discarded oil cans. Therefore, a large amount of wastewater containing waste mineral oil will be generated during the recycling and cleaning process. This wastewater contains various toxic substances such as heavy metals and benzene series. Direct discharge will cause serious pollution to the environment and indirectly harm human health. In addition, waste mineral oil is a kind of waste with high recycling value. Through recycling, energy products such as fuel oil and diesel can be regenerated. Therefore, by separating waste mineral oil from wastewater through appropriate treatment, on the one hand, environmental pollution can be reduced, and on the other hand, the recycling of energy can be improved.

[0003] However, the current wastewater treatment process can only choose to remove waste mineral oil or recover the oil layer suspended on the water surface formed by the oil liquid with a particle size greater than 100 μm in the wastewater, and it is difficult to recover the oil liquid with a particle size less than 100 μm, especially less than 25 μm, dispersed in the water, resulting in poor recovery effect of waste mineral oil and poor treatment effect of wastewater, and further causing waste of energy and environmental pollution. Summary of the Invention

[0004] In order to improve the recovery of waste mineral oil in wastewater treatment, the present application provides a process for treating wastewater to recover waste mineral oil.

[0005] In a first aspect, a process for treating wastewater to recover mineral oil includes the following steps:

[0006] Step 1: Add acid to the wastewater to adjust the pH to 4.8 - 5.2, then add a demulsifier and mix. After standing for 2 - 3 h, extract the upper oil layer to obtain the first treated wastewater;

[0007] Step 2: Perform air flotation treatment on the first treated wastewater for 30 - 60 min, then add a demulsifier and mix for 20 - 40 min, then add an oil-absorbing resin. After standing for 2 - 3 h, take out the oil-absorbing resin to obtain the second treated wastewater;

[0008] Step 3: Add acid to the second treated wastewater to adjust the pH to 2 - 4, and then perform a Fenton reaction to obtain the third treated wastewater;

[0009] Step 4: Add alkali to the third treated wastewater to adjust the pH to 7 - 9, add an adsorbent, and after standing for 4 - 6 h, recover the adsorbent and discharge it.

[0010] By adopting the above technical solution, metal hydroxides in water are dissolved by adding acid, so that the small molecule oil attached to the hydroxides is released into the water, facilitating demulsification. In addition, there are still insoluble particles with smaller particle sizes after acid dissolution, which can serve as flocculation cores during the demulsification process, improving the flocculation and demulsification effects. Optimizing the standing time can improve the effects of demulsification and flocculation to form precipitation, and at the same time reduce the re-formation of emulsions of dispersed oil and water in the wastewater, thereby improving the recovery of waste mineral oil. Extracting the upper-layer oil can collect most of the oil in the wastewater with a particle size greater than or equal to 100 μm, so that only oil with a smaller particle size remains in the wastewater.

[0011] The wastewater after the first treatment is subjected to air flotation treatment, so that the suspended pollutants that are difficult to flocculate and precipitate in the wastewater adhere to the surface of the bubbles and float up with the bubbles, forming a foam layer of bubbles, water and pollutants on the water surface, which is convenient for removal; adding a demulsifier again to demulsify the re-formed emulsion in the wastewater and improve the adsorption effect of the subsequent oil-absorbing resin on the oil; adding an oil-absorbing resin to recover and adsorb the oil in the wastewater with a particle size less than or equal to 100 μm, thereby completing the recovery of large-particle-size and small-particle-size oil.

[0012] The pH of the wastewater after the third treatment is further adjusted by adding acid to reduce the formation of iron hydroxide from ferrous ions, thereby reducing the reduction of the catalytic performance in the Fenton reaction due to the decrease in the content of ferrous ions in the wastewater, reducing the degradation rate of organic impurities, and reducing the wastewater treatment effect; in addition, adjusting the pH to about 2-4 can reduce the degradation of hydrogen peroxide, thereby improving the oxidation ability of hydrogen peroxide in the wastewater and improving the degradation of organic impurities. Adjusting the pH of the wastewater after the third treatment by adding base can form metal precipitates in the wastewater and adjust the water quality, and be absorbed by the adsorbent to reduce environmental pollution. In addition, adjusting the pH of the wastewater to weakly alkaline is also closer to the national requirements for discharge.

[0013] Preferably, the process raw materials for treating and recovering waste mineral oil from the wastewater, by weight, comprise the following components: 1000 parts of wastewater, 40-80 parts of demulsifier, 50-60 parts of oil-absorbing resin and 10-30 parts of adsorbent.

[0014] Typically but not restrictively, the adsorbent is a composition of one or more of activated carbon, bentonite and carbon fiber.

[0015] By adopting the above technical solution and optimizing the raw material components in the process, the treatment of wastewater can be completed and most of the waste mineral oil in the wastewater can be recovered with less raw material consumption, which is economical and environmentally friendly and suitable for large-scale industrial wastewater treatment.

[0016] Preferably, the weight ratio of the demulsifier in step one to the demulsifier in step two is (2-4):1.

