Sewage treatment process for acrylonitrile production device

Abstract

The invention discloses an acrylonitrile production device sewage treatment process and belongs to the technical field of sewage treatment. The method comprises the following steps: sewage enters an ozone oxidation device to be treated, and the pH value of effluent of the ozone oxidation device is controlled to be below 4; the effluent overflows into a first-stage UV / H2O2 photo-promoted Fenton device, Fe < 3 + > salt and hydrogen peroxide are added, and the hydraulic retention time is 0.1-3 h; the effluent overflows into a second-stage UV / H2O2 photo-induced Fenton device, and the effluent of the second-stage UV / H2O2 photo-induced Fenton device flows back to the inlet of the ozone oxidation device; the effluent overflows and enters a third-stage UV / H2O2 photo-promoted Fenton device, and the hydraulic retention time is 0.1-3 h; and adding caustic soda into the effluent to adjust the pH value to 6.5-8.5, and sequentially carrying out A / A / O process and biological filter EBF treatment, so as to realize up-to-standard discharge. According to the treatment process, degradation-resistant nitrification-inhibiting substances in the sewage can be effectively removed, the BOD5 / COD (Biochemical Oxygen Demand / Chemical Oxygen Demand) value of the sewage is greatly improved, the biodegradability of the treated sewage is remarkably improved, sulfate radicals or other anions are not introduced, the process is safe and non-toxic, and the operation cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a sewage treatment process for an acrylonitrile production device. Background Art

[0002] Acrylonitrile production unit wastewater refers to the wastewater generated during the refining of acrylonitrile in the acrylonitrile production unit, that is, acrylonitrile refined water, specifically the condensate of the four-effect evaporator in the acrylonitrile production unit. The wastewater from the acrylonitrile production unit contains a large amount of nitriles and inorganic cyanide compounds, which are difficult to biodegrade, difficult to degrade, high chemical oxygen demand COD and high nitrogen content wastewater. Pollutants such as nitriles and inorganic cyanide compounds in the wastewater are biologically toxic and can inhibit the nitrification reaction of the biochemical system and affect the effect of biological denitrification. If effective pretreatment is not carried out and it directly enters the biochemical system, the nitrification and denitrification effects of the biochemical system cannot be improved simply by increasing the denitrification filler and optimizing the type and method of adding carbon sources.

[0003] Traditional Fenton reaction or Fenton-like reaction uses Fe 2+ Catalyzing hydrogen peroxide to produce highly oxidizing hydroxyl radicals can effectively treat COD and difficult-to-oxidize substances in sewage, and has been widely used in the sewage treatment industry. Photochemical synergistic oxidation process, namely photo-promoted Fenton oxidation, is a new development in water treatment, mainly used to remove organic pollutants that are difficult to remove by classical treatment methods. However, in the process of Fenton or other Fenton-like processes, as the reaction proceeds, the total cyanide in the sewage increases rapidly. The toxicity of cyanide leads to extremely poor biodegradability. At the same time, free cyanide evaporates into the gas phase in the form of HCN, which poses a great safety risk. In order to maintain the strong oxidizing property of Fenton or Fenton-like processes, it is necessary to continuously add strong acidic substances to maintain the pH value of 2-4, and the pH must be adjusted to neutral when entering the biochemical unit of the sewage field. Therefore, this process will bring too much salt to the sewage, such as introducing too much sulfate, and finally forming high-salt wastewater, which is not conducive to meeting the discharge standards.

[0004] The ozone oxidation process has no special requirements for pH value and can be carried out in a wide range, mainly generating carboxylic acid compounds, but the effect of removing COD from sewage is not obvious. If it is necessary to significantly reduce the COD of sewage, the power consumption of the ozone generator is high, which affects the application scope of ozone to remove COD.

[0005] Patent CN103304096A discloses a method for treating acrylonitrile wastewater by ozone catalysis coupled with biological nitrification. The wastewater first enters a regulating tank for water quality adjustment, then flows through a pre-oxidation tower and a catalytic oxidation tower, and then passes through an ozone removal tank to remove residual ozone in the water. Then, ammonia nitrogen is removed through a nitrification tank, and the effluent is discharged from a clear water tank. This invention pre-oxidizes and catalytically oxidizes the effluent from the regulating tank, which increases the operating cycle of the sewage treatment plant and does not fundamentally solve the problem of the biodegradability of the sewage.

