A device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation.

Abstract

This invention provides an apparatus and method for deep denitrification and synergistic greenhouse gas emission reduction in biogas slurry driven by airlift circulation. This invention reduces the demand for carbon sources and alkalinity in biogas slurry treatment through anaerobic / aerobic / anoxic operation modes. The aerobic zone of this invention, which performs short-cut nitrification + anaerobic ammonium oxidation, is the main denitrification unit. The nitrate nitrogen produced in the anaerobic ammonium oxidation process is removed in the subsequent anoxic stage through endogenous short-cut denitrification + anaerobic ammonium oxidation. The carbon source in the wastewater is first converted into endogenous carbon in the anaerobic zone, providing a substrate for endogenous short-cut denitrification in the anoxic zone and reducing the carbon source addition in the anoxic zone. Simultaneously, it avoids the rapid growth of heterotrophic bacteria caused by excessive carbon sources in the aerobic zone, providing a suitable environment for the enrichment of anaerobic ammonium oxidizing bacteria. This invention replaces the stirring system in traditional plug-flow wastewater treatment facilities with airlift circulation and achieves N2O gas absorption and treatment through a step-by-step airlift circulation method.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation. Background Technology

[0002] Currently, wastewater treatment plants account for 1.6% of global carbon emissions, with direct carbon emissions from the treatment process accounting for as much as 86%. Therefore, there is an urgent need to promote a method that can collect and treat greenhouse gases emitted during wastewater treatment in situ, and this method should also be feasible and have low retrofit costs. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides an apparatus and method for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by airlift circulation. The device includes an anaerobic zone, an aerobic zone, an intermediate zone, and an anoxic zone, which are sequentially connected by a wastewater pipeline. Each of the aerobic, intermediate, and anoxic zones is equipped with packing assemblies to increase biomass loading. The anaerobic zone is used for biogas slurry influent, converting COD in the wastewater into endogenous carbon, reducing the COD to 400-800 mg / L before transporting it to the aerobic zone. The aerobic zone is used for short-cut nitrification and anaerobic digestion of the wastewater. The wastewater undergoes ammonia oxidation treatment, and is then transported to the intermediate zone. This intermediate zone serves as an aerobic zone during the initial startup phase and when the treatment load is low, maintaining a dissolved oxygen concentration of 0.5–1 mg / L. When the nitrogen and total nitrogen in the effluent from the aerobic zone meet the requirements, it becomes an anoxic zone, controlling dissolved oxygen to <0.1 mg / L. The effluent is then transported to the anoxic zone. The anoxic zone is used for short-cut denitrification and anaerobic ammonia oxidation treatment, ensuring that the effluent meets the requirements of ammonia nitrogen <45 mg / L, total nitrogen <70 mg / L, and COD <500 mg / L. The anaerobic zone, aerobic zone, intermediate zone, and anoxic zone are all equipped with covers; the aerobic zone, intermediate zone, anoxic zone, and anaerobic zone are also connected sequentially by gas pipelines; the aerobic zone is also used for the intake of waste gas from the plant area, and the odorous components in the waste gas are adsorbed and oxidized into CO2 by aerobic bacteria, while NH3 and H2S are oxidized by ammonia-oxidizing bacteria and sulfur-oxidizing bacteria and then transported to the intermediate zone; when the intermediate zone is used as an anoxic functional zone, it, along with the anoxic zone, is used to assimilate CO2 from the waste gas using anaerobic ammonia-oxidizing bacteria and heterotrophic denitrifying bacteria. The intermediate zone, when serving as an aerobic functional zone, is used for the intake of waste gas from the plant area and the waste gas is transported to the anoxic zone. The anoxic zone is used for the assimilation of CO2 and the reduction of N2O in the waste gas by anaerobic ammonia-oxidizing bacteria or sulfur-autotrophic denitrifying bacteria, and the waste gas is transported to the anaerobic zone. The anaerobic zone is used for the reduction of N2O in the waste gas by organic matter to remove more than 95% of N2O.

[0005] Furthermore, the device also includes a sedimentation tank located at the effluent end of the anoxic zone; the sedimentation tank is used to settle the effluent from the anoxic zone and return a portion of the sludge to the anaerobic zone through a first sludge return pipe; when the intermediate zone is used as an anoxic functional zone, a portion of the sludge is returned to the intermediate zone through a second sludge return pipe; when the intermediate zone is used as an aerobic functional zone, the sludge is returned to the anoxic zone through a third sludge return pipe; the top of the sedimentation tank is provided with an upper effluent outlet for discharging treated wastewater; the bottom of the sedimentation tank is used to discharge excess sludge.

