Sludge anaerobic digestion treatment system and treatment method

Abstract

The application discloses a sludge anaerobic digestion treatment system and treatment method, and relates to the field of sludge treatment.The system comprises a sludge slurry tank, a dilution cooling tank and an anaerobic digestion tank which are sequentially connected; a plurality of membrane assemblies are arranged in the anaerobic digestion tank; the membrane assemblies are connected with an acid tank through a circulating pump; dilute acid is circulated in the membrane assemblies; and the free ammonia is spontaneously transferred from the sludge to the acid tank through the difference between the free ammonia partial pressures inside and outside the membrane assemblies, so as to reduce the concentration of free ammonia in the sludge, promote the organic carbon conversion and anaerobic digestion of the sludge; the bottom of the anaerobic digestion tank is connected with a sludge dewatering machine, so that the sludge can be reused after dewatering treatment; and a biogas collecting pipeline is arranged at the top of the anaerobic digestion tank, part of the biogas is recirculated into the anaerobic digestion tank for membrane surface flushing and sludge stirring, and the other part of the biogas is output outside the system for resource utilization.The application has the advantages of simple operation, low energy consumption, stable operation and the like, and improves the overall operation economic benefits of the anaerobic digestion system.

Description

Technical Field

[0001] This invention belongs to the field of sludge anaerobic digestion treatment technology, specifically relating to a sludge anaerobic digestion treatment system and treatment method. Background Technology

[0002] Currently, research focusing on reducing free ammonia concentration during anaerobic digestion mainly employs methods such as biological inoculation, in-tank anaerobic ammonia oxidation, adsorption, sedimentation, ultrasonic degradation, microwave degradation, and membrane separation. Biological inoculation faces challenges in selecting microorganisms adapted to the existing system environment. Furthermore, the inoculated microorganisms may compete with native microorganisms, resulting in a relatively low inoculation success rate. In-tank anaerobic ammonia oxidation suffers from extremely slow growth of anaerobic ammonia-oxidizing bacteria, high sensitivity to environmental changes, and stringent control precision requirements. Adsorption and sedimentation methods require external reagents, and the resulting crystals tend to settle at the bottom of the tank, making cleaning difficult. Ultrasonic and microwave methods inactivate and disintegrate bacteria in the sludge and consume excessive energy; therefore, these technologies have not been applied in actual production processes.

[0003] High-solids-content anaerobic digestion feedstocks require solid-liquid separation before membrane treatment. The sludge containing high ammonia concentrations undergoes membrane treatment before being combined with the solids, a process that is cumbersome and time-consuming. Current membrane separation technology utilizes the partial pressure difference of free ammonia between the two liquid phases inside and outside the hollow fiber membrane as a driving force, causing free ammonia to spontaneously transfer from the organic matter in the digester to the dilute acid inside the membrane. Therefore, compared to other methods, membrane separation technology has advantages such as low energy consumption, convenient control, and good free ammonia removal efficiency, making it a technology with excellent commercial value and promising prospects for large-scale industrial application.

[0004] However, hollow fiber membrane separation technology also has some inherent disadvantages. For example, the biofilm formed by bacteria on the membrane surface and impurities in the sludge can easily cause membrane clogging, thus affecting the efficiency of free ammonia treatment. Therefore, in existing research, this technology is generally used to reduce the concentration of free ammonia in media with low solids content (<3%), such as wastewater. In some studies that directly place hollow fiber membranes inside anaerobic digesters to reduce free ammonia concentration, the organic matter being anaerobic digested is generally livestock and poultry manure, with a solids content usually below 3%. Hollow fiber membranes are extremely prone to clogging when treating media with high solids content, causing difficulties in system operation. Existing research on using membrane technology to reduce the concentration of free ammonia in high-solids-content organic matter usually requires pretreatment of the organic matter, i.e., first performing solid-liquid separation on the sludge, and then mixing the liquid with the solids after removing free ammonia. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a sludge anaerobic digestion treatment system and method that is compact in structure, simple in operation, low in energy consumption, and highly stable in operation.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An anaerobic digestion system for sludge includes a sludge pulping tank, a dilution and cooling tank, and an anaerobic digestion tank connected in sequence. The sludge pulping tank is used to pulp the sludge raw material, the dilution and cooling tank is used to dilute and cool the pulped sludge, and the anaerobic digestion tank is used to perform anaerobic digestion on the cooled sludge. The anaerobic digestion tank is equipped with multiple membrane modules, which are connected to an external acid tank via a circulation pump. Dilute acid circulates within the membrane modules, and the pressure difference of free ammonia inside and outside the membrane modules promotes the spontaneous release of free ammonia. The sludge is transferred from the anaerobic digester to the acidic solution in the membrane module to reduce the concentration of free ammonia in the sludge and promote organic carbon conversion and anaerobic digestion. The bottom of the anaerobic digester is connected to a sludge dewatering machine, which is used to dewater the anaerobic digested sludge to enable sludge reuse. The top of the anaerobic digester is equipped with a biogas collection pipe, and part of the biogas is recirculated into the anaerobic digester through a compressor to flush the membrane surface and agitate the sludge, while the other part of the biogas is output outside the system for resource utilization.

