JP7763433B2 - Processing system and control method thereof - Google Patents

Description

The present invention relates to a treatment system and its control method, which includes a flocculant addition unit that adds a flocculant to the material to be treated to form a floc, and a solid-liquid separation unit that separates the floc into a solid and liquid to form a concentrate.

A known treatment system for reducing the volume of materials to be treated, such as sewage sludge and biomass, involves adding a flocculant, such as a polymer flocculant, to the material to aggregate the solids contained in the material and form flocculated flocs (also called "coarse flocs"). The flocculated flocs are then subjected to solid-liquid separation to produce a concentrate with a reduced moisture content. In such treatment systems, if the flocculant addition rate relative to the material (also referred to herein as the "flocculant addition rate") is low, the flocculant may be insufficient, resulting in insufficient floc formation and insufficient solid-liquid separation of the flocculant in the solid-liquid separation section, which may prevent the moisture content of the concentrate from being reduced to the target value. Conversely, if the flocculant addition rate is high, excessive flocculant may be added to the flocculant, resulting in some flocculant not being used to aggregate the material and being discharged unreacted as a separated liquid in the solid-liquid separation section, resulting in a deterioration in life cycle cost (LCC) and potentially causing overloading of the solid-liquid separation section. Furthermore, if the separated liquid containing unreacted coagulant is returned to a biological treatment facility using aerobic treatment such as activated sludge, it may have a negative impact on the biological treatment facility. Therefore, in treatment systems, it is desirable to control the coagulant addition rate relative to the material being treated within an appropriate range.

In response, technology has been proposed that detects the solids concentration of the concentrate discharged from the solid-liquid separation section and controls the flocculant addition rate based on the detection results (see, for example, Patent Document 1). In the treatment system described in Patent Document 1, the amount of flocculant input and solids concentration, the flow rate and turbidity of the separated water discharged by solid-liquid separation, and the amount of concentrate discharged are measured, and the solids concentration of the concentrate is calculated from these measurement results.

JP 2013-000692 A

In a configuration such as that described in Patent Document 1, in which the solids concentration of the concentrate is detected and the detection results are used to control the flocculant addition rate, a certain amount of time is required to detect the solids concentration of the concentrate, resulting in a delay in controlling the flocculant addition rate. Therefore, the flocculant addition rate cannot follow relatively rapid fluctuations in the solids concentration of the concentrate, and the actual flocculant addition rate may deviate from the appropriate range. Furthermore, the accuracy of detecting the solids concentration of the concentrate is not very high, as it is heavily dependent on the measurement accuracy of each parameter used for the detection. Therefore, controlling the flocculant addition rate based on detection results with low accuracy may result in the actual flocculant addition rate deviating from the appropriate range.
In view of this situation, the main object of the present invention is to provide a technology in a treatment system in which a flocculant is added to a material to be treated and then solid-liquid separation is performed, which maintains the flocculant addition rate within an appropriate range to prevent deterioration of LCC due to excessive addition of flocculant and overload in the solid-liquid separation section, while improving the flocculation floc properties of the floc by adding an appropriate amount of flocculant without shortage, thereby enabling good and stable solid-liquid separation of the flocculant in the solid-liquid separation section.

A first characteristic configuration of the treatment system according to the present invention is a treatment system including a flocculant adding unit that adds a flocculant to a material to be treated to form a floc, and a solid-liquid separating unit that separates the floc into a solid and liquid to form a concentrate,
a storage section that is installed on an inlet side or an outlet side of the solid-liquid separation section and that temporarily stores the flocculate or the concentrate;
a reservoir liquid level measuring unit that measures a reservoir liquid level, which is the liquid level of the aggregate or the concentrate in the reservoir;
and a control unit that controls the rate at which the flocculant is added to the material to be treated by the flocculant adding unit based on the liquid level in the storage unit.
A characteristic configuration of the control method for a treatment system according to the present invention is a control method for a treatment system including a flocculant adding unit that adds a flocculant to a treatment object to form a floc, and a solid-liquid separating unit that separates the floc into a solid and liquid to form a concentrate,
measuring a liquid level in a reservoir, which is the liquid level of the flocculant or the concentrate in a reservoir that is installed on the inlet side or the outlet side of the solid-liquid separation section and that temporarily stores the flocculant or the concentrate;
The feature is that a flocculant addition rate control is executed to control the rate at which the flocculant is added to the object to be treated by the flocculant adding unit based on the liquid level in the storage unit.

According to this configuration, when the flocculant addition rate for the material to be treated changes, the properties of the flocculant flocs formed in the flocculant-added material, such as viscosity, fineness, and strength (hereinafter referred to as "floc properties"), change, which in turn changes the ease with which the solid-liquid separation section can absorb the flocs and separate the water. As a result, the liquid level in the reservoir at the inlet or outlet of the solid-liquid separation section changes. Therefore, it is possible to determine whether the flocculant addition rate is excessive or insufficient based on the liquid level in the reservoir measured by the reservoir liquid level measuring section and its rate of change. The control section then executes the flocculant addition rate control, controlling the flocculant addition rate based on the liquid level in the reservoir, thereby maintaining the liquid level in the reservoir within as appropriate a range as possible.
Therefore, the present invention can provide a technology that, in a treatment system in which a flocculant is added to a material to be treated and then solid-liquid separation is performed, can maintain the flocculant addition rate within an appropriate range to prevent deterioration of LCC due to excessive addition of flocculant and overload in the solid-liquid separation section, while improving the flocculation floc properties of the floc by adding an appropriate amount of flocculant without shortage, thereby enabling good and stable solid-liquid separation of the flocculant in the solid-liquid separation section.

A second characteristic feature of the treatment system of the present invention is that, in the flocculant addition rate control, the control unit executes a temporary addition rate increase process that temporarily increases the flocculant addition rate from the time the liquid level in the reservoir exceeds a predetermined temporary increase judgment value until the liquid level in the reservoir reaches a predetermined return judgment value that is lower than the temporary increase judgment value.

With this configuration, when the liquid level in the storage section exceeds the temporary increase judgment value, it is determined that there is a shortage of flocculant in the floc, and the execution of the temporary addition rate increase process is initiated, increasing the flocculant addition rate. This suppresses deterioration of floc properties, such as a decrease in floc strength and fragmentation, due to a shortage of flocculant in the floc, and prevents excessive increases in the liquid level in the storage section due to the deterioration of floc properties. Then, after the execution of the temporary addition rate increase process is initiated, the liquid level in the storage section decreases as the flocculant addition rate increases, and when the liquid level in the storage section decreases to the return judgment value, the execution of the temporary addition rate increase process is terminated, and the flocculant addition rate is returned to the level before the increase. This suppresses as much as possible deterioration in LCC due to an increase in the flocculant addition rate.

A third characteristic feature of the treatment system of the present invention is that, in the flocculant addition rate control, the control unit increases the flocculant addition rate by a predetermined increase correction amount when the liquid level in the reservoir exceeds a predetermined increase correction judgment value that is equal to or greater than the temporary increase judgment value, and executes an addition rate correction process that decreases the flocculant addition rate by a predetermined decrease correction amount when the liquid level in the reservoir falls below a predetermined decrease correction judgment value that is less than the return judgment value.

