Method and system for treating stainless steel cold rolling mixed acid wastewater

Abstract

The application provides a stainless steel cold-rolled mixed-acid wastewater treatment method and system, which comprises the following steps: performing lime neutralization treatment, liquid alkali neutralization treatment and flocculation and sedimentation treatment on the stainless steel cold-rolled mixed-acid wastewater to obtain first effluent; judging whether sodium hypochlorite solution needs to be added for ammonia and nitrogen removal treatment according to the ammonia and nitrogen concentration in the first effluent, and obtaining second effluent; performing flocculation and sedimentation treatment on the second effluent to obtain third effluent; judging whether hydrochloric acid needs to be added for pH adjustment treatment according to the total nitrogen concentration in the third effluent, and obtaining fourth effluent; and performing biological denitrification treatment and sludge-water separation treatment on the fourth effluent to obtain biochemical sludge and biochemical sedimentation effluent. The application uses liquid alkali to replace part of the lime to neutralize the stainless steel cold-rolled mixed-acid wastewater, can reduce the hardness of the wastewater, reduce the output of solid waste and save the cost of softening and calcium removal agents; and uses sodium hypochlorite to remove ammonia and nitrogen, so that the influence of wastewater with high-concentration ammonia and nitrogen on the effluent stability of the subsequent biochemical system is avoided.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method and system for treating mixed acid wastewater from stainless steel cold rolling. Background Technology

[0002] The stainless steel cold rolling pickling unit will generate mixed acid (nitric acid and hydrofluoric acid) wastewater during the production process. This mixed acid wastewater contains pollutants such as total nitrogen, ammonia nitrogen, fluoride ions, iron, nickel, and chromium ions. It must be effectively treated before it can be discharged or recycled.

[0003] Currently, the common treatment method for this mixed acidic wastewater is a combination of lime slurry physicochemical defluorination and biological denitrification. For details, please refer to [link to relevant documentation]. Figure 1 , Figure 1 A schematic diagram of the stainless steel cold rolling mixed acid wastewater treatment process provided by existing technology. (Example) Figure 1 As shown, the existing treatment process for stainless steel cold rolling mixed acid wastewater is as follows: First, lime slurry is added to the stainless steel cold rolling mixed acid wastewater for lime neutralization, causing fluoride ions in the wastewater to combine with calcium ions to form calcium fluoride precipitate. Simultaneously, heavy metal ions form metal hydroxide precipitates under alkaline conditions, thereby removing most of the fluoride and heavy metal ions. To ensure that the effluent fluoride concentration meets the requirements of the "Water Pollutant Discharge Standard for Iron and Steel Industry" (GB13456-2012), coagulants (such as polyaluminum chloride) and flocculants are added to the lime-neutralized wastewater for coagulation and sedimentation treatment, achieving fine fluoride removal. Next, the clarified liquid after coagulation and sedimentation treatment undergoes biological denitrification treatment (including anoxic denitrification and aerobic nitrification) by adding an external carbon source (such as methanol). Finally, the effluent after biological denitrification treatment undergoes sedimentation treatment to obtain precipitated effluent, and the effluent quality meets all the discharge standards required by the "Water Pollutant Discharge Standard for Iron and Steel Industry" (GB13456-2012).

[0004] However, the conventional treatment process for the above-mentioned stainless steel cold rolling mixed acid wastewater has the following problems: To ensure that fluoride ions and heavy metal ions fully form precipitates, excessive lime slurry is usually added to the wastewater, resulting in a huge amount of solid waste. The lime neutralization and precipitation effluent has high hardness, which in turn leads to high hardness in the subsequent biological treatment system influent. High-hardness wastewater entering the biological treatment system leads to a decrease in activated sludge concentration. Especially during biological denitrification, the denitrification reaction generates a large amount of alkalinity, which reacts with the high concentration of calcium ions in the influent to form a large amount of insoluble precipitates. This increases the inorganic content in the denitrification sludge and reduces microbial activity, further decreasing the denitrification efficiency. In addition, high-hardness wastewater easily causes scaling on pumps, pipes, and tank walls during production, increasing equipment maintenance costs.

[0005] To address the issue of high calcium ion concentrations at the upstream stage affecting downstream biological denitrification, current improvements primarily involve adding a softening and calcium removal process before the biological denitrification process. This involves adding sodium carbonate or sodium sulfate to the lime-neutralized effluent, causing calcium ions to precipitate as calcium carbonate or calcium sulfate, thereby reducing wastewater hardness. While this method effectively addresses the impact of high calcium ion concentrations on biological denitrification, it has several drawbacks in practical application: First, the large amount of chemical agents used for softening and calcium removal significantly increases the cost of wastewater treatment chemicals. Second, this method cannot address the issue of large fluctuations in ammonia nitrogen concentration in the upstream influent, leading to unstable effluent from the biological system. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for treating mixed acid wastewater from stainless steel cold rolling, in order to solve one or more of the problems existing in the prior art, such as high hardness of the effluent from lime neutralization and precipitation, high cost of adding softening and calcium removal agents, and large fluctuations in the ammonia nitrogen concentration of the upstream water, which leads to unstable effluent from the biological system.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for treating mixed acid wastewater from stainless steel cold rolling, comprising:

[0008] The stainless steel cold rolling mixed acid wastewater was neutralized with lime to obtain a first mixture;

[0009] The first mixture was neutralized with liquid alkali to obtain a second mixture;

[0010] The second mixture is subjected to flocculation and sedimentation treatment to obtain the first effluent;

[0011] Based on the ammonia nitrogen concentration in the first effluent, determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal treatment, and obtain the second effluent;

[0012] The second effluent is subjected to coagulation and sedimentation treatment to obtain the third effluent;

[0013] Based on the total nitrogen concentration in the third effluent, determine whether hydrochloric acid needs to be added for pH adjustment, and obtain the fourth effluent.

[0014] The fourth effluent was subjected to biological denitrification treatment to obtain a mud-water mixture;

[0015] The mud-water mixture is subjected to mud-water separation treatment to obtain biochemical sludge and biochemical sedimentation effluent.

[0016] Optionally, the step of neutralizing the stainless steel cold-rolling mixed acid wastewater with lime to obtain a first mixture includes: adding lime slurry with a mass concentration of 5% to 16% to the stainless steel cold-rolling mixed acid wastewater, causing the stainless steel cold-rolling mixed acid wastewater to undergo a lime neutralization reaction with the lime slurry, and controlling the pH value during the lime neutralization reaction to be between 1 and 6, with a reaction time of 0.5 hours to 1 hour, to obtain the first mixture; the method further includes: adjusting the amount of lime slurry added based on the fluoride ion concentration in the second mixture to control the fluoride ion concentration in the second mixture to be within 1%. The concentration of fluoride ions in the second mixture is 5 mg / L to 25 mg / L; wherein the feedback adjustment includes: when the concentration of fluoride ions in the second mixture is between 15 mg / L and 25 mg / L, keeping the amount of lime slurry added constant; when the concentration of fluoride ions in the second mixture is less than 15 mg / L, reducing the amount of lime slurry added until the concentration of fluoride ions in the second mixture is not less than 15 mg / L; when the concentration of fluoride ions in the second mixture is greater than 25 mg / L, increasing the amount of lime slurry added until the concentration of fluoride ions in the second mixture is not greater than 25 mg / L.

[0017] Optionally, the step of neutralizing the first mixture with liquid alkali to obtain the second mixture includes: adding liquid alkali to the first mixture and adjusting the pH of the first mixture to 8.8-9.5, so that the first mixture and the liquid alkali undergo a neutralization reaction to obtain the second mixture.