[0007] As a further improvement of the present invention, the membrane assembly includes a support frame and a water-proof and breathable membrane, and multiple water-proof and breathable membranes are arranged parallel to each other in the support frame in a vertical direction. As a further improvement of the present invention, the spacing between adjacent waterproof and breathable membranes is greater than 10 cm, and the total surface area of ​​all waterproof and breathable membranes in each membrane module is greater than 12 m². 2 . As a further improvement of the present invention, the waterproof and breathable membrane is made of expanded polytetrafluoroethylene (PTFE), and the external dimensions of a single waterproof and breathable membrane are greater than 100 cm × 50 cm × 1 cm, the filtration pore size is 1 nm to 5 nm, the porosity is 85% to 90%, the tensile strength is greater than 80 N, and the air permeability is greater than 7.0 × 10⁻⁶. 2 cm 3 / cm 2 / s / cm Hg, pH tolerance range is 0~14. As a further improvement of the present invention, the density range of the membrane module deployed in the digested sludge is: membrane area : sludge amount = 1 : 1 to 10 (m³). 2 / m 3 ). As a further improvement of the present invention, the anaerobic digester is also provided with multiple aeration discs. Each membrane module is surrounded by aeration discs. The aeration discs are connected to the compressor through pipes. The compressor delivers pressurized biogas to the aeration discs. The pressurized biogas provides continuous surface scouring to the membrane module through nozzles arranged in a ring on the aeration discs. As a further improvement of the present invention, the diameter of the aeration disc is 50 cm to 100 cm, and 10 to 20 nozzles are evenly arranged in a ring on each aeration disc, with each nozzle at a 40° angle to the aeration disc. o ~50 o The angle is oriented towards the center of the aeration disc. As a further improvement of the present invention, the bottom of the anaerobic digester is also provided with a stirring branch pipe, which is connected to the compressor through a pipeline. The compressor delivers pressurized biogas to the stirring branch pipe, and the pressurized biogas is evenly sprayed at the bottom of the anaerobic digester through the stirring branch pipe to achieve sludge circulation and stirring. As a general technical concept, the present invention also provides a sludge anaerobic digestion treatment method for the above-mentioned sludge anaerobic digestion treatment system, comprising the following steps: Step S1: The excess sludge from the municipal wastewater treatment plant with a solids content of 15% to 25% is pulped in a sludge pulping tank at a temperature of 70℃ to 90℃. The pulped sludge is then cooled to 56℃ to 58℃ in a dilution and cooling tank and diluted to a solids content of 10% to 12%, before being transported to an anaerobic digester for anaerobic digestion. During the anaerobic digestion process, the sludge remains in the anaerobic digester for 20 to 25 days, and the temperature is maintained at 55℃ to 57℃. Step S2: The membrane module with a water-proof and breathable membrane is placed in the digested sludge in the anaerobic digester. The circulating liquid inside the membrane is dilute sulfuric acid with a concentration of 10-130 mmol / L, and the flow rate of the dilute sulfuric acid is controlled at 2-5 m / s. The free ammonia in the sludge is exchanged into the acid liquid by utilizing the partial pressure difference of free ammonia inside and outside the membrane. Step S3: The biogas produced in the anaerobic digester is divided into first biogas and second biogas. The first biogas is pressurized by a compressor and then divided into first pressurized biogas and second pressurized biogas. The first pressurized biogas enters the stirring branch pipe at the bottom of the anaerobic digester to achieve sludge circulation and stirring. The second pressurized biogas enters the aeration disc around the membrane module and provides continuous surface scouring for the membrane module through the nozzles arranged in a ring on the aeration disc. The second biogas is discharged from the tank for resource utilization. Step S4: The sludge after anaerobic digestion is transported to a sludge dewatering machine for dewatering treatment. Both the sludge and filtrate obtained from dewatering are utilized as resources.

