A device system for denitrification and dephosphorization of sewage and in-situ sludge reduction and a treatment method thereof

Abstract

The application provides a device system and a treatment method for sewage denitrification and phosphorus removal coupled with in-situ sludge reduction, the device system comprising an electrochemical reaction device, an AAO device and a sedimentation tank; the AAO device comprising an anaerobic tank, an anoxic tank and an aerobic tank connected in sequence; the aerobic tank being connected with the sedimentation tank; a sludge outlet of the sedimentation tank being connected with an inlet of the electrochemical reaction device; an outlet of the electrochemical reaction device being connected with a sludge inlet of the anaerobic tank; the electrochemical reaction device being a sealed reaction tank; a cathode and an anode being arranged in the reaction tank, the cathode and the anode being respectively and independently connected with a power supply; the anode being an iron electrode; a first stirring device being arranged in the reaction tank; and sponge filling being placed at the bottom of the reaction tank. By adding the iron anode electrochemical reaction device, the denitrification and phosphorus removal efficiency in the traditional biochemical treatment unit of sewage treatment is improved, the in-situ sludge reduction is realized, and the demand for external carbon source is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater biological treatment technology, and relates to a device system and treatment method for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction. Background Technology

[0002] Currently, biological treatment is widely used for wastewater denitrification, with heterotrophic denitrification being the most common and applied in the vast majority of wastewater treatment plants. Carbon sources play a crucial role in common heterotrophic denitrification processes. While sufficient carbon sources are beneficial for denitrification reactions, they also result in a large amount of excess sludge. Furthermore, carbon limitation (C / N < 6) can lead to a total nitrogen (TN) removal efficiency of less than 50% in biological nutrient removal processes.

[0003] Wastewater from developing countries typically has a C / N ratio of less than 5. Therefore, to meet stringent effluent standards and achieve high nitrogen removal efficiency, adding carbon sources is the preferred method. However, pollution transfer is unavoidable in this process. While adding organic carbon sources ensures a sufficient and stable supply of organic matter as electron donors, it also significantly increases the amount of excess sludge due to sufficient anabolism, severely impacting the goal of cost-effective wastewater treatment. Treatment and disposal costs account for more than 50% of the total operating costs of wastewater treatment plants. This problem is exacerbated by increasing influent nitrogen content. Therefore, it is necessary to explore a method that balances improving nitrogen removal efficiency with reducing excess sludge.

[0004] Existing technologies indicate that inserting an oligotrophic anaerobic reactor (side-flow reactor) into the sludge return line of a traditional activated sludge system promotes pyrolysis-cryptic growth, thus achieving a promising and cost-effective sludge reduction method. Intracellular organic matter is released into the extracellular space through biomass pyrolysis, while particulate organic matter hydrolyzes into dissolved organic matter (DOM), which facilitates cryptic growth, realizing sludge resource utilization and reducing excess sludge production. However, the above method has limited improvements in nitrogen and phosphorus removal, long hydraulic retention times, large equipment footprint, and limited sludge reduction rate.

[0005] In summary, providing a wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction device and treatment method with low external carbon source input, small equipment footprint, and simple operation is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a device system and treatment method for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction. By adding an iron anode electrochemical reaction device in the side flow zone, the denitrification and phosphorus removal efficiency in the traditional biochemical treatment unit of wastewater treatment can be effectively improved, achieving in-situ sludge reduction (reducing the yield of excess sludge), reducing the demand for external carbon sources, and with low cost and low equipment and operation requirements.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a device system for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction, the device system comprising an electrochemical reaction device, an AAO device, and a sedimentation tank;

[0009] The AAO device includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence.

[0010] The anaerobic tank has an inlet on its side wall; the aerobic tank is connected to the sedimentation tank; and the sedimentation tank has an outlet on its side wall.

[0011] The sludge outlet of the sedimentation tank is connected to the inlet of the electrochemical reaction device; the outlet of the electrochemical reaction device is connected to the sludge inlet of the anaerobic tank.

[0012] The electrochemical reaction device is a sealed reaction tank; a cathode and an anode are provided in the reaction tank, and the cathode and the anode are independently connected to a power source; the anode is an iron electrode; a first stirring device is provided in the reaction tank; and sponge packing is placed at the bottom of the reaction tank.

[0013] In this invention, the electrochemical reaction device is a side-flow reaction device.

