A method for short-range nitrification-iron coupled sulfur cycle biological denitrification

Abstract

This invention discloses a short-cut nitrification-iron coupled sulfur cycle biological denitrification method, belonging to the field of nitrogen-containing wastewater treatment technology. This method utilizes domesticated nitrite-reducing bacteria to convert ammonia nitrogen in wastewater into nitrite; then, a composite bacterial agent obtained by inoculating sulfate-reducing bacteria and denitrifying thiobacilli together in a culture medium containing iron or ferrous ions further removes nitrite and nitrate from the wastewater. Through sulfate reduction and sulfur autotrophic denitrification coupled with iron, sulfate in the wastewater is converted into electron donors, forming a carbon-nitrogen-sulfur-iron biological co-reaction system. This overcomes the shortcomings of single-species denitrification systems, enhances denitrification efficiency, and reduces energy consumption and cost.

Description

Technical Field

[0001] This invention relates to the field of nitrogen-containing wastewater treatment technology, and in particular to a short-cut nitrification-iron coupled sulfur cycle biological denitrification method. Background Technology

[0002] With the development of the national economy and the improvement of people's living standards, the discharge of nitrogen-containing wastewater has increased dramatically, especially low-carbon nitrogen-containing wastewater. Among these, the removal of ammonia nitrogen presents many challenges. Traditional biological denitrification processes, such as sequencing batch reactor (SBR) activated sludge processes and anaerobic / anoxic / aerobic processes, are mature, stable, and effective, but they are complex to operate and require high energy consumption. Newer biological denitrification processes, such as anaerobic ammonia oxidation, simultaneous nitrification-denitrification, and short-cut nitrification-denitrification, offer advantages such as higher efficiency and lower energy consumption. However, they also face challenges due to environmental sensitivity and stringent operational requirements. Therefore, process selection must be based on actual needs.

[0003] In practical applications, short-cut nitrification processes suffer from unstable nitrite accumulation during the short-cut nitrification stage. Compared to heterotrophic denitrification, biological autotrophic denitrification offers the advantage of lower sludge production, reducing subsequent sludge disposal costs. Common electron donors for autotrophic denitrification include hydrogen, iron, and sulfur. Autotrophic denitrification can significantly reduce the cost of adding organic carbon sources. Sulfur autotrophic denitrification (SAD), currently the mainstream autotrophic denitrification process, refers to the biological process of reducing nitrite by oxidizing reduced sulfur with sulfur-oxidizing bacteria under anoxic or anaerobic conditions, utilizing sulfur as an electron donor, thus exhibiting significant carbon reduction benefits. However, SAD also has certain drawbacks, such as: S... 2- It is prone to loss in the system, etc. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a short-cut nitrification-iron coupled sulfur cycle biological denitrification method. In the short-cut nitrification process, nitrite-oxidizing bacteria first convert ammonia nitrogen into nitrite. In the sulfur cycle microbial system, Fe... 2+ By forming an iron carrier in the form of FeS, sulfides are effectively fixed in the system, preventing their escape. Moreover, when the electron donor in the system is insufficient, it can serve as a substitute electron donor for biological denitrification, reducing the demand for external organic carbon sources. Sodium sulfate, as the sulfur source for sulfur autotrophic denitrification, transforms sulfate pollutants in wastewater into electron donors through a combination of sulfate reduction and sulfur autotrophic denitrification, forming a carbon-nitrogen-sulfur biological co-reaction system. This overcomes the shortcomings of single-species denitrification systems. The iron carrier in the form of FeS can also promote the activity of key enzymes in biological denitrification in the biological system, enhance the system's resistance to shock loads, and thus enhance denitrification stability.

[0005] To achieve the above objectives, the present invention provides a short-cut nitrification-iron coupled sulfur cycle biological denitrification method. The method first uses domesticated nitrite-reducing bacteria to convert ammonia nitrogen in wastewater into nitrite; then, sulfate-reducing bacteria and denitrifying thiobacilli are inoculated together into a culture medium containing iron ions or ferrous ions to further remove nitrite and nitrate from the wastewater using a domesticated composite bacterial agent.

