Method for treating high-ammonia-nitrogen wastewater containing ammonium bifluoride

Abstract

The invention relates to the technical field of ammonia-nitrogen-containing wastewater treatment, in particular to a method for treating ammonium hydrogen fluoride-containing high-ammonia-nitrogen wastewater, which comprises the following steps: S1, adding lime slurry, polyacrylamide and phosphate into the ammonium hydrogen fluoride-containing high-ammonia-nitrogen wastewater, stirring and standing to obtain primary wastewater; s2, adjusting the pH value of the first-stage wastewater to 10-11.5, and introducing air for air stripping to obtain second-stage wastewater; s3, introducing the secondary wastewater into a biological reaction tank, and carrying out nitrification and denitrification reactions to obtain biologically treated wastewater; s4, the wastewater subjected to biological treatment enters a sedimentation tank, and after sludge is separated, the wastewater reaches the standard and is discharged. By adopting the method, the ammonia nitrogen in the wastewater can be efficiently removed, the concentration of the ammonia nitrogen can be reduced from the initial 2000mg / L to below 30mg / L, the high efficiency and high speed of chemical precipitation are utilized, the cost advantages of air stripping and biological treatment are also exerted, the overall operation cost is relatively low, the whole treatment process only needs 34-38 hours, and the time is relatively short. Compared with a traditional air stripping method, the cost of the process is reduced by 25-30%.

Description

Technical Field

[0001] The present application relates to the technical field of treatment of wastewater containing ammonia nitrogen, and more specifically, to a method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen. Background Art

[0002] Industrial production processes in industries such as the fluorine chemical industry, electronics, photovoltaics, and electroplating generate wastewater containing ammonium bifluoride and high ammonia nitrogen concentrations, with ammonia nitrogen concentrations reaching as high as 2000 mg / L. To reduce ammonia nitrogen levels in wastewater, stripping, biological methods, and membrane separation technologies are currently the primary methods used. Stripping can effectively reduce ammonia nitrogen concentrations to below 120 mg / L. However, the stripping process can easily cause secondary pollution, requiring the installation of an ammonia nitrogen absorption device. Furthermore, ammonia nitrogen removal efficiency is low at low temperatures, and adjusting the pH to an alkaline state requires the addition of a certain amount of calcium hydroxide, which can easily cause scale buildup, impacting equipment operation and hindering the continuous treatment of large quantities of wastewater. Biological methods can generally achieve ammonia nitrogen removal rates exceeding 99%. However, wastewater containing ammonium bifluoride and high ammonia nitrogen concentrations contains a large number of toxic and hazardous substances, which can affect microbial activity and treatment effectiveness, significantly reducing the effectiveness of ammonia nitrogen treatment. Membrane separation technology has a high ammonia nitrogen recovery rate, no secondary pollution, and a simple process flow, but the membrane cost is high, and the membrane is easily contaminated and clogged during operation, especially wastewater containing ammonium bifluoride and high ammonia nitrogen is more prone to clogging. The membrane needs to be replaced or cleaned and maintained regularly, which increases the operating cost and difficulty of operation.

[0003] The above methods have the problems of low efficiency, high cost or complicated operation, and are not suitable for high ammonia nitrogen wastewater containing ammonium bifluoride. Therefore, there is an urgent need for an efficient, economical and easy-to-operate process to treat such wastewater. Summary of the Invention

[0004] In order to reduce the ammonia nitrogen content of ammonium bifluoride-containing high-ammonia nitrogen wastewater while reducing cost and efficiency, the present application provides a method for treating ammonium bifluoride-containing high-ammonia nitrogen wastewater, comprising the following steps: S1. Add lime slurry, polyacrylamide and phosphate to the wastewater containing ammonium bifluoride and high ammonia nitrogen, stir, and let it stand to obtain primary wastewater; S2. Adjust the pH of the primary wastewater to 10-11.5, and introduce air for stripping to obtain secondary wastewater; S3, introducing the secondary wastewater into the biological reaction tank to undergo nitrification and denitrification reactions to obtain biologically treated wastewater; S4. The biologically treated wastewater is sent to the sedimentation tank and discharged after the sludge is separated and meets the discharge standards.

