Sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process and system

Abstract

The invention discloses a sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process and system, and the process comprises the following steps: S1, pumping sewage into an A1 anoxic zone, and carrying out heterotrophic denitrification; s2, enabling the sewage treated by the anoxic zone A1 to enter an anoxic zone A2, and carrying out carbon-sulfur synergistic denitrification; s3, the sewage treated by the anoxic zone A2 enters an aerobic zone O1 for nitrification; s4, enabling the sewage treated by the O1 aerobic zone to enter an O2 aerobic zone, and carrying out deep nitrification / adsorption; s5, enabling the sewage treated by the O2 aerobic zone to enter an SAD sulfur autotrophic denitrification zone, and carrying out sulfur autotrophic denitrification; wherein the effluent part of the SAD sulfur autotrophic denitrification zone flows back to the A1 anoxic zone. According to the invention, high-efficiency denitrification is realized under the condition of low addition or no addition of an organic carbon source, the adaptability and stability of the system to high ammonia nitrogen and high total nitrogen load are improved, the operation energy consumption, the carbon source addition amount and the sludge yield are reduced, and the effluent is stable.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and biological denitrification technology, specifically relating to a treatment method for high ammonia nitrogen and low carbon-to-nitrogen ratio wastewater collected from toilets in railway EMU depots, and particularly to a multi-stage coupled deep denitrification treatment process and system that combines traditional biological denitrification process with sulfur autotrophic denitrification process. Background Technology

[0002] Wastewater from toilets in railway EMU depots is a typical type of difficult-to-treat industrial wastewater, characterized by extremely high concentrations of ammonia nitrogen (NH3-N) and total nitrogen (TN) (ammonia nitrogen can reach over 1400 mg / L), high COD concentration but poor biodegradability, extremely low overall carbon-to-nitrogen ratio (C / N) (usually below 3), large fluctuations in water quality and quantity, and high requirements for operational stability.

[0003] At present, the traditional biological denitrification process with AO (anaerobic-aerobic) as the core is generally used in engineering. However, this type of process is mature and reliable in treating urban domestic sewage, but it has obvious shortcomings when dealing with special sewage such as toilet sewage collected in railway depots: (1) Due to the low C / N ratio, the denitrification process lacks sufficient electron donors, and a large amount of external organic carbon sources (such as methanol and sodium acetate) must be added to meet the denitrification requirements, resulting in high operating costs; (2) In order to maintain the nitrification effect, high-intensity aeration is required, and the aeration volume and return ratio are large, resulting in huge energy consumption; (3) The large-scale reproduction of heterotrophic bacteria leads to a large sludge production, which increases the burden of subsequent sludge treatment and disposal and greenhouse gas emissions; (4) Under the conditions of high load, low temperature or drastic fluctuations in water quality, the denitrification stability of the system is insufficient, and the effluent water quality is difficult to guarantee.

[0004] Sulfur autotrophic denitrification technology uses elemental sulfur or sulfur-containing compounds as electron donors to reduce nitrates / nitrites without the need for external organic carbon sources. It offers advantages such as low energy consumption, low sludge production, and low operating costs. However, when a single sulfur autotrophic denitrification process is directly applied to high-COD and high-ammonia-nitrogen wastewater, it is prone to problems such as insufficient removal of upstream organic matter, limited nitrification, and accumulation of nitrite.

[0005] To address the aforementioned problems, existing technologies attempt to introduce novel denitrification processes. For example: Chinese Patent Publication No. CN112520849A discloses a wastewater treatment process and system with low carbon-to-nitrogen ratio and high ammonia nitrogen. It is designed for wastewater with low carbon-to-nitrogen ratio and high ammonia nitrogen in highway service areas. It adopts a combination of multi-stage nitrification-denitrification and sulfur autotrophic denitrification (SAD) to reduce the amount of carbon source and alkalinity added. However, this process is mainly designed for service area wastewater with relatively low ammonia nitrogen concentrations (usually <200 mg / L). The AO-SAD-O-SAD-O process it employs still relies on the traditional A / O approach in its overall structure. It does not fully consider the pressure and stability of the system under extremely high ammonia nitrogen loads. The excessive load on the pre-nitrification unit can easily lead to a decrease in nitrification efficiency or even pH instability, causing the entire process to collapse. It also fails to consider that although the wastewater collected from the toilets in the train depot has an extremely low carbon-to-nitrogen ratio (C / N), the ammonia nitrogen concentration is extremely high, and the COD influent concentration is also relatively high compared to conventional water quality. Directly placing the sulfur autotrophic denitrification unit in the conventional biological treatment process allows heterotrophic microorganisms to easily dominate, inhibiting the enrichment and stable growth of sulfur autotrophic denitrifying bacteria and affecting the continuous nitrogen removal effect of sulfur autotrophic denitrification. At the same time, this process does not classify and regulate the synergistic relationship between heterotrophic denitrification and sulfur autotrophic denitrification under ultra-low carbon-to-nitrogen ratio conditions. When the influent water quality fluctuates greatly, the system's ability to withstand shock loads is limited, making it difficult to achieve long-term stable deep denitrification.

[0006] Chinese patent publication numbers CN111661924A, CN108483655A, and CN118343921A employ a combination of short-cut nitrification / anaerobic ammonium oxidation and sulfur autotrophic short-cut denitrification. Theoretically, this type of process boasts extremely high nitrogen removal efficiency and very low energy consumption; however, its successful operation highly depends on precise control of parameters such as dissolved oxygen (DO), temperature, and substrate ratio. For sewage collected from toilets in railway depots, where water quality and quantity fluctuate drastically and contain complex organic matter, the short-cut nitrification / anaerobic ammonium oxidation process has stringent operating conditions in practical engineering applications. Its process control is complex, and long-term stable operation is difficult. Furthermore, anaerobic ammonium oxidizing bacteria are highly sensitive to changes in the concentration of organic matter in the influent; under conditions of fluctuation or accumulation of organic matter, bacterial activity is easily inhibited, thus affecting the overall nitrogen removal efficiency.

