A method for treating painting wastewater

Abstract

The application discloses a kind of coating wastewater treatment methods, high concentration degreasing wastewater is collected separately with low concentration electrophoresis wastewater, surface adjustment wastewater, washing wastewater, and the method of pickling precipitation is used to treat coating degreasing wastewater, and after the degreasing wastewater treated by acidification demulsification is mixed with the remaining other wastewater, it is treated by fenton oxidation and neutralization flocculation precipitation method, to a certain extent, the difficulty of wastewater treatment is reduced, the operation cost of coating wastewater is reduced, and a new idea is provided for vehicle coating industry water pollution prevention and control.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and specifically to a method for treating coating wastewater. Background Technology

[0002] In recent years, my country's industrial development has been rapid, which has led to the leapfrog development of the coating industry. During the processing and manufacturing of mechanical equipment, the coating process generates a large amount of wastewater, such as electrophoresis wastewater, degreasing wastewater, surface conditioning wastewater, and washing wastewater.

[0003] Typically, in the production of automotive parts, to ensure aesthetic appearance, performance, and corrosion resistance of the steel, automotive painting is a primary measure for protecting and decorating the vehicle. As a crucial step in the automotive production process, it involves subjecting the assembled, exposed steel body to a series of chemical anti-corrosion treatments. This ultimately forms several layers of chemical coatings and related protective media on the surface of the steel substrate, including its internal cavities. Its main function is to prevent corrosion of the body panels and enhance the vehicle's appearance. The automotive painting process includes pretreatment, electrophoretic coating, electrophoretic sanding, PVC material sealing, intermediate coat coating, intermediate coat sanding, color paint coating, clear coat coating, baking, finishing and delivery, spot repair, door sill black paint, cavity waxing, and final assembly rework. Painting wastewater mainly originates from the pretreatment processes (pre-degreasing, degreasing, surface conditioning, phosphating, passivation, etc.), cathodic electrophoresis, and intermediate and topcoat spraying processes. Degreasing agents, phosphating agents, surface conditioners, and phosphoric acid are the main pollutants in automotive painting wastewater. Based on this, coating wastewater has the following characteristics: it has many types of wastewater, complex composition, uneven water quality, high pollutant concentration, and poor biodegradability. If it is not properly treated, it will cause serious pollution to the environment.

[0004] Currently, conventional treatment processes for coating wastewater mainly employ physical, chemical, biological, and physicochemical methods. Physical treatment methods include separation, filtration, and centrifugation. Chemical treatment methods mainly include neutralization, coagulation, and oxidation-reduction methods, which involve adding appropriate acids, alkalis, flocculants, oxidants, and reducing agents to the wastewater. Biological treatment, also known as biochemical treatment, utilizes the metabolic processes of microorganisms to oxidize and decompose complex organic matter in the wastewater into carbon dioxide, methane, and water. Physicochemical methods mainly include ion exchange, electrodialysis, and reverse osmosis. However, any of these methods may have drawbacks such as long treatment cycles, large land areas required, high treatment costs, and unstable treatment effects.

[0005] Therefore, most existing coating wastewater treatment processes employ mixed treatment methods, such as initial lime coagulation and sedimentation followed by anaerobic reaction and aerobic oxidation. Because degreasing agents and surface conditioners used in automotive coating processes contain phosphates, and coating additives also contain heavy metals such as zinc, nickel, and manganese, the total phosphorus and heavy metals in the coating wastewater are difficult to meet discharge standards through primary sedimentation. Furthermore, surfactants in the wastewater strongly inhibit acid-producing and methanogenic bacteria during anaerobic reactions, and lipids in the wastewater are difficult to treat to compliance using only aerobic oxidation systems. Additionally, anaerobic and aerobic treatments have specific requirements regarding the pH, temperature, and salinity of the wastewater. Therefore, this treatment method has limitations and its effectiveness is not ideal.

[0006] Another typical coating wastewater treatment process generally involves first adding lime slurry to clarify the solution and adjusting the pH value to 10-11. Most of the phosphates in the wastewater are precipitated and removed. The lime slurry also neutralizes the phosphate while removing it. Then, subsequent treatments such as acid addition, Fenton oxidation, coagulation and sedimentation are carried out. However, this treatment method is also not ideal and consumes a lot of acid and alkali. Summary of the Invention

[0007] 1. The problem to be solved

[0008] To address the problem that existing methods for treating coating wastewater are not effective enough, this invention provides a method for treating coating wastewater.