[0006] Furthermore, the volume ratio of the anaerobic zone, aerobic zone, intermediate zone, and anoxic zone is 1:1:1:1.

[0007] Furthermore, the filling ratio of the packing components in the aerobic zone, intermediate zone, and anoxic zone is 60% of the tank volume.

[0008] Furthermore, a dissolved oxygen probe is installed in the aerobic zone to monitor dissolved oxygen; the dissolved oxygen probe is also connected to a PLC to control the air intake pump to pump waste gas from the plant into the aerobic zone.

[0009] Furthermore, the device also includes an aerobic zone gas circulation pump connected to the aerobic zone for aeration from the bottom of the aerobic zone and maintaining an upward flow rate to achieve a uniform mixing of mud and water; a circulation pump connected to the intermediate zone for circulating aeration from the bottom of the intermediate zone to maintain an upward flow rate; an anoxic zone gas circulation pump connected to the anoxic zone for aeration from the bottom of the anoxic zone; and an anaerobic zone gas circulation pump connected to the anaerobic zone for aeration from the bottom of the anaerobic zone to mix mud and water and increase N2O solubility.

[0010] Further, an air outlet is provided on the anaerobic zone for discharging the treated gas; a tail gas treatment module is further provided at the rear end of the air outlet, and the tail gas treatment module is used to treat aerosols and toxic and harmful gases by means of activated carbon adsorption and catalytic oxidation.

[0011] Further, the middle zone is also connected to the anaerobic zone; when the middle zone serves as an anoxic functional zone, it is used to receive the mud-water mixture with an influent ratio of 20-40% of the anaerobic zone to reduce the endogenous carbon loss in the aerobic zone; the middle zone is also used to set an external carbon source.

[0012] The present invention also provides a method for deep denitrification of biogas slurry and synergistic reduction of greenhouse gases driven by air-lift circulation, and this method is applied to the device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gases driven by air-lift circulation as described above; this method includes: the biogas slurry enters from the anaerobic zone, and the COD in the sewage is converted into endogenous carbon. After the COD drops to 400-800 mg / L, it enters the aerobic zone; the aerobic zone performs short-cut nitrification treatment and anaerobic ammonia oxidation treatment on the sewage, and then transports the sewage to the middle zone; the middle zone serves as an aerobic functional zone in the initial stage of the device startup and when the treatment load is low, and maintains the dissolved oxygen concentration at 0.5-1 mg / L; when the ammonia nitrogen and total nitrogen in the effluent at the end of the aerobic zone meet the requirements, it serves as an anoxic functional zone, and the dissolved oxygen is controlled to be <0.1 mg / L; and the effluent is transported to the anoxic zone; the anoxic zone performs short-cut denitrification treatment and anaerobic ammonia oxidation treatment on the sewage, so that the effluent meets the requirements of ammonia nitrogen <45 mg / L, total nitrogen <70 mg / L and COD <500 mg / L; The plant exhaust gas enters from the aerobic zone, and the malodorous components in the exhaust gas are adsorbed and oxidized by aerobic bacteria into CO2, and NH3 and H2S are oxidized by ammonia-oxidizing bacteria and sulfur-oxidizing bacteria and then transported to the middle zone; when the middle zone serves as an anoxic functional zone, both the middle zone and the anoxic zone use anaerobic ammonia-oxidizing bacteria and heterotrophic denitrifying bacteria to assimilate CO2 and reduce N2O in the exhaust gas, and use sulfur autotrophic denitrifying bacteria to remove the residual H2S, and transport the outlet gas to the anaerobic zone; when the middle zone serves as an aerobic functional zone, the plant exhaust gas also enters from the middle zone and transports the exhaust gas to the anoxic zone; the anoxic zone uses anaerobic ammonia-oxidizing bacteria or sulfur autotrophic denitrifying bacteria to assimilate CO2 and reduce N2O in the exhaust gas, and transports the outlet gas to the anaerobic zone; the anaerobic zone uses organic matter to reduce N2O in the exhaust gas to remove more than 95% of N2O.

[0013] Further, the parameters of the biogas slurry are C:N = 2-5, 1 < BOD5 / TN < 2.5, and the ammonia nitrogen concentration is 1000-1800 mg / L; the requirements for the effluent at the end of the aerobic zone are that the ammonia nitrogen concentration is less than 100 mg / L and the total nitrogen concentration is less than 250 mg / L.

