In-situ capacity expansion system and control method thereof

Abstract

The application provides an in-situ capacity expansion system and a control method thereof. The in-situ capacity expansion system is applied to a biochemical treatment system, and comprises a sludge screening device and a membrane separation tank. The operation mode of the in-situ capacity expansion system has a first mode, a second mode and a third mode. The in-situ capacity expansion system and the control method thereof can adjust the operation strategy of the in-situ capacity expansion system in real time according to the water inflow load, water quality change, biochemical reaction state and membrane tank pollution condition, and have higher operation flexibility and adaptability.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and in particular to an in-situ expansion system and its control method. Background Technology

[0002] With the continuous advancement of urbanization and the growth of population and industry, sewage discharge has been increasing year by year. Existing sewage treatment plants generally face the problem of insufficient treatment capacity during long-term operation, especially during the rainy season, which makes it difficult for the effluent quality to meet standards stably or requires frequent load reduction, affecting sewage treatment efficiency and quality. At the same time, the existing sewage treatment system has poor flexibility. When the inflow water fluctuates, especially when it is close to the load capacity of the sewage treatment system, such fluctuations will have a significant impact on the normal operation of the sewage treatment system. Summary of the Invention

[0003] In view of this, the purpose of this application is to propose an in-situ capacity expansion system and its control method to solve the above-mentioned technical problems.

[0004] A first aspect of this application provides an in-situ expansion system for use in a biochemical treatment system, the biochemical treatment system comprising, in sequence, an inlet pipeline, a biochemical reaction zone, a first connecting pipeline, a secondary sedimentation tank, and a first drainage pipeline; the bottom of the secondary sedimentation tank is connected to the biochemical reaction zone via a sludge return pipeline; the in-situ expansion system includes:

[0005] A sludge screening device includes a sludge screening body and an overflow port at the top, a bottom flow port at the bottom, and a first feed port on the side wall of the sludge screening body. The first feed port is connected to the sludge return pipeline and the first connecting pipeline through a first feed pipeline and a second feed pipeline, respectively. The bottom flow port is connected to the biochemical reaction zone through the first return pipeline. The overflow port is connected to a second drainage pipeline to discharge the overflow products to the outside of the system.

[0006] The membrane separation tank is equipped with a second feed inlet, a drain outlet, and a sludge discharge outlet. A membrane module for separating sludge and water is installed between the second feed inlet and the drain outlet. The second feed inlet is connected to the underflow outlet and the first connecting pipeline via a third feed pipeline and a fourth feed pipeline, respectively. The sludge discharge outlet is connected to the biochemical reaction zone via a second return pipeline. The drain outlet is connected to a third drain pipeline to discharge the permeate from the membrane separation tank to the outside of the system.

[0007] The in-situ expansion system has three operating modes: a first mode, a second mode, and a third mode. In the first mode, the sludge screening device, the first feed pipeline, the first return pipeline, and the second drainage pipeline are in operation; the membrane separation tank and the second feed pipeline are in non-operational state.

[0008] In the second mode, the membrane separation tank, the fourth feed pipeline, the second return pipeline and the third drainage pipeline are in operation, while the sludge screening device is in non-operational state.

[0009] In the third mode, the sludge screening device, the membrane separation tank, the second feed pipeline, the third feed pipeline, the second return pipeline, the second drainage pipeline, and the third drainage pipeline are in operation, while the first feed pipeline, the first return pipeline, and the fourth feed pipeline are in non-operational state.

[0010] Furthermore, the biochemical reaction zone includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence;

[0011] The bottom of the secondary sedimentation tank is connected to the anaerobic tank via the sludge return pipeline;

[0012] And / or, the bottom of the aerobic tank is connected to the anoxic tank via an internal reflux pipeline.

[0013] Furthermore, the in-situ expansion system also includes a backwashing device, which is connected to the third drainage pipeline for adding cleaning agents to the membrane separation tank.

[0014] And / or, the in-situ expansion system further includes a dosing device connected to the third feed line for adding flocculant to the membrane separation tank through the third feed line.

[0015] A second aspect of this application provides a control method for an in-situ capacity expansion system as described in the first aspect above, the control method comprising:

[0016] Determine the required water volume to be treated by the biological treatment system;

[0017] Determine the first water volume used to characterize the hydraulic load capacity of the secondary sedimentation tank in the biochemical treatment system;

[0018] In response to the fact that the water volume to be processed is greater than the first water volume and less than or equal to a preset water volume threshold, the in-situ expansion system is controlled to operate in the first mode.

[0019] In response to the water volume to be treated being greater than the preset water volume threshold, the rate of increase of the transmembrane pressure difference in the membrane module in the membrane separation tank is obtained;

[0020] In response to the transmembrane pressure differential growth rate being less than or equal to a preset first rate threshold, the in-situ expansion system is controlled to operate in a second mode.

[0021] In response to the transmembrane pressure difference growth rate being greater than a preset first rate threshold, the in-situ expansion system is controlled to operate in a third mode.

[0022] Furthermore, after the control in-situ expansion system operates in the first mode, it also includes:

[0023] Monitor the concentration of suspended particulate matter in the effluent from the secondary sedimentation tank;

[0024] The flow rate distribution between the underflow port and the overflow port of the hydrocyclone is adjusted based on the concentration of suspended particulate matter, so that the flow rate ratio between the underflow port and the overflow port decreases as the concentration of suspended particulate matter increases.

[0025] Furthermore, the flow distribution between the underflow port and the overflow port of the hydrocyclone is adjusted based on the concentration of the suspended particulate matter, including:

[0026] In response to the concentration of suspended particulate matter being less than or equal to a preset first concentration threshold, the flow ratio between the underflow port and the overflow port of the hydrocyclone is adjusted to a first ratio.

[0027] In response to the suspended particulate matter concentration being greater than the first concentration threshold and less than or equal to a preset second concentration threshold, the flow ratio between the underflow port and the overflow port of the hydrocyclone is adjusted to a second ratio.

[0028] In response to the concentration of suspended particulate matter being greater than the second concentration threshold, the flow ratio of the underflow port to the overflow port of the hydrocyclone is adjusted to a third ratio.

[0029] The first ratio, the second ratio, and the third ratio decrease sequentially.

[0030] Furthermore, after the control in-situ expansion system operates in the third mode, it also includes:

[0031] Monitor the specific resistance parameters of the feed sludge at the first inlet and the discharge sludge at the underflow outlet;

[0032] Calculate the ratio of the specific resistance parameters of the discharged sludge to that of the fed sludge to obtain the sludge specific resistance ratio.

[0033] In response to the sludge resistivity ratio being greater than a preset first sludge resistivity threshold, the dosing device is controlled to open to add flocculant into the third feed pipeline.

[0034] Furthermore, the control method further includes:

[0035] In response to the transmembrane pressure differential growth rate being greater than a preset second rate threshold, the backwashing device is activated to add cleaning agent to the membrane separation tank through the third drainage pipeline.

[0036] Wherein, the second rate threshold is greater than the first rate threshold.

[0037] Further, determining the required water volume of the biochemical treatment system includes:

[0038] Acquire historical inflow data and historical water supply data of the service area within the historical preset first time window of the biochemical treatment system;

[0039] Obtain the predicted weather information for the next preset second time window and the future date characteristics information for the corresponding time period;

[0040] Based on a pre-built water volume prediction model, the water volume in a future preset second time window is predicted using the historical water inflow data, the historical water supply data, predicted weather information, and the future date feature information, thereby obtaining the water volume to be treated.

[0041] Further, the determination of the first water volume used to characterize the hydraulic loading capacity of the secondary sedimentation tank in the biochemical treatment system includes:

[0042] Acquire historical influent water quality and historical operation data of the biochemical treatment system within the historically preset third time window;

[0043] Based on the pre-constructed sludge volume index prediction model, the sludge volume index for a future preset second time window is predicted using the historical influent water quality and the historical operating data, thus obtaining the predicted sludge volume index.

[0044] The solids flux threshold of the secondary sedimentation tank is determined based on the predicted sludge volume index.

[0045] Based on the solid flux threshold, the amount of water that the secondary sedimentation tank can process in a future preset second time window is determined, and the first water volume is obtained.

[0046] As can be seen from the above, this application provides an in-situ expansion system and its control method, which can improve the hydraulic load capacity of the biological treatment system. It allows for the individual or simultaneous operation of the sludge screening device and membrane separation tank based on the opening status of each pipeline, thereby achieving multiple operating modes, including a first mode, a second mode, and a third mode. The appropriate operating mode can be flexibly selected based on the operating status of the biological treatment system, changes in influent load, and the treatment needs of the wastewater treatment plant. When the influent load is low and the operation of the biological treatment system meets the influent load, the in-situ expansion system can be controlled to be in a non-operating state, relying solely on the secondary sedimentation tank to complete sludge-water separation, thus reducing energy consumption and operating costs. When the proportion of light sludge in the returned sludge increases, or when problems such as decreased sludge settling performance occur in the secondary sedimentation tank, the first mode can be activated, i.e., only the sludge screening device is operated. By classifying and screening the returned sludge, the light sludge with poor settling performance is discharged with the overflow, while the heavy sludge with good settling performance is returned to the biological treatment system, thereby improving sludge properties and stabilizing the operation of the biological treatment system. When the influent flow rate increases significantly, or the hydraulic load and solids flux of the secondary sedimentation tank cannot meet the demand, the second mode can be activated. This mode operates only the membrane separation tank, allowing the effluent from the biological reaction zone to undergo direct membrane separation. This replaces part of the separation task of the secondary sedimentation tank, enhancing the treatment capacity of the biological treatment system and achieving in-situ expansion. When the mixed liquor entering the membrane tank contains an increase in light sludge, fine particles, or colloidal components that easily clog membrane pores, the third mode can be activated. This mode operates the sludge screening device and the membrane separation tank simultaneously. The sludge screening device discharges the light mixed liquor, which is prone to membrane fouling, from the overflow outlet, allowing the heavy sludge-water mixed liquor to enter the membrane separation tank for solid-liquid separation. This effectively reduces the fouling load entering the membrane modules, slows down the development of membrane fouling, and maintains the stability of membrane flux. Through the first, second, and third modes of the in-situ expansion system, the system can adjust its operating strategy in real time according to changes in influent load, water quality, biological reaction status, and membrane fouling status, providing greater operational flexibility and adaptability. This multi-mode operation mechanism not only enhances the overall processing capacity and ability to cope with load fluctuations of the in-situ expansion system, but also reduces the operating costs and maintenance frequency caused by membrane fouling, thereby achieving efficient, stable and flexible operation of the system. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of a sludge screening device in an embodiment of this application;

[0049] Figure 2 This is a schematic diagram of an in-situ capacity expansion system according to an embodiment of this application;

[0050] Figure 3 This is a schematic flowchart of a control method for an in-situ capacity expansion system according to an embodiment of this application;

[0051] Figure 4 This is another schematic diagram of the control method flow of an in-situ expansion system in an embodiment of this application.