According to this configuration, when the liquid level in the reservoir exceeds the increase correction judgment value, it is determined that there is a shortage of flocculant in the flocculant, and the flocculant addition rate is increased by the increase correction width. Furthermore, when the liquid level in the reservoir falls below the decrease correction judgment value, it is determined that there is an excess of flocculant in the flocculant, and the flocculant addition rate is decreased by the decrease correction width. This allows the flocculant addition rate to be appropriately corrected in a timely manner so that the liquid level in the reservoir is maintained within a range that is equal to or less than the increase correction judgment value and equal to or greater than the decrease correction judgment value.
Furthermore, the increase correction judgment value, which serves as the criterion for determining whether to increase the flocculant addition rate by the addition rate correction process, is set to be equal to or greater than the temporary increase judgment value, which serves as the criterion for determining whether to start the execution of the above-mentioned temporary addition rate increase process.As a result, in cases where the temporary increase in the flocculant addition rate by starting the execution of the addition rate temporary increase process is not enough to resolve the flocculant shortage and does not contribute to preventing the liquid level in the reservoir from rising, the flocculant addition rate can be increased and corrected by the addition rate correction process by the increase correction width, thereby reliably preventing an excessive rise in the liquid level in the reservoir.
Furthermore, the decrease correction judgment value, which is the criterion for judging whether the flocculant addition rate is decreased by the addition rate correction process, is set to be less than the return judgment value, which is the criterion for judging whether the execution of the temporary addition rate increase process described above is terminated. As a result, in cases where the temporary decrease in the flocculant addition rate due to the termination of the execution of the temporary addition rate increase process is not enough to resolve the excessive addition of flocculant and to prevent a drop in the liquid level in the reservoir, the flocculant addition rate can be reduced and corrected by the decrease correction width by the addition rate correction process, thereby reliably preventing an excessive drop in the liquid level in the reservoir.

A fourth characteristic configuration of the treatment system according to the present invention is a treatment system including, as the storage unit, an inlet-side storage unit that is installed on an inlet side of the solid-liquid separation unit and that temporarily stores the aggregates immediately before being introduced into the solid-liquid separation unit,
the reservoir internal liquid level measuring unit includes an inlet-side reservoir internal liquid level measuring unit that measures an inlet-side reservoir internal liquid level, which is a reservoir internal liquid level of the aggregate in the inlet-side reservoir,
The control unit executes, as the flocculant addition rate control, a first flocculant addition rate control that controls the flocculant addition rate based on the liquid level in the inlet-side reservoir.

According to this configuration, if the flocculant addition rate is too low, the flocculation properties of the flocs deteriorate, making it harder for the flocs to be absorbed from the inlet reservoir of the solid-liquid separation unit, resulting in an increase in the liquid level in the inlet reservoir. Therefore, the control unit executes the first flocculant addition rate control and controls the flocculant addition rate based on the liquid level in the inlet reservoir, thereby maintaining the liquid level in the inlet reservoir within as appropriate a range as possible. This prevents deterioration of LCC due to excessive addition of flocculant and overloading of the solid-liquid separation unit, while improving the flocculation properties of the flocs by adding an appropriate amount of flocculant, improving the absorption of the flocs from the inlet reservoir of the solid-liquid separation unit, and enabling good and stable solid-liquid separation of the flocs in the solid-liquid separation unit.

A fifth characteristic configuration of the treatment system according to the present invention is that the storage unit includes an outlet-side storage unit that is installed on the outlet side of the solid-liquid separation unit and that temporarily stores the concentrate immediately before being discharged from the solid-liquid separation unit and introduced into a subsequent treatment unit,
the reservoir internal liquid level measuring unit includes an outlet side reservoir internal liquid level measuring unit that measures an outlet side reservoir internal liquid level, which is a reservoir internal liquid level of the concentrate in the outlet side reservoir,
The control unit executes, as the flocculant addition rate control, a second flocculant addition rate control that controls the flocculant addition rate based on the liquid level in the outlet-side reservoir.

According to this configuration, if the flocculant addition rate is too low, the flocculation properties of the floc will deteriorate, making it harder for water to separate in the solid-liquid separation section, lowering the solids concentration of the concentrate, and causing an increase in the liquid level in the outlet-side reservoir. Therefore, the control unit executes the second flocculant addition rate control and controls the flocculant addition rate based on the liquid level in the outlet-side reservoir, thereby maintaining the liquid level in the outlet-side reservoir within as appropriate a range as possible. This prevents deterioration of LCC and overload in the solid-liquid separation section due to excessive addition of flocculant, while improving the flocculation properties of the floc by adding an appropriate amount of flocculant, improving the ease of water separation in the solid-liquid separation section, preventing a decrease in the solids concentration of the concentrate, and enabling good and stable solid-liquid separation of the flocculant in the solid-liquid separation section.

1 is a schematic configuration diagram of a processing system according to the present embodiment; FIG. 1 is a flowchart showing the flow of a control method for a processing system according to an embodiment of the present invention. Flow diagram showing the flow of first flocculant addition rate control Flow diagram showing the flow of second flocculant addition rate control Flow diagram showing another form of second flocculant addition rate control

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A processing system and a control method thereof according to an embodiment of the present invention will be described with reference to the accompanying drawings.
1, the treatment system 100 according to this embodiment is provided with a flocculant supply pump 2 (an example of a flocculant adding section) that adds a flocculant F to organic waste S1 (an example of a material to be treated) containing sludge supplied from a previous treatment section 1, such as a sludge storage tank, a sludge supply pump, or a concentrator, to form flocculated sludge S2 (an example of a flocculant), and a solid-liquid separation section 10 that performs solid-liquid separation on the flocculated sludge S2 to which the flocculant F has been added to form concentrated sludge S3 (an example of a concentrate). In this embodiment, the flocculant F is added to the organic waste S1 being stirred in the sludge coagulation tank 5, but it may also be added to the organic waste S1 before it is supplied to the sludge coagulation tank 5.
The organic waste S1 to which the flocculant F has been added is stirred in the sludge coagulation tank 5 to promote the generation of flocculated flocs, and the flocculated sludge S2 containing the generated flocs is supplied from the sludge coagulation tank 5 to the solid-liquid separation section 10 in the subsequent stage.
As the flocculant F, any known flocculant used for flocculating sludge, such as cationic, amphoteric, and polymer flocculants such as polyamidine, can be used.
Furthermore, in the treatment system 100 of this embodiment, the organic waste S1 including sludge is treated as the material to be treated, but biomass or the like may also be used as the material to be treated.

The solid-liquid separation section 10 is configured to separate the coagulated sludge S2 supplied from the sludge coagulation tank 5 into solid and liquid, and to discharge the concentrated sludge S3 obtained by separating the water content through the solid-liquid separation. It may be called a concentrator or a dehydrator depending on the degree of concentration. While there is no clear distinction between a concentrator and a dehydrator, a device that has a higher solid concentration in the treated product than a concentrator is generally called a dehydrator. For example, a solid-liquid separation section 10 that increases the solid concentration of the solid content to about 1% to 15% is called a concentrator, and a device that increases the solid concentration of the solid content more than a concentrator is called a dehydrator.
Furthermore, the concentrated sludge S3 corresponds to the concentrated sludge S3 as long as it has been subjected to solid-liquid separation in the solid-liquid separation section 10, regardless of the solid concentration.
The treatment system 100 may include a system having only a thickener, a system having only a dehydrator, or a system having a thickener and a dehydrator arranged in series as the solid-liquid separation section 10. The characteristic configuration of the present invention can be applied to both or either of the thickener and the dehydrator. Furthermore, when a thickener and a dehydrator are provided as the solid-liquid separation section 10, a sludge transport pump may be provided to transport sludge discharged from the thickener in the preceding stage to the dehydrator in the following stage.

