Wastewater treatment system and method based on sulfur recovery and denitrification

Abstract

The invention discloses a wastewater treatment system and method based on sulfur recovery and denitrification, and belongs to the technical field of wastewater biological treatment. The system comprises an anaerobic reactor, a low-oxygen reactor, a primary precipitator, an aerobic-anoxic reactor and a secondary precipitator which are communicated in sequence. The method comprises the following steps: wastewater enters an anaerobic reactor for sulfate reduction; anaerobic effluent enters a low-oxygen reactor to oxidize sulfide into elemental sulfur; sulfur-containing sludge separated by the primary precipitator enters an anoxic section of the aerobic-anoxic reactor after wall breaking, and nitrate nitrogen is reduced into nitrogen by utilizing elemental sulfur and an organic carbon source in the sludge as electron donors for sulfur autotrophic denitrification and heterotrophic denitrification respectively. Through the process of anaerobic sulfur production, low-oxygen sulfur fixation and oxygen-deficient sulfur utilization, oriented conversion and resource recovery of sulfur elements are achieved, the requirement for an external carbon source is lowered, and the method has the advantages of being high in denitrification efficiency, low in sludge yield and low in treatment cost.

Description

Technical Field

[0001] This invention belongs to the field of wastewater biological treatment technology, specifically relating to a wastewater treatment system and method based on sulfur recovery and synergistic denitrification. Background Technology

[0002] Industrial wastewater from industries such as pharmaceuticals, chemicals, and printing and dyeing typically contains high concentrations of chemical oxygen demand (COD), total nitrogen (TN), and sulfate (SO4). 2- Wastewater containing pollutants such as carbon, nitrogen, and sulfur, if discharged directly without proper treatment, will cause serious harm to the aquatic environment. How to achieve the synergistic removal of multiple pollutants such as carbon, nitrogen, and sulfur economically and efficiently, while simultaneously realizing the effective recovery of sulfur resources, has always been a technical challenge in the field of industrial wastewater treatment.

[0003] Traditional treatment processes often combine physicochemical and biological methods. For sulfates, chemical precipitation (e.g., adding lime to generate calcium sulfate) or membrane separation are commonly used for removal. However, these physicochemical methods suffer from high reagent dosages, high operating costs, and secondary pollution problems such as the generation of large amounts of saline chemical sludge. For COD and total nitrogen removal, separate biological units are typically used. If the wastewater's carbon-to-nitrogen ratio is insufficient, external carbon sources such as methanol and sodium acetate must be added. This treatment model results in a lengthy process flow, low total nitrogen removal rate, high power consumption, and significant carbon source waste. When using traditional nitrification-denitrification processes, organic carbon sources in the wastewater that could serve as electron donors are largely consumed in the aerobic stage, while the denitrification stage has to rely on external carbon sources, creating a dual dilemma of resource waste and increased costs. While the A / O process addresses the waste of organic carbon sources to some extent, internal recirculation increases power consumption and limits the total nitrogen removal rate. More importantly, sulfates in the wastewater are almost entirely unutilized in this process, becoming a pollutant requiring additional treatment.

[0004] In recent years, biological treatment technologies based on sulfur autotrophic denitrification have become a research hotspot in the field of simultaneous nitrogen and sulfur removal due to their advantages such as no need for external carbon sources and low sludge production. Existing technologies, such as CN117819712A, disclose a deep nitrogen removal device based on sulfur autotrophic denitrification, which achieves autotrophic denitrification by setting up a layer of elemental sulfur packing; CN111777179B involves a sulfur autotrophic denitrification filter and its application, which maintains stable system operation by retaining elemental sulfur. A common feature of these technologies is that processes such as sulfate reduction, sulfide oxidation, and sulfur autotrophic denitrification are dispersed in different units. Sulfur autotrophic denitrification units typically exist as independent filters and rely on external elemental sulfur (such as sulfur particles) as electron donors. Although these technologies have made breakthroughs in specific aspects, they still have not escaped the limitations of "unit fragmentation and unidirectional material flow"—sulfates in the raw water are not converted into usable resources, sulfur-containing sludge is only treated as waste, and there is a lack of organic synergy between the carbon, nitrogen, and sulfur removal processes.

