Treatment system and control method of the same

Abstract

To provide a treatment system for adding a coagulant agent to an object to be treated and performing solid-liquid separation in a screw press type solid-liquid separation part, which maintains a coagulant agent addition rate in an appropriate range, suppresses deterioration of LCC by excessive addition of the coagulant agent and an overload in the solid-liquid separation part, improves a coagulant floc property in a coagulant by addition of a sufficient and adequate amount of coagulant agent, and improves and stabilizes the coagulant in the solid-liquid separation part and performs solid-liquid separation.SOLUTION: A treatment system executes coagulant agent addition rate control of detecting a screw load value Ls indicating a rotation load of a screw 12 in a solid-liquid separation part 10, and controlling a coagulant agent addition rate x that is an addition rate of a coagulant agent F to an object S1 to be treated by a coagulant agent addition part 2 on the basis of the screw load value Ls.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a treatment system comprising an addition unit that adds a flocculant to an object to be treated to form a floc, and a solid-liquid separation unit that separates the floc into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured in a screw press type that solid-liquid separates the floc by rotational driving of a screw, and a control method thereof.

Background Art

[0002] As a treatment system for reducing the volume of objects to be treated such as sewage sludge and biomass, by adding a flocculant such as a polymer flocculant to the object to be treated, the solid content of the object to be treated contained in the object to be treated is aggregated to form flocculated flocs (also referred to as "coarse flocs"), and by solid-liquid separating the flocs containing such flocculated flocs, a concentrate with a reduced water content is produced. In such a treatment system, when the addition rate of the flocculant to the object to be treated (also referred to as the "flocculant addition rate" in the present application) is low, the flocculant is insufficient in the flocs, the formation of flocculated flocs becomes insufficient, and the flocs cannot be properly solid-liquid separated in the solid-liquid separation unit, and the water content of the concentrate may not be reduced to the target value. Conversely, when the flocculant addition rate is high, the flocculant is excessively added to the flocs, and some of the flocculant is not used for aggregating the object to be treated and is discharged as a separation liquid in the solid-liquid separation unit without reaction, which deteriorates the LCC (life cycle cost), and there may be a problem of overload in the solid-liquid separation unit. In addition, when the separation liquid containing the unreacted flocculant is returned to a biological treatment facility performing aerobic treatment such as the activated sludge method, it may have an adverse effect on the biological treatment facility. Therefore, in the treatment system, it is desirable to control the flocculant addition rate to the object to be treated within an appropriate range.

[0003] Therefore, a technique has been proposed in which the solid content concentration of the concentrate discharged from the solid-liquid separation section is detected, and the flocculant addition rate is controlled based on the detection result (see, for example, Patent Document 1). In the processing system described in Patent Document 1, a detection body is rotationally driven in the concentrate stored in the receiving tank, and the rotational resistance of the detection body (the current value of the drive motor) is measured as a value indicating the solid content concentration of the concentrate. Further, in the processing system described in Patent Document 1, the solid-liquid separation section is configured as a screw press type that separates the aggregates by rotational driving of the screw.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a configuration in which the solid content concentration of the concentrate is detected as in Patent Document 1 and the detection result is used to control the flocculant addition rate, since it takes a certain amount of time to detect the solid content concentration of the concentrate, there is a delay in controlling the flocculant addition rate. Therefore, it is impossible to make the flocculant addition rate follow a relatively rapid change in the solid content concentration of the concentrate, and there is a risk that the actual flocculant addition rate will deviate from the appropriate range. Further, since the detection accuracy of the solid content concentration of the concentrate greatly depends on the measurement accuracy of each parameter used for the detection, it is not very high. Therefore, when controlling the flocculant addition rate based on a detection result with low accuracy, the actual flocculant addition rate may deviate from the appropriate range. In view of this situation, the main problem of the present invention is to maintain the flocculant addition rate within an appropriate range in a treatment system that adds a flocculant to the object to be treated and then performs solid-liquid separation in a screw press type solid-liquid separation unit, while suppressing the deterioration of LCC due to excessive addition of the flocculant and the overload in the solid-liquid separation unit, and improving the floc properties of the flocs in the flocs by adding an appropriate amount of the flocculant without shortage, so as to be able to perform good and stable solid-liquid separation of the flocs in the solid-liquid separation unit.

