A method for treating and reusing chemical wastewater containing oligomers

Abstract

This application provides a method for treating and reusing chemical wastewater containing oligomers, comprising the following steps: 1) subjecting the chemical wastewater containing oligomers to be treated to a crosslinking reaction with an initiator and a crosslinking agent in a crosslinking unit; 2) introducing the crosslinked wastewater from the crosslinking unit into an air flotation unit, adding a flotation agent, and performing air flotation treatment; 3) introducing the air flotation effluent from the air flotation unit into a biochemical unit for biochemical treatment; 4) introducing the effluent from the biochemical unit into an advanced treatment unit for further treatment; 5) introducing the effluent from the advanced treatment unit into a membrane treatment unit for membrane treatment, wherein the membrane-treated water can be reused in chemical water production or as makeup water for circulating water systems. This invention has the advantages of good treatment effect and low treatment cost, solves the problem of reusing treated styrene-butadiene rubber wastewater, and saves water resources.

Description

Technical Field

[0001] This invention relates to a method for the pretreatment of chemical wastewater, and more particularly to a method for the treatment and reuse of chemical wastewater containing oligomers. Background Technology

[0002] Synthetic rubber, such as styrene-butadiene rubber, requires the addition of large amounts of coagulants, dispersants, regulators, and polymerization inhibitors during production, resulting in wastewater containing high concentrations of organic matter that is extremely difficult to degrade. These organic substances are mostly unreacted monomers and oligomers, and conventional methods are difficult to achieve satisfactory results, making advanced treatment and reuse quite challenging.

[0003] Currently, the treatment of wastewater from synthetic rubber production primarily employs a combination of pretreatment and biological treatment methods, with research and development focusing on improving both pretreatment and biological treatment efficiency. Pretreatment measures for synthetic rubber production wastewater mainly include coagulation sedimentation, coagulation flotation, electrolytic flocculation, and catalytic oxidation. Subsequent biological treatment measures mainly include hydrolysis acidification, contact oxidation, activated sludge, and the use of highly efficient beneficial bacteria. From engineering practice in treating synthetic rubber production wastewater, although the combination of pretreatment and biological treatment can significantly remove pollutants, the presence of some non-biodegradable substances in the wastewater results in poor effluent quality after biological treatment, affecting compliance with discharge standards. Furthermore, the presence of oligomers in the wastewater makes desalination and reuse difficult.

[0004] Regarding the advanced treatment and reuse of synthetic rubber production wastewater under secondary biochemical treatment, some people have proposed methods such as coagulation sedimentation, activated carbon adsorption, and reverse osmosis. However, these methods generally suffer from limitations such as unsatisfactory treatment effects, high treatment costs, and unstable operation, making it difficult to achieve industrial application.

[0005] Patent CN101723526 discloses a membrane treatment method for synthetic rubber production wastewater that has undergone secondary biochemical treatment. This method employs a treatment process of "catalytic oxidation + coagulation sedimentation + ultrafiltration + reverse osmosis." First, hydrogen peroxide is used as the oxidant and ferrous sulfate as the catalyst to catalytically oxidize the wastewater, primarily removing recalcitrant COD. Then, coagulation sedimentation removes iron and suspended solids, followed by ultrafiltration to remove colloids and residual particulate matter. Finally, reverse osmosis is used for desalination. Because the pretreatment effectively removes organic matter that significantly impacts the operation of the membrane system, this method results in excellent effluent quality.

[0006] However, this method cannot effectively remove oligomers from wastewater, and it cannot prevent oligomers from clogging the membrane, thus limiting the long-term operation of the membrane facility. Furthermore, the wastewater treatment process using Fenton's reagent results in large volumes of waste residue and significant acid and alkali consumption.

[0007] Therefore, it is necessary to adopt practical and feasible methods to treat chemical wastewater containing oligomers so that the treated wastewater can be recycled and reused. Summary of the Invention

[0008] The purpose of this invention is to provide a method for treating and reusing chemical wastewater containing oligomers, particularly a method for treating and reusing synthetic rubber wastewater.

[0009] A method for treating and reusing chemical wastewater containing oligomers includes the following steps:

[0010] 1) The chemical wastewater containing oligomers to be treated undergoes a crosslinking reaction with the initiator and crosslinking agent in the crosslinking unit;

[0011] 2) The cross-linked wastewater from the cross-linking unit is fed into the air flotation unit, flotation agent is added, and air flotation treatment is performed;

[0012] 3) The effluent from the air flotation unit is fed into the biological treatment unit for biological treatment;

[0013] 4) The effluent from the biochemical unit is fed into the advanced treatment unit for further treatment.

