Iron-manganese modified biochar and application thereof in anaerobic ammonia oxidation denitrification system

Abstract

The present application relates to the technical field of water treatment, and particularly relates to iron-manganese modified biochar and application of the same in an anaerobic ammonia oxidation denitrification system. The present application provides iron-manganese modified biochar, which is prepared by pyrolysis of biochar modified by iron salt and manganese salt. The present application loads iron and manganese on the surface of biochar to construct a porous carrier with stable redox activity and interface catalytic function, so as to use the carrier as a biological attachment substrate and a trace element slow-release source of anaerobic ammonia oxidation bacteria, thereby improving the denitrification performance and operation stability of the system. The use of the iron-manganese modified biochar can promote the enrichment and metabolic activity of anaerobic ammonia oxidation bacteria, enhance the buffering capacity of the system to nitrite fluctuation, and promote the further reduction of nitrate under the condition of no additional organic carbon source, so as to finally realize the significant improvement of total nitrogen removal efficiency and the efficient and stable effluent water quality.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to an iron-manganese modified biochar and its application in an anaerobic ammonia oxidation denitrification system. Background Technology

[0002] Compared to traditional nitrification-denitrification processes, anaerobic ammonia oxidation (ANAO) has become a research hotspot in wastewater treatment and resource recovery due to its significant advantages, including no need for external organic carbon sources, significantly reduced aeration requirements, and substantial savings in infrastructure and operating costs. This process directly converts ammonia nitrogen and nitrite into nitrogen gas using anaerobic ammonia-oxidizing bacteria. This not only avoids the economic and environmental burdens of carbon source addition and high-energy-consuming aeration in traditional processes, but also results in extremely low sludge production, thus significantly reducing sludge treatment and disposal costs and the risk of secondary pollution. The significant reduction in energy consumption also directly reduces indirect carbon emissions during wastewater treatment, giving ANAO technology the dual advantages of high-efficiency nitrogen removal and low-carbon operation, aligning with the current development direction of improving the quality and efficiency of wastewater treatment plants and the "dual-carbon" strategy.

[0003] However, anaerobic ammonia oxidation (ANAO) still faces multiple challenges in its engineering application and long-term stable operation. On the one hand, ANAO bacteria grow slowly and are sensitive to environmental conditions, making the process relatively fragile. External disturbances such as temperature fluctuations, imprecisely controlled micro-aeration, and changes in influent nitrogen load can easily cause fluctuations in the reaction system, affecting the stable formation and accumulation of nitrite, and thus disrupting the substrate balance required for the ANAO reaction. On the other hand, from a reaction stoichiometric perspective, the theoretical nitrogen removal efficiency of ANAO is approximately 89%, and the process is accompanied by the production of about 10% nitrate as a byproduct. The aforementioned operational instability and the inherent nitrate byproduct problem combine to cause nitrate to continuously accumulate within the system, becoming a key bottleneck restricting the deep removal of total nitrogen in the effluent and further improvement of the process's nitrogen removal efficiency.

[0004] To enhance the efficiency of anaerobic ammonia oxidation, the addition of biochar as a conductive material or microbial carrier has been widely studied. However, this approach still has significant limitations. The physicochemical properties of biochar are highly dependent on its biomass feedstock, pyrolysis conditions, and subsequent activation methods. Differences in these factors significantly affect the pore structure, the type and quantity of surface functional groups, and the conductivity and redox activity of biochar, leading to inconsistent performance of materials from different batches or sources in the complex microbial-electron transport system, resulting in insufficient reliability and repeatability of the enhancement effect. More importantly, the addition of biochar alone may primarily promote the conversion of nitrate to nitrite or enhance interspecies electron transport, potentially causing a sharp increase or peak in the concentration of bioavailable nitrite in the short term. Since anaerobic ammonia oxidizing bacteria are extremely sensitive to nitrite toxicity, such instantaneous high-concentration exposure can easily lead to inhibition of bacterial activity, slow metabolic recovery, and even the collapse and instability of the entire reaction system, thereby increasing the risk of process operation.