[0005] It is noteworthy that in processes where sulfides are oxidized to generate elemental sulfur, the elemental sulfur typically adheres to the sludge surface, forming sulfur-containing sludge. Current technologies generally treat this type of sludge as conventional waste sludge, failing to recognize its dual resource attributes: enrichment of both elemental sulfur and adsorption as an internal carbon source. In fact, sulfur-containing sludge can serve as an electron donor for autotrophic denitrification and a supplementary carbon source for heterotrophic denitrification, possessing the potential to become an "endogenous electron donor pool." However, no technical solution has yet been found to integrate this attribute into the system design, achieving in-situ reuse of sulfur resources and cascade utilization of carbon sources.

[0006] In summary, existing industrial wastewater treatment technologies generally suffer from several drawbacks when dealing with complex water quality containing multiple pollutants such as carbon, nitrogen, and sulfur. These include lengthy process flows, fragmented unit functions, significant carbon source waste, high sulfate removal costs, ineffective sulfur resource recovery and utilization, and neglect of the resource value of sulfur-containing sludge. Developing an integrated treatment system and method that breaks down unit boundaries, achieves in-situ sulfate conversion, efficient recovery of elemental sulfur, resource utilization of sulfur-containing sludge, and synergistic removal of carbon and nitrogen pollutants is of great significance for improving industrial wastewater treatment efficiency, reducing operating costs, and realizing resource recovery. Summary of the Invention

[0007] To address the aforementioned existing technologies, this invention provides a wastewater treatment system and method based on sulfur recovery and synergistic denitrification. The system comprises an anaerobic reactor, a hypoxic reactor, a primary sedimentation tank, an aerobic-anoxic reactor, and a secondary sedimentation tank, connected in sequence. The method includes: wastewater entering the anaerobic reactor for sulfate reduction; the anaerobic effluent entering the hypoxic reactor to oxidize sulfides into elemental sulfur; and sulfur-containing sludge separated from the primary sedimentation tank being broken down and then entering the anoxic section of the aerobic-anoxic reactor, where elemental sulfur and organic carbon sources in the sludge are used as electron donors for sulfur autotrophic and heterotrophic denitrification, respectively, to reduce nitrate nitrogen to nitrogen gas. This invention achieves targeted conversion and resource recovery of sulfur through the "anaerobic sulfur production - hypoxic sulfur fixation - anoxic sulfur utilization" process, reducing the demand for external carbon sources and offering advantages such as high denitrification efficiency, low sludge production, and low treatment costs.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a wastewater treatment system based on sulfur recovery and synergistic denitrification, comprising an anaerobic reactor, a low-oxygen reactor, a primary sedimentation tank, an aerobic-anoxic reactor, and a secondary sedimentation tank connected in sequence; wherein the anaerobic reactor, the primary sedimentation tank, and the secondary sedimentation tank are all equipped with sludge discharge pipes.

[0009] The anaerobic reactor is enriched with sulfate-reducing bacteria to reduce sulfate ions in the influent to sulfides, controlling the pH value to 6.5-7.5; the exhaust end of the top of the anaerobic reactor is connected to the air inlet end of the bottom of the desulfurization scrubber; the effluent end of the anaerobic reactor is connected to the inlet end of the low-oxygen reactor.

[0010] The desulfurization scrubber is used to collect and treat gases rich in hydrogen sulfide, and uses a mixture from a low-oxygen reactor to wash away the hydrogen sulfide from the gas; the top inlet and bottom outlet of the desulfurization scrubber are respectively connected to the low-oxygen reactor; the treated gas is discharged from the top of the desulfurization scrubber.

[0011] The low-oxygen reactor is enriched with sulfur-oxidizing bacteria and the dissolved oxygen concentration is controlled at 0-0.5 mg / L. It is used to oxidize sulfides in the influent into elemental sulfur. The outlet of the low-oxygen reactor is connected to the influent of the primary sedimentation tank.

[0012] The primary sedimentation tank is used to receive the effluent from the low-oxygen reactor and perform mud-water separation; the supernatant outlet of the primary sedimentation tank is connected to the inlet of the aerobic section of the aerobic-anoxic reactor. The aerobic-anoxic reactor includes an aerobic section and an anoxic section connected in series. The aerobic section is equipped with an aeration device to oxidize ammonia nitrogen into nitrate nitrogen. The anoxic section is equipped with a mixing and stirring device to reduce nitrate nitrogen into nitrogen gas. The anoxic section is connected to the sludge discharge pipe of the primary reactor and receives sludge containing elemental sulfur. The organic carbon source and elemental sulfur in the sludge are used as electron donors for heterotrophic denitrification and sulfur autotrophic denitrification, respectively, to reduce nitrate nitrogen from the mixed liquor of the aerobic section into nitrogen gas.

