WO2012042728A1 - Water treatment system and method for controlling aeration air quantity thereof - Google Patents

Abstract

A reclaimed water production system (1) is provided with a series biological reactor (10) comprising an anaerobic tank (3), an anoxic tank (4) and an aerobic tank (5), a first ammonia meter (31) for measuring the ammonia nitrogen concentration of raw water, an aeration air quantity computing unit (41) for generating a target operation quantity, and an aeration air quantity control unit (91) for controlling the aeration air quantity of an aeration device (9) on the basis of the target operation quantity. The aeration air quantity computing unit (41) has a feed forward control system (48) including a feed-forward (FF) operation quantity function F₁(x) element (71) for generating a target operation quantity advance signal on the basis of the ammonia nitrogen concentration of the raw water and a waste time element (75) for correcting the time required for the raw water to flow into the aerobic tank (5) relative to the target operation quantity advance signal, and a feedback control system (49) for performing feedback control on the basis of the ammonia nitrogen concentration of the aerobic tank. Meanwhile, the follow-up properties of ammonia decomposing ability relative to variations in the ammonia nitrogen concentration of the aerobic tank is enhanced, thereby reducing the aeration air quantity in the aggregate.

Description

Water treatment system and aeration air volume control method thereof

The present invention relates to a water treatment system provided with a biological reaction tank including an aerobic tank provided in a sewage treatment facility or the like. In particular, in the said water treatment system, it is related with control of the aeration air volume of an aerobic tank.

Conventionally, a reclaimed water production system for producing reclaimed water by treating with a membrane separation activated sludge method (MBR: Membrane Bio-Reactor) is known as one of sewage water treatment systems such as domestic wastewater. Such a reclaimed water production system is, for example, a raw water tank that stores raw water (inflow sewage), a series of biological reaction tanks that biologically treat pollutants in raw water with activated sludge, and a mixed liquid in which raw water and activated sludge are mixed. A membrane separation tank for separating the sludge from the membrane and a filtered water tank into which the filtered treated water flows. The series of biological reaction tanks includes an anaerobic tank, an oxygen-free tank, an aerobic tank equipped with an aeration apparatus, and the like. In these biological reaction tanks, pollutants contained in raw water such as carbon-based organic substances, nitrogen-containing compounds and phosphorus-containing compounds are removed.

The aerobic tank of the above reclaimed water production system is equipped with an aeration device for aeration of the aerobic tank. By supplying fine bubbles into the mixture of the aerobic tank raw water and activated sludge in the aeration device, the dissolved oxygen in the mixture required for microbial activity is increased or the mixture is stirred. be able to. If the amount of air supplied to the mixed liquid in the aerobic tank by the aeration apparatus (hereinafter referred to as the aeration air volume) is insufficient, the quality of the treated water is deteriorated. Therefore, conventionally, an aerobic tank is provided with a dissolved oxygen concentration meter, and the amount of aeration air is controlled so that the measured value of the dissolved oxygen concentration meter becomes the set target value of the dissolved oxygen concentration. However, since it is based on an indirect indicator of dissolved oxygen concentration, a high dissolved oxygen concentration target value must be set in order to maintain the quality of the treated water within the regulation value, and the system has an excessive amount of aeration air at all times. Is being driven. Therefore, the aeration apparatus that requires energy for operation has hindered the reduction of the operation cost and the energy saving of the reclaimed water production system.

Therefore, in Patent Document 1, since the nitrification rate of nitrifying bacteria is slower than the rate of organic matter removal and phosphorus absorption, supplying oxygen necessary for nitrification is necessary for organic matter removal, phosphorus absorption and nitrogen removal. Based on the idea that a large aeration air volume can be secured, an aeration air volume control device that controls the aeration air volume of an aerobic tank based on the ammonia nitrogen concentration in the aerobic tank has been proposed. This aeration air volume control device includes an ammonia meter for measuring the ammonia nitrogen concentration in the aerobic tank, a target setting means for setting a target value of the ammonia nitrogen concentration of the effluent water in the aerobic tank, and the measured ammonia And a controller for calculating a target value of the aeration air volume so as to bring the nitrogen concentration close to the set target value.

JP 2005-199116 A

In the reclaimed water production system as described above, if the raw water tank functioning as a buffer has a large capacity, a sudden change in the ammonia nitrogen concentration of the raw water flowing into the biological reaction tank is absorbed by the raw water tank. However, if the raw water tank has a small capacity, the ammonia nitrogen concentration of the raw water flowing into the biological reaction tank may fluctuate rapidly. In addition, the growth rate of nitrifying bacteria that nitrify ammonia nitrogen in the aerobic tank is slower than that of heterotrophic bacteria in normal activated sludge. For this reason, when the ammonia nitrogen concentration of the raw water flowing into the biological reaction tank rapidly increases, it is detected that the ammonia nitrogen concentration in the aerobic tank is increased as described in Patent Document 1. Even if the aeration volume is increased, the nitrification reaction (ammonia decomposition reaction) by nitrifying bacteria cannot follow the increase in the ammonia nitrogen concentration in the aerobic tank, and the ammonia nitrogen concentration of the treated water discharged from the aerobic tank is regulated. It can happen that the value is exceeded.

In view of the above, in the water treatment system provided in the sewage treatment facility, the present invention controls the amount of aeration air in the aerobic tank based on the ammonia nitrogen concentration of the raw water, thereby preventing variations in the ammonia nitrogen concentration in the aerobic tank. The purpose is to improve the follow-up ability of ammonia decomposition capacity and to reduce the aeration air volume as a whole. Eventually, the purpose is to save energy in the operation of the water treatment system.