[0052] Figure labeling: 100-Biological treatment system; 110-Inlet pipeline; 120-Biological reaction zone; 121-Anaerobic tank; 122-Anoxic tank; 123-Aerobic tank; 130-First connecting pipeline; 140-Secondary sedimentation tank; 150-First drainage pipeline; 160-Sludge return pipeline; 170-Internal return pipeline; 200-In-situ expansion system; 210-Sludge screening device; 211-First feed pipeline; 2 12-Second feed line; 213-First return line; 214-Second drainage line; 215-Main feed line; 220-Membrane separator; 221-Third feed line; 222-Second return line; 223-Third drainage line; 224-Fourth feed line; 230-Backwashing device; 240-Dosing device; 31-Sludge screening body; 32-First feed inlet; 33-Overflow outlet; 34-Bottom flow outlet. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0054] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0055] With the continuous advancement of urbanization and the growth of population and industry, sewage discharge is increasing year by year, and existing sewage treatment plants generally face the problem of insufficient treatment capacity during long-term operation. Many sewage treatment facilities were designed with parameters determined based on the drainage scale and water quality load at the time. As the flow rate and pollution load increase, the design redundancy of the original system is gradually exhausted, resulting in the difficulty of consistently meeting effluent standards or the need for frequent load reduction operation. Building new sewage treatment plants can meet the sewage treatment needs, but it is costly, difficult, and time-consuming, and cannot solve the current problems in a timely manner. In-situ expansion is a quick and effective way to improve the hydraulic load capacity of sewage treatment plants, that is, to add some equipment and devices to the original treatment process to improve the overall hydraulic load capacity.

[0056] Wastewater treatment can be divided into three stages: pretreatment, biological treatment, and advanced treatment. In the pretreatment stage, larger particles and suspended solids are removed primarily through physical units such as screens, grit chambers, and primary sedimentation tanks to reduce the load on subsequent treatment units. In the biological treatment stage, biochemical processes such as activated sludge, contact oxidation, or biofilm processes are used to remove biodegradable organic pollutants from the wastewater; this is the core and most demanding stage of wastewater treatment. In the advanced treatment stage, processes such as filtration, denitrification, adsorption, or disinfection are typically employed to further remove nitrogen, phosphorus, and trace organic matter, ensuring that the effluent meets discharge or reuse standards.

[0057] In the entire wastewater treatment process, the treatment load and upper limit of output capacity mainly depend on the biological treatment stage. The biological treatment stage not only undertakes the core task of removing the main organic pollutants in wastewater, but its operating load also directly affects the stability of subsequent sedimentation and effluent quality. When the influent flow or pollution load continues to rise, if the treatment capacity of the biological treatment stage is insufficient, the stability of the effluent and the overall treatment capacity of the wastewater treatment plant will be limited.

[0058] For the biological treatment stage, the treatment capacity of the secondary sedimentation tank often becomes the key factor limiting its hydraulic load capacity. The secondary sedimentation tank is responsible for separating sludge from the effluent from the biological treatment process, and its treatment performance depends on factors such as surface area, hydraulic retention time, and sludge settling properties. To ensure effluent quality, the secondary sedimentation tank needs to maintain sufficient retention time to allow suspended sludge to settle fully. When the influent flow rate increases, the hydraulic retention time shortens, and the solid-liquid separation efficiency decreases, easily leading to sludge carryover in the effluent and excessive suspended solids. This makes the secondary sedimentation tank a major bottleneck restricting further upgrades and capacity expansion of the system.

[0059] In view of this, this application provides an in-situ expansion system 200, applied to a biochemical treatment system 100, which can effectively improve the hydraulic load capacity of the biochemical treatment system 100, such as... Figures 1-2As shown, the biochemical treatment system includes an inlet pipeline 110, a biochemical reaction zone 120, a first connecting pipeline 130, a secondary sedimentation tank 140, and a first drainage pipeline 150 connected in sequence; the bottom of the secondary sedimentation tank 140 is connected to the biochemical reaction zone 120 through a sludge return pipeline 160; the in-situ expansion system 200 includes:

[0060] The sludge screening device 210 includes a sludge screening body 31 and an overflow port 33 at the top, a bottom flow port 34 at the bottom, and a first feed port 32 on the side wall of the sludge screening body 31. The first feed port 32 is connected to the sludge return pipe 160 and the first connecting pipe 130 through a first feed pipe 211 and a second feed pipe 212, respectively. The bottom flow port 34 is connected to the biochemical reaction zone 120 through a first return pipe 213. The overflow port 33 is connected to a second drainage pipe 214 to discharge the overflow products to the outside of the system.

[0061] The membrane separation tank 220 is provided with a second feed inlet, a drain outlet, and a sludge discharge outlet. A membrane module for separating sludge and water is installed between the second feed inlet and the drain outlet. The second feed inlet is connected to the underflow outlet 34 and the first connecting pipeline 130 through a third feed pipeline 221 and a fourth feed pipeline 224, respectively. The sludge discharge outlet is connected to the biochemical reaction zone 120 through a second return pipeline 222. The drain outlet is connected to a third drain pipeline 223 to discharge the permeate from the membrane separation tank 220 to the outside of the system.

[0062] The in-situ expansion system 200 has three operating modes: a first mode, a second mode, and a third mode. In the first mode, the sludge screening device 210, the first feed pipeline 211, the first return pipeline 213, and the second drainage pipeline 214 are in operation; the membrane separation tank 220 and the second feed pipeline 212 are in non-operational state.

[0063] In the second mode, the membrane separation tank 220, the fourth feed pipeline 224, the second return pipeline 222 and the third drainage pipeline 223 are in operation, while the sludge screening device 210 is in non-operational state.

[0064] In the third mode, the sludge screening device 210, the membrane separation tank 220, the second feed pipeline 212, the third feed pipeline 221, the second return pipeline 222, the second drainage pipeline 214, and the third drainage pipeline 223 are in operation, while the first feed pipeline 211, the first return pipeline 213, and the fourth feed pipeline 224 are in non-operational state.

[0065] Specifically, the in-situ expansion system 200 also has a non-operation mode. In the non-operation mode, only the biochemical treatment system 100 operates within the entire in-situ expansion system 200. When the in-situ expansion system 200 is in non-operation mode, the sludge screening device 210, membrane separation tank 220, first feed pipeline 211, second feed pipeline 212, third feed pipeline 221, fourth feed pipeline 224, first return pipeline 213, second return pipeline 222, second drainage pipeline 214, and third drainage pipeline 223 are all in a non-operational state. Specifically, the non-operational state includes a series of inactive states such as standby state and shutdown state.

[0066] The biological treatment system 100 typically employs the activated sludge process for wastewater treatment. In this process, the physicochemical properties and biological activity of the sludge are key factors determining the system's operating efficiency and hydraulic load capacity. During long-term operation or when treating high-concentration, recalcitrant industrial wastewater, the activated sludge within the system is prone to deterioration, manifesting as loose sludge floc structure, reduced particle size, and decreased settling performance. When the sludge structure is loose and settling performance is poor, the sedimentation time required is longer; that is, the hydraulic retention time of the secondary sedimentation tank 140 needs to be set longer to ensure that the effluent quality meets requirements. However, measures to increase the hydraulic retention time of the secondary sedimentation tank 140 mainly involve reducing the treatment flow rate or increasing the surface area of ​​the secondary sedimentation tank 140, both of which are difficult to implement in actual operation. When the sludge flocs are compact, have high density, and good settling performance, sludge-water separation can be completed in a short time. The hydraulic retention time required for the secondary settling tank 140 is short. The system can still maintain clear effluent and low suspended solids concentration under high influent flow rate, thereby significantly improving the overall hydraulic load-bearing capacity.

[0067] A hydrocyclone is a highly efficient separation device that uses centrifugal force to separate mixtures of different densities. By tangentially feeding water, a high-speed rotating vortex is formed inside. The strong centrifugal force generated causes the heavier components with larger density or particle size to be thrown against the wall of the device and spiraled downwards to be discharged from the bottom flow, while the lighter components with smaller density or particle size are discharged from the overflow in the center with the inner vortex, thereby achieving rapid separation of the mixture. It can be used for sludge thickening and dewatering.

[0068] The sludge screening device 210 can be a hydrocyclone. The first feed inlet 32 ​​is tangentially set, and the material enters the sludge screening body 31 tangentially from the first feed inlet 32. A rotating flow from top to bottom is formed inside the sludge screening body 31. Under the action of centrifugal force, the materials with higher density and mass move radially towards the wall and downward, and are finally discharged from the bottom outlet 34. The materials with lower density and mass gradually move towards the center and upward, and finally flow out from the top overflow outlet 33.

[0069] In the first mode of this application, only the sludge screening device 210 is operated. The return sludge portion of the sludge return pipeline 160 enters the first feed pipeline 211, and then enters the sludge screening body 31 of the sludge screening device 210 through the first feed inlet 32 ​​for screening. Heavy sludge with a compact floc structure, high density, and good settling performance gradually settles to the bottom under the action of swirling flow and flows out from the bottom outlet 34, and finally returns to the biological treatment system 100 through the first return pipeline 213; sludge with a loose floc structure, low density, and poor settling performance... The light sludge gradually moves upward under the action of swirling flow and flows out from the overflow port 33. Finally, it is discharged to the outside of the system through the second drainage pipeline 214. This realizes the sludge screening in the biological treatment system 100, and removes the light sludge with deteriorated performance and poor settling performance to the outside of the system, while returning the heavy sludge with good settling performance to the biological treatment system 100. This improves the sludge settling performance of the entire biological treatment system 100, thereby improving the treatment capacity of the secondary sedimentation tank 140 and the biological treatment system 100, and thus the hydraulic load capacity of the entire system.

[0070] In membrane separation tank 220, sludge-water separation is achieved by selectively retaining the sludge-water mixture through membrane modules. Specifically, the membrane pore size of the membrane modules can effectively retain activated sludge and suspended particulate matter, while clean water is generated by permeating through the membrane surface. The membrane modules can be microfiltration membrane modules or ultrafiltration membrane modules; other membrane modules capable of sludge-water separation can also be used in this application, and there are no specific limitations.

