System and method for treating biogas slurry by coupling nitrosation and anaerobic ammonia oxidation with bioflocculation

Abstract

This invention belongs to the field of wastewater treatment technology, specifically relating to a system and method for treating biogas slurry using a coupled bioflocculation process of nitrification and anaerobic ammonia oxidation. The system includes a nitrification reactor, an anaerobic ammonia oxidation reactor, and several flocculation devices connected in sequence. The nitrification reactor treats the biogas slurry through nitrification; the anaerobic ammonia oxidation reactor denitrifies the biogas slurry after nitrification; and the flocculation devices perform bioflocculation on the denitrified biogas slurry, discharging the sludge produced by bioflocculation and collecting the liquid generated during the bioflocculation process. Using the system described in this invention, biogas slurry is ultimately treated to achieve ammonia and nitrogen removal. The treated wastewater has a low COD content, and suspended solids and most colored substances in the biogas slurry are removed, while simultaneously improving treatment efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a system and method for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation. Background Technology

[0002] Biogas slurry is a high-concentration organic wastewater produced through anaerobic fermentation. It is characterized by high levels of total nitrogen, total phosphorus, and COD, and poor biodegradability. Direct discharge of biogas slurry would damage the ecological environment. Anaerobic ammonia oxidation (ANAO) technology has demonstrated significant advantages in wastewater nitrogen and phosphorus removal. Nitrification is a crucial pre-reaction in ANAO, providing the necessary nitrite for the process. The principle of ANAO is that anaerobic ammonia-oxidizing bacteria utilize nitrite (NO2) under anaerobic conditions. - -N) acts as an electron acceptor for NH4 + -N oxidation eventually releases most of the nitrogen as nitrogen gas.

[0003] Because biogas slurry contains a large amount of NH4 + Pollutants such as nitrogen (NH4) and carbon dioxide (COD) are present, but the C / N ratio is low, resulting in poor biodegradability. Therefore, nitrification-denitrification processes are used to remove NH4. + The availability of carbon sources is difficult when nitrogen is present, resulting in low treatment efficiency. Nitrification and anammox processes are fully autotrophic, so denitrification can be carried out without the need for external carbon sources. However, the biogas slurry treated by nitrification and anammox in the existing technology still has high levels of suspended solids and COD. Furthermore, the start-up time for nitrification and anammox technologies is relatively long, resulting in low treatment efficiency. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing short-cut nitrification-anammox technologies, which still result in high levels of suspended solids and COD in the treated biogas slurry, as well as low treatment efficiency. Therefore, this invention proposes a system and method for treating biogas slurry by coupling nitrification and anammox with bioflocculation. This system first performs independent two-stage start-up treatments for nitrification and anammox. After both reactions are successfully started, the biogas slurry is first pumped into the nitrification unit for nitrification treatment. The treated wastewater is then used as influent for anammox and further treated in the anammox reactor to achieve denitrification. Finally, the effluent from anammox undergoes bioflocculation, ultimately achieving deammoniation and denitrification of the biogas slurry.

[0005] The first aspect of this invention proposes a system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation. The system includes a nitrification reactor, an anaerobic ammonia oxidation reactor, and several flocculation devices connected in sequence. The nitrification reactor performs nitrification treatment on the biogas slurry, the anaerobic ammonia oxidation reactor is used to denitrify the biogas slurry after nitrification treatment, and the flocculation devices are used to perform bioflocculation on the denitrified biogas slurry, discharge the sludge generated by bioflocculation, and collect the liquid generated by bioflocculation treatment.

[0006] Preferably, the system further includes a liquid storage device connected to the anaerobic ammonia oxidation reactor, the liquid storage device being used to supply the solution required by the anaerobic ammonia oxidation bacteria during the start-up culture phase to the anaerobic ammonia oxidation reactor.

[0007] Preferably, an aeration stone is provided on the inner bottom of the nitrification reaction device, the aeration stone is connected to an air pump, and a gas flow meter is provided on the connecting pipe between the aeration stone and the air pump. The gas flow meter is used to control the aeration mode in the nitrification reaction device to be intermittent aeration. A first temperature controller probe, a first pH value monitoring probe, a first dissolved oxygen monitoring probe, and a first stirrer are installed inside the nitrification reaction device. A first heating plate is installed on the outer wall of the nitrification reaction device.

[0008] Preferably, the anaerobic ammonia oxidation reactor is equipped with a second temperature controller probe, a second pH monitoring probe, a second dissolved oxygen monitoring probe, and a second stirrer; a second heating plate is installed on the outer wall of the anaerobic ammonia oxidation reactor.

[0009] Preferably, a first valve and a first pump are sequentially installed on the connecting pipe between the nitrification reactor and the anaerobic ammonia oxidation reactor along the flow direction of the biogas slurry after nitrification. The first valve is closed when the nitrifying bacteria in the nitrification reactor or the anaerobic ammonia oxidizing bacteria in the anaerobic ammonia oxidation reactor are in the start-up cultivation stage. A second valve and a second pump are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reactor and the flocculation device along the flow direction of the biogas slurry after denitrification. A second liquid flow meter and a fourth pump are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reactor and the storage device along the flow direction of the solution required by the anaerobic ammonia oxidizing bacteria during the start-up cultivation stage.

[0010] Preferably, the system further includes a biogas slurry storage tank, which is connected to a nitrification reaction device. A first liquid flow meter and a third pump are sequentially installed on the connecting pipe between the biogas slurry storage tank and the nitrification reaction device along the flow direction of the biogas slurry.

