Treatment method of passivation wastewater

Abstract

The invention relates to the field of pickling passivation wastewater, and particularly discloses a passivation wastewater treatment method. The treatment method of the passivation wastewater comprises the following steps: adding a modified adsorbent into the passivation wastewater, stirring, adding sodium hydroxide and calcium chloride, adjusting the pH value, precipitating and separating aluminum ions and fluorine ions; adding an oxidizing agent to remove high-concentration ammonia nitrogen in the wastewater; and finally, sequentially carrying out aerobic treatment, anoxic treatment, precipitation treatment and disinfection treatment to achieve the effect of efficiently removing total nitrogen. According to the method, aluminum ions, fluorine ions and total nitrogen in the passivation wastewater can be efficiently removed.

Description

Technical Field

[0001] The invention relates to the field of pickling passivation wastewater, in particular to a method for treating passivation wastewater. Background Art

[0002] Aluminum-containing pickling and passivation wastewater is usually wastewater generated during the manufacturing process of aluminum-containing products. In the manufacturing process of aluminum products, it is often necessary to use hydrofluoric acid and other fluorine-containing substances for pickling, and then use organic matter containing amino functional groups for surface treatment. Therefore, in addition to a large amount of aluminum ions, aluminum-containing pickling and passivation wastewater often contains a large amount of fluoride ions and high concentrations of ammonia nitrogen.

[0003] The existing sewage treatment plant processes the aluminum pickling and passivation wastewater as follows: pretreatment - primary treatment - biochemical treatment - deep treatment. Since the aluminum pickling and passivation wastewater contains a large amount of aluminum ions and fluoride ions, it is easy to inhibit the activity of microorganisms, destroy the sludge structure, and reduce the efficiency of biochemical reaction treatment. Therefore, before biochemical treatment, it is necessary to remove a large amount of aluminum ions and fluoride ions in the alumina electroplating wastewater.

[0004] At present, the conventional treatment method for removing aluminum ions and fluoride ions in sewage treatment plants is mainly to add calcium hydroxide. Aluminum ions generate aluminum hydroxide flocs under neutral and weakly alkaline conditions, and fluoride ions generate calcium fluoride precipitates with calcium ions under alkaline conditions. However, excessive addition of calcium hydroxide can easily make the pH of the wastewater too high, affecting subsequent biological treatment. Therefore, when a certain amount of calcium hydroxide is added, a certain amount of calcium chloride will be added to continue to precipitate fluoride ions. However, the above method has limited effect on removing fluoride ions and aluminum ions. At the same time, calcium ions that do not participate in the precipitation reaction can easily increase the salinity of the wastewater, reducing the efficiency of subsequent biochemical reactions. Therefore, there is still room for improvement. Summary of the invention

[0005] In order to improve the removal efficiency of aluminum ions and fluoride ions in aluminum oxide electroplating wastewater without reducing the treatment efficiency of biochemical reactions, the present application provides a method for treating passivation wastewater.

[0006] In the first aspect, the present application provides a method for treating passivation wastewater, which adopts the following technical solution: A method for treating passivation wastewater, the process steps of which include pretreatment, flocculation and sedimentation, ammonia nitrogen stripping, and denitrification: S1, pretreatment: adding a modified adsorbent to the passivation wastewater and stirring, then adding sodium hydroxide and calcium chloride, adjusting the pH to 6-7, stirring, and separating by precipitation to obtain pretreated wastewater, wherein the modified adsorbent is obtained by grinding activated carbon, calcium-based bentonite and acetic acid in a weight ratio of (4-6): (1-2): 0.5, and the weight ratio of the passivation wastewater to the modified adsorbent is 1000: 20-30; S2, flocculation precipitation: add polydimethyldiallylammonium chloride, polyaluminium chloride, chitosan and polyacrylamide into the pretreated wastewater, and the mass concentrations of polydimethyldiallylammonium chloride, polyaluminium chloride and chitosan in the pretreated wastewater are 20-25mg / L, 6-8mg / L, 5mg / L and 30-40mg / L respectively, and then stir and filter to obtain secondary treated wastewater.