[0006] Patent CN116354490A proposes a photo-Fenton wastewater treatment method and device for simultaneous denitrification and removal of refractory organic matter, the method comprising the following steps: 2 O 2 The photo-Fenton catalyst and anaerobic ammonia-oxidizing bacteria are introduced to form a reaction system, which reacts under light conditions to remove nitrogen and difficult-to-degrade organic matter in the wastewater. This patent uses photo-Fenton to remove difficult-to-degrade organic matter, but because denitrification is carried out through a multi-species community with Anammox as the core, the process cost is relatively high and the operation requirements are relatively strict. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a wastewater treatment process for an acrylonitrile production plant, which can effectively remove the refractory and nitrification-inhibiting substances in the wastewater and significantly improve the BOD of the wastewater. 5 / COD value, which significantly improves the biodegradability of the treated sewage. At the same time, this treatment process does not introduce sulfate or other anions, the process is safe and non-toxic, and the operating cost is low.

[0008] In order to achieve the above object, according to one aspect of the present invention, a wastewater treatment process for an acrylonitrile production device is provided, comprising the following steps: (1) The wastewater from the acrylonitrile production unit enters the ozone oxidation unit, where ozone is introduced for ozone oxidation treatment, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4; (2) The water overflow from the ozone oxidation device enters the first stage UV / H 2 O 2 Photo-Fenton device, adding Fe 3+ Salt and hydrogen peroxide, hydraulic retention time 0.1-3h; (3) The water overflow from step (2) enters the second stage UV / H 2 O 2 Photo-Fenton device, second stage UV / H 2 O 2 The effluent from the photo-Fenton device is refluxed to the inlet of the ozone oxidation device, with a reflux ratio of 50%-1000%; (4) The water overflow from step (3) enters the third stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 0.1-3h; (5) The effluent from step (4) is treated by adding caustic soda to adjust the pH value to 6.5-8.5, and then treated by the A / A / O process and the EBF biofilter in sequence to meet the discharge standards.

[0009] In some embodiments, in step (1), the dosage of ozone is 10-1000 mg / L, and the hydraulic retention time is 0.5-5 h.

[0010] In some embodiments, in step (2), the Fe 3+ The salt is selected from at least one of ferric sulfate and ferric chloride, wherein the Fe 3+ The dosage of salt is 10-100 mg / L.

[0011] In some embodiments, in step (2), the Fe 3+ The dosage of salt is 30-60 mg / L.

[0012] In some embodiments, in step (2), the dosage of the hydrogen peroxide is 50-1000 mg / L.

[0013] In some embodiments, in step (3), the second stage UV / H 2 O 2 The hydraulic retention time in the photo-Fenton device is 0.5-5h.

[0014] In some embodiments, in step (3), the second stage UV / H 2 O 2 The reflux ratio of the effluent from the photo-Fenton device is 100%-500%.

[0015] In some embodiments, the BOD of the effluent from step (4) is 5 / COD value>0.5.

[0016] In some embodiments, in step (5), the A / A / O process conditions are: the hydraulic retention time of the anaerobic tank is 15-30 hours, the hydraulic retention time of the anoxic tank is 20-30 hours, and the hydraulic retention time of the aerobic tank is 20-40 hours.

[0017] In some embodiments, in step (5), the hydraulic retention time of the biological filter EBF is 2-4 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides an ozone oxidation with internal reflux and three-stage UV / H 2 O 2 Photo-Fenton coupled wastewater treatment process, by controlling the process conditions of each step and the second stage UV / H 2 O 2 The reflux ratio of the effluent from the photo-Fenton unit can effectively remove the difficult-to-degrade and nitrification-inhibiting substances in the wastewater of the acrylonitrile production unit, and significantly increase the BOD of the wastewater. 5 / COD value, which significantly improves the biodegradability of the treated sewage and effectively avoids the problem of increased total cyanide caused by the addition of strong acid in the Fenton process.

[0019] (2) Sulfate or other anions are not introduced into the treatment process of the present invention, so the salt content in the sewage is low, the process is safe and non-toxic, the operating cost is low, and the effluent quality can meet the direct discharge water quality requirements of GB31571-2015. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 This is a process flow chart of wastewater treatment in an acrylonitrile production device according to an embodiment of the present invention.