[0007] In summary, existing technologies either fail to effectively address the dual challenges of ultra-high ammonia nitrogen and high COD, or are overly complex and difficult to operate stably in engineering. Therefore, there is an urgent need to develop a novel coupled denitrification process that can efficiently treat ultra-high ammonia nitrogen, adapt to low carbon-to-nitrogen ratios and high COD impacts, and is stable and cost-effective. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention proposes a sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment process and system. By innovatively introducing a multi-stage functional reactor and a sulfur autotrophic denitrification unit into the traditional biological treatment process, it achieves efficient nitrogen removal under conditions of low or no added organic carbon source, improves the system's adaptability and stability to high ammonia nitrogen and high total nitrogen loads, reduces operating energy consumption, carbon source dosage and sludge production, and ensures stable effluent that meets the Class B requirements of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015).

[0009] This invention is implemented as follows: a sulfur autotrophic denitrification enhanced nitrogen removal coupling process, specifically including the following steps: S1. Pump the wastewater into the A1 anoxic zone for heterotrophic denitrification; wherein, the wastewater concentration is >1400mg / L, C / N ratio <3, COD concentration >3300mg / L, and total nitrogen (TN) concentration >1600mg / L. S2. Wastewater treated in the A1 anoxic zone in step S1 enters the A2 anoxic zone for carbon-sulfur synergistic denitrification. S3. Wastewater treated in the anoxic zone A2 of step S2 enters the aerobic zone O1 for nitrification. S4. Wastewater treated in the O1 aerobic zone in step S3 enters the O2 aerobic zone for deep nitrification / adsorption. S5. Wastewater treated in the O2 aerobic zone in step S4 enters the SAD sulfur autotrophic denitrification zone for sulfur autotrophic denitrification. In this process, a portion of the effluent from the SAD sulfur autotrophic denitrification zone is recirculated to the A1 anoxic zone.

[0010] In the above technical solution, preferably, porous packing material is added to the A1 anoxic zone. This packing material is selected from ceramsite packing material, biochar packing material or a combination thereof. This packing material is used to enrich heterotrophic denitrifying bacteria, improve biomass retention capacity, remove part of COD and start heterotrophic denitrification, alleviate subsequent load, improve the system's shock resistance, and provide some alkalinity.

[0011] In the above technical solution, preferably, carbon-sulfur synergistic denitrification composite packing is added to the A2 anoxic zone. This packing is used to form a carbon-sulfur synergistic denitrification environment, realize the synergistic denitrification of heterotrophic denitrification and sulfur autotrophic denitrification, and maintain a high denitrification rate under low C / N conditions.

[0012] In the above technical solution, preferably, porous packing material is added to the O1 aerobic zone. This packing material is selected from ceramsite packing material, modified plastic packing material or a combination thereof. This packing material is used to enrich nitrifying bacteria, convert ammonia nitrogen into nitrate, continuously aerate, and maintain the activity of nitrifying bacteria.

[0013] In the above technical solution, preferably, a packing material with adsorption properties is added to the O2 aerobic zone. This packing material is selected from zeolite packing material or modified zeolite packing material. This packing material is used to enrich nitrifying bacteria, enhance nitrification, and adsorb and buffer ammonia nitrogen and nitrite nitrogen, thereby reducing the risk of nitrite nitrogen accumulation.

[0014] In the above technical solution, preferably, both the O1 aerobic zone and the O2 aerobic zone are equipped with aeration devices.

[0015] In the above technical solution, preferably, elemental sulfur particles or sulfur-based composite packing are added to the SAD sulfur autotrophic denitrification zone to use elemental sulfur as an electron donor for deep denitrification, without the need for an external organic carbon source, resulting in high total nitrogen removal efficiency.

[0016] In the above technical solution, preferably, the effluent from the SAD autotrophic denitrification reactor is partially recycled to the A1 anoxic reactor, with a recycling ratio of 50% to 400% of the influent flow rate, which can be adjusted according to the influent ammonia nitrogen concentration, total nitrogen load and system operating status.

[0017] In the above technical solution, preferably, during system operation, the dissolved oxygen (DO) in the A1 anoxic zone and the A2 anoxic zone is ≤0.5 mg / L; the dissolved oxygen in the O1 aerobic zone and the O2 aerobic zone is 2.0~3.0 mg / L; the system hydraulic retention time is set to 24~72 h according to the influent load, and the system temperature is set to 12~35℃ to ensure the stable denitrification effect of the system under ultra-high ammonia nitrogen conditions.

[0018] A sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment system includes an A1 anoxic reactor, an A2 anoxic reactor, an O1 aerobic reactor, an O2 aerobic reactor, a SAD sulfur autotrophic denitrification reactor connected in sequence, and a return pipeline connected between the outlet of the SAD sulfur autotrophic denitrification reactor and the inlet of the A1 anoxic reactor.

[0019] In the above technical solution, preferably, the A1 anoxic reactor is used to perform heterotrophic denitrification using organic matter in wastewater.

[0020] The A1 anoxic reactor is a closed or semi-closed structure. The A1 anoxic reactor is equipped with a stirring device or a hydraulic mixing structure to ensure that the sewage and return liquid are fully mixed in the reactor. The A1 anoxic reactor has an inlet at the bottom or side wall and an outlet or overflow at the top.