[0006] The culture medium formula for acclimatizing nitrifying bacteria is: 0.2–2 g / L NH4Cl, 0.5–2 g / L NaHCO3; acclimatization conditions are: DO ≤ 0.5 mg / L, 15–40℃, 80–200 rpm, acclimatization time is 7–20 days; the pH of the culture medium is 7–9, adjusted using sodium bicarbonate or sodium carbonate. The preferred sodium bicarbonate dosage is 1 g / L.

[0007] The ferric ion is selected from at least one of ferric sulfate, ferric nitrate, and ferric chloride; the ferrous ion is selected from at least one of ferrous sulfate, ferrous chloride, ferrous sulfate, and ferrous nitrate.

[0008] The culture medium containing ferrous ions is formulated as follows: 0.4–2 g / L C6H 12 O6, 0.2-3 g / L NaNO2, 0.1-0.5 g / L Na2SO4, 0.04-0.1 g / L KH2PO4, 0.1-0.3 g / L FeSO4; the ferrous ion-containing culture medium formula is to replace 0.1-0.3 g / L FeSO4 in the aforementioned ferrous ion-containing culture medium formula with 0.1-0.4 g / L Fe2(SO4)3.

[0009] The acclimatization conditions for the sulfate-reducing bacteria and denitrifying thiobacilli were 15–40°C, 80–200 rpm, anaerobic in the dark, for 3–5 days; the pH of the culture medium was 6–9, adjusted using sulfuric acid solution and sodium hydroxide solution. Preferably, a 1 mol / L sulfuric acid solution and a 1 mol / L sodium hydroxide solution were used.

[0010] Furthermore,

[0011] The inoculation volume ratio of sulfate-reducing bacteria and denitrifying thiobacilli during acclimatization was 1–5; the concentration range of both sulfate-reducing bacteria and denitrifying thiobacilli in the acclimatized bacterial agent was 10. 4 ~10 5 cfu / mL.

[0012] The concentration range of nitrifying bacteria after acclimation is 10. 3 ~10 5 cfu / mL.

[0013] The acclimatized nitrifying bacteria were inoculated into nitrogen-containing wastewater at a volume ratio of 0.5 to 5. Inorganic carbon sources were added to make the inorganic C / N ratio 0.3 to 1.5. The ammonia nitrogen in the wastewater was converted into nitrite under low dissolved oxygen conditions (DO ≤ 0.5 mg / L), 15–40℃, 80–200 rpm, and pH 8–9. The conversion time was 6–24 hours.

[0014] The compound bacterial agent, after being acclimated with ferrous or ferrous ions, is inoculated into nitrogen-containing wastewater at a volume ratio of 0.5 to 5. An organic carbon source is added to bring the COD / N ratio to 1.6 to 3.7. The wastewater is then cultured under anaerobic dark conditions at 15 to 40°C, 80 to 200 rpm, and pH 6 to 9 to remove nitrite and nitrate nitrogen from the wastewater.

[0015] The denitrification time is 6–24 hours.

[0016] The concentrations of nitrite nitrogen and nitrate nitrogen in nitrogen-containing wastewater are controlled at 50–1000 mg / L.

[0017] The inorganic carbon source is selected from at least one of sodium bicarbonate and sodium carbonate.

[0018] The organic carbon source is selected from at least one of glucose, sucrose, and xylose.

[0019] The method of this invention is used to treat wastewater containing ammonia nitrogen, nitrate and nitrite.

[0020] Sulfate reduction: Under anaerobic conditions, sulfate-reducing bacteria in the bacterial agent utilize electrons provided by organic carbon sources to reduce sulfate to H2S and H2S. - and S 2- Sulfides provide electron donors for sulfur autotrophic denitrification.

[0021] Sulfate autotrophic denitrification: Under anaerobic conditions, the denitrifying thiobacilli in the inoculant use sulfides generated from sulfate reduction as electron donors to provide electrons to nitrite nitrogen in the water sample. Nitrite nitrogen is converted into nitrogen gas, and sulfides are converted back into sulfate ions. Using sulfides as electron donors solves the problem of poor mass transfer efficiency in traditional sulfur autotrophic denitrification.