[0014] 5) The effluent from the deep treatment unit is fed into the membrane treatment unit for membrane treatment. The membrane-treated water can be reused for chemical water production or circulating water replenishment.

[0015] In the crosslinking unit of step 1 of the present invention, the initiator can be persulfate, hydrogen peroxide, sodium hypochlorite, preferably persulfate, such as potassium persulfate, and the amount of initiator added can be 50-1000 ppm, preferably 100-500 ppm.

[0016] The crosslinking agent can be N,N'-dimethylenebisacrylamide, hydroxyethyl acrylate, benzoyl peroxide, glutaraldehyde, etc., preferably N,N'-dimethylenebisacrylamide; the dosage of the crosslinking agent can be 0.1-80 ppm, preferably 1-10 ppm; the reaction time of the crosslinking reaction can be 2-200 minutes, preferably 10-100 minutes; the reaction temperature can be greater than 15℃, preferably 30℃-80℃.

[0017] In step 2 of the present invention, the air flotation unit may employ one or more of dissolved air flotation, aeration flotation, and electrolytic flotation, with dissolved air flotation being preferred. The conditions for performing the air flotation treatment may be: dissolved air pressure of 0.2–0.4 MPa and air-to-water volume ratio of 0.04–0.08:1.

[0018] The flotation agent can be one or more commonly used flotation agents such as aluminum salts, iron salts, polyaluminum chloride, polyferric chloride, and polyacrylamide, preferably a combination of polyaluminum chloride and polyacrylamide. The dosage of polyaluminum chloride is 1-5000 mg / L, preferably 10-200 mg / L; the dosage of polyacrylamide is 0.05-100 mg / L, preferably 1-20 mg / L.

[0019] In step 3 of this invention, the biochemical unit preferably employs a treatment process of hydrolysis acidification + denitrification + MBBR. Specifically, it consists of a hydrolysis acidification tank + denitrification tank + MBBR tank + secondary sedimentation tank. The temperature of the biochemical unit is 10-40℃. The conditions for the hydrolysis acidification tank are: dissolved oxygen less than 1 mg / L, hydraulic retention time 3-16 h; dissolved oxygen less than 1 mg / L, hydraulic retention time 2-12 h, sludge concentration 2-4 g / L; MBBR conditions are: dissolved oxygen 2-4 mg / L, hydraulic retention time 30-80 h, sludge concentration 2-4 g / L; and the hydraulic retention time of the secondary sedimentation tank is 1-4 h. A portion of the mixed liquor from the MBBR tank outlet is recycled to the inlet of the denitrification tank, with a recycling rate of 100%-400%. A portion of the sludge from the bottom of the secondary sedimentation tank is recycled to the denitrification tank, with a sludge recycling rate of 50%-150%.

[0020] In step 4 of this invention, the deep treatment unit preferably employs an ozone oxidation + BAF treatment process. The ozone oxidation section includes an ozone reaction tank and an ozone buffer tank. The hydraulic retention time in the ozone reaction tank is 0.1-2 hours, the hydraulic retention time in the ozone buffer tank is 0.5-4 hours, and the ozone dosage concentration is 20-200 mg / L. The retention time in the BAF reaction tank is 0.2-16 hours, preferably 0.5-8 hours.

[0021] In step 5 of the present invention, the membrane treatment unit preferably uses a combination of ultrafiltration and reverse osmosis, specifically sand filtration + multi-media filtration + ultrafiltration + security filter + reverse osmosis. The sand filtration uses quartz sand with a filtration rate <15 m / h; the multi-media filtration uses both anthracite and quartz sand media with a filtration rate <10 m / h; and the ultrafiltration uses a ceramic membrane with a flux of 18-30 L / m³. 2 • h, backwash time with clean water is 15-20 min: 1 min, the precision of the security filter is 5 μm; the reverse osmosis operating flux is 18-20 L / m 2 •h, with a recovery rate of 65-75%.

[0022] Compared with existing technologies, this invention has the advantages of good treatment effect and low treatment cost, solves the problem of recycling synthetic rubber wastewater after treatment, and saves water resources. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0024] Table 1 shows the water quality of styrene-butadiene rubber wastewater from a petrochemical enterprise.