[0017] By adopting the above technical solution, the dosage of the demulsifier in the process is further optimized, and by using the demulsifier step by step, even with a small dosage of the demulsifier, a good demulsification effect can still be achieved, improving the effect of wastewater treatment and saving costs.

[0018] Preferably, the demulsifier comprises calcium chloride, polyaluminum chloride and anionic polyacrylamide in a weight ratio of (1 - 1.2):(1 - 1.1):(0.7 - 0.85).

[0019] By adopting the above technical solution, a large amount of calcium ions are formed in the wastewater by calcium chloride. The calcium ions can destroy the stable oil-water two-phase interfacial film in the emulsion, reduce the stability of the emulsion, and then separate the oil from the emulsion into the wastewater for easy recovery. In addition, the surface of the oil is negatively charged, and the calcium ions can adsorb small-sized oil droplets through electrostatic attraction to form larger-sized oil droplets, improving the recovery effect of waste mineral oil. Adding polyaluminum chloride forms positively charged flocculent gel clusters, which play a role in compressing the double electric layer, thereby coagulating the negatively charged impurity suspensions in the wastewater to form multiple short-chain flocs. Adding anionic polyacrylamide, through the bridging effect, further combines the short-chain flocs formed by coagulation in the wastewater to form floc clusters, and the floc clusters can further adsorb the suspensions in the wastewater, thus achieving better demulsification and flocculation effects and improving the recovery of waste mineral oil and the treatment effect of wastewater. However, if an excessive amount of calcium chloride is added, the content of calcium ions in the wastewater is too high, which will cause a change in the surface charge of the oil, thus affecting the separation of the oil from the emulsion and the recovery of waste mineral oil and the treatment effect of wastewater.

[0020] However, if an excessive amount of polyaluminum chloride is added, it will also destroy the charge balance between the suspended solid particles, reduce the stability of the flocs, and affect the effect of wastewater treatment; if an excessive amount of anionic polyacrylamide is added, a large amount of negative charges will be formed on the surface of the flocs, forming a greater electrostatic repulsion, affecting the agglomeration performance of the flocs, and thus affecting the effect of wastewater treatment. Through the compounding and synergy of calcium chloride, polyaluminum chloride and anionic polyacrylamide, a better wastewater treatment effect can be achieved with a reduced dosage of the demulsifier, and the recovery of waste mineral oil in the wastewater can be improved.

[0021] Preferably, the oil-absorbing resin is a modified polyacrylate, and the modified polyacrylate comprises the following components in parts by weight: 18 - 26 parts of octadecyl methacrylate, 8 - 12 parts of butyl methacrylate, 1.2 - 2.4 parts of styrene, 1 - 3 parts of magnetic iron oxide fibers, 1 - 3 parts of initiator, 2 - 4 parts of crosslinking agent, 0.6 - 1 part of pore-forming agent.

[0022] Typically but not restrictively, the initiator is one of ammonium persulfate, sodium persulfate or azobisisobutyronitrile.

[0023] By adopting the above technical solutions, octadecyl methacrylate with a longer chain length is used as a polymerization monomer. The molecular chain of the synthesized oil-absorbing resin is longer, which improves the oil absorption capacity of the oil-absorbing resin and can reduce the dosage of the oil-absorbing resin. Magnetic iron oxide fibers are used to modify polyacrylate. On the one hand, for the polyacrylate resin modified by magnetic iron oxide fibers, due to the filling of inorganic materials, the pore size of the oil-absorbing resin is further reduced, and a large number of metal ions are carried on the pores, which can improve the absorption rate of small-particle-size oil, enhance the steric hindrance effect of the oil-absorbing resin, and make it difficult for large oil droplets to escape from the resin due to the steric hindrance effect after the oil droplets aggregate to form large droplets in the resin, thus improving the recovery effect of waste mineral oil. In addition, under the action of an external magnetic field, magnetic iron oxide fibers can improve the adsorption capacity for small-particle-size oil in wastewater and reduce the escape of oil from the inside of the oil-absorbing resin back into the wastewater.

[0024] After the treatment, the adsorbed waste mineral oil on the oil-absorbing resin can be desorbed by changing the external magnetic field, which improves the recovery efficiency of the waste mineral oil. The oil-absorbing resin prepared by this method can be reused repeatedly, saving costs and reducing waste consumption. By controlling the dosages of the initiator, styrene, cross-linking agent, and pore-forming agent, the cross-linking degree and pore size of the oil-absorbing resin are adjusted, and the pores and spatial structure of the polyacrylate resin are further improved by magnetic iron oxide fibers, further enhancing the ability of the oil-absorbing resin to recover waste mineral oil.

[0025] Preferably, the magnetic iron oxide fibers are obtained by growing magnetic iron oxide on the surface of straw by the template method. The raw materials of the magnetic iron oxide fibers include the following components in parts by weight: 0.3 - 0.9 part of straw, 4 - 8 parts of iron acetate, and 1 - 1.5 parts of silane coupling agent.

