JP2020199474A - Control devices, control method and computer program - Google Patents

Abstract

To provide a control device, a control method and a computer program capable of maintaining an activated sludge concentration of a biological reaction tank more appropriately in a water treatment system including a solid-liquid separation means using membrane and a decomposition means of pollutants using activated sludge.SOLUTION: A control device according to an embodiment is used in a water treatment system including a solid-liquid separation means using membrane and a pollutant decomposition means using an activated sludge method. The control device includes a circulation unit and a first control unit. The circulation unit circulates a part of water to be treated in a biological reaction tank by returning a part of the water to be treated in an aerobic tank or a membrane tank including the solid-liquid separation means using membrane, to an oxygen-free tank. The first control unit adjusts a circulation amount of the water to be treated by the circulation unit using MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank or the membrane tank as an index.SELECTED DRAWING: Figure 2

Description

Embodiments of the present invention relate to control devices, control methods and computer programs.

One of the solid-liquid separation methods in water treatment is a method using a fine filter called a "membrane". Further, as one of the methods for decomposing pollutants in water, an activated sludge method for decomposing pollutants using activated sludge is known. A water treatment method that combines solid-liquid separation with these membranes and an activated sludge method is called a membrane separation activated sludge method (MBR: Membrane Bioreactor). With its use, the membrane gradually becomes clogged by the fine solids contained in the water to be treated adhering to the membrane surface and pores, and the higher the activated sludge concentration, the more the membrane tends to clog. It is known to be large. Since activated sludge has the property of increasing according to the amount of decomposed pollutants, it is necessary for MBR to periodically extract the activated sludge that accumulates in the biological reaction tank and control its concentration appropriately. Specifically, if the amount of activated sludge in the water to be treated is excessively small, the ability to decompose pollutants is reduced, and if it is excessively large, membrane blockage is promoted. Therefore, the amount of activated sludge in the water to be treated needs to be controlled so as not to promote membrane occlusion more than necessary while maintaining the required decomposition ability.

However, it is not really easy to perform the operation of extracting the activated sludge that constantly grows intermittently while appropriately grasping the balance between the amount of growth and the amount of extraction. In addition, if the amount of withdrawal is too large, it becomes difficult to recover the state of the biological reaction tank, so that the determination of withdrawal is delayed, and the activated sludge may not always be withdrawn at the optimum timing. Against this background, it is desired to establish a technique for appropriately controlling the activated sludge concentration of the water to be treated in the MBR.

Japanese Unexamined Patent Publication No. 2013-188650 Japanese Unexamined Patent Publication No. 2015-24368 Japanese Unexamined Patent Publication No. 2008-155080

The problem to be solved by the present invention is a control capable of more appropriately maintaining the activated sludge concentration in the biological reaction tank in a water treatment system including a solid-liquid separation means by a membrane and a means for decomposing pollutants by active sludge. It is to provide devices, control methods and computer programs.

The control device of the embodiment is used in a water treatment system including a solid-liquid separation means by a membrane and a pollutant decomposition means by an activated sludge method. The control device includes a circulation unit and a first control unit. The circulation unit circulates a part of the water to be treated in the biological reaction tank by returning a part of the water to be treated in the aerobic tank or the membrane tank provided with the solid-liquid separation means by the membrane to the oxygen-free tank. .. The first control unit adjusts the circulation amount of the water to be treated by the circulation unit using the MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank or the membrane tank as an index.

The figure which shows the specific example of the structure of the water treatment system 100 in 1st Embodiment. The block diagram which shows the specific example of the functional structure of the control device 3 in 1st Embodiment. The figure which shows typically the change of the concentration gradient of the MLSS concentration in the biological reaction tank 2 of 1st Embodiment. The flowchart which shows the flow of the process which control device 3 adjusts the circulation amount of nitrification liquid in 1st Embodiment. The figure which shows the specific example of the structure of the water treatment system 100a in the 2nd Embodiment. The block diagram which shows the specific example of the functional structure of the control device 3a in the 2nd Embodiment. FIG. 5 is a flowchart showing a flow of a process in which the control device 3a adjusts the circulation amount of the nitrifying liquid and the extraction amount of activated sludge in the second embodiment.