[0025] Table 1. Water quality of styrene-butadiene rubber wastewater

[0026]

[0027] As can be seen from the data in Table 1, the wastewater has a high COD, poor biodegradability, high total nitrogen, and high content of oligomeric suspended solids.

[0028] For this wastewater, some companies use long-process biochemical treatment technology to make the wastewater meet the discharge standards, but due to the presence of oligomers, it is impossible to use dual membrane treatment for desalination and reuse. However, the method of this invention can achieve reuse.

[0029] Example 1

[0030] The water sample was taken from the homogenization tank of a certain refining and chemical enterprise, which contained styrene-butadiene rubber wastewater. The water quality is shown in Table 1.

[0031] 1) Introduce wastewater into the crosslinking unit, add 100 ppm of persulfate and 3 ppm of N,N'-dimethylenebisacrylamide, and react at 60°C for 60 min.

[0032] 2) After the cross-linking reaction, the wastewater enters the dissolved air flotation unit and 30 ppm of polyaluminum chloride and 2 ppm of polyacrylamide are added for dissolved air flotation reaction. The dissolved air pressure is controlled at 0.3 MPa and the air-water volume ratio is 0.06:1.

[0033] 3) Wastewater from the air flotation reaction enters the biological treatment unit, which consists of a hydrolysis acidification tank + denitrification tank + MBBR tank + secondary sedimentation tank. The control conditions for the biological treatment unit are as follows: temperature 20-35℃; dissolved oxygen less than 0.5 mg / L in the hydrolysis acidification tank, hydraulic retention time 10 h; dissolved oxygen less than 1 mg / L in the denitrification tank, hydraulic retention time 8 h, sludge concentration 2-4 g / L; dissolved oxygen 2-4 mg / L in the MBBR tank, hydraulic retention time 50 h, sludge concentration 2-4 g / L; hydraulic retention time in the secondary sedimentation tank 2 h. A portion of the mixed liquor from the MBBR tank outlet is recycled to the denitrification tank inlet, with a recycling rate of 200%. A portion of the sludge from the bottom of the secondary sedimentation tank is recycled to the denitrification tank, with a sludge recycling rate of 100%.

[0034] 4) The wastewater after the biochemical reaction enters the advanced treatment unit, which adopts an ozone oxidation + BAF treatment process. The ozone oxidation section includes an ozone reactor and an ozone buffer tank. The hydraulic retention time in the ozone reactor is 0.5 h, and the hydraulic retention time in the ozone buffer tank is 1.5 h. The ozone dosage concentration is 50 mg / L. The retention time in the BAF reactor is 3 h.

[0035] 5) Wastewater treated by the advanced treatment unit enters the membrane treatment unit, which employs a combination of sand filtration, multi-media filtration, ultrafiltration, security filter, and reverse osmosis. The sand filtration uses quartz sand at a filtration rate of 10 m / h; the multi-media filtration uses both anthracite and quartz sand media at a filtration rate of 8 m / h; and the ultrafiltration uses a ceramic membrane with a flux of 20 L / m³. 2 • h, backwash time with clean water is 20 min: 1 min, the precision of the security filter is 5 μm; the reverse osmosis operating flux is 18 L / m 2 •h, with a recovery rate of 70%.

[0036] The dual-membrane unit in Implementation 1 operated stably for 3 months without a decrease in membrane flux, and the effluent could be used as makeup water for both circulating water and chemical water treatment. The water quality of the treated wastewater is shown in the table below.

[0037] Table 1. Treatment effect of Example 1

[0038]

[0039] Example 2

[0040] The water sample was taken from the homogenization tank of a certain refining and chemical enterprise, which contained styrene-butadiene rubber wastewater. The water quality is shown in Table 1.

[0041] 1) Introduce wastewater into the crosslinking unit, add 150 ppm of persulfate and 5 ppm of N,N'-dimethylenebisacrylamide, and react at 60°C for 60 min.

[0042] 2) After the cross-linking reaction, the wastewater enters the dissolved air flotation unit and 30 ppm of polyaluminum chloride and 2 ppm of polyacrylamide are added for dissolved air flotation reaction. The dissolved air pressure is controlled at 0.3 MPa and the air-water volume ratio is 0.06:1.