[0011] A second aspect of this invention proposes a method for treating biogas slurry based on the coupled bioflocculation of nitrification and anaerobic ammonia oxidation using the system described above. This method includes the following steps:

[0012] Step S1: Input biogas slurry into a nitrification reactor containing nitrifying bacteria, and start the nitrifying bacteria culture using an intermittent aeration mode; at the same time, supply the solution required for the anaerobic ammonia oxidizing bacteria in the start-up culture stage to the anaerobic ammonia oxidizing reactor, and start the anaerobic ammonia oxidizing bacteria culture using a gradient acclimatization method.

[0013] Step S2: The nitrifying bacteria in the nitrification reactor and the anaerobic ammonia oxidation bacteria in the anaerobic ammonia oxidation reactor are successfully started. The biogas slurry is transported to the nitrification reactor for nitrification. The biogas slurry after nitrification is transported to the anaerobic ammonia oxidation reactor for denitrification. The denitrified biogas slurry is then transported to the flocculation device for flocculation, sedimentation, and solid-liquid separation in sequence.

[0014] Preferably, in step S1, the conditions for starting the nitrifying bacteria culture using intermittent aeration mode are: temperature 28-32℃, hydraulic retention time 1-3 days, aeration rate 50-100 mL / L*min, pH value 8.0-8.5, and stirring rate 100-200 r / min; the intermittent aeration mode is based on a 24-hour cycle, first performing 10 min of water inlet, 60 min of anaerobic digestion, and 60 min of aeration, then cycling the water inlet, anaerobic digestion, and aeration 11 times, and finally performing 60 min of anaerobic digestion, 60 min of sedimentation, and 10 min of effluent discharge.

[0015] Preferably, the specific method for initiating the anaerobic ammonia oxidizing bacteria using a gradient acclimation approach is as follows: artificially prepared water is delivered to the anaerobic ammonia oxidation reactor, where the anaerobic ammonia oxidizing bacteria undergo a first culture in the artificially prepared water; after the first culture, a mixed solution formed by the biogas slurry treated by nitrification and water is delivered to the anaerobic ammonia oxidation reactor, where the anaerobic ammonia oxidizing bacteria, after the first culture, undergo a second culture in the mixed solution; after the second culture, the biogas slurry treated by nitrification is delivered to the anaerobic ammonia oxidation reactor, where the anaerobic ammonia oxidizing bacteria, after the second culture, undergo a third culture in the biogas slurry treated by nitrification.

[0016] More preferably, the artificially prepared water contains water, inorganic salts, trace elements, and NH4. + -N and NO2 - -N, and NH4 + -N and NO2 - The concentration ratio of -N is 1:1.32; the dissolved oxygen content in the artificially prepared water is ≤0.5mg / L, and the pH value of the artificially prepared water is 7.4-7.6; the mass concentration of the mixed solution is 25-50%.

[0017] Preferably, in step S2, the flocculation device contains a bio-flocculator and calcium oxide, and the volume ratio of biogas slurry to bio-flocculator is 25:1-2, and the volume ratio of biogas slurry to calcium oxide is 500:1-2.

[0018] The system and method for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation as described in this invention have the following beneficial effects:

[0019] (1) In this invention, the nitrification reaction is first started in the nitrification reactor. At the same time, the anaerobic ammonia oxidation bacteria are domesticated and treated in the anaerobic ammonia oxidation reactor using a gradient treatment method to achieve rapid start-up of the anaerobic ammonia oxidation reactor, thereby achieving stable and efficient denitrification. After the nitrification reaction and the anaerobic ammonia oxidation reaction are successfully started, the biogas slurry is first pumped into the nitrification reactor for nitrification treatment. The treated wastewater is used as the influent for anaerobic ammonia oxidation and enters the anaerobic ammonia oxidation reactor for further treatment to achieve denitrification. Finally, the effluent from anaerobic ammonia oxidation is subjected to bio-flocculation to achieve denitrification and denitrification of the biogas slurry. The solid suspended matter and most of the colored substances in the biogas slurry are removed, and the COD content in the treated wastewater is low, while improving the treatment efficiency.

[0020] (2) In the preferred case, the temperature, pH value and dissolved oxygen content in the nitrification reaction and the anaerobic ammonia oxidation reaction are controlled to promote the reaction to proceed more fully, so that the total nitrogen removal rate of the final treated biogas slurry is more than 85%, the total phosphorus removal rate is more than 90%, the COD removal rate is more than 65%, and the suspended solids removal rate is more than 90%. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation, according to one embodiment of the present invention.

[0022] Figure Labels

[0023] 1. Nitrification reactor; 2. Anaerobic ammonia oxidation reactor; 3. Flocculation device; 4. Liquid storage device; 5. First valve; 6. First pump; 7. Second valve; 8. Second pump; 9. Aeration stone; 10. Air pump; 11. Gas flow meter; 12. First temperature controller probe; 13. First pH value monitoring probe; 14. First dissolved oxygen monitoring probe; 15. First stirrer; 16. First heating plate; 17. Second temperature controller probe; 18. Second pH value monitoring probe; 19. Second dissolved oxygen monitoring probe; 20. Second stirrer; 21. Second heating plate; 22. Sewage valve; 23. Third stirrer; 24. Biogas slurry storage tank; 25. First liquid flow meter; 26. Third pump; 27. Second liquid flow meter; 28. Fourth pump; 29. ​​Temperature controller; 30. pH and dissolved oxygen detector; 31. Motor; 32. Third valve; 33. Fourth valve. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] Even after anaerobic ammonia oxidation treatment, biogas slurry still exhibits characteristics such as high levels of suspended solid particles and high COD. Flocculation technology can effectively address these issues. Flocculation involves adding flocculants to the water to reduce the repulsive forces between particles, causing them to become unstable. The particles then aggregate and settle under the influence of charge neutralization, adsorption bridging, and other processes. Flocculation is characterized by its excellent removal of turbidity, color, and COD, and it offers advantages such as low cost, low dosage, and simple operation. It also avoids the secondary pollution problems associated with the use of chemical flocculants.