[0005] To address the issue of nitrate accumulation, the introduction of iron-based materials for modification is considered a potential strategy. Single iron-modified materials (such as iron-supported biochar) can promote the metabolic activity of anaerobic ammonia oxidizing bacteria and sludge granulation to a certain extent by providing iron ions or iron oxides. However, excessive accumulation of iron (especially Fe(II)) in the system or excessively high local concentrations may cause hysteretic inhibition or alter the microbial community structure, leading to a shift in the ecological niche of functional bacteria. Simultaneously, the iron phase is prone to oxidation precipitation, surface passivation, or the formation of a coating layer during long-term operation, resulting in a gradual reduction of effective catalytic active sites and a decline or fluctuation in the enhancement effect. Current technologies still lack a path to systematically overcome the upper limit of total nitrogen removal under low-carbon or even no-external-carbon source conditions to address the inherent nitrate byproduct problem of anaerobic ammonia oxidation. Common deep denitrification schemes often require the addition of additional organic carbon sources to drive heterotrophic denitrification or the introduction of complex coupled systems such as sulfur-based autotrophic denitrification, which undoubtedly increases the complexity of the process, operating costs, and the risk of secondary pollution. Therefore, developing a low-carbon reinforcing material and technology that can simultaneously stabilize the anaerobic ammonia oxidation process, control the risk of nitrite, and reduce nitrate accumulation in situ has become a key requirement to promote the widespread engineering application of this process. Summary of the Invention

[0006] To address the aforementioned shortcomings in existing technologies, the present invention aims to provide an iron-manganese modified biochar composite material, its preparation method, and its application in an anaerobic ammonia oxidation denitrification system. This composite material constructs a porous carrier with stable redox activity and interfacial catalytic function by synergistically loading iron and manganese onto the surface of biochar. This carrier serves as a bio-attachment matrix for anaerobic ammonia oxidizing bacteria and a slow-release source of trace elements, thereby improving the system's denitrification performance and operational stability. The application of the iron-manganese modified biochar described in this invention can promote the enrichment and metabolic activity of anaerobic ammonia oxidizing bacteria, enhance the system's buffering capacity against nitrite fluctuations, and further reduce nitrates without the addition of external organic carbon sources, ultimately achieving a significant improvement in total nitrogen removal efficiency and highly efficient and stable effluent quality.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an iron-manganese modified biochar, which is prepared by composite modification of iron salt and manganese salt and pyrolysis. Its surface contains Fe-Mn composite oxide crystal phase, including one or more of MnFe2O4, Fe3O4 and Mn3O4.

[0008] Preferably, the iron salt is FeCl3·6H2O, the manganese salt is MnCl2·4H2O, and the molar ratio of the iron salt to the manganese salt is 1.8~2.2:1.

[0009] This invention provides a method for preparing the iron-manganese modified biochar, comprising the following steps: (1) After sieving the biochar, soak it in deionized water, rinse it and dry it; (2) Under anaerobic conditions, the biochar treated in step (1) was mixed with an aqueous solution of iron and manganese salts and ultrasonically treated to maintain the pH of the system at 9-11. (3) Stir the mixture from step (2) for 20-28 hours. After solid-liquid separation, rinse with water and anhydrous ethanol alternately until neutral, and then dry. (4) The dried material is pyrolyzed under a nitrogen atmosphere; (5) After pyrolysis, rinse with water until neutral, and vacuum dry to obtain iron-manganese modified biochar.

[0010] Preferably, the iron salt in step (2) is FeCl3·6H2O, the manganese salt is MnCl2·4H2O, the iron salt concentration is 0.2~0.4 M, and the manganese salt concentration is 0.1~0.2 M.

[0011] Preferably, the ultrasonic treatment time in step (2) is 50~70 min, the ultrasonic treatment frequency is 40 kHz and the power is 120 W.

[0012] Preferably, the pyrolysis temperature in step (2) is 750~850℃ and the time is 50~70min.

[0013] This invention provides the application of the iron-manganese modified biochar in an anaerobic ammonia oxidation denitrification system, which can be achieved by adding the modified biochar into the anaerobic ammonia oxidation reactor.

[0014] Preferably, the anaerobic ammonia oxidation reactor is an upflow anaerobic sludge bed reactor, and the dosage of the iron-manganese modified biochar is 8~12 g / L.

[0015] Preferably, the anaerobic ammonia oxidation reactor operates at a temperature of 33-37°C, with a hydraulic retention time of 4-5 hours and an operating time of 80-200 days. The anaerobic ammonia oxidation biological nitrogen removal system also includes a nutrient solution. The nutrient solution comprises a trace element mixture I and a mixture II, wherein mixture I contains 5.00 g / L EDTA and 9.14 g / L FeSO4·7H2O, and mixture II contains 5.00 g / L EDTA and 0.19 g / L NiCl2·6H2O, 0.99 g / L MnCl2·4H2O, 0.24 g / L CoCl2·7H2O, 0.22 g / L Na2MoO4·2H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO3, 0.25 g / L CuSO4·H2O, and 0.21 g / L... Na2SeO4·10H2O.