The water treatment system according to the present invention has an aerobic tank equipped with an aeration apparatus, and at least one anaerobic tank or an oxygen-free tank provided on the upstream side of the aerobic tank, and is based on the activated sludge method. A series of biological reaction tanks for water treatment, a first ammonia meter for measuring the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks, and an aeration air volume calculation device for generating a target manipulated variable of the aeration apparatus And an aeration air volume control device that controls the aeration air volume of the aeration device based on the generated target operation amount,
The aeration air volume calculation device is configured to generate a target operation amount advance signal based on the ammonia nitrogen concentration of the raw water, and the raw water is supplied to the aerobic tank with respect to the target operation amount advance signal. It has a feedforward control system including a dead time element for performing correction corresponding to the time required for inflow.

Similarly, an aeration air volume control method for a water treatment system according to the present invention includes an aerobic tank provided with an aeration apparatus, and at least one anaerobic tank or an anaerobic tank provided upstream of the aerobic tank. And an aeration air volume control method for a water treatment system comprising a series of biological reaction tanks for water treatment based on the activated sludge method,
Measuring the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks, generating a target manipulated variable preceding signal based on the measured ammonia nitrogen concentration of the raw water, for the target manipulated variable preceding signal, Correcting the dead time corresponding to the time required for the raw water flowing into the series of biological reaction tanks to flow into the aerobic tank, and generating a target operation amount based on the corrected target operation amount preceding signal, The aeration air volume of the aeration apparatus is controlled based on the generated target operation amount.

According to the above-mentioned water treatment system or the aeration air volume control method of the water treatment system, the fluctuation of the ammonia concentration of the mixed liquid (liquid in which raw water and activated sludge are mixed) flowing into the aerobic tank at the ammonia nitrogen concentration of the raw water is predicted. Thus, the amount of aeration in the aerobic tank can be changed. In particular, nitrifying bacteria that nitrify ammonia nitrogen in an aerobic tank take time to be activated as compared with other activated sludge microorganisms. However, depending on the water treatment system or the method for controlling the aeration air volume of the water treatment system, For example, the nitrifying bacteria can be activated by increasing the aeration air volume in advance until the discontinuous surface where the ammonia nitrogen concentration of the mixed solution rapidly changes reaches the aerobic tank. In this way, by changing the amount of aeration air according to the increase or decrease of the ammonia nitrogen concentration of the raw water, the ability of the ammonia decomposition ability in the aerobic tank to follow the fluctuation of the ammonia concentration of the mixed liquid flowing into the aerobic tank can be improved. Get higher. For this reason, it is no longer necessary to constantly activate the nitrifying bacteria in preparation for sudden fluctuations in the ammonia concentration, maintaining a low aeration amount during normal times and reducing the aeration amount only when necessary. Increased operation is possible. As a result, the amount of aeration air in the aerobic tank can be reduced as a whole, and energy saving in the operation of the water treatment system can be achieved.

The water treatment system according to the present invention further includes a second ammonia meter for measuring the ammonia nitrogen concentration in the aerobic tank, and the aeration air amount calculation device includes the ammonia nitrogen concentration and ammonia in the aerobic tank. A feedback control system including a second operation amount calculation element that generates a target operation amount feedback signal based on a deviation from the state nitrogen concentration set value, the corrected target operation amount preceding signal, and the target operation amount feedback signal And an addition element for adding.

Similarly, an aeration air volume control method for a water treatment system according to the present invention includes an aerobic tank provided with an aeration apparatus, and at least one anaerobic tank or an anaerobic tank provided upstream of the aerobic tank. And an aeration air volume control method for a water treatment system comprising a series of biological reaction tanks for water treatment based on the activated sludge method,
Measuring the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks, generating a target manipulated variable preceding signal based on the measured ammonia nitrogen concentration of the raw water, for the target manipulated variable preceding signal, The dead time corresponding to the time required for the raw water flowing into the series of biological reaction tanks to flow into the aerobic tank is corrected, the ammonia nitrogen concentration in the aerobic tank is measured, and the ammonia in the aerobic tank is measured. A target operation amount feedback signal is generated based on the deviation between the state nitrogen concentration and the ammonia nitrogen concentration set value, and the target operation amount feedback signal is added to the target operation amount feedback signal and the target operation amount feedback signal is added. And aeration air volume of the aeration apparatus is controlled based on the generated target operation amount.

According to the water treatment system or the aeration air volume control method of the water treatment system, the target operation amount of the aeration air volume by the feedforward control can be compensated by feedback control. As a result, the aeration air volume can be increased or decreased by following the change of the ammonia nitrogen concentration of the mixed liquid flowing into the aerobic tank, and the ammonia state of the mixed liquid (or treated water) flowing out from the series of biological reaction tanks. The nitrogen concentration can be controlled more reliably.

Further, in the water treatment system, the feedforward control system of the aeration air volume calculating device may set the target operation amount preceding signal to a target operation amount corresponding to an increase or decrease in the amount of the mixed liquid flowing into the aerobic tank. It is preferable to further include an aerobic tank inflow amount correction element that corrects to increase or decrease. Here, the “mixed liquid” refers to a liquid in which the raw water flowing into the biological reaction tank and the activated sludge in the biological reaction tank are mixed, that is, an activated sludge mixed liquid.

Similarly, in the aeration air volume control method of the water treatment system, the target operation amount preceding signal is further increased or decreased in response to an increase or decrease in the amount of the mixed liquid flowing into the aerobic tank. It is better to correct it.

According to the water treatment system or the aeration air volume control method of the water treatment system, the aeration air volume is increased in response to an increase in ammonia nitrogen to be treated with an increase in the amount of the mixed liquid flowing into the aerobic tank. be able to.

In the water treatment system, the feedforward control system of the aeration air amount calculation device decreases or increases the target operation amount preceding signal corresponding to an increase / decrease in the moving average of the aeration air amount of the aeration device. It is preferable to further include an aeration air volume moving average correction element that corrects as described above.

Similarly, in the aeration air volume control method of the water treatment system, the target operation amount preceding signal is further corrected so that the target operation amount decreases or increases in accordance with the increase or decrease of the moving average of the aeration air volume of the aeration device. It is good to do.

