Method for rapid start-up and improvement of operation efficiency of anaerobic ammonia oxidation under low-oxygen condition

Abstract

The application discloses a method for quickly starting up anaerobic ammonia oxidation under low-oxygen condition and improving operation efficiency, and comprises the following steps: S1, inoculating anaerobic ammonia oxidation sludge into a reactor; S2, feeding water into the reactor, wherein the water is not subjected to deoxygenation treatment, the ratio of ammonia nitrogen to nitrite nitrogen in the water is (1.5-2.5):1, and the hydraulic retention time is 3-3.9h; S3, operating the reactor until the total nitrogen removal efficiency of the reactor reaches 75% and is kept stable for at least 14 days, and the ammonia nitrogen removal efficiency and the nitrite nitrogen removal efficiency are both maintained above 90%, so that the quick start-up of anaerobic ammonia oxidation under low-oxygen condition is realized; and S4, adjusting the hydraulic retention time to 2-2.9h, and continuing to operate the reactor for no more than 20 days, so that the operation efficiency of the reactor is improved. According to the method, the quick start-up of anaerobic ammonia oxidation under micro-oxygen condition can be successfully realized within 40 days, and the operation efficiency of anaerobic ammonia oxidation can be improved within 20 days, thereby breaking through the limitation of a long start-up period and low operation efficiency of traditional anaerobic ammonia oxidation.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, specifically to a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions. Background Technology

[0002] Anaerobic ammonia oxidation (AAO) is a highly efficient autotrophic nitrogen removal technology that directly converts ammonia nitrogen and nitrite into nitrogen gas under anaerobic conditions. Compared to the traditional nitrification-denitrification process, AAO requires no external carbon source, has low energy consumption, and produces less sludge, thus holding significant application value in wastewater treatment. However, the slow growth of AAO bacteria and their sensitivity to environmental conditions, especially during the initial startup phase, lead to long system start-up times and poor stability, limiting its widespread application in practical wastewater treatment projects.

[0003] Currently, anammox is typically started up using sludge inoculation or biofilm immobilization, and system stability is improved through a short-cut nitrification-anammox process. The short-cut nitrification-anammox process utilizes ammonia-oxidizing bacteria to oxidize some ammonia nitrogen into nitrite nitrogen, providing electron acceptors for the anammox bacteria. However, the short-cut nitrification-anammox process still faces many challenges in practical applications. For example, the anammox bacteria must contend with the influence of dissolved oxygen present in the upstream short-cut nitrification process or the wastewater itself, making its practical application undoubtedly difficult.

[0004] Therefore, there is an urgent need to provide a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation (ANAO) under hypoxic conditions. By constructing a "short-range nitrification-ANAO" system under microaerobic conditions, and utilizing the synergistic mechanism of ammonia-oxidizing and anaerobic ammonia-oxidizing bacteria, rapid start-up and efficient operation of the ANAO system are achieved. This method can successfully achieve rapid start-up of ANAO within 40 days under microaerobic conditions and improve its operational efficiency within 20 days, overcoming the limitations of long start-up cycles and low operational efficiency of traditional ANAO systems, and improving engineering operability.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions, comprising the following steps:

[0008] S1. Inoculate the reactor with anaerobic ammonia oxidation sludge;

[0009] S2. Water is introduced into the reactor. The water has not been deoxygenated, and the ratio of ammonia nitrogen to nitrite nitrogen in the water is (1.5-2.5):1, with a hydraulic retention time of 3-3.9 h.

[0010] S3. Run the reactor until the total nitrogen removal efficiency in the reactor reaches 75% and remains stable for at least 14 days, while the ammonia nitrogen removal efficiency and nitrite nitrogen removal efficiency are both maintained above 90%, thereby achieving rapid start-up of anaerobic ammonia oxidation under low oxygen conditions.

[0011] S4. Adjust the hydraulic retention time to 2-2.9 hours and continue operating the reactor for no more than 20 days to improve the reactor's operating efficiency.

[0012] The regulation of the ammonia nitrogen:nitrite nitrogen ratio and hydraulic retention time is crucial for the initiation of anaerobic ammonium oxidation. An appropriate hydraulic retention time helps regulate the competitive relationship among ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and anaerobic ammonium-oxidizing bacteria. Furthermore, the ammonia nitrogen:nitrite nitrogen ratio directly affects the substrate supply for anaerobic ammonium-oxidizing bacteria; proper regulation can optimize the balance between electron donors and acceptors, promote the proliferation of anaerobic ammonium-oxidizing bacteria, and simultaneously avoid the inhibition of anaerobic ammonium-oxidizing bacteria by excess nitrite nitrogen, thereby improving the system's nitrogen removal performance.

