Treatment process of wastewater with high nitrile content

Abstract

The invention discloses a treatment process of high-nitrile-content wastewater, and belongs to the technical field of wastewater treatment. The method comprises the following steps: (1) pretreatment: adding an alkaline substance into the high-nitrile-content wastewater to adjust the pH value of the wastewater to 9-12, and adding sodium percarbonate for reaction to obtain pretreated wastewater; and (2) sequentially treating the pretreated wastewater through an A / A / O process and a biological filter EBF, and discharging after reaching the standard. According to the treatment process, the treatment cost of the high-nitrile-content wastewater can be effectively reduced, the content of nitrile compounds in the wastewater can be rapidly reduced, the biodegradability of the wastewater can be remarkably improved, and the wastewater can be discharged after reaching the standard.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a treatment process for wastewater with high nitrile content. Background Art

[0002] Nitrile is a kind of organic matter containing the organic group -C≡N, which is a highly toxic substance. Nitrile-containing wastewater refers to industrial wastewater containing nitrile compounds, which is mainly produced from the industrial production processes of acrylic fiber, acrylonitrile, acetonitrile and related downstream enterprises. These industrial wastewaters contain high levels of nitrile, often containing hundreds of mg / L of acrylonitrile, acetonitrile, butenedinitrile, cyanopyridine and other nitrile compounds, which affect the smooth operation of the subsequent biochemical units of the sewage field, especially causing the nitrification reaction to fail to proceed smoothly, and then the chemical oxygen demand COD and total nitrogen of the effluent cannot meet the external discharge requirements. Therefore, the biochemical compliance of high nitrile-containing wastewater has always been a difficult problem in the industry.

[0003] At present, the main treatment processes for nitrile-containing wastewater are: chemical method (combustion method, chemical coagulation, chemical oxidation and internal electrolysis), biological method (SBR method, biological contact oxidation method, pressurized aerobic biochemical method, acidification pretreatment, biological filter tower and addition of special bacteria), physical and chemical method (membrane distillation technology and membrane separation method). Among them, the biochemical method is suitable for low nitrile compound content. When it is greater than a certain concentration (such as nitrile compound concentration higher than 50mg / L), it will inhibit the nitrification reaction, thereby affecting the treatment effect of the biochemical method. The physical and chemical method is prone to membrane clogging, and the clogging of the membrane will reduce the effective water permeability, thereby affecting the treatment effect of nitrile-containing wastewater. The chemical method is currently a widely used method for treating nitrile-containing wastewater, but there are still some problems, mainly manifested in: it is difficult for the treated effluent to meet the biochemical standard, in addition to COD, the ammonia nitrogen content in the effluent is also high; the cost is high.

[0004] Patent CN102115271A discloses a method for treating high-concentration cyanide or nitrile organic wastewater. First, under alkaline conditions, Cu 2+ The first step is to oxidize the wastewater to remove inorganic cyanide by adding alkali to adjust the pH value, and then alkaline hydrolysis of organic nitrile is carried out at a certain temperature for 2-4 hours; finally, under alkaline conditions, oxidant hydrogen peroxide is added to the wastewater to remove cyanide by the second step. 2+ , in fact, new pollutants are introduced into the sewage, making the sewage non-biodegradable and unable to meet discharge standards.

[0005] Patent CN103420473B discloses a method for treating wastewater in the process of acrylonitrile production and refining. The wastewater and oxygen-containing gas enter a catalytic wet oxidation reactor to cause free radical reaction between organic matter and oxygen, thereby continuously degrading the organic matter and finally generating non-toxic and harmless substances such as H2O, CO2 and N2. This process can effectively remove COD, but it is carried out in high-temperature and high-pressure equipment, and the process is complex and the investment is high. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a treatment process for high-nitrile-containing wastewater, which can effectively reduce the treatment cost of high-nitrile-containing wastewater, quickly reduce the content of nitrile compounds in the wastewater, significantly improve the biodegradability of the wastewater, and make the wastewater meet discharge standards.

