A method for treating fluorescent whitening agent wastewater

Abstract

The present application relates to the technical field of industrial wastewater treatment, and particularly discloses a method for treating fluorescent whitening agent wastewater. The method comprises the following steps: firstly, acid precipitation and impurity removal are performed at a specific pH and temperature; secondly, reverse osmosis concentration is performed; and thirdly, secondary acid precipitation and impurity removal are performed at a specific pH and temperature. A large amount of organic matter in the fluorescent whitening agent wastewater is removed in advance, the pressure of a micro-electrolysis process is reduced, and the treatment efficiency of the micro-electrolysis is improved. Meanwhile, the micro-electrolysis is coupled with a Fenton oxidation technology, and the degradation degree of various organic matters in the wastewater is further improved, so that the treated wastewater can directly meet the discharge standard. The whole treatment process is simple, safe and controllable, and is suitable for treating various fluorescent whitening agent wastewater. The whole treatment process does not need to be subjected to biochemical treatment, the treatment cost of the wastewater is effectively reduced, meanwhile, a by-product salt with high added value is obtained, the comprehensive treatment and resource utilization of the fluorescent whitening agent wastewater are realized, and the present application has high practical value.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for treating fluorescent whitening agent wastewater. Background Technology

[0002] Optical brighteners are fluorescent dyes widely used in textiles, detergents, papermaking, printing, leather, plastics, synthetic fibers, paints, inks and other industries. The production process of optical brighteners will discharge a large amount of high-concentration, difficult-to-treat organic wastewater, which will seriously pollute the water environment and restrict the survival and development of enterprises. The wastewater from the production of optical brighteners has the following characteristics: (1) The wastewater has a complex composition. The organic pollutants in it mainly include benzene and its derivatives containing amino, nitro and sulfonic acid groups. These organic pollutants will inhibit the activity of microorganisms, resulting in extremely poor biodegradability of the wastewater; (2) The wastewater contains a high salt content, which will greatly affect the osmotic pressure balance of biological cells in the biochemical reaction unit, thus leading to the death of microorganisms. In addition, the presence of certain inorganic salts will also act as biological inhibitors to inhibit the action of biological enzymes, thereby inhibiting the growth of microorganisms; (3) Optical brighteners are mostly artificially synthesized macromolecular organic compounds with relative molecular masses ranging from hundreds to thousands. Most optical brighteners themselves cannot be degraded by microorganisms. Their degradation effect mainly comes from the adsorption of activated sludge. Therefore, due to the complex and variable composition, high toxicity, and poor biodegradability of wastewater from the production of fluorescent whitening agents, the use of biological treatment units cannot meet the wastewater discharge requirements.

[0003] Currently, most domestic treatment methods for fluorescent whitening agent wastewater involve first subjecting it to advanced physical and chemical oxidation followed by biochemical treatment. This process is lengthy and complex. Existing technologies disclose methods for treating fluorescent whitening agent wastewater using electrocatalytic oxidation, micro-electrolysis, and biochemical methods. However, these methods treat only a single type of wastewater, and the electrocatalytic oxidation process generates chlorine gas, posing safety and secondary pollution risks. Therefore, there is an urgent need for an economical and efficient method for treating fluorescent whitening agent wastewater that does not generate secondary pollution. Summary of the Invention

[0004] To address the problems of high treatment difficulty, single-source wastewater treatment, and secondary pollution caused by existing fluorescent whitening agent wastewater treatment methods, this invention provides a method for treating fluorescent whitening agent wastewater. This method primarily utilizes acid precipitation for impurity removal, reverse osmosis concentration, secondary acid precipitation for impurity removal, and iron-carbon micro-electrolysis coupled with Fenton oxidation technology. This achieves deep degradation of various recalcitrant organic compounds in the fluorescent whitening agent wastewater, while also yielding high-quality by-product salts, realizing the resource utilization of the production wastewater without secondary pollution problems, thus demonstrating high economic and environmental benefits.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0006] A method for treating fluorescent whitening agent wastewater includes the following steps:

