Method for strengthening formation and denitrification performance of salt-tolerant aerobic granular sludge in high-salinity wastewater treatment

Abstract

The invention discloses a method for strengthening formation and denitrification performance of salt-tolerant aerobic granular sludge in high-salinity wastewater treatment, which comprises the following specific implementation processes: culturing S-AGS by taking activated sludge of a town sewage treatment system and salt-tolerant sludge of an industrial wastewater treatment system as a mixed inoculum, and optimizing the operating conditions of an SBR (sequencing batch reactor); 16SrRNA high-throughput sequencing and co-occurrence network analysis are applied to identify S-AGS core species, a theoretical basis is provided for directional strengthening of structural stability and denitrification performance of the S-AGS core species, screening and expanding culture are performed on core functional strains, Thaura T-1 and PseudofuvimonasP-1 obtained through screening and expanding culture are compounded to prepare a composite functional microbial inoculum, and on the basis of mixed inoculum and reactor conditions, the composite functional microbial inoculum can be used for preparing the high-efficiency denitrification agent for the S-AGS. The composite functional microbial agent is added, so that the synergistic strengthening effect on the denitrification performance of the S-AGS is achieved. According to the method, mixed sludge is inoculated, efficient nitrogen and carbon removal performance is achieved under high salt stress, a core strain is screened and subjected to expanding culture and compounded to serve as a composite functional bacterial agent, and the nitrogen removal efficiency of nitrification / denitrification in the biological treatment process under salt stress can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of biological enhancement treatment of high-salt organic wastewater, and specifically relates to a method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment. Background Art

[0002] Aerobic granular sludge (AGS) technology has the advantages of good sedimentation performance, high tolerance load, and strong resistance to salt stress, and has great application potential in the treatment of high-salt organic wastewater. However, the AGS process under high salt stress has engineering difficulties such as unstable particle structure and limited removal of pollutants (especially nitrogen pollution), which restricts its engineering application. The key is to cultivate salt-tolerant aerobic granular sludge (S-AGS) with stable structure and efficient nitrogen removal. At present, S-AGS cultivation mostly uses conventional activated sludge as inoculum to first cultivate granular sludge, and then gradually increase the salinity to promote the improvement of community salt tolerance. However, it is difficult to cultivate S-AGS with stable particles and strong salt tolerance using a single sludge inoculum source. Researchers usually use biochemical activated sludge with rich species diversity and good sedimentation performance as inoculum to cultivate AGS, but its tolerance to salinity is limited and its performance under high salt stress is unstable; compared with conventional activated sludge, the bacterial community derived from high-salt habitats such as industrial wastewater has higher tolerance to salinity and diverse metabolic pathways, but such bacterial communities have poor self-flocculation ability and are difficult to form granular sludge with stable structure. In addition, when the salinity increases step by step, the activity of microorganisms generally decreases and sludge loss is serious, especially the denitrification functional bacteria (such as denitrifying bacteria, ammonia oxidizing bacteria, and nitrite oxidizing bacteria) that are very sensitive to salinity. The metabolism is severely inhibited, resulting in the collapse of the process denitrification performance. In this regard, in order to solve the above problems, we should make full use of the characteristics of AGS bacterial community zoning colonization and functional interaction, and propose a S-AGS enhanced cultivation method from the perspective of inoculum sludge selection, operation condition optimization, and functional bacterial agent enhancement to achieve efficient and stable denitrification of S-AGS under high salt stress. Summary of the invention

[0003] In view of the above problems, the object of the present invention is to provide a method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment.