[0007] In order to achieve the above object, according to one aspect of the present invention, a treatment process for high nitrile-containing wastewater is provided, comprising the following steps: (1) Pretreatment: adding alkaline substances to the wastewater with high nitrile content to adjust the pH value of the wastewater to 9-12, adding sodium percarbonate to react, and obtaining pretreated wastewater; (2) The pretreated wastewater is processed by the A / A / O process and the EBF biofilter in turn before it can meet the discharge standards.

[0008] In some embodiments, in step (1), in step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0009] In some embodiments, in step (1), alkaline substances are added to the wastewater with high nitrile content to adjust the pH value of the wastewater to 10-11.

[0010] In some embodiments, in step (1), the amount of sodium percarbonate used is 50-1000 mg / L.

[0011] In some embodiments, in step (1), the molar ratio of sodium percarbonate to -C≡N groups in wastewater is (0.01-1):1.

[0012] In some embodiments, in step (1), the temperature for adding sodium percarbonate to react is room temperature, and the reaction time is 0.1-2.0 hours.

[0013] In some embodiments, the BOD5 / COD value of the pretreated wastewater is higher than 0.5.

[0014] In some embodiments, the content of nitrile compounds in the pretreated wastewater is less than 0.33 mg / L.

[0015] In some embodiments, in step (2), 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 20-40 hours, and the hydraulic retention time of the aerobic tank is 10-30 hours.

[0016] In some embodiments, in step (2), the process conditions of the biological filter EBF are: the hydraulic retention time is 2-4h.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides an efficient and low-cost pretreatment technology for high-nitrile-containing wastewater. By adding a small amount of alkaline substance to the high-nitrile-containing wastewater to adjust the pH value of the wastewater, and adding a specific amount of sodium percarbonate for reaction, the nitrile compounds in the wastewater can be quickly converted into the corresponding ammonium carboxylates, thereby fundamentally removing the toxicity of the nitrile compounds and significantly improving the biodegradability of the wastewater. The BOD5 / COD value of the pretreated wastewater is higher than 0.5, and can be directly used for biochemical treatment.

[0018] (2) The high nitrile content wastewater treatment process of the present invention is simple to operate, low in cost, and the effluent quality can meet the direct discharge water quality requirements of GB31571-2015. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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 flow chart of a process for treating wastewater containing high nitrile content according to an embodiment of the present invention; Figure 2 This is a graph showing the changes in ammonia nitrogen content and conductivity of the wastewater in Comparative Example 8 as a function of the amount of sodium hydroxide added. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The present invention provides a treatment process for wastewater with high nitrile content, which is characterized by comprising the following steps: (1) Pretreatment: adding alkaline substances to the wastewater with high nitrile content to adjust the pH value of the wastewater to 9-12, adding sodium percarbonate to react, and obtaining pretreated wastewater; (2) The pretreated wastewater is processed by the A / A / O process and the EBF biofilter in turn before it can meet the discharge standards.

[0025] In the present invention, the high nitrile-containing wastewater refers to wastewater with a total nitrile group content higher than 10 mg / L. The present invention does not specifically limit the source of the high nitrile-containing wastewater, including but not limited to industrial wastewater containing nitrile compounds generated by industries such as acrylonitrile production, acrylic fiber, nitrile rubber or latex, and ABS engineering resin.

[0026] In some embodiments, in step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The alkaline substance in the present invention is used to adjust the pH value of the nitrile-containing wastewater, thereby providing necessary conditions for subsequent reactions.

[0027] In some preferred embodiments, in step (1), an alkaline substance is added to the wastewater with high nitrile content to adjust the pH value of the wastewater to 10-11. The present invention can provide a suitable environment for the carboxylation reaction of the nitrile group under specific alkaline conditions by adding an alkaline substance to the wastewater with high nitrile content to adjust the pH value of the wastewater. If the pH value is low, the nitrile compound is not easy to be carboxylated; if the pH value is high, the cost of adding alkali is too high, and too much salt will be brought into the subsequent biochemical unit, making it difficult to biodegrade.

[0028] In some embodiments, in step (1), the amount of sodium percarbonate used is 50-1000 mg / L. It can be understood that the amount 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.

[0029] Furthermore, in step (1), the amount of sodium percarbonate used is preferably 100-1000 mg / L.

