Efficient denitrification method based on anaerobic ammonia oxidation process

Abstract

The invention relates to the technical field of biological sewage treatment, and discloses a high-efficiency denitrification method based on an anaerobic ammonia oxidation process, the method is operated based on a sequencing batch reactor, and the method comprises a composite conductive matrix construction step and a time sequence pulse maintenance operation step, the method comprises the following steps: firstly, adding ferroferric oxide and ferrous sulfide powder into a sludge mixed solution to construct a composite magnetic biological carrier; in the water inlet stage, local acid microenvironment construction, protective pulse activation and mainstream water inlet and in-situ reconstruction operation are sequentially executed. By controlling the pH value and the dosing sequence, the acidic environment is utilized to trigger ferrous sulfide to release reducing components so as to protect the hydroxylamine metabolism activator from being oxidized, and then the pH value is adjusted back by utilizing mainstream inlet water to induce dissolved ions to generate in-situ flocculation. According to the method, the utilization rate of the activating agent is effectively increased, the problems of carrier surface passivation and sludge loss are solved, and the denitrification efficiency and the operation stability of the system are remarkably enhanced.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, specifically to a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process. Background Technology

[0002] Anaerobic ammonia oxidation (AAO) technology, as a novel autotrophic nitrogen removal process, utilizes anaerobic ammonia-oxidizing bacteria to directly convert ammonia nitrogen and nitrite nitrogen into nitrogen gas under anaerobic conditions. It boasts significant advantages such as requiring no external organic carbon source, low sludge production, and low energy consumption. However, anaerobic ammonia-oxidizing bacteria are extremely slow-growing chemoautotrophic bacteria with long doubling times and are highly sensitive to changes in environmental conditions. In practical engineering applications, they often face challenges such as long start-up periods, weak resistance to shock loads, and susceptibility to instability under high loads. Therefore, it is urgent to improve the system's reaction rate and stability through exogenous enhancement methods.

[0003] Although adding conductive materials to construct a composite matrix can promote electron transfer, the carrier surface is easily passivated by inorganic precipitates or extracellular polymers during long-term operation, significantly weakening its conductivity. Simultaneously, under the hydraulic shearing action of the reactor, the structure of aged sludge is prone to loosening and disintegration, leading to the separation and loss of functional carriers from biomass, making it difficult to maintain a high concentration of activated sludge and limiting the increase in denitrification load.

[0004] Furthermore, while the addition of activators such as hydroxylamine can enhance metabolic activity, their chemically reactive nature makes them highly susceptible to abiotic oxidative decomposition under normal neutral or weakly alkaline conditions. This results in the agent being consumed by the environmental medium before it can penetrate into the cell, leading to extremely low bioavailability. Increasing the dosage to ensure effectiveness not only significantly increases operating costs but may also cause toxic inhibition of microorganisms due to excessively high local concentrations. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation (ANAO) technology. This method solves the problems of slow proliferation of functional bacteria and susceptibility to environmental fluctuations during long-term operation of existing ANAO processes, easy passivation of magnetic carrier surfaces leading to decreased electron transfer efficiency, low utilization rate of metabolic activators due to non-biological oxidation and decomposition under normal conditions, and loose structure of granular sludge that is easily lost.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process, which is based on sequencing batch reactor operation and includes a composite conductive matrix construction step and a time-sequential pulse maintenance operation step;

[0007] The composite conductive matrix construction steps include: adding iron oxide powder and ferrous sulfide powder to the anaerobic ammonia oxidation sludge mixture in the reactor, and using hydraulic shearing to form a composite magnetic biological carrier.

[0008] The time-series pulse maintenance operation steps include: during the influent phase of the sequencing batch reactor's operating cycle, sequentially performing the local acidic microenvironment construction operation, the protective pulse activation operation, and the mainstream influent and in-situ reconstruction operation;

[0009] In this process, by controlling the pH value of the influent and the order of chemical addition, an acidic environment is first created locally in the reactor to trigger the release of reducing components from ferrous sulfide. After adding hydroxylamine metabolic activators, the pH value of the mainstream influent is adjusted to induce in-situ flocculation of dissolved ions.

[0010] By employing the above technical solution, this invention utilizes the spatiotemporal characteristics of the SBR process and the chemical response mechanism of inorganic components to achieve in-situ repair and enhancement of the reaction system. The specific mechanism of action is as follows:

[0011] First, by utilizing the acid-sensitive properties of ferrous sulfide, a trace amount of acid dissolution is induced in the local acidic environment at the initial stage of water influent, releasing dissolved hydrogen sulfide and ferrous ions. Dissolved hydrogen sulfide has strong reducing properties and preferentially reacts with dissolved oxygen and oxidizing free radicals in the microenvironment, rapidly reducing the local redox potential and creating an instantaneous reducing protective environment.

[0012] Secondly, the pulsed injection of hydroxylamine metabolic activators (such as hydroxylamine sulfate) in the aforementioned reducing environment prevents hydroxylamine from being consumed by non-biological oxidation before entering the cells, allowing it to penetrate into the granular sludge in a highly active state and be captured by hydrazine synthase, thereby significantly improving the substrate metabolism rate of functional bacteria. At the same time, the acidic environment combined with reducing components can effectively reduce and strip the oxidized passivation layer on the surface of the iron oxide carrier, restoring its electron conduction activity.

[0013] Finally, by utilizing the alkalinity introduced by the subsequent mainstream influent, the pH value of the reactor naturally rises back to the weakly alkaline range, causing the previously dissolved ferrous ions and sulfide ions to exceed the solubility product constant and undergo reverse co-precipitation. The generated nascent ferrous sulfide microparticles and ferric colloids have a large specific surface area and adsorption activity. Through netting and bridging, they re-fix the free bacteria and small fragments onto the magnetic framework, realizing the online densification and reorganization of the physical structure of granular sludge.

[0014] Preferably, in the composite conductive matrix construction step, the mass ratio of the iron oxide powder to the ferrous sulfide powder is 5:1 to 10:1; the total amount of the composite magnetic biological carrier added is 5% to 10% of the dry weight of the suspended solids in the mixture in the reactor.

[0015] By adopting the above technical solution, the density of iron(III) oxide as the electronic framework is guaranteed, and an appropriate amount of acid-sensitive sulfur source is provided to avoid biological toxicity caused by excessive release of sulfides, or failure of the reduction protection function due to insufficient content.

[0016] Preferably, in the process of creating the localized acidic microenvironment, the reactor stirring device is stopped, and acidic liquid is pumped in through the bottom inlet of the reactor to control the local pH value of the sludge layer area at the bottom of the reactor to be 6.0 to 6.5.

[0017] By adopting the above technical solution, the diffusion of acidic liquid is limited by the static state of the fluid, and a micro-reaction zone is constructed only in the high-concentration sludge area at the bottom, thus achieving targeted acid washing of the carrier and avoiding the inhibition of the main microbial activity by the total mixed acid shock.

[0018] Preferably, the duration of the local acidic microenvironment construction operation is the first 3% to 8% of the water inlet cycle; the acidic liquid is prepared by mixing raw water and dilute sulfuric acid.

[0019] By adopting the above technical solution, the maintenance window of the acidic environment is limited, ensuring that ferrous sulfide has enough time to undergo phase transformation and release effective components, while preventing the hydrolysis of extracellular polymers or the shedding of biofilm caused by prolonged acid immersion.