[0022] Ferrocarrier strengthening: Fe 2+ By forming an iron support in the form of FeS, S is effectively absorbed. 2- It is fixed in the system to prevent it from escaping, and when the electron donor in the system is insufficient, it can serve as an alternative electron donor for biological denitrification, reducing the demand for external organic carbon sources. At the same time, it can enhance the system's resistance to shock loads. Iron carriers in the form of FeS can also promote the activity of key enzymes in biological denitrification in biological systems.

[0023] Compared with existing technologies, this invention provides a short-range nitrification-iron coupled sulfur cycle biological denitrification method, which has the following advantages:

[0024] (1) This invention makes full use of the water quality characteristics of common low-carbon nitrogen-containing wastewater. This type of wastewater contains pollutants such as sulfate. Nitrifying bacteria first convert ammonia nitrogen into nitrite, and iron-carrier-enhanced sulfur-cycle biological denitrification bacteria then use sulfate-reducing bacteria to reduce sulfate into H2S and H2S. - and S 2- Sulfides provide electron donors for sulfur autotrophic denitrification. Denitrifying thiobacilli can utilize sulfides in water to achieve autotrophic denitrification and remove nitrite, while ferrous iron can react with sulfur... 2- The formation of FeS precipitate effectively removes S. 2- It is fixed in the system to prevent it from escaping. When ferric iron is added to the system, it can be converted into ferrous iron. Moreover, when there is insufficient electron donor in the system, it can serve as a substitute electron donor for biological denitrification. Iron carriers in the form of FeS can also promote the activity of key enzymes in biological denitrification in biological systems, while also enhancing the flocculation effect of microorganisms, enhancing the system's resistance to shock loads, and thus enhancing the system's denitrification stability.

[0025] (2) The nitrifying bacteria have a high oxidation rate for ammonia nitrogen. Under inorganic C / N ratio of 0.3-1.5 and low dissolved oxygen conditions, the highest accumulation of nitrite in the culture medium with ammonia nitrogen as the only nitrogen source reached 230 mg / L. This shows that short-cut nitrifying bacteria have great application potential in degrading ammonia nitrogen in wastewater.

[0026] (3) Both nitrifying bacteria and iron-coupled sulfur cycle biological systems have a certain degree of salt tolerance and can be used for the conversion of ammonia nitrogen in saline wastewater.

[0027] (4) The iron-coupled sulfur cycle microbial system of the present invention has high efficiency in low carbon denitrification performance and is suitable for denitrification treatment of low carbon wastewater. At 15-40℃ and COD / N of 2.6-3.7, the nitrite nitrogen removal rate reaches 100%, which shows that the iron-coupled sulfur cycle biological system has great application potential for degrading nitrite nitrogen in wastewater. Attached Figure Description

[0028] Figure 1 The nitrite accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different inorganic C / N ratios;

[0029] Figure 2 The nitrate accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different inorganic C / N ratios;

[0030] Figure 3 The figure shows the nitrite accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different sulfate concentrations;

[0031] Figure 4 The figure shows the nitrate accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different sulfate concentrations;

[0032] Figure 5 The figure shows the nitrite accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different chloride concentrations;

[0033] Figure 6 The figure shows the nitrate accumulation of the short-cut nitrifying microbial denitrifying agent in Example 1 under different chloride concentrations;

[0034] Figure 7 The graph shows the nitrite removal effect of the sulfur cycle microbial denitrification agent in Example 3 under different carbon-nitrogen ratios.

[0035] Figure 8 The graph shows the nitrate removal effect of the sulfur cycle microbial denitrification agent in Example 3 under different carbon-nitrogen ratios.

[0036] Figure 9 The graph shows the nitrite removal effect of the iron-carrier enhanced sulfur cycle microbial denitrification agent in Example 3 under different carbon-nitrogen ratios.

[0037] Figure 10 The graph shows the nitrate removal effect of the iron-carrier enhanced sulfur cycle microbial denitrification agent in Example 3 under different carbon-nitrogen ratios.

[0038] Figure 11 This is a comparison diagram of the NAR / NIR enzyme activity of the iron-carrier-enhanced sulfur-cycling microbial denitrifying agent and the sulfur-cycling microbial denitrifying agent in Example 6.

