Treatment method of high-concentration ammonia-nitrogen wastewater

Abstract

The invention provides a treatment method of high-concentration ammonia-nitrogen wastewater, and relates to the technical field of wastewater treatment. The method comprises the following steps: firstly, adjusting the pH value of the high-concentration ammonia-nitrogen wastewater to 12, then carrying out stirring and air stripping pretreatment, and then sequentially adding phosphate and magnesium salt into the treated wastewater to carry out MAP method treatment. According to the method, key parameters are strictly regulated and controlled, so that efficient treatment of the high-concentration ammonia-nitrogen wastewater is realized. The pH value of the wastewater subjected to air stripping pretreatment is 10-11, so that the method is suitable for an MAP method, and the pH value does not need to be additionally adjusted. According to the treatment method disclosed by the invention, the concentration of ammonia nitrogen in the wastewater is remarkably reduced, and the concentration of ammonia nitrogen pollutants in the effluent is lower than 30mg / L and meets the A2 / O process requirements. The whole treatment process is carried out in the same unit, the process is simplified, the cost is reduced, the generated magnesium ammonium phosphate can be recycled as a fertilizer, and economic and environmental benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating high-concentration ammonia nitrogen wastewater. Background Art

[0002] Ammonia nitrogen is one of the common pollutants in the water environment and a representation of the pollution status of the water environment, so the content of ammonia nitrogen in water is an important indicator of water quality. The sources of ammonia nitrogen wastewater are very wide, and industrial wastewater, agricultural wastewater and domestic sewage are its main sources. Industrial wastewater containing ammonia nitrogen mainly comes from the petroleum industry, metal smelting industry, chemical industry, aquaculture and agricultural and sideline food processing industry; nitrogen fertilizers commonly used in agricultural production will be washed into groundwater, rivers and lakes with water flow, leading to eutrophication of water bodies; in terms of domestic sewage, the ammonia nitrogen content in human daily excrement and the infiltration liquid of domestic garbage is relatively high, but only 20% of domestic sewage has been effectively treated, and most of the domestic sewage is directly discharged into natural water bodies, causing great pollution and damage to nearby water bodies.

[0003] There are mainly physical, chemical and biological methods for treating ammonia nitrogen in wastewater. The stripping method mainly uses the volatility of ammonia nitrogen. After adjusting the wastewater to alkaline, ammonia will dissociate and escape from the wastewater. The purpose of removing ammonia nitrogen from the wastewater can be achieved by blowing away the ammonia gas with air or steam. However, the stripping method has high process conditions and poor nitrogen removal effect.

[0004] Chemical precipitation is a method of converting pollutants dissolved in water into insoluble or slightly soluble solid particles by using precipitates produced by chemical reactions to purify water. Magnesium ammonium phosphate precipitation (MAP) is a commonly used method in chemical precipitation to remove ammonia nitrogen. Its process principle is to add a certain proportion of phosphate and magnesium salt to wastewater containing ammonia nitrogen, which reacts with ammonia nitrogen to form magnesium ammonium phosphate precipitate. However, similar to the stripping method, the treatment effect of using chemical precipitation to treat high-concentration ammonia nitrogen wastewater is also limited.

[0005] The biological method uses microorganisms to convert a series of organic nitrogen into ammonia nitrogen, and then converts the ammonia nitrogen into nitrogen gas through the nitrification and denitrification of nitrifying bacteria and denitrifying bacteria, thereby achieving the purpose of removing ammonia nitrogen. 2 / O process), short-range nitrification and denitrification, anaerobic ammonium oxidation and other technologies are all wastewater treatment technologies derived from the category of biological treatment. The biological method is better than the physical and chemical methods in treating ammonia nitrogen pollutants, so it has become a common technology for treating ammonia nitrogen pollutants in major sewage treatment plants today. However, traditional A 2 The C / N ratio is increased to improve the nitrogen removal effect.

[0006] Therefore, it is necessary to develop a combined treatment method for ammonia nitrogen wastewater, in order to achieve the same effect as traditional A 2 / O process has the same processing effect.