[0014] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages: This invention replaces the mixing system in traditional plug-flow wastewater treatment facilities with an air-lift circulation system, and achieves N2O gas absorption and treatment through a step-by-step air-lift circulation method. Furthermore, this invention can reduce the pressure on the plant's odor treatment system to a certain extent and ensure that the effluent meets reuse standards. Simultaneously, this invention also achieves intelligent and efficient operation and management by constructing a smart dissolved oxygen control system for the wastewater treatment plant.

[0015] This invention provides a sealing cover for a plug-flow wastewater treatment device, which can prevent the emission of gases from the wastewater treatment plant, facilitate centralized treatment of waste gas, meet the environmental protection requirements of some plant areas, and has extremely low modification costs.

[0016] This invention achieves homogenization through air-lift circulation, which replaces the stirring system in traditional plug-flow sewage treatment devices. This reduces the construction and maintenance costs associated with the installation, operation, aging, and failure of the stirring system, and greatly reduces the difficulty of operation and maintenance. In addition, the air-lift circulation stirring method of this invention provides a larger internal space in the tank, providing more space for the placement of packing components, while effectively avoiding the generation of dead zones in the stirring.

[0017] This invention reduces the demand for carbon source and alkalinity in wastewater treatment by employing an anaerobic / aerobic / anoxic operating mode. The aerobic zone of this invention, which performs short-cut nitrification + anaerobic ammonium oxidation, is the main nitrogen removal unit. The nitrate nitrogen produced during anaerobic ammonium oxidation is removed in the subsequent anoxic stage through endogenous short-cut denitrification + anaerobic ammonium oxidation. Carbon sources in the wastewater are first converted into endogenous carbon in the anaerobic zone, providing substrate for endogenous short-cut denitrification in the anoxic zone and reducing the carbon source addition required in the anoxic zone. Simultaneously, it avoids the rapid growth of heterotrophic bacteria due to excessive carbon sources in the aerobic zone, providing a suitable environment for the enrichment of anaerobic ammonium oxidizing bacteria. Furthermore, the dual sludge recirculation system brings the alkalinity generated during endogenous short-cut denitrification back to the front end, preventing excessive alkalinity consumption during short-cut nitrification and thus reducing the alkalinity addition required in the aerobic stage. Furthermore, since the present invention has independent airlift circulation in each compartment, it is convenient to adjust the ratio of anaerobic / aerobic / anoxic conditions, and to adjust it according to the effect during actual operation.

[0018] This invention achieves greenhouse gas emission reduction through a step-by-step airlift circulation method. After collection, the odorous gas from the plant area is first supplied to the aerobic zone. In the aerobic zone, short-range nitrifying bacteria utilize the oxygen to oxidize ammonia nitrogen into nitrite nitrogen, a process that produces some NO and N2O (nitric oxide and nitrous oxide, major greenhouse gases). Subsequently, the gas enters the intermediate reaction zone, further consuming oxygen. Then, the gas, with extremely low oxygen content, enters the anoxic zone, providing mixing and upward flow velocity for the sludge in this area. In the anoxic zone, endogenous denitrifying bacteria reduce some N2O to N2, while also reducing some NO2. - The gases are reduced to NO and N2O. Therefore, the final gas will be returned to the anaerobic zone for further reaction, allowing the denitrifying bacteria in the anaerobic zone to completely remove NO and N2O, thereby achieving greenhouse gas emission reduction.

[0019] This invention achieves precise regulation of the entire wastewater treatment process through intelligent control, further enhancing the treatment effect. The invention adds a dissolved oxygen monitoring probe to the aerobic zone and connects it to the PLC host. When the dissolved oxygen level in the aerobic zone is low, the air pump is controlled to extract odorous gases from the plant area and inject them into the top space of the aerobic zone, providing a stable reaction environment for the wastewater treatment facilities. Attached Figure Description

[0020] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments, and unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0021] Figure 1 This is an embodiment of the present invention.

[0022] In the diagram, 1 is biogas slurry, 2 is anaerobic zone, 3 is aerobic zone, 4 is intermediate zone, 5 is anoxic zone, 6 is sedimentation tank, 7 is upper effluent, 8 is excess sludge, 9 is packing assembly, 10 is cover plate, 11 is exhaust gas, 12 is aerobic zone gas circulation pump, 13 is tail gas, 14 is circulation pump, 15 is intermediate zone tail gas, 16 is anoxic zone gas circulation pump, 17 is anoxic zone tail gas, 18 is anaerobic zone gas circulation pump, 19 is air outlet, 20 is third sludge return pipe, 21 is second sludge return pipe, 22 is first sludge return pipe, 23 is dissolved oxygen probe, 24 is PLC, and 25 is air intake pump. Detailed Implementation

[0023] In recent years, the increasing prevalence of underground sewage treatment plants and the addition of sewage tank covers to meet environmental protection requirements have provided basic conditions for collecting escaping greenhouse gases, but effective in-situ treatment methods for greenhouse gases are still lacking. This invention, building upon the traditional sewage treatment process which only focuses on sewage flow design, adds gas recirculation and gas flow direction design, enabling the in-situ reduction and fixation of greenhouse gases using microorganisms.