[0014] The device system provided by this invention, by adding an electrochemical reaction device (electrochemical iron-driven low-carbon deep treatment device) at the side flow of the AAO device, can avoid the addition of external organic carbon sources in the case of low carbon-to-nitrogen ratio wastewater, significantly improving the denitrification and phosphorus removal efficiency of the device system, and achieving a low-carbon wastewater treatment process in conjunction with the efficient in-situ sludge reduction process in the main flow zone (AAO device).

[0015] It is worth noting that by adding an electrochemical reactor at the side flow of the AAO device, with an iron electrode as its anode, the electrochemical iron-driven low-carbon deep treatment device promotes the stable proliferation of characteristic functional bacteria and the release of endogenous carbon sources in the sludge, thereby enhancing endogenous denitrification and improving the biodegradation of extracellular polymers, thus reducing the amount of organic components in the sludge. Furthermore, the dynamic oxidation-reduction of iron occurs in the electrochemical reactor, promoting the electron transfer process of microorganisms. This not only enables the autotrophic denitrification process of iron-autotrophic bacteria but also accelerates the degradation and utilization of organic matter. It also allows for the co-precipitation of phosphates in the electrochemical reactor and the mainstream zone, enabling the synergistic reduction of sludge through deep nitrogen and phosphorus removal.

[0016] As a preferred embodiment of the present invention, the cathode comprises a graphite electrode.

[0017] Preferably, the distance between the cathode and the anode is 4.5 to 5.5 cm, for example, it can be 4.6 cm, 4.7 cm, 4.8 cm, 4.9 cm, 5 cm, 5.1 cm, 5.2 cm, 5.3 cm or 5.4 cm, but is not limited to the listed values, and other values ​​within the range are also applicable.

[0018] As a preferred embodiment of the present invention, the sponge filler is made of polyurethane.

[0019] Preferably, the filling volume of the sponge filler is 25% to 35% of the volume of the electrochemical reaction device, for example, it can be 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33% or 34%, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0020] As a preferred embodiment of the present invention, a second stirring device is provided in the anaerobic tank.

[0021] Preferably, a third stirring device is provided in the anoxic pool.

[0022] Preferably, a nitrification liquid return pipeline is connected between the aerobic tank and the anoxic tank.

[0023] Preferably, the aerobic tank is equipped with an aeration device.

[0024] Preferably, the sludge outlet of the sedimentation tank is connected to two pipes, one of which returns the sludge to the electrochemical reaction device, and the other of which discharges it externally.

[0025] Secondly, the present invention provides a wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction treatment method, wherein the treatment method is carried out using the device system described in the first aspect, specifically including:

[0026] Wastewater is continuously fed into the anaerobic tank, and then flows sequentially into the anoxic tank and the aerobic tank. The effluent from the aerobic tank undergoes sludge-water separation in the sedimentation tank. The separated water is discharged, while some of the separated sludge is returned to the electrochemical reactor through the sludge return pipe. Subsequently, under the action of DC power and stirring, the sludge undergoes an electrochemical reaction in the electrochemical reactor. Finally, the sludge after the electrochemical reaction flows into the anaerobic tank.

[0027] In this invention, a certain amount of sludge from a municipal wastewater treatment plant is inoculated into the electrochemical reaction device before the device system is started; after the device system is started, no more sludge is inoculated. The wastewater includes actual wastewater or simulated wastewater.

[0028] The treatment method provided by this invention has the advantages of simple operation, high cost and efficiency, deep nitrogen and phosphorus removal, in-situ sludge reduction, and low external carbon source input, which is beneficial to practical engineering applications.

[0029] As a preferred technical solution of the present invention, the carbon-to-nitrogen ratio of the wastewater is ≥3.5, for example, it can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0030] Preferably, the concentration of sludge in the electrochemical reactor is 6000-7000 mg / L, for example, it can be 6100 mg / L, 6200 mg / L, 6300 mg / L, 6400 mg / L, 6500 mg / L, 6600 mg / L, 6700 mg / L, 6800 mg / L or 6900 mg / L, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0031] As a preferred technical solution of the present invention, the hydraulic retention time of the anaerobic tank is 70 to 120 minutes, for example, it can be 75 minutes, 80 minutes, 85 minutes, 90 minutes, 95 minutes, 100 minutes, 105 minutes, 110 minutes or 115 minutes, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0032] Preferably, the hydraulic retention time of the anoxic tank is 160 to 200 minutes, for example, it can be 165 minutes, 170 minutes, 175 minutes, 180 minutes, 185 minutes, 190 minutes or 195 minutes, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0033] As a preferred technical solution of the present invention, the dissolved oxygen content in the aerobic tank is ≥4mg / L, for example, it can be 4.5mg / L, 5mg / L, 5.5mg / L, 6mg / L, 6.5mg / L or 7mg / L, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0034] Preferably, the hydraulic retention time of the aerobic tank is 7 to 9 hours, for example, it can be 7.2 hours, 7.5 hours, 7.8 hours, 8 hours, 8.2 hours, 8.5 hours or 8.7 hours, but is not limited to the listed values. Other values ​​within the range are also applicable.

