Anaerobic-aerobic multi-cycle treatment system and method for fresh landfill leachate

Abstract

The application discloses a fresh garbage leachate anaerobic-AOAO multi-cycle treatment system, which comprises a regulating tank, a primary settling tank, an intermediate tank, an anaerobic reactor, a circulating tank, an intermediate sedimentation tank, a first-stage anoxic tank, a first-stage aerobic tank, a second-stage anoxic tank, a second-stage aerobic tank and a secondary settling tank which are sequentially connected in communication, the intermediate tank is connected in communication with the anaerobic reactor and the first-stage anoxic tank through a liquid inlet pipe and a bypass pipe respectively, the first-stage anoxic tank, the first-stage aerobic tank, the second-stage anoxic tank and the second-stage aerobic tank are connected in a head-to-tail mode, the tail end of the first-stage aerobic tank is connected to the first-stage anoxic tank through a pipeline, the bottom of the secondary settling tank is connected to the intermediate sedimentation tank and the first-stage anoxic tank through pipelines respectively, and the water outlet of the secondary settling tank is connected in communication with the regulating tank. The application further discloses a fresh garbage leachate anaerobic-AOAO multi-cycle treatment method, and solves the problem that the existing method is difficult to remove dissolved microbial products, reduces the inhibition of ammonia nitrogen to microorganisms to below the inhibitory concentration, and thus improves the activity of sludge and the pollutant removal rate.

Description

Technical Field

[0001] This invention belongs to the technical field of organic wastewater treatment methods, specifically relating to an anaerobic-AOAO multi-cycle treatment system for fresh landfill leachate, and also to a method for anaerobic-AOAO multi-cycle treatment of fresh landfill leachate. Background Technology

[0002] Further removal of residual organic matter (EfOM) from the effluent of biologically treated organic wastewater is crucial for improving treatment efficiency. Studies have shown that EfOM is primarily composed of soluble microbial products (SMPs) generated during the treatment process, which cannot be effectively degraded using traditional methods. Due to the extremely high concentration of SMPs in fresh leachate, and because the amount of SMPs produced is positively correlated with the concentration of the original wastewater, the concentration of SMPs in the fresh leachate effluent is very high, severely impacting effluent quality. Some studies suggest that traditional wastewater treatment methods are insufficient to remove SMPs, requiring additional treatment to further reduce them. Simultaneously, fresh leachate has a high ammonia nitrogen concentration, necessitating efficient denitrification and COD removal simultaneously to meet treatment standards. Currently, the mainstream method for treating fresh leachate follows the landfill leachate technology, which mostly adopts coagulation and treatment-anaerobic-aerobic-anoxic biological treatment plus advanced oxidation and microfiltration plus nanofiltration plus reverse osmosis. However, the concentrated liquid produced after nanofiltration (NF) and (RO) methods, which accounts for about 35-45% of the original wastewater volume, contains high concentrations of salinity and recalcitrant organic matter. It cannot be returned to the system for treatment, and there is no economically reasonable treatment and disposal technology available.

[0003] The aforementioned "fresh leachate" refers to leachate from municipal solid waste incineration power plants and municipal solid waste transfer stations, and its properties are different from those of leachate from landfills. Summary of the Invention

[0004] The first objective of this invention is to provide an anaerobic-AOAO multi-cycle biological treatment system for fresh landfill leachate, which solves the problem that existing wastewater treatment methods are unable to remove microbial products.

[0005] The second objective of this invention is to provide an anaerobic-AOAO multi-cycle biological treatment method for fresh landfill leachate, which significantly reduces the concentration of organic matter in the effluent, overcomes the excessive reliance on membrane methods in traditional technologies, and lays the foundation for reducing costs and overcoming the problem of concentrated liquid retained by membranes.

[0006] The first technical solution adopted in this invention is: a fresh landfill leachate anaerobic-AOAO multi-cycle treatment system, comprising an equalization tank, a primary sedimentation tank, an intermediate tank, an anaerobic reactor, an external circulation tank, an intermediate sedimentation tank, a primary anoxic tank, a primary aerobic tank, a secondary anoxic tank, a secondary aerobic tank, and a secondary sedimentation tank connected in sequence. The intermediate tank is connected to the anaerobic reactor and the primary anoxic tank through an inlet pipe and a bypass pipe, respectively. The primary anoxic tank, the primary aerobic tank, the secondary anoxic tank, and the secondary aerobic tank are connected end to end. The end of the primary aerobic tank is connected to the primary anoxic tank through a pipe. The bottom of the secondary sedimentation tank is connected to the intermediate sedimentation tank and the primary anoxic tank through pipes, respectively. The outlet of the secondary sedimentation tank is connected to the equalization tank.

[0007] The first technical solution adopted in this invention is further characterized by:

[0008] Agitators are installed in the primary and secondary anoxic tanks, and aeration devices are installed in the primary and secondary aerobic tanks. The volume ratio of the primary anoxic tank to the primary aerobic tank to the secondary anoxic tank to the secondary aerobic tank is 30:50~53:8~12:8~10.

[0009] The second technical solution adopted in this invention is: an anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate, specifically implemented according to the following steps:

[0010] Step 1: The original leachate flow rate Q1 is mixed with the effluent return flow rate Q2 from the secondary sedimentation tank in the equalization tank;

[0011] Step 2: The mixed leachate is pumped into the primary sedimentation tank, where most of the suspended solids are removed by sedimentation, and then it enters the intermediate tank.