[0020] Preferably, in the protective pulse activation operation, under the condition of maintaining a local acidic environment at the bottom, a hydroxylamine sulfate solution is injected into the bottom region in a pulse manner; the amount of hydroxylamine sulfate solution added is calculated based on the effective volume of the reactor, so that its theoretical final concentration in the reactor, expressed as nitrogen, is 2 mg / L to 5 mg / L.

[0021] By adopting the above technical solution and utilizing the aforementioned reducing protection mechanism, even extremely low concentrations of hydroxylamine can reach the effective intracellular activation threshold, significantly reducing drug costs and eliminating the potential inhibitory risk of high concentrations of hydroxylamine.

[0022] Preferably, the protective pulse activation operation is performed immediately after the local acidic microenvironment construction operation, and the pulse injection lasts for 1 to 3 minutes; during this period, hydrogen sulfide generated by the acidolysis of ferrous sulfide is used as a reducing barrier to protect hydroxylamine sulfate from oxidation.

[0023] By adopting the above technical solution, hydroxylamine is ensured to enter the system at the moment when its reducing power is strongest, thereby maximizing its bioavailability.

[0024] Preferably, in the main influent and in-situ reconstruction operation, the bottom influent and chemical dosing are stopped, the main influent system of the reactor is turned on and the stirring device is turned on, and raw water with a pH of 7.5 to 8.2 is pumped in at full speed; the alkalinity of the raw water is used to neutralize the acidic area at the bottom, so that the overall pH of the mixture in the reactor rises to 7.8 to 8.2 within 10 to 20 minutes, thereby inducing dissolved ferrous ions and sulfur ions to co-precipitate in situ.

[0025] By adopting the above technical solution, the acidic area can be naturally neutralized by the buffering capacity of the raw water itself, without the need for additional alkali solution; the gentle pH rise process is conducive to the formation of co-precipitated products with good crystallinity and excellent settling performance, further enhancing the mechanical strength of sludge particles.

[0026] Preferably, the particle size distribution of the iron oxide powder is 200 mesh to 400 mesh; and the particle size distribution of the ferrous sulfide powder is 100 mesh to 200 mesh.

[0027] By adopting the above technical solution, a multi-level porous structure is constructed using different particle sizes. The finer ferric oxide provides a larger specific surface area to promote electron transfer, while the coarser ferrous sulfide serves as a slow-release source that remains in the sludge for a long time.

[0028] Preferably, the method further includes a reaction stage, in which the reaction temperature is controlled at 30℃~35℃ and the dissolved oxygen concentration is lower than 0.1 mg / L after the water intake is completed, and the anaerobic ammonia oxidation denitrification reaction is carried out using the activated composite magnetic biological carrier.

[0029] By adopting the above technical solutions, a suitable metabolic environment is provided for the functional microbial community after cleaning, activation and reconstruction, ensuring continuous and efficient denitrification performance.

[0030] Preferably, before the composite conductive matrix construction step, a raw material premixing treatment is further included: iron oxide powder and ferrous sulfide powder are placed in a dry powder mixer and mechanically mixed at room temperature for 10 to 15 minutes to obtain a composite conductive medium dry powder with uniform color.

[0031] By adopting the above technical solution, the contact sites of the two inorganic components are increased, which is conducive to the formation of a composite carrier core with uniform composition during the subsequent biofilm formation process and prevents local performance differences caused by component separation.

[0032] This invention provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation. It has the following beneficial effects:

[0033] 1. This invention creates a locally acidic microenvironment during the influent stage, triggering the in-situ release of highly reducing hydrogen sulfide from ferrous sulfide, thus constructing a chemical protective barrier for the subsequent pulsed addition of hydroxylamine metabolic activators. This mechanism effectively inhibits the ineffective oxidative decomposition of hydroxylamine in non-intracellular processes, ensuring that it can penetrate into the granular sludge in a highly active state and be captured by hydrazine synthase, thereby significantly improving the metabolic activity and denitrification load of anaerobic ammonia-oxidizing bacteria at low dosages.

[0034] 2. This invention induces a reverse co-precipitation reaction between ferrous ions and sulfide ions released from the initial acidification process by controlling the pH rise caused by the main influent. The resulting nascent inorganic microparticles have high surface energy and can act as an in-situ binder to re-fix free bacteria and small fragments onto the magnetic framework, achieving online repair and densification of the granular sludge's physical structure. This effectively solves the problem of biomass loss under high hydraulic shear and improves the system's settling performance.

[0035] 3. This invention effectively removes the oxide passivation layer and inert metabolites accumulated on the surface of the iron oxide carrier through periodic acidic pulse cleaning, maintaining the unobstructed and active electron conduction interface. Combined with ferrous sulfide as an acid-responsive buffer, it avoids the inhibition of the host microorganisms by acid shocks, ensures the long-term stability of the electron transport channels, significantly extends the stable operating cycle of the reaction system, and enhances its resistance to shock loads. Attached Figure Description

[0036] Figure 1 This is a flowchart of the method of the present invention;

[0037] Figure 2 This is a comparison graph showing the change of dissolved ferrous ion concentration over time in the microenvironment at the bottom of the reactor between embodiments and comparative examples of the present invention.

[0038] Figure 3 This is a comparison graph showing the change of sulfide concentration over time in the microenvironment at the bottom of the reactor between embodiments and comparative examples of the present invention.

[0039] Figure 4 The following are the decay kinetic curves of hydroxylamine sulfate concentration over time in different microenvironment systems for the embodiments and comparative examples of the present invention;

[0040] Figure 5 This is a bar chart comparing the half-life of hydroxylamine sulfate in the embodiments and comparative examples of the present invention;

[0041] Figure 6 This is a graph showing the trend of total nitrogen removal rate over time during long-term operation of the embodiments and comparative examples of the present invention.

[0042] Figure 7 The figures show a comparison of sludge biological activity and key enzyme activity under long-term operating conditions between the embodiments and comparative examples of the present invention. (a) is a graph showing the change in anaerobic ammonia oxidation activity, (b) is a graph showing the change in the activity of the key enzyme hydrazine synthase, and (c) is a graph showing the change in the activity of the electron transport system.

[0043] Figure 8 This is a comparative diagram showing the correlation between sludge settling performance and EPS component characteristics in the embodiments and comparative examples of the present invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products:

[0046] Iron(III) oxide (Fe3O4), commercially available industrial-grade powder, CAS No. 1317-61-9, purity ≥90%, particle size distribution between 200 mesh and 400 mesh, is used as the electron conduction framework and magnetic carrier core in this invention.

[0047] Ferrous sulfide (FeS), commercially available industrial-grade powder, CAS No. 1317-37-9, with a purity ≥95% and a particle size distribution between 100 mesh and 200 mesh, is used as a pH-responsive redox buffer and in-situ iron source in this invention.

[0048] Hydroxylamine sulfate ((NH2OH)2·H2SO4), commercially available industrial-grade crystalline powder, CAS No. 10039-54-0, purity ≥98%, is prepared into an aqueous solution with a mass concentration of 30%-50% with deionized water before use, and is used as a metabolic activator and cleaning and reducing agent in this invention.