[0026] The first aspect of this invention proposes a system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation, such as... Figure 1 As shown, the system includes a nitrification reaction device 1, an anaerobic ammonia oxidation reaction device 2, and several flocculation devices 3 connected in sequence.

[0027] The nitrification reactor 1 is used to treat the biogas slurry through nitrification reaction. The anaerobic ammonia oxidation reactor 2 is used to denitrify the biogas slurry after nitrification reaction. The flocculation reactor 3 is used to perform bioflocculation on the denitrified biogas slurry, discharge the sludge produced by bioflocculation, and collect the liquid produced by bioflocculation treatment.

[0028] The nitrification reaction is initiated by intermittent aeration under the dual inhibition of free ammonia and low dissolved oxygen. This inhibits NOB bacteria (nitrite-oxidizing bacteria), ensuring the reaction proceeds only to the nitrification stage. The nitrification reaction provides substrate for the subsequent anaerobic ammonia oxidation reaction. In a specific embodiment of the system described in this invention, an aeration stone 9 is installed on the inner bottom of the nitrification reaction device 1. The aeration stone 9 is connected to an air pump 10, and a gas flow meter 11 is installed on the connecting pipe between the aeration stone 9 and the air pump 10. The aeration devices, including the aeration stone 9, are used to increase the dissolved oxygen in the system to achieve the conditions for the nitrification reaction. The gas flow meter 11 is used to control the aeration mode within the nitrification reaction device 1 to be intermittent aeration.

[0029] In a specific embodiment of the system described in this invention, the system further includes a biogas slurry storage tank 24, which is connected to a nitrification reaction device 1. A first liquid flow meter 25 and a third pump 26 are sequentially installed on the connecting pipe between the biogas slurry storage tank 24 and the nitrification reaction device 1 along the flow direction of the biogas slurry. The first liquid flow meter 25 and the third pump 26 are used to quantitatively transfer the biogas slurry to the nitrification reaction device 1 to initiate the nitrification reaction.

[0030] In a specific embodiment of the system described in this invention, the nitrosation reaction device 1 is internally equipped with a first temperature controller probe 12, a first pH value monitoring probe 13, and a first dissolved oxygen monitoring probe 14, which can be used to detect the temperature, pH value, and dissolved oxygen content during the nitrosation reaction process to achieve optimal nitrosation reaction conditions. The nitrosation reaction device 1 is also internally equipped with a first stirrer 15, which is powered by a motor 31. The first stirrer 15 is used for thorough mixing, accelerating the nitrosation reaction, and making the reaction more uniform. A first heating plate 16 is installed on the outer wall of the nitrosation reaction device 1 to heat the nitrosation reaction to the temperature required for the complete formation of nitrous acid.

[0031] In a specific embodiment of the system described in this invention, the anaerobic ammonia oxidation reactor 2 is internally equipped with a second temperature controller probe 17, a second pH monitoring probe 18, and a second dissolved oxygen monitoring probe 19, which are used to detect the temperature, pH value, and dissolved oxygen content during the anaerobic ammonia oxidation reaction process, so as to achieve the optimal anaerobic ammonia oxidation reaction conditions. The anaerobic ammonia oxidation reactor 2 is also internally equipped with a second stirrer 20, and a motor 31 provides power to the second stirrer 20. The second stirrer 20 is used to fully mix the anaerobic ammonia oxidizing bacteria and the influent, promoting a more complete reaction. A second heating plate 21 is installed on the outer wall of the anaerobic ammonia oxidation reactor 2, which is used to enable the anaerobic ammonia oxidizing bacteria to fully denitrify.

[0032] In a specific embodiment of the system described in this invention, the first temperature controller probe 12 and the second temperature controller probe 17 can be probes on the same temperature controller 29; the first pH value monitoring probe 13, the first dissolved oxygen monitoring probe 14, the second pH value monitoring probe 18 and the second dissolved oxygen monitoring probe 19 can be probes on the same pH and dissolved oxygen detector 30.

[0033] In a specific embodiment of the system described in this invention, a first valve 5 and a first pump 6 are sequentially installed on the connecting pipe between the nitrification reaction device 1 and the anaerobic ammonia oxidation reaction device 2 along the flow direction of the biogas slurry after nitrification reaction treatment; the first valve 5 is used to isolate the nitrification reaction device 1 and the anaerobic ammonia oxidation reaction device 2, so that the two reactions can be started and cultured in two stages. The first valve 5 is closed when the nitrifying bacteria in the nitrification reaction device 1 or the anaerobic ammonia oxidation bacteria in the anaerobic ammonia oxidation reaction device 2 are in the start-up culture stage; the first pump 6 is used to transport the biogas slurry after nitrification reaction treatment to the anaerobic ammonia oxidation reaction device 2.

[0034] In a specific embodiment of the system described in this invention, a second valve 7 and a second pump 8 are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reactor 2 and the flocculation device 3, along the flow direction of the denitrified biogas slurry. During actual operation, after the denitrification reaction in the anaerobic ammonia oxidation reactor 2 is completed, the second valve 7 is opened, and the second pump 8 is used to transport the denitrified biogas slurry to the flocculation device 3.