The solid-liquid separation section 10 is configured as a screw press type in which a screw 12 housed in an outer cylindrical screen 11 is rotated by a drive motor 13, and the flocculated sludge S2 introduced from an inlet side hopper 20 is pressurized in a pressure chamber 15 formed between the outer cylindrical screen 11 and the screw 12 to separate the solid and liquid, and the concentrated sludge S3 after the solid-liquid separation is discharged into an outlet side hopper 23.
In the present invention, the solid-liquid separation section 10 may be of a type different from the above-mentioned screw press type.

In the solid-liquid separation section 10, an inlet hopper 20 (an example of an inlet storage section) is provided at the inlet side where the flocculated sludge S2 is supplied, for temporarily storing the flocculated sludge S2. An outlet hopper 23 (an example of an outlet storage section) is provided at the outlet side where the thickened sludge S3 is discharged, for temporarily storing the thickened sludge S3. Specifically, the flocculated sludge S2 supplied from the sludge flocculation tank 5 is temporarily stored in the inlet hopper 20, and the flocculated sludge S2 stored in the inlet hopper 20 is then sucked into the pressurized chamber 15 by the rotation of the screw 12. Furthermore, the thickened sludge S3 discharged from the pressurized chamber 15 is temporarily stored in the outlet hopper 23, and the thickened sludge S3 stored in the outlet hopper 23 is then fed into a downstream processing section 30, such as a conveying pump or a dewatering device. The outlet hopper 23 is usually equipped in the solid-liquid separation section 10 itself, such as a thickener, but it may also be the inlet hopper of the treatment section 30 installed downstream. The inlet hopper 20 and outlet hopper 23 may have any structure as long as they are capable of storing flocculated sludge S2 and concentrated sludge S3, and may also be a storage tank separate from the solid-liquid separation section 10.

Furthermore, the inlet hopper 20 is provided with a level sensor 21 that functions as an inlet hopper liquid level measuring unit (an example of an inlet reservoir liquid level measuring unit) that measures the inlet hopper liquid level li (an example of an inlet reservoir liquid level), which is the liquid level in the hopper of the flocculated sludge S2 in the inlet hopper 20. On the other hand, the outlet hopper 23 is provided with a level sensor 24 that functions as an outlet hopper liquid level measuring unit (an example of an outlet reservoir liquid level measuring unit) that measures the outlet hopper liquid level lo (an example of an outlet reservoir liquid level), which is the liquid level in the hopper of the concentrated sludge S3 in the outlet hopper 23.

The treatment system 100 is provided with a control device 50 that controls the operation of the flocculant supply pump 2, the drive motor 13 of the solid-liquid separation section 10, etc. The control device 50 executes a predetermined computer program to function as a control unit that controls the flocculant addition rate x, which is the rate at which flocculant F is added to the organic waste S1 by the flocculant supply pump 2, based on the liquid levels li and lo in the hopper measured by the level sensors 21 and 24.
The flocculant addition rate is the value obtained by dividing the amount of solids in the flocculant by the amount of solids in the sludge, and can generally be calculated using the following formula.
Flocculant addition rate = (chemical solution concentration × chemical supply amount) / (sludge solids concentration × sludge supply amount)

That is, as shown in FIG. 2, the control device 50 executes a first flocculant addition rate control (step #1) and a second flocculant addition rate control (step #2), which will be described in detail later. The control device 50 determines the flocculant addition rate base value x0, which is the base value of the flocculant addition rate x, and the increase width variables Δx1i, Δx2i, Δx1o, and Δx2o, which are the increase widths of the flocculant addition rate x. Then, in step #3, the flocculant addition rate x is determined by adding these increase width variables Δx1i, Δx2i, Δx1o, and Δx2o to the flocculant addition rate base value x0. The flocculant addition rate x thus determined is then multiplied by the supply rate vs of organic waste S1 from the upstream processing unit 1 to determine the flocculant addition amount vh. The output of the flocculant supply pump 2 is set so that the flocculant F equivalent to the determined flocculant addition amount vh is added to the organic waste S1.
In this embodiment, the initial value of the flocculant addition rate basic value x0, which is the basic value of the flocculant addition rate x, is set to a value between 0.1% and 2.5%, preferably about 1.8%, and the initial values of the increase width variables Δx1i, Δx2i, Δx1o, and Δx2o, which are the increase widths, are set to 0 points.
The first flocculant addition rate control (step #1 in FIG. 2) and the second flocculant addition rate control (step #2 in FIG. 2) will be described in detail below.

[First flocculant addition rate control]
As the above-mentioned flocculant addition rate control (step #1 in Figure 2), the control device 50 executes a first flocculant addition rate control, which controls the flocculant addition rate x based on the liquid level li in the inlet side hopper measured by the level sensor 21 (see Figure 1), as shown in Figure 3.
1 , if the flocculant addition rate x is too low, the flocculation flocculation properties of the flocculated sludge S2 deteriorate, making it difficult for the solid-liquid separation section 10 to absorb the flocculated sludge S2 from the inlet hopper 20, resulting in an increase in the liquid level li in the inlet hopper. Therefore, by controlling the flocculant addition rate x based on the liquid level li in the inlet hopper through the first flocculant addition rate control, the liquid level li in the inlet hopper is maintained within as appropriate a range as possible. Therefore, while deterioration of the LCC due to excessive addition of flocculant F and overloading of the solid-liquid separation section 10 are suppressed, the addition of an appropriate amount of flocculant F improves the flocculation flocculation properties of the flocculated sludge S2, improving the absorption of the flocculated sludge S2 from the inlet hopper 20 of the solid-liquid separation section 10, resulting in good and stable solid-liquid separation of the flocculated sludge S2 in the solid-liquid separation section 10.

The first flocculant addition rate control shown in Figure 3 controls the flocculant addition rate x by comparing the liquid level li in the inlet hopper with various judgment values Li1, Li2, Li3, Li4, and Li5. This first flocculant addition rate control includes a first addition rate temporary increase process for determining the first addition rate increase range variable Δx1i, a second addition rate temporary increase process for determining the second addition rate increase range variable Δx2i, and an addition rate correction process for determining the flocculant addition rate basic value x0. Details of each process are explained below. In each process, five judgment values Li1, Li2, Li3, Li4, and Li5 are set, in descending order, as judgment values for the liquid level li in the inlet hopper. Furthermore, the constants Ai, Bi, Ci, and Di related to the increase/decrease ranges set for the variables x0, Δx1i, and Δx2i that make up the flocculant addition rate x are all positive numbers greater than zero. Also, in the following explanation, the names of the judgment values Li1, Li2, Li3, Li4, and Li5 will be in accordance with the processing, but judgment values with the same symbol are set to the same value.

(First addition rate temporary increase process)
The first addition rate temporary increase process in the first flocculant addition rate control is a process for temporarily increasing the flocculant addition rate x from when the liquid level li in the inlet hopper exceeds a predetermined temporary increase judgment value Li1 until the liquid level li in the inlet hopper reaches a predetermined return judgment value Li3 that is lower than the temporary increase judgment value Li1. This first addition rate temporary increase process is made up of steps #1-03, #1-04, #1-06, and #1-07 shown in Figure 3, and step #3 shown in Figure 2.