[0008] As a further improvement of the present invention, in step S2, when the pH value of the acid solution is greater than 6, the dilute sulfuric acid containing ammonia is discharged, and at the same time, some fresh dilute sulfuric acid is added; magnesium oxide and sodium phosphate are added to the waste dilute sulfuric acid solution containing ammonia, and sodium hydroxide is added to adjust the pH value of the solution to be greater than 8, thereby obtaining fertilizer magnesium ammonium phosphate crystals. Compared with the prior art, the advantages of the present invention are as follows: 1. The sludge anaerobic digestion treatment system of the present invention connects a sludge pulping tank, a dilution and cooling tank, and an anaerobic digestion tank in sequence. The sludge pulping tank is used to pulp municipal sludge raw materials, the dilution and cooling tank is used to dilute and cool the pulped sludge, and finally the anaerobic digestion tank is used to anaerobic digest the cooled sludge. This eliminates the need for solid-liquid separation of the anaerobic fermentation raw materials, achieving ammonia removal within the anaerobic digestion tank for high-solids-content organic solid waste. The system is easy to operate and has low maintenance costs. Furthermore, multiple membrane modules are installed inside the anaerobic digestion tank, and these membrane modules are connected to an external acid pool via a circulation pump. Dilute acid circulates within the membrane modules, and the pressure difference of free ammonia inside and outside the membrane modules causes free ammonia to spontaneously transfer from the sludge in the anaerobic digestion tank to the acid pool in the membrane modules, thereby reducing the concentration of free ammonia in the sludge and improving the organic carbon conversion rate and anaerobic digestion gas production rate of the sludge. Meanwhile, the bottom of the anaerobic digester is connected to a sludge dewatering machine, which dewaters the sludge after anaerobic digestion. The dewatered sludge is then used for landscaping, incineration, and building materials, achieving sludge reuse. A biogas collection pipe is installed at the top of the anaerobic digester, with a portion of the biogas being recirculated back into the digester via a compressor for membrane surface rinsing and sludge agitation. The remaining biogas is output outside the system for resource utilization. The biogas produced during anaerobic digestion can be used to rinse the membrane modules, slowing down membrane clogging, extending the membrane cleaning and replacement cycle, and saving operating costs. Furthermore, the biogas also agitates the materials inside the digester, making the mixture more uniform and improving the biogas production rate during anaerobic digestion.

[0009] 2. The sludge anaerobic digestion treatment method of the present invention utilizes dilute acid circulating within a water-resistant and breathable membrane. This membrane is directly installed inside the anaerobic digester. The dilute acid circulates within the membrane, and the partial pressure difference between the inside and outside of the membrane reduces the concentration of free ammonia in the sludge within the digester. This achieves the goal of increasing the organic carbon conversion rate of the sludge and the amount of biogas produced during continuous reactor operation. Simultaneously, the generated biogas flushes the surface of the water-resistant and breathable membrane, slowing down the fouling rate of the membrane module and ensuring stable process operation. The ammonia-containing wastewater, after being adjusted to alkalinity, can be crystallized into magnesium ammonium phosphate by adding magnesium salts and phosphates, serving as an excellent nitrogen and phosphorus fertilizer resource, thus improving the overall economic benefits of the system. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating the structural principle of the sludge anaerobic digestion treatment system of the present invention.