[0071] In the second mode of this application, the membrane separator 220, the fourth feed line 224, the second return line 222, and the third drainage line 223 are all operational. A portion of the effluent from the biochemical reaction zone 120 enters the secondary sedimentation tank 140 directly via the first connecting line 130, while the other portion enters the membrane separator 220 via the third feed line 221 for solid-liquid separation. Sludge is retained in the membrane reaction tank by the membrane module and returned to the biochemical treatment system 100 via the second return line 222 to continue participating in biochemical treatment. Clean water permeates through the membrane module and is discharged outside the system via the third drainage line 223 for subsequent treatment. Operating the membrane separator 220 to share the treatment pressure of the secondary sedimentation tank 140 can effectively reduce the hydraulic load and solids flux of the secondary sedimentation tank 140. On the one hand, it keeps the sludge-water separation performance of the secondary sedimentation tank 140 stable; on the other hand, the membrane separator 220 can achieve stable solid-liquid separation under high sludge concentration, effectively increasing the overall system's treatment capacity limit, improving the stability of effluent quality, and enhancing the operational flexibility and hydraulic load capacity of the in-situ expansion system 200 under fluctuating influent conditions.

[0072] Membrane separator 220, as a highly efficient wastewater biological treatment and solid-liquid separation device, has been widely used in municipal wastewater and industrial wastewater treatment due to its advantages such as excellent effluent quality, small footprint, and low sludge production. However, with the large-scale engineering application of membrane separation technology, its inherent technical bottlenecks have become increasingly prominent, seriously restricting the economic benefits and long-term stable operation of this technology. During the operation of membrane separator 220, soluble microbial products, extracellular polymers, and other viscous substances in the activated sludge mixture, as well as fine sludge flocs and colloidal particles, will irreversibly adsorb and deposit on the membrane surface and inside the membrane pores of the membrane module, leading to a sharp decrease in membrane flux and a continuous increase in transmembrane pressure (TMP). To maintain permeate flow, frequent backwashing and chemical cleaning of the membrane separator 220 are necessary. This significantly increases operating energy consumption and reagent costs, and severely shortens the lifespan of the membrane modules. Membrane replacement requires shutdown and evacuation, which takes a long time and affects wastewater treatment efficiency. Furthermore, membrane replacement is expensive, substantially increasing the operating costs of the wastewater treatment plant. Especially during long-term operation or when treating high-concentration, recalcitrant industrial wastewater, the activated sludge in the system is prone to deterioration, exhibiting characteristics such as loose sludge floc structure, reduced particle size, and decreased settling performance. This "inferior" sludge mixture has extremely poor filtration properties, directly exacerbating the membrane fouling rate and preventing the system from operating stably at the designed flux. Due to these membrane fouling and sludge efficiency issues, the design of the membrane separator 220 is typically conservative, with actual operating flux far lower than the theoretical value of the membrane material. When faced with fluctuations in influent flow or the need for upgrades and capacity expansion, the system lacks flexibility and struggles to operate at full capacity or even under short-term overload. Forcibly increasing the operating load will lead to a rapid acceleration of membrane fouling and a significant increase in the risk of system failure.

[0073] In the third mode of this application, the sludge screening device 210, membrane separation tank 220, second feed pipeline 212, third feed pipeline 221, second return pipeline 222, and third drainage pipeline 223 operate. Part of the effluent from the biochemical reaction zone 120 directly enters the secondary sedimentation tank 140 via the first connecting pipeline 130 for sludge-water separation through settling and sedimentation. The other part enters the sludge screening device 210 via the second feed pipeline 212. Light sludge, characterized by loose floc structure, small particle size, and poor settling performance, is discharged from the overflow port 33, while heavy sludge, characterized by dense floc structure, large particle size, and good settling performance, flows out from the bottom outlet 34 and enters the membrane separation tank 220 via the third feed pipeline 221 for sludge-water separation. Sludge containing viscous substances, fine particles, colloids, etc., which easily exacerbate membrane fouling, is typically characterized by low density, small particle size, and light weight, and is included in light sludge. Therefore, in the third mode, the effluent from the biochemical reaction zone 120 is classified by the sludge screening device 210, allowing viscous substances, fine sludge particles, and colloidal components that are prone to clogging the membrane modules to be preferentially discharged along the overflow path. This reduces the pollutant load entering the membrane separation tank 220, delays membrane pore clogging, improves membrane flux stability, and ensures the system's wastewater treatment capacity. Simultaneously, the heavy sludge mixed liquor received by the membrane separation tank 220 is more conducive to efficient sludge-water separation, enabling the system to maintain stable water production performance even under high loads, further enhancing the overall operating efficiency and treatment capacity of the in-situ expansion system 200.

[0074] The transmembrane pressure differential growth rate (TMP growth rate) can be calculated by obtaining the initial and final values ​​of the transmembrane pressure differential of the membrane module over a period of time, and dividing the difference between the two values ​​by the time interval. For example, when the time unit is days, the unit can be expressed as kPa / day. It can be the stable operating range between two cleaning cycles or a fixed length of time during continuous operation, without any specific limitation. The initial and final values ​​of the transmembrane pressure differential can be obtained from the pressure gauge of the third drainage pipeline, the liquid level pressure of the membrane separation tank, or the negative pressure signal at the inlet of the permeate pump. Other methods and instruments for obtaining the transmembrane pressure differential can also be used in this application, without any specific limitation.

[0075] In this application, the in-situ expansion system 200 includes a sludge screening device 210 and a membrane separation tank 220. Depending on the opening status of each pipeline, the sludge screening device 210 and the membrane separation tank 220 can be operated individually or simultaneously, thereby realizing multiple operating modes including the first mode, the second mode and the third mode. The applicable operating mode can be flexibly selected according to the operating status of the biochemical treatment system 100, changes in influent load and the treatment needs of the wastewater treatment plant. When the influent load is low and the operation of the biological treatment system 100 meets the influent load, the in-situ expansion system 200 can be kept inactive, relying solely on the secondary sedimentation tank 140 to complete sludge-water separation, thereby reducing energy consumption and operating costs. When the proportion of light sludge in the returned sludge increases, or when the sludge settling performance of the secondary sedimentation tank 140 declines, the first mode can be activated, i.e., only the sludge screening device 210 is operated. By classifying and screening the returned sludge, the light sludge with poor settling performance is discharged with the overflow, while the heavy sludge with good settling performance is returned to the biological treatment system 100, thereby improving sludge properties and stabilizing the operation of the biological treatment system. When the influent volume increases significantly, and the hydraulic load and solids flux of the secondary sedimentation tank 140 cannot meet the demand, the second mode can be activated, i.e., only the membrane separation tank 220 is operated, allowing the effluent from the biological reaction zone 120 to undergo membrane separation directly, replacing part of the separation task of the secondary sedimentation tank 140, enhancing the treatment capacity of the biological treatment system 100, and achieving in-situ expansion. When the amount of light sludge, fine particles, or colloidal components that easily clog membrane pores in the mixed liquor entering the membrane tank increases, the third mode can be activated, which simultaneously operates the sludge screening device 210 and the membrane separation tank 220. The sludge screening device 210 discharges the light mixed liquor that is prone to causing membrane fouling from the overflow port 33, allowing the heavy sludge-water mixed liquor to enter the membrane separation tank 220 for solid-liquid separation. This effectively reduces the fouling load entering the membrane module, slows down the development of membrane fouling, and maintains the stability of membrane flux.

[0076] Through the first, second, and third modes of the in-situ expansion system 200, the system can adjust its operating strategy in real time according to factors such as influent load, water quality changes, biochemical reaction status, and membrane fouling conditions, exhibiting greater operational flexibility and adaptability. This multi-mode operation mechanism not only enhances the overall treatment capacity and load fluctuation response of the in-situ expansion system 200 but also reduces operating costs and maintenance frequency caused by membrane fouling, thereby achieving efficient, stable, and flexible system operation.

[0077] In some embodiments, in a first mode, the flow rate of the underflow port 34 to the overflow port 33 of the sludge screening device 210 is controlled to be 0.05~0.3; in a third mode, the flow rate ratio of the underflow port 34 to the overflow port 33 of the sludge screening device 210 is controlled to be 4~8, which is within a second range. In the first mode, the material entering the sludge screening device 210 comes from the sludge return pipeline 160, and has a high solid content and high sludge concentration. In this mode, by controlling the flow rate of the underflow port 34 to be much smaller than the flow rate of the overflow port 33, most of the light sludge is discharged with the overflow port 33, while the dense, well-settling heavy sludge is discharged from the underflow port 34 and returned to the biochemical reaction zone 120. This allows for more effective screening of high-quality heavy sludge, thereby improving the sludge properties of the biochemical system. In the third mode, the material entering the sludge screening device 210 is the effluent from the biochemical reaction zone 120. This mixture has not undergone sedimentation separation, and the sludge is mainly in a suspended state. If the overflow port 33 has an excessively large flow rate, a large amount of unseparated sludge-water mixture may be discharged through the overflow port 33, affecting the stable operation of subsequent processes. Therefore, in the third mode, the flow rate of the underflow port 34 is set to be much greater than that of the overflow port 33. Most of the mixture is output from the underflow port 34 to the membrane separation tank 220 for sludge-water separation, while the light sludge is discharged with the overflow port 33. This effectively reduces the amount of polluting particles entering the membrane separation tank 220, while ensuring that most of the mixture enters the membrane tank for solid-liquid separation, thus balancing membrane fouling control and the system's hydraulic load treatment capacity.

[0078] In some embodiments, valves are installed on the first feed line 211, the second feed line 212, the third feed line 221, the fourth feed line 224, and the first return line 213 to switch between operating and non-operating states. Valves may also be installed on the second return line 222, the second drainage line 214, and the third drainage line 223 to switch between operating and non-operating states, or valves may not be installed and they may remain normally open. The switching between operating and non-operating states follows the changes in the state of the sludge screening device 210 or the membrane separation tank 220 connected to them. Specifically, when the membrane separator 220 is in operation, the second return pipeline 222 receives sludge from the sludge discharge port of the membrane separator 220, and the third drainage pipeline 223 receives clean water from the drainage port, and is also in operation. When the membrane separator 220 is not in operation, there is no sludge discharge from the sludge discharge port of the membrane separator 220, no water production from the drainage port, and the second return pipeline 222 and the third drainage pipeline 223 have no operating flow, and are also in operation. When the sludge screening device 210 is in operation, the second drainage pipeline 214 receives material from the overflow port 33, and is also in operation. When the sludge screening device 210 is not in operation, there is no material discharged from the overflow port 33, and the second drainage pipeline 214 has no operating flow, and is also in operation.