[0007] S3, ammonia nitrogen stripping: add strong oxidant to the secondary treated wastewater, stir, strip and absorb in the absorption tower to obtain low ammonia nitrogen wastewater; S4, denitrification: The low ammonia nitrogen wastewater is subjected to aerobic treatment, anoxic treatment, sedimentation treatment and disinfection treatment in sequence to obtain the treated passivated wastewater.

[0008] By adopting the above technical scheme, in the pretreatment stage, the modified adsorbent can efficiently adsorb organic matter, heavy metal ions and other pollutants in the wastewater, reduce their concentration, and facilitate subsequent purification. Among them, the activated carbon has a porous structure and a high specific surface area, which can effectively adsorb organic matter, heavy metal ions and other pollutants in the wastewater; calcium-based bentonite has good adsorption and ion exchange properties, which can further enhance the removal effect of pollutants in the wastewater; acetic acid promotes the refinement of carbon and calcium-based bentonite particles and increases the surface active sites, thereby improving the adsorption performance. By adding sodium hydroxide to adjust the pH of the wastewater to 6-7, the aluminum ions in the wastewater react with hydroxide to form aluminum hydroxide flocs, and further combine with fluoride ions in the water to form a sodium hexafluoroaluminate precipitate, and then add calcium chloride and fluoride ions to form calcium fluoride to remove the remaining fluoride ions in the wastewater. This method can remove a large amount of aluminum ions and fluoride ions in the wastewater, and the additional sodium ions are also removed at the same time, which is not easy to increase the cation concentration of the passivated wastewater and affect the subsequent biochemical reactions.

[0009] However, since calcium fluoride has a certain solubility in water, and a small amount of calcium fluoride still exists in the wastewater in a suspended state, it is difficult to remove it by gravity sedimentation. Therefore, if you want to efficiently remove the residual calcium fluoride in the water, you need to combine other technical means. In this application document, polydimethyldiallyl ammonium chloride, polyaluminium chloride, and chitosan composite flocculation are also used to remove the residual calcium fluoride in the wastewater. By using the spatial sites inside chitosan and the electrostatic attraction points to adsorb the dissolved calcium fluoride in the water, the network molecular chains formed by polydimethyldiallyl ammonium chloride and polyaluminium chloride capture the suspended calcium fluoride in the wastewater. At the same time, the long-chain structure in polydimethyldiallyl ammonium chloride and polyaluminium chloride can also combine with the active sites on the surface of chitosan to form flocs connected by multiple flocs, further improving the removal efficiency of residual calcium fluoride in the wastewater. At the same time, polyacrylamide can form a network structure in water through its long-chain molecular structure, effectively capture and bridge suspended particles and colloidal particles in the wastewater, enhance the coagulation effect, and help remove tiny particles and soluble pollutants in the wastewater.

[0010] In the ammonia nitrogen stripping stage, a strong oxidant is added to the pre-treated wastewater, which converts the ammonia nitrogen in the wastewater into nitrogen and ammonia. After stripping and absorption in the absorption tower, the high concentration of ammonia nitrogen in the wastewater is removed. The remaining low concentration of ammonia nitrogen, nitrate nitrogen and nitrite nitrogen in the wastewater is converted into nitrogen in various forms through the total nitrogen integrated equipment, thereby achieving the effect of reducing the total nitrogen in the wastewater.

[0011] Preferably, the weight of the strong oxidant is 3 / 1000-5 / 1000 of the weight of the passivation wastewater.

[0012] Preferably, in step S1, the mass ratio of wastewater to sodium hydroxide and calcium hydroxide is 10000:2:(2-3).

[0013] By adopting the above technical solution, by optimizing the dosage of strong oxidants, adding a specific proportion of sodium hydroxide and calcium chloride can effectively remove aluminum ions and fluoride ions in the water. At the same time, it is not easy to increase the content of sodium ions and calcium ions in the wastewater, resulting in an increase in the salinity of the wastewater and a reduction in the efficiency of subsequent biochemical reactions.

