Method for advanced denitrification of low carbon-nitrogen ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation

Abstract

The present application relates to the field of wastewater treatment, and particularly relates to a method for advanced denitrification of low carbon-nitrogen ratio wastewater based on short-cut nitrification and denitrification and anaerobic ammonia oxidation, which establishes an activated sludge bioaugmentation system by adding biochar immobilized ZB403 strain into an SBR activated sludge system, and domesticates the activated sludge bioaugmentation system by adjusting the component and content of simulated wastewater and optimizing the operation conditions of the bioaugmentation system, and optimizes the biological community structure in the system. The activated sludge bioaugmentation system is used for treating low carbon-nitrogen ratio wastewater, the inorganic nitrogen removal rate is above 99%, the COD removal rate is above 97%, and the sludge yield coefficient Yobs is 0.27-0.29 kgVSS / kgCOD.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more particularly to a method for deep denitrification of wastewater with a low C / N ratio based on short-cut nitrification-denitrification and anaerobic ammonia oxidation. Background Technology

[0002] In recent years, with the rapid development of industry, a large amount of wastewater has been generated from production and daily life. If municipal sewage fails to meet discharge standards, it will adversely affect the water quality of receiving water bodies such as rivers and lakes. The current Urban Wastewater Discharge Standard (GB18918-2002) requires that the effluent quality of urban wastewater treatment plants meet the Class A standard, requiring total nitrogen to be less than 15 mg / L and ammonia nitrogen to be less than 5 mg / L. However, in the actual operation of wastewater treatment plants, due to changes in the quality and quantity of receiving wastewater, as well as the low carbon source content in the wastewater, the effluent quality fluctuates, making it difficult to meet nitrogen and phosphorus standards. Meanwhile, the carbon-to-nitrogen ratio in urban wastewater generally fluctuates between 3 and 5, while traditional biological denitrification requires 55 g COD / g N. Therefore, the limited carbon source in actual wastewater treatment leads to instability in biological wastewater treatment, incomplete ammonia nitrogen removal, and the need to add large amounts of easily degradable carbon sources for nitrification and denitrification, resulting in high operating costs and low efficiency in actual wastewater treatment. Therefore, how to efficiently and stably remove ammonia nitrogen from wastewater with a low carbon-to-nitrogen ratio has become a key issue that urgently needs to be addressed in biological wastewater treatment. Summary of the Invention

[0003] To overcome the above problems, the purpose of this invention is to provide a method for deep denitrification of low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation, which can achieve efficient denitrification of low C / N ratio wastewater.

[0004] To achieve the above objectives, the present invention provides a method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation, characterized by comprising the following steps:

[0005] (1) Preparation of biochar-coupled ZB403 strain complex:

[0006] A biochar-coupled ZB403 strain complex was prepared by mixing Citrobacter freundii ZB403 with biochar using an adsorption-immobilization method.

[0007] (2) Pre-acclimatization of activated sludge:

[0008] Activated sludge was inoculated into the SBR reactor and pre-acclimation simulated wastewater with a carbon-to-nitrogen ratio of 6 and an inorganic nitrogen concentration of 300 mg / L was injected to acclimate the activated sludge. The pre-acclimatization conditions were as follows: the SBR reactor operated for 24 hours, continuous aeration for 12 hours, and aeration stopped for 12 hours. The DO during the aeration phase was 3.0–4.0 mg / L, and the DO during the aeration stop phase was below 0.5 mg / L. The stirring rate was 400 ± 20 rpm. After the activated sludge stabilized, an activated sludge acclimatization system was formed.

[0009] (3) Establishment of activated sludge bio-enhancing system:

[0010] The biochar-coupled ZB403 strain complex obtained in step (1) was added to the activated sludge acclimatization system to form an activated sludge bio-enhanced system.

[0011] (4) Acclimation of the activated sludge bio-enhanced system:

[0012] The acclimation of the activated sludge bioaugmentation system is divided into three stages. The next stage is initiated after the system has stabilized in the previous stage. The operating conditions for all three stages are: a 24-hour operating cycle, 12 hours of continuous aeration, and 12 hours of aeration stoppage. The dissolved oxygen (DO) concentration (DO) during the aeration stage is 3.0–4.0 mg / L, and the DO concentration during the aeration stoppage stage is below 0.5 mg / L. The parameters of the simulated wastewater used for the acclimation of the activated sludge bioaugmentation system are as follows: [Parameters for the simulated wastewater used in the first stage of acclimation are not provided in the original text.] The carbon-to-nitrogen ratio in the first stage was 2.0, the inorganic nitrogen was ammonia nitrogen, the inorganic nitrogen concentration was 300 mg / L, and the COD concentration was 600 mg / L. In the second stage, the carbon-to-nitrogen ratio in the simulated wastewater was 1.5, the inorganic nitrogen was ammonia nitrogen, the inorganic nitrogen concentration was 300 mg / L, and the COD concentration was 450 mg / L. In the third stage, the carbon-to-nitrogen ratio in the simulated wastewater was 2.0, the inorganic nitrogen was a composite inorganic nitrogen source of ammonia nitrogen and nitrate, the total nitrogen concentration was 300 mg / L, and the COD concentration was 600 mg / L.

[0013] After three stages of acclimatization, the activated sludge bio-enhanced system is transformed into an activated sludge enhanced denitrification system.