[0035] In a specific embodiment of the system described in this invention, the system further includes a liquid storage device 4 connected to the anaerobic ammonia oxidation reactor 2, the liquid storage device 4 being used to supply the solution required by the anaerobic ammonia oxidation bacteria during the start-up culture stage to the anaerobic ammonia oxidation reactor 2.

[0036] In a preferred embodiment of the system described in this invention, a second liquid flow meter 27 and a fourth pump 28 are sequentially arranged on the connecting pipe between the anaerobic ammonia oxidation reactor 2 and the storage device 4 along the flow direction of the solution required by the anaerobic ammonia oxidizing bacteria during the start-up culture stage. The second liquid flow meter 27 and the fourth pump 28 are used to quantitatively deliver the solution required by the anaerobic ammonia oxidizing bacteria during the start-up culture stage to the anaerobic ammonia oxidation reactor 2.

[0037] In a specific embodiment of the system described in this invention, a drain valve 22 is provided at the bottom of the flocculation device 3, which is used to discharge the sludge generated by bioflocculation; a third agitator 23 is installed inside the flocculation device 3, which fully mixes the flocculant with the anaerobic ammonia oxidation effluent.

[0038] In a specific embodiment of the system described in this invention, a valve is provided between several flocculation devices 3. The valve is used to transport the wastewater generated by the previous flocculation device 3 to the next flocculation device 3 for bioflocculation. Specifically, in order to reduce energy consumption and save energy, the system is provided with 2-4 flocculation devices 3.

[0039] In the actual operation of the system described in this invention, the nitrification reaction and the anammox reaction are first started and cultured. First valve 5, first pump 6, second valve 7, and second pump 8 are closed, allowing the nitrification reaction device 1 and the anammox reaction device 2 to achieve two-stage independent start-up and culture. First liquid flow meter 25 and third pump 26 are opened to quantitatively transport the biogas slurry from the biogas slurry storage tank 24 to the nitrification reaction device 1. Intermittent aeration is used to start the nitrifying bacteria culture in the nitrification reaction device 1. Simultaneously, the anammox reaction... Device 2 employs a gradient acclimation method under anaerobic conditions to acclimate anaerobic ammonia-oxidizing bacteria, enabling rapid start-up of the anaerobic ammonia oxidation system. The storage device 4, the second liquid flow meter 27, and the fourth pump 28 provide the liquid preparation containers for the gradient acclimation and quantitatively transfer a portion of the influent. During the artificial water preparation stage, the storage device 4 is filled with artificial water, and the second liquid flow meter 27 and the fourth pump 28 are turned on. The artificial water is quantitatively delivered to the anaerobic ammonia oxidation reactor 2 through the second liquid flow meter 27 and the fourth pump 28, where the anaerobic ammonia-oxidizing bacteria undergo their first culture. The artificial water preparation stage then concludes. Afterwards, the mixing and influent stage begins. First valve 5 and first pump 6 are opened, connecting the nitrification reactor 1 and the anammox reactor 2. The nitrified biogas slurry is pumped to the anammox reactor 2 via first pump 6, where it is mixed with water to form a mixed solution. The anammox bacteria, after their first incubation, undergo a second incubation in this mixed solution. After the mixing and influent stage, the nitrification and biogas slurry influent stage begins. The nitrified biogas slurry continues to be pumped to the anammox reactor 2 via first pump 6, where the anammox bacteria, after their second incubation, undergo a second incubation in this mixed solution. After the nitrification reaction, the biogas slurry is cultured for the third time. After the nitrification biogas slurry influent stage is completed, the anaerobic ammonia oxidation bacteria in the anaerobic ammonia oxidation reactor 2 are successfully started and cultured. The biogas slurry in the biogas slurry storage tank 24 is quantitatively transported to the nitrification reactor 1 for nitrification reaction. The biogas slurry after nitrification reaction is transported to the anaerobic ammonia oxidation reactor through the first pump 6 for denitrification. The second valve 7 and the second pump 8 are opened, and the denitrified biogas slurry is transported to the flocculation device for flocculation, sedimentation and solid-liquid separation in sequence to obtain the final treated biogas slurry.

[0040] A second aspect of this invention proposes a method for treating biogas slurry based on the coupled bioflocculation of nitrification and anaerobic ammonia oxidation using the system described above. This method includes the following steps:

[0041] Step S1: The biogas slurry is fed into the nitrification reactor 1 containing nitrifying bacteria, and the nitrifying bacteria are started up using an intermittent aeration mode; at the same time, the solution required for the anaerobic ammonia oxidizing bacteria in the start-up culture stage is supplied to the anaerobic ammonia oxidizing reactor 2, and the anaerobic ammonia oxidizing bacteria are started up using a gradient acclimatization method.

[0042] Step S2: The nitrifying bacteria in the nitrification reactor 1 and the anaerobic ammonia oxidation bacteria in the anaerobic ammonia oxidation reactor 2 are successfully started. The biogas slurry is transported to the nitrification reactor 1 for nitrification reaction. The biogas slurry after nitrification reaction is transported to the anaerobic ammonia oxidation reactor 2 for denitrification. The denitrified biogas slurry is transported to the flocculation device 3 for flocculation, sedimentation and solid-liquid separation in sequence.

[0043] In a specific embodiment of the method described in this invention, in step S1, the nitrifying bacteria can be nitrite oxidizing bacteria (NOB).