[0014] Preferably, the molecular weight of the polyacrylamide is 500-2000.

[0015] By adopting the above technical solution, the molecular weight of polyacrylamide is optimized, the dispersion of polyacrylamide in waste liquid is improved, its coagulation effect is increased, and the ability to remove tiny particles and soluble pollutants in wastewater is improved.

[0016] Preferably, in S2, the strong oxidant is composed of sodium hypochlorite and potassium ferrate in a mass ratio of 3:(4-5).

[0017] By adopting the above technical solution, sodium hypochlorite and potassium ferrate in a specific ratio are used as strong oxidants to oxidize ammonia nitrogen in the passivation wastewater into nitrogen and ammonia, which is conducive to further improving the removal efficiency of ammonia nitrogen. Before the wastewater enters the ammonia nitrogen, the ammonia nitrogen content in the wastewater is effectively reduced, and it is not easy to be insufficient to meet the nutrient elements required for subsequent biochemical reactions due to the low COD content and small carbon-nitrogen ratio in the wastewater.

[0018] Preferably, the average particle size of the activated carbon is 30-50 microns, and the average particle size of the calcium-based bentonite is 100-200 microns.

[0019] By adopting the above technical solution, the average particle size of activated carbon and calcium-based bentonite is optimized, the surface area of ​​both is increased, and the adsorption of impurities in the wastewater is improved, which is beneficial to the subsequent removal of aluminum ions, fluoride ions and various ammonia nitrogen substances.

[0020] Preferably, the low-ammonia nitrogen wastewater needs to be exposed to sunlight before step S4, using a xenon arc lamp for irradiation with a wavelength of 350-400nm and an irradiance of 40-55W / m 2 nm.

[0021] By adopting the above technical solution, the organic matter in the wastewater undergoes photochemical reaction through exposure to the sun, generating free radicals and active oxygen species. These substances have strong oxidizing ability, can decompose organic pollutants and reduce the COD of wastewater. At the same time, the temperature of the wastewater rises slightly, increasing the metabolic activity of microorganisms and the activity of enzymes, thereby improving the biological treatment efficiency of the subsequent denitrification and denitrification step.

[0022] Preferably, the dissolved oxygen concentration of the aerobic treatment is 5-6 mg / L; the dissolved oxygen concentration of the anoxic treatment is 0.5-1 mg / L.

[0023] By adopting the above technical scheme, the dissolved oxygen concentrations in the aerobic zone and the anaerobic zone are adjusted respectively to provide a suitable growth environment for the microorganisms in each zone, so that the aerobic zone can fully convert ammonia nitrogen into nitrate nitrogen or nitrite nitrogen, and the nitrate nitrogen or nitrite nitrogen can be reduced to nitrogen gas in the anaerobic zone, thereby further improving the removal efficiency of total nitrogen.

[0024] Preferably, the particle size of the aerobic granular sludge in the aerobic treatment is >2.0 mm.

[0025] By adopting the above technical solution and using aerobic granular sludge with a particle size greater than 2.0 mm, there is a wider anoxic and anaerobic area in the center of the aerobic granular sludge, which can improve the efficiency of denitrification and enhance the conversion efficiency of nitrate nitrogen and nitrite nitrogen.

[0026] Preferably, the hydraulic retention time of aerobic treatment is 4-8 hours; the hydraulic retention time of anaerobic treatment is 8-16 hours.

[0027] By adopting the above technical solution and using different hydraulic retention times in the aerobic zone and the anaerobic zone respectively, it can be ensured that the microorganisms in the biochemical reaction process can further improve the removal efficiency of total nitrogen through nitrification and denitrification reactions while maintaining normal life activities.