[0014] (5) Using an activated sludge enhanced denitrification system to directly denitrify low carbon-to-nitrogen ratio wastewater: The low carbon-to-nitrogen ratio wastewater is directly injected into a reactor equipped with an activated sludge enhanced denitrification system for denitrification reaction. The low carbon-to-nitrogen ratio wastewater has a C / N ratio ≥ 2 and an inorganic nitrogen concentration ≤ 400 mg / L.

[0015] As a preferred embodiment, in step (1), the Citrobacter freundii has the accession number CCTCC No: M20221764, the depository is the China Center for Type Culture Collection (CCTCC), the culture name is Citrobacter freundii ZB 403, the deposit date is November 11, 2022, and the deposit address is Wuhan University, Wuhan, China.

[0016] As a preferred embodiment, in step (1), the preparation process of the biochar is as follows:

[0017] 1) Raw material selection: Use moso bamboo as raw material, and crush it to a particle size of 0.5-1mm;

[0018] 2) Pyrolysis: Under nitrogen protection, the temperature is increased to 500-600℃ at 10℃ / min and held at the temperature for 2-3 hours for continuous pyrolysis;

[0019] 3) Activation: Soak in H3PO4, then wash with NaOH solution until neutral, and then dry;

[0020] 4) Modification: The iron-modified biochar is formed by impregnation with FeCl3 solution for 10-14 hours and calcination.

[0021] As a preferred embodiment, in step (2), the carbon-to-nitrogen ratio of the simulated wastewater used for initial acclimatization to the activated sludge is 3-4:1 by volume; the components of the simulated wastewater used for initial acclimatization are: C4H4Na2O4·6H2O 10.125g / L, (NH4)2SO4 1.416g / L, NaHCO3 0.11g / L, KH2PO4 1.097g / L, MgSO4·7H2O 0.067g / L, MnSO4·H2O 0.0038g / L, CaCl2 0.006g / L, and trace amounts of FeSO4·7H2O, with an initial COD influent concentration of 1200mg / L.

[0022] As a preferred embodiment, in step (3), the amount of biochar coupled with ZB403 strain complex added is 1.0 to 2.0 g / L.

[0023] As a preferred embodiment, in step (4), during the three stages of acclimatization, the system temperature is 30–32°C, and the pH of the simulated wastewater used for acclimatization is 7.5–8.0. 30–32°C is the optimal temperature for anammox bacteria, which is conducive to their growth. By adding an appropriate amount of NaHCO3 to adjust the pH of the simulated wastewater to 7.5–8.0, the activity of nitrite-oxidizing bacteria (NOB) can be effectively inhibited.

[0024] As a preferred embodiment, in step (4),

[0025] The simulated wastewater used in the first stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 3.375 g / L, (NH4)2SO4 1.416 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 600 mg / L.

[0026] The simulated wastewater used in the second stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 2.531 g / L, (NH4)2SO4 1.416 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 450 mg / L.

[0027] The simulated wastewater used in the third stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 3.375 g / L, (NH4)2SO4 1.178 g / L, KNO3 0.361 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 600 mg / L.

[0028] As a preferred embodiment, in step (5), the denitrification conditions of the activated sludge biological enhancement system are as follows: an operating cycle of 24 hours, continuous aeration for 12 hours, and aeration stopped for 12 hours; the DO concentration during the aeration phase is 3.0–4.0 mg / L, and the DO concentration during the aeration stop phase is below 0.5 mg / L; the temperature is 29–31℃, and the pH is 7.0–7.5. Maintaining a temperature of 29–31℃ improves the removal of inorganic nitrogen from the wastewater. Additionally, maintaining a pH of 7.0–7.5 (generally 7–8) and keeping the alkalinity at 7.0–7.5 reduces the economic cost of adjusting alkalinity at wastewater treatment plants.

[0029] As a preferred embodiment, in step (5), the inorganic nitrogen is a composite nitrogen source, including ammonia nitrogen and nitrate.

[0030] As a preferred option, the activated sludge enhanced denitrification system is used to treat wastewater with a low carbon-to-nitrogen ratio. The inorganic nitrogen removal rate is over 99%, the COD removal rate is over 97%, and the sludge yield coefficient Yobs is 0.27-0.29 kgVSS / kgCOD.

[0031] The mechanism of this invention is as follows:

[0032] This invention employs a three-pronged deep denitrification strategy of "adsorption-mass transfer-microbial community regulation," utilizing a synergistic denitrification pathway of short-cut nitrification-anammox-denitrification. Specifically, this invention first establishes an activated sludge bio-enhanced system by adding biochar-immobilized ZB403 strain to the SBR activated sludge system. Then, by adjusting the composition and content of simulated wastewater and optimizing the operating conditions of the bio-enhanced system, the activated sludge bio-enhanced system is acclimatized to achieve activated sludge reduction and the activation and enrichment of short-cut nitrification / denitrification bacteria and anammox bacteria. During the denitrification process of domestic wastewater with a C / N ratio of 2-4 in the acclimatized activated sludge bio-enhanced system, during a 12-hour full aeration process (aerobic stage), the activated and enriched nitrifying bacteria and ZB403 strain in the acclimatized activated sludge undergo short-cut nitrification, utilizing the carbon source in the wastewater to reduce NH4+. + -N is converted to NO2 - -N and N2, the nitration reaction is controlled at nitrite (NO2) - -N) stage; then during the 12-hour aeration shutdown process (anaerobic stage), the anaerobic ammonia oxidizing bacteria (Anammox) and denitrifying bacteria activated and enriched in the acclimated activated sludge simultaneously carry out anaerobic ammonia oxidation and short-cut denitrification reactions. The anaerobic ammonia oxidation reaction uses NH4+ in the wastewater as the fuel. + -N is an electron donor, NO2 - -N acts as an electron acceptor to generate N2. The iron-modified biochar in the biochar-coupled HN-AD strain complex can act as an electron shuttle to accelerate the anaerobic ammonium oxidation reaction, thereby reducing unreacted NO2. - -N is further reduced to N2 through short-cut denitrification.

