Alkali washing wastewater treatment and recycling method

Abstract

The invention relates to a method for treating and recycling alkali washing wastewater, and belongs to the technical field of wastewater treatment. Through the fine control process steps of pretreatment, ultrafiltration separation, nanofiltration separation and the like, the wastewater complexity is effectively reduced, and the sodium hydroxide recovery efficiency is improved. According to the pretreatment step of the alkali washing wastewater, an adsorbent prepared from bagasse is combined with copper ion loading and calcium acrylate introduction, and sodium alginate is further added, so that the adsorption capacity of organic matters and oils is remarkably enhanced, waste resource utilization is realized, and favorable conditions are created for subsequent membrane separation. Besides, a special membrane cleaning agent is also prepared, and the reliability and economical efficiency of the wastewater treatment process are improved by optimizing the formula design, efficiently cleaning the membrane component, keeping the membrane permeability, prolonging the service life and ensuring the stable operation of the membrane separation system.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment and relates to a method for treating and recycling alkali washing wastewater. Background Art

[0002] When using methanol to olefins technology to produce propylene, ethylene and other products, the olefin separation unit usually uses sodium hydroxide solution to wash the acidic gas in the reaction gas. This process produces alkaline washing wastewater containing a large amount of pollutants. Alkaline washing wastewater has the characteristics of high pH value, high oil content and high COD, which is difficult to treat. If it is directly discharged into the biochemical system of the sewage treatment plant, it will cause serious impact on the wastewater treatment process and cannot operate normally.

[0003] The oil in the alkaline washing wastewater can be either of two types: one is that ketones or aldehydes react with alkali to produce aldol condensation reactions, producing unsaturated ketones or aldehydes, which then polymerize into butter; the other is that unsaturated olefins or dienes dissolved in the alkaline solution produce free radicals and undergo coupling reactions.

[0004] The classification of oil substances can be mainly divided into dissolved oil, emulsified oil, dispersed oil and floating oil according to the specific form of oil in water and the differences in the source of oil-containing wastewater. Different types of oil are suitable for different oil-water separation methods. Floating oil and dispersed oil are generally separated by physical methods using the difference in oil and water density. However, the diameter of emulsified oil is too small to form a stable oil-water interface with water molecules, so special demulsification technology must be used for two-phase separation. At present, demulsification and oil removal technologies include physical demulsification, chemical demulsification and biological demulsification. The principle of physical demulsification is to destroy the stable oil-water interface film in wastewater by physical methods, so as to separate oil and water. Commonly used physical technologies include ultrasonic method, adsorption method, air flotation method, membrane separation method, microwave method, etc. The chemical demulsification method is to add a demulsifier to make it adsorb the oil-water interface film in a stable emulsified state, reduce the membrane strength and break it, so as to separate oil and water. The chemical demulsification method has high demulsification efficiency and fast demulsification speed, but the added demulsifier is generally not recyclable, the use cost is high, and it may produce new pollution, increasing the difficulty of sewage treatment.

[0005] There are many studies on the treatment of waste alkali liquid at home and abroad, and alkaline wastewater is treated by flotation + three-effect evaporation crystallization. The waste alkali liquid enters the oil-water separation and flotation integrated machine for oil removal, or is temporarily stored in the waste alkali liquid accident pool, and then is lifted into the oil-water separation and flotation integrated machine for oil removal. After oil removal, the waste alkali liquid is lifted to the three-effect evaporator for evaporation and crystallization treatment. The evaporated condensate enters the sewage treatment biochemical unit, and the crystallized waste alkali residue is treated as solid hazardous waste outsourced. The most typical technology for waste alkali liquid is wet air oxidation, which can completely treat the sulfide and organic matter in the waste alkali liquid, but the investment and operating costs are high, and it is not suitable for treating the waste alkali liquid of methanol to olefins unit. The incineration method is widely used in the industry, but the direct burning treatment cost is high, and the particulate matter content in the flue gas is easy to exceed the standard, which poses a great environmental risk.