[0049] The inoculated sludge was taken from anaerobic ammonia oxidation granular sludge from an urban wastewater treatment plant. The sludge concentration (MLSS) was approximately 3000–5000 mg / L, the ratio of volatile suspended solids concentration (MLVSS) to MLSS was approximately 0.7–0.8, and the specific anaerobic ammonia oxidation activity (SAA) was approximately 0.3–0.5 kgN / (kgVSS·d). The experimental water was simulated high ammonia nitrogen wastewater prepared from ammonium chloride and sodium nitrite, with an influent total nitrogen concentration of 200–800 mg / L and a pH value adjusted to 7.5–8.2.

[0050] Preparation Example 1:

[0051] This preparation example provides a method for preparing an iron-based composite magnetic biological carrier, including the following steps:

[0052] Raw material weighing and premixing: Accurately weigh industrial grade iron tetroxide (Fe3O4) powder and ferrous sulfide (FeS) powder, put them into a dry powder mixer at a mass ratio of 8:1, and mechanically mix them at room temperature for 10 to 15 minutes until the color is uniform when observed with the naked eye, to obtain composite conductive medium dry powder.

[0053] Inoculation and addition: In the sequencing batch reactor (SBR) containing anaerobic ammonia oxidation granular sludge, the mixed liquor suspended solids concentration (MLSS) in the reactor is measured. The aforementioned composite conductive medium dry powder is weighed at 8% of the dry weight of MLSS and added directly to the reactor mixture in one go.

[0054] In-situ biofilm formation: Start the reactor stirring device and set the speed to 150-180 rpm. Under the conditions of temperature 33±2℃ and pH 7.8-8.2, maintain the reactor in the conventional influent-reaction-drainage mode for 48-72 hours. This allows the composite conductive medium dry powder and anaerobic ammonia oxidation granular sludge to complete self-assembly under the hydraulic shear and extracellular polymer (EPS) adhesion, thus obtaining an iron-based composite magnetic biological carrier.

[0055] Preparation Example 2:

[0056] This preparation example provides a method for preparing an iron-based composite magnetic biological carrier, including the following steps:

[0057] Raw material weighing and premixing: Accurately weigh industrial grade iron tetroxide (Fe3O4) powder and ferrous sulfide (FeS) powder, put them into a dry powder mixer at a mass ratio of 10:1, and mix them evenly to obtain composite conductive dielectric dry powder.

[0058] Inoculation and addition: The aforementioned composite conductive medium dry powder is added to the sequencing batch reactor (SBR) containing anaerobic ammonia oxidation granular sludge in a single batch at a ratio of 5% of the dry weight of MLSS.

[0059] In-situ biofilm formation: Start the reactor stirring device and set the speed to 150 rpm. Under the conditions of temperature 33±2℃ and pH 7.8~8.2, maintain the reactor in circulation for 48 hours, so that the composite conductive medium dry powder and anaerobic ammonia oxidation granular sludge can complete self-assembly under hydraulic shear and bioadhesion to obtain iron-based composite magnetic biological carrier.

[0060] Preparation Example 3:

[0061] This preparation example provides a method for preparing an iron-based composite magnetic biological carrier, including the following steps:

[0062] Raw material weighing and premixing: Accurately weigh industrial grade iron tetroxide (Fe3O4) powder and ferrous sulfide (FeS) powder, put them into a dry powder mixer at a mass ratio of 5:1, and mix them evenly to obtain composite conductive dielectric dry powder.

[0063] Inoculation and addition: The aforementioned composite conductive medium dry powder is added to the sequencing batch reactor (SBR) containing anaerobic ammonia oxidation granular sludge in a single batch at a ratio of 10% of the dry weight of MLSS.

[0064] In-situ biofilm formation: Start the reactor stirring device and set the speed to 150 rpm. Under the conditions of temperature 33±2℃ and pH 7.8~8.2, maintain the reactor in circulation for 48 hours, so that the composite conductive medium dry powder and anaerobic ammonia oxidation granular sludge can complete self-assembly under hydraulic shear and bioadhesion to obtain iron-based composite magnetic biological carrier.

[0065] Preparation Example 4:

[0066] This preparation example provides a method for preparing an iron-based composite magnetic biological carrier, including the following steps:

[0067] Raw material weighing and premixing: Accurately weigh industrial grade iron tetroxide (Fe3O4) powder and ferrous sulfide (FeS) powder, put them into a dry powder mixer at a mass ratio of 5:1, and mix them evenly to obtain composite conductive dielectric dry powder.

[0068] Inoculation and addition: The aforementioned composite conductive medium dry powder is added to the sequencing batch reactor (SBR) containing anaerobic ammonia oxidation granular sludge in a single addition at a ratio of 3% of the dry weight of MLSS.

[0069] In-situ biofilm formation: Start the reactor stirring device and set the speed to 150 rpm. Under the conditions of temperature 33±2℃ and pH 7.8~8.2, maintain the reactor in circulation for 48 hours, so that the composite conductive medium dry powder and anaerobic ammonia oxidation granular sludge can complete self-assembly under hydraulic shear and bioadhesion to obtain iron-based composite magnetic biological carrier.

[0070] Example 1:

[0071] Reference Appendix Figure 1 This embodiment provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process.

[0072] The iron-based composite magnetic biological carrier prepared in Example 1 was used to construct the reaction system. The reactor was a sequencing batch reactor (SBR), and the operating temperature was controlled at 33°C.

[0073] During the influent stage of the SBR reactor, the first step is to construct a local acidic microenvironment: the agitator is turned off to allow the fluid inside the reactor to remain still. A mixture of raw water and dilute sulfuric acid is pumped in through a micro-influent system at the bottom of the reactor, with the influent volume accounting for 5% of the total influent volume for this cycle. The amount of acid added is adjusted to stabilize the local pH value of the sludge layer area at the bottom of the reactor at 6.2. This process lasts for 5 minutes, using the weakly acidic environment to trigger the trace release of hydrogen sulfide and ferrous ions from ferrous sulfide.

[0074] The protective pulse activation step is then performed: with the stirrer off, hydroxylamine sulfate solution is rapidly pulsed into the acidified bottom area through the bottom micro-injection system for 2 minutes. The dosage is controlled so that the theoretical final concentration of hydroxylamine sulfate in the entire reactor is 3 mg / L (as N). During this process, the released hydrogen sulfide preferentially consumes the oxidant in the environment to protect hydroxylamine and assist in cleaning the carrier surface.

[0075] Finally, the main influent and in-situ reconstruction steps are carried out: the agitator is turned on and the speed is set to 150 rpm, while the bottom influent is stopped and the main influent system in the upper part of the reactor is switched to pump in conventional raw water with a pH of 7.8 at full speed. The alkalinity of the raw water is used to neutralize the acidic area at the bottom, so that the overall pH of the mixed liquid in the reactor naturally rises to 8.0 within 15 minutes. As the pH rises, dissolved iron ions and sulfur ions undergo in-situ co-precipitation, which strengthens the sludge floc structure.

[0076] After the water intake is completed, the anaerobic ammonia oxidation reaction stage begins, with a reaction time of 4 hours. After the reaction is completed, stirring is stopped, and the mixture is allowed to settle for 30 minutes before the supernatant is discharged.

[0077] Example 2:

[0078] This embodiment provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process.

[0079] The reaction system was constructed using the iron-based composite magnetic biological carrier (high magnetic skeleton ratio) prepared in Example 2. The reactor was a sequencing batch reactor (SBR), and the operating temperature was controlled at 33℃.