[0009] A further proposed solution can address the problem of high acid and / or alkali consumption in existing coating wastewater treatment processes.

[0010] 2. Technical Solution

[0011] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0012] A method for treating coating wastewater, the method comprising the following steps:

[0013] S1. Acidify and demulsify the wastewater;

[0014] S2. The effluent from the acidification and demulsification treatment is subjected to Fenton oxidation treatment;

[0015] S3. Perform flocculation and sedimentation treatment on the effluent after Fenton oxidation;

[0016] In step S1, the pH of the wastewater is adjusted to ≤2 using acid to form a solid-liquid blend, and then solid-liquid separation is performed to obtain the effluent from the acidification and demulsification treatment.

[0017] It should be noted that the coating process generates a large amount of wastewater, typically including electrophoresis wastewater, degreasing wastewater, surface conditioning wastewater, and washing wastewater. In S1, the wastewater refers to degreasing wastewater generated during the coating process; the pollutants in this degreasing wastewater are mainly:

[0018] Emulsified oil, content 900–1200 mg / L;

[0019] Surfactant, content 300-400 mg / L;

[0020] COD, content 2000-2500 mg / L;

[0021] Phosphorus content, 80–100 mg / L;

[0022] Zinc, content 15-20 mg / L.

[0023] Furthermore, in step S1, an aeration process is performed.

[0024] It should be noted that in step S1, adjusting the pH of the wastewater to ≤2 using acid is crucial for generating solid precipitates of pollutants and achieving significant removal of pollutants. Therefore, it is preferable to adjust the pH of the wastewater to <2 using acid. In fact, simply adjusting the pH of the wastewater to >2, such as between 2 and 3, only slightly reduces the transparency of the wastewater; it cannot form large flocculent precipitates and achieve solid-liquid gravity separation.

[0025] Based on this, in some embodiments of the present invention, in step S1, an acid solution can be added to the wastewater using a metering pump, thoroughly mixed and aerated, and the pH adjusted to ≤2. After the wastewater is demulsified, a solid-liquid mixture is formed, and most pollutants are converted into solids.

[0026] Furthermore, in step S2, ferrous ions and hydrogen peroxide are added to perform Fenton oxidation treatment;

[0027] The calculation is based on the amount of COD in the water body; the amount of ferrous ions added is 0.04 to 0.1 times the amount of COD; or, the amount of ferrous ions added is 0.1 to 0.2 g / L.

[0028] The mass ratio of added hydrogen peroxide to ferrous ions is (5-8):1.

[0029] It should be noted that, under normal circumstances, the effluent after acidification and demulsification can be directly subjected to Fenton oxidation treatment without the need for additional acid to adjust the pH, which greatly saves on the amount of acid used.

[0030] Furthermore, in S2, the hydraulic residence time during Fenton oxidation treatment is 1 to 2 hours.

[0031] In some embodiments of the present invention, if necessary, a metering pump or other dosing device can be used to add acid to the water. Then, ferrous sulfate is added as ferrous ions, along with hydrogen peroxide; finally, thorough aeration and stirring are performed, and the wastewater retention time is maintained at 1 to 2 hours to fully oxidize and remove organic pollutants from the wastewater.

[0032] Furthermore, in step S3, lime and flocculant are added for flocculation treatment, and the pH value of the water body needs to be adjusted to 7-8; based on this, generally, the amount of lime added is 8-10 g / L; the amount of flocculant added is 0.2-0.5 g / L.

[0033] In some embodiments of the present invention, a dosing device can be used to add lime water to the water body, adjust the pH to neutral, and then add flocculant and stir thoroughly before sedimentation to achieve solid-liquid separation and remove suspended solids, phosphorus, nickel, manganese, zinc and other pollutants from the wastewater.