[0006] In summary, various treatment methods for alkaline washing wastewater have problems such as no recycling of alkali solution, large investment in treatment equipment, high operating cost, low efficiency, and environmental risks. Summary of the invention

[0007] The purpose of the present invention is to provide a method for treating and recycling alkali-washing wastewater. In the methanol-to-olefins process, an olefin separation unit uses sodium hydroxide solution to wash acidic reaction gas. This process produces alkali-washing wastewater containing a large amount of pollutants. The alkali-washing wastewater has the characteristics of high alkali concentration, high COD, high oil content, etc. The present invention removes suspended matter and organic matter in the wastewater through pretreatment, and then uses membrane technology to recover sodium hydroxide.

[0008] The purpose of the present invention can be achieved through the following technical solutions: A method for treating and recycling alkali washing wastewater, the specific steps of the recycling method are as follows: S1. Pretreatment: adding the adsorbent to the alkali-washing wastewater, stirring at 40-45 °C and 550-650 r / min for 30-60 min to obtain a pretreated mixed solution; S2, ultrafiltration membrane separation: the pretreated mixed liquid is subjected to plate and frame filter pressing, and the plate and frame filtrate is further passed through the ultrafiltration membrane to remove suspended solids and macromolecular substances in the liquid. The filtration temperature is 35~70 ℃, the filtration precision is 0.05~0.5 μm, and the recovery rate of the ultrafiltration membrane is controlled at 90%~95%. After operation, the ultrafiltration membrane is cleaned with a membrane cleaning agent. The mass concentration of the membrane cleaning agent is 0.5%~2%, the cleaning temperature is set to 40~80 ℃, and the cleaning time is 30~60 min. After cleaning, the flux of the ultrafiltration membrane is restored; S3, nanofiltration membrane separation: The ultrafiltration membrane filtrate is filtered through a rolled nanofiltration membrane to remove residual organic matter in the liquid and recover sodium hydroxide. When cleaning the rolled nanofiltration membrane, first use a membrane cleaning agent with a mass concentration of 0.1%~0.5% for 30~60 minutes, and the cleaning temperature is set to 30~40 ℃. After cleaning, the flux of the rolled nanofiltration membrane is restored.

[0009] As a preferred technical solution of the present invention, the suspended matter content in the alkali washing wastewater in S1 is 200-300 mg / L, the oil content is 800-1300 mg / L, the COD content is 10000-12000 mg / L, and the sodium hydroxide content is 0.5wt%-0.8wt%.

[0010] As a preferred technical solution of the present invention, the preparation method of the adsorbent in S1 is as follows: S3-1: 10-20 parts by weight of bagasse powder was added to 80-90 parts by weight of deionized water, and ultrasonicated for 20-40 minutes. Then, 1-2 parts by weight of copper chloride was added, and stirred at a speed of 200-300 r / min for 6-10 hours. The mixture was placed in a vacuum drying oven at 60°C and dried for 12 hours. The mixture was then transferred to a crucible and calcined in a muffle furnace under nitrogen protection for 1-2 hours to obtain powder A. S3-2: 15-25 parts by weight of powder A are added to 100 parts by weight of deionized water, ultrasonicated for 10 min, 15-25 parts by weight of a calcium source are added, stirred at a speed of 500-600 r / min for 30 min, and then acrylic acid in an equal molar ratio to the calcium source is added, stirred at a speed of 700-800 r / min for 1-2 h, and dried in a vacuum drying oven at 60-80 °C for 12-24 h to obtain powder B; S3-3: Powder B and sodium alginate are mixed in a mass ratio of (3-5):1, and the mixture is placed in a ball mill for 2-4 h to obtain the adsorbent.

[0011] As a preferred technical solution of the present invention, the dosage of the adsorbent in S1 is 0.5% to 5% of the weight of the alkali washing wastewater.

[0012] As a preferred technical solution of the present invention, the calcination temperature of the muffle furnace in S3-1 is 500-700°C.

[0013] As a preferred technical solution of the present invention, the calcium source in S3-2 is one of calcium oxide or calcium hydroxide.