[0080] During the influent stage of the SBR reactor, the agitator is first turned off to maintain fluid stillness. A mixture of raw water and dilute sulfuric acid is pumped in through the micro-influent system at the bottom of the reactor. The influent volume accounts for 4% of the total influent volume for this cycle. The acid addition is precisely adjusted to lower the local pH value of the sludge layer area at the bottom of the reactor and maintain it at 6.0. This process lasts for 5 minutes. The lower pH value promotes the dissolution of low-content FeS.

[0081] While maintaining a static state, hydroxylamine sulfate solution is pulsedly injected into the bottom region through a bottom micro-injection system. The pulse injection duration is 1 minute. The injection amount is controlled so that the theoretical final concentration of hydroxylamine sulfate in the entire reactor is 2 mg / L (calculated as N). The activity of low-dose hydroxylamine is ensured by utilizing a locally high concentration of reducing protective layer.

[0082] Then, the agitator was turned on and the speed was set to 150 rpm. The bottom liquid inlet was stopped, and the main water inlet system was turned on to pump in raw water with a pH of 8.0, so that the overall pH of the mixture in the reactor would rise to 7.9 within 12 minutes, completing the reorganization of the floc structure.

[0083] After the water intake is completed, the reaction stage begins. Dissolved oxygen is controlled to be below 0.1 mg / L, and the reaction time is 4 hours. After sedimentation for 30 minutes, the water is drained.

[0084] Example 3:

[0085] This embodiment provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process.

[0086] The reaction system was constructed using the iron-based composite magnetic biological carrier (high functional component ratio) prepared in Example 3. The reactor was a sequencing batch reactor (SBR), and the operating temperature was controlled at 35°C.

[0087] During the influent stage of the SBR reactor, the agitator is turned off, and a mixture of raw water and dilute sulfuric acid is pumped in through the micro-influent system at the bottom of the reactor. The influent volume accounts for 5% of the total influent volume in this cycle. Since the FeS content in the carrier is high, the acid addition is adjusted to maintain the local pH value of the sludge layer area at the bottom of the reactor at 6.5 to meet the release requirements. This process lasts for 5 minutes.

[0088] While maintaining a static state, hydroxylamine sulfate solution was pulsedly injected into the bottom region through a bottom micro-injection system for 3 minutes. The injection rate was increased to achieve a theoretical final concentration of hydroxylamine sulfate in the entire reactor of 5 mg / L (calculated as N), thereby achieving deep activation of bacterial metabolic activity.

[0089] Then, the agitator was turned on and the speed was gradually increased to 180 rpm. The bottom liquid inlet was stopped, and raw water with a pH of 8.2 was quickly pumped in through the main water inlet system. By using strong hydraulic shear and the process of the pH rising back to 8.1 within 18 minutes, not only was chemical flocculation achieved, but the loose and aged biofilm was also further removed.

[0090] After the water intake is completed, the reaction stage begins, which lasts for 3 hours. After settling for 20 minutes, the water is drained.

[0091] Example 4:

[0092] This embodiment provides a highly efficient nitrogen removal method based on anaerobic ammonia oxidation process.

[0093] The iron-based composite magnetic biological carrier prepared in Example 1 was used to construct the reaction system. The reactor was a sequencing batch reactor (SBR), and the operating temperature was controlled at 33°C.

[0094] During the influent stage of the SBR reactor, the agitator is turned off, and a mixture of raw water and dilute sulfuric acid is pumped in through the micro-influent system at the bottom of the reactor to increase the bottom influent proportion to 8% of the total influent volume for this cycle. The acid addition is adjusted to maintain the local pH value of the expanded sludge layer at the bottom of the reactor at 6.2. This process lasts for 8 minutes to create a larger volume of acidic plug flow region and increase the contact time between the carrier and the acidic environment.

[0095] While maintaining a static state, hydroxylamine sulfate solution is pulsedly injected into the bottom region through the bottom micro-injection system. The pulse injection duration is 2 minutes, and the injection amount is controlled so that the theoretical final concentration of hydroxylamine sulfate in the entire reactor is 3 mg / L (calculated as N).

[0096] Then, turn on the stirrer to 150 rpm, stop the bottom inlet, and turn on the main inlet water system to pump in raw water with a pH of 7.8. Since the bottom acidic volume is large, control the main inlet water flow rate so that the overall pH of the mixture in the reactor rises back to 8.0 within 20 minutes.

[0097] After the water intake is completed, the reaction stage begins, which lasts for 4 hours. After settling for 30 minutes, the water is drained.

[0098] Comparative Example 1:

[0099] Compared with Example 1, the difference is that this comparative example is a blank control group without any enhancement measures. Specifically, no iron(III) oxide (Fe3O4) and ferrous sulfide (FeS) composite carrier were added to the reaction system, which only contained an equal amount of ordinary anaerobic ammonia oxidation granular sludge; and during operation, no local acidic microenvironment was constructed or hydroxylamine sulfate was pulsedly added, and the conventional SBR influent and reaction mode were always maintained, with all other aspects remaining the same.

[0100] Comparative Example 2:

[0101] Compared to Example 1, the difference lies in the omission of the key component ferrous sulfide (FeS). Specifically, only iron(III) oxide (Fe3O4) is used as the single carrier in the preparation process, without the addition of ferrous sulfide; in the operation process, although the local acidification and hydroxylamine sulfate addition steps are performed in the same way, due to the lack of FeS acidolysis buffer, it is impossible to build a high concentration of reducing sulfur barrier locally, while the rest are the same.

[0102] Comparative Example 3:

[0103] Compared to Example 1, the difference lies in the omission of the key metabolic activator hydroxylamine sulfate. Specifically, in the protective pulse activation step, only an equal volume of deoxygenated deionized water was pulsed in to simulate hydraulic disturbance, without the addition of hydroxylamine sulfate, thus relying solely on physical cleaning and FeS chemical action for operation; all other steps remained the same.

[0104] Comparative Example 4:

[0105] Compared to Example 1, the difference lies in the omission of the local acidic microenvironment construction step (i.e., no pH differential). Specifically, dilute sulfuric acid is not pumped in during the influent stage; instead, an equal dose of hydroxylamine sulfate is added directly under a normal pH environment (pH 7.8). Due to the lack of an acidic environment to drive the process, FeS cannot effectively release ferrous ions and hydrogen sulfide, and hydroxylamine is directly exposed to a non-acidic oxidizing environment. All other aspects remain the same.

[0106] Comparative Example 5:

[0107] Compared to Example 1, the difference lies in the use of a soluble sulfur source instead of solid ferrous sulfide (FeS). Specifically, FeS is not added during carrier preparation, but in the pulse activation step, an additional sodium sulfide (Na2S) solution with the same molar sulfur content as FeS in Example 1 is added; the dosage is controlled so that the theoretical initial concentration of sulfur ions in the reactor is 15 mg / L (aimed at simulating the sulfide level released by FeS under acidic conditions in Example 1). Since Na2S is a fast-soluble strong reducing agent, it cannot achieve the slow release and in-situ acid response function of solid FeS, but everything else is the same.

[0108] Comparative Example 6:

[0109] Compared to Example 1, the difference lies in the change of the process sequence (the order of chemical addition is reversed). Specifically, the operation sequence of first acidifying and then adding the chemical followed by the return of the feed water is cancelled. Instead, the main feed water is added first, and after the pH in the reactor naturally rises to 8.0, the same amount of hydroxylamine sulfate is added to the system. At this point, the system is already in an alkaline environment, thus missing the surface cleaning and protection window under acidic conditions. Everything else is the same.