[0026] Typically but not restrictively, the silane coupling agent is one of KH-560 or KH-570.

[0027] By adopting the above technical solutions, the template method is used to grow magnetic iron oxide along the surface of straw, thereby forming a dense three-dimensional crystal structure, which can improve the steric hindrance effect of the oil-absorbing resin, and further increase the adsorption rate of small-particle-size oil droplets under the action of a magnetic field, thereby accelerating the solvation rate of the resin polymer chains, enhancing the stretching of the internal molecular chains of the resin, increasing the swelling of the resin, and thus improving the recovery effect of the oil-absorbing resin on waste mineral oil. The surface of the magnetic iron oxide fibers is modified with a silane coupling agent to introduce active groups on its surface, improving the binding performance between the magnetic iron oxide fibers and polyacrylate and enhancing the recovery performance of the oil-absorbing resin. Moreover, the magnetic iron oxide fibers prepared by this method have a stable structure, which can increase the number of times the oil-absorbing resin can be used. The combination of the magnetic iron oxide fibers and the polyacrylate resin is relatively stable and not easily detached and dispersed into the wastewater to form new pollution.

[0028] Preferably, the magnetic iron oxide fibers are prepared according to the following steps:

[0029] S1. Dissolve iron acetate in absolute ethanol and water to form an iron acetate solution. Then add straw to the iron acetate solution, and after standing for 12 - 24 h, take it out to obtain iron acetate fibers.

[0030] S2. After washing and drying the iron acetate fibers, calcine them at 600 - 800 °C for 3 - 6 h to obtain powder particles.

[0031] S3. Perform secondary calcination on the powder particles at 800 - 900 °C for 40 - 70 min, and then blend them with a silane coupling agent for 30 - 50 min to obtain magnetic iron oxide fibers.

[0032] Typically but not restrictively, the volume ratio of water to absolute ethanol is 1:1.

[0033] By adopting the above technical solution, dissolve iron acetate in water and absolute ethanol to form an iron acetate solution. After adding straw, iron acetate can combine with the cellulose on the surface of the straw through electrostatic attraction, van der Waals force, hydrogen bond and other forces, so that ferrous ions can adhere to the surface of the cellulose. Then through primary calcination, the iron acetate on the fiber surface is calcined to form iron oxide or magnetic iron oxide. Due to the fact that iron oxide or magnetic iron oxide is adsorbed on the surface of the straw, the formed magnetic iron oxide particles retain the hierarchical structure of the straw fiber and have an irregular pore structure, thus improving the adsorption capacity for small - particle - size oil. Then through secondary combustion, the iron oxide is fully oxidized to form magnetic iron oxide, improving the effect of the oil - absorbing resin in recovering waste mineral oil.

[0034] Preferably, the pore - forming agent is one of ethyl acetate or a composition of ethyl acetate and n - octanol.

[0035] By adopting the above technical solution, using the above - mentioned type of pore - forming agent can significantly improve the pore structure of the oil - absorbing resin, so that the polyacrylate resin can better cooperate with the magnetic oxide, further improving the recovery effect of the oil - absorbing resin on waste mineral oil. Using ethyl acetate as the pore - forming agent and modifying with magnetic iron oxide fibers, the formed oil - absorbing resin has a more suitable pore size, which can improve the recovery effect of the oil - absorbing resin on waste mineral oil.

[0036] Preferably, the cross - linking agent is one of 1,4 - dibutyl dimethacrylate, divinylbenzene or N,N'-methylenebisacrylamide.

[0037] In this application, 1,4 - dibutyl dimethacrylate is further preferably adopted.

[0038] By adopting the above technical scheme and the above-mentioned type of cross-linking agent, the cross-linking degree of the oil-absorbing resin can be significantly improved, the steric hindrance effect of the oil-absorbing resin can be increased, and the pore size of the oil-absorbing resin can be improved, thereby improving the recovery effect of the oil-absorbing resin on waste mineral oil; by adopting 1,4-dibutanol butyl dimethacrylate as a cross-linking agent, the internal structure of the oil-absorbing resin formed by cross-linking is more complex, the internal pores are more numerous and the pore size is smaller, and the adsorption effect on small-particle oil can be improved.

[0039] Preferably, the preparation process of the oil absorbing resin is prepared by the following steps:

[0040] The temperature of octadecyl methacrylate is raised to 80-90°C, and then butyl methacrylate, styrene, magnetic iron oxide fiber, initiator, crosslinking agent and porogen are added and mixed for reaction for 4-8 hours. After washing, the mixture is frozen at -5-0°C for 6-8 hours, filtered and washed to obtain an oil-absorbing resin.

[0041] By adopting the above technical scheme and optimizing the preparation process parameters of the oil absorbing resin, the adsorption effect of the oil absorbing resin can be improved. In addition, by freezing, the oil absorbing resin is formed into a block structure, which is convenient for separating the oil absorbing resin from wastewater and improving the adsorption performance of the oil absorbing resin, thereby improving the effect of wastewater treatment and the recovery effect of waste mineral oil.