[0033] The advantages of this invention are as follows: Compared with the conventional invention, this invention has the following advantages:

[0034] (1) This invention establishes an activated sludge bio-enhanced system by adding biochar-immobilized ZB403 strain to the SBR activated sludge system. Furthermore, the activated sludge bio-enhanced system is acclimatized by adjusting the composition and content of the simulated wastewater and optimizing the operating conditions of the bio-enhanced system. This optimizes the biological community structure within the system, reduces sludge accumulation, and controls the nitrification process within the nitrite (NO2) range. -In the -N) stage, short-cut nitrification and denitrification are achieved.

[0035] (2) This invention employs intermittent aeration, specifically 12 hours of full aeration followed by 12 hours of aeration cessation. This intermittent aeration method couples short-cut denitrification and anaerobic ammonium oxidation. The activated sludge bio-enhancing system after acclimation treatment activates and enriches anaerobic ammonium oxidizing bacteria (Anammox) and denitrifying bacteria. Anaerobic ammonium oxidation promotes NH4+. + Electron donor, NO2 - -N acts as an electron acceptor to generate N2, which is NO2 produced from incomplete anaerobic ammonium oxidation. - -N is further reduced to N2 through short-cut denitrification.

[0036] (3) The activated sludge bio-enhanced system of the present invention has both short-cut nitrification and denitrification capabilities and anaerobic ammonia oxidation capabilities. Compared with the traditional activated sludge process, the activated sludge bio-enhanced system of the present invention has excellent denitrification capabilities. Especially for low C / N wastewater, the short-cut nitrification and denitrification process requires less organic carbon source in the denitrification stage, while the anaerobic ammonia oxidation process does not require any external carbon source. Combining the two processes can reduce the dependence on external carbon sources. For C / N ratios of 2 to 4, the denitrification efficiency is above 99%.

[0037] (4) The method for deep denitrification of low carbon-to-nitrogen ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation of the present invention has a sludge yield coefficient Yobs of 0.27-0.29 kgVSS / kgCOD compared with the traditional activated sludge method, and a sludge production rate coefficient of 0.34 kgVSS / kgCOD compared with the blank control activated sludge.

[0038] (5) The biochar-coupled HN-AD strain complex of the present invention uses iron-modified biochar. First, iron-modified biochar has excellent carbon source adsorption capacity. In the aerobic stage, it can quickly adsorb the carbon source in the wastewater onto the biochar-coupled HN-AD strain complex, which is conducive to the efficient nitrification reaction of the HN-AD strain in the biochar-coupled HN-AD strain complex, that is, to utilize the adsorbed carbon source to remove NH4 in the wastewater. + -N is converted to NO2 - -N and N2; secondly, iron-modified biochar enhances electron transport capacity and can act as an electron shuttle to accelerate anaerobic ammonium oxidation reaction, using NH4+ in wastewater. + -N is an electron donor, NO2 - -N is an electron acceptor that generates N2.

[0039] (6) The process of denitrification of low C / N wastewater using the activated sludge biological enhancement system of the present invention is simple. Traditional denitrification of low C / N wastewater requires pretreatment in an anaerobic reactor before entering the reactor for denitrification, which is very complicated and increases the treatment cost of wastewater treatment plants. The present invention directly adds low C / N wastewater to the activated sludge enhanced denitrification system for reaction without the need to transfer the reactor, which significantly reduces the cost of wastewater treatment. Attached Figure Description

[0040] Figure 1 This is a 2μm electron microscope scan image of the biochar in Example 1;

[0041] Figure 2 This is a 1 μm electron microscope scan image of the biochar from Example 1;

[0042] Figure 3 This is a schematic diagram of the SBR reactor in Example 2;

[0043] Figure 4 This is a diagram showing the horizontal distribution of phylum (a) in the communities of reactors R1 and R4 in Example 4;

[0044] Figure 5 This is a diagram showing the horizontal distribution of community genus (b) in reactors R1 and R4 in Example 4;

[0045] Figure 6 This is a graph showing the relative abundance of relevant nitrogen cycle genes in reactors R1 and R4 in Example 4;

[0046] Figure 7 This is a diagram of the nitrogen circulation pathway in reactor R4 in Example 4;

[0047] Figure 8 This is a graph showing the changes in ammonia nitrogen concentration in the influent and effluent of Example 5. Detailed Implementation

[0048] To better understand the present invention, the invention will be described in detail below with reference to the accompanying drawings and specific examples.

[0049] Example 1: Preparation of a biochar-coupled ZB403 strain complex using Citrobacter freundii immobilized in biochar.

[0050] The culture medium and its components used in this embodiment are:

[0051] LB medium: 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride;

[0052] Inorganic salt culture medium: 0.1 g / L KH2PO4, 1.133 g / L Na2HPO4·12H2O, 0.3 g / L NH4Cl, 0.04 g / L MgSO4·7H2O, 0.0045 g / L CaCl2, 0.005 g / L FeSO4·7H2O.