[0021] The A1 anoxic reactor is filled with porous packing material, which is selected from ceramsite packing material, biochar packing material or a combination thereof. The packing material filling rate is 20% to 40% of the effective volume of the A1 anoxic reactor, which is used to enrich heterotrophic denitrifying bacteria and improve biomass retention capacity.

[0022] With the above structural design, organic matter in the influent can be fully utilized as an electron donor under low dissolved oxygen conditions to achieve efficient heterotrophic denitrification, while enhancing the system's buffering capacity against fluctuations in water quality and quantity.

[0023] In the above technical solution, preferably, the A2 anoxic reactor is used for carbon-sulfur synergistic denitrification.

[0024] The A2 anoxic reactor has a similar structure to the A1 anoxic reactor, being a closed or semi-closed structure. The A2 anoxic reactor has an inlet at the bottom or side wall and an outlet or overflow at the top.

[0025] The A2 anoxic reactor is equipped with a packing zone for filling carbon-sulfur synergistic denitrification composite packing. The packing zone is set in the form of a packing frame, packing basket or fixed bed to prevent packing loss and facilitate subsequent packing replenishment.

[0026] The packing material filling rate of the A2 anoxic reactor is 20% to 50% of the effective volume of the A2 anoxic reactor, so that a reaction environment in which heterotrophic denitrification and sulfur autotrophic denitrification occur synergistically is formed in the A2 anoxic reactor.

[0027] Through the above structural design, sulfur autotrophic denitrifying bacteria can be enriched in advance while organic matter is gradually consumed at the front end, providing a biological basis for the stable operation of the subsequent SAD sulfur autotrophic denitrification reactor.

[0028] In the above technical solution, preferably, the O1 aerobic reactor is used to carry out the nitration reaction, oxidizing ammonia nitrogen into nitrate nitrogen.

[0029] The O1 aerobic reactor is equipped with an aeration device, which is a microporous aerator or a perforated aeration pipe. The aeration device is located at the bottom or lower side wall of the O1 aerobic reactor and is used to continuously supply oxygen to the O1 aerobic reactor. The O1 aerobic reactor has an inlet at the bottom and an outlet and an exhaust port at the top.

[0030] The O1 aerobic reactor is filled with porous packing material for the attachment and growth of nitrifying bacteria. The packing material is selected from ceramsite packing material, modified plastic packing material or a combination thereof, and the packing material filling rate is 20% to 40% of the effective volume of the O1 aerobic reactor.

[0031] With the above structural setup, the O1 aerobic reactor can bear the main nitrification load of the system, stably converting high-concentration ammonia nitrogen into nitrate nitrogen, and reducing the load pressure on subsequent reactors.

[0032] In the above technical solutions, the preferred method is an O2 aerobic reactor, which is used for deep nitrification and organic matter adsorption.

[0033] The O2 aerobic reactor is located after the O1 aerobic reactor. It also contains an aeration device, which is either a microporous aerator or a perforated aeration pipe. The aeration device is located at the bottom or lower side wall of the O2 aerobic reactor to continuously supply oxygen to the reactor. The O2 aerobic reactor has an inlet at the bottom and an outlet and exhaust port at the top.

[0034] The O2 aerobic reactor is filled with packing material with adsorption properties. This packing material is zeolite packing material or modified zeolite packing material, and the packing material filling rate is 10% to 30% of the effective volume of the O2 aerobic reactor.

[0035] The O2 aerobic reactor buffers and further removes residual ammonia nitrogen and nitrite nitrogen through the synergistic effect of adsorption and biological action, thereby reducing the risk of water quality fluctuations entering the subsequent SAD sulfur autotrophic denitrification reactor.

[0036] In the above technical solutions, the preferred method is the SAD sulfur autotrophic denitrification reactor, which uses elemental sulfur as an electron donor to reduce nitrate nitrogen to nitrogen gas.

[0037] The SAD (sulfur-autotrophic denitrification) reactor is equipped with a sulfur-based denitrification packing bed, which is arranged in the form of a fixed bed, packing basket, or modular packing unit to ensure stable distribution of the packing within the reactor. The reactor has an inlet at the bottom and an outlet and exhaust port at the top to promptly remove nitrogen gas generated during denitrification.

[0038] The SAD sulfur autotrophic denitrification reactor is filled with elemental sulfur particles or sulfur-based composite packing material. The particle size of the packing material is 1-6 mm, and the packing material filling rate is 20%-50% of the effective volume of the SAD sulfur autotrophic denitrification reactor.

[0039] With the above structural design, efficient reduction of nitrate nitrogen can be achieved without the need for an external organic carbon source, thus completing the system's deep denitrification.

[0040] The treatment process of this invention sequentially comprises an A1 anoxic stage (heterotrophic denitrification), an A2 anoxic stage (carbon-sulfur synergistic denitrification), an O1 aerobic stage (nitrification), an O2 aerobic stage (deep nitrification / adsorption), and a SAD sulfur autotrophic denitrification stage, with effluent recirculation to the upstream anoxic stage at the end. This invention, through the series connection and coupling of multi-stage functional reactors, efficiently removes high concentrations of ammonia nitrogen and total nitrogen without or with only a small amount of external organic carbon source. This process is particularly suitable for treating difficult-to-treat wastewater, such as sewage from railway depots, characterized by extremely high ammonia nitrogen (>1400 mg / L), high COD, but an ultra-low carbon-to-nitrogen ratio (C / N<3), effectively solving the problems of high operating costs and poor stability of traditional processes, ensuring stable effluent compliance.

