Sewage nitrogen and phosphorus removal coupled in-situ sludge reduction device system and treatment method

Abstract

The invention provides a sewage nitrogen and phosphorus removal coupled in-situ sludge reduction device system and a treatment method. The device system comprises an electrochemical reaction device, an AAO device and a sedimentation tank, the AAO device comprises an anaerobic tank, an anoxic tank and an aerobic tank which are connected in sequence; the aerobic tank is connected with the sedimentation tank; a sludge outlet of the sedimentation tank is connected with an inlet of the electrochemical reaction device; an outlet of the electrochemical reaction device is connected with a sludge inlet of the anaerobic tank; the electrochemical reaction device is a sealed reaction tank; a cathode and an anode are arranged in the reaction tank, and the cathode and the anode are respectively and independently connected with a power supply; the anode is an iron electrode; a first stirring device is arranged in the reaction tank; a sponge filler is placed at the bottom of the reaction tank. By additionally arranging the iron anode electrochemical reaction device, the nitrogen and phosphorus removal efficiency in a traditional biochemical treatment unit for sewage treatment is improved, in-situ sludge reduction is realized, and the demand quantity of an exogenous carbon source is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage biological treatment, and relates to a sewage denitrification and dephosphorization coupled with in-situ sludge reduction device system and a treatment method. Background Art

[0002] At present, biological treatment has been widely used in wastewater denitrification, and heterotrophic denitrification process is the most common and is used by most sewage treatment plants. Carbon source plays a vital role in the common heterotrophic denitrification process. Although sufficient carbon source is conducive to denitrification reaction, the output of residual sludge is huge; and carbon limitation (C / N<6) may cause the total nitrogen (TN) removal efficiency of the biological nutrient removal process to be less than 50%.

[0003] Actual sewage in developing countries usually has the characteristic of C / N less than 5. Therefore, in the face of strict effluent standards, in order to meet the denitrification efficiency, adding carbon sources is the first choice, but in the process, pollution transfer is inevitable. Although the addition of organic carbon sources can ensure that there is enough organic matter as an electron donor that can be continuously and stably provided, the significant increase in excess sludge on the basis of sufficient anabolism highly affects the goal of economically friendly wastewater treatment, and its treatment and disposal expenses account for more than 50% of the total operating cost of sewage treatment plants. This problem is exacerbated with the increase of influent nitrogen content. Therefore, it is necessary to explore a method to maintain a balance between improving nitrogen removal rate and reducing excess sludge.

[0004] Prior art shows that inserting a oligotrophic anaerobic reactor (side stream reaction device) into the sludge return line of a traditional activated sludge system is conducive to lysis-hidden growth, thereby achieving a promising and cost-effective sludge reduction method. Intracellular organic matter is released into the extracellular space through biomass lysis, and particulate organic matter is hydrolyzed into soluble organic matter (DOM), which helps hidden growth, realizes sludge resource utilization, and reduces the amount of excess sludge. However, the above method has limited improvement in nitrogen and phosphorus removal, long hydraulic retention time, large device footprint, and limited sludge reduction rate.

[0005] In summary, it is an urgent problem to be solved by technical personnel in this field to provide a device system and treatment method for sewage nitrogen and phosphorus removal coupled with in-situ sludge reduction, which has low external carbon source input, small equipment footprint, and simple operation. Summary of the invention

[0006] The purpose of the present invention is to provide a device system and treatment method for sewage 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 sewage treatment can be effectively improved, in-situ sludge reduction can be achieved (reducing the residual sludge yield), and the demand for exogenous carbon sources can be reduced, with low cost and low equipment and operation requirements.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a device system for wastewater nitrogen 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 comprises an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence;

[0010] The side wall of the anaerobic tank is provided with a water inlet; the aerobic tank is connected to the sedimentation tank; the side wall of the sedimentation tank is provided with a water outlet;

[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 pool; a cathode and an anode are arranged in the reaction pool, and the cathode and the anode are independently connected to a power source respectively; the anode is an iron electrode; a first stirring device is arranged in the reaction pool; a sponge filler is placed at the bottom of the reaction pool.