[0079] In some embodiments, a booster pump is provided between the first feed pipeline 211, the second feed pipeline 212, and the first feed inlet 32. The sludge screening device 210 is controlled to be in an operating or non-operating state by turning the booster pump on and off. Optionally, as... Figure 2 As shown, a main feed pipeline 215 is connected to the first feed inlet 32. The first feed pipeline 211 and the second feed pipeline 212 are both connected to the main feed pipeline 215. A booster pump is installed on the main feed pipeline 215. When the sludge screening device 210 needs to be switched to the operating state, the booster pump is turned on. The suction effect of the booster pump creates a suction flow in the main feed pipeline 215, causing a portion of the material from the sludge return pipeline 160 or the first connecting pipeline 130 to enter the first feed pipeline 211 or the second feed pipeline 212, thereby allowing the corresponding material to enter the sludge screening device 210. Within the sludge screening device 210, a swirling flow occurs, achieving material classification and separation. When the sludge screening device 210 needs to be switched to the non-operating state, the booster pump is turned off.

[0080] In some embodiments, a permeate pump is installed on the third drainage pipeline 223. The membrane separation tank 220 is switched between operating and non-operating states by turning the permeate pump on and off. When the membrane separation tank 220 needs to be operated, the permeate pump is turned on, creating a suction flow on the third drainage pipeline 223. The clean water in the membrane separation tank 220 permeates through the membrane module into the third drainage pipeline 223 under the action of pressure difference, while the sludge is retained in the tank by the membrane module, thereby achieving sludge-water separation in the membrane separation tank 220.

[0081] In some embodiments, an aeration component is provided at the bottom of the membrane module. The aeration component creates an upward airflow and turbulence around the membrane module. Through the shear force and turbulence generated by the aeration bubbles, the concentration polarization layer on the membrane surface is disrupted, and sticky pollutants such as sludge particles, colloidal substances, soluble microbial products (SMP), and extracellular polymeric substances (EPS) adhering to the membrane surface are shed. This effectively slows down the fouling rate of the membrane module and maintains a stable increase in transmembrane pressure gradient (TMP). The aeration device can operate intermittently to maintain effective cleaning of the membrane surface while controlling energy consumption. The aeration intensity can be approximately 0.3-0.6 Nm³ / (m²·h) to ensure the stability of the membrane module during the water production process.

[0082] In some embodiments, such as Figure 2 As shown, the biochemical reaction zone 120 includes an anaerobic tank 121, an anoxic tank 122 and an aerobic tank 123 connected in sequence.

[0083] The bottom of the secondary sedimentation tank 140 is connected to the anaerobic tank 121 through the sludge return pipeline 160;

[0084] And / or, the bottom of the aerobic tank 123 is connected to the anoxic tank 122 via an internal return pipeline 170.

[0085] Specifically, the anaerobic tank 121 is used to release phosphorus from the sludge flocs in an environment without dissolved oxygen and nitrates, promoting phosphorus release by polyphosphate-accumulating bacteria; the anoxic tank 122 lacks dissolved oxygen but contains nitrates, which can be reduced to nitrogen gas by denitrifying bacteria, achieving denitrification; the aerobic tank 123 is an oxygen-rich environment where microorganisms carry out organic matter degradation, nitrification, and phosphorus uptake by polyphosphate-accumulating bacteria, and is the main area for organic matter removal and nitrification in the biological treatment system 100. The bottom of the secondary sedimentation tank 140 is connected to the anaerobic tank 121 through the sludge return pipeline 160 to achieve sludge external return, so that the settled activated sludge is returned to the anaerobic tank 121 to continue participating in the biological reaction, maintaining the sludge concentration and sludge age of the system. The bottom of the aerobic tank is connected to the anoxic tank 122 via an internal return pipeline 170, enabling internal sludge return. The internal return pipeline 170 is used to return the nitrate-nitrogen mixed liquor from the aerobic tank to the anoxic tank 122, allowing the anoxic tank 122 to obtain sufficient nitrates as electron acceptors for the denitrification reaction, thereby improving the system's denitrification capacity. Specifically, the return ratio of internal sludge return can be 100%~200%, and the return ratio of external sludge return can be 50%~100%.

[0086] In some embodiments, the in-situ expansion system 200 further includes a backwashing device 230, which is connected to the third drainage pipeline 223 for adding cleaning agents to the membrane separation tank 220.

[0087] And / or, the in-situ expansion system 200 further includes a dosing device 240, which is connected to the third feed line 221 for adding flocculant to the membrane separation tank 220 through the third feed line 221.

[0088] Specifically, such as Figure 2As shown, the backwashing device 230 includes a backwashing pipeline and a first chemical storage tank. The backwashing pipeline connects to a third drainage pipeline 223 and the first chemical storage tank. The first chemical storage tank stores cleaning agents. A valve and a first dosing pump are also installed on the backwashing pipeline. When the backwashing device 230 needs to be operated, the first feed inlet 32 ​​of the membrane separation tank 220 and the permeate pump are closed. The valve and the first dosing pump on the backwashing pipeline are opened, and the cleaning agent in the first chemical storage tank is pumped back into the membrane separation tank 220 through the third drainage pipeline 223 to perform online cleaning of organic contaminants on the membrane surface. After cleaning is completed, the first dosing pump and the valve on the backwashing pipeline are closed. The cleaning agents include any one or more of sodium hypochlorite, citric acid, oxalic acid, and hydrogen peroxide. Other cleaning agents that can be used in this application may also be used, and no specific limitation is imposed.

[0089] like Figure 2 As shown, the dosing device 240 includes a dosing pipeline and a second storage tank. The dosing pipeline connects to a third feed pipeline 221 and the second storage tank, which stores flocculant. The dosing pipeline is also equipped with a valve and a second dosing pump. When flocculant needs to be added to the membrane separation tank 220, the valve on the dosing pipeline and the second dosing pump are opened, and the flocculant in the second storage tank is pumped into the membrane separation tank 220 via the third feed pipeline 221 through the second dosing pump. When flocculant does not need to be added to the membrane separation tank 220, the second dosing pump and the valve on the dosing pipeline are closed. The flocculant may include any one or more of polyaluminum chloride, polyacrylamide, aluminum sulfate, and iron salt flocculants (such as ferrous sulfate and ferric chloride), or it may be a targeted metal chelating agent, or it may be the flocculant described in the patent publication texts CN115448573B and CN117534189B. Other agents that can be used to enhance sludge particles and improve sedimentation may also be used in this application, without any specific restrictions.

[0090] By installing the backwashing device 230, the membrane module can be chemically cleaned when the transmembrane pressure difference increases, the membrane flux decreases, or the membrane surface fouling intensifies. This removes pollutants such as sticky substances, colloidal particles, and soluble microbial metabolites adhering to the membrane surface, thereby restoring the membrane module's water production capacity. When the proportion of fine particles in the mixed liquor increases, the sludge floc structure becomes loose, membrane module fouling intensifies, or the membrane flux drops rapidly, the dosing device 240 can be activated to add flocculants. This promotes particle aggregation in the feed mixed liquor to the membrane reactor, causing fine particles to form a more stable floc structure, thereby reducing the fouling load entering the membrane module and improving membrane separation efficiency.

[0091] Optionally, flow meters can be installed on the inlet pipeline 110, the first feed pipeline 211, the second drain pipeline 214, the first return pipeline 213, and the third drain pipeline 223 to obtain the flow rate of the corresponding pipelines; suspended particulate matter concentration meters can be installed on the inlet pipeline 110 and the first drain pipeline 150 to detect the suspended particulate matter concentration of the corresponding pipelines; an online sludge concentration meter can be installed in the membrane separation tank 220 to monitor its sludge concentration; pressure transmitters can be installed on the main feed pipeline 215, the first return pipeline 213, and the third drain pipeline 223 to detect the pressure of the corresponding pipelines; other instruments can also be installed according to actual conditions, without any specific restrictions.

[0092] Based on the same inventive concept, this application also provides a control method for an in-situ expansion system, such as... Figure 3 As shown, an in-situ capacity expansion system is applied to any of the foregoing embodiments; the control method includes:

[0093] S101. Determine the required water volume to be treated by the biochemical treatment system;

[0094] Specifically, the required amount of water to be treated can be determined based on the historical water volume treated by the biochemical treatment system, such as the historical treatment volume of the same season and date in the previous year, or the actual inflow volume of the sewage treatment plant in the past month or period. Alternatively, the required amount of water to be treated can be predicted based on a water volume prediction model. Other methods for determining the required amount of water to be treated by the biochemical treatment system can also be applied in this application, without any specific limitations.

[0095] S102. Determine the first water volume used to characterize the hydraulic load capacity of the secondary sedimentation tank of the biochemical treatment system;

[0096] Specifically, the first water volume can be the design capacity of the secondary sedimentation tank. The design capacity of the secondary sedimentation tank refers to the maximum influent flow rate that the tank can stably withstand over a long period, under given tank type, surface area, depth, hydraulic retention time, and tank structure, while ensuring effective sludge-water separation and stable effluent quality. The design capacity of the secondary sedimentation tank is determined at the initial stage of the biological treatment system design based on the actual needs of the wastewater treatment plant and relevant regulations.

[0097] S103. In response to the fact that the amount of water to be processed is greater than the first amount of water and less than or equal to a preset water volume threshold, control the in-situ expansion system to operate in the first mode.

[0098] In response to the water volume to be treated being greater than the preset water volume threshold, the rate of increase of the transmembrane pressure difference in the membrane module in the membrane separation tank is obtained;

[0099] In response to the transmembrane pressure differential growth rate being less than or equal to a preset first rate threshold, the in-situ expansion system is controlled to operate in a second mode.

[0100] In response to the transmembrane pressure difference growth rate being greater than a preset first rate threshold, the in-situ expansion system is controlled to operate in a third mode.

[0101] Specifically, the first water volume can be represented by Q. a This indicates that the preset water volume threshold can be based on the first water volume Q. a For example, it can be 1.3 times the first water volume, i.e., 1.3Q. a It can also be set to 1.1, 1.15, 1.2, 1.25, 1.35, or 1.4 times the first water volume, i.e., 1.1Q. a 1.15Q a 1.2Q a 1.25Q a 1.35Q a 1.4Q a The first rate threshold can be set to 0.3 kPa / day, or it can be set to 0.1, 0.15, 0.2, 0.25, 0.35, or 0.4 kPa / day, or other values ​​can be set according to actual conditions. In the second mode, the membrane separation tank can be set to constant flux operation, with a flux set to 15 LMH and an on / off ratio of 7:1. An aeration device is installed at the bottom of the membrane module to control membrane fouling, with an aeration intensity of 0.3-0.6 Nm³ / (m²·h), and the rate of change of the transmembrane pressure differential is monitored in real time.