[0018] Optionally, determining whether to add sodium hypochlorite solution for ammonia nitrogen removal based on the ammonia nitrogen concentration in the first effluent and obtaining the second effluent includes: when the ammonia nitrogen concentration in the first effluent is greater than a preset threshold for ammonia nitrogen concentration, adding sodium hypochlorite solution to the first effluent and ensuring that the ammonia nitrogen concentration in the first effluent is not greater than the preset threshold for ammonia nitrogen concentration, thereby obtaining the second effluent; when the ammonia nitrogen concentration in the first effluent is not greater than the preset threshold for ammonia nitrogen concentration, not adding the sodium hypochlorite solution, and using the first effluent as the second effluent.

[0019] Optionally, the preset threshold value of ammonia nitrogen concentration ranges from 25 mg / L to 30 mg / L.

[0020] Optionally, the coagulation and sedimentation treatment of the second effluent to obtain the third effluent includes: adding flocculant and coagulant to the second effluent to carry out a coagulation reaction to obtain a coagulated mixture; performing solid-liquid separation on the coagulated mixture, and using the clarified liquid as the third effluent; the method further includes: real-time monitoring of the fluoride ion concentration in the third effluent, and adjusting the dosage of the coagulant based on the monitoring results to maintain the fluoride ion concentration in the third effluent within the target range; wherein, adjusting the dosage of the coagulant based on the monitoring results includes When the fluoride ion concentration in the third effluent is within the target range, the dosage of the coagulant is kept constant; when the fluoride ion concentration in the third effluent is less than the lower limit of the target range, the dosage of the coagulant is reduced until the fluoride ion concentration in the third effluent is within the target range; when the fluoride ion concentration in the third effluent is greater than the upper limit of the target range, the dosage of the coagulant is increased until the fluoride ion concentration in the third effluent is within the target range.

[0021] Optionally, the target range for the fluoride ion concentration is 5 mg / L to 10 mg / L.

[0022] Optionally, determining whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration in the third effluent to obtain the fourth effluent includes: when the total nitrogen concentration in the third effluent is less than a first threshold, not adding hydrochloric acid to the third effluent and using the third effluent as the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the first threshold and less than a second threshold, adding hydrochloric acid to the third effluent and adjusting the pH value of the third effluent to a first preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the second threshold and less than a third threshold, adding hydrochloric acid to the third effluent and adjusting the pH value of the third effluent to a second preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the third threshold and less than a fourth threshold... Hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to a third preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the fourth threshold and less than the fifth threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to a fourth preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the fifth threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to a fifth preset pH range to obtain the fourth effluent; wherein, the first threshold < the second threshold < the third threshold < the fourth threshold < the fifth threshold; the first preset pH range > the second preset pH range > the third preset pH range > the fourth preset pH range > the fifth preset pH range.

[0023] Optionally, the first threshold is 400 mg / L, the second threshold is 600 mg / L, the third threshold is 800 mg / L, the fourth threshold is 1000 mg / L, and the fifth threshold is 1200 mg / L; the first preset pH range is greater than 6.5 and not greater than 7.0, the second preset pH range is greater than 6.0 and not greater than 6.5, the third preset pH range is greater than 5.5 and not greater than 6.0, the fourth preset pH range is greater than 5.0 and not greater than 5.5, and the fifth preset pH range is not less than 4.5 and not greater than 5.0.

[0024] To achieve the above objectives, the present invention also provides a stainless steel cold rolling mixed acid wastewater treatment system, comprising, in sequence, a lime neutralization unit, a liquid alkali neutralization unit, a flocculation sedimentation unit, an ammonia nitrogen removal unit, a coagulation sedimentation unit, a pH adjustment unit, a biological denitrification unit, and a sludge-water separation unit; the lime neutralization unit is configured to: neutralize the stainless steel cold rolling mixed acid wastewater with lime to obtain a first mixture; the liquid alkali neutralization unit is configured to: neutralize the first mixture with liquid alkali to obtain a second mixture; the flocculation sedimentation unit is configured to: perform flocculation sedimentation on the second mixture to obtain a first effluent; the ammonia nitrogen removal unit is configured to: obtain the first... The ammonia nitrogen concentration in the effluent is determined, and based on the ammonia nitrogen concentration, it is determined whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal treatment to obtain a second effluent; the coagulation and sedimentation unit is configured to perform coagulation and sedimentation treatment on the second effluent to obtain a third effluent; the pH adjustment unit is configured to obtain the total nitrogen concentration in the third effluent, and based on the total nitrogen concentration, it is determined whether hydrochloric acid needs to be added for pH adjustment treatment to obtain a fourth effluent; the biological denitrification unit is configured to perform biological denitrification treatment on the fourth effluent to obtain a mud-water mixture; the mud-water separation unit is configured to perform mud-water separation treatment on the mud-water mixture to obtain biochemical sludge and biochemical sedimentation effluent.

[0025] Compared with the prior art, the stainless steel cold rolling mixed acid wastewater treatment method and system provided by the present invention have the following beneficial effects:

[0026] The present invention provides a method for treating stainless steel cold rolling mixed acid wastewater, comprising: neutralizing the stainless steel cold rolling mixed acid wastewater with lime to obtain a first mixture; neutralizing the first mixture with liquid alkali to obtain a second mixture; subjecting the second mixture to flocculation and sedimentation to obtain a first effluent; determining whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal based on the ammonia nitrogen concentration in the first effluent, and obtaining a second effluent; subjecting the second effluent to coagulation and sedimentation to obtain a third effluent; determining whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration in the third effluent, and obtaining a fourth effluent; subjecting the fourth effluent to biological denitrification to obtain a sludge-water mixture; and subjecting the sludge-water mixture to sludge-water separation to obtain biochemical sludge and biochemical sedimentation effluent. Therefore, the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention, compared with the existing technology that only adds lime slurry to neutralize the stainless steel cold rolling mixed acid wastewater, uses both lime neutralization and liquid alkali neutralization treatments. By using liquid alkali to replace part of the lime neutralization, the method avoids the introduction of high concentrations of calcium ions, which not only reduces wastewater hardness and solid waste production, but also saves on softening and calcium removal agent costs and reduces equipment maintenance costs. Furthermore, after obtaining the third effluent through flocculation and sedimentation, the ammonia nitrogen concentration in the first effluent is used to determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal. This ensures that the ammonia nitrogen concentration in the wastewater is stably maintained within a suitable range, thus preventing high-concentration ammonia nitrogen wastewater from affecting the effluent stability of the subsequent biological treatment system. Simultaneously, it ensures that the residual chlorine concentration in the water is maintained at a low level, effectively preventing residual chlorine from entering the subsequent biological treatment system and killing activated sludge, thereby enhancing the subsequent biological treatment system's resistance to shock loads. Furthermore, after obtaining the third effluent through coagulation and sedimentation, the total nitrogen concentration in the third effluent is used to determine whether hydrochloric acid needs to be added for pH adjustment. This ensures that the pH of the wastewater entering the subsequent biological treatment system is maintained within the suitable range for microorganisms, avoiding problems such as low denitrification efficiency and inhibited sludge activity caused by excessively high pH. This ensures that the biological treatment system can still operate stably and meet discharge standards even under high total nitrogen shock loads. The stainless steel cold rolling mixed acid wastewater treatment method provided by this invention can effectively solve the problem of unstable effluent from the biological treatment system caused by excessively high calcium ion concentration and large fluctuations in upstream ammonia nitrogen concentration, while reducing wastewater hardness and solid waste production. Ultimately, the effluent quality consistently meets the requirements of the "Water Pollutant Discharge Standard for Iron and Steel Industry" (GB13456-2012).

[0027] Since the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention and the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention belong to the same inventive concept, the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention has at least all the advantages of the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention. For the advantages of the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention, please refer to the relevant description of the beneficial effects of the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention, which will not be repeated here. Attached Figure Description

[0028] Figure 1 A schematic diagram of the stainless steel cold rolling mixed acid wastewater treatment process provided by existing technology;

[0029] Figure 2 This is a schematic diagram of the overall steps of a method for treating mixed acid wastewater from stainless steel cold rolling according to Embodiment 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of a specific process for treating mixed acid wastewater from stainless steel cold rolling, provided in Embodiment 1 of the present invention.