[0039] Figure 12 This is a scanning electron microscope image of the iron-carrier-enhanced sulfur cycle microbial denitrification agent in Example 7;

[0040] Figure 13 This is a scanning electron microscope image of the sulfur-cycling microbial denitrifying agent in Example 7;

[0041] Figure 14 This is a comparison diagram of X-ray diffraction (XRD) analysis of the iron-carrier-enhanced sulfur-cycling microbial denitrifying agent and the sulfur-cycling microbial denitrifying agent in Example 8. Detailed Implementation

[0042] Example 1

[0043] (1) The nitrifying bacteria were purchased from the “China Microbial Strains Query Network” platform, and the platform number for the nitrifying bacteria is bio-67412.

[0044] The domestication of the nitrifying bacteria agent of the present invention: nitrifying bacteria are inoculated into a culture medium for domestication to obtain a nitrifying denitrifying bacteria agent. The culture medium contains 0.5 g / L NH4Cl and 1 g / L NaHCO3.

[0045] The acclimatization conditions were: DO ≤ 0.5 mg / L, 30℃, 130 rpm, and an acclimatization time of 12 days; the pH of the culture medium was 8, adjusted using sodium bicarbonate. After acclimatization, the concentration of nitrifying bacteria in the inoculum ranged from 10... 3 ~10 5 cfu / mL.

[0046] Nitrifying bacteria were applied to an ammonia nitrogen degradation experiment, with an ammonia nitrogen concentration of 60±3 mg / L. The nitrogen source added to the wastewater was NH4Cl (i.e., ammonia nitrogen), the inorganic carbon source was NaHCO3, and the concentration of the biological agent was 10 mg / L. 3 ~10 5 The concentration of cfu / mL was 1:1 with the wastewater, and the degradation conditions were: temperature 30℃, time 6h, and pH 8.

[0047] The short-range nitrifying biological agent prepared in Example 1 was applied to an ammonia nitrogen degradation experiment. Figure 1 and Figure 2 The figures show the nitrite and nitrate accumulation of short-cut nitrifying microbial denitrifying agents under different inorganic C / N ratios, respectively. Figure 1 It can be seen that there are high nitrite accumulation rates when the inorganic C / N ratio is between 0.9 and 1.3, and the nitrite accumulation reaches 30 mg / L when the inorganic C / N ratio is between 1.2 and 1.3. Figure 3 and Figure 4 The figures show the accumulation of nitrite and nitrate with short-cut nitrifying microbial denitrifying agents at different sulfate concentrations when the inorganic carbon-to-nitrogen ratio is 1. Figure 3 It can be seen that when the sulfate concentration is 0-8 g / L, the nitrite accumulation is the highest when the sulfate concentration is 3.2 g / L, reaching 31 mg / L; Figure 5 and Figure 6 To investigate the accumulation of nitrite and nitrate by short-cut nitrifying microbial denitrifying agents at different chloride concentrations with an inorganic carbon-to-nitrogen ratio of 1, from... Figure 5 It can be seen that the nitrite accumulation is similar at chloride concentrations of 0 and 1.6 g / L, and the nitrite accumulation reaches 30 mg / L, indicating that this nitrifying bacterium has a certain degree of salt tolerance. Figure 2 , Figure 4 and Figure 6It can be seen that the nitrate accumulation is all below 4 mg / L. Table 1 shows the nitrite accumulation effect of short-range nitrifying microbial agents during long-term operation. When the initial ammonia nitrogen concentration is 289.5 mg / L, the highest nitrite accumulation can reach 232.3 mg / L after 48 hours of reaction, and the highest nitrate accumulation can reach 44.2 mg / L. The conversion efficiency of ammonia nitrogen to nitrite is relatively high.

[0048] Table 1. Nitrite accumulation effect of short-range nitrifying microbial inoculants after long-term operation.

[0049]

[0050] Example 2: Domestication of iron-carrier-enhanced sulfur cycling microbial denitrifying agents

[0051] The sulfate-reducing bacteria and denitrifying thiobacillus used in this embodiment were purchased from the "China Microbial Strains Query Network" platform. The platform number for sulfate-reducing bacteria is bio-00232, and the platform number for denitrifying thiobacillus is bio-72703.