[0034] In some embodiments of the present invention, after solid-liquid separation, an upper clear liquid and a lower sludge are generated. The upper clear liquid can be directly used as the "effluent from flocculation and sedimentation treatment" for filtration treatment; the lower sludge can be fed into a high-pressure plate and frame filter press for filtration, and the supernatant generated during the filtration process can be returned to the "effluent from flocculation and sedimentation treatment".

[0035] The flocculant can be any one or more of aluminum sulfate, aluminum chloride, ferric sulfate, ferric chloride, polyaluminum chloride (PAC), polyaluminum sulfate (PAS), polyferric chloride (PFC), polyacrylamide (PAM), and polyferric sulfate (PFS).

[0036] Furthermore, in step S1, solid-liquid separation is performed to obtain an upper clear liquid, "effluent from acidification and demulsification treatment," and a lower sludge layer.

[0037] The sludge can be subjected to pressure filtration to obtain filtrate;

[0038] The filtrate is refluxed to the effluent from the acidification and demulsification treatment.

[0039] In some embodiments of the present invention, sludge can be fed into a high-pressure plate and frame filter press for filtration, and the supernatant generated during the filtration process can be returned to the "effluent from acidification and demulsification treatment".

[0040] Furthermore, in practice, conventional coating wastewater treatment often involves mixing the various types of wastewater mentioned above.

[0041] The technical solution of this invention classifies the wastewater generated during the coating process. In particular, the degreasing wastewater is first collected and acidified to form a solid-liquid blend. Solid-liquid separation is then performed to obtain the effluent from the acidification and demulsification treatment. Then, other types of low-concentration wastewater generated during the coating process are mixed and homogenized with the aforementioned effluent from the acidification and demulsification treatment. The next step of Fenton oxidation treatment can be carried out directly, or in special cases, only a very small amount of acid is needed to fine-tune the pH of the liquid.

[0042] The low-concentration wastewater includes any one or more of the following: electrophoretic wastewater, surface conditioning wastewater, and washing wastewater generated during the coating process. The coating process generates a large amount of wastewater, typically including electrophoretic wastewater, degreasing wastewater, surface conditioning wastewater, and washing wastewater. The main pollutants and their concentrations in each type of wastewater are as follows:

[0043] (1) Electrophoresis wastewater, the main pollutants are:

[0044] COD, content 200-250 mg / L;

[0045] Phosphorus, content 8-10 mg / L;

[0046] (2) The main pollutants in the surface treatment wastewater are:

[0047] Surfactant, content 10-20 mg / L;

[0048] COD, content 20-50 mg / L;

[0049] Phosphorus, content 100-150 mg / L;

[0050] Zinc, content 1-2 mg / L.

[0051] (3) Washing wastewater, the main pollutants are:

[0052] Surfactant, content 30-50 mg / L;

[0053] COD, content 90-100 mg / L;

[0054] Phosphorus, content 30-50 mg / L;

[0055] The total amount of nickel, manganese, and zinc shall not exceed 12 mg / L. More specifically: nickel, 1-2 mg / L; manganese, 2-5 mg / L; zinc, 2-5 mg / L.

[0056] Therefore, when introducing low-concentration wastewater into the effluent of the acidification and demulsification treatment, the flow rate of the low-concentration wastewater is 3-4 L / L.

[0057] Furthermore, the method for treating coating wastewater further includes step S4, which involves filtering the effluent from the flocculation and sedimentation treatment. Specifically, the effluent from the flocculation and sedimentation treatment is passed through a sand filter tank for further filtration to remove suspended solids.

[0058] Beneficial effects

[0059] 1. This invention separates high-concentration degreasing wastewater from low-concentration electrophoresis wastewater, surface conditioning wastewater, and washing wastewater, and prioritizes the treatment of degreasing wastewater through acidification and demulsification, which can significantly reduce surfactants and suspended solids in the wastewater and has an extremely high pollutant removal effect on degreasing wastewater.

[0060] Based on this, the effluent from acidification and demulsification can be directly subjected to Fenton oxidation treatment, which can effectively improve the effect of Fenton oxidation.

[0061] Alternatively, the degreasing wastewater that has undergone acidification and demulsification treatment can be mixed with other low-concentration wastewater and then subjected to Fenton oxidation treatment. Compared with conventional wastewater mixing treatment, this method can effectively reduce the difficulty and cost of treatment.