[0102] Taking the example of valves installed on each pipeline, we will further explain how to control the switching of various operating modes of the in-situ expansion system.

[0103] When the in-situ expansion system is running in the first mode, the booster pump is turned on, and the valves on the first feed line, first return line, and second drain line are opened. The valves on the second feed line, third feed line, and fourth feed line are closed, and the pressure P1 on the main feed line 215 of the sludge screening device is controlled to be less than 0.2 MPa. When running in the second mode, the permeate pump is turned on, and the valves on the fourth feed line, second return line, and third drain line are opened. The valves on the booster pump, first feed line, second feed line, third feed line, first return line, and second drain line are closed. When running in the third mode, the booster pump and permeate pump are turned on, and the valves on the second feed line, third feed line, second return line, second drain line, and third drain line are opened. The pressure P1 on the main feed line 215 of the sludge screening device is controlled to be less than 0.2 MPa, and the valves on the first feed line, first return line, and fourth feed line are closed. In this application, the ability of the biological treatment system to meet wastewater treatment needs is determined based on the required treatment volume and the initial volume. When the required treatment volume exceeds the carrying capacity of the secondary sedimentation tank but is less than or equal to a preset volume threshold, it indicates that the incoming water may exceed the load of the secondary sedimentation tank, but the excess is small. In this case, only the sludge screening device is operated to classify and separate the returned sludge, thereby improving the actual volume of water that the secondary sedimentation tank can handle by improving the sludge settling performance. When the required treatment volume further increases beyond the preset volume threshold, the appropriate operating mode for the in-situ expansion system is further determined based on the transmembrane pressure difference growth rate of the membrane module. When the transmembrane pressure difference growth rate is less than or equal to a preset first rate threshold, it indicates that the membrane module is operating normally and membrane fouling is minimal. Within a controllable range, the membrane flux can meet the current water demand. At this time, the in-situ expansion system is controlled to operate in the second mode, with only the membrane separation tank operating to handle part of the sludge-water separation load, thereby effectively diverting the secondary sedimentation tank and improving the overall hydraulic treatment capacity of the system. When the transmembrane pressure difference growth rate is high, i.e., greater than the first rate threshold, it indicates that the membrane fouling rate is relatively serious, and the content of light sludge with stickiness and small particles is high. At this time, the in-situ expansion system is controlled to operate in the third mode, so that the sludge screening device and the membrane separation tank operate simultaneously. The light sludge is discharged through the sludge screening device, reducing the content of polluting particles in the membrane tank feed, thereby effectively delaying membrane fouling, stabilizing membrane flux, and achieving dynamic protection of the membrane module.

[0104] Through the above-mentioned multi-mode linkage strategy, this application can realize timely identification of water load status and membrane fouling status, and switch the operating mode in a timely manner when water volume changes or membrane fouling intensifies. This enables the system to automatically select the optimal treatment path under different load conditions, thereby improving the operational stability, treatment flexibility and adaptability of the in-situ expansion system, significantly reducing the operational risks caused by sudden load increases or membrane fouling, and significantly improving the hydraulic load capacity of the system.

[0105] In some embodiments, the method further includes: controlling the in-situ expansion system to be in a non-operating state in response to the required water volume being less than or equal to the first water volume. When the required water volume is less than or equal to the first water volume, it indicates that the hydraulic load capacity of the secondary sedimentation tank is sufficient to meet the system's inflow water demand. At this time, only the biological treatment system is operated, and the in-situ expansion system is controlled to be in a non-operating state. That is, the sludge screening device, membrane separation tank, and connected pipelines (i.e., the first feed pipeline, the second feed pipeline, the third feed pipeline, the fourth feed pipeline, the second drainage pipeline, the third drainage pipeline, the first return pipeline, and the second return pipeline) are all in a non-operating state, thereby reducing operating costs.

[0106] In some embodiments, after the control in-situ capacity expansion system operates in a first mode, it further includes:

[0107] Monitor the concentration of suspended particulate matter in the effluent from the secondary sedimentation tank;

[0108] The flow rate distribution between the underflow port and the overflow port of the hydrocyclone is adjusted based on the concentration of suspended particulate matter, so that the flow rate ratio between the underflow port and the overflow port decreases as the concentration of suspended particulate matter increases.

[0109] Specifically, a suspended particulate matter concentration meter can be installed on the first drainage pipeline to monitor the suspended particulate matter concentration in the effluent from the secondary sedimentation tank. In this embodiment, the flow distribution between the underflow and overflow outlets of the sludge screening device is adjusted based on the suspended particulate matter concentration in the effluent from the secondary sedimentation tank. This causes the flow ratio between the underflow and overflow outlets to decrease as the particulate matter concentration increases. When the suspended particulate matter concentration in the effluent from the secondary sedimentation tank is high, it indicates that the sludge settling performance in the biological treatment system is poor. Therefore, the flow rate at the underflow outlet can be reduced, and the flow rate at the overflow outlet can be increased. This allows the sludge screening device to output more overflow when the particulate matter concentration is high, thereby discharging more light sludge from the overflow path, reducing the proportion of light and loose sludge entering subsequent treatment units, and further improving the separation effect of the secondary sedimentation tank. By reducing the underflow ratio and increasing the overflow discharge under suspended particulate matter concentration conditions, it is possible to effectively prevent fine flocs and difficult-to-settle particles from entering the membrane separation tank or subsequent treatment unit with the underflow, thereby improving the sludge-water separation effect and enhancing the system's operational stability and adaptability under fluctuating water quality conditions.

[0110] In some embodiments, adjusting the flow rate distribution between the underflow outlet and the overflow outlet of the hydrocyclone based on the concentration of suspended particulate matter includes:

[0111] In response to the concentration of suspended particulate matter being less than or equal to a preset first concentration threshold, the flow ratio between the underflow port and the overflow port of the hydrocyclone is adjusted to a first ratio.

[0112] In response to the suspended particulate matter concentration being greater than the first concentration threshold and less than or equal to a preset second concentration threshold, the flow ratio between the underflow port and the overflow port of the hydrocyclone is adjusted to a second ratio.

[0113] In response to the concentration of suspended particulate matter being greater than the second concentration threshold, the flow ratio of the underflow port to the overflow port of the hydrocyclone is adjusted to a third ratio.

[0114] The first ratio, the second ratio, and the third ratio decrease sequentially.

[0115] Specifically, the first ratio ranges from 0.2 to 0.3, for example, it can be 0.22, 0.24, 0.25, 0.26, 0.28, 0.29, or 0.3. It can also be set to other values ​​within or outside this range depending on the actual situation; there are no specific restrictions. The second ratio ranges from 0.1 to 0.2, for example, it can be 0.12, 0.14, 0.15, 0.16, 0.18, 0.19, or 0.2. It can also be set to other values ​​within or outside this range depending on the actual situation; there are no specific restrictions. The third ratio ranges from 0.05 to 0.1, for example, it can be 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1. It can also be set to other values ​​within or outside this range depending on the actual situation; there are no specific restrictions.

[0116] The first concentration threshold can be set to 50 mg / L, or 40, 45, 55, or 60 mg / L, or other values ​​depending on the actual situation; there are no specific restrictions. The second concentration threshold can be set to 100 mg / L, or 80, 85, 90, 95, 105, 110, or 115 mg / L, or other values ​​depending on the actual situation; there are no specific restrictions.

[0117] The appropriate concentration thresholds are set according to different suspended particulate matter concentrations, and different flow ratios of the bottom outlet and overflow outlet are assigned to each concentration range, so that the sludge screening device can automatically match the appropriate grading intensity under different water quality conditions. When the suspended particulate matter concentration is low, it indicates good separation in the secondary settling tank, indirectly reflecting good sludge settling performance. In this case, the flow ratio between the bottom flow and the overflow should be adjusted to a larger first ratio, allowing more mixed liquor to be discharged through the bottom flow, thereby enhancing the recovery capacity of heavy particles and maintaining a moderate classification effect. When the suspended particulate matter concentration is in the middle range, the flow ratio should be adjusted to a smaller second ratio to reduce the bottom flow discharge and increase the overflow ratio, making the classification effect more biased towards the discharge of light sludge. When the suspended particulate matter concentration is high, it indicates poor separation in the secondary settling tank, indirectly reflecting poor sludge settling performance, with a large proportion of light sludge that is loose, small in size, and has poor settling performance. In this case, the flow ratio should be adjusted to a smaller third ratio, allowing more mixed liquor to be discharged through the overflow path, so as to remove a large number of fine flocs and light sludge in time and prevent them from entering subsequent treatment units with the bottom flow, thus affecting the sludge-water separation efficiency.

[0118] Through the aforementioned concentration threshold-based graded control method, the sludge screening device can dynamically change the distribution ratio of overflow and underflow according to real-time water quality changes. This allows for precise adjustment of the grading direction and intensity, increasing the return of heavy sludge at low concentrations and prioritizing the removal of light sludge at high concentrations, achieving a separation effect that better conforms to water quality variation patterns. This not only improves the system's adaptability to fluctuating water quality conditions but also effectively ensures the stable operation of the secondary sedimentation tank and membrane separation tank, significantly enhancing the operational reliability and treatment efficiency of the entire in-situ expansion system.

[0119] In some embodiments, after the control in-situ capacity expansion system operates in a third mode, it further includes:

[0120] Monitor the specific resistance parameters of the feed sludge at the first inlet and the discharge sludge at the underflow outlet;

[0121] Calculate the ratio of the specific resistance parameters of the discharged sludge to that of the fed sludge to obtain the sludge specific resistance ratio.

[0122] In response to the sludge resistivity ratio being greater than a preset first sludge resistivity threshold, the dosing device is controlled to open to add flocculant into the third feed pipeline.

[0123] Specifically, the first sludge resistivity threshold can be set to 0.5, or to a ratio of 0.4, 0.45, 0.55, 0.6, etc., or to other ratios depending on the actual situation. There are no specific restrictions.