[0042] In summary, this application has the following beneficial effects:

[0043] 1. Recover large-particle oil after demulsification, and use oil-absorbing resin to recover small-particle oil after flotation and secondary demulsification. Cooperate with the operation to improve the recovery of waste mineral oil while treating wastewater.

[0044] 2. Modify the polyacrylate resin with magnetic iron oxide fiber to accelerate the adsorption rate of waste mineral oil by the oil-absorbing resin just after it is put into the wastewater, thereby accelerating the solvation rate of the resin polymer, accelerating the extension rate of the molecular chain inside the resin, accelerating the swelling of the resin, and thus accelerating the adsorption rate of the oil-absorbing resin to the oil; in addition, improve the steric hindrance and pore size of the polyacrylate resin, increase the adsorption of the oil-absorbing resin to small-particle oil, and at the same time increase the oil retention rate of the oil-absorbing resin, thereby improving the recovery effect of the waste mineral oil. In addition, the magnetic iron oxide fiber also gives the polyacrylate resin the ability to adsorb and desorb oil under the action of a magnetic field, so that the oil-absorbing resin can quickly collect waste mineral oil and will not cause secondary water pollution due to chemical recovery.

[0045] 3. The template method is used to form a hierarchical structure and a pore structure of magnetic iron oxide, and then the surface is modified by a silane coupling agent to improve the synergistic effect and bonding strength of magnetic iron oxide fiber and polyacrylate, thereby improving the recovery performance of oil-absorbing resin. DETAILED DESCRIPTION

[0046] The raw materials used in the examples and preparation examples can all be commercially available and are described in detail. The present application will be further described in detail below in conjunction with the examples.

[0047] Preparation of magnetic iron oxide fibers

[0048] Preparation Example 1-1, a kind of magnetic iron oxide fiber, is prepared by the following method:

[0049] S1. Dissolve 6 g of iron acetate in 200 mL of absolute ethanol and 200 mL of water to form an iron acetate solution. Then add 0.6 g of straw to the iron acetate solution, and take it out after standing for 18 h to obtain iron acetate fibers;

[0050] S2. After washing and drying the iron acetate fibers, calcine them at 700 °C for 4.5 h to obtain powder particles;

[0051] S3. Calcine the powder particles at 850 °C for the second time, with the calcination time being 55 min, and then blend them with KH-570 for 40 min to obtain magnetic iron oxide fibers.

[0052] Preparation Example 1-2, a kind of magnetic iron oxide fiber, is prepared by the following method:

[0053] S1. Dissolve 8 g of iron acetate in 200 mL of absolute ethanol and 200 mL of water to form an iron acetate solution. Then add 0.9 g of straw to the iron acetate solution, and take it out after standing for 24 h to obtain iron acetate fibers;

[0054] S2. After washing and drying the iron acetate fibers, calcine them at 800 °C for 3 h to obtain powder particles;

[0055] S3. Calcine the powder particles at 800 °C for the second time, with the calcination time being 70 min, and then blend them with KH-570 for 40 min to obtain magnetic iron oxide fibers.

[0056] Preparation Example 1-3, a kind of magnetic iron oxide fiber, is prepared by the following method:

[0057] S1. Dissolve 4 g of iron acetate in 200 mL of absolute ethanol and 200 mL of water to form an iron acetate solution. Then add 0.3 g of straw to the iron acetate solution, and take it out after standing for 12 h to obtain iron acetate fibers;

[0058] S2. After washing and drying the iron acetate fibers, calcine them at 600 °C for 6 h to obtain powder particles;

[0059] S3. Calcine the powder particles at 900 °C for the second time, with the calcination time being 40 min, and then blend them with KH-560 for 40 min to obtain magnetic iron oxide fibers.

[0060] Preparation Example 1-4, a magnetic iron oxide fiber, was prepared by the following method:

[0061] S1. Dissolve 6 g of iron acetate in 200 mL of absolute ethanol and 200 mL of water to form an iron acetate solution. Then, add 0.6 g of straw to the iron acetate solution, and after standing for 18 h, take it out to obtain iron acetate fiber;

[0062] S2. After washing and drying the iron acetate fiber, calcine it at 700 °C for 4.5 h to obtain powder particles;

[0063] S3. Subject the powder particles to secondary calcination at 850 °C for 55 min to obtain magnetic iron oxide fiber.

[0064] Preparation Example 1-5, a magnetic iron oxide fiber, was prepared by the following method:

[0065] S1. Dissolve 6 g of iron acetate in 200 mL of absolute ethanol and 200 mL of water to form an iron acetate solution. Then, add 0.6 g of straw to the iron acetate solution, and after standing for 18 h, take it out to obtain iron acetate fiber;

[0066] S2. After washing and drying the iron acetate fiber, calcine it at 700 °C for 5.5 h, and then blend it with KH-570 for 40 min to obtain magnetic iron oxide fiber.