[0005] By adopting this technical solution, ammonia nitrogen can be efficiently removed from wastewater, reducing the ammonia nitrogen concentration from an initial 2000 mg / L to below 30 mg / L. This utilizes the high efficiency and rapidity of chemical precipitation while leveraging the cost advantages of air stripping and biological treatment. Overall operating costs are relatively low, and the entire treatment process takes only 34-38 hours. Compared to traditional air stripping methods, this process reduces costs by 25-30%, offering excellent economic and environmental benefits. It provides an efficient, economical, and easy-to-operate solution for the treatment of high-ammonia nitrogen wastewater containing ammonium bifluoride.

[0006] In step S1, lime slurry is added to the wastewater containing ammonium bifluoride and high ammonia nitrogen, and the ammonium ions in the ammonium bifluoride are converted into ammonia nitrogen by adjusting the pH value of the wastewater to alkaline. At the same time, the Ca in the lime slurry is converted into 2 + Reacts with fluoride ions to form calcium fluoride precipitate, initially reducing the fluoride concentration in the wastewater. Polyacrylamide acts as a flocculant, promoting the flocculation and precipitation of suspended matter and colloidal particles. Phosphate reacts with ammonia nitrogen to form magnesium ammonium phosphate precipitate, further removing ammonia nitrogen and phosphorus from the wastewater. This synergistic effect not only reduces the load of subsequent stripping but also reduces the content of other harmful substances in the wastewater.

[0007] In step S2, the pH of the primary wastewater is adjusted to 10-11.5, and air is introduced for stripping. Under alkaline conditions, ammonia nitrogen exists primarily as free ammonia. The introduction of air transfers ammonia nitrogen from the liquid phase to the vapor phase, thereby removing it. By optimizing the stripping tower design and controlling parameters such as air flow and wastewater residence time, ammonia nitrogen concentrations can be reduced to below 500 mg / L, creating favorable conditions for subsequent biological treatment.

[0008] In step S3, the secondary wastewater is introduced into a biological reactor for nitrification and denitrification. Nitrification converts ammonia nitrogen into nitrate nitrogen, while denitrification converts nitrate nitrogen into nitrogen gas, achieving deep nitrogen removal. After biological treatment, the ammonia nitrogen concentration in the wastewater is further reduced, while organic matter and other nitrogen compounds are also effectively removed.

[0009] In step S4, the biologically treated wastewater enters a sedimentation tank, where gravity sedimentation separates the sludge, further removing suspended solids and some colloidal impurities, ensuring that the effluent quality meets discharge standards. The sedimentation tank also removes some ammonia nitrogen that hasn't been fully treated, ensuring the effluent ammonia nitrogen concentration remains below 30 mg / L.

[0010] Preferably, in step S1, 0.5-1 kg of lime slurry, 0.05-0.15 kg of polyacrylamide, and 1.0-1.6 kg of phosphate need to be added per cubic meter of wastewater.