[0014] As a preferred technical solution of the present invention, the ball milling speed in S3-3 is 200~300 r / min.

[0015] As a preferred technical solution of the present invention, the ultrafiltration membrane structure in S2 is one of tubular, plate, curtain or roll ultrafiltration membranes, and the ultrafiltration membrane material is one of ceramic, stainless steel and PTFE.

[0016] As a preferred technical solution of the present invention, the components and mass percentages of the membrane cleaning agent are 5% to 15% sodium hydroxide, 10% to 25% tetrasodium ethylenediaminetetraacetic acid, 0.5% to 1.5% propanol, 0.5% to 1% ethylene glycol, 0.5% to 1% polyvinyl alcohol, 0.5% to 1.5% sodium dodecylbenzene sulfonate, 0.3% to 0.5% fatty alcohol polyoxyethylene ether, 0.05% to 0.5% ether, and the balance deionized water.

[0017] As a preferred technical solution of the present invention, the rolled nanofiltration membrane filtrate in S3 can be subjected to secondary nanofiltration membrane filtration to further improve the quality of the recovered sodium hydroxide.

[0018] Regarding the characteristics of alkaline washing wastewater, including high suspended solid concentration, high oil content, high COD value and containing sodium hydroxide. The oil in the wastewater mainly exists in an emulsified state, with complex components, including organic substances such as olefins, alkanes, aldehydes, ketones, etc. These characteristics make it difficult for the traditional air flotation method to effectively remove oil, and the removal of oil and suspended solids becomes a major challenge in the pretreatment stage.

[0019] As a by-product of the sugarcane industry, sugarcane bagasse is not only widely sourced and inexpensive, but also provides a rich raw material for the preparation of highly efficient adsorbents. Using sugarcane bagasse to prepare adsorbents not only realizes the resource utilization of waste, but also reduces the production cost of adsorbents. The porous structure and high specific surface area characteristics of sugarcane bagasse itself provide a good physical basis for its use as an adsorbent, enabling the adsorbent to come into full contact with and interact with organic substances and oil molecules in alkaline wastewater.

[0020] Copper ions and sugarcane bagasse are placed in a solution and mixed for a certain time, and then copper ions are stably loaded on the surface and pores of sugarcane bagasse-based biochar by high-temperature roasting. After high-temperature roasting and ball milling treatment, the porous structure and specific surface area of sugarcane bagasse-based biochar are further optimized, improving the adsorption performance; at the same time, copper ions, as an effective adsorption site, can further enhance the adsorption capacity of the adsorbent for organic substances and oil. Copper ions can interact with heteroatoms such as nitrogen and sulfur in organic compounds by forming π complex bonds, thereby effectively separating and adsorbing these organic compounds. In addition, copper-loaded biochar also has the ability to activate persulfate substances in alkaline wastewater, generating reactive species such as singlet oxygen and superoxide radicals, which can promote the degradation of organic pollution in alkaline wastewater and further improve the wastewater treatment efficiency.

[0021] Calcium acrylate is generated by reacting a calcium source with acrylic acid under certain conditions. The carboxyl groups in the calcium acrylate molecules can react with the hydroxyl and carboxyl groups on the surface of biochar to form covalent bonds or ionic bonds, thereby enhancing the stability and adsorption performance of the adsorbent. When the adsorbent is added to alkaline washing wastewater, due to the presence of a certain amount of organic substances in the alkaline washing wastewater, the organic substances can act as cross-linking agents or initiators for calcium acrylate, causing calcium acrylate to undergo a polymerization reaction, exciting the double chains in the acrylate molecular structure to form monomer free radicals. When monomer free radicals meet new monomers, they are extremely easy to combine and transfer this excitation effect in turn, repeating in a cycle, and the molecules are interconnected to form a planar chain-like or three-dimensional network structure. The formation of this structure further increases the adsorption surface area and adsorption sites of the adsorbent, thus significantly improving its adsorption capacity for organic substances and oil molecules in alkaline wastewater.