[0007] The invention patent with publication number CN101555077A provides a method for treating high-concentration ammonia nitrogen wastewater with poor biodegradability by combining multiple technologies. In the method, the ammonia nitrogen wastewater first enters a pH adjustment tank to adjust the pH value to 11-12.5, and then enters a stripping tower to be stripped at a gas-liquid ratio of 3000-4500. After stripping, the wastewater enters a chemical precipitation tank, and magnesium salt and phosphate are added at a molar ratio of Mg:N:P of 1.4-1.7:1:1. The reaction generates magnesium ammonium phosphate precipitation to remove ammonia nitrogen. The effluent enters a breakpoint chlorination tank, and a chlorine-containing oxidant is added at a weight ratio of effective chlorine to ammonia nitrogen Cl / N of 9-12:1. After the reaction, it is transferred to a reduction tank, and a reducing agent is added at 1-1.1 times the theoretical molar value of complete reaction with residual chlorine. The wastewater can be discharged directly after the reaction. Although this method can treat high-concentration ammonia nitrogen wastewater, its stripping and MAP method need to be carried out in two treatment units and before the MAP method, the pH of the wastewater needs to be adjusted. This undoubtedly increases the wastewater treatment cost and the complexity of the process, and the economic efficiency needs to be improved. Summary of the invention

[0008] In view of this, the present invention provides a method for treating high-concentration ammonia nitrogen wastewater, which combines stirring stripping pretreatment with MAP method, and achieves efficient treatment of high-concentration ammonia nitrogen wastewater by strictly regulating key parameters of the treatment process. The treatment process of the present invention can be carried out in the same treatment unit without the need for an additional pH process, thereby simplifying the treatment process of high-concentration ammonia nitrogen wastewater and improving treatment efficiency.

[0009] The method for treating high-concentration ammonia nitrogen wastewater provided by the present invention comprises the following steps:

[0010] S1. Adjust the pH of high-concentration ammonia nitrogen wastewater and then perform stirring and stripping pretreatment;

[0011] S2. Add phosphate and magnesium salt to the wastewater after stripping treatment in sequence, stir the reaction and then let it stand to separate and precipitate, thus completing the treatment of high-concentration ammonia nitrogen wastewater.

[0012] Preferably, the pH of the high-concentration ammonia nitrogen wastewater after adjustment is 12.

[0013] Preferably, the rotation speed of the stirring and stripping pretreatment is 300 to 1200 r / min, and the treatment time is 2 to 3 hours.

[0014] Preferably, the pH of the high-concentration ammonia nitrogen wastewater after the stirring and stripping treatment is 10-11.

[0015] Preferably, the phosphate is at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate, and the magnesium salt is magnesium sulfate and / or magnesium chloride.

[0016] Preferably, after adding phosphate and magnesium salt, the molar ratio of nitrogen, phosphorus and magnesium in the high-concentration ammonia nitrogen wastewater is n(N):n(P):n(Mg)=1:1.2:1.2.

[0017] Preferably, the stirring reaction time is 30 to 50 minutes, and the standing time after the stirring reaction is 30 to 60 minutes.

[0018] Compared with the prior art, the present invention can significantly reduce the ammonia nitrogen concentration in high-concentration ammonia nitrogen wastewater by combining stirring and air stripping pretreatment with MAP method, and the ammonia nitrogen pollutant concentration in the effluent is lower than 30 mg / L, which meets the requirements of A 2 / O process treatment requirements. The treatment process of the present invention can be carried out in the same treatment unit, and there is no need for an additional pH adjustment process, which greatly simplifies the treatment process and reduces the operation complexity and operating costs. At the same time, the present invention adjusts the pH of the high-concentration ammonia nitrogen wastewater to improve the efficiency of the stirring and stripping pretreatment. The pH of the treated wastewater is 10-11, which is suitable for the MAP method. There is no need to additionally adjust the pH value of the wastewater before MAP. The present invention optimizes the reaction conditions of the MAP method and improves the precipitation efficiency. The generated magnesium ammonium phosphate can be used as a fertilizer to achieve resource recycling, which has both economic and environmental benefits. The entire treatment process does not produce harmful by-products, is environmentally friendly, and meets the requirements of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 The test results of the effect of air stripping pretreatment process on ammonia nitrogen removal effect;

[0021] Figure 2 The test results of the effect of air stripping time on ammonia nitrogen removal effect;

[0022] Figure 3 The test results of the effect of pH on ammonia nitrogen removal are shown;

[0023] Figure 4 The test results of the effect of MAP reaction time on ammonia nitrogen removal efficiency;

[0024] Figure 5 is the SEM image of the precipitate of Example 1;

[0025] Figure 6 This is the XRD spectrum of the precipitate in Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for treating high-concentration ammonia nitrogen wastewater, which specifically comprises the following steps:

[0028] S1. Adjust the pH of high-concentration ammonia nitrogen wastewater and then perform stirring and stripping treatment;

[0029] S2. Add phosphate and magnesium salt to the wastewater after stripping treatment in sequence, stir the reaction and then let it stand to separate and precipitate, thus completing the treatment of high-concentration ammonia nitrogen wastewater.