[0013] In the present invention, the electrochemical reaction device is a lateral flow reaction device.

[0014] The device system provided by the present invention can avoid the addition of exogenous organic carbon source in the case of low carbon-nitrogen ratio sewage by adding an electrochemical reaction device (electrochemical iron-driven low-carbon deep treatment device) at the side stream of the AAO device, thereby significantly improving the nitrogen removal and phosphorus removal efficiency of the device system, and coordinating the efficient in-situ sludge reduction process in the mainstream area (AAO device) to realize a low-carbon sewage treatment process.

[0015] It is worth noting that by adding an electrochemical reaction device at the side stream of the AAO device, and its anode is an iron electrode, the electrochemical iron-driven low-carbon deep treatment device promotes the stable proliferation of characteristic functional bacteria, while promoting the release of endogenous carbon sources in the sludge, achieving enhanced endogenous denitrification, and enhancing the biodegradation of extracellular polymers, thereby achieving the reduction of organic components in the sludge; and the dynamic oxidation and reduction of iron occurs in the electrochemical reaction device, which promotes the microbial electron transfer process, not only realizing the autotrophic denitrification process of iron autotrophic bacteria, but also accelerating the degradation and utilization of organic matter, and giving the electrochemical reaction device and the mainstream area phosphate co-precipitation, so that deep denitrification and phosphorus removal and synergistic sludge reduction can be achieved.

[0016] As a preferred technical solution of the present invention, the cathode includes a graphite electrode.

[0017] Preferably, the distance between the cathode and the anode is 4.5-5.5 cm, for example, 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 numerical range are also applicable.

[0018] As a preferred technical solution of the present invention, the material of the sponge filler includes 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 numerical range are also applicable.

[0020] As a preferred technical solution 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 tank.

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

[0023] Preferably, an aeration device is provided in the aerobic tank.

[0024] Preferably, the sludge outlet of the sedimentation tank is connected to two pipelines, one pipeline is for returning to the electrochemical reaction device, and the other pipeline is for external discharge.

[0025] In a second aspect, the present invention provides a treatment method for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction, the treatment method being carried out using the device system described in the first aspect, and specifically comprising:

[0026] The sewage is continuously passed into the anaerobic tank, and then flows into the anoxic tank and the aerobic tank in turn. The effluent from the aerobic tank is then separated into mud and water in the sedimentation tank, and the separated water is discharged. Part of the separated sludge is returned to the electrochemical reaction device through the sludge return pipe, and then an electrochemical reaction is carried out in the electrochemical reaction device under the action of a DC power supply and stirring. Finally, the sludge after the electrochemical reaction flows into the anaerobic tank.

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

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

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

[0030] Preferably, the concentration of the sludge in the electrochemical reaction device 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, but is not limited to the listed values, and other values ​​within the numerical 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 min, for example, it can be 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min or 115 min, but is not limited to the listed values, and other values ​​within the numerical range are also applicable.

[0032] Preferably, the hydraulic retention time of the anoxic tank 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, but is not limited to the listed values, and other values ​​within the numerical range are also applicable.

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

[0034] Preferably, the hydraulic retention time of the aerobic pool 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, and other values ​​within the numerical range are also applicable.

[0035] Preferably, the nitrification liquid in the aerobic tank flows back to the anoxic tank through the nitrification liquid reflux pipe.

[0036] Preferably, the nitrification liquid reflux ratio of the aerobic pool is 220% to 280% of the water inlet flow rate, for example, it can be 225%, 230%, 235%, 240%, 245%, 250%, 255%, 260% or 270%, but is not limited to the listed values, and other values ​​within the numerical range are equally 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, and other values ​​within the numerical range are also applicable.

[0038] Preferably, the sludge return ratio of the sedimentation tank is 70% to 90% of the inlet 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 numerical 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, but is not limited to the listed values, and other values ​​within the numerical range are also applicable.