[0022] Sodium alginate and powder B are mixed in a certain mass ratio. Sodium alginate and calcium acrylate can work together to form a more stable cross-linked structure, which not only improves the mechanical strength of the adsorbent, but also facilitates the adsorption and fixation of the target pollutants by the adsorbent. In addition, the addition of sodium alginate further enhances the adhesion and synergy between the raw materials, and helps to stabilize the copper element loaded on the bagasse-based biochar, making the entire adsorbent system more stable and efficient.

[0023] In view of the characteristics of alkaline washing wastewater, the membrane cleaning agent prepared by the present invention can effectively remove organic pollutants such as grease and protein and inorganic pollutants such as metal ions remaining on the membrane through reasonable component ratio and concentration setting, prevent membrane pollution and clogging, and restore membrane flux.

[0024] Among them, sodium hydroxide has a strong decontamination ability and can effectively decompose grease, protein and certain organic dirt. It converts grease into soap and glycerol through saponification reaction, and cooperates with tetrasodium ethylenediaminetetraacetic acid to enhance the chelation of metal ions and prevent metal ions from damaging the membrane. Tetrasodium ethylenediaminetetraacetic acid and propanol can improve the permeability and solubility of the cleaning agent. Propanol has good solubility and volatility, can dissolve grease, grease and other oily substances, and completely remove them. Ethylene glycol has good solubility and stability, and at the same time helps to separate oil and water and reduce the cost of drainage treatment. Polyvinyl alcohol, as a high molecular polymer, has lubricating and moisturizing effects, which helps to reduce the mechanical damage of the cleaning agent to the membrane, and synergizes with surfactants to enhance the lubricity and protective properties of the cleaning agent. Fatty alcohol polyoxyethylene ether, as a non-ionic surfactant, has excellent emulsification, dispersing and decontamination capabilities, and synergizes with sodium dodecylbenzene sulfonate anionic surfactant to significantly enhance the emulsification effect and decontamination ability of the cleaning agent. Ether helps to accelerate the volatilization and drying process of the cleaning agent, prevents the cleaning agent from remaining on the membrane surface, and works with other ingredients to improve the volatility and drying performance of the cleaning agent.

[0025] Beneficial effects of the present invention: (1) The treatment and recycling method of the present invention introduces a series of process steps such as pretreatment, ultrafiltration separation and nanofiltration separation, and finely controls the parameters of each step. Through this comprehensive treatment process, the complexity and treatment difficulty of wastewater are effectively reduced, while the recovery efficiency of sodium hydroxide is improved.

[0026] (2) In view of the characteristics of alkaline washing wastewater, an adsorbent was prepared for pretreatment. The porous structure and high specific surface area of ​​bagasse were used, combined with the loading of copper ions and the introduction of calcium acrylate, to significantly optimize the adsorption performance. Copper ions, as effective adsorption sites, interact with heterocyclic atoms in organic matter through π complex bonds, enhancing the adsorption capacity for organic matter and oils; at the same time, copper-loaded biochar activates persulfate to produce active species, promoting the degradation of organic pollution. The polymerization reaction of calcium acrylate forms a planar chain or three-dimensional network structure, further increasing the adsorption surface area and sites. The introduction of sodium alginate further improves the stability of the adsorption system, significantly improving the adsorption capacity for organic matter and oil molecules in alkaline wastewater, realizing the resource utilization of waste and improving the efficiency of wastewater treatment, and providing more favorable conditions for subsequent membrane separation processes.

[0027] (3) In view of the special water quality of the alkaline washing waste liquid, the present invention prepares a membrane cleaning agent, which has an optimized formula designed for the pollutant components in the alkaline washing waste liquid and has an excellent cleaning effect. By using the membrane cleaning agent to regularly and efficiently clean the membrane assembly, the permeability of the membrane is maintained, the service life of the membrane is extended, the stable operation of the membrane separation system is ensured, and the reliability and economy of the entire wastewater treatment process are improved. DETAILED DESCRIPTION