Hereinafter, the control device, the control method, and the computer program of the embodiment will be described with reference to the drawings.

(First Embodiment)
FIG. 1 is a diagram showing a specific example of the configuration of the water treatment system 100 according to the first embodiment. The water treatment system 100 includes a solid-liquid separation means using a membrane and a means for decomposing pollutants by activated sludge, and is a system that performs water treatment by the membrane separation activated sludge method (MBR: Membrane Bioreactor). It is provided with a biological reaction tank 2 and a control device 3. More specifically, the water treatment system 100 is a system assuming a circulation type nitrification denitrification method MBR that circulates a part of the water to be treated in the biological reaction tank 2. The circulation type nitrification denitrification method MBR is one of the forms of a water treatment system that realizes so-called advanced treatment that enables removal of nitrogen and phosphorus in the water to be treated.

The first sedimentation reservoir 1 is a reservoir for storing the water to be treated (hereinafter referred to as "water to be treated") sent to the water treatment system 100. Initially, in the sedimentation pond 1, a relatively large solid substance is separated from the water to be treated by sedimentation, and the supernatant water is sent to the biological reaction tank 2.

In the biological reaction tank 2, the water to be treated and the activated sludge are mixed, and the pollutants in the water to be treated are decomposed by the action of microorganisms in the activated sludge. The water to be treated in which the pollutant is decomposed is separated from the activated sludge by a membrane and discharged from the water treatment system 100 as treated water (hereinafter referred to as "treated water").

Specifically, the biological reaction tank 2 includes an oxygen-free tank 21, an aerobic tank 22, and a membrane unit 23 installed by being immersed in water to be treated in the aerobic tank 22.

The oxygen-free tank 21 is a water storage tank that initially stores the water to be treated sent from the sedimentation pond 1 in a state where air is not supplied. The water to be treated sent to the oxygen-free tank 21 is sent to the aerobic tank 22 after staying for a predetermined time. Generally, the residence time of the water to be treated in the oxygen-free tank 21 is designed to be about 3 hours. Therefore, the oxygen-free tank 21 is generally considered to have a capacity capable of storing the amount of inflow water for 3 hours.

The aerobic tank 22 is a water storage tank that supplies air to the water to be treated sent from the oxygen-free tank 21. The water to be treated sent to the aerobic tank 22 is sent to the membrane unit 23 after staying for a predetermined time. As with the oxygen-free tank 21, the capacity of the aerobic tank 22 is generally sufficient as long as it can store the amount of inflow water for 3 hours.

On the other hand, a part of the water to be treated in the aerobic tank 22 is returned to the oxygen-free tank 21 by the nitrifying liquid circulation pump 221 (an example of the circulation part and the sludge extraction part). Hereinafter, the water to be treated returned to the oxygen-free tank 21 by the nitrifying liquid circulation pump 221 is referred to as "nitrifying liquid". In the circulation type nitrification denitrification method MBR, the nitrification liquid is returned for the purpose of removing the nitrogen content in the water to be treated. The flow rate of the returned nitrifying liquid is adjusted by controlling the output of the nitrifying liquid circulation pump 221 or the opening degree of the flow valve V1 provided in the middle of the return flow path.

Specifically, in the aerobic tank 22, the nitrifying bacteria in the activated sludge are activated by supplying air to the water to be treated, and the activation of the nitrifying bacteria promotes the nitrification reaction in the water to be treated. By this nitrification reaction, ammonia in the water to be treated is oxidized to nitric acid. On the other hand, in the anoxic tank 21, denitrification bacteria in the activated sludge are activated by not supplying air to the water to be treated, and the denitrification reaction in the water to be treated is promoted by the activation of the denitrification bacteria. By this denitrification reaction, nitric acid is reduced to nitrogen gas and released into the atmosphere. In such a nitrification-denitrification reaction, the nitrification solution plays a role of a medium for supplying nitric acid to the anoxic tank 21, and promotes the nitrification-denitrification reaction in the biological reaction tank 2. As a result, the nitrogen content in the water to be treated is removed.

