Petrochemical wastewater treatment method

Abstract

The invention belongs to the technical field of water treatment, and particularly discloses a petrochemical wastewater treatment method which comprises the following steps: S1, mixing petrochemical wastewater with acid, controlling the pH value of the wastewater to be 5-5.5, and standing for defoaming; s2, introducing the wastewater into a first reaction unit, adding an oxidizing agent and ferrous sulfate, and mixing; then introducing into a second reaction unit, adding the oxidizing agent and the ferrous sulfate again, mixing, and standing for 20-30 minutes; wherein one part of the water in the second reaction unit flows back to the first reaction unit, the reflux ratio of the water to the inlet water is 200%-300%, the other part of the water flows back to the S1 to adjust the pH value of the wastewater, and the reflux ratio is 50%-200%; s3, entering a neutralization tank to regulate the pH value to 7.0-7.5, staying for 10-15 minutes, and then entering a degassing tank to stay for 40-60 minutes; s4, water is introduced into a flocculation tank, a flocculant is added for mixing, finally, the water is introduced into a final sedimentation tank for clarification, discharged clear liquid is lower than a discharge limit value, and up-to-standard discharge is achieved. The oxidation method is used for treating the wastewater, the process is simple, and the wastewater treatment efficiency is high.

Description

Technical Field

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

[0002] Petrochemical production involves thousands of raw materials, products and intermediate products, resulting in a large number of pollutants in wastewater. According to incomplete tests, it contains oil, sulfur, phenol, cyanide, COD, polycyclic aromatic hydrocarbons, aromatic amine compounds and heterocyclic compounds.

[0003] Due to the different production processes of petrochemical industry in the park, the pollutants contained in petrochemical wastewater are diverse and the water quality is very complex. Therefore, the long-term stable quality of the effluent from the wastewater treatment in the petrochemical park is still a major problem that needs to be overcome. At present, the main methods for removing pollutants include biochemical method, physicochemical method and advanced oxidation method. Biochemical method is the most widely used method for treating organic wastewater, mainly including activated sludge, biofilm method, aerobic-anaerobic method, etc. When the composition of petrochemical wastewater is complex, the proportion of refractory wastewater is large, and it contains toxic substances or bio-refractory organic matter, the treatment effect of biological method is poor or even cannot be treated; there are few literature reports on the treatment of refractory organic pollutants by physicochemical method, mainly including adsorption method, extraction method, etc. Advanced oxidation technology is often used for pre-treatment or deep treatment of biological treatment. Generally, under the action of catalyst, chemical oxidants are used to treat organic wastewater to improve the biodegradability of wastewater, or directly oxidize and degrade organic matter in wastewater to stabilize it. However, advanced oxidation method will increase the volume of sludge produced, and excessive input of reagents will cause secondary pollution. Summary of the invention

[0004] The invention provides a method for treating petrochemical wastewater, which utilizes an oxidation method to treat the wastewater, has a simple process and high wastewater treatment efficiency.

[0005] In order to achieve the above objectives, the present invention adopts the following technical scheme: a method for treating petrochemical wastewater, comprising the following steps: S1, the acid-adding and lifting unit adds acid to the petrochemical wastewater and mixes it, controls the pH of the wastewater to 5.0~5.5, and then stops to defoam; S2, the wastewater treated by the composite reaction unit S1 is introduced into the first reaction unit, and an oxidant and ferrous sulfate are added for mixing, and the residence time of the wastewater is 5-10s; then it is introduced into the second reaction unit, and an oxidant and ferrous sulfate are added again for mixing, and the wastewater is retained for 20-30min; a part of the water in the second reaction unit is returned to the first reaction unit, and the ratio of the water flow to the inlet water flow is 200%-300%, and the other part is returned to S1 for adjusting the pH of the wastewater, and the reflux ratio is 50%-200%; S3, neutralization and degassing unit S2 effluent enters the neutralization tank, adds alkaline substances to adjust the pH to 7.0-7.5, stays for 10-15 minutes, and then enters the degassing tank to stay for 40-60 minutes; S4, the water treated by loading clarification unit S3 is introduced into the flocculation tank, flocculant is added for mixing, and finally introduced into the final sedimentation tank for clarification. The discharged clear liquid is lower than the discharge limit, achieving standard discharge.