[0052] The domestication of the siderophore-enhanced sulfur cycling compound bacterial agent of this invention: Sulfate-reducing bacteria and denitrifying thiobacilli were inoculated into a culture medium at a volume ratio of 1:1 for domestication, resulting in a siderophore-enhanced sulfur cycling microbial denitrifying agent. The culture medium contained 0.5 g / L 6H. 12 O6, 1g / L NaNO2, 0.1g / L Na2SO4, 0.06g / L KH2PO4, 0.1g / L FeSO4;

[0053] The acclimatization conditions were 30℃, 130 rpm, anaerobic darkness, and an acclimatization period of 7 days. The pH of the culture medium was 7, adjusted using 1 mol / L sulfuric acid solution and 1 mol / L sodium hydroxide solution. After acclimatization, the concentrations of sulfate-reducing bacteria and denitrifying thiobacilli in the inoculum were both within the range of 10. 4 ~10 5 cfu / mL.

[0054] Meanwhile, a sulfur-cycle compound bacterial agent was prepared as a control. The preparation of this bacterial agent differed from that of the iron-carrier-enhanced sulfur-cycle compound bacterial agent in that FeSO4 was not added to the culture medium, while the other cultivation and acclimatization steps were the same.

[0055] Example 3: Enhanced nitrogen removal capacity of iron-carrier-enhanced sulfur-cycle compound bacterial agent compared to sulfur-cycle compound bacterial agent under different carbon-nitrogen ratio conditions.

[0056] The iron-carrier-enhanced sulfur cycling composite bacterial agent and the sulfur cycling composite bacterial agent prepared in Example 2 were added to simulated nitrogen-containing wastewater, with a wastewater to composite bacterial agent volume ratio of 3:1. NO2 - The -N concentration was 60±3 mg / L, and the simulated nitrogen-containing wastewater was supplemented with C6H4O as the organic carbon source.12 O6 was used as the sulfur source (Na2SO4) and the nitrogen source (NaNO2, i.e., nitrite nitrogen). Organic carbon and nitrogen sources were added to achieve COD / N ratios of 1.6, 2.1, 2.6, 3.2, and 3.7, respectively. The reaction was carried out under anaerobic, dark conditions at 30℃, 120 rpm, and pH 7. The removal capacity of the sulfur-cycling composite bacterial agent and the iron-carrier-enhanced sulfur-cycling composite bacterial agent for nitrite was measured after 6 hours of reaction. The results are as follows: Figure 7 and Figure 9 As shown, the sulfur-cycle compound bacterial agent and the iron carrier-enhanced sulfur-cycle compound bacterial agent have the following results regarding their ability to remove nitrite: Figure 8 and Figure 10 As shown, the iron-carrier-enhanced sulfur cycling compound bacterial agent can achieve a nitrite removal rate of over 80% when COD / N is 2.1, over 92% when COD / N is between 2.6 and 3.2, and 100% when COD / N is between 3.2 and 3.7. In contrast, the sulfur cycling compound bacterial agent achieves a nitrite removal rate of 69% when COD / N is 2.1, and while it achieves over 89% when COD / N is between 2.6 and 3.2, it achieves a nitrite removal rate of 96% when COD / N is between 3.2 and 3.7. After 6 hours of reaction, the nitrate concentration of the iron-carrier-enhanced sulfur cycling compound bacterial agent is below 1 mg / L. This indicates that the iron-carrier-enhanced sulfur cycling compound bacterial agent has a higher denitrification efficiency under low carbon-to-nitrogen ratio conditions compared to the sulfur cycling compound bacterial agent, reducing the amount of organic carbon source used and demonstrating better economic benefits.

[0057] Example 4: The improved denitrification capacity of the iron-carrier-enhanced sulfur cycling compound bacterial agent acclimated with ferrous iron compared to the sulfur cycling compound bacterial agent with added ferrous iron according to the present invention.

[0058] Example 4 differs from Example 3 in that the COD / N ratio is 2.6, the influent nitrite nitrogen concentration is 200±5 mg / L, and 1 mM ferrous ions are added to the wastewater of the sulfur-cycle compound bacterial agent. As shown in Table 2, compared with the sulfur-cycle compound bacterial agent with added ferrous ions, the iron carrier-enhanced sulfur-cycle compound bacterial agent after long-term ferrous acclimation has a higher nitrite nitrogen degradation efficiency. Within 24 hours, the nitrite concentration was reduced from 200.74 mg / L to 0.07 mg / L, with a degradation efficiency of 99.97%, and the nitrate concentration was reduced from 18.08 mg / L to 0.02 mg / L, with a degradation efficiency of 99.88%. The sulfur-cycle compound bacterial agent had a nitrite removal rate of 81.17% and a nitrate removal rate of 78.74% within 24 hours, indicating that the iron carrier-enhanced sulfur-cycle compound bacterial agent has a better denitrification effect after long-term acclimation.