[0012] Step 3: Pump the leachate in the intermediate tank into the anaerobic reactor and directly into the primary anoxic tank through the bypass pipe. The flow rate into the anaerobic reactor is Q3, and the flow rate into the primary anoxic tank is Q4.

[0013] Step 4: The effluent from the anaerobic reactor enters the external circulation tank, and a portion of it returns to the anaerobic reactor from the bottom of the external circulation tank. The flow rate of this portion is Q5.

[0014] Step 5: The overflow water from the top of the external circulation tank and a portion of the remaining sludge R2 from the secondary sedimentation tank are mixed in the pipeline and then enter the intermediate sedimentation tank.

[0015] Step 6: The effluent from the intermediate sedimentation tank enters the primary anoxic tank, and then passes through the primary anoxic tank, primary aerobic tank, secondary anoxic tank, and secondary aerobic tank that are connected end to end in sequence.

[0016] At the end of the primary aerobic tank, the mud-water mixture containing nitrate nitrogen, i.e., the nitrified liquid, is returned to the primary anoxic tank. The nitrified liquid return flow rate is Q6.

[0017] Step 7: The sludge-water mixture after two stages of anoxic and aerobic treatment is separated in the secondary sedimentation tank. A portion of the residual sludge R2 from the lower sedimentation tank is returned to the intermediate sedimentation tank, where it mixes with the incoming water and settles before being discharged as residual sludge. Another portion of the sludge R1 from the secondary sedimentation tank is returned to the primary anoxic tank to maintain the sludge concentration required by the AOAO system. The flow rate Q3+Q4 of the sludge R1 returned from the secondary sedimentation tank and the flow rate Q3+Q4 entering the primary anoxic tank is called the sludge return ratio, which is 1. A portion of the supernatant from the secondary sedimentation tank is returned to the equalization tank according to the effluent return ratio Q2 / Q1 to mix with and dilute the original leachate. The remaining supernatant from the secondary sedimentation tank overflows and becomes the treated effluent of this system, with an effluent flow rate of Q7.

[0018] The second technical solution adopted in this invention is further characterized by:

[0019] The ratio of the flow rate of the effluent recirculated to that of the original leachate in step 1 is called the effluent recirculation ratio, i.e., Q2 / Q1, and the effluent recirculation ratio is 5-7.

[0020] In step 3, the flow rate Q3 pumped into the anaerobic reactor and the wastewater Q4 directly entering the primary anoxic tank through the bypass pipe are allocated in the ratio Q3:Q4 = 7-8:2-3.

[0021] In step 4, a portion of the effluent from the external circulation tank enters the anaerobic reactor from the bottom via a circulation pump, increasing the upflow velocity. This portion of the effluent, Q5, is used to maintain the expansion state of the sludge bed in the anaerobic reactor. Its size depends on the type of anaerobic reactor and can be calculated using formula (1):

[0022]

[0023] Where U refers to the upward flow velocity of the liquid in the empty tower within the reactor, in m / h; and A is the horizontal cross-sectional area of ​​the anaerobic reactor, in m². 2 The units for Q3 and Q5 are in meters. 3 / h.

[0024] In step 6, the primary and secondary anoxic tanks achieve nitrogen removal by converting nitrate nitrogen into nitrogen gas, while also reducing some organic carbon.

[0025] In step 6, the primary and secondary aerobic tanks remove a large amount of organic matter while converting ammonia nitrogen into nitrate nitrogen.

[0026] In step 6, the ratio of the nitrification liquor return flow rate Q6 to the water volume entering the anoxic tank Q3 plus Q4, Q6 / (Q3+Q4), is called the nitrification liquor return ratio, which is 3-4.

[0027] Agitators are installed in the primary and secondary anoxic tanks to maintain the suspended state of the microbial sludge and ensure good mixing between the sludge and wastewater. Aeration devices are installed in the primary and secondary aerobic tanks to introduce air into the sludge-water mixture, maintaining a certain dissolved oxygen concentration and the suspended state of the sludge. The effective volume ratio of each tank is as follows: 30% for the primary anoxic tank, 50-53% for the primary aerobic tank, 8.0-12% for the secondary anoxic tank, and 8.0-10% for the secondary aerobic tank.

[0028] The beneficial effects of this invention are:

[0029] 1. The multi-cycle treatment method of this invention uses reflux dilution to adjust the influent concentration, ensuring that solid-liquid separation of high-concentration leachate takes place under free settling conditions, thus solving the problem of difficult solid-liquid separation of high-concentration wastewater. In this invention, multi-reflux control can effectively dilute the pollutant concentration of high-concentration fresh leachate stock solution, reducing the inhibition of ammonia nitrogen on microorganisms to below the inhibition concentration, thereby improving sludge activity and maintaining the stable operation of the biological treatment system. At the same time, the high proportion of multi-stage reflux control effectively degrades SMP in EfOM, effectively improving the treatment efficiency of easily degradable organic wastewater.

[0030] 2. The multi-cycle treatment method of this invention does not use any chemicals or membranes in the biological treatment stage and does not produce concentrated liquid. Without the use of chemicals, membranes, or advanced treatment, it achieves a removal rate of over 98% for COD, total nitrogen, ammonia nitrogen, and total phosphorus, meeting the standards for total nitrogen, ammonia nitrogen, and total phosphorus (Level I standard of the "Pollutant Control Standard for Municipal Solid Waste Landfills" (GB16889–2008)). Simultaneously, it significantly reduces the concentration of organic matter, laying the foundation for simplified post-treatment methods, enabling post-treatment to fully meet the national Level I standard without the use of any membranes.