ア ン モ ニ ア Ammonia nitrogen decomposing ability due to the activity of activated sludge microorganisms in the aerobic tank depends on the history of aeration volume. Therefore, according to the water treatment system or the aeration air volume control method of the water treatment system, the target is to reduce the aeration air volume when the moving average of the aeration air volume is large and increase the aeration air volume when the moving average of the aeration air volume is small. A more efficient aeration can be performed by correcting the operation amount.

Further, in the water treatment system or the aeration air volume control method of the water treatment system, the target manipulated variable preceding signal is generated based on a function determined from a relationship between the ammonia nitrogen concentration of the raw water and the ammonia nitrogen concentration of the treated water. It is good to be done. Here, “treated water” refers to a liquid after water treatment released from a series of biological reaction tanks.

According to the above, since the target operation amount preceding signal can be generated based on the ammonia concentration of the raw water in accordance with the target value of the treated water ammonia concentration, more efficient according to the target value of the treated water ammonia concentration. Aeration can be performed.

According to the present invention, in the reclaimed water production system, energy saving can be realized by optimizing the aeration air volume of the aeration apparatus provided in the aerobic tank.

FIG. 1 is a diagram showing a schematic configuration of a reclaimed water production system according to an embodiment of the present invention. FIG. 2 is a block diagram showing a control configuration of the reclaimed water production system. FIG. 3 is a block diagram showing a signal flow of the aeration air volume calculation unit. FIG. 4 is a chart showing characteristics of the FF manipulated variable function. FIG. 5 is a chart showing characteristics of the inflow amount correction function. FIG. 6 is a chart showing characteristics of the aeration air volume moving average correction function. FIG. 7 is a chart showing a time-series change in the target manipulated variable in which the aeration air volume is controlled.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

The reclaimed water production system according to this embodiment is a water treatment system for purifying sewage using a membrane separation activated sludge method (MBR: Membrane Bio-Reactor). As shown in FIG. 1, the reclaimed water production system 1 includes a raw water tank 2, a series of biological reaction tanks 10 comprising an anaerobic tank 3, an oxygen-free tank 4 and an aerobic tank 5, a membrane separation tank 6, and a filtered water tank 7. And. The raw water tank 2 functions as a buffer tank that temporarily stores the inflowing sewage. The outflow side of the raw water tank 2 is connected to the inflow side of the anaerobic tank 3 located on the most upstream side of the series of biological reaction tanks 10 by a pipe 52. The pipe 52 is provided with a supply pump 51 that pumps the raw water stored in the raw water tank 2 to the anaerobic tank 3.

The biological reaction tank 10 is provided in the order of the anaerobic tank 3, the anoxic tank 4, and the aerobic tank 5 from the upstream side. The raw water that has flowed into the biological reaction tank 10 exists as an activated sludge mixed solution (hereinafter also simply referred to as “mixed solution”) with activated sludge. In this Embodiment, the anaerobic tank 3 and the anoxic tank 4 are formed by dividing one reaction tank into two, and the anaerobic tank 3 and the anaerobic tank 4 are connected. The outflow side of the anaerobic tank 4 is connected to the inflow side of the aerobic tank 5 through a pipe 53. Further, the outflow side of the aerobic tank 5 is connected to the inflow side of the membrane separation tank 6 through a pipe 54. The membrane separation tank 6 is provided with a separation membrane 8 for separating sludge from the mixed liquid. The separation membrane 8 is provided at the inlet of a pipe 56 that connects the membrane separation tank 6 and the filtered water tank 7. The pipe 56 is provided with a discharge pump 55 that pumps the treated water filtered by the separation membrane 8. The discharge pump 55 is intermittently driven by a target value operation in the membrane separation tank 6. Then, the amount of treated water discharged by the discharge pump 55 is detected by a level switch (not shown), and the supply pump 51 is driven in accordance with the discharged treated water amount to correspond to the treated water amount flowing out from the membrane separation tank 6. The amount of raw water to be supplied is supplied to the anaerobic tank 3 and the anoxic tank 4. By supplying an overflow amount of the mixed solution from the anaerobic tank 4 to the aerobic tank 5 and from the aerobic tank 5 to the membrane separation tank 6, the entire retained water amount of the biological reaction tank 10 is maintained.

The aerobic tank 5 is provided with an aeration device 9. The aeration device 9 blows air into the mixed solution in the aerobic tank 5 to stir the mixed solution to make the microorganisms survive, and to supply oxygen necessary for removing nitrogen, phosphorus and organic substances by the microorganisms. . The aeration apparatus 9 according to the present embodiment is configured to supply fine bubbles from the bottom of the aerobic tank 5 into the mixed liquid in the aerobic tank 5. The amount of fine bubbles supplied to the liquid mixture in the aerobic tank 5 by the aeration device 9 (hereinafter referred to as “aeration air amount”) is controlled by the control device 40.

At the bottom of the membrane separation tank 6, a circulating water outlet 6a, a return sludge outlet 6b and an excess sludge outlet 6c are opened. The circulating water outlet 6 a of the membrane separation tank 6 and the anoxic tank 4 are connected by a pipe 61 provided with a circulation pump 62. Through this pipe 61, circulating water (mixed liquid having advanced nitrification) is supplied from the membrane separation tank 6 to the anoxic tank 4. The return sludge outlet 6b of the membrane separation tank 6 and the bottom of the anaerobic tank 3 are connected by a pipe 63 having a sludge return pump 64. A part of the sludge is returned from the membrane separation tank 6 to the anaerobic tank 3 through the pipe 63. Furthermore, a pipe 59 provided with an excess sludge pump 60 is connected to the excess sludge outlet 6 c of the membrane separation tank 6. Excess sludge is discharged from the membrane separation tank 6 through the pipe 59.