Further, in the aerobic tank 22, a surplus sludge drawing pump 222 for pulling out activated sludge that grows and accumulates in the tank is installed. Since the activated sludge in the aerobic tank 22 causes clogging of the membrane in the membrane unit 23, it is pulled out by the excess sludge extraction pump 222 so that its concentration does not become excessively high, and an external process (for example, sludge disposal) (for example, sludge disposal) (not shown) is drawn. It is sent to the process etc.). The amount of activated sludge drawn out is adjusted by controlling the output of the excess sludge drawing pump 222 or the opening degree of the flow valve V2 provided in the middle of the water supply flow path to the external process.

The membrane unit 23 is a device that separates the treated water from the water to be treated and discharges it by filtering the water to be treated in the aerobic tank 22. The membrane unit 23 includes one or more membrane modules 231 and supplies water to be treated to each membrane module 231. The membrane unit 23 collects and discharges the treated water separated from the water to be treated by each membrane module 231.

The membrane used for the membrane module 231 may be any kind of membrane as long as it can separate the treated water from the water to be treated. For example, the membrane module 231 may use a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), or a nanofiltration membrane (NF membrane). ) May be used, or a reverse osmosis membrane (RO membrane) may be used.

Further, when the film unit 23 includes a plurality of film modules 231, the positional relationship and the connection relationship of each film module 231 are not limited to a specific mode. For example, the membrane unit 23 may have one or more membrane modules 231 arranged in series with respect to the flow of water to be treated, or may be arranged in parallel. Further, the membrane unit 23 does not necessarily have to be installed in the aerobic tank 22. For example, the membrane unit may be installed in a water tank (also referred to as a membrane tank) dedicated to membrane treatment provided in the subsequent stage in the aerobic tank.

The control device 3 has a function of adjusting the circulation amount of the nitrifying liquid in the biological reaction tank 2 by controlling the operation of the nitrifying liquid circulation pump 221. Specifically, the control device 3 controls the amount of nitrified liquid drawn out by the nitrifying liquid circulation pump 221 based on the MLSS (Mixed Liquor Suspended Solids) concentration in the aerobic tank 22. Here, the MLSS concentration is the concentration of suspended solids (MLSS) in the sample (here, the water to be treated), and is a value generally used as a control index for the amount of activated sludge in the biological reaction tank 2. For this control, an MLSS concentration meter 223 is installed in the aerobic tank 22.

FIG. 2 is a block diagram showing a specific example of the functional configuration of the control device 3 according to the first embodiment. The control device 3 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like connected by a bus, and executes a program. The control device 3 functions as a device including a communication unit 31, a storage unit 32, a measurement data acquisition unit 33, and a first control unit 34 by executing a program. All or part of each function of the control device 3 may be realized by using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a flexible disk, a magneto-optical disk, a portable medium such as a ROM or a CD-ROM, or a storage device such as a hard disk built in a computer system. The program may be transmitted over a telecommunication line.

The communication unit 31 is a communication interface that communicates with the MLSS concentration meter 223, the ORP meter 211, the nitrifying liquid circulation pump 221 and the excess sludge extraction pump 222. The communication unit 31 may be a wired communication interface or a wireless communication interface.

The storage unit 32 is configured by using a storage device such as a magnetic hard disk device or a semiconductor storage device. The storage unit 32 stores various setting information necessary for the operation of the control device 3.

The measurement data acquisition unit 33 acquires the measurement data of the MLSS concentration meter 223 and the ORP meter 211 via the communication unit 31. The measurement data acquisition unit 33 stores each acquired measurement data in the storage unit 32. The measurement data acquisition unit 33 accumulates the measurement data in the storage unit 32 by repeatedly executing the acquisition and storage of the measurement data.