[0007] Step a: Adjust the pH of the fluorescent whitening agent wastewater to 1-4, add activated carbon, heat to 60℃-85℃ and keep warm for 0.5h-2h, add filter aid, filter, and obtain the first filtrate;

[0008] Step b: Adjust the pH of the first filtrate to neutral, and concentrate it by reverse osmosis to obtain concentrated wastewater;

[0009] Step c: Adjust the pH of the concentrated wastewater to 3-4, add activated carbon, heat to 60℃-85℃ and keep warm for 0.5h-2h, add filter aid, filter, and obtain the second filtrate;

[0010] Step d: Adjust the pH of the second filtrate to 1-4, add iron-carbon packing material, and add hydrogen peroxide to the system while performing aeration and micro-electrolysis. After micro-electrolysis, adjust the pH to 6-9, add activated carbon and flocculant, filter, and obtain the third filtrate.

[0011] Step e: Concentrate the third filtrate to obtain by-product salt.

[0012] Compared to existing technologies, the method for treating fluorescent whitening agent wastewater provided by this invention first removes impurities through acid precipitation at a specific pH and temperature, followed by reverse osmosis concentration and a second acid precipitation at a specific pH and temperature. This pre-removal of a large amount of organic matter in the fluorescent whitening agent wastewater reduces the pressure on the micro-electrolysis process and improves its treatment efficiency. Simultaneously, the micro-electrolysis coupled with Fenton oxidation technology further enhances the degradation of various organic substances in the wastewater, enabling the treated wastewater to directly meet discharge standards. This invention, through simple two-stage acid precipitation removal combined with micro-electrolysis and Fenton oxidation technology, reduces the COD of the treated wastewater to below 200 mg / L. This not only reduces wastewater treatment costs but also yields high-quality by-product salts, realizing the resource utilization of fluorescent whitening agent wastewater and demonstrating high application prospects.

[0013] The entire process of this invention is simple, safe, and controllable, and is applicable to the treatment of various fluorescent whitening agent wastewaters. The entire process does not require biochemical treatment, effectively reducing the cost of wastewater treatment. At the same time, it also yields high-value-added by-product salts, realizing the comprehensive treatment and resource utilization of fluorescent whitening agent production wastewater. It effectively solves the problem of fluorescent whitening agent wastewater treatment, has high economic and environmental benefits, and high practical value.

[0014] It should be noted that the fluorescent whitening agent wastewater described in this invention refers to triazine aminostilbene type or modified fluorescent whitening agents. These whitening agents have high solubility in water, with COD levels in the wastewater reaching approximately 10,000 mg / L and TOC exceeding 4,000 mg / L. They are resistant to strong acids and alkalis, making them difficult to treat. The fluorescent whitening agent wastewater treatment method provided by this invention is not only applicable to triazine aminostilbene type or modified fluorescent whitening agents, but also to the treatment of various other types of whitening agent wastewater. It achieves excellent treatment results for different types of whitening agent wastewater, providing a new method for treating fluorescent whitening agent wastewater without biochemical treatment, which is of great significance for achieving clean production of fluorescent whitening agents.

[0015] Preferably, in step a, the activated carbon is at least one of wood-based carbon, coal-based carbon, or coconut shell carbon, and its addition amount is 5‰ to 2% of the mass of the fluorescent whitening agent wastewater.

[0016] During their experiments, the inventors discovered that commonly used methods in wastewater treatment, such as micro-electrolysis, advanced Fenton oxidation, or a combination of micro-electrolysis and staged oxidation, failed to effectively degrade fluorescent whitening agent wastewater and thus could not meet wastewater discharge requirements. The inventors analyzed that this was because fluorescent whitening agent wastewater, especially modified triazine aminostilbene type fluorescent whitening agent wastewater, had a high organic content. Simple micro-electrolysis and / or advanced Fenton oxidation methods were insufficient to completely degrade the high organic content in the wastewater. Therefore, the inventors creatively proposed a method to pre-remove some organic matter before micro-electrolysis treatment, so that the organic matter content in the wastewater reached the limit for micro-electrolysis treatment. However, after numerous experiments, the inventors found that pre-removing organic matter from the wastewater was difficult. Although some methods could remove some organic matter to a certain extent, the remaining organic matter content in the wastewater remained high, and subsequent oxidation treatment still could not effectively reduce the COD of the wastewater. Through ingenuity, the inventors discovered that only by using a method of acid precipitation followed by concentration and then acid precipitation at specific pH and temperature can organic matter in wastewater be removed as much as possible, thereby achieving complete degradation of organic matter in subsequent micro-electrolysis and Fenton synergistic degradation processes.