[0021] Among them, 1 ozone oxidation device; 2 first-stage UV / H 2 O 2 Photo-Fenton device; 3 second-stage UV / H 2 O 2 Photo-Fenton device; 4 third-level UV / H 2 O 2 Photo-Fenton device; 5A / A / O process device; 6 EBF biological filter; 7 return pipe; 8 other sewage input pipes in the factory area; 9 effluent discharge. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0024] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0025] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0026] The sewage of the present invention refers to the sewage generated during the refining process of acrylonitrile in an acrylonitrile production device, namely, acrylonitrile refined water, specifically the condensate of the four-effect evaporator in the acrylonitrile production device, referred to as four-effect evaporator condensate.

[0027] The present invention provides a wastewater treatment process for an acrylonitrile production device, comprising the following steps: (1) The wastewater from the acrylonitrile production unit enters the ozone oxidation unit, where ozone is introduced for ozone oxidation treatment, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4; (2) The water overflow from the ozone oxidation device enters the first stage UV / H 2 O 2 Photo-Fenton device, adding Fe 3+ Salt and hydrogen peroxide, hydraulic retention time 0.1-3h; (3) The water overflow from step (2) enters the second stage UV / H 2 O 2 Photo-Fenton device, second stage UV / H 2 O 2 The effluent from the photo-Fenton device is refluxed to the inlet of the ozone oxidation device, with a reflux ratio of 50-1000%; (4) The water overflow from step (3) enters the third stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 0.1-3h; (5) The effluent from step (4) is treated by adding caustic soda to adjust the pH value to 6.5-8.5, and then treated by the A / A / O process and the EBF biofilter in sequence to meet the discharge standards.

[0028] In the present invention, in step (1), wastewater from the acrylonitrile production unit enters an ozone oxidation unit, and ozone is introduced for ozone oxidation treatment, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4. Specifically, the pH value of the effluent from the ozone oxidation unit can be controlled by adjusting the ozone dosage and the hydraulic retention time. The present invention has no specific restrictions on the ozone oxidation unit, and a conventional ozone oxidation unit in the art can be used. The ozone oxidation can be either pure ozone oxidation or catalytic ozone oxidation. The wastewater after ozone oxidation treatment meets the requirements of level 3 UV / H 2 O 2 The pH range required by the photo-Fenton device does not require UV / H 2O 2 The photo-Fenton device injects strong acidic substances, such as sulfuric acid, so the salt content in the wastewater is controlled at a lower range.

[0029] According to the treatment process of the present invention, in some embodiments, in step (1), the dosage of ozone is 10-1000 mg / L. It can be understood that the dosage of ozone can be 10 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, 450 mg / L, 500 mg / L, 550 mg / L, 600 mg / L, 650 mg / L, 700 mg / L / L, 750mg / L, 800mg / L, 850mg / L, 900mg / L, 950mg / L, 1000mg / L or any value in the range of 10-1000mg / L; the hydraulic retention time is 0.5-5h, it can be understood that the hydraulic retention time can be any specific value among 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any value in the range of 0.5-5h.

[0030] In the present invention, in step (2), the water overflow from the ozone oxidation device enters the first stage UV / H 2 O 2 Photo-Fenton device, adding Fe 3+ Salt and hydrogen peroxide, the hydraulic retention time is 0.1-3h. In some embodiments, the Fe 3+ The salt is selected from at least one of ferric sulfate and ferric chloride, wherein the Fe 3+ The dosage of salt is 10-100 mg / L. It can be understood that the Fe 3+The dosage of salt can be any specific value among 10mg / L, 20mg / L, 30mg / L, 40mg / L, 50mg / L, 60mg / L, 70mg / L, 80mg / L, 90mg / L, 100mg / L or any value within the range of 10-100mg / L. In some embodiments, the dosage of the hydrogen peroxide is 50-1000 mg / L. It can be understood that the dosage of the hydrogen peroxide can be any specific value of 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, 450 mg / L, 500 mg / L, 550 mg / L, 600 mg / L, 650 mg / L, 700 mg / L, 750 mg / L, 800 mg / L, 850 mg / L, 900 mg / L, 950 mg / L, 1000 mg / L or any value within the range of 50-1000 mg / L.

[0031] Further, in some embodiments, in step (2), the Fe 3+ The dosage of salt is preferably 30-60 mg / L. In some embodiments, in step (2), the dosage of hydrogen peroxide is preferably 100-500 mg / L.