Means for Solving the Problem

[0006] The first characteristic configuration of the treatment system according to the present invention includes an addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that performs solid-liquid separation on the flocs to obtain a concentrate, and the solid-liquid separation unit is configured in a screw press type that performs solid-liquid separation on the flocs by rotational driving of a screw, and a screw load value detection unit that detects a screw load value indicating the rotational load of the screw in the solid-liquid separation unit, and a control unit that executes flocculant addition rate control for controlling the flocculant addition rate to the object to be treated by the flocculant addition unit based on the screw load value. Further, the characteristic configuration of the control method of the treatment system according to the present invention includes an addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that performs solid-liquid separation on the flocs to obtain a concentrate, and is a control method of a treatment system in which the solid-liquid separation unit is configured in a screw press type that performs solid-liquid separation on the flocs by rotational driving of a screw, and detects a screw load value indicating the rotational load of the screw in the solid-liquid separation unit, and executes flocculant addition rate control for controlling the flocculant addition rate to the object to be treated by the flocculant addition unit based on the screw load value.

[0007] According to this configuration, when the coagulant addition rate to the object to be treated changes, the properties of the coagulation flocs formed in the aggregate to which the coagulant is added, such as the viscosity, size, and strength of the coagulation flocs (hereinafter referred to as "coagulation floc properties"), change. As a result, the rotational load of the screw in the solid-liquid separation section configured in a screw press type changes. Therefore, it is possible to determine the excess or deficiency of the coagulant addition rate from the screw load value detected by the screw load value detection section. Then, the control section executes the coagulant addition rate control and controls the coagulant addition rate based on the screw load value, so that the rotational load of the screw can be maintained within an appropriate range as much as possible. Therefore, according to the present invention, in a treatment system for solid-liquid separation after adding a coagulant to sludge, while maintaining the coagulant addition rate within an appropriate range and suppressing the deterioration of LCC due to excessive addition of the coagulant and the overload in the solid-liquid separation section, it is possible to provide a technique capable of improving the coagulation floc properties in the aggregate by adding an appropriate amount of the coagulant without shortage and stably performing solid-liquid separation of the aggregate in the screw press type solid-liquid separation section.

[0008] The second characteristic configuration of the treatment system according to the present invention is that, in the coagulant addition rate control, the control section executes an addition rate temporary decrease process for temporarily decreasing the coagulant addition rate during the period from when the screw load value exceeds a predetermined temporary decrease determination value to when the screw load value reaches a predetermined return determination value.

[0009] According to this configuration, when the screw load value exceeds the temporary decrease determination value, it is determined that the flocculant is excessively added in the aggregates, and the execution of the addition rate temporary decrease process is started, and the flocculant addition rate is decreased. By this, deterioration of the floc properties such as an increase in the viscosity and subdivision of the floc due to the excessive addition of the flocculant in the aggregates is suppressed, and an excessive increase in the rotational load of the screw can be avoided. Then, after the execution of the addition rate temporary decrease process is started, as the flocculant addition rate decreases, the driving load of the screw decreases, and when the screw load value decreases to the return determination value, the execution of the addition rate temporary decrease process is terminated, and the flocculant addition rate is returned to that before the decrease. By this, deterioration of the ease of water separation in the solid-liquid separation section due to the decrease in the flocculant addition rate can be suppressed as much as possible, and the solid content concentration of the concentrate can be kept as high as possible.

[0010] A third characteristic configuration of the processing system according to the present invention is that, in the flocculant addition rate control, when the screw load value continuously falls below a predetermined increase correction determination value that is less than the return determination value for a predetermined set time, the control unit executes an addition rate correction process of increasing the flocculant addition rate by a predetermined increase correction width.