[0011] Figure 2 This is a schematic diagram of the structural principle of the membrane module in the sludge anaerobic digestion treatment system of the present invention.

[0012] Figure 3This is a schematic diagram of the anaerobic digestion treatment method for sludge according to the present invention.

[0013] Figure 4 This is a schematic diagram showing the changes in ammonia nitrogen concentration and sludge VSS content over operating time in a specific embodiment 3 of the present invention.

[0014] Figure 5 This is a schematic diagram showing the change of biogas production rate with operating time in specific embodiment 3 of the present invention.

[0015] Legend: 1. Sludge slurry tank; 2. Dilution and cooling tank; 3. Anaerobic digester; 4. Acid tank; 5. Circulation pump; 6. Membrane module; 61. Support frame; 62. Waterproof and breathable membrane; 7. Compressor; 8. Mixing branch pipe; 9. Aeration disc; 10. Sludge dewatering machine; G1. First biogas; G2. Second biogas; G11. First pressurized biogas; G12. Second pressurized biogas; L1. Digester feed; L2. Digester discharge; L3. Dry sludge; L4. Sludge filtrate. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0017] Example 1 like Figure 1 and Figure 2 As shown, the sludge anaerobic digestion system of the present invention includes a sludge pulping tank 1, a dilution and cooling tank 2, and an anaerobic digestion tank 3 connected in sequence. The sludge pulping tank 1 is used to pulp the sludge raw material; the dilution and cooling tank 2 is used to dilute and cool the pulped sludge; and the anaerobic digestion tank 3 is used to perform anaerobic digestion on the cooled sludge. The anaerobic digestion tank 3 is equipped with multiple membrane modules 6. The membrane modules 6 are connected to an external acid tank 4 via a circulation pump 5. Dilute acid circulates within the membrane modules 6, and the partial pressure difference of free ammonia inside and outside the membrane modules 6 causes free ammonia to spontaneously transfer from the sludge in the anaerobic digestion tank 3 to the acid in the membrane modules 6, thereby reducing the concentration of free ammonia in the sludge and promoting organic carbon conversion and anaerobic digestion. The bottom of the anaerobic digestion tank 3 is connected to a sludge dewatering machine 10, which is used to dewater the anaerobically digested sludge to achieve sludge reuse. The top of the anaerobic digester 3 is equipped with a biogas collection pipe, and part of the biogas is recirculated into the anaerobic digester 3 through the compressor 7 for membrane surface flushing and sludge stirring, while the other part of the biogas is output outside the system for resource utilization.

[0018] In this embodiment, in-tank ammonia removal can be directly achieved, eliminating the need for solid-liquid separation of the anaerobic fermentation material and the subsequent mixing with solid materials after liquid ammonia removal. This reduces operational steps, improves operational efficiency, and lowers operating costs. Furthermore, it does not occupy external tank space and can achieve in-tank ammonia removal under normal pressure, resulting in low cost.

[0019] like Figure 2 As shown, in this embodiment, the membrane module 6 includes a support frame 61 and a water-proof and breathable membrane 62, with multiple water-proof and breathable membranes 62 arranged parallel to each other in the support frame 61 along the vertical direction. By having the water-proof and breathable membranes 62 directly contact the activated sludge, the concentration of free ammonia, an inhibitory factor in the anaerobic digestion process, is reduced, thereby improving the organic carbon conversion rate and biogas production rate during anaerobic digestion, and ultimately enhancing the economic benefits of the anaerobic digestion system.

[0020] In membrane module 6, the spacing between adjacent waterproof and breathable membranes 62 is greater than 10 cm, and the total surface area of ​​all waterproof and breathable membranes 62 in each membrane module 6 is greater than 12 m². 2 .

[0021] Furthermore, the waterproof and breathable membrane 62 is made of expanded polytetrafluoroethylene (ePTFE). The external dimensions of a single waterproof and breathable membrane 62 are greater than 100 cm × 50 cm × 1 cm, the filtration pore size is 1 nm to 5 nm, the porosity is 85% to 90%, the tensile strength is greater than 80 N, and the air permeability is greater than 7.0 × 10⁻⁶. 2 cm 3 / cm 2 / s / cm Hg, pH tolerance range is 0~14.