[0030] The first step of the present invention is to adjust the pH of the high-concentration ammonia nitrogen wastewater and then perform a stirring and stripping treatment. In a specific embodiment of the present invention, the pH of the high-concentration ammonia nitrogen wastewater after adjustment is preferably 12. In some specific embodiments of the present invention, a NaOH solution is used to adjust the pH of the high-concentration ammonia nitrogen wastewater. In some preferred embodiments of the present invention, a 20% NaOH solution is used to adjust the pH of the high-concentration ammonia nitrogen wastewater.

[0031] In a specific embodiment of the present invention, the rotation speed of the stirring and blowing treatment is preferably 300-1200 r / min, and the treatment time is preferably 2-3 hours. In some preferred embodiments of the present invention, the rotation speed of the stirring and blowing treatment is 1200 r / min, and the treatment time is 2 hours.

[0032] Stripping treatment is a method for treating wastewater by using the theory of gas-liquid phase equilibrium and mass transfer rate. Common methods of stripping treatment mainly include aeration stripping or stirring stripping. However, the present invention strictly limits the stripping treatment method to stirring stripping. The reason is that stirring stripping has a good ammonia nitrogen removal rate in the system of the present invention, while the ammonia nitrogen removal effect of aeration stripping is very limited. In addition, aeration stripping generally needs to be carried out in a separate treatment unit, and compared with stirring stripping, the equipment required for aeration stripping is simpler, which not only reduces the equipment investment cost, but also simplifies operation and maintenance. At the same time, the mass transfer rate can be controlled by adjusting the stirring speed, the treatment effect is optimized, the operation is more flexible, and the adaptability is strong. Finally, the effluent of general stripping treatment requires an additional pH adjustment process, but because the present invention adjusts the process of degassing pretreatment and adjusts the pH of high-concentration ammonia nitrogen wastewater before degassing pretreatment, MAP can be directly carried out in the same treatment unit after stripping pretreatment without additional adjustment of the pH of the wastewater, which simplifies the treatment process, saves treatment costs, and improves treatment efficiency.

[0033] In a specific embodiment of the present invention, the pH of the high-concentration ammonia nitrogen wastewater after the stripping treatment is preferably 10 to 11. The second step of the present invention is to use the MAP method to complete the treatment of the high-concentration ammonia nitrogen wastewater. The pH of the wastewater after the stripping treatment of the present invention is 10 to 11, which is the optimal pH for the MAP method of the present invention. Therefore, there is no need to adjust the pH of the wastewater after the stripping pretreatment, and MAP treatment can be performed.

[0034] In a specific embodiment of the present invention, the phosphate is at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate, and the magnesium salt is magnesium sulfate and / or magnesium chloride. In some specific embodiments of the present invention, the phosphate is disodium hydrogen phosphate, and the magnesium salt is magnesium sulfate.

[0035] In a specific embodiment of the present invention, the molar ratio of nitrogen, phosphorus and magnesium in the high-concentration ammonia nitrogen wastewater after adding phosphate and magnesium salt is n(N):n(P):n(Mg)=1:1.2:1.2.

[0036] The biggest advantage of the MAP method is that the ammonia nitrogen component contained in the wastewater is chemically reacted to generate magnesium ammonium phosphate precipitate by adding magnesium source and phosphorus source, so as to achieve the purpose of final recycling and reuse. Therefore, strictly controlling the ratio of nitrogen, phosphorus and magnesium in the wastewater has a significant impact on the treatment method of the MAP method. In combination with the pretreatment process of the present invention and the process parameters involved in the MAP method, the present invention strictly limits the wastewater after adding magnesium source and phosphorus source to n(N):n(P):n(Mg)=1:1.2:1.2. Only under this condition can the expected treatment effect be achieved.

[0037] In a specific embodiment of the present invention, the stirring reaction time is preferably 30 to 50 minutes, and the standing time after the reaction is preferably 60 minutes. In some specific embodiments of the present invention, the stirring reaction time is 30 minutes.

[0038] In order to further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0039] Unless otherwise specified, all experiments were repeated 3 times and the results were expressed as mean values.

[0040] Example 1 Effect of air stripping pretreatment process on ammonia nitrogen removal effect

[0041] The simulated wastewater with an ammonia nitrogen concentration of 150 mg / L and a pH of 12 was prepared, and the wastewater was pretreated by aeration stripping and stirring stripping. The gas-liquid ratio of aeration stripping was 3600, and the stirring rates of stirring stripping were 300 r / min and 1200 r / min. After stripping for 2 hours, the ammonia nitrogen removal rate was measured. The results are as follows: Figure 1As shown, group 1 is used for treating wastewater by aeration stripping, group 2 is used for treating wastewater by 300r / min stirring stripping, and group 3 is used for treating wastewater by 1200r / min stirring stripping.