[0044] In step S1, the conditions for initiating the cultivation of nitrifying bacteria using intermittent aeration mode are as follows: temperature 28-32℃, below 28℃ the activity of nitrifying bacteria decreases, above 28℃ the activity of nitrifying bacteria decreases, and above 32℃ the bacteria die; water retention time 1-3 days, less than one day the bacteria have insufficient time to grow and reproduce and the enrichment is insufficient, more than three days the cultivation cycle is too long; aeration rate 50-100 mL / L*min; pH value 8.0-8.5, the suitable growth environment pH value too high or too low will cause the bacteria to lose activity or even die; stirring rate 100-200 r / min; the intermittent aeration mode is based on a 24-hour cycle, first performing 10 min of water intake, 60 min of anaerobic digestion, 60 min of aeration, then cycling the water intake, anaerobic digestion and aeration 11 times, and finally performing 60 min of anaerobic digestion, 60 min of sedimentation, and 10 min of effluent.

[0045] In a specific embodiment of the method described in this invention, in step S1, the anaerobic ammonia oxidizing bacteria in the anaerobic ammonia oxidation reactor 2 are dark red spherical aggregates with a diameter of 0.5-2.0 mm. The main genera are Candidatus Brocadia, a certain amount of Candidatus Kuenenia and a small amount of other genera. The initial inoculation volume accounts for 15-20% of the working volume of the anaerobic ammonia oxidation reactor 2.

[0046] In a specific embodiment of the method described in this invention, the temperature of the anaerobic ammonia oxidation reactor 2 is maintained at 28-32℃, with approximately 2L of water added each time, and one operating cycle is 24 hours. Specifically, one operating cycle of the anaerobic ammonia oxidation reactor 2 is set as follows: 10 minutes of water inlet, 23 hours of anaerobic operation, 40 minutes of sedimentation, and 10 minutes of drainage. During the anaerobic operation, stirring is performed at a stirring rate of 100 r / min.

[0047] In step S1, a gradient acclimatization method is used to acclimatize and cultivate anaerobic ammonia-oxidizing bacteria to achieve rapid start-up of the anaerobic ammonia oxidation reaction system. The gradient cultivation method involves sequentially introducing the anaerobic ammonia-oxidizing bacteria into three stages: artificial water distribution, mixed water intake, and nitrification of the entire biogas slurry. In practice, the artificial water distribution stage lasts 30-40 days, the mixed water intake stage lasts 50-60 days, and the nitrification of the entire biogas slurry intake stage lasts 15-25 days.

[0048] The artificial water preparation stage uses tap water, inorganic salts, and trace elements. The specific added components are: 20 mg / L KH₂PO₄, 107 mg / L CaCl₂·2H₂O, 45 mg / L MgSO₄·7H₂O, and 1350 mg / L KHCO₃. The trace elements are a mixture of Trace Element Concentrate I (1 mL / L) and Trace Element Concentrate II. The specific composition of the trace elements is shown in Table 1. Additionally, the artificially prepared water also contains NH₄⁺. + -N and NO2 - -N, and NH4 + -N and NO2 - The concentration ratio of -N is 1:1.32. In the specific implementation process, NH4 + -N and NO2 - -N is provided by NH4Cl and NaNO2, respectively.

[0049] Table 1. Trace element content in artificially prepared water

[0050]

[0051] During the artificial water preparation stage, the first valve 5 and the first pump 6 are closed, allowing the nitrification reactor 1 and the anaerobic ammonia oxidation reactor 2 to operate independently. In this process, the nitrification reactor 1 uses intermittent aeration for the initial nitrification reaction. In a specific embodiment, a second liquid flow meter 27 and a fourth pump 28 are sequentially installed along the flow direction of the artificial water on the connecting pipe between the anaerobic ammonia oxidation reactor 2 and the storage device 4. When the second liquid flow meter 27 and the fourth pump 28 are opened, the storage device 4 supplies artificial water to the anaerobic ammonia oxidation reactor 2, allowing the anaerobic ammonia oxidizing bacteria in the reactor 2 to undergo their first culture in the artificial water. In actual operation, high-purity nitrogen gas is introduced into the artificial water for 5 minutes before each infusion to reduce the dissolved oxygen (DO) to below 0.5 mg / L. Then, the pH of the artificial water is adjusted to 7.5 ± 0.1 using dilute hydrochloric acid or NaOH solution before being added to the anaerobic ammonia oxidation reactor 2. When the NH4+ in the artificial water... + -N and NO2 - The content of -N is close to that of NH4 in the biogas slurry. + -N and NO2 - The first culture is complete when the -N content reaches the required level for the influent biogas slurry and the activity of anaerobic ammonia oxidizing bacteria meets the requirements.

[0052] After the first incubation, the first valve 5 and the first pump 6 are opened to connect the nitrification reactor 1 and the anammox reactor 2. The biogas slurry treated by the nitrification reaction is then transported to the anammox reactor 2. Simultaneously, water is introduced into the anammox reactor 2 to form a mixed solution for the initial incubation. The mass concentration of this mixed solution is 25-50%, which is the mixing influent stage. During this stage, the temperature of the mixed solution is 29-31℃, the dissolved oxygen (DO) is reduced to below 0.5 mg / L, and the pH is adjusted to 7.5 ± 0.1. The anammox bacteria, after the first incubation, undergo a second incubation in the mixed solution. When the NH4+ in the mixed solution... + -N, NO2 - The removal rates of -N and TN reached approximately 95%, 85%, and 70% or more, respectively, indicating that the anaerobic ammonia-oxidizing bacteria had adapted to the concentration of biogas slurry, and the second culture was completed.