[0028] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0029] Example 1 A method for treating and recycling alkali washing wastewater, the specific steps of the recycling method are as follows: S1. Pretreatment: adding the adsorbent to the alkali-washing wastewater, wherein the alkali-washing wastewater has a suspended solid content of 218 mg / L, an oil content of 1235 mg / L, a COD content of 11800 mg / L, and a sodium hydroxide content of 0.6wt%. The amount of the adsorbent added is 0.5% of the weight of the alkali-washing wastewater. Stirring at 40°C and 600 r / min for 30 min to obtain a pretreated mixed solution. S2, ultrafiltration membrane separation: the pretreated mixed liquid is subjected to plate and frame filter pressing, and the plate and frame filtrate is further passed through the ultrafiltration membrane to remove suspended solids and macromolecular substances in the liquid. The ultrafiltration membrane is a ceramic roll membrane, the filtration temperature is 40 °C, the filtration accuracy is 0.2 μm, and the recovery rate of the ultrafiltration membrane is controlled at 95%. After operation, the ultrafiltration membrane is cleaned with a membrane cleaning agent, the mass concentration of the membrane cleaning agent added is 1.5%, the cleaning temperature is set to 80 °C, and the cleaning time is 30 min. After cleaning, the flux of the ceramic ultrafiltration membrane is restored; S3, nanofiltration membrane separation: The ultrafiltration membrane filtrate is filtered through a rolled nanofiltration membrane to remove residual organic matter in the liquid and recover sodium hydroxide. When cleaning the rolled nanofiltration membrane, a membrane cleaning agent with a mass concentration of 0.4% is first used for 60 minutes, and the cleaning temperature is set to 40 °C. After cleaning, the flux of the rolled nanofiltration membrane is restored.

[0030] Wherein, the preparation method of the adsorbent in S1 is as follows: S3-1: 15 parts by weight of bagasse powder was added to 85 parts by weight of deionized water, and ultrasonicated for 30 min. Then, 1.5 parts by weight of copper chloride was added, and stirred at 250 r / min for 8 h. The mixture was placed in a vacuum drying oven at 60 °C for 12 h, and then transferred to a crucible, and then placed in a muffle furnace for calcination under nitrogen protection for 1.5 h at a calcination temperature of 600 °C to obtain powder A. S3-2: 20 parts by weight of powder A were added to 100 parts by weight of deionized water, ultrasonicated for 10 min, 20 parts by weight of calcium oxide were added, stirred at 550 r / min for 30 min, acrylic acid in an equal molar ratio to calcium oxide was added, stirred at 750 r / min for 1.5 h, and dried in a vacuum drying oven at 70 °C for 16 h to obtain powder B; S3-3: Powder B and sodium alginate were mixed in a mass ratio of 4:1, and the mixture was placed in a ball mill for 3 h at a ball mill speed of 250 r / min to obtain the adsorbent.

[0031] The components and mass percentages of the membrane cleaning agent are 10% sodium hydroxide, 17% tetrasodium ethylenediaminetetraacetic acid, 1% propanol, 0.8% ethylene glycol, 0.8% polyvinyl alcohol, 1% sodium dodecylbenzene sulfonate, 0.4% fatty alcohol polyoxyethylene ether, 0.3% ethyl ether, and the balance deionized water.

[0032] Test results: The recovered nanofiltration membrane filtrate contained 5 mg / L of suspended solids, 65 mg / L of oil, 230 mg / L of COD, 0.73 wt% of sodium hydroxide, and a sodium hydroxide recovery rate greater than 100%.