[0041] The advantages and positive effects of this invention are: This invention utilizes a multi-stage anoxic zone, aerobic zone, and sulfur autotrophic denitrification zone to achieve highly efficient removal of high concentrations of ammonia nitrogen and total nitrogen by employing the synergistic effects of heterotrophic denitrification, nitrification, and sulfur autotrophic denitrification. This treatment process is suitable for special wastewater systems with extremely low carbon-to-nitrogen ratios, extremely high ammonia nitrogen concentrations, and large fluctuations in water quality. It is particularly suitable for the stable treatment of difficult-to-treat nitrogen-containing wastewater, such as sewage from toilets in railway depots, to achieve compliance with treatment standards.

[0042] 1) Highly targeted: Specifically designed for sewage from toilets in railway EMU depots with ultra-high ammonia nitrogen (>1400mg / L), high COD (>3300mg / L), and ultra-low carbon-to-nitrogen ratio (C / N<3), solving a global problem in the treatment of this type of wastewater.

[0043] 2) Robust process: It abandons the anammox process, which has extremely harsh operating conditions, and adopts a mature nitrification / denitrification pathway. The load is shared by multiple reactors, which has strong resistance to shocks. The multi-stage buffer and functional zoning greatly enhance the system's adaptability to water quality and quantity fluctuations and its long-term operational stability.

[0044] 3) Low cost: The raw water carbon source is maximized through the A1 anoxic section, and the main denitrification load is finally undertaken by the SAD sulfur autotrophic denitrification section to complete deep denitrification, which significantly reduces or even completely avoids the need for external carbon sources and greatly reduces operating costs; it also reduces aeration requirements and heterotrophic sludge production.

[0045] 4) Excellent efficiency: Experiments show that under the condition that the influent TN is as high as 1600 mg / L or more, the removal rate of COD, ammonia nitrogen and nitrate nitrogen by this treatment process can reach more than 90%, 99% and 90% respectively, and the effluent water quality meets the standards and can stably reach the GB / T31962-2015 Class B standard. Attached Figure Description

[0046] Figure 1 This is a flowchart of the sulfur autotrophic denitrification enhanced denitrification coupling treatment system provided in the embodiments of the present invention. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] The following is in conjunction with the appendix Figure 1 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] like Figure 1 As shown, a sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment process includes the following steps: S1. Pump the wastewater into the A1 anoxic zone for heterotrophic denitrification; wherein, the wastewater concentration is >1400mg / L, C / N ratio <3, COD concentration >3300mg / L, and total nitrogen (TN) concentration >1600mg / L. S2. Wastewater treated in the A1 anoxic zone in step S1 enters the A2 anoxic zone for carbon-sulfur synergistic denitrification. S3. Wastewater treated in the anoxic zone A2 of step S2 enters the aerobic zone O1 for nitrification. S4. Wastewater treated in the O1 aerobic zone in step S3 enters the O2 aerobic zone for deep nitrification / adsorption. S5. Wastewater treated in the O2 aerobic zone in step S4 enters the SAD sulfur autotrophic denitrification zone for sulfur autotrophic denitrification. In this process, a portion of the effluent from the SAD sulfur autotrophic denitrification zone is recirculated to the A1 anoxic zone.

[0052] In a preferred embodiment, porous packing material is added to the A1 anoxic zone. This packing material is selected from ceramsite packing material, biochar packing material, or a combination thereof. This packing material is used to enrich heterotrophic denitrifying bacteria, improve biomass retention capacity, remove part of COD and start heterotrophic denitrification, alleviate subsequent load, improve the system's shock resistance, and provide some alkalinity.

[0053] As a preferred embodiment, carbon-sulfur synergistic denitrification composite packing is added to the A2 anoxic zone. This packing is used to form a carbon-sulfur synergistic denitrification environment. It uses elemental sulfur as the main material and is compounded with other inorganic components. It can serve as an electron donor for sulfur autotrophic denitrification and as a biological carrier for carrying microorganisms, so as to achieve synergistic denitrification of heterotrophic denitrification and sulfur autotrophic denitrification, and maintain a high denitrification rate under low C / N conditions.

[0054] In a preferred embodiment, porous packing material is added to the O1 aerobic zone. This packing material is selected from ceramsite packing material, modified plastic packing material, or a combination thereof. This packing material is used to enrich nitrifying bacteria, convert ammonia nitrogen into nitrate, and continuously aerate to maintain the activity of nitrifying bacteria.

[0055] In a preferred embodiment, a packing material with adsorption properties is added to the O2 aerobic zone. This packing material is selected from zeolite packing material or modified zeolite packing material. This packing material is used to enrich nitrifying bacteria, enhance nitrification, and adsorb and buffer ammonia nitrogen and nitrite nitrogen, thereby reducing the risk of nitrite nitrogen accumulation.

[0056] In a preferred embodiment, both the O1 aerobic zone and the O2 aerobic zone are equipped with aeration devices.

[0057] As a preferred embodiment, elemental sulfur particles or sulfur-based composite packing are added to the SAD sulfur autotrophic denitrification zone, using elemental sulfur as an electron donor for deep denitrification, without the need for an external organic carbon source, resulting in high total nitrogen removal efficiency.

[0058] In a preferred embodiment, a portion of the effluent from the SAD (sulfur autotrophic denitrification) reactor is recycled to the A1 anoxic reactor at a recycling ratio of 50% to 400% of the influent flow rate, which can be adjusted according to the influent ammonia nitrogen concentration, total nitrogen load, and system operating status. By implementing this recycling method, on the one hand, the concentration of pollutants in the upstream influent can be diluted, mitigating the instantaneous load shock in the A1 anoxic zone; on the other hand, the alkalinity generated by sulfur autotrophic denitrification in the recycled liquid can compensate for the alkalinity consumed during aerobic nitrification, which helps maintain system pH stability and reduces the amount of external alkalinity added.