[0035] Preferably, the nitrified liquid in the aerobic tank is returned to the anoxic tank via a nitrified liquid return pipe.

[0036] Preferably, the nitrification liquor recirculation ratio of the aerobic tank is 220% to 280% of the influent flow rate, for example, it can be 225%, 230%, 235%, 240%, 245%, 250%, 255%, 260% or 270%, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0037] As a preferred technical solution of the present invention, the mud-water separation time is 1 to 4 hours, for example, it can be 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 3.8 hours, but is not limited to the listed values. Other values ​​within the range are also applicable.

[0038] Preferably, the sludge return ratio of the sedimentation tank is 70% to 90% of the influent flow rate, for example, it can be 72%, 75%, 78%, 80%, 82%, 85%, 86% or 88%, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0039] As a preferred technical solution of the present invention, the current of the DC power supply is 3 to 8 mA, for example, it can be 3.5 mA, 4 mA, 4.5 mA, 5 mA, 5.5 mA, 6 mA, 6.5 mA, 7 mA or 7.5 mA, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0040] Preferably, the stirring speed is 150 to 250 rpm, for example, it can be 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm or 240 rpm, but is not limited to the listed values, other values ​​within the range are also applicable.

[0041] Preferably, in the electrochemical reaction, the iron electrode simultaneously performs autotrophic denitrification and endogenous heterotrophic denitrification.

[0042] It is worth noting that the iron electrode not only improves heterotrophic denitrification by increasing the bioavailable COD yield, but also provides electrons for Fe(II)-based autotrophic denitrification. The specific reaction process is shown in the following equation:

[0043] Iron electrode reaction: Fe - 2e - =Fe(Ⅱ) (1)

[0044] 4Fe(II) + 2NO2 - +8H + →4Fe(Ⅲ)+N2+4H2O (2)

[0045] 10Fe(II) + 2NO3 - +12H + →10Fe(Ⅲ)+N2+6H2O (3)

[0046] As autotrophic and endogenous heterotrophic denitrification proceeds, Fe(II) is oxidized by nitrates and nitrites through iron autotrophic processes. The presence of phosphates causes Fe(II) and Fe(III) to chemically precipitate, with Fe(III) predominating in the precipitate. This means Fe(II) is oxidized to Fe(III) through denitrification and co-precipitates with phosphates, thus enhancing the simultaneous denitrification and phosphorus removal process. Furthermore, Fe(III) reduction also occurs in the electrochemical reactor. With the accumulation of Fe(III), this electron acceptor, under the active influence of iron-reducing bacteria, participates in the reduction of organic matter, promoting the release and transformation of endogenous organic matter in the system, such as the production of volatile fatty acids (VFAs). The increase in dissolved organic matter, in turn, can stimulate microorganisms to reduce Fe(III) to Fe(II). Fe(II) can further reduce and transform organic matter and nitrate nitrogen. Through the dynamic cycle between Fe(II) and Fe(III), electron shuttle in the microbial carbon and nitrogen metabolism process is further stimulated, creating favorable conditions for enzyme metabolism and accelerating electron transfer.

[0047] Preferably, the electrochemical reaction time is 160 to 200 min, for example, it can be 165 min, 170 min, 175 min, 180 min, 185 min, 190 min or 195 min, etc., but is not limited to the listed values, and other values ​​within the range are also applicable.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The device system and treatment method provided by the present invention, by adding an electrochemical reaction device at the side flow of the AAO device, and the anode of the device is an iron electrode, can avoid the addition of external organic carbon sources in the case of low carbon-nitrogen ratio wastewater, significantly improve the denitrification and phosphorus removal efficiency of the device system, and achieve a low carbon wastewater treatment process in conjunction with the efficient in-situ sludge reduction process in the mainstream zone.