[0006] Optionally, when acid is added in S1 to adjust the pH, it is divided into a coarse adjustment pool and a fine adjustment pool. Concentrated sulfuric acid is used in the coarse adjustment pool to adjust the pH to between 5.5 and 6.5, and water refluxed from the second reaction unit is used in the fine adjustment pool to adjust the pH to between 5 and 5.5.

[0007] Optionally, the residence time of wastewater in the rough adjustment tank is 2-4 minutes; the residence time in the fine adjustment tank is 3-6 minutes. The function of the defoaming tank is: petrochemical wastewater may contain some carbonate and bicarbonate pollutants, which will release a large amount of heat and CO2 after adding sulfuric acid; the CO2 release process will cause a lot of bubbles and foam to be generated on the surface of the reaction tank. Setting up a defoaming tank can reduce the foam entering the subsequent units. The intermediate water tank is used as a buffer tank for entering the first reaction unit to prevent the water in the defoaming tank from directly entering the first reaction unit. Bubbles and foams can easily cause cavitation in the water inlet pump, affecting the flow of the water inlet pump and damaging the water pump.

[0008] Optionally, when defoaming in S1, the residence time in the defoaming pool is 6 to 8 minutes, and the residence time in the intermediate water pool is 20 to 40 minutes.

[0009] Optionally, the mass concentration of the oxidant in the first reaction unit in S2 is 0.08~0.15mL / L, and the amount of ferrous sulfate added is 250~300mg / L; the mass concentration of the oxidant in the second reaction unit is 0.05~0.1mL / L, and the amount of ferrous sulfate added is 50~100mg / L.

[0010] Optionally, the oxidant in S2 is one or more of O3, H2O2, and KMnO4.

[0011] Optionally, a catalytic filler is added to the second reaction unit, the filler has a particle size of 3-8 mm and a density of 1.1-1.5 kg / m 3 , surface loaded with metal.

[0012] Optionally, the carrier of the filler is one or more of Al2O3, SiO2, industrial ceramics, and molecular sieves; the loaded metals are iron, manganese and copper, and one or more of nickel, molybdenum and cobalt are also loaded; wherein the loading amount of iron, manganese and copper on the carrier is 5%~10%, and the loading amount of one or more of nickel, molybdenum and cobalt is 1%~4%.

[0013] Optionally, the flocculant in S4 is PAM, the addition amount is 0.75~1.5 mg / L, and the residence time is 3~8 min.

[0014] Optionally, the surface load of the final sedimentation tank is 15-30m 3 / (m 2 •h); before the end of the flocculation tank enters the final sedimentation tank, add quartz sand of 80-160μm, with an addition amount of 10-15kg / 10,000 tons of water.

[0015] The present invention has the following beneficial effects: 1. The water quality and quantity of petrochemical wastewater fluctuate greatly and the water quality is complex. The present invention uses a combined process of acid addition + composite reaction + loading clarification to efficiently remove the difficult-to-degrade organic matter in the wastewater. Specifically, in the composite reaction unit, the strong oxidizing property of ferrous ions catalyzing the oxidant under weak acidic conditions to produce hydroxyl free radicals (•OH) is used for removal. Taking H2O2 as an oxidant as an example, the chemical formula involved in the advanced oxidation reaction in the composite reaction unit is: .

[0016] The present invention sets two-stage reflux to make full use of the intermediate products produced in the advanced oxidation process, wherein the first reflux is to reflux the water in the second reaction unit to the first reaction unit, and utilize the Fe 2+ The oxidant added by catalysis increases the yield of free radicals (OH·) in the oxidant of the first reaction unit; during the second reflux, the water of the second reaction unit is refluxed to the acid addition unit to reuse the H + , reducing the dosage of concentrated sulfuric acid in the acid-adding and lifting unit, and reducing the dosage of alkali solution in the later neutralization and degassing unit. The two-stage reflux of the present invention can greatly reduce the dosage of chemical agents.