[0011] By adopting the above technical solution, the dosage of lime slurry, polyacrylamide and phosphate is optimized, other harmful substances in the wastewater are reduced, the biodegradability of the wastewater is improved, and a more favorable environment is created for subsequent treatment. The addition of lime slurry can quickly increase the pH value of the wastewater to alkaline, prompting the ammonium ions in ammonium bifluoride to be converted into ammonia nitrogen, creating favorable conditions for subsequent stripping. At the same time, the Ca in the lime 2 + reacts with F- in the wastewater to form an insoluble CaF2 precipitate, thereby effectively reducing the fluoride concentration in the wastewater and reducing its interference with subsequent treatment processes. Polyacrylamide, as a flocculant, can effectively promote the flocculation and precipitation of suspended matter, colloidal particles, and pollutants bound to them in the wastewater. Through charge neutralization and bridging effects, it aggregates fine particles into larger flocs, accelerates the precipitation rate, improves the efficiency of solid-liquid separation, and significantly improves the clarity of the wastewater, removing more impurities for subsequent treatment. Phosphate reacts with ammonia nitrogen to form magnesium ammonium phosphate precipitate, which directly removes part of the ammonia nitrogen and reduces the load of stripping and biological treatment. The synergistic effect of the three can reduce the ammonia nitrogen concentration in the wastewater from the initial 2000mg / L to below 500mg / L.

[0012] Preferably, the pH value in the nitrification stage is controlled between 7.8-8.5, the DO control value is 2-4 mg / L, the nitrification liquid reflux ratio is 200%-300%, and the hydraulic retention time in the digestion stage is 12-16 hours.

[0013] By adopting the above technical solution, efficient biological treatment of high-ammonia nitrogen wastewater containing ammonium bifluoride can be achieved. The pH value in the nitrification stage is controlled between 7.8-8.5 to ensure that nitrifying bacteria are in a suitable growth environment, improve the efficiency of the nitrification reaction, and stably remove ammonia nitrogen from the wastewater. Controlling the dissolved oxygen (DO) at 2-4 mg / L can not only meet the oxygen demand of nitrifying bacteria, but also avoid excessive energy consumption and reduce operating costs. Setting the nitrification liquid reflux ratio at 200%-300% effectively promotes the nitrification process, enhances the system's ability to resist shock loads, and further improves the ammonia nitrogen removal rate. The hydraulic retention time in the digestion stage is controlled at 8-12 hours to ensure sufficient reaction time for the full degradation of organic matter and ammonia nitrogen, while avoiding energy waste caused by excessive residence time.

[0014] Preferably, the pH value in the denitrification stage is controlled between 7.5-7.8, the DO value is controlled between 0.2-0.5 mg / L, the hydraulic retention time in the reverse digestion stage is 8-12 h, and the MLSS is controlled between 2000-2500 mg / L.

[0015] By adopting the above technical solutions, the pH value in the denitrification stage is controlled between 7.5-7.8, which is conducive to maintaining microbial activity and improving the efficiency of ammonia nitrogen conversion; the dissolved oxygen (DO) is controlled at 0.2-0.5 mg / L, which can reduce the inhibitory effect of oxygen on the denitrification process and promote the growth and metabolism of denitrifying bacteria; the hydraulic retention time is set to 4-6 hours to ensure that the reaction is fully carried out and further improve the ammonia nitrogen removal effect; the mixed liquor suspended solids concentration (MLSS) is controlled at 2000-2500 mg / L, which can maintain an appropriate amount of microorganisms and enhance the treatment capacity, while avoiding excessive sludge concentration leading to unstable system operation.

[0016] Preferably, during the stripping process, the gas-liquid ratio is maintained at (2500-3000):1, and the stripping time is 4-6 hours.

[0017] By adopting the above technical solution, high-ammonia nitrogen wastewater containing ammonium bifluoride is efficiently treated. By maintaining a gas-liquid ratio of 2500-3000:1, the ammonia nitrogen removal efficiency during the stripping process is significantly improved, reducing residual ammonia nitrogen in the wastewater and lowering the risk of secondary pollution. Controlling the stripping time to 1-2 hours ensures the process's efficiency and cost-effectiveness, effectively removing ammonia nitrogen in a relatively short period of time and avoiding the increased energy consumption and reduced equipment utilization associated with excessively long treatment times.

[0018] Preferably, in step S2, a multi-stage stripping method or a countercurrent stripping method is adopted.