[0053] A method for preparing a biochar-coupled ZB403 strain complex, comprising the following steps:

[0054] (1) Preparation of bacterial culture: *Citrobacter freundii* (CCTCC No.: M20221764, deposited at the China Center for Type Culture Collection (CCTCC) on November 11, 2022, Wuhan University, Wuhan, China) was cultured on LB medium at 28℃ and 200 rpm for 24 h until the logarithmic growth phase. The bacterial culture was collected and centrifuged at 4℃ (5000 rpm) for 10 min. The supernatant was discarded, and the cells were washed three times with sterile water. The cells were then resuspended in physiological saline (0.9% sodium chloride solution) and the cell concentration was adjusted to OD600 = 5.0 (approximately 10). 9 The sample (CFU / mL) was stored at 4°C for later use. This Citrobacter freundii ZB403 has a high ammonia nitrogen degradation capacity with aerobic nitrification and heterotrophic denitrification capabilities. To simplify the description of Citrobacter freundii ZB403, the term "ZB403 strain" will be used instead of "Citrobacter freundii ZB403 strain" below.

[0055] (2) Preparation of biochar:

[0056] Raw material: Agricultural waste (bamboo), crushed to a particle size of 0.5-1mm;

[0057] Pyrolysis: Under nitrogen protection, the temperature was increased to 500℃ at 10℃ / min and held at the same temperature for 2 hours for continuous pyrolysis;

[0058] Activation: Soak in 1 mol / L H3PO4 for 24 h, then wash with 0.1 mol / L NaOH solution until neutral, and then dry at 80℃;

[0059] Modification: The biochar was impregnated with 0.1 mol / L FeCl3 solution for 12 h, with the mass ratio of biochar to FeCl3 solution controlled at 1:4. The mixture of biochar and FeCl3 solution was then heated to 700℃ under limited oxygen conditions and held for 1.5 h. Afterwards, it was washed with deionized water and dried at 80℃ for 24 h to obtain iron-modified biochar. The iron-modified biochar exhibits enhanced electron transport capacity, thus improving mass transfer efficiency in wastewater treatment.

[0060] The biochar obtained in this step was examined using electron microscopy. Figure 1 and Figure 2 As shown in the figure, the biochar obtained in this embodiment has a large number of pores on its surface, resulting in a high specific surface area (521.7 m²). 2 The abundant pore structure (pore size 1-3 mm) significantly improved the loading efficiency and metabolic activity of strain ZB403.

[0061] (3) Biochar-coupled ZB403 strain complex:

[0062] Add 5% (v / v) of the bacterial suspension obtained in step (1) and 3% (w / v) of the biochar obtained in step (2) to the inorganic salt culture medium. Incubate at 28°C and 200 rpm for 24 h for immobilization. Finally, filter the inorganic salt culture medium through a 0.15 μm nylon sieve to separate the biochar-coupled ZB403 strain complex. Wash with sterile water and store at 4°C for later use.

[0063] Example 2: Pre-acclimatization of activated sludge

[0064] (1) The activated sludge used in this embodiment was taken from the aeration tank of the wastewater treatment plant in Jiangxia District, Wuhan City. The activated sludge was washed and screened to remove large particulate impurities before use. The mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) of the inoculated sludge were 2.16 g / L and 1.73 g / L, respectively.

[0065] (2) Operation of the activated sludge denitrification system:

[0066] The experimental sequencing batch reactor (SBR reactor) was used, such as... Figure 3 As shown, the reactor is 24.5 cm high, with a bottom length and width of 16 cm, a volume of 3 L, and an effective volume of 1.8 L. The SBR reactor contains 1.8 L of simulated wastewater. The components of the simulated wastewater used for initial acclimatization are: C4H4Na2O4·6H2O 10.125 g / L (added according to a C / N ratio of 6), (NH4)2SO4 1.416 g / L (added according to NH4). + The following ingredients were added: -N concentration of 300 mg / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and FeSO4·7H2O in trace amounts. The initial COD influent concentration was 1200 mg / L.

[0067] Combination Figure 3 As shown, the SBR reactor has a sludge discharge port and an aeration head at the bottom, and a sampling port and an outlet on the side wall. The SBR reactor is equipped with a mechanical stirring device to thoroughly mix the activated sludge and simulated wastewater, and a gas flow meter is used to control the aeration rate. 600 mL of activated sludge is added to the SBR reactor. The SBR reactor operates on a 24-hour cycle, with continuous aeration for 12 hours and aeration stopped for 12 hours. During the aeration phase, the dissolved oxygen (DO) (mg / L) is 3.0–4.0, and during the aeration-stop phase, it is below 0.5 mg / L. The influent pH is controlled at 7.0–7.5, the temperature at 30–35℃, and the stirring speed at 400±20 rpm. Water samples are taken every 24 hours to measure the COD and NH4+ in the influent and effluent. + -N, NO3 - -N, NO2 - -N concentration, sludge samples were taken at the end of each stage of operation to measure sludge characteristic indicators. After 10 days, the various indicators of the activated sludge system (effluent inorganic nitrogen content, COD content, and activated sludge MLSS, MLVSS, SVI, EPS indicators) tended to stabilize, at which point the initial acclimatization process of activated sludge was completed.