[0050] (2) The device system provided by the present invention promotes the stable proliferation of characteristic functional bacteria by adding an electrochemical iron-driven low-carbon deep treatment device, promotes the release of endogenous carbon sources in sludge, realizes enhanced endogenous denitrification, and enhances the biodegradation of extracellular polymers, thereby achieving the reduction of organic components in sludge; at the same time, the dynamic oxidation-reduction of iron occurs in the electrochemical reaction device, which promotes the electron transfer process of microorganisms, not only realizing the autotrophic denitrification process of iron autotrophic bacteria, but also accelerating the degradation and utilization of organic matter, and providing co-precipitation of phosphates in the electrochemical reaction device and the mainstream zone, so that the deep denitrification and phosphorus removal synergistic sludge reduction can be achieved. Attached Figure Description

[0051] Figure 1This is a schematic diagram of the wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction device system provided in Example 1;

[0052] Figure 2 A schematic diagram of the electrochemical reaction apparatus provided in Example 1;

[0053] Among them, 1-anaerobic tank, 2-anoxic tank, 3-aerobic tank, 4-sedimentation tank, 5-electrochemical reaction device, 6-second stirring device, 7-third stirring device, 8-aeration device, 51-DC power supply, 52-stirring device, 53-sealing cover, 54-sponge packing, 55-inlet, 56-outlet.

[0054] Figure 3 The graph shows the results of the endogenous denitrification rate and the maximum accumulated concentrations of VFA and COD in the side-flow reactors of Example 1 and Comparative Example 1.

[0055] Figure 4 The graph shows the EPS concentration results in the side-flow reactor and AAO device in Example 1 and Comparative Example 1.

[0056] Figure 5 The graph shows the activity results of TTC-ETS in the side-flow reaction device and AAO device in Example 1 and Comparative Example 1.

[0057] Figure 6 The diagram shows the relative abundance of functional bacteria in the side-flow reaction device and its packing material in Example 1 and Comparative Example 1. Detailed Implementation

[0058] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0060] In the following examples and comparative examples, a certain amount of sludge from a municipal wastewater treatment plant was inoculated into the electrochemical reactor before the system was started; after the system was started, no more sludge was inoculated. The wastewater in the following examples and comparative examples was simulated domestic wastewater, using sodium acetate, glucose, and peptone as a composite carbon source, and ammonium chloride and potassium dihydrogen phosphate as simulated nitrogen and phosphorus pollutants. The concentration of ammonia nitrogen in the simulated domestic wastewater was 50 mg / L, the concentration of total phosphorus was 5 mg / L, and the concentration of COD was 175 mg / L. All concentrations in the following examples and comparative examples are mass concentrations.

[0061] Example 1

[0062] This embodiment provides a device system and treatment method for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction. The device system (such as...) Figure 1 (As shown) includes an electrochemical reaction device 5, an AAO device, and a sedimentation tank 4;

[0063] The AAO device includes an anaerobic tank 1, an anoxic tank 2, and an aerobic tank 3 connected in sequence; an inlet is provided on the side wall of the anaerobic tank 1; a second stirring device 6 is provided in the anaerobic tank 1; a third stirring device 7 is provided in the anoxic tank 2; a nitrification liquid return pipeline is connected between the aerobic tank 3 and the anoxic tank 2; and an aeration device 8 is provided in the aerobic tank 3.

[0064] The aerobic tank 3 is connected to the sedimentation tank 4; the sedimentation tank 4 is provided with an outlet on its side wall; the sludge outlet of the sedimentation tank 4 is connected to two pipes, one pipe returns to the electrochemical reaction device 5, and the other pipe discharges externally.

[0065] The outlet of the electrochemical reaction device 5 is connected to the sludge inlet of the anaerobic tank 1, and the electrochemical reaction device 5 is a side-flow reaction device; the electrochemical reaction device 5 (e.g. Figure 2 (As shown) is a sealed reaction tank 53; the reaction tank is equipped with a cathode and an anode, which are independently connected to a DC power supply 51; the anode is an iron electrode; the cathode is a graphite electrode; the dimensions of the anode are 8cm × 4cm × 0.2cm (height × width × thickness), and the distance between the cathode and the anode is 5cm; a first stirring device 52 is provided in the reaction tank; a sponge packing 54 is placed at the bottom of the reaction tank; the material of the sponge packing 54 is polyurethane; the filling volume of the sponge packing 54 is 30% of the volume of the electrochemical reaction device;

[0066] The treatment method includes: continuously feeding simulated domestic sewage into anaerobic tank 1 at a flow rate of 11L / day and retaining it for 90 minutes, then flowing it into anoxic tank 2 and retaining it for 180 minutes, then flowing it into aerobic tank 3 and retaining it for 8 hours. The nitrified liquid in aerobic tank 3 is returned to anoxic tank 2 through a nitrified liquid return pipe. Then, the effluent from aerobic tank 3 is subjected to sludge-water separation in sedimentation tank 4 for 2 hours. The separated water is discharged, and part of the separated sludge is returned to electrochemical reaction device 5 through a sludge return pipe. Subsequently, under the action of a DC power supply with a current of 5mA and a stirring speed of 200rpm, an electrochemical reaction is carried out in electrochemical reaction device 5 for 180 minutes. Finally, the sludge after the electrochemical reaction flows into anaerobic tank 1.