In the vicinity of the outflow side of the raw water tank 2, the concentration of ammonia nitrogen in the raw water flowing into the series of biological reaction tanks 10 (here, the most upstream anaerobic tank 3) (hereinafter referred to as "raw water ammonia nitrogen concentration"). A first ammonia meter 31 for measuring x)) is provided. Further, in the vicinity of the outflow side of the aerobic tank 5, a second ammonia meter 32 that measures the ammonia nitrogen concentration of the treated water flowing out of the aerobic tank 5 (hereinafter referred to as “aerobic tank ammonia nitrogen concentration”). Is provided. Further, the filtered water tank 7 is provided with a third ammonia meter 33 for measuring the ammonia nitrogen concentration of the treated water discharged to the filtered water tank 7 (hereinafter referred to as “treated water ammonia nitrogen concentration”).

Next, the control configuration of the reclaimed water production system 1 will be described. FIG. 2 is a block diagram showing a control configuration of the reclaimed water production system. In the figure, the control of the aeration apparatus 9 is shown in detail, and the remainder is omitted. As shown in FIG. 2, the control device 40 that controls the entire reclaimed water production system 1 is communicably connected to a supply pump 51, a discharge pump 55, a circulation pump 62, a sludge return pump 64, and an excess sludge pump 60. . In addition, the ammonia meters 31, 32, and 33 are all communicably connected to the control device 40, and the measurement signals of the ammonia meters 31, 32, and 33 are transmitted to the control device 40. And the control apparatus 40 performs operation | movement of the supply pump 51, the discharge pump 55, the circulation pump 62, the sludge return pump 64, the excess sludge pump 60, and the aeration apparatus 9 based on the measurement signal of each ammonia meter 31, 32, 33. Control. Thereby, the control apparatus 40 is the amount of raw | natural water inflow, the amount of treated water discharge | release, the flow volume of circulating fluid, the flow volume of returned sludge, excess sludge so that nitrogen, phosphorus, and organic substance of treated water may not exceed each regulation value. The amount of extraction and the amount of aeration are controlled to appropriate values.

In the reclaimed water production process by the reclaimed water production system 1 configured as described above, organic substances, nitrogen, phosphorus, etc. contained in the raw water are removed. Hereinafter, the mechanism of nitrogen / phosphorus removal in this reclaimed water production process will be briefly described.

(Removal of nitrogen)
The raw water flowing into the anaerobic tank 3 from the raw water tank 2 contains ammonia nitrogen (NH ₄ -N) and organic nitrogen. In the anaerobic tank 3, the anoxic tank 4 and the aerobic tank 5, the organic nitrogen changes to ammonia nitrogen. Furthermore, in the aerobic tank 5, ammonia nitrogen is oxidized to nitrite nitrogen (NO ₂ -N) and nitrate nitrogen (NO ₃ -N) by nitrifying bacteria. Nitrite nitrogen and nitrate nitrogen (NO ₃ -N) contained in the circulating water sent from the membrane separation tank 6 to the anoxic tank 4 by the circulation pump 62 are nutrient sources of organic matter in the raw water under anoxic conditions. It is reduced to nitrogen gas (N ₂ ) and released out of the system by nitrate respiration or nitrite respiration by denitrifying bacteria.

(Phosphorus removal)
In the anaerobic tank 3, the phosphorus accumulating bacteria in the activated sludge take in organic substances in the raw water such as acetic acid into the body and release the retained phosphoric acid (PO ₄ ). In the aerobic tank 5, the phosphorus-accumulating bacteria that excessively ingest phosphorus under aerobic conditions take in more phosphoric phosphorus released in the anaerobic tank 3. The activated sludge accumulating phosphorus is discharged from the membrane separation tank 6 through the pipe 59 as excess sludge.

(Removal of organic matter)
The organic matter in the mixed liquid comes into contact with the activated sludge and is adsorbed (condensed) on the surface of the activated sludge, and is decomposed by heterotrophic organisms in the activated sludge under the aerobic condition of the aerobic tank 5 or in the activated sludge. Accumulated in. Furthermore, as described above, the organic matter in the raw water is consumed in the anaerobic tank 3 and the anoxic tank 4. In this way, most of the organic substances contained in the mixed solution are adsorbed by the activated sludge and then used by the activated sludge microorganisms to be removed from the mixed solution.

Here, the control of the aeration apparatus 9 by the control apparatus 40 will be described with reference to FIGS. The control device 40 is composed of one or a plurality of computers. Each computer is a CPU (Central Processing Unit), a main storage device that rewrites a program executed by the CPU and data used in the program, and a CPU executes the program. It is sometimes equipped with a secondary storage device that temporarily stores data, an interface for connecting the CPU and external devices, an internal path for connecting these, and the like (none of which are shown). Then, by executing a predetermined program by the CPU, each functional unit (aeration air volume calculation unit 41, moving average calculation unit 42 and aeration air volume control unit 91 described later) of the control device 40 shown in FIG. 2 is realized. .

The control device 40 includes an aeration air amount calculation unit 41 that calculates a target operation amount corresponding to the aeration air amount of the aeration device 9 and a moving average calculation unit 42 that calculates a moving average of the target operation amount of the aeration air amount. Further, the control device 40 operates an operation amount of a rotation speed (not shown) of a blower provided in the aeration device 9 or an operation amount of an adjustment actuator (not shown) provided in a supply path of air discharged from the aeration device 9. An aeration air volume control unit 91 for adjusting In the present embodiment, the aeration air volume control unit 91 is provided in the control device 40, but the aeration air volume control unit 91 may be provided in the aeration device 9. The aeration air volume control unit 91 is configured to adjust the operation amount of the rotation speed of the blower or the operation amount of the adjusting actuator based on the target operation amount commanded from the aeration air volume calculation unit 41.