[0016] This invention provides an anaerobic ammonia oxidation denitrification system, comprising the aforementioned iron-manganese modified biochar and anaerobic ammonia oxidizing bacteria.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Effectively regulates nitrite and enhances system stability: The material of this invention, through the chemical and biocatalytic action of surface MnOx, can precisely regulate nitrite (NO2) in the reaction system. - The dynamics of NO2 generation and consumption significantly reduce NO2. - Peak concentration and cumulative exposure. Under adverse conditions such as fluctuating influent load, shocks, or localized accumulation, this material can effectively buffer NO2. - This instantaneous impact helps prevent the anaerobic ammonia-oxidizing bacteria from losing activity and becoming unstable due to nitrite inhibition.

[0018] 2. Overcoming nitrate accumulation limitations to achieve deep denitrification: Targeting the nitrate (NO3) produced as a byproduct of anaerobic ammonium oxidation. -The present invention addresses the bottleneck in total nitrogen removal caused by [unspecified issue]. Under operating conditions without relying on external organic carbon sources (or extremely low COD), the material of this invention can stimulate and enhance the autotrophic or low-carbon denitrification potential within the system, promoting the production of byproduct NO3. - Further reduction occurs in situ. This not only reduces the net accumulation and formation coefficient of nitrates, but also raises the total nitrogen removal rate and denitrification load of the system to a higher level, achieving a deeper and more economical denitrification effect, and avoiding the cost and secondary pollution risks caused by adding carbon sources or adding complex process units.

[0019] 3. Establishing a manganese recycling synergistic mechanism to ensure long-term enhancement: Compared to single-dosage manganese agents or single manganese-modified materials that are easily consumed, dissolved, and have diminishing effects, this invention constructs a "Mn" synergistic mechanism to ensure long-term enhancement. 2+ The synergistic cycling mechanism of "controlled slow release" and "in-situ regeneration of surface MnOx" ensures that the manganese active component remains stably within the efficient promotion window during long-term operation. This reversible MnOx... 2+ The MnOx cycle continuously optimizes the electron transport chain of microorganisms, significantly improving related metabolic indicators such as electron transport system (ETS) activity and heme c content, thereby enhancing the energy metabolism efficiency and substrate conversion capacity of anaerobic ammonia-oxidizing bacteria in the long term, and greatly improving the long-term operational stability and shock resistance of the system.

[0020] 4. Enhancing the overall performance by coupling the advantages of multiple materials: This invention efficiently couples the excellent porous structure, microbial adhesion, and conductive framework of biochar with the rich valence state changes and interfacial catalytic activity of iron and manganese components. Compared with ordinary biochar that only provides physical adsorption or limited electron transfer, and with pure iron or pure manganese materials that have a single function, the material of this invention exhibits a more significant and stable synergistic enhancement effect in several key performance indicators, such as nitrite control, nitrate reduction, increased upper limit of total nitrogen removal, and system recovery speed.

[0021] 5. Diverse material forms and environmentally friendly, facilitating engineering applications: The material of this invention can be flexibly prepared into various forms such as powder, granules, or immobilized fillers according to actual engineering needs. After operation, the material can be easily recovered and recycled through simple methods such as sedimentation, filtration, magnetic separation, or direct removal of the carrier. Simultaneously, the amount of metal leaching in the reaction system is effectively controlled, ensuring the safety of the biological environment and providing a guarantee for long-term stable operation, demonstrating excellent prospects for engineering applications. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 The images show the infrared spectra of biochar before and after modification.

[0024] Figure 2 The images show the XRD patterns of biochar before and after modification.

[0025] Figure 3 The XRD patterns of iron-manganese modified biochar before and after the continuous flow reaction are shown.

[0026] Figure 4 This is a cyclic voltammetric curve of biochar.

[0027] Figure 5 The cyclic voltammetric characteristic curves of iron-modified biochar are shown.

[0028] Figure 6 The cyclic voltammetric curves of iron-manganese modified biochar are shown.

[0029] Figure 7 The images show the electrochemical impedance spectroscopy (EIS) spectra of biochar before and after modification.