[0017] Preferably, in step a, the filter aid is at least one of diatomaceous earth, perlite, cellulose, asbestos, graphite powder, sawdust, or paper pulp, and its addition amount is 1‰ to 2‰ of the mass of the fluorescent whitening agent wastewater.

[0018] Adding activated carbon and filter aids after acid precipitation can effectively adsorb colored impurities in wastewater and improve filtration efficiency, thereby effectively improving the wastewater treatment efficiency.

[0019] In one specific embodiment of the present invention, in step a, hydrochloric acid, sulfuric acid, or nitric acid is used to adjust the pH of the wastewater to 1-4. Within this pH range, a large amount of organic matter and sodium carbonate precipitate out of the wastewater, effectively reducing the pressure of subsequent micro-electrolysis treatment and improving the efficiency of subsequent reverse osmosis concentration.

[0020] It should be noted that, in order to obtain a single-component by-product salt, the same acid is used to adjust the pH in steps a and c. Hydrochloric acid is preferably used to adjust the pH of the system.

[0021] Preferably, in step b, 70% to 80% of the water is removed by reverse osmosis concentration.

[0022] Concentrating the wastewater after the first acid washing can increase the amount of organic matter released during the second acid precipitation, thereby effectively reducing the pressure on subsequent micro-electrolysis treatment.

[0023] The freshwater obtained after reverse osmosis concentration has a COD ≤ 100 mg / L, a total salt content ≤ 50 ppm, and a chloride ion content ≤ 40 ppm, and can be directly reused in the production of fluorescent whitening agents.

[0024] Preferably, in step b, neutrality refers to a pH of 6 to 7.

[0025] In one specific embodiment of the present invention, in step b, sodium hydroxide, potassium hydroxide, ammonia water, or ammonia gas are used to adjust the pH of the system to 6-7.

[0026] It should be noted that, in order to obtain a single by-product salt, the same base is used to adjust the pH in steps b and d. Sodium hydroxide is preferably used to adjust the pH of the system.

[0027] Preferably, in step c, the activated carbon is at least one of wood-based carbon, coal-based carbon, or coconut shell carbon, and its addition amount is 5‰ to 2% of the mass of concentrated wastewater.

[0028] Preferably, in step c, the filter aid is at least one of diatomaceous earth, perlite, cellulose, asbestos, graphite powder, sawdust, or paper pulp, and its addition amount is 1‰ to 2‰ of the mass of the concentrated wastewater.

[0029] Preferably, in step d, the amount of hydrogen peroxide added is 0.2% to 1% of the mass of the second filtrate.

[0030] Furthermore, in step d, the hydrogen peroxide is added to the system multiple times, preferably in four separate additions.

[0031] For example, in step d, the concentration of the hydrogen peroxide is 28wt% to 30wt%.

[0032] Preferably, in step d, the iron-carbon filler is granular carbon and iron filings in a mass ratio of 1 to 3:1, and its addition amount is 8% to 12% of the mass of the second filtrate wastewater.

[0033] Preferably, in step d, the micro-electrolysis time is 1h to 4h.

[0034] Preferably, in step d, the flocculant is at least one of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, or polyferric sulfate, and its addition amount is 1‰ to 5‰ of the mass of the second filtrate.

[0035] Preferably, in step d, the activated carbon is at least one of wood-based charcoal, coal-based charcoal, or coconut shell charcoal, and its addition amount is 1% to 3% of the mass of the second filtrate.

[0036] The above-mentioned optimized process conditions can reduce the COD in the wastewater after micro-electrolysis to below 200 mg / L, meeting the wastewater discharge standards.

[0037] In one specific embodiment of the present invention, plate and frame filtration is used for all filtration processes.