FIG. 3 is a block diagram showing a signal flow of the aeration air volume calculation unit 41. As shown in FIG. 3, the aeration air amount calculation unit 41 generates a feedforward manipulated variable (hereinafter referred to as FF manipulated variable) that is a target manipulated variable preceding signal based on the raw water ammonia nitrogen concentration x. Hereinafter referred to as FF control system 48) and a feedback control system (hereinafter referred to as FB control amount) that generates a feedback operation amount (hereinafter referred to as FB operation amount) which is a target operation amount feedback signal using the aerobic tank ammonia nitrogen concentration as a control amount. System 49). The FF control system 48 and the FB control system 49 function in cooperation, and the FF operation amount generated by the FF control system 48 and the FB operation amount generated by the FB control system 49 are added by the addition element 77. The target operation amount of the aeration apparatus 9 is generated. The target operation amount is output from the aeration air amount calculation unit 41 to the aeration air amount control unit 91.

First, the contents of the FB control system 49 will be described. The FB control system 49 generates a deviation operation element 78 for calculating a deviation between the aerobic tank ammonia nitrogen concentration (control value) and the ammonia nitrogen concentration set value of the aerobic tank 5, and generates an FB manipulated variable from this deviation. FB manipulated variable calculation element 79 to be included. An output signal (FB operation amount) of the FB control system 49 is input to the addition element 77. The FB manipulated variable computation element 79 can be a computation element that calculates the FB manipulated variable using, for example, a PID control method, a P control method, or a PI control method. The aerobic tank ammonia nitrogen concentration is a measurement value of the second ammonia meter 32 provided in the aerobic tank 5. Further, the ammonia nitrogen concentration set value of the aerobic tank 5 is a value that is appropriately determined based on a target value (for example, environmental regulation value) of the ammonia nitrogen concentration of the treated water.

Next, the contents of the FF control system 48 will be described. The FF control system 48 includes an FF manipulated variable function F ₁ (x) element 71, an inflow rate correction function F ₂ (u) element 72, an aeration air volume moving average correction function F ₃ (v) element 73, and their calculation. An integration element 74 for multiplying signals, a dead time element 75, and a feed forward gain element 76 are included. An output signal (FF operation amount) of the FF control system 48 is input to the addition element 77.

The FF manipulated variable function F ₁ (x) is used to control the treated water ammonia nitrogen concentration based on the raw water ammonia nitrogen concentration x, and the raw water ammonia nitrogen concentration x and the aeration air flow manipulated variable (in particular, the FF manipulated variable). Is a function of the relationship between the static characteristics and Therefore, the FF manipulated variable function F ₁ (x) is a function of the raw water ammonia nitrogen concentration x. The raw water ammonia nitrogen concentration x is the ammonia nitrogen concentration of raw water flowing into the anaerobic tank 3, and is a measurement value of the first ammonia meter 31 provided in the raw water tank 2 in the present embodiment. Since the FF manipulated variable function F ₁ (x) is affected by the treatment capacity of the entire water treatment system, the use environment, and the like, it is preferable to set the FF manipulated variable function F ₁ (x) for each water treatment system. The FF manipulated variable F ₁ (x) may be obtained experimentally or by simulation.

FIG. 4 is a chart showing the characteristics of the FF manipulated variable function F ₁ (x). The vertical axis y represents the FF manipulated variable (L / min), and the horizontal axis x represents the raw water ammonia nitrogen concentration (mg / L). Is shown. The FF manipulated variable (L / min) represents the aeration air volume, and Y1 is the minimum air volume. The minimum air volume Y1 is the minimum air volume required to maintain the entire system. The minimum air flow required to maintain the entire system is a heterotrophic organism that agitates sludge in the aerobic tank and grows using carbon-based organic matter under the aerobic condition of the aerobic tank 5. This is the minimum amount of aeration air that provides oxygen necessary for active sludge microorganisms such as nitrifying bacteria that nitrify ammonia nitrogen to maintain the living body. The minimum airflow Y1 is appropriately determined according to the number of activated sludge microorganisms in the aerobic tank 5 and the capacity of the aerobic tank 5, correction of the standard operation amount (moving average of raw water inflow and aeration airflow), and feed forward The amount of correction is set by the gain parameter. When the aeration air volume is operated at the minimum air volume Y1, the dissolved oxygen concentration of the mixed solution in the aerobic tank 5 is close to zero.

As shown in the chart of FIG. 4, the FF manipulated variable y is constant at the minimum airflow Y1 when the raw water ammonia nitrogen concentration x ranges from 0 to the first concentration X1. This first concentration X1 is the maximum raw water ammonia nitrogen concentration at which the ammonia nitrogen concentration of the treated water is not more than the target value when the aeration air volume is the minimum air volume Y1. In addition, the target value of the ammonia nitrogen concentration of the treated water is appropriately determined based on the environmental regulation value. Then, in the range where the raw water ammonia nitrogen concentration x is not less than the first concentration X1, the FF manipulated variable y increases as the raw water ammonia nitrogen concentration x increases.

To add dynamics to the FF operation amount function F _{1 (x),} FF manipulated variable y obtained from the FF operation amount function F _{1 (x)} is adjusted by the dead time and the feedforward gain K _f. The dead time (also referred to as shift time) is, as a rule, a mixture of raw water whose ammonia nitrogen concentration has been measured by the first ammonia meter 31 flowing into a series of biological reaction tanks 10 and mixed with activated sludge. This is the time required to flow into the aerobic tank 5. However, since the growth rate of nitrifying bacteria that nitrify ammonia nitrogen in the aerobic tank 5 is slower than that of heterotrophic bacteria in ordinary activated sludge, the discontinuous surface of the ammonia nitrogen concentration in the mixed solution is the aerobic tank 5. The aeration air volume is increased before reaching the aeration, and when the discontinuous surface reaches the aerobic tank 5, the activated sludge microorganisms are activated so as to cope with the rapid increase in the ammonia nitrogen concentration. Is desirable. That is, the dead time is desirably set to a time shorter than the time required for the raw water whose ammonia nitrogen concentration is measured by the first ammonia meter 31 to flow into the aerobic tank 5. Such dead time can be obtained experimentally or computationally as a time including a residence time from flowing into the anaerobic tank 3 to flowing out from the anaerobic tank 4. As an example, in a reclaimed water production system with a maximum throughput of 55 ton / day, the time required for raw water to flow into the anaerobic tank 3 and out of the anaerobic tank 4 is about 2 hours including the residence time. The feedforward gain _Kf is a ratio between a change amount of the raw water ammonia nitrogen concentration x as an input value and a change amount of the FF manipulated variable y as an output value, and is appropriately set.