[0031] 3. The reflux of the multi-circulation treatment system of the present invention enables the effective degradation of effluent organic matter (EfOM) and dissolved microbial products (SMP); the external circulation reflux of the anaerobic reactor circulation tank increases the upflow velocity of the anaerobic reactor and maintains the expansion state of the sludge bed in the anaerobic reactor, thereby improving the mass transfer efficiency between wastewater organic matter and granular sludge. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the multi-loop processing system structure of the present invention;

[0033] Figure 2 This is a flowchart of the multi-loop processing method of the present invention.

[0034] 1. Equalization tank, 2. Primary sedimentation tank, 3. Intermediate tank, 4. Anaerobic reactor, 5. External circulation tank, 6. Intermediate sedimentation tank, 7. Primary anoxic tank, 8. Primary aerobic tank, 9. Secondary anoxic tank, 10. Secondary aerobic tank, 11. Secondary sedimentation tank, Q1. Raw leachate flow rate, Q2. Effluent return flow rate, Q3. Flow rate from intermediate tank to anaerobic reactor, Q4. Flow rate from intermediate tank to primary anoxic tank, Q5. External circulation tank flow rate, Q6. Nitrified liquor return flow rate, Q7. Effluent flow rate, R1. Returned sludge, R2. Excess sludge. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0036] like Figure 1 As shown, this invention provides an anaerobic-AOAO multi-cycle biological treatment system for landfill leachate, comprising an equalization tank 1, a primary sedimentation tank 2, an intermediate tank 3, an anaerobic reactor 4, an external circulation tank 5, an intermediate sedimentation tank 6, a primary anoxic tank 7, a primary aerobic tank 8, a secondary anoxic tank 9, a secondary aerobic tank 10, and a secondary sedimentation tank 11, connected in sequence. The intermediate tank 3 is directly connected to the anaerobic reactor 4 and also connected to the primary anoxic tank 7 via a bypass pipe. The primary anoxic tank 7, primary aerobic tank 8, secondary anoxic tank 9, and secondary aerobic tank 10 are connected end-to-end. The end of the primary aerobic tank 8 is connected to the front of the primary anoxic tank 7 via a pipe. The bottom of the secondary sedimentation tank 11 is connected to the intermediate sedimentation tank 6 and the primary anoxic tank 7 via pipes. The outlet of the secondary sedimentation tank 11 is connected to the equalization tank 1. The volume ratio of the primary anoxic tank 7 to the primary aerobic tank 8 to the secondary anoxic tank 9 to the secondary aerobic tank 10 is 30:50~53:8~12:8~10.

[0037] This invention also provides an anaerobic-AOAO multi-cycle biological treatment method for fresh landfill leachate, such as... Figure 2 As shown, the multi-loop processing system described above is implemented through the following steps:

[0038] Step 1: The original leachate flow rate Q1 is mixed with the supernatant effluent return flow rate Q2 from the secondary sedimentation tank 11 in the equalization tank 1. The ratio of the supernatant return flow rate from the secondary sedimentation tank to the original leachate flow rate Q2 / Q1 is called the effluent return ratio, which is taken as 5 to 7.

[0039] Step 2: The mixed leachate is pumped into the primary sedimentation tank 2, where most of the suspended solids are removed by sedimentation, and then it enters the intermediate tank 3.

[0040] Step 3: The leachate in the intermediate tank 3 is pumped into the anaerobic reactor 4 and directly into the primary anoxic tank 7 through the bypass pipe. The flow rate into the anaerobic reactor 4 is Q3, and the flow rate into the primary anoxic tank 7 is Q4. The ratio of Q3 / Q4 is between 8:2 and 7:3. The purpose of allowing some wastewater to enter the primary anoxic tank directly through the bypass pipe is to adjust the amount of organic matter in the primary anoxic tank to meet the carbon source requirements of the denitrification process.

[0041] Step 4: The effluent from anaerobic reactor 4 enters the external circulation tank 5. A portion of it returns to anaerobic reactor 4 from the bottom of the external circulation tank 5. This portion has a flow rate of Q5. The purpose is to increase the mass transfer effect by increasing the upflow velocity of the liquid in the anaerobic reactor, while simultaneously eliminating some microbial products (SMP). The flow rate Q5 depends on the type of anaerobic reactor and can be calculated using the following formula:

[0042]

[0043] Equation (1) is also the definition of the upflow velocity U, where U refers to the upflow velocity of the liquid in the empty tower inside the reactor, in m / h; A is the horizontal cross-sectional area of ​​the anaerobic reactor, in m². 2 The units for Q3 and Q5 are in meters. 3 / h; for upflow anaerobic sludge blanket (UASB) reactors, U is between 0.5 and 1.5 m / h; for expanded granular sludge blanket (EGSB) reactors, U is between 1.5 and 3.0 m / h. Based on the above parameters, the circulation ratio (Q5 / Q3) and the value of Q5 of the anaerobic reactor can be calculated and determined. Since the upflow velocity has a large range, Q5 also has a relatively loose range. This invention suggests that the anaerobic reactor should preferably be a high-load expanded granular sludge blanket reactor. When using a high-load reactor, the effluent from the external circulation tank 5 is recirculated into the reactor to maintain a high upflow velocity in the reactor so that the "bed" formed by the biological granular sludge in the reactor is in an expanded state, which can improve the efficient mass transfer between organic matter and biomass in the wastewater. The three-phase separator installed in the anaerobic reactor keeps the sludge (microorganisms) in the reactor and separates the generated biogas from the water, realizing the three-phase separation of clean water, biogas and sludge.