[0067] Preparation Example 1-6, a magnetic iron oxide fiber, was prepared by the following method:

[0068] S1. After washing and drying the iron acetate, calcine it at 700 °C for 4.5 h to obtain powder particles;

[0069] S2. Subject the powder particles to secondary calcination at 850 °C for 55 min, and then blend it with KH-570 for 40 min to obtain magnetic iron oxide.

[0070] Preparation of oil-absorbing resin

[0071] Preparation Example 2-1, an oil-absorbing resin, was prepared by the following steps:

[0072] Heat 22 g of octadecyl methacrylate to 85 °C, then add 10 g of butyl methacrylate, 1.8 g of styrene, 2 g of magnetic iron oxide fiber, 2 g of azobisisobutyronitrile, 3 g of 1,4-dibutyl dimethacrylate, and 0.8 g of ethyl acetate, and mix and react for 6 h. Wash the reaction product alternately with ethanol and water, and then freeze-dry it at -3 °C for 7 h to obtain the oil-absorbing resin.

[0073] Among them, the magnetic iron oxide fiber is derived from Preparation Example 1-1.

[0074] Preparation Example 2-2, an oil-absorbing resin, was prepared by the following steps:

[0075] Heat 26 g of octadecyl methacrylate to 90 °C, then add 8 g of butyl methacrylate, 1.2 g of styrene, 3 g of magnetic iron oxide fibers, 1 g of azobisisobutyronitrile, 4 g of 1,4-dibutyl dimethacrylate, and 1 g of ethyl acetate, and react for 8 h. Wash the reaction product alternately with ethanol and water, and then freeze-dry at -5 °C for 6 h to obtain the oil-absorbing resin.

[0076] Among them, the magnetic iron oxide fibers are derived from Preparation Example 1-2.

[0077] Preparation Example 2-4, an oil-absorbing resin, was prepared by the following steps: Heat 22 g of octadecyl methacrylate to 85 °C, then add 10 g of butyl methacrylate, 1.8 g of styrene, 2 g of magnetic iron oxide fibers, 2 g of ammonium persulfate, 3 g of divinylbenzene, 0.7 g of ethyl acetate, and 0.1 g of n-octanol, and react for 6 h. Wash the reaction product alternately with ethanol and water, and then freeze-dry at -3 °C for 7 h to obtain the oil-absorbing resin.

[0078] Among them, the magnetic iron oxide fibers are derived from Preparation Example 1-1.

[0079] Preparation Example 2-5, an oil-absorbing resin, was prepared by the following steps:

[0080] Heat 22 g of octadecyl methacrylate to 85 °C, then add 10 g of butyl methacrylate, 1.8 g of styrene, 2 g of magnetic iron oxide fibers, 2 g of azobisisobutyronitrile, 3 g of 1,4-dibutyl dimethacrylate, and 0.8 g of ethyl acetate, and react for 6 h. Wash the reaction product alternately with ethanol and water, and dry to obtain the oil-absorbing resin (without freezing treatment). Among them, the magnetic iron oxide fibers are derived from Preparation Example 1-1.

[0081] Preparation Example 2-6, an oil-absorbing resin, is different from Preparation Example 2-1 in that the magnetic iron oxide fibers are derived from Preparation Example 1-4.

[0082] Preparation Example 2-7, an oil-absorbing resin, is different from Preparation Example 2-1 in that the magnetic iron oxide fibers are derived from Preparation Example 1-5.

[0083] Preparation Example 2-8, an oil-absorbing resin, is different from Preparation Example 2-1 in that the magnetic iron oxide fibers are derived from Preparation Example 1-6.

[0084] Preparation Example 2-9, an oil-absorbing resin, is different from Preparation Example 2-1 in that the octadecyl methacrylate is replaced with an equal amount of methyl methacrylate.

[0085] Preparation Example 2-10, an oil-absorbing resin, which is different from Preparation Example 2-1 in that the magnetic iron oxide fibers are replaced with an equal amount of straw, and the straw is powdery straw with a particle size of 10-18 mesh.

[0086] Example

[0087] Example 1, a process for treating wastewater to recover mineral oil, which adopts the following steps:

[0088] Step 1: Add hydrochloric acid to 1000 kg of wastewater to adjust the pH to 5, then add 45 kg of demulsifier and mix. After standing for 2.5 h, extract the upper oil layer to obtain the first-treated wastewater.

[0089] Step 2: Perform air flotation treatment on the first-treated wastewater for 45 min, then add 15 kg of demulsifier and mix for 30 min. Then add 55 kg of oil-absorbing resin and stand for 2.5 h under the action of an external magnetic field. Take out the oil-absorbing resin to obtain the second-treated wastewater.