[0011] According to this configuration, when the addition rate correction process is executed and the screw load value continuously falls below the increase correction determination value for the set time, it is determined that the flocculant is surely insufficient in the aggregates, and the flocculant addition rate is increased by the increase correction width. By this, the flocculant addition rate can be appropriately corrected to avoid as much as possible a decrease in the solid content concentration of the concentrate accompanied by a continuous decrease in the rotational load of the screw. Furthermore, an increase correction determination value, which serves as a criterion for determining an increase in the flocculant addition rate by the above addition rate correction process, is set to be less than the above return determination value, which serves as a criterion for determining the end of the execution of the above addition rate temporary decrease process. By doing so, when the temporary decrease in the flocculant addition rate due to the end of the execution of the addition rate temporary decrease process alone does not eliminate the shortage of the flocculant and cannot contribute to avoiding a decrease in the rotational load of the screw, the addition rate correction process is also used to increase the flocculant addition rate by the above increase correction width for correction, so that an excessive decrease in the rotational load of the screw can be reliably avoided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0013] As shown in FIG. 1, in the processing system 100 according to the present embodiment, a flocculant supply pump 2 (an example of a flocculant addition unit) that adds a flocculant F to organic waste S1 (an example of a material to be processed), which includes sludge supplied from a front-stage processing unit 1 such as a sludge storage tank, a sludge supply pump, and a concentration device, to form flocculated sludge S2 (an example of a flocculate), and a solid-liquid separation unit 10 that separates the flocculated sludge S2 to which the flocculant F has been added into concentrated sludge S3 (an example of a concentrate) are provided. In the present embodiment, the flocculant F is added to the organic waste S1 being stirred in the sludge flocculation tank 5, but it may also be added to the organic waste S1 before it is supplied to the sludge flocculation tank 5. Then, by stirring the organic waste S1 to which the flocculant F has been added in the sludge flocculation tank 5, the generation of flocculant flocs is promoted, and the flocculated sludge S2 containing the generated flocculant flocs is supplied from the sludge flocculation tank 5 to the subsequent solid-liquid separation unit 10. As the flocculant F, any known flocculant used for sludge flocculation, such as a cationic, amphoteric, or polyamidine polymer flocculant, can be used. In addition, in the processing system 100 of the present embodiment, although the organic waste S1 containing sludge is used as the object to be processed, biomass or the like may also be used as the object to be processed.

[0014] The solid-liquid separation unit 10 is configured to perform solid-liquid separation on the flocculated sludge S2 supplied from the sludge flocculation tank 5 and discharge the concentrated sludge S3 obtained by separating moisture through the solid-liquid separation. Depending on the degree of concentration, it may be referred to as a concentration device or a dehydration device. Note that there is no specific distinction between the concentration device and the dehydration device, but generally, a device with a higher solid concentration of the processed material obtained after treatment than that of the concentration device is called a dehydration device. For example, the solid-liquid separation unit 10 that increases the solid concentration of the solid content from about 1% to about 15% is called a concentration device, and a device that increases the solid concentration of the solid content higher than that of the concentration device is called a dehydration device. In addition, the concentrated sludge S3 corresponds to the concentrated sludge S3 regardless of the solid concentration as long as it is solid-liquid separated by the solid-liquid separation unit 10. Note that as the processing system 100, there are those equipped with only a concentration device as the solid-liquid separation unit 10, those equipped with only a dehydration device, and those equipped with these concentration devices and dehydration devices arranged in parallel in series. However, the characteristic configuration of the present invention is applicable to both or either of the concentration device and the dehydration device. Further, when the concentration device and the dehydration device are provided as the solid-liquid separation unit 10, a sludge transfer pump may be provided to transfer the sludge discharged from the previous-stage concentration device to the subsequent-stage dehydration device.

[0015] The solid-liquid separation unit 10 is configured as a screw press type that rotationally drives a screw 12 housed in an outer cylinder screen 11 by a drive motor 13, pressurizes the flocculated sludge S2 introduced from the inlet-side hopper 20 in a pressure chamber 15 formed between the outer cylinder screen 11 and the screw 12 for solid-liquid separation, and discharges the concentrated sludge S3 after the solid-liquid separation to the outlet-side hopper 23.

[0016] In the solid-liquid separation unit 10, an inlet-side hopper 20 for temporarily storing the flocculated sludge S2 is provided on the inlet side where the flocculated sludge S2 is supplied, and an outlet-side hopper 23 for temporarily storing the concentrated sludge S3 is provided on the outlet side where the concentrated sludge S3 is discharged. That is, the flocculated sludge S2 supplied from the sludge flocculation tank 5 is temporarily stored in the inlet-side hopper 20 once, and the flocculated sludge S2 stored in the inlet-side hopper 20 is swallowed into the pressurizing chamber 15 by the rotational drive of the screw 12. Further, the concentrated sludge S3 discharged from the pressurizing chamber 15 is temporarily stored in the outlet-side hopper 23 once, and the concentrated sludge S3 stored in the outlet-side hopper 23 is fed into the subsequent processing unit 30 such as a transfer pump or a dewatering device. Incidentally, the outlet-side hopper 23 is usually equipped in the solid-liquid separation unit 10 itself such as a concentrator, but it may be an inlet-side hopper of the processing unit 30 installed in the subsequent stage. Incidentally, the inlet-side hopper 20 and the outlet-side hopper 23 are not limited in structure as long as they can store the flocculated sludge S2 and the concentrated sludge S3, and may be a storage tank placed separately from the solid-liquid separation unit 10.