[0044] Step 5: The overflow water from the upper part of the external circulation tank 5 and the residual sludge R2 from the secondary sedimentation tank 11 are mixed in the pipeline and enter the intermediate sedimentation tank 6. The sedimented sludge at the bottom is discharged as residual sludge. The overflow from the upper part of the intermediate sedimentation tank 6 enters the primary anoxic tank 7.

[0045] Step 6: The effluent from intermediate sedimentation tank 6 enters primary anoxic tank 7, and then passes through primary anoxic tank 7, primary aerobic tank 8, secondary anoxic tank 9 and secondary aerobic tank 10 in sequence. Primary anoxic tank 7 and secondary anoxic tank 9 achieve the purpose of nitrogen removal by converting nitrate nitrogen into nitrogen gas, while also reducing some organic carbon.

[0046] In step 6, the primary aerobic tank 8 and the secondary aerobic tank 10 remove a large amount of organic matter while converting ammonia nitrogen into nitrate nitrogen;

[0047] At the end of the primary aerobic tank 8, the mud-water mixture containing nitrate nitrogen, i.e. nitrified liquid, is returned to the primary anoxic tank 7. The nitrified liquid return flow rate is Q6. The nitrified liquid return ratio Q6 / (Q3+Q4) recommended by this invention is between 3 and 4.

[0048] Step 7: The sludge-water mixture after two stages of anoxic and aerobic treatment is separated into sludge and water in the secondary sedimentation tank 11. A portion of the residual sludge R2 in the lower sedimentation tank 11 is returned to the intermediate sedimentation tank 6, where it is mixed with the incoming water and settled before being discharged as residual sludge. A portion of the returned sludge R1 in the secondary sedimentation tank is returned to the primary anoxic tank 7 to maintain the sludge concentration required by the AOAO system. The flow rate Q3+Q4 of the returned sludge R1 in the secondary sedimentation tank and the flow rate Q3+Q4 entering the primary anoxic tank is called the sludge return ratio. The sludge return ratio recommended in this invention is 1.0. As mentioned above, a portion of the supernatant in the secondary sedimentation tank 11 is returned to the equalization tank according to the effluent return ratio Q2 / Q1 to mix with and dilute the original leachate. The remaining supernatant in the secondary sedimentation tank 11 overflows and becomes the treated effluent of this system, with an effluent flow rate of Q7.

[0049] Agitators are installed in the primary anoxic tank 7 and the secondary anoxic tank 9 to maintain the suspension of the microbial sludge and the good mixing of sludge and wastewater; aeration devices are installed in the primary aerobic tank 8 and the secondary aerobic tank 10 to introduce air into the sludge-water mixture to maintain a certain dissolved oxygen concentration and the suspension of sludge.

[0050] The AOAO system in this invention uses a relatively high effective volume of the primary anoxic tank A1. The effective volume of each tank accounts for the following proportions: primary anoxic tank 7 is 30%, primary aerobic tank 8 is 50-53%, secondary anoxic tank 9 is 8.0-12%, and secondary aerobic tank 10 is 8.0-10%.

[0051] The method of the present invention will be further illustrated below through examples.

[0052] Example 1

[0053] Example 1 describes the treatment of leachate from a municipal solid waste incineration power plant, using a method similar to... Figure 2As shown, the anaerobic reactor is an expanded granular sludge bed (EGSB) reactor. Equalization tank 1 receives raw leachate and effluent from the secondary sedimentation tank. The raw leachate flow rate Q1 is mixed with the effluent return flow rate Q2 from the supernatant of the secondary sedimentation tank 11 in equalization tank 1. In this embodiment 1, the ratio of the effluent return flow rate Q2 from the supernatant of the secondary sedimentation tank 11 to the raw leachate flow rate Q1, known as the "effluent return ratio," is 7.0. Under these conditions, the concentration of the mixed water in equalization tank 1 is between 5000 and 6000 mg COD / L.

[0054] The equalization tank 1 is equipped with a mixer for mixing. The hydraulic retention time in the equalization tank 1 is approximately 6 hours. The primary sedimentation tank 2 has no different requirements from a typical wastewater primary sedimentation tank, with a hydraulic load of 1.0 m. 3 / m 2 The intermediate tank 3 is designed for continuous influent to the anaerobic reactor, with an HRT of approximately 1 hour. The mixed liquid after mixing in the equalization tank enters the primary sedimentation tank 2. After sedimentation to remove most of the suspended solids, it enters the intermediate tank 3, where the EGSB reactor 4 is pumped in at a flow rate of Q3. At the same time, a portion of the influent from the intermediate tank 3 enters the primary anoxic tank 7 directly through the bypass pipe at a flow rate of Q4.

