Low carbon-nitrogen ratio wastewater advanced denitrification process

Abstract

This invention relates to the field of wastewater denitrification technology, specifically to a deep denitrification process for low C / N ratio wastewater. The process includes the following steps: constructing an MBBR-SADN reaction system, preparing functionalized carriers, directionally enriching denitrifying bacteria, optimizing operating parameters, and acclimatizing with actual wastewater gradients. Through a three-pronged technical approach of functionalized carrier modification, directional bacterial regulation, and synergistic optimization of process parameters, the modified carrier promotes SOB enrichment and EPS secretion, thereby accelerating biofilm formation, significantly shortening the biofilm formation cycle, and maintaining effluent TN stably below 4 mg / L, achieving a denitrification efficiency of over 99.4%. Engineering verification has been conducted on low C / N ratio wastewater (C / N = 1.4–3). During 90 days of continuous operation, the effluent TN remained consistently below 3.8 mg / L, indicating that this denitrification process has good stability and adaptability in practical applications. It provides a solution to key challenges in current sulfur autotrophic denitrification technologies, such as long biofilm formation cycles, low denitrification efficiency, and poor shock resistance.

Description

Technical Field

[0001] This invention relates to the field of wastewater denitrification technology, specifically to a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio. Background Technology

[0002] With the rapid development of global industrialization and agricultural activities, nitrate pollution has become increasingly serious, posing a severe threat to human health and ecosystems. According to new industry standards, the upper limit for total nitrogen (TN) in wastewater treatment plant effluent has been reduced from 10 mg / L to 5 mg / L. However, currently, 80% of wastewater treatment plants in my country have an influent BOD5 / TN ratio of <3.6, indicating insufficient organic matter concentration in the raw water. This severely restricts the TN removal rate of the biological treatment stage, making efficient removal of nitrogenous pollutants, especially low-carbon pollutants, from wastewater with low C / N ratios a key challenge in upgrading and retrofitting wastewater.

[0003] Traditional heterotrophic denitrification processes suffer from high carbon source dependence, large sludge production, low nitrogen removal efficiency, high carbon emissions, and high costs, making it difficult to meet the requirements of new emission standards. In contrast, sulfur autotrophic denitrification (SADN) technology requires no external organic carbon source, produces less sludge, and can effectively solve the nitrogen removal problem of wastewater with low C / N ratios. However, SADN technology still faces two major bottlenecks in practical applications: First, the growth rate of sulfur autotrophic denitrifying bacteria (SOB) is low, and traditional carriers such as polyurethane foam (PUF) are insufficient for SOB immobilization, resulting in a long biofilm settling period (>30 days), and the biofilm is easily detached by hydraulic shear. Second, actual wastewater often contains heavy metals, heterotrophic bacteria, and trace organic matter, which can inhibit SOB activity and trigger byproducts. Accumulation of microorganisms leads to fluctuations in denitrification efficiency. Existing research mostly focuses on optimizing single parameters (such as HRT or pH control), lacking a synergistic optimization mechanism involving the carrier, microbial community, and process parameters, making it difficult to achieve stable and efficient engineering applications.

[0004] Based on the above problems, this invention proposes a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio. By designing functionalized carriers and coordinating the control of multi-dimensional parameters, it overcomes the technical limitations of existing sulfur autotrophic denitrification technologies. Summary of the Invention

[0005] For ease of description, Table 1 lists the Chinese descriptions of the symbols and abbreviations involved in this invention.

[0006] Table 1. Chinese descriptions of the symbols and abbreviations involved in this invention.

[0007] To achieve the technical objectives described in the background section, this invention provides a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio.

[0008] S1. Constructing the MBBR-SADN reaction system: The MBBR-SADN reaction system consists of a moving bed biofilm reactor (MBBR), which uses an external water bath with a temperature of 25~35℃ to ensure the stable operation of the sulfur autotrophic denitrification process. S2. Preparation of biomembrane carriers: Amine-modified polyurethane foam (PUF@NH2 carrier) was used as a biofilm carrier. The surface of the biofilm carrier has a multi-level rough structure and -NH2 functional groups, which can efficiently fix sulfur autotrophic denitrifying bacteria through electrostatic adsorption and hydrogen bonding, and achieve the adsorption and enrichment of nitrate, providing a favorable microenvironment for subsequent biofilm formation and denitrification reactions. S3, Targeted enrichment of microbial communities: A sulfur-autotrophic bacterial community dominated by *Thiobacillus* and *Thiomonas* was selected. A simulated wastewater was designed based on the actual wastewater composition, and a gradient enrichment process was performed in the simulated wastewater. During the gradient enrichment process, the ratio of sulfur source to nitrogen source was controlled at 1:1. OD was obtained through isothermal shaking culture at 25–35℃ and 130–150 rpm. 600 Enriched bacterial solutions with a concentration of ≥0.8 were used for subsequent biofilm formation. S4. Rapid biofilm attachment: The enriched bacterial solution and biofilm carrier were mixed at a mass ratio of 2:1. The dynamic biofilm formation parameters were adjusted, and the enriched bacterial solution was periodically replenished to promote rapid growth of biomass on the carrier surface, so that the ATP content reached 0.68 μmol / g VSS within 12 days, achieving efficient biofilm formation. Note: An MBBR-SADN system based on a biofilm carrier was constructed for biofilm initiation experiments. The results showed that a multi-level rough structure was formed on the surface of the biofilm carrier, increasing the biofilm attachment area. Simultaneously, the protonation of surface -NH2 was enriched through electrostatic interactions. This provides a localized high-concentration substrate environment for SOB, promoting the secretion of extracellular polymeric substances (EPS) and the targeted enrichment of functional microbial communities, shortening the biofilm formation period to 12 days, a 40% reduction compared to the unmodified carrier, and achieving a denitrification efficiency of 99.4%. High-throughput sequencing shows that the microbial community on the surface of the biofilm carrier has the highest biodiversity and species richness. Compared to the unmodified PUF, the biofilm carrier increases the relative abundance of Thiobacillus and Sulfurimonas from 0.41% and 0.27% on day 1 of biofilm formation to 20.83% and 5.81% on day 12, respectively, taking an absolute dominant position. This change in the microbial community is the key reason for the optimal denitrification performance of the biofilm carrier system. S5. Actual wastewater gradient acclimatization: The actual wastewater proportion was gradually increased in stages of 25%, 50%, 75%, and 100%, with each stage running for 6 days. The succession of the microbial community was monitored and the synergistic operating parameters were adjusted to ensure that the TN concentration in the effluent reached the set target.