[0019] By adopting the above technical solutions, multi-stage or countercurrent stripping can significantly improve the removal efficiency of ammonia nitrogen. Compared with traditional single-stage stripping, multi-stage or countercurrent stripping can more fully utilize the gas-liquid contact area, promoting the transfer of ammonia nitrogen from the wastewater to the gas phase, thereby reducing the ammonia nitrogen concentration in the wastewater. At the same time, this method can also reduce the secondary contamination of ammonia nitrogen during the stripping process to a certain extent, improving the stability and reliability of the entire treatment process.

[0020] Specifically, multi-stage stripping or countercurrent stripping methods effectively improve the removal rate of ammonia nitrogen by optimizing the gas-liquid flow direction and contact time, ensuring the influent quality in the subsequent biological treatment stage, and providing an important guarantee for the efficient and economical treatment of high-ammonia nitrogen wastewater containing ammonium bifluoride.

[0021] Preferably, polyaluminium chloride is added in step S4 in an amount of 0.3-0.5 kg / m3.

[0022] By adopting the above technical solution, polyaluminum chloride can be added before the biologically treated wastewater enters the sedimentation tank to further improve the coagulation effect of suspended matter and impurities in the wastewater, promote the sedimentation and separation of sludge, and thus improve the clarity of the wastewater and the discharge compliance rate.

[0023] Preferably, before step S1, the wastewater containing ammonium bifluoride and high ammonia nitrogen is filtered using activated adsorption carbon.

[0024] By adopting the above technical solution, some organic pollutants and toxic and hazardous substances can be effectively removed from ammonium bifluoride-containing high-ammonia nitrogen wastewater. Using activated adsorption carbon filtration before step S1 can pre-absorb organic matter and harmful impurities in the wastewater, providing a purer wastewater environment for subsequent lime slurry, polyacrylamide, and phosphate treatment, reducing the burden of subsequent treatment steps and improving overall treatment efficiency and effectiveness.

[0025] In summary, this application has the following beneficial effects: 1. By adding lime slurry, polyacrylamide and phosphate to the wastewater for pretreatment, some pollutants in the wastewater can be effectively removed, the subsequent treatment load can be reduced, scale formation can be reduced, and equipment operation stability can be improved; 2. Adopt multi-stage or countercurrent stripping mode and precisely control the gas-liquid ratio and stripping time to significantly improve the ammonia nitrogen removal efficiency, reduce the risk of secondary pollution, and adapt to efficient treatment under low temperature conditions; 3. Combined with the nitrification and denitrification treatment of the biological reactor, key parameters such as pH value, dissolved oxygen and hydraulic retention time are optimized to overcome the impact of toxic substances in wastewater on microbial activity and ensure stable and efficient ammonia nitrogen removal rate. DETAILED DESCRIPTION Example

[0026] The high ammonia nitrogen wastewater containing ammonium bifluoride to be treated has an ammonia nitrogen concentration of 2000 mg / L, a fluoride ion concentration of 300 mg / L, a wastewater temperature of 22°C, a pH value of 8.0, and a treatment capacity of 1m 3 .

[0027] Lime slurry: Prepare 10% lime slurry. First, pour 9 kg of water into a container, then slowly add 1 kg of quicklime, stirring while adding until the slurry is uniform.

[0028] Example 1 A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen content comprises the following steps: S1, into the ammonium bifluoride-containing high ammonia nitrogen wastewater, add 0.5Kg lime slurry, 0.05Kg polyacrylamide and 1Kg phosphate (sodium phosphate), stir, stand, and obtain first-level wastewater, and the treatment time is 1h; S2. Adjust the pH of the primary wastewater to 10, introduce air for stripping, and adopt multi-stage stripping to obtain secondary wastewater; During the stripping process, the gas-liquid ratio was maintained at 2500:1 and the stripping time was 4 hours.