[0053] After the second cultivation, the effluent ratio from nitrification is gradually increased until the entire biogas slurry after nitrification is subjected to anaerobic ammonia oxidation treatment, i.e., the influent stage of the biogas slurry after nitrification. The anaerobic ammonia oxidizing bacteria, after the second cultivation, undergo a third cultivation in the biogas slurry after nitrification. When NO2... - -N removal rate greater than 90%, NH4 +The nitrogen (N) removal rate dropped to approximately 70% on average, but the total nitrogen (TN) removal rate did not change significantly and was close to the TN removal rate in artificially prepared water. Therefore, the anaerobic ammonia oxidation reactor can be considered successfully started up, and the third culture is complete. Once all three cultures of the anaerobic ammonia oxidizing bacteria have been completed, the anaerobic ammonia oxidation reaction is considered successfully started.

[0054] In actual operation, after both the nitrification reaction and the anaerobic ammonium oxidation reaction are successfully started, the treatment process sequence of the biogas slurry is as follows: the biogas slurry in the biogas slurry storage tank 24 is first pumped into the nitrification reaction device 1 for nitrification reaction. The treated wastewater is then used as the influent for anaerobic ammonium oxidation and enters the anaerobic ammonium oxidation reaction device 2 for further treatment, thereby achieving denitrification. Finally, the effluent from anaerobic ammonium oxidation enters the flocculation device 3 for biological flocculation, sedimentation, and solid-liquid separation, ultimately achieving denitrification and carbon removal purification of the biogas slurry.

[0055] In a specific embodiment of the method described in this invention, in step S2, during the flocculation process, the stirring rate is 300-500 min / r and the settling time is 15-30 min.

[0056] In a specific embodiment of the method described in this invention, in step S2, the flocculation device 3 contains a bioflocculator and calcium oxide. The volume ratio of biogas slurry to bioflocculator is 25:1-2, and the volume ratio of biogas slurry to calcium oxide is 500:1-2. Specifically, the bioflocculator mainly consists of polysaccharides and proteins, and also contains small amounts of nucleic acids and other components.

[0057] In a preferred embodiment of the method described in this invention, step S2 further includes subjecting the supernatant obtained from solid-liquid separation to a series of flocculation, sedimentation, and solid-liquid separation processes in the flocculation device 3. More preferably, the denitrified biogas slurry undergoes two bioflocculation processes in the flocculation device 3, with the flocculant content added in the second bioflocculation being 30-60% of the flocculant content added in the first bioflocculation.

[0058] The following examples further illustrate the system and method for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation, as described in this invention. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following examples.

[0059] Example 1

[0060] A system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation, such as Figure 1As shown, the system includes a biogas slurry storage tank 24, a nitrification reaction device 1, an anaerobic ammonia oxidation reaction device 2, and two flocculation devices 3 connected in sequence. The anaerobic ammonia oxidation reaction device 2 is connected to a storage device 4. A first liquid flow meter 25 and a third pump 26 are sequentially installed along the flow direction of the biogas slurry on the connecting pipe between the biogas slurry storage tank 24 and the nitrification reaction device 1. A first valve 5 and a first pump 6 are sequentially installed along the flow direction of the biogas slurry after nitrification on the connecting pipe between the nitrification reaction device 1 and the anaerobic ammonia oxidation reaction device 2. A second liquid flow meter 27 and a fourth pump 28 are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reaction device 2 and the storage device 4, along the flow direction of the solution required by the anaerobic ammonia oxidation bacteria during the start-up culture stage. A second valve 7 and a second pump 8 are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reaction device 2 and the primary flocculation device 3, along the flow direction of the denitrified biogas slurry. A third valve 32 is installed between the primary flocculation device 3 and the secondary flocculation device 3. A fourth valve 33 is installed on the side wall of the secondary flocculation device 3. A drain valve 22 is installed at the bottom of both the primary flocculation device 3 and the secondary flocculation device 3.

[0061] An aeration stone 9 is installed on the inner bottom of the nitrification reactor 1. The aeration stone 9 is connected to an air pump 10. A gas flow meter 11 is installed on the connecting pipe between the aeration stone 9 and the air pump 10. The gas flow meter 11 is used to control the aeration mode of the nitrification reactor 1 to be intermittent aeration. A first temperature controller probe 12, a first pH value monitoring probe 13, a first dissolved oxygen monitoring probe 14, and a first stirrer 15 are installed inside the nitrification reactor 1. A first heating plate 16 is installed on the outer wall of the nitrification reactor 1. A second temperature controller probe 17 and a second pH value monitoring probe 18 are installed inside the anaerobic ammonia oxidation reactor 2. The device includes a head 18, a second dissolved oxygen monitoring probe 19, and a second stirrer 20; a second heating plate 21 is installed on the outer wall of the anaerobic ammonia oxidation reaction device 2; the first temperature controller probe 12 and the second temperature controller probe 17 can be probes on the same temperature controller 29; the first pH value monitoring probe 13, the first dissolved oxygen monitoring probe 14, the second pH value monitoring probe 18, and the second dissolved oxygen monitoring probe 19 can be probes on the same pH and dissolved oxygen detector 30; a third stirrer 23 is installed inside the primary flocculation device 3 and the secondary flocculation device 3; the first stirrer 15, the second stirrer 20, and the third stirrer 23 are all powered by a motor 31.