[0009] Furthermore, the moving bed biofilm reactor in S1 has a hollow cylindrical structure with a height-to-diameter ratio of 2 to 2.2:1; an agitator is installed at the central axis of the moving bed biofilm reactor, with a diameter of 50 to 55% of the diameter of the moving bed biofilm reactor, and the height of the agitator from the bottom is 7.5 to 8% of the height of the moving bed biofilm reactor; an external water bath layer with a thickness of 3 to 3.5 cm is installed on the outside of the moving bed biofilm reactor, and intermittent heating is used to maintain a constant temperature.

[0010] Note: The height-to-diameter ratio (2~2.2:1) of the moving bed biofilm reactor optimizes liquid mixing uniformity and reduces sludge loss; the design of the ratio of the agitator diameter to the reactor diameter (50~55%) and the height from the bottom (7.5~8%) incorporates fluid dynamics simulation results to ensure carrier fluidization efficiency (pressure drop <0.3 kPa) and avoid excessive biofilm shearing; the insulation layer thickness (3~3.5 cm) is maintained at a constant temperature of 30±1℃ through intermittent heating to ensure the basic activity of functional bacteria.

[0011] Furthermore, Let n be the multiplier and n∈R + Therefore, the amount of enriched bacterial solution added to S4 is [8,12]n mL, and the amount of biofilm carrier added is [1.8,2.2]ng; The method for adjusting the dynamic biofilm formation parameters in S4 is as follows: S4-1. During the initial 12-day biofilm formation stage, an additional enriched bacterial solution is added daily as a supplement, with the amount of enriched bacterial solution added being 0.5-1% of the total simulated wastewater volume; S4-2, Through online monitoring The concentration change controls the amount of sulfur source added. The sulfur source is a composite system of sodium thiosulfate and ferrous sulfate, with a molar ratio of 2:1. S4-3. Dynamic biofilm formation is considered complete when the EPS content reaches 60 mg / g VSS.

[0012] Note: During the dynamic biofilm formation stage, supplement with 0.5-1% enriched bacterial solution daily, combined with a sodium thiosulfate-ferrous sulfate composite sulfur source, through Fe... 2+ The redox buffering effect reduces the ineffective decomposition of thiosulfate, and experiments show that this combination can increase the denitrification rate by 15%; EPS content reaches 60 mg / g. The criterion for VSS is based on the strong correlation between ATP and EPS (R). 2=0.91), at which point the biofilm maturity meets the requirements for hydraulic shear resistance; the biofilm formation period is shortened to 12 days (40% less than that of the unmodified carrier), which is attributed to the protonation of the -NH2 groups on the PUF@NH2 surface promoting SOB enrichment and enhancing biofilm stability through EPS secretion (protein accounting for 89.6%).

[0013] Furthermore, the method for monitoring microbial community succession in S5 is as follows: S5A-1: Online monitoring of ATP content and EPS component dynamic changes; triggering the microbial community activation program when ATP < 0.4 μmol / g VSS. S5A-1-1, Increase ATP content: Promote the metabolic activity of functional bacteria by optimizing substrate supply and environmental conditions; S5A-1-2, Adjust EPS components: Enhance biofilm stability and reduce microbial loss due to EPS loss; S5A-2: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, a sulfur oxidation-denitrification metabolic chain is established to keep the effluent TN concentration stable below 4 mg / L. S5A-3: The thickness of the biofilm on the carrier surface is measured every 15 days, and the thickness is controlled within the range of 80~120 μm. S5A-4: The relative abundance of functional bacterial communities is monitored by real-time sequencing of 16S rRNA, maintaining their proportion >20%.

[0014] Furthermore, the method for adjusting the HRT-carrier filling rate-pH-stirring rate parameters in S5A-2 is as follows: S5A-2-1, Determine the HRT range as 6~8 h and the carrier filling rate range as 30~40%. S5A-2-2: When the influent C / N ratio is less than 3, the pH compensation system is automatically activated to maintain the system pH at 7~8.5. S5A-2-3. The stirring rate of the moving bed biofilm reactor is dynamically adjusted to 30~40 rpm by monitoring the fluidization state of the carrier.

[0015] Note: HRT = 6~8 h: To ensure the integrity of the sulfur oxidation-denitrification metabolic chain and avoid sulfur oxidation. 2- Accumulation (<5 mg / L); Carrier filling rate 30~40%: maximizes biofilm reaction sites, while avoiding clogging through the fluidization characteristics of the moving bed biofilm reactor (pressure drop <0.3 kPa); pH=7~8.5: achieved by adding NaHCO3 to maintain bacterial activity and inhibit ineffective decomposition of thiosulfate; Furthermore, the method for adjusting the cooperative operation parameters in S5 is as follows: S5B-1 uses a biotoxic buffer to eliminate heavy metal inhibition. The biotoxic buffer is cysteine, and the dosage is 0.5~0.7 mmol / L. S5B-2, Set up a heterotrophic bacteria competitive inhibition module: Pulse-add chloramphenicol once every 48 hours, with a single duration of 1 hour and an addition concentration of 10 mg / L. The trigger condition is that the abundance of heterotrophic bacteria is >15%. S5B-3. When COD > 30 mg / L, start the auxiliary carbon source addition system. The carbon source is made from sugar or agricultural waste through fermentation.

[0016] Note: The dosage of the composite carbon source needs to be dynamically adjusted according to actual process requirements and the carbon-to-nitrogen ratio (C / N), as shown in the following formula: Where Y: dosage of composite carbon source; Q: influent flow rate (m³ / h) 3 / d); ΔTN: the difference between total nitrogen in the influent and total nitrogen in the effluent (mg / L); ΔCOD: the difference between COD in the influent and COD in the effluent (mg / L); E: COD equivalent of the carbon source.

[0017] Furthermore, the preparation method of the biomembrane carrier in S2 is as follows: S2-1, Acidification Modification: Let n be the multiplier and n∈R + First, [0.3, 0.5] ng potassium permanganate and [0.4, 0.45] n mL concentrated sulfuric acid were added sequentially to [60, 65] n mL of ultrapure water and mixed thoroughly. The mixture was stirred continuously at 50 °C for 8-12 min. Then, [1.8, 2.2] ng PUF was added and heated at 50 °C for 13-17 min. Finally, the reaction product was filtered out and washed to obtain the PUF@COOH carrier. S2-2, Amination Modification: Let n be the multiplier and n∈R + [95,105] mL of DETA was heated in a constant temperature oil bath at 80 °C, and then [3.8,4.2] ng of aluminum chloride was slowly added. After the reaction was complete, [0.8,1.2] ng of PUF@COOH carrier was added, and the reaction was carried out at 80 °C for 1 h. After the reaction was complete, the reaction product was filtered out and washed, and finally dried to obtain amination-modified polyurethane foam, i.e., biofilm carrier. Note: Potassium permanganate-concentrated sulfuric acid induces the breaking of CO single bonds in the PUF molecular chain through strong oxidation, promoting the formation of carboxyl groups (-COOH), so that the amount of -COOH grafted on the PUF surface can reach 1.79 mmol / g; Under the catalysis of aluminum chloride, the amine-NH2 groups on the DETA surface undergo an amide reaction with -COOH, grafting amine groups onto the PUF surface at a grafting amount of 1.50 mmol / g. Pseudo-first-order kinetics show that PUF@NH2 has a significant effect on... The maximum adsorption capacity reaches 5.85 mg / g (R 2 =0.9926), which is a significant improvement over the unmodified carrier.