[0013] The secondary sedimentation tank has its inlet end connected to the outlet end of the aerobic-anoxic reactor for solid-liquid separation. The supernatant from the secondary sedimentation tank is discharged in compliance with standards, and the bottom sludge is returned to the aerobic section of the aerobic-anoxic reactor.

[0014] The anaerobic reactor, primary sedimentation tank, and secondary sedimentation tank are all equipped with sludge discharge pipes to discharge their respective excess sludge.

[0015] Preferably, the anaerobic reactor is an upflow anaerobic sludge bed or an expanded granular sludge bed, and the sulfate volumetric loading is controlled at 1-3 kg SO4. 2- / m 3 .d.

[0016] Preferably, the low-oxygen reactor is a low-oxygen upflow internal circulation reactor or a completely mixed reactor. When an upflow internal circulation reactor is used, the first-stage precipitator in the system is omitted.

[0017] Preferably, the low-oxygen reactor controls the sulfide volumetric loading at 0.5-1.5 kg S. 2- / m 3 .d.

[0018] In a second aspect, the present invention provides a wastewater treatment method based on sulfur recovery and synergistic denitrification, comprising the following steps: (1) Sulfate reduction stage: Wastewater enters the anaerobic reactor and utilizes sulfate-reducing bacteria cultivated in the anaerobic reactor (by creating suitable conditions, the small amount of sulfate-reducing bacteria that originally existed in the wastewater are screened and enriched into the dominant bacteria group in the anaerobic reactor) to reduce sulfate in the wastewater to sulfide, while degrading part of COD, so as to achieve the synergistic removal of COD and sulfate. After the reaction, anaerobic effluent containing sulfide is obtained. (2) Sulfide oxidation stage: Anaerobic effluent enters the low oxygen reactor and is mixed with activated sludge returned from the primary sedimentation tank. Under micro-oxygen conditions (dissolved oxygen concentration of 0-0.5 mg / L), the sulfur-oxidizing bacteria enriched in the activated sludge oxidize the sulfides in the wastewater into elemental sulfur. (3) Primary mud-water separation stage: The effluent from the low-oxygen reactor enters the primary sedimentation tank, and the sulfur-containing activated sludge that settles is then returned to the low-oxygen reactor to ensure the continuous biochemical reaction. The supernatant after sedimentation enters the aerobic section of the aerobic-anoxic reactor; the sulfur-containing sludge after sedimentation is broken down and then enters the anoxic section of the aerobic-anoxic reactor.

[0019] (4) Aerobic-Anoxic Synergistic Denitrification Stage: The supernatant from the primary sedimentation tank is mixed with the return sludge from the secondary sedimentation tank and enters the aerobic section. Nitrifying bacteria are used to oxidize ammonia nitrogen in the wastewater into nitrate nitrogen under aerobic conditions. Then it enters the anoxic section and is mixed with sulfur-containing sludge from the primary sedimentation tank. The elemental sulfur in the sludge is used as the electron donor for sulfur autotrophic denitrification, and the organic carbon source in the sludge is used as the electron donor for heterotrophic denitrification. Through the synergistic effect of sulfur autotrophic denitrifying bacteria and heterotrophic denitrifying bacteria, the nitrate nitrogen produced in the aerobic section is reduced to nitrogen gas, and pollutants such as COD in the wastewater are degraded simultaneously. (5) Secondary mud-water separation stage: The effluent from the anoxic section enters the secondary sedimentation tank, and the supernatant after sedimentation meets the discharge standards. The sludge is returned to the aerobic section to maintain the sludge age of the system. (6) Residual sludge disposal stage: The residual sludge generated by the anaerobic reactor and the secondary sedimentation tank is dewatered and then transported off-site for disposal; the residual sludge containing elemental sulfur generated by the primary sedimentation tank is dewatered and dried and then recycled to realize the resource-based disposal of pollutants.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. Targeted Conversion and Resource Utilization of Sulfur: Through an anaerobic sulfur production-low-oxygen sulfur fixation-oxygen-deficient sulfur utilization chain, sulfides are directionally converted into elemental sulfur, with an elemental sulfur conversion rate of ≥80%. This enables the resource recovery of sulfur and the utilization of SO4. 2- Degradation.