[0062] 2. The coating wastewater treatment process provided by this invention has a high pollutant removal rate, mature technology, and stable operation, which can ensure that the wastewater from the coating industry meets the standards for a long time after treatment, providing a new approach to water pollution prevention and control in the coating industry. Attached Figure Description

[0063] Figure 1 This is a process flow diagram of the technical solution in an embodiment of the present invention. Detailed Implementation

[0064] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field;

[0065] The essential features and significant effects of the present invention can be seen from the following embodiments. The described embodiments are some, but not all, of the embodiments of the present invention. Therefore, they do not limit the present invention in any way. Any non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are within the protection scope of the present invention.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terms used herein and / or include any and all combinations of one or more of the associated listed items.

[0067] The coating process generates a large amount of wastewater, typically including electrophoresis wastewater, degreasing wastewater, surface conditioning wastewater, and washing wastewater. However, it should be noted that in actual production, even wastewater from the same source and using the same process can exhibit fluctuating contaminant levels. The wastewater samples with the following specifications used in this embodiment are provided to illustrate the invention's solution. The purpose is merely to better explain the technical solution and does not imply that the invention itself is incomplete or limited to treating wastewater with the indicated specifications.

[0068] Table 1 shows the indicators of the wastewater treated in the examples.

[0069]

[0070]

[0071] In this embodiment of the invention, the apparatus used in the process of treating coating wastewater includes, in sequence: a degreasing wastewater collection tank, an acidification and demulsification tank, a sedimentation tank, a comprehensive equalization tank, a Fenton oxidation tank, a flocculation sedimentation tank, a sand filter tank, and a discharge tank.

[0072] It also includes: sludge thickening tank and plate and frame filter press.

[0073] In terms of methodology:

[0074] The degreasing wastewater collection tank is used to collect degreasing wastewater. In step 1, the degreasing wastewater enters the degreasing wastewater collection tank, where ordinary homogenization and other operations can be performed. Then, it is pumped into the acidification and demulsification tank.

[0075] The acidification demulsification tank is used for acidification demulsification. In step 2, acid solution (sulfuric acid is used in the following examples) is added to the acidification demulsification tank using a metering pump, and the mixture is thoroughly mixed, aerated, and stirred. The pH is adjusted to ≤2. After the wastewater is demulsified, it forms a solid-liquid mixture, and most of the pollutants are converted into solids.

[0076] The sedimentation tank is used to achieve solid-liquid separation of the wastewater after the acidification and demulsification tank treatment. In step 3, the wastewater from the acidification and demulsification tank enters the sedimentation tank for solid-liquid separation. The supernatant enters the general equalization tank, and the sludge in the lower layer enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press, and the filtrate can be returned to the general equalization tank.

[0077] The integrated equalization tank is used to collect the supernatant effluent after solid-liquid separation in the sedimentation tank from the acidified demulsification wastewater, which is the "effluent after acidification demulsification treatment". In step 4, the effluent from the sedimentation tank is thoroughly mixed and homogenized with low-concentration wastewater such as electrophoresis wastewater, surface conditioning wastewater, and washing wastewater in the integrated equalization tank.

[0078] The Fenton oxidation tank is used for Fenton oxidation treatment. In step 5, the wastewater from the general equalization tank enters the Fenton oxidation tank. (If necessary, sulfuric acid can be added to the general equalization tank using a dosing device to adjust the pH to 3, but under normal circumstances, no adjustment is needed to meet the pH requirements for Fenton oxidation treatment.) Ferrous ions (ferrous sulfate is used in this example) and hydrogen peroxide are added, followed by thorough aeration and stirring. The wastewater retention time is maintained at 1 to 2 hours to fully oxidize and remove organic pollutants from the wastewater.

[0079] The flocculation sedimentation tank is used for flocculation and sedimentation. In step 6, the effluent from the Fenton oxidation tank enters the flocculation sedimentation tank. Lime water is added to the general equalization tank using a dosing device to adjust the pH to neutral. After adding solutions such as PAC and PAM and stirring thoroughly, sedimentation is achieved to separate solids and liquids, removing suspended solids, phosphorus, nickel, manganese, zinc, and other pollutants from the wastewater. The resulting lower layer sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press. The filtrate can be returned to the general equalization tank. At the same time, the supernatant enters the sand filter tank for further filtration to remove suspended solids.