[0022] In this embodiment, a belt-type water-proof and breathable membrane 62 is used instead of a traditional hollow fiber membrane, which can effectively prevent acid from seeping out from the inside of the membrane, causing a decrease in pH inside the anaerobic digester and inhibiting the anaerobic digestion process. Moreover, the water-proof and breathable membrane 62 also alleviates the problem of membrane clogging and difficulty in cleaning, extends the operating time of a single membrane module, and improves the stability of the anaerobic digestion system.

[0023] In this embodiment, the density range of the membrane module 6 deployed in the digested sludge is: membrane area : sludge amount = 1 : 1 to 10 (m³). 2 / m 3 This approach not only improves the efficiency of anaerobic digestion of sludge but also does not increase the operating cost of the system.

[0024] In this embodiment, the partial pressure difference between the inside and outside of the water-proof and breathable membrane 62 is used to directly transfer free ammonia from the sludge to the circulating acid solution inside the membrane, thereby reducing the concentration of free ammonia in the sludge, reducing the inhibitory effect of high free ammonia concentration on the metabolism of anaerobic fermentation bacteria, and improving the biogas production rate and sludge organic carbon conversion rate in anaerobic digestion.

[0025] like Figure 1 As shown in this embodiment, the anaerobic digester 3 is also equipped with multiple aeration discs 9. Each membrane module 6 is evenly distributed with aeration discs 9 around its periphery. The aeration discs 9 are connected to the compressor 7 through pipes. The compressor 7 delivers pressurized biogas to the aeration discs 9. The pressurized biogas provides continuous surface scouring to the membrane module 6 through nozzles arranged in a ring on the aeration discs 9.

[0026] Furthermore, the diameter of the aeration disc 9 is 50 cm to 100 cm, and 10 to 20 nozzles are evenly arranged in a ring on each aeration disc 9, with each nozzle at a 40° angle to the aeration disc 9. o ~50 o The angle is oriented towards the center of the aeration disc 9.

[0027] like Figure 1 As shown in this embodiment, the bottom of the anaerobic digester 3 is also provided with a stirring branch pipe 8. The stirring branch pipe 8 is connected to the compressor 7 through a pipe. The compressor 7 delivers pressurized biogas to the stirring branch pipe 8. The pressurized biogas is evenly sprayed at the bottom of the anaerobic digester 3 through the stirring branch pipe 8 to achieve sludge circulation and stirring.

[0028] Excessive free ammonia concentration in sludge is one of the main inhibitory factors in the anaerobic digestion process. Directly reducing the free ammonia concentration within the digester is beneficial to improving the overall utilization rate of organic carbon conversion to methane in the sludge, thereby increasing the biogas production rate of anaerobic digestion. In this embodiment, the biogas produced by anaerobic digestion is used to stir the digester, which can achieve uniform material distribution within the digester. The biogas is also used to flush the membrane surface, which can slow down the membrane fouling rate and increase the operating time of a single membrane module.

[0029] Example 2 like Figure 3 As shown, the sludge anaerobic digestion treatment method of the present invention is implemented based on the anaerobic digestion treatment system in Example 1, and includes the following steps: Step S1: The excess sludge from the municipal wastewater treatment plant with a solids content of 15% to 25% is pulped in sludge pulping tank 1 at a pulping temperature of 70℃ to 90℃. The pulped sludge is then cooled to 56℃ to 58℃ in dilution and cooling tank 2 and diluted to a solids content of 10% to 12%, before being transported to anaerobic digester 3 for anaerobic digestion. During anaerobic digestion, the sludge stays in anaerobic digester 3 for 20 to 25 days, and the temperature is maintained at 55℃ to 57℃.

