A method for treating high-ammonia nitrogen wastewater

Abstract

The present invention relates to the field of wastewater treatment. To address the time-consuming issue of short-term nitrification treatment of high-ammonia nitrogen wastewater, a method for treating high-ammonia nitrogen wastewater is provided. The method comprises the following steps: the high-ammonia nitrogen wastewater enters an aeration tank through an air stripping device, where it fully contacts biological fillers and is separated into clear water and muddy water after sedimentation. The muddy water then re-enters the air stripping device after aeration to initiate a new cycle; the biological fillers are attached with ammonia-forming bacteria that decompose organic nitrogen into ammonia nitrogen. Utilizing the principle of short-term denitrification, the process has a stronger denitrification capacity than traditional multi-stage AO processes, achieving a denitrification efficiency exceeding 95%. In actual operation, the process can reduce oxygen supply by approximately 25%, reduce residual sludge discharge by approximately 50%, and lower operating costs.

Description

Technical Field

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

[0002] With the rapid growth of industries like fertilizer and petrochemicals, the resulting high-ammonia nitrogen wastewater has become a limiting factor in their development. Therefore, effectively and economically controlling high-concentration pollution has become a key research topic for environmentalists. In recent years, several new denitrification processes have emerged both domestically and internationally, providing novel approaches for denitrifying high-concentration ammonia nitrogen wastewater. These include short-cut nitrification and denitrification, aerobic denitrification, and anaerobic ammonium oxidation.

[0003] Short-range nitrification can shorten the denitrification reaction process, improve denitrification efficiency, and remove organic matter and total phosphorus from wastewater while denitrifying. Gent Microbial Ecology Laboratory took advantage of the difference in kinetic characteristics that nitrite bacteria have a stronger affinity for dissolved oxygen than nitrate bacteria, and gradually eliminated nitrate bacteria under low dissolved oxygen conditions to achieve the purpose of short-range nitrification. Thus, they proposed the OLAND process. Du Bing et al. (Development and Research of New Nitrite Process, Water Supply and Drainage, 2006, 32(9)) used a long sludge age and low oxygen process to control the nitrite reaction, making ammonia-oxidizing bacteria the dominant bacterial community. They successfully developed a new nitrite process. However, the average ammonia nitrogen conversion rate of this process was 68.1%, and the nitrite nitrogen generation rate was 63.7%. Short-range nitrification mostly remains in the laboratory stage. In actual application, there are still problems such as instability and long startup time of the nitrification process. Therefore, an ideal solution is needed. Summary of the Invention

[0004] In order to overcome the problem that short-range nitrification treatment of high-ammonia nitrogen wastewater takes a long time, the present invention provides a method for treating high-ammonia nitrogen wastewater, which improves denitrification capacity and denitrification efficiency through cyclic treatment.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for treating high-ammonia nitrogen wastewater comprises the following steps: the high-ammonia nitrogen wastewater enters an aeration tank through an air stripping device, fully contacts with biological fillers in the aeration tank, and is separated into clear water and muddy water after sedimentation. The muddy water re-enters the air stripping device after aeration to start a new cycle; ammonia-forming bacteria that decompose organic nitrogen into ammonia nitrogen are attached to the biological fillers.

[0007] Preferably, the dissolved oxygen content in the aeration tank is 0.5-2 mg / L, the pH is 6-8, the ORP is 50-200 mV, and the temperature is 15-40°C; the surface load of the pool used for the precipitation is 1-1.2 m 3 / (m 2 ·h).

[0008] Preferably, several ropes are suspended in the aeration tank, and the biofiller is fixed to the ropes. The biofiller is a hollow sphere filled with polyurethane reticulated foam. Anaerobic or facultative aerobic bacteria grow in the polyurethane reticulated foam, while aerobic bacteria grow in the hollow sphere. The biofiller is then filled with polyurethane reticulated foam to form the hollow sphere. Anaerobic or facultative aerobic bacteria grow inside the biofiller, while aerobic bacteria grow outside. In this way, each carrier acts as a microreactor, enabling simultaneous nitrification and denitrification reactions, thereby improving treatment efficiency.