[0017] 2. The present invention sets a coarse adjustment tank and a fine adjustment tank in the acid addition and lifting link. The coarse adjustment tank adds concentrated sulfuric acid in a short time, which will release a large amount of heat and reduce the pH; then enters the fine adjustment tank to use the H refluxed from the second reaction unit + Fine-tune the pH so that the pH of the effluent from the fine-tuning pool meets the requirements of subsequent treatment (adjust the appropriate pH to 5.0-5.5), so that the H in the second reaction unit can be fully utilized. + And reduce the heat of the intermediate water pool for defoaming. Through two-stage acid adjustment, the utilization efficiency of concentrated sulfuric acid can be improved, the waste of reagents can be reduced, and then enter the defoaming pool and the intermediate water pool for buffering, which can fully release the CO2 and other gases produced by the reaction of carbonates and bicarbonates in petrochemical wastewater under acidic conditions, reducing the impact on the back-end composite reaction process.

[0018] 3. In the composite reaction process of the present invention, the removal of refractory organic pollutants in this unit mainly involves two processes: mineralization removal process and polymerization enrichment removal process.2+ As a catalyst, it activates the oxidant to generate hydroxyl radicals (•OH), decomposes organic pollutants into CO2 and H2O, and improves the mineralization removal effect of difficult-to-degrade organic pollutants in petrochemical wastewater. Specifically, the composite reaction process is divided into two reaction units: the first reaction unit and the second reaction unit. In the first reaction unit, a part of the oxidant and ferrous sulfate are added in a short time. On the one hand, it can activate the reaction system, pre-treat and catalyze the oxidation of macromolecular substances in the wastewater, and reduce the addition of oxidants and ferrous sulfate reagents in the second reaction unit at the back end; on the other hand, the H generated in the first reaction unit + , which will reduce the pH value of the wastewater and increase the acidity of the wastewater, which is more conducive to the smooth operation of the second reaction unit and reduces the addition of concentrated sulfuric acid reagents in the upstream acid addition and lifting tank. 2+ The dosage of ferrous sulfate in the first reaction unit can be reduced; in the second unit, a solid-phase catalyst is also added, and the iron salt produced in the reaction unit has a coagulation effect. Under the action of the catalyst, the coupling and polymerization of the difficult-to-degrade organic matter in the petrochemical wastewater are achieved, and a thick layer is enriched on the surface of the solid-phase catalyst, thereby achieving the purpose of removing the difficult-to-degrade organic pollutants in the water.

[0019] 4. Loading clarification process: the iron mud flocs produced after the composite reaction have a small density and a slow sedimentation speed. The traditional sedimentation process occupies a large area. The present invention adds micro sand with a smaller particle size to the sedimentation tank during the sedimentation stage. The micro sand provides the core for the flocculation reaction. Through the adsorption and bridging effect of PAM, the aggregation between the iron mud flocs, suspended solids and micro sand is accelerated to form high-density flocs, improve the sedimentation performance, and then shorten the sedimentation time, which is conducive to the rapid and efficient separation of the sedimentation tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart of the method in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0022] Example 1 The wastewater from a petrochemical industry mainly comes from the fertilizer and chemical industry area and the chlorofluorine chemical industry area, and is treated by the secondary biochemical treatment of the sewage treatment plant. Figure 1 As shown, the following steps are included: S1, acid addition and lifting unit The petrochemical wastewater from the secondary sedimentation tank is introduced into the coarse adjustment tank with a residence time of 2 minutes. Concentrated sulfuric acid is added to mix and the pH of the wastewater is adjusted to 5.3; then it enters the fine adjustment tank with a residence time of 4 minutes. When the system is just started, acid is added to adjust the pH to 5.5. Subsequently, the water refluxed from the second reaction unit is used to adjust the pH to 5.3; then it enters the defoaming tank with a residence time of 6 minutes and the intermediate water tank with a residence time of 25 minutes.