[0031] Figure 4 This is a structural block diagram of a stainless steel cold rolling mixed acid wastewater treatment system provided in Embodiment 2 of the present invention;

[0032] Figure 5 A schematic diagram of a stainless steel cold rolling mixed acid wastewater treatment system provided in Embodiment 2 of the present invention;

[0033] The annotations in the attached figures are explained as follows:

[0034] 1-Lime neutralization unit, 11-First reaction tank, 12-Lime slurry dosing device;

[0035] 2-Liquid alkali neutralization unit, 21-Second reaction tank, 22-Liquid alkali dosing device, 23-First fluoride ion concentration detector;

[0036] 3-Flocculation and sedimentation unit, 31-Flocculation and sedimentation tank, 32-First flocculant dosing device;

[0037] 4-Ammonia nitrogen removal unit, 41-Third reaction tank, 42-Sodium hypochlorite dosing device, 43-Ammonia nitrogen concentration detector;

[0038] 5-Coagulation and sedimentation unit, 51-Coagulation and sedimentation tank, 52-Second flocculant dosing device, 53-Coagulator dosing device, 54-Second fluoride ion concentration detector;

[0039] 6-pH adjustment unit, 61-pH adjustment tank, 62-total nitrogen concentration detector, 63-hydrochloric acid dosing device, 64-pH detector;

[0040] 7-Biological denitrification unit, 71-Anoxic tank, 72-Aerobic tank, 73-Carbon source addition device;

[0041] 8-Sludge-water separation unit, 81-Secondary sedimentation tank. Detailed Implementation

[0042] The following detailed description of the stainless steel cold rolling mixed acid wastewater treatment method and system proposed in this invention, in conjunction with the accompanying drawings and specific embodiments, will further illustrate these features. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, used only to facilitate and clarify the illustration of the embodiments of this invention. Please refer to the drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this invention. Any modifications to the structure, changes in proportions, or adjustments to the size, provided that the effects and objectives achieved by this invention are the same or similar, should still fall within the scope of the technical content disclosed in this invention. Specific design features of the invention disclosed herein, including, for example, specific dimensions, orientations, positions, and shapes, will be determined in part by the specific application and usage environment. Furthermore, in the embodiments described below, the same reference numerals are sometimes used across different drawings to denote the same parts or parts having the same function, omitting repeated descriptions.

[0043] Example 1

[0044] This embodiment provides a method for treating mixed acid wastewater from stainless steel cold rolling. For details, please refer to... Figure 2 , Figure 2 This is a schematic diagram illustrating the overall steps of the stainless steel cold rolling mixed acid wastewater treatment method provided in this embodiment. From... Figure 2 As can be seen, the method includes:

[0045] S100: The stainless steel cold rolling mixed acid wastewater is neutralized with lime to obtain a first mixture;

[0046] S200: The first mixture is subjected to liquid alkali neutralization treatment to obtain a second mixture;

[0047] S300: The second mixture is subjected to flocculation and sedimentation treatment to obtain the first effluent;

[0048] S400: Based on the ammonia nitrogen concentration in the first effluent, determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal treatment, and obtain the second effluent;

[0049] S500: The second effluent is subjected to coagulation and sedimentation treatment to obtain the third effluent;

[0050] S600: Based on the total nitrogen concentration in the third effluent, determine whether hydrochloric acid needs to be added for pH adjustment, and obtain the fourth effluent;

[0051] S700: The fourth effluent is subjected to biological denitrification treatment to obtain a mud-water mixture;

[0052] S800: The mud-water mixture is subjected to mud-water separation treatment to obtain biochemical sludge and biochemical sedimentation effluent.

[0053] Therefore, the stainless steel cold rolling mixed acid wastewater treatment method provided in this embodiment, compared with the existing technology that only adds lime slurry to neutralize the stainless steel cold rolling mixed acid wastewater, uses both lime neutralization and liquid alkali neutralization to treat the stainless steel cold rolling mixed acid wastewater. By using liquid alkali to replace part of the lime neutralization, it avoids the introduction of high concentrations of calcium ions, which not only reduces wastewater hardness and solid waste production, but also saves on softening and calcium removal agent costs and reduces equipment maintenance costs. Furthermore, after obtaining the third effluent through flocculation and sedimentation, the ammonia nitrogen concentration in the first effluent is used to determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal. This ensures that the ammonia nitrogen concentration in the wastewater is stably maintained within a suitable range, thus preventing high-concentration ammonia nitrogen wastewater from affecting the effluent stability of the subsequent biological treatment system. Simultaneously, it ensures that the residual chlorine concentration in the water is maintained at a low level, effectively preventing residual chlorine from entering the subsequent biological treatment system and killing activated sludge, thereby enhancing the subsequent biological treatment system's resistance to shock loads. Furthermore, after obtaining the third effluent through coagulation and sedimentation, the total nitrogen concentration in the third effluent is used to determine whether hydrochloric acid needs to be added for pH adjustment. This ensures that the pH of the wastewater entering the subsequent biological treatment system is maintained within the suitable range for microorganisms, avoiding problems such as low denitrification efficiency and inhibited sludge activity caused by excessively high pH. This ensures that the biological treatment system can still operate stably and meet discharge standards under high total nitrogen shock loads. The stainless steel cold rolling mixed acid wastewater treatment method provided in this embodiment can effectively solve the problem of unstable effluent from the biological treatment system caused by excessively high calcium ion concentration and large fluctuations in ammonia nitrogen concentration in upstream water, while reducing wastewater hardness and solid waste production. Ultimately, the effluent quality can stably meet the requirements of the "Water Pollutant Discharge Standard for Iron and Steel Industry" (GB13456-2012).

[0054] For example, please see Figure 3 , Figure 3 This is a schematic diagram of the specific process for treating mixed acid wastewater from stainless steel cold rolling provided in this embodiment, as shown below. Figure 3As shown, in some embodiments, step S100 specifically includes: introducing the stainless steel cold rolling mixed acid wastewater into a first reaction tank 11, adding lime slurry with a mass concentration of 5%~16% into the first reaction tank 11, so that the stainless steel cold rolling mixed acid wastewater and the lime slurry undergo a lime neutralization reaction in the first reaction tank 11, and controlling the pH value during the lime neutralization reaction to be between 1 and 6, with a reaction time of 0.5 hours to 1 hour, to obtain the first mixture; step S200 specifically includes: introducing the first mixture into a second reaction tank 21, adding liquid alkali into the second reaction tank 21, and adjusting the pH value of the first mixture to be between 8.8 and 9.5, so that the first mixture and the liquid alkali undergo a liquid alkali neutralization reaction in the second reaction tank 21, to obtain the second mixture; in addition, the stainless steel cold rolling mixed acid wastewater treatment method provided in this embodiment further includes: based on the fluoride ions in the second mixture The concentration feedback adjustment adjusts the amount of lime slurry added to control the fluoride ion concentration in the second mixture between 15 mg / L and 25 mg / L. This feedback adjustment includes: when the fluoride ion concentration in the second mixture is between 15 mg / L and 25 mg / L, the amount of lime slurry added remains constant, and the pH value during the lime neutralization reaction remains constant; when the fluoride ion concentration in the second mixture is less than 15 mg / L, to avoid introducing high concentrations of calcium ions, the amount of lime slurry added can be appropriately reduced, causing the pH value during the lime neutralization reaction to decrease until the fluoride ion concentration in the second mixture is not less than 15 mg / L; when the fluoride ion concentration in the second mixture is greater than 25 mg / L, to improve the defluorination effect, the amount of lime slurry added can be appropriately increased, causing the pH value during the lime neutralization reaction to increase until the fluoride ion concentration in the second mixture is not greater than 25 mg / L. Therefore, by first adding lime slurry with a mass concentration of 5% to 16% to the mixed acid wastewater from stainless steel cold rolling, a lime neutralization reaction occurs between the wastewater and the lime slurry. Controlling the pH value during the lime neutralization reaction to 1 to 6 and the reaction time to 0.5 to 1 hour reduces the consumption of lime slurry and avoids the introduction of high concentrations of calcium ions, thereby reducing wastewater hardness and solid waste generation. Then, by adding liquid alkali to the first mixture obtained after the lime neutralization reaction and adjusting the pH value of the first mixture to 8.8 to 9.5, not only do the fluoride and sulfate ions in the first mixture react fully with calcium ions under slightly alkaline conditions to form calcium fluoride and calcium sulfate precipitates respectively, but the first mixture also undergoes a liquid alkali neutralization reaction, causing heavy metal ions such as iron, nickel, and chromium in the first mixture to form hydroxide precipitates under slightly alkaline conditions.In addition, by adjusting the amount of lime slurry added based on the fluoride ion concentration in the second mixture, the fluoride ion concentration in the second mixture can be controlled at 15 mg / L to 25 mg / L. This can reduce the consumption of lime slurry while ensuring the fluoride removal effect and avoid introducing high concentrations of calcium ions, thereby reducing the hardness of wastewater and the amount of solid waste generated.