The inflow amount correction function F ₂ (u) is a function of a correction coefficient for the FF manipulated variable based on the inflow amount of the mixed liquid into the aerobic tank 5 (hereinafter referred to as “aerobic tank inflow amount u”). is there. If the aerobic tank inflow u increases, the amount of ammonia nitrogen to be treated increases, so the amount of aeration air must be increased. FIG. 5 is a chart showing the characteristics of the inflow rate correction function F ₂ (u), where the vertical axis α indicates the correction coefficient, and the horizontal axis u indicates the aerobic tank inflow rate u (L / min). . In the present embodiment, the flow rate of the discharge pump 55 is detected and set as the aerobic tank inflow amount u. However, the aerobic tank inflow u may be the flow rate of the supply pump 51 or the flow rate of the water pipe provided between the aerobic tank 5 and the membrane separation tank 6.

As shown in the chart of FIG. 5, when the aerobic tank inflow u is 0, the correction coefficient α is α1 smaller than 1 (F ₂ (0) = α1, α1 <1). When the aerobic tank inflow rate u is the reference flow rate U1, the correction coefficient α is 1 (F ₂ (U1) = 1). When the aerobic tank inflow rate u is the maximum flow rate U2, the correction coefficient α is α2 larger than 1 (F ₂ (U2) = α2, α2> 1). Thus, the correction coefficient α increases from α1 smaller than 1 to α2 larger than 1, with the aerobic tank inflow u being the reference flow rate U1, as the aerobic tank inflow u increases. As a preferred example of the correction coefficient α, α1 = 0.5 and α2 = 1.5. The reference flow rate U1 of the aerobic tank inflow rate u is determined by the treatment capacity of the reclaimed water production system 1, and the maximum flow rate U2 is determined by the capacity of the discharge pump 55 in addition to the treatment capacity of the reclaimed water production system 1.

The aeration air volume moving average correction function F ₃ (v) is a function of the FF manipulated variable correction coefficient based on the history of the aeration air volume of the aeration apparatus 9. The inventors confirmed that the ability to decompose ammonia nitrogen of activated sludge microorganisms (aerobic microorganisms active under aerobic conditions) such as nitrifying bacteria in the aerobic tank 5 depends on the history of aeration air volume Has been. For example, after the operation was continued with the aeration air volume as the minimum air volume Y1, even if the aeration air volume was increased, the decomposition rate of ammonia nitrogen corresponding to the aeration air volume could not be obtained. Therefore, the activated sludge microorganisms are activated and ammonia is maintained from the state in which the aeration air volume in the aerobic tank 5 is maintained at the minimum air volume Y1 and the dissolved oxygen concentration is almost zero and the activated sludge microorganisms are only maintained in the living body. In order to increase the ability to decompose nitrogen, it is effective to increase the amount of aeration air more than the calculated target operation amount and rapidly activate the activity of activated sludge microorganisms. On the contrary, in a state where the activated sludge microorganisms in the aerobic tank 5 are already active, it is possible to obtain the decomposition rate of ammonia nitrogen as needed with an aeration air amount smaller than the calculated target operation amount. . Therefore, based on the history of the aeration air volume of the aeration apparatus 9, the FF manipulated variable is corrected for the aeration air volume moving average so that the aeration air volume is small when the moving average of the aeration air volume is large and the aeration air volume is large when the moving average is small. Efficient aeration is performed by correcting with the function F ₃ (v).

FIG. 6 is a chart showing the characteristics of the aeration air volume moving average correction function F ₃ (v). The vertical axis β represents a correction coefficient, and the horizontal axis v represents a moving average (L / min) of the aeration air volume. Yes. Here, the moving average of the aeration air volume is a moving average of the target operation amount of the aeration air volume. The moving average calculation unit 42 of the control device 40 calculates the moving average of the target operation amount of the aeration air volume and provides it to the aeration air volume calculation unit 41. The moving average calculation unit 42 reads the target operation amount data of the aeration air amount stored in the aeration operation amount database 43 and calculates the moving average v of the target operation amount of the aeration air amount. The moving average v of the target operation amount of the aeration air volume is an average value of the n target operation amounts including the previous time. The number n of moving average treatments can be determined as appropriate according to the sensitivity (time required for activation) of the activated sludge microorganisms.

As shown in the chart of FIG. 6, when the moving average v of the aeration air volume is the minimum air volume V1 smaller than the reference flow rate V0, the correction coefficient β is β2 larger than 1 (F ₃ (V1) = β2, β2). > 1). When the moving average v is the reference flow rate V0, the correction coefficient β is 1 (F ₃ (V0) = 1). When the moving average v is the maximum flow rate V2 greater than the reference flow rate V0, the correction coefficient β is β1 smaller than 1 (F ₃ (V2) = β1, β1 <1). Thus, the correction coefficient β is 1 when the moving average v is the reference flow rate V0, and decreases from β2 larger than 1 to β1 smaller than 1 as the moving average v increases. As a preferred example of the correction coefficient β, β1 = 0.5 and β2 = 1.5 can be set. Note that the minimum air volume V1 of the moving average v is substantially equal to the above-mentioned minimum air volume Y1.

The target operation amount of the aeration device 9 generated by the aeration air amount calculation unit 41 as described above is output to the aeration air amount control unit 91, and the aeration device 9 generates bubbles of the aeration air amount according to the target operation amount in the aerobic tank 5. Into the mixture. The target manipulated variable of the aeration apparatus 9 is the sum of the FF manipulated variable and the FB manipulated variable. The FF control system 48 serves as a base for the target manipulated variable based on the raw water ammonia nitrogen concentration x which is a preceding signal. The FF manipulated variable is calculated, and the FB manipulated variable is calculated in such a manner that the FB control system 49 compensates the FF manipulated variable.