[0023] S2, composite reaction unit The wastewater treated by S1 was introduced into the first reaction unit, with a residence time of 5s, and 27% hydrogen peroxide and 30% ferrous sulfate were added for mixing, with the addition amounts of 0.15mL / L and 300mg / L respectively; then introduced into the second reaction unit, 27% hydrogen peroxide and 30% ferrous sulfate were added again for mixing, with the addition amounts of 0.1mL / L and 100mg / L respectively, and stayed for 22min; part of the water in the second reaction unit was refluxed to the first reaction unit, with a reflux ratio of 250%, and the other part was refluxed to S1 for adjusting the pH of the wastewater, with a reflux ratio of 100%; the second reaction unit was filled with a solid phase catalyst with a filling rate of 25%, and the main components were iron, manganese, copper and nickel, wherein the loading amounts of iron, manganese and copper on the carrier were 5%, 7% and 5% respectively, and the loading amount of nickel was 2%.

[0024] S3, neutralization and degassing unit The water treated by S2 enters the neutralization tank, adds alkaline substance sodium hydroxide, adjusts the pH to 7.0-7.5, stays for 12 minutes, and then enters the degassing tank and stays for 40 minutes; S4, the water treated by loading clarification unit S3 is introduced into the flocculation tank, and the flocculant PAM 0.75 mg / L is added to mix, and the residence time is 5 minutes. Before entering the final sedimentation tank at the end of the flocculation tank, a quartz sand carrier with a particle size of 80-160 μm is added, and the addition amount is 10 kg / 10,000 tons of water. Finally, it is introduced into the final sedimentation tank for clarification. The discharged clear liquid is lower than the emission limit, achieving standard emission. The specific key indicators are shown in Table 1.

[0025] Example 2 The treatment of petrochemical wastewater from a certain plant includes the following steps: S1, acid addition and lifting unit The petrochemical wastewater is introduced into the rough adjustment tank with a residence time of 4 minutes. Concentrated sulfuric acid is added to mix and the pH of the wastewater is adjusted to 5.5; then it enters the fine adjustment tank with a residence time of 3 minutes. When the system is just started, acid is added to adjust the pH to 5.5. Subsequently, the water refluxed from the second reaction unit is used to adjust the pH to 5.0; then it enters the defoaming tank with a residence time of 8 minutes and the intermediate water tank with a residence time of 40 minutes.

[0026] S2, composite reaction unit The wastewater treated by S1 is introduced into the first reaction unit, and the residence time is 10s. 27% hydrogen peroxide and 30% ferrous sulfate are added for mixing, and the addition amounts are 0.08mL / L and 250mg / L respectively. Then the wastewater is introduced into the second reaction unit, and 27% hydrogen peroxide and 30% ferrous sulfate are added again for mixing, and the addition amounts are 0.05mL / L and 50mg / L respectively, and the mixture is retained for 20min. Part of the water in the second reaction unit flows back to the first reaction unit, and the reflux ratio is 300%, and the other part flows back to S1 for adjusting the pH of the wastewater, and the reflux ratio is 150%. The second reaction unit is filled with a solid phase catalyst, and the filling rate is 30%. The main components are iron, manganese, copper, nickel and cobalt, and the loading amounts of iron, manganese and copper on the carrier are 7%, 8% and 10% respectively, the loading amount of nickel is 1%, and the loading amount of cobalt is 4%.