[0124] Sludge specific resistance is used to characterize the resistance of sludge during the filtration process. It reflects the floc structure, colloidal content, and filterability of the sludge. A higher specific resistance indicates that the sludge is more difficult to filter, more likely to form a cake layer on the membrane module surface, and exacerbates membrane fouling. In the third mode, the mixed liquor output from the underflow outlet enters the membrane separation tank for solid-liquid separation. Therefore, by simultaneously monitoring the sludge specific resistance at the first inlet and the underflow outlet, the degree of improvement in sludge filterability after hydrocyclone classification can be determined.

[0125] When the calculated sludge resistivity ratio is greater than the first sludge resistivity threshold (e.g., 0.5), it indicates that the hydrocyclone can no longer further improve the filterability of the sludge under the current operating parameters. The underflow still contains a high proportion of fine particles or colloidal substances, resulting in high filtration resistance and easy fouling of the membrane module. Since this type of sludge characteristic is a limitation inherent to the sludge itself and cannot be solved by adjusting the hydrocyclone flow rate ratio, when the sludge resistivity ratio exceeds the first sludge resistivity threshold, flocculant is added to the third feed line to enhance sludge particle aggregation and form larger, denser flocs. This reduces the sludge resistivity of the feed sludge to the membrane separation tank, resulting in better filtration performance of the mixed liquor entering the membrane separation tank, reducing membrane fouling, and improving the continuous operation stability of the system.

[0126] Specifically, the amount of flocculant added increases with the increase of the sludge specific resistance ratio. When the sludge specific resistance ratio is greater than the preset first sludge specific resistance threshold and less than the second sludge specific resistance threshold, the flocculant dosage is set to make the flocculant concentration in the feed mixture of the membrane separator 10–30 mg / L. When the sludge specific resistance ratio is greater than or equal to the second sludge specific resistance threshold, the flocculant dosage is set to make the flocculant concentration in the feed mixture of the membrane separator 20–60 mg / L. The second sludge specific resistance threshold can be 0.8, or it can be set to 0.7, 0.75, 0.85, 0.9, etc., or other ratios can be set according to actual conditions; there are no specific restrictions.

[0127] In some implementations, the control method further includes:

[0128] In response to the transmembrane pressure difference growth rate being greater than a preset second rate threshold, the backwashing device is activated to add cleaning agents to the membrane separation tank through the third drain pipeline.

[0129] Wherein, the second rate threshold is greater than the first rate threshold.

[0130] Specifically, the second rate threshold can be 0.5 kPa / day, or it can be set to 0.3, 0.4, 0.6, or 0.7 kPa / day, or other ratios depending on the actual situation; there are no specific restrictions. Taking sodium hypochlorite solution as the cleaning agent as an example, the cleaning agent can be prepared as a 500 mg / L sodium hypochlorite solution and added at a dosage of 2 L / m² according to the membrane module area.

[0131] When the rate of increase in transmembrane pressure difference exceeds a preset second rate threshold, it indicates that the membrane fouling is developing rapidly, and the fouling layer accumulated on the membrane surface can no longer be effectively alleviated by the grading action of the sludge screening device or conventional aeration cleaning alone. If operation continues in the current state, it will lead to a rapid decrease in membrane flux, increased energy consumption, and affect the system's treatment capacity. At this time, by turning on the backwash device and adding cleaning agents to the membrane separation tank, organic pollutants, colloidal substances, soluble microbial metabolites (SMP), and biofouling attached to the membrane module surface can be chemically cleaned, thereby effectively removing the fouling layer, restoring the filtration performance of the membrane module, reducing the rate of increase in transmembrane pressure difference, ensuring the stable operation of the membrane separation tank, and extending the service life of the membrane module.

[0132] In some embodiments, determining the required water volume to be treated by the biochemical treatment system includes:

[0133] Acquire historical inflow data and historical water supply data of the service area within the historical preset first time window of the biochemical treatment system;

[0134] Obtain the predicted weather information for the next preset second time window and the future date characteristics information for the corresponding time period;

[0135] Based on a pre-built water volume prediction model, the water volume in a future preset second time window is predicted using the historical water inflow data, the historical water supply data, predicted weather information, and the future date feature information, thereby obtaining the water volume to be treated.

[0136] Specifically, historical water inflow data includes historical water inflow, corresponding date characteristic information, and weather information. Date characteristic information includes date information, seasonal information, and holiday information, among which holiday information is used to identify whether the corresponding date is a weekend or a statutory holiday (such as the Spring Festival, National Day, etc.) or a non-working day or a working day.

[0137] Historical water supply data for the service area can provide information on the tap water supply volume of the biochemical treatment system within a pre-set historical time window, including daily, hourly, or time-segmented water supply. Since water consumption by residents or businesses in the area is strongly correlated with wastewater discharge, historical water supply data can reflect the actual water consumption levels and living and production patterns in the service area, and provides a good indication of trends in water volume changes.

[0138] The inflow to wastewater treatment plants is not only related to the regional water supply but also affected by external factors such as weather, seasons, and holidays. Specifically, on weekdays, industrial enterprises, commercial establishments, schools, and other units are operating normally, and the combined industrial and commercial wastewater from production and business activities with domestic wastewater results in a generally higher inflow. On weekends or public holidays, production and business activities of these units decrease or are suspended, leading to a significant drop in industrial and commercial wastewater, thus the overall inflow is usually lower than on weekdays. When there is rainfall, rainwater infiltration, external water inflow, or combined sewer overflows can significantly increase the amount of water entering the wastewater treatment plant. Under sunny conditions, the impact of external water inflow is relatively small, and the inflow is mainly determined by domestic and industrial wastewater, which is usually more stable. Temperature changes also affect regional water use behavior. For example, in hot weather, residents use more water for showering and washing, which may lead to an increase in domestic wastewater and inflow. In cold weather, outdoor activities decrease and some water use behavior declines, generally resulting in a lower inflow. Seasonal changes also lead to different trends in water inflow: Spring and autumn bring mild weather and relatively stable water usage patterns, resulting in smaller fluctuations in inflow; summer sees more high temperatures, usually accompanied by increased domestic water consumption, leading to higher inflows; winter's low temperatures may cause reduced water usage in some areas or other seasonal changes in water usage habits, causing a downward trend in inflows. Therefore, using date-specific information (including weekends, holidays, and seasonal types), weather information (such as rainfall and temperature), and historical inflow and supply data as inputs to water volume prediction models can more comprehensively reflect the key factors affecting inflows. This allows the water volume prediction model to learn the mechanisms by which different external factors influence inflow changes, thereby improving the accuracy and reliability of future inflow predictions.

[0139] The water volume prediction model is constructed using a sliding window-based Long Short-Term Memory (LSTM) network. LSTM is a type of recurrent neural network, a special kind of recurrent neural network, capable of analyzing inputs using time series data. LSTM is an improved recurrent neural network that, by introducing forget gates, input gates, and output gates, can retain or discard historical information at different time scales, thus possessing the ability to capture long-term dependencies and complex temporal features. Compared to traditional neural networks, LSTM can more effectively handle nonlinear, periodic, and highly abrupt time series data, making it particularly suitable for multi-factor time series data such as wastewater inflow, which is influenced by weather, holidays, seasonal variations, and human drainage habits.

[0140] In LSTM, a sliding window is used to construct model input samples from continuous time series, allowing a fixed-length historical data segment to be used as input for a single prediction. For example, if the sliding window length is 7 days, when the model predicts the water inflow for a certain day, it will use the water inflow data of the previous 7 days as input; when moving forward one day to predict the water inflow for the next day, the window also slides forward, using the most recent 7 days of data (such as data from days 2 to 8) as new input. By continuously sliding the window and generating new input sequences, LSTM can continuously learn from the latest historical patterns, thereby improving the accuracy of future water inflow predictions and its responsiveness to water flow trends.

[0141] The water volume prediction model can be constructed through the following steps: obtaining the first training data, which includes historical water inflow data of multiple consecutive historical moments of the biochemical treatment system and historical water supply data of the service area; constructing an initial model based on a long short-term memory neural network; pre-training the initial model using the first training data until a preset termination condition is reached, determining the model parameters at the time of training termination as the final model parameters, and applying the final model parameters to the initial model to obtain the water volume prediction model.

[0142] Specifically, the first time window is preset to 5 days, but it can also be set to 7, 6, 4, 3, 2, or 1 days, or other times depending on the actual situation; there are no specific restrictions. The second time window is preset to 3 days, but it can also be set to 1, 2, or 4 days, or other times depending on the actual situation; there are no specific restrictions. For example, when the first time window is preset to 5 days and the second time window to 3 days, it means that the water volume prediction model uses historical water inflow data from the past 5 days and historical water supply data of the area it serves to predict the water inflow for the next 3 days, thus obtaining the amount of water that needs to be treated.

[0143] When the preset second time window is greater than one day, the water volume prediction model uses historical water inflow data, historical water supply data, predicted weather information, and future date characteristics to predict the water inflow for the next day. Then, the water inflow for the next day is used as historical water inflow data for the next day's prediction, ultimately obtaining the water inflow for the preset second time window. For example, if the preset first time window is 5 days and the preset second time window is 3 days, it means that the water volume prediction model uses historical water inflow data from the past 5 days and historical water supply data for the area it serves to predict the water volume for the first day. When predicting the water volume for the second day, the predicted water volume for the first day is used as historical data for the second day's prediction. When predicting the water volume for the third day, the predicted water volumes for the first and second days are used as historical data for the third day's prediction, thus achieving the prediction of the water inflow for the next 3 days and ultimately obtaining the water volume to be treated.

[0144] By incorporating predictions of future water volume requirements into the control process, the system can anticipate water volume trends within a pre-set second time window before the actual inflow arrives. When the prediction indicates that the future water volume may exceed the safe treatment capacity of the secondary sedimentation tank or approach the system's load limit, the control strategy can adjust the operating mode in advance, such as by activating the in-situ expansion system ahead of time. This effectively avoids problems such as sludge runoff, excessive effluent, or unstable treatment caused by sudden increases in water volume. Compared to the traditional passive adjustment method that relies on real-time flow changes, the proactive control method based on the water volume prediction model in this application significantly improves the system's adaptability to peak water volumes, rainy season fluctuations, and periodic changes during holidays. This gives the in-situ expansion system greater operational flexibility and safety margin, ensuring stable and compliant operation even under fluctuating water volume conditions.

[0145] In some embodiments, determining the first water volume used to characterize the hydraulic loading capacity of the secondary sedimentation tank of the biochemical treatment system includes:

[0146] Acquire historical influent water quality and historical operation data of the biochemical treatment system within the historically preset third time window;

[0147] Based on the pre-constructed sludge volume index prediction model, the sludge volume index for a future preset second time window is predicted using the historical influent water quality and the historical operating data, thus obtaining the predicted sludge volume index.