[0040] Preferably, the stirring speed is 150-250 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, and other values ​​within the numerical 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 nitrate and nitrite through the iron autotrophic process, and the presence of phosphate causes Fe(II) and Fe(III) to chemically precipitate with it. Fe(III) accounts for the majority of the precipitation, that is, Fe(II) is oxidized to Fe(III) through the denitrification reaction and co-precipitates with phosphate, achieving the enhancement of the simultaneous denitrification and phosphorus removal process. In addition, the reduction of Fe(III) also occurs in the electrochemical reaction device. As Fe(III) accumulates, this electron acceptor participates in the reduction of organic matter under the active performance of iron-reducing bacteria, promoting the release and transformation of endogenous organic matter in the system, such as the production of volatile fatty acids (VFA). The increase in soluble organic matter can in turn stimulate microorganisms to reduce Fe(III) to Fe(II), and Fe(II) can further reduce and transform organic matter and nitrate nitrogen. Through the dynamic cycle between Fe(II) and Fe(III), the electron shuttle in the carbon and nitrogen metabolism of microorganisms is further stimulated, and favorable conditions are created for enzyme metabolism, accelerating electron transfer.

[0047] Preferably, the electrochemical reaction time is 160 to 200 min, for example, 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 numerical 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 stream of the AAO device, and its anode is an iron electrode, the addition of an exogenous organic carbon source can be avoided in the case of low carbon-nitrogen ratio sewage, and the nitrogen removal and phosphorus removal efficiency of the device system can be greatly improved, and the efficient in-situ sludge reduction process in the mainstream area is coordinated to achieve a low-carbon sewage treatment process;

[0050] (2) The device system provided by the present invention promotes the stable proliferation of characteristic functional bacteria, 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 redox 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 the electrochemical reaction device with the co-precipitation of phosphate in the mainstream area, so that deep denitrification and phosphorus removal and sludge reduction can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1A schematic diagram of the structure of the device system for wastewater nitrogen and phosphorus removal coupled with in-situ sludge reduction provided in Example 1;

[0052] Figure 2 A schematic diagram of the structure of the electrochemical reaction device 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 filler, 55-inlet, 56-outlet;

[0054] Figure 3 The result diagram of the endogenous denitrification rate of the side stream reaction device and the maximum accumulation concentration of VFA and COD in Example 1 and Comparative Example 1;

[0055] Figure 4 The EPS concentration results in the side stream reaction device and the AAO device in Example 1 and Comparative Example 1 are shown;

[0056] Figure 5 The results of TTC-ETS activity in the lateral flow reaction device and the AAO device in Example 1 and Comparative Example 1 are shown;

[0057] Figure 6 Graph showing the relative abundance of functional bacteria in the lateral flow reaction device and its filler in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0058] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0059] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only 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 shall be subject to the claims.

[0060] In the following examples and comparative examples, before the device system is started, a certain amount of sludge from a municipal sewage treatment plant is inoculated into the electrochemical reaction device; when the device system is started, no sludge is inoculated. The sewage in the following examples and comparative examples is simulated domestic sewage, with sodium acetate, glucose, and peptone as composite carbon sources, and ammonium chloride and potassium dihydrogen phosphate as simulated domestic sewage N and P pollutants. The concentration of ammonia nitrogen in the simulated domestic sewage is 50 mg / L, the concentration of total phosphorus is 5 mg / L, and the concentration of COD is 175 mg / L. The concentrations in the following examples and comparative examples are all mass concentrations.