[0042] Depend on Figure 1 It can be seen that the ammonia nitrogen removal rate of the stirring stripping is significantly higher than that of the aeration stripping, which shows that the aeration stripping method is not suitable for the present invention. In addition, when the stirring speed is 300r / min, after 2h of stripping, the ammonia nitrogen concentration in the solution is reduced from 150mg / L to 95.10mg / L, and the ammonia nitrogen removal rate is 36.60%. After the speed is increased to 1200r / min, the ammonia nitrogen concentration in the solution is reduced to 78.37mg / L, and the ammonia nitrogen removal rate is 47.75%, indicating that increasing the speed can improve the ammonia nitrogen removal rate. In the actual wastewater treatment process, a suitable stirring rate can be selected according to the actual situation of the wastewater to achieve a balance between cost and treatment effect.

[0043] Example 2 Effect of stripping time on ammonia nitrogen removal effect

[0044] Take the simulated wastewater prepared in Example 1, stir and blow off at 1200r / min for a period of time (30min, 60min, 90min, 120min, 150min, 180min). After the stripping is completed, the concentration of ammonia nitrogen in the wastewater is measured and the ammonia nitrogen removal rate is calculated. The results are as follows: Figure 2 shown.

[0045] Depend on Figure 2 It can be seen that after 2 hours of stirring and stripping, the concentration of ammonia nitrogen in the wastewater dropped from 150.00 mg / L to 76.44 mg / L, and the ammonia nitrogen removal rate was 49.04%. When the stirring time was increased, the ammonia nitrogen removal rate did not increase significantly. In the actual wastewater treatment process, the appropriate treatment time can be selected according to the actual situation of the wastewater to achieve a balance between cost and treatment effect.

[0046] Example 3 Effect of pH on Ammonia Nitrogen Removal

[0047] The ammonia nitrogen concentration was set to 150 mg / L, and the pH was adjusted to 9, 10, 11, 12, and 13, respectively. The stripping was carried out at 1200 r / min for 2 hours. After the stripping was completed, the ammonia nitrogen concentration and pH in the wastewater were measured and the ammonia nitrogen removal rate was calculated. The results are as follows: Figure 3 shown.

[0048] Depend on Figure 3 It can be seen that air stripping can produce two effects on denitrification: one is to reduce the concentration of nitrogen in the solution, and the other is to reduce the pH of the solution. The present invention strictly controls the air stripping pretreatment process to ensure the ammonia nitrogen removal effect of the pretreatment process while maintaining the pH of the treated wastewater within the most suitable range for the MPA method, without the need to adjust the pH.

[0049] Example 4 Effect of MAP reaction time on ammonia nitrogen removal effect

[0050] Prepare simulated wastewater with an ammonia nitrogen concentration of 150 mg / L and a pH of 12. After stirring and stripping at 1200 r / min for 2 hours, add disodium hydrogen phosphate and then magnesium sulfate to the wastewater in a molar ratio of nitrogen, phosphorus and magnesium of n(N):n(P):n(Mg)=1:1.2:1.2. After reacting at 20°C for a period of time (10 min, 20 min, 30 min, 40 min, 50 min), let it stand for 60 min, measure the ammonia nitrogen concentration in the wastewater and calculate the ammonia nitrogen removal rate. The results are as follows: Figure 4 shown.

[0051] Depend on Figure 4 It can be seen that when the reaction time is 0-30 minutes, the ammonia nitrogen removal rate increases with the increase of reaction time; but when the reaction time increases to 40-50 minutes, the ammonia nitrogen removal rate decreases with the increase of reaction time, and the ammonia nitrogen removal rate is as high as 78.62% at 30 minutes.

[0052] Example 5 Effect of MAP reaction pH on ammonia nitrogen removal efficiency

[0053] Prepare simulated wastewater with an ammonia nitrogen concentration of 150 mg / L and a pH of 7, 8, 9, 10, 11, 12, and 13, respectively. After stirring and stripping at 1200 r / min for 2 h, disodium hydrogen phosphate and then magnesium sulfate were added to the wastewater in a molar ratio of nitrogen, phosphorus, and magnesium of n(N):n(P):n(Mg)=1:1.2:1.2. After reacting at 20°C for 30 min, let it stand for 60 min. The ammonia nitrogen concentration in the wastewater was determined and the ammonia nitrogen removal rate was calculated.