[0018] Furthermore, the gradient enrichment method described in S3 is as follows: First, the bacterial solution of sulfur autotrophic bacteria was centrifuged at 8000 rpm to obtain a precipitated bacterial solution, which was then resuspended: the precipitated bacterial solution was redispersed uniformly in simulated wastewater at a mass ratio of 2:1 to obtain a resuspended bacterial solution; then, enrichment was carried out: the resuspended bacterial solution was mixed with simulated wastewater at a mass ratio of 5:1 and enriched in a constant temperature water bath shaker at 30℃ and 150 rpm for 1 day to obtain an enriched bacterial solution; Explanation: Gradient enrichment mainly involves: first resuspension treatment, then concentration treatment; the purpose of resuspension treatment is to use new culture medium to break up and dilute the tightly packed bacterial precipitate, so that it becomes a uniformly dispersed suspension again; while the purpose of concentration treatment is to obtain a uniform bacterial solution with higher purity and concentration than the original bacterial solution.

[0019] Furthermore, the composition of the simulated wastewater in S3 is as follows: NaNO3: 1 g / L, Na2S2O3·5H2O: 1 g / L, K2HPO4: 220 mg / L, CaCl2: 1 mg / L, NaH2PO4·2H2O: 150 g / L, NaHCO3: 400 g / L, MgCl2·6H2O: 5 g / L, MnCl2: 64 mg / L, CoCl2·6H2O: 200 mg / L, (NH4)6Mo7O2·4H2O: 55 mg / L, FeSO4·7H2O: 500 mg / L, EDTA: 500 mg / L, ZnCl2: 70 mg / L, NiCl2·6H2O: 24 mg / L, CuSO4: 2 mg / L, H3BO3: 6 mg / L; COD: 18.03~25.77 mg / L, 8.36~11.24 mg / L :0.2~1.71 mg / L, TP: 0.52~1.57 mg / L, DO: 2.3~4.32 mg / L.

[0020] Note: The culture medium formula is designed based on the metabolic requirements of sulfur-autotrophic denitrifying bacteria, with sodium thiosulfate and sodium nitrate serving as the sulfur and nitrogen sources, respectively, supplemented with specific trace elements (such as Fe). 2+Co 2+ Mo 6+ To activate SOB enzyme activity; via OD 600 Dynamic monitoring and optimization ensure bacterial activity.

[0021] As another aspect of the present invention, a low C / N ratio wastewater deep denitrification process designed by the present invention is applied to the deep treatment of wastewater with a C / N ratio of 1.4 to 3; the wastewater treated by the above process has an effluent TN ≤ 5 mg / L and no nitrite accumulation.

[0022] Compared with existing wastewater denitrification processes, the beneficial effects of this invention are: This invention solves the problems of long biofilm formation period, low nitrogen removal efficiency, and weak shock resistance in sulfur autotrophic denitrification technology through a three-pronged technical solution of functionalized carrier modification, targeted microbial community regulation, and synergistic optimization of process parameters. Specific advantages include: (1) High efficiency denitrification: The modified carrier promotes SOB enrichment and EPS secretion, shortens the biofilm formation period to 12 days (40% less than traditional carriers), and ensures that the effluent TN is stable at <4 mg / L and the denitrification efficiency is ≥99.4%; (2) Rapid start-up: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, the efficiency of sulfur oxidation-denitrification coupled metabolism is increased by 50%, and there is no accumulation of nitrite nitrogen; (3) Strong resistance to shocks: The system integrates ATP monitoring and microbial activation programs, combined with cysteine ​​toxicity buffering and chloramphenicol heterotrophic bacteria inhibition, to improve the system's ability to resist environmental changes. Attached Figure Description

[0023] Figure 1 These are SEM images of the surface of the experimental PUF@NH2 carrier. Among them, (a) is the image at 3 µm after 1 day of biofilm formation, (b) is the image at 10 µm after 1 day of biofilm formation, (c) is the image at 30 µm after 1 day of biofilm formation, (d) is the image at 3 µm after 12 days of biofilm formation, (e) is the image at 10 µm after 12 days of biofilm formation, and (f) is the image at 30 µm after 12 days of biofilm formation. Figure 2 This is a diagram showing the nitrogen removal effect of the biofilm start-up experiment in Section 4 of the experimental examples. In the diagram, (a) is the effluent. Concentration, (b) is the effluent concentration. Concentration, (c) is the effluent concentration. Concentration, (d) is Removal rate, (e) is the S / N ratio of the effluent, and (f) is the pH of the effluent. Detailed Implementation

[0024] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0025] Example 1: The content of this example describes a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio.