That is, in this first addition rate temporary increase process, as shown primarily in Figure 3, when it is determined that the liquid level li in the inlet hopper exceeds the temporary increase judgment value Li1 (yes in step #1-03), it is determined that there is a shortage of flocculant F in the flocculated sludge S2, and the first addition rate increase amount variable Δx1i is changed from 0 to the first temporary increase amount Ai (e.g., 0.05 to 0.50 points) (step #1-04). Then, in step #3 (see Figure 2), the flocculant addition rate x is temporarily increased by the first temporary increase amount Ai. This suppresses deterioration of floc properties, such as a decrease in floc strength and fragmentation, due to a shortage of flocculant F in the flocculated sludge S2, and prevents an excessive rise in the liquid level li in the inlet hopper due to the deterioration of floc properties. Furthermore, the increase in the flocculant addition rate x through the first addition rate temporary increase process (step #1-04, step #3 (see Figure 2)) is highly urgent in order to prevent the flocculated sludge S2 from overflowing from the inlet hopper 20, and is therefore executed immediately when it is determined that the liquid level li in the inlet hopper has exceeded the temporary increase determination value Li1 (yes in step #1-03).

Furthermore, as the liquid level li in the inlet hopper decreases with the increase in the flocculant addition rate x by the first temporary increase Ai, when it is determined that the liquid level li in the inlet hopper has reached the return judgment value Li3 (yes in step #1-06), the first addition rate increase variable Δx1i is returned to 0 (step #1-07). Then, in step #3 (see Figure 2), the temporary increase in the flocculant addition rate x by the first temporary increase Ai is terminated, and the flocculant addition rate x is returned to its pre-increase state. This minimizes the deterioration of LCC caused by the increase in the flocculant addition rate x by the first temporary increase Ai. The reduction in the flocculant addition rate x (step #1-07, step #3 (see Figure 2)) due to the end of the first addition rate temporary increase process is immediately executed when it is determined that the liquid level li in the inlet hopper has reached the return judgment value Li3 (yes in step #1-06). The reduction of the flocculant addition rate x (step #1-07, step #3 (see Figure 2)) due to the completion of the first addition rate temporary increase process is less urgent than an increase, and can therefore be performed when it is determined that the liquid level li in the inlet hopper has remained below the recovery judgment value Li3 for a set time (e.g., 5 to 30 minutes). The set time is set taking into account the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10. For example, it can be set to the sum of the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10.

(Second addition rate temporary increase process)
The second addition rate temporary increase process in the first flocculant addition rate control is a process of temporarily increasing the flocculant addition rate x from when the liquid level li in the inlet hopper exceeds a predetermined temporary increase judgment value Li2 until the liquid level li in the inlet hopper reaches a predetermined return judgment value Li4 that is lower than the temporary increase judgment value Li2, similar to the first addition rate temporary increase process described above. This second addition rate temporary increase process is composed of steps #1-01, #1-02, #1-08, and #1-09 shown in FIG. 3, and step #3 shown in FIG. 2.

That is, in this second addition rate temporary increase process, as shown primarily in Figure 3, when it is determined that the liquid level li in the inlet hopper exceeds the temporary increase judgment value Li2 (yes in step #1-01), it is determined that there is a shortage of flocculant F in the flocculated sludge S2, and the second addition rate increase amount variable Δx2i is changed from 0 to the second temporary increase amount Bi (e.g., 0.10 points) (step #1-02). Then, in step #3 (see Figure 2), the flocculant addition rate x is temporarily increased by the second temporary increase amount Bi. This suppresses deterioration of floc properties, such as a decrease in floc strength and fragmentation, due to a shortage of flocculant F in the flocculated sludge S2, and prevents an excessive rise in the liquid level li in the inlet hopper due to the deterioration of floc properties. Furthermore, the increase in the flocculant addition rate x through the second addition rate temporary increase process (steps #1-02 and #3 (see Figure 2)) is highly urgent in order to prevent the flocculated sludge S2 from overflowing from the inlet hopper 20, and is therefore executed immediately when it is determined that the liquid level li in the inlet hopper has exceeded the temporary increase determination value Li2 (yes in step #1-03).

Furthermore, as the liquid level li in the inlet hopper decreases with the increase in the flocculant addition rate x by the second temporary increase Bi, when it is determined that the liquid level li in the inlet hopper has reached the return judgment value Li4 (yes in step #1-08), the second addition rate increase variable Δx2i is returned to 0 (step #1-09). Then, in step #3 (see Figure 2), the temporary increase in the flocculant addition rate x by the second temporary increase Bi is terminated, and the flocculant addition rate x is returned to its pre-increase state. This minimizes the deterioration of LCC caused by the increase in the flocculant addition rate x by the second temporary increase Bi. The reduction in the flocculant addition rate x (step #1-09, step #3 (see Figure 2)) due to the end of the second addition rate temporary increase process is immediately executed when it is determined that the liquid level li in the inlet hopper has reached the return judgment value Li4 (yes in step #1-08). The reduction of the flocculant addition rate x (step #1-09, step #3 (see Figure 2)) due to the completion of the second addition rate temporary increase process is less urgent than an increase, and can therefore be performed when it is determined that the liquid level li in the inlet hopper has remained below the recovery judgment value Li4 for a set time (e.g., 5 to 30 minutes). The set time is set taking into account the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10. For example, it can be set to the sum of the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10.

In this embodiment, in order to perform a temporary increase of the flocculant addition rate x in stages, two types of addition rate temporary increase processes, the first addition rate temporary increase process and the second addition rate temporary increase process, are performed using different temporary increase judgment values Li1, Li2 and return judgment values Li3, Li4. The temporary increase judgment value Li1, which is the judgment criterion for the liquid level li in the inlet hopper when the temporary increase of the flocculant addition rate x is started in the first addition rate temporary increase process, is set higher than the temporary increase judgment value Li2, which is the judgment criterion for the liquid level li in the inlet hopper when the temporary increase of the flocculant addition rate x is started in the second addition rate temporary increase process. That is, when the liquid level li in the inlet hopper rises and exceeds the temporary increase judgment value Li2, the second addition rate temporary increase process starts a temporary increase of the flocculant addition rate x by the second temporary increase width Bi. Furthermore, when the liquid level li in the inlet-side hopper continues to rise and exceeds the temporary increase judgment value Li1 even after the flocculant addition rate x is increased by the second temporary increase width Bi, a temporary increase of the flocculant addition rate x by the first temporary increase width Ai through the first addition rate temporary increase process is also started. For this reason, in order to reliably lower the liquid level li in the inlet-side hopper when the liquid level li in the inlet-side hopper exceeds the temporary increase judgment value Li1, it is preferable to set the first temporary increase width Ai (e.g., 0.05 to 0.50 points) in the first addition rate temporary increase process larger than the second temporary increase width Bi (e.g., 0.10 points) in the second addition rate temporary increase process, and it is preferable to set it to, for example, about twice the second temporary increase width Bi.
It should be noted that the configuration may be such that only one of the first addition rate temporary increase processing and the second addition rate temporary increase processing is executed.