[0030] In some embodiments, in step (1), the molar ratio of sodium percarbonate to -C≡N groups in wastewater is (0.01-1):1. It can be understood that the molar ratio can be any specific value among 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1 or any value within the range of (0.01-1):1.

[0031] In the present invention, the role of adding sodium percarbonate is to promote the hydrolysis of nitrile compounds to generate corresponding ammonium carboxylates. The applicant has also found that by further controlling the molar ratio of sodium percarbonate and -C≡N groups in wastewater, the nitrile compounds can be completely hydrolyzed within 1 hour, the toxicity caused by the nitrile compounds in the wastewater is quickly eliminated, and the biodegradability of the wastewater is significantly improved. If the molar ratio of sodium percarbonate to -C≡N groups in wastewater is low, the carboxylation process of nitrile compounds takes a long time and has low efficiency. If the molar ratio of sodium percarbonate to -C≡N groups in wastewater is high, the cost of adding auxiliary agents is high, and excessive salt will be brought into the subsequent biochemical unit and it is not easy to biodegrade.

[0032] In some embodiments, in step (1), the temperature for adding sodium percarbonate to react is room temperature, and the reaction time is 0.1-2.0 h. It can be understood that the time can be any specific value of 0.1 h, 0.5 h, 1 h, 1.5 h, 2 h or any value within the range of 0.1-2.0 h.

[0033] In some embodiments, the BOD5 / COD value of the pretreated wastewater is higher than 0.5.

[0034] In the present invention, BOD5 (Biochemical Oxygen Demand) is an important indicator that indirectly indicates the degree of organic pollution in water bodies by the amount of dissolved oxygen consumed by microbial metabolism. Generally, 5 days is used as the standard time for measuring BOD, so it is called five-day biochemical oxygen demand, expressed as BOD5. The ratio of BOD5 / COD can be used to judge the biodegradability of influent water. A ratio lower than 0.3 indicates that the biodegradability is extremely poor and cannot be treated by biochemical methods; a BOD5 / COD value higher than 0.5 indicates that the biodegradability of the wastewater is extremely high and almost completely biodegradable.

[0035] In some embodiments, the content of nitrile compounds in the wastewater after pretreatment is less than 0.33 mg / L, indicating that the treatment process of the present invention can achieve complete hydrolysis of nitrile compounds in the wastewater, completely eliminate the toxicity of nitrile compounds, and significantly improve the biodegradability of the wastewater.

[0036] In some embodiments, in step (2), 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 20-40 hours, and the hydraulic retention time of the aerobic tank is 10-30 hours.

[0037] 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%.

[0038] In the present invention, the A / A / O process is the abbreviation of Anaerobic-Anoxic-Oxic in English (biological denitrification and phosphorus removal), also known as anaerobic-anoxic-aerobic method. In some specific embodiments, the wastewater and the return sludge first enter the anaerobic tank and are completely mixed. After a certain period of anaerobic decomposition, part of the nitrogen-containing compounds are converted into N2 (denitrification) and released, and the polyphosphate microorganisms (polyphosphate bacteria, etc.) in the return sludge release phosphorus to meet the bacteria's demand for phosphorus. Then the sewage flows into the anoxic tank, and the denitrifying bacteria in the pool use the undecomposed carbon-containing organic matter in the sewage as a carbon source to reduce the nitrate ions that flow back through the internal circulation in the aerobic tank to N2 and release. Next, the sewage flows into the aerobic tank, and the ammonia nitrogen in the water undergoes nitrification to generate nitrate ions. At the same time, the organic matter in the water is oxidized and decomposed to supply energy to the phosphorus-absorbing microorganisms. The microorganisms absorb phosphorus from the water, and the phosphorus enters the cell tissue and is enriched in the microorganisms. After precipitation and separation, it is discharged from the system in the form of phosphorus-rich sludge.