[0024] Furthermore, anaerobic digestion effluent (hereinafter referred to as biogas slurry), as a typical type of wastewater with a low carbon-to-nitrogen ratio and high ammonia nitrogen content, typically requires the addition of a large amount of carbon source to ensure sufficient nitrate nitrogen removal in order to meet effluent quality standards during treatment. This invention is the first to propose a plug-flow AOA (anaerobic-aerobic-anoxic) process, utilizing packing material to enrich anaerobic ammonia-oxidizing bacteria in the aerobic and anoxic zones, thereby reducing the amount of carbon source and alkalinity added. Unlike current AOA processes, which are mostly used for low-concentration municipal wastewater, this invention has already achieved effective treatment of high-concentration wastewater in the early experimental stage. Without adding an external carbon source, the effluent quality meets the Class B standard of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T31962-2015).

[0025] The present invention will now be described in detail with reference to specific embodiments.

[0026] This invention provides a device (hereinafter referred to as a wastewater treatment facility) and method for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas stripping circulation, specifically including the following components and steps: The wastewater treatment facility of this invention includes an anaerobic zone 2, an aerobic zone 3, an intermediate zone 4, an anoxic zone 5, and a sedimentation tank 6. The volume ratio of zones 2 to 5 is 1:1:1:1. The flocculent sludge concentration in the anaerobic and aerobic zones should be maintained at 3000-5000 mg / L, and the sludge concentration in the anoxic zone should be maintained at 4500-65000 mg / L. Furthermore, packing components 9 should be added in zones 3 to 5 to promote the enrichment of anaerobic ammonia-oxidizing bacteria, with a packing ratio of 60% of the tank volume. The hydraulic retention time of the entire wastewater treatment facility should be set at 3-6 days.

[0027] Biogas slurry 1 (actually measured C:N = 2 - 5, 1 < BOD5 / TN < 2.5, and the ammonia nitrogen concentration is about 1000 - 1800 mg / L) enters the anaerobic zone 2 in the sewage treatment facility. First, the COD in the sewage is converted into endogenous carbon, reducing the COD to about 400 - 800 mg / L. Subsequently, the sewage enters the aerobic zone 3 for the short-cut nitrification + anaerobic ammonia oxidation process. The dissolved oxygen in this area should be maintained at 0.5 - 1 mg / L to maintain a sufficient short-cut nitrification rate and avoid the inhibition of anaerobic ammonia oxidation bacteria by dissolved oxygen. The monitoring of dissolved oxygen is achieved by the dissolved oxygen probe 23 and, after feedback through the PLC 24, controls the operation of the air intake pump 25 to inject sufficient plant exhaust gas into the top space of the aerobic zone 3. At the end of this area, the ammonia nitrogen concentration should be less than 100 mg / L, and the total nitrogen concentration should be less than 250 mg / L. In the initial startup stage and when the treatment load is low, the intermediate zone 4 is converted into an aerobic functional zone, and the dissolved oxygen concentration in it is maintained at 0.5 - 1 mg / L to make the ammonia nitrogen and total nitrogen in the effluent of this area meet the corresponding requirements. When the effluent at the end of the aerobic zone 3 can meet the requirements, the intermediate zone 4 is converted into an anoxic functional zone (dissolved oxygen < 0.1 mg / L). Subsequently, the sewage enters the anoxic zone 5 for the endogenous (short-cut) denitrification + anaerobic ammonia oxidation process. The effluent from the anoxic zone should meet the Class B standards in the "Quality Standards for Wastewater Discharged into Urban Sewage Systems" (GB / T 31962 - 2015) with ammonia nitrogen < 45 mg / L, total nitrogen < 70 mg / L, and COD < 500 mg / L.

[0028] The present invention also includes a sludge return system. After sedimentation in the sedimentation tank 6, part of the sedimented sludge is returned to the anaerobic zone 2 through the first sludge return pipe 22. And when the intermediate zone 4 exists as an anoxic functional zone, part of the sludge is returned to the intermediate zone 4 through the second sludge return pipe 21. When the intermediate zone exists as an aerobic functional zone, the sludge is returned from the third sludge return pipe 20 to the anoxic zone 5. The above sludge return ratios are all 100 - 500% of the influent to maintain the sludge concentration requirements in the corresponding areas and dilute the influent. The upper effluent 7 is discharged from the treatment facility, and steps such as disinfection can be carried out according to the corresponding environmental protection requirements. The excess sludge 8 is discharged.

