Sewage treatment device and method for achieving enhanced nitrogen and phosphorus removal and n 2o emission reduction by means of AOA process

Abstract

The present invention belongs to the fields of energy conservation, consumption reduction and carbon neutralization in terms of sewage treatment, and provides a sewage treatment device and method for achieving enhanced nitrogen and phosphorus removal and N2O emission reduction by means of an AOA process. The device mainly comprises a raw sewage tank, an AOA reactor and a sedimentation basin. Sewage firstly enters the AOA reactor and sequentially passes through an anaerobic zone, an aerobic zone and an anoxic zone in a water flow direction. Anaerobic phosphorus release and internal carbon source storage processes are mainly performed in the anaerobic zone; nitrification and aerobic phosphorus absorption are performed in the aerobic zone; and endogenous denitrification and anaerobic ammonia oxidation are performed in the anoxic zone. In addition, the escape of N2O in the aerobic zone is reduced by controlling dissolved oxygen, the carbon sequestration capability of the rear anoxic zone is fully utilized, and a large amount of dissolved-state N2O generated in the aerobic zone is removed. The present application mainly provides a brand-new solution for a key low-carbon denitrification technique for sewage treatment, and the technique can effectively reduce energy and chemicals required for aeration, excess sludge yield and N2O emissions during operation, and has application prospects.

Description

AOA process for wastewater treatment devices and methods to achieve enhanced nitrogen and phosphorus removal and N2O emission reduction.

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese Patent Application No. 202410510273.4, filed on April 26, 2024, entitled “Wastewater Treatment Device and Method for Enhanced Denitrification, Phosphorus Removal and N2O Emission Reduction via AOA Process”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of environmental engineering wastewater treatment and carbon neutrality, and specifically relates to wastewater treatment devices and methods for achieving enhanced nitrogen and phosphorus removal and N2O emission reduction using the AOA process. Background Technology

[0004] The concept of carbon neutrality presents the wastewater treatment industry with the challenge of transforming from an energy-intensive sector to a green and low-carbon one. Simultaneously, stringent wastewater discharge standards and improved wastewater treatment rates are beneficial for environmental protection and water pollution control. Therefore, technological innovation is essential to achieve even stricter standards while reducing carbon emissions and consumption.

[0005] The anaerobic / aerobic / anoxic (AOA) process is a novel biological treatment process in which microorganisms can store most of the influent organic matter within their cells in the anaerobic zone, and then utilize the intracellular carbon source in the anoxic zone to achieve endogenous denitrification and nitrogen removal. This process employs post-denitrification, and theoretically, can achieve near 100% nitrogen removal efficiency under sufficient carbon source conditions. Anaerobic ammonia oxidation is carried out by anaerobic ammonia-oxidizing bacteria under anoxic conditions, converting NH4+ into nitrogen. + With NO2 - It is converted into N2, CO2 is fixed, and NO3 is produced. - Anaerobic ammonia oxidation (AOA) is a biological process that does not produce N2O and requires no aeration or organic carbon source, making it the most economical and efficient wastewater denitrification technology currently available. Combining AOA with anaerobic ammonia oxidation effectively solves the bottleneck problems of insufficient carbon sources, including difficulties in deep nitrogen and phosphorus removal, energy conservation, and carbon emission reduction in wastewater.

[0006] Nitrogen gas (N2O) is a greenhouse gas with a 100-year global warming potential 265 times that of carbon dioxide and 28 times that of methane. It is a major greenhouse gas emitted during wastewater treatment. Currently, the rate of increase in global N2O emissions due to human activities exceeds the predictions of the Intergovernmental Panel on Climate Change (IPCC) and the Paris Agreement. A 1% N2O emission factor will increase the carbon footprint of wastewater treatment plants by approximately 30%. Therefore, it is imperative to develop effective strategies to reduce N2O emissions. The denitrification zone is the only N2O sink in wastewater treatment processes. Denitrifying microbial communities possess an extremely high N2O reduction capacity, which is 2-10 times their production capacity. N2O mainly exists in liquid form in the anoxic zone, where it is removed by denitrifying bacteria as an electron acceptor, with only a small portion escaping into the atmosphere. Developing processes that can fully utilize the N2O sink capacity of the anoxic zone offers a promising prospect for further reducing the carbon footprint of wastewater treatment plants.