[0027] S3, neutralization and degassing unit The water treated by S2 enters the neutralization tank, adds alkaline substance sodium hydroxide, adjusts the pH to 7.0-7.5, stays for 12 minutes, and then enters the degassing tank and stays for 40 minutes; S4, the water treated by loading clarification unit S3 is introduced into the flocculation tank and mixed with flocculant PAM 1.0 mg / L, and the residence time is 7 minutes. Before entering the final sedimentation tank at the end of the flocculation tank, quartz sand carrier with a particle size of 80-160 μm is added, and the addition amount is 12 kg / 10,000 tons of water. Finally, it is introduced into the final sedimentation tank for clarification. The discharged clear liquid is lower than the emission limit, achieving standard emission. The key indicators are shown in Table 1.

[0028] Example 3 The treatment of petrochemical wastewater from a certain plant includes the following steps: S1, acid addition and lifting unit The petrochemical wastewater from the secondary sedimentation tank is introduced into the rough adjustment tank with a residence time of 2 minutes. Concentrated sulfuric acid is added to mix and the pH value of the wastewater is adjusted to 5.4. Then it enters the fine adjustment tank with a residence time of 6 minutes. When the system is just started, acid is added to adjust the pH value to 5.4. Subsequently, the water refluxed from the second reaction unit is used to adjust the pH value to 5.0. Then it enters the defoaming tank with a residence time of 6 minutes and the intermediate water tank with a residence time of 30 minutes.

[0029] S2, composite reaction unit The wastewater treated by S1 is introduced into the first reaction unit, and the residence time is 10s. 27% hydrogen peroxide and 30% ferrous sulfate are added for mixing, and the addition amounts are 0.12mL / L and 275mg / L respectively. Then the wastewater is introduced into the second reaction unit, and 27% hydrogen peroxide and 30% ferrous sulfate are added again for mixing, and the addition amounts are 0.075mL / L and 80mg / L respectively, and the mixture is retained for 20min. Part of the water in the second reaction unit is returned to the first reaction unit, and the reflux ratio with the influent water is 300%, and the other part is returned to S1 for adjusting the pH of the wastewater, and the reflux ratio is 150%. The second reaction unit is filled with a solid phase catalyst, and the filling rate is 30%. The main components are iron, manganese, copper, cobalt and molybdenum, and the loading amounts of iron, manganese and copper on the carrier are 7%, 7% and 9% respectively, the loading amount of cobalt is 1%, and the loading amount of molybdenum is 2%.

[0030] S3, neutralization and degassing unit The water treated by S2 enters the neutralization tank, adds alkaline substance sodium hydroxide, adjusts the pH to 7.0-7.5, stays for 11 minutes, and then enters the degassing tank and stays for 35 minutes; S4, the water treated by loading clarification unit S3 is introduced into the flocculation tank and mixed with flocculant PAM 1.2 mg / L, and the residence time is 6 minutes. Before entering the final sedimentation tank at the end of the flocculation tank, quartz sand carrier with a particle size of 80-160 μm is added, and the addition amount is 11 kg / 10,000 tons of water. Finally, it is introduced into the final sedimentation tank for clarification. The discharged clear liquid is lower than the emission limit, achieving standard emission. The key indicators are shown in Table 1.

[0031] Comparative Example 1 Comparative Example 1 is based on Example 1, except that the first reflux is not provided.

[0032] The wastewater was the same as in Example 1, and the key indicators before and after treatment are shown in Table 1.

[0033] Comparative Example 2 Comparative Example 2 is based on Example 2, except that the second reaction unit does not have a solid-phase catalytic filler. The key indicators before and after treatment are shown in Table 1.

[0034] Comparative Example 3 Comparative Example 3 is based on Example 3, except that the second reflux is not provided, and the pH of both the coarse adjustment tank and the fine adjustment tank is adjusted by concentrated sulfuric acid.

[0035] The specific processing method includes the following steps: S1, acid addition and lifting unit The petrochemical wastewater from the secondary sedimentation tank is introduced into the coarse adjustment tank with a residence time of 2 minutes. Concentrated sulfuric acid is added and mixed to adjust the pH value of the wastewater to 5.4. Then it enters the fine adjustment tank with a residence time of 6 minutes. The pH value is adjusted to 5.0 by concentrated sulfuric acid in the fine adjustment tank. Then it enters the defoaming tank with a residence time of 6 minutes and the intermediate water tank with a residence time of 30 minutes.

