Method for quickly starting anaerobic ammonia oxidation reaction and improving denitrification performance by utilizing sulfuration modified nano zero-valent iron

Abstract

The invention belongs to the technical field of sewage treatment, and provides a method for quickly starting anaerobic ammonia oxidation and improving denitrification performance. Inoculating sludge is added into the ASBR reactor, the inoculating sludge is taken from activated sludge of an aerobic tank of an urban sewage treatment plant, and the volatile suspended solid concentration of initial mixed liquid is 4.8 + / -0.1 g / L; respectively adding vulcanized nano zero-valent iron into the reactor on the 30th day and the 52th day; feeding water is manually distributed, the pH value of the feeding water is adjusted to 7.5-8.0, dissolved oxygen in the water is removed through N2 aeration, the dissolved oxygen in the feeding water is made to be lower than 0.3 mg / L, and the anaerobic environment is kept; continuously operating the reactor for 140 days under the conditions of 35 + / -1 DEG C, 150r. Min <-1 > and light shielding, and analyzing the performance of the reactor during the period; the time required for starting the anaerobic ammonia oxidation process is shortened, the denitrification efficiency of the system is improved, and theoretical support and technical parameters are provided for engineering application of the anaerobic ammonia oxidation process.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a method for rapidly starting an anaerobic ammonium oxidation reaction and improving nitrogen removal performance by using sulfur-modified nano zero-valent iron. Background Art

[0002] Since the birth of the anaerobic ammonium oxidation (Anammox) process, it has been widely used in sewage denitrification due to its high efficiency and sustainability. Under anaerobic conditions, the Anammox process relies on autotrophic anaerobic ammonium-oxidizing bacteria to directly oxidize ammonia (NH 2 - -N) to nitrogen gas (N 4 + -N) using nitrite (NO 2 ). However, due to the characteristics of slow growth rate, long generation cycle, and temperature sensitivity of anaerobic ammonium-oxidizing bacteria, it is difficult to enrich anaerobic ammonium-oxidizing bacteria, significantly prolonging the start-up period of the reactor and presenting difficulties in mainstream applications.

[0003] Studies have found that anaerobic ammonium-oxidizing bacteria contain a large amount of cellular iron in the form of heme and sulfur-iron proteins, and the presence of iron promotes the growth of anaerobic ammonium-oxidizing bacteria. Nano zero-valent iron (nZVI) has the characteristics of small volume, large specific surface area, and high activity, and can accelerate the start-up of the anammox process (84 d). The reason why nZVI can improve the nitrogen removal efficiency (NRE) is that nZVI improves the activity of the quorum sensing system and thus the activity of anaerobic ammonium-oxidizing bacteria. In addition, the combined effect of the shell structure covered by the nZVI precipitation corrosion product and the buffering effect of extracellular polymeric substances (EPS) avoids the sharp change of pH. However, due to the high surface energy and magnetism of nZVI, it is easy to quickly aggregate into large particles, reducing the surface area and reaction activity, and nZVI is easily oxidized and difficult to be evenly distributed in the liquid phase.

[0004] To improve this problem, researchers have proposed using modified nZVI to improve applicability and activity. Adding sulfur element during the preparation of nZVI can obtain sulfur-modified nano zero-valent iron (S-nZVI), which improves the reaction activity and electron selectivity of nZVI. Introducing sulfur element into the Anammox system increases the abundance of Ca. Brocadia and also stimulates the relative abundances of anaerobic ammonium-oxidation genes such as hao, hzsA, and hzsC. Relatively low sulfide significantly increases the biomass and heme c concentration.

[0005] S-nZVI has better long-term stability than nZVI and can reduce inactivation caused by aggregation. At the same time, FeS formed on the surface of S-nZVI xIt has reducibility and can remove nitrate nitrogen. The anaerobic system inoculated with S-nZVI and anaerobic sludge can improve the secretion of EPS and the activities of several key enzymes, enrich functional bacteria, and improve biodiversity. Based on these characteristics of S-nZVI, it can be speculated that it has a promoting effect on the anaerobic ammonium oxidation process, can shorten the start-up time of the Anammox process and improve the Anammox denitrification performance. Summary of the Invention

[0006] In order to solve the problems of slow start-up and low denitrification performance of anaerobic ammonium oxidation, the present invention proposes a method for rapidly starting anaerobic ammonium oxidation reaction and improving denitrification performance by using sulfur-modified nano-zero valent iron. The present invention proposes to add sulfur-modified nano-zero valent iron S-nZVI to the reactor to shorten the start-up time of anaerobic ammonium oxidation and improve the denitrification performance, and explore its mechanism of action. The purpose of the present invention is to reveal the application of S-nZVI in anaerobic ammonium oxidation, in order to provide a new idea for the rapid start-up and stable operation of anaerobic ammonium oxidation.

[0007] The present invention prepares S-nZVI by liquid phase reduction method, and characterizes the surface morphology and structure of the prepared material. In the ASBR reactor, the effects of adding S-nZVI on the rapid start-up, long-term operation characteristics of the Anammox process, and nitrogen conversion law are explored, the change characteristics of the microbial community structure are analyzed, and the influence of S-nZVI on the start-up of the anaerobic ammonium oxidation process is explored, providing theoretical support and technical parameters for the engineering application of the Anammox process.