[0043] 3) Wastewater from the air flotation reaction enters the biological treatment unit, which consists of a hydrolysis acidification tank + denitrification tank + MBBR tank + secondary sedimentation tank. The control conditions for the biological treatment unit are: temperature 20-35℃; dissolved oxygen in the hydrolysis acidification tank <0.5 mg / L, hydraulic retention time 10 h; dissolved oxygen in the denitrification tank <1 mg / L, hydraulic retention time 8 h, sludge concentration 2-4 g / L; dissolved oxygen in the MBBR tank 2-4 mg / L, hydraulic retention time 50 h, sludge concentration 2-4 g / L; hydraulic retention time in the secondary sedimentation tank 2 h. A portion of the mixed liquor from the MBBR tank outlet is recycled to the inlet of the denitrification tank, with a recycling rate of 200%. A portion of the sludge from the bottom of the secondary sedimentation tank is recycled to the denitrification tank, with a sludge recycling rate of 100%.

[0044] 4) The wastewater after the biochemical reaction enters the advanced treatment unit, which adopts an ozone oxidation + BAF treatment process. The ozone oxidation section includes an ozone reactor and an ozone buffer tank. The hydraulic retention time in the ozone reactor is 0.5 h, and the hydraulic retention time in the ozone buffer tank is 1.5 h. The ozone dosage concentration is 50 mg / L. The retention time in the BAF reactor is 3 h.

[0045] 5) Wastewater treated by the advanced treatment unit enters the membrane treatment unit, which employs a combination of sand filtration, multi-media filtration, ultrafiltration, security filter, and reverse osmosis. The sand filtration uses quartz sand at a filtration rate of 10 m / h; the multi-media filtration uses both anthracite and quartz sand media at a filtration rate of 8 m / h; and the ultrafiltration uses a ceramic membrane with a flux of 20 L / m³. 2 • h, backwash time with clean water is 20 min: 1 min, the precision of the security filter is 5 μm; the reverse osmosis operating flux is 18 L / m 2 • h, recovery rate 70%. The water quality of the treated wastewater is shown in the table below.

[0046] Table 2. Treatment effect of Example 2

[0047]

[0048] Example 3

[0049] The water sample was taken from the homogenization tank of a certain refining and chemical enterprise, which contained styrene-butadiene rubber wastewater. The water quality is shown in Table 1.

[0050] 1) Introduce wastewater into the crosslinking unit, add 200 ppm of persulfate and 8 ppm of N,N'-methylenebisacrylamide, and react at 60°C for 80 min.

[0051] 2) After the cross-linking reaction, the wastewater enters the dissolved air flotation unit and 30 ppm of polyaluminum chloride and 2 ppm of polyacrylamide are added for dissolved air flotation reaction. The dissolved air pressure is controlled at 0.3 MPa and the air-water volume ratio is 0.06:1.

[0052] 3) Wastewater from the air flotation reaction enters the biological treatment unit, which consists of a hydrolysis acidification tank + denitrification tank + MBBR tank + secondary sedimentation tank at a temperature of 20-35℃. The control conditions for the biological treatment unit are as follows: dissolved oxygen in the hydrolysis acidification tank is less than 0.5 mg / L, with a hydraulic retention time of 10 h; dissolved oxygen in the denitrification tank is less than 1 mg / L, with a hydraulic retention time of 8 h and a sludge concentration of 2-4 g / L; dissolved oxygen in the MBBR tank is 2-4 mg / L, with a hydraulic retention time of 50 h and a sludge concentration of 2-4 g / L; and the hydraulic retention time in the secondary sedimentation tank is 2 h. A portion of the mixed liquor from the MBBR tank outlet is recycled to the inlet of the denitrification tank, with a recycling rate of 200%. A portion of the sludge from the bottom of the secondary sedimentation tank is recycled to the denitrification tank, with a sludge recycling rate of 100%.

[0053] 4) The wastewater after the biochemical reaction enters the advanced treatment unit, which adopts an ozone oxidation + BAF treatment process. The ozone oxidation section includes an ozone reactor and an ozone buffer tank. The hydraulic retention time in the ozone reactor is 0.5 h, and the hydraulic retention time in the ozone buffer tank is 1.5 h. The ozone dosage concentration is 50 mg / L. The retention time in the BAF reactor is 3 h.

[0054] 5) Wastewater treated by the advanced treatment unit enters the membrane treatment unit, which employs a combination of sand filtration, multi-media filtration, ultrafiltration, security filter, and reverse osmosis. The sand filtration uses quartz sand at a filtration rate of 10 m / h; the multi-media filtration uses both anthracite and quartz sand media at a filtration rate of 8 m / h; and the ultrafiltration uses a ceramic membrane with a flux of 20 L / m³. 2 • h, backwash time with clean water is 20 min: 1 min, the precision of the security filter is 5 μm; the reverse osmosis operating flux is 18 L / m 2 •h, with a recovery rate of 70%.