[0033] Example 2 A method for treating and recycling alkali washing wastewater, the specific steps of the recycling method are as follows: S1. Pretreatment: adding the adsorbent to the alkali-washing wastewater, wherein the alkali-washing wastewater has a suspended solid content of 285 mg / L, an oil content of 825 mg / L, a COD content of 10030 mg / L, and a sodium hydroxide content of 0.8 wt %. The amount of the adsorbent added is 4.5% of the weight of the alkali-washing wastewater. Stirring at 550 r / min for 40 min at 42 °C to obtain a pretreated mixed solution. S2, ultrafiltration membrane separation: the pretreated mixed liquid was subjected to plate and frame filter pressing, and the plate and frame filtrate was further passed through a stainless steel ultrafiltration membrane to remove suspended solids and macromolecular substances in the liquid. The filtration temperature was 60 °C, the filtration precision was 0.05 μm, and the recovery rate of the stainless steel ultrafiltration membrane was controlled at 95%. After operation, the stainless steel ultrafiltration membrane was cleaned with a membrane cleaning agent. The mass concentration of the membrane cleaning agent was 2%, the cleaning temperature was set to 55 °C, and the cleaning time was 45 min. After cleaning, the flux of the stainless steel ultrafiltration membrane was restored; S3, nanofiltration membrane separation: The filtrate of the stainless steel ultrafiltration membrane is filtered by a rolled nanofiltration membrane, and the filtrate of the stainless steel membrane enters the nanofiltration membrane for the first separation, and then the first filtrate is filtered by a second nanofiltration membrane to remove residual organic matter in the liquid and recover sodium hydroxide. When cleaning the rolled nanofiltration membrane, first use a membrane cleaning agent with a mass concentration of 0.5% for 40 minutes, and the cleaning temperature is set to 45 °C. After cleaning, the flux of the rolled nanofiltration membrane is restored.

[0034] Wherein, the preparation method of the adsorbent in S1 is as follows: S3-1: 10 parts by weight of bagasse powder was added to 90 parts by weight of deionized water, ultrasonicated for 20 min, and then 1 part by weight of copper chloride was added, stirred at 200 r / min for 6 h, placed in a 60 °C vacuum drying oven for 12 h, then transferred to a crucible, and then placed in a muffle furnace under nitrogen protection for 1 h. The calcination temperature was 500 °C to obtain powder A; S3-2: 15 parts by weight of powder A were added to 100 parts by weight of deionized water, ultrasonicated for 10 min, 15 parts by weight of calcium hydroxide were added, stirred at 500 r / min for 30 min, acrylic acid in an equal molar ratio to calcium hydroxide was added, stirred at 700 r / min for 1 h, and dried in a vacuum drying oven at 60 °C for 12 h to obtain powder B; S3-3: Powder B and sodium alginate were mixed in a mass ratio of 3:1, and the mixture was placed in a ball mill for 2 h at a ball mill speed of 200 r / min to obtain the adsorbent.

[0035] The components and mass percentages of the membrane cleaning agent are 5% sodium hydroxide, 10% tetrasodium ethylenediaminetetraacetic acid, 0.5% propanol, 0.5% ethylene glycol, 0.5% polyvinyl alcohol, 0.5% sodium dodecylbenzene sulfonate, 0.3% fatty alcohol polyoxyethylene ether, 0.05% ethyl ether, and the balance deionized water.

[0036] Test results: No suspended matter was detected in the recovered secondary nanofiltration membrane filtrate, the oil content was 15 mg / L, the COD content was 23 mg / L, the sodium hydroxide content was 0.92 wt%, and the recovery rate of sodium hydroxide was greater than 100%.

[0037] Example 3 A method for treating and recycling alkali washing wastewater, the specific steps of the recycling method are as follows: S1. Pretreatment: adding the adsorbent to the alkali-washing wastewater, wherein the alkali-washing wastewater has a suspended solid content of 205 mg / L, an oil content of 1025 mg / L, a COD content of 11280 mg / L, and a sodium hydroxide content of 0.5 wt %. The amount of the adsorbent added is 5% of the weight of the alkali-washing wastewater. Stirring at 45 °C and 650 r / min for 60 min, a pretreated mixed solution is obtained. S2, ultrafiltration membrane separation: the pretreated mixed liquid is subjected to plate and frame filter pressing, and the plate and frame filtrate is further passed through the ultrafiltration membrane to remove suspended solids and macromolecular substances in the liquid. The ultrafiltration membrane is a curtain membrane made of PTFE, the filtration temperature is 35 °C, the filtration accuracy is 0.5 μm, and the recovery rate of the ultrafiltration membrane is controlled at 90%. After operation, the ultrafiltration membrane is cleaned with a membrane cleaning agent, the mass concentration of the membrane cleaning agent added is 0.5%, the cleaning temperature is set to 40 °C, and the cleaning time is 60 min. After cleaning, the flux of the ultrafiltration membrane is restored; S3, nanofiltration membrane separation: The ultrafiltration membrane filtrate is filtered through a rolled nanofiltration membrane to remove residual organic matter in the liquid and recover sodium hydroxide. When cleaning the rolled nanofiltration membrane, a membrane cleaning agent with a mass concentration of 0.3% is first used for 60 minutes, and the cleaning temperature is set to 40 °C. After cleaning, the flux of the rolled nanofiltration membrane is restored.