[0054] The results showed that when the pH was 10-11, the ammonia nitrogen removal rate was as high as 92.24%, which was significantly higher than that under other pH conditions, and the treated wastewater met the requirements of A 2 It can be seen that the optimal reaction pH of the MPA method of the present invention is 10-11, which is consistent with the pH of the wastewater after the stirring and stripping pretreatment. Therefore, before the MPA method is carried out, there is no need to adjust the pH of the wastewater.

[0055] Example 6 A method for treating high-concentration ammonia nitrogen wastewater, the steps are as follows:

[0056] S1. Use 20% NaOH solution to adjust the pH of high-concentration ammonia nitrogen wastewater to 12, and stir and blow off at 1200r / min for 2h;

[0057] S2. First add disodium hydrogen phosphate and then magnesium sulfate to the wastewater in a molar ratio of nitrogen, phosphorus and magnesium of n(N):n(P):n(Mg)=1:1.2:1.2. After stirring the reaction for 30 minutes, let it stand for 60 minutes, separate the precipitation, and complete the treatment of high-concentration ammonia nitrogen wastewater.

[0058] The wastewater is wastewater generated by a carbon fiber production workshop, and the water quality indicators are shown in Table 1.

[0059] Table 1 Water quality indicators of wastewater

[0060]

[0061]

[0062] After treatment, the water quality indicators are shown in Table 2.

[0063] Table 2 Water quality indicators after treatment

[0064]

[0065] Comparative Example 1

[0066] The same as Example 6, except that disodium hydrogen phosphate is first added to the wastewater and then magnesium sulfate is added according to the molar ratio of nitrogen, phosphorus and magnesium being n(N):n(P):n(Mg)=1:1:1.4.

[0067] After testing, the ammonia nitrogen removal rate of this embodiment is 78.51%.

[0068] Comparative Example 1

[0069] Same as Example 6, except that: before step S2, the pH of the wastewater is adjusted to 9.5. The specific steps are:

[0070] S1. Use 20% NaOH solution to adjust the pH of high-concentration ammonia nitrogen wastewater to 12, stir and blow off at 1200r / min for 2h, and then adjust the pH of the wastewater to 9.5;

[0071] S2. First add disodium hydrogen phosphate and then magnesium sulfate to the wastewater in a molar ratio of nitrogen, phosphorus and magnesium of n(N):n(P):n(Mg)=1:1.2:1.2. After stirring the reaction for 30 minutes, let it stand for 60 minutes, separate the precipitation, and complete the treatment of high-concentration ammonia nitrogen wastewater.

[0072] After testing, the ammonia nitrogen removal rate of this embodiment is 70.19%.

[0073] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for treating high-concentration ammonia nitrogen wastewater, characterized in that: The following steps are involved: S1. Adjust the pH of high-concentration ammonia nitrogen wastewater and then perform stirring and stripping pretreatment; S2. Add phosphate and magnesium salt to the wastewater after stripping treatment in sequence, stir the reaction and then let it stand to separate and precipitate, thus completing the treatment of high-concentration ammonia nitrogen wastewater.

2. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: After adjustment, the pH value of the high-concentration ammonia nitrogen wastewater is 12.

3. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: The rotation speed of the stirring and stripping pretreatment is 300-1200 r / min, and the treatment time is 2-3 hours.

4. A method for treating high-concentration ammonia nitrogen wastewater according to claim 3, characterized in that: The rotation speed of the stirring and stripping pretreatment is 1200 r / min, and the treatment time is 2 h.

5. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: The pH of high-concentration ammonia nitrogen wastewater after stirring and stripping treatment is 10-11.

6. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: The phosphate is at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate, and the magnesium salt is magnesium sulfate and / or magnesium chloride.

7. A method for treating high-concentration ammonia nitrogen wastewater according to claim 6, characterized in that: The phosphate is disodium hydrogen phosphate, and the magnesium salt is magnesium sulfate.

8. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: After adding phosphate and magnesium salt, the molar ratio of nitrogen, phosphorus and magnesium in the high-concentration ammonia nitrogen wastewater is n(N):n(P):n(Mg)=1:1.2:1.

2.

9. A method for treating high-concentration ammonia nitrogen wastewater according to claim 1, characterized in that: The stirring reaction time is 30 to 50 minutes, and the standing time after the stirring reaction is 30 to 60 minutes.

10. A method for treating high-concentration ammonia nitrogen wastewater according to claim 9, characterized in that: The stirring reaction time is 30 min.

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