[0067] The nitrification liquor return flow rate of the aerobic tank 3 is 27.5 L / day; the sludge return flow rate of the sedimentation tank 4 is 8.8 L / day; in the electrochemical reaction, the iron electrode simultaneously performs autotrophic denitrification and endogenous heterotrophic denitrification; the inlet flow rate and outlet flow rate of the electrochemical reaction device 5 are kept consistent.

[0068] Examples 2-5 and Comparative Examples 1-2

[0069] The side-flow reactor setup, packing configuration, packing volume, and DC power supply current were modified as shown in Table 1. All other conditions remained the same as in Example 1.

[0070] Table 1

[0071]

[0072] Where “ / ” indicates that the corresponding parameters are not set. The conventional side-flow reaction device in Comparative Example 1 can be set with reference to the side-flow reaction zone provided in CN111977793A.

[0073] When the carbon-to-nitrogen ratio of the simulated domestic wastewater was 3.5, the device system and treatment method provided in the above examples and comparative examples were continuously operated for 70 days. The mass concentrations of total nitrogen, total phosphorus, and COD in the effluent were determined by ion chromatography, and the sludge yield in the effluent of the side-flow reactor was determined by sludge growth and COD consumption. The results are shown in Table 2.

[0074] Table 2

[0075]

[0076]

[0077] As shown in Table 2:

[0078] (1) The device system and treatment method provided by the present invention can effectively improve the denitrification and phosphorus removal efficiency in the traditional biochemical treatment unit of sewage treatment by adding a side-flow iron anode electrochemical reaction device, realize in-situ sludge reduction, and reduce the demand for external carbon sources.

[0079] (2) Comparison of Examples 1 and 2-3 and Comparative Example 2 shows that when no polyurethane sponge packing is set or the amount of polyurethane sponge packing is too small, the internal carbon source of the sludge is not fully released due to the low enrichment of functional bacteria, and the sludge reduction is not obvious; when the amount of polyurethane sponge packing is too large, the excessive enrichment of hydrolytic acidifying bacteria leads to the excessive release of internal carbon source by the sludge, and the COD concentration of the effluent increases.

[0080] (3) Comparing Example 1 and Example 4-5, it can be seen that when the current of the external DC power supply is too small, the extracellular electron flow is reduced, resulting in an insignificant improvement in community activity and a decrease in phosphorus removal effect; when the current of the external DC power supply is too large, cell stress causes apoptosis, leading to the death of functional bacteria and excessive sludge decomposition.

[0081] (4) Comparison of Example 1 and Comparative Example 1 shows that when a conventional side-flow reactor is used, the denitrification and phosphorus removal process is hindered due to insufficient carbon source, resulting in high total nitrogen and total phosphorus content in the effluent. In addition, the sludge reduction rate is limited.

[0082] Performance testing and mechanism

[0083] (I) Denitrification and phosphorus removal effect

[0084] To verify the nitrogen and phosphorus removal efficiency of wastewater under different carbon-nitrogen ratios, the device system and treatment method provided in Example 1 and Comparative Example 1 were used. The concentrations of nitrate nitrogen, total nitrogen, and total phosphorus in the effluent were measured by ion chromatography when the carbon-nitrogen ratio of the influent was 3.5 and 8, respectively, and the removal rates of total nitrogen, total phosphorus, and COD were calculated.

[0085] When the influent carbon-to-nitrogen ratio was 3.5, the ammonia nitrogen concentration was 52 mg / L, the total phosphorus concentration was 5.3 mg / L, and the COD concentration was 182 mg / L, the effluent nitrate nitrogen concentration in Example 1 was 7.8 mg / L, the total nitrogen concentration was 8.8 mg / L, the total phosphorus concentration was 0.2 mg / L, and the COD removal rate was 91.7%. In Comparative Example 1, the effluent nitrate nitrogen concentration was 16.7 mg / L, the total nitrogen concentration was 17.9 mg / L, the total phosphorus concentration was 3.9 mg / L, and the COD removal rate was 89.2%. Compared with Comparative Example 1, Example 1 reduced the nitrate nitrogen concentration in the effluent by 53.3%, and improved both the total nitrogen removal rate and the total phosphorus removal rate.