[0013] In this invention, the inventors innovatively introduce a "short-cut nitrification-anaerobic ammonium oxidation" system into the rapid start-up process of anaerobic ammonium oxidation. Under hypoxic conditions, the anaerobic ammonium oxidizing bacteria and ammonia oxidizing bacteria in the anaerobic ammonium oxidation bacterial community cooperate by regulating the ammonia nitrogen:nitrite nitrogen ratio, oxidizing ammonium ions in wastewater into nitrite to supply the anaerobic ammonium oxidizing bacteria. Furthermore, as aerobic bacteria, the ammonia oxidizing bacteria can consume limited dissolved oxygen, thus creating the anoxic conditions required for the survival of anaerobic ammonium oxidizing bacteria. The method of this invention enables the rapid start-up of the anaerobic ammonium oxidation system under non-deoxygenated wastewater conditions and achieves stable and efficient operation, which is of great significance for the practical engineering application of anaerobic ammonium oxidation technology.

[0014] In some preferred embodiments of the present invention, the biomass concentration of the anaerobic ammonia oxidation sludge inoculated in the reactor, based on volatile solids concentration (VSS), is 0.5–5 g·L⁻¹. -1 For example, the dosage can be 0.5, 1, 2, 3, 4, or 5 g·L. -1 wait.

[0015] In some preferred embodiments of the present invention, the reactor is a continuously stirred reactor to ensure that the microbial community in the reactor is in full contact with the culture medium.

[0016] In some preferred embodiments of the present invention, the pH of the influent is 7.6 to 7.8, and for example, it can be 7.6, 7.7, 7.8, etc.; the water temperature of the influent is 20 to 28°C, and for example, it can be 20, 21, 22, 23, 24, 25, 26, 27, 28°C, etc.

[0017] In step S2 of this invention, the dissolved oxygen concentration in the influent is ≤0.29 mg·L. -1 For example, the values ​​can be 0, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, or 0.29 mg·L. -1 wait.

[0018] In step S2 of the present invention, the total nitrogen in the influent consists of ammonia nitrogen and nitrite nitrogen, wherein the ratio of ammonia nitrogen to nitrite nitrogen needs to be controlled at (1.5 to 2.5):1. For example, it can be 1.5:1, 2:1, 2.5:1, etc., preferably 2:1.

[0019] Furthermore, when the ratio of ammonia nitrogen to nitrite nitrogen is 2:1, the total nitrogen concentration in the influent is 60–150 mg·L⁻¹. -1 For example, the values ​​can be 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 mg·L. -1 The concentration of ammonia nitrogen in the influent is 40–100 mg / L. -1 For example, the values ​​can be 40, 50, 60, 70, 80, 90, or 100 mg·L. -1 The concentration of nitrite nitrogen in the influent is 20–50 mg / L. -1 For example, the concentrations can be 20, 30, 40, or 50 mg / L. -1 In some preferred embodiments of the present invention, when the ratio of ammonia nitrogen to nitrite nitrogen is 2:1, the total nitrogen concentration in the influent is 90 mg·L⁻¹. -1 The concentration of ammonia nitrogen was 60 mg·L⁻¹. -1 The concentration of nitrite nitrogen is 30 mg·L⁻¹. -1 .

[0020] Furthermore, the ratio of ammonia nitrogen to nitrite nitrogen in the influent can be adjusted by adding ammonia nitrogen and nitrite nitrogen to the influent. Specifically, ammonia nitrogen and nitrite nitrogen are added to the influent from the first day of reactor operation to control the ratio. In some specific embodiments, the ammonia nitrogen source is ammonium chloride, and the nitrite nitrogen source is sodium nitrite.

[0021] Furthermore, the influent can be simulated wastewater. In some preferred embodiments of the present invention, the influent contains NH4Cl, NaNO2, and C6H4Cl. 12 O6, CaCl2·2H2O, MgCl2·6H2O, KHCO3, NaH2PO4, trace element I stock solution and trace element II stock solution. The trace element I stock solution is prepared from EDTA·2Na and FeSO4·7H2O; the trace element II stock solution contains: MnCl2, ZnSO4·7H2O, CuSO4·5H2O, Na2MoO4·4H2O, H3BO3, CoCl2·6H2O, NiCl2·6H2O, and vitamin tablets.

[0022] In step S2 of the present invention, the hydraulic residence time of the incoming water needs to be controlled to be 3 to 3.9 hours. For example, it can be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 hours, etc., preferably 3.6 hours.