[0021] 2. Cascade utilization of carbon source and sulfur: The sulfur-containing sludge from the primary sedimentation tank is directionally recycled to the anoxic zone. The "internal carbon source" carried by the sludge itself and elemental sulfur drive heterotrophic and autotrophic denitrification respectively, reducing the demand for external carbon source.

[0022] 3. Aerobic-Anoxic Synergistic Denitrification: Ammonia nitrogen in wastewater is first oxidized to nitrate nitrogen in the aerobic zone, and then reduced to nitrogen gas in the anoxic zone. The denitrification process does not require digester reflux, and the nitrate nitrogen is fully reduced, achieving efficient removal of total nitrogen.

[0023] 4. Highly efficient synergistic removal of multiple pollutants: Sulfate reduction, sulfide detoxification, nitrification, and dual-pathway denitrification are simultaneously completed within a single coupled system, removing COD and SO4. 2- The removal rates of NH3-N and total nitrogen can reach over 95%, 90%, 95%, and 90%, respectively.

[0024] 5. Reduce system carbon emissions: The coupled process reduces power consumption by about 20% by eliminating internal recirculation and reducing aeration volume, and reduces sludge volume by 30% by reducing the addition of carbon sources and chemical agents, thus achieving low-carbon operation. Attached Figure Description

[0025] Figure 1 This is a flow chart for wastewater treatment based on sulfur recovery and synergistic denitrification. Detailed Implementation

[0026] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0027] The specific embodiments of the present invention will be described in further detail below with reference to examples. The following detailed descriptions are illustrative and intended to provide further explanation of this application, rather than limiting the scope of the invention.

[0028] Example: The industrial wastewater treated in this embodiment is pharmaceutical wastewater, with a treatment volume of 50m³. 3 / d, its water quality indicators are as follows: COD=2000-3000mg / L, NH3-N=200-280mg / L, TN=220-300mg / L, SO4 2- =1000-1500mg / L, pH=6.5-7.5, and the treatment should meet the requirements of GB21907 standard, namely: COD=100mg / L, NH3-N=15mg / L, TN=50mg / L.

[0029] Using the processing system described in this invention, the parameters of each reactor are set as follows: The anaerobic reactor used is a UASB reactor with an effective volume of 38 m³. 3 Hydraulic retention time 18h, pH adjusted to 6.5-7.5, sludge concentration 10g / L, sulfate volumetric loading ≤2kg SO4 2- / m 3 •d. Hydrogen sulfide gas collected at the top vent is desulfurized by washing with wastewater from the low-oxygen reactor and then discharged into the air. The washing liquid is then returned to the low-oxygen reactor.

[0030] The effective volume of the low-oxygen reactor is 18m³. 3 Hydraulic retention time 8 hours, pH adjusted to 7.5, sludge concentration 6 g / L, sulfide volumetric loading ≤ 1.2 kg S 2- / m 3 •d. A perforated tube aerator and a submersible mixer were used for mixing, and the dissolved oxygen concentration was controlled below 0.5 mg / L.

[0031] The primary sedimentation tank is a horizontal flow sedimentation tank with a surface loading of 0.8 m³. 3 / (m 2 ·h), with a sedimentation area of ​​2.6m. 2 The sludge return ratio is 80%, and the amount of sulfur-containing sludge transported to the anoxic zone is 0.8 m³. 3 / d.

[0032] The effective volume of the aerobic-anoxic reactor is 56 m³. 3 The effective volume of the aerobic section is 38m³. 3 The hydraulic retention time is 18 hours, and a microporous aerator is used to control the dissolved oxygen concentration at 1.5-2.5 mg / L; the effective volume of the anoxic section is 20 m³. 3 The hydraulic retention time is 10 hours, and a submersible mixer is used for mixing to control the dissolved oxygen concentration to within 0.5 mg / L.

[0033] The secondary sedimentation tank is a horizontal flow sedimentation tank with a surface loading of 0.6 m³. 3 / (m 2 •h), with an effective sedimentation area of ​​3.5m. 2 The sludge return ratio is 100%.

[0034] The processing steps are as follows: (1) Sulfate reduction stage: After pretreatment by screen and grit chamber, pharmaceutical wastewater enters the UASB reactor, where sulfate-reducing bacteria reduce SO4 in the wastewater. 2- It is reduced to sulfides, while simultaneously degrading approximately 75% of COD. The anaerobic effluent has a COD of 550-650 mg / L and SO4 content of [missing value]. 2- The removal rate is ≥90%, and the sulfide concentration is 90-120 mg / L.