[0007] Summary of the Invention

[0008] The purpose of this application is to provide a novel process and method for deep nitrogen and phosphorus removal and N2O reduction in wastewater such as low C / N ratio municipal sewage and landfill leachate. In this device, wastewater first enters the anaerobic zone of the AOA reactor from the raw water tank for organic matter removal, phosphorus release, and denitrification. Denitrifying bacteria absorb organic matter from the wastewater in the anaerobic zone, converting it into internal carbon sources such as PHAs and Gly, which are stored intracellularly. Simultaneously, the denitrifying bacteria utilize the organic matter in the raw water to remove NO3 from the returned sludge. - and NO2 - Furthermore, PAOs decompose poly-P within their bodies to generate energy, and use this energy to absorb organic matter in wastewater, converting it into an internal carbon source. This process is accompanied by PO4. 3- The NH4+ is released. It then enters the aerobic zone for nitrification and aerobic phosphorus uptake, removing NH4+ from the water. + With PO4 3- AOB and NOB utilize dissolved oxygen to remove NH4 from wastewater. + Oxidized to NO3 - and NO2 - PAOs utilize intracellular carbon sources previously stored in the anaerobic zone to convert extracellular PO4 into carbon dioxide. 3- Phosphorus is transported into cells for resynthesis of poly-P, and then removed through the discharge of excess sludge, achieving phosphorus removal in the AOA system. Furthermore, the remaining, non-bioavailable COD from the anaerobic zone is further removed in the aerobic zone. Finally, it enters the anoxic zone for endogenous denitrification, anaerobic ammonium oxidation, and denitrification phosphorus removal. NO3 produced during nitrification... - NO2 -When N2O enters the anoxic zone, denitrifying bacteria utilize the internal carbon source stored in the anaerobic zone to complete the denitrification process. Anaerobic ammonia oxidizing bacteria use CO2 as their inorganic carbon source, achieving deep nitrogen removal in the anoxic zone without aeration or organic carbon source, and anaerobic ammonia oxidation does not produce N2O. Furthermore, the remaining PO4... 3- Further removal is possible in the hypoxic zone, accompanied by NO3. - or NO2 - The reduction. This application can utilize the internal carbon source fully stored in the anaerobic zone to remove NO3 through denitrification. - It removes NO2 and fully utilizes the carbon sink capacity of the post-anoxic zone to remove dissolved N2O without the need for an external carbon source. At the same time, it can save the aeration volume of the aerobic zone, and has the advantages of deep pollutant reduction, low sludge production and carbon saving and consumption reduction. Attached Figure Description

[0009] Figure 1 is a schematic diagram of a wastewater treatment device that achieves enhanced nitrogen and phosphorus removal and N2O emission reduction using the AOA process;

[0010] Wherein, 1 represents the raw wastewater tank, 2 represents the AOA bioreactor, and 3 represents the sedimentation tank; 1.1 represents the influent pump, 1.2 represents the first sludge return pump, and 1.3 represents the second sludge return pump; 2.1 represents the anaerobic zone, 2.2 represents the aerobic zone, 2.3 represents the anoxic zone, 2.4 represents the aeration device, 2.5 represents the stirring device, 2.6 represents the pH / DO online monitoring system, 2.7 represents the N2O online monitoring system, and 2.8 represents the biological packing material.

[0011] Figure 2a shows the changes in nitrogen pollutant and COD concentrations along the AOA process; Figure 2b shows the changes in dissolved N2O concentration and gaseous N2O emission rate along the AOA process.

[0012] Where Inf represents inlet water, A n0 A represents the theoretical zone after the influent and the first return sludge are mixed. n1 The first cell represents anaerobic digestion, A. n2 O1 represents the first anaerobic zone, O2 represents the first aerobic zone, O3 represents the third aerobic zone, A0 represents the theoretical zone after the aerobic effluent and the second return sludge are mixed, A1 represents the first anoxic zone, A2 represents the second anoxic zone, A3 represents the third anoxic zone, A4 represents the fourth anoxic zone, A5 represents the fifth anoxic zone, and Eff represents the effluent. Detailed Implementation

[0013] The present application will be further described below with reference to the accompanying drawings and embodiments:

[0014] A wastewater treatment device and method for enhanced nitrogen and phosphorus removal and N2O reduction using the AOA process, characterized by: a raw wastewater tank (1), an AOA biochemical reactor (2), a sedimentation tank (3); an influent pump (1.1), a first sludge return pump (1.2), a second sludge return pump (1.3); an anaerobic zone (2.1), an aerobic zone (2.2), an anoxic zone (2.3), an aeration device (2.4), a stirring device (2.5), an online pH / DO monitoring system (2.6), an online N2O monitoring system (2.7), and biological packing material (2.8). Wastewater passes sequentially through the anaerobic, aerobic, and anoxic zones of the AOA biochemical reactor from the raw wastewater tank, and then flows out through the sedimentation tank. The total hydraulic retention time is set at 12-16 hours, with the anaerobic zone accounting for 20-30%, the aerobic zone for 25-40%, and the anoxic zone for 35%-50%. The volume ratio can be flexibly adjusted according to the operating conditions. Part of the sludge is returned to the front end of the anaerobic zone via a first sludge return pump, with a return ratio R1 controlled at 80-120%. Another part is returned to the front end of the anoxic zone via a second sludge return pump, with a return ratio R2 controlled at 80-120%. An online N2O monitoring system is installed at the end of the anoxic zone to monitor the N2O concentration in the effluent from the biological treatment tank in real time. The aeration rate is flexibly adjusted through the aeration device to control dissolved oxygen below 2 mg / L, reducing aeration energy consumption and N2O emission. Extending the proportion of the anoxic zone's hydraulic retention time to over 50% of the total hydraulic retention time fully utilizes the carbon sequestration potential of the downstream anoxic zone and removes dissolved N2O carried by the upstream aerobic zone. Biological packing material is used to enrich anaerobic ammonia-oxidizing bacteria, with a packing ratio of 20-30%.

[0015] The specific steps are as follows:

[0016] 1) Start-up phase:

[0017] First, inoculate with nitrifying and denitrifying flocculent sludge, setting the volume ratio of the anaerobic, aerobic, and anoxic zones to 2:3:3. The first sludge return ratio R1 and the second sludge return ratio R2 are both 80-120%. Dissolved oxygen in the aerobic zone is controlled at 1-4 mg / L. After gradual acclimatization, the sludge concentration is increased to 3000-5000 mg / L. Wait until the NH4+ ions reach the end of the aerobic zone... + When the nitrogen concentration is controlled at 1-2 mg / L, the endogenous denitrification rate reaches 0.2-0.6 mgN / gVSS / h, the total nitrogen concentration in the effluent is controlled below 15 mg / L, and the total phosphorus concentration is controlled below 0.5 mg / L and can be maintained for more than one week, it indicates that the system has been successfully started.

[0018] In the formula: NO3 refers to the hypoxic phase --N concentration change; MLVSS refers to the volatile solids concentration of the sludge mixture in the anoxic zone; Δt refers to the hydraulic retention time in the anoxic zone.

[0019] 2) Enhance the endogenous denitrification stage:

[0020] First, the dissolved oxygen in the aerobic zone is precisely controlled at 1-2 mg / L to avoid excessive nitrification and unnecessary loss of internal carbon sources. Simultaneously, 10-20% of the aerobic zone volume is switched to anoxic operation, thereby increasing the endogenous denitrification time in the anoxic zone and preventing the influent carbon source from being primarily used to reduce NO3 in the returned sludge in the anaerobic zone. - -N and NO2 - -N increases the internal carbon source storage rate. When the internal carbon source storage rate reaches 90% or higher at the end of the anaerobic process, NH4+ will be used at the end of the aerobic process. + When the nitrogen concentration is controlled at 1-2 mg / L, the endogenous denitrification rate reaches above 0.6 mgN / gVSS / h, the total nitrogen concentration in the effluent is controlled below 10 mg / L, and the total phosphorus concentration is controlled below 0.5 mg / L and can be maintained for more than one week, it indicates that the enhanced endogenous denitrification of the system is successful.

[0021] In the formula: ΔCOD refers to the change in COD concentration in the anaerobic zone; NO3 in the anaerobic zone - -N concentration change; NO2 in the anaerobic zone - -N concentration change; 2.86 and 1.71 are denitrification units NO3. - -N and NO2 - -N required COD concentration.

[0022] 3) Stable operation phase:

[0023] The system sludge concentration is maintained at 3000-5000 mg / L, the hydraulic retention time is 12-16 h, the effluent COD is less than 50 mg / L, the total nitrogen is less than 5 mg / L, and the NH4+ is less than 5 mg / L. + The concentrations of -N (-N) less than 2 mg / L, N2O-N less than 0.1 mg / L, and total phosphorus less than 0.5 mg / L indicate that the system is operating stably.

[0024] 4) Energy conservation, emission reduction, and carbon reduction measures:

[0025] After the system stabilizes, reduce the aeration rate to lower the dissolved oxygen concentration at the aerobic end to 0.5-1 mg / L, reducing the amount of N2O stripped from the liquid phase into the atmosphere and fully utilizing the carbon sequestration capacity of the post-anoxic zone. Furthermore, add biological packing material to the anoxic zone at a filling ratio of 20-30% to enrich anaerobic ammonia-oxidizing bacteria. When the endogenous denitrification rate reaches above 1.0 mg N / g VSS / h, the second sludge return can be shut off to reduce energy consumption. Once the nitrogen removal contribution from anaerobic ammonia oxidation reaches over 20%, the NH4+ ions at the effluent aerobic end will be reduced. + When the N2O-N concentration is less than 1 mg / L, the total nitrogen is less than 5 mg / L, and the undissolved N2O-N concentration in the anoxic state is less than 0.01 mg / L and can be maintained for more than a week, it indicates that the system has successfully achieved energy conservation, consumption reduction, and carbon emission reduction.