[0009] Preferably, the preparation method of the polyurethane reticulated foam is:

[0010] (1) Stir polyether polyol, hexanediol, castor oil and additives uniformly; add isocyanate and zirconium phosphate and continue stirring to obtain a mixture;

[0011] (2) The mixture is injected into a foaming chamber for vacuum foaming, and then reticulated to obtain polyurethane reticulated foam. Vacuum foaming can produce polyurethane reticulated foam plastic with large pores, which has high stability and safety.

[0012] As a biological carrier material, polyurethane reticulated foam is an important habitat for microorganisms to survive and metabolize. It can improve sewage treatment capabilities and promote the in-situ decomposition of excess sludge, thereby reducing excess sludge. Therefore, the performance of polyurethane reticulated foam is critical. The pore-forming agent of the present invention imparts macropores to the polyurethane reticulated foam. When three different alcohols, polyether polyol, hexylene glycol, and castor oil, are polymerized with isocyanate, the cross-linking of the branches forms a reticulated pore. Zirconium phosphate is a mesoporous material with small pores, and the presence of zirconium phosphate facilitates foaming. Therefore, the polyurethane reticulated foam produced by the present invention has three different pore sizes, which increase adhesion and retention efficiency, thereby improving the efficiency of microbial sludge treatment.

[0013] Preferably, the weight fractions of the raw materials in step (1) are: 10-50 parts by weight of polyether polyol, 6-10 parts by weight of hexanediol, 6-10 parts by weight of castor oil, 5-10 parts by weight of zirconium phosphate, and 40-50 parts by weight of isocyanate. The additives include 0.5-1 parts by weight of a foam stabilizer, 2-4 parts by weight of a blowing agent, 3-5 parts by weight of a cross-linking agent, 0.2-0.5 parts by weight of a pore-opening agent, and 3-5 parts by weight of a catalyst. When the three different alcohols, polyether polyol, hexanediol, and castor oil, are polymerized with isocyanate, the branches intersect to form a network of pores. In particular, the interaction of long-chain castor oil, hexanediol, and short-chain polyether polyol increases the complexity of the interlaced pores. However, the ratio of the three must be controlled. Furthermore, castor oil increases the viscosity of the mixed system, affecting the foaming performance, so its usage must be controlled within a reasonable range.

[0014] Preferably, in step (1), the isocyanate is TDI or MDI; the catalyst is a tertiary amine; the foam stabilizer is a polysiloxane polyether copolymer; the foaming agent is water; and the cross-linking agent is an alcoholamine compound.

[0015] Preferably, the vacuum foaming conditions in step (2) are as follows: injecting the stirred mixture into a foaming chamber equipped with an air valve connected to a vacuum pump for foaming, closing the foaming chamber after 150 to 200 seconds, and simultaneously opening the air valve connected to the vacuum pump for vacuuming, until the pressure in the foaming chamber reaches 0.05 to 0.07 MPa, and then closing the air valve.

[0016] Preferably, the sedimentation is achieved by using inclined tube packing, so that the mud and water mixture passing through the area is separated, the sludge sinks to the bottom and flows to the return aeration area, and the supernatant flows out from the outlet weir and enters the subsequent treatment unit.

[0017] Therefore, the beneficial effects of the present invention are as follows: (1) Utilizing the principle of short-range denitrification, the process has a stronger denitrification capacity than the traditional multi-stage AO process, with a denitrification efficiency of over 95%. In actual operation, the process can reduce oxygen supply by approximately 25%, reduce residual sludge discharge by approximately 50%, and reduce operating costs. (2) The self-made polyurethane reticulated foam improves its efficiency in treating sludge. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below through specific embodiments.