[0030] Step S2: The membrane module 6 with a water-proof and breathable membrane 62 is placed in the digested sludge within the anaerobic digester 3. The circulating liquid inside the membrane is dilute sulfuric acid with a concentration of 10–130 mmol / L, and the flow rate of the dilute sulfuric acid is controlled at 2–5 m / s. The partial pressure difference of free ammonia inside and outside the membrane facilitates the exchange of free ammonia in the sludge into the acid solution. The partial pressure difference of free ammonia inside and outside the water-proof and breathable membrane 62 is the main driving force for the transfer of free ammonia from the sludge outside the membrane to the acid solution inside the membrane, thereby reducing the concentration of free ammonia in the sludge. The partial pressure difference of free ammonia inside and outside the membrane is affected by various factors such as temperature, pH, and the degree of membrane fouling. Maintaining the partial pressure difference of free ammonia inside and outside the water-proof and breathable membrane and achieving stable operation of the membrane module is one of the key technologies of this technical solution.

[0031] Step S3: The biogas produced in the anaerobic digester 3 is divided into first biogas G1 and second biogas G2. First biogas G1 is pressurized by compressor 7 and then divided into first pressurized biogas G11 and second pressurized biogas G12. First pressurized biogas G11 enters the stirring branch pipe 8 at the bottom of the anaerobic digester 3 to achieve sludge circulation and stirring. Second pressurized biogas G12 enters the aeration disc 9 around the membrane module 6, providing continuous surface scouring to the membrane module 6 through the annularly arranged nozzles on the aeration disc 9. Second biogas G2 is discharged from the tank for resource utilization such as power generation, boilers, and compressed natural gas (CNG). Further, the biogas flow rate after pressurization by compressor 7 is 10 m / s to 15 m / s.

[0032] Step S4: The anaerobic digested sludge is transported to the sludge dewatering machine 10 for dewatering. Both the dewatered sludge and the filtrate are utilized for resource recovery. Specifically, the dewatered sludge is used for landscaping, incineration, building materials, and other applications. The filtrate produced by dewatering undergoes biochemical + membrane treatment and is used as sludge dilution water and production water.

[0033] In this embodiment, the method of reducing ammonia nitrogen concentration inside the anaerobic digester can promote the conversion rate of organic carbon in anaerobic digestion and increase biogas production. Using the biogas produced by anaerobic fermentation to flush the membrane surface extends the membrane's operating cycle and saves operating costs.

[0034] In step S2 of this embodiment, when the pH value of the acid solution is greater than 6, the dilute sulfuric acid containing ammonia is discharged, while some fresh dilute sulfuric acid is added. Magnesium oxide and sodium phosphate are added to the waste dilute sulfuric acid solution containing ammonia, and sodium hydroxide is added to adjust the pH value of the solution to be greater than 8, thereby obtaining fertilizer magnesium ammonium phosphate crystals. Further resource utilization of ammonia in the waste acid solution saves resources and improves economic efficiency.

[0035] Example 3 Municipal waste sludge with a solids content of 20% and a VSS content of 40% was heated to 90°C with steam in sludge slurry tank 1, and then cooled to a solids content of 11.6% and a temperature of 57.6°C in dilution and cooling tank 2. This sludge L1 was then added to anaerobic digester 3, where it was stored for 20 days at a temperature of 55°C. The water-proof and breathable membrane was made of expanded polytetrafluoroethylene (PTFE), with a single membrane size of 200 × 100 × 3 cm, a filtration pore size of 1 nm, a porosity of 85%, a tensile strength of 100 N, and an air permeability of 7.0 × 10⁻⁶. 2 cm 3 / cm 2 / s / cm Hg, the surface area of ​​each membrane module is 4.18 m². 2 They are installed in a parallel and vertical manner, with a spacing of 20 cm between each membrane module. The total surface area of ​​each membrane module is approximately 20 m². 2 The ratio of inner membrane area to sludge volume in the tank is 2:1m². 2 / m 3 The initial concentration of dilute sulfuric acid in acid tank 4 is 100 mmol / L. The circulation flow rate of dilute sulfuric acid inside the membrane is maintained at 4 m / s by adjusting the circulation pump 5.

[0036] The biogas produced in the anaerobic digester is divided into primary biogas G1 and secondary biogas G2. Primary biogas G1, after being pressurized by compressor 7, flows at a velocity of 10 m / s and is further divided into primary pressurized biogas G11 and secondary pressurized biogas G12. Primary pressurized biogas G11 enters the stirring branch pipe 8 at the bottom of the tank to achieve sludge circulation and stirring. Secondary pressurized biogas G12 enters the aeration discs 9 surrounding the membrane module 6. The aeration discs have a diameter of 75 cm and provide continuous surface scouring to the membrane module 6 through 10 nozzles arranged in a ring on each aeration disc. Secondary biogas G2 is discharged from the tank for resource utilization.