[0055] For further details, please continue to see [link / reference]. Figure 3 ,like Figure 3 As shown, in some embodiments, step S300 specifically includes: allowing the second mixture to enter the flocculation sedimentation tank 31, adding flocculant to the flocculation sedimentation tank 31 to form larger dense flocs from the insoluble matter in the second mixture, then separating the dense flocs (i.e., settled sludge) from the supernatant, the settled sludge being transported to the sludge dewatering system for treatment, and the supernatant being used as the first effluent flowing into the subsequent treatment unit.

[0056] For the preferred options, please continue reading. Figure 3 ,like Figure 3 As shown, in some embodiments, step S400 specifically includes: allowing the first effluent to enter the third reaction tank 41; when the ammonia nitrogen concentration in the first effluent is greater than a preset threshold for ammonia nitrogen concentration, adding sodium hypochlorite solution to the first effluent to reduce the ammonia nitrogen concentration in the first effluent to no greater than the preset threshold for ammonia nitrogen concentration, thereby obtaining the second effluent; when the ammonia nitrogen concentration in the first effluent is not greater than the preset threshold for ammonia nitrogen concentration, not adding sodium hypochlorite solution, and using the first effluent as the second effluent. Thus, sodium hypochlorite solution is only added to the first effluent when the ammonia nitrogen concentration in the first effluent is greater than the preset threshold for ammonia nitrogen concentration, utilizing the strong oxidizing properties of sodium hypochlorite solution to treat the first effluent for ammonia nitrogen removal, ensuring that the ammonia nitrogen concentration in the first effluent is not greater than the preset threshold for ammonia nitrogen concentration before flowing into the subsequent treatment unit. This not only avoids the impact of high-concentration ammonia nitrogen wastewater on the effluent stability of the subsequent biological treatment system, but also ensures that the residual chlorine concentration in the water is maintained at a low level, effectively preventing residual chlorine from entering the subsequent biological treatment system to kill activated sludge, and enhancing the subsequent biological treatment system's resistance to shock loads.

[0057] It should be noted that the present invention does not impose excessive limitations on the specific value of the preset threshold for ammonia nitrogen concentration or the mass concentration of the sodium hypochlorite solution. For example, in some embodiments, the preset threshold for ammonia nitrogen concentration ranges from 25 mg / L to 30 mg / L, and the mass concentration of the sodium hypochlorite solution can be 10%.

[0058] For further details, please continue to see [link / reference]. Figure 3 ,like Figure 3As shown, in some embodiments, step S500 specifically includes: allowing the second effluent to enter a coagulation sedimentation tank 51; adding flocculant and coagulant to the coagulation sedimentation tank 51 to carry out a coagulation reaction to obtain a coagulated mixture; performing solid-liquid separation on the coagulated mixture, and using the clarified liquid as the third effluent; furthermore, the stainless steel cold rolling mixed acid wastewater treatment method provided in this embodiment also includes: real-time monitoring of the fluoride ion concentration in the third effluent, and adjusting the dosage of the coagulant based on the monitoring results to maintain the fluoride ion concentration in the third effluent within the target range; wherein, the step of adjusting the dosage based on the monitoring results... The feedback adjustment of the coagulant dosage includes: when the fluoride ion concentration in the third effluent is within the target range, maintaining the coagulant dosage unchanged; when the fluoride ion concentration in the third effluent is less than the lower limit of the target range, reducing the coagulant dosage until the fluoride ion concentration in the third effluent is within the target range; and when the fluoride ion concentration in the third effluent is greater than the upper limit of the target range, increasing the coagulant dosage until the fluoride ion concentration in the third effluent is within the target range. Therefore, by monitoring the fluoride ion concentration in the third effluent in real time and adjusting the coagulant dosage accordingly, not only can the fluoride ion concentration in the wastewater be further reduced, but the costs of coagulant / defluorinating agents can also be saved, the amount of chemical sludge generated can be reduced, and the burden of subsequent sludge dewatering and disposal can be reduced.

[0059] Preferably, in some embodiments, the target range for the fluoride ion concentration is 5 mg / L to 10 mg / L.

[0060] To better understand the present invention, the coagulation and sedimentation treatment process of the second effluent is described below by way of example.

[0061] First, after the second effluent enters the coagulation sedimentation tank 51, a coagulant (such as polyaluminum chloride) and a flocculant are added to the coagulation sedimentation tank 51, causing the fluoride ions in the second effluent to react and form insoluble substances, resulting in large, dense flocs. Then, these dense flocs (i.e., settled sludge) are separated from the clarified liquid, with the clarified liquid becoming the third effluent. Simultaneously, the fluoride ion concentration in the third effluent is monitored in real time, and the coagulant dosage is adjusted based on the monitoring results: when the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L, the coagulant dosage remains unchanged; when the fluoride ion concentration in the third effluent is below 5 mg / L, the coagulant dosage is reduced until the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L; when the fluoride ion concentration in the third effluent is above 10 mg / L, the coagulant dosage is increased until the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L. Ultimately, the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L, allowing the third effluent to flow into the subsequent treatment unit, and the settled sludge to be transported to the sludge dewatering system for treatment.

[0062] It should be noted that stainless steel cold rolling mixed acid wastewater is characterized by high total nitrogen concentration and low ammonia nitrogen concentration (the ratio of ammonia nitrogen concentration to total nitrogen concentration is usually less than 0.025). During biological denitrification treatment of this type of wastewater, denitrification (alkali production) occurs during total nitrogen removal, while nitrification (acid production) occurs during ammonia nitrogen removal. However, due to the high total nitrogen concentration and low ammonia nitrogen concentration in the stainless steel cold rolling mixed acid wastewater, alkali production exceeds acid production, resulting in an excessively high pH value in the wastewater, which affects denitrification efficiency and effluent quality. Therefore, to solve the above problems, this invention adds step S600 after step S500.

[0063] For details, please continue to see Figure 3 ,like Figure 3As shown, in some embodiments, step S600 specifically includes: allowing the third effluent to enter a pH adjustment tank 61; when the total nitrogen concentration in the third effluent is less than a first threshold, not adding hydrochloric acid to the pH adjustment tank 61, and using the third effluent as the fourth effluent, directly entering the subsequent treatment unit; when the total nitrogen concentration in the third effluent is not less than the first threshold and less than a second threshold, adding hydrochloric acid to the pH adjustment tank 61, and adjusting the pH value of the third effluent to a first preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the second threshold and less than the third threshold, adding hydrochloric acid to the pH adjustment tank 61, and adjusting the pH value of the third effluent to a second preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the third threshold and less than the fourth threshold... When the total nitrogen concentration in the third effluent is not less than the fourth threshold and less than the fifth threshold, hydrochloric acid is added to the pH adjustment tank 61, and the pH value of the third effluent is adjusted to the fourth preset pH range to obtain the fourth effluent; when the total nitrogen concentration in the third effluent is not less than the fifth threshold, hydrochloric acid is added to the pH adjustment tank 61, and the pH value of the third effluent is adjusted to the fifth preset pH range to obtain the fourth effluent; wherein, the first threshold < the second threshold < the third threshold < the fourth threshold < the fifth threshold; the first preset pH range > the second preset pH range > the third preset pH range > the fourth preset pH range > the fifth preset pH range. Therefore, the amount of hydrochloric acid added can be dynamically adjusted according to the total nitrogen concentration in the third effluent, so that the pH value of the third effluent is adjusted to a suitable range. This can effectively prevent the inhibition of microbial activity by high pH value, ensure the biological denitrification effect and effluent quality, avoid excessive chemical addition and waste, reduce operating costs and improve the shock resistance of the biological system.