[0068] Example 3: Establishment of an activated sludge bio-enhancing system

[0069] The biochar-coupled ZB403 strain complex obtained in Example 1 was added to the SBR activated sludge system after acclimatization in Example 2. The addition of the biochar-coupled ZB403 strain complex to bio-enhance the SBR activated sludge system resulted in a bio-enhanced activated sludge system. The specific addition ratio was: 1.8 L of simulated wastewater used for initial acclimatization, 600 mL of activated sludge, and 1.0 g / L of the biochar-coupled ZB403 strain complex.

[0070] Example 4: Acclimation of the Activated Sludge Bioenhanced System

[0071] The acclimation treatment of the bioaugmentation system specifically includes two aspects: adjusting the composition and content of components in the simulated wastewater (specifically, setting an appropriate initial ammonia nitrogen concentration in the simulated wastewater and adjusting the C / N ratio and inorganic nitrogen components during the acclimation process), and optimizing the operating conditions of the bioaugmentation system. The acclimation treatment of the bioaugmentation system aims to activate and enrich short-cut nitrification and denitrification bacteria and anaerobic ammonia-oxidizing bacteria in the activated sludge, as well as to reduce the volume of activated sludge. Specific acclimation parameters are shown in Table 1. Water samples were taken every 24 hours to measure COD, NH4+-N concentrations in the influent and effluent. At the end of each stage of operation, the COD removal rate and inorganic nitrogen removal rate data after the system stabilized were statistically analyzed, and sludge samples were taken to measure sludge characteristic indicators. The results are shown in Table 1.

[0072] Table 1. Acclimation of the activated sludge bio-enhanced system

[0073]

[0074]

[0075] Example 4 also included a blank control group: without the addition of biochar coupled with the ZB403 strain complex, the activated sludge SBR system acclimated in the early stages of Example 2 was run directly according to the parameters in Table 2, with the operating conditions identical to Example 4, to investigate the effect of bioaugmentation on the microbial community structure in the SBR system. For simplicity, the blank control group was named reactor R1, and in this Example 4, it was named reactor R4. Activated sludge samples from reactors R1 and R4 were extracted on days 53, 90, and 180 to detect changes in microbial community structure, combined with... Figure 4 and Figure 5 As shown, compared with the sludge from different stages of R1, the content of bacterial phyla that promote anaerobic ammonium oxidation was significantly increased in reactor R4. Furthermore, the sludge in reactor R4 contained most of the dominant microbial genera, demonstrating that the microbial activity and sludge activity in reactor R4 were better, and thus more conducive to short-cut nitrification, denitrification, and anaerobic ammonium oxidation. Combined with... Figure 6 and Figure 7 As shown, the nitrogen cycle pathway of the activated sludge bioaugmentation system can be seen, with NO3 added to the influent. - Following the -N designation, the abundance of the napA gene (nitrate reductase) significantly increased (0.46), driving NO3 uptake. - -N→NO2 - The conversion of -N. This process provides ample substrate for short-cut denitrification, increasing the abundance of the nirS gene (nitrite reductase) to 0.18, promoting NO2 conversion. - The reduction of N₂O into NO and then into N₂O was observed. Simultaneous expression of the norB gene (0.27) and the nosZ gene (0.09) indicated a near-complete denitrification chain, with N₂O being further reduced to N₂, thus reducing greenhouse gas emissions. The coupling of anaerobic ammonia oxidation with short-cut nitrification was also validated in gene expression, with restored ammonia-oxidizing bacteria (AOB) activity (amoC = 0.36), converting some NH₄⁺ into N₂. + -N is oxidized to NO2 - -N provides substrates for anaerobic ammonium oxidation. Figure 6 The expression of the hzs gene (hydrazine synthase) in AnAOB shows that AnAOB utilizes NH4+. + -N and NO2 - -N is converted into N2, achieving efficient nitrogen removal. Biochar adsorbs NO3- to form N2. - -N and NH4 +-N forms localized high-concentration areas, promoting the co-localization of short-cut denitrifying bacteria and AnAOB. ​​The conductivity of its Fe3O4-supported biochar accelerates electron transfer, enhancing the catalytic efficiency of napA and hzsB. This coupled pathway (short-cut nitrification-anaerobic ammonium oxidation) has low carbon source requirements, reducing dependence on full-process nitrification and effectively lowering the demand for influent carbon source content.

[0076] The calculation process for activated sludge reduction is as follows: According to the environmental protection technical document "Guidelines for Best Feasible Technologies for Pollution Prevention and Control in Sludge Treatment and Disposal of Urban Wastewater Treatment Plants (Trial) (HJ-BAT-002)", the output of residual activated sludge in wastewater treatment systems using the activated sludge process and its modified processes should be calculated using the following formula (1):

[0077]

[0078] In formula (1): ΔX2——remaining activated sludge amount, kg / d;

[0079] The ratio of f = MLVSS / MLSS is typically 0.5-0.75 for domestic sewage.

[0080] Lr = La-Le;

[0081] Lr — Organic matter concentration and degradation rate, kg / m³ 3 ;

[0082] La—Concentration of organic matter in reactor influent, kg / m³ 3 ;

[0083] Le—Concentration of organic matter in reactor effluent, kg / m³ 3 ;

[0084] V—Effective volume of the reactor; m 3；

[0085] Xv — Concentration of volatile organic compounds in the mixture, kg / m³ 3 ;

[0086] Q—Design average daily wastewater flow rate, kg / m³ 3 ;

[0087] a——Sludge production rate coefficient, kgVss / kgBOD5, usually taken as 0.5-0.65;

[0088] b—Sludge self-oxidation rate, kg / d, usually taken as 0.05-0.1.