[0038] In one specific embodiment of the present invention, in step e, MVR evaporation and concentration are used. The COD of the water obtained by evaporation and concentration is ≤100ppm, which can be directly recycled back to the production process of fluorescent whitening agent. The liquid obtained by evaporation and concentration is separated by centrifuge, and the by-product salt and mother liquor are obtained. The mother liquor is recycled back to step a and combined with the fluorescent whitening agent wastewater for treatment.

[0039] The method for treating fluorescent whitening agent wastewater provided by this invention is simple to operate, has low energy consumption, and can completely reduce the high content of organic matter in the wastewater without the need for traditional biochemical treatment. At the same time, the recovered high-value-added by-product salt can be sold as an industrial product, which also helps to reduce the treatment cost of fluorescent whitening agent wastewater. Therefore, this invention not only effectively solves the problem of fluorescent whitening agent wastewater treatment, but also realizes the comprehensive treatment and resource utilization of wastewater, which has high economic and environmental benefits and extremely high promotion value. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] To better illustrate the present invention, further examples are provided below.

[0042] In the following examples and comparative examples, the fluorescence intensity of the fluorescent whitening agent wastewater was 0.95, the pH was 9.6 (25℃), the COD was 11000 mg / L, the TOC was 4150 mg / L, and the chloride ion content was 13000 mg / L.

[0043] Example 1

[0044] This embodiment provides a method for treating fluorescent whitening agent wastewater, including the following steps:

[0045] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 3 over 25 minutes. Then add activated carbon at 5‰ of the wastewater's mass, heat to 60℃ and maintain the temperature for 0.5 hours. Next, add diatomaceous earth at 1‰ of the wastewater's mass, and filter through a plate and frame filter for 25 minutes to obtain the first filtrate. The first filtrate contains 14000 mg / L chloride ions, 5000 mg / L COD, 0.46 fluorescence intensity, and 2700 mg / L TOC.

[0046] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 6, then concentrate the wastewater through a reverse osmosis membrane. After concentrating the wastewater and removing 80% of the water, stop the concentration. The resulting concentrated wastewater has 62,000 mg / L chloride ions, 22,700 mg / L COD, 2.0 fluorescence intensity, and 13,300 mg / L TOC. The resulting freshwater has 75 mg / L COD, 36 ppm total salt, and ≤20 ppm chloride ions.

[0047] Step 3: Slowly add hydrochloric acid to the concentrated wastewater to adjust the pH to 3 over 30 minutes. Add activated carbon at 8‰ of the concentrated wastewater mass, heat to 60℃ and maintain the temperature for 0.5 hours. After the temperature maintenance is complete, add diatomaceous earth at 1‰ of the concentrated wastewater mass, filter through a plate and frame filter for 30 minutes to obtain the second filtrate. The second filtrate contains 62700 mg / L chloride ions, 6253 mg / L COD, 0.52 fluorescence intensity, and 3000 mg / L TOC.

[0048] Step 4: The second filtrate is subjected to iron-carbon micro-electrolysis. The iron-carbon packing material is granular carbon and iron filings in a mass ratio of 2:1, and its addition amount is 10% of the mass of the second filtrate wastewater. During aeration and micro-electrolysis, 30% hydrogen peroxide is added in four portions, with a total addition amount of 0.5% of the mass of the second filtrate. The aeration and micro-electrolysis time is 1 hour. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 7. Then, 1.5% of the mass of the second filtrate activated carbon and 1‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain the third filtrate. The third filtrate contains 62950 mg / L chloride ions, 152 mg / L COD, 0.002 fluorescence intensity, 22 mg / L TOC, and 60 color.

[0049] Step 5: The third filtrate is concentrated by MVR evaporation to 82%. The concentrate is centrifuged and dried to obtain white solid sodium chloride with a purity of 99.7%. The evaporation product water has a COD of 65 ppm. The centrifuged mother liquor is returned to Step 1.