[0064] Preferably, in some embodiments, the first threshold is 400 mg / L, the second threshold is 600 mg / L, the third threshold is 800 mg / L, the fourth threshold is 1000 mg / L, and the fifth threshold is 1200 mg / L; the first preset pH range is greater than 6.5 and not greater than 7.0, the second preset pH range is greater than 6.0 and not greater than 6.5, the third preset pH range is greater than 5.5 and not greater than 6.0, the fourth preset pH range is greater than 5.0 and not greater than 5.5, and the fifth preset pH range is not less than 4.5 and not greater than 5.0.

[0065] It should be noted that the mass concentration of the added hydrochloric acid can be set according to the actual treatment scenario. For example, in some embodiments, the mass concentration of the added hydrochloric acid can be 30%.

[0066] For example, please continue to see Figure 3 ,like Figure 3 As shown, in some embodiments, step S700 specifically includes: first, the fourth effluent is introduced into an anoxic tank 71, and a carbon source is added to the anoxic tank 71 to reduce nitrate nitrogen in the fourth effluent to nitrogen gas through the metabolic action of denitrifying bacteria; then, the fourth effluent is introduced into an aerobic tank 72, and under aerobic conditions, ammonia nitrogen in the fourth effluent is oxidized to nitrate nitrogen through the action of nitrifying bacteria; subsequently, part of the mixed liquor in the aerobic tank 72 is returned to the anoxic tank 71, and nitrate nitrogen is removed again through biological anoxic denitrification reaction; finally, through multi-stage circulation reaction, a sludge-water mixture rich in activated sludge is obtained.

[0067] It should be noted that the present invention does not impose excessive limitations on the type and mass concentration of the added carbon source. For example, in some embodiments, the added carbon source may be methanol with a mass concentration of 95%, and the amount of methanol added may be adjusted according to the total nitrogen concentration.

[0068] For example, please continue to see Figure 3 ,like Figure 3 As shown, in some embodiments, step S800 specifically includes: allowing the mud-water mixture to enter a secondary sedimentation tank 81 for mud-water separation treatment to obtain biochemical sludge and biochemical sedimentation effluent.

[0069] Example 2

[0070] This embodiment provides a wastewater treatment system for mixed acid wastewater from stainless steel cold rolling. For details, please refer to... Figure 4 , Figure 4 This is a structural block diagram of the stainless steel cold-rolling mixed acid wastewater treatment system provided in this embodiment. From... Figure 4As can be seen, the system includes, in sequence, a lime neutralization unit 1, a liquid alkali neutralization unit 2, a flocculation and sedimentation unit 3, an ammonia nitrogen removal unit 4, a coagulation and sedimentation unit 5, a pH adjustment unit 6, a biological denitrification unit 7, and a mud-water separation unit 8; the lime neutralization unit 1 is configured to neutralize the stainless steel cold rolling mixed acid wastewater with lime to obtain a first mixture; the liquid alkali neutralization unit 2 is configured to neutralize the first mixture with liquid alkali to obtain a second mixture; the flocculation and sedimentation unit 3 is configured to flocculate and sedimentate the second mixture to obtain a first effluent; and the ammonia nitrogen removal unit 4 is configured to obtain the ammonia nitrogen concentration in the first effluent. The system is configured to: measure the total nitrogen concentration in the second effluent and determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal based on the ammonia nitrogen concentration, thereby obtaining a second effluent; the coagulation and sedimentation unit 5 is configured to: perform coagulation and sedimentation treatment on the second effluent to obtain a third effluent; the pH adjustment unit 6 is configured to: obtain the total nitrogen concentration in the third effluent and determine whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration, thereby obtaining a fourth effluent; the biological denitrification unit 7 is configured to: perform biological denitrification treatment on the fourth effluent to obtain a mud-water mixture; the mud-water separation unit 8 is configured to: perform mud-water separation treatment on the mud-water mixture to obtain biochemical sludge and biochemical sedimentation effluent.