[0080] In step 7, the effluent from the sand filter tank enters the discharge pool and is discharged after passing the test.

[0081] The present invention will be further described below with reference to specific embodiments.

[0082] Example 1

[0083] This embodiment provides a method for treating coating wastewater, the steps of which are as follows:

[0084] In step 1, the degreasing wastewater enters the degreasing wastewater collection tank, and then enters the acidification and demulsification tank through a booster pump.

[0085] In step 2, sulfuric acid is added to the acidification demulsification tank using a metering pump, and the mixture is thoroughly mixed, aerated, and stirred. The pH is adjusted to 1.5, and the hydraulic retention time is 20 minutes. After the wastewater is demulsified, a solid-liquid mixture is formed, and the pollutants are converted into solids.

[0086] In step 3, the wastewater from the acidification and demulsification tank (i.e. the effluent after acidification and demulsification treatment) enters the sedimentation tank for solid-liquid separation. The upper clear liquid enters the comprehensive equalization tank, and the lower sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press, and the filtrate can be returned to the comprehensive equalization tank.

[0087] In step 4, the effluent from the sedimentation tank is thoroughly mixed and homogenized with low-concentration wastewater such as electrophoresis wastewater, surface conditioning wastewater, and washing wastewater in the integrated equalization tank.

[0088] In this embodiment, the low-concentration wastewater includes electrophoresis wastewater, surface conditioning wastewater, and washing wastewater, with a volume ratio of 5:1:70.

[0089] The ratio of the amount of low-concentration wastewater introduced to the amount of degreasing wastewater in step 1 is 7:2.

[0090] In step 5, the wastewater from the general equalization tank enters the Fenton oxidation tank, where ferrous sulfate and hydrogen peroxide are added and the tank is fully aerated and stirred. The wastewater retention time is maintained at 1 hour to fully oxidize and remove organic pollutants from the wastewater.

[0091] Ensure that the concentration of the added ferrous ions is 0.1 g / L;

[0092] The concentration of added hydrogen peroxide is 0.6 g / L.

[0093] In step 6, the effluent from the Fenton oxidation tank enters the flocculation sedimentation tank. Lime water is added to the general equalization tank using a dosing device to adjust the pH to neutral. After adding PAC solution and PAM solution and stirring thoroughly, sedimentation is achieved to separate solids and liquids, removing suspended solids, phosphorus, nickel, manganese, zinc and other pollutants from the wastewater. The resulting lower layer sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press. The filtrate can be returned to the general equalization tank. At the same time, the supernatant enters the sand filter tank for further filtration to remove suspended solids.

[0094] Calculated based on the amounts of lime, PAC, and PAM.

[0095] The concentration of the added lime is 8 g / L;

[0096] The concentration of PAC added is 0.2 g / L.

[0097] The concentration of PAM added was 2 mg / L.

[0098] In step 7, the effluent from the sand filter tank enters the discharge pool and is discharged after passing the test.

[0099] Example 2

[0100] This embodiment provides a method for treating coating wastewater, which is basically the same as that in Embodiment 1, except that:

[0101] In step 2, sulfuric acid is added to the acidification and demulsification tank using a metering pump, and the mixture is thoroughly aerated and stirred to adjust the pH to 2.

[0102] The rest is the same as in Example 1.

[0103] Example 3

[0104] This embodiment provides a method for treating coating wastewater, the steps of which are as follows:

[0105] In step 1, the degreasing wastewater enters the degreasing wastewater collection tank, and then enters the acidification and demulsification tank through a booster pump.

[0106] In step 2, sulfuric acid is added to the acidification demulsification tank using a metering pump, and the mixture is thoroughly mixed, aerated, and stirred. The pH is adjusted to <2, and the hydraulic retention time is 20 minutes. After the wastewater is demulsified, a solid-liquid mixture is formed, and the pollutants are converted into solids.

[0107] In step 3, the wastewater from the acidification and demulsification tank (i.e. the effluent after acidification and demulsification treatment) enters the sedimentation tank for solid-liquid separation. The upper clear liquid enters the comprehensive equalization tank, and the lower sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press, and the filtrate can be returned to the comprehensive equalization tank.