[0090] Step 3: Add sulfuric acid to the second-treated wastewater to adjust the pH to 3, then add 200 L of 10 mol / L hydrogen peroxide and 120 L of 1 mol / L ferrous sulfate, and react for 3 h to obtain the third-treated wastewater.

[0091] Step 4: Add sodium hydroxide to the third-treated wastewater to adjust the pH to 8, add 20 kg of activated carbon, stand for 5 h, then recover the activated carbon and discharge it.

[0092] The demulsifier is obtained by mixing 1.1 parts of calcium chloride, 1.1 parts of polyaluminum chloride and 0.7 parts of polyacrylamide; the oil-absorbing resin is from Preparation Example 2-1.

[0093] Example 2, a process for treating wastewater to recover mineral oil, which adopts the following steps:

[0094] Step 1: Add hydrochloric acid to 1000 kg of wastewater to adjust the pH to 5.2, then add 64 kg of demulsifier and mix. After standing for 2 h, extract the upper oil layer to obtain the first-treated wastewater.

[0095] Step 2: Perform air flotation treatment on the first-treated wastewater for 30 min, then add 16 kg of demulsifier and mix for 20 min. Then add 50 kg of oil-absorbing resin and stand for 3 h under the action of an external magnetic field to obtain the second-treated wastewater.

[0096] Step 3: Add sulfuric acid to the second-treated wastewater to adjust the pH to 2, then add 200 L of 10 mol / L hydrogen peroxide and 120 L of 1 mol / L ferrous sulfate, and react for 3 h to obtain the third-treated wastewater.

[0097] Step 4: Add sodium hydroxide to the wastewater after the third treatment to adjust the pH to 7, add 10 kg of activated carbon, let it stand for 6 h, recover the activated carbon, and discharge it externally.

[0098] Among them, the demulsifier is obtained by mixing 1 part of calcium chloride, 1 part of polyaluminum chloride and 0.85 part of polyacrylamide; the oil-absorbing resin is from Preparation Example 2-2.

[0099] Example 4, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-4.

[0100] Example 5, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-5.

[0101] Example 6, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-6.

[0102] Example 7, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-7.

[0103] Example 8, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-8.

[0104] Example 9, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-9.

[0105] Example 10, a process for treating wastewater to recover mineral oil, is different from Example 1 in that the oil-absorbing resin is from Preparation Example 2-10.

[0106] Comparative Example

[0107] Comparative Example 1, a process for treating wastewater to recover mineral oil, adopts the following steps:

[0108] Step 1: Add hydrochloric acid to 1000 kg of wastewater to adjust the pH to 5, then add 45 kg of demulsifier and mix. After standing for 2.5 h, extract the upper oil layer to obtain the wastewater after the first treatment;

[0109] Step 2: Perform air flotation treatment on the wastewater after the first treatment for 45 min, then add 15 kg of demulsifier and mix for 30 min, and extract the upper oil layer to obtain the wastewater after the second treatment;

[0110] Step 3: Add sulfuric acid to the wastewater after the second treatment to adjust the pH to 3, and then perform Fenton reaction to obtain the wastewater after the third treatment;

[0111] Step 4: Add sodium hydroxide to the wastewater after the third treatment to adjust the pH to 8, add 20 kg of activated carbon, let it stand for 5 h, then recover the activated carbon and discharge the wastewater.

[0112] The demulsifier is obtained by mixing 1.1 parts of calcium chloride, 1.1 parts of polyaluminum chloride and 0.7 parts of polyacrylamide; the oil-absorbing resin is from Preparation Example 2-1.

[0113] Comparative Example 2, a process for treating and recovering mineral oil from wastewater, comprises the following steps:

[0114] Step 1: Add hydrochloric acid to 1000 kg of wastewater to adjust the pH to 5, then perform air flotation for 45 min, add 55 kg of oil-absorbing resin, let it stand for 2.5 h under the action of an external magnetic field, take out the oil-absorbing resin to obtain the wastewater after the first treatment;

[0115] Step 2: Add sulfuric acid to the wastewater after the first treatment to adjust the pH to 3, then perform Fenton reaction to obtain the wastewater after the third treatment;

[0116] Step 3: Add sodium hydroxide to the wastewater after the second treatment to adjust the pH to 8, add 20 kg of activated carbon, let it stand for 5 h, then recover the activated carbon and discharge the wastewater (i.e., no demulsification treatment).

[0117] Among them, the oil-absorbing resin is from Preparation Example 2-1.

[0118] Comparative Example 3, a process for treating and recovering mineral oil from wastewater, comprises the following steps:

[0119] Step 1: Add hydrochloric acid to 1000 kg of wastewater to adjust the pH to 5, then add 60 kg of demulsifier and mix, after standing for 2.5 h, extract the upper oil layer, then add 55 kg of oil-absorbing resin, let it stand for 2.5 h under the action of an external magnetic field, take out the oil-absorbing resin to obtain the wastewater after the first treatment;

[0120] Step 2: Add sulfuric acid to the wastewater after the first treatment to adjust the pH to 3, then perform Fenton reaction to obtain the wastewater after the second treatment;

[0121] Step 3: Add sodium hydroxide to the wastewater after the second treatment to adjust the pH to 8, add 20 kg of activated carbon, let it stand for 5 h, then recover the activated carbon and discharge the wastewater (omit the air flotation step and add the demulsifier at one time).