[0029] The core innovation of this invention is the addition of a gas recirculation path to achieve greenhouse gas emission reduction in the wastewater treatment process. When the dissolved oxygen in aerobic zone 3 is <0.5 or the treatment effect cannot meet the requirements, PLC 24 controls air intake pump 25 to pump in the plant's exhaust gas 11. Subsequently, the top gas is extracted by aerobic zone gas circulation pump 12 and aerated to maintain the dissolved oxygen concentration in aerobic zone 3. The wastewater treatment facility is equipped with a cover plate 10 to maintain a sealed environment for gas collection and recirculation. The aerobic zone gas circulation pump 12 is normally open and maintains an upward flow rate (usually 0.3~0.8 m / h, mainly to maintain a uniform mixing state of sludge and water). During this process, odorous components in the plant's exhaust gas 11, such as ethanol, acetaldehyde, propionaldehyde, ethyl acetate, methanethiol, dimethyl disulfide, and olefins, are adsorbed and oxidized into CO2 by aerobic bacteria in aerobic zone 3, while NH3 and H2S are oxidized into NO2 by ammonia-oxidizing bacteria and sulfur-oxidizing bacteria in aerobic zone 3. - SO3 - SO4 - Afterwards, it enters intermediate zone 4. It should be noted that when intermediate zone 4 is used as an anoxic zone, intermediate zone 4 and anoxic zone 5 will treat the oxidized waste gas together. When intermediate zone 4 is used as an aerobic zone, the waste gas is directly transported to anoxic zone 5 for treatment. In anoxic zone 5 and the anoxic functional zones, anaerobic ammonia-oxidizing bacteria process the residual NH4+. + and NO2 -The residual H2S is removed by sulfur-autotrophic denitrifying bacteria, thereby treating the escaping odorous gases and reducing the pressure on odor control in the plant area. Furthermore, the short-cut nitrification process in the aerobic phase releases greenhouse gases such as N2O, so the resulting tail gas 13 can enter the intermediate zone 4 for further treatment via pressure difference. When the intermediate zone 4 functions as an aerobic zone, the intake pump 25 pumps gas into both the aerobic zone 3 and the intermediate zone 4 simultaneously, further increasing the CO2 and N2O content in the top gas. This gas is then circulated and aerated by the intermediate zone gas circulation pump 14 to maintain the upward flow rate. When the intermediate zone 4 functions as an anoxic zone, the intake pump 25 only pumps plant exhaust gas into the aerobic zone 3. The pressure difference causes the low-oxygen tail gas 13 from the aerobic zone to enter the intermediate zone, where it is circulated and aerated by the circulation pump 14 to maintain the upward flow rate. During this period, the CO2 and N2O produced in aerobic zone 3 serve as the inorganic carbon source required for the growth of anaerobic ammonia-oxidizing bacteria and the reaction substrate for endogenous denitrifying bacteria (this reaction reduces N2O to N2), thereby achieving greenhouse gas emission reduction. The exhaust gas 15 from the intermediate zone enters the anoxic zone 5 due to the pressure difference generated by N2 production and aeration in the aerobic zone. This zone is similar to the anoxic intermediate zone, primarily involving CO2 assimilation and N2O reduction, with mixing provided by the anoxic zone gas circulation pump 16. However, due to the low C / N ratio at this stage, N2O cannot be completely removed. Therefore, the anoxic zone exhaust gas 17 is returned to anaerobic zone 2 for N2O reduction, and mixing is provided by the anaerobic zone gas circulation pump 18, increasing N2O solubility and enhancing the N2O removal efficiency of denitrifying bacteria. Actual measurements show that up to 95% N2O removal can be achieved. The treated gas is discharged through outlet 19, and subsequent exhaust gas treatment (such as activated carbon adsorption, catalytic oxidation, etc.) can be carried out according to the corresponding environmental protection requirements to avoid the emission of aerosols and toxic and harmful gases.

[0030] When the ammonia nitrogen level in the effluent is too high and cannot meet the standards, intermediate zone 4 can be converted into an aerobic zone, and the dissolved oxygen in aerobic zone 3 and intermediate zone 4 can be increased to 0.8~1.5 mg / L to ensure that the ammonia nitrogen is fully oxidized and meets the effluent requirements.

