A process and device for large-scale extraction of extracellular polymers from excess sludge

Abstract

The present invention relates to a process and apparatus for large-scale extraction of extracellular polymers from excess sludge. The process comprises collecting excess sludge into a sludge buffer tank; concentrating the sludge through a spiral centrifuge; performing heat exchange and temperature increase; transferring the heated sludge to an alkaline heating tank for reaction and separation of extracellular polymers; exchanging heat with normal-temperature sludge in a heat exchanger after the reaction; performing solid-liquid separation of the alkaline sludge after the heat exchange in a horizontal centrifuge, and collecting an extracellular polymer solution; acidifying the extracellular polymer solution in an acidification tank; separating colloidal extracellular polymers from the acidified solution in a disc centrifuge, and storing the colloidal extracellular polymers in a storage tank. The process provided by the present invention has the advantages of large extracellular polymer extraction volume and saving manual operation. The extracellular polymers obtained by the process can be used in the fields of pollutant control, soil improvement, papermaking and textiles, and have extremely high economic value.

Description

Technical Field

[0001] The invention relates to a process and a device for large-scale extraction of extracellular polymers from excess sludge, belonging to the technical field of sewage treatment resource utilization. Background Art

[0002] Wastewater treatment plants generate a large amount of excess sludge during operation. Conventional treatment methods for this excess sludge include sludge incineration and landfilling. These methods are not only costly but also have negative environmental impacts. Therefore, it is necessary to promote the resource utilization of excess sludge, achieve sludge reduction, and mitigate the negative environmental impact of the sludge treatment process.

[0003] Extracellular polymeric substances (EPS) can account for as much as 10% to 40% of the dry weight of excess sludge from sewage treatment plants. These substances primarily originate from biomacromolecules produced during microbial growth, secretion, and apoptosis and degradation in activated sludge. These substances form a network structure with adsorption properties through physical and chemical reactions, protecting the activated sludge from external conditions and maintaining its reactivity. The primary components of EPS in excess sludge are polysaccharides and proteins, along with some nucleic acids and humic acid. EPS have great potential and commercial value in areas such as pollutant remediation, soil improvement, papermaking, textiles, and the construction industry.

[0004] Although both physical and chemical methods can be used to extract EPS from residual sludge, such as centrifugation, ultrasound, heating, ethylenediaminetetraacetic acid, cation exchange resin, formamide sodium hydroxide, formaldehyde-NaOH, hydrothermal sodium carbonate, acid treatment, etc., chemical extraction methods generally have higher EPS yields than physical extraction methods. However, compared with physical methods, chemical methods introduce more chemical pollution. Among all extraction methods, EPS extraction under alkaline conditions has a higher yield. Studies have shown that alkaline conditions can destroy disulfide bonds in proteins and hydrolyze polysaccharides, which is conducive to the extraction of negatively charged components, which has a good effect on the stripping of EPS. However, this method is currently difficult to directly apply to the large-scale extraction of extracellular polymers. The main reasons are as follows: (1) The extraction process requires a lot of manual operation, the process is complicated and consumes a lot of labor costs. (2) Low scale yield: The extraction process is not a continuous flow, and the centrifuge capacity is generally less than 250ml, the extraction volume is small and the efficiency is low. (3) A weakly alkaline sodium carbonate aqueous solution is used to adjust the pH, and the dosage is large. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] In order to solve the above problems in the prior art, the present invention provides a process and apparatus for large-scale extraction of extracellular polymers from excess sludge.

[0007] (2) Technical solution

[0008] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] A process for large-scale extraction of extracellular polymers from excess sludge comprises the following steps:

[0010] S1, transporting the excess activated sludge with high water content to the sludge storage tank;

[0011] S2. Transfer the excess sludge with high water content in the sludge storage tank in step S1 to a snail press, add flocculant, dehydrate it through the snail press, and collect the concentrated sludge;

[0012] S3, transferring the concentrated sludge at room temperature in step S2 to a heat exchanger, where the temperature of the concentrated sludge is increased through heat exchange in the heat exchanger;

[0013] S4, continuously transferring the concentrated sludge after the heating in step S3 to an alkaline heating tank, where the concentrated sludge is stirred and heated to adjust the concentration of the sludge to alkaline;