[0148] The solids flux threshold of the secondary sedimentation tank is determined based on the predicted sludge volume index.

[0149] Based on the solid flux threshold, the amount of water that the secondary sedimentation tank can process in a future preset second time window is determined, and the first water volume is obtained.

[0150] Specifically, historical influent water quality includes parameters such as Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), and Sludge Volume Index (SVI) of the historical influent; historical operational data includes operational parameters such as water temperature, pH, amount of added carbon source, and sludge concentration in the biochemical reaction zone. COD, TN, and TP are used to characterize the concentrations of organic matter, nitrogenous pollutants, and phosphorus-containing pollutants in wastewater, respectively, and are important water quality indicators reflecting the biodegradability of wastewater, nutrient balance, and microbial growth conditions.

[0151] The sludge volume index (SVI) is influenced by a combination of factors, including microbial growth status, floc structure, sludge age, nutrient ratio, and aquatic environmental conditions. Therefore, historical influent water quality and operational data can be used to predict future SVI. Specifically, influent COD and the amount of added carbon source determine the amount of organic matter available for microbial use, affecting sludge yield and floc formation characteristics. Essentially, it reflects the organic load and is one of the core factors influencing SVI. At low organic loads, microorganisms are in a state of starvation; filamentous bacteria, with their larger surface area, have a higher absorption rate of low-concentration substrates, giving them an advantage in competition and making them prone to low-load sludge bulking and increased SVI. At high organic loads, the flocs grow rapidly, entering an exponential growth phase, making it difficult to form dense flocs and reducing settling performance.

[0152] TN and TP represent indicators of microbial nutrient balance, affecting the nitrogen and phosphorus nutrient supply to microorganisms. A suitable carbon-nitrogen-phosphorus ratio contributes to the stability of activated sludge systems. Excess carbon sources are converted into glycogen or extracellular polymeric substances (EPS) by microorganisms and stored within the body or secreted externally. A large amount of hydrophilic EPS leads to increased water content in sludge flocs, resulting in a loose, viscous structure, non-filamentous bulking, and increased SVI.

[0153] Water temperature and pH are core environmental factors affecting the structure and metabolic activity of microbial communities. When the water temperature is between 15-35℃, flocs and filamentous bacteria are in dynamic equilibrium, resulting in well-structured sludge flocs and a relatively normal SVI (Sludge Volume Index). At low temperatures (<15℃), microbial metabolism slows down, but filamentous bacteria have a better ability to utilize the substrate than floc bacteria, gaining a growth advantage and multiplying, leading to filamentous bacteria expansion and an increase in SVI. High temperatures (>35℃) accelerate the reaction, causing excessive consumption of dissolved oxygen (DO), creating an anoxic environment within the flocs and providing growth conditions for filamentous bacteria. At excessively low pH (<6), some fungal filamentous bacteria survive preferentially, inhibiting the activity of floc bacteria, causing floc disintegration and an increase in SVI. The sludge concentration in the biochemical reaction zone affects the sludge volume index (SVI) by influencing the system's feed-to-microbe ratio (F / M) and dissolved oxygen gradient. F / M (food-to-microbe ratio) refers to the organic pollutant load borne by a unit mass of activated sludge microorganisms per unit time. Its calculation formula is usually F / M = (total amount of organic matter entering the biochemical reaction zone) / (total amount of microorganisms in the system). It is a core parameter for regulating the health and balance of the activated sludge system.

[0154] Therefore, by acquiring historical influent water quality and historical operation data, we can reflect the microbial growth conditions and sludge generation characteristics of the biochemical treatment system over a period of time. This allows the sludge volume index prediction model to learn the correlation between the above factors and SVI changes, thereby achieving accurate prediction of the sludge volume index for the future preset second time window.

[0155] The sludge volume index prediction model is constructed using a sliding window-based long short-term memory network. Specifically, it is constructed through the following steps: acquiring second training data, which includes historical influent water quality and historical operational data of the biochemical treatment system at multiple consecutive historical moments; constructing an initial model based on the long short-term memory neural network; pre-training the initial model using the second training data until a preset termination condition is reached; determining the model parameters at the termination of training as the final model parameters; and applying the final model parameters to the initial model to obtain the sludge volume index prediction model. Specifically, the preset third time window can be 5 days, or it can be set to 6, 4, 3, 2, or 1 day. It can be the same as or different from the preset first time window, or it can be set to other times according to actual conditions; there are no specific restrictions.

[0156] Specifically, the solids flux threshold is used to represent the maximum allowable solids flux of the secondary sedimentation tank. Solids flux refers to the mass load of solids (suspended solids, sludge) acting on the surface area of ​​the secondary sedimentation tank per unit time. The maximum allowable solids flux refers to the maximum solids flux that the secondary sedimentation tank can withstand while maintaining stable settling and meeting effluent standards. It is a key parameter that determines the maximum water treatment capacity of the system.

[0157] The Sludge Volume Index (SVI) characterizes the settling performance and floc structure of sludge, and is a key indicator affecting the sludge-water separation efficiency of secondary settling tanks. A higher SVI value indicates looser sludge flocs, poorer compressibility, and worse settling performance, resulting in a thicker sludge layer in the secondary settling tank and thus a lower solids flux that the tank can handle. Conversely, a lower SVI indicates better sludge settling performance, allowing the secondary settling tank to operate stably under higher solids flux conditions. Therefore, there is a certain correlation between SVI and the maximum allowable solids flux parameter of the secondary settling tank (refer to design manuals such as ATV-DVWK-A131). For example, when the SVI is approximately 100 mL / g, the maximum allowable solids flux in the secondary sedimentation tank is approximately 4–6 kg / (m²·h); when the SVI is approximately 150 mL / g, the maximum allowable solids flux is approximately 3–4 kg / (m²·h); when the SVI is approximately 200 mL / g, the maximum allowable solids flux is approximately 2–3 kg / (m²·h); and when the SVI is greater than 250 mL / g, the maximum allowable solids flux is less than 2 kg / (m²·h), making it difficult for the secondary sedimentation tank to operate under high loads. Therefore, a correlation between the sludge volume index and the maximum allowable solids flux can be pre-established based on wastewater characteristics and treatment experience. After obtaining the predicted sludge volume, the corresponding maximum allowable solids flux, i.e., the solids flux threshold, can be determined based on the pre-established correlation.

[0158] The maximum allowable solids flux of the secondary sedimentation tank directly determines the upper limit of its treatable water volume. A higher solids flux means the secondary sedimentation tank can receive and settle more mixed liquor containing suspended solids per unit time, thus allowing for a higher influent flow rate. When the maximum solids flux decreases, the influent flow rate of the secondary sedimentation tank must be reduced to avoid sludge floating, sludge runoff, or turbid effluent, thus decreasing the overall treatable water volume of the system. Therefore, after obtaining the solids flux threshold, the future treatable water volume can be further deduced.

[0159] Specifically, after obtaining the solid flux threshold, the first water volume can be calculated according to the following formula:

[0160] Q a =(G·A) / (R·10) 6 / SVI 测 );

[0161] Among them, Q a For the first water volume, SVI 测 To predict the sludge volume index, G is the solids flux threshold, A is the surface area of ​​the secondary sedimentation tank, and R is the sludge external return ratio.

[0162] The following relationship exists between the solid flux threshold and water volume in the secondary sedimentation tank: G = (Q a +Q r )·MLSS / A, where Q r The sludge return volume is the amount of sludge returned to the sludge return pipeline, and MLSS is the mixed liquor suspended solids concentration (kg / m³ or g / L).

[0163] The following relationship exists between MLSS, the returned sludge concentration RSS, and the external sludge return ratio R: MLSS = [R / (1 + R)]·RSS. The external sludge return ratio R = Q. r / Q a .

[0164] RSS can be used to predict the sludge volume index SVI. 测 Approximate estimate, i.e.: RSS=10 6 / SVI 测 For example, SVI 测 =150mL / g, then RSS≈10 6 / 150≈6667mg / L≈6.67 kg / m³.

[0165] Finally, set MLSS = [R / (1+R)]·RSS and R = Q. r / Q a SVI 测 Substituting into the formula for calculating G, we can derive: Q a= (G·A ) / (R·RSS )= (G·A ) / (R·10 6 / SVI 测 ).

[0166] Therefore, based on the predicted sludge volume index and the corresponding solid flux threshold, the hydraulic load capacity of the secondary sedimentation tank in the future can be predicted, thus obtaining the first water volume.

[0167] In this embodiment, the solids flux capacity of the secondary sedimentation tank can be known in advance before a preset second time window by using the predicted sludge volume index (SVI). Since the SVI reflects the settling performance and floc structure of sludge and is a key factor determining the maximum solids flux capacity of the secondary sedimentation tank, the future SVI can be predicted based on historical influent water quality and historical operating data. Based on this, the solids flux threshold of the secondary sedimentation tank can be determined, and the maximum water volume that the secondary sedimentation tank can treat in the future can be quantitatively calculated. This allows the system to determine in advance whether the secondary sedimentation tank may experience excessive solids flux, obstructed sludge-water separation, or sludge leakage risk before the actual wastewater volume arrives. This provides a basis for switching the operating mode of the in-situ expansion system in advance and for starting the sludge screening device and membrane separation tank, avoiding instability caused by sudden load increases. This effectively improves the operational safety and adaptability of the in-situ expansion system, and enhances its overall stability under fluctuating water quality and quantity conditions.

[0168] The control method of this application will be further described below through a specific embodiment.

[0169] The original biological treatment system of a wastewater treatment plant adopts a typical anaerobic-anoxic-aerobic (AAO) process. As the amount of wastewater in the service area increases year by year, the solids flux of the secondary sedimentation tank is gradually approaching its limit, and the overall treatment capacity of the system is reaching a bottleneck. It is urgent to expand the capacity in situ without taking up new land.

[0170] Therefore, the in-situ expansion system of this application is used to expand the existing biological treatment system in situ. The control method of the in-situ expansion system proposed in this application is used to predict the system's treatable water volume and dynamically regulate the operation of the in-situ expansion system to improve overall treatment capacity and operational stability. The control method of this application will be further explained below using an example of a biological reaction zone including an anaerobic tank, an anoxic tank, and an aerobic tank.

[0171] The control method for the in-situ expansion system can be executed using an electronic control unit, or it can be executed using other independently operating controllers; there are no specific restrictions. The following explanation uses a controller as an example to further illustrate this control method.