[0004] The invention proposes to cultivate S-AGS by using activated sludge from a municipal sewage treatment system and salt-tolerant sludge from an industrial wastewater treatment system as mixed inoculum. On the basis of optimizing the inoculum sludge, the invention develops a S-AGS cultivation method with strong aeration, short sedimentation and gradient salinity acclimation. Then, 16S rRNA high-throughput sequencing and co-occurrence network analysis are used to identify the core species of S-AGS, so as to provide a theoretical basis for directional enhancement of its structural stability and denitrification performance. The core functional strain screening and expansion cultivation are carried out, and Thauera T-1 and Pseudofulvimonas P-1 obtained by screening and expansion cultivation are compounded to prepare a composite functional bacterial agent, which is put into an SBR reactor to exert the synergistic enhancement effect of Thauera spp. and Pseudofulvimonas spp. on the denitrification performance of S-AGS, endow S-AGS with the potential of simultaneous nitrification and denitrification under high salt stress, and enhance the denitrification performance of high-salt wastewater treatment in the process.

[0005] The specific technical solutions are as follows:

[0006] A method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment comprises the following steps:

[0007] 1) Using activated sludge from urban sewage treatment systems and salt-tolerant sludge from industrial wastewater treatment systems as mixed inoculum to cultivate S-AGS and optimize the operating conditions of the SBR reactor;

[0008] 2) Use 16S rRNA high-throughput sequencing and co-occurrence network analysis to identify the core species with good salt tolerance in S-AGS, and provide a theoretical basis for the targeted enhancement of its structural stability and denitrification performance;

[0009] 3) Based on step 2), the core functional strains are screened and expanded, and Thauera T-1 and Pseudofulvimonas P-1 obtained by screening and expansion are compounded to prepare a composite functional bacterial agent, and the composite functional bacterial agent is added based on the mixed inoculum and reactor conditions in step 1) to exert the effects of Thauera spp. and

[0010] Synergistic enhancement of the nitrogen removal performance of S-AGS by Pseudofulvimonas spp.

[0011] Furthermore, the treatment salinity of the salt-tolerant sludge in step 1) is ≥1%, the mixing mass ratio of activated sludge and salt-tolerant sludge is 2:1-1:1, and the salt-tolerant sludge of the industrial wastewater treatment system is taken from wastewater treatment systems such as pharmaceutical chemicals, fine chemicals, coal chemicals, petrochemicals, etc. (mother liquor) and wastewater regeneration concentrate from papermaking, printing and dyeing, power plant desulfurization, etc. The proportion of salt-tolerant sludge in industrial wastewater should not exceed 50%, otherwise the sludge granulation process will be slow and the particle structure will be difficult to stabilize.

[0012] Further, the effective volume of the sequencing batch reactor (SBR) in step 1) is 4.0±0.2L, the height-to-diameter ratio is 5:1, the volume exchange ratio is 50%, the ambient temperature is 25±2°C, the reactor is provided with oxygen through the bottom aeration head, the surface gas velocity is 1.2cm / s, the dissolved oxygen is 7.5-8.5mg / L, and different from the conventional operation mode, a stronger aeration is set to produce a higher hydraulic shear force to stimulate microorganisms to secrete extracellular polymers (EPS) and form a higher hydraulic selection pressure to promote particle formation. The operation cycle is 4h, including 3min water inlet, 35min standing, 187-192min aeration, 5-10min sedimentation, 5min water outlet, the sludge discharge is not strictly controlled, and the pH value is controlled at 7.0± 0.2, setting a shorter sedimentation time is conducive to discharging sludge with poor sedimentation performance as early as possible in the drainage stage and promoting the retention of granular sludge with good performance in the system. The gradient acclimation method is used to enhance the salt tolerance of the sludge. The long-term operation of the reactor is divided into six stages. In terms of NaCl, the influent salinity is 0, 10, 20, 30, 35, and 40 g / L, the influent COD is 800-1000 mg / L, and the COD / TN is 20:1 to promote microbial growth. The operation time of each stage is 15-20 days. After observing the stability of COD and TN removal performance, the salinity can be increased; the gradient salinity condition is conducive to the adaptive change of the microbial community and avoids cell death caused by high osmotic pressure under instantaneous salt stress.

[0013] Furthermore, in step 2), the dynamic succession of the microbial community structure with salinity changes was explored to clarify the impact of salinity on the S-AGS microbial community, and 16S rRNA high-throughput sequencing and co-occurrence network analysis were used to identify the core species Thauera spp. and Pseudofulvimonas spp. with good salt tolerance.