[0032] In the present invention, the second level UV / H 2 O 2 The photo-Fenton device has an internal reflux pipeline, through which the second stage UV / H 2 O 2 The effluent from the photo-Fenton device flows back to the inlet of the ozone oxidation device. 2 O 2 The photo-Fenton device includes a reactor body, which includes but is not limited to a stainless steel tank. An ultraviolet lamp is arranged in the center of the reactor body, and a quartz glass sleeve is covered on the outer surface of the ultraviolet lamp. An inlet pipe, an outlet pipe and a reflux pipe are arranged on the tank body, and the reflux pipe is connected to the inlet of the ozone oxidation device.

[0033] The present invention has a first-level UV / H 2 O 2 Photo-Fenton device and third-stage UV / H 2 O 2 There is no specific limitation on the photo-Fenton device, and conventional UV / H 2 O 2Photo-Fenton device. For example, the reaction device may include a reactor body, which includes but is not limited to a stainless steel tank, a UV lamp is arranged in the center of the reactor body, a quartz glass sleeve is covered on the UV lamp, the upper and lower ends of the tank body are connected by a pipeline, and an electromagnetic metering pump is used to promote the flow of liquid in the tank.

[0034] Furthermore, the various levels of UV / H 2 O 2 The wavelength of ultraviolet light in the photo-Fenton device is 250-260nm, and the irradiation power of the ultraviolet lamp is 0.3-0.6kw·h / m 3 .

[0035] According to the treatment process of the present invention, in some embodiments, in step (3), the second stage UV / H 2 O 2 The hydraulic retention time in the photo-Fenton device is 0.5-5h. It can be understood that the hydraulic retention time can be any specific value of 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any value within the range of 0.5-5h.

[0036] According to the treatment process of the present invention, in some embodiments, in step (3), the second stage UV / H 2 O 2 The reflux ratio of the effluent from the photo-Fenton device is 50-1000%, preferably 100-500%. 2 O 2 The reflow ratio of the effluent from the photo-Fenton device can achieve the goals of wastewater decarbonization (i.e., reducing COD) and improving biodegradability with less ozone and hydrogen peroxide dosage; if the reflow ratio is too low, the wastewater decarbonization rate will be low and there will be too much residual hydrogen peroxide in the effluent, affecting the biodegradability; if the reflow ratio is too high, it will easily cause excessive energy consumption of the reflux pump and increase the cost of wastewater treatment.

[0037] According to the treatment process of the present invention, in some embodiments, the third level UV / H 2 O 2 BOD of effluent from photo-Fenton device 5 The / COD value is greater than 0.5, indicating that the treatment process of the present invention can completely remove the difficult-to-degrade, nitrification-inhibiting substances and toxic substances in the sewage, and improve the biodegradability of the sewage.

[0038] The inventors of the present invention have found that the wastewater from the acrylonitrile production plant can be treated with ozone oxidation and multi-stage UV / H in a specific order. 2 O 2The photo-Fenton process significantly improves the biodegradability of the treated effluent, while the salt content in the wastewater is extremely low. First, the ozone oxidation process can oxidize most of the nitrogen-containing compounds in the wastewater, especially nitrile compounds, into amides or ammonium carboxylates, while providing three levels of UV / H 2 O 2 The pH value required for the photo-Fenton process. 2 O 2 The photo-Fenton process can effectively reduce COD in wastewater without the need for UV / H 2 O 2 The photo-promoted Fenton device injects strong acidic substances, so the salt content in the wastewater is controlled at a lower range, and at the same time effectively avoids the problem of increased total cyanide in the Fenton process.

[0039] According to the treatment process of the present invention, in some embodiments, in step (5), the caustic soda can be in the form of an aqueous solution, and the mass concentration of the caustic soda aqueous solution can be 30-50%. It can be understood that the mass concentration of the caustic soda aqueous solution can be any specific value of 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50% or any value within the range of 30-50%.

[0040] In the present invention, the sewage is further treated by the A / A / O process and the biofilter EBF. 2 O 2 The wastewater treated by the photo-Fenton device can be treated by the A / A / O process and the biofilter EBF together with other wastewater in the plant, for example, it can be treated by the A / A / O process and the biofilter EBF together with the circulating water wastewater and the desalted water station wastewater in the plant. The present invention has no special restrictions on this and can be adjusted according to actual conditions.