[0071] For example, please see Figure 5 , Figure 5 This is a schematic diagram of the stainless steel cold-rolling mixed acid wastewater treatment system provided in this embodiment. Figure 5As shown, in some embodiments, the lime neutralization unit 1 includes a first reaction tank 11 and a lime slurry dosing device 12 for adding lime slurry to the first reaction tank 11. The first reaction tank 11 is used to receive stainless steel cold rolling mixed acid wastewater and to allow the stainless steel cold rolling mixed acid wastewater and the lime slurry to undergo a lime neutralization reaction in the first reaction tank 11 for 0.5 hours to 1 hour, outputting a first mixture. The liquid alkali neutralization unit 2 includes a second reaction tank 21 and a liquid alkali dosing device 22 for adding liquid alkali to the second reaction tank 21. The second reaction tank 21 is used to receive the first mixture and to allow the first mixture and the liquid alkali to undergo a liquid alkali neutralization reaction in the second reaction tank 21, outputting a second mixture. The liquid alkali neutralization unit 2 also includes a first fluoride ion concentration detector 23 for monitoring the fluoride ion concentration in the second mixture in the second reaction tank 21. The first fluoride ion concentration detector 23 is interlocked with the lime slurry dosing device 12: when the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second mixture is 15 mg / L... When the concentration is 25 mg / L, the dosage of the lime slurry dosing device 12 is kept constant. When the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second mixture is less than 15 mg / L, the dosage of the lime slurry dosing device 12 is reduced until the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second mixture is not less than 15 mg / L. When the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second mixture is greater than 25 mg / L, the dosage of the lime slurry dosing device 12 is increased until the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second mixture is not greater than 25 mg / L. The flocculation sedimentation unit 3 includes a flocculation sedimentation tank 31 and a first flocculant dosing device 32 for adding flocculant to the flocculation sedimentation tank 31. The flocculation sedimentation tank 31 is used to receive the second mixture and cause the second mixture to undergo a flocculation sedimentation reaction in the flocculation sedimentation tank 31, outputting the first effluent.The ammonia nitrogen removal unit 4 includes a third reaction tank 41 for receiving the first effluent, a sodium hypochlorite dosing device 42 for adding sodium hypochlorite solution to the third reaction tank 41, and an ammonia nitrogen concentration detector 43 for obtaining the ammonia nitrogen concentration in the first effluent from the third reaction tank 41. The ammonia nitrogen concentration detector 43 and the sodium hypochlorite dosing device 42 are interlocked: when the ammonia nitrogen concentration detector 43 detects that the ammonia nitrogen concentration in the first effluent is not greater than a preset ammonia nitrogen concentration threshold, it controls the sodium hypochlorite dosing device 42 to be in a closed state; when the ammonia nitrogen concentration detector 43 detects that the ammonia nitrogen concentration in the first effluent is greater than the preset ammonia nitrogen concentration threshold, it controls the sodium hypochlorite dosing device 42 to add sodium hypochlorite solution to the third reaction tank 41 until the ammonia nitrogen concentration detector 43 detects that the ammonia nitrogen concentration in the first effluent is not greater than the preset ammonia nitrogen concentration threshold. The coagulation and sedimentation unit 5 includes a coagulation and sedimentation tank 51, a second flocculant dosing device 52 for adding flocculant to the coagulation and sedimentation tank 51, and a colocculant dosing device 53 for adding coagulant to the coagulation and sedimentation tank 51. The coagulation and sedimentation tank 51 is used to receive the second effluent output from the third reaction tank 41, causing the second effluent to undergo a coagulation reaction in the coagulation and sedimentation tank 51 to obtain a coagulated mixture. The coagulated mixture is then subjected to solid-liquid separation to obtain a clear liquid as the third effluent. The coagulation and sedimentation unit 5 also includes a second fluoride ion concentration detector 54 for monitoring the fluoride ion concentration in the third effluent in the coagulation and sedimentation tank 51. The second fluoride ion concentration detector 54 is interlocked with the colocculant dosing device 53: when the second fluoride ion concentration detector 54... When the fluoride ion concentration in the third effluent is detected to be between 5 mg / L and 10 mg / L, the dosage of the coagulant dosing device 53 is kept constant. When the second fluoride ion concentration detector 54 detects that the fluoride ion concentration in the third effluent is less than 5 mg / L, the dosage of the coagulant dosing device 53 is reduced until the second fluoride ion concentration detector 54 detects that the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L. When the second fluoride ion concentration detector 54 detects that the fluoride ion concentration in the third effluent is greater than 10 mg / L, the dosage of the coagulant dosing device 53 is increased until the second fluoride ion concentration detector 54 detects that the fluoride ion concentration in the third effluent is between 5 mg / L and 10 mg / L.The pH adjustment unit 6 includes a pH adjustment tank 61 for receiving the third effluent, a total nitrogen concentration detector 62 for acquiring the total nitrogen concentration in the third effluent from the pH adjustment tank 61, a hydrochloric acid dosing device 63 for adding hydrochloric acid to the pH adjustment tank 61, and a pH detector 64 for detecting the pH value of the third effluent from the pH adjustment tank 61. The total nitrogen concentration detector 62, the hydrochloric acid dosing device 63, and the pH detector 64 are interlocked: when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is low... When the concentration is 400 mg / L, the hydrochloric acid dosing device 63 is kept in the off state. When the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 400 mg / L and less than 600 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 6.5 and not greater than 7.0. When the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 600 mg / L and less than 800 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61. The dosing device 63 adds hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 6.0 and not greater than 6.5; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 800 mg / L and less than 1000 mg / L, the hydrochloric acid dosing device 63 controls the addition of hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 5.5 and not greater than 6.0; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 800 mg / L and less than 1000 mg / L, the hydrochloric acid dosing device 63 adds hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 5.5 and not greater than 6.0; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is greater than 800 mg / L and less than 1000 mg / L, the hydrochloric acid dosing device 63 adds hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 5.5 and not greater than 6.0; when the total nitrogen concentration in the third effluent is greater than 800 mg / L and less than 1000 mg / L, the hydrochloric acid dosing device 63 adds hydrochloric acid to the pH adjustment tank 61 until the pH value of the third effluent is greater than 5.5 and not greater than 6.0. When the nitrogen concentration is not less than 1000 mg / L and less than 1200 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 5.0 and not greater than 5.5; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 1200 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is not less than 4.5 and not greater than 5.0. The biological denitrification unit 7 includes an anoxic tank 71 and an aerobic tank 72 arranged sequentially, and a carbon source dosing device 73 for adding a carbon source to the anoxic tank 71; the anoxic tank 71 is used to receive the fourth effluent from the pH adjustment and the return liquid from the aerobic tank 72, and to cause the fourth effluent and the return liquid to undergo denitrification in the anoxic tank 71; the aerobic tank 72 is used to receive the wastewater from the anoxic tank 71, to cause the wastewater to undergo nitrification in the aerobic tank 72, and to output the return liquid to the anoxic tank 71 and output a sludge-water mixture rich in activated sludge.The mud-water separation unit 8 includes a secondary sedimentation tank 81, which is used to receive the mud-water mixture and settle it to achieve mud-water separation, outputting biochemical sludge and biochemical sedimentation effluent.

[0072] To facilitate understanding of the present invention, the following exemplary embodiments are described in conjunction with... Figure 5 The process of treating stainless steel cold rolling mixed acid wastewater using the stainless steel cold rolling mixed acid wastewater treatment system provided by the present invention is illustrated by way of example.

[0073] First, the stainless steel cold rolling mixed acid wastewater is transported to the first reaction tank 11 in the lime neutralization unit 1. Lime slurry with a mass concentration of 5% to 16% is added to the first reaction tank 11 through the lime slurry dosing device 12, so that the stainless steel cold rolling mixed acid wastewater and lime slurry undergo a lime neutralization reaction in the first reaction tank 11. The pH value of the wastewater in the first reaction tank 11 is controlled at 1 to 6, and the hydraulic retention time of the first reaction tank 11 is 1 hour, to obtain the first mixture. The first mixture flows into the second reaction tank 21 in the liquid alkali neutralization unit 2. Liquid alkali with a mass concentration of 30% is added to the second reaction tank 21 through the liquid alkali dosing device 22, raising the pH value of the wastewater to 8.8~9.5. At this time, the fluoride ions and sulfate ions in the first mixture react fully with calcium ions under slightly alkaline conditions to form calcium fluoride precipitate and calcium sulfate precipitate, respectively. The first mixture undergoes a liquid alkali neutralization reaction with the liquid alkali, causing the heavy metal ions such as iron, nickel, and chromium in the first mixture to form hydroxide precipitates under slightly alkaline conditions. The hydraulic retention time of the second reaction tank 21 is 1 hour, resulting in the second mixture. Simultaneously, the fluoride ion concentration in the second reaction tank 21 is monitored in real time by the first fluoride ion concentration detector 23, and the dosage of lime slurry is adjusted according to the fluoride ion concentration feedback: when the fluoride ion concentration is between 15 mg / L and 25 mg / L, the dosage of lime slurry dosing device 12 is kept constant, and the pH value of the wastewater in the first reaction tank 11 remains constant; when the fluoride ion concentration is less than 15 mg / L, the dosage of lime slurry dosing device 12 is reduced, so that the pH value of the wastewater in the first reaction tank 11 decreases until the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second reaction tank 21 is not less than 15 mg / L; when the fluoride ion concentration is greater than 25 mg / L, the dosage of lime slurry dosing device 12 is increased, so that the pH value of the wastewater in the first reaction tank 11 increases until the first fluoride ion concentration detector 23 detects that the fluoride ion concentration in the second reaction tank 21 is not greater than 25 mg / L.

[0074] Then, the second mixture flows into the flocculation sedimentation tank 31 in the flocculation sedimentation unit 3. The hydraulic retention time of the flocculation sedimentation tank 31 is 1.5 hours. Polyacrylamide with a concentration of 5 mg / L is added to the flocculation sedimentation tank 31 through the first flocculant dosing device 32, so that the insoluble matter in the second mixture forms large dense flocs. Then, the dense flocs (i.e., settled sludge) are separated from the supernatant. The settled sludge is transported to the sludge dewatering system for treatment, and the supernatant is used as the first effluent.

[0075] Next, the first effluent flows into the third reaction tank 41 in the subsequent ammonia nitrogen removal unit 4. The hydraulic retention time of the third reaction tank 41 is 0.5 hours. The ammonia nitrogen concentration in the first effluent in the third reaction tank 41 is monitored by the ammonia nitrogen concentration detector 43 and found to be greater than 25 mg / L. At this time, the sodium hypochlorite dosing device 42 is controlled to add a 10% sodium hypochlorite solution to the third reaction tank 41. The strong oxidizing property of sodium hypochlorite is used to remove ammonia nitrogen from the first effluent. After the ammonia nitrogen concentration in the first effluent is not greater than 25 mg / L, it flows into the subsequent coagulation and sedimentation unit 5.