[0014] Furthermore, in the composite functional bacterial agent in step 3), Thauera T-1 and Pseudofulvimonas P-1 are compounded in a biomass ratio of 2:1 to 1:2.

[0015] Furthermore, the added amount of the composite functional bacterial agent is 3% to 10% of the biomass.

[0016] Further, the screening and expansion process in step 3) is as follows: S-AGS is obtained from a stably operated SBR reactor as a source of salt-tolerant co-cultured bacteria, the granular sludge is fully ground and dispersed, the strain is separated by the dilution multiple method, and the diluted bacterial suspension is evenly coated on a solid culture medium containing 100 mg / L LB, and a salt stress habitat is simulated by adding different concentrations of NaCl. Subsequently, the culture medium is sealed with a sealing film and inverted in an incubator for overnight culture. After a single colony grows, several salt-tolerant strains are finally screened out after multiple plate coating and streaking. When the culture medium salinity is 10 g / L, the screened strains are subcultured three times and frozen in a -80°C refrigerator with 50% glycerol, followed by 16S rDNA gene sequencing, and a phylogenetic tree is generated using the BLAST (basic local alignment search tool) algorithm to screen out the strain most similar to Thaueraspp. (named Thauera T-1). Similarly, when the salinity of the culture medium was 30 g / L, the strain most similar to Pseudofulvimonas spp. (named Pseudofulvimonas P-1) was screened out and used as the reserve core functional bacteria for exogenous enhancement of the reactor.

[0017] The beneficial effects of the present invention are:

[0018] 1) The present invention proposes to cultivate S-AGS using activated sludge from a municipal sewage treatment system and salt-tolerant sludge from an industrial wastewater treatment system as mixed inoculum. Compared with single sludge inoculation, this method combines the advantages of activated sludge being easy to agglomerate and granulate and industrial sludge being strong in salt tolerance, and can cultivate S-AGS with dense particles and good strength, thereby imparting efficient nitrogen removal and carbon removal performance under high salt stress;

[0019] 2) The present invention develops a S-AGS cultivation method with strong aeration, short settling time and gradient salinity acclimation, which can stimulate microorganisms to secrete extracellular polymers and form a high hydraulic selection pressure to promote particle formation, which is beneficial to discharge sludge with poor settling performance as early as possible in the drainage stage and promote the retention of granular sludge with good performance in the system, which is beneficial to the adaptive change of microbial community and avoids cell death caused by high osmotic pressure under instantaneous salt stress; 3) With the goal of directional enhancement of S-AGS structural stability and denitrification performance, the present invention targetedly identified the core species of S-AGS and screened and expanded the culture to obtain a composite functional bacterial agent (ThaueraT-1+Pseudofulvimonas P-1). Both microorganisms are functional bacteria with simultaneous nitrification and denitrification. The strong EPS secretion ability of Thauera T-1 is beneficial to maintaining the stability of S-AGS particles, and Pseudofulvimonas P-1 is beneficial to maintaining the stability of S-AGS particles. The strong salt tolerance of P-1 is beneficial to improving the salt stress resistance of S-AGS. The two synergistically endow S-AGS with the potential for simultaneous nitrification and denitrification under high salt stress, thereby enhancing the denitrification performance of the process for high-salt wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The performance results of the three groups of different sludge inoculation conditions in Example 1, (a) is the particle size of salt-tolerant aerobic granular sludge, (b) is the influent COD and removal rate, (c) is the influent TN and its removal rate, (d) is NH4 + -N and removal rate;

[0021] Figure 2 Optical microscope images of sludge samples at 4% salinity in Example 1, (a) is the R1 reactor, (b) is the R2 reactor, and (c) is the R3 reactor;

[0022] Figure 3 This is the microbial colinearity network diagram of the R3 reactor sludge at 1-4% salinity in Example 2;

[0023] Figure 4 NH4 for RC and RTP nitrogen conversion processes + -N, NO2 - -N and NO3 - -N degradation curves, (a) and (e) are the ammonia oxidation process of the RC group and the RTP group, (b) and (f) are the nitrite oxidation process of the RC group and the RTP group, (c) and (g) are the nitrite reduction process of the RC group and the RTP group, (d) and (h) are the nitrate reduction process of the RC group and the RTP group. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the embodiments and the accompanying drawings, but the protection scope of the present invention is not limited thereto.