Hereinafter, the aeration air volume control by the aeration air volume calculating unit 41 will be described with a specific example with reference to FIG. In the chart shown in FIG. 7, the horizontal axis represents time, one vertical axis represents the target operation amount of the aeration air volume, and the other vertical axis represents the ammonia nitrogen concentration. The solid line shows the time series change of the target manipulated variable of the aeration air volume, the chain line shows the time series change of the raw water ammonia nitrogen concentration, and the one-dot chain line shows the time series change of the aerobic tank ammonia nitrogen concentration.

As shown in FIG. 7, the reclaimed water production system 1 is operated with the aeration air volume maintained at the minimum air volume Y1 until the raw water ammonia nitrogen concentration reaches the first concentration X1. When the raw water ammonia nitrogen concentration exceeds the first concentration X1 at time T1, the FF control system 48 of the aeration air amount calculation unit 41 sets the aeration air amount at time T2 after the elapse of the shift time (dead time) from time T1. The target manipulated variable is increased corresponding to the increase of the raw water ammonia nitrogen concentration. As a result, when the discontinuous surface (especially a discontinuous surface that rapidly increases) of the ammonia nitrogen concentration of the mixed solution reaches the aerobic tank 5, the aeration apparatus 9 does not delay the rapid change of the ammonia nitrogen concentration. The aeration air volume has already been changed so that it can follow.

If the aerobic tank ammonia nitrogen concentration exceeds the ammonia nitrogen concentration set value of the aerobic tank at time T3 without being able to cope with the increase in the aeration air volume by the feedforward control, the FB control system 49 of the aeration air volume calculating unit 41 Immediately increases the target operation amount of the aeration air volume corresponding to the increase in the aerobic tank ammonia nitrogen concentration. In this way, when the aerobic tank ammonia nitrogen concentration becomes lower than the set value of ammonia nitrogen concentration in the aerobic tank and the raw water ammonia nitrogen concentration becomes lower than the first concentration X1 at time T4, the aeration air amount calculation unit. 41 returns the target operation amount of the aeration air volume to the minimum air volume Y1, and the operation of the reclaimed water production system 1 is continued with the aeration air volume maintained at the minimum air volume Y1.

Although the raw water ammonia nitrogen concentration is maintained below the first concentration X1, the aerobic tank ammonia nitrogen concentration may exceed the ammonia nitrogen concentration set value of the aerobic tank for some reason. For example, at time T5, the raw water ammonia nitrogen concentration is less than the first concentration X1 even if the shift time is traced back from here, but the aerobic tank ammonia nitrogen concentration exceeds the ammonia nitrogen concentration set value of the aerobic tank. Yes. In such a case, the FB control system 49 of the aeration air amount calculation unit 41 immediately increases the target operation amount of the aeration air amount in response to the increase in the aerobic tank ammonia nitrogen concentration. In this way, when the aerobic tank ammonia nitrogen concentration increases without prior notice, it cannot be handled by feedforward control, but this can be compensated by feedback control. When the aerobic tank ammonia nitrogen concentration becomes smaller than the ammonia nitrogen concentration set value in the aerobic tank at time T6 due to the increase in the aeration volume, the aeration air volume calculation unit 41 returns the target operation volume of the aeration air volume to the minimum air volume Y1. The operation of the reclaimed water production system 1 is continued with the aeration air volume maintained at the minimum air volume Y1.

As described above, in the aeration air volume control according to the present embodiment, the mixed liquid is obtained by cooperatively performing the feedforward control based on the raw water ammonia nitrogen concentration and the feedback control based on the aerobic tank ammonia nitrogen concentration. The aeration air volume can be increased following a rapid change in the ammonia nitrogen concentration without delay.

Further, in the above-described aeration air volume control, when the raw water ammonia nitrogen concentration is smaller than the first concentration X1, the aeration air volume is maintained at the minimum air volume Y1, and according to the change in the raw water ammonia nitrogen concentration or the aerobic tank ammonia nitrogen concentration. The aeration air volume is increased. As described above, the minimum air volume Y1 of the aeration air volume in the aerobic tank 5 is the minimum air volume necessary for maintaining the entire system, and correction of the standard operation amount (raw water inflow amount, moving average of aeration air volume), and The correction amount is set according to the parameter of the feed forward gain. By controlling the aeration air volume in this way, it is possible to follow abrupt changes in the ammonia nitrogen concentration without delay, so in addition to increasing the aeration amount when necessary, it is possible to operate at the minimum air volume when the raw water ammonia nitrogen concentration is low. Since it can do, the surplus ventilation of the aeration apparatus 9 is reduced and the amount of aeration air can be reduced as a whole. Thereby, maintenance of the quality of treated water and reduction of energy and cost of operation of reclaimed water manufacturing system 1 (especially aeration device 9) can be aimed at.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, the structure of the reclaimed water production system 1 is not limited to the above embodiment. For example, although the aerobic tank 5 and the membrane separation tank 6 are formed in separate tanks, they can be configured integrally. For example, although both the anaerobic tank 3 and the anaerobic tank 4 are provided, at least one of the anaerobic tank 3 and the anoxic tank 4 may be provided. Further, the aeration apparatus 9 is configured to adjust the aeration air volume based on the operation amount of the rotation speed of the blower or the operation amount of the adjusting actuator. However, according to the structure of the aeration apparatus 9, the operation speed of the blower is controlled. The amount of aeration can be controlled by both the amount and the operation amount of the adjusting actuator. The third ammonia meter 33 may be a concentration meter that continuously measures the ammonia concentration. However, the ammonia concentration may be measured by an arbitrary method by sampling periodically or irregularly. You can also.