[0108] In step 4, the effluent from the sedimentation tank is thoroughly mixed and homogenized with low-concentration wastewater such as electrophoresis wastewater, surface conditioning wastewater, and washing wastewater in the integrated equalization tank.

[0109] In this embodiment, the low-concentration wastewater includes electrophoresis wastewater, surface conditioning wastewater, and washing wastewater, with a ratio of 5:1:70.

[0110] The ratio of the amount of low-concentration wastewater introduced to the amount of degreasing wastewater in step 1 is 7:2.

[0111] In step 5, the wastewater from the general equalization tank enters the Fenton oxidation tank, where ferrous sulfate and hydrogen peroxide are added and the tank is fully aerated and stirred. The wastewater retention time is maintained at 2 hours to fully oxidize and remove organic pollutants from the wastewater.

[0112] Ensure that the concentration of the added ferrous ions is 0.1 g / L;

[0113] The concentration of added hydrogen peroxide is 0.6 g / L.

[0114] In step 6, the effluent from the Fenton oxidation tank enters the flocculation sedimentation tank. Lime water is added to the general equalization tank using a dosing device to adjust the pH to neutral. After adding PAC solution and PAM solution and stirring thoroughly, sedimentation is achieved to separate solids and liquids, removing suspended solids, phosphorus, nickel, manganese, zinc and other pollutants from the wastewater. The resulting lower layer sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press. The filtrate can be returned to the general equalization tank. At the same time, the supernatant enters the sand filter tank for further filtration to remove suspended solids.

[0115] Calculated based on the amounts of lime, PAC, and PAM.

[0116] The concentration of the added lime is 8 g / L;

[0117] The concentration of PAC added is 0.2 g / L.

[0118] The concentration of PAM added was 2 mg / L.

[0119] In step 7, the effluent from the sand filter tank enters the discharge pool and is discharged after passing the test.

[0120] Example 4

[0121] This embodiment provides a method for treating coating wastewater, the steps of which are as follows:

[0122] In step 1, the degreasing wastewater enters the degreasing wastewater collection tank, and then enters the acidification and demulsification tank through a booster pump.

[0123] In step 2, sulfuric acid is added to the acidification demulsification tank using a metering pump, and the mixture is thoroughly mixed, aerated, and stirred. The pH is adjusted to 1.5, and the hydraulic retention time is 20 minutes. After the wastewater is demulsified, a solid-liquid mixture is formed, and the pollutants are converted into solids.

[0124] In step 3, the wastewater from the acidification and demulsification tank (i.e. the effluent after acidification and demulsification treatment) enters the sedimentation tank for solid-liquid separation. The upper clear liquid enters the comprehensive equalization tank, and the lower sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press, and the filtrate can be returned to the comprehensive equalization tank.

[0125] In step 4, the effluent from the sedimentation tank is thoroughly mixed and homogenized with low-concentration wastewater such as electrophoresis wastewater, surface conditioning wastewater, and washing wastewater in the integrated equalization tank.

[0126] In this embodiment, the low-concentration wastewater includes electrophoresis wastewater, surface conditioning wastewater, and washing wastewater, with a volume ratio of 5:1:70.

[0127] The ratio of the amount of low-concentration wastewater introduced to the amount of degreasing wastewater in step 1 is 7:2.

[0128] In step 5, the wastewater from the general equalization tank enters the Fenton oxidation tank, where ferrous sulfate and hydrogen peroxide are added and the tank is fully aerated and stirred. The wastewater retention time is maintained at 1 hour to fully oxidize and remove organic pollutants from the wastewater.

[0129] Ensure that the concentration of the added ferrous ions is 0.2 g / L;

[0130] The concentration of hydrogen peroxide added is 1 g / L.

[0131] In step 6, the effluent from the Fenton oxidation tank enters the flocculation sedimentation tank. Lime water is added to the general equalization tank using a dosing device to adjust the pH to neutral. After adding PAC solution and PAM solution and stirring thoroughly, sedimentation is achieved to separate solids and liquids, removing suspended solids, phosphorus, nickel, manganese, zinc and other pollutants from the wastewater. The resulting lower layer sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press. The filtrate can be returned to the general equalization tank. At the same time, the supernatant enters the sand filter tank for further filtration to remove suspended solids.