[0025] Example 1 Optimization of inoculated sludge and reactor operating conditions

[0026] Three groups of SBR reactors were set up to investigate the effect of inoculation sludge source on the cultivation performance of S-AGS: the inoculum of the R1 reactor was the aeration tank sludge of a certain urban sewage treatment plant, with MLSS (mixed liquor suspended solids concentration) of 4000±110 mg / L and MLVSS (mixed liquor volatile suspended solids concentration) of 2568±70 mg / L; the inoculum of the R2 reactor was the secondary sedimentation tank sludge of a certain pharmaceutical and chemical sewage treatment plant, and the sludge was collected and then exposed to air and then inoculated. The MLSS of the industrial salt-tolerant sludge was 4000±120 mg / L and MLVSS was 2238±60 mg / L; in order to maintain the same biomass, the R3 reactor was inoculated with a mixture of the above urban sludge and industrial sludge, and the MLSS of both was 2000 mg / L.

[0027] The effective volume of the SBR reactor system of the above three groups is 4.0±0.2L, the height-diameter ratio (H / D) is 5:1, the volume exchange ratio is 50%, the ambient temperature is 25±2℃, the reactor is provided with oxygen through the bottom aeration head, the surface gas velocity is 1.2cm / s, the dissolved oxygen is 7.5~8.5mg / L, the SBR operation cycle is 4h, including water inlet (3min), standing (35min), aeration (190min), sedimentation (7min), water outlet (5min), the sludge discharge is not strictly controlled, and the pH value is controlled at 7.0±0.2. The reactor runs for a total of 145 days, divided into six stages, the influent COD is 800mg / L, TN is 40mg / L, and the influent salinity (in terms of NaCl) in the six stages is 0, 10, 20, 30, 35, 40g / L respectively.

[0028] like Figure 1 As shown in (a), the initial AGS particle size of the reactors was relatively small, with average particle sizes of 112.2±11μm (R1), 90.1±13μm (R2), and 103.5±9μm (R3). After 20 days of sludge screening, the particle size of the sludge in the three groups of reactors increased, and the sludge gradually changed from the initial flocculent form to fine particles. As the salinity continued to increase, the average particle size of the granular sludge in the R3 reactor reached about 1200±44μm, while the final average particle size of the sludge in the R2 and R1 reactors was only 600±26μm and 650±33μm, respectively. This shows that under high salt stress, R3 has stronger aggregation performance after inoculation with mixed sludge, can tolerate higher salinity, and form larger particles. Figure 2 As shown, optical microscope observation of sludge samples at 4% salinity revealed that the AGS structure in R3 was dense, with clear boundary structure and yellow color ( Figure 2 (c) in R1, the sludge stratification is not obvious and the structure is relatively loose ( Figure 2(a) in R2, while the sludge in R2 still retains a lot of flocculent and white ( Figure 2 (b) in the figure. The above results show that the R3 reactor inoculated with urban-industrial mixed sludge formed granular sludge with larger particles and higher density. This method has solved the problems of poor sedimentation performance of single sludge inoculated under high stress and difficulty in retaining functional bacteria to a certain extent.

[0029] The COD concentration of reactor influent and COD removal rate are as follows: Figure 1 As shown in (b), at the beginning of salinity addition, the COD removal rates of the three groups of reactors fluctuated greatly, but could be stabilized at around 90% within 10 days. Within a salinity of 2%, all three groups of reactors could maintain good carbon removal efficiency. When the salinity reached 4%, the COD removal rates of R1 and R2 dropped to below 85% and 90%, which were significantly lower than those of R3 (94.1±0.4%). The results showed that the sludge microorganisms in R3 had a strong tolerance to salinity and their metabolic activity was not significantly inhibited.