(Addition rate correction process)
The addition rate correction process in the first flocculant addition rate control is a process in which the flocculant addition rate x is increased by a predetermined increase correction width Ci when the liquid level li in the inlet hopper exceeds a predetermined increase correction judgment value Li1, and the flocculant addition rate x is decreased by a predetermined decrease correction width Di when the liquid level li in the inlet hopper falls below a predetermined decrease correction judgment value Li5 that is lower than the increase correction judgment value Li1. This addition rate correction process is made up of steps #1-03, #1-05, #1-10, #1-11, and #1-12 shown in Figure 3, and step #3 shown in Figure 2.

Specifically, as shown primarily in FIG. 3, in this addition rate correction process, when it is determined that the liquid level li in the inlet hopper exceeds the predetermined increase correction judgment value Li1 (yes in step #1-03), it is determined that there is a shortage of flocculant F in the flocculating sludge S2, and the flocculant addition rate basic value x0 is increased by an increase correction width Ci (e.g., 0.05 points) (step #1-05). Then, in step #3 (see FIG. 2), the flocculant addition rate x is increased by the increase correction width Ci, which is the same as the increase in the flocculant addition rate basic value x0. Note that this increase in the flocculant addition rate x through the temporary addition rate increase process (step #1-05, step #3 (see FIG. 2)) is highly urgent in order to prevent the flocculating sludge S2 from overflowing from the inlet hopper 20, and is therefore executed immediately when it is determined that the liquid level li in the inlet hopper exceeds the increase correction judgment value Li1 (yes in step #1-03).

Furthermore, when it is determined that the liquid level li in the inlet hopper has fallen below the predetermined decrease correction value Li5 (yes in step #1-10), it is determined that excessive flocculant F has been added to the flocculated sludge S2, and the basic flocculant addition rate value x0 is reduced by the decrease correction width Di (e.g., 0.05 points) (step #1-12). Then, in step #3 (see Figure 2), the flocculant addition rate x is reduced by the decrease correction width Di, which is the same as the reduction in the basic flocculant addition rate value x0. Furthermore, while the reduction in the flocculant addition rate x through the addition rate correction process (steps #1-12 and #3 (see Figure 2)) may be performed immediately, in this embodiment, it is less urgent than an increase. Therefore, it is performed when it is determined that the liquid level li in the inlet hopper has continued to fall below the decrease correction value Li5 for a set time T1 (e.g., 5 to 30 minutes) (yes in step #1-11) (yes in step #1-10). The above set time is set taking into consideration the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the coagulated sludge S2 is supplied to the solid-liquid separation section 10. For example, it can be set to the sum of the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the coagulated sludge S2 is supplied to the solid-liquid separation section 10. Furthermore, when it is determined that the liquid level li in the inlet hopper has fallen below the decrease correction judgment value Li5 (yes in step #1-10), the coagulant addition rate x can be immediately reduced through addition rate correction processing (steps #1-12 and #3 (see Figure 2)).

By performing the above-described addition rate correction process, the coagulant addition rate x is corrected in a timely manner to an appropriate value so that the liquid level li in the inlet side hopper is maintained within the range between the increase correction judgment value Li1 on the highest side and the decrease correction judgment value Li5 on the lowest side.
In this embodiment, the increase correction judgment value Li1, which is the criterion for determining whether to increase the flocculant addition rate x through the addition rate correction process, is set to the same value as the temporary increase judgment value Li1, which is the criterion for determining whether to start the first addition rate temporary increase process described above. However, a different value may be used. Furthermore, it is desirable to set the increase correction judgment value, which is the criterion for determining whether to increase the flocculant addition rate x through the addition rate correction process, to a value greater than the temporary increase judgment value, which is the criterion for determining whether to start the addition rate temporary increase process described above. By setting it in this manner, even if the temporary increase in the flocculant addition rate x resulting from the start of the addition rate temporary increase process is not enough to resolve the shortage of flocculant F and to prevent the liquid level li in the inlet-side hopper from rising, the flocculant addition rate x is also increased and corrected by the increase correction width Ci through the addition rate correction process, thereby reliably preventing an excessive rise in the liquid level li in the inlet-side hopper.

Furthermore, the decrease correction judgment value Li5, which serves as the criterion for determining whether the flocculant addition rate x is decreased by the addition rate correction process, is less than the return judgment values Li3 and Li4, which serve as the criterion for determining whether the execution of the temporary addition rate increase process described above is terminated. As a result, even if the temporary decrease in the flocculant addition rate x due to the termination of the temporary addition rate increase process does not resolve the excessive addition of flocculant F and does not contribute to preventing a drop in the liquid level li in the inlet hopper, the flocculant addition rate x is also reduced and corrected by the decrease correction width Di by the addition rate correction process, thereby reliably preventing an excessive drop in the liquid level li in the inlet hopper.

Note that the increase correction range Ci (e.g., 0.05 points) and decrease correction range Di (e.g., 0.05 points) in the addition correction process described above are not intended to temporarily increase or decrease the addition rate temporary increase process described above, but rather to increase or decrease the flocculant addition rate basic value x0 itself, which forms the basis for the flocculant addition rate x. Therefore, it is preferable to set these ranges smaller than the first temporary increase range Ai (e.g., 0.05 to 0.50 points) and the second temporary increase range Bi (e.g., 0.10 points) in the addition rate temporary increase process described above.

[Control of second flocculant addition rate]
As the above-mentioned flocculant addition rate control (step #2 in Figure 2), the control device 50 executes a second flocculant addition rate control, which controls the flocculant addition rate x based on the liquid level lo in the outlet side hopper measured by the level sensor 24 (see Figure 1), as shown in Figure 4.
1 , if the flocculant addition rate x is too low, the flocculation floc properties of the flocculated sludge S2 deteriorate, which reduces the ease of water separation in the solid-liquid separation section 10 and reduces the solid concentration of the concentrated sludge S3, resulting in an increase in the liquid level l0 in the outlet hopper. Therefore, by executing the second flocculant addition rate control and controlling the flocculant addition rate x based on the liquid level l0 in the outlet hopper, the liquid level l0 in the outlet hopper is maintained within as appropriate a range as possible. Therefore, while deterioration of LCC due to excessive addition of flocculant F and overloading of the solid-liquid separation section 10 are suppressed, the addition of an appropriate amount of flocculant F improves the flocculation floc properties of the flocculated sludge S2, improving the ease of water separation in the solid-liquid separation section 10 and suppressing a decrease in the solid concentration of the concentrated sludge S3, resulting in good and stable solid-liquid separation of the flocculated sludge S2 in the solid-liquid separation section 10.

The second flocculant addition rate control shown in Figure 4 controls the flocculant addition rate x by comparing the liquid level lo in the outlet hopper with various judgment values Lo1, Lo2, Lo3, Lo4, and Lo5. This second flocculant addition rate control includes a first addition rate temporary increase process for determining the first addition rate increase range variable Δx1o, a second addition rate temporary increase process for determining the second addition rate increase range variable Δx2o, and an addition rate correction process for determining the flocculant addition rate basic value x0. Details of each process are explained below. In each process, five judgment values Lo1, Lo2, Lo3, Lo4, and Lo5 are set, in descending order, as judgment values for the liquid level lo in the outlet hopper. Furthermore, the constants Ao, Bo, Co, and Do related to the increase/decrease ranges set for the variables x0, Δx1o, and Δx2o that make up the flocculant addition rate x are all positive numbers greater than zero. Also, in the following explanation, the names of the judgment values Lo1, Lo2, Lo3, Lo4, and Lo5 will be in accordance with the processing, but judgment values with the same symbol are set to the same value.