[0132] Calculated based on the amounts of lime, PAC, and PAM.

[0133] The concentration of the added lime is 10 g / L;

[0134] The concentration of PAC added was 0.45 g / L.

[0135] The concentration of PAM added was 2 mg / L.

[0136] In step 7, the effluent from the sand filter tank enters the discharge pool and is discharged after passing the test.

[0137] Comparative Example 1

[0138] This comparative example provides another type of method for treating coating wastewater, the steps of which are as follows: basically the same as in Example 1 above, except that...

[0139] In step 2, sulfuric acid is added to the acidification and demulsification tank using a metering pump, and the mixture is thoroughly mixed, aerated, and stirred. The pH is then adjusted to 4, and the rest is the same as in Example 1.

[0140] Comparative Example 2

[0141] This comparative example provides another type of coating wastewater treatment method, the steps of which are as follows: basically the same as the above embodiment 1, except that the coating wastewater is not classified for treatment. That is, in step 1, the mixed coating wastewater (degreasing wastewater, electrophoresis wastewater, surface conditioning wastewater, and washing wastewater) is put into the wastewater collection tank and then pumped into the acidification and demulsification tank.

[0142] The rest is the same as in Example 1.

[0143] Comparative Example 3

[0144] This comparative example provides another type of treatment method for coating wastewater. The difference between the other examples 1 and the previous ones is that the treatment sequence is: first adding alkali to neutralize and flocculate, then adding acid for Fenton oxidation, and then adding alkali to neutralize and flocculate again.

[0145] Specifically as follows:

[0146] Replace steps 2 and 3 of the acidification demulsification and solid-liquid separation in Example 1 with the following steps:

[0147] The mixed coating wastewater (degreasing wastewater, electrophoresis wastewater, surface conditioning wastewater, and washing wastewater) is fed into a wastewater equalization tank for mixing and homogenization. The effluent then enters a neutralization and flocculation sedimentation tank, where lime, PAC, and PAM are added for neutralization, flocculation, and sedimentation to remove suspended solids, phosphorus, nickel, manganese, zinc, and other pollutants from the wastewater. The resulting lower layer sludge is concentrated and stored in a sludge thickening tank, and subsequently treated by a plate and frame filter press. The filtrate can be returned to the integrated equalization tank. At the same time, the supernatant enters a pH adjustment tank to adjust the pH to 2.

[0148] The concentration of the added lime is 8 g / L;

[0149] The concentration of PAC added was 0.2 g / LB.

[0150] The concentration of PAM added was 2 mg / L.

[0151] Wastewater from the pH adjustment tank enters the Fenton oxidation tank. Ferrous sulfate and hydrogen peroxide are added, and the tank is fully aerated and stirred. The wastewater retention time is maintained at 1 hour to fully oxidize and remove organic pollutants from the wastewater.

[0152] Ensure that the concentration of the added ferrous ions is 0.1 g / L;

[0153] The concentration of added hydrogen peroxide is 0.6 g / L.

[0154] The effluent from the Fenton oxidation tank enters the flocculation sedimentation tank. Lime water is added to the general equalization tank using a dosing device to adjust the pH to neutral. After adding PAC solution and PAM solution and stirring thoroughly, sedimentation is achieved to separate solids and liquids, removing suspended solids, phosphorus, nickel, manganese, zinc and other pollutants from the wastewater. The resulting lower layer sludge enters the sludge thickening tank for concentration and storage. Subsequently, it is treated by a plate and frame filter press. The filtrate can be returned to the general equalization tank. At the same time, the supernatant enters the sand filter tank for further filtration to remove suspended solids.

[0155] Calculated based on the amounts of lime, PAC, and PAM.

[0156] The concentration of the added lime is 8 g / L;

[0157] The concentration of PAC added was 0.2 g / LB.

[0158] The concentration of PAM added was 2 mg / L.

[0159] The effluent from the sand filter tank enters the discharge pool and is discharged only after passing the test.