[0030] 3 groups of reactors TN, NH4 + -N removal rates are as follows Figure 1 As shown in (c) and (d) in the figure, before adding salinity, the TN removal rates of R1, R2, and R3 were 70.1±3.1%, 64.6±2.2%, and 68.2±1.3%, respectively, and NH4 + -N removal rates were 96.0±2.7%, 83.2±1.9%, and 90.6±2.2%, respectively. After gradually increasing the salinity, the denitrification performance of the three groups of reactors was affected in a short period of time. At 3% salinity, TN and NH4 + -N removal rate can be stabilized at 81±1.3% and 98±1.2% in the end, while the removal rates of R1 and R2 are only 77±1.9%, 95±2.2% and 89±0.9%, 91±1.3%, respectively. In the later high salinity condition, the TN removal rate of R3 has been maintained at a high level (78.8±0.9%), higher than R1 (59.1±0.7%) and R2 (60.3±1.2%). The order of reactor stability during the acclimation process of different salinity gradients is R3>R2>R1 (based on denitrification and carbon removal performance). It can be seen that compared with single inoculated sludge, inoculated mixed sludge can couple the denitrification function of urban sewage activated sludge and the salt tolerance function of industrial wastewater sludge, giving R3 efficient denitrification and carbon removal performance under high salt stress.

[0031] Example 2 Identification of core species in salt-tolerant aerobic granular sludge

[0032] Using 16S rRNA high-throughput sequencing, we focused on the R3 group to explore the dynamic succession of the microbial community structure with salinity changes (1-4%) to clarify the impact of salinity on the S-AGS microbial community. As the salinity increased, the relative abundance of the dominant AGS genera Rhodobacter spp., Hyphomonas spp., and Flavobacterium spp. under salt-free conditions decreased from 14.25%, 11.98%, and 9.59% to 1.59%, 5.10%, and 1.29%, respectively, indicating that their competitiveness under high salinity decreased and it was difficult for them to compete and survive under excessively high salt conditions. Thauera spp. was significantly enriched when the salinity was higher than 2%, and its abundance increased from 4.57% to 38.89% with the increase of salinity, while the abundance of Pseudofulvimonas spp. increased from 1.20% to 10.02%. When the salinity reached 4%, the dominant species in the system were Thauera spp. (30.55%) and Pseudofulvimonas spp. (6.95%). Among them, Thauera spp. had a strong EPS secretion ability and played an important role in the S-AGS stabilization process. It also had the ability of simultaneous nitrification and denitrification. Pseudofulvimonas spp. was a heterotrophic nitrifying-aerobic denitrifying bacterium, which was reported to have a stronger tolerance to salinity (above 30 g / L NaCl). Therefore, under salinity stress, the high enrichment of Thaueraspp. functional bacteria stimulates EPS secretion to maintain good sludge agglomeration. At the same time, the salt-tolerant denitrification functional bacteria Pseudofulvimonas spp. in the aerobic granular sludge system can ensure that the system can maintain a high nitrogen metabolism efficiency and enhance the salt tolerance of the entire aerobic granular sludge reactor system.

[0033] Analysis of the niche width and correlation network of the S-AGS microbial community showed that under 1-4% salinity, functional bacteria such as Thauera spp. and Pseudofulvimonas spp. not only had high abundance (>1%) under high salt stress, but also occupied a wide niche (niche width scores ranked in the top 50). Therefore, Thauera spp. and Pseudofulvimonas spp. are the dominant bacterial communities in S-AGS. Through correlation network analysis ( Figure 3), the positive correlation ratio of interactions between microbial community networks was 70.15%, and the negative correlation ratio was 29.85%; the S-AGS microbial network includes multiple important modules, among which the modules represented by Thauera spp. and Pseudofulvimonas spp. have the characteristics of large nodes / high centrality. Combined with the above, Thauera spp. and Pseudofulvimonas spp. have important ecological functions, high stability and adaptability at 1% to 4% salinity, and are the core species of S-AGS, playing an important role in the structural stability and functional diversity of aerobic granular sludge.