[0059] Table 2. Denitrification effect of iron-carrier-enhanced sulfur cycling compound microbial agent acclimated to ferrous sulfate and sulfur cycling compound microbial agent with added ferrous sulfate.

[0060]

[0061] Example 5: Improved nitrogen removal capacity of iron-carrier-enhanced sulfur-cycle compound bacterial agent compared to sulfur-cycle compound bacterial agent under high-concentration nitrite wastewater load.

[0062] Example 5 differs from Example 3 in that the COD / N ratio is 2.6, and the influent nitrite nitrogen concentration is 180–227 mg / L. Tables 3 and 4 show that, compared to the sulfur-cycle compound bacterial agent, the iron-carrier-enhanced sulfur-cycle compound bacterial agent achieved a nitrite removal rate of over 99% and a nitrate removal rate of over 95% after 24 hours of reaction under different nitrite loads. In contrast, the sulfur-cycle compound bacterial agent still showed nitrite accumulation after 24 hours of reaction under different nitrite loads, with nitrite removal rates between 80% and 90% and nitrate removal rates between 70% and 90%. The nitrite removal rate gradually decreased with increasing nitrite concentration. This indicates that the iron-carrier-enhanced sulfur-cycle compound bacterial agent can enhance the resistance to shock loads caused by water quality fluctuations and improve the denitrification efficiency under different nitrite loads.

[0063] Table 3. Nitrogen removal effect of iron-carrier-enhanced sulfur cycling compound bacterial agent under high-concentration nitrite wastewater load.

[0064]

[0065] Table 4. Denitrification effect of sulfur-cycle compound bacterial agent under high-concentration nitrite wastewater load.

[0066]

[0067] Example 6: Enhanced activity of key denitrification enzymes by siderophore-enhanced sulfur cycling compound bacterial agent compared to sulfur cycling compound bacterial agent.

[0068] The sulfur-cycling compound bacterial agent (iron-0) and the siderophore-enhanced sulfur-cycling compound bacterial agent (iron-1) were centrifuged at 4000 rpm, 4°C, for 10 min. The mixture was then washed twice with 0.1 M PBS buffer, and this step was repeated three times. The mixture was resuspended in 0.1 M PBS buffer for the final wash, followed by sonication at 20 kHz, 5 min, and 4°C. The mixture was then centrifuged at 10000 g, 4°C, for 10 min, and the supernatant was extracted. This supernatant was the crude enzyme solution, used to determine the activity of key denitrification enzymes. The activities of nitrate reductase (NAR) and nitrite reductase (NIR) in different groups of crude enzyme solutions were measured. Figure 11 As shown, compared with the sulfur-cycle compound bacterial agent, the iron-supported sulfur-cycle compound bacterial agent improved the activity of two key enzymes under the condition of COD / N of 2.1, thus promoting the removal of nitrite. This indicates that the iron-supported sulfur-cycle compound bacterial agent accelerates the removal rate of nitrite and nitrate by enhancing the activity of key denitrification enzymes.

[0069] Example 7: Comparison of SEM and EDS of Ferrocarrier-Enhanced Sulfur Cycling Compound Microbial Agent and Sulfur Cycling Compound Microbial Agent

[0070] SEM images of the iron-carrier-enhanced sulfur cycling compound microbial agent and the sulfur cycling compound microbial agent are as follows: Figure 12 and Figure 13 As shown. From Figure 13 It can be seen that the surface of the sulfur-cycle compound microbial agent is smooth, and there are certain gaps between the microbial cells. Figure 12 Dense, fine-particle-size precipitates appeared on the surface of the iron-carrier-enhanced sulfur-cycling composite bacterial agent. These precipitates almost filled the gaps between bacteria, making the sludge surface structure more compact. The precipitates caused microorganisms to aggregate into bacterial flocs, resulting in better flocculation. Tables 5 and 6 show that the iron-carrier-enhanced sulfur-cycling composite bacterial agent, compared to the sulfur-cycling composite bacterial agent, had a higher Fe mass, generating FeS precipitate. This FeS-based iron carrier can effectively remove sulfur... 2- It is fixed in the system to prevent it from escaping, and when there is insufficient electron donor in the system, it can serve as an alternative electron donor for biological denitrification, reducing the demand for external organic carbon sources and enhancing the system's denitrification stability.