[0062] A method for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation according to the system described in Example 1, the method comprising the following steps:

[0063] Step S1: Place 0.5L of nitrified sludge into the nitrification reactor 1. Use the first liquid flow meter 25 and the third pump 26 to quantitatively deliver the biogas slurry into the nitrification reactor 1. After the biogas slurry is fed into the reactor, turn on the first heating plate 16 to control the temperature of the nitrification reactor 1 at 35.5℃, the pH at 8.3, and the stirring speed at 100r / min. Turn on the air pump 10 to start pumping air into the nitrification reactor 1. Control the aeration rate at 100ml / L*min. Set the aeration mode to intermittent aeration mode: 24h is one cycle, with a combination of 10min of water inlet, 60min of anaerobic digestion, and 60min of aeration for 11 cycles. Finally, perform 60min of anaerobic digestion, 40min of sedimentation, and 10min of effluent discharge. Each influent intake is 2L, with a hRT of approximately 1.25 days. Under this mode, the start-up period lasts 58 days. During this operation, the first valve 5 is closed, and the nitrification reactor 1 and the anammox reactor 2 are separated. The anammox reaction is started simultaneously with the nitrification reaction. Anammox bacteria, primarily Candidatus Brocadia, are inoculated into anammox reactor 2 at a sludge volume / working volume ratio of 0.167. The temperature of the entire anammox reactor 2 is maintained at 32℃, with each influent intake being approximately 2L, and one operating cycle lasting 2 days. The gradient acclimatization stages set for the start-up period of anaerobic ammonia oxidation were: artificial water preparation stage (30 days), mixed water intake stage (78 days), and post-nitrification biogas slurry stage (105 days). One operating cycle of anaerobic ammonia oxidation reactor 2 was set as follows: 10 minutes of water intake, 23 hours of anaerobic operation, 40 minutes of sedimentation, and 10 minutes of drainage. During the anaerobic operation, stirring was carried out at a rate of 100 r / min. In the artificial water preparation stage, high-purity nitrogen gas was introduced into the water for 5 minutes each time to reduce the dissolved oxygen to below 0.5 mg / L. After adjusting the pH of the influent to 7.6 with dilute hydrochloric acid, it was then added to anaerobic ammonia oxidation reactor 2.

[0064] Step S2: After both the nitrification and anaerobic ammonium oxidation reactions have been successfully started, open the first valve 5 and the first pump 6 to allow the nitrified effluent to enter the anaerobic ammonium oxidation reactor 2. The anaerobic ammonium oxidation process will stably denitrify the nitrified effluent using the above-mentioned operating mode, with a cycle of 24 hours. Open the second valve 7 and pump the effluent treated by the anaerobic ammonium oxidation into the primary flocculation device 3 using the second pump 8. Add 8 mL of biological flocculant and 0.4 g of calcium oxide per 100 mL of biogas slurry. Turn on the third stirrer 23. The stirring rate is 500 r / min, the stirring time is 5 min, the sedimentation time is 30 min, the drain valve 22 is opened to discharge the bottom flocculent sludge; the third valve 32 is opened to bring the supernatant of the primary flocculated biogas slurry into the secondary flocculation device 3, 4 mL of biological flocculant and 0.3 g of calcium oxide are added to every 100 mL of biogas slurry, the third stirrer 23 is opened, the stirring rate is 500 r / min, the stirring time is 5 min, the sedimentation time is 30 min, the drain valve 22 is opened to discharge the bottom flocculent sludge, and the fourth valve 33 is opened to discharge the treated wastewater.

[0065] Before treatment, the TN concentration of the biogas slurry was 908.8 mg / L, the COD concentration was 1562.7 mg / g, the TP concentration was 54.5 mg / L, and the turbidity was 256.3 NTU. After treatment with the biogas slurry treated by the coupled bioflocculation method of nitrification and anaerobic ammonia oxidation described in this invention, the suspended solids and most of the colored substances in the biogas slurry were removed. The final TN concentration of the treated biogas slurry was 103.7 mg / L, the COD concentration was 506.1 mg / g, the TP concentration was 2.5 mg / L, and the turbidity was 5.92 NTU, indicating that the pollutants in the biogas slurry were effectively removed.

[0066] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation, characterized in that, It includes a liquid storage device connected to the anaerobic ammonia oxidation reactor, a nitrification reactor, an anaerobic ammonia oxidation reactor, and several flocculation devices connected in sequence. The nitrification reactor treats the biogas slurry through nitrification. The anaerobic ammonium oxidation reactor denitrifies the biogas slurry after nitrification. The flocculation device performs bioflocculation on the denitrified biogas slurry, discharges the sludge produced by bioflocculation, and collects the liquid produced by bioflocculation. The storage device supplies the solution required by the anaerobic ammonium oxidizing bacteria during the start-up and cultivation phase to the anaerobic ammonium oxidizing reactor. An aeration stone is installed on the inner bottom of the nitrification reactor, which is connected to an air pump. A gas flow meter is installed on the connecting pipe between the aeration stone and the air pump to control the aeration mode in the nitrification reactor to be intermittent aeration. A first valve and a first pump are sequentially installed on the connecting pipe between the nitrification reactor and the anaerobic ammonium oxidizing reactor along the flow direction of the biogas slurry after nitrification. The first valve is closed when the nitrifying bacteria in the nitrification reactor or the anaerobic ammonium oxidizing bacteria in the anaerobic ammonium oxidizing reactor are in the start-up and cultivation phase. The nitrification reactor and the anammox reactor undergo two independent start-up and cultivation stages. Biogas slurry from the storage tank is transported to the nitrification reactor, where intermittent aeration is used to start the nitrifying bacteria culture. The anammox reactor, under anaerobic conditions, employs a gradient acclimation method to acclimate the anammox bacteria. In the artificial water distribution stage, artificial water is loaded into the storage tank and transported to the anammox reactor, where the anammox bacteria undergo their first cultivation. Then, in the mixed water intake stage, the nitrification reactor and the anammox reactor are connected, and the nitrified biogas slurry is transported to the anammox reactor. The device mixes the nitrified biogas slurry with water to form a mixed solution. Anaerobic ammonia oxidizing bacteria, after the first culture, undergo a second culture in the mixed solution. Then, it enters the whole biogas slurry influent stage for nitrification. The nitrified biogas slurry is then transported to the anaerobic ammonia oxidation reactor. The anaerobic ammonia oxidizing bacteria, after the second culture, undergo a third culture in the biogas slurry treated by the nitrification reaction. The biogas slurry in the biogas slurry storage tank is then transported to the nitrification reactor for nitrification. The biogas slurry treated by the nitrification reaction is then transported to the anaerobic ammonia oxidation reactor for denitrification. The denitrified biogas slurry is then transported to the flocculation device for flocculation, sedimentation, and solid-liquid separation in sequence.