[0017] Furthermore, a screw load value detection unit 17 for detecting a screw load value ls indicating the rotational load of the screw 12 in the solid-liquid separation unit 10 is provided. In the present embodiment, the screw load value detection unit 17 is configured to detect, as v, a value obtained by multiplying the rotational speed of the drive motor 13 corresponding to the rotational speed of the screw 12 and the current value of the drive motor 13 corresponding to the rotational torque of the screw 12. However, for example, a configuration in which only the power consumption or the current value of the drive motor 13 is detected as the screw load value ls may be adopted.

[0018] The processing system 100 is provided with a control device 50 for controlling the operations of the flocculant supply pump 2, the drive motor 13 of the solid-liquid separation unit 10, and the like. Then, the control device 50 functions as a control unit that executes flocculant addition rate control for controlling the flocculant addition rate x, which is the addition rate of the flocculant F to the organic waste S1 by the flocculant supply pump 2, based on the screw load value ls detected by the screw load value detection unit 17 by executing a predetermined computer program. The coagulant addition rate is the value obtained by dividing the solid content of the coagulant by the solid content in the sludge, and generally can be obtained by the following calculation formula. Coagulant addition rate = (chemical solution dissolution concentration × chemical supply amount) / (sludge solid concentration × sludge supply amount)

[0019] That is, although details will be described later, as shown in FIG. 2, the control device 50 executes coagulant addition rate control to determine the coagulant addition rate basic value x0 that becomes the basic value of the coagulant addition rate x and the decrease width variables Δx1 and Δx2 that become the decrease width of the coagulant addition rate x. Then, in step #12, the coagulant addition rate x is determined as a value obtained by subtracting these decrease width variables Δx1 and Δx2 from the coagulant addition rate basic value x0. Then, the coagulant addition amount vh is determined by multiplying the thus determined coagulant addition rate x by the supply amount vs of the organic waste S1 from the previous treatment unit 1. The output of the coagulant supply pump 2 is set so as to add the coagulant F corresponding to the determined coagulant addition amount vh to the organic waste S1. In this embodiment, the initial value of the coagulant addition rate basic value x0 that becomes the basic value of the coagulant addition rate x is set to a value of 0.1% to 0.9%, preferably about 0.4%, and the initial values of the decrease width variables Δx1 and Δx2 that become the increase width are set to 0 points. Hereinafter, details of the coagulant addition rate control will be described with reference to FIG. 2.

[0020] 〔Coagulant addition rate control〕 As shown in FIG. 2, the control device 50 executes coagulant addition rate control for controlling the coagulant addition rate x based on the screw load value ls detected by the screw load value detection unit 17. That is, when the coagulant addition rate x changes, the floc properties in the coagulated sludge S2 change, and as a result, the rotational load of the screw 12 in the solid-liquid separation unit 10 configured in a screw press type changes. Therefore, the excess or deficiency of the coagulant addition rate x is determined from the screw load value ls detected by the screw load value detection unit 17. Then, by performing the flocculant addition rate control and controlling the flocculant addition rate x based on the screw load value ls, the rotational load of the screw 12 is maintained within an appropriate range as much as possible. Therefore, while suppressing the deterioration of LCC due to excessive addition of the flocculant F and the overload in the solid-liquid separation section 10, the floc properties in the flocculated sludge S2 are improved by adding an appropriate amount of the flocculant F without shortage, and the flocculated sludge S2 is separated from solid to liquid well and stably in the screw press type solid-liquid separation section 10. In addition, considering the time until the filling of the flocculated sludge S2 into the solid-liquid separation section 10 is completed at startup, the control device 50 starts the flocculant addition rate control after a certain time (for example, 180 min) has elapsed since startup.