[0008] The present invention is realized by the following technical solutions: a method for rapidly starting anaerobic ammonium oxidation reaction and improving denitrification performance by using sulfur-modified nano-zero valent iron, adding inoculated sludge to the ASBR reactor, and the initial concentration of mixed liquid volatile suspended solids MLVSS is 4.8 ± 0.1 g / L; adding sulfur-modified nano-zero valent iron S-nZVI to the reactor on the 30th day and the 52nd day respectively; the influent is artificial wastewater, and the influent pH is 7.5-8.0, and the dissolved oxygen in the water is removed by aerating N 2 to make the dissolved oxygen in the influent lower than 0.3 mg / L, and maintain an anaerobic environment; the reactor operates continuously for 140 d at 35 ± 1 °C and 150 r·min -1 under the condition of avoiding light, and analyze the reactor performance during this period; S-nZVI is prepared by liquid phase synthesis method: FeSO 4 ·7H 2 O is dissolved in an ethanol solution with a concentration of 75%, adding Na 2 S·9H 2 O, under the N 2 atmosphere, the NaOH solution containing NaBH 4 is dropped into FeSO4 ·7H 2 In the O mixture, continuously stir at 1000 rpm for 60 min; the obtained S-nZVI is washed successively with deionized water and absolute ethanol, and then dried in a vacuum drying oven at 60 °C for 24 h; The influent water contains 20-100 mg / L NH 4 Cl, 26.4-100 mg / L Na 2 NO 2 , 500 mg / L NaHCO 3 , 180 mg / L CaCl 2 , 100 mg / L MgSO 4 ·7H 2 O, 27 mg / L KH 2 PO 4 , and in addition, 1 ml / L of trace element I and trace element II are added; the components of the trace element solution are as follows: .

[0009] The specific surface area and pore size of the S-nZVI are: S BET (m 2 / g): 64.7; D m (nm): 74.1.

[0010] Specifically, it includes the following steps: (1) Inoculate sludge and add nZVI and S-nZVI: The inoculated sludge is taken from the activated sludge in the aerobic tank of a municipal wastewater treatment plant, left to stand for 24 h, and the supernatant is discarded. The concentration of mixed liquid volatile suspended solids (MLVSS) is 4.8 ± 0.1 g / L; Take 200 mL of sludge and inoculate it into the reactor, and add 50 mg·L -1 of nZVI and S-nZVI to the reactor on the 30th day and the 52nd day respectively; (2) Reactor operation: Place the reactor in a constant temperature shaking incubator at 35 °C and 150 r·min -1 for operation; Intermittent influent is adopted, and the HRT is controlled to be 12-48 h; The reactor operates continuously for 140 d, divided into four stages: stage I cell lysis stage, stage II transition stage, stage III activity improvement stage, and stage IV activity stabilization stage; Stage I is from 1 to 30 d, and the influent NO 2 - -N concentration is 26.4 mg·L -1 , and the influent NH 4 + -N concentration is 20 mg·L -1 ; Stage II is from 31 to 70 d, and the influent NO2 - The concentration of -N is 66 mg·L -1 , and the influent NH 4 + -N concentration is 50 mg·L -1 ; Phase III is from 71 to 90 d, and the influent NO 2 - -N concentration is 66 mg·L -1 , and the influent NH 4 + -N concentration is 50 mg·L -1 ; Phase IV is from 90 to 140 d, among which from 90 to 112 d, the influent NO 2 - -N concentration is 75 mg·L -1 , and the influent NH 4 + -N concentration is 85 mg·L -1 , and from 113 to 140 d, the influent NO 2 - -N concentration is 100 mg·L -1 , and the influent NH 4 + -N concentration is 100 mg·L -1 ; (3) Performance analysis: Water samples were collected from the ASBR reactor every two days and filtered using a 0.45 μm filter membrane; the established standard methods were used to measure the concentrations of NH 4 + -N, NO 2 - -N, NO 3 - -N and MLVSS; the concentration of ferrous ions in the sludge was measured by the phenanthroline spectrophotometry method; the pH was measured using a pHS-3C pH meter; EPS extraction was carried out by the thermal extraction method; the protein PN content was quantified by the BCA method, and the polysaccharide PS content was determined by the anthrone-sulfuric acid method; the PN and PS contents in EPS were detected every 70 d, and each sample was analyzed 3 times to obtain accurate results; (4) Correlation network analysis: Spearman correlation analysis was used to explore the association relationships among the top 50 abundant genera; significant correlations were determined based on a coefficient greater than 0.5 and a p-value less than 0.05; network visualization analysis was implemented using Gephi software.

[0011] The effective volume of the reactor is 200 mL.

[0012] The sludge sample was subjected to microbial sequencing analysis. The method used was to extract the sample DNA with a kit. The primers for the V3-V4 region of 16S rRNA were 341F: 5'-CCTACGGGAGGCAGCAG-3' and 805R: 5'-GACTACHVGGGTATCTAATCC-3', and Illumina high-throughput sequencing was performed.

[0013] By analyzing the changes in the effluent nitrogen concentration, nitrogen removal efficiency, Fe 2+ content, EPS content, and microbial community structure, the present invention proves the feasibility of S-nZVI promoting the rapid start-up of Anammox and improving the denitrification performance, providing a new way for the stable operation of Anammox.