[0034] Example 3 Composite functional bacterial agent strengthens the salt tolerance and denitrification function of S-AGS

[0035] S-AGS was obtained from a stably operated SBR reactor as a source of salt-tolerant co-cultured bacteria. The granular sludge was fully ground and dispersed, and the strains were isolated by the dilution multiple method. The diluted bacterial suspension was evenly coated on a solid culture medium containing 100 mg / L LB, and a salt stress habitat was simulated by adding different concentrations of NaCl. Subsequently, the culture medium was sealed with a sealing film and inverted in an incubator for overnight culture. After a single colony grew up, several salt-tolerant strains were finally screened out after multiple plate coating and streaking. When the culture medium salinity was 10 g / L, the selected strains were subcultured three times and frozen in a -80°C refrigerator with 50% glycerol, followed by 16S rDNA gene sequencing. The BLAST (basic local alignment search tool) algorithm was used to generate a phylogenetic tree, and the strain most similar to Thauera spp. (named Thauera T-1) was screened out. Similarly, when the salinity of the culture medium was 30 g / L, the strain most similar to Pseudofulvimonas spp. (named Pseudofulvimonas P-1) was screened out and used as the reserve core functional bacteria for exogenous enhancement of the reactor.

[0036] Thauera T-1 and Pseudofulvimonas P-1 were obtained from S-AGS and compounded in a 1:1 biomass ratio to prepare a composite functional bacterial agent. The enhancement effect of the functional bacterial agent on the nitrification / denitrification pathway of S-AGS under high salt stress was evaluated through batch experiments. The composite functional bacterial agent was added at a dosage of 5% (biomass ratio, w / w) as the RTP group, and the heat-inactivated strain was added as the control RC group. The sludge specific activity of ammonia oxidation, digestion and denitrification reactions of sludge was analyzed. The batch experiment was sampled and tested 10 times to monitor NH4 + -N, NO2 - -N, NO3 -The concentration of -N changes, the consumption rate of the substrate in the system is obtained by linear fitting and related calculations are performed to evaluate its denitrification performance.

[0037] NH4 + -N, NO2 - -N and NO3 - -N degradation curve Figure 4 As shown in the figure, the RTP group rapidly denitrified under 2% salinity conditions, and the nitrogen pollutants were basically completely removed within 2 hours. The denitrification process followed the first-order reaction kinetics. The control group Rc observed NH4 + -N in small amounts with NO2 - -N accumulated in large quantities, indicating that the ammonia oxidation and nitrification processes were inhibited by salinity. Analysis of the denitrification process of the Rc group ( Figure 4 (b) to (d)) found NO2 - -N reduction was not affected but NO3 - -N accumulation, indicating NO2 - -N oxidation process is inhibited. Compared with nitrification process, ammonia oxidation process is less affected by salinity, and nitrite oxidizing bacteria (NOB) obtain less energy from ammonia and nitrite oxidation process. Therefore, salt stress has an adverse effect on the activity and enrichment of NOB. At this time, Rc sludge mainly realizes nitrogen conversion through short-range nitrification-denitrification.

[0038] The specific activities of nitrogen transformation-related processes were calculated from the sludge nitrogen degradation curve. Compared with the control group, the specific activities of ammonia oxidation, nitrite oxidation, nitrite reduction and nitrate reduction in RTP sludge were higher, which were 4.18, 3.62, 4.47 and 5.82 mg N / (g·VSS·h), respectively, and increased by 19.8±0.8%, 19.1±0.3%, 22.1±1.1% and 38.9±1.2% respectively compared with the control group RC. The nitrite oxidation rate in RBC was significantly increased, resulting in rapid utilization of nitrite, so no nitrite accumulation was observed in the batch experiment. Thauera T-1 and Pseudofulvimonas P-1 are both heterotrophic nitrification-aerobic denitrification bacteria, and have the ability of simultaneous nitrification-denitrification under aerobic conditions. Compared with conventional denitrifying bacteria, HN-AD bacteria have a faster growth rate, a higher tolerance load, and a greater denitrification potential under salt stress. As an emerging bio-augmentation strain, its addition and enrichment can help improve the nitrification / denitrification denitrification efficiency of the biological treatment process under salt stress, and it has good environmental adaptability to support the nitrogen conversion potential of simultaneous nitrification and denitrification.