[0031] When the effluent nitrate nitrogen is too high, causing the total nitrogen to fail to meet the standard, intermediate zone 4 can be converted into an anoxic functional zone, and a sludge bypass system can be set up. This involves drawing 20-40% of the influent sludge-water mixture from the end of anaerobic zone 2 into intermediate zone 4 to reduce the endogenous carbon loss in the aerobic zone. If the requirements are still not met, external carbon sources such as sodium acetate, glucose, methanol, and digestate can be added in appropriate amounts to the initial section of intermediate zone 4.

[0032] This invention pioneered the application of plug-flow AOA technology in the treatment of high-concentration biogas slurry, solving the problems of high carbon source and alkalinity addition in the process, and reducing the difficulty of treatment. Existing operating methods for treating biogas slurry from kitchen waste, food processing, and livestock manure are mostly limited to anaerobic-anoxic-aerobic (AAO) operation modes, as exemplified by invention patents: CN202410461442.X, CN202110503901.2, CN202210586769.0, CN202011587813.7, etc. This operating mode (referring to AAO) is characterized by strong shock resistance and low carbon source demand. However, this method requires a large reflux ratio to ensure that the effluent nitrate nitrogen meets the standards, making it difficult to operate and with limited effectiveness. It also produces a large amount of sludge, putting considerable pressure on subsequent treatment. Some existing biogas slurry treatments also use anaerobic ammonium oxidation (AAO) systems as the mainstream nitrogen removal method, such as invention patents: CN202211495510.1, CN202211520869.X, CN202410198168.1, etc. The use of short-cut nitrification-anaerobic ammonium oxidation increases the system load, reduces sludge production, and reduces the addition of carbon source and alkalinity. However, the mainstream short-cut nitrification-anaerobic ammonium oxidation process also requires a subsequent AO or multi-stage AO process to remove residual nitrate nitrogen due to its own metabolic pathway limitations. Furthermore, carbon source addition is still required during this process to achieve effective nitrate nitrogen removal. Furthermore, due to the long growth cycle of anammox microorganisms, pretreatment units such as high-aeration tanks and multi-stage AO are required before the short-cut nitrification-anammox functional unit to prevent excessive carbon sources from entering the anammox unit and causing heterotrophic bacteria to compete for its ecological niche. This invention pioneers the application of plug-flow AOA technology in high-concentration biogas slurry treatment. By converting organic matter into endogenous carbon through denitrifying polysaccharide bacteria in the anaerobic zone, excessive carbon sources are prevented from entering the aerobic zone, thus avoiding excessive heterotrophic bacteria proliferation. Simultaneously, the endogenous carbon undergoes endogenous short-cut denitrification in the anoxic zone, achieving short-cut denitrification with little or no added carbon source, reducing the pressure on carbon source addition and sludge treatment. Moreover, since the alkalinity consumed by short-cut nitrification is only 30% of that consumed in the nitrification process, the alkalinity required for this operating mode is far less than that of the AAO operating mode.

[0033] Based on this, the present invention solves the problems of difficulty and high cost in upgrading and retrofitting wastewater treatment plants. The present invention is based on the plug-flow structure widely used in existing wastewater treatment plants, achieving denitrification and exhaust gas treatment by adding covers and air passages. Previously, invention patent CN 118812013 A used the AOA (Automatic Aeration) operation mode to treat high-concentration biogas slurry; however, this patent is difficult to directly modify the surface of existing plants, increasing construction costs. Furthermore, this patent uses Sequencing Batch Reactor (SBR), which has a long idle period in actual operation and is relatively difficult to operate and maintain. Especially for the increasingly popular underground wastewater treatment plants and those that have added covers to meet exhaust gas treatment requirements, the present invention has a lower implementation threshold and is more feasible.

[0034] This invention solves the problems of agitator aging and difficult operation and maintenance in existing wastewater treatment processes. This invention pioneers the use of air-lift circulation to achieve homogenization in plug-flow wastewater treatment facilities, avoiding agitator failures caused by biological and salinity corrosion. Furthermore, the air-lift circulation mixing method provides more effective tank volume, allowing for the addition of more packing material, which contributes to improved treatment efficiency.

[0035] The most important innovation of this invention is solving the problem of excessive greenhouse gas emissions from wastewater treatment plants. While previous invention patent CN113998782B proposed collecting waste gas from the plant area for aeration in the aerobic and intermediate zones of the AOA process, this only addressed odorous gases such as H2S and CH4. A significant amount of N2O was still emitted into the atmosphere with the aeration from the aerobic zone, contradicting the wastewater treatment industry's "carbon neutrality" goal. Although invention patent CN119263488A proposed adding a cover plate to the plug-flow AOA process to facilitate N2O collection and tail gas treatment, thereby achieving greenhouse gas emission reduction, it increased the burden on subsequent gas treatment. This invention first proposes a gas recirculation method that differentiates between water and air flow directions, achieving in-situ N2O emission reduction and microbial absorption through gas flow design. This method greatly reduces the difficulty of subsequent treatment and also lowers treatment costs.