[0014] The results show that the start-up of Anammox can be promoted by adding S-nZVI in the Anammox reactor. Compared with the control group and the nZVI reactor, the start-up time of S-nZVI was shortened by 32 d and 14 d respectively, and the NRE was increased by 4.7% and 2.4% respectively. The Fe 2+ content in the sludge increased by 23.3% - 68.9%, and the EPS content increased by 39.8 mg / L. The relative abundances of anaerobic ammonium-oxidizing bacteria were increased, and the relative abundances of Candidatus Brocadia and Candidatus Anammoxoglobus were increased from 0.07% and 0% to 15.62% and 0.23% respectively.

[0015] By adding S-nZVI to the ASBR reactor, the present invention shortened the time required for the start-up of anammox and improved the denitrification efficiency of the system, and explored the changes in the effluent nitrogen concentration, denitrification efficiency, Fe 2+ content in the sludge, the secretion of EPS content, and the microbial community structure during the reaction process. The enrichment of anaerobic ammonium-oxidizing functional bacteria and the improvement of their activity are necessary conditions for the stable operation of anaerobic ammonium oxidation. The present invention provides a new way for this. Description of the Drawings

[0016] Figure 1 : Scanning electron microscope images of nZVI and S-nZVI, (a) Scanning electron microscope image of nZVI; (b) Scanning electron microscope image of S-nZVI (Fe / S = 10); (c) Element distribution of nZVI; (d) Element distribution of S-nZVI (Fe / S = 10); Figure 2 : Denitrification performance of S0 (control group), S1 (adding nZVI), and S2 (adding S-nZVI), (a) Inlet and outlet NH 4 + -N concentration; (b) Inlet and outlet NO 2- -N concentration; (c) influent and effluent NO 3 - -N concentration; (d) nitrogen removal efficiency (NRE); Figure 3 For the performance characterization of anaerobic ammonium oxidation sludge; In the figure: (a) Fe2+ content in anaerobic ammonium oxidation sludge; (b) EPS concentration and protein-polysaccharide ratio (PN / PS); Figure 4 For the microbial community structure composition of the reactor; In the figure: (a) compositional changes at the phylum level, (b) compositional changes at the genus level; Figure 5 For the genus-level species correlation network; Figure 6 For the community function prediction based on KEGG; (a) nitrogen-converting enzyme content; (b) metabolic function; Figure 7 For the XPS spectra of nZVI and S-nZVI; In the figure: (a) Fe XPS spectrum of nZVI; (b) Fe XPS spectrum of S-nZVI; (c) S XPS spectrum of nZVI; (d) S XPS spectrum of S-nZVI. Specific implementation manners

[0017] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The materials cited herein and their citations will be incorporated by reference.

[0019] Equivalent technologies of the specific embodiments described that can be understood by those skilled in the art through routine experiments will be included in this application.

[0020] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The instrument and equipment used in the following embodiments are all conventional laboratory instrument and equipment unless otherwise specified; the experimental materials used in the following embodiments are all obtained from conventional biochemical reagent stores unless otherwise specified.

[0021] I. Reaction apparatus and method: Three ASBRs were used in the experiment, namely S0 (without material), S1 (containing nZVI), and S2 (containing S-nZVI, Fe / S = 10). The reactors were continuously operated for 140 d at 35 ± 1 °C under dark conditions. The dosages of nZVI and S-nZVI were fixed at 50 mg·L -1 . The experiment was divided into 4 stages, and the load was continuously increased by changing the hydraulic retention time (HRT) and influent concentration.

[0022] 1. Preparation of nZVI and S-nZVI: Preparation of nZVI: The liquid-phase reduction method was used to prepare nZVI. Weigh 4.9643 g of FeSO4·7H 2 O and dissolve it in 50 mL of water. Pour the mixed solution into a 250 mL three-necked flask. Add 20 mL of absolute ethanol to the three-necked flask and stir evenly at a speed of 450 rpm to dilute and disperse the solute, making the particle size of the synthesized iron particles smaller. Weigh 2.0266 g of NaBH 4 (excess Fe 2 + :BH 4 - = 1:3) and dissolve it in 20 mL (0.025 mol / L) of NaOH solution. Add the NaOH solution containing NaBH 4 to the constant-pressure funnel and drip it into the three-necked flask at a speed of 2 drops / second, and stir at a speed of 450 rpm. After the dripping is completed, continue to stir for 0.5 h to make the reaction complete. Filter the mixed solution with a Buchner funnel, and wash the prepared solid particles twice with deionized water and once with absolute ethanol. The separated precipitate was dried in a vacuum drying oven at 60 °C for 24 h, ground, and the sample was collected in a centrifuge tube, sealed, and stored in a refrigerator at 4 °C for later use.

[0023] Preparation of S-nZVI: The liquid-phase reduction method was used to prepare S-nZVI. Weigh 3.723 g of FeSO 4 ·7H 2 O and dissolve it in 110 mL of water. Pour the mixed solution into a 250 mL three-necked flask and stir at a speed of 450 rpm for 0.5 h. Add 7.5 mL of (1 mol / L) NaOH to the three-necked flask at a speed of 1 drop / second, and stir for 0.5 h after adding. Weigh 1.0165 g of NaBH 4 and dissolve it in 40 mL of water. Add 13.06 mL (0.1 mol / L) of Na 4 S·9H 2 O to the NaBH 2 solution. The NaBH 2 containing Na 2 S·9H4 The solution was added dropwise to the three-necked flask through a constant-pressure funnel at a rate of 2 drops per second, and stirred for 0.5 h to make the reaction sufficient. The mixture was filtered through a Buchner funnel, and the prepared solid particles were rinsed twice with deionized water and once with absolute ethanol. The separated precipitate was dried in a vacuum drying oven at 60 °C for 24 h, ground, and the sample was collected and sealed in a centrifuge tube and stored refrigerated at 4 °C in the refrigerator for later use.