[0039] In some embodiments, in step (2), the process conditions of the biological filter EBF are: the hydraulic retention time is 2-4h.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In the present invention, the testing methods of various performance parameters in the embodiments and comparative examples are as follows: Conductivity: Tested in accordance with GB / T 6908-2018; Chemical oxygen demand CODcr: dichromate method, tested according to HJ828-2017 standard; Five-day biochemical oxygen demand BOD5: tested according to HJ505-2009 standard; Total organic carbon TOC: tested according to HJ 501-2009 standard; Total nitrogen content TN: tested according to BSEN12260-2003 standard; Ammonia nitrogen NH3-N content: tested according to HJ / T 195-2005 standard; Total cyanide content: tested according to HJ 484-2009 standard; Suspended matter content: tested according to GB / T 11901-1989 standard; The contents of acrylonitrile and acrylic acid are determined in accordance with JY / T 0574-2020 General Rules for Gas Chromatography, using headspace gas chromatography-mass spectrometry, and 5 mg / L, 10 mg / L, and 50 mg / L acrylonitrile as internal standard curves.

[0044] Example 1 The high nitrile-containing wastewater treatment process described in this embodiment is as follows: Figure 1As shown. Specifically, it includes the following steps: a rubber synthesis process discharges industrial wastewater containing acrylonitrile (acrylonitrile content is 660mg / L, COD is 3120mg / L, TN is 610mg / L, ammonia nitrogen is undetectable, and pH is 8.51), sodium hydroxide is added to adjust its pH to 11.0, 100mg / L sodium percarbonate is added, the molar ratio of sodium percarbonate to -C≡N group in the wastewater is 0.03:1, the pH value of the wastewater is still maintained at 11.0, and the reaction is carried out at room temperature for 1h to obtain the pretreated wastewater. After testing, the pH of the pretreated wastewater is 10.7, the acrylonitrile content is undetectable, the ammonia nitrogen increases to 143mg / L, and the BOD5 / COD value is 0.66.

[0045] The pretreated wastewater enters the anaerobic tank, anoxic tank and aerobic tank of the A / A / O biochemical system in turn, where the hydraulic retention time of the anaerobic tank is 30 hours, the hydraulic retention time of the anoxic tank is 20 hours, and the hydraulic retention time of the aerobic tank is 10 hours. The wastewater treated in the aerobic tank enters the secondary sedimentation tank for sedimentation separation, and the nitrification liquid and sludge in the secondary sedimentation tank are returned to the anoxic tank, where the nitrification liquid return ratio is 300%, and the sludge return ratio is 50%. Then the effluent enters the biological filter EBF, and the empty tower hydraulic retention time is 2.6 hours. The treated effluent is directly discharged.

[0046] After testing, the effluent COD was 50-75mg / L, TOC was 18-30mg / L, TN was 25-32mg / L, NH3-N was 1.1-3.8mg / L, suspended solids was 10-15mg / L, and total cyanide content was 0.15-0.39mg / L. The water quality fully met the direct discharge water quality requirements of GB31571-2015.

[0047] Example 2 The high nitrile-containing wastewater treatment process described in this embodiment is as follows: Figure 1 As shown. Specifically, the following steps are included: a certain acrylic fiber production process discharges industrial wastewater (acrylonitrile content is 86mg / L, acrylic acid is 36mg / L, COD is 1100mg / L, TN is 216mg / L, ammonia nitrogen is undetectable, and pH is 5.51), sodium hydroxide is added to adjust its pH to 10.0, 200mg / L sodium percarbonate is added at room temperature, the molar ratio of sodium percarbonate to -C≡N group in the wastewater is 0.45:1, and the reaction is carried out at room temperature for 0.16h to obtain pretreated wastewater. After testing, the acrylonitrile content in the pretreated wastewater is undetectable, while the acrylic acid root reaches 143mg / L, the ammonia nitrogen increases to 27.3mg / L, and the BOD5 / COD value is 0.68.

[0048] The pretreated wastewater enters the anaerobic tank, anoxic tank and aerobic tank of the A / A / O biochemical system in turn, where the hydraulic retention time of the anaerobic tank is 30 hours, the hydraulic retention time of the anoxic tank is 30 hours, and the hydraulic retention time of the aerobic tank is 20 hours. The wastewater treated in the aerobic tank enters the secondary sedimentation tank for sedimentation separation, and the nitrification liquid and sludge in the secondary sedimentation tank are returned to the anoxic tank, where the nitrification liquid return ratio is 400%, and the sludge return ratio is 70%. It enters the biological filter EBF, and the empty tower hydraulic retention time is 2.5 hours. The treated effluent is directly discharged.