(First addition rate temporary increase process)
The first addition rate temporary increase process in the second flocculant addition rate control is a process for temporarily increasing the flocculant addition rate x from when the liquid level lo in the outlet hopper exceeds a predetermined temporary increase judgment value Lo1 until the liquid level lo in the outlet hopper reaches a predetermined return judgment value Lo3 that is lower than the temporary increase judgment value Lo1. This first addition rate temporary increase process is made up of steps #2-03, #2-04, #2-06, and #2-07 shown in Figure 4, and step #3 shown in Figure 2.

That is, in this first addition rate temporary increase process, as shown primarily in Figure 4, when it is determined that the liquid level lo in the outlet hopper exceeds the temporary increase judgment value Lo1 (yes in step #2-03), it is determined that there is a shortage of flocculant F in the flocculated sludge S2, and the first addition rate increase width variable Δx1o is changed from 0 to the first temporary increase width Ao (e.g., 0.05 to 0.50 points) (step #2-04). Then, in step #3 (see Figure 2), the flocculant addition rate x is temporarily increased by the first temporary increase width Ao. This suppresses deterioration of floc properties, such as a decrease in floc strength and fragmentation, due to a shortage of flocculant F in the flocculated sludge S2, and prevents an excessive rise in the liquid level lo in the outlet hopper due to the deterioration of floc properties. Furthermore, the increase in the flocculant addition rate x through the first addition rate temporary increase process (step #2-04, step #3 (see Figure 2)) is highly urgent in order to prevent the flocculated sludge S2 from overflowing from the outlet hopper 23, and is therefore executed immediately when it is determined that the liquid level lo in the outlet hopper has exceeded the temporary increase determination value Lo1 (yes in step #2-03).

Furthermore, as the liquid level lo in the outlet hopper decreases with the increase in the flocculant addition rate x by the first temporary increase Ao, when it is determined that the liquid level lo in the outlet hopper has reached the return judgment value Lo3 (yes in step #2-06), the first addition rate increase variable Δx1o is returned to 0 (step #2-07). Then, in step #3 (see Figure 2), the temporary increase in the flocculant addition rate x by the first temporary increase Ao is terminated, and the flocculant addition rate x is returned to its pre-increase state. This minimizes the deterioration of LCC caused by the increase in the flocculant addition rate x by the first temporary increase Ao. The reduction in the flocculant addition rate x (step #2-07, step #3 (see Figure 2)) due to the end of the first addition rate temporary increase process is immediately executed when it is determined that the liquid level lo in the outlet hopper has reached the return judgment value Lo3 (yes in step #2-06). The reduction of the flocculant addition rate x (step #2-07, step #3 (see Figure 2)) due to the completion of the first addition rate temporary increase process is less urgent than an increase, and can therefore be performed when it is determined that the liquid level lo in the outlet hopper has remained below the recovery judgment value Lo3 for a set time (e.g., 5 to 30 minutes). The set time is set taking into account the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10. For example, it can be set to the sum of the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10.

(Second addition rate temporary increase process)
The second addition rate temporary increase process in the second flocculant addition rate control, like the first addition rate temporary increase process described above, is a process for temporarily increasing the flocculant addition rate x from when the liquid level lo in the outlet hopper exceeds a predetermined temporary increase judgment value Lo2 until the liquid level lo in the outlet hopper reaches a predetermined return judgment value Lo4 that is lower than the temporary increase judgment value Lo2. This second addition rate temporary increase process is composed of steps #2-01, #2-02, #2-08, and #2-09 shown in Figure 4, and step #3 shown in Figure 2.

That is, in this second addition rate temporary increase process, as shown primarily in Figure 4, when it is determined that the liquid level lo in the outlet hopper exceeds the temporary increase judgment value Lo2 (yes in step #2-01), it is determined that there is a shortage of flocculant F in the flocculated sludge S2, and the second addition rate increase width variable Δx2o is changed from 0 to the second temporary increase width Bo (e.g., 0.10 points) (step #2-02). Then, in step #3 (see Figure 2), the flocculant addition rate x is temporarily increased by the second temporary increase width Bo. This suppresses deterioration of floc properties, such as a decrease in floc strength and fragmentation, due to a shortage of flocculant F in the flocculated sludge S2, and prevents an excessive rise in the liquid level lo in the outlet hopper due to the deterioration of floc properties. Furthermore, the increase in the flocculant addition rate x through the second addition rate temporary increase process (steps #2-02 and #3 (see Figure 2)) is highly urgent in order to prevent the flocculated sludge S2 from overflowing from the outlet hopper 23, and is therefore executed immediately when it is determined that the liquid level lo in the outlet hopper has exceeded the temporary increase determination value Lo2 (yes in step #2-03).

Furthermore, as the liquid level lo in the outlet hopper decreases with the increase in the flocculant addition rate x by the second temporary increase Bo, when it is determined that the liquid level lo in the outlet hopper has reached the return judgment value Lo4 (yes in step #2-08), the second addition rate increase variable Δx2o is returned to 0 (step #2-09). Then, in step #3 (see Figure 2), the temporary increase in the flocculant addition rate x by the second temporary increase Bo is terminated, and the flocculant addition rate x is returned to its pre-increase state. This minimizes the deterioration of LCC due to the increase in the flocculant addition rate x by the second temporary increase Bo. The reduction in the flocculant addition rate x (step #2-09, step #3 (see Figure 2)) resulting from the end of the second addition rate temporary increase process is immediately executed when it is determined that the liquid level lo in the outlet hopper has reached the return judgment value Lo4 (yes in step #2-08). The reduction of the flocculant addition rate x (step #2-09, step #3 (see Figure 2)) due to the completion of the second addition rate temporary increase process is less urgent than an increase, and can therefore be executed when it is determined that the liquid level lo in the outlet hopper has remained below the recovery judgment value Lo4 for a set time (e.g., 5 to 30 minutes). The set time is set taking into account the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10. For example, it can be set to the sum of the hydraulic retention time (HRT) of the sludge coagulation tank 5 and the time until the flocculated sludge S2 is supplied to the solid-liquid separation section 10.

In this embodiment, in order to perform a temporary increase of the flocculant addition rate x in stages, two types of addition rate temporary increase processes, the first addition rate temporary increase process and the second addition rate temporary increase process, are performed using different temporary increase judgment values Lo1, Lo2 and return judgment values Lo3, Lo4. The temporary increase judgment value Lo1, which is the judgment criterion for the liquid level lo in the outlet-side hopper when the temporary increase of the flocculant addition rate x is started in the first addition rate temporary increase process, is set higher than the temporary increase judgment value Lo2, which is the judgment criterion for the liquid level lo in the outlet-side hopper when the temporary increase of the flocculant addition rate x is started in the second addition rate temporary increase process. That is, when the liquid level lo in the outlet-side hopper rises and exceeds the temporary increase judgment value Lo2, the second addition rate temporary increase process starts a temporary increase of the flocculant addition rate x by the second temporary increase width Bo. Furthermore, when the liquid level lo in the outlet-side hopper continues to rise and exceeds the temporary increase judgment value Lo1 even after the flocculant addition rate x is increased by the second temporary increase width Bo, a temporary increase of the flocculant addition rate x by the first temporary increase width Ao through the first addition rate temporary increase process is also started. For this reason, in order to reliably lower the liquid level lo in the outlet-side hopper when the liquid level lo in the outlet-side hopper exceeds the temporary increase judgment value Lo1, it is preferable to set the first temporary increase width Ao (e.g., 0.05 to 0.50 points) in the first addition rate temporary increase process larger than the second temporary increase width Bo (e.g., 0.10 points) in the second addition rate temporary increase process, and it is preferable to set it to, for example, about twice the second temporary increase width Bo.
It should be noted that the configuration may be such that only one of the first addition rate temporary increase processing and the second addition rate temporary increase processing is executed.