[0024] The morphological characteristics and the distributions of C, O, Fe, and S of nZVI and S-nZVI were studied by SEM-EDS. Figure 1 Figures a and 1b are the SEM images of nZVI and S-nZVI. Compared with nZVI, the surface of S-nZVI particles is relatively rough, and the generated iron sulfide adheres to the surface, reducing the chain-like aggregation phenomenon between particles. EDS analysis ( Figure 1 d) also confirmed the loading of S on the surface of S-nZVI, with a weight fraction of 1.50%. The XPS spectra ( Figure 7 a and b) showed the presence of Fe(II) and Fe(III) in both materials. From Figure 7 c and d, it can be seen that nZVI only contains SO 4 2- (168.2 eV), which is due to the FeSO 4 ·7H 2 O selected when preparing the material. The S element in S-nZVI mainly exists in the forms of S 2- (162.0 eV), S 2 2- (162.9 eV), S n 2- (163.9 eV) and SO 4 2- (168.2 eV). This indicates that the surface composition of S-nZVI is mainly FeS, Fe 2 , FeS n , and a small amount of FeSO4, etc. The BET specific surface areas and pore diameters of nZVI and S-nZVI are 15.4 and 64.7 m 2 / g, 28.6 and 74.1 nm, respectively. The higher BET surface area and pore diameter of S-nZVI may provide more potential sites for microbial adhesion.

[0025] 2. Inoculated sludge and simulated wastewater: The inoculated sludge was taken from the activated sludge in the aerobic tank of a municipal wastewater treatment plant, and the initial concentration of mixed liquid volatile suspended solids (MLVSS) was 4.8 ± 0.1 g / L. Artificial water was used in the experiment, with NH 4 Cl and NaNO 2 as raw materials, and NaHCO 3Use inorganic carbon source to maintain the influent pH at 7.5 - 8.0. Add trace elements required for microbial growth (1 ml / L) to the influent. NH 4 + -N and NO 2 - -N have initial concentrations of 20 mg / L and 26 mg / L respectively, and are adjusted during the experiment. Remove dissolved oxygen (DO) in water by aeration to make the DO in the influent lower than 0.3 mg / L. 2 4

[0026] Artificial influent contains NH 4 Cl (50 - 75 mg·L -1 ), Na 2 NO 2 (70 - 100 mg / L), NaHCO 3 (500 mg / L), CaCl 2 (180 mg / L), MgSO 4 ·7H 2 O (100 mg / L), 27 mg / L KH 2 PO 4 (27 mg / L), 1 mL / L of trace element Ⅰ and trace element Ⅱ. The ratio of trace elements is shown in Table 1. Adjust the pH with 0.1 mol·L -1 of HCl and NaOH.

[0027] Table 1: Components of trace element solution 3. Reactor operation parameters: The reactor operates for a total of 140 days, divided into four stages, and the time of each stage is shown in Table 2.

[0028] Table 2: Reactor operation stages 4. Collect water samples from the ASBR reactor every two days and filter them using a 0.45 μm filter membrane. Determine the concentrations of NH 4 + -N, NO 2 - -N, NO 3 - -N and MLVSS using the established standard methods. Determine ferrous ions (Fe 2+Concentration. The pH was measured using a pHS-3C pH meter. EPS extraction was performed using the thermal extraction method. The protein (PN) content was quantified by the BCA method, and the polysaccharide (PS) content was determined by the anthrone-sulfuric acid method. The PN and PS contents in EPS were detected every 70 d, and each sample was analyzed 3 times to obtain accurate results. In addition, sludge samples were taken at the end of the operation (140 d), and the sample DNA was extracted using a kit. The primers for the V3-V4 region of 16S rRNA were 341F (CCTACGGGAGGCAGCAG) and 805R (GACTACHVGGGTATCTAATCC), and high-throughput sequencing was performed using the Illumina system.

[0029] 5. Calculation method: The nitrogen removal rate (NRE) and NO 2 - -N removal rate described in the text are calculated as follows: ; where C i refers to the influent substance concentration (mg·L -1 ), and C e refers to the effluent substance concentration.

[0030] II. Experimental results 1. The start-up process of the three ASBR reactors (S 0 , S 1 and S 2 ), the change in the effluent nitrogen concentration, and the denitrification performance are as Figure 2 shown.

[0031] The first stage is the cell lysis stage. At the beginning of the reactor operation, the effluent NH 4 + -N concentration was significantly higher than the influent concentration (20 mg / L), but the effluent NO 2 - -N concentration was significantly lower than the influent concentration (26 mg / L). This is mainly because some microorganisms in the inoculated sludge failed to adapt to the new environment, resulting in autolysis and releasing a large amount of NH 4 + -N. In addition, an appropriate amount of organic matter was produced during the cell lysis process, which contributed to the denitrification of nitrite and thus reduced the effluent NO 2 --N. The cell lysis durations of S0, S1, and S2 were 26 days, 26 days, and 18 days, respectively. During this stage, the significant decrease in nitrite concentration in the effluent of each reactor was attributed to denitrifying bacteria. The average NREs of S0, S1, and S2 were 26.8±16.4%, 38.0±19.5%, and 38.3±19.6%, respectively. Therefore, the nitrogen removal efficiencies of the three reactors showed a similar trend during the cell lysis stage, which was the result of the combined action of nitrifying bacteria, denitrifying bacteria, and anaerobic ammonium oxidation bacteria in the inoculated sludge.