[0055] In this embodiment 1, the ratio of wastewater flow rates entering anaerobic reactor 4 and primary anoxic tank 7 is Q3:Q4 = 8:2. The effluent from anaerobic reactor 4 enters external circulation tank 5, where the anaerobic effluent is recirculated back into the bottom of EGSB reactor by a circulation pump. In this embodiment, the ratio of external circulation tank flow rate Q5 to anaerobic influent flow rate Q3 is Q5 / Q3 = 8, and the upflow velocity of EGSB reactor is 2.3 m / h.

[0056] The remaining overflow from the external circulation tank 5 and the remaining sludge from the secondary sedimentation tank 11 are mixed in the pipeline and then enter the intermediate sedimentation tank 6. The settled sludge is discharged as the system's remaining sludge. The supernatant from the intermediate sedimentation tank overflows into the primary anoxic tank 7, where it mixes with the influent from the bypass pipe. Therefore, the wastewater flow rate entering the primary anoxic tank is equal to Q3 plus Q4.

[0057] The first-stage anoxic pool 7, the first-stage aerobic pool 8, the second-stage anoxic pool 9, and the second-stage aerobic pool 10, which are connected end to end, are the main structures of the AOAO method. In this embodiment 1, the effective volume ratio of these four pools is 30:50:12:8.

[0058] The primary anoxic tank 7 and the secondary anoxic tank 9 achieve nitrogen removal by converting nitrate nitrogen into nitrogen gas, while also reducing some organic carbon. The primary aerobic tank 8 and the secondary aerobic tank 10 remove a large amount of organic matter while converting ammonia nitrogen into nitrate nitrogen. At the end of the primary aerobic tank 8, the sludge-water mixture containing nitrate nitrogen, i.e., the nitrified liquid, is returned to the primary anoxic tank 7 to provide nitrate nitrogen for the primary anoxic tank. The ratio of the nitrified liquid return flow rate Q6 to the flow rate (Q3+Q4) entering the primary anoxic tank is called the nitrified liquid return ratio. In this embodiment, Q6 / (Q3+Q4) = 3 is taken, which can meet the requirement of 98% removal of total nitrogen and ammonia nitrogen.

[0059] The secondary anoxic tank 9 denitrifies nitrates from the wastewater in the primary aerobic tank 8 to generate nitrogen gas, achieving further denitrification. The aeration in the secondary aerobic tank 10 increases the dissolved oxygen level of the wastewater, preventing sludge from floating due to fermentation gas generated in the anaerobic state after the wastewater enters the secondary sedimentation tank 11. At the same time, the aeration further converts the remaining ammonia nitrogen into nitrate nitrogen. This nitrate nitrogen will also enter the front end of the system with the return flow of Q2 and will eventually be removed through denitrification.

[0060] The sludge-water mixture treated by the AOAO system achieves sludge-water separation in the secondary sedimentation tank 11. A portion of the supernatant is returned to the equalization tank 1 to mix with the original leachate according to the required flow rate of "effluent return ratio Q2 / Q1". In this embodiment 1, Q2 / Q1 = 7.0. The remaining supernatant from the secondary sedimentation tank 11 overflows and is discharged from the system, which is the system's effluent flow rate Q7. Ignoring the water carried away by the residual sludge, Q7 is equal to the original leachate flow rate Q1 entering the system. In addition, a portion of the sludge R1 from the secondary sedimentation tank 11 is returned to the primary anoxic tank. The sludge return ratio R1 / (Q3+Q4) is similar to that of the general activated sludge process. In this embodiment 1, the sludge return ratio is taken as 1.0. The remaining sludge R2 from the secondary sedimentation tank is returned to the effluent pipeline of the external circulation tank 5 and mixed with the anaerobic effluent. Then, it enters the intermediate sedimentation tank 6, where it adsorbs some of the organic matter in the anaerobic effluent and settles before being discharged as residual sludge.

[0061] The surface loading of intermediate sedimentation tank 6 is 2m. 3 / m 2 The four tanks, namely, the primary anoxic tank (7), the primary aerobic tank (8), the secondary anoxic tank (9), and the secondary aerobic tank (10), are interconnected corridor-type tanks. The total effective volume of these four tanks is calculated based on a COD / m³ ratio of 1.2 kg / m³. 3 The volumetric loading rate and treated water volume calculation for .d are as follows: Secondary sedimentation tank 11 is a typical radial flow sedimentation tank with a surface loading rate of 0.8 m³ / s. 3 / m 2 .d.

[0062] The main effects of the treatment:

[0063] The homogeneous concentrations of total nitrogen, ammonia nitrogen, and total phosphorus in the effluent from the secondary sedimentation tank were 24, 14, and 1.0 mg / L, respectively, all meeting the Class I standard of the national discharge standard (GB 16889-2008); the average concentration of COD in the effluent was 540 mg / L; and the removal rates of COD, total nitrogen, ammonia nitrogen, and total phosphorus were all greater than 98%.

[0064] Example 2

[0065] The method flow of this embodiment 2 is similar to that of embodiment 1, with the main differences being: 1) the anaerobic reactor adopts an upflow anaerobic sludge blanket (UASB) reactor; 2) the specific method parameters vary slightly depending on the equipment; and 3) the object being treated is also leachate from a municipal solid waste incineration power plant.