[0089] Every 7 days, the MLSS and MLVSS of the activated sludge in the reactor were measured during the first stage (1-52 days), the second stage (53-90 days), and the third stage (91-180 days) of operation. The average values ​​were then taken, and the data are shown in Table 2. The amount of excess sludge was calculated using the formula above. The activated sludge enhanced denitrification system constructed using this invention can effectively reduce the yield of excess sludge. In this embodiment (reactor R4), the sludge yield coefficient (Yobs) is 0.28 kgVSS / kgCOD, which is 17.6% lower than the blank control activated sludge (reactor R1) (0.34 kgVSS / kgCOD), and can reduce excess sludge by a maximum of 17.37 kg / d.

[0090] Table 2 Activated sludge data for reactors R1 and R4

[0091] VSS / SS stage Lr La Le Xv △X2 0.934132 1 S1 0.2318 0.25 0.0182 3.34 124.072 0.991758 1 S4 0.2367 0.25 0.0133 3.64 119.3331 0.817708 2 S1 0.1875 0.1875 0 3.84 114.6491 0.784047 2 S4 0.1875 0.1875 0 5.14 119.5712 0.716475 3 S1 0.25 0.25 0 5.22 174.4644 0.77758 3 S4 0.24431 0.25 0.00569 5.62 157.0955

[0092] As can be seen from Example 4, the activated sludge enhanced denitrification system has a stronger multi-pathway synergistic denitrification capacity of "short-cut nitrification-anammox-denitrification". Among them, the Anammox pathway contributed 38% of the denitrification efficiency, while short-cut denitrification reduced carbon source consumption. In addition, biochar significantly improved the system's resistance to shock loads by adsorbing free ammonia and inhibiting the proliferation of filamentous bacteria. EPS remained stable at 154-200 mg / g, and MLSS remained at 5.0-5.4 g / L (decay rate <5%), which is >25% compared to the R1 blank control group. The activated sludge reduction effect is significant. Based on the sludge yield model calculation, the amount of residual sludge in the R4 reactor was reduced by 17.37 kg / d.

[0093] Example 5: Activated sludge enhanced denitrification system for deep denitrification of wastewater with a C / N ratio of 4 and inorganic nitrogen concentration of 300 mg / L.

[0094] The activated sludge enhanced denitrification system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 4 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 6.75 g / L (added according to a C / N ratio of 4), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The concentration of FeSO4·7H2O was trace at 0.006 g / L, and the influent COD concentration was 1200 mg / L. The SBR unit operated for 24 hours at a time for 10 days, with 30 minutes each for influent and effluent, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, repeating this cycle. The water exchange ratio was 100%. The aeration rate was adjusted to maintain DO at 3-5 mg / L during aeration, and the turbine speed was adjusted to maintain DO below 0.5 mg / L when aeration was stopped. The effluent quality and sludge settling performance were continuously monitored daily, combined with... Figure 8 As shown, the denitrification efficiency of this embodiment is stable at 100%. Due to the large number of effluent data and activated sludge graphs, in order to more intuitively demonstrate the denitrification performance of the embodiment, the effluent and activated sludge data of the following embodiment are presented in tabular form, as shown in Table 3 below.

[0095] Example 6: The acclimated activated sludge bio-enhanced system was used for deep denitrification of wastewater with a C / N ratio of 4 and inorganic nitrogen concentration of 400 mg / L.

[0096] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 4 and an inorganic nitrogen concentration of 400 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 6.75 g / L (added according to a C / N ratio of 4), (NH4)2SO4 1.888 g / L (added according to an NH4+-N concentration of 400 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0097] Example 7: The acclimated activated sludge bio-enhanced system was used for deep denitrification of wastewater with a C / N ratio of 3 and inorganic nitrogen concentration of 300 mg / L.

[0098] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 3 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 5.062 g / L (added according to a C / N ratio of 3), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR unit operated for 10 days, with a cycle of 24 hours for each influent and effluent, followed by 720 minutes of aeration and 720 minutes of aeration stoppage. The water exchange ratio was 100%. The aeration rate was adjusted to maintain DO at 3-5 mg / L during aeration and the turbine speed was adjusted to maintain DO below 0.5 mg / L when aeration was stopped. The effluent quality and sludge settling performance were continuously monitored daily, as shown in Table 3. Table 3 shows that the total nitrogen removal rate was 100%. In addition, the nitrite nitrogen accumulation rate, Anammox activity, and activated sludge reduction data were measured during the denitrification process. The nitrite nitrogen accumulation rate was stable at 90%, and the Anammox activity was 0.35 kgN / (m³). 3 ·d),

[0099] Example 8: The acclimated activated sludge bio-enhanced system was used for deep denitrification of wastewater with a C / N ratio of 2 and inorganic nitrogen concentration of 300 mg / L.

[0100] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 2 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 3.375 g / L (added according to a C / N ratio of 2), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0101] Example 9: The acclimated activated sludge bio-enhanced system was used for deep denitrification of wastewater with a C / N ratio of 2 and a combined inorganic nitrogen concentration of 300 mg / L.