[0014] S5, transferring the high-temperature alkaline sludge treated in step S4 to the heat exchanger in S3; exchanging heat with the room-temperature sludge in S3, while reducing the temperature of the high-temperature excess sludge treated in step S4;

[0015] S6. Transferring the alkaline sludge after heat exchange in step S5 to a horizontal centrifuge; performing solid-liquid separation of the alkaline sludge in the horizontal centrifuge; collecting the liquid phase containing extracellular polymeric substances and entering the acidification tank, and discharging the solid phase sludge as waste;

[0016] S7. Acidification is performed in the acidification tank, and the acidified solution is continuously transferred out of the acidification tank. The polysaccharides and proteins in the extracellular polymers are denatured into colloids in the acidic environment, which facilitates separation from the aqueous solution;

[0017] S8. The acidified aqueous phase in step S7 is transferred to a disc centrifuge to separate the colloidal extracellular polymers from the aqueous phase, and the colloidal extracellular polymers are transferred to a storage tank or barrel for storage.

[0018] In the process as described above, preferably, in step S1, the water content of the excess activated sludge is 93-98%, and the sludge is flocculent sludge, granular sludge or biofilm sludge generated from biological treatment facilities such as urban sewage, industrial wastewater and food processing.

[0019] In the process described above, preferably, in step S2, the flocculant is polyacrylamide, and the added content is 0.5% of the dry sludge mass; the dehydration and concentration operating parameters of the screw stack are a centrifuge angle of 30 degrees and a centrifuge main shaft speed of 55-65 rpm; and the moisture content of the concentrated sludge after dehydration is 90-92%.

[0020] In the process described above, preferably, in step S3, the temperature of the concentrated sludge is increased to 40-55°C; in step S4, the stirring rate is 150-220 rpm, the temperature is heated to 75-85°C, and sodium hydroxide solution is added to the alkaline heating tank to adjust the pH value to 9.5-11.

[0021] In the process as described above, preferably, in step S6, the horizontal centrifuge is a sedimentation type, and the operating parameters are a drum speed of 2000 rpm and an initial differential speed between the rotor and the screw of 5-15 rpm.

[0022] In the process described above, preferably, in step S7, the acidification is performed by adjusting the pH value of the liquid in the acidification tank to maintain at 2-3 using a 1 mol / L hydrochloric acid solution; and in step S8, the rotation speed of the disc centrifuge is 3500-4500 rpm.

[0023] In the process as described above, preferably, in step S2, the flow rate transmitted to the screw stacking machine is 400~800L / hour, in step S3, the amount of flocculant added is 40~80g / hour; in step S4, the concentrated sludge enters and flows out of the alkaline heating tank at a flow rate of 400L~800L / hour.

[0024] A device for large-scale extraction of extracellular polymers from excess sludge comprises a sludge storage tank, a screw stack, a heat exchanger, an alkaline heating tank, a horizontal centrifuge, an acidification tank, a disc centrifuge and a storage tank, which are connected in sequence. The outlet of the alkaline heating tank is connected to the heat exchanger and then to the inlet of the horizontal centrifuge through the heat exchanger. A stirring device and a pH regulating device are provided in both the alkaline heating tank and the acidification tank, and a heating device is also provided in the alkaline heating tank.

[0025] As described above, preferably, the alkaline heating tank includes a reaction tank body, a first stirring device, a heating device and a first pH adjusting device, the outer layer of the reaction tank body is coated with an insulation layer, and the left and right ends of the reaction tank body are respectively provided with a sludge inlet and an outlet, the sludge inlet is connected to the heat exchanger, and the outlet is connected to the horizontal centrifuge; the first stirring device is arranged in the center of the reaction tank body, and the heating device is arranged at the central bottom of the reaction tank body; the first pH adjusting device includes a first dosing pump, a first drug storage barrel, a first online pH meter and a first programmable logic controller, the first online pH meter is arranged at the front end of the reaction tank body, and a first dosing port is provided on the reaction tank body opposite the first online pH meter; the first online pH meter is connected to the first programmable logic controller, and the first programmable logic controller is connected to the first dosing pump and the heating device; the liquid inlet pipe of the first dosing pump is connected to the first drug storage barrel, and the liquid outlet is connected to the first dosing port.