[0055] The dual-membrane unit in Implementation 3 operated stably for 3 months without a decrease in membrane flux, and the effluent could be used as makeup water for both circulating water and chemical water treatment. The water quality of the treated wastewater is shown in the table below.

[0056] Table 3. Treatment effect of Example 3

[0057]

[0058] Comparative Example 1

[0059] Other examples are similar to Example 3, except that step 1 is omitted. In Comparative Example 1, the dual-membrane device operated for one month, and the membrane flux decreased significantly. Chemical cleaning could not restore the membrane flux. The water quality of the treated wastewater within one month is shown in the table below.

[0060] Table 4 shows the treatment effect of Comparative Example 1.

[0061]

[0062] Comparative Example 2

[0063] Other examples are similar to Example 3, except that step 1 employs the following catalytic oxidation method:

[0064] Adjust the pH of the wastewater to 3, add 200 ppm of persulfate and 200 ppm of ferrous sulfate, react for 80 minutes, then adjust the pH to 7 and let it settle for 2 hours.

[0065] In Comparative Example 2, the dual-membrane unit experienced a significant decrease in membrane flux after one month of operation, and chemical cleaning was unable to restore the flux. The water quality of the treated wastewater over one month is shown in the table below.

[0066] Table 5. Treatment effect of Comparative Example 2

[0067]

Claims

1. A method for treating and reusing chemical wastewater containing oligomers, comprising the following steps: 1) The chemical wastewater containing oligomers to be treated is subjected to a crosslinking reaction with an initiator and a crosslinking agent in a crosslinking unit. The initiator is selected from one or more of persulfate, hydrogen peroxide, and sodium hypochlorite. The crosslinking agent is selected from one or more of N,N'-dimethylenebisacrylamide, hydroxyethyl acrylate, benzoyl peroxide, and glutaraldehyde. 2) The cross-linked wastewater from the cross-linking unit is fed into the air flotation unit, flotation agent is added, and air flotation treatment is performed; 3) The effluent from the air flotation unit is fed into the biological treatment unit for biological treatment; 4) The effluent from the biochemical unit is fed into the advanced treatment unit for further treatment; 5) The effluent from the deep treatment unit is fed into the membrane treatment unit for membrane treatment, and the resulting membrane-treated water is reused.

2. The method according to claim 1, wherein, The dosage of the initiator is 50-1000 ppm.

3. The method according to claim 1, wherein, The dosage of the initiator is 100-500 ppm.

4. The method according to claim 1, wherein, The dosage of the crosslinking agent is 0.1-80 ppm.

5. The method according to claim 1, wherein, The dosage of the crosslinking agent is 1-10 ppm.

6. The method according to claim 1, wherein, The reaction time for the cross-linking reaction is 2-200 minutes.

7. The method according to claim 1, wherein, The reaction time for the cross-linking reaction is 10-100 minutes.

8. The method according to claim 1, wherein, The reaction temperature is 30℃-80℃.

9. The method according to claim 1, wherein, The air flotation treatment employs one or more of the following methods: dissolved air flotation, aeration flotation, and electrolytic flotation. The conditions for air flotation treatment are: dissolved air pressure of 0.2–0.4 MPa and air-to-water volume ratio of 0.04–0.08:

1.

10. The method according to claim 1, wherein, The flotation agent is selected from a combination of polyaluminum chloride and polyacrylamide, with the dosage of polyaluminum chloride being 1-5000 mg / L and the dosage of polyacrylamide being 0.05-100 mg / L.

11. The method according to claim 1, wherein, The flotation agent is selected from a combination of polyaluminum chloride and polyacrylamide, with the dosage of polyaluminum chloride being 10-200 mg / L and the dosage of polyacrylamide being 1-20 mg / L.

12. The method according to claim 1, wherein, The biochemical unit employs a hydrolysis acidification + denitrification + MBBR treatment process.

13. The method according to claim 1, wherein, The deep processing unit employs an ozone oxidation + BAF treatment process.

14. The method according to claim 1, wherein, The membrane treatment unit employs an ultrafiltration + reverse osmosis process.

15. The method according to claim 1, wherein, The chemical wastewater containing oligomers is wastewater generated during the production of synthetic rubber.

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