[0026] S1. Constructing the MBBR-SADN reaction system: The MBBR-SADN reaction system consists of a moving bed biofilm reactor (MBBR), which uses an external water bath at 25°C to control the temperature and ensure the stable execution of the sulfur autotrophic denitrification process. The aforementioned moving bed biofilm reactor is a hollow cylinder with a height of 18 cm and a diameter of 9 cm. An agitator with a diameter of 4.5 cm and a height of 1.35 cm from the bottom is installed at the central axis of the MBBR reactor. A 3 cm thick insulation layer is installed on the outside of the MBBR reactor, and intermittent heating is used to maintain a constant temperature. S2. Preparation of biomembrane carriers: Amine-modified polyurethane foam was used as a biofilm carrier. The surface of the biofilm carrier has a multi-level rough structure and –NH2 functional groups, which can efficiently fix sulfur autotrophic denitrifying bacteria through electrostatic adsorption and hydrogen bonding, and achieve the adsorption and enrichment of nitrate, providing a favorable microenvironment for subsequent biofilm formation and denitrification reactions. The preparation method of the biomembrane carrier is as follows: S2-1, Acidification Modification: First, add 0.3 g of potassium permanganate and 0.4 mL of concentrated sulfuric acid to 60 mL of ultrapure water and mix well. Stir continuously at 50 °C for 8 min. Then add 1.8 g of PUF and heat at 50 °C for 13-17 min. Finally, filter out the reaction product and wash to obtain the PUF@COOH support. S2-2, Amination Modification: 95 mL of DETA was heated in a constant temperature oil bath at 80℃, and then 3.8 g of aluminum chloride was slowly added. After the reaction was complete, 0.8 g of PUF@COOH carrier was added, and the reaction was carried out at 80℃ for 1 h. After the reaction was complete, the reaction product was filtered out and washed. Finally, the product was dried to obtain amination-modified polyurethane foam, i.e., biofilm carrier. S3, Targeted enrichment of microbial communities: A sulfur-autotrophic bacterial community dominated by *Thiobacillus* and *Thiomonas* was selected. A simulated wastewater was designed based on the actual wastewater composition, and gradient enrichment was performed in the simulated wastewater. During the gradient enrichment process, the ratio of sulfur source to nitrogen source was controlled at 1:1. OD was obtained through isothermal shaking culture at 30℃ and 150rpm. 600Enriched bacterial solutions with a concentration of ≥0.8 were used for subsequent biofilm formation. The gradient enrichment method is as follows: In this embodiment, the bacterial solution of the sulfur autotrophic bacteria includes Thiobacillus and Sulfurimonas, both of which were purchased from the official store of the Water Country, and the mass ratio of the two is 1:1. First, the bacterial solution of sulfur autotrophic bacteria was centrifuged at 8000 rpm to obtain a precipitated bacterial solution, which was then resuspended: the precipitated bacterial solution was redispersed uniformly in simulated wastewater at a mass ratio of 2:1 to obtain a resuspended bacterial solution; then, enrichment was carried out: the resuspended bacterial solution was mixed with simulated wastewater at a mass ratio of 5:1 and enriched in a constant temperature water bath shaker at 25℃ and 130 rpm for 1 day to obtain an enriched bacterial solution; The components of the simulated wastewater are: NaNO3: 1 g / L, Na2S2O3·5H2O: 1 g / L, K2HPO4: 220 mg / L, CaCl2: 1 mg / L, NaH2PO4·2H2O: 150 g / L, NaHCO3: 400 g / L, MgCl2·6H2O: 5 g / L, MnCl2: 64 mg / L, CoCl2·6H2O: 200 mg / L, (NH4)6Mo7O2·4H2O: 55 mg / L, FeSO4·7H2O: 500 mg / L, EDTA: 500 mg / L, ZnCl2: 70 mg / L, NiCl2·6H2O: 24 mg / L, CuSO4: 2 mg / L, H3BO3: 6 mg / L; COD: 18.03 mg / L, 8.36 mg / L :0.2 mg / L, TP: 0.52 mg / L, DO: 2.3 mg / L; S4. Rapid biofilm attachment: 8 mL of enriched bacterial solution was mixed with 1.8 g of biofilm carrier. Dynamic biofilm attachment parameters were adjusted, and the enriched bacterial solution was periodically replenished to promote rapid growth of biomass on the carrier surface, so that the ATP content reached 0.68 μmol / g VSS within 12 days, achieving efficient biofilm attachment. The method for adjusting dynamic biofilm formation parameters is as follows: S4-1. During the initial 12-day biofilm formation stage, an additional enriched bacterial solution was added daily as a supplement, with the amount of enriched bacterial solution added being 0.5% of the total simulated wastewater volume. S4-2, Through online monitoring The concentration change controls the amount of sulfur source added. The sulfur source is a composite system of sodium thiosulfate and ferrous sulfate, with a molar ratio of 2:1. S4-3. Dynamic biofilm formation is considered complete when the EPS content reaches 60 mg / g VSS. S5. Actual wastewater gradient acclimatization: The actual wastewater proportion was gradually increased in the proportions of 25%, 50%, 75%, and 100%, with each stage running for 6 days. The succession of the microbial community was monitored and the synergistic operating parameters were adjusted to ensure that the TN concentration in the effluent reached the set target. The methods for monitoring microbial community succession are as follows: S5A-1: Online monitoring of ATP content and EPS component dynamic changes; triggering the microbial community activation program when ATP < 0.4 μmol / g VSS. S5A-1-1, Increase ATP content: Promote the metabolic activity of functional bacteria by optimizing substrate supply and environmental conditions; Substrate supply optimization: The dosage of the composite sulfur source was dynamically adjusted based on the online monitoring of sulfide concentration to maintain the sulfur-to-nitrogen ratio within the range of 1.2:1; when ATP decreased, additional Fe was added. 2+ (1 mg / L) and Mg 2+ (0.5 mg / L); Environmental condition control: Maintain dissolved oxygen (DO) at the bottom of the reactor at 0.5 mg / L (to promote sulfur oxidation) and DO at 1.5 mg / L in the middle and upper parts of the reactor at microporous aeration (to promote denitrification); when ATP is below the threshold for two consecutive days, increase the water bath temperature (maximum value 35℃) to accelerate microbial metabolism; S5A-1-2, Adjusting EPS components: Enhances biofilm stability and reduces microbial loss due to EPS leaching. When EPS loss is detected, stop the water intake for 30 minutes to encourage the detached microorganisms to reattach to the carrier. S5A-2: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, a sulfur oxidation-denitrification metabolic chain is established to keep the effluent TN concentration stable below 4 mg / L. The methods for adjusting the parameters HRT, carrier filling rate, pH, and stirring rate are as follows: S5A-2-1, Determine the HRT range as 6 hours and the carrier filling rate range as 30%. S5A-2-2: When the influent C / N ratio is less than 3, the pH compensation system is automatically activated to maintain the system pH at 7. S5A-2-3, The stirring rate of the moving bed biofilm reactor is dynamically adjusted to 30 rpm by monitoring the fluidization state of the carrier; S5A-3: The thickness of the biofilm on the carrier surface is measured every 15 days, and the thickness is controlled within the range of 80 μm. S5A-4: The relative abundance of functional bacterial communities was monitored through real-time 16S rRNA sequencing, maintaining their proportion >20%; The method for adjusting the parameters of coordinated operation is as follows: S5B-1 uses a biotoxic buffer to eliminate heavy metal inhibition. The biotoxic buffer is cysteine, and the dosage is 0.5 mmol / L. S5B-2, Set up a heterotrophic bacteria competitive inhibition module: Pulse-add chloramphenicol once every 48 hours, with a single duration of 1 hour and an addition concentration of 10 mg / L. The trigger condition is that the abundance of heterotrophic bacteria is >15%. S5B-3. When COD > 30 mg / L, the auxiliary carbon source addition system is started. The carbon source is made from fermented waste straw.