2. The system for treating biogas slurry by coupled nitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, The nitrification reaction device is equipped with a first temperature controller probe, a first pH value monitoring probe, a first dissolved oxygen monitoring probe, and a first stirrer. A first heating plate is installed on the outer wall of the nitrosation reaction device; The anaerobic ammonia oxidation reactor is equipped with a second temperature controller probe, a second pH value monitoring probe, a second dissolved oxygen monitoring probe, and a second stirrer. A second heating plate is installed on the outer wall of the anaerobic ammonia oxidation reactor.

3. The system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation according to claim 2, characterized in that, The connecting pipe between the anaerobic ammonia oxidation reactor and the flocculation device is equipped with a second valve and a second pump in sequence along the flow direction of the denitrified biogas slurry. A second liquid flow meter and a fourth pump are sequentially installed on the connecting pipe between the anaerobic ammonia oxidation reactor and the storage device, along the flow direction of the solution required by the anaerobic ammonia oxidizing bacteria during the start-up culture stage.

4. The system for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation according to claim 1, characterized in that, The system also includes a biogas slurry storage tank, which is connected to a nitrification reaction device. A first liquid flow meter and a third pump are sequentially installed on the connecting pipe between the biogas slurry storage tank and the nitrification reaction device along the flow direction of the biogas slurry.

5. A method for treating biogas slurry by coupling nitrification and anaerobic ammonia oxidation with bioflocculation based on the system described in any one of claims 1-4, characterized in that, The method includes the following steps: Step S1: Input biogas slurry into a nitrification reactor containing nitrifying bacteria, and start the nitrifying bacteria culture using an intermittent aeration mode; at the same time, supply the solution required for the anaerobic ammonia oxidizing bacteria in the start-up culture stage to the anaerobic ammonia oxidizing reactor, and start the anaerobic ammonia oxidizing bacteria culture using a gradient acclimatization method. Step S2: The nitrifying bacteria in the nitrification reactor and the anaerobic ammonia oxidation bacteria in the anaerobic ammonia oxidation reactor are successfully started. The biogas slurry is transported to the nitrification reactor for nitrification. The biogas slurry after nitrification is transported to the anaerobic ammonia oxidation reactor for denitrification. The denitrified biogas slurry is then transported to the flocculation device for flocculation, sedimentation, and solid-liquid separation in sequence.

6. The method for treating biogas slurry by coupled nitrification and anaerobic ammonia oxidation according to claim 5, characterized in that, In step S1, the conditions for starting the culture of the nitrifying bacteria using intermittent aeration mode are: temperature 28-32℃, hydraulic retention time 1-3 days, aeration rate 50-100 mL / L*min, pH value 8.0-8.5, and stirring rate 100-200 r / min. The intermittent aeration mode operates on a 24-hour cycle, first performing 10 minutes of water intake, 60 minutes of anaerobic digestion, and 60 minutes of aeration, then cycling the water intake, anaerobic digestion, and aeration cycle 11 times, and finally performing 60 minutes of anaerobic digestion, 60 minutes of sedimentation, and 10 minutes of effluent discharge.

7. The method for treating biogas slurry by coupled nitrification and anaerobic ammonia oxidation according to claim 5, characterized in that, In step S1, the specific method for starting the anaerobic ammonia oxidizing bacteria culture using a gradient acclimatization approach is as follows: artificial water is delivered to the anaerobic ammonia oxidation reactor, and the anaerobic ammonia oxidizing bacteria are cultured for the first time in the artificial water. After the first culture is completed, the mixed solution of biogas slurry treated by nitrification reaction and water is transported to the anaerobic ammonia oxidation reactor, and the anaerobic ammonia oxidizing bacteria after the first culture are cultured for the second time in the mixed solution. After the second culture is completed, the biogas slurry treated by the nitrification reaction is transported to the anaerobic ammonia oxidation reactor (2), and the anaerobic ammonia oxidizing bacteria after the second culture are cultured for the third time in the biogas slurry treated by the nitrification reaction.

8. The method for treating biogas slurry by coupled nitrification and anaerobic ammonia oxidation according to claim 7, characterized in that, The artificially prepared water contains water, inorganic salts, trace elements, and NH4. + -N and NO2 - -N, and NH4 + -N and NO2 - The concentration ratio of -N is 1:1.32; the dissolved oxygen content in the artificially prepared water is ≤0.5mg / L, and the pH value of the artificially prepared water is 7.4-7.6; the mass concentration of the mixed solution is 25-50%.

9. The method for treating biogas slurry by coupled nitrification and anaerobic ammonia oxidation according to claim 5, characterized in that, In step S2, the flocculation device contains a bio-flocculator and calcium oxide, and the volume ratio of biogas slurry to bio-flocculator is 25:1-2, and the volume ratio of biogas slurry to calcium oxide is 500:1-2.

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