[0059] As a preferred embodiment, during system operation, the dissolved oxygen (DO) in the A1 and A2 anoxic zones is ≤0.5 mg / L; the dissolved oxygen in the O1 and O2 aerobic zones is 2.0–3.0 mg / L; the system hydraulic retention time is set to 24–72 h according to the influent load, and the system temperature is set to 12–35℃ to ensure stable denitrification effect of the system under ultra-high ammonia nitrogen conditions.

[0060] A sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment system includes an A1 anoxic reactor, an A2 anoxic reactor, an O1 aerobic reactor, an O2 aerobic reactor, a SAD sulfur autotrophic denitrification reactor connected in sequence, and a return pipeline connected between the outlet of the SAD sulfur autotrophic denitrification reactor and the inlet of the A1 anoxic reactor.

[0061] As a preferred embodiment, the A1 anoxic reactor is used for heterotrophic denitrification using organic matter in wastewater.

[0062] The A1 anoxic reactor is a closed or semi-closed structure. The A1 anoxic reactor is equipped with a stirring device or a hydraulic mixing structure to ensure that the sewage and return liquid are fully mixed in the reactor. The A1 anoxic reactor has an inlet at the bottom or side wall and an outlet or overflow at the top.

[0063] The A1 anoxic reactor is filled with porous packing material, which is selected from ceramsite packing material, biochar packing material or a combination thereof. The packing material filling rate is 20% to 40% of the effective volume of the A1 anoxic reactor, which is used to enrich heterotrophic denitrifying bacteria and improve biomass retention capacity.

[0064] With the above structural design, organic matter in the influent can be fully utilized as an electron donor under low dissolved oxygen conditions to achieve efficient heterotrophic denitrification, while enhancing the system's buffering capacity against fluctuations in water quality and quantity.

[0065] As a preferred embodiment, the A2 anoxic reactor is used for carbon-sulfur synergistic denitrification.

[0066] The A2 anoxic reactor has a similar structure to the A1 anoxic reactor, being a closed or semi-closed structure. The A2 anoxic reactor has an inlet at the bottom or side wall and an outlet or overflow at the top.

[0067] The A2 anoxic reactor is equipped with a packing zone for filling carbon-sulfur synergistic denitrification composite packing. The packing zone is set in the form of a packing frame, packing basket or fixed bed to prevent packing loss and facilitate subsequent packing replenishment.

[0068] The packing material filling rate of the A2 anoxic reactor is 20% to 50% of the effective volume of the A2 anoxic reactor, so that a reaction environment in which heterotrophic denitrification and sulfur autotrophic denitrification occur synergistically is formed in the A2 anoxic reactor.

[0069] Through the above structural design, sulfur autotrophic denitrifying bacteria can be enriched in advance while organic matter is gradually consumed at the front end, providing a biological basis for the stable operation of the subsequent SAD sulfur autotrophic denitrification reactor.

[0070] As a preferred embodiment, the O1 aerobic reactor is used to carry out the nitration reaction, oxidizing ammonia nitrogen to nitrate nitrogen.

[0071] The O1 aerobic reactor is equipped with an aeration device, which is a microporous aerator or a perforated aeration pipe. The aeration device is located at the bottom or lower side wall of the O1 aerobic reactor and is used to continuously supply oxygen to the O1 aerobic reactor. The O1 aerobic reactor has an inlet at the bottom and an outlet and an exhaust port at the top.

[0072] The O1 aerobic reactor is filled with porous packing material for the attachment and growth of nitrifying bacteria. The packing material is selected from ceramsite packing material, modified plastic packing material or a combination thereof, and the packing material filling rate is 20% to 40% of the effective volume of the O1 aerobic reactor.

[0073] With the above structural setup, the O1 aerobic reactor can bear the main nitrification load of the system, stably converting high-concentration ammonia nitrogen into nitrate nitrogen, and reducing the load pressure on subsequent reactors.

[0074] As a preferred embodiment, an O2 aerobic reactor is used for deep nitrification and organic matter adsorption.

[0075] The O2 aerobic reactor is located after the O1 aerobic reactor. It also contains an aeration device, which is either a microporous aerator or a perforated aeration pipe. The aeration device is located at the bottom or lower side wall of the O2 aerobic reactor to continuously supply oxygen to the reactor. The O2 aerobic reactor has an inlet at the bottom and an outlet and exhaust port at the top.

[0076] The O2 aerobic reactor is filled with packing material with adsorption properties. This packing material is zeolite packing material or modified zeolite packing material, and the packing material filling rate is 10% to 30% of the effective volume of the O2 aerobic reactor.

[0077] The O2 aerobic reactor buffers and further removes residual ammonia nitrogen and nitrite nitrogen through the synergistic effect of adsorption and biological action, thereby reducing the risk of water quality fluctuations entering the subsequent SAD sulfur autotrophic denitrification reactor.

[0078] As a preferred embodiment, the SAD sulfur autotrophic denitrification reactor is used to reduce nitrate nitrogen to nitrogen gas by using elemental sulfur as an electron donor.

[0079] The SAD (sulfur-autotrophic denitrification) reactor is equipped with a sulfur-based denitrification packing bed, which is arranged in the form of a fixed bed, packing basket, or modular packing unit to ensure stable distribution of the packing within the reactor. The SAD reactor has an inlet at the bottom and an outlet and exhaust port at the top to promptly remove nitrogen gas generated during denitrification.