[0066] The main differences in parameters include:

[0067] 1) The supernatant reflux ratio (Q2 / Q1) of the secondary sedimentation tank 11 is 5.0, and the COD concentration in the equalization tank is between 5500 and 6500 mg / L;

[0068] 2) Nitrification liquor reflux ratio Q5 / (Q3+Q4)=4.0;

[0069] 3) Sludge return ratio R1 / (Q3+Q4)=0.8;

[0070] 4) The recirculation ratio (Q5 / Q3) of the circulating tank of the UASB reactor is 3.0, and the corresponding upflow velocity in the UASB reactor is 1.0 m / h;

[0071] 5) The effective volume ratio of the four pools in the AOAO system is 30:53:8.5:8.5; other methods and conditions are the same as in Example 1.

[0072] The processing effect obtained under the conditions of Example 2 is as follows:

[0073] The average concentrations of COD, TN, and ammonia nitrogen in the effluent from the secondary sedimentation tank were 493, 12.9, and 8.8 mg / L, respectively; their removal rates were in the ranges of 97.5–99.5%, 97.7–98.7%, and 99.3–99.7%, respectively; among them, TN and ammonia nitrogen met the Class I standard of the national discharge standard (GB 16889–2008).

[0074] Example 3

[0075] The method and process of this embodiment 3 are the same as those of embodiments 1 and 2. The main differences are: 1) the anaerobic reactor is an EGSB reactor; 2) the specific method parameters vary slightly depending on the equipment; 3) the effective volume ratios of the four tanks of the AOAO system are 30%, 53%, 8% and 9% respectively.

[0076] The main differences in parameters include:

[0077] 1) Q2 / Q1 = 6.0, under this condition the average concentration in the equalization tank is 5980 mg COD / L;

[0078] 2) The EGSB recirculation ratio Q5 / Q3 = 5.0, and the corresponding upflow velocity in the EGSB reactor is 1.7 m / h;

[0079] 3) The ratio of the flow rate Q3 directly entering the EGSB reactor from the intermediate tank 3 to the flow rate Q4 entering the primary anoxic tank through the bypass pipe is 7:3.

[0080] The nitration liquor reflux ratio Q6 / (Q3+Q4)=3.0;

[0081] The sludge return ratio R1 / (Q3+Q4)=1.0;

[0082] Other structural and method parameters are the same as those in the previous two embodiments.

[0083] Under these conditions, the average value of the dissolved COD concentration, i.e., the dissolved organic matter (DOM), was 293 mg COD / L; the total nitrogen, total phosphorus, and ammonia nitrogen all met the Class I standard of the national emission standard (GB 16889–2008).

[0084] The working principle of the multi-loop processing method of this invention is as follows:

[0085] 1. Preprocessing stage

[0086] This invention's multi-cycle treatment method abandons the commonly used chemical coagulation and sedimentation method in the pretreatment stage, and adopts a high-proportion recirculation dilution of the influent from the secondary sedimentation tank 11. Its main functions include: 1) reducing the high viscosity and suspended solids concentration of ultra-high concentration wastewater, transforming the sedimentation state of the wastewater in the primary sedimentation tank from disturbed sedimentation to free sedimentation, thereby significantly improving the removal efficiency of suspended solids; 2) utilizing the weakly alkaline properties of the effluent to adjust the acidic leachate influent to near neutral and increase bicarbonate alkalinity, thereby improving the pH buffering capacity of the wastewater and making it more suitable for the next step of biological treatment; 3) a high proportion of recirculation dilution. For example, reflux can dilute the influent, reducing the inhibitory effect of toxic compounds in the influent on microorganisms, especially reducing the toxicity of high concentrations of ammonia nitrogen in the raw water to anaerobic bacteria; 4) Not using coagulants not only reduces the cost of chemical dosing, but also avoids the inhibitory effect of chemicals (such as the most commonly used aluminum chloride and sulfate) on microorganisms, which can improve the effect of biological treatment and greatly reduce the amount of biological sludge, thereby reducing sludge treatment and chemical costs and lowering operating costs; 5) Pretreatment without the use of coagulants converts more organic matter into renewable energy methane, realizing resource utilization and reducing carbon emissions.

[0087] The key function of the high-proportion recirculation in the multi-cycle treatment method of this invention is to eliminate SMPs in wastewater. Since these are the dominant components in biologically treated effluent, their concentration determines the concentration of organic matter in the effluent. Because SMP concentration is positively correlated with substrate concentration, the SMP problem is more prominent in high-concentration wastewater, becoming a bottleneck that hinders the improvement of biological treatment efficiency for high-concentration wastewater. Recent studies have found that SMPs generated during biological treatment require a long hydraulic retention time or the addition of new treatment units to degrade. Direct discharge of effluent from the secondary sedimentation tank prevents SMPs from undergoing degradation, a significant reason for high effluent concentrations. Recirculation, however, can effectively degrade SMPs, significantly improving the efficiency of biological treatment.

[0088] 2. Anaerobic biological treatment stage

[0089] The significance of the multi-cycle treatment method for anaerobic biological treatment in this invention lies in: 1) recovering renewable energy—methane—from organic wastewater, achieving a balance between resource utilization and pollutant emission reduction; achieving greenhouse gas emission reduction; and degrading pollutants at the lowest cost (no need for aeration power, low sludge production). Therefore, the first step of biological treatment, the anaerobic reactor, eliminates the most pollutants with the smallest reactor volume. However, the anaerobic treatment process also produces the most SMP. This patent specifically proposes to recirculate the sludge from the secondary sedimentation tank (mainly microbial cells) to contact the anaerobic effluent. The aerobic microbial cells in the starved state of the recirculated sludge can adsorb a large amount of SMP in the anaerobic effluent in a short time. After the sludge adsorbs SMP, it is discharged from the intermediate sedimentation tank, achieving the effect of reducing SMP. This process is different from the conventional process of discharging excess sludge from the secondary sedimentation tank.