[0049] After testing, the effluent COD was 60-70mg / L, TOC was 25-29mg / L, TN was 11-15mg / L, NH3-N was 0.1-1.1mg / L, suspended solids was 10-15mg / L, and total cyanide content was 0.11-0.30mg / L. The water quality fully met the direct discharge quality requirements of GB31571-2015.

[0050] Example 3 The high nitrile-containing wastewater treatment process described in this embodiment is as follows: Figure 1 As shown. Specifically, the following steps are included: industrial wastewater (total nitrile group content of 1726 mg / L, COD of 15,500 mg / L, TN of 2620 mg / L, ammonia nitrogen content of 200 mg / L, pH value of 5.7) generated in a certain acrylonitrile refining process, 1000 mg / L of sodium hydroxide is added to adjust the pH value to 11.0, 1000 mg / L of sodium percarbonate is added, the molar ratio of sodium percarbonate to -C≡N group in the wastewater is 0.05:1, react at room temperature for 1 hour, and obtain pretreated wastewater. After testing, the acrylonitrile content in the pretreated wastewater cannot be detected, while the ammonia nitrogen increases to 1120 mg / L, and the BOD5 / COD is 0.53.

[0051] The pretreated wastewater enters the anaerobic tank, anoxic tank and aerobic tank of the A / A / O biochemical system in turn, where the hydraulic retention time of the anaerobic tank is 30 hours, the hydraulic retention time of the anoxic tank is 30 hours, and the hydraulic retention time of the aerobic tank is 20 hours. The wastewater 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, where the nitrification liquid return ratio is 300%, and the sludge return ratio is 50%. It enters the biological filter EBF, the empty tower hydraulic retention time is 3 hours, and the treated effluent is directly discharged.

[0052] After testing, the effluent COD was 55-66mg / L, TOC was 20-30mg / L, TN was 27-33mg / L, NH3-N was 1.7-7.9mg / L, suspended solids was 10-15mg / L, total cyanide content was 0.25-0.45mg / L, and the water quality fully met the direct discharge quality requirements of GB31571-2015.

[0053] Comparative Example 1 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that sodium percarbonate is replaced with hydrogen peroxide. According to the hydrogen peroxide content in sodium percarbonate, the amount of hydrogen peroxide added is 32.5 mg / L, and the reaction is carried out at room temperature for 0.5-2 h to obtain pretreated wastewater.

[0054] After the reaction, the pH value and the content of acrylonitrile and ammonia nitrogen in the wastewater were tested; the pH value of the wastewater was adjusted to 7.5, and its BOD5 / COD ratio was tested. The various indicators of the wastewater after pretreatment, the specific data are shown in Table 1. Since the biodegradability of the wastewater is too low, it cannot be put into the biochemical system for subsequent treatment.

[0055] Table 1 Various indicators of wastewater after pretreatment at different reaction times in Comparative Example 1 .

[0056] Comparative Example 2 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that sodium percarbonate is replaced with sodium carbonate. According to the sodium carbonate content in sodium percarbonate, 67.5 mg / L of sodium carbonate is added and reacted at room temperature for 0.5-2 h to obtain pretreated wastewater.

[0057] After the reaction, the pH value of the wastewater and the content of acrylonitrile and ammonia nitrogen were tested; the pH value of the wastewater was adjusted to 7.5, and its BOD5 / COD ratio was tested. The various indicators of the wastewater after pretreatment, the specific data are shown in Table 2. Since the biodegradability of the wastewater is too low, it cannot be put into the biochemical system for subsequent treatment.

[0058] Table 2 Various indicators of wastewater after pretreatment at different reaction times in Comparative Example 2 .

[0059] Comparative Example 3 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that sodium percarbonate is replaced with sodium carbonate and hydrogen peroxide. According to the sodium carbonate and hydrogen peroxide content in sodium percarbonate, 67.5 mg / L of sodium carbonate and 32.5 mg / L of hydrogen peroxide are added, and the reaction is carried out at room temperature for 0.5-2 hours to obtain pretreated wastewater.