[0122] The demulsifier is obtained by mixing 1.1 parts of calcium chloride, 1.1 parts of polyaluminum chloride and 0.7 parts of polyacrylamide; the oil-absorbing resin is from Preparation Example 2-1.

[0123] Comparative Example 4, a method for treating emulsified oil wastewater, comprises the following steps:

[0124] 1) Adjust the water volume in the separate-quality regulation tank and remove the floating oil on the upper layer; the high-concentration emulsified oil waste liquid is discharged and stored in the separate-quality regulation tank for treatment. The hydraulic retention time is 10 d, which can play a role in adjusting the water quality and volume. The floating oil on the upper layer of the wastewater is intercepted by the oil separation board and then removed manually regularly or removed automatically by setting up a float skimmer. The emulsified oil wastewater after removing the floating oil is lifted to the demulsification tank by a submersible pump located 1.0 m from the bottom of the tank. The impurities with a relatively large specific gravity that may be carried in the original wastewater sink to the bottom of the tank as sediment and are removed regularly.

[0125] 2) Pump the wastewater after removing the floating oil on the upper layer into the demulsification tank and add chemical agents for demulsification;

[0126] The wastewater in the above steps enters the demulsification tank for demulsification. Quicklime (CaO) is used as the demulsifying agent, and the dosage is 10 g / L. The demulsification tank operates intermittently. The operation time of one cycle is 2.5 h, in which the reaction time is controlled within 0.5 h, the static settling time is 1.0 h, and the drainage time is 0.5 h. The operation steps of this embodiment are as follows: The lift pump in the separate-quality regulation tank pumps the oil-containing wastewater into the demulsification tank. When the upper liquid level of the demulsification tank is reached, the water inlet is stopped. At the same time, the metering pump quantitatively pumps the CaO emulsion into the tank. Subsequently, the stirring motor of the demulsification tank is started to make the wastewater react with the demulsifying agent. The reaction time is 0.5 h. When the reaction ends, the stirring motor is stopped and the static settling starts. After 1.0 h of static settling, the valves of the floating slag pipe and the sediment pipe are opened respectively, and the floating slag and sediment after demulsification are discharged into the sludge storage tank by gravity; then the drain pipe is opened to discharge the clarified liquid after demulsification into the intermediate tank.

[0127] 3) Pump the wastewater after the demulsification tank into the intermediate tank for a short stay and then pump it into the membrane bioreactor;

[0128] The clarified liquid after demulsification drains into the intermediate tank by gravity. In this embodiment, the hydraulic retention time HRT of the intermediate tank is 1.0 d. The intermediate tank is the link between the intermittently operating demulsification tank and the continuously operating membrane bioreactor and provides an appropriate place for the addition of nutrients. According to the co-degradation theory, glucose is added to the intermediate tank. In this embodiment, it is added in the ratio of 1 kg of wastewater COD: 1 kg of glucose, and a certain amount of ammonium bicarbonate and ammonium dihydrogen phosphate are added appropriately to supplement the N and P required for the growth of microorganisms.

[0129] 4) The wastewater after demulsification is further deoiled and the COD is degraded in the membrane bioreactor. The treated water is separated by the membrane and directly discharged by the membrane suction pump.

[0130] Performance test The water discharged from Examples 1-10 and Comparative Examples 1-4 was sampled and tested, and untreated water was set as a blank control. The test was conducted 6 times in parallel and the average value was taken. The results are shown in Table 1. Compared with the first-level standard of the national sewage discharge standard GB13456-92, COD ≤ 100 mg / L, oil ≤ 8 mg / L, ammonia nitrogen ≤ 15 mg / L, and sulfide ≤ 1 mg / L.

[0131] The waste mineral oil collected in each treatment group was weighed and the mass was recorded. The results are shown in Table 1.

[0132] Table 1: Treatment results of Examples 1-10, Comparative Examples 1-4 and Blank Control

[0133]

[0134] Combining Examples 1-4 and Comparative Example 4 and Table 1, it can be seen that the technical solution of the present application has a better treatment effect than the conventional treatment of oily wastewater, the wastewater fully meets the national first-level standard, and the available waste mineral oil is recovered; in addition, the process of the present application is simple, and the process raw materials used are widely available, and most of the raw materials can be reused, which is economical and environmentally friendly, and has good applicability, and can play a good treatment and recovery role for various types of oily wastewater. The reason is that in the process of the present application, a demulsifier is first used to break the emulsion in the water and produce a flocculation effect, so that the water and oil are separated, and the large-particle oil can be directly recovered, and then the flotation and demulsification process is used to disperse the small-particle oil in the water as much as possible, and then the oil-absorbing resin prepared by the present application that can quickly adsorb the small-particle oil is used for further collection, so that most of the waste mineral oil can be collected and a better treatment effect is produced.