[0090] 3. AOAO System Part

[0091] In the multi-cycle treatment system of this invention, in the "anoxic tank (section A) - aerobic tank (section O) - anoxic tank (A) - aerobic tank (O)" treatment system, the microorganisms in the anoxic tank have a denitrification effect, which converts the nitrate nitrogen returned from the oxidation tank into nitrogen gas and releases it into the atmosphere from the liquid phase, thereby completing the denitrification process. This process can only be achieved under the condition that BOD / TN>4. In conventional biological treatment, about 95% of BOD is consumed in anaerobic treatment. Thus, if the anaerobic effluent directly enters the AOAO system for denitrification, the biodegradable organic matter (BOD) used for denitrification will inevitably be lacking, and the denitrification effect cannot be achieved. In order to make up for the lack of organic matter, this invention proposes to allocate the wastewater entering the anaerobic reactor and directly entering the first-stage anoxic tank in a certain proportion.

[0092] In the multi-cycle treatment system of this invention, the nitrification process in the primary aerobic tank 8 oxidizes ammonia nitrogen into nitrate nitrogen, and then provides nitrate nitrogen for the denitrification process to the primary anoxic tank 7 through nitrification liquor recirculation. Based on the properties of fresh leachate, this invention proposes a nitrification liquor recirculation ratio (Q6 / (Q3+Q4)) of 3-4:1. Field studies have shown that the removal efficiency of COD and ammonia nitrogen by this method is greater than 98.0%.

[0093] Compared with the prior art, the present invention has the following advantages:

[0094] 1. The multi-cycle treatment method of the present invention uses reflux dilution to adjust the influent concentration, ensuring that the solid-liquid separation of high-concentration leachate is carried out under free sedimentation conditions, thus solving the problem of difficult solid-liquid separation of high-concentration wastewater;

[0095] 2. The original leachate from the multi-cycle treatment system of this invention is acidic, with a pH of 4.6–5.8, while the optimal pH for microorganisms in the treatment system is around 7. This invention utilizes the weak alkalinity of the return water (pH between 8.0 and 8.5) to mix the effluent with the original leachate by regulating the return flow, raising the pH to around 7.0. Simultaneously, the increased alkalinity enhances the pH buffering capacity of the wastewater, preventing acidification. This process saves on the cost of alkali solutions required for pH adjustment and contributes to stable operation.

[0096] 3. In the multi-cycle treatment method of the present invention, in order to avoid the use of external commercial carbon sources, part of the leachate is directly introduced into the AOAO system through the bypass pipe to provide the carbon source required for denitrification in the primary anoxic tank;

[0097] 4. The multi-circulation treatment method of this invention can effectively dilute the pollutant concentration of high-concentration fresh leachate stock solution, reduce the inhibition of ammonia nitrogen on microorganisms to below the inhibition concentration, thereby improving the activity of sludge and maintaining the stable operation of the biological treatment system.

[0098] 5. The multi-cycle treatment method of the present invention utilizes a high proportion of multi-stage reflux control to effectively degrade SMP in EfOM, thereby effectively improving the treatment efficiency of easily degradable organic wastewater.

[0099] 6. The multi-cycle treatment method of the present invention adopts the method of mixing the residual sludge return and the effluent from the anaerobic reactor into the intermediate sedimentation tank. During this process, the residual sludge can absorb some of the organic matter that is difficult to degrade in the anaerobic process and settle together with the sludge and be discharged with the residual sludge, which plays the role of biological coagulation and sedimentation, and can effectively reduce the organic matter concentration of the anaerobic effluent.

[0100] 7. The external circulation of the anaerobic reactor circulation tank in the multi-circulation treatment system of this invention increases the upflow velocity of the anaerobic reactor and maintains the expansion state of the anaerobic reactor sludge bed, which is the basis for high-efficiency mass transfer between wastewater organic matter and granular sludge.

[0101] 8. The multi-circulation treatment method of the present invention includes multi-recirculation control of anaerobic effluent, nitrification liquor, secondary sedimentation tank effluent, sludge recirculation from the secondary sedimentation tank to the primary anoxic tank, and residual sludge recirculation to the intermediate sedimentation tank. The recirculation rate of each part can be controlled according to the method requirements to ensure the treatment effect.