[0029] S3. Introducing the secondary wastewater into the biological reactor for nitrification and denitrification reactions to obtain biologically treated wastewater; during the nitrification stage, the pH value is controlled at 7.8, the DO value is controlled at 2 mg / L, the nitrification liquid reflux ratio is 200%, and the hydraulic retention time during the digestion stage is 12 hours; The pH value in the denitrification stage was controlled at 7.5, the DO value was controlled at 0.2 mg / L, the hydraulic retention time in the de-digestion stage was 12 h, and the MLSS was controlled at 2000 mg / L; S4. The biologically treated wastewater is sent to the sedimentation tank for 5 hours, and the sludge is separated and then discharged in compliance with the standards.

[0030] Example 2 A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen content comprises the following steps: S1, into the ammonium bifluoride-containing high ammonia nitrogen wastewater, add 0.8Kg lime slurry, 0.1Kg polyacrylamide and 1.4Kg phosphate (sodium phosphate), stir, stand, and obtain first-level wastewater, and the treatment time is 1h; S2. Adjust the pH of the primary wastewater to 11, introduce air for stripping, and adopt countercurrent stripping to obtain secondary wastewater; During the stripping process, the gas-liquid ratio was maintained at 2800:1 and the stripping time was 5 hours.

[0031] S3. The secondary wastewater is introduced into the biological reactor for nitrification and denitrification to obtain biologically treated wastewater; the pH value of the nitrification stage is controlled between 8.1, the DO value is controlled at 3 mg / L, the nitrification liquid reflux ratio is 250%, and the hydraulic retention time of the digestion stage is 14 hours; The pH value of the denitrification stage is controlled between 7.6, the DO value is controlled at 0.3 mg / L, the hydraulic retention time of the denitrification stage is 10 h, and the MLSS is controlled at 2300 mg / L; S4. The biologically treated wastewater is sent to the sedimentation tank for 4 hours and discharged after the sludge is separated and meets the discharge standards.

[0032] Example 3 A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen content comprises the following steps: S1, into the ammonium bifluoride-containing high ammonia nitrogen wastewater, add 1Kg lime slurry, 0.15Kg polyacrylamide and 1.6Kg phosphate (sodium dihydrogen phosphate), stir, stand, and obtain first-level wastewater, and the treatment time is 1h; S2. Adjust the pH of the primary wastewater to 11.5, introduce air for stripping, and adopt multi-stage stripping to obtain secondary wastewater; During the stripping process, the gas-liquid ratio was maintained at 3000:1 and the stripping time was 6 hours.

[0033] S3. The secondary wastewater is introduced into the biological reactor for nitrification and denitrification to obtain biologically treated wastewater; the pH value in the nitrification stage is controlled between 8.5, the DO value is controlled at 4 mg / L, the nitrification liquid reflux ratio is 300%, and the hydraulic retention time in the digestion stage is 16 hours; The pH value of the denitrification stage is controlled between 7.8, the DO value is controlled at 0.5 mg / L, the hydraulic retention time of the denitrification stage is 8 hours, and the MLSS is controlled at 2500 mg / L; S4. The biologically treated wastewater is sent to the sedimentation tank for 3 hours, and the sludge is separated and then discharged in compliance with the standards.

[0034] Example 4 A method for treating high-ammonia nitrogen wastewater containing ammonium bifluoride. The difference between this embodiment and embodiment 1 is that: in step S4, polyaluminum chloride is added to the sedimentation tank in an amount of 0.3 kg / m 3 .

[0035] Example 5 A method for treating high-ammonia nitrogen wastewater containing ammonium bifluoride. The difference between this embodiment and embodiment 1 is that: in step S4, polyaluminum chloride is added to the sedimentation tank in an amount of 0.5 kg / m 3 .

[0036] Example 6 A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen content. The difference between this embodiment and embodiment 1 is that before step S1, the wastewater containing ammonium bifluoride and high ammonia nitrogen content is filtered using activated adsorption carbon.