[0110] Test Example 1: FeS Response and Component Release Characteristics Test under Locally Acidic Environment

[0111] This test case aims to verify the material rheological process of the pH-responsive release and reducing protection mechanism described in this invention in actual processes.

[0112] Experimental steps:

[0113] Three groups of SBR reactors with stable operation were selected, corresponding to Example 1 (Fe3O4 / FeS support + local acidification process), Comparative Example 4 (Fe3O4 / FeS support + conventional pH process) and Comparative Example 2 (single Fe3O4 support + local acidification process).

[0114] A rapid sampling tube is pre-installed at the center of the sludge layer at the bottom of each reactor (5 cm from the bottom plate), and the end of the sampling tube is connected to a vacuum sampling device with a 0.45 μm filter membrane.

[0115] Each reactor group simultaneously entered the water inlet stage. In Example 1 and Comparative Example 2, the bottom micro-acid inlet system was turned on to control the bottom pH to be maintained within the preset acidic range (pH 6.0-6.2). After 5 minutes, the acid inlet was stopped and the main inlet was switched (pH adjustment). Comparative Example 4 did not introduce acid and maintained a neutral environment throughout the process.

[0116] Taking the acid initiation start time as 0, 5 mL of mixed solution sample is extracted from the bottom sampling tube every minute within the first 10 minutes.

[0117] Solid-liquid separation was performed immediately after sample collection. The supernatant was divided into two portions: one portion was treated with zinc acetate for fixation of sulfides (S). 2- / HS - The determination of ferrous ions (Methylene blue spectrophotometry) was performed using a separate sample containing hydroxylamine hydrochloride and o-phenanthroline chromogenic reagent. 2+ ) Determination (o-phenanthroline spectrophotometric method).

[0118] Experimental data:

[0119] Table 1. Dynamic changes in ion concentration in the bottom microenvironment of different systems during the water influent stage.

[0120] Time (min) <![CDATA[Example 1 Fe 2+ (mg / L)]]> <![CDATA[Example 1 S 2- (mg / L)]]> <![CDATA[Comparative Example 4 Fe 2+ (mg / L)]]> <![CDATA[Comparative Example 4 S 2- (mg / L)]]> <![CDATA[Comparative Example 2 Fe 2+ (mg / L)]]> <![CDATA[Comparative Example 2 S 2- (mg / L)]]> Remark 0 0.12 0.05 0.15 0.04 0.11 0.03 initial state 1 5.34 2.11 0.14 0.04 0.42 0.03 Acidification begins 2 18.76 6.89 0.16 0.05 0.85 0.04 3 22.45 11.23 0.13 0.06 1.24 0.03 4 28.82 14.56 0.15 0.04 1.56 0.05 peak region 5 26.10 13.44 0.14 0.05 1.88 0.04 Stop acid feeding 6 22.34 7.65 0.16 0.05 1.92 0.03 pH adjustment begins 7 8.56 2.89 0.15 0.04 1.76 0.04 Rapid sedimentation 8 2.11 0.54 0.14 0.05 1.65 0.03 9 0.45 0.12 0.13 0.04 1.54 0.04 10 0.18 0.06 0.15 0.05 1.48 0.03 Return to normal

[0121] Conclusion Analysis:

[0122] Based on the test data in Table 1, refer to the appendix. Figure 2 -Appendix Figure 3 In Example 1, dissolved Fe was detected during the local acidification phase lasting 0–5 minutes. 2+ With S 2- The concentration increased exponentially in a synchronous manner, reaching its peak at around the 4th minute (Fe). 2+ Approximately 41.82 mg / L, S 2- (Approximately 14.56 mg / L). In contrast, although Comparative Example 4 contained the same FeS component, its ion concentration remained at an extremely low background level (<0.2 mg / L) due to the lack of acidic excitation conditions, confirming the chemical stability of ferrous sulfide under normal neutral pH conditions and indicating that its release process is pH-dependent. Although Comparative Example 2 constructed an acidic environment, only trace amounts of Fe were detected due to the lack of an FeS source. 2+ Increased levels (originating from trace acid dissolution of Fe3O4 or endogenous release from sludge), with almost no detectable S. 2- This confirms that the high concentration of reducing components does indeed originate from the acidolysis of FeS.

[0123] During the 5-10 minute phase, as the acidic influent stopped and the mainstream alkaline raw water was introduced, the Fe in Example 1... 2+ With S 2-The concentration rapidly decreased to the initial level. This rapid formation and rapid disappearance dynamic characteristic verifies the in-situ reconstruction mechanism proposed in this invention: that is, during the pH adjustment process, the dissolved iron and sulfur exceeded the solubility product constant (Ksp), resulting in a reverse co-precipitation reaction. This process not only eliminates the potential risk of iron and sulfur loss in the effluent, but also, through adsorption bridging, the nascent FeS particles and iron colloids generated during the precipitation process re-fix the free sludge under the impact of the influent onto the magnetic framework, achieving online repair of the physical structure. Simultaneously, the high concentration of S formed in the 2nd to 5th minutes... 2- The microenvironment provided a reducing barrier sufficient to consume the surrounding dissolved oxygen for the subsequently added hydroxylamine, verifying the feasibility of constructing an in-situ reducing barrier.

[0124] Test Example 2: Stability and Half-Life Test of Hydroxylamine (HA) in a Reducing Microenvironment

[0125] This test case aims to quantitatively evaluate the impact of different process environments on the chemical stability of hydroxylamine sulfate (HA), a key metabolic activator, and to verify the protective effect of FeS acidolysis products on hydroxylamine.

[0126] Experimental steps:

[0127] Three sealed conical flasks with an effective volume of 1L were used as static reaction containers, and equal amounts of anaerobic ammonia oxidation washing sludge and supernatant were added to each. The three containers correspond to Example 1 (Fe3O4 / FeS system), Comparative Example 2 (Fe3O4 / FeS-free system), and Comparative Example 6 (Fe3O4 / FeS / post-dosing system), respectively.

[0128] The environment inside each container was pre-controlled: In Example 1 and Comparative Example 2, the pH was adjusted to 6.2 by adding a trace amount of sulfuric acid and left to stand for 5 minutes. In Example 1, the FeS acidolysis reaction occurred in advance in the container. In Comparative Example 6, the pH was adjusted to 8.0 to simulate a conventional alkaline environment.

[0129] Hydroxylamine sulfate stock solution was simultaneously injected into three containers in one go to achieve an initial theoretical concentration of 3.00 mg / L (as N). The containers were then immediately sealed and placed on a magnetic stirrer and stirred at a low speed of 100 rpm to avoid introducing external oxygen.

[0130] The addition time was set to 0 min. At the 0, 5, 15, 30, 60, 90 and 120 minutes of the reaction, 5 mL of the mixture was extracted through the sampling port and immediately filtered through a 0.22 μm filter membrane to terminate the reaction.

[0131] The residual concentration of hydroxylamine in the filtrate was determined by the 8-hydroxyquinoline spectrophotometric method. Based on the concentration-time curve, a first-order reaction kinetic equation was used. Fitted decay rate constant ( ), and calculate the half-life of hydroxylamine in each system ( ).