[0028] In summary, this application has the following beneficial effects: 1. Through the stirring of specific adsorbents, sodium hydroxide is added to adjust the pH of the wastewater to 6-7. The aluminum ions in the wastewater react with hydroxide to form aluminum hydroxide flocs, which are further combined with fluoride ions in the water to form sodium hexafluoroaluminate precipitation. The remaining fluoride ions in the wastewater are then removed by sodium chloride. This method can remove a large amount of aluminum ions and fluoride ions in the wastewater, and the additional sodium ions are also removed at the same time. It is not easy to further increase the cation concentration of the passivated wastewater and affect the subsequent biochemical reactions. The residual calcium fluoride in the wastewater is removed by composite flocculation of polydimethyldiallyl ammonium chloride, polyaluminium chloride, chitosan and polyacrylamide. The calcium fluoride dissolved in the water is adsorbed by utilizing the spatial sites inside chitosan and the electrostatic attraction points. The network molecular chains formed by polydimethyldiallyl ammonium chloride and polyaluminium chloride capture the suspended calcium fluoride in the wastewater. At the same time, the long chain structure in polydimethyldiallyl ammonium chloride and polyaluminium chloride can also combine with the active sites on the surface of chitosan to form flocs connected by multiple flocs, further improving the removal efficiency of residual calcium fluoride in the wastewater.

[0029] 2. By using sodium hypochlorite and potassium ferrate in a specific proportion as strong oxidants, the ammonia nitrogen in the passivation wastewater can be oxidized into nitrogen and ammonia, effectively reducing the ammonia nitrogen content in the wastewater. It is not easy to completely remove the ammonia nitrogen in the wastewater through subsequent biochemical reactions due to the low COD content and small carbon-nitrogen ratio in the wastewater, which is conducive to further improving the removal efficiency of ammonia nitrogen. DETAILED DESCRIPTION

[0030] The present application is further described in detail below with reference to the embodiments.

[0031] The raw materials of the following examples and comparative examples are all commercially available, as follows: Polydimethyldiallylammonium chloride was purchased from Yunfu Haixing Environmental Protection Technology Co., Ltd., model number HX-2W20.

[0032] Polyaluminium chloride was purchased from Henan Haiyun Environmental Protection Technology Co., Ltd. and was of superior grade.

[0033] Chitosan was purchased from Jinan Huijinchuan Trading Co., Ltd., with a CAS number of 9012-76-4.

[0034] Preparation Example 1 The preparation of artificial passivation wastewater is as follows: Take 4.46g of aluminum chloride hexahydrate and dissolve it in pure water, then add 1.95g of ammonium fluoride and stir evenly, and make the volume to 1000mL with pure water, and then use 0.1mol / L sodium hydroxide solution and 0.1mol / L hydrochloric acid solution to adjust the pH of the solution to 6 to obtain artificial passivation wastewater, which is stored for later use.

[0035] Example 1 A method for treating passivation wastewater, the process steps of which include pretreatment, flocculation and sedimentation, ammonia nitrogen stripping, and denitrification: S1, pretreatment: add 20g of modified adsorbent to 1L of passivation wastewater and stir, the modified adsorbent is composed of activated carbon, calcium-based bentonite and acetic acid in a weight ratio of 4:1:0.5, the average particle size of activated carbon is 30 microns, the average particle size of calcium-based bentonite is 100 microns, then add 0.2g of sodium hydroxide and 0.2g of calcium chloride, adjust the pH to 6, stir at a speed of 150r / min for 30 minutes, settle for 20 minutes, filter, and obtain pretreated wastewater; S2, flocculation precipitation: add 20 mg of polydimethyldiallylammonium chloride, 6 mg of polyaluminium chloride, 5 mg of chitosan and 30 mg of polyacrylamide to the pretreated wastewater, the molecular weight of polyacrylamide is 500, stir at a speed of 150 r / min for 20 minutes, precipitate for 10 minutes, filter, and obtain secondary treated wastewater; S3, ammonia nitrogen stripping: add 0.3g sodium hypochlorite and 0.4g potassium ferrate to the secondary treated wastewater, stir at a speed of 150r / min for 30 minutes, and then strip and absorb in an absorption tower to obtain low ammonia nitrogen wastewater; S4, denitrification: The low ammonia nitrogen wastewater is subjected to aerobic treatment, anoxic treatment, sedimentation treatment and disinfection treatment in sequence. The hydraulic retention time of aerobic treatment is adjusted to 4 hours, the dissolved oxygen concentration is 6 mg / L, and aerobic granular sludge with a particle size > 2.0 mm is added; the hydraulic retention time of anaerobic treatment is 16 hours, and the dissolved oxygen concentration in the anoxic zone is 0.5 mg / L, so as to obtain the treated passivated wastewater.