[0021] The flocculant addition rate control shown in FIG. 2 controls the flocculant addition rate x by comparing the screw load value ls itself with various determination values Ls1, Ls2, Ls3, Ls4, Ls5. This flocculant addition rate control includes a first addition rate temporary decrease process for determining the first addition rate decrease width variable Δx1, a second addition rate temporary decrease process for determining the second addition rate decrease width variable Δx2, and an addition rate correction process for determining the flocculant addition rate basic value x0. The details of each process will be described below. In each process, five determination values Ls1, Ls2, Ls3, LS4, Ls5 are set in order from the higher side as determination values for the screw load value ls. Also, the constants As, Bs, Cs regarding the increase and decrease widths set for the variables x0, Δx1, Δx2 constituting the flocculant addition rate x are all positive numbers greater than 0. In the following description, the names of the determination values Ls1, Ls2, Ls3, Ls4, Ls5 are made to match the process, but those with the same sign are determination values set to the same value.

[0022] (First addition rate temporary decrease process) In the first addition rate temporary decrease process in the flocculant addition rate control, the flocculant addition rate x is temporarily decreased from when the screw load value ls exceeds a predetermined determination value Ls1 for temporary decrease until the screw load value ls becomes a predetermined return determination value Ls3 lower than the temporary decrease determination value Ls1. This first addition rate temporary decrease process is composed of step #03, step #04, step #05, step #06, and step #12 shown in FIG. 2.

[0023] That is, in this first addition rate temporary decrease process, when it is determined (yes in step #03) that the screw load value ls exceeds the temporary decrease determination value Ls1, it is judged that the flocculant F is excessively added in the flocculated sludge S2, and the first addition rate decrease width variable Δx1 is changed from 0 to the first temporary decrease width As (for example, 0.05 points) (step #04). Then, in step #12, the flocculant addition rate x is temporarily decreased by the first temporary decrease width As. By this, the deterioration of the floc properties such as the increase in viscosity and subdivision of the floc due to the excessive addition of the flocculant F in the flocculated sludge S2 is suppressed, and the excessive increase in the screw load value ls due to the deterioration of the floc properties is avoided. Incidentally, since the decrease in the flocculant addition rate x (step #04, step #12) by the above first addition rate temporary decrease process is highly urgent from the viewpoint of preventing the overload of the solid-liquid separation section 10, it is immediately executed when it is determined (yes in step #03) that the screw load value ls exceeds the temporary decrease determination value Ls1.

[0024] Furthermore, as the screw load value ls decreases by the amount of the first temporary decrease width As of the flocculant addition rate x, when it is determined that the screw load value ls has reached the return determination value Ls3 (yes in step #05), the first addition rate decrease width variable Δx1 is reset to 0 (step #06). Then, in step #12, the temporary decrease by the amount of the first temporary decrease width As of the flocculant addition rate x ends, and the flocculant addition rate x is restored to the value before the decrease. This suppresses as much as possible the deterioration of the ease of water separation in the solid-liquid separation section 10 due to the decrease in the flocculant addition rate x, and keeps the solid content concentration of the concentrated sludge S3 as high as possible. The increase in the flocculant addition rate x due to the end of the first addition rate temporary decrease process (steps #06 and #12) is immediately executed when it is determined that the screw load value ls has reached the return determination value Ls3 (yes in step #05). Incidentally, since the increase in the flocculant addition rate x due to the end of the first addition rate temporary decrease process (steps #06 and #12) is less urgent than during the decrease, it can also be executed when it is determined that the screw load value ls has remained below the return determination value Ls3 for a set time (for example, 120 minutes).

[0025] (Second addition rate temporary decrease process) The second addition rate temporary decrease process in the flocculant addition rate control is a process of temporarily decreasing the flocculant addition rate x from when the screw load value ls exceeds a predetermined temporary decrease determination value Ls2 until the screw load value ls reaches a predetermined return determination value Ls4 lower than the temporary decrease determination value Ls2, similar to the above-described first addition rate temporary decrease process. This second addition rate temporary decrease process is composed of steps #01, #02, #07, #08, and #12 shown in FIG. 2.