[0132] Experimental data:

[0133] Table 2. Record of hydroxylamine (HA) concentration decay and kinetic parameters in different microenvironment systems.

[0134] Time (min) Example 1: HA concentration (mg / L) Comparative Example 2: HA concentration (mg / L) Comparative Example 6: HA concentration (mg / L) 0 2.98 3.01 2.95 5 2.92 2.85 2.54 15 2.86 2.62 1.88 30 2.78 2.31 1.12 60 2.64 1.84 0.45 90 2.51 1.48 0.18 120 2.39 1.15 0.07 kinetic parameters <![CDATA[Decay rate constant k (min −1 )]]> 0.0018 0.0081 0.0305 <![CDATA[Half-life t 1 / 2 (min)]]> 385.1 85.6 22.7 <![CDATA[Fitting correlation coefficient R 2 > 0.992 0.988 0.995

[0135] Conclusion Analysis:

[0136] Based on the test data in Table 2, refer to the appendix. Figure 4 -Appendix Figure 5 The stability of hydroxylamine varied significantly under different process conditions. In the simulated conventional alkaline environment (pH 8.0) of Comparative Example 6, hydroxylamine exhibited instability, with its concentration rapidly dropping below 1.2 mg / L within the first 30 minutes, and a half-life of only 22.7 minutes. This is because hydroxylamine readily undergoes auto-oxidation under alkaline conditions, and the residual dissolved oxygen and high-valent nitrogen oxides in the reaction system accelerate its oxidative decomposition, resulting in the ineffective loss of most of the hydroxylamine before it enters bacterial cells.

[0137] Although Comparative Example 2 constructed the same acidic environment as Example 1 (pH 6.2), its half-life was extended to 85.6 minutes. This indicates that the acidic conditions alone inhibited the auto-oxidation rate of hydroxylamine to some extent. However, due to the lack of FeS component, there were no reducing substances in the system that actively consumed the oxidant. Hydroxylamine was still continuously consumed by oxidizing substances in the environment, resulting in its decay rate constant (k=0.0081) being significantly higher than that of Example 1.

[0138] In Example 1, under the combined effects of acidity and FeS, hydroxylamine exhibited optimal stability, with a residual concentration as high as 2.39 mg / L after 120 minutes and a calculated half-life of 385.1 minutes, which were 4.5 times that of Comparative Example 2 and 16.9 times that of Comparative Example 6, respectively. This result confirms the in-situ reduction barrier mechanism proposed in this invention: the release of hydrogen sulfide (H2S) and ferrous ions (Fe2+) by FeS under localized acidic conditions. 2+ Hydroxylamine preferentially reacts with dissolved oxygen and oxidative free radicals in the environment, lowering the redox potential (ORP) of the microenvironment and thus creating a chemically safe pathway for it. This high stability ensures that low dosages of hydroxylamine can maintain an effective concentration for a long time, sufficient to penetrate into the granular sludge and be captured and utilized by the hydrazine synthase (HZS) of functional bacteria, which is a key prerequisite for achieving low-consumption and high-efficiency activation.

[0139] Test Example 3: Comparison of Denitrification Efficiency and Stability under Long-Term Operation

[0140] This test case aims to examine the actual impact of different process modes on the denitrification stability and shock resistance of the reaction system under continuous high-load operation conditions.

[0141] Experimental steps:

[0142] Ten identical SBR reactors were constructed, each with an effective volume of 5L, corresponding to the process conditions of Examples 1 to 4 and Comparative Examples 1 to 6, respectively. Each reactor was inoculated with an equal amount of homogeneous anaerobic ammonia oxidation granular sludge, and the initial sludge concentration (MLVSS) was controlled at 3500 mg / L.

[0143] Continuous operation testing was initiated, with a total operating cycle of 60 days (180 cycles). The influent substrate was artificially prepared, and the total nitrogen (TN) concentration was adjusted to maintain the volumetric nitrogen loading (NLR) of all reactors at a uniform 0.80 kgN / (m³). 3 ·d) At high load levels, the molar ratio of nitrite nitrogen to ammonia nitrogen in the influent is controlled at 1.32:1.

[0144] Each reactor group strictly followed its corresponding process flow. Examples 1-4 and Comparative Examples 2-6 performed pH adjustment and chemical dosing operations according to the set program; Comparative Example 1 maintained conventional SBR operation. During operation, the reaction temperature was controlled at 33±1℃ (35℃ for Example 3), and the water quality indicators of the influent and effluent were monitored and recorded daily.

[0145] After each cycle, effluent samples were collected, and the total nitrogen concentration was determined according to the standard "Methods for Monitoring and Analysis of Water and Wastewater". The daily average total nitrogen removal rate and nitrogen removal load (NRR) of each reactor were calculated, and the standard deviation (SD) of 60 days of operating data was calculated to quantify the system's volatility and stability.

[0146] Experimental data:

[0147] Table 3. Statistical table of nitrogen removal efficiency of each reaction system during long-term operation (60 days)

[0148] Group Average total nitrogen removal rate (%) Removal rate standard deviation (SD) <![CDATA[Average nitrogen removal rate (NRR, kgN / m 3 ·d)]]> Total nitrogen concentration range in effluent (mg / L) Remark Example 1 91.42 1.15 0.73 12.5～18.4 Standard mode Example 2 88.75 1.84 0.71 18.2～24.6 Low power consumption mode Example 3 92.88 0.96 0.74 10.2～～15.3 Enhanced Mode Example 4 89.56 1.52 0.72 16.5～22.1 Hydraulic optimization Comparative Example 1 68.34 8.45 0.55 45.2～110.5 Blank control Comparative Example 2 76.21 4.32 0.61 35.6～58.9 FeS-free Comparative Example 3 79.45 2.12 0.64 32.1～44.5 Hydroxylamine Comparative Example 4 81.02 3.56 0.65 28.5～48.2 No pH difference Comparative Example 5 77.83 5.67 0.62 30.2～65.4 <![CDATA[Replacement of Na2S]]> Comparative Example 6 83.15 2.98 0.67 25.4～38.6 Reversed order

[0149] Conclusion Analysis:

[0150] Based on the statistical data in Table 3, refer to the appendix. Figure 6 The combined process proposed in this invention demonstrates advantages in both processing efficiency and system stability. Examples 1 and 3 were performed at 0.80 kgN / (m³). 3Under the high-load impact of ·d), the average total nitrogen removal rates reached 91.42% and 92.88%, respectively, with extremely low standard deviations (SD < 1.2), indicating that the system has a strong anti-interference ability. This is attributed to the synergistic effect of acid-assisted reduction and in-situ remediation mechanisms: on the one hand, periodic micro-acidic washing removes inert metabolites from the surface of the magnetic framework, maintaining the unobstructed electron transport channels; on the other hand, hydroxylamine, under the protection of the reducing barrier constructed by FeS, effectively activates the HZS enzyme activity of functional bacteria, enabling the system to maintain a high metabolic level at all times.

[0151] In contrast, the removal rate of Comparative Example 1 (blank group) was only 68.34%, and the standard deviation was as high as 8.45. The operational data showed that its efficiency declined significantly in the later stage, which confirmed that conventional SBR is difficult to overcome the problems of sludge aging and activity loss under high load when there is no external enhancement method.