[0080] The SAD sulfur autotrophic denitrification reactor is filled with elemental sulfur particles or sulfur-based composite packing material. The particle size of the packing material is 1-6 mm, and the packing material filling rate is 20%-50% of the effective volume of the SAD sulfur autotrophic denitrification reactor.

[0081] With the above structural design, efficient reduction of nitrate nitrogen can be achieved without the need for an external organic carbon source, thus completing the system's deep denitrification.

[0082] The core of this invention lies in constructing a multi-stage coupled denitrification process system of A1 (anoxic) → A2 (anoxic) → O1 (aerobic) → O2 (aerobic) → SAD (sulfur autotrophic denitrification). Each functional reaction section is set in series along the water flow direction. Through the functional zoning of the reaction and the gradual distribution of the reaction load, stable and efficient denitrification treatment of wastewater with ultra-high ammonia nitrogen and low carbon-to-nitrogen ratio is achieved.

[0083] As the first reaction unit of the system, the A1 anoxic reaction section makes full use of the relatively high amount of biodegradable organic matter in the raw wastewater. Under low dissolved oxygen conditions, heterotrophic denitrification occurs preferentially, rapidly reducing nitrate and nitrite nitrogen in the return water and influent. At the same time, it consumes easily degradable organic matter, thereby reducing the organic load of the subsequent aerobic section. Through the heterotrophic denitrification reaction, a certain alkalinity is generated under anoxic conditions at the front end, providing a buffer for the inevitable alkalinity consumption in the subsequent nitrification reaction and sulfur autotrophic denitrification process, thus contributing to the overall pH stability of the system.

[0084] Building upon the A1 anoxic reaction section, the A2 anoxic reaction section introduces a carbon-sulfur synergistic denitrification mechanism. By installing a carbon-sulfur synergistic denitrification composite packing material within the reactor, heterotrophic denitrification and sulfur autotrophic denitrification proceed synergistically in the same reaction environment. In this stage, residual organic matter and sulfur-based electron donors jointly participate in the denitrification reaction, further improving total nitrogen removal efficiency and facilitating the gradual enrichment and acclimatization of sulfur autotrophic denitrifying bacteria. This achieves a smooth transition from heterotrophic to autotrophic denitrification, preventing the inhibition of sulfur autotrophic denitrification under high COD conditions.

[0085] The O1 and O2 aerobic reaction sections are arranged in a two-stage series configuration. The O1 aerobic reaction section bears the main nitrification load, oxidizing high-concentration ammonia nitrogen to nitrate nitrogen under sufficient oxygen supply. The O2 aerobic reaction section further removes and stabilizes residual ammonia nitrogen and nitrite nitrogen through further nitrification and the adsorption and buffering effect of the packing material. By implementing the nitrification process in stages, the impact of ultra-high ammonia nitrogen on a single aerobic reactor is effectively dispersed, improving the stability of the nitrification system under high load and water quality fluctuation conditions.

[0086] The SAD (sulfur autotrophic denitrification) reaction section, serving as the final deep nitrogen removal unit of the system, utilizes elemental sulfur as an electron donor to efficiently reduce nitrate nitrogen produced in the preceding nitrification stage to nitrogen gas without the need for an external organic carbon source, thus achieving deep nitrogen removal. This reaction section is independent of the influent organic matter concentration and is less affected by water quality fluctuations, making it a key guarantee for the system to achieve stable and compliant emissions under low carbon-to-nitrogen ratio conditions.

[0087] By setting up the above-mentioned reflux method, on the one hand, the effluent from the SAD sulfur autotrophic denitrification reactor can be refluxed back to the upstream A1 anoxic zone, which plays a role in diluting and buffering the high-concentration influent, reducing the instantaneous load impact on the A1 anoxic zone, and improving the system's adaptability to fluctuations in water quality and quantity. On the other hand, the nitrate nitrogen carried in the reflux liquid can preferentially participate in the heterotrophic denitrification reaction in the A1 anoxic zone, using the residual organic matter in the raw water as an electron donor for reduction, thereby generating a certain alkalinity under upstream anoxic conditions to compensate for the alkalinity consumed in the subsequent aerobic nitrification and sulfur autotrophic denitrification processes. This is beneficial for maintaining the overall pH stability of the system and reducing the dependence on external alkalinity adjustment during operation.

[0088] Through the synergistic effect of the above-mentioned multi-stage reactors, the present invention achieves a reasonable division of labor and coupling between heterotrophic denitrification, nitrification reaction and sulfur autotrophic denitrification in time and space, overcoming the problems of high operating cost and poor stability of traditional processes when treating wastewater with ultra-high ammonia nitrogen and low carbon-to-nitrogen ratio. The system can achieve efficient and stable denitrification treatment without or with only a small amount of external carbon source.

[0089] The treatment process of this invention sequentially comprises an A1 anoxic stage (heterotrophic denitrification), an A2 anoxic stage (carbon-sulfur synergistic denitrification), an O1 aerobic stage (nitrification), an O2 aerobic stage (deep nitrification / adsorption), and a SAD sulfur autotrophic denitrification stage, with effluent recirculation to the upstream anoxic stage at the end. This invention, through the series connection and coupling of multi-stage functional reactors, efficiently removes high concentrations of ammonia nitrogen and total nitrogen without or with only a small amount of external organic carbon source. This process is particularly suitable for treating difficult-to-treat wastewater, such as sewage from railway depots, characterized by extremely high ammonia nitrogen (>1400 mg / L), high COD, but an ultra-low carbon-to-nitrogen ratio (C / N<3), effectively solving the problems of high operating costs and poor stability of traditional processes, ensuring stable effluent compliance.

[0090] To better understand the above embodiments of the present invention, they are further described below.