[0030] Figure 8 This is a schematic diagram of a continuous flow anaerobic ammonia oxidation reactor.

[0031] Figure 9 The graph shows the changes in nitrogen concentrations in the influent and effluent of the continuous flow bioreactor R1.

[0032] Figure 10 The graph shows the changes in nitrogen concentrations in the influent and effluent of the continuous flow bioreactor R2.

[0033] Figure 11 This is a graph showing the changes in nitrogen concentrations in the influent and effluent of the continuous flow bioreactor R3. Detailed Implementation

[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] Example 1: A method for preparing iron-manganese modified biochar, comprising the following steps: (1) After sieving the biochar through an 80-mesh sieve, take the sieved activated carbon for later use.

[0036] (2) Soak the activated carbon treated in step (1) in deionized water, and then rinse it repeatedly with deionized water to remove residual impurities. Dry the rinsed activated carbon for later use. (3) Pass sufficient N2 into 200 mL of deionized water to remove dissolved oxygen; add 20 g of biochar, stir well, add 16.22 g FeCl3·6H2O (0.3 M) and 5.94 g MnCl2·4H2O (0.15 M) to the above system, and place the mixed solution in an ultrasonic bath for 1 h to allow the metal ions to be completely adsorbed and the carbon particles to be evenly dispersed. During the process, ensure that the pH value of the solution is maintained at approximately 10.

[0037] (4) The mixed solution after step (3) is placed at room temperature and stirred for 24 hours. Then, the solid and liquid are separated, and the solid is collected. The solid is washed alternately with deionized water and anhydrous ethanol until the pH value is neutral, and then dried and stored.

[0038] (5) The modified biochar was pyrolyzed in a muffle furnace under N2 atmosphere: the pyrolysis temperature was 800℃ and the pyrolysis time was 1h. (6) After pyrolysis, the char is rinsed with deionized water until the pH value is neutral, and then dried in a vacuum dryer to obtain iron-manganese modified biochar.

[0039] Example 2 The only difference from Example 1 is that in step (3), only FeCl3·6H2O (0.3 M) is added to the system, and MnCl2·4H2O is not added.

[0040] Application Example 1 (1) Three identical UASB reactors (Xinyuan Acrylic Glass Products Processing Plant) were constructed and named R1, R2, and R3 respectively for cultivating anaerobic ammonia oxidation sludge. The effective volume of each reactor was 1 liter. The inoculum sludge was mixed sludge cultivated by the Water Pollution Control Laboratory of the School of Environmental and Safety Engineering, Fuzhou University. The sludge concentrations (MLSS) in the reactors before material addition were 12.13 g / L, 12.14 g / L, and 11.34 g / L, respectively.

[0041] (2) In R1, only mixed sludge was inoculated (as a blank group); in R2, in addition to inoculating mixed sludge, 10g of iron-modified activated carbon (Fe-BC, as the iron-modified activated carbon group; prepared by the method in Example 2) was added; in R3, in addition to inoculating mixed sludge, 10g of iron-manganese-modified activated carbon (Fe-Mn-BC, as the iron-modified activated carbon group; prepared by the method in Example 1) was added.

[0042] (3) The anaerobic ammonia oxidation system is cultured continuously for 130 days, with NH4+ as the influent. +-N and NO2--N are used as substrates, and trace elements required for microbial growth are added to the influent substrate; the entire culture process is carried out under darkness, the reactor temperature is controlled at 33-37℃, the pH value is controlled at 7-7.8, and the hydraulic retention time is 4.5 hours.

[0043] (4) The nutrient solution of the anaerobic ammonia oxidation biological denitrification system includes trace element mixture I and mixture II. Mixture I contains 5.00 g / L EDTA and 9.14 g / L FeSO4·7H2O, while mixture II contains 5.00 g / L EDTA and 0.19 g / L NiCl2·6H2O, 0.99 g / L MnCl2·4H2O, 0.24 g / L CoCl2·7H2O, 0.22 g / L Na2MoO4·2H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO3, 0.25 g / L CuSO4·H2O and 0.21 g / L Na2SeO4·10H2O.

[0044] (5) Based on the removal of ammonia nitrogen and nitrite in the reactor effluent, after the removal rates of ammonia nitrogen and nitrite in the influent both exceeded 90% and the effluent stabilized for a period of time, the influent ammonia nitrogen and nitrite loads were increased, and the concentrations of ammonia nitrogen and nitrite in the influent were eventually increased to 120 mg / L and 150 mg / L, respectively. During the cultivation process, the changes in nitrogen content in the reactor effluent were measured, and the changes in the valence state of elements on the surface of the materials before and after the reaction were also measured.