[0060] After the reaction, the pH value of the wastewater and the content of acrylonitrile and ammonia nitrogen were tested; the pH value of the wastewater was adjusted to 7.5, and its BOD5 / COD ratio was tested. The various indicators of the wastewater after pretreatment, the specific data are shown in Table 3. Since the biodegradability of the wastewater is too low, it cannot be put into the biochemical system for subsequent treatment.

[0061] Table 3 Various indicators of wastewater after pretreatment at different reaction times in Comparative Example 3 .

[0062] Comparative Example 4 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that sodium hydroxide is added in the pretreatment step to adjust the pH value of the wastewater to 13.0. The reaction is carried out at room temperature for 0.5-2.0 hours to obtain pretreated wastewater.

[0063] After the reaction, the pH value and the content of acrylonitrile and ammonia nitrogen in the wastewater were tested; the pH value of the wastewater was adjusted to 7.5, and its BOD5 / COD ratio was tested. The various indicators of the wastewater after pretreatment, the specific data are shown in Table 4. Since the biodegradability of the wastewater is too low, it cannot be put into the biochemical system for subsequent treatment.

[0064] Table 4 Various indicators of wastewater after pretreatment at different reaction times in Comparative Example 4 .

[0065] Comparative Example 5 The wastewater quality and wastewater pretreatment process are the same as those in Example 3, except that sodium percarbonate is replaced with sodium persulfate in the pretreatment step, and 758 mg / L of sodium persulfate is added according to the content of hydroxyl radicals generated by hydrogen peroxide in sodium percarbonate. The reaction is carried out at room temperature for 1 hour to obtain pretreated wastewater.

[0066] After the reaction, the pH value of the wastewater and the content of acrylonitrile and ammonia nitrogen were tested; the pH value of the wastewater was adjusted to 7.5, and its BOD5 / COD ratio was tested. After testing, the acrylonitrile content in the pretreated wastewater was 221 mg / L, while the ammonia nitrogen increased to 75 mg / L, and the BOD5 / COD was 0.04, which made it impossible to carry out biochemical reactions.

[0067] Comparative Example 6 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that the dosage of sodium percarbonate in the pretreatment step is 10 mg / L, the molar ratio of sodium percarbonate to -C≡N group in the wastewater is 0.003:1, and the reaction is performed for 1 hour to obtain pretreated wastewater.

[0068] After testing, the acrylonitrile content in the pretreated wastewater was 221 mg / L, while the ammonia nitrogen increased to 75 mg / L, and the BOD5 / COD was 0.05, making it impossible to undergo biochemical reactions.

[0069] Comparative Example 7 The wastewater quality and wastewater pretreatment process are the same as those in Example 1, except that the dosage of sodium percarbonate in the pretreatment step is 5000 mg / L, the molar ratio of sodium percarbonate to -C≡N group in the wastewater is 1.45:1, and the reaction is carried out for 1 hour to obtain pretreated wastewater.

[0070] After testing, the acrylonitrile content in the pretreated wastewater was 0.2 mg / L, while the ammonia nitrogen content increased to 140 mg / L, but the conductivity reached 19,000 μs / cm, becoming high-salt wastewater, with a BOD5 / COD of 0.09, making it unable to undergo biochemical reactions.

[0071] Comparative Example 8 The wastewater quality and pretreatment process are the same as those in Example 3, except that sodium percarbonate is not added in the pretreatment step, and only different amounts of sodium hydroxide are added to adjust the pH value, and the changes in the ammonia nitrogen content and conductivity of the wastewater with the addition of sodium hydroxide are detected. The specific results are shown in Figure 2 shown.

[0072] Through Example 3 and Comparative Example 8 and Figure 2 It can be seen that as the amount of sodium hydroxide added increases, the ammonia nitrogen content generated by the conversion of nitrile groups in the wastewater of Comparative Example 4 becomes higher and higher, and the two are in direct proportion. At the same time, the electrical conductivity of the wastewater is also getting higher and higher. When the equivalent effect of removing nitrile compounds and ammonia nitrogen content as in Example 3 is achieved, the electrical conductivity of the wastewater reaches 15,000 μs / cm, becoming a high-salt wastewater, and its BOD5 / COD value is only 0.21, and the biodegradability does not reach the effect of Example 3.