[0026] In the formula: 2.06 refers to the stoichiometric coefficient contributed by anaerobic ammonia oxidation; NH4 during the hypoxic phase + -N concentration change; ΔTIN refers to the total nitrogen concentration change in the hypoxic area.

[0027] The experimental results show that after energy saving and consumption reduction and stabilization (as shown in Figure 2), the COD of urban sewage effluent after passing through the AOA process is less than 50 mg / L, and NH4 is less than 50 mg / L. + -N is below 1 mg / L, N₂O₃-N is below 0.01 mg / L, total nitrogen is below 5 mg / L, and total phosphorus is below 0.5 mg / L. This process can save 30% of aeration energy consumption, reduce excess sludge production by 20%, and has a carbon emission reduction potential of 1.54 × 10⁻⁶ mg / L. 6 kgCO2-eq / a / 10 4 t.

[0028] The above are specific embodiments of this application, which are intended to help those skilled in the art to better understand and apply this application. The implementation of this application is not limited to these embodiments. Therefore, any simple improvements made to this application by those skilled in the art are within the scope of this application.

Claims

1. A wastewater treatment device that achieves enhanced nitrogen and phosphorus removal and N2O emission reduction using the AOA process, characterized in that: The device includes a raw wastewater tank (1), an AOA bioreactor (2), a sedimentation tank (3); an influent pump (1.1), a first sludge return pump (1.2), a second sludge return pump (1.3); an anaerobic zone (2.1), an aerobic zone (2.2), an anoxic zone (2.3), an aeration device (2.4), a stirring device (2.5), an online pH / DO monitoring system (2.6), an online N2O monitoring system (2.7), and biological packing material (2.8). Wastewater passes through the raw wastewater tank sequentially through the anaerobic zone, aerobic zone, and anoxic zone of the AOA bioreactor, and then flows out through the sedimentation tank. The total hydraulic retention time is set to 12-16 hours, with the anaerobic zone accounting for 20-30%, the aerobic zone for 25-40%, and the anoxic zone for 35%-50%. Part of the sludge is returned to the front end of the anaerobic zone via a first sludge return pump, with a return ratio R1 controlled at 80-120%. The other part is returned to the front end of the anoxic zone via a second sludge return pump, with a return ratio R2 controlled at 80-120%. An online N2O monitoring system is installed at the end of the anoxic zone to monitor the N2O concentration in the effluent from the biological treatment tank in real time. The biological packing material filling ratio is 20-30%.

2. The method of using the apparatus as described in claim 1, characterized in that, Includes the following steps: 1) Start-up phase: First, nitrifying and denitrifying flocculent sludge is inoculated, and the volume ratio of the anaerobic zone, aerobic zone, and anoxic zone is set to 2:3:

3. The first sludge return ratio R1 and the second sludge return ratio R2 are both 80-120%. Dissolved oxygen in the aerobic zone is controlled at 1-4 mg / L, and NH4+ is removed from the aerobic zone. + -N concentration controlled at 1-2 mg / L; sludge concentration 3000-5000 mg / L; 2) Enhance the endogenous denitrification stage: First, the dissolved oxygen in the aerobic zone is further precisely controlled at 1-2 mg / L. Then, 10-20% of the volume of the aerobic zone is switched to anoxic operation, thereby increasing the endogenous denitrification time in the anoxic zone and avoiding the need for influent. Carbon sources in anaerobic zones are primarily used to reduce NO3 in returned sludge. - -N and NO2 - -N increases the internal carbon source storage rate of the anaerobic end to over 90%; 3) Energy conservation, emission reduction, and carbon emission reduction measures: Reduce the dissolved oxygen concentration at the end of the aerobic process to 0.5-1 mg / L to reduce the amount of N2O stripped from the liquid phase into the atmosphere and fully utilize the carbon sequestration capacity of the post-anoxic zone. In addition, add biological packing material to the anoxic zone at a filling ratio of 20-30% to enrich anaerobic ammonia-oxidizing bacteria. When the endogenous denitrification rate reaches 1.0 mg N / g VSS / h or higher, shut off the second sludge return flow to reduce energy consumption. Use an online N2O monitoring system to monitor the N2O-N concentration in real time.

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