The first control unit 34 has a function of adjusting the circulation amount of the nitrifying liquid according to the change of the MLSS concentration by controlling the nitrifying liquid circulation pump 221. Specifically, the first control unit 34 observes a change in the MLSS concentration of the water to be treated in the aerobic tank 22 based on the measurement data of the MLSS concentration meter 223, and nitrifies according to the magnitude of the short-term change. Determine the flow rate of the liquid. The first control unit 34 determines a control instruction value for discharging the nitrifying liquid of the determined flow rate to the nitrification liquid circulation pump 221 and sends a control signal for notifying the determined control instruction value to the nitrification liquid circulation pump via the communication unit 31. Output to 221.

Since the membrane unit 23 is arranged on the downstream side of the aerobic tank 22, the MLSS concentration on the downstream side of the aerobic tank 22 has a great influence on the clogging of the membrane. Therefore, by increasing the amount of activated sludge returned from the downstream side of the aerobic tank 22, the progress of membrane clogging in the membrane unit 23 can be delayed.

FIG. 3 is a diagram schematically showing a change in the concentration gradient of the MLSS concentration in the biological reaction tank 2 of the first embodiment. The vertical axis of the graph shown in FIG. 3 represents the MLSS concentration of the water to be treated in the biological reaction tank 2, and the horizontal axis represents the position of the water to be treated in the biological reaction tank 2. The horizontal axis represents the position in the flow direction of the water to be treated (horizontal direction in FIG. 1). Here, the straight line L1 shows the concentration gradient when the nitrifying liquid is circulated at a normal flow rate, and the straight line L2 shows the concentration gradient when the circulating amount of the nitrifying liquid is increased. For the sake of simplicity, the change in the concentration gradient of the MLSS concentration in the biological reaction tank 2 is shown by a straight line, but it is actually affected by the DO (Dissolved Oxygen) concentration and activated sludge concentration at each position. It may be curved.

Generally, in the circulating nitrification denitrification method MBR, the oxygen required for the decomposition reaction (denitrification reaction) in the anoxic tank is in the form of nitrate ion and nitrite ion in the water to be treated returned from the aerobic tank as a nitrification solution. Be supplied. Further, in the anoxic tank and the aerobic tank, activated sludge is generated by decomposition reaction (nitrification reaction and denitrification reaction) in addition to movement of activated sludge by circulation of nitrification liquid. From these facts, in the circulation type nitrification denitrification method MBR, the distribution of the MLSS concentration is not uniform in the biological reaction tank in principle, and there is a concentration gradient as shown in the straight line L1, for example. As shown by the straight line L1, in the circulation type nitrification denitrification method MBR, generally, from the upstream part (specifically, the upstream part of the oxygen-free tank) to the downstream part (specifically, the downstream part of the aerobic tank) of the biological reaction tank. The MLSS concentration increases.

In anoxic tanks and aerobic tanks where such a concentration gradient occurs, when the decomposition treatment of pollutants is ideally advanced, the pollutants flowing into the biological reaction tank are decomposed during the residence time in the tank. To. For example, assuming that the residence time of the water to be treated in the oxygen-free tank and the aerobic tank is 3 hours each, the pollutant that has flowed in is decomposed over 6 hours, which is the total residence time of each tank. This means that the amount of pollutants flowing into the biological reaction tank affects the amount of activated sludge in the tank for as long as 6 hours from the time of inflow.

On the other hand, in order to operate the membrane treatment stably, it is necessary to keep the progress rate of membrane clogging constant. Furthermore, since the progress rate of membrane clogging depends on the MLSS concentration in the aerobic tank (or membrane tank), the MLSS concentration in the aerobic tank does not become excessively high for stable operation of the membrane treatment. Must be done. Conventionally, the MLSS concentration in the tank is controlled by pulling out the activated sludge in the tank, but it may be difficult to recover the state when the activated sludge is pulled out too much, and the MLSS concentration tends to change over a long period of time. It is often done by looking at. Therefore, in the conventional water treatment system by the circulation type nitrification denitrification method MBR, it is difficult to suppress the influence of the short-term change of the MLSS concentration on the clogging of the membrane.