Claims

1. A method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment, characterized in that: The steps include: 1) Using activated sludge from urban sewage treatment systems and salt-tolerant sludge from industrial wastewater treatment systems as mixed inoculum to cultivate S-AGS and optimize the operating conditions of the SBR reactor; 2) Use 16S rRNA high-throughput sequencing and co-occurrence network analysis to identify the core species with good salt tolerance in S-AGS, and provide a theoretical basis for the targeted enhancement of its structural stability and denitrification performance; 3) Based on step 2), the core functional strains are screened and cultured, and Thauera T-1 and Pseudofulvimonas P-1 obtained by screening and culture are compounded to prepare a composite functional bacterial agent, and the composite functional bacterial agent is added based on the mixed inoculum and reactor conditions in step 1) to exert the synergistic enhancement effect of the core functional strains on the denitrification performance of S-AGS.

2. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 1, characterized in that: The treatment salinity of the salt-tolerant sludge in step 1) is ≥1%, and the mixing mass ratio of the activated sludge and the salt-tolerant sludge is 2:1-1:

1.

3. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 1, characterized in that: The SBR reactor in step 1) is provided with oxygen through a bottom aeration head, the surface gas velocity is 1.2 cm / s, the dissolved oxygen is 7.5-8.5 mg / L, the operation cycle is 4 hours, including 3 minutes of water inlet, 35 minutes of standing, 187-192 minutes of aeration, 5-10 minutes of sedimentation, and 5 minutes of water outlet. The pH value is controlled at 7.0±0.2, and the salt tolerance of the sludge is enhanced by gradient acclimation. In terms of NaCl, the influent salinity is 0, 10, 20, 30, 35, and 40 g / L, respectively, and the influent COD is 800-1000 mg / L. COD / TN is 20:

1.

4. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 3, characterized in that: In step 2), the dynamic succession of the microbial community structure with salinity changes was explored to clarify the impact of salinity on the S-AGS microbial community, and 16S rRNA high-throughput sequencing and co-occurrence network analysis were used to identify the core species Thauera spp. and Pseudofulvimonas spp. with good salt tolerance.

5. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 4, characterized in that: The screening and expansion process in step 3) is as follows: S-AGS is obtained from a stably operated SBR reactor as a source of salt-tolerant co-cultured bacteria, the granular sludge is fully ground and dispersed, the strain is separated by the dilution multiple method, the diluted bacterial suspension is evenly coated on a solid culture medium containing LB, and a salt stress habitat is simulated by adding different concentrations of NaCl. The culture medium is sealed with a sealing film and inverted in an incubator for overnight culture. After a single colony grows, it is plated and streaked multiple times to finally screen out several salt-tolerant strains. When the salinity of the culture medium is 10 g / L, the screened strains are subcultured three times and then frozen in a -80°C refrigerator with 50% glycerol, followed by 16S rDNA gene sequencing. A phylogenetic tree is generated using the BLAST algorithm, and the strain most similar to Thauera spp. is screened out, recorded as Thauera T-1, and when the salinity of the culture medium is 30 g / L, the strain most similar to Pseudofulvimonas spp. is screened out as Pseudofulvimonas P-1.

6. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 1, characterized in that: In the composite functional bacterial agent in step 3), Thauera T-1 and Pseudofulvimonas P-1 are compounded in a biomass ratio of 2:1 to 1:

2.

7. The method for enhancing the formation of salt-tolerant aerobic granular sludge and its denitrification performance in high-salt wastewater treatment according to claim 6, characterized in that: The addition amount of composite functional bacterial agent is 3% to 10% of the biomass.

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