[0061] Example 1

[0062] This embodiment provides a device system and a treatment method for wastewater nitrogen 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 comprises an anaerobic tank 1, an anoxic tank 2, and an aerobic tank 3 which are connected in sequence; a water 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 reflux pipeline is connected between the aerobic tank 3 and the anoxic tank 2; an aeration device 8 is provided in the aerobic tank 3;

[0064] The aerobic tank 3 is connected to the sedimentation tank 4; a water outlet is provided on the side wall of the sedimentation tank 4; the sludge outlet of the sedimentation tank 4 is connected to two pipes, one pipe is returned to the electrochemical reaction device 5, and the other pipe is discharged outside;

[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 stream reaction device; the electrochemical reaction device 5 (such as Figure 2 ) is a sealed reaction pool 53; a cathode and an anode are arranged in the reaction pool, and the cathode and the anode are independently connected to a DC power supply 51; the anode is an iron electrode; the cathode is a graphite electrode; the size of the anode is 8cm×4cm×0.2cm (height×width×thickness), and the distance between the cathode and the anode is 5cm; a first stirring device 52 is arranged in the reaction pool; a sponge filler 54 is placed at the bottom of the reaction pool; the material of the sponge filler 54 is polyurethane; the filling volume of the sponge filler 54 is 30% of the volume of the electrochemical reaction device;

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

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

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

[0069] The parameters such as the setting of the lateral flow reaction device, the setting of the filler, the filling volume of the filler and the current of the DC power supply were changed, as shown in Table 1. The other conditions were the same as those in Example 1.

[0070] Table 1

[0071]

[0072] Wherein, “ / ” indicates that the corresponding parameters are not set, and the conventional lateral flow reaction device in Comparative Example 1 can refer to the lateral flow reaction zone setting provided in CN111977793A;

[0073] When the carbon-nitrogen ratio of the simulated domestic sewage is 3.5, the device system and treatment method provided in the above embodiment and the comparative example are continuously operated for 70 days, and the mass concentrations of total nitrogen, total phosphorus and COD in the effluent are measured by ion chromatography, and the sludge growth and COD consumption are used to measure the sludge yield in the effluent of the side stream reaction device. The results are shown in Table 2.

[0074] Table 2

[0075]

[0076]

[0077] From Table 2, we can see that:

[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, achieve in-situ sludge reduction, and reduce the demand for exogenous carbon sources;

[0079] (2) By comparing Example 1 with Examples 2-3 and Comparative Example 2, it can be seen that when no polyurethane sponge filler is provided or the amount of the polyurethane sponge filler is too little, 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 the polyurethane sponge filler is too much, the endogenous carbon source released by the sludge is too much due to the enrichment of excessive hydrolytic acidifying bacteria, and the effluent COD concentration increases;

[0080] (3) From the comparison between Example 1 and Examples 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 effect on the improvement of the community activity and a reduced phosphorus removal effect; when the current of the external DC power supply is too large, apoptosis occurs due to cell stress, resulting in the death of functional bacteria and excessive sludge lysis;

[0081] (4) By comparing Example 1 with Comparative Example 1, it can be seen that when a conventional side stream reaction device is used, the denitrification and phosphorus removal process is hindered due to insufficient carbon source, the total nitrogen and total phosphorus content in the effluent is high, and the sludge reduction rate is limited.

[0082] Performance test and mechanism

[0083] (I) Nitrogen removal and phosphorus removal effect

[0084] In order to verify the denitrification and phosphorus removal effects of sewage under different carbon-nitrogen ratios, the device system and treatment method provided in the above-mentioned Example 1 and Comparative Example 1 were used, and the concentrations of nitrate nitrogen, total nitrogen and total phosphorus in the effluent when the carbon-nitrogen ratio of the inlet water was 3.5 and 8, respectively, were determined by ion chromatograph, and the removal rates of total nitrogen, total phosphorus and COD were calculated.

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

[0086] When the carbon-nitrogen ratio of the influent 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 nitrate nitrogen concentration of the effluent in Example 1 is 3.8 mg / L, the total nitrogen concentration is 4.9 mg / L, the total phosphorus concentration of the effluent is 0.11 mg / L, and the COD removal rate is 96.2%; the nitrate nitrogen concentration of the effluent in Comparative Example 1 is 10.7 mg / L, the total nitrogen concentration is 11.2 mg / L, the total phosphorus concentration of the effluent is 1.6 mg / L, and the COD removal rate is 93.3%; the nitrate nitrogen concentration of the effluent in Example 1 is reduced by 56.2% compared with Comparative Example 1, and the total nitrogen removal rate and the total phosphorus removal rate are both improved.