[0036] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation, characterized in that, The device includes an anaerobic zone (2), an aerobic zone (3), an intermediate zone (4) and an anoxic zone (5), which are connected in sequence by sewage pipelines; each of the aerobic zone (3), the intermediate zone (4) and the anoxic zone (5) is equipped with a packing assembly (9) to improve biomass loading; The anaerobic zone (2) is used for the influent of biogas slurry (1) and converts the COD in the wastewater into endogenous carbon, so that the COD is reduced to 400~800mg / L before being transported to the aerobic zone (3). The aerobic zone (3) is used to perform short-cut nitrification and anaerobic ammonia oxidation on the wastewater before it is transported to the intermediate zone (4). The intermediate zone (4) is used as an aerobic functional zone during the initial startup of the device and when the treatment load is low, and the dissolved oxygen concentration is maintained at 0.5~1mg / L; when the nitrogen and total nitrogen in the effluent at the end of the aerobic zone (3) meet the requirements, it is used as an anoxic functional zone, and the dissolved oxygen is controlled at <0.1mg / L; and the effluent is transported to the anoxic zone (5). The anoxic zone (5) is used for short-cut denitrification and anaerobic ammonia oxidation of wastewater, so that the effluent meets the requirements of ammonia nitrogen <45mg / L, total nitrogen <70mg / L and COD <500mg / L; The anaerobic zone (2), aerobic zone (3), intermediate zone (4) and anoxic zone (5) are all equipped with cover plates (10); the aerobic zone (3), intermediate zone (4), anoxic zone (5) and anaerobic zone (2) are also connected in sequence by gas pipelines; The aerobic zone (3) is also used for the intake of waste gas (11) in the factory area, and the malodorous components in the waste gas are adsorbed and oxidized into CO2 by aerobic bacteria, while NH3 and H2S are oxidized by ammonia-oxidizing bacteria and sulfur-oxidizing bacteria and then transported to the intermediate zone (4). When the intermediate zone (4) is used as an anoxic functional zone, it is used in the same way as the anoxic zone (5) to assimilate CO2 and reduce N2O in the exhaust gas with anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria, remove residual H2S with sulfur autotrophic denitrifying bacteria, and transport the exhaust gas to the anaerobic zone (2). When the intermediate zone (4) is used as an aerobic functional zone, it is used for the intake of waste gas (11) from the plant area and to transport the waste gas to the anoxic zone (5); the anoxic zone (5) is used to assimilate CO2 and reduce N2O in the waste gas by anaerobic ammonia oxidizing bacteria or sulfur autotrophic denitrifying bacteria and to transport the exhaust gas to the anaerobic zone (2). The anaerobic zone (2) is used to reduce N2O in the waste gas with organic matter to remove more than 95% of N2O.

2. The device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation according to claim 1, characterized in that, The device also includes a sedimentation tank (6) located at the outlet of the anoxic zone (5); The sedimentation tank (6) is used to settle the effluent from the anoxic zone (5) and return a portion of the sludge to the anaerobic zone (2) through the first sludge return pipe (22); when the intermediate zone (4) is an anoxic functional zone, a portion of the sludge is returned to the intermediate zone (4) through the second sludge return pipe (21); when the intermediate zone (4) is an aerobic functional zone, the sludge is returned to the anoxic zone (5) through the third sludge return pipe (20). The sedimentation tank (6) is provided with an upper effluent (7) at the top for discharging treated wastewater; The bottom of the sedimentation tank (6) is used to discharge excess sludge (8).

3. The device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation according to claim 1, characterized in that, The volume ratio of the anaerobic zone (2), aerobic zone (3), intermediate zone (4) and anoxic zone (5) is 1:1:1:

1.

4. The device for deep denitrification of biogas slurry and synergistic emission reduction of greenhouse gases driven by gas lift circulation according to claim 1, characterized in that, The filling ratio of the packing components (9) in the aerobic zone (3), intermediate zone (4) and anoxic zone (5) is 60% of the tank volume.

5. The device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation according to claim 1, characterized in that, A dissolved oxygen probe (23) is installed in the aerobic zone (3) to monitor dissolved oxygen; The dissolved oxygen probe (23) is also connected to a PLC (24) to control the air intake pump (25) to pump the waste gas (11) from the plant into the aerobic zone (3).