Based on such a background and the principle of MLSS concentration, the control device 3 of the first embodiment reduces the concentration gradient of MLSS concentration in the biological reaction tank 2 by increasing the circulation amount of the nitrifying solution. Specifically, the control device 3 returns the nitrifying solution from the most downstream part of the aerobic tank 22 having the maximum concentration to the most upstream part of the anoxic tank 21 having the minimum concentration, so that the aerobic tank 3 is used. It reduces the MLSS concentration in the most downstream part of 22. By performing such control, the control device 3 can reduce the concentration gradient of the MLSS concentration in the biological reaction tank 2 from, for example, the state of the straight line L1 to the state of the straight line L2.

FIG. 4 is a flowchart showing a flow of processing in which the control device 3 adjusts the circulation amount of the nitrifying liquid in the first embodiment. First, the first control unit 34 determines whether or not the first determination timing has arrived (step S101). The first determination timing is the timing for determining the magnitude of the amount of change in the MLSS concentration. For example, the interval of the first determination timing is set to an interval in which the magnitude of a short-term change (for example, a change in the past 1 hour) of the MLSS concentration can be observed. The interval of the first determination timing may be set according to the magnitude of the change in the MLSS concentration that can occur in the water treatment system 100, the rate of change, the magnitude of the short-term change to be detected, and the like.

When the first determination timing has not arrived (step S101-NO), the first control unit 34 repeatedly executes the determination process of step S101 until the first determination timing arrives. On the other hand, when the first determination timing has arrived (step S101-YES), the first control unit 34 determines the MLSS concentration in the past predetermined period based on the measurement data of the MLSS concentration stored in the storage unit 32. The amount of change is acquired (step S102), and it is determined whether or not the amount of change has reached a predetermined threshold value (step S103). Here, the period for acquiring the amount of change in the MLSS concentration may be set according to the magnitude of the short-term change to be observed, the rate of change, and the like. For example, this period may be set to the same period as the interval of the first determination timing.

When the amount of change in the MLSS concentration has not reached the threshold value (step S103-NO), the first control unit 34 returns the process to step S101 and waits for the arrival of the next first determination timing. On the other hand, when the amount of change in the MLSS concentration has reached the threshold value (step S103-YES), the first control unit 34 determines the circulation amount of the nitrifying solution based on the magnitude of the amount of change (step S104). For example, the first control unit 34 may determine the circulation amount of the nitrifying liquid based on the correspondence between the amount of change in the MLSS concentration and the increment of the nitrifying liquid flow rate. In this case, it is assumed that the information indicating the correspondence relationship (hereinafter referred to as "first correspondence information") is stored in the storage unit 32 in advance. The amount of change in the MLSS concentration may be represented by the ratio of the amount of change (that is, the rate of change) to the MLSS concentration before or after the change.

Here, when the circulation amount of the nitrifying liquid is increased, the concentration gradient of the DO concentration in the biological reaction tank 2 also changes in the direction of becoming more uniform. Then, excessively increasing the circulation amount of the nitrifying liquid may adversely affect the denitrification reaction in the oxygen-free tank 21. Therefore, it is desirable that the increase in the circulation amount be limited to the minimum increase amount that can achieve the required nitrogen removal rate.

Therefore, the first control unit 34 may determine the circulation amount of the nitrifying solution in consideration of the DO value (or the pH that correlates with the DO value) of the oxygen-free tank 21 in addition to the MLSS concentration. However, in this case, a DO meter (or pH meter) for measuring the DO value (or pH) of the oxygen-free tank 21 is required. On the other hand, it is known that the ORP (Oxidation-Reduction Potential) value, which is an index value of the amount of activated sludge, also correlates with the DO value, and activated sludge is used in water treatment systems based on the activated sludge method. An ORP meter is often provided for volume control. Therefore, in the water treatment system 100 provided with the ORP meter 211 in the oxygen-free tank 21, the first control unit 34 may determine the circulation amount of the nitrifying solution based on the measurement data of the MLSS concentration meter 223 and the ORP meter 211. ..

For example, the first correspondence information may be generated as information indicating a correspondence relationship between the amount of change (or rate of change) in the MLSS concentration and the permissible increment of the nitrification liquid flow rate with respect to the change amount.