[0041] In the present invention, the A / A / O process is the abbreviation of Anaerobic-Anoxic-Oxic (biological denitrification and phosphorus removal), also known as anaerobic-anoxic-aerobic process. In some specific embodiments, the sewage and the return sludge are firstly mixed in the anaerobic tank, and then anaerobic decomposition is carried out for a certain period of time to convert some nitrogen-containing compounds into N 2 The phosphorus is released by the phosphorus-accumulating microorganisms (phosphorus-accumulating bacteria, etc.) in the return sludge to meet the phosphorus demand of bacteria. Then the sewage flows into the anoxic tank, where the denitrifying bacteria use the undecomposed carbon-containing organic matter in the sewage as a carbon source and reduce the nitrate ions returned from the aerobic tank through the internal circulation to N 2Then the sewage flows into the aerobic pool, where the ammonia nitrogen in the water undergoes nitrification to generate nitrate ions, while the organic matter in the water is oxidized and decomposed to provide energy for phosphorus-absorbing microorganisms. The microorganisms absorb phosphorus from the water, and the phosphorus enters the cell tissues and is enriched in the microorganisms. After precipitation and separation, it is discharged from the system in the form of phosphorus-rich sludge.

[0042] According to the treatment process of the present invention, in some embodiments, in step (5), the A / A / O process conditions are: the hydraulic retention time of the anaerobic tank is 15-30 hours, the hydraulic retention time of the anoxic tank is 20-30 hours, and the hydraulic retention time of the aerobic tank is 20-40 hours.

[0043] In the present invention, the sewage treated in the anoxic tank enters the aerobic tank for nitrification treatment, part of the nitrification effluent is returned to the anoxic tank, the remaining effluent enters the sedimentation tank for sedimentation separation, part of the sludge is returned to the anoxic tank, and the supernatant is discharged as treated effluent to the subsequent process. The present invention can adopt conventional process parameters of the A / A / O process, for example, the return ratio of the nitrification effluent can be 200-600%, and the return ratio of the sedimentation tank sludge can be 30-90%.

[0044] EBF, or engineered bacteria biofilter, forms a fixed bed biofilter by loading bio-enhanced engineered strains into porous materials such as activated carbon and ceramsite to remove COD that is difficult to biodegrade in sewage. In actual operation, the pool is aerated from the bottom, the dissolved oxygen is maintained at 1-6 mg / L, and the water flows from bottom to top through the fixed bed, which can remove most of the difficult to biodegrade COD in the water.

[0045] According to the treatment process of the present invention, in some embodiments, in step (5), the hydraulic retention time of the biological filter EBF is 2-4 hours.

[0046] The present invention has no special limitation on the A / A / O tank and the biological filter EBF, and conventional A / A / O tanks and biological filter EBF in the art can be used.

[0047] The present invention will be described in detail below by way of examples. It should be understood that the following examples are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0048] In the present invention, the testing methods of various performance parameters in the embodiments and comparative examples are as follows: Chemical oxygen demand CODcr: dichromate method, tested according to HJ828-2017 standard; Five-day biochemical oxygen demand BOD 5 : Tested according to HJ505-2009 standard; Total organic carbon TOC: tested according to HJ501-2009 standard; Total nitrogen content TN: tested according to BSEN12260-2003 standard; Ammonia nitrogen NH 3 -N content: tested according to HJ / T195-2005 standard; NO 3 -N content: tested according to HJ / T198-2005 standard; Total cyanide content: tested according to HJ484-2009 standard; Total phosphorus content: tested according to DINENISO6878-2004 standard; Suspended matter content: tested according to GB / T11901-1989 standard; The contents of acrylonitrile, acrolein, cyanopyridine, succinonitrile, propionitrile, diazine and 2-hydroxy-4,6-dimethylpyrimidine are determined according to the general rules for gas chromatography JY / T0574-2020, and are detected by headspace gas chromatography-mass spectrometry, with 5 mg / L, 10 mg / L and 50 mg / L acrylonitrile solutions as internal standard curves.

[0049] In the present invention, the wastewater to be treated used in the embodiments and comparative examples is the condensate of the four-effect evaporator of a certain acrylonitrile production device, and the conventional water quality is shown in Table 1. The content of characteristic pollutants in the condensate of the four-effect evaporator is measured by gas chromatography-mass spectrometry as shown in Table 2. This wastewater has low biodegradability, BOD 5 / COD value is about 0.004.