[0032] On the 30th day, nZVI and S-nZVI were added to S1 and S2, respectively. After 48 h of reaction, there was no significant difference in NRE among the three reactors, which might be because the microbial community in the reactors was complex at this stage, and the nitrogen removal was coordinated by multiple microorganisms.

[0033] The second stage was the transition stage. During this stage, the nitrate nitrogen production in each reactor was much higher than the theoretical value of 0.26, and the ratios at 70 d were 0.945, 0.750, and 0.785, respectively. The reason for this result might be that some ammonia-oxidizing bacteria could survive under low DO conditions and produce nitrate nitrogen. At the same time, it also made the NRE of each reactor lower than 70% in the first 70 days.

[0034] When nZVI and S-nZVI were added again on the 52nd day, a significant decrease in NO 3 - -N was observed in S1 and S2. This might be due to the chemical reaction between nZVI and nitrate to produce NH 4 + -N. At the same time, microorganisms used zero-valent iron or divalent iron and endogenous organic carbon as electron donors to reduce nitrate or nitrite to N 2 .

[0035] The third stage was the activity improvement stage, and the nitrate nitrogen production in each reactor began to gradually decrease. On the 80th day, the total nitrogen removal rate of S2 reached over 80.0%. On the 94th day, the total nitrogen removal rate of S1 was 82.3%. At this time, the total nitrogen removal rate of S0 was only above 75%, and its total nitrogen removal rate reached above 80% for the first time on the 112th day. During this stage, the NREs of S0, S1, and S2 were 71.5±4.6%, 74.7±5.3%, and 78.2±5.2%, respectively. This indicated that adding nZVI and S-nZVI could both shorten the start-up time of anaerobic ammonium oxidation and improve the nitrogen removal efficiency, but the performance of S-nZVI was better. This was mainly because the sulfide-iron compounds on the surface of S-nZVI had higher conductivity and hydrophobicity, which could accelerate electron transfer and slow down the passivation reaction. Therefore, its reaction activity and antioxidant ability were stronger than those of nZVI.

[0036] The fourth stage is the active stable stage. By increasing the influent NH 4 + -N and NO 2 - -N concentrations of the reactor, the total nitrogen load of the reactor is increased. During the 90 - 112 d, the NLR of each reactor is 0.32 kg TN / m 3 / d. During this stage, the NREs of S0, S1 and S2 are 77.1±3.2%, 82.3±2.3% and 84.2±2.5% respectively. On the 112th d, the influent NH 4 + -N and NO 2 - -N concentrations are increased again. At this time, the NLR is 0.4 kg TN / m3 / d. During the 112 - 140 d, the NREs of S0, S1 and S2 are 79.5±3.8%, 81.8±4.6% and 84.2±3.5% respectively. Although the effluent NH 4 + -N and NO 2 - -N concentrations of the three reactors all increase to some extent, they still maintain relatively high NREs. This indicates that the microbial community in the reactor already has a certain degree of anti-disturbance ability. To sum up, the use of S-nZVI can not only shorten the start-up time of the anaerobic ammonium oxidation process, but also resist shock loads during the stable operation period.

[0037] 2. Changes in Fe 2+ in sludge: The Fe 2+ content of the sludge is as Figure 3 shown. During the second, third and fourth stages, the Fe 2 + content of S1 is 13.8% - 40.5% higher than that of S0, while during the same stages, the Fe 2+ content of S2 is 23.3% - 68.9% higher than that of S0. The presence of nZVI and S-nZVI both increases the Fe 2+ content of the reactor sludge, and the presence of S-nZVI has a more obvious promotion effect on the Fe 2+ content of the sludge. This may be because the sulfided nZVI contains more Fe 2+ on its surface, which is convenient for cells to directly absorb and utilize. The synthesis of heme c requires the embedding of Fe 2+ to form an active region. The Fe 2+ content in the sludge is positively correlated with heme c. With the addition of iron-containing materials, the synthesis of heme c is promoted. Previous studies have shown that heme c is related to the denitrification performance of the reactor, and the higher the heme c content, the stronger the denitrification performance. In this study, the Fe 2+The change trend of the content is almost the same as that of NRE. In summary, the addition of S-nZVI can promote the intracellular Fe 2+ content, thereby promoting the synthesis of heme c and improving the denitrification performance of the reactor. 3. Changes in EPS in the reactor: The EPS content of the sludge is as Figure 3 shown. After the reactor operates for 140 d, the EPS contents of S0, S1, and S2 are 32.1 mg / g VSS, 47.9 mg / g VSS, and 55.5 mg / g VSS, respectively, showing a significant increase compared with 14.8 mg / g VSS, 18.9 mg / g VSS, and 15.7 mg / g VSS during the initial startup period, with the increase rates being 50.8%, 60.5%, and 71.7%, respectively. The higher EPS content in S2 is caused by the combined action of ZVI and S2-. The introduction of S2- will cause bacteria to produce self-protection, form a protective barrier through extracellular proteins, and promote the release of EPS. After operating for 140 d, the PN / PS values of the three reactors S0, S1, and S2 all increase, being 2.9, 3.8, and 4.5, respectively. The reactors with the addition of S-nZVI show a better tendency to increase EPS and PN secretion, which helps to protect cell structure, promote cell growth and metabolic processes, improve the hydrophobicity of sludge, and enhance the stability of the anaerobic ammonia oxidation system.