[0091] The following three examples use a five-stage column reactor to construct an AAOO-SAD coupled system to simulate the continuous operation of sewage from a high-speed train toilet.

[0092] Example 1 Continuous operation under typical operating conditions This embodiment constructs a laboratory-scale AAOO-SAD five-stage series sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment system. The effective volumes of each reactor are as follows: A1 anoxic reactor: 5 L; A2 anoxic reactor: 5 L; O1 aerobic reactor: 10 L; O2 aerobic reactor: 5 L; and SAD sulfur autotrophic denitrification reactor: 5 L. The influent simulates sewage collected from toilets in a railway depot, with the following water quality parameters: ammonia nitrogen concentration 1450±50 mg / L, total nitrogen (TN) concentration 1650±50 mg / L, COD concentration 3400±100 mg / L, and C / N ≈ 2.0.

[0093] The A1 anoxic reactor, A2 anoxic reactor, O1 aerobic reactor, and O2 aerobic reactor were all fed with different packing materials (all with a filling rate of 30%), among which: The A1 anoxic reactor is filled with 2-4mm ceramsite. Sulfur particles with a diameter of 1-6 mm are added to the A2 anoxic reactor; The O1 and O2 aerobic reactors use microporous aeration, with DO controlled at 2.0-3.0 mg / L; The SAD sulfur autotrophic denitrification reactor is filled with elemental sulfur particles (1-6 mm in diameter) and has no external carbon source. The effluent from the SAD sulfur autotrophic denitrification reactor is refluxed to the A1 anoxic reactor at a 200% reflux ratio.

[0094] The system operating parameters are set as follows: dissolved oxygen in the A1 and A2 anoxic reactors is controlled below 0.5 mg / L; dissolved oxygen in the O1 and O2 aerobic reactors is controlled between 2.0 and 3.0 mg / L; the SAD autotrophic denitrification reactor operates in anoxic mode; the SAD effluent is recirculated to the A1 anoxic reactor at a recirculation ratio of 100% to 300% of the influent flow rate; and the total hydraulic retention time of the system is 36 to 60 h.

[0095] After the system has been running continuously and stabilized, the ammonia nitrogen concentration in the effluent is consistently below 15 mg / L and the total nitrogen concentration is consistently below 30 mg / L, indicating that the overall denitrification effect of the system is good. No additional organic carbon source needs to be added during operation, and only a small amount of alkalinity needs to be adjusted according to the operating conditions, resulting in high system stability.

[0096] Example 2 Stability test under high load impact Based on Example 1, the influent ammonia nitrogen concentration was increased to 1800 mg / L, COD to 3600 mg / L, and C / N ≈ 1.6, while other conditions remained unchanged. The system quickly stabilized after a 10-day shock, and the effluent TN remained below 35 mg / L, indicating that the process of this invention has excellent resistance to high-load shocks.

[0097] Example 3 Operating performance under low temperature conditions The system was placed in a constant temperature environment of 12°C, and the influent water quality was the same as in Example 1. Although the nitrification rate decreased, thanks to the design of the O1 / O2 dual aerobic stage and the characteristic that the SAD sulfur autotrophic denitrification stage is not significantly affected by low temperature, the system stabilized again after 20 days, and the final effluent TN was 38 mg / L, proving that this process still has good denitrification capacity at low temperatures.

[0098] The experimental results of Examples 1-3 show that the system operates stably and all indicators meet the expected goals, verifying the feasibility and superiority of the present invention.

[0099] Comparative Example 1 Comparative Example 1 uses a conventional A / O process to treat the wastewater described in Example 1. The system only includes a single-stage anoxic reactor and a single-stage aerobic reactor, without the A2 anoxic reactor, O2 aerobic reactor, and SAD sulfur autotrophic denitrification reactor. The other operating conditions are basically the same as in Example 1.

[0100] The operational results show that under low carbon-to-nitrogen ratio conditions, the process requires the addition of a large amount of external organic carbon source to maintain the denitrification reaction, resulting in high system operating costs. Furthermore, when the influent ammonia nitrogen load is high or the water quality fluctuates, the total nitrogen in the effluent fluctuates beyond the standard, indicating poor long-term operational stability.

[0101] Comparative Example 2 Based on Example 1, the aerobic reactor and the SAD sulfur autotrophic denitrification reactor were removed, and heterotrophic denitrification was carried out solely by the front-end anoxic reactor, while the rest of the structure and operating parameters remained unchanged.

[0102] Operational results show that under conditions of low influent carbon-to-nitrogen ratio, it is difficult to achieve stable deep denitrification by relying solely on heterotrophic denitrification. It is necessary to continuously add external organic carbon sources to maintain denitrification efficiency, and the system has limited adaptability to fluctuations in water quality and quantity.

[0103] As can be seen from the comparison of the above embodiments and comparative examples, the AAOO-SAD coupled denitrification process proposed in this invention has comprehensive advantages such as high denitrification efficiency, low operating cost, strong resistance to shocks, and good system stability when treating sewage from the toilets of high-speed train depots with ultra-high ammonia nitrogen, high COD, and ultra-low carbon-nitrogen ratio.