[0037] The anaerobic digested sludge L2 is processed by sludge dewatering machine 10. The dewatered dry sludge L3 is used for landscaping, incineration, building materials and other applications. The filtrate L4 produced by dewatering is treated by biochemical + membrane treatment and used as sludge dilution water and production water supplement.

[0038] Magnesium oxide and sodium phosphate were added to a waste dilute sulfuric acid solution containing ammonia. After adjusting the pH of the solution to 8.5 with sodium hydroxide, magnesium ammonium phosphate hexahydrate crystals with a purity of 53.7% could be obtained.

[0039] Data monitoring showed the following trends in ammonia nitrogen concentration and sludge VSS content within the tank over the 92 days following the start of the process: Figure 4As shown, the ammonia nitrogen concentration in the tank gradually decreased from 2311 mg / L to around 1350 mg / L and then stabilized. The pH value in the tank was 7.99. Simultaneously, the VSS content of the sludge in the tank showed a similar trend, decreasing from 33% to around 28% and then stabilizing, while the degradation rate increased from 25% to 40%. On the 12th day of operation, the ammonia nitrogen concentration in the tank increased. At this point, the pH of the circulating acid solution was greater than 6. After partially replacing the circulating dilute sulfuric acid with fresh sulfuric acid, the ammonia nitrogen concentration gradually decreased. This method was used to maintain the ammonia nitrogen concentration in the tank at a low level. The decrease in the VSS content of the sludge also resulted in a reduction of approximately 15% in the chemical consumption of the sludge dewatering machine (per ton of dry sludge).

[0040] Biogas production rate monitoring data during operation, such as Figure 5 As shown, the biogas production per cubic meter is calculated based on the amount of mud added per ton. Figure 5 Data shows that the amount of biogas produced in the anaerobic digester gradually increases and eventually stabilizes. Compared with the initial state of the system, the biogas production in the stable state increases by about 31%.

[0041] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A sludge anaerobic digestion treatment system, characterized in that, The system includes a sludge pulping tank (1), a dilution and cooling tank (2), and an anaerobic digestion tank (3) connected in sequence. The sludge pulping tank (1) is used to pulp the sludge raw material, the dilution and cooling tank (2) is used to dilute and cool the pulped sludge, and the anaerobic digestion tank (3) is used to anaerobic digest the cooled sludge. The anaerobic digestion tank (3) is equipped with multiple membrane modules (6) inside. Each membrane module (6) includes a support frame (61) and a water-proof and breathable membrane (62). Multiple water-proof and breathable membranes (62) are arranged parallel to each other in the vertical direction. In the support frame (61); the membrane module (6) is connected to the external acid tank (4) through a circulation pump (5), using dilute acid to circulate in the membrane module (6), and through the partial pressure difference of free ammonia inside and outside the membrane module (6), free ammonia is spontaneously transferred from the sludge in the anaerobic digester (3) to the acid in the membrane module (6), thereby reducing the concentration of free ammonia in the sludge in the anaerobic digester (3) and promoting the organic carbon conversion and anaerobic digestion of the sludge; the bottom of the anaerobic digester (3) is connected to the sludge dewatering machine (10), and the sludge dewatering machine (10) is connected to the sludge dewatering machine (10). 0) Used for dewatering sludge after anaerobic digestion to achieve sludge reuse; the top of the anaerobic digester (3) is equipped with a biogas collection pipe, and part of the biogas is recirculated into the anaerobic digester (3) through the compressor (7) for rinsing the surface of the membrane module (6) and stirring the sludge, while the other part of the biogas is output outside the system for resource utilization; the anaerobic digester (3) is also equipped with multiple aeration discs (9), and aeration discs (9) are evenly distributed around the periphery of each group of membrane modules (6), and the aeration discs (9) are connected to the system through pipes. The compressor (7) is connected to the aeration disc (9), which delivers pressurized biogas to the aeration disc (9). The pressurized biogas provides continuous surface scouring to the membrane module (6) through the nozzles arranged in a ring on the aeration disc (9). The bottom of the anaerobic digester (3) is also provided with a stirring branch pipe (8), which is connected to the compressor (7) through a pipe. The compressor (7) delivers pressurized biogas to the stirring branch pipe (8), and the pressurized biogas is evenly sprayed at the bottom of the anaerobic digester (3) through the stirring branch pipe (8) to achieve sludge circulation and stirring. The waterproof and breathable membrane (62) is made of expanded polytetrafluoroethylene, and the external dimensions of a single waterproof and breathable membrane (62) are greater than 100 cm. 50 cm 1 cm, filter pore size 1nm~5nm, porosity 85%~90%, tensile strength greater than 80 N, air permeability greater than 7.0×10 2 cm 3 / cm 2 / s / cm Hg, pH tolerance range is 0~14; The diameter of the aeration disc (9) is 50 cm to 100 cm, and 10 to 20 nozzles are evenly arranged in a ring on each aeration disc (9), with each nozzle at a 40° angle to the aeration disc (9). o ~50 o The angle is oriented toward the center of the aeration disc (9).