Further, for example, the first control unit 34 may determine the circulation amount of the nitrifying liquid by using a model formula for determining an appropriate circulation amount based on the change amount (or change rate) of the ORP value and the MLSS concentration. ..

Further, for example, the first control unit 34 gradually sets the circulation amount determined based on the change amount (or change rate) of the MLSS concentration as a target value within a range in which the ORP value does not deviate from a predetermined allowable range. The circulation amount may be increased.

The method in which the first control unit 34 controls the circulation amount of the nitrifying liquid may be any feedback control with the determined circulation amount as the target value. For example, the circulation amount of the nitrifying solution may be controlled by PID control (Proportional-Integral-Differential Controller).

The first control unit 34 controls the nitrification liquid circulation pump 221 so as to realize the circulation amount of the nitrification liquid determined in this way (step S105).

The control device 3 of the first embodiment configured in this way determines the circulation amount of the nitrified liquid in the circulating nitrification denitrification method MBR based on the magnitude of the short-term change in the MLSS concentration in the aerobic tank 22. By doing so, the MLSS concentration in the biological reaction tank 2 can be maintained more appropriately. According to the water treatment system 100 of the first embodiment, the control device 3 maintains the MLSS concentration in the biological reaction tank 2 at an appropriate value, so that the quality of the treated water is not deteriorated and the membrane is clogged. It becomes possible to suppress. Further, the progress of the clogging of the membrane is suppressed, so that the power consumption of the water treatment system can be reduced. In addition, since the progress of membrane clogging is suppressed, the frequency of membrane cleaning is reduced, so that the equipment operating rate can be improved. In addition, by reducing the frequency of membrane cleaning, labor costs and chemical costs related to membrane cleaning can be reduced.

In the first embodiment, the configuration for adjusting the nitrifying liquid circulation amount based on the MLSS concentration in the aerobic tank 22 is shown, but when the MLSS concentration meter 223 is provided in the anoxic tank 21, there is no such structure. The nitrifying liquid circulation amount may be adjusted based on the MLSS concentration of the oxygen tank 21.

(Second Embodiment)
FIG. 5 is a diagram showing a specific example of the configuration of the water treatment system 100a according to the second embodiment. The water treatment system 100a is different from the water treatment system 100 of the first embodiment in that the control device 3a is provided instead of the control device 3. Since other configurations are the same as those of the first embodiment, the same configurations will be designated by the same reference numerals as those in FIG.

FIG. 6 is a block diagram showing a specific example of the functional configuration of the control device 3a according to the second embodiment. The control device 3a is different from the control device 3 of the first embodiment in that the second control unit 35 is further provided. Since the other functional units are the same as those of the control device 3 of the first embodiment, the description thereof will be omitted by assigning the same reference numerals to the same functional units as those in FIG.

The second control unit 35 has a function of adjusting the amount of activated sludge drawn from the aerobic tank 22 according to the change in the MLSS concentration by controlling the excess sludge drawing pump 222. Specifically, the second control unit 35 observes the change in the MLSS concentration of the water to be treated in the aerobic tank 22 based on the measurement data of the MLSS concentration meter 223, and favorably according to the magnitude of the long-term change. The amount of activated sludge to be withdrawn from the air tank 22 is determined. The second control unit 35 determines a control instruction value for extracting the determined withdrawal amount of activated sludge to the excess sludge extraction pump 222, and extracts a control signal for notifying the determined control instruction value via the communication unit 31. Output to pump 222.

FIG. 7 is a flowchart showing a flow of processing in which the control device 3a adjusts the circulation amount of the nitrifying liquid and the extraction amount of the activated sludge in the second embodiment. First, the second control unit 35 determines whether or not the second determination timing has arrived (step S201). The second determination timing is the same as the first determination timing in that the magnitude of the change in the MLSS concentration is determined, but the first determination timing observes a short-term change in the MLSS concentration. Although it was the timing, it differs from the first determination timing in that it is the timing for observing a long-term change in the MLSS concentration. Therefore, the interval of the second determination timing is set to a period longer than the interval of the first determination timing.