[0050] Example 1 The wastewater treatment process of the acrylonitrile production device described in this embodiment is as follows: Figure 1 The specific steps include: (1) The wastewater from the acrylonitrile production unit enters the ozone oxidation unit and is treated by ozone oxidation. The ozone dosage is 500 mg / L, the hydraulic retention time is 2 h, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4. (2) The water overflow from the ozone oxidation device enters the first stage UV / H 2 O 2 The photo-Fenton device was used to add ferric chloride and hydrogen peroxide, and the hydraulic retention time was 1.5 h. 3+ Based on salt, the dosage of ferric chloride is 50mg / L, and the dosage of hydrogen peroxide is 480mg / L; (3) First level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the second stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 1.5h, second stage UV / H 2 O 2The effluent from the photo-Fenton device is refluxed to the inlet of the ozone oxidation device at a reflux ratio of 300%; (4) Second level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the third-stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 1.5h; (5) Level 3 UV / H 2 O 2 Caustic soda is added to the effluent of the photo-Fenton device to adjust the pH value to 7.8, and the effluent enters the anaerobic tank, anoxic tank and aerobic tank of the A / A / O biochemical system in sequence together with an equal amount of circulating water sewage and desalted water station sewage. The hydraulic retention time in the anaerobic tank is 30 hours, the hydraulic retention time in the anoxic tank is 30 hours, and the hydraulic retention time in the aerobic tank is 40 hours. The sewage treated in the aerobic tank enters the secondary sedimentation tank for sedimentation and separation, and the nitrification liquid and sludge in the secondary sedimentation tank are returned to the anoxic tank, wherein the nitrification liquid return ratio is 300%, and the sludge return ratio is 50%. Then the effluent enters the biological filter EBF with a hydraulic retention time of 2 hours, and the treated effluent is directly discharged.

[0051] After testing, the third level UV / H 2 O 2 The conventional water quality of the effluent from the photo-Fenton device is shown in Table 1. The third-level UV / H 2 O 2 The characteristic pollutant contents in the effluent of the photo-Fenton device are shown in Table 2. 2 O 2 BOD of effluent from photo-Fenton device 5 / COD value is 0.53, which has good biodegradability. The EBF effluent quality meets the direct discharge water quality requirements of GB31571-2015. The specific data are shown in Table 3.

[0052] Example 2 The wastewater treatment process of the acrylonitrile production device described in this embodiment is as follows: Figure 1 The specific steps include: (1) The wastewater from the acrylonitrile production unit enters the ozone oxidation unit and is treated by ozone oxidation. The ozone dosage is 100 mg / L, the hydraulic retention time is 4 h, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4. (2) The water overflow from the ozone oxidation device enters the first stage UV / H 2 O 2 The photo-Fenton device was used to add ferric sulfate and hydrogen peroxide, and the hydraulic retention time was 3h. 3+Based on salt, the dosage of ferric sulfate is 60mg / L, and the dosage of hydrogen peroxide is 50mg / L; (3) First level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the second stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 5h, second stage UV / H 2 O 2 The effluent from the photo-Fenton device is refluxed to the inlet of the ozone oxidation device at a reflux ratio of 500%; (4) Second level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the third-stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 3h; (5) Level 3 UV / H 2 O 2 Caustic soda is added to the effluent of the photo-Fenton device to adjust the pH value to 6.8, and the effluent enters the anaerobic tank, anoxic tank and aerobic tank of the A / A / O biochemical system in sequence together with an equal amount of circulating water sewage and desalted water station sewage. The hydraulic retention time of the anaerobic tank is 20 hours, the hydraulic retention time of the anoxic tank is 20 hours, and the hydraulic retention time of the aerobic tank is 20 hours. The sewage treated in the aerobic tank enters the secondary sedimentation tank for sedimentation and separation, and the nitrification liquid and sludge in the secondary sedimentation tank are returned to the anoxic tank, wherein the nitrification liquid return ratio is 300%, and the sludge return ratio is 50%. Then the effluent enters the biological filter EBF with a hydraulic retention time of 4 hours, and the treated effluent is directly discharged.