[0050] Example 2

[0051] This embodiment provides a method for treating fluorescent whitening agent wastewater, including the following steps:

[0052] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 1 over 35 minutes. Then add activated carbon at 2% of the wastewater's mass, heat to 70°C and keep warm for 2 hours. Next, add diatomaceous earth at 2‰ of the wastewater's mass, and filter through a plate and frame filter for 28 minutes to obtain the first filtrate. The first filtrate contains 14850 mg / L chloride ions, 4952 mg / L COD, 0.45 fluorescence intensity, and 2697 mg / L TOC.

[0053] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 7, then concentrate the wastewater through a reverse osmosis membrane. After concentrating the wastewater and removing 75% of the water, stop the concentration. The resulting concentrated wastewater has 59350 mg / L chloride ions, 19800 mg / L COD, 1.77 fluorescence intensity, and 10690 mg / L TOC. The resulting freshwater has 79 mg / L COD, 37 ppm total salt, and ≤22 ppm chloride ions.

[0054] Step 3: Slowly add hydrochloric acid to the concentrated wastewater to adjust the pH to 4, taking 25 minutes. Add activated carbon at 5‰ of the concentrated wastewater mass, heat to 75℃ and keep warm for 2 hours. After the warming period, add diatomaceous earth at 1.5‰ of the concentrated wastewater mass, filter by plate and frame filter for 28 minutes to obtain the second filtrate. The second filtrate contains 60329 mg / L chloride ions, 5545 mg / L COD, 0.5 fluorescence intensity, and 3020 mg / L TOC.

[0055] Step 4: The second filtrate is subjected to iron-carbon micro-electrolysis. The iron-carbon packing material is granular carbon and iron filings in a 1:1 mass ratio, and its addition amount is 8% of the mass of the second filtrate wastewater. During aeration and micro-electrolysis, 30% hydrogen peroxide is added in four portions, with a total addition amount of 0.2% of the mass of the second filtrate. The aeration and micro-electrolysis time is 4 hours. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 9. Then, 3% of the mass of the second filtrate activated carbon and 5‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain the third filtrate. The third filtrate contains 60554 mg / L chloride ions, 139 mg / L COD, 0.0018 fluorescence intensity, 20 mg / L TOC, and 58 color.

[0056] Step 5: The third filtrate is concentrated by MVR evaporation to 83%. The concentrate is centrifuged and dried to obtain white solid sodium chloride with a purity of 99.6%. The evaporation product water has a COD of 57 ppm. The centrifuged mother liquor is returned to Step 1.

[0057] Example 3

[0058] This embodiment provides a method for treating fluorescent whitening agent wastewater, including the following steps:

[0059] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 4 over 20 minutes. Then add activated carbon at 1% of the wastewater's mass, heat to 85°C and keep warm for 1 hour. Next, add diatomaceous earth at 1.5‰ of the wastewater's mass, filter through a plate and frame filter for 30 minutes to obtain the first filtrate. The first filtrate contains 13980 mg / L chloride ions, 4997 mg / L COD, 0.46 fluorescence intensity, and 2706 mg / L TOC.

[0060] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 6, then concentrate it through a reverse osmosis membrane. The wastewater is concentrated to remove 70% of the water. Concentration is then stopped. The resulting concentrated wastewater has 46586 mg / L chloride ions, 16646 mg / L COD, 1.47 fluorescence intensity, and 9746 mg / L TOC. The resulting freshwater has 64 mg / L COD, 30 ppm total salt, and ≤17 ppm chloride ions.

[0061] Step 3: Slowly add hydrochloric acid to the concentrated wastewater to adjust the pH to 3, taking 26 minutes. Add 2% activated carbon (by weight of the concentrated wastewater), heat to 85℃ and hold for 0.5 hours. After holding, add 2‰ diatomaceous earth (by weight of the concentrated wastewater), filter by plate and frame filter for 26 minutes to obtain the second filtrate. The second filtrate contains 46735 mg / L chloride ions, 5497 mg / L COD, 0.485 fluorescence intensity, and 2958 mg / L TOC.