[0036] Example 2 A method for treating passivation wastewater, the process steps of which include pretreatment, flocculation and sedimentation, ammonia nitrogen stripping, and denitrification: S1, pretreatment: add 25g of modified adsorbent to 1L of passivation wastewater and stir, the modified adsorbent is composed of activated carbon, calcium-based bentonite and acetic acid in a weight ratio of 5:1.5:0.5, the average particle size of the activated carbon is 40 microns, and the average particle size of the calcium-based bentonite is 150 microns, then add 0.2g of sodium hydroxide and 0.3g of calcium chloride, adjust the pH to 7, stir at a speed of 150r / min for 30 minutes, precipitate for 20 minutes, filter, and obtain pretreated wastewater; S2, flocculation precipitation: add 25 mg of polydimethyldiallylammonium chloride, 8 mg of polyaluminium chloride, 5 mg of chitosan and 35 mg of polyacrylamide to the pretreated wastewater, the molecular weight of polyacrylamide is 1000, stir at a speed of 150 r / min for 20 minutes, precipitate for 10 minutes, filter, and obtain secondary treated wastewater; S3, ammonia nitrogen stripping: add 0.3g sodium hypochlorite and 0.5g potassium ferrate to the secondary treated wastewater, stir at a speed of 150r / min for 30 minutes, then strip and absorb in an absorption tower to obtain low ammonia nitrogen wastewater; S4, denitrification: The low ammonia nitrogen wastewater is subjected to aerobic treatment, anoxic treatment, sedimentation treatment and disinfection treatment in sequence. The hydraulic retention time of aerobic treatment is adjusted to 8 hours, the dissolved oxygen concentration is 6 mg / L, and aerobic granular sludge with a particle size of >2.0 mm is added; the hydraulic retention time of anaerobic treatment is 16 hours, and the dissolved oxygen concentration in the anoxic zone is 1 mg / L, so as to obtain the treated passivated wastewater.

[0037] Example 3 A method for treating passivation wastewater, the process steps of which include pretreatment, flocculation and sedimentation, ammonia nitrogen stripping, and denitrification: S1, pretreatment: add 30g of modified adsorbent to 1L of passivation wastewater and stir, the modified adsorbent is composed of activated carbon, calcium-based bentonite and acetic acid in a weight ratio of 6:2:0.5, the average particle size of the activated carbon is 50 microns, and the average particle size of the calcium-based bentonite is 200 microns, then add 0.2g of sodium hydroxide and 0.25g of calcium chloride, adjust the pH to 6.5, stir at a speed of 150r / min for 30 minutes, precipitate for 20 minutes, filter, and obtain pretreated wastewater; S2, flocculation precipitation: add 22.5 mg of polydimethyldiallylammonium chloride, 7 mg of polyaluminium chloride, 5 mg of chitosan and 40 mg of polyacrylamide to the pretreated wastewater, the molecular weight of polyacrylamide is 2000, stir at a speed of 150 r / min for 20 minutes, precipitate for 10 minutes, filter, and obtain secondary treated wastewater; S3, ammonia nitrogen stripping: add 0.3g sodium hypochlorite and 0.45g potassium ferrate to the secondary treated wastewater, stir at a speed of 150r / min for 30 minutes, and then strip and absorb in an absorption tower to obtain low ammonia nitrogen wastewater; S4, denitrification: The low ammonia nitrogen wastewater is subjected to aerobic treatment, anoxic treatment, sedimentation treatment and disinfection treatment in sequence. The hydraulic retention time of aerobic treatment is adjusted to 6 hours, the dissolved oxygen concentration is 5.5 mg / L, and aerobic granular sludge with a particle size of >2.0 mm is added; the hydraulic retention time of anaerobic treatment is 12 hours, and the dissolved oxygen concentration in the anoxic zone is 0.75 mg / L, so as to obtain the treated passivated wastewater.