[0027] Example 2: The content of this example describes a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio under another set of parameters.

[0028] S1. Constructing the MBBR-SADN reaction system: The MBBR-SADN reaction system consists of a moving bed biofilm reactor (MBBR), which uses an external water bath at 30°C to control the temperature and ensure the stable operation of the sulfur autotrophic denitrification process. The aforementioned moving bed biofilm reactor is a hollow cylinder with a height of 18.9 cm and a diameter of 9 cm. An agitator is installed at the central axis inside the MBBR reactor, with a diameter of 4.77 cm equal to the diameter of the MBBR reactor, and the agitator is 1.47 cm above the bottom. A 3.3 cm thick insulation layer is installed on the outside of the MBBR reactor, and intermittent heating is used to maintain a constant temperature. S2. Preparation of biomembrane carriers: Amine-modified polyurethane foam was used as a biofilm carrier. The surface of the biofilm carrier has a multi-level rough structure and –NH2 functional groups, which can efficiently fix sulfur autotrophic denitrifying bacteria through electrostatic adsorption and hydrogen bonding, and achieve the adsorption and enrichment of nitrate, providing a favorable microenvironment for subsequent biofilm formation and denitrification reactions. The preparation method of the biomembrane carrier is as follows: S2-1, Acidification Modification: First, add 0.4 g of potassium permanganate and 0.42 mL of concentrated sulfuric acid to 62 mL of ultrapure water and mix well. Stir continuously at 50 °C for 10 min. Then add 2 g of PUF and heat at 50 °C for 15 min. Finally, filter out the reaction product and wash to obtain the PUF@COOH support. S2-2, Amination Modification: 100 mL of DETA was heated in a constant temperature oil bath at 80℃, and then 4 g of aluminum chloride was slowly added. After the reaction was complete, 1 g of PUF@COOH carrier was added, and the reaction was carried out at 80℃ for 1 h. After the reaction was complete, the reaction product was filtered out and washed, and finally dried to obtain amination-modified polyurethane foam, i.e., biofilm carrier. S3, Targeted enrichment of microbial communities: A sulfur-autotrophic bacterial community dominated by *Thiobacillus* and *Thiomonas* was selected. A simulated wastewater was designed based on the actual wastewater composition, and gradient enrichment was performed in the simulated wastewater. During the gradient enrichment process, the ratio of sulfur source to nitrogen source was controlled at 1:1. OD was obtained through isothermal shaking culture at 30℃ and 150rpm. 600 Enriched bacterial solutions with a concentration of ≥0.8 were used for subsequent biofilm formation. The gradient enrichment method is as follows: In this embodiment, the bacterial solution of the sulfur autotrophic bacteria includes Thiobacillus and Sulfurimonas, both of which were purchased from the official store of the Water Country, and the mass ratio of the two is 1:1. First, the bacterial solution of sulfur autotrophic bacteria was centrifuged at 8000 rpm to obtain a precipitated bacterial solution, which was then resuspended: the precipitated bacterial solution was redispersed uniformly in simulated wastewater at a mass ratio of 2:1 to obtain a resuspended bacterial solution; then, enrichment was carried out: the resuspended bacterial solution was mixed with simulated wastewater at a mass ratio of 5:1 and enriched in a constant temperature water bath shaker at 30℃ and 140 rpm for 1 day to obtain an enriched bacterial solution; The components of the simulated wastewater are: NaNO3: 1 g / L, Na2S2O3·5H2O: 1 g / L, K2HPO4: 220 mg / L, CaCl2: 1 mg / L, NaH2PO4·2H2O: 150 g / L, NaHCO3: 400 g / L, MgCl2·6H2O: 5 g / L, MnCl2: 64 mg / L, CoCl2·6H2O: 200 mg / L, (NH4)6Mo7O2·4H2O: 55 mg / L, FeSO4·7H2O: 500 mg / L, EDTA: 500 mg / L, ZnCl2: 70 mg / L, NiCl2·6H2O: 24 mg / L, CuSO4: 2 mg / L, H3BO3: 6 mg / L; COD: 22.25 mg / L, 9.18 mg / L :1.35 mg / L, TP: 1.12 mg / L, DO: 3.11 mg / L; S4. Rapid biofilm attachment: 10 mL of enriched bacterial solution was mixed with 2 g of biofilm carrier. Dynamic biofilm attachment parameters were adjusted, and the enriched bacterial solution was periodically replenished to promote rapid growth of biomass on the carrier surface, so that the ATP content reached 0.68 μmol / g VSS within 12 days, achieving efficient biofilm attachment. The method for adjusting dynamic biofilm formation parameters is as follows: S4-1. During the initial 12-day biofilm formation stage, an additional enriched bacterial solution was added daily as a supplement, with the amount of enriched bacterial solution added being 0.8% of the total simulated wastewater volume. S4-2, Through online monitoring The concentration change controls the amount of sulfur source added. The sulfur source is a composite system of sodium thiosulfate and ferrous sulfate, with a molar ratio of 2:1. S4-3. Dynamic biofilm formation is considered complete when the EPS content reaches 60 mg / g VSS. S5. Actual wastewater gradient acclimatization: The actual wastewater proportion was gradually increased in the proportions of 25%, 50%, 75%, and 100%, with each stage running for 6 days. The succession of the microbial community was monitored and the synergistic operating parameters were adjusted to ensure that the TN concentration in the effluent reached the set target. The methods for monitoring microbial community succession are as follows: S5A-1: Online monitoring of ATP content and EPS component dynamic changes; triggering the microbial community activation program when ATP < 0.4 μmol / g VSS. S5A-1-1, Increase ATP content: Promote the metabolic activity of functional bacteria by optimizing substrate supply and environmental conditions; Substrate supply optimization: The dosage of the composite sulfur source was dynamically adjusted based on the online monitoring of sulfide concentration to maintain the sulfur-nitrogen ratio within the range of 1.35:1; when ATP decreased, additional Fe was added. 2+ (1.5 mg / L) and Mg 2+ (0.7 mg / L); Environmental condition control: Maintain dissolved oxygen (DO) at the bottom of the reactor at 0.7 mg / L (to promote sulfur oxidation) and DO at 2 mg / L in the middle and upper parts of the reactor at microporous aeration (to promote denitrification); when ATP is below the threshold for two consecutive days, increase the water bath temperature (maximum value 35℃) to accelerate microbial metabolism; S5A-1-2, Adjust EPS components: Enhance biofilm stability and reduce microbial loss due to EPS loss; When EPS loss is detected, water intake is stopped for 45 minutes to encourage the detached microorganisms to reattach to the carrier. S5A-2: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, a sulfur oxidation-denitrification metabolic chain is established to keep the effluent TN concentration stable below 4 mg / L. The methods for adjusting the parameters HRT, carrier filling rate, pH, and stirring rate are as follows: S5A-2-1, Determine the HRT range as 7 hours and the carrier filling rate range as 35%. S5A-2-2: When the influent C / N ratio is <3, the pH compensation system is automatically activated to maintain the system pH = 8. S5A-2-3, The stirring rate of the moving bed biofilm reactor is dynamically adjusted to 35 rpm by monitoring the fluidization state of the carrier; S5A-3: The thickness of the biofilm on the carrier surface is measured every 15 days, and the thickness is controlled within 100 μm. S5A-4: The relative abundance of functional bacterial communities was monitored through real-time 16S rRNA sequencing, maintaining their proportion >20%; The method for adjusting the parameters of coordinated operation is as follows: S5B-1 uses a biotoxic buffer to eliminate heavy metal inhibition. The biotoxic buffer is cysteine, and the dosage is 0.6 mmol / L. S5B-2, Set up a heterotrophic bacteria competitive inhibition module: Pulse-add chloramphenicol once every 48 hours, with a single duration of 1 hour and an addition concentration of 10 mg / L. The trigger condition is that the abundance of heterotrophic bacteria is >15%. S5B-3. When COD > 30 mg / L, the auxiliary carbon source dosing system is activated. The carbon source is made from fermented waste straw.