Claims

1. A method for anaerobic-AOAO multi-cycle treatment of fresh landfill leachate, characterized in that, This is implemented through a multi-loop processing system, specifically following these steps: Step 1: The original leachate flow rate Q1 is mixed with the effluent return flow rate Q2 from the secondary sedimentation tank (1) in the equalization tank (1); Step 2: The mixed leachate is pumped into the primary sedimentation tank (2), and after sedimentation to remove most of the suspended solids, it enters the intermediate tank (3). Step 3: Pump the leachate in the intermediate tank (3) into the anaerobic reactor (4) and directly into the primary anoxic tank (7) through the bypass pipe. The flow rate into the anaerobic reactor (4) is Q3, and the flow rate into the primary anoxic tank (7) is Q4. Step 4: The effluent from the anaerobic reactor (4) enters the external circulation tank (5), and a portion of it returns to the anaerobic reactor (4) from the bottom of the external circulation tank (5). The flow rate of this portion is Q5. Step 5: The overflow water from the upper part of the external circulation tank (5) and a portion of the remaining sludge R2 from the secondary sedimentation tank (11) are mixed in the pipeline and then enter the intermediate sedimentation tank (6). Step 6: The effluent from the intermediate sedimentation tank (6) enters the primary anoxic tank (7) and passes through the primary anoxic tank (7), primary aerobic tank (8), secondary anoxic tank (9) and secondary aerobic tank (10) connected end to end in sequence; At the end of the primary aerobic tank (8), the mud-water mixture containing nitrate nitrogen, i.e. nitrified liquid, is returned to the primary anoxic tank (7), and the nitrified liquid return flow rate is Q6. Step 7: The sludge-water mixture after two stages of anoxic and aerobic treatment is separated into sludge and water in the secondary sedimentation tank (11). A portion of the residual sludge R2 in the lower sedimentation tank (11) is returned to the intermediate sedimentation tank (6), where it is mixed with the incoming water and settled before being discharged as residual sludge. Another portion of the sludge R1 in the secondary sedimentation tank is returned to the primary anoxic tank (7) to maintain the sludge concentration required by the AOAO system. The flow rate Q3+Q4 of the sludge R1 returned from the secondary sedimentation tank and the flow rate Q3+Q4 entering the primary anoxic tank is called the sludge return ratio. The sludge return ratio is 1. A portion of the supernatant in the secondary sedimentation tank (11) is returned to the equalization tank according to the effluent return ratio Q2 / Q1 to mix with and dilute the original leachate. The remaining supernatant in the secondary sedimentation tank (11) overflows and becomes the treated effluent of this system. The effluent flow rate is Q7. The multi-cycle treatment system includes an equalization tank (1), a primary sedimentation tank (2), an intermediate tank (3), an anaerobic reactor (4), an external circulation tank (5), an intermediate sedimentation tank (6), a primary anoxic tank (7), a primary aerobic tank (8), a secondary anoxic tank (9), a secondary aerobic tank (10), and a secondary sedimentation tank (11) connected in sequence. The intermediate tank (3) is connected to the anaerobic reactor (4) and the primary anoxic tank (7) through an inlet pipe and a bypass pipe, respectively. The primary anoxic tank (7), the primary aerobic tank (8), the secondary anoxic tank (9), and the secondary aerobic tank (10) are connected end to end. The end of the primary aerobic tank (8) is connected to the primary anoxic tank (7) through a pipe. The bottom of the secondary sedimentation tank (11) is connected to the intermediate sedimentation tank (6) and the primary anoxic tank (7) through pipes, respectively. The outlet of the secondary sedimentation tank (11) is connected to the equalization tank (1). Agitators are installed in the primary anoxic tank (7) and the secondary anoxic tank (9), and aeration devices are installed in the primary aerobic tank (8) and the secondary aerobic tank (10). The volume ratio of the primary anoxic tank (7) to the primary aerobic tank (8) is 30:50~53:8~12:8~10.

2. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, The ratio of the flow rate of the effluent recirculated to the flow rate of the original leachate in step 1 is called the effluent recirculation ratio, i.e., Q2 / Q1, and the effluent recirculation ratio is 5-7.

3. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, In step 3, the flow rate Q3 pumped into the anaerobic reactor (4) and the flow rate Q4 directly entering the primary anoxic tank (7) through the bypass pipe are allocated in the following ratio: Q3:Q4 = 7-8:2-3.

4. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, In step 4, a portion of the effluent from the external circulation tank (5) enters the anaerobic reactor (4) from the bottom via a circulation pump, increasing the upflow velocity of the reactor. This portion of the effluent, Q5, is used to maintain the expansion state of the sludge bed in the anaerobic reactor (4). Its size depends on the type of anaerobic reactor and can be calculated according to formula (1): Where U refers to the upward flow velocity of the liquid in the empty tower within the reactor, in m / h; and A is the horizontal cross-sectional area of ​​the anaerobic reactor, in m². 2 The units for Q3 and Q5 are in meters. 3 / h.

5. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, In step 6, the primary anoxic tank (7) and the secondary anoxic tank (9) achieve the purpose of nitrogen removal by converting nitrate nitrogen into nitrogen gas, while also reducing a portion of organic carbon.

6. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, In step 6, the primary aerobic tank (8) and the secondary aerobic tank (10) remove a large amount of organic matter while converting ammonia nitrogen into nitrate nitrogen.

7. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to claim 1, characterized in that, In step 6, the ratio of the nitrification liquor return flow rate Q6 to the water volume entering the anoxic tank Q3+Q4 is called the nitrification liquor return ratio, which is 3-4.

8. The anaerobic-AOAO multi-cycle treatment method for fresh landfill leachate according to any one of claims 1-7, characterized in that, Agitators are installed in the primary anoxic tank (7) and the secondary anoxic tank (9) to maintain the suspended state of the microbial sludge and the good mixing of sludge and wastewater. Aeration devices are installed in the primary aerobic tank (8) and the secondary aerobic tank (10) to introduce air into the sludge-water mixture to maintain a certain dissolved oxygen concentration and the suspended state of the sludge. The effective volume ratio of each tank is as follows: 30% for the primary anoxic tank (7), 50-53% for the primary aerobic tank (8), 8.0-12% for the secondary anoxic tank (9), and 8.0-10% for the secondary aerobic tank (10).

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