[0023] Furthermore, the anaerobic ammonia oxidation can be rapidly started within 40 days. That is, by controlling the ratio of ammonia nitrogen to nitrite nitrogen in the influent to (1.5-2.5):1 and adjusting the hydraulic retention time to 3-3.9 hours, the anaerobic ammonia oxidation reaction can be successfully started and stabilized within 40 days, achieving efficient nitrogen removal of the system.

[0024] Furthermore, in step S4, after the anaerobic ammonia oxidation reactor is rapidly started, the hydraulic retention time is adjusted to 2–2.9 hours, and the reactor continues to operate for no more than 20 days, thereby improving the reactor's operational efficiency. Here, improved operational efficiency refers to an increase in the system's nitrogen removal efficiency.

[0025] In this invention, after the rapid start-up of anaerobic ammonia oxidation, the hydraulic retention time needs to be adjusted to 2 to 2.9 hours. For example, it can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or 2.9 hours, preferably 2.4 hours.

[0026] In this invention, by optimizing the hydraulic retention time to 2–2.9 h, it is beneficial for ammonia-oxidizing bacteria to consume some ammonia nitrogen and convert it into nitrite nitrogen, ensuring sufficient substrate for the anammox reaction and achieving nitrogen balance. The shorter hydraulic retention time provides nutrients for the anammox bacteria, creating an environment suitable for their growth, thus improving operational efficiency.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This invention constructs a "short-cut nitrification-anaerobic ammonium oxidation" system under microaerobic conditions, utilizing the synergistic mechanism of ammonium-oxidizing and anaerobic ammonium-oxidizing bacteria to achieve rapid start-up and efficient operation of the anaerobic ammonium oxidation system. Within 40 days, the anaerobic ammonium oxidation reaction was successfully started and stabilized, achieving stable system operation and efficient nitrogen removal. This overcomes the limitations of the long start-up cycle of traditional anaerobic ammonium oxidation systems, improves engineering operability, and provides a more adaptable start-up strategy for practical applications.

[0029] 2. After the rapid start-up of anaerobic ammonia oxidation, this invention further improves the operating efficiency of the reactor within 20 days by optimizing the hydraulic retention time, ensuring efficient operation, enhancing the stability and adaptability of the anaerobic ammonia oxidation process, and broadening its application scope in wastewater treatment.

[0030] 3. Experiments have shown that the method of the present invention can effectively overcome the problem of slow growth of anaerobic ammonia-oxidizing bacteria, accelerate their enrichment, and significantly improve the denitrification performance of the system. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] In the following examples and comparative examples, the specific composition of the simulated wastewater used is as follows: ammonia nitrogen (prepared according to experimental requirements), nitrite nitrogen (prepared according to experimental requirements), and KHCO3 1500 mg·L⁻¹. -1 MgCl2·6H2O 1500mg·L -1 56 mg / L CaCl2·2H2O -1 NaH2PO4 10 mg·L -1 Trace element I and trace element II stock solutions were prepared, with water as the solvent. The composition of trace element I stock solution was: EDTA·2Na 5 g·L⁻¹ -1 FeSO4·7H2O 9.14 g·L -1 The composition of the trace element II stock solution is: MnCl2 0.63 g·L⁻¹ -1 ZnSO4·7H2O 0.43g·L -1 CuSO4·5H2O 0.219 g·L -1Na₂MoO₄·4H₂O 0.184 g·L⁻¹ -1 H3BO3 0.014 g·L -1 CoCl2·6H2O 0.228g·L -1 NiCl2·6H2O 0.195 g·L -1 Vitamin tablets 0.317g / L -1 .

[0034] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods, and the materials and reagents used are commercially available.

[0035] Experiment 1

[0036] This experiment provides a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under hypoxic conditions. The specific steps are as follows:

[0037] S1. A continuous stirred reactor with an effective volume of 1L was used. Mature anaerobic ammonia oxidizing sludge with a relative abundance of 7.14% for the anaerobic ammonia oxidizing bacteria *Candidatus Kuenenia*, 0.04% for the anaerobic ammonia oxidizing bacteria genus, and almost zero relative abundance for the ammonia oxidizing bacteria genus *Nitrosomonas* was used as the inoculum source. After inoculation, the biomass in the reactor, expressed as volatile solids concentration (VSS), was 1.20 g·L⁻¹. -1 .