[0045] The experimental results are as follows: (1) Material characterization Figure 1 The images show the infrared and XRD spectra of biochar before and after modification according to the methods in Examples 1 and 2.

[0046] FTIR results showed that Fe / Mn modification not only introduced metal-oxygen bonds but also significantly reconstructed the chemical environment of oxygen-containing functional groups on the biochar surface. Compared with BC (pure biochar), Fe-BC (prepared in Example 2) and Fe-Mn-BC (prepared in Example 1) showed improvements in the 700-500 cm⁻¹ range. -1 New characteristic absorption peaks of metal-oxygen (MO) appear in the low wavenumber region, located at 628 cm⁻¹. -1 With 599 cm -1 Furthermore, the peak position shifted significantly after the introduction of Mn, indicating a change in the vibrational mode of the metal-oxygen framework and the possible formation of a more complex Fe-O-Mn composite structure.

[0047] At the same time, 1650 cm -1 The nearby characteristic peak is at 1657 cm⁻¹ BC. -1 Moved to 1635 cm of Fe-BC-1 It rearranges to 1646 cm⁻¹ in Fe-Mn-BC. -1 Combined with ~1050 cm -1 Interval (1053 / 1057 / 1046 cm) -1 The synchronous migration of C=O / aromatic structure-related vibrations and CO (or COC) vibrations indicates that the local chemical environment of these vibrations has changed. It is speculated that this is due to the coordination / bonding between oxygen-containing functional groups and metal centers (such as MOC or surface complex structures), which leads to the adjustment of bond strength and vibration frequency.

[0048] Figure 2 XRD results showed that Fe / Mn modification significantly altered the mineral phase composition of the biochar surface and constructed a stable Fe-Mn oxide framework. The original biochar (BC) mainly exhibited a broad diffuse peak at 2θ≈20-30° and a weak characteristic peak near ~43°, reflecting that it was dominated by an amorphous / low-graphitized carbon framework and lacked a significant crystalline inorganic phase.

[0049] After Fe modification (Fe-BC), a set of distinct sharp diffraction peaks appeared in the 30-65° range, belonging to spinel-type iron oxides such as Fe3O4, indicating that Fe species had been successfully introduced and anchored on the carbon substrate surface in the form of crystalline oxides. Building on this, the Fe-Mn composite modified sample (Fe-Mn-BC), in addition to retaining the broad peaks of the carbon phase, further exhibited characteristic peaks of the Fe-Mn spinel phase such as MnFe2O4, accompanied by Fe3Mn3O8 and (FeO)0. 497 (MnO)0. 503 The presence of mixed oxide signals indicates that Mn has successfully incorporated into the Fe oxide structure, forming a more complex composite oxide / solid solution framework. Combined with the appearance and shift of the MO vibrational peak in FTIR and the verification of metal-oxidation chemical states and mixed valence states by XPS, it can be confirmed that Fe / Mn species exist as stable metal-oxygen bonds and crystalline mineral structures. This FTIR conclusion is corroborated by the appearance of Fe / Mn oxide crystalline phases in XRD and the changes in the chemical states of metal-oxygen related components (MO / M-OH) and oxygen-containing functional groups in XPS, suggesting that Fe / Mn species are anchored to the carbon framework surface in the form of stable oxygen bonds rather than simple physical mixing. Further electrochemical characterization revealed that although metal loading may lead to a decrease in some electrochemically accessible surface areas (CV area in the order BC>Fe-Mn-BC>Fe-BC), Fe-Mn-BC exhibits lower interfacial impedance in the high-frequency region of EIS (curve shifted to the left). This indicates that the Fe / Mn composite sites and the reconstruction of oxygen-containing functional groups on the surface jointly promote interfacial charge transfer and potential electron exchange processes, providing more effective interfacial reaction sites and electron transfer basis for the material in anaerobic ammonia oxidation systems.

[0050] Figure 3 The elemental analysis of iron-modified activated carbon was performed using X-ray energy dispersive spectroscopy before and after the reaction.