[0029] Example 3: The content of this example describes a deep denitrification process for wastewater with a low carbon-to-nitrogen ratio under another set of parameters.

[0030] S1. Constructing the MBBR-SADN reaction system: The MBBR-SADN reaction system consists of a moving bed biofilm reactor (MBBR), which uses an external water bath at 35°C to control the temperature and ensure the stable execution of the sulfur autotrophic denitrification process. The aforementioned moving bed biofilm reactor is a hollow cylinder with a height of 19.8 cm and a diameter of 9 cm. An agitator is installed at the central axis inside the MBBR reactor, with a diameter of 4.95 cm equal to the diameter of the MBBR reactor, and the agitator is 1.58 cm above the bottom. A 3.5 cm thick insulation layer is installed on the outside of the MBBR reactor, and intermittent heating is used to maintain a constant temperature. S2. Preparation of biomembrane carriers: Amine-modified polyurethane foam was used as a biofilm carrier. The surface of the biofilm carrier has a multi-level rough structure and –NH2 functional groups, which can efficiently fix sulfur autotrophic denitrifying bacteria through electrostatic adsorption and hydrogen bonding, and achieve the adsorption and enrichment of nitrate, providing a favorable microenvironment for subsequent biofilm formation and denitrification reactions. The preparation method of the biomembrane carrier is as follows: S2-1, Acidification Modification: First, add 0.5 g of potassium permanganate and 0.45 mL of concentrated sulfuric acid to 65 mL of ultrapure water and mix well. Stir continuously at 50 °C for 12 min. Then add 2.2 g of PUF and heat at 50 °C for 17 min. Finally, filter out the reaction product and wash to obtain the PUF@COOH support. S2-2, Amination Modification: 105 mL of DETA was heated in a constant temperature oil bath at 80℃, and then 4.2 g of aluminum chloride was slowly added. After the reaction was complete, 1.2 g of PUF@COOH carrier was added, and the reaction was carried out at 80℃ for 1 h. After the reaction was complete, the reaction product was filtered out and washed. Finally, the product was dried to obtain amination-modified polyurethane foam, i.e., biofilm carrier. S3, Targeted enrichment of microbial communities: A sulfur-autotrophic bacterial community dominated by *Thiobacillus* and *Thiomonas* was selected. A simulated wastewater was designed based on the actual wastewater composition, and gradient enrichment was performed in the simulated wastewater. During the gradient enrichment process, the ratio of sulfur source to nitrogen source was controlled at 1:1. OD was obtained through isothermal shaking culture at 30℃ and 150rpm. 600 Enriched bacterial solutions with a concentration of ≥0.8 were used for subsequent biofilm formation. The gradient enrichment method is as follows: In this embodiment, the bacterial solution of the sulfur autotrophic bacteria includes Thiobacillus and Sulfurimonas, both of which were purchased from the official store of the Water Country, and the mass ratio of the two is 1:1. First, the bacterial solution of sulfur autotrophic bacteria was centrifuged at 8000 rpm to obtain a precipitated bacterial solution, which was then resuspended: the precipitated bacterial solution was redispersed uniformly in simulated wastewater at a mass ratio of 2:1 to obtain a resuspended bacterial solution; then, enrichment was carried out: the resuspended bacterial solution was mixed with simulated wastewater at a mass ratio of 5:1 and enriched in a constant temperature water bath shaker at 35℃ and 150 rpm for 1 day to obtain an enriched bacterial solution; The components of the simulated wastewater are: NaNO3: 1 g / L, Na2S2O3·5H2O: 1 g / L, K2HPO4: 220 mg / L, CaCl2: 1 mg / L, NaH2PO4·2H2O: 150 g / L, NaHCO3: 400 g / L, MgCl2·6H2O: 5 g / L, MnCl2: 64 mg / L, CoCl2·6H2O: 200 mg / L, (NH4)6Mo7O2·4H2O: 55 mg / L, FeSO4·7H2O: 500 mg / L, EDTA: 500 mg / L, ZnCl2: 70 mg / L, NiCl2·6H2O: 24 mg / L, CuSO4: 2 mg / L, H3BO3: 6 mg / L; COD: 25.77 mg / L, 11.24 mg / L :1.71 mg / L, TP: 1.57 mg / L, DO: 4.32 mg / L; S4. Rapid biofilm attachment: 12 mL of enriched bacterial solution was mixed with 2.2 g of biofilm carrier. Dynamic biofilm attachment parameters were adjusted, and the enriched bacterial solution was periodically replenished to promote rapid growth of biomass on the carrier surface, so that the ATP content reached 0.68 μmol / g VSS within 12 days, achieving efficient biofilm attachment. The method for adjusting dynamic biofilm formation parameters is as follows: S4-1. During the initial 12-day biofilm formation stage, an additional enriched bacterial solution was added daily as a supplement, with the amount of enriched bacterial solution added being 1% of the total simulated wastewater volume. S4-2, Through online monitoring The concentration change controls the amount of sulfur source added. The sulfur source is a composite system of sodium thiosulfate and ferrous sulfate, with a molar ratio of 2:1. S4-3. Dynamic biofilm formation is considered complete when the EPS content reaches 60 mg / g VSS. S5. Actual wastewater gradient acclimatization: The actual wastewater proportion was gradually increased in the proportions of 25%, 50%, 75%, and 100%, with each stage running for 6 days. The succession of the microbial community was monitored and the synergistic operating parameters were adjusted to ensure that the TN concentration in the effluent reached the set target. The methods for monitoring microbial community succession are as follows: S5A-1: Online monitoring of ATP content and EPS component dynamic changes; triggering the microbial community activation program when ATP < 0.4 μmol / g VSS. S5A-1-1, Increase ATP content: Promote the metabolic activity of functional bacteria by optimizing substrate supply and environmental conditions; Substrate supply optimization: The dosage of the composite sulfur source was dynamically adjusted based on the online monitoring of sulfide concentration to maintain the sulfur-to-nitrogen ratio within the range of 1.5:1; when ATP decreased, additional Fe was added. 2+ (2 mg / L) and Mg 2+ (1 mg / L); Environmental condition control: Maintain dissolved oxygen (DO) at the bottom of the reactor at 1.0 mg / L (to promote sulfur oxidation) and DO at 2.5 mg / L in the middle and upper parts of the reactor at microporous aeration (to promote denitrification); when ATP is below the threshold for two consecutive days, increase the water bath temperature (maximum value 35℃) to accelerate microbial metabolism; S5A-1-2, Adjust EPS components: Enhance biofilm stability and reduce microbial loss due to EPS loss; When EPS loss is detected, stop the water intake for 60 minutes to encourage the detached microorganisms to reattach to the carrier. S5A-2: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, a sulfur oxidation-denitrification metabolic chain is established to keep the effluent TN concentration stable below 4 mg / L. The methods for adjusting the parameters HRT, carrier filling rate, pH, and stirring rate are as follows: S5A-2-1, Determine the HRT range as 8 hours and the carrier filling rate range as 40%. S5A-2-2: When the influent C / N ratio is less than 3, the pH compensation system is automatically activated to maintain the system pH at 8.5. S5A-2-3, The stirring rate of the moving bed biofilm reactor is dynamically adjusted to 40 rpm by monitoring the fluidization state of the carrier; S5A-3: The thickness of the biofilm on the carrier surface is measured every 15 days, and the thickness is controlled within the range of 120 μm. S5A-4: The relative abundance of functional bacterial communities was monitored through real-time 16S rRNA sequencing, maintaining their proportion >20%; The method for adjusting the parameters of coordinated operation is as follows: S5B-1 uses a biotoxic buffer to eliminate heavy metal inhibition. The biotoxic buffer is cysteine, and the dosage is 0.7 mmol / L. S5B-2, Set up a heterotrophic bacteria competitive inhibition module: Pulse-add chloramphenicol once every 48 hours, with a single duration of 1 hour and an addition concentration of 10 mg / L. The trigger condition is that the abundance of heterotrophic bacteria is >15%. S5B-3. When COD > 30 mg / L, the auxiliary carbon source dosing system is activated. The carbon source is made from fermented waste straw.