[0036] S2, composite reaction unit The wastewater treated by S1 is introduced into the first reaction unit, and the residence time is 10s. 27% hydrogen peroxide and 30% ferrous sulfate are added for mixing, and the addition amounts are 0.12mL / L and 275mg / L respectively. Then the wastewater is introduced into the second reaction unit, and 27% hydrogen peroxide and 30% ferrous sulfate are added again for mixing, and the addition amounts are 0.075mL / L and 80mg / L respectively, and the mixture is retained for 20min. Part of the water in the second reaction unit is returned to the first reaction unit, and the reflux ratio with the influent water is 300%, and the other part is returned to S1 for adjusting the pH of the wastewater, and the reflux ratio is 150%. The second reaction unit is filled with a solid phase catalyst, and the filling rate is 30%. The main components are iron, manganese, copper, cobalt and molybdenum, and the loading amounts of iron, manganese and copper on the carrier are 7%, 7% and 9% respectively, the loading amount of cobalt is 1%, and the loading amount of molybdenum is 2%.

[0037] S3, neutralization and degassing unit The water treated by S2 enters the neutralization tank, adds alkaline substance sodium hydroxide, adjusts the pH to 7.0-7.5, stays for 11 minutes, and then enters the degassing tank and stays for 35 minutes; S4, loading clarification unit S3 treated water introduced into the flocculation tank, added flocculant PAM 1.2mg / L mixed, retention time 6min, before the end of the flocculation tank into the final sedimentation tank, add quartz sand carrier with a particle size of 80-160μm, the addition amount is 11kg / 10,000 tons of water, and finally introduced into the final sedimentation tank for clarification, and the clear liquid is discharged. The key indicators before and after treatment are shown in Table 1.

[0038] Comparative Example 4 Comparative Example 4 is based on Example 2, the only difference being that the catalyst filled in the second reaction unit only carries three metals of iron, manganese and copper.

[0039] The specific process includes the following steps: S1, acid addition and lifting unit The petrochemical wastewater from the secondary sedimentation tank is introduced into the rough adjustment tank with a residence time of 4 minutes. Concentrated sulfuric acid is added to mix and the pH value of the wastewater is adjusted to 5.5. Then it enters the fine adjustment tank with a residence time of 3 minutes. When the system is just started, acid is added to adjust the pH value to 5.5. Subsequently, the water refluxed from the second reaction unit is used to adjust the pH value to 5.0. Then it enters the defoaming tank with a residence time of 8 minutes and the intermediate water tank with a residence time of 40 minutes.

[0040] S2, composite reaction unit The wastewater treated by S1 was introduced into the first reaction unit, with a residence time of 10s, and 27% hydrogen peroxide and 30% ferrous sulfate were added for mixing, with the addition amounts of 0.08mL / L and 250mg / L respectively; then introduced into the second reaction unit, 27% hydrogen peroxide and 30% ferrous sulfate were added again for mixing, with the addition amounts of 0.05mL / L and 50mg / L respectively, and stayed for 20min; part of the water in the second reaction unit was refluxed to the first reaction unit, and its reflux ratio with the influent water was 300%, and the other part was refluxed to S1 for adjusting the pH of the wastewater, with a reflux ratio of 150%; the second reaction unit was filled with a solid phase catalyst with a filling rate of 30%, and the main components were iron, manganese and copper, and the loading amounts on the carrier were 5%, 9% and 12% respectively.

[0041] S3, neutralization and degassing unit The water treated by S2 enters the neutralization tank, adds alkaline substance sodium hydroxide, adjusts the pH to 7.0-7.5, stays for 12 minutes, and then enters the degassing tank and stays for 40 minutes; S4, loading clarification unit S3 treated water introduced into the flocculation tank, added flocculant PAM 1.0mg / L mixed, retention time 7min, before the end of the flocculation tank into the final sedimentation tank, add quartz sand carrier with a particle size of 80-160μm, the addition amount is 12kg / 10,000 tons of water, and finally introduced into the final sedimentation tank for clarification, and the clear liquid is discharged. The key indicators before and after treatment are shown in Table 1.