[0038] 3. Changes in the microbial community structure in the reactor: Figure 4 It is the analysis of the composition and succession of the microbial community structure in the reactor. Figure 4 a shows the microbial composition at the phylum level. At the phylum level, the initially inoculated sludge samples are mainly composed of Planctomycetota (31.67%), Proteobacteria (19.87%), Bacteroidota (11.73%), Patescibacteria (9.56%), and Chloroflexi (8.96%). After the reactor operates for 140 d, the main dominant phyla in S0, S1, and S2 do not change significantly, being Planctomycetota (22.04%, 20.55%, 22.71%), Proteobacteria (15.61%, 20.55%, 22.71%), Bacteroidota (4.82%, 4.62%, 6.13%), and Chloroflexi (17.15%, 17.48%, 17.44%), respectively. The relative abundances of Bacteroidota in S1 and S2 decrease significantly, which may be related to the weakening of denitrification reactions in the reactor. There is literature indicating that Fe 2+Promote the dissimilatory nitrate reduction to ammonium (DNRA) process by inhibiting denitrification. Acidobacteriota in S1 and S2 were 9.67% and 8.78% respectively, while only 4.23% was contained in SY0. This may be because the added nZVI and S-nZVI promoted the participation of the Feammox system in the nitrogen cycle process, and Acidobacteria belong to typical Feammox bacteria. Research shows that some microorganisms belonging to Acidobacteria have the ability to use various simple organic acids (such as acetate) as alternative electron donors to dissimilate iron reduction under anaerobic conditions.

[0039] Figure 4 b shows the differences in relative abundances at the genus level. Only Candidatus Brocadia was detected in the inoculated sludge, with a relative abundance of 0.07%. While both Candidatus Brocadia and Candidatus Anammoxoglobus were detected in S0, S1, and S2, with relative abundances of 13.74%, 11.69%, 15.62% and 0.17%, 0.22% and 0.23% respectively. And Candidatus Jettenia was also detected in S0 and S1, with relatively low contents of 0.01% and 0.02% respectively. The relatively high relative abundance of Candidatus Brocadia in the three reactors may be related to its high growth rate. The increase in the abundance of anaerobic ammonia-oxidizing bacteria in S2 was related to the higher NRE ( Figure 2 d). After the 140-day experiment, the total relative abundance of anaerobic ammonia-oxidizing bacteria in S2 was 15.86%, which was 1.88% and 3.93% higher than that in S0 and S1 respectively. This indicates that compared with nZVI, S-nZVI can further enrich anaerobic ammonia-oxidizing bacteria. In addition, the start-up times of the anaerobic ammonia-oxidation processes in the S0, S1, and S2 reactors were 112, 94, and 82 days respectively, further indicating that the increase in the abundance of anaerobic ammonia-oxidizing bacteria contributed to the successful start-up of the reactor. The relative abundance of the ammonia-oxidizing bacterium Nitrosomonas in S2 was 1.44%, higher than that in S0 (0.35%) but lower than that in S1 (2.65%). At the same time, the relative abundance of the nitrite-oxidizing bacterium Nitrospira was 0.32%, also lower than that in S0 (0.52%) and S1 (0.36%). This shows that the reducing S-nZVI inhibits the growth of nitrifying bacteria by reducing the ORP, ensuring the performance of anaerobic ammonia oxidation under low DO conditions and contributing to the growth of anaerobic ammonia-oxidizing bacteria.

[0040] Unclassified_Anaerolineacea, Unclassified_SJA-28, Unclassified_Sapro - spiraceae, and Norank_Comamonadacea were found in all three reactors, and they may play a key role in hydrolyzing complex organic matter and fermenting it into smaller organic molecules. Unclassified_Anaerolineacea is an anaerobic bacterium capable of fermenting and hydrolyzing carbohydrates and is the primary fermenter for carbohydrate decomposition. Unclassified_SJA28 is a previously reported fermentative, monoploid H 2 -oxidizing autotroph that can degrade EPS. In addition, the presence of Norank_Comamonadacea indicates the removal of bio-nutrients and reduced sludge production under anoxic conditions. In addition, a large number of bacteria with denitrification activity (Denitratisoma, Ferruginibacter, Terrimonas, norank_PHOS-HE36, Norank_Gemmatimonadaceae, and OLB17) were also detected in this study. Denitratisoma is a heterotrophic denitrifying bacterium that uses dead cells as a carbon source for denitrification. Ferruginibacter is well-known for its heterotrophic denitrification metabolism and also exhibits hydrolytic activity, promoting the decomposition of complex organic matter and EPS. Terrimonas is a denitrifying bacterium that not only participates in denitrification but also secretes EPS to promote the aggregation of anaerobic bacteria, thereby improving the nitrogen removal efficiency. Thermomonas is the main autotrophic denitrifying bacterium detected in most sulfur autotrophic denitrification reactors, and the relative abundances of Thermomonas in S1 and S2 are 0.012% and 0.014%, respectively. This may be due to the addition of S-nZVI promoting the growth of sulfur autotrophic denitrifying bacteria. The presence of Nar and Nrf genes in norank_PHOS-HE36 indicates that it may be involved in DNRA, and its content in S2 is higher than that in S1 (0.36% in S2 and 0.12% in S1). Denitrifying bacteria in the anaerobic ammonium oxidation system can use EPS or endogenous organic matter to provide electrons for reducing nitrate. There is a complex synergistic mechanism between denitrifying bacteria and anaerobic ammonium oxidizing bacteria, jointly responsible for nitrogen removal. Denitrifying bacteria in the anaerobic ammonium oxidation system can promote the decomposition of complex organic matter, increase EPS secretion, and use endogenous organic matter to provide electrons for reducing nitrate.