For example, a long-term change in MLSS concentration can be obtained as a deviation between a moving average value of MLSS concentration in the past 24 hours and a predetermined control target value of MLSS concentration. Further, the interval of the second determination timing depends on the magnitude and rate of change of the MLSS concentration that can occur in the water treatment system 100a, the magnitude of the long-term change to be detected, and the like, as in the case of the first determination timing. Should be set.

When the second determination timing has not arrived (step S201-NO), the second control unit 35 repeatedly executes the determination process of step S201 until the second determination timing arrives. On the other hand, when the second determination timing has arrived (step S201-YES), the second control unit 35 determines the MLSS concentration in the past predetermined period based on the measurement data of the MLSS concentration stored in the storage unit 32. The amount of change is acquired (step S202), and it is determined whether or not the amount of change has reached a predetermined threshold value (step S203). Here, the period for acquiring the amount of change in the MLSS concentration may be set according to the magnitude of the long-term change to be observed, the rate of change, and the like. For example, this period may be set to the same period as the interval of the second determination timing.

When the amount of change in the MLSS concentration has not reached the threshold value (step S203-NO), the second control unit 35 returns the process to step S201 and waits for the arrival of the next second determination timing. On the other hand, when the amount of change in the MLSS concentration has reached the threshold value (step S203-YES), the second control unit 35 determines the amount of activated sludge extracted based on the magnitude of the amount of change (step S204). For example, the second control unit 35 may determine the amount of activated sludge extracted based on the correspondence between the amount of change in the MLSS concentration and the amount of extracted activated sludge. In this case, it is assumed that the information indicating the correspondence relationship (hereinafter referred to as "second correspondence information") is stored in the storage unit 32 in advance. The amount of change in the MLSS concentration may be represented by the ratio of the amount of change (that is, the rate of change) to the MLSS concentration before or after the change.

Here, if the amount of activated sludge in the water to be treated is excessively small, the ability to decompose pollutants is reduced, and if it is excessively large, membrane blockage is promoted. Further, if the amount of extraction is too large, it becomes difficult to restore the state of the biological reaction tank 2. Therefore, the amount of activated sludge extracted needs to be determined so as not to promote membrane occlusion more than necessary while maintaining the required decomposition ability.

For example, the second correspondence information may be generated as information indicating a correspondence relationship between the amount of change (or rate of change) in the MLSS concentration and the amount of extraction allowed for the amount of change. In addition, a slightly smaller amount of extraction may be set so that the activated sludge is not extracted too much.

Further, for example, the second control unit 35 may determine the amount of activated sludge extracted by using a model formula for determining an appropriate amount of extraction based on the amount of change (or rate of change) in the MLSS concentration.

Further, for example, the second control unit 35 sets the extraction amount determined based on the change amount (or change rate) of the MLSS concentration as the overall target value, and achieves the target value by a plurality of extractions each time. The withdrawal amount may be determined.

The second control unit 35 controls the excess sludge withdrawal pump 222 so as to realize the activated sludge withdrawal amount determined in this way (step S205).

The control device 3a of the second embodiment configured in this way determines the circulation amount of the nitrified liquid in the circulating nitrification denitrification method MBR based on the magnitude of the short-term change in the MLSS concentration in the aerobic tank 22. In addition, by determining the amount of activated sludge extracted based on the magnitude of long-term change in the MLSS concentration in the aerobic tank 22, a solid-liquid separation means using a film and a means for decomposing pollutants by the activated sludge are provided. In the water treatment system, the MLSS concentration in the biological reaction vessel can be maintained more appropriately.