6. The device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation according to claim 1, characterized in that, The device also includes an aerobic zone gas circulation pump (12) connected to the aerobic zone (3), which is used to aerate from the bottom of the aerobic zone (3) and maintain an upward flow rate so as to achieve a uniform mixing state of mud and water. A circulation pump (14) connected to the intermediate zone (4) is used to circulate aeration from the bottom of the intermediate zone (4) to maintain an upward flow rate; The anoxic zone gas circulation pump (16) connected to the anoxic zone (5) is used for aeration from the bottom of the anoxic zone (5); An anaerobic zone gas circulation pump (18) connected to the anaerobic zone (2) is used to aerate from the bottom of the anaerobic zone (2) to mix the mud and water and increase the solubility of N2O.

7. The device for deep denitrification of biogas slurry and synergistic emission reduction of greenhouse gases driven by gas lift circulation according to claim 1, characterized in that, The anaerobic zone (2) is provided with an outlet (19) for discharging the treated gas; The exhaust port (19) is further provided with an exhaust gas treatment module at its rear end. The exhaust gas treatment module is used to treat aerosols and toxic and harmful gases by means of activated carbon adsorption and catalytic oxidation.

8. The device for deep denitrification of biogas slurry and synergistic emission reduction of greenhouse gases driven by gas lift circulation according to claim 1, characterized in that, The intermediate zone (4) is also connected to the anaerobic zone (2); When the intermediate zone (4) is used as an anoxic functional zone, it is used to receive a mud-water mixture with a 20-40% influent ratio from the anaerobic zone (2) to reduce the endogenous carbon loss of the aerobic zone (3); the intermediate zone (4) is also used to set up an external carbon source.

9. A method for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by gas lift circulation, characterized in that, This method is applied to a device for deep denitrification of biogas slurry and synergistic reduction of greenhouse gas emissions driven by air-lift circulation as described in any one of claims 1 to 8; The method includes: The biogas slurry (1) enters the anaerobic zone (2) and converts the COD in the wastewater into endogenous carbon. After the COD drops to 400~800mg / L, it enters the aerobic zone (3). The aerobic zone (3) performs short-cut nitrification and anaerobic ammonia oxidation on the wastewater, and then transports the wastewater to the intermediate zone (4). The intermediate zone (4) serves as an aerobic functional zone during the initial startup of the device and when the treatment load is low, and maintains a dissolved oxygen concentration of 0.5~1 mg / L; when the ammonia nitrogen and total nitrogen in the effluent at the end of the aerobic zone (3) meet the requirements, it serves as an anoxic functional zone, and controls the dissolved oxygen <0.1 mg / L; and the effluent is then transported to the anoxic zone (5). The anoxic zone (5) performs short-cut denitrification and anaerobic ammonia oxidation on the wastewater to ensure that the effluent meets the requirements of ammonia nitrogen <45mg / L, total nitrogen <70mg / L and COD <500mg / L; The waste gas (11) enters from the aerobic zone (3) and the odorous components in the waste gas are adsorbed and oxidized into CO2 by aerobic bacteria. NH3 and H2S are oxidized by ammonia-oxidizing bacteria and sulfur-oxidizing bacteria and then transported to the intermediate zone (4). When the intermediate zone (4) is used as an anoxic functional zone, both the anoxic zone (5) and the anoxic zone (2) use anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria to assimilate CO2 and reduce N2O in the exhaust gas, use sulfur autotrophic denitrifying bacteria to remove residual H2S, and transport the exhaust gas to the anoxic zone (2). When the intermediate zone (4) is used as an aerobic functional zone, the waste gas (11) of the plant area also enters from the intermediate zone (4) and is transported to the anoxic zone (5); the anoxic zone (5) uses anaerobic ammonia oxidizing bacteria or sulfur autotrophic denitrifying bacteria to assimilate CO2 and reduce N2O in the waste gas, and transports the effluent to the anaerobic zone (2). The anaerobic zone (2) uses organic matter to reduce N2O in the waste gas, thereby removing more than 95% of N2O.

10. The method for deep denitrification of biogas slurry and synergistic emission reduction of greenhouse gases driven by gas lift circulation according to claim 9, characterized in that, The parameters of the biogas slurry (1) are C:N = 2~5, 1< BOD5 / TN < 2.5, and ammonia nitrogen concentration of 1000~1800mg / L; The aerobic zone (3) is required to have an ammonia nitrogen concentration of less than 100 mg / L and a total nitrogen concentration of less than 250 mg / L at the end of the effluent.

Images