[0053] After testing, the third level UV / H 2 O 2 The conventional water quality of the effluent from the photo-Fenton device is shown in Table 1. The third-level UV / H 2 O 2 The characteristic pollutant contents in the effluent of the photo-Fenton device are shown in Table 2. 2 O 2 BOD of effluent from photo-Fenton device 5 / COD value is 0.56, with good biodegradability. EBF effluent quality meets the direct discharge water quality requirements of GB31571-2015, and the specific data are shown in Table 3.

[0054] Table 1 Four-effect evaporator condensate and third-stage UV / H 2 O 2 Conventional water quality of photo-Fenton effluent .

[0055] Table 2 Four-effect evaporator condensate and third-stage UV / H 2 O 2 Characteristic pollutants in photo-Fenton effluent .

[0056] Table 3 EBF effluent quality in the examples and GB31571-2015 direct discharge quality .

[0057] Comparative Example 1 The wastewater treatment process of the acrylonitrile production unit in this comparative example is the same as that in Example 1, except that the second stage UV / H 2 O 2 The effluent from the photo-Fenton device is not refluxed. 2 O 2 The effluent COD of the photo-Fenton device was 2326 mg / L. The residual hydrogen peroxide in the wastewater was 100 mg / L as detected by hydrogen peroxide test paper. 5 / COD value is 0.21. It can be seen that the biodegradability of the sewage is low and it fails to achieve the water quality effect in the embodiment, so it cannot be put into the biochemical system for subsequent treatment.

[0058] Comparative Example 2 The wastewater treatment process of the acrylonitrile production plant in this comparative example is the same as that in Example 1, except that only one UV / H 2 O 2 Photo-Fenton device. After testing, UV / H 2 O 2 BOD of the effluent from the photo-Fenton device 5 / COD value is 0.13. Since the biodegradability of sewage is too low, it cannot be put into the biochemical system for subsequent treatment.

[0059] Comparative Example 3 The wastewater treatment process of the acrylonitrile production unit in this comparative example is the same as that in Example 1, except that the second stage UV / H 2 O 2 The effluent from the photo-Fenton device is returned to the inlet of the ozone oxidation device at a 45% reflux ratio. 2 O 2 The effluent COD of the photo-Fenton device was 2192 mg / L. The residual hydrogen peroxide in the wastewater was 50 mg / L as detected by hydrogen peroxide test paper. 5 / COD value is 0.23. Since the biodegradability of sewage is too low, it cannot be put into the biochemical system for subsequent treatment.

[0060] Comparative Example 4 The wastewater treatment process of the acrylonitrile production unit in this comparative example is the same as that in Example 1, except that the second stage UV / H 2 O 2 The effluent from the photo-Fenton device is refluxed to the inlet of the ozone oxidation device at a reflux ratio of 1100%. 2 O 2 BOD of the effluent from the photo-Fenton device 5 The / COD value is 0.32, which is biodegradable. However, due to excessive reflux, it will lead to excessive energy consumption in industrial production and is not feasible.

[0061] Comparative Example 5 The wastewater treatment process of the acrylonitrile production device in this comparative example is the same as that in Example 1, except that the wastewater first enters the three-stage UV / H 2 O 2 The photo-Fenton device is used for treatment, and then enters the ozone oxidation device. The specific steps are as follows: (1) Wastewater from the acrylonitrile production unit enters the first-stage UV / H 2 O 2 The photo-Fenton device was used to add ferric chloride and hydrogen peroxide, and sulfuric acid was added to adjust the pH value of the sewage to 3.5. The hydraulic retention time was 1.5 h. 3+ Based on salt, the dosage of ferric chloride is 50mg / L, and the dosage of hydrogen peroxide is 480mg / L; (2) First level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the second stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 1.5h; (3) Second level UV / H 2 O 2 The effluent from the photo-Fenton device overflows into the third-stage UV / H 2 O 2 Photo-Fenton device, hydraulic retention time is 1.5h; (4) Level 3 UV / H 2 O 2 The effluent from the photo-Fenton device enters the ozone oxidation device, where ozone is introduced for ozone oxidation treatment. 500 mg / L of ozone is added, and the hydraulic retention time is 2 h. The inventors found that in the process of comparative example 5, after sulfuric acid was added in step (1) to adjust the pH value to 3.5, the total cyanide content continued to increase during the oxidation process. 2 O 2The total cyanide content of the effluent from the photo-Fenton device was 105 mg / L, which formed highly toxic wastewater and brought hidden dangers to production safety. After subsequent treatment, the total cyanide content of the effluent from ozone oxidation was still as high as 93 mg / L. Both production safety and water quality did not achieve the effects in the embodiments of the present invention and were not feasible.