[0086] When the influent carbon-to-nitrogen ratio is 8 (sufficient carbon source), the ammonia nitrogen concentration is 50 mg / L, the total phosphorus concentration is 5 mg / L, and the COD concentration is 400 mg / L, the effluent nitrate nitrogen concentration in Example 1 is 3.8 mg / L, the total nitrogen concentration is 4.9 mg / L, the total phosphorus concentration is 0.11 mg / L, and the COD removal rate is 96.2%. In Comparative Example 1, the effluent nitrate nitrogen concentration is 10.7 mg / L, the total nitrogen concentration is 11.2 mg / L, the total phosphorus concentration is 1.6 mg / L, and the COD removal rate is 93.3%. Compared with Comparative Example 1, Example 1 reduces the nitrate nitrogen concentration in the effluent by 56.2%, and improves both the total nitrogen removal rate and the total phosphorus removal rate.

[0087] This indicates that when the C / N ratio of domestic sewage is ≥3.5, the addition of an electrochemical iron-driven low-carbon deep treatment device promotes deep nitrogen and phosphorus removal, compensates for the insufficient carbon source caused by low C / N ratio, avoids the addition of external carbon sources, and ensures significant removal of nitrogen, phosphorus, and organic matter under high C / N conditions, while ensuring that the total Fe concentration in the effluent is less than 2 mg / L, thus achieving low-carbon and efficient deep sewage treatment.

[0088] (II) In-situ sludge reduction effect

[0089] To verify the in-situ sludge reduction effect under different carbon-nitrogen ratios, the device system and treatment method provided in Example 1 and Comparative Example 1 were used. The sludge yield in the effluent of the side-flow reactor was measured by sludge growth and COD consumption when the carbon-nitrogen ratio of the influent was 3.5 and 8. The results are shown in Table 3.

[0090] Table 3

[0091]

[0092]

[0093] Table 3 shows that under low C / N conditions, the sludge reduction rate of Example 1 is 37.5% higher than that of Comparative Example 1; under high C / N conditions, the sludge reduction rate of Example 1 is 44.3% higher than that of Comparative Example 1. This indicates that the electrochemical iron-driven low-carbon deep treatment device promotes the in-situ sludge reduction process, resulting in a significant reduction in the amount of excess sludge.

[0094] (III) Enhancement of endogenous denitrification process

[0095] The sludge recirculation carried a certain amount of nitrate nitrogen and phosphate. To determine the effect of the iron electrode on the deep denitrification efficiency in the electrochemical reactor, the endogenous denitrification rate and the maximum accumulation concentrations of VFA and COD in the side-stream reactors of Example 1 and Comparative Example 1 were tested. The results are as follows: Figure 3 As shown.

[0096] Depend on Figure 3 It can be seen that the electrochemical reaction device in Example 1 has a significant denitrification effect, with an endogenous denitrification rate of 6.7 mgN / h, while that in Comparative Example 1 is only 0.5 mgN / h. Meanwhile, with the continuous accumulation of DOM released from the hydrolysis of particulate organic matter and the conversion of EPS (extracellular polymeric substances in sludge), the maximum accumulation concentrations of VFA and COD in Example 1 reach 12.3 mg / L and 22.1 mg / L, respectively. In contrast, the maximum accumulation concentrations of VFA and COD in Comparative Example 1 are only 2.6 mg / L and 9.1 mg / L, respectively.

[0097] Since heterotrophic bacteria favor VFAs produced through hydrolysis and fermentation, higher COD concentrations can provide more opportunities for VFA production, thereby improving the heterotrophic denitrification process. Furthermore, the iron electrode used in this invention not only improves heterotrophic denitrification by increasing the bioavailable COD yield, but also provides electrons for Fe(II)-based autotrophic denitrification.

[0098] (iv) Release and utilization of extracellular polymers

[0099] Activated sludge comprises four main components: active microorganisms, apoptotic microorganisms, microbial metabolites, and inorganic matter. In-situ sludge reduction caused by microbial metabolism primarily involves the reduction of organic components in the activated sludge. Extracellular polymers account for 50%–90% of the total organic content of the sludge; therefore, reducing the concentration of extracellular polymers can significantly decrease the sludge concentration, thereby reducing excess sludge production. Dissolved organic matter is the final form of insoluble organic matter after undergoing biochemical reactions such as hydrolysis.

[0100] To determine the effect of the electrochemical reaction device setup on the release and utilization of extracellular polymeric substances (EPS), the EPS concentrations in the side-flow reaction device and AAO device of Example 1 and Comparative Example 1 were tested. The results are as follows: Figure 4 As shown.