[0102] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 2 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 3.375 g / L (added according to a C / N ratio of 2), (NH4)2SO4 1.178 g / L (added according to an NH4+-N concentration of 250 mg / L), KNO3 0.361 g / L (added according to an NO3-N concentration of 50 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0103] This embodiment introduces a composite nitrogen source (NH4). + -N+NO3 --N) to simulate the components of real wastewater, where TN in typical wastewater is in the form of ammonia nitrogen (NH4) + -N), nitrates (NO3) - The presence of nitrogen (NH4+) in the influent from a composite nitrogen source intensifies the competitive conversion of nitrogen forms within the system, placing higher demands on the performance of the denitrification system. This embodiment introduces a composite nitrogen source (NH4+). + -N+NO3 - After nitrogen removal (N), the nitrogen removal efficiency reaches 100%, demonstrating that the activated sludge bio-enhanced system of this invention has excellent adaptability to complex nitrogen-containing wastewater.

[0104] Comparative Example 1: The acclimated activated sludge bio-enhanced system was used for denitrification of wastewater with a C / N ratio of 1.5.

[0105] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 1.5 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 2.531 g / L (added according to a C / N ratio of 1.5), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0106] Comparative Example 2: The acclimated activated sludge bio-enhanced system was used for denitrification of wastewater with a C / N ratio of 1.

[0107] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 1 and an inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 1.688 g / L (added according to a C / N ratio of 1), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0108] Comparative Example 3: The acclimated activated sludge bio-enhanced system was used for denitrification of wastewater with a C / N ratio of 0.5.

[0109] The activated sludge bio-enhancing system obtained in Example 4 above was applied to the deep denitrification of wastewater with a C / N ratio of 0.5 and inorganic nitrogen concentration of 300 mg / L. The wastewater composition was as follows: C4H4Na2O4·6H2O 0.844 g / L (added according to a C / N ratio of 0.5), (NH4)2SO4 1.416 g / L (added according to an NH4+-N concentration of 300 mg / L), NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 The influent COD concentration was 1600 mg / L, with a trace amount of FeSO4·7H2O. The SBR device operated for 24 hours each time, for a total of 10 days. The influent and effluent were each for 30 minutes, followed by 720 minutes of aeration and then 720 minutes of aeration stoppage, and this cycle was repeated. The water exchange ratio was 100%. The aeration rate was adjusted to keep the DO at 3-5 mg / L during the aeration period, and the rotation speed was adjusted to keep the DO below 0.5 mg / L when aeration was stopped. The effluent water quality and sludge settling performance indicators were continuously monitored daily, as shown in Table 3 below.

[0110] Table 3. Effluent water quality and sludge settling performance indicators

[0111]

[0112]

[0113] Examples 5-9 show that the activated sludge enhanced denitrification system is effective for wastewater with low C / N ratio (C / N = 2.0-4.0) and high ammonia nitrogen (300 mg / L ≤ NH4). + -N≤400mg / L) exhibits excellent denitrification performance: NH4 + The nitrogen removal rate is consistently above 99%, the COD removal rate is ≥97%, and the total nitrogen (TN) removal efficiency is ≥99%. Furthermore, the sludge performance is stable (SVI ≤ 87 mL / g, EPS > 170 mg / g). The activated sludge bio-enhanced system of this invention exhibits excellent sludge reduction performance, with a sludge yield coefficient (Yobs) of 0.27–0.29 kgVSS / kgCOD, a 17.6% reduction compared to the control group's 0.34 kgVSS / kgCOD. Generally, a higher C / N ratio in wastewater leads to better bacterial growth; therefore, it is reasonable to deduce that a C / N ratio greater than 4.0 results in better nitrogen removal from the wastewater. As can be seen from Comparative Examples 1-3, the ammonia nitrogen removal efficiency of the system decreases significantly when the C / N ratio is less than 2. A C / N ratio of 1.5 exceeds the tolerance threshold of nitrifying bacteria. When the C / N ratio is less than 2, the denitrification process stalls due to insufficient carbon source, leading to nitrate accumulation and inhibiting the activity of nitrifying bacteria. In addition, under low C / N conditions, microorganisms may secrete more extracellular polymers (EPS) to cope with external stress, but the accumulation of these EPS can clog the pores of biochar and weaken the mass transfer efficiency. Therefore, the C / N ratio of wastewater has a significant impact on the nitrogen removal effect, and maintaining a C / N ratio above 2.0 is key to maintaining efficient nitrogen removal.