[0038] S2. Four continuous stirred reactors, each with an effective volume of 1.0 L, were set up and named Y1, Y2, Y3, and Y4, respectively. Y1 served as the experimental group, while Y2, Y3, and Y4 served as control groups. Simulated wastewater without deoxygenation treatment was used as the influent, and the ratio of ammonia nitrogen to nitrite nitrogen in the influent was adjusted according to Table 1. The hydraulic retention time was controlled at 3.6 h, and the sludge was started up at 24℃ and influent pH = 7.6.

[0039] Table 1. Ratio and dosage of ammonia nitrogen and nitrite nitrogen in influent.

[0040]

[0041] (1) After 40 days of start-up culture, the average denitrification efficiency of Y1 was 80.27%, the ammonia nitrogen removal rate reached 93.09%, and the nitrite nitrogen removal rate reached 92.18%. The average denitrification efficiency of Y2 and Y4 was around 65%, with Y2 achieving an ammonia nitrogen removal rate of 73.12% and a nitrite nitrogen removal rate of 68.18%, and Y4 achieving an ammonia nitrogen removal rate of 82.37% and a nitrite nitrogen removal rate of 76.95%. The average denitrification efficiency of Y3 was 60.84%, with an ammonia nitrogen removal rate of 90.66% and a nitrite nitrogen removal rate of 86.47%. Since the denitrification efficiency of Y1 gradually increased and remained stable throughout the start-up culture period, it can be considered that the anaerobic ammonia oxidation start-up was successful. However, the total nitrogen denitrification efficiency of Y2, Y3, and Y4 fluctuated and continued to decline, which can be considered as the failure of the anaerobic ammonia oxidation start-up.

[0042] (2) On day 40, an ex-situ batch experiment was conducted on the sludge from the four reactors for 6 hours to detect the anaerobic ammonia oxidation activity and ammonia oxidation activity. The results showed that: Y1 achieved the highest total nitrogen removal rate of 75.46% and ammonia nitrogen removal rate of 93.09%; Y2 achieved a total nitrogen removal rate of 62.47% and ammonia nitrogen removal rate of 86.09%; while Y3 achieved a total nitrogen removal rate of only 53.52% and ammonia nitrogen removal rate of 68.09%; and Y4 achieved a total nitrogen removal rate of 63.85% and ammonia nitrogen removal rate of 85.20%.

[0043] Based on the average denitrification efficiency and the results of the ex-situ batch experiments, it can be demonstrated that the ratio of ammonia nitrogen to nitrite nitrogen is 2:1 (ammonia nitrogen concentration 60 mg·L⁻¹). -1 Nitrite nitrogen concentration 30 mg·L -1 When the anaerobic ammonia oxidation reaction in the reactor was started successfully.

[0044] (3) On day 40, the microbial community diversity of each reactor in (2) was analyzed by sequencing. The results are shown in Table 2.

[0045] Table 2. Relative abundance of various bacterial genera in the reactor.

[0046]

[0047] Referring to Table 2, compared to Y2, Y3, and Y4, the relative abundance of anaerobic ammonia oxidizing bacteria and ammonia oxidizing bacteria was more balanced in Y1. This indicates that, due to the presence of dissolved oxygen, increasing the influent substrate ratio (ammonia nitrogen:nitrite nitrogen ratio) promotes the activity of ammonia oxidizing bacteria, causing them to dominate the anaerobic ammonia oxidation system. This results in the production of excessive nitrite nitrogen, leading to nitrogen accumulation and an imbalance in the anaerobic ammonia oxidation reaction. However, when using a conventional influent substrate ratio, the activity of ammonia oxidizing bacteria is low, making it impossible for them to consume dissolved oxygen in the water, thus affecting the anaerobic ammonia oxidation reaction.

[0048] Therefore, through the optimization experiment of the influent ammonia nitrogen: nitrite nitrogen matrix ratio, it was demonstrated that anaerobic ammonia oxidation starts up rapidly when the ammonia nitrogen: nitrite nitrogen ratio is 2:1.

[0049] Experiment 2

[0050] This experiment provides a method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under hypoxic conditions. The specific steps are as follows:

[0051] Three continuous stirred reactors with an effective volume of 1 L were set up and named R1, R2, and R3, respectively. Anaerobic ammonia oxidation sludge from reactor Y1 was used as the inoculum source. After inoculation, the biomass in each reactor, expressed as volatile solids concentration (VSS), was 1.44 g·L⁻¹. -1 With a concentration of 60 mg / L -1 ammonia nitrogen and 30 mg·L -1 Simulated wastewater containing nitrite nitrogen without deoxygenation treatment was used as the influent. The reactor's operating efficiency was improved under the conditions of 24℃ and influent pH=7.6. Among them, R1 was the experimental group with a hydraulic retention time of 2.4h; R2 and R3 were the control groups with hydraulic retention times of 3.6h and 1.2h, respectively.