(Addition rate correction process)
The addition rate correction process in the second flocculant addition rate control is a process in which the flocculant addition rate x is increased by a predetermined increase correction width Co when the liquid level lo in the outlet hopper exceeds a predetermined increase correction judgment value Lo1, and the flocculant addition rate x is decreased by a predetermined decrease correction width Do when the liquid level lo in the outlet hopper falls below a predetermined decrease correction judgment value Lo5 that is lower than the increase correction judgment value Lo1. This addition rate correction process is composed of steps #2-03, #2-05, #2-10, #2-11, and #2-12 shown in Figure 4, and step #3 shown in Figure 2.

Specifically, as shown primarily in FIG. 4, in this addition rate correction process, when it is determined that the liquid level lo in the outlet hopper exceeds the predetermined increase correction judgment value Lo1 (yes in step #2-03), it is determined that there is a shortage of flocculant F in the flocculated sludge S2, and the flocculant addition rate basic value x0 is increased by the increase correction width Co (e.g., 0.10 points) (step #2-05). Then, in step #3 (see FIG. 2), the flocculant addition rate x is increased by the increase correction width Co, which is the same as the increase in the flocculant addition rate basic value x0. Note that this increase in the flocculant addition rate x through the temporary addition rate increase process (step #2-05, step #3 (see FIG. 2)) is highly urgent in order to prevent the flocculated sludge S2 from overflowing from the outlet hopper 23, and is therefore executed immediately when it is determined that the liquid level lo in the outlet hopper exceeds the increase correction judgment value Lo1 (yes in step #2-03).

Furthermore, when it is determined that the liquid level lo in the outlet hopper has fallen below the predetermined decrease correction value Lo5 (yes in step #2-10), it is determined that excessive flocculant F has been added to the flocculated sludge S2, and the basic flocculant addition rate value x0 is reduced by the decrease correction width Do (e.g., 0.10 points) (step #2-12). Then, in step #3 (see Figure 2), the flocculant addition rate x is reduced by the decrease correction width Do, which is the same as the reduction in the basic flocculant addition rate value x0. Furthermore, while the reduction in the flocculant addition rate x through the addition rate correction process (step #2-12, step #3 (see Figure 2)) may be performed immediately, in this embodiment, it is less urgent than an increase. Therefore, it is performed when it is determined that the liquid level lo in the outlet hopper has continued to fall below the decrease correction value Lo5 for a set time T2 (e.g., 5 to 30 minutes) (yes in step #2-11) (yes in step #2-10). Furthermore, when it is determined that the liquid level lo in the outlet hopper has fallen below the decrease correction judgment value Lo5 (yes in step #2-10), the flocculant addition rate x may be immediately reduced through the addition rate correction process (step #2-12, step #3 (see Figure 2)).

In this embodiment, the addition rate correction process in the second flocculant addition rate control serves as an emergency response when the addition rate correction process in the first flocculant addition rate control described above is insufficient to correct the flocculant addition rate x. Therefore, the process of reducing the flocculant addition rate x (steps #2-10 to #2-12), which is less urgent, can be omitted from the addition rate correction process in the second flocculant addition rate control. Furthermore, in cases where the addition rate correction process in the first flocculant addition rate control described above is sufficient to correct the flocculant addition rate x, or in cases where the solid-liquid separation unit 10 is a dewatering device that rarely experiences concentration failures that cause a sudden rise in the liquid level lo in the outlet hopper, the addition rate correction process in the second flocculant addition rate control itself can be omitted.

By performing the above-described addition rate correction process, the coagulant addition rate x is corrected in a timely manner to an appropriate value so that the liquid level lo in the outlet side hopper is maintained within the range between the increase correction judgment value Lo1 on the highest side and the decrease correction judgment value Lo5 on the lowest side.
Furthermore, the increase correction judgment value Lo1, which is the criterion for determining whether to increase the flocculant addition rate x by the addition rate correction process, is set to be equal to or greater than the temporary increase judgment values Lo1 and Lo2, which are the criterion for determining whether to start the execution of the above-mentioned temporary addition rate increase process.As a result, in cases where the temporary increase in the flocculant addition rate x by starting the execution of the above-mentioned temporary addition rate increase process is not enough to resolve the shortage of flocculant F and cannot contribute to preventing an increase in the liquid level lo in the outlet-side hopper, the flocculant addition rate x is also increased and corrected by the increase correction width Co by the addition rate correction process, and an excessive increase in the liquid level lo in the outlet-side hopper is reliably prevented.

In addition, the decrease correction judgment value Lo5, which serves as the criterion for determining whether the flocculant addition rate x is decreased by the addition rate correction process, is less than the return judgment values Lo3 and Lo4, which serve as the criterion for determining whether the execution of the temporary addition rate increase process described above is terminated. As a result, even if the temporary decrease in the flocculant addition rate x due to the termination of the temporary addition rate increase process does not resolve the excessive addition of flocculant F and does not contribute to preventing a drop in the liquid level lo in the outlet hopper, the flocculant addition rate x is also reduced and corrected by the decrease correction width Do by the addition rate correction process, thereby reliably preventing an excessive drop in the liquid level lo in the outlet hopper.

In addition, the increase correction range Co (e.g., 0.10 points) and decrease correction range Do (e.g., 0.10 points) in the above-mentioned addition correction process are not intended to temporarily increase or decrease the addition rate by the above-mentioned temporary addition rate increase process, but rather to increase or decrease the basic value x0 of the flocculant addition rate, which is the basis for the flocculant addition rate x.Therefore, it is preferable to set them to be smaller than the first temporary increase range Ao (e.g., 0.05 to 0.50 points) and the second temporary increase range Bo (e.g., 0.10 points) in the above-mentioned temporary addition rate increase process. Furthermore, the addition rate correction process in the second flocculant addition rate control serves as an emergency response when the addition rate correction process in the first flocculant addition rate control described above is insufficient to correct the flocculant addition rate x. Therefore, the increase correction range Co (e.g., 0.10 points) and decrease correction range Do (e.g., 0.10 points) in the addition correction process in the second flocculant addition rate control described above are preferably slightly larger than the increase correction range Ci (e.g., 0.05 points) and decrease correction range Di (e.g., 0.05 points) in the addition rate correction process in the first flocculant addition rate control described above.