[0031] Experimental Example: The description of this experimental example is based on the scheme described in Example 2, and aims to illustrate the practical application effect of the present invention.

[0032] Denitrification effect analysis Biofilm initiation experiments were conducted using a constant-temperature water bath shaker and shake flasks. 200 mL of prepared simulated wastewater was placed in four 500 mL Erlenmeyer flasks and shaken in a constant-temperature water bath at 30℃ and 150 rpm to simulate the reaction environment within the MBBR. Then, 2 g of modified carrier was placed in R1 and R3, and 1 g of unmodified carrier in R2 and R4, respectively. Initial biofilm formation was completed in R1 and R2, while 10 mL of enriched resuspended bacterial solution was added to each of R3 and R4, thus forming four reaction systems: R1 (modified carrier fixed bacteria), R2 (unmodified carrier fixed bacteria), R3 (modified carrier free bacteria), and R4 (unmodified carrier free bacteria), for a 20-day initial biofilm formation period. Water was replaced every 6 hours from the top of the shake flasks to maintain a HRT of 6 hours. Before water replacement, the shake flasks were allowed to stand for 30 minutes. An additional 1 mL of enriched and concentrated bacterial solution was added daily during the operation.

[0033] During the 12-day biofilm formation start-up phase, reactors containing modified PUF fixed bacteria (R1), unmodified PUF fixed bacteria (R2), modified PUF free bacteria (R3), and unmodified PUF free bacteria (R4) were used to treat simulated wastewater. The removal effect is as follows Figure 2 As shown. The initial concentration was 35 mg / L. Results showed that R1 was significantly more effective than the other systems in treating the simulated wastewater among the four systems. Specifically, on day 12, R1 showed the best performance in treating the simulated wastewater. The removal rate stabilizes at 94.31%, about a week faster than traditional PUF biofilm formation. Furthermore, R1 remains stable between 98.36% and 99.4% during the subsequent 8 days of operation, ultimately achieving high effluent removal rates by day 12. The concentration was reduced to 0.15 mg / L, indicating that the modified PUF-fixed bacteria possess excellent denitrification stability and high efficiency. The mechanism is as follows: 1) Through oxidative-amine modification, a multi-level rough structure is formed on the PUF@NH2 surface, increasing the biofilm adhesion area. Simultaneously, the protonation of surface -NH2 enriches the biofilm through electrostatic interactions. 1) Provides a local high-concentration substrate environment for SOB; 2) Immobilization technology covalently binds the functional bacterial community SOB to the PUF@NH2 surface, avoiding the loss of biomass caused by hydraulic shear of free bacteria.

[0034] In contrast, the suspended carrier in the R2 system... The removal rate showed a gradual upward trend. It increased from 4% on day 1 to 94.72% on day 18, finally reaching 96.49% on day 12. This result indicates that although the unmodified carrier lacks surface functionalization, a high denitrification efficiency can still be achieved by extending the biofilm attachment time (>18 days). However, its performance fluctuated significantly (e.g., the removal rate plummeted to 47% on day 9), possibly related to the weak biofilm adhesion caused by the smooth surface of the unmodified PUF. Furthermore, in R3, high denitrification efficiency was observed for the first 6 days, but significant fluctuations followed (removal rate range 2.54%~13.55%). This may be because the free bacterial solution initially had more sufficient contact with the simulated wastewater and the carrier, resulting in brief adhesion. However, as the operating time increased, the free bacteria that failed to adhere to the suspended PUF surface gradually lost due to hydraulic shear, leading to reduced biomass and decreased metabolic activity. R4 exhibited the worst denitrification effect and the greatest fluctuation. Compared to R3, R4's disadvantages further highlight the necessity of carrier modification: unmodified PUF cannot promote bacterial adhesion through surface roughness, nor does it have chemically active sites for substrate enrichment, resulting in low metabolic efficiency of free bacteria. In addition, the removal rate of R4 plummeted to 2.54% on day 15, possibly due to the lack of a protective mechanism leading to bacterial inactivation under environmental stress.