In the water treatment system 100a of the second embodiment, the control device 3a is configured to adjust the amount of activated sludge drawn out together with the adjustment of the nitrification liquid circulation amount described in the first embodiment. May be good. For example, the control device 3a first adjusts the concentration by increasing or decreasing the nitrification liquid circulation amount in response to the change in the MLSS concentration, and pulls out the activated sludge when the adjustment of the MLSS concentration cannot be dealt with by increasing or decreasing the nitrification liquid circulation amount. It may be configured to increase or decrease the amount. In this case, for example, the upper limit value, the lower limit value, and the standard value are set for each of the nitrification liquid circulation amount and the activated sludge extraction amount in the control device 3a, and the adjustment of the MLSS concentration cannot be dealt with by increasing or decreasing the nitrification liquid circulation amount. In some cases (for example, when the nitrifying liquid circulation amount is out of the range from the lower limit value to the upper limit value), the amount of activated sludge drawn out may be increased or decreased. On the other hand, when returning the nitrification liquid circulation amount and the activated sludge withdrawal amount increased or decreased for adjusting the MLSS concentration to the standard values, the control device 3a first returns the activated sludge withdrawal amount to the standard values and then nitrifies. It may be configured to return the liquid circulation amount to the standard value.

According to at least one embodiment described above, the circulation amount of the water to be treated by the nitrification liquid circulation pump 221 is measured by using the MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank 22 (or the membrane tank) as an index. By having the first control unit 34 to be adjusted, it is possible to more appropriately maintain the activated sludge concentration in the biological reaction tank in a water treatment system including a solid-liquid separation means by a film and a means for decomposing pollutants by active sludge. A capable control device, control method and computer program can be provided.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

100, 100a ... water treatment system, 1 ... first sedimentation pond, 2 ... biological reaction tank, 21 ... anoxic tank, 211 ... ORP (Oxidation-Reduction Potential) meter, 22 ... aerobic tank, 221 ... nitrification liquid circulation pump, 222 ... Excess sludge extraction pump, 223 ... MLSS concentration meter, 23 ... Membrane unit, 231 ... Membrane module, 3, 3a ... Control device, 31 ... Communication unit, 32 ... Storage unit, 33 ... Measurement data acquisition unit, 34 ... 1 control unit, 35 ... second control unit, V1 ... flow valve, V2 ... flow valve

Claims (6)

A control device used in a water treatment system including solid-liquid separation means using a membrane and decomposing means for pollutants by the activated sludge method.
A circulation unit that circulates a part of the water to be treated in the biological reaction tank by returning a part of the water to be treated in the aerobic tank or the membrane tank provided with the solid-liquid separation means by the membrane to the oxygen-free tank.
A first control unit that adjusts the circulation amount of the water to be treated by the circulation unit using the MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank or the membrane tank as an index.
A control device comprising. The first control unit adjusts the circulation amount of the water to be treated by the circulation unit according to a short-term change in the MLSS concentration of the water to be treated in the aerobic tank or the membrane tank.
The control device according to claim 1. In addition to the short-term change in the MLSS concentration, the first control unit adjusts the circulation amount based on the ORP (Oxidation-Reduction Potential) value or pH of the anoxic tank.
The control device according to claim 2. A sludge extraction part that extracts activated sludge from the aerobic tank,
A second control unit that adjusts the amount of activated sludge extracted by the sludge extraction unit according to a long-term change in the MLSS concentration.
Further prepare
The control device according to claim 2 or 3. It is a control method in a water treatment system including a solid-liquid separation means by a membrane and a pollutant decomposition means by an activated sludge method.
A circulation step of circulating a part of the water to be treated in the biological reaction tank by returning a part of the water to be treated in the aerobic tank or the membrane tank provided with the solid-liquid separation means by the membrane to the oxygen-free tank.
A first control step for adjusting the circulation amount of the water to be treated in the circulation step using the MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank or the membrane tank as an index.
Control method having. For computers used to control water treatment systems that include solid-liquid separation means by membrane and decomposition means of pollutants by activated sludge method.
A circulation step of circulating a part of the water to be treated in the biological reaction tank by returning a part of the water to be treated in the aerobic tank or the membrane tank provided with the solid-liquid separation means by the membrane to the oxygen-free tank.
A first control step for adjusting the circulation amount of the water to be treated in the circulation step using the MLSS (Mixed Liquor Suspended Solids) concentration of the water to be treated in the aerobic tank or the membrane tank as an index.
A computer program to run.

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