[0038] Example 4 That is, the difference from Example 3 is that sodium hypochlorite is replaced by an equal amount of chlorine dioxide.

[0039] Example 5 That is, the difference from Example 3 is that potassium permanganate is used instead of potassium ferrate in an equal amount.

[0040] Example 6 The difference from Example 3 is that the low-ammonia nitrogen wastewater needs to be exposed to sunlight before the S4 step, using a xenon arc lamp for irradiation with a wavelength of 350nm and an irradiance of 40W / m 2 nm.

[0041] Example 7 The difference from Example 3 is that the low-ammonia nitrogen wastewater needs to be exposed to sunlight before step S4, using a xenon arc lamp for irradiation with a wavelength of 400 nm and an irradiance of 55 W / m 2 nm.

[0042] Example 8 The difference from Example 3 is that the molecular weight of the polyacrylamide is 2500.

[0043] Example 7 The difference from Example 3 is that the hydraulic retention time of the aerobic treatment is 3 hours, and the hydraulic retention time of the anaerobic zone is 6 hours.

[0044] Example 8 The difference from Example 3 is that the hydraulic retention time of the aerobic treatment is 9 hours, and the hydraulic retention time of the anaerobic zone is 18 hours.

[0045] Example 9 The difference from Example 3 is that the dissolved oxygen concentration in the aerobic treatment is 4 mg / L; and the dissolved oxygen concentration in the anoxic zone is 0.3 mg / L.

[0046] Example 10 The difference from Example 3 is that the dissolved oxygen concentration in the aerobic treatment is 7 mg / L; and the dissolved oxygen concentration in the anoxic zone is 1.2 mg / L.

[0047] Embodiment 11 The difference from Example 3 is that the particle size of the aerobic granular sludge in the aerobic treatment is <2.0 mm.

[0048] Comparative Example 1 The difference from Example 3 is that no modified adsorbent is added to S1.

[0049] Comparative Example 2 The difference from Example 3 is that the modified adsorbent in S1 is composed of activated carbon and acetic acid in a weight ratio of 5:0.5.

[0050] Comparative Example 3 The difference from Example 3 is that the modified adsorbent is composed of calcium-based bentonite and acetic acid in a weight ratio of 5:0.5.

[0051] Comparative Example 4 The difference from Example 3 is that acetic acid is not added to S1.

[0052] Comparative Example 5 The difference from Example 3 is that in S2, no polyacrylamide is added.

[0053] Comparative Example 6 The difference from Example 3 is that in S2, an equal amount of 2-acrylamide-2-methylpropanesulfonic acid is used to replace polyaluminium chloride.

[0054] Comparative Example 7 The difference from Example 3 is that in S2, an equal amount of sodium alginate is used instead of chitosan.

[0055] Comparative Example 8 The difference from Example 3 is that no polydimethyldiallylammonium chloride is added to S2.

[0056] Comparative Example 9 The difference from Example 3 is that the low ammonia nitrogen wastewater is subjected to anoxic treatment, aerobic treatment, sedimentation treatment and disinfection treatment in sequence.

[0057] Experiment 1 Aluminum ion determination The passivation wastewater treated in the above examples and comparative examples was taken, and the aluminum ion content was determined by the rose red ammonium trihydroxylate spectrophotometric method in accordance with GB / T 9734-2008 "General Method for Determination of Aluminum in Chemical Reagents", and the aluminum removal rate (%) was calculated.

[0058] Experiment 2 Determination of fluoride, nitrite and nitrate Take the passivation wastewater treated in the above embodiments and comparative examples, and determine the contents of fluoride ion, nitrate nitrogen and nitrite nitrogen in the treated wastewater according to GB / T 14642-2009 "Ion chromatography for determination of fluoride, chlorine, phosphate, nitrite, nitrate and sulfate in industrial circulating cooling water and boiler water", and calculate the removal efficiency (%) respectively.