[0135] It can be seen from Example 1 and Example 5 and Table 1 that freezing the oil absorbing resin to form a block resin can improve the recovery effect of waste mineral oil.

[0136] Combining Example 1, Examples 6-10 and Comparative Example 1, it can be seen that the preparation and modification of the oil-absorbing resin greatly affects the collection of waste mineral oil. In addition, since the content of waste mineral oil in the wastewater is not high, it is reflected that the oil-absorbing resin plays a role in the recovery of waste mineral oil. The reason is that the modification of the polyacrylate resin by magnetic iron oxide fiber has a synergistic effect on the recovery of waste mineral oil, and the distribution process designed by the present application also has a significant recovery effect on the small-particle oil that is difficult to collect, so that the waste mineral oil in the wastewater is fully recovered.

[0137] It can be seen from the combination of Example 1 and Comparative Examples 2-3 that without using demulsification or air flotation to treat the wastewater, both the treatment effect of the wastewater and the recovery amount of waste mineral oil are affected. The reason is that there is also a synergistic effect between the process steps of this application, and only through the treatment of different processes can a better treatment of the wastewater be completed and a better recovery of waste mineral oil be achieved.

[0138] This specific embodiment is only an explanation of this application and does not limit this application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions according to needs, but as long as they are within the scope of the claims of this application, they are protected by the patent law.

Claims

1. A process for treating wastewater to recover waste mineral oil, characterized in that, It includes the following steps: Step 1: Add acid to the wastewater to adjust the pH to 4.8 - 5.2, add a demulsifier and mix. After standing for 2 - 3 h, extract the upper oil layer to obtain the first treated wastewater. Step 2: Conduct air flotation treatment on the first treated wastewater for 30 - 60 min, then add a demulsifier and mix for 20 - 40 min. Then add an oil-absorbing resin. After standing for 2 - 3 h, take out the oil-absorbing resin to obtain the second treated wastewater. Step 3: Add acid to the second treated wastewater to adjust the pH to 2 - 4, and then conduct a Fenton reaction to obtain the third treated wastewater. Step 4: Add alkali to the third treated wastewater to adjust the pH to 7 - 9, add an adsorbent. After standing for 4 - 6 h, recover the adsorbent and discharge it. The weight ratio of the demulsifier in Step 1 to the demulsifier in Step 2 is (2 - 4):

1. The process raw materials for treating wastewater to recover waste mineral oil, by weight, include the following components: 1000 parts of wastewater, 40 - 80 parts of demulsifier, 50 - 60 parts of oil-absorbing resin, and 10 - 30 parts of adsorbent. The oil-absorbing resin uses modified polyacrylate, and the modified polyacrylate includes the following components by weight: 18 - 26 parts of octadecyl methacrylate, 8 - 12 parts of butyl methacrylate, 1.2 - 2.4 parts of styrene, 1 - 3 parts of magnetic iron oxide fiber, 1 - 3 parts of initiator, 2 - 4 parts of crosslinking agent, 0.6 - 1 part of pore-forming agent. The magnetic iron oxide fiber is obtained by growing magnetic iron oxide on the surface of straw through a template method. The raw materials of the magnetic iron oxide fiber include the following components by weight: 0.3 - 0.9 parts of straw, 4 - 8 parts of iron acetate, and 1 - 1.5 parts of silane coupling agent. The magnetic iron oxide fiber is prepared according to the following steps: S1. Dissolve iron acetate in absolute ethanol and water to form an iron acetate solution. Then add straw to the iron acetate solution. After standing for 12 - 24 h, take it out to obtain iron acetate fiber. S2. Wash and dry the iron acetate fiber, and then calcine it at 600 - 800 °C for 3 - 6 h to obtain powder particles. S3. Conduct secondary calcination on the powder particles at 800 - 900 °C for 40 - 70 min, and then blend them with the silane coupling agent for 30 - 50 min to obtain magnetic iron oxide fiber. The pore-forming agent uses ethyl acetate or a composition of ethyl acetate and n-octanol. The crosslinking agent uses divinylbenzene or N,N'-methylenebisacrylamide. The preparation process of the oil-absorbing resin is obtained by the following steps: Heat octadecyl methacrylate to 80 - 90 °C, then add butyl methacrylate, styrene, magnetic iron oxide fiber, initiator, crosslinking agent, and pore-forming agent and mix and react for 4 - 8 h. After washing, freeze at -5 - 0 °C for 6 - 8 h, filter and wash to obtain the oil-absorbing resin.

2. The process for treating wastewater to recover waste mineral oil according to claim 1, characterized in that, The demulsifier includes calcium chloride, polyaluminum chloride, and anionic polyacrylamide with a weight ratio of (1 - 1.2):(1 - 1.1):(0.7 - 0.85).

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