[0026] That is, in this second addition rate temporary decrease process, when it is determined that the screw load value ls exceeds the temporary decrease determination value Ls2 (yes in step #01), it is judged that the flocculant F is excessively added in the flocculated sludge S2, and the second addition rate decrease width variable Δx2 is changed from 0 to the second temporary decrease width Bs (for example, 0.05 points) (step #02). Then, in step #12, the flocculant addition rate x is temporarily decreased by the second temporary decrease width Bs. By this, the deterioration of the floc properties such as the increase in viscosity and subdivision of the floc formed by the excessive addition of the flocculant F in the flocculated sludge S2 is suppressed, and the excessive increase in the screw load value ls due to the deterioration of the floc properties is avoided. Note that the decrease in the flocculant addition rate x (steps #02 and #12) by the above first addition rate temporary decrease process is highly urgent from the viewpoint of preventing the overload of the solid-liquid separation unit 10, and thus is immediately executed when it is determined that the screw load value ls exceeds the temporary decrease determination value Ls1 (yes in step #03).

[0027] Furthermore, as the screw load value ls decreases with the decrease of the second temporary decrease width Bs of the flocculant addition rate x, and when it is determined that the screw load value ls has reached the return determination value Ls4 (yes in step #07), the second addition rate decrease width variable Δx2 is reset to 0 (step #08). Then, in step #12, the temporary decrease of the flocculant addition rate x by the second temporary decrease width Bs is completed, and the flocculant addition rate x is restored to the value before the above decrease. By this, the deterioration of the ease of water separation in the solid-liquid separation unit 10 due to the decrease of the flocculant addition rate x is suppressed as much as possible, and the solid content concentration of the concentrated sludge S3 is maintained as high as possible. The increase in the flocculant addition rate x (steps #08 and #12) due to the end of the above second addition rate temporary decrease process is immediately executed when it is determined that the screw load value ls has reached the return determination value Ls4 (yes in step #07). Note that the increase in the flocculant addition rate x (steps #08 and #12) due to the end of the above second addition rate temporary decrease process is less urgent than during the decrease, and thus it can also be executed when it is determined that the screw load value ls has continued to be equal to or less than the return determination value Ls4 for a set time (for example, 120 min).

[0028] In this embodiment, in order to gradually execute a temporary decrease in the flocculant addition rate x, as the addition rate temporary decrease process, two types of the first addition rate temporary decrease process and the second addition rate temporary decrease process with different temporary decrease determination values Ls1 and Ls2 and return determination values Ls3 and Ls4 are executed. And, the temporary decrease determination value Ls1, which is the determination criterion for the screw load value ls when starting the temporary decrease in the flocculant addition rate x in the first addition rate temporary decrease process, is set higher than the temporary decrease determination value Ls2, which is the determination criterion for the screw load value ls when starting the temporary decrease in the flocculant addition rate x in the second addition rate temporary decrease process. That is, when the screw load value ls rises and exceeds the temporary decrease determination value Ls2, a temporary decrease by the second temporary decrease width Bs of the flocculant addition rate x by the second addition rate temporary decrease process is started. Further, when the screw load value ls continues to rise and exceeds the temporary decrease determination value Ls1 even after the flocculant addition rate x is decreased by the second temporary decrease width Bs, a temporary decrease by the first temporary decrease width As of the flocculant addition rate x by the first addition rate temporary decrease process is also started. For example, in this embodiment, both the first temporary decrease width As and the second temporary decrease width Bs are set to the same value, for example, 0.05 points. However, in order to surely decrease the screw load value ls when the screw load value ls exceeds the temporary decrease determination value Ls1, the first temporary decrease width As in the first addition rate temporary decrease process can also be set larger than the second temporary decrease width Bs in the second addition rate temporary decrease process. Note that only one of the first addition rate temporary decrease process and the second addition rate temporary decrease process may be configured to be executed.

[0029] (Addition rate correction process) The addition rate correction process in the flocculant addition rate control is a process of increasing the flocculant addition rate x by a predetermined increase correction width Cs when the screw load value ls falls below a predetermined increase correction determination value Ls5. This addition rate correction process is composed of step #09, step #10, step #11, and step #12.

[0030] That is, in this addition rate correction process, when it is determined that the screw load value ls is less than a predetermined increase correction determination value Ls5 (yes in step #09), it is determined that the flocculant F is surely insufficient in the flocculated sludge S2, and the basic flocculant addition rate x0 is increased by an increase correction width Cs (for example, 0.10 point) (step #11). Then, in step #12, the flocculant addition rate x is increased by the same increase correction width Cs as the increase amount of the basic flocculant addition rate x0. Further, the increase in the flocculant addition rate x by the addition rate correction process (steps #11 and #12) may be executed immediately, but in this embodiment, since the urgency is low, when it is determined that the screw load value ls continues (yes in step #10) for a set time T (for example, 120 min) and is less than the increase correction determination value Ls5 (yes in step #09), it is executed. Incidentally, when it is determined that the screw load value ls is less than the increase correction determination value Ls5 (yes in step #09), the increase in the flocculant addition rate x by the addition rate correction process (steps #11 and #12) may be immediately performed.