[0114] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonium oxidation, characterized in that, Including the following steps: (1) Preparation of biochar-coupled ZB403 strain complex: A biochar-coupled ZB403 strain complex was prepared by mixing Citrobacter freundii ZB403 with biochar using an adsorption-immobilization method. (2) Pre-acclimatization of activated sludge: Activated sludge was inoculated into the SBR reactor and pre-acclimation simulated wastewater with a carbon-to-nitrogen ratio of 6 and an inorganic nitrogen concentration of 300 mg / L was injected to acclimate the activated sludge. The pre-acclimatization conditions were as follows: the SBR reactor operated for 24 hours, continuous aeration for 12 hours, and aeration stopped for 12 hours. The DO during the aeration phase was 3.0–4.0 mg / L, and the DO during the aeration stop phase was below 0.5 mg / L. The stirring rate was 400 ± 20 rpm. After the activated sludge stabilized, an activated sludge acclimatization system was formed. (3) Establishment of activated sludge bio-enhancing system: The biochar-coupled ZB403 strain complex obtained in step (1) was added to the activated sludge acclimatization system to form an activated sludge bio-enhanced system. (4) Acclimation of the activated sludge bio-enhanced system: The acclimation of the activated sludge bioaugmentation system is divided into three stages. The next stage is initiated after the system has stabilized in the previous stage. The operating conditions for all three stages are: a 24-hour operating cycle, 12 hours of continuous aeration, and 12 hours of aeration stoppage. The dissolved oxygen (DO) concentration (DO) during the aeration stage is 3.0–4.0 mg / L, and the DO concentration during the aeration stoppage stage is below 0.5 mg / L. The parameters of the simulated wastewater used for the acclimation of the activated sludge bioaugmentation system are as follows: [Parameters for the simulated wastewater used in the first stage of acclimation are not provided in the original text.] The carbon-to-nitrogen ratio in the first stage was 2.0, the inorganic nitrogen was ammonia nitrogen, the inorganic nitrogen concentration was 300 mg / L, and the COD concentration was 600 mg / L. In the second stage, the carbon-to-nitrogen ratio in the simulated wastewater was 1.5, the inorganic nitrogen was ammonia nitrogen, the inorganic nitrogen concentration was 300 mg / L, and the COD concentration was 450 mg / L. In the third stage, the carbon-to-nitrogen ratio in the simulated wastewater was 2.0, the inorganic nitrogen was a composite inorganic nitrogen source of ammonia nitrogen and nitrate, the total nitrogen concentration was 300 mg / L, and the COD concentration was 600 mg / L. After three stages of acclimatization, the activated sludge bio-enhanced system is transformed into an activated sludge enhanced denitrification system. (5) Using an activated sludge enhanced denitrification system to directly denitrify low carbon-to-nitrogen ratio wastewater: The low carbon-to-nitrogen ratio wastewater is directly injected into a reactor equipped with an activated sludge enhanced denitrification system for denitrification reaction. The low carbon-to-nitrogen ratio wastewater has a C / N ratio ≥ 2 and an inorganic nitrogen concentration ≤ 400 mg / L.

2. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (1), the Citrobacter freundii ZB403 has the preservation number CCTCC No: M20221764 and is named Citrobacter freundii ZB 403.

3. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (1), the preparation process of the biochar is as follows: 1) Raw material selection: Use moso bamboo as raw material, and crush it to a particle size of 0.5-1mm; 2) Pyrolysis: Under nitrogen protection, the temperature is increased to 500-600℃ at 10℃ / min and held at the temperature for 2-3 hours for continuous pyrolysis; 3) Activation: Soak in H3PO4, then wash with NaOH solution until neutral, and then dry; 4) Modification: The activated biochar is impregnated with FeCl3 solution for 10-14 hours and then calcined to form iron-modified biochar.

4. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (2), the volume ratio of simulated wastewater to activated sludge used for initial acclimatization is 3-4:1; the components of the simulated wastewater used for initial acclimatization are: C4H4Na2O4·6H2O 10.125g / L, (NH4)2SO4 1.416g / L, NaHCO3 0.11g / L, KH2PO4 1.097g / L, MgSO4·7H2O 0.067g / L, MnSO4·H2O 0.0038g / L, CaCl2 0.006g / L, and trace amounts of FeSO4·7H2O, with an initial COD influent concentration of 1200mg / L.

5. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (3), the amount of biochar coupled with ZB403 strain complex added is 1.0 to 2.0 g / L.

6. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (4), during the three stages of acclimatization, the temperature of the system is 30-32℃, and the pH of the simulated wastewater used for acclimatization is 7.5-8.

0.

7. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (4), The simulated wastewater used in the first stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 3.375 g / L, (NH4)2SO4 1.416 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 600 mg / L. The simulated wastewater used in the second stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 2.531 g / L, (NH4)2SO4 1.416 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 450 mg / L. The simulated wastewater used in the third stage of acclimatization consisted of the following components: C4H4Na2O4·6H2O 3.375 g / L, (NH4)2SO4 1.178 g / L, KNO3 0.361 g / L, NaHCO3 0.11 g / L, KH2PO4 1.097 g / L, MgSO4·7H2O 0.067 g / L, MnSO4·H2O 0.0038 g / L, CaCl2 0.006 g / L, and trace amounts of FeSO4·7H2O. The initial COD concentration in the influent was 600 mg / L.

8. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (5), the denitrification conditions of the activated sludge bio-enhanced system are as follows: the operating cycle is 24h, continuous aeration is 12h, aeration is stopped for 12h, the DO during the aeration stage is 3.0~4.0mg / L, the DO during the aeration stop stage is below 0.5mg / L, the temperature is 29~31℃, and the pH is 7.0~7.

5.

9. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to claim 1, characterized in that, In step (5), the inorganic nitrogen is a composite nitrogen source, including ammonia nitrogen and nitrate.

10. The method for deep nitrogen removal from low C / N ratio wastewater based on short-cut nitrification-denitrification and anaerobic ammonia oxidation according to any one of claims 1 to 9, characterized in that, The activated sludge enhanced denitrification system was used to treat wastewater with a low carbon-to-nitrogen ratio. The inorganic nitrogen removal rate was over 99%, the COD removal rate was over 97%, and the sludge yield coefficient Yobs was 0.27–0.29 kgVSS / kgCOD.

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