[0026] As described above, preferably, the acidification tank includes an acidification reaction tank body, a second stirring device and a second pH adjustment device, the front and rear ends of the acidification reaction tank body are provided with a liquid inlet and a liquid outlet, and the second stirring device is arranged in the center of the acidification reaction tank body; the second pH adjustment device includes a second dosing pump, a second medicine storage barrel, a second online pH meter and a second programmable logic controller; the front and rear ends of the acidification reaction tank body are respectively provided with a second online pH meter and a second dosing port, the second online pH meter is connected to the second programmable logic controller, and the second programmable logic controller is connected to control the start and stop of the second dosing pump; the liquid inlet pipe of the second dosing pump is connected to the second medicine storage barrel, and the liquid outlet of the second dosing pump is connected to the second dosing port.

[0027] (3) Beneficial effects

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a process and apparatus for large-scale extraction of extracellular polymers from excess sludge. This process can extract extracellular polymers on a large scale, with a processing capacity exceeding 800 liters per hour, enabling large-scale treatment of excess sludge. The extracellular polymers obtained after treatment can be used in pollutant control, soil improvement, papermaking, textiles, and other fields, and have extremely high economic value. The apparatus provided by the present invention for large-scale extraction of extracellular polymers from excess sludge has a small footprint, is easy to install, requires low investment, offers stable output, and does not require continuous personnel monitoring. Furthermore, the process achieves high EPS extraction efficiency and lower power and chemical consumption per unit of output.

[0030] The process of the present invention is continuously operated, the extraction process reduces manual operation and saves labor, and the heat exchange system is provided to reduce energy consumption in operation and save operation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1A process flow chart for large-scale extraction of extracellular polymers provided for the implementation of the present invention;

[0032] Figure 2 Schematic diagram of the structure of the alkaline heating pool;

[0033] Figure 3 Schematic diagram of the acidification tank structure.

[0034] [Description of Reference Numerals]

[0035] 1: reaction cell body;

[0036] 2: Insulation layer;

[0037] 3: Sludge inlet;

[0038] 4: Export;

[0039] 5: first stirring device;

[0040] 6: Heating device;

[0041] 7: The first dosing pump;

[0042] 8: The first medicine storage barrel;

[0043] 9: First online pH meter;

[0044] 10: First programmable logic controller;

[0045] 11: First dosing port;

[0046] 12: Acidification reaction tank body;

[0047] 13: second stirring device;

[0048] 14: liquid inlet;

[0049] 15: Liquid outlet;

[0050] 16: Second dosing pump;

[0051] 17: Second medicine storage barrel;

[0052] 18: Second online pH meter;

[0053] 19: Second programmable logic controller;

[0054] 20: The second dosing port. DETAILED DESCRIPTION

[0055] The present invention relates to a process and apparatus for large-scale extraction of extracellular polymeric substances from excess sludge. The process can extract extracellular polymeric substances from activated sludge in large quantities and efficiently through the steps of sludge concentration, alkaline heat extraction, decanter centrifuge separation, acidification, and disc centrifuge separation.

[0056] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0057] Example 1

[0058] A process for continuously and massively extracting extracellular polymeric substances from excess sludge comprises the following steps:

[0059] S1: Transport 1m³ of municipal excess activated sludge with a moisture content between 97% and 98% to unit 1 - sludge storage tank

[0060] S2: The residual sludge in the unit 1-sludge storage tank is transferred to the unit 2-snail stacker at a flow rate of 500L / hour, and flocculants are added to assist. The unit 2-snail stacker reduces the sludge moisture content to 90%, and collects the concentrated sludge. The flocculant is a polyacrylamide material, and the added content is 0.5% of the dry sludge mass, that is, the flocculant is added at a rate of 50g / hour. The addition of flocculants is used to improve the dehydration efficiency of the snail stacker; the operating parameters of the snail stacker are a centrifuge angle of 30 degrees and a centrifuge spindle speed of 60rpm.

[0061] S3: The concentrated sludge at room temperature is transferred to unit 3 - heat exchanger, which heats the room temperature sludge to 50°C. The heat exchanger adopts shell and tube heat exchanger.