[0035] In summary, the modified PUF immobilized bacteria technology, through the dual optimization of surface functionalization and bacterial community immobilization, significantly improves the denitrification performance and stability of the MBBR-SADN system. Its effluent... The concentration can be stably kept below 1 mg / L, meeting the deep denitrification requirements mentioned above.

Claims

1. A deep denitrification process for wastewater with a low carbon-to-nitrogen ratio, characterized in that, Includes the following steps: S1. Constructing the MBBR-SADN reaction system: The MBBR-SADN reaction system consists of a moving bed biofilm reactor, which is temperature-controlled by an external water bath layer at 25~35℃ to ensure the stable execution of the sulfur autotrophic denitrification process. S2. Preparation of biomembrane carriers: Amine-modified polyurethane foam is used as a biofilm carrier. The surface of the biofilm carrier has a multi-level rough structure and –NH2 functional groups, which can efficiently fix sulfur autotrophic denitrifying bacteria through electrostatic adsorption and hydrogen bonding, and achieve the adsorption and enrichment of nitrate, providing a favorable microenvironment for subsequent biofilm formation and denitrification reactions. S3, Targeted enrichment of microbial communities: A sulfur-autotrophic bacterial community dominated by *Thiomonas* and *Thiobacillus* was selected. A simulated wastewater was designed based on the actual wastewater composition, and gradient enrichment was performed in the simulated wastewater. During the gradient enrichment process, the ratio of sulfur source to nitrogen source was controlled at 1:

1. OD was obtained through isothermal shaking culture at 25–35℃ and 130–150 rpm. 600 Enriched bacterial solutions with a concentration of ≥0.8 were used for subsequent biofilm formation. S4. Rapid biofilm attachment: The enriched bacterial solution was mixed with a biofilm carrier, the dynamic biofilm formation parameters were adjusted, and the enriched bacterial solution was periodically replenished to promote rapid growth of biomass on the carrier surface, so that the ATP content reached 0.68 μmol / g VSS within 12 days, achieving efficient biofilm formation. S5. Actual wastewater gradient acclimatization: The actual wastewater proportion was gradually increased in the proportions of 25%, 50%, 75%, and 100%, with each stage running for 6 days. The succession of the microbial community was monitored and the synergistic operating parameters were adjusted to ensure that the TN concentration in the effluent reached the set target. Let n be the multiplier and n∈R + Therefore, the amount of enriched bacterial solution added in S4 is [8,12]n mL, and the amount of biofilm carrier added is [1.8,2.2]ng; The method for adjusting the dynamic biofilm formation parameters in S4 is as follows: S4-1. During the initial 12-day biofilm formation stage, an additional enriched bacterial solution is added daily as a supplement, with the amount of enriched bacterial solution added being 0.5-1% of the total simulated wastewater volume; S4-2, Through online monitoring The concentration change controls the amount of sulfur source added. The sulfur source adopts a composite system of sodium thiosulfate and ferrous sulfate, and the molar ratio of the two is 2:

1. S4-3. Dynamic biofilm formation is considered complete when the EPS content reaches 60 mg / g VSS. The method for monitoring microbial community succession described in S5 is as follows: S5A-1: Online monitoring of ATP content and EPS component dynamic changes; triggering the microbial community activation program when ATP < 0.4 μmol / g VSS. S5A-1-1, Increase ATP content: Promote the metabolic activity of functional bacteria by optimizing substrate supply and environmental conditions; S5A-1-2, Adjust EPS components: Enhance biofilm stability and reduce microbial loss due to EPS loss; S5A-2: By adjusting the parameters of HRT-carrier filling rate-pH-stirring rate, a sulfur oxidation-denitrification metabolic chain is established to keep the effluent TN concentration stable below 4 mg / L. S5A-3: The thickness of the biofilm on the carrier surface is measured every 15 days, and the thickness is controlled within the range of 80~120 μm. S5A-4: The relative abundance of functional bacterial communities was monitored through real-time 16S rRNA sequencing, maintaining their proportion >20%; The method for adjusting the HRT-carrier filling rate-pH-stirring rate parameters described in S5A-2 is as follows: S5A-2-1, Determine the HRT range as 6~8 h and the carrier filling rate range as 30~40%. S5A-2-2: When the influent C / N ratio is less than 3, the pH compensation system is automatically activated to maintain the system pH at 7~8.

5. S5A-2-3, The stirring rate of the moving bed biofilm reactor is dynamically adjusted to 30~40 rpm by monitoring the fluidization state of the carrier; The method for adjusting the cooperative operation parameters described in S5 is as follows: S5B-1, using a biotoxic buffer to eliminate heavy metal inhibition, wherein the biotoxic buffer is cysteine, and the dosage is 0.5~0.7 mmol / L; S5B-2, Set up a heterotrophic bacteria competitive inhibition module: Pulse-add chloramphenicol once every 48 hours, with a single duration of 1 hour and an addition concentration of 10 mg / L. The trigger condition is that the abundance of heterotrophic bacteria is >15%. S5B-3. When COD > 30 mg / L, the auxiliary carbon source dosing system is started. The carbon source is a carbon source made by fermentation of sugars or agricultural waste.

2. The deep denitrification process for low C / N ratio wastewater as described in claim 1, characterized in that, The moving bed biofilm reactor described in S1 has a hollow cylindrical structure with a height-to-diameter ratio of 2 to 2.2:

1. An agitator is installed at the central axis of the moving bed biofilm reactor. The diameter of the agitator is 50 to 55% of the diameter of the moving bed biofilm reactor, and the height of the agitator from the bottom is 7.5 to 8% of the height of the moving bed biofilm reactor. An external water bath layer with a thickness of 3 to 3.5 cm is installed on the outside of the moving bed biofilm reactor, and intermittent heating is used to maintain a constant temperature.

3. The application of the deep denitrification process for low C / N ratio wastewater as described in any one of claims 1 to 2, characterized in that, It is suitable for advanced wastewater treatment with a C / N ratio of 1.4 to 3, with effluent TN ≤ 4 mg / L and no nitrite accumulation.

Images