[0038] Wherein, the preparation method of the adsorbent in S1 is as follows: S3-1: 20 parts by weight of bagasse powder were added to 90 parts by weight of deionized water, ultrasonicated for 40 min, and then 2 parts by weight of copper chloride were added, stirred at 300 r / min for 10 h, placed in a 60 °C vacuum drying oven for 12 h, then transferred to a crucible, and then placed in a muffle furnace under nitrogen protection for 2 h. The calcination temperature was 700 °C to obtain powder A; S3-2: 25 parts by weight of powder A were added to 100 parts by weight of deionized water, ultrasonicated for 10 min, 25 parts by weight of calcium oxide were added, stirred at 600 r / min for 30 min, acrylic acid in an equal molar ratio to calcium oxide was added, stirred at 800 r / min for 2 h, and dried in a vacuum drying oven at 80 °C for 24 h to obtain powder B; S3-3: Powder B and sodium alginate were mixed in a mass ratio of 5:1, and the mixture was placed in a ball mill for 4 h at a ball mill speed of 300 r / min to obtain the adsorbent.

[0039] The components and mass percentages of the membrane cleaning agent are 15% sodium hydroxide, 25% tetrasodium ethylenediaminetetraacetic acid, 1.5% propanol, 1% ethylene glycol, 1% polyvinyl alcohol, 1.5% sodium dodecylbenzene sulfonate, 0.5% fatty alcohol polyoxyethylene ether, 0.5% ethyl ether, and the balance deionized water.

[0040] Test results: The recovered nanofiltration membrane filtrate contained 2 mg / L of suspended solids, 35 mg / L of oil, 85 mg / L of COD, and 0.63 wt% of sodium hydroxide. The recovery rate of sodium hydroxide was greater than 100%.

[0041] Comparative Example 1 No copper chloride was added during the preparation of the adsorbent, and the remaining steps were the same as those in Example 1.

[0042] The recovered nanofiltration membrane filtrate contained 16 mg / L of suspended matter, 114 mg / L of oil, 415 mg / L of COD, and 0.46 wt% of sodium hydroxide.

[0043] Comparative Example 2 The preparation of the adsorbent does not involve step S3-2, and the remaining steps are the same as those in Example 1.

[0044] The recovered nanofiltration membrane filtrate contained 21 mg / L of suspended matter, 136 mg / L of oil, 302 mg / L of COD, and 0.52 wt% of sodium hydroxide.

[0045] Comparative Example 3 No sodium alginate was added during the preparation of the adsorbent, and the remaining steps were the same as those in Example 1.

[0046] The recovered nanofiltration membrane filtrate contained 19 mg / L of suspended solids, 97 mg / L of oil, 289 mg / L of COD, and 0.56 wt% of sodium hydroxide.