[0019] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0020] Example 1

[0021] A method for treating high-ammonia nitrogen wastewater, wherein the high-ammonia nitrogen wastewater enters an aeration tank through an air stripping device, fully contacts with biological fillers in the aeration tank, and is separated into clear water and muddy water after sedimentation. The muddy water re-enters the air stripping device after aeration to start a new round of circulation.

[0022] The aeration tank has a dissolved oxygen content of 0.5-2 mg / L, a pH of 6-8, an ORP of 50-200 mV, and a temperature of 15-40°C. Several ropes are suspended in the aeration tank, secured with commercially available biofillers. These biofillers are attached to ammonia-forming bacteria that decompose organic nitrogen into ammonia. The biofillers are hollow spheres filled with commercially available polyurethane reticulated foam. Anaerobic bacteria grow in the polyurethane reticulated foam, while aerobic bacteria grow in the hollow spheres. The biofillers are created by filling the hollow spheres with polyurethane reticulated foam.

[0023] The surface load of the pool used for the sedimentation is 1-1.2 m3 / (m 2 h). The sedimentation is achieved by inclined tube packing, which separates the mud and water mixture passing through this area. The sludge sinks to the bottom and flows to the return aeration area. The supernatant flows out from the outlet weir and enters the subsequent treatment unit.

[0024] Example 2

[0025] The difference from Example 1 is that the polyurethane reticulated foam is homemade, and the preparation method is as follows:

[0026] (1) Mix 15 parts of ethylene glycol polyether polyol, 7 parts of hexanediol, 8 parts of castor oil and additives (1 part of polysiloxane polyether copolymer, 3 parts of water, 4 parts of alcoholamine crosslinking agent, 0.5 parts of pore opening agent, and 4 parts of tertiary amine catalyst) by mass and mix them evenly; add 40 parts of toluene diisocyanate and 5 parts of zirconium phosphate and continue stirring to obtain a mixture;

[0027] (2) The stirred mixture was injected into a foaming chamber equipped with an air valve connected to a vacuum pump for foaming. After 150 seconds, the foaming chamber was closed and the air valve connected to the vacuum pump was opened to evacuate the chamber until the pressure in the foaming chamber was 0.05-0.07 MPa and the air valve was closed. The polyurethane soft foam system was then immersed in a reticulation liquid (a mixture of 40 wt% NaOH aqueous solution, isopropyl alcohol, and propylene glycol in a weight ratio of 5:2:1) for 20 minutes. After being taken out, the system was rinsed with distilled water for 4 minutes, and then placed in a 2 wt% acetic acid solution for 10 minutes. After being taken out, the system was rinsed with distilled water for 4 minutes and dried.

[0028] Example 3

[0029] The difference from Example 2 is that castor oil is not added in step (1) of preparing the polyurethane reticulated foam, and its mass is supplemented by ethylene glycol polyether polyol.

[0030] Example 4

[0031] The difference from Example 2 is that hexanediol is not added in step (1) of preparing the polyurethane reticulated foam, and its mass is supplemented by ethylene glycol polyether polyol.

[0032] Example 5

[0033] The difference from Example 2 is that zirconium phosphate is not added in step (1) of preparing the polyurethane reticulated foam.

[0034] Example 6

[0035] The difference from Example 2 is that the amount of castor oil used in step (1) of preparing the polyurethane reticulated foam is 15 parts.

[0036] Comparative Example 1

[0037] The difference from Example 1 is that the traditional multi-stage AO process is used to treat the sludge.

[0038] Example 1 uses the principle of short-range denitrification, and the sludge concentration in the aeration tank can reach 8000-10000 mg / L. Compared with the sludge concentration of 3000-4000 mg / L of the traditional multi-stage AO process in Comparative Example 1, it has a stronger denitrification capacity and a denitrification efficiency of up to 96%. In actual operation, the oxygen supply can be reduced by about 25%, the residual sludge discharge can be reduced by about 50%, and the operating cost is reduced.