[0059] Experiment 3: Ammonia nitrogen determination Take the passivation wastewater treated in the above embodiments and comparative examples, and determine the ammonia nitrogen in accordance with DZ / T 0064.57-2021 "Groundwater Quality Analysis Method Part 57: Determination of Ammonia Nitrogen by Nessler's Reagent Spectrophotometry", and calculate the ammonia nitrogen removal rate (%).

[0060] The above experimental test data are detailed in Table 1.

[0061] Table 1 Experimental data of Examples 1-14 and Comparative Examples 1-9 According to the data comparison of Example 3 and Comparative Example 1 in Table 1, Example 3 can effectively remove aluminum ions and fluoride ions in water by adopting the above-mentioned treatment method, and has a good removal effect on various forms of nitrogen in wastewater; Comparative Example 1 replaces sodium hydroxide with an equal amount of calcium hydroxide, and the removal effect of aluminum ions and fluoride ions is reduced, and the removal effects of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen all decrease to varying degrees. In Comparative Examples 2-3, too high or too low hydroxide ions are likely to hinder the formation of aluminum hydroxide, resulting in a decrease in flocculation and sedimentation efficiency. It shows that by optimizing the composition and dosage of the adsorbent, the aluminum ions in the wastewater react with hydroxide to form floccules of aluminum hydroxide, and further combine with fluoride ions in the water to form a precipitate of sodium hexafluoroaluminate, and then remove the remaining fluoride ions in the wastewater by sodium chloride. This method can remove a large amount of aluminum ions and fluoride ions in the wastewater. The removal efficiency of fluoride ions in the wastewater in Comparative Examples 4-7 is reduced, indicating that methyldiallylammonium chloride, polyaluminum chloride, and chitosan composite flocculation have a good removal effect on calcium fluoride. The removal efficiency of fluoride ions and various forms of nitrogen in wastewater in Comparative Example 9 was reduced, indicating that aerobic treatment and anoxic treatment had a positive effect on the removal of fluoride ions and various forms of nitrogen in wastewater.

[0062] According to the data comparison of Example 3 and Examples 4-5 in Table 1, it can be obtained that by using sodium hypochlorite and potassium ferrate in a specific ratio as strong oxidants, the ammonia nitrogen in the passivation wastewater can be oxidized into nitrogen and ammonia, thereby effectively reducing the ammonia nitrogen content in the wastewater.

[0063] According to the data comparison between Example 3 and Example 6-7 in 1, it can be obtained that the removal efficiency of fluoride ions and various forms of nitrogen in wastewater in Example 6-7 is improved, and fluoride ions in water can be effectively removed, and at the same time, various forms of nitrogen in wastewater have good removal effects.

[0064] According to the data comparison between Example 3 and Example 9 in 1, it can be obtained that the fluoride ion removal effect of Example 9 is reduced, and the removal effects of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen all decrease to varying degrees, indicating that optimizing the molecular weight of polyacrylamide is beneficial to the removal of fluoride ions and various forms of nitrogen in water.

[0065] According to the data comparison between Example 3 and Example 9 in Table 1, a thorough denitrification reaction is carried out in the subsequent anoxic stage to reduce the content of nitrate nitrogen and nitrite nitrogen in the water, thereby achieving the effect of efficient removal of total nitrogen.

[0066] According to the data comparison between Example 3 and Examples 10-11 in Table 1, it can be obtained that a lower hydraulic retention time cannot allow the nitrogen in the wastewater to fully participate in the reaction, resulting in a higher nitrogen content in the treated wastewater; a higher hydraulic retention time cannot provide sufficient nutrition to the microorganisms in the water, resulting in a decrease in the nitrogen treatment efficiency. The use of an appropriate hydraulic retention time can ensure that various forms of nitrogen in the water can smoothly undergo nitrification and denitrification reactions, thereby further improving the removal efficiency of total nitrogen.