[0052] (1) After 20 days of operation, the average denitrification efficiency of R1 was 88.23%, that of R2 was 79.41%, and that of R3 was 71.26%. This indicates that when the hydraulic retention time is 2.4 h, ammonia-oxidizing bacteria can consume some ammonia nitrogen and convert it into nitrite nitrogen, so that the substrate for anaerobic ammonia oxidation reaction is sufficient and nitrogen balance is achieved. The shorter hydraulic retention time provides nutrients for anaerobic ammonia-oxidizing bacteria. However, the short hydraulic retention time has a significant impact on the survival of microorganisms in the reactor, resulting in a decrease in operating efficiency.

[0053] On day 20, a 6-hour ex-situ batch experiment was conducted on the sludge from the three reactors to detect the anaerobic ammonia oxidation (AAO) and ammonia oxidation (AO) activities. The results showed that R1 achieved the highest total nitrogen removal rate of 90.12% and ammonia nitrogen removal rate of 95.19%; R2 achieved a total nitrogen removal rate of 86.47% and ammonia nitrogen removal rate of 86.22%; while R3 achieved only 73.42% of total nitrogen removal and 69.84% of ammonia nitrogen removal. Therefore, it was concluded that the shorter the hydraulic retention time, the higher the AAO activity and the lower the AO activity. When the influent ammonia nitrogen to nitrite nitrogen ratio was 2:1 and the concentration remained constant, continuously increasing the hydraulic retention time increased the nitrogen load in the reactor, and the activity of AAO bacteria increased simultaneously. This indicates that the system environment was conducive to the growth of AAO bacteria, resulting in better treatment performance. This demonstrates that a hydraulic retention time of 2.4 hours significantly improved the reactor's operating efficiency.

[0054] In summary, this experiment achieved rapid start-up of anaerobic ammonia oxidation by controlling the influent ammonia nitrogen:nitrite nitrogen substrate ratio to 2:1, enabling the system to operate stably for 40 days. Simultaneously, optimizing the hydraulic retention time to 2.4 hours significantly improved the reactor's operating efficiency within 20 days. This invention not only provides a new research perspective and data support for the rapid start-up and stable operation of anaerobic ammonia oxidation in practical applications, but also provides a scientific basis for optimizing biological nitrogen removal process parameters and improving engineering applicability.

[0055] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions, characterized in that, Includes the following steps: S1. Inoculate the reactor with anaerobic ammonia oxidation sludge; S2. Water is introduced into the reactor. The water has not been deoxygenated and the ratio of ammonia nitrogen to nitrite nitrogen in the water is (1.5~2.5):1, with a hydraulic retention time of 3~3.9h. S3. Run the reactor until the total nitrogen removal efficiency in the reactor reaches 75% and remains stable for at least 14 days, while the ammonia nitrogen removal efficiency and nitrite nitrogen removal efficiency are both maintained above 90%, thereby achieving rapid start-up of anaerobic ammonia oxidation under low oxygen conditions; S4. Adjust the hydraulic retention time to 2~2.9 h and continue to operate the reactor for no more than 20 days, thereby improving the operating efficiency of the reactor; In step S2, the dissolved oxygen concentration in the influent is ≤0.29 mg·L⁻¹. -1 The pH of the influent is 7.6–7.8, and the water temperature is 20–28℃. In step S3, the anaerobic ammonia oxidation rapid start-up time shall not exceed 40 days.

2. The method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions according to claim 1, characterized in that, In step S1, the reactor is a continuous stirred reactor.

3. The method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions according to claim 1, characterized in that, In step S1, the biomass concentration of the anaerobic ammonia oxidation sludge inoculated into the reactor is 0.5–5 g·L⁻¹, calculated as volatile solids concentration (VSS). -1 .

4. The method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions according to claim 1, characterized in that, In step S2, the ratio of ammonia nitrogen to nitrite nitrogen in the influent is 2:1, and the hydraulic retention time is 3.6 h.

5. The method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions according to claim 1, characterized in that, In step S2, the total nitrogen concentration of the influent is 60–150 mg·L⁻¹. -1 The concentration of ammonia nitrogen is 40–100 mg·L⁻¹. -1 The concentration of nitrite nitrogen is 20–50 mg·L⁻¹. -1 .

6. The method for rapid start-up and improved operational efficiency of anaerobic ammonia oxidation under low-oxygen conditions according to claim 1, characterized in that, In step S4, the hydraulic residence time is adjusted to 2.4 h.

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