[0076] Then, the second effluent from the third reaction tank 41 enters the coagulation sedimentation tank 51 in the coagulation sedimentation unit 5. Flocculant is added to the coagulation sedimentation tank 51 through the second flocculant dosing device 52 and polyaluminum chloride is added to the coagulation sedimentation tank 51 through the coagulator dosing device 53. The hydraulic retention time of the coagulation sedimentation tank 51 is 1.5 hours. After the coagulation reaction, the fluoride ions in the second effluent react to form insoluble substances and form large dense flocs. After sedimentation, the dense flocs (i.e., settled sludge) are separated from the clear liquid, and the clear liquid is used as the third effluent. Simultaneously, the concentration of fluoride ions in the third effluent from the coagulation sedimentation tank 51 is monitored in real time by a second fluoride ion concentration detector 54, and the dosage of coagulant is adjusted based on the monitoring results: when the second fluoride ion concentration detector 54 detects that the concentration of fluoride ions in the third effluent is between 5 mg / L and 10 mg / L, the dosage of coagulant added by the device 53 is kept constant; when the second fluoride ion concentration detector 54 detects that the concentration of fluoride ions in the third effluent is less than 5 mg / L, the dosage of coagulant added by the device 53 is reduced until the concentration of fluoride ions in the third effluent is between 5 mg / L and 10 mg / L; when the second fluoride ion concentration detector 54 detects that the concentration of fluoride ions in the third effluent is greater than 10 mg / L, the dosage of coagulant added by the device 53 is increased until the concentration of fluoride ions in the third effluent is between 5 mg / L and 10 mg / L. After the fluoride ion concentration in the third effluent is set at 5 mg / L to 10 mg / L, it is then introduced into the subsequent pH adjustment unit 6.

[0077] Next, the third effluent from the coagulation and sedimentation unit 5 enters the pH adjustment tank 61 in the pH adjustment unit 6. The total nitrogen concentration in the third effluent is monitored in real time by the total nitrogen concentration detector 62, and the pH value of the third effluent is monitored in real time by the pH detector 64. Based on the total nitrogen concentration in the third effluent, it is determined whether hydrochloric acid with a mass concentration of 30% needs to be added to the pH adjustment tank 61 through the hydrochloric acid dosing device 63: when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is less than 400 mg / L, the hydrochloric acid dosing device 63 is controlled to be in the off state. When the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 400 mg / L and less than 600 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 6.5 and not greater than 7.0; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 600 mg / L and less than 800 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the total nitrogen concentration in the third effluent is greater than 6.5 and not greater than 7.0. When the pH value of the third effluent is detected by the pH meter 64 to be greater than 6.0 and not greater than 6.5; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 800 mg / L and less than 1000 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH value of the third effluent is detected by the pH meter 64 to be greater than 5.5 and not greater than 6.0; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 1000 mg / L and less than 1200 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61. The dosing device 63 adds hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is greater than 5.0 and not greater than 5.5; when the total nitrogen concentration detector 62 detects that the total nitrogen concentration in the third effluent is not less than 1200 mg / L, the hydrochloric acid dosing device 63 is controlled to add hydrochloric acid to the pH adjustment tank 61 until the pH detector 64 detects that the pH value of the third effluent is not less than 4.5 and not greater than 5.0; the hydraulic retention time of the pH adjustment tank 61 is 0.5 hours, and the fourth effluent is output from the pH adjustment tank 61.

[0078] Subsequently, the fourth effluent from the pH adjustment unit 6 enters the anoxic tank 71 in the biological denitrification unit 7. Methanol with a mass concentration of 95% is added to the anoxic tank 71 through the carbon source addition device 73. The nitrate nitrogen in the fourth effluent is reduced to nitrogen gas by the metabolic action of denitrifying bacteria. Then, the fourth effluent enters the aerobic tank 72. Under aerobic conditions, the ammonia nitrogen in the fourth effluent is oxidized to nitrate nitrogen by the action of nitrifying bacteria. Next, part of the mixed liquor in the aerobic tank 72 is returned to the anoxic tank 71, and nitrate nitrogen is removed again through biological anoxic denitrification reaction. Through multi-stage circulation reaction, a sludge-water mixture rich in activated sludge is output.

[0079] Finally, the mud-water mixture output from the biological denitrification unit 7 enters the secondary sedimentation tank 81 in the mud-water separation unit 8, and after sedimentation in the secondary sedimentation tank 81, biochemical sludge and biochemical sedimentation effluent are obtained.

[0080] Since the stainless steel cold rolling mixed acid wastewater treatment system provided in this embodiment belongs to the same inventive concept as the stainless steel cold rolling mixed acid wastewater treatment method provided in any of the above embodiments, the stainless steel cold rolling mixed acid wastewater treatment system provided in this embodiment has at least all the advantages of the stainless steel cold rolling mixed acid wastewater treatment methods provided in the above embodiments. For the advantages of the stainless steel cold rolling mixed acid wastewater treatment system provided in this embodiment, please refer to the relevant descriptions of the beneficial effects of the stainless steel cold rolling mixed acid wastewater treatment methods provided in the above embodiments, which will not be repeated here.

[0081] In summary, the stainless steel cold rolling mixed acid wastewater treatment method and system provided by the present invention have the following advantages: The stainless steel cold rolling mixed acid wastewater treatment method provided by the present invention includes: neutralizing the stainless steel cold rolling mixed acid wastewater with lime to obtain a first mixture; neutralizing the first mixture with liquid alkali to obtain a second mixture; subjecting the second mixture to flocculation and sedimentation to obtain a first effluent; determining whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal based on the ammonia nitrogen concentration in the first effluent, and obtaining a second effluent; subjecting the second effluent to coagulation and sedimentation to obtain a third effluent; determining whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration in the third effluent, and obtaining a fourth effluent; subjecting the fourth effluent to biological denitrification to obtain a sludge-water mixture; and subjecting the sludge-water mixture to sludge-water separation to obtain biochemical sludge and biochemical sedimentation effluent. Therefore, the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention, compared with the existing technology that only adds lime slurry to neutralize the stainless steel cold rolling mixed acid wastewater, uses both lime neutralization and liquid alkali neutralization treatments. By using liquid alkali to replace part of the lime neutralization, the method avoids the introduction of high concentrations of calcium ions, which not only reduces wastewater hardness and solid waste production, but also saves on softening and calcium removal agent costs and reduces equipment maintenance costs. Furthermore, after obtaining the third effluent through flocculation and sedimentation, the ammonia nitrogen concentration in the first effluent is used to determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal. This ensures that the ammonia nitrogen concentration in the wastewater is stably maintained within a suitable range, thus preventing high-concentration ammonia nitrogen wastewater from affecting the effluent stability of the subsequent biological treatment system. Simultaneously, it ensures that the residual chlorine concentration in the water is maintained at a low level, effectively preventing residual chlorine from entering the subsequent biological treatment system and killing activated sludge, thereby enhancing the subsequent biological treatment system's resistance to shock loads. Furthermore, after obtaining the third effluent through coagulation and sedimentation, the total nitrogen concentration in the third effluent is used to determine whether hydrochloric acid needs to be added for pH adjustment. This ensures that the pH of the wastewater entering the subsequent biological treatment system is maintained within the suitable range for microorganisms, avoiding problems such as low denitrification efficiency and inhibited sludge activity caused by excessively high pH. This ensures that the biological treatment system can still operate stably and meet discharge standards even under high total nitrogen shock loads. The stainless steel cold rolling mixed acid wastewater treatment method provided by this invention can effectively solve the problem of unstable effluent from the biological treatment system caused by excessively high calcium ion concentration and large fluctuations in upstream ammonia nitrogen concentration, while reducing wastewater hardness and solid waste production. Ultimately, the effluent quality consistently meets the requirements of the "Water Pollutant Discharge Standard for Iron and Steel Industry" (GB13456-2012).