In addition, the FF control system 48 of the aeration air amount calculation unit 41 multiplies the FF manipulated variable function F ₁ (x), the inflow amount correction function F ₂ (u), and the aeration air amount moving average correction function F ₃ (v). to those combined by multiplying the dead time and the feedforward gain K _f, but calculates the FF operation amount, a method of calculating the FF operation amount it is not limited thereto. For example, the FF manipulated variable can be calculated using at least one of the inflow rate correction function F ₂ (u) and the aeration air volume moving average correction function F ₃ (v) as a constant (= 1).

The present invention is useful for controlling the amount of aeration air in an aerobic tank in a water treatment system including an aerobic tank in which aeration is performed.

1 Reclaimed water production system (water treatment system)
2 Raw water tank 3 Anaerobic tank 4 Anaerobic tank 5 Aerobic tank 6 Membrane separation tank 7 Filtration water tank 8 Separation membrane 9 Aeration device 10 Biological reaction tank 31 First ammonia meter 32 Second ammonia meter 40 Control device 41 Aeration air volume calculation Unit 42 moving average calculation unit 43 aeration operation amount database 48 feedforward control system 49 feedback control system 91 aeration air amount control unit 51 supply pump 55 discharge pump 71 FF operation amount function F ₁ (x) element (first operation amount calculation element )
72 Inflow amount correction function F ₂ (u) element 73 Aeration air volume moving average correction function F ₃ (v) element 75 Dead time element 79 FB manipulated variable calculation element (second manipulated variable calculation element)

Claims (10)

A series of biological reaction tanks having an aerobic tank provided with an aeration apparatus, and at least one anaerobic tank or an oxygen-free tank provided upstream of the aerobic tank, and performing water treatment based on an activated sludge method When,
A first ammonia meter for measuring the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks;
An aeration air volume calculating device for generating a target operation amount of the aeration apparatus;
An aeration air volume control device that controls the aeration air volume of the aeration device based on the generated target operation amount;
The aeration air volume calculation device is:
A first manipulated variable calculation element for generating a target manipulated variable preceding signal based on the ammonia nitrogen concentration of the raw water;
A feedforward control system including a dead time element for performing correction corresponding to the time required for the raw water to flow into the aerobic tank with respect to the target operation amount preceding signal,
Water treatment system. The water treatment system further includes a second ammonia meter for measuring the ammonia nitrogen concentration in the aerobic tank,
The aeration air volume calculation device includes a second operation amount calculation element that generates a target operation amount feedback signal based on a deviation between the ammonia nitrogen concentration of the aerobic tank and the ammonia nitrogen concentration set value. The water treatment system according to claim 1, further comprising: an addition element that adds the corrected target operation amount preceding signal and the target operation amount feedback signal. The feedforward control system of the aeration air volume calculation device is:
An aerobic tank inflow amount correction element that further corrects the target operation amount preceding signal so that the target operation amount increases or decreases in response to an increase or decrease in the inflow amount of the mixed liquid into the aerobic tank. The water treatment system of Claim 1 or Claim 2. The feedforward control system of the aeration air volume calculation device is:
The aeration air volume moving average correction element further corrects the target operation amount preceding signal so that the target operation amount decreases or increases in response to an increase or decrease in the moving average of the aeration air volume of the aeration apparatus. The water treatment system according to any one of 3. The first manipulated variable calculation element is a calculation element that generates the target manipulated variable preceding signal based on a function determined from a relationship between the ammonia nitrogen concentration of raw water and the ammonia nitrogen concentration of treated water. The water treatment system according to any one of 1 to 4. A series of biological reaction tanks having an aerobic tank provided with an aeration apparatus, and having at least one anaerobic tank or an oxygen-free tank provided upstream of the aerobic tank, and performing water treatment based on the activated sludge method A method for controlling the aeration air volume of a water treatment system comprising:
Measure the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks,
Generate a target manipulated variable preceding signal based on the measured ammonia nitrogen concentration of the raw water,
Correcting the dead time corresponding to the time required for the raw water flowing into the series of biological reaction tanks to flow into the aerobic tank with respect to the target operation amount preceding signal,
Generating a target operation amount based on the corrected target operation amount preceding signal;
A method of controlling the amount of aeration air of the aeration device based on the generated target operation amount. A series of biological reaction tanks having an aerobic tank provided with an aeration apparatus, and having at least one anaerobic tank or an oxygen-free tank provided upstream of the aerobic tank, and performing water treatment based on the activated sludge method A method for controlling the aeration air volume of a water treatment system comprising:
Measure the ammonia nitrogen concentration of raw water flowing into the series of biological reaction tanks,
Generate a target manipulated variable preceding signal based on the measured ammonia nitrogen concentration of the raw water,
Correcting the dead time corresponding to the time required for the raw water flowing into the series of biological reaction tanks to flow into the aerobic tank with respect to the target operation amount preceding signal,
Measure the ammonia nitrogen concentration in the aerobic tank,
Based on the deviation between the ammonia nitrogen concentration of the aerobic tank and the ammonia nitrogen concentration set value, a target manipulated variable feedback signal is generated,
A target operation amount is generated by adding the corrected target operation amount preceding signal and the target operation amount feedback signal,
A method of controlling the amount of aeration air of the aeration device based on the generated target operation amount. The target operation amount preceding signal is further corrected so that the target operation amount increases or decreases in response to an increase or decrease in the amount of the mixed liquid flowing into the aerobic tank. Aeration flow control method for water treatment system. The target operation amount preceding signal is further corrected so that the target operation amount decreases or increases in response to an increase or decrease in the moving average of the aeration air amount of the aeration apparatus. Aeration air volume control method for water treatment system in Japan. The water treatment according to any one of claims 6 to 9, wherein the target manipulated variable preceding signal is generated based on a function determined from a relationship between the ammonia nitrogen concentration of the raw water and the ammonia nitrogen concentration of the treated water. A method for controlling aeration air volume of the system.

Images