[0087] This shows that when the C / N of domestic sewage is ≥3.5, the addition of an electrochemical iron-driven low-carbon deep treatment device can promote deep nitrogen and phosphorus removal, compensate for the lack of carbon source at low C / N and cause the nitrogen and phosphorus removal process to be blocked and avoid the addition of exogenous carbon source. At the same time, it can ensure the substantial removal of nitrogen, phosphorus and organic matter under high C / N conditions, and ensure that the total Fe concentration in the effluent is less than 2 mg / L, achieving low-carbon and high-efficiency deep sewage treatment.

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

[0089] In order to verify the in-situ sludge reduction effect under different carbon-nitrogen ratios, the device system and treatment method provided in the above-mentioned Example 1 and Comparative Example 1 were used. The sludge growth rate and COD consumption were used to determine the sludge yield in the effluent water of the side stream reaction device when the carbon-nitrogen ratio of the inlet water was 3.5 and 8. The results are shown in Table 3.

[0090] Table 3

[0091]

[0092]

[0093] It can be seen from Table 3 that under low C / N conditions, the sludge reduction rate of Example 1 is increased by 37.5% compared with that of Comparative Example 1; under high C / N conditions, the sludge reduction rate of Example 1 is increased by 44.3% compared with that of Comparative Example 1. This shows that the electrochemical iron-driven low-carbon deep treatment device promotes the in-situ sludge reduction process, which greatly reduces the excess sludge production.

[0094] 3. Strengthening of endogenous denitrification process

[0095] The sludge return carries a certain amount of nitrate nitrogen and phosphate. In order to determine the effect of the iron electrode on the deep denitrification efficiency in the electrochemical reaction device, the endogenous denitrification rate and the maximum accumulation concentration of VFA and COD in the side stream reaction device in Example 1 and Comparative Example 1 were tested respectively. The results are as follows: Figure 3 shown.

[0096] Depend on Figure 3 It can be seen that the denitrification effect of the electrochemical reaction device in Example 1 is obvious, and its endogenous denitrification rate is 6.7 mgN / h, while that of Comparative Example 1 is only 0.5 mgN / h. At the same time, with the continuous accumulation of DOM released by the hydrolysis of particulate organic matter and the conversion of EPS (sludge extracellular polymers), the maximum accumulation concentrations of VFA and COD in Example 1 reached 12.3 mg / L and 22.1 mg / L respectively. The maximum accumulation concentrations of VFA and COD in Comparative Example 1 were only 2.6 mg / L and 9.1 mg / L.

[0097] Since the VFA favored by heterotrophic bacteria are produced by hydrolysis and fermentation, a higher COD concentration can provide more opportunities for the production of VFA, thereby improving the heterotrophic denitrification process. In addition, the iron electrode used in the present invention not only improves heterotrophic denitrification by increasing the bio-effective COD yield, but also provides electrons for Fe(II)-based autotrophic denitrification.

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

[0099] Activated sludge includes four major components, namely active microorganisms, apoptotic microorganisms, microbial metabolites, and inorganic matter. The in-situ sludge reduction caused by microbial biological metabolism is mainly the attenuation of organic components in activated sludge, among which the organic content of extracellular polymers accounts for 50% to 90% of the total organic content of sludge. Therefore, the attenuation of extracellular polymer concentration can significantly weaken the sludge concentration, thereby reducing the excess sludge production. Soluble organic matter is the final form of insoluble organic matter after biochemical reactions such as hydrolysis.

[0100] In order to determine the effect of the setting of the electrochemical reaction device on the release and utilization of extracellular polymers, the EPS concentrations in the lateral flow reaction device and the AAO device in Example 1 and Comparative Example 1 were tested. The results are as follows: Figure 4 shown.