[0039] Performance Testing

[0040] The polyurethane reticulated foams of the above examples were subjected to performance tests using the biofilm forming ability evaluation method described in CN112960766B. The results are shown in the following table.

[0041]

[0042] As can be seen from the table, Example 1 uses ordinary commercially available polyurethane reticulated foam, and Example 2 uses homemade polyurethane reticulated foam. The comprehensive performance of Example 2 is significantly higher than that of Example 1, indicating that the various reagents added during the preparation of the polyurethane reticulated foam of the present invention do play a role.

[0043] Compared with Example 2: Example 3 does not add castor oil because castor oil can increase viscosity, which is beneficial for improving the foaming performance of polyurethane. On the other hand, its hydroxyl groups can participate in the polymerization of polyurethane, affecting the formed network structure, which is ultimately reflected in the performance as a prolonged biofilm formation time and a decreased bioburden. However, in Example 6, the performance also decreased due to the excessive addition of castor oil, indicating that the amount of castor oil needs to be within a reasonable range to achieve the best effect. Example 4 does not add hexylene glycol, which has a smaller impact than Example 3. Example 5 does not add zirconium phosphate because zirconium phosphate is a mesoporous material with small pores, which adds a different form of pores to the polyurethane reticulated foam, which can improve adsorption capacity. On the other hand, it can serve as a crystal nucleus to promote foaming. Therefore, the adhesion and retention efficiency of Example 5 are not as good as those of Example 2.

[0044] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for treating high-ammonia nitrogen wastewater, characterized in that: The following steps are involved: High-ammonia nitrogen wastewater enters the aeration tank through the air stripping device, where it fully contacts the biological filler and is separated into clean water and muddy water after sedimentation. The muddy water re-enters the air stripping device after aeration, starting a new cycle. The biological filler is attached with ammonia-forming bacteria that decompose organic nitrogen into ammonia nitrogen. The dissolved oxygen content in the aeration tank is 0.5-2 mg / L. The biological filler is a hollow sphere filled with polyurethane reticulated foam, the polyurethane reticulated foam grows anaerobic bacteria or facultative aerobic bacteria, and the hollow sphere grows aerobic bacteria; The preparation method of polyurethane reticulated foam is as follows: (1) Stir polyether polyol, hexanediol, castor oil and additives uniformly; add isocyanate and zirconium phosphate and continue stirring to obtain a mixture; (2) The mixed material is injected into a foaming cavity for vacuum foaming, and then reticulated to obtain polyurethane reticulated foam.

2. The method according to claim 1, wherein The pH in the aeration tank is 6-8, the ORP is 50-200 mV, and the temperature is 15-40°C; the surface load of the pool used for the precipitation is 1-1.2 m 3 / (m 2 ·h).

3. The method according to claim 1, characterized in that A number of ropes are hung in the aeration tank, and the biological fillers are fixed on the ropes.

4. The method according to claim 1, wherein The raw materials in step (1) are, by mass, 10-50 parts of polyether polyol, 6-10 parts of hexanediol, 6-10 parts of castor oil, 5-10 parts of zirconium phosphate and 40-50 parts of isocyanate; the auxiliary agents are 0.5-1 parts of foam stabilizer, 2-4 parts of foaming agent, 3-5 parts of crosslinking agent, 0.2-0.5 parts of cell opener and 3-5 parts of catalyst.

5. The method according to claim 4, characterized in that The isocyanate is TDI or MDI.

6. The method according to claim 4, characterized in that The catalyst is a tertiary amine.

7. The method according to claim 4, characterized in that The foam stabilizer is a polysiloxane polyether copolymer.

8. The method according to claim 4, characterized in that The foaming agent is water.

9. The method according to claim 4, characterized in that The cross-linking agent is an alcoholamine compound.

10. The method according to claim 1 or 2, characterized in that The precipitation is achieved by inclined tube packing.

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