[0101] Depend on Figure 4 As can be seen, in Example 1, the electrochemical reactor successfully released EPS, reaching a concentration of 43.2 mg / gVSS. This EPS was fed back to the system as endogenous organic matter for endogenous denitrification. Furthermore, the released extracellular polymers were utilized by heterotrophic denitrifying bacteria within the AAO device, reducing the EPS concentration at the end of the AAO device to 19.2 mg / gVSS, thus enhancing sludge reduction. In contrast, in Comparative Example 1, the extracellular polymer concentration fluctuation was not significant, with only a 4.1 mg / gVSS concentration difference between the side-flow reactor and the AAO device. This demonstrates that the electrochemical reactor of this invention can enhance sludge reduction.

[0102] (V) Electron transport activity assessment

[0103] TTC-ETS (triphenyltetrazolium chloride dehydrogenase) can characterize the electron transfer activity within a device system, and thus be used to characterize the efficiency of redox (denitrification and phosphorus removal) reactions within the device system. Therefore, the TTC-ETS activity in the side-flow reactor and AAO device of Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 5 As shown.

[0104] Depend on Figure 5 It can be seen that the TTC-ETS value of the electrochemical reaction device in Example 1 can reach 38.5 μg / (mg·h), while the TTC-ETS value of the side-flow reaction device in Comparative Example 1 is only 11.4 μg / (mg·h), making Example 1 237.7% higher than Comparative Example 1. Furthermore, the TTC-ETS value of the AAO device in Example 1 can reach 47.7 μg / (mg·h), while the TTC-ETS value of the AAO device in the Comparative Example is only 24.5 μg / (mg·h). This indicates that the electrochemical reaction device (iron anode) is more likely to undergo biochemical reactions such as denitrification and phosphorus removal than the conventional side-flow process, and allows additional intracellular substances to be released extracellularly, promoting the degradation of more endogenous organic matter in the AAO device and maintaining its stronger biochemical activity.

[0105] (vi) Targeted regulation of microbial communities

[0106] To determine the directional regulation of the microbial community, the relative abundance of functional bacteria in the side-flow reactor and its packing material in Example 1 and Comparative Example 1 was tested. The results are as follows: Figure 6 As shown.

[0107] Depend on Figure 6 It can be seen that the relative abundance of functional bacteria in the electrochemical reaction device and its packing material in Example 1 is higher than that in Comparative Example 1.

[0108] The electrochemical reactor (iron anode) is a crucial factor in achieving deep denitrification and phosphorus removal coupled with in-situ sludge reduction. First, the transformation of complex organic matter within activated sludge cells is a primary process for effectively providing bioavailable carbon sources. Hydrolysis and fermentation convert macromolecular organic matter into simpler compounds and produce VFAs. Some bacteria, such as *Terrimonas* and *Thermomonas*, proliferate stably in the electrochemical reactor, promoting the production of soluble organic matter. Second, cultivating more denitrifying bacteria in the electrochemical reactor improves endogenous denitrification efficiency and COD release consumption rate. *Feruginibacter* is a dominant genus, with a higher content in the electrochemical reactor of Example 1 compared to the side-flow reactor in Comparative Example 1, supporting its metabolism of complex organic polymers (such as extracellular polymers) and nitrate nitrogen. Other heterotrophic denitrifying bacteria also expand their survival advantage with the introduction of the iron electrode and can fully utilize the released endogenous carbon source to achieve denitrification and MLSS reduction. Dechloromonas, an iron-based autotrophic denitrifying bacterium, saw a significant increase in its content within the electrochemical reactor to meet the demands of efficient iron electron absorption. Third, the response of specific bacteria to iron-rich electron conditions can stimulate the survival of other functional bacteria in nutrient-poor environments. Caldilinea, an autotrophic bacterium, provides nutrients to heterotrophic bacteria under nutrient-deficient conditions, maintaining their growth. When the denitrification process in the electrochemical reactor ends, Zoogloea can stimulate EPS production, further improving the survival environment of dominant heterotrophic bacteria. Chryseobacterium, with its low nutrient requirements, strong adaptability to environmental changes, and strong proteolytic activity, can hydrolyze EPS to provide nutrients for other heterotrophic bacteria. These bacteria actively regulate and improve the multi-bacterial symbiotic environment in the device system of Example 1, thereby further promoting the positive response of genes to Fe(II). Fourth, iron metabolism-related bacteria proliferate in large numbers within the electrochemical reactor and enhance electron transfer during the removal of organic matter and nitrogen. Geothrix can produce chelating agents that dissolve ferric iron solid precipitates and release electron shuttle compounds for microbial interactions on iron surfaces. It can also utilize nitrates and iron for respiration. Therefore, the microbial community exhibits positive changes in functional biomass, accelerates endogenous organic metabolism, and promotes the transfer of various electron donors to nitrate / nitrite reduction processes.