[0082] Since the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention and the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention belong to the same inventive concept, the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention has at least all the advantages of the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention. For the advantages of the stainless steel cold rolling mixed acid wastewater treatment system provided by this invention, please refer to the relevant description of the beneficial effects of the stainless steel cold rolling mixed acid wastewater treatment method provided by this invention, which will not be repeated here.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for treating mixed acid wastewater from stainless steel cold rolling, characterized in that, The method includes: The stainless steel cold rolling mixed acid wastewater was neutralized with lime to obtain a first mixture; The first mixture was neutralized with liquid alkali to obtain a second mixture; The second mixture is subjected to flocculation and sedimentation treatment to obtain the first effluent; Based on the ammonia nitrogen concentration in the first effluent, determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal treatment, and obtain the second effluent; The second effluent is subjected to coagulation and sedimentation treatment to obtain the third effluent; Based on the total nitrogen concentration in the third effluent, determine whether hydrochloric acid needs to be added for pH adjustment, and obtain the fourth effluent. The fourth effluent was subjected to biological denitrification treatment to obtain a mud-water mixture; The mud-water mixture is subjected to mud-water separation treatment to obtain biochemical sludge and biochemical sedimentation effluent.

2. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 1, characterized in that, The process of neutralizing the stainless steel cold-rolling mixed acid wastewater with lime to obtain a first mixture includes: Lime slurry with a mass concentration of 5% to 16% is added to the stainless steel cold rolling mixed acid wastewater, so that the stainless steel cold rolling mixed acid wastewater and the lime slurry undergo a lime neutralization reaction. The pH value during the lime neutralization reaction is controlled at 1 to 6, and the reaction time is 0.5 hours to 1 hour to obtain the first mixture. The method further includes: adjusting the dosage of lime slurry based on the fluoride ion concentration in the second mixture to control the fluoride ion concentration in the second mixture between 15 mg / L and 25 mg / L; wherein the feedback adjustment includes: when the fluoride ion concentration in the second mixture is between 15 mg / L and 25 mg / L, keeping the dosage of lime slurry constant; when the fluoride ion concentration in the second mixture is less than 15 mg / L, reducing the dosage of lime slurry until the fluoride ion concentration in the second mixture is not less than 15 mg / L; when the fluoride ion concentration in the second mixture is greater than 25 mg / L, increasing the dosage of lime slurry until the fluoride ion concentration in the second mixture is not greater than 25 mg / L.

3. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 1, characterized in that, The process of neutralizing the first mixture with liquid alkali to obtain the second mixture includes: Liquid alkali is added to the first mixture, and the pH value of the first mixture is adjusted to 8.8~9.5, so that the first mixture and the liquid alkali undergo a liquid alkali neutralization reaction to obtain the second mixture.

4. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 1, characterized in that, The step of determining whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal based on the ammonia nitrogen concentration in the first effluent, and obtaining the second effluent, includes: When the ammonia nitrogen concentration in the first effluent exceeds a preset threshold for ammonia nitrogen concentration, sodium hypochlorite solution is added to the first effluent to ensure that the ammonia nitrogen concentration in the first effluent does not exceed the preset threshold for ammonia nitrogen concentration, thereby obtaining the second effluent. When the ammonia nitrogen concentration in the first effluent is not greater than the preset threshold for ammonia nitrogen concentration, the sodium hypochlorite solution is not added, and the first effluent is used as the second effluent.

5. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 4, characterized in that, The preset threshold value for ammonia nitrogen concentration ranges from 25 mg / L to 30 mg / L.

6. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 1, characterized in that, The process of treating the second effluent with coagulation and sedimentation to obtain the third effluent includes: Flocculant and coagulant are added to the second effluent to carry out a coagulation reaction and obtain a coagulated mixture. The coagulated mixture is subjected to solid-liquid separation, and the clear liquid is used as the third effluent. The method further includes: real-time monitoring of the fluoride ion concentration in the third effluent, and adjusting the dosage of the coagulant based on the monitoring results to maintain the fluoride ion concentration in the third effluent within the target range; wherein, adjusting the dosage of the coagulant based on the monitoring results includes: when the fluoride ion concentration in the third effluent is within the target range, keeping the dosage of the coagulant constant; when the fluoride ion concentration in the third effluent is less than the lower limit of the target range, reducing the dosage of the coagulant until the fluoride ion concentration in the third effluent is within the target range; and when the fluoride ion concentration in the third effluent is greater than the upper limit of the target range, increasing the dosage of the coagulant until the fluoride ion concentration in the third effluent is within the target range.

7. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 6, characterized in that, The target range for fluoride ion concentration is 5 mg / L to 10 mg / L.

8. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 1, characterized in that, The step of determining whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration in the third effluent, and obtaining the fourth effluent, includes: When the total nitrogen concentration in the third effluent is less than the first threshold, hydrochloric acid is not added to the third effluent, and the third effluent is used as the fourth effluent. When the total nitrogen concentration in the third effluent is not less than the first threshold and less than the second threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to a first preset pH range to obtain the fourth effluent. When the total nitrogen concentration in the third effluent is not less than the second threshold and less than the third threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to the second preset pH range to obtain the fourth effluent. When the total nitrogen concentration in the third effluent is not less than the third threshold and less than the fourth threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to a third preset pH range to obtain the fourth effluent. When the total nitrogen concentration in the third effluent is not less than the fourth threshold and less than the fifth threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to the fourth preset pH range to obtain the fourth effluent. When the total nitrogen concentration in the third effluent is not less than the fifth threshold, hydrochloric acid is added to the third effluent, and the pH value of the third effluent is adjusted to the fifth preset pH range to obtain the fourth effluent. Wherein, the first threshold < the second threshold < the third threshold < the fourth threshold < the fifth threshold; the first preset pH range > the second preset pH range > the third preset pH range > the fourth preset pH range > the fifth preset pH range.

9. The method for treating mixed acid wastewater from stainless steel cold rolling as described in claim 8, characterized in that, The first threshold is 400 mg / L, the second threshold is 600 mg / L, the third threshold is 800 mg / L, the fourth threshold is 1000 mg / L, and the fifth threshold is 1200 mg / L; the first preset pH range is greater than 6.5 and not greater than 7.0, the second preset pH range is greater than 6.0 and not greater than 6.5, the third preset pH range is greater than 5.5 and not greater than 6.0, the fourth preset pH range is greater than 5.0 and not greater than 5.5, and the fifth preset pH range is not less than 4.5 and not greater than 5.

0.

10. A stainless steel cold-rolling mixed acid wastewater treatment system, characterized in that, The system includes, in sequence, a lime neutralization unit, a liquid alkali neutralization unit, a flocculation and sedimentation unit, an ammonia nitrogen removal unit, a coagulation and sedimentation unit, a pH adjustment unit, a biological denitrification unit, and a mud-water separation unit; The lime neutralization unit is configured to: neutralize the stainless steel cold rolling mixed acid wastewater with lime to obtain a first mixture; The liquid alkali neutralization unit is configured to: neutralize the first mixture with liquid alkali to obtain a second mixture; The flocculation and sedimentation unit is configured to: perform flocculation and sedimentation treatment on the second mixture to obtain the first effluent; The ammonia nitrogen removal unit is configured to: obtain the ammonia nitrogen concentration in the first effluent, and determine whether sodium hypochlorite solution needs to be added for ammonia nitrogen removal based on the ammonia nitrogen concentration, so as to obtain the second effluent; The coagulation and sedimentation unit is configured to: perform coagulation and sedimentation treatment on the second effluent to obtain the third effluent; The pH adjustment unit is configured to: obtain the total nitrogen concentration in the third effluent, and determine whether hydrochloric acid needs to be added for pH adjustment based on the total nitrogen concentration, so as to obtain the fourth effluent; The biological denitrification unit is configured to: perform biological denitrification treatment on the fourth effluent to obtain a mud-water mixture; The mud-water separation unit is configured to perform mud-water separation treatment on the mud-water mixture to obtain biochemical sludge and biochemical sedimentation effluent.

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