[0071] Table 5. Elemental weight and atomic percentage corresponding to the EDS energy spectrum of the iron-carrier-enhanced sulfur cycling compound microbial agent.

[0072] element weight percentage Atomic percentage carbon 70.5％ 90.3％ sulfur 7.4％ 3.6％ iron 22.1％ 6.1％ total 100％ 100％

[0073] Table 6. Elemental weights and atomic percentages corresponding to the EDS energy dispersive spectroscopy (EDS) spectra of sulfur-cycle compound microbial agents.

[0074] element weight percentage Atomic percentage carbon 72.42％ 91.8％ nitrogen 3.39％ 1.61％ sulfur 24.19％ 6.59％ total 100％ 100％

[0075] Example 8: XRD Comparison of Iron-Carrier Enhanced Sulfur Cycling Compound Microbial Agent and Sulfur Cycling Compound Microbial Agent

[0076] X-ray diffraction (XRD) analysis revealed the crystal structure changes of the iron-supported enhanced sulfur cycling composite bacterial agent and the sulfur cycling composite bacterial agent. Iron-0 and iron-1 represent the XRD patterns of the sulfur cycling composite bacterial agent and the iron-supported enhanced sulfur cycling composite bacterial agent, respectively. Figure 14As shown, no characteristic peaks were observed in the un-iron-acclimated sulfur-cycling compound bacterial agent, while the iron-carrier-enhanced sulfur-cycling compound bacterial agent exhibited sulfur and iron peaks at 27.6°, 21.1°, 52.2°, and 43.9°. Comparison with the PDF#49-1632 card confirmed that the substance was ferrous sulfide (FeS), consistent with previous SEM and EDS analyses. Therefore, the precipitate formed on the sludge surface can be identified as FeS. Ferrous sulfide, as the main component of natural pyrrhotite, has a scaly structure similar to graphite and belongs to the hexagonal crystal system. Thiobacillus can utilize it for denitrification, and both Fe and S within it can serve as electron donors for denitrification. The resulting FeS can improve the nitrogen removal performance of the biological system and enhance its denitrification stability.

[0077] Example 9: Short-range nitrification nitrite accumulation effect and denitrification performance of iron-carrier enhanced sulfur cycling compound bacterial agent

[0078] The nitrifying bacteria agent from Example 1 was applied to an ammonia nitrogen degradation experiment, with a concentration of 10... 3 ~10 5 The concentration of CFU / mL was 1:1 with wastewater, the ammonia nitrogen concentration was 60.33 mg / L, the inorganic C / N ratio was 1, and the degradation conditions were 30℃, 6h, and pH 8. The effluent from short-cut nitrification was then treated with the iron-carrier-enhanced sulfur cycle composite bacterial agent prepared in Example 2. The volume ratio of short-cut nitrification effluent to iron-carrier-enhanced sulfur cycle composite bacterial agent was 3:1. NO2 - The -N concentration was 23.51 mg / L, and an organic carbon source was added to bring the COD / N ratio to 2.6. The reaction was carried out under anaerobic darkness, at 30℃, 120 rpm, and pH 7. The removal capacity of the iron-carrier-enhanced sulfur-cycle composite bacterial agent on nitrite in the short-cut nitrification effluent was measured after 3 hours of reaction. Table 7 shows that the nitrite accumulation reached 29.81 mg / L after 6 hours of reaction. Subsequently, the effluent was treated with the iron-carrier-enhanced sulfur-cycle composite bacterial agent, and after 3 hours of reaction, the residual nitrite concentration was 0.17 mg / L, achieving a removal rate of 99%. Table 7 also shows that the residual nitrate concentration after 3 hours of reaction was 1.98 mg / L, indicating that the iron-carrier-enhanced sulfur-cycle composite bacterial agent can also achieve a high nitrite removal rate in the short-cut nitrification effluent.