[0041] Figure 5Shows the correlations among the top 50 genera in the sample. In the ASBR, the ratio of positive to negative correlations remains similar, indicating that the characteristics of microbial interactions are more complementary rather than obvious cooperation or competition, which is the main driving factor of community structure. Cadidatus Brocadia is the main functional microorganism in the anaerobic ammonium oxidation process and is positively correlated with UTCFX1 of the Anaerolineaceae. In addition, Denitratisoma and norank_mle1-8 (Planctomycetota) are also positively correlated with Cadidatus Brocadia. Denitratisoma is a typical heterotrophic denitrifying bacterium, showing a significant positive correlation with Cadidatus Brocadia and similar abundance changes, providing favorable conditions for nitrogen removal in the anaerobic ammonium oxidation system. In terms of connectors, Chloroflexi, Proteobacteria, and Bacteroidota are composed of a large number of microorganisms related to nitrogen metabolism. These microorganisms contribute to the stability and functional expression of the anaerobic ammonium oxidizing bacteria community by sharing molybdenum cofactors, extracellular polysaccharides, amino acids, and folic acid with the anaerobic ammonium oxidizing bacteria. However, the role of non-key species cannot be ignored. For example, microorganisms under the Microbacteriaceae, which often appear in the microbial network, can be cross-fed by anaerobic ammonium oxidizing bacteria and heterotrophic microorganisms, contributing to the stability of the microbial system. Therefore, the correlated effects among multiple microorganisms jointly promote the growth and metabolism of anaerobic ammonium oxidizing bacteria.

[0042] Figure 6 Shows the content of enzymes related to NO 2 − -N transformation (predicted using PICRUSTs based on the KEGG database), Figure 6 As shown in a, in addition to being removed by anaerobic ammonium oxidation, nitrite can also be reduced to nitrogen gas through denitrification (NO 2 − -N → N 2 ), or reduced to ammonium through DNRA (NO 2 − -N → NH 4 + -N). The nitrite reductase (ammonia production) in S2 is significantly higher than that in S1, but the contents of nitrite reductase (NO production) and NO reductase in it are significantly lower than those in S1. This is mainly because S-nZVI contains sulfide (S 2- ), and some DNRA bacteria can use sulfide (S 2- ) or elemental sulfur (S 0 ) as electron donors for the DNRA process. Some studies have found that Fe 2+The addition improved DNRA and inhibited denitrification. In this study, the iron ions and sulfur ions released by S-nZVI promoted the occurrence of the DNRA process.

[0043] Figure 6 b shows the predicted metabolic functions of the reactor communities. The results indicate that the metabolic function of S2 is slightly higher than that of S1 and S0. This also shows that adding S-nZVI to the anaerobic ammonia oxidation reactor can promote the metabolism of microorganisms.

[0044] This invention verified that: under the condition of 35±1°C, exogenous addition of S-nZVI can shorten the startup time of Anammox and improve the nitrogen removal efficiency. The entire Anammox startup experiment lasted for 140 days. The startup times of S0, S1, and S2 were 80 d, 94 d, and 112 d respectively. Moreover, the nitrogen removal efficiency of S2 increased by 4.7% compared with S0 and 2.4% compared with S1.

[0045] Fe in the sludge 2+ content increased. In the second, third, and fourth stages, the Fe 2+ content of S1 was 13.8% - 40.5% higher than that of S0. And in the same stage, the Fe 2+ content of S2 was 23.3% - 68.9% higher than that of S0. Adding S-nZVI can promote the intracellular Fe 2+ content, thereby promoting the synthesis of heme c and improving the nitrogen removal performance of the reactor.

[0046] The EPS content of the sludge increased. After the reactor operated for 140 d, the EPS contents of S0, S1, and S2 were 32.1 mg / gVSS, 47.9 mg / g VSS, and 55.5 mg / g VSS respectively, showing a significant increase compared with 14.8 mg / g VSS, 18.9 mg / g VSS, and 15.7 mg / g VSS at the initial startup stage. The increase rates were 50.8%, 60.5%, and 71.7% respectively. The reactors with S-nZVI addition showed a better tendency of increased EPS secretion, which helps to protect cell structures, promote cell growth and metabolic processes, improve the hydrophobicity of the sludge, and enhance the stability of the anaerobic ammonia oxidation system.