[0152] Comparative Example 3 (without hydroxylamine) maintained good stability (SD=2.12), but the average removal rate remained at 79.45%, failing to break through the 80% bottleneck. This indicates that while the physicochemical effects of FeS and Fe3O4 can stabilize the environment, the lack of direct electron pumping by the metabolic activator (hydroxylamine) prevents the deep activation of substrate affinity in the cells, thus limiting the upper limit of the reaction rate.

[0153] The average removal rate of Comparative Example 6 (process sequence reversed) was 83.15%, lower than that of Example 1. This result confirms the criticality of process timing: hydroxylamine was added later under alkaline conditions, and due to the lack of FeS dissolution protection in an acidic environment, most of the hydroxylamine was consumed by non-biological oxidation and failed to effectively act on intracellular enzymes. At the same time, the in-situ flocculation window during the pH adjustment phase was missed, resulting in the sludge structure not being periodically reinforced, and the effluent quality fluctuation (SD=2.98) was approximately 2.6 times that of Example 1. In addition, the high standard deviation (SD=5.67) of Comparative Example 5 (Na2S replacement) indicates that although direct addition of soluble sulfides can provide short-term reducing power, it is prone to local toxicity or insufficient sulfur source due to its rapid loss with the effluent and difficulty in precise concentration control, and cannot achieve on-demand slow release and in-situ retention like solid FeS in Example 1.

[0154] Test Example 4: Determination of Sludge Specific Activity (SAA) and Key Metabolic Enzyme Activities

[0155] This test case verifies the mechanism by which the process of this invention enhances the physiological activity of anaerobic ammonia oxidizing bacteria (AnAOB) from the micro-metabolic level through quantitative analysis of biochemical indicators.

[0156] Experimental steps:

[0157] When each reactor had been running continuously for 45 days, granular sludge samples were collected from the sampling port in the middle of the reactors of Example 1 (combined process), Comparative Example 1 (blank control), Comparative Example 3 (no hydroxylamine addition), and Comparative Example 4 (constant pH / no acid washing).

[0158] The collected sludge samples were washed three times with anoxic phosphate buffer (PBS, pH 7.2) to remove residual matrix and suspended impurities on the surface, and then centrifuged (3000 g, 5 min) to determine the content of volatile organic compounds (VSS) in suspended solids to calibrate biomass.

[0159] Anaerobic ammonia oxidation activity (SAA) determination: Equal volumes of washed sludge were inoculated into 120 mL serum bottles, and NH4+ was added. + -N and NO2 - Substrate solutions of 50 mg / L each of -N were prepared, and nitrogen gas was introduced for 10 minutes to maintain a strictly anaerobic environment. The solutions were then incubated in a constant temperature shaker at 33°C. The total nitrogen concentration in the liquid phase was measured every hour, and the SAA value was calculated using the slope of linear regression.

[0160] Heme c content determination: Take the cleaned sludge, extract it with 1M NaOH solution in a 90℃ water bath for 20 minutes, centrifuge and collect the supernatant, use a UV-Vis spectrophotometer to measure the difference in absorbance at 550 nm between the oxidized state (with potassium ferricyanide) and the reduced state (with sodium dithionite), and calculate the Heme c content.

[0161] Hydrazine synthase (HZS) activity assay: Intracellular crude enzyme solution was extracted by low-temperature ultrasonic disruption. Hydroxylamine was used as the electron donor and cytochrome c as the electron acceptor. The relative enzyme activity units of HZS were characterized by monitoring the reduction rate of cytochrome c at 550 nm in an anaerobic cuvette.

[0162] Experimental data:

[0163] Table 4. Results of sludge biological activity and key enzyme activity indicators for each group on day 45 of operation.

[0164] Group Compared with anaerobic ammonia oxidation activity, SAA (gN / (gVSS·d)) Heme c content (μmol / gVSS) Relative activity of hydrazine synthase (HZS) (U / mg protein) Remark Example 1 0.584 1.42 18.45 Synergistic enhancement Comparative Example 1 0.215 0.46 6.12 Activity decline Comparative Example 3 0.392 1.15 9.87 Lack of HA activation Comparative Example 4 0.315 1.08 10.35 Channel blockage

[0165] Conclusion Analysis:

[0166] Based on the test data in Table 4, refer to the appendix. Figure 7Example 1 demonstrated superiority across all biokinetic parameters, confirming the regulatory role of process parameters on micrometabolism. Specifically, the SAA value of Example 1 reached 0.584 gN / (gVSS·d), approximately 2.7 times that of Comparative Example 1 (blank group). The extremely low Heme c content (0.46 μmol / gVSS) in Comparative Example 1 indicates that, under conventional operating conditions lacking carrier protection and chemical activation, high influent loads led to a significant decrease in functional bacterial abundance and biomass loss.

[0167] Compared to Example 1 and Comparative Example 3 (without hydroxylamine), although the FeS carrier in Comparative Example 3 maintained a high cell abundance (Heme c 1.15 μmol / g VSS, not significantly different from 1.42 in Example 1 compared to SAA), its HZS enzyme activity (9.87 U / mg) was only about 53% of that in Example 1 (18.45 U / mg). This data directly confirms that the addition of hydroxylamine was not merely consumed as a nitrogen source, but rather upregulated the catalytic activity of the core enzyme HZS by intervening in the hydrazine synthesis metabolic pathway, thus achieving higher activity with the same cell count. Compared to Example 1 and Comparative Example 4 (without pH differential), the SAA value of Comparative Example 4 (0.315) was lower than that of Example 1. Although Comparative Example 4 also contained FeS and hydroxylamine, the lack of periodic acidic pulse washing made the sludge surface and pores easily covered by extracellular polymers (EPS) and inorganic precipitates. This not only increased the substrate mass transfer resistance but also hindered the penetration of hydroxylamine into the intracellular enzyme active site, resulting in limited metabolic activation efficiency. This result indicates that in-situ acid washing is a necessary physical prerequisite for ensuring the long-term operation of the hydroxylamine activation mechanism.

[0168] Test Example 5: Sludge Physical Settling Properties and Extracellular Polymer (EPS) Characteristics Test

[0169] This test case aims to examine the physical structural stability of granular sludge and the changes in extracellular polymer components in various reaction systems after long-term operation, in order to verify the in-situ reconstruction mechanism proposed in this invention on the repair of sludge morphology.

[0170] Experimental steps:

[0171] After the experiment ended (day 60), 50 mL of well-mixed sludge samples were taken from the reactors of Example 1 (combined process), Example 4 (hydraulic optimization), Comparative Example 1 (blank control), and Comparative Example 5 (Na2S substitution), respectively. The sludge was gently rinsed with 0.9% NaCl solution to remove loose impurities adhering to the surface.

[0172] Place the cleaned sludge sample in a standard 1000 mL graduated cylinder, add water to the mark, let stand for 30 minutes, and read the sludge settling volume (SV). 30The settled sludge was then dried to constant weight, and the mixed liquor suspended solids concentration (MLSS) was measured to calculate the sludge volume index (SVI). 30 ).

[0173] Fifty intact sludge particles were randomly selected from each group and placed in a sedimentation column (50 cm high) filled with clean water. The time it took for a single particle to travel a specific distance was recorded, and the average sedimentation velocity was calculated.