[0062] Step 4: The second filtrate is subjected to iron-carbon micro-electrolysis. The iron-carbon packing material is granular carbon and iron filings in a mass ratio of 3:1, and its addition amount is 12% of the mass of the second filtrate wastewater. During aeration and micro-electrolysis, 28% hydrogen peroxide is added in four portions, with a total addition amount of 1% of the mass of the second filtrate. The aeration and micro-electrolysis time is 2 hours. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 6. Then, 1% of the mass of the second filtrate activated carbon and 1‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain the third filtrate. The third filtrate contains 47032 mg / L chloride ions, 138 mg / L COD, 0.001 fluorescence intensity, 12 mg / L TOC, and 47 color.

[0063] Step 5: The third filtrate is concentrated by MVR evaporation to 80%. The concentrate is centrifuged and dried to obtain white solid sodium chloride with a purity of 99.6%. The evaporation product water has a COD of 51 ppm. The centrifuged mother liquor is returned to Step 1.

[0064] In the above Examples 1 to 3, the use of other acids or bases as defined in this invention to adjust the pH, as well as other filter aids or other flocculants, can achieve technical effects comparable to those in the corresponding examples.

[0065] Comparative Example 1

[0066] This comparative example provides a method for treating fluorescent whitening agent wastewater, which differs from Example 1 only in that acid precipitation is not performed before micro-electrolysis. Specifically, it includes the following steps:

[0067] Step 1: The fluorescent whitening agent wastewater is subjected to iron-carbon micro-electrolysis. The iron-carbon filler is granular carbon and iron filings in a mass ratio of 2:1, and its addition amount is 10% of the mass of the fluorescent whitening agent wastewater. During aeration and micro-electrolysis, 30% hydrogen peroxide is added in four portions, with a total addition amount of 0.5% of the mass of the fluorescent whitening agent wastewater. The aeration and micro-electrolysis time is 1 hour. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 7. Then, 1.5% of the mass of the fluorescent whitening agent wastewater, activated carbon, and 1‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain micro-electrolyzed water. The micro-electrolyzed water has a chloride ion concentration of 13100 mg / L, a COD of 6800 mg / L, a fluorescence intensity of 0.54, and an effluent color of red.

[0068] Comparative Example 2

[0069] This comparative example provides a method for treating fluorescent whitening agent wastewater, which differs from Example 1 only in that the secondary acid precipitation for impurity removal in step three is omitted. The specific steps are as follows:

[0070] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 3 over 25 minutes. Then add activated carbon at 5‰ of the wastewater's mass, heat to 60℃ and maintain the temperature for 0.5 hours. Next, add diatomaceous earth at 1‰ of the wastewater's mass, and filter through a plate and frame filter for 25 minutes to obtain the first filtrate. The first filtrate contains 14032 g / L chloride ions, 5078 mg / L COD, 0.46 fluorescence intensity, and 2713 mg / L TOC.

[0071] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 6, then concentrate the wastewater through a reverse osmosis membrane. After concentrating the wastewater and removing 80% of the water, stop the concentration. The resulting concentrated wastewater has 62,173 mg / L chloride ions, 22,060 mg / L COD, 2.2 fluorescence intensity, and 13,398 mg / L TOC. The resulting freshwater has 78 mg / L COD, 37 ppm total salt, and ≤20 ppm chloride ions.

[0072] Step 3: Perform iron-carbon micro-electrolysis on the concentrated wastewater. The iron-carbon packing material is granular carbon and iron filings in a mass ratio of 2:1, and its addition amount is 10% of the concentrated wastewater mass. During aeration and micro-electrolysis, 30% hydrogen peroxide is added in four portions, with a total addition amount of 0.5% of the concentrated wastewater mass. The aeration and micro-electrolysis time is 1 hour. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 7. Then, 1.5% of the concentrated wastewater mass of activated carbon and 1‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain micro-electrolyzed water. The micro-electrolyzed water has a chloride ion concentration of 62314 mg / L, a COD concentration of 5896 mg / L, a fluorescence intensity of 0.5, a TOC concentration of 3083 mg / L, and a dark reddish-brown color.