[0042] Table 1

[0043] The above embodiments describe the preferred implementation of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for treating petrochemical wastewater, characterized in that: The following steps are involved: S1, the acid-adding and lifting unit adds acid to the petrochemical wastewater and mixes it, controls the pH of the wastewater to 5.0~5.5, and then stops to defoam; S2, the wastewater treated by the composite reaction unit S1 is introduced into the first reaction unit, and an oxidant and ferrous sulfate are added for mixing, and the residence time of the wastewater is 5-10s; then it is introduced into the second reaction unit, and an oxidant and ferrous sulfate are added again for mixing, and the wastewater is retained for 20-30min; a part of the water in the second reaction unit is returned to the first reaction unit, and the ratio of the water flow to the inlet water flow is 200%-300%, and the other part is returned to S1 for adjusting the pH of the wastewater, and the reflux ratio is 50%-200%; S3, neutralization and degassing unit S2 effluent enters the neutralization tank, adds alkaline substances to adjust the pH to 7.0-7.5, stays for 10-15 minutes, and then enters the degassing tank to stay for 40-60 minutes; S4, the water treated by loading clarification unit S3 is introduced into the flocculation tank, flocculant is added for mixing, and finally introduced into the final sedimentation tank for clarification. The discharged clear liquid is lower than the discharge limit, achieving standard discharge.

2. The method according to claim 1, characterized in that: When acid is added to adjust the pH in S1, it is divided into a rough adjustment pool and a fine adjustment pool. Concentrated sulfuric acid is used in the rough adjustment pool to adjust the pH to between 5.5 and 6.5, and the water refluxed from the second reaction unit is used in the fine adjustment pool to adjust the pH to between 5 and 5.

5.

3. The method according to claim 2, characterized in that: The residence time of wastewater in the coarse adjustment tank is 2-4 minutes; the residence time in the fine adjustment tank is 3-6 minutes.

4. The method according to claim 1, characterized in that: When defoaming in S1, the residence time in the defoaming pool is 6 to 8 minutes, and the residence time in the intermediate water pool is 20 to 40 minutes.

5. The method according to claim 1, characterized in that: The mass concentration of the oxidant in the first reaction unit of S2 is 0.08~0.15mL / L, and the dosage of ferrous sulfate is 250~300mg / L; the mass concentration of the oxidant in the second reaction unit is 0.05~0.1mL / L, and the dosage of ferrous sulfate is 50~100mg / L.

6. The method according to claim 5, characterized in that: The oxidant in S2 is one or more of O3, H2O2, and KMnO4.

7. The method according to any one of claims 1 to 6, characterized in that: Catalytic fillers are also added to the second reaction unit. The particle size of the fillers is 3-8 mm and the density is 1.1-1.5 kg / m 3 , surface loaded with metal.

8. The method according to claim 7, characterized in that: The carrier of the filler is one or more of Al2O3, SiO2, industrial ceramics, and molecular sieves; the loaded metals are iron, manganese and copper, and one or more of nickel, molybdenum and cobalt are also loaded; the loading amount of iron, manganese and copper on the carrier is 5%~10%, and the loading amount of one or more of nickel, molybdenum and cobalt is 1%~4%.

9. The method according to claim 1, characterized in that: The flocculant in S4 is PAM, the addition amount is 0.75~1.5mg / L, and the residence time is 3~8min.

10. The method according to claim 1, characterized in that: Surface load of S4 final sedimentation tank 15-30m 3 / (m 2 •h); before the end of the flocculation tank enters the final sedimentation tank, add quartz sand of 80-160μm, with an addition amount of 10-15kg / 10,000 tons of water.

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