[0062] S4: The concentrated sludge heated in step S3 is continuously transferred to the alkaline heating tank in unit 4 at a rate of 500 L / hour. A 1 mol / L sodium hydroxide solution is added to adjust the pH to 9.5-11. After stirring and heating in the alkaline heating tank to extract extracellular polymers (ECPs), the mixed sludge is continuously discharged from the tank at a rate of 500 L / hour. The alkaline heating environment hydrolyzes the proteins and polysaccharides in the excess sludge, facilitating the removal of ECPs.

[0063] S5: The 80°C mixed sludge treated in step S4 is transferred to unit 3-heat exchanger for heat exchange, and heat is exchanged with the original room temperature sludge initially added in step S3. After the heat is exchanged with the room temperature sludge, the temperature of the 80°C mixed sludge treated in step S4 is reduced to 40°C.

[0064] S6: The 40°C mixed sludge after heat exchange in step S5 is transferred to Unit 5 - a horizontal centrifuge. The horizontal centrifuge is a decanter type, operating at a drum speed of 2000 rpm and an initial differential speed between the rotor and the screw of 5-15 rpm. The mixed sludge undergoes solid-liquid separation in Unit 5 - a horizontal centrifuge. The liquid phase containing extracellular polymeric substances is collected, and the solid sludge residue is discharged as waste.

[0065] S7: The extracellular polymer solution collected in step S6 is continuously transferred to unit 6, the acidification tank. A 1 mol / L hydrochloric acid solution is added to the acidification tank to maintain the pH of the liquid in the acidification tank at 2-3. The acidified solution is stirred and continuously transferred out of the acidification tank. The polysaccharides and proteins in the extracellular polymer are denatured into colloids in the acidic environment, facilitating their separation from the aqueous solution.

[0066] S8: The acidified aqueous phase from step S7 is transferred to unit 7, a disc centrifuge. The disc centrifuge is operated at 4000 rpm. The disc centrifuge separates the colloidal extracellular polymeric substances from the aqueous phase and transfers the colloidal extracellular polymeric substances to unit 8, a storage tank (or storage barrel) for storage. In this step, 95% of the colloidal extracellular polymeric substances in the original solution can be separated and extracted.

[0067] The above process can be carried out using a large-scale device for extracting extracellular polymers from excess sludge, which includes a sludge storage tank, a screw stack, a heat exchanger, an alkaline heating tank, a return heat exchanger, a horizontal centrifuge, an acidification tank, a disc centrifuge and a storage tank connected in sequence;

[0068] Among them, alkaline heating pools such as Figure 2 As shown, it is a device for providing heating, stirring and alkaline conditions for the extracellular polymer extraction process. The alkaline heating tank comprises a reaction tank body 1, a first stirring device, a heating device and a first pH regulating device.

[0069] The reaction tank body 1 is made of stainless steel and is square. Its length, width and height are 1m×0.4m×0.6m. The outer layer of the reaction tank body 1 is covered with an insulation layer 2, and the insulation layer 2 is composed of 3 cm thick polyurethane. The left and right ends of the reaction tank body 1 are respectively provided with a sludge inlet 3 and an outlet 4. The sludge inlet is connected to the heat exchanger, and the outlet is connected to the horizontal centrifuge. During operation, the sludge flows in and out continuously from the sludge inlet 3 and the outlet 4 at a flow rate of 100L / hour. A first stirring device 5 is provided in the middle of the reaction tank body 1. The first stirring device 5 is a stirring paddle driven by a motor and is evenly distributed in the tank body. A heating device 6 is provided at the bottom of the reaction tank body 1, which is heated by an electric heating wire. The electric heating wire is evenly distributed at the bottom of the tank body. The reaction tank liquid is adjusted to 80°C by temperature control.

[0070] The first pH adjustment device comprises a first dosing pump 7, a first drug storage tank 8, a first online pH meter 9, and a first programmable logic controller 10. A first dosing port 11 and the first online pH meter 9 are respectively positioned in the middle of the two long sides of the reaction tank. The first online pH meter is connected to the first programmable logic controller, which controls the start and stop of the first dosing pump. The first dosing pump's inlet pipe is connected to the first drug storage tank, and the first dosing pump's outlet is connected to the first dosing port. The pH of the liquid in the reaction tank is maintained between 9.5 and 11. Specifically, when the first online pH meter detects that the pH of the liquid in the tank is less than 9.5, the first programmable logic controller activates the dosing pump, transferring the sodium hydroxide solution from the first drug storage tank to the reaction tank. Dosing stops when the first online pH meter detects that the pH of the liquid in the tank is higher than 11.