[0051] It can be seen that FE-MN-BC underwent significant mineral phase evolution before and after the reaction. The original sample before the reaction exhibited a broad peak at 2θ≈20-30°, indicating that the material is dominated by an amorphous / low-graphitized carbon framework. Characteristic diffraction peaks of Fe-Mn binary oxides such as MnFe2O4 and signals from some low-valence mixed oxides were also observed, indicating successful Fe / Mn loading. The used sample after the reaction showed and significantly enhanced characteristic diffraction peaks of Fe3O4 (mainly distributed around ~30°, ~35°, ~43°, ~57°, and ~62°), while the related peaks of manganese oxides such as Mn3O4 and MnO2 were also clearer, indicating that the Fe-Mn composite oxide underwent phase transformation and remineralization deposition during reactor operation. These results suggest that the Fe / Mn species underwent a reduction-reoxidation cycle during operation, accompanied by a dissolution-redeposition process. The Fe3O4 and other mineral phases formed / enriched after the reaction can provide the system with more reversible redox sites and potential conductive electron transport pathways, thus providing structural and mineralogical evidence for the material to promote the reaction process.

[0052] Figures 4-7 The cyclic voltammetry (CV) curves of biochar and modified biochar are shown. Electrochemical tests indicate that Fe / Mn loading significantly alters the charge storage and interfacial charge transfer characteristics of biochar. Within the potential window of -1.0 to +1.0 V, the CV curves of all three materials exhibit quasi-capacitive hysteresis loops, and change with the scan rate (20-200 mV s⁻¹). -1 The increase in current and overall outward expansion indicates that the material possesses a certain charge storage and buffering capacity. A comparison of different materials shows that BC has the largest current response and loop area (200 mV s). -1 The current amplitude was approximately ±0.12 A, with Fe-Mn-BC in the middle (approximately ±0.07 A) and Fe-BC the smallest (approximately ±0.055 A). This indicates that Fe loading may have shielded some pore / capacitive sites, while the introduction of Mn can alleviate the loss of electrochemical activity to some extent. EIS (Nyquist) further showed that the Fe-Mn-BC curve shifted significantly to the left in the high-frequency region, corresponding to a lower real impedance at the same virtual impedance level, suggesting a reduction in interfacial charge transfer resistance and an enhancement of electron transport kinetics. Combining the CV and EIS results, although Fe-Mn composite modification may reduce the accessibility of some capacitive sites, it significantly improves the interfacial charge transfer efficiency, providing electrochemical evidence for the enhancement of electron transport in subsequent reaction systems.

[0053] (2) Denitrification status Figures 9-11The figure shows the changes in ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen concentrations in the influent and effluent during the cultivation of the anaerobic ammonia oxidation system. As can be seen from the figure, during the 130 days of operation, the influent ammonia nitrogen and nitrite nitrogen concentrations gradually increased from 50 mg / L and 60 mg / L to 120 mg / L and 150 mg / L, respectively. With the increase in influent load, all three reactors maintained a relatively high NH4 concentration. + -N and NO2 - While it has good TN removal capacity, reactor R3 exhibits higher TN removal rate and lower NO3 removal rate. - -N residue.

[0054] Overall statistics during the dosing period show that the TN removal rate of R3 was 84.83±4.18%, significantly higher than that of R2 (80.72±5.64%) and R1 (78.83±3.88%); the NO3 removal rate in the effluent from R3 was... - -N was 27.02 ± 4.90 mg·L. -1 Compared with R1 (38.58±10.32 mg·L), -1 The level decreased by approximately 29.96%, compared to R2 (34.15 ± 7.54 mg·L⁻¹). -1 The NO2 content of R3 decreased by approximately 20.86%. - -N effluent average (0.79±1.33 mg·L) -1 The result was lower than R1 (1.29 ± 2.07 mg·L⁻¹). -1 R2 (1.11 ± 1.78 mg·L) -1 (and exhibits stronger peak-shaving ability at higher quantiles: NO2) - -N effluent 95th percentile is 6.82 mg·L⁻¹. -1 It decreased to 3.03 mg·L⁻¹ for R3. -1 This indicates that Fe-Mn-BC can significantly reduce the risk of nitrite exposure during short-term fluctuations. ΔNO2 in the three reactors... - / ΔNH4 + The medians were all close to 1.32 (R1: 1.320; R2: 1.353; R3: 1.350), indicating that after the addition of NH4... + Removal remained primarily Anammox-based, and the material did not alter the dominant reaction pathway. However, ΔNO3... - / ΔNH4 + Significant differences exist among the reactors, with a median R1 of 0.434 (significantly higher than the theoretical 0.26), R2 of 0.355, and R3 of 0.277. These results suggest that the core of the material effect is not "enhancing NH4+". + or NO2 - The main reaction was not removed, but the NO3 was significantly altered.- The "formation and accumulation balance" raises the overall TN removal ceiling.