[0035] (2) Sulfide oxidation stage: Anaerobic effluent enters the low oxygen reactor and mixes with the activated sludge returned from the primary sedimentation tank. Sulfur oxidizing bacteria oxidize sulfides into elemental sulfur. Elemental sulfur adheres to the sludge surface to form sulfur-containing sludge. The sulfide concentration in the effluent of the low oxygen reactor is ≤5mg / L and the elemental sulfur conversion rate is ≥90%.

[0036] (3) Primary sludge-water separation stage: The effluent from the low-oxygen reactor enters the primary sedimentation tank. After sludge-water separation, the supernatant has COD=150-200mg / L, NH3-N=100-120mg / L, and TN=120-150mg / L; the sulfur-containing sludge is returned to the low-oxygen reactor, and the remaining 0.6m of sulfur-containing sludge... 3 / d is conveyed to the sludge wall-breaking machine, and the remainder is discharged.

[0037] (4) Sludge cell breaking stage: The sludge cell breaking adopts the ambient temperature alkaline hydrolysis process. After the sulfur-containing sludge enters the cell breaking device and reacts for 3 hours, the sulfur-containing sludge after cell breaking enters the anoxic section of the aerobic-anoxic reactor.

[0038] (5) Aerobic-anoxic synergistic denitrification stage: The supernatant is mixed with the return sludge from the secondary sedimentation tank and enters the aerobic section. Nitrifying bacteria oxidize ammonia nitrogen into nitrate nitrogen. The mixed liquid from the aerobic section flows into the anoxic section by gravity and mixes with sulfur-containing sludge. Sulfate autotrophic denitrifying bacteria and heterotrophic denitrifying bacteria work together to reduce nitrate nitrogen into nitrogen gas.

[0039] (6) Secondary mud-water separation stage: The effluent from the anoxic section enters the secondary sedimentation tank. After solid-liquid separation, the supernatant has COD≤80mg / L, NH3-N≤5mg / L, TN≤15mg / L, and SO42-≤5mg / L. 2- ≤500mg / L, discharge meets the standard; settled sludge is returned to the aerobic section, and the remaining sludge is discharged.

[0040] (7) Residual sludge disposal stage: The system generates a total of 13 t / a of residual sludge, of which 6 t / a of residual sludge generated by the anaerobic reactor and the secondary sedimentation tank is dewatered and transported off-site for disposal; 7 t / d of sulfur-containing sludge, part of which (about 3.5 t / a) is returned to the anoxic section of the aerobic-anoxic reactor, and the remaining part is dewatered and dried to recover elemental sulfur.

[0041] The treatment effect of this embodiment shows that, using the system and method of the present invention, COD and SO4 in pharmaceutical wastewater can be reduced. 2- Simultaneous and efficient removal of NH3-N and TN, COD removal rate ≥95%, SO4 2- The removal rate is ≥60%, the NH3-N removal rate is ≥98%, and the TN removal rate is ≥92%. No external carbon source or sulfur matrix needs to be added. The sludge production is reduced by more than 40% compared with the traditional process, and the treatment cost is reduced by 35%, achieving the dual benefits of synergistic removal of pollutants and resource recovery.

[0042] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A wastewater treatment system based on sulfur recovery and synergistic denitrification, characterized in that, It includes an anaerobic reactor, a low-oxygen reactor, a primary sedimentation tank, an aerobic-anoxic reactor, and a secondary sedimentation tank connected in sequence; the anaerobic reactor, the primary sedimentation tank, and the secondary sedimentation tank are all equipped with sludge discharge pipes; The anaerobic reactor is enriched with sulfate-reducing bacteria. Its inlet end is connected to the inlet pipe, its outlet end is connected to the inlet end of the low-oxygen reactor, and its top exhaust end is connected to the air inlet end of the desulfurization scrubber. The low-oxygen reactor is enriched with sulfur-oxidizing bacteria, and its outlet is connected to the inlet of the primary sedimentation tank. The supernatant outlet of the primary sedimentation tank is connected to the inlet of the aerobic section of the aerobic-anoxic reactor; the sulfur-containing activated sludge after sedimentation is divided into two parts. The first part of the sulfur-containing activated sludge is returned to the low-oxygen reactor, and the second part of the sulfur-containing activated sludge is connected to the sludge inlet of the anoxic section of the aerobic-anoxic reactor after being treated by the sludge wall breaker. The aerobic-anoxic reactor includes an aerobic section and an anoxic section connected in series. An aeration device is installed in the aerobic section, and a mixing and stirring device is installed in the anoxic section. The anoxic section is also provided with a sludge inlet that is connected to the sludge discharge pipe of the primary sedimentation unit. The secondary sedimentation tank has its inlet end connected to the outlet end of the anoxic section of the aerobic-anoxic reactor, and its bottom is equipped with a sludge return pipe connected to the aerobic section of the aerobic-anoxic reactor.