[0104] This invention achieves the complementary advantages of sulfur autotrophic denitrification and traditional biological denitrification by constructing a multi-stage AAOO-SAD coupled denitrification process. It is particularly suitable for the efficient, low-consumption, and stable treatment of sewage collected from toilets in railway EMU depots and has good prospects for engineering promotion and application.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A sulfur autotrophic denitrification enhanced nitrogen removal coupling process, characterized in that, Includes the following steps: S1. Pump the wastewater into the A1 anoxic zone for heterotrophic denitrification; wherein, the wastewater concentration is >1500mg / L, C / N ratio <3, COD concentration >3300mg / L, and total nitrogen (TN) concentration >1600mg / L. S2. Wastewater treated in the A1 anoxic zone in step S1 enters the A2 anoxic zone for carbon-sulfur synergistic denitrification. S3. Wastewater treated in the anoxic zone A2 of step S2 enters the aerobic zone O1 for nitrification. S4. Wastewater treated in the O1 aerobic zone in step S3 enters the O2 aerobic zone for deep nitrification / adsorption. S5. Wastewater treated in the O2 aerobic zone in step S4 enters the SAD sulfur autotrophic denitrification zone for sulfur autotrophic denitrification. In this process, a portion of the effluent from the SAD sulfur autotrophic denitrification zone is recirculated to the A1 anoxic zone.

2. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, Porous packing material is added to the A1 anoxic zone. This packing material is selected from ceramsite packing material, biochar packing material, or a combination thereof. The packing material filling rate is 20% to 40% of the effective volume of the A1 anoxic reactor. This packing material is used to enrich heterotrophic denitrifying bacteria, improve biomass retention capacity, remove part of COD and start heterotrophic denitrification, alleviate subsequent load, improve the system's shock resistance, and provide some alkalinity.

3. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, Carbon-sulfur synergistic denitrification composite packing is added to the A2 anoxic zone. The packing filling rate is 20% to 50% of the effective volume of the A2 anoxic reactor. This packing is used to form a carbon-sulfur synergistic denitrification environment to achieve synergistic denitrification of heterotrophic denitrification and sulfur autotrophic denitrification.

4. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, Porous packing material is added to the O1 aerobic zone. This packing material is selected from ceramsite packing material, modified plastic packing material, or a combination thereof. The packing material filling rate is 20% to 40% of the effective volume of the O1 aerobic reactor. This packing material is used to enrich nitrifying bacteria, convert ammonia nitrogen into nitrate, and maintain the activity of nitrifying bacteria.

5. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, The O2 aerobic zone is filled with adsorption-capable packing material, with a packing rate of 10% to 30% of the effective volume of the O2 aerobic reactor. This packing material is selected from zeolite packing or modified zeolite packing. This packing material is used to enrich nitrifying bacteria, enhance nitrification, and adsorb and buffer ammonia nitrogen and nitrite nitrogen.

6. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, The SAD sulfur autotrophic denitrification zone is filled with elemental sulfur particles or sulfur-based composite packing material with a particle size of 1-6 mm and a packing filling rate of 20%-50% of the effective volume of the SAD sulfur autotrophic denitrification reactor. Elemental sulfur is used as an electron donor for deep denitrification without the need for an external organic carbon source.

7. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, The effluent from the SAD sulfur autotrophic denitrification reactor is partially recycled to the A1 anoxic reactor, with a recycling ratio of 50% to 400% of the influent flow rate.

8. The sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment process according to claim 1, characterized in that, During system operation, the dissolved oxygen in the A1 and A2 anoxic zones is ≤0.5 mg / L; the dissolved oxygen in the O1 and O2 aerobic zones is 2.0–3.0 mg / L; the system temperature is set to 12–35℃; and the system hydraulic retention time is set to 24–72 h according to the influent load.

9. A sulfur autotrophic denitrification enhanced nitrogen removal coupling treatment system, used to implement the process described in any one of claims 1-8, characterized in that, It includes an A1 anoxic reactor, an A2 anoxic reactor, an O1 aerobic reactor, an O2 aerobic reactor, a SAD sulfur autotrophic denitrification reactor connected in sequence, and a return pipeline connecting the outlet of the SAD sulfur autotrophic denitrification reactor and the inlet of the A1 anoxic reactor.

10. The sulfur autotrophic denitrification enhanced nitrogen removal coupled treatment system according to claim 9, characterized in that, The A1 anoxic reactor is used to perform heterotrophic denitrification using organic matter in wastewater. The A1 anoxic reactor is a closed or semi-closed structure. The A1 anoxic reactor is equipped with a stirring device or a hydraulic mixing structure inside. The A1 anoxic reactor has an inlet at the bottom or side wall and an outlet or overflow at the top. The A2 anoxic reactor is used for carbon-sulfur co-denitrification; the A2 anoxic reactor is a closed or semi-closed structure, with an inlet at the bottom or side wall and an outlet or overflow at the top; the packing zone inside the A2 anoxic reactor is set in the form of a packing frame, a packing basket or a fixed bed. The O1 aerobic reactor is used for nitrification to oxidize ammonia nitrogen into nitrate nitrogen. An aeration device, which is a microporous aerator or a perforated aeration pipe, is installed inside the O1 aerobic reactor at the bottom or lower side wall to continuously supply oxygen to the O1 aerobic reactor. The O1 aerobic reactor has an inlet at the bottom and an outlet and an exhaust port at the top. The O2 aerobic reactor is used for deep nitrification and organic matter adsorption. An aeration device is installed inside the O2 aerobic reactor. The aeration device is a microporous aerator or a perforated aeration pipe, which is set at the bottom or lower side wall of the O2 aerobic reactor to continuously supply oxygen into the O2 aerobic reactor. The bottom of the O2 aerobic reactor is provided with an inlet, and the top is provided with an outlet and an exhaust port. The SAD sulfur autotrophic denitrification reactor is used to reduce nitrate nitrogen to nitrogen gas by using elemental sulfur as an electron donor. The SAD sulfur autotrophic denitrification reactor is equipped with a sulfur-based denitrification packing bed, which is set in the form of a fixed bed, packing basket or modular packing unit. The SAD sulfur autotrophic denitrification reactor is provided with an inlet at the bottom and an outlet and an exhaust port at the top.

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