[0071] Acidification tank is a device that adjusts the extracellular polymer solution to acidity, such as Figure 3 The device comprises an acidification reaction tank body 12, a second stirring device 13 and a second pH regulating device.

[0072] The acidification reaction tank body 12 is made of stainless steel and is equipped with a liquid inlet 14 and a liquid outlet 15 at its front and rear ends. The liquid inlet is connected to a horizontal centrifuge, and the liquid outlet is connected to a disc centrifuge. A second stirring device 13 is located in the center of the acidification reaction tank. The stirring device is a motor-driven stirring paddle and is located in the center of the acidification reaction tank.

[0073] The pH adjustment device consists of a second dosing pump 16, a second drug storage tank 17, a second online pH meter 18, and a second programmable logic controller 19. The second online pH meter 18 and a second dosing port 20 are respectively provided at the front and rear ends of the acidification reaction tank body 12. The second online pH meter 18 is connected to the second programmable logic controller 19, which is connected to control the second dosing pump 16. The liquid inlet pipe of the second dosing pump 16 is connected to the second drug storage tank 17, and the liquid outlet of the second dosing pump 16 is connected to the second dosing port 20.

[0074] The second drug storage tank is filled with a 1 mol / L hydrochloric acid solution, which is used to adjust the pH of the liquid in the acidification tank to maintain a range of 2 to 3. That is, when the online pH meter detects that the pH of the liquid in the tank is greater than 3, the programmable logic controller starts the dosing pump to transport the hydrochloric acid in the drug storage tank to the acidification tank. The dosing stops when the online pH meter detects that the pH of the liquid in the tank is less than 2.

[0075] The process of large-scale extraction of extracellular polymers from residual sludge using the above-mentioned device can extract extracellular polymers on a large scale, with a processing capacity of more than 500 liters / hour, and the process flow runs continuously. The extraction process reduces manual operations and saves labor; the setting of a heat exchange system reduces energy consumption during operation and saves costs.

[0076] Comparative Example

[0077] The method for extracting extracellular polymers from residual sludge used in the prior art includes the following steps: (1) manually adding activated sludge to a centrifuge tube, centrifuging it with a centrifuge, and slowly pouring out the supernatant to obtain concentrated sludge; (2) transferring the concentrated sludge at the bottom of the centrifuge tube to a beaker with a key, adding a sodium carbonate aqueous solution to adjust the pH of the sludge solution to 9-10; (3) heating the sludge in a water bath to 80°C; (4) heating and stirring the solution for 2 hours; (5) transferring the reaction solution to a centrifuge tube, centrifuging and collecting the supernatant; (6) adjusting the pH to 2.2; and (7) transferring it to a centrifuge tube and collecting the extracellular polymers in the upper layer after centrifugation. This method has significant disadvantages compared to the method of the present invention, with lower yield, low efficiency, and requiring a lot of manual operation.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the above-disclosed embodiments into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above-disclosed embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention shall remain within the scope of protection of the present invention.