2. The sludge anaerobic digestion treatment system according to claim 1, characterized in that, The spacing between adjacent waterproof and breathable membranes (62) is greater than 10 cm, and the total surface area of ​​all waterproof and breathable membranes (62) in each membrane module (6) is greater than 12 m². 2 .

3. The sludge anaerobic digestion treatment system according to claim 1, characterized in that, The density range of the membrane module (6) in the digested sludge is: membrane area: sludge amount = 1: 1 to 10.

4. A method for anaerobic digestion of sludge based on the anaerobic digestion system according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: The residual sludge from the municipal wastewater treatment plant with a solids content of 15% to 25% is pulped in a sludge pulping tank (1) at a pulping temperature of 70℃ to 90℃. The pulped sludge is then cooled to 56℃ to 58℃ in a dilution and cooling tank (2) and diluted to a solids content of 10% to 12%. It is then transported to an anaerobic digestion tank (3) for anaerobic digestion. During the anaerobic digestion process, the sludge stays in the anaerobic digestion tank (3) for 20 to 25 days, and the temperature is maintained at 55℃ to 57℃. Step S2: The membrane module (6) with a water-proof and breathable membrane (62) is placed in the digested sludge in the anaerobic digester (3). The circulating liquid inside the membrane is dilute sulfuric acid with a concentration of 10-130 mmol / L, and the flow rate of the dilute sulfuric acid is controlled at 2-5 m / s. The free ammonia in the sludge is exchanged into the acid liquid by utilizing the partial pressure difference of free ammonia inside and outside the membrane. Step S3: The biogas produced in the anaerobic digester (3) is divided into first biogas (G1) and second biogas (G2). The first biogas (G1) is pressurized by the compressor (7) and then divided into first pressurized biogas (G11) and second pressurized biogas (G12). The first pressurized biogas (G11) enters the stirring branch pipe (8) at the bottom of the anaerobic digester (3) to realize sludge circulation and stirring. The second pressurized biogas (G12) enters the aeration disc (9) around the membrane module (6) and provides continuous surface flushing to the membrane module (6) through the nozzles arranged in a ring on the aeration disc (9). The second biogas (G2) is discharged from the tank for resource utilization. Step S4: The sludge after anaerobic digestion is transported to a sludge dewatering machine (10) for dewatering treatment. The sludge and filtrate obtained after dewatering are both utilized as resources.

5. The anaerobic digestion treatment method for sludge according to claim 4, characterized in that, In step S2, when the pH value of the acid solution is greater than 6, the dilute sulfuric acid containing ammonia is discharged, and fresh dilute sulfuric acid is added at the same time; magnesium oxide and sodium phosphate are added to the waste dilute sulfuric acid solution containing ammonia, and sodium hydroxide is added to adjust the pH value of the solution to be greater than 8, thereby obtaining fertilizer magnesium ammonium phosphate crystals.

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