[0101] Depend on Figure 4 It can be seen that the electrochemical reaction device in Example 1 successfully releases EPS, and its concentration reaches 43.2 mg / gVSS, and is fed back to the device system in the form of endogenous organic matter for endogenous denitrification, and the released extracellular polymers are used by heterotrophic denitrifying bacteria in the AAO device, so that the EPS concentration at the end of the AAO device is reduced to 19.2 mg / gVSS, achieving enhanced sludge reduction. In Comparative Example 1, the fluctuation of extracellular polymers is not obvious, and there is only a concentration difference fluctuation of 4.1 mg / gVSS between the side flow reaction device and the AAO device. This shows that the electrochemical reaction device set in the present invention can enhance sludge reduction.

[0102] (V) Evaluation of electron transfer activity

[0103] TTC-ETS (chlorotriphenyltetrazolium dehydrogenase) can characterize the electron transfer activity in the device system, and further be used to characterize the redox (denitrification and phosphorus removal) reaction efficiency in the device system. Therefore, the TTC-ETS activity in the side stream reaction device and the AAO device in Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 5 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 38.5μg / (mg·h), while the TTC-ETS value of the lateral flow reaction device in Comparative Example 1 is only 11.4μg / (mg·h), and Example 1 is 237.7% higher than Comparative Example 1. In addition, the TTC-ETS value of the AAO device in Example 1 can reach 47.7μg / (mg·h), while the TTC-ETS value of the AAO device in the comparative example is only 24.5μg / (mg·h). This shows that the electrochemical reaction device (iron anode) is more likely to undergo biochemical reactions such as denitrification and dephosphorization than the conventional lateral flow process, and allows additional intracellular substances to be released outside the cell, promoting the degradation of more endogenous organic matter in the AAO device, so that it maintains stronger biochemical activity.

[0105] 6. Targeted regulation of microbial communities

[0106] In order to determine the directional regulation of the microbial community, the relative abundance of functional bacteria in the lateral flow reaction device and its filler in Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 6 shown.

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

[0108] The electrochemical reaction device (iron anode) is an important reason for achieving deep denitrification and phosphorus removal coupled with in-situ sludge reduction. First, the conversion of complex organic matter in activated sludge cells is the main process for effectively providing biologically available carbon sources. Hydrolysis and fermentation convert macromolecular organic matter into simple compounds and produce VFAs. Some bacteria, such as Terrimonas and Thermomonas, stably proliferate in electrochemical reaction devices and can promote the production of soluble organic matter. Second, culturing more denitrifying bacteria in electrochemical reaction devices improves endogenous denitrification efficiency and COD release and consumption rate. Ferruginibacter is the dominant genus among them. Compared with the lateral flow reaction device in Comparative Example 1, the content in the electrochemical reaction device in Example 1 is higher, which supports its role in metabolizing complex organic polymers (such as extracellular polymers) and nitrate nitrogen. Other heterotrophic denitrifying bacteria also expand their survival advantages in the equipment with the introduction of iron electrodes, and can make full use of the released endogenous carbon source to achieve denitrification and MLSS reduction. Dechloromonas (Deoxymonas) is an iron-based autotrophic denitrifying bacteria, and its content in the electrochemical reaction device is greatly increased to meet the efficient reception of iron electrons. Third, the response of specific bacteria to iron-rich electron conditions can stimulate other functional bacteria to survive in a poor nutrient environment. Caldilinea (Warm Rope Bacteria) is an autotrophic bacterium that provides nutrition for heterotrophic bacteria under conditions of nutrient deficiency to maintain its growth. When the denitrification process in the electrochemical reaction device ends, Zoogloea (Mobilinium) can stimulate the production of EPS and further improve the living environment of dominant heterotrophic bacteria. Chryseobacterium (Golden Bacillus) has low nutritional requirements, strong adaptability to environmental changes, strong proteolytic activity, and can hydrolyze EPS to provide nutrition for other heterotrophic bacteria. These bacteria actively regulate and improve the multi-bacteria symbiotic environment in the device system of Example 1, thereby further promoting the positive response function of genes to Fe (II). Fourth, bacteria related to iron metabolism multiply in the electrochemical reaction device and enhance electron transfer during the removal of organic matter and nitrogen. Geothrix can produce chelating agents that can dissolve ferric iron solid precipitates and release electron shuttle compounds for microbial interaction on iron surfaces and can also use nitrate and iron substances for respiration. As a result, the microbial community showed positive changes in the corresponding functional biomass, accelerated endogenous organic metabolism, and promoted the transfer of multiple electron donors to nitrate / nitrite reduction processes.