[0079] Table 7. Effects of Short-Range Nitrification Nitrite Accumulation on Nitrogenation Performance of Iron-Carrier Enhanced Sulfur Cycling Compound Microbial Agent

[0080]

[0081]

[0082] Therefore, the present invention employs the above-mentioned method for preparing and applying a short-range nitrification-iron coupled sulfur cycle biological denitrification agent, which can not only remove ammonia nitrogen, nitrite nitrogen and nitrate nitrogen under low-carbon conditions, but also adapt to complex wastewater in actual process operation. This method has good application prospects for removing ammonia nitrogen, nitrite nitrogen and nitrate nitrogen from low-carbon wastewater.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for short-cut nitrification-iron coupled sulfur cycle biological denitrification, characterized in that, The method comprises the following steps: First, the ammonia nitrogen in the wastewater is converted into nitrite by using the acclimated nitrosation bacteria; then, the composite bacteria obtained by inoculating the sulfate-reducing bacteria and the Thiobacillus denitrificans into the culture medium containing iron ions or ferrous ions are used to further remove the nitrite and nitrate in the wastewater; The culture medium formula of the acclimated nitrosobacteria agent is: 0.2-2 g / L NH4Cl, 0.5-2 g / L NaHCO3; the acclimation conditions are: DO≤0.5 mg / L, 15-40 ℃, 80-200 rpm, and the acclimation time is 7-20 days; the pH of the culture medium is 7-9, and the pH is adjusted by using sodium bicarbonate or sodium carbonate; the culture medium formula containing ferrous ions is: 0.4-2 g / L C6H 12 O6, 0.2-3 g / L NaNO2, 0.1-0.5 g / L Na2SO4, 0.04-0.1 g / L KH2PO4, 0.1-0.3 g / L FeSO4; the culture medium formula containing iron ions is that 0.1-0.3 g / L FeSO4 in the culture medium formula containing ferrous ions is replaced by 0.1-0.4 g / L Fe2(SO4)3; the acclimation conditions of the sulfate-reducing bacteria and the Thiobacillus denitrificans are: 15-40 ℃, 80-200 rpm, anaerobic darkness, and the acclimation time is 3-5 days; the pH of the culture medium is 6-9, and the pH is adjusted by using sulfuric acid solution and sodium hydroxide solution; the inoculation volume ratio of the sulfate-reducing bacteria and the Thiobacillus denitrificans during acclimation is 1-5, and the concentration of the sulfate-reducing bacteria and the Thiobacillus denitrificans in the agent after acclimation is both in the range of 10 4 -10 5 cfu / mL; the concentration of the nitrosobacteria agent after acclimation is in the range of 10 3 -10 5 cfu / mL; the acclimated nitrosobacteria agent is inoculated into the nitrogen-containing wastewater, the volume ratio of the wastewater to the agent is 0.5-5, inorganic carbon source is added to the inorganic C / N is 0.3-1.5, and the ammonia nitrogen in the wastewater is converted into nitrite under the conditions of low dissolved oxygen DO≤0.5 mg / L, 15-40 ℃, 80-200 rpm, and pH 8-9; the conversion time is 6-24 h; the compound agent after the iron ion or ferrous ion acclimation is inoculated into the nitrogen-containing wastewater, the volume ratio of the wastewater to the compound agent is 0.5-5, organic carbon source is added to the COD / N is 1.6-3.7, and the nitrite nitrogen and nitrate nitrogen in the wastewater are further removed under the conditions of anaerobic darkness, 15-40 ℃, 80-200 rpm, and pH 6-9; the denitrification time is 6-24 h.

2. The method of claim 1, wherein, The concentration of the nitrite nitrogen and the nitrate nitrogen in the nitrogen-containing wastewater is controlled at 50-1000 mg / L.

3. The method of claim 1, wherein, The inorganic carbon source is at least one of sodium bicarbonate and sodium carbonate, and the organic carbon source is at least one of glucose, sucrose and xylose.

4. The method of claim 1, wherein, The method is used for treating wastewater containing ammonia nitrogen, nitrate and nitrite.

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