[0067] According to the data comparison of Example 3 and Examples 12-13 in Table 1, it can be seen that lower dissolved oxygen causes part of the ammonia nitrogen to be unable to be completely oxidized into nitrate nitrogen or nitrite nitrogen, resulting in the accumulation of ammonia nitrogen; higher dissolved oxygen is not conducive to denitrification, resulting in higher nitrate nitrogen and nitrite nitrogen contents in the treated wastewater. The dissolved oxygen concentrations in the aerobic zone and the anaerobic zone are adjusted separately to provide a suitable growth environment for the microorganisms in each zone, which can improve the effects of nitrification and denitrification.

[0068] According to the data comparison of Example 3 and Example 14 in Table 1, it can be obtained that the aerobic granular sludge with a particle size greater than 2.0 mm is cultivated, and there are anoxic and anaerobic areas in the center of the aerobic granular sludge, which can improve the efficiency of denitrification and enhance the conversion rate of nitrate nitrogen and nitrite nitrogen.

[0069] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for treating passivation wastewater, characterized in that: The process steps include pretreatment, flocculation and sedimentation, ammonia nitrogen stripping, and denitrification: S1, pretreatment: adding a modified adsorbent to the passivation wastewater and stirring, then adding sodium hydroxide and calcium chloride, adjusting the pH to 6-7, stirring, and separating by precipitation to obtain pretreated wastewater, wherein the modified adsorbent is obtained by grinding activated carbon, calcium-based bentonite and acetic acid in a weight ratio of (4-6): (1-2): 0.5, and the amount of the modified adsorbent is 20-30 g / L; S2, flocculation precipitation: adding polydimethyldiallylammonium chloride, polyaluminium chloride, chitosan and polyacrylamide to the pretreated wastewater, wherein the mass concentrations of polydimethyldiallylammonium chloride, polyaluminium chloride and chitosan in the pretreated wastewater are 20-25 mg / L, 6-8 mg / L, 5 mg / L and 30-40 mg / L, respectively, and then stirring and filtering to obtain secondary treated wastewater; S3, ammonia nitrogen stripping: add strong oxidant to the secondary treated wastewater, stir, strip and absorb in the absorption tower to obtain low ammonia nitrogen wastewater; S4, denitrification: The low ammonia nitrogen wastewater is subjected to aerobic treatment, anoxic treatment, sedimentation treatment and disinfection treatment in sequence to obtain the treated passivated wastewater.

2. A method for treating passivation wastewater according to claim 1, characterized in that: In the step S1, the mass ratio of wastewater to sodium hydroxide and calcium hydroxide is 10000:2:(2-3).

3. A method for treating passivation wastewater according to claim 1, characterized in that: The weight of the strong oxidant is 3 / 1000-5 / 1000 of the weight of the passivation wastewater.

4. A method for treating passivation wastewater according to claim 3, characterized in that: In the step S2, the strong oxidant is obtained by mixing sodium hypochlorite and potassium ferrate in a weight ratio of 3:(4-5).

5. A method for treating passivation wastewater according to claim 1, characterized in that: The molecular weight of the polyacrylamide is 500-2000.

6. A method for treating passivation wastewater according to claim 5, characterized in that: The average particle size of the activated carbon is 30-50 microns, and the average particle size of the calcium-based bentonite is 100-200 microns.

7. A method for treating passivation wastewater according to claim 5, characterized in that: The low-ammonia nitrogen wastewater needs to be exposed to sunlight before the S4 step, using a xenon arc lamp for irradiation, with a wavelength of 350-400nm and an irradiance of 40-55W / m²nm.

8. A method for treating passivation wastewater according to claim 5, characterized in that: The dissolved oxygen concentration in the aerobic treatment is 5-6 mg / L; the dissolved oxygen concentration in the anoxic treatment is 0.5-1 mg / L.

9. A method for treating passivation wastewater according to claim 5, characterized in that: The particle size of the aerobic granular sludge in the aerobic treatment is >2.0 mm.

10. A method for treating passivation wastewater according to claim 5, characterized in that: The hydraulic retention time of the aerobic treatment is 4-8 hours; the hydraulic retention time of the anaerobic treatment is 8-16 hours.

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