2. The wastewater treatment system according to claim 1, characterized in that, The anaerobic reactor is configured to control the sulfate volumetric loading at 1-3 kg SO4. 2- / m 3 ·d.

3. The wastewater treatment system according to claim 1, characterized in that, The low-oxygen reactor controls the sulfide volumetric loading at 0.5-1.5 kg S. 2- / m 3 ·d.

4. A wastewater treatment method based on sulfur recovery and synergistic denitrification, characterized in that, The system according to any one of claims 1-3 includes the following steps: (1) Sulfate reduction stage: Wastewater enters the anaerobic reactor, and sulfate-reducing bacteria are used to reduce the sulfate ions in the wastewater to sulfides, resulting in anaerobic effluent containing sulfides; (2) Sulfide oxidation stage: Anaerobic effluent enters the low oxygen reactor and is mixed with the first part of sulfur-containing activated sludge returned from the primary sedimentation tank. Sulfide oxidizing bacteria are used to oxidize sulfides into elemental sulfur. (3) Primary mud-water separation stage: The effluent from the low-oxygen reactor enters the primary sedimentation tank for mud-water separation. The supernatant after sedimentation enters the aerobic section of the aerobic-anoxic reactor. The second part of sulfur-containing sludge after sedimentation enters the anoxic section of the aerobic-anoxic reactor after cell wall breaking. (4) Aerobic-anoxic synergistic denitrification stage: The supernatant from the primary precipitator is mixed with the return sludge from the secondary precipitator and enters the aerobic section to oxidize ammonia nitrogen into nitrate nitrogen; then it enters the anoxic section and is mixed with sulfur-containing sludge from the primary precipitator. The elemental sulfur and organic carbon source in the sludge are used as electron donors for sulfur autotrophic denitrification and heterotrophic denitrification, respectively, to reduce nitrate nitrogen into nitrogen gas; (5) Secondary sludge-water separation stage: The effluent from the anoxic section enters the secondary sedimentation tank for solid-liquid separation. The supernatant from the secondary sedimentation tank meets the discharge standards, and the sludge from the secondary sedimentation tank is returned to the aerobic section to maintain the sludge age of the system. (6) Residual sludge disposal stage: The residual sludge generated by the anaerobic reactor and the secondary sedimentation tank is transported off-site for disposal after dewatering treatment; the residual sludge containing elemental sulfur generated by the primary sedimentation tank is dewatered and dried to recover elemental sulfur.

5. The wastewater treatment method according to claim 4, characterized in that, In step (3), the amount of sulfur-containing sludge entering the anoxic zone is calculated using the following formula: (1) When the effluent contains SO4 2- When there are no control requirements: Where: q is the sulfur-containing sludge return flow rate, in kg / d; C0 is the COD concentration of the wastewater entering the aerobic-anoxic reactor, in mg / L; C e COD concentration of the effluent from the secondary sedimentation tank, in mg / L; N0 is the total nitrogen concentration of the wastewater entering the aerobic-anoxic reactor, in mg / L; N e The total nitrogen concentration in the effluent from the secondary sedimentation tank is mg / L; Q is the wastewater treatment capacity, in m³. 3 / d;X a The percentage of elemental sulfur in sulfur-containing sludge, expressed as % . (2) When the effluent contains SO4 2- When there are control requirements: In the formula: q is the sulfur-containing sludge recirculation rate, in kg / d; S a SO4 in the effluent 2- Concentration is controlled, in mg / L; Q is the wastewater treatment capacity, in m³. 3 / d;X a The percentage of elemental sulfur in sulfur-containing sludge, in units of %.

6. The wastewater treatment method according to claim 4, characterized in that, In step (1), the pH value inside the anaerobic reactor is controlled to be 6.5-7.

5.

7. The wastewater treatment method according to claim 4, characterized in that, In step (2), the dissolved oxygen concentration in the low-oxygen reactor is controlled to be 0-0.5 mg / L.

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