[0062] It can be seen from Example 1 and Comparative Example 1 that the second-stage UV / H 2 O 2 The effluent from the photo-Fenton device is not refluxed, and the third-stage UV / H 2 O 2 BOD of effluent from photo-Fenton device 5 / COD value is significantly lower than that of Example 1. It can be seen from Example 1 and Comparative Example 2 that Comparative Example 2 has only one level of UV / H 2 O 2 Photo-Fenton device to detect BOD 5 / COD value is also significantly lower than that in Example 1. It can be seen from Example 1 and Comparative Examples 3-4 that the second-stage UV / H 2 O 2 If the effluent reflow ratio of the photo-Fenton device is too low or too high, it will have a great impact on the sewage treatment results or will not be industrially feasible due to high energy consumption, which means that controlling the reflow ratio within the appropriate range is not a conventional choice. 2 O 2 The order of the photo-Fenton device and the ozone oxidation device, the safety and water quality of the sewage treatment process are quite different, which shows that the ozone oxidation device and UV / H 2 O 2 The order of the photo-Fenton devices cannot be interchanged.

[0063] It can be seen that the present invention designs an ozone oxidation with internal reflux and a three-stage UV / H 2 O 2 Photo-Fenton coupled wastewater treatment process, and further control of process conditions of each step and second-stage UV / H 2 O 2 The reflux ratio of the effluent from the photo-Fenton unit can effectively remove the difficult-to-degrade and nitrification-inhibiting substances in the wastewater of the acrylonitrile production unit, and significantly increase the BOD of the wastewater. 5 / COD value, which significantly improves the biodegradability of the treated sewage.

[0064] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A wastewater treatment process for an acrylonitrile production device, characterized in that: The steps include: (1) The wastewater from the acrylonitrile production unit enters the ozone oxidation unit, where ozone is introduced for ozone oxidation treatment, and the pH value of the effluent from the ozone oxidation unit is controlled to be below 4; (2) The water overflow from the ozone oxidation device enters the first-stage UV / H2O2 photo-Fenton device, where Fe 3+ Salt and hydrogen peroxide, hydraulic retention time 0.1-3h; (3) The effluent from step (2) overflows into the second-stage UV / H2O2 photo-Fenton device, and the effluent from the second-stage UV / H2O2 photo-Fenton device flows back to the inlet of the ozone oxidation device, with a reflux ratio of 50%-1000%; (4) The effluent from step (3) overflows into the third-stage UV / H2O2 photo-Fenton device, with a hydraulic retention time of 0.1-3h; (5) The effluent from step (4) is treated by adding caustic soda to adjust the pH value to 6.5-8.5, and then treated by the A / A / O process and the EBF biofilter in sequence to meet the discharge standards.

2. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (1), the dosage of ozone is 10-1000 mg / L, and the hydraulic retention time is 0.5-5 h.

3. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (2), the Fe 3+ The salt is selected from at least one of ferric sulfate and ferric chloride, wherein the Fe 3+ The dosage of salt is 10-100 mg / L.

4. The wastewater treatment process for acrylonitrile production equipment according to claim 3, characterized in that: In step (2), the Fe 3+ The dosage of salt is 30-60 mg / L.

5. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (2), the dosage of the hydrogen peroxide is 50-1000 mg / L.

6. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (3), the hydraulic retention time in the second-stage UV / H2O2 photo-Fenton device is 0.5-5h.

7. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (3), the reflux ratio of the effluent from the second-stage UV / H2O2 photo-Fenton device is 100-500%.

8. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: The BOD5 / COD value of the effluent from step (4) is greater than 0.

5.

9. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (5), the A / A / O process conditions are: the hydraulic retention time of the anaerobic tank is 15-30 hours, the hydraulic retention time of the anoxic tank is 20-30 hours, and the hydraulic retention time of the aerobic tank is 20-40 hours.

10. The wastewater treatment process for acrylonitrile production equipment according to claim 1, characterized in that: In step (5), the hydraulic retention time of the biological filter EBF is 2-4h.

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