[0109] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A device system for wastewater nitrogen and phosphorus removal coupled with in-situ sludge reduction, characterized in that, The device system includes an electrochemical reaction device, an AAO device, and a precipitation tank; The AAO device includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. The anaerobic tank has an inlet on its side wall; the aerobic tank is connected to the sedimentation tank; and the sedimentation tank has an outlet on its side wall. The sludge outlet of the sedimentation tank is connected to the inlet of the electrochemical reaction device; the outlet of the electrochemical reaction device is connected to the sludge inlet of the anaerobic tank; the sludge outlet of the sedimentation tank is connected to two pipes, one pipe returns the sludge to the electrochemical reaction device, and the other pipe discharges the sludge. The electrochemical reaction device is a sealed reaction tank; a cathode and an anode are provided in the reaction tank, and the cathode and the anode are independently connected to a power source; the anode is an iron electrode; a first stirring device is provided in the reaction tank; and sponge packing is placed at the bottom of the reaction tank. The filling volume of the sponge filler is 25% to 35% of the volume of the electrochemical reaction device.

2. The device system according to claim 1, characterized in that, The cathode includes a graphite electrode.

3. The device system according to claim 1, characterized in that, The distance between the cathode and the anode is 4.5~5.5cm.

4. The device system according to claim 1, characterized in that, The sponge filler is made of polyurethane.

5. The device system according to claim 1, characterized in that, A second stirring device is installed inside the anaerobic tank.

6. The device system according to claim 1, characterized in that, A third stirring device is installed in the anoxic pool.

7. The device system according to claim 1, characterized in that, A nitrification liquid return pipeline connects the aerobic tank and the anoxic tank.

8. The device system according to claim 1, characterized in that, An aeration device is installed in the aerobic tank.

9. A wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction method, characterized in that, The processing method is performed using the apparatus system described in any one of claims 1-8, specifically including: Wastewater is continuously fed into the anaerobic tank, and then flows sequentially into the anoxic tank and the aerobic tank. The effluent from the aerobic tank undergoes sludge-water separation in the sedimentation tank. The separated water is discharged, while some of the separated sludge is returned to the electrochemical reactor through the sludge return pipe. Subsequently, under the action of DC power and stirring, the sludge undergoes an electrochemical reaction in the electrochemical reactor. Finally, the sludge after the electrochemical reaction flows into the anaerobic tank.

10. The processing method according to claim 9, characterized in that, The wastewater has a carbon-to-nitrogen ratio of ≥3.

5.

11. The processing method according to claim 9, characterized in that, The concentration of sludge in the electrochemical reactor is 6000~7000 mg / L.

12. The processing method according to claim 9, characterized in that, The hydraulic retention time in the anaerobic tank is 70-120 minutes.

13. The processing method according to claim 9, characterized in that, The hydraulic retention time in the anoxic pool is 160-200 min.

14. The processing method according to claim 9, characterized in that, The dissolved oxygen content in the aerobic tank is ≥4 mg / L.

15. The processing method according to claim 9, characterized in that, The hydraulic retention time of the aerobic tank is 7-9 hours.

16. The processing method according to claim 9, characterized in that, The nitrified liquid in the aerobic tank is returned to the anoxic tank through the nitrified liquid return pipe.

17. The processing method according to claim 9, characterized in that, The nitrification liquor recirculation ratio of the aerobic tank is 220% to 280% of the influent flow rate.

18. The processing method according to claim 9, characterized in that, The mud-water separation time is 1-4 hours.

19. The processing method according to claim 9, characterized in that, The sludge return ratio of the sedimentation tank is 70% to 90% of the influent flow rate.

20. The processing method according to claim 9, characterized in that, The DC power supply has a current of 3~8mA.

21. The processing method according to claim 9, characterized in that, The stirring speed is 150~250 rpm.

22. The processing method according to claim 9, characterized in that, In the electrochemical reaction, the iron electrode simultaneously undergoes autotrophic denitrification and endogenous heterotrophic denitrification.

23. The processing method according to claim 9, characterized in that, The electrochemical reaction takes 160-200 minutes.

Images