[0047] S-nZVI can promote the enrichment of Anammox functional bacteria and the increase in the abundances of DNR bacteria and fermentative bacteria, thereby maintaining the stable nitrogen removal of the Anammox system under nitrogen changes. Cadidatus Brocadia is the key genus for Anammox startup, with relative abundances of 13.74%, 11.69%, and 15.62% in S0, S1, and S2, respectively. In addition, the relative abundances of Denitratisoma, UTCFX1, and norank_mle1-8 all increase together with Cadidatus Brocadia.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rapidly starting anaerobic ammonium oxidation reaction and improving denitrification performance using sulfide-modified nano zero-valent iron, characterized in that: The inoculum sludge was added to the ASBR reactor, and the initial mixed liquid volatile suspended solids (MLVSS) concentration was 4.8±0.1 g / L. 50 mg·L was added to the reactor on the 30th and 52nd days, respectively. -1 Sulfurized modified nano zero-valent iron S-nZVI; the influent water is artificially distributed water, using 0.1 mol·L -1 The pH of the influent was adjusted to 7.5-8.0 by adding HCl and NaOH, and the dissolved oxygen in the water was removed by N2 exposure, so that the dissolved oxygen in the influent was less than 0.3 mg / L to maintain an anaerobic environment. The reactor was operated at 35 ± 1℃ and 150 r·min -1 The reactor was operated continuously for 140 days under light-proof conditions, during which the performance of the reactor was analyzed; S-nZVI was prepared by liquid phase synthesis: 3.723 g FeSO4·7H2O was dissolved in 110 mL water and stirred at 450 rpm for 0.5 h; 7.5 mL of 1 mol / L NaOH was added at 1 drop / s and stirred for 0.5 h after addition; 1.0165 g NaBH4 was dissolved in 40 mL water, and 13.06 mL of 0.1 mol / L Na2S·9H2O was added to the NaBH4 solution; The NaBH4 solution containing Na2S·9H2O was added to the FeSO4 solution at a rate of 2 drops / second, and stirred for 0.5 h to allow the reaction to be complete; the obtained S-nZVI was washed with deionized water and anhydrous ethanol in turn, and then dried in a vacuum oven at 60°C for 24 h; the obtained S-nZVI sample was refrigerated and stored at 4°C for later use; The influent water contains 20-100 mg / L NH4Cl, 26.4-100 mg / L Na2NO2, 500 mg / L NaHCO3, 180 mg / L CaCl2, 100 mg / L MgSO4·7H2O, 27 mg / L KH2PO4, and 1 ml / L trace element I and trace element II are added; wherein the trace element solution components are as follows: 。 2. The method according to claim 1, characterized in that: The specific surface area and pore size of the S-nZVI are: BET :64.7m 2 / g;D m :74.1nm.

3. The method according to claim 1, characterized in that: The specific steps include: (1) Inoculation of sludge and addition of S-nZVI: The inoculated sludge was taken from the activated sludge in the aerobic tank of the municipal sewage treatment plant. The sludge was allowed to stand for 24 h, and the supernatant was discarded. The MLVSS concentration of the mixed liquid was 4.8±0.1 g / L. 200 mL of sludge was inoculated into the reactor, and 50 mg·L S-nZVI was added to the reactor on the 30th and 52nd days, respectively. -1 S-nZVI; (2) Reactor operation: The reactor was placed at 35°C and 150 r / min -1 The reactor was operated in a constant temperature oscillating box; intermittent water inflow was used, and the HRT was controlled at 12 to 48 hours; the reactor was operated continuously for 140 days, which was divided into four stages: stage I cell lysis stage, stage II transition stage, stage III activity enhancement stage, and stage IV activity stabilization stage; Phase I is 1~30 days, with influent NO2 - -N concentration was 26.4 mg·L -1 , influent NH4 + -N concentration was 20 mg·L -1 ; Phase II is 31~70 days, influent NO2 - -N concentration was 66 mg·L -1 , influent NH4 + -N concentration is 50 mg·L -1 ; Stage III is 71~90 days, influent NO2 - -N concentration was 66 mg·L -1 , influent NH4 + -N concentration is 50 mg·L -1 ; Stage IV is 90-140 days, of which 90-112 days are influent NO2 - -N concentration is 75 mg·L -1 , influent NH4 + -N concentration is 85 mg·L -1 , 113~140 d influent NO2 - -N concentration is 100 mg·L -1 , influent NH4 + -N concentration is 100 mg·L -1 ; (3) Performance analysis: Water samples were collected from the ASBR reactor every two days and filtered using a 0.45 μm filter membrane; NH4 + -N, NO2 - -N、NO3 - -N and MLVSS concentrations; the concentration of ferrous ions in the sludge was determined by o-phenanthroline spectrophotometry; pH ​​was measured using a pHS-3C pH meter; EPS was extracted using the thermal extraction method; the protein PN content was quantified using the BCA method, and the polysaccharide PS content was determined by the anthrone-sulfuric acid method; The PN and PS contents in EPS were tested every 70 days, and each sample was analyzed three times to obtain accurate results; (4) Correlation network analysis: Spearman correlation analysis was used to explore the correlation between the top 50 abundant genera; significant correlation was determined based on a coefficient greater than 0.5 and a p-value less than 0.05; network visualization analysis was achieved using Gephi software.

4. The method according to claim 3, characterized in that: The effective volume of the reactor is 200 mL.

5. The method according to claim 3, characterized in that: Microbial sequencing analysis was performed on the sludge samples. The sample DNA was extracted using a kit and the primers for the V3-V4 region of 16SrRNA were 341F: 5'-CCTACGGGAGGCAGCAG-3' and 805R: 5'-GACTACHVGGGTATCTAATCC-3', and Illumina high-throughput sequencing was performed.

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