[0073] Comparative Example 3

[0074] This comparative example provides a method for treating fluorescent whitening agent wastewater, which differs from Example 1 only in the pH value adjusted in steps one and five. Specifically, it includes the following steps:

[0075] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 5, then add 5‰ activated carbon (by weight of the fluorescent whitening agent wastewater), heat to 60℃ and keep warm for 0.5h, then add 1‰ diatomaceous earth (by weight of the fluorescent whitening agent wastewater), filter by plate and frame filter to obtain the first filtrate; the first filtrate contains 13400mg / L chloride ions, 9600mg / L COD, 0.92 fluorescence intensity, and 12950mg / L TOC.

[0076] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 6. Concentrate the wastewater through a reverse osmosis membrane. When 62% of the water is removed by the concentration, the reverse osmosis membrane becomes clogged, and the concentration is stopped. The resulting concentrated wastewater has 35,620 mg / L chloride ions, 27,000 mg / L COD, 2.59 fluorescence intensity, and 40,460 mg / L TOC. The resulting freshwater has 78 mg / L COD, 37 ppm total salt, and ≤20 ppm chloride ions.

[0077] Step 3: Slowly add hydrochloric acid to the concentrated wastewater to adjust the pH to 5, add activated carbon at 8‰ of the concentrated wastewater mass, heat to 60℃ and keep warm for 0.5h. After the holding time is completed, add diatomaceous earth at 1‰ of the concentrated wastewater mass, filter by plate and frame for 3h to obtain the second filtrate; the second filtrate contains chloride ions 35700mg / L, COD 19200mg / L, fluorescence intensity 1.35, and TOC 9400mg / L.

[0078] Step 4: The second filtrate is subjected to iron-carbon micro-electrolysis. The iron-carbon packing material is granular carbon and iron filings in a mass ratio of 2:1, and its addition amount is 10% of the mass of the second filtrate wastewater. During aeration and micro-electrolysis, 30% hydrogen peroxide is added in four portions, with a total addition amount of 0.5% of the mass of the second filtrate. The aeration and micro-electrolysis time is 1 hour. After the micro-electrolysis is completed, sodium hydroxide is added to adjust the pH to 7. Then, 1.5% of the mass of the second filtrate activated carbon and 1‰ of polyaluminum chloride are added. The mixture is then filtered through a plate and frame filter to obtain the third filtrate. The third filtrate contains 35720 mg / L chloride ions, 10005 mg / L COD, 1.1 fluorescence intensity, and 75200 mg / L TOC. The effluent is reddish-brown.

[0079] Comparative Example 4

[0080] This comparative example provides a method for treating fluorescent whitening agent wastewater, which differs from Example 1 only in that micro-electrolysis and Fenton oxidation are performed in steps, specifically including the following steps:

[0081] Step 1: Slowly add hydrochloric acid to the fluorescent whitening agent wastewater to adjust the pH to 3 over 25 minutes. Then add activated carbon at 5‰ of the wastewater's mass, heat to 60℃ and maintain the temperature for 0.5 hours. Next, add diatomaceous earth at 1‰ of the wastewater's mass, and filter through a plate and frame filter for 25 minutes to obtain the first filtrate. The first filtrate contains 13740 mg / L chloride ions, 6050 mg / L COD, 0.49 fluorescence intensity, and 2803 mg / L TOC.

[0082] Step 2: Add sodium hydroxide to the first filtrate to adjust the pH to 6, then concentrate the wastewater through a reverse osmosis membrane. After concentrating the wastewater and removing 80% of the water, stop the concentration. The resulting concentrated wastewater has 68,700 mg / L chloride ions, 30,250 mg / L COD, 2.23 fluorescence intensity, and 14,000 mg / L TOC. The resulting freshwater has 80 mg / L COD, 39 ppm total salt, and ≤20 ppm chloride ions.

[0083] Step 3: Slowly add hydrochloric acid to the concentrated wastewater to adjust the pH to 3 over 30 minutes. Add activated carbon at 8‰ of the concentrated wastewater mass, heat to 60℃ and maintain the temperature for 0.5 hours. After the temperature maintenance is complete, add diatomaceous earth at 1‰ of the concentrated wastewater mass, filter through a plate and frame filter for 30 minutes to obtain the second filtrate. The second filtrate contains 69,000 mg / L chloride ions, 6,300 mg / L COD, 0.54 fluorescence intensity, and 3012 mg / L TOC.