In the treatment system 100 of this embodiment, when the control device 50 controls the flocculant addition rate x, the first flocculant addition rate control is executed preferentially based on the liquid level li in the inlet hopper. If the first flocculant addition rate control fails to fully optimize the flocculant addition rate x, the second flocculant addition rate control is executed based on the liquid level lo in the outlet hopper as a follow-up. In particular, when the concentrated sludge S3 in the outlet hopper 23 is transported to the downstream treatment section 30 by the transfer pump, the transfer pump is controlled to maintain the liquid level lo in the outlet hopper within an appropriate range. Therefore, the first flocculant addition rate control based on the liquid level li in the inlet hopper is used to control the flocculant addition rate x preferentially. Only if the control of the transfer pump fails to maintain the liquid level lo in the outlet hopper within an appropriate range will the second flocculant addition rate control based on the liquid level lo in the outlet hopper be used to control the flocculant addition rate x. In this embodiment, both the first flocculant addition rate control and the second flocculant addition rate control are executed, but it is also possible to execute only one of them.

[Another form of second flocculant addition rate control]
In the second flocculant addition rate control described above (see Figure 4), the flocculant addition rate x is controlled by comparing the liquid level lo in the outlet hopper itself with the judgment values Lo1, Lo2, Lo3, Lo4, and Lo5. However, the flocculant addition rate x can also be controlled using conditions such as the rate of change of the liquid level lo in the outlet hopper rather than the liquid level lo in the outlet hopper itself. For example, as shown in Figure 5, the rate of rise Δlo of the liquid level lo in the outlet hopper can be compared with the judgment value ΔLo1 to control the flocculant addition rate x.
In another form of second flocculant addition rate control shown in Figure 5, when it is determined (step #2-21) that the increase rate Δlo of the liquid level lo in the outlet hopper exceeds a predetermined increase correction judgment value ΔLo1, such as when poor concentration occurs in the solid-liquid separation section 10, the flocculant addition rate basic value x0 is increased by an increase correction width Eo (e.g., 0.20 to 0.30 points) (step #2-22). Then, in step #3 (see Figure 2), the flocculant addition rate x is increased by the increase correction width Eo, which is the same as the increase in the flocculant addition rate basic value x0.

In the processing system 100 of this embodiment, when the solid-liquid separation unit 10 is a concentration device in which there is a possibility of a sudden rise in the liquid level Lo in the outlet hopper due to poor concentration, for example, another form of second flocculant addition rate control shown in FIG. 5 is executed in addition to the second flocculant addition rate control shown in FIG. 4. However, it is also possible to configure the system to execute either one of these forms of second flocculant addition rate control. Furthermore, when executing the second flocculant addition rate control shown in FIG. 4, the other form of second flocculant addition rate control shown in FIG. 5 may be incorporated instead of the addition rate correction process (steps #2-03, #2-05, #2-10, #2-11, and #2-12) in the second flocculant addition rate control.

1 Processing section 2 Flocculant supply pump (flocculant addition section)
5 Sludge coagulation tank 10 Solid-liquid separation section 20 Inlet side hopper (inlet side storage section)
21 Level sensor (liquid level measurement unit in inlet reservoir)
23 Outlet side hopper (outlet side storage section)
24 Level sensor (liquid level measurement unit in outlet side reservoir)
30: Subsequent processing unit 50: Control device (control unit)
100 Treatment system S1 Organic waste (material to be treated)
S2 Flocculated sludge (floc)
S3 Thickened sludge (concentrate)
F Flocculant li Liquid level in inlet hopper lo Liquid level in outlet hopper x Flocculant addition rate Ci Increase correction width Co Increase correction width Di Decrease correction width Do Decrease correction width Eo Increase correction width Li1 Judgment value for increase correction, judgment value for temporary increase Li2 Judgment value for temporary increase Li3 Judgment value for return Li4 Judgment value for return Li5 Judgment value for decrease correction Lo1 Judgment value for increase correction, judgment value for temporary increase Lo2 Judgment value for temporary increase Lo3 Judgment value for return Lo4 Judgment value for return Lo5 Judgment value for decrease correction ΔLo1 Judgment value for increase correction

Claims (5)

A treatment system including a flocculant adding unit that adds a flocculant to a material to be treated to form a floc, and a solid-liquid separating unit that separates the floc into a solid and liquid to form a concentrate,
a storage section that is installed on an inlet side or an outlet side of the solid-liquid separation section and that temporarily stores the flocculate or the concentrate;
a reservoir liquid level measuring unit that measures a reservoir liquid level, which is the liquid level of the aggregate or the concentrate in the reservoir;
a control unit that executes flocculant addition rate control to control the flocculant addition rate to the object to be treated by the flocculant addition unit based on the liquid level in the storage unit ,
A processing system in which the control unit executes a temporary addition rate increase process in the flocculant addition rate control, which temporarily increases the flocculant addition rate from the time when the liquid level in the storage section exceeds a predetermined temporary increase judgment value until the liquid level in the storage section reaches a predetermined return judgment value that is lower than the temporary increase judgment value . The processing system described in claim 1, wherein the control unit, in the flocculant addition rate control, increases the flocculant addition rate by a predetermined increase correction range when the liquid level in the storage section exceeds a predetermined increase correction judgment value that is equal to or greater than the temporary increase judgment value, and performs an addition rate correction process that decreases the flocculant addition rate by a predetermined decrease correction range when the liquid level in the storage section falls below a predetermined decrease correction judgment value that is less than the return judgment value. The storage section includes an inlet-side storage section that is installed on the inlet side of the solid-liquid separation section and that temporarily stores the aggregates immediately before being introduced into the solid-liquid separation section,
the reservoir internal liquid level measuring unit includes an inlet-side reservoir internal liquid level measuring unit that measures an inlet-side reservoir internal liquid level, which is a reservoir internal liquid level of the aggregate in the inlet-side reservoir,
The treatment system according to claim 1 or 2, wherein the control unit executes a first flocculant addition rate control as the flocculant addition rate control, which controls the flocculant addition rate based on a liquid level in the inlet-side reservoir. The storage unit includes an outlet-side storage unit that is installed on the outlet side of the solid-liquid separation unit and that temporarily stores the concentrate immediately before it is discharged from the solid-liquid separation unit and introduced into a subsequent processing unit,
the reservoir internal liquid level measuring unit includes an outlet side reservoir internal liquid level measuring unit that measures an outlet side reservoir internal liquid level, which is a reservoir internal liquid level of the concentrate in the outlet side reservoir,
The treatment system according to claim 1 or 2, wherein the control unit executes second flocculant addition rate control as the flocculant addition rate control, which controls the flocculant addition rate based on the liquid level in the outlet-side reservoir. A control method for a treatment system including a flocculant adding unit that adds a flocculant to a material to be treated to form a floc, and a solid-liquid separating unit that separates the floc into a solid and liquid to form a concentrate,
measuring a liquid level in a reservoir, which is the liquid level of the flocculant or the concentrate in a reservoir that is installed on the inlet side or the outlet side of the solid-liquid separation section and that temporarily stores the flocculant or the concentrate;
performing a flocculant addition rate control for controlling a flocculant addition rate to the object to be treated by the flocculant addition unit based on the liquid level in the storage unit ;
A control method for a treatment system, characterized in that in the flocculant addition rate control, a temporary addition rate increase process is executed to temporarily increase the flocculant addition rate from the time when the liquid level in the storage section exceeds a predetermined temporary increase judgment value until the liquid level in the storage section reaches a predetermined return judgment value that is lower than the temporary increase judgment value .