[0160] Example 4

[0161] Table 2 shows the treatment effect of coating wastewater after Fenton oxidation treatment in Examples 1-3 and Comparative Examples 1-2 above:

[0162]

[0163] Note: The wastewater treated in Table 2 is a mixture of degreasing wastewater, electrophoresis wastewater, surface conditioning wastewater, and washing wastewater.

[0164] Table 3 shows the treatment effect of coating wastewater after demulsification treatment in Examples 1-2 and Comparative Examples 1-2 above:

[0165]

[0166] Note: In Table 3, Examples 1 and 2, and Comparative Examples 1 and 2 represent the pollutant removal rates after acidification and demulsification treatment of degreasing wastewater;

[0167] Comparative Example 3 is the wastewater resulting from the mixture of degreasing wastewater, electrophoresis wastewater, surface conditioning wastewater, and washing wastewater, and represents the pollutant removal rate after neutralization, flocculation, and sedimentation with lime.

[0168] Table 4 shows the amount of acid and lime consumed in the treatment of coating wastewater in Example 1 and Comparative Examples 1-2 above:

[0169]

[0170]

[0171] It should be noted that other painting wastewater can also be treated using the method of this invention. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of this invention shall be determined by the claims.

Claims

1. A method for treating coating wastewater, characterized in that, The method for treating the coating wastewater includes the following steps: S1. First, the wastewater is subjected to acidification and demulsification treatment; the wastewater is degreasing wastewater generated during the coating process; The degreasing wastewater contains 900-1200 mg / L of emulsified oil, 300-400 mg / L of surfactant, 2000-2500 mg / L of COD, 80-100 mg / L of phosphorus, and no more than 20 mg / L of zinc. Then, low-concentration wastewater is introduced into the effluent from the acidification and demulsification treatment; The amount of low-concentration wastewater introduced is 3 to 4 times that of the wastewater in S1; The low-concentration wastewater includes any one or more of the following: electrophoretic wastewater, surface conditioning wastewater, and washing wastewater generated during the coating process; S2. Perform Fenton oxidation treatment on the effluent from the acidification and demulsification process; S3. Perform flocculation and sedimentation treatment on the effluent after Fenton oxidation; In step S1, the pH of the wastewater is adjusted to ≤2 using acid to form a solid-liquid blend, and then solid-liquid separation is performed to obtain the effluent from the acidification and demulsification treatment.

2. The method for treating coating wastewater according to claim 1, characterized in that, In step S1, aeration treatment is performed.

3. The method for treating coating wastewater according to claim 1, characterized in that, In S2, ferrous ions and hydrogen peroxide are added to perform Fenton oxidation treatment; The amount of ferrous ions added is calculated based on the amount of COD in the water body, which is 0.04 to 0.1 times the amount of COD. The mass ratio of added hydrogen peroxide to ferrous ions is (5~8):

1.

4. The method for treating coating wastewater according to claim 3, characterized in that, In S2, the amount of ferrous ions added is 0.1~0.2 g / L.

5. The method for treating coating wastewater according to claim 1, characterized in that, In step S3, lime and flocculant are added for flocculation treatment; wherein... The amount of lime added is 8~10g / L; The amount of flocculant added is 0.2~0.5g / L.

6. The method for treating coating wastewater according to any one of claims 1 to 5, characterized in that, In step S1, solid-liquid separation is performed to obtain effluent from acidification and demulsification treatment, as well as sludge. The sludge is subjected to pressure filtration to obtain filtrate; The filtrate is refluxed to the effluent from the acidification and demulsification treatment.

7. The method for treating coating wastewater according to claim 6, characterized in that, The electrophoresis wastewater contains 200-250 mg / L COD and 8-10 mg / L phosphorus; The surface-treated wastewater contains 10-20 mg / L of surfactant, 20-50 mg / L of COD, 100-150 mg / L of phosphorus, and no more than 2 mg / L of zinc; The washing wastewater contains 30-50 mg / L of surfactant, 90-100 mg / L of COD, 30-50 mg / L of phosphorus, and a total of no more than 12 mg / L of nickel, manganese, and zinc.

8. The method for treating coating wastewater according to any one of claims 1 to 5, characterized in that, It also includes the following steps: S4. Filter the effluent from the flocculation and sedimentation treatment.

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