Claims

1. A process for large-scale extraction of extracellular polymers from excess sludge, characterized in that: It includes the following steps: S1. transporting excess activated sludge with high moisture content to a sludge storage tank, wherein the excess activated sludge has a moisture content of 93-98%; S2. Transfer the excess sludge with high water content in the sludge storage tank in step S1 to a snail press, add flocculant, dehydrate it through the snail press, and collect the concentrated sludge; S3, transferring the concentrated sludge at room temperature in step S2 to a heat exchanger, where the temperature of the concentrated sludge is raised to 50°C through heat exchange; S4, continuously transferring the concentrated sludge after heating in step S3 to an alkaline heating tank, where it is stirred and heated to adjust the concentrated sludge to alkaline; S5, transferring the high-temperature alkaline sludge treated in step S4 to the heat exchanger in S3; exchanging heat with the room-temperature sludge in S3, while reducing the temperature of the high-temperature residual sludge treated in step S4 to 40°C; S6. Transferring the alkaline sludge after heat exchange in step S5 to a horizontal centrifuge; performing solid-liquid separation in the alkaline sludge in the horizontal centrifuge; wherein the horizontal centrifuge is a sedimentation type, and the operating parameters are a drum speed of 2000 rpm and an initial differential speed between the drum and the screw of 5-15 rpm; collecting the liquid phase containing extracellular polymeric substances and entering the acidification tank, and discharging the solid phase sludge as waste; S7. Acidification is performed in an acidification tank, and the acidified solution is continuously transferred out of the acidification tank; polysaccharides and proteins in extracellular polymers are denatured into colloids under an acidic environment, which is conducive to separation from the aqueous solution; S8, transferring the acidified aqueous phase in step S7 to a disc centrifuge at a speed of 3500-4500 rpm to separate the colloidal extracellular polymeric substances from the aqueous phase, and transferring the colloidal extracellular polymeric substances to a storage tank or barrel for storage; In step S2, the flocculant is polyacrylamide, and the added content is 0.5% of the dry sludge mass; the dehydration and concentration operating parameters of the spiral stacker are a centrifuge angle of 30 degrees and a centrifuge main shaft speed of 55-65 rpm; the moisture content of the concentrated sludge after dehydration is 90-92%; In step S3, the temperature of the concentrated sludge is raised to 40-55°C; in step S4, the temperature is heated to 75-85°C at a stirring rate of 150-220 rpm, and sodium hydroxide solution is added to the alkaline heating tank to adjust the pH value to 9.5-11; In step S7, the acidification is performed by adjusting the pH value of the liquid in the acidification tank to maintain at 2-3 using a 1 mol / L hydrochloric acid solution.

2. The process according to claim 1, wherein In step S1 , the sludge is flocculent sludge, granular sludge or biofilm sludge generated from urban sewage, industrial wastewater and food processing biological treatment facilities.

3. The process according to claim 1, wherein In step S2, the flow rate transmitted to the spiral stacking machine is 400~800L / hour, in step S3, the flocculant is added at a rate of 40~80g / hour; in step S4, the concentrated sludge enters and flows out of the alkaline heating tank at a flow rate of 400~800L / hour.

4. A device for large-scale extraction of extracellular polymers from excess sludge, comprising a sludge storage tank, a screw stack, a heat exchanger, an alkaline heating tank, a horizontal centrifuge, an acidification tank, a disc centrifuge and a storage tank connected in sequence, wherein: The outlet of the alkaline heating pool is connected to the heat exchanger, and then to the inlet of the horizontal centrifuge through the heat exchanger. The alkaline heating pool and the acidification pool are both equipped with a stirring device and a pH regulating device. The alkaline heating pool is also equipped with a heating device. The alkaline heating tank includes a reaction tank body, a first stirring device, a heating device and a first pH adjustment device. The outer layer of the reaction tank body is coated with an insulation layer. The left and right ends of the reaction tank body are respectively provided with a sludge inlet and an outlet. The sludge inlet is connected to a heat exchanger, and the outlet is connected to a horizontal centrifuge. The first stirring device is arranged in the center of the reaction tank body, and the heating device is arranged at the central bottom of the reaction tank body. The first pH adjustment device includes a first dosing pump, a first drug storage barrel, a first online pH meter and a first programmable logic controller. The first online pH meter is arranged at the front end of the reaction tank body, and a first dosing port is provided on the reaction tank body opposite the first online pH meter. The first online pH meter is connected to the first programmable logic controller, and the first programmable logic controller is connected to the first dosing pump and the heating device. The liquid inlet pipe of the first dosing pump is connected to the first drug storage barrel, and the liquid outlet is connected to the first dosing port. The acidification tank includes an acidification reaction tank body, a second stirring device and a second pH adjustment device. The front and rear ends of the acidification reaction tank body are provided with a liquid inlet and a liquid outlet. The liquid inlet is connected to a horizontal centrifuge, and the liquid outlet is connected to a disc centrifuge. The second stirring device is arranged in the center of the acidification reaction tank body. The second pH adjustment device includes a second dosing pump, a second medicine storage barrel, a second online pH meter and a second programmable logic controller. The front and rear ends of the acidification reaction tank body are respectively provided with a second online pH meter and a second dosing port. The second online pH meter is connected to the second programmable logic controller, and the second programmable logic controller is connected to control the start and stop of the second dosing pump. The liquid inlet pipe of the second dosing pump is connected to the second medicine storage barrel, and the liquid outlet of the second dosing pump is connected to the second dosing port.

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