[0172] like Figure 4As shown, the controller invokes a pre-built water volume prediction model. Based on the historical inflow and supply data of the biochemical treatment system over the past 5 days, as well as the predicted weather information for the next 3 days (e.g., sunny, rainy, etc.) and future date characteristics (e.g., holidays, weekdays, weekends, etc.), it predicts the inflow volume for the next 3 days and obtains the water volume to be treated. The required treatment volume can be expressed as the average inflow rate over the 3 days, in m³ / h.

[0173] The controller invokes a pre-built sludge volume index prediction model, using historical influent water quality (such as COD, TP, TND, SVI, etc.) and historical operating data (water temperature, pH) of the biological treatment system to predict the sludge volume index for the next 3 days, thus obtaining the predicted sludge volume. The predicted sludge volume can be represented by the average sludge volume index over the 3 days. Then, based on the predicted sludge volume index, the corresponding solids flux threshold is determined, thereby determining the hydraulic loading capacity of the secondary sedimentation tank for the next 3 days, i.e., obtaining the first water volume. The first water volume can be represented by the average influent flow rate over the 3 days, in m³ / h.

[0174] like Figure 3 As shown, the controller acquires a preset water volume threshold and compares it with the water volume to be treated. When the water volume to be treated is greater than a first water volume but less than or equal to the preset water volume threshold, the controller controls the in-situ expansion system to operate in a first mode. During the operation of the first mode, the controller acquires the suspended particulate matter concentration of the secondary sedimentation tank effluent in real time and adjusts the flow distribution between the hydrocyclone's underflow port and overflow port based on the suspended particulate matter concentration. When the suspended particulate matter concentration is less than or equal to a preset first concentration threshold, the controller controls the valve opening of the underflow port and overflow port to make the flow ratio between the hydrocyclone's underflow port and overflow port a first ratio; when the suspended particulate matter concentration is greater than the first concentration threshold but less than or equal to a preset second concentration threshold, the flow ratio between the hydrocyclone's underflow port and overflow port is adjusted to a second ratio; when the suspended particulate matter concentration is greater than the second concentration threshold, the flow ratio between the hydrocyclone's underflow port and overflow port is adjusted to a third ratio.

[0175] When the volume of water to be treated exceeds a preset threshold, the controller acquires the transmembrane pressure differential growth rate of the membrane modules in the membrane separator. If the membrane separator has never been turned on, the transmembrane pressure differential growth rate can be directly determined to be 0. If the membrane separator has been turned on for a period of time, paused for a period of time, and then restarted, the transmembrane pressure differential growth rate measured during the most recent operation can be acquired to determine the membrane fouling situation. The controller further acquires a first rate threshold. When the transmembrane pressure differential growth rate is determined to be less than or equal to the preset first rate threshold, the in-situ expansion system is controlled to operate in the second mode; when the transmembrane pressure differential growth rate is greater than the preset first rate threshold, the in-situ expansion system is controlled to operate in the third mode. After controlling the in-situ expansion system to operate in the second mode, the transmembrane pressure differential growth rate continues to be monitored, and when the transmembrane pressure differential growth rate increases too rapidly, it is switched to the third mode in a timely manner.

[0176] After the in-situ expansion system is operated in the third mode, the controller calculates the sludge specific resistance ratio by obtaining the specific resistance parameters of the feed sludge at the first inlet and the discharge sludge at the underflow outlet; when the sludge specific resistance ratio is greater than the preset first sludge specific resistance threshold, the dosing device is turned on to add flocculant into the third feed pipeline.

[0177] Meanwhile, when the controller detects that the rate of increase of the transmembrane pressure difference is greater than the preset second rate threshold, it controls the backwashing device to start so as to add cleaning agent into the membrane separation tank through the third drainage pipeline to clean the membrane module in the separation tank.

[0178] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.

[0179] Furthermore, given that details have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that embodiments of this application may be practiced without these details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0180] To simplify the description and discussion, and to avoid obscuring the embodiments of this application, well-known power / ground connections to other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be shown in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be fully understood by those skilled in the art). While specific details have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application may be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0181] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. The embodiments of this application are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A control method for an in-situ capacity expansion system, characterized in that, The in-situ expansion system is applied to the biochemical treatment system, which includes an inlet pipeline, a biochemical reaction zone, a first connecting pipeline, a secondary sedimentation tank, and a first drainage pipeline connected in sequence. The bottom of the secondary sedimentation tank is connected to the biochemical reaction zone via a sludge return pipeline; the in-situ expansion system includes: A sludge screening device includes a sludge screening body and an overflow port at the top, a bottom flow port at the bottom, and a first feed port on the side wall of the sludge screening body. The first feed port is connected to the sludge return pipeline and the first connecting pipeline through a first feed pipeline and a second feed pipeline, respectively. The bottom flow port is connected to the biochemical reaction zone through the first return pipeline. The overflow port is connected to a second drainage pipeline to discharge the overflow products to the outside of the system. The membrane separation tank is equipped with a second feed inlet, a drain outlet, and a sludge discharge outlet. A membrane module for separating sludge and water is installed between the second feed inlet and the drain outlet. The second feed inlet is connected to the underflow outlet and the first connecting pipeline via a third feed pipeline and a fourth feed pipeline, respectively. The sludge discharge outlet is connected to the biochemical reaction zone via a second return pipeline. The drain outlet is connected to a third drain pipeline to discharge the permeate from the membrane separation tank to the outside of the system. The in-situ expansion system has three operating modes: a first mode, a second mode, and a third mode. In the first mode, the sludge screening device, the first feed pipeline, the first return pipeline, and the second drainage pipeline are in operation; the membrane separation tank and the second feed pipeline are in non-operational state. In the second mode, the membrane separation tank, the fourth feed pipeline, the second return pipeline and the third drainage pipeline are in operation, while the sludge screening device is in non-operational state. In the third mode, the sludge screening device, the membrane separation tank, the second feed pipeline, the third feed pipeline, the second return pipeline, the second drainage pipeline, and the third drainage pipeline are in operation, while the first feed pipeline, the first return pipeline, and the fourth feed pipeline are in non-operational state. The control method includes: Determine the required water volume to be treated by the biological treatment system; Determine the first water volume used to characterize the hydraulic load capacity of the secondary sedimentation tank in the biochemical treatment system; In response to the fact that the water volume to be processed is greater than the first water volume and less than or equal to a preset water volume threshold, the in-situ expansion system is controlled to operate in the first mode. In response to the water volume to be treated being greater than the preset water volume threshold, the rate of increase of the transmembrane pressure difference in the membrane module in the membrane separation tank is obtained; In response to the transmembrane pressure differential growth rate being less than or equal to a preset first rate threshold, the in-situ expansion system is controlled to operate in a second mode. In response to the transmembrane pressure difference growth rate being greater than a preset first rate threshold, the in-situ expansion system is controlled to operate in a third mode.

2. The control method according to claim 1, characterized in that, The biochemical reaction zone includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. The bottom of the secondary sedimentation tank is connected to the anaerobic tank via the sludge return pipeline; And / or, the bottom of the aerobic tank is connected to the anoxic tank via an internal reflux pipeline.

3. The control method according to claim 1, characterized in that, The in-situ expansion system also includes a backwashing device, which is connected to the third drainage pipeline for adding cleaning agents to the membrane separation tank. And / or, the in-situ expansion system further includes a dosing device connected to the third feed line for adding flocculant to the membrane separation tank through the third feed line.

4. The control method according to claim 1, characterized in that, After the control in-situ capacity expansion system operates in the first mode, it also includes: Monitor the concentration of suspended particulate matter in the effluent from the secondary sedimentation tank; The flow rate distribution between the underflow port and the overflow port of the sludge screening device is adjusted based on the concentration of suspended particulate matter, so that the flow rate ratio between the underflow port and the overflow port decreases as the concentration of suspended particulate matter increases.

5. The control method according to claim 4, characterized in that, The flow distribution between the underflow and overflow outlets of the sludge screening device is controlled based on the concentration of suspended particulate matter, including: In response to the suspended particulate matter concentration being less than or equal to a preset first concentration threshold, the flow ratio between the underflow port and the overflow port of the sludge screening device is adjusted to a first ratio. In response to the suspended particulate matter concentration being greater than the first concentration threshold and less than or equal to a preset second concentration threshold, the flow ratio between the bottom outlet and the overflow outlet of the sludge screening device is adjusted to a second ratio. In response to the suspended particulate matter concentration being greater than the second concentration threshold, the flow ratio between the underflow outlet and the overflow outlet of the sludge screening device is adjusted to a third ratio. The first ratio, the second ratio, and the third ratio decrease sequentially.

6. The control method according to claim 3, characterized in that, After the control in-situ expansion system operates in the third mode, it also includes: Monitor the specific resistance parameters of the feed sludge at the first inlet and the discharge sludge at the underflow outlet; Calculate the ratio of the specific resistance parameters of the discharged sludge to that of the fed sludge to obtain the sludge specific resistance ratio. In response to the sludge resistivity ratio being greater than a preset first sludge resistivity threshold, the dosing device is controlled to open to add flocculant into the third feed pipeline.

7. The control method according to claim 3, characterized in that, The control method further includes: In response to the transmembrane pressure differential growth rate being greater than a preset second rate threshold, the backwashing device is controlled to be turned on to add cleaning agent to the membrane separation tank through the third drainage pipeline; Wherein, the second rate threshold is greater than the first rate threshold.

8. The control method according to claim 1, characterized in that, Determining the required water volume for the biochemical treatment system includes: Acquire historical inflow data and historical water supply data of the service area within the historical preset first time window of the biochemical treatment system; Obtain the predicted weather information for the next preset second time window and the future date characteristics information for the corresponding time period; Based on a pre-built water volume prediction model, the water volume in a future preset second time window is predicted using the historical water inflow data, the historical water supply data, predicted weather information, and the future date feature information, thereby obtaining the water volume to be treated.

9. The control method according to claim 1, characterized in that, The determination of the first water volume used to characterize the hydraulic loading capacity of the secondary sedimentation tank in the biochemical treatment system includes: Acquire historical influent water quality and historical operation data of the biochemical treatment system within the historically preset third time window; Based on the pre-constructed sludge volume index prediction model, the sludge volume index for a future preset second time window is predicted using the historical influent water quality and the historical operating data, thus obtaining the predicted sludge volume index. The solids flux threshold of the secondary sedimentation tank is determined based on the predicted sludge volume index. Based on the solid flux threshold, the amount of water that the secondary sedimentation tank can process in a future preset second time window is determined, and the first water volume is obtained.

Images