[0047] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for treating and recycling alkali washing wastewater, characterized in that: The specific steps of the recycling method are as follows: S1. Pretreatment: adding the adsorbent to the alkali-washing wastewater, stirring at 40-45 °C and 550-650 r / min for 30-60 min to obtain a pretreated mixed solution; S2, ultrafiltration membrane separation: the pretreated mixed liquid is subjected to plate and frame filter pressing, and the plate and frame filtrate is further passed through the ultrafiltration membrane to remove suspended solids and macromolecular substances in the liquid. The filtration temperature is 35~70 ℃, the filtration precision is 0.05~0.5 μm, and the recovery rate of the ultrafiltration membrane is controlled at 90%~95%. After operation, the ultrafiltration membrane is cleaned with a membrane cleaning agent. The mass concentration of the membrane cleaning agent is 0.5%~2%, the cleaning temperature is set to 40~80 ℃, and the cleaning time is 30~60 min. After cleaning, the flux of the ultrafiltration membrane is restored; S3, nanofiltration membrane separation: The ultrafiltration membrane filtrate is filtered through a rolled nanofiltration membrane to remove residual organic matter in the liquid and recover sodium hydroxide. When cleaning the rolled nanofiltration membrane, first use a membrane cleaning agent with a mass concentration of 0.1%~0.5% for 30~60 min, and the cleaning temperature is set to 30~40 ℃. After cleaning, the flux of the rolled nanofiltration membrane is restored.

2. The method for treating and recycling alkali washing wastewater according to claim 1, characterized in that: The alkali washing wastewater in S1 has a suspended solid content of 200-300 mg / L, an oil content of 800-1300 mg / L, a COD content of 10000-12000 mg / L, and a sodium hydroxide content of 0.5wt%-0.8wt%.

3. The method for treating and recycling alkali washing wastewater according to claim 1, characterized in that: The preparation method of the adsorbent in S1 is as follows: S3-1: 10-20 parts by weight of bagasse powder was added to 80-90 parts by weight of deionized water, and ultrasonicated for 20-40 min. Then, 1-2 parts by weight of copper chloride was added, and stirred at a speed of 200-300 r / min for 6-10 h. The mixture was placed in a vacuum drying oven at 60 °C and dried for 12 h. Then, the mixture was transferred to a crucible, and then placed in a muffle furnace and calcined under nitrogen protection for 1-2 h to obtain powder A. S3-2: 15-25 parts by weight of powder A are added to 100 parts by weight of deionized water, ultrasonicated for 10 min, 15-25 parts by weight of a calcium source are added, stirred at a speed of 500-600 r / min for 30 min, and then acrylic acid in an equal molar ratio to the calcium source is added, stirred at a speed of 700-800 r / min for 1-2 h, and dried in a vacuum drying oven at 60-80 °C for 12-24 h to obtain powder B; S3-3: Powder B and sodium alginate are mixed in a mass ratio of (3-5):1, and the mixture is placed in a ball mill for 2-4 h to obtain the adsorbent.

4. The method for treating and recycling alkali washing wastewater according to claim 1, characterized in that: The dosage of the adsorbent in S1 is 0.5% to 5% of the weight of the alkali washing wastewater.

5. The method for treating and recycling alkali washing wastewater according to claim 3, characterized in that: The calcination temperature of the muffle furnace in S3-1 is 500-700°C.

6. The method for treating and recycling alkali-washing wastewater according to claim 3, characterized in that: The calcium source in S3-2 is one of calcium oxide and calcium hydroxide.

7. The method for treating and recycling alkali-washing wastewater according to claim 3, characterized in that: The ball milling speed in S3-3 is 200-300 r / min.

8. The method for treating and recycling alkali-washing wastewater according to claim 1, characterized in that: The ultrafiltration membrane structure in S2 is one of tubular, plate, curtain or roll ultrafiltration membranes, and the ultrafiltration membrane material is one of ceramic, stainless steel and PTFE.

9. The method for treating and recycling alkali washing wastewater according to claim 1, characterized in that: The components and mass percentages of the membrane cleaning agent are 5%-15% sodium hydroxide, 10%-25% tetrasodium ethylenediaminetetraacetic acid, 0.5%-1.5% propanol, 0.5%-1% ethylene glycol, 0.5%-1% polyvinyl alcohol, 0.5%-1.5% sodium dodecylbenzene sulfonate, 0.3%-0.5% fatty alcohol polyoxyethylene ether, 0.05%-0.5% ethyl ether, and the balance deionized water.

10. The method for treating and recycling alkali washing wastewater according to claim 1, characterized in that: The rolled nanofiltration membrane filtrate in S3 can be subjected to secondary nanofiltration membrane filtration to further improve the quality of the recovered sodium hydroxide.