[0084] Step 4: The second filtrate is subjected to iron-carbon micro-electrolysis. The iron-carbon packing material is granular carbon and iron filings in a mass ratio of 2:1. The amount added is 10% of the mass of the second filtrate wastewater. The aeration and micro-electrolysis time is 1 hour to obtain micro-electrolyzed water. The micro-electrolyzed water has 66920 mg / L of chloride ions, 4370 mg / L of COD, 0.34 of fluorescence intensity, 2200 mg / L of TOC, and the effluent is reddish-brown.

[0085] Step 5: Add 2% ferrous sulfate (by mass) to the micro-electrolyzed water and 30% hydrogen peroxide (by mass) in four portions at room temperature, with a total addition of 0.5% of the mass of the micro-electrolyzed water. Oxidize for 1 hour, then add sodium hydroxide to adjust the pH to 7. Next, add 1.5% activated carbon (by mass of the micro-electrolyzed water) and 1‰ polyaluminum chloride. Filter using a plate and frame filter. The filtrate contains 62950 mg / L chloride ions, 2200 mg / L COD, 0.2 fluorescence intensity, and 1750 mg / L TOC. The effluent is red.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating fluorescent whitening agent wastewater, wherein the fluorescent whitening agent wastewater refers to wastewater containing triazine aminostilbene type or modified thereof fluorescent whitening agents, characterized in that, Includes the following steps: Step a: Adjust the pH of the fluorescent whitening agent wastewater to 1-4, add activated carbon, heat to 60℃-85℃ and keep warm for 0.5h-2h, add filter aid, filter, and obtain the first filtrate; Step b: Adjust the pH of the first filtrate to neutral, and remove 70% to 80% of the water by reverse osmosis concentration to obtain concentrated wastewater; Step c: Adjust the pH of the concentrated wastewater to 3-4, add activated carbon, heat to 60℃-85℃ and keep warm for 0.5h-2h, add filter aid, filter, and obtain the second filtrate; Step d: Adjust the pH of the second filtrate to 1-4, add iron-carbon packing material, and add hydrogen peroxide to the system while performing aeration and micro-electrolysis. After micro-electrolysis, adjust the pH to 6-9, add activated carbon and flocculant, filter, and obtain the third filtrate. Step e: Concentrate the third filtrate to obtain by-product salt.

2. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step a, the activated carbon is at least one of wood-based charcoal, coal-based charcoal, or coconut shell charcoal, and its addition amount is 5‰~2% of the mass of the fluorescent whitening agent wastewater; and / or In step a, the filter aid is at least one of diatomaceous earth, perlite, cellulose, asbestos, graphite powder, sawdust, or paper pulp, and its addition amount is 1‰ to 2‰ of the mass of the fluorescent whitening agent wastewater.

3. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step b, neutrality refers to a pH of 6-7.

4. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step c, the activated carbon is at least one of wood-based charcoal, coal-based charcoal, or coconut shell charcoal, and its addition amount is 5‰~2% of the mass of the concentrated wastewater; and / or In step c, the filter aid is at least one of diatomaceous earth, perlite, cellulose, asbestos, graphite powder, sawdust, or paper pulp, and its addition amount is 1‰ to 2‰ of the mass of the concentrated wastewater.

5. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step d, the amount of hydrogen peroxide added is 0.2% to 1% of the mass of the second filtrate.

6. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step d, the iron-carbon filler is granular carbon and iron filings in a mass ratio of 1 to 3:1, and its addition amount is 8% to 12% of the mass of the second filtrate wastewater.

7. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step d, the micro-electrolysis time is 1h to 4h.

8. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step d, the flocculant is at least one of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, or polyferric sulfate, and its addition amount is 1‰ to 5‰ of the mass of the second filtrate.

9. The method for treating fluorescent whitening agent wastewater as described in claim 1, characterized in that, In step d, the activated carbon is at least one of wood-based carbon, coal-based carbon, or coconut shell carbon, and its addition amount is 1% to 3% of the mass of the second filtrate.