[0109] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition 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 sedimentation tank; The AAO device comprises an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence; The side wall of the anaerobic tank is provided with a water inlet; the aerobic tank is connected to the sedimentation tank; the side wall of the sedimentation tank is provided with a water outlet; 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 electrochemical reaction device is a sealed reaction pool; a cathode and an anode are arranged in the reaction pool, and the cathode and the anode are independently connected to a power source respectively; the anode is an iron electrode; a first stirring device is arranged in the reaction pool; a sponge filler is placed at the bottom of the reaction pool.

2. The device system according to claim 1, characterized in that: The cathode comprises a graphite electrode; Preferably, the distance between the cathode and the anode is 4.5-5.5 cm.

3. The device system according to claim 1 or 2, characterized in that: The material of the sponge filler includes polyurethane; Preferably, the filling volume of the sponge filler is 25% to 35% of the volume of the electrochemical reaction device.

4. The device system according to any one of claims 1 to 3, characterized in that: A second stirring device is provided in the anaerobic tank; Preferably, a third stirring device is provided in the anoxic tank; Preferably, a nitrification liquid reflux pipeline is connected between the aerobic tank and the anoxic tank; Preferably, an aeration device is provided in the aerobic tank; Preferably, the sludge outlet of the sedimentation tank is connected to two pipelines, one pipeline is for returning to the electrochemical reaction device, and the other pipeline is for external discharge.

5. A treatment method for wastewater denitrification and phosphorus removal coupled with in-situ sludge reduction, characterized in that: The treatment method is carried out using the device system according to any one of claims 1 to 4, and specifically comprises: The sewage is continuously passed into the anaerobic tank, and then flows into the anoxic tank and the aerobic tank in turn. The effluent from the aerobic tank is then separated into mud and water in the sedimentation tank, and the separated water is discharged. Part of the separated sludge is returned to the electrochemical reaction device through the sludge return pipe, and then an electrochemical reaction is carried out in the electrochemical reaction device under the action of a DC power supply and stirring. Finally, the sludge after the electrochemical reaction flows into the anaerobic tank.

6. The processing method according to claim 5, characterized in that: The carbon-nitrogen ratio of the sewage is ≥3.5; Preferably, the concentration of sludge in the electrochemical reaction device is 6000-7000 mg / L.

7. The processing method according to claim 5 or 6, characterized in that: The hydraulic retention time of the anaerobic tank is 70 to 120 minutes; Preferably, the hydraulic retention time of the anoxic tank is 160 to 200 minutes.

8. The processing method according to any one of claims 5 to 7, characterized in that: The dissolved oxygen content in the aerobic pool is ≥4 mg / L; Preferably, the hydraulic retention time of the aerobic pool is 7 to 9 hours; Preferably, the nitrification liquid in the aerobic tank flows back to the anoxic tank through the nitrification liquid reflux pipe; Preferably, the nitrification liquid reflux ratio of the aerobic pool is 220% to 280% of the inlet water flow rate.

9. The processing method according to any one of claims 5 to 8, characterized in that: The time for mud-water separation is 1 to 4 hours; Preferably, the sludge return ratio of the sedimentation tank is 70% to 90% of the inlet water flow rate.

10. The processing method according to any one of claims 5 to 9, characterized in that: The current of the DC power supply is 3-8 mA; Preferably, the stirring speed is 150 to 250 rpm; Preferably, in the electrochemical reaction, the iron electrode simultaneously performs autotrophic denitrification and endogenous heterotrophic denitrification; Preferably, the electrochemical reaction time is 160 to 200 minutes.

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