[0073] It can be seen from Example 1 and Comparative Examples 1-4, Example 3 and Comparative Examples 5 that the present invention first adjusts the pH of the wastewater in a specific range in the wastewater pretreatment step, and then uses sodium percarbonate to process, and the nitrile compound content in the obtained pre-treated wastewater is almost 0, and the biodegradability of the pre-treated wastewater is significantly improved, and the BOD5 / COD ratio can reach more than 0.5, and after A / A / O pool and biofilter EBF treatment, the direct drainage of GB31571-2015 can be achieved; and sodium carbonate, hydrogen peroxide, sodium carbonate and hydrogen peroxide, sodium persulfate are used respectively in the comparative example, and the BOD5 / COD ratio of the pre-treated wastewater obtained after reaction 1h is all below 0.2, and biodegradability does not meet the requirements. In addition, it can be seen from Example 1 and Comparative Examples 4 that in the pre-treatment step, the pH of the wastewater is too high and the decomposition effect of the nitrile compounds in the wastewater is seriously reduced, thereby affecting the biodegradability of the pre-treated wastewater. It can be seen from Example 1 and Comparative Examples 6 and 7 that the amount of sodium percarbonate added in the pretreatment step has a great influence on the decomposition of nitrile compounds and the biodegradability of wastewater after pretreatment. If the amount of sodium percarbonate added is too low or too high, the pretreatment effect is not ideal. Therefore, the present invention adopts a specific pretreatment step, firstly adjusts the pH of the nitrile-containing wastewater to 9-12, and simultaneously adds 100-2000 mg / L of sodium percarbonate, controls the molar ratio of sodium percarbonate to -C≡N groups in the wastewater to (0.01-1): 1, and can completely hydrolyze nitrile compounds within 1 hour without introducing too much salt, thereby effectively improving the biodegradability of sewage; after A / A / O biochemical pool treatment and biological filter EBF deep decarbonization, the direct discharge water quality of GB31571-2015 can be achieved.

[0074] 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 process for treating wastewater containing high nitrile content, characterized in that: The steps include: (1) Pretreatment: adding alkaline substances to the wastewater with high nitrile content to adjust the pH value of the wastewater to 9-12, adding sodium percarbonate to react, and obtaining pretreated wastewater; (2) The pretreated wastewater is processed by the A / A / O process and the EBF biofilter in turn before it can meet the discharge standards.

2. The process for treating high nitrile-containing wastewater according to claim 1, wherein: In step (1), the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

3. The treatment process for high nitrile-containing wastewater according to claim 1, wherein In step (1), alkaline substances are added to the wastewater with high nitrile content to adjust the pH value of the wastewater to 10-11.

4. The process for treating high nitrile-containing wastewater according to claim 1, wherein: In step (1), the amount of sodium percarbonate used is 50-1000 mg / L.

5. The process for treating wastewater containing high nitrile content according to claim 1, wherein: In step (1), the molar ratio of sodium percarbonate to -C≡N groups in wastewater is (0.01-1):

1.

6. The process for treating wastewater containing high nitrile content according to claim 1, wherein: In step (1), the temperature for adding sodium percarbonate to react is room temperature, and the reaction time is 0.1-2.0h.

7. The process for treating wastewater containing high nitrile content according to claim 1, wherein: The BOD5 / COD value of the pretreated wastewater is higher than 0.

5.

8. The process for treating wastewater containing high nitrile content according to claim 1, wherein: The content of nitrile compounds in the pretreated wastewater is less than 0.33 mg / L.

9. The process for treating wastewater containing high nitrile content according to claim 1, wherein: In step (2), 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 20-40 hours, and the hydraulic retention time of the aerobic tank is 10-30 hours.

10. The process for treating wastewater containing high nitrile content according to claim 1, wherein: In step (2), the process conditions of the biological filter EBF are: hydraulic retention time is 2-4h.

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