[0031] By executing the addition rate correction process as described above, the flocculant addition rate x is appropriately corrected in a timely manner to be maintained at or above the increase correction determination value Ls5. Furthermore, the increase correction determination value Ls5 serving as the determination criterion for the increase in the flocculant addition rate x by the above addition rate correction process is set to be less than the return determination values Ls3 and Ls4 which are the determination criteria for the end of the execution of the above addition rate temporary decrease process. Thus, in a case where the shortage of the flocculant F cannot be eliminated only by the temporary increase in the flocculant addition rate x due to the end of the execution of the above addition rate temporary decrease process and the decrease in the screw load value ls cannot be avoided, the flocculant addition rate x is increased and corrected by the increase correction width Cs by the above addition rate correction process in combination, and an excessive decrease in the screw load value ls is surely avoided.

[0032] Incidentally, the increase correction width Cs (for example, 0.10 point) in the above addition correction process is not for the purpose of temporary increase or decrease by the above addition rate temporary decrease process, but for the purpose of surely avoiding excessive decrease in the screw load value ls. Therefore, it is preferably set to be larger than the temporary decrease widths As and Bs (for example, 0.05 point) in the above addition rate temporary decrease process. For example, it is preferably set to about twice the temporary decrease widths As and Bs.

[0033] Incidentally, in the present embodiment, in the addition rate correction process, only the correction of the coagulant addition rate x to the increasing side is performed, and the correction of the coagulant addition rate x to the decreasing side is not performed. However, it can also be configured to perform the correction of the coagulant addition rate x to the decreasing side. In that case, when it is determined that the screw load value ls exceeds the predetermined decrease correction determination value Ls1, it can be configured that it is determined that the coagulant F is excessively added in the flocculated sludge S2, and the basic value x0 of the coagulant addition rate is decreased by the predetermined decrease correction width.

[0034] Although not shown, when the screw load value ls exceeds a determination value larger than the determination value Ls1, it can also be configured to perform processes such as alarm output and operation stop on the assumption that there is a high possibility that the solid-liquid separation unit 10 is malfunctioning.

Explanation of Reference Numerals

[0035] 2 Coagulant supply pump (coagulant addition unit) 10 Solid-liquid separation unit 12 Screw 17 Screw load value detection unit 50 Control device (control unit) 100 Processing system S1 Organic waste (object to be treated) S2 Flocculated sludge (flocculated product) S3 Concentrated sludge (concentrated product) F Coagulant ls Screw load value x Coagulant addition rate Cs Increase correction width Ls1 Temporary decrease determination value Judgment value for temporary decrease of Ls2 Judgment value for return of Ls3 Judgment value for return of Ls4 Judgment value for increase correction of Ls5 Set time T

Claims

1. An addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that separates the flocs into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured as a screw press type that separates the flocs by rotational driving of a screw, and a screw load value detection unit that detects a screw load value indicating the rotational load of the screw in the solid-liquid separation unit, and a control unit that executes a flocculant addition rate control for controlling the flocculant addition rate to the object to be treated by the flocculant addition unit based on the screw load value.

2. The processing system according to claim 1, wherein the control unit executes an addition rate temporary decrease process of temporarily decreasing the flocculant addition rate during the period from when the screw load value exceeds a predetermined temporary decrease determination value until the screw load value reaches a predetermined return determination value in the flocculant addition rate control.

3. The processing system according to claim 2, wherein the control unit executes an addition rate correction process of increasing the flocculant addition rate by a predetermined increase correction width when the screw load value falls below a predetermined increase correction determination value that is less than the return determination value and continues for a predetermined set time in the flocculant addition rate control.

4. An addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that separates the flocs into a concentrate by solid-liquid separation, and a control method for a processing system, wherein the solid-liquid separation unit is configured as a screw press type that separates the flocs by rotational driving of a screw, and detecting a screw load value indicating the rotational load of the screw in the solid-liquid separation unit, and executing a flocculant addition rate control for controlling the flocculant addition rate to the object to be treated by the flocculant addition unit based on the screw load value.

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