[0055] The combined results from different load stages during the combined addition period show that ΔNO2 / ΔNH4 ≈ 1.32 for all three reactors, indicating that Anammox is still NH4. + The primary pathway for TN removal was observed; material differences were mainly reflected in the significant variations in the deviation of ΔNO3 / ΔNH4. The control group (R1) and Fe-BC (R2) exhibited substantial excess NO3 accumulation (median ΔNO3 / ΔNH4 ratios of 0.434 and 0.355 respectively during the dosing period), resulting in the upper limit of TN removal being limited by NO3. - Residual limitation; while Fe-Mn-BC (R3) significantly reduces NO3 accumulation and makes the stoichiometric ratio revert to theoretical values ​​(median ΔNO3 / ΔNH4 = 0.277, and NO3 "excess" ≈ 0 / negative under high load), while suppressing NO2. - High exposure values ​​result in a more significant and stable overall nitrogen removal advantage during high-load phases.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An iron-manganese modified biochar, characterized in that, The biochar is prepared by pyrolysis after composite modification with iron and manganese salts, and its surface contains Fe-Mn composite oxide crystal phase, including one or more of MnFe2O4, Fe3O4 and Mn3O4.

2. The iron-manganese modified biochar according to claim 1, characterized in that, The iron salt is FeCl3·6H2O, the manganese salt is MnCl2·4H2O, and the molar ratio of iron salt to manganese salt is 1.8~2.2:

1.

3. A method for preparing iron-manganese modified biochar according to claim 1 or 2, characterized in that, Includes the following steps: (1) After sieving the biochar, soak it in water, rinse it and dry it; (2) Under anaerobic conditions, the biochar treated in step (1) was mixed with an aqueous solution of iron and manganese salts and ultrasonically treated to maintain the pH of the system at 9-11. (3) Stir the mixture from step (2) for 20-28 hours. After solid-liquid separation, rinse with water and anhydrous ethanol alternately until neutral, and then dry. (4) The dried material is pyrolyzed under a nitrogen atmosphere; (5) After pyrolysis, rinse with water until neutral, and vacuum dry to obtain iron-manganese modified biochar.

4. The preparation method according to claim 3, characterized in that, The iron salt in step (2) is FeCl3·6H2O, the manganese salt is MnCl2·4H2O, the iron salt concentration is 0.2~0.4 M, and the manganese salt concentration is 0.1~0.2 M.

5. The preparation method according to claim 3, characterized in that, The ultrasonic treatment in step (2) lasts for 50 to 70 minutes, with a frequency of 40 kHz and a power of 120 W.

6. The preparation method according to claim 3, characterized in that, The pyrolysis temperature in step (2) is 750~850℃ and the time is 50~70min.

7. The application of the iron-manganese modified biochar according to claim 1 or 2 in an anaerobic ammonia oxidation denitrification system, characterized in that, The modified biochar can be added to an anaerobic ammonia oxidation reactor.

8. The application according to claim 7, characterized in that, The anaerobic ammonia oxidation reactor is an upflow anaerobic sludge bed reactor, and the dosage of the iron-manganese modified biochar is 8~12 g / L.

9. The application according to claim 7, characterized in that, The anaerobic ammonia oxidation reactor operates at a temperature of 33-37℃, with a hydraulic retention time of 4-5 hours and an operating time of 80-200 days. The anaerobic ammonia oxidation biological nitrogen removal system also includes a nutrient solution. This nutrient solution comprises two mixtures: a trace element mixture I and a mixture II. Mixture I contains 5.00 g / L EDTA and 9.14 g / L FeSO4·7H2O, while mixture II contains 5.00 g / L EDTA, 0.19 g / L NiCl2·6H2O, 0.99 g / L MnCl2·4H2O, 0.24 g / L CoCl2·7H2O, 0.22 g / L Na2MoO4·2H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO3, 0.25 g / L CuSO4·H2O, and 0.21 g / L Na2SeO4·10H2O.

10. An anaerobic ammonia oxidation denitrification system, characterized in that, It includes the iron-manganese modified biochar as described in claim 1 or 2, and anaerobic ammonia-oxidizing bacteria.

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