[0037] Comparative Example Comparative Example 1 A method for treating ammonium bifluoride-containing high-ammonia nitrogen wastewater. The difference between this comparative example and Example 1 is that only lime slurry is added to the ammonium bifluoride-containing high-ammonia nitrogen wastewater, and the amount used is the same as in step S1 of the present invention (0.5 kg), and the mixture is stirred and allowed to stand.

[0038] Comparative Example 2 A method for treating high-ammonia nitrogen wastewater containing ammonium bifluoride. The difference between this comparative example and Example 1 is that step S2 is performed first and then step S1.

[0039] Comparative Example 3 A method for treating high-ammonia nitrogen wastewater containing ammonium bifluoride. The difference between this comparative example and Example 1 is that step S2 is omitted.

[0040] Detection method / test method The ammonia nitrogen content and fluoride ion concentration of Examples 1-6 and Comparative Examples 1-3 were recorded as shown in Table 1: Table 1 Experimental data of Examples 1-6 and Comparative Examples 1-3 It can be seen from the experimental data of Example 1 and Comparative Examples 1-3 that the method of the present application for treating high-ammonia nitrogen wastewater containing ammonium bifluoride can greatly improve the efficiency of removing ammonia nitrogen and fluoride ions, while greatly shortening the treatment time.

[0041] It can be seen from the experimental data of Example 1 and Examples 4-5 that by adding an appropriate amount of polyaluminum chloride in step S4, the efficiency of removing ammonia nitrogen and fluoride ions can be greatly improved.

[0042] It can be seen from the experimental data of Example 1 and Example 6 that the efficiency of removing ammonia nitrogen and fluoride ions can be greatly improved by filtering the high-ammonia nitrogen wastewater containing ammonium bifluoride using activated adsorption carbon.

[0043] 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 non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen, characterized in that: The following steps are involved: S1. Add lime slurry, polyacrylamide and phosphate to the wastewater containing ammonium bifluoride and high ammonia nitrogen, stir, and let it stand to obtain primary wastewater; S2. Adjust the pH of the primary wastewater to 10-11.5, and introduce air for stripping to obtain secondary wastewater; S3, introducing the secondary wastewater into the biological reaction tank to undergo nitrification and denitrification reactions to obtain biologically treated wastewater; S4. The biologically treated wastewater is sent to the sedimentation tank and discharged after the sludge is separated and meets the discharge standards.

2. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 1, characterized in that: In step S1, about 0.5-1 kg of lime slurry, 0.05-0.15 kg of polyacrylamide, and 1.0-1.6 kg of phosphate need to be added per cubic meter of wastewater.

3. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 2, characterized in that: The phosphate includes at least one of phosphate, dihydrogen phosphate and hydrogen phosphate.

4. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 1, characterized in that: The pH value in the nitrification stage is controlled between 7.8 and 8.5, the DO value is controlled between 2 and 4 mg / L, the nitrification liquid reflux ratio is 200% to 300%, and the hydraulic retention time in the digestion stage is 12 to 16 hours.

5. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 4, characterized in that: The pH value of the denitrification stage is controlled between 7.5 and 7.8, the DO value is controlled between 0.2 and 0.5 mg / L, the hydraulic retention time of the reverse digestion stage is 8 to 12 hours, and the MLSS is controlled between 2000 and 2500 mg / L.

6. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 4, characterized in that: During the stripping process, the gas-liquid ratio is maintained at (2500-3000):1, and the stripping time is 4-6h.

7. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 1, characterized in that: In step S2, a multi-stage stripping method or a countercurrent stripping method is adopted.

8. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 1, characterized in that: In step S4, polyaluminium chloride is added in an amount of 0.3-0.5 kg / m 3 .

9. A method for treating wastewater containing ammonium bifluoride and high ammonia nitrogen according to claim 1, characterized in that: Before step S1, the wastewater containing ammonium bifluoride and high ammonia nitrogen is filtered using activated adsorption carbon.

Images