[0174] Extracellular polymeric substances (EPS) were extracted from sludge using a thermal extraction method. The sludge suspension was heated in an 80°C water bath for 30 minutes, centrifuged at 4000 rpm for 15 minutes, and the supernatant was collected. The protein (PN) and polysaccharide (PS) contents in the extract were determined using the Folin-phenol reagent method and the anthrone-sulfuric acid method, respectively, and the PN / PS ratio was calculated.

[0175] Experimental data:

[0176] Table 5. Results of physical settling properties of sludge and EPS component analysis at the end of operation.

[0177] Group <![CDATA[Sludge Volume Index SVI 30 (mL / g)]]> Mean settlement velocity (m / h) Total EPS content (mg / gVSS) Protein PN (mg / g VSS) Polysaccharide PS (mg / gVSS) PN / PS ratio Example 1 36.4 68.5 145.2 112.4 32.8 3.43 Example 4 34.8 74.2 138.6 105.3 33.3 3.16 Comparative Example 1 62.8 34.2 86.5 45.8 40.7 1.12 Comparative Example 5 55.3 41.6 102.4 64.5 37.9 1.70

[0178] Conclusion Analysis:

[0179] Based on the test data in Table 5, refer to the appendix. Figure 8 The embodiments of the present invention demonstrate significant advantages in terms of sludge physical structure and biochemical properties, confirming the in-situ solidification effect of the process on granular sludge. Example 1's SVI 30 The pH value was as low as 36.4 mL / g, while the average settling velocity was as high as 68.5 m / h, indicating that the sludge particles had a dense structure and excellent solid-liquid separation performance. This is mainly due to the unique pH adjustment mechanism of this invention: during the periodic fluctuation of pH from 6.0 to 7.5, dissolved Fe... 2+ With S 2- In-situ co-precipitation occurs within the pores of the sludge, generating nanoscale FeS crystal nuclei that act as an inorganic framework, effectively filling the voids within the particles and increasing the specific gravity and mechanical strength of the sludge. In contrast, Comparative Example 1 (blank control) showed SVI... 30 The concentration was as high as 62.8 mL / g, the settling velocity was only 34.2 m / h, and the PN / PS ratio in EPS was only 1.12. The data indicate that under long-term high-load operation, due to the lack of external enhancement, the sludge showed obvious aging and hollowing phenomena, and the loss of extracellular protein (PN) led to a decrease in particle hydrophobicity and a weakening of the aggregation ability of bacterial flocs.

[0180] Although Comparative Example 5 (Na2S substitution) introduced a sulfur source, its SVI 30The concentration (55.3 mL / g) is still higher than in Example 1, and the improvement in the PN / PS ratio (1.70) is limited. This is because the directly added soluble Na2S mainly reacts in the liquid phase, and the resulting sulfide precipitates are mostly in suspension, making it difficult to accurately deposit inside the granular sludge. The lack of endogenous inorganic framework support makes its effect on improving sludge density far less than the in-situ remediation strategy based on acidolysis-reconstruction in Example 1.

[0181] Furthermore, the higher PN / PS ratios (>3.0) in Examples 1 and 4 further confirm that the trace iron ions generated by FeS acid hydrolysis stimulated the bacteria to secrete more extracellular proteins. The high concentration of proteins not only provided stronger bioadhesion but also further stabilized the connection between metal ions and bacteria through complexation, forming an inorganic-organic interpenetrating network structure, thereby enhancing the system's resistance to hydraulic shear. In Example 4, due to the introduction of hydraulic vortex optimization, the physical screening effect further increased its settling velocity to 74.2 m / h, but its biochemical composition was similar to that of Example 1, indicating that chemical modification is the fundamental reason for improving sludge quality.

[0182] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A highly efficient nitrogen removal method based on anaerobic ammonia oxidation process, characterized in that, The method is based on a sequencing batch reactor operation and includes a composite conductive matrix construction step and a time-series pulse maintenance operation step. The composite conductive matrix construction steps include: adding iron oxide powder and ferrous sulfide powder to the anaerobic ammonia oxidation sludge mixture in the reactor, and using hydraulic shearing to form a composite magnetic biological carrier. The time-series pulse maintenance operation steps include: during the influent phase of the sequencing batch reactor's operating cycle, sequentially performing the local acidic microenvironment construction operation, the protective pulse activation operation, and the mainstream influent and in-situ reconstruction operation; In this process, by controlling the pH value of the influent and the order of chemical addition, an acidic environment is first created locally in the reactor to trigger the release of reducing components from ferrous sulfide. After adding hydroxylamine metabolic activators, the pH value of the mainstream influent is adjusted to induce in-situ flocculation of dissolved ions.

2. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 1, characterized in that, In the composite conductive matrix construction step, the mass ratio of the iron oxide powder to the ferrous sulfide powder is 5:1 to 10:1; the total amount of the composite magnetic biological carrier added is 5% to 10% of the dry weight of the suspended solids in the mixture in the reactor.

3. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 1, characterized in that, In the process of constructing the localized acidic microenvironment, the reactor stirring device is stopped, and acidic liquid is pumped in through the bottom inlet of the reactor to control the local pH value of the sludge layer area at the bottom of the reactor to be 6.0 to 6.

5.

4. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 3, characterized in that, The duration of the local acidic microenvironment construction operation is the first 3% to 8% of the water inlet cycle; the acidic liquid is prepared by mixing raw water and dilute sulfuric acid.

5. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 1, characterized in that, The hydroxylamine metabolic activator is hydroxylamine sulfate. In the protective pulse activation operation, hydroxylamine sulfate solution is injected into the bottom region in a pulse manner while maintaining a local acidic environment at the bottom. The amount of hydroxylamine sulfate solution added is calculated based on the effective volume of the reactor, so that its theoretical final concentration in the reactor, expressed as nitrogen, is 2 mg / L to 5 mg / L.

6. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 5, characterized in that, The protective pulse activation operation is performed immediately after the local acidic microenvironment construction operation, and the pulse injection lasts for 1 to 3 minutes. During this period, hydrogen sulfide generated by the acidolysis of ferrous sulfide is used as a reducing barrier to protect hydroxylamine sulfate from oxidation.

7. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 1, characterized in that, During the main influent and in-situ reconstruction operation, the bottom influent and chemical dosing are stopped, the main influent system of the reactor is turned on and the stirring device is turned on, and raw water with a pH of 7.5 to 8.2 is pumped in at full speed. By utilizing the alkalinity of the raw water to neutralize the acidic region at the bottom, the overall pH value of the mixed solution in the reactor rises to 7.8-8.2 within 10-20 minutes, thereby inducing in-situ co-precipitation of dissolved ferrous ions and sulfur ions.

8. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 1, characterized in that, The particle size distribution of the iron oxide powder is 200 mesh to 400 mesh; the particle size distribution of the ferrous sulfide powder is 100 mesh to 200 mesh.

9. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 7, characterized in that, The method includes a reaction stage. After the water intake is completed, the reaction temperature is controlled at 30℃~35℃ and the dissolved oxygen concentration is lower than 0.1 mg / L. The activated composite magnetic biological carrier is used to carry out anaerobic ammonia oxidation denitrification reaction.

10. The efficient nitrogen removal method based on anaerobic ammonia oxidation process according to claim 7, characterized in that, Before the composite conductive matrix construction step, a raw material premixing treatment is also included: iron oxide powder and ferrous sulfide powder are placed in a dry powder mixer and mechanically mixed at room temperature for 10 to 15 minutes to obtain a composite conductive medium dry powder with uniform color.

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