JP7743201B2 - Coagulant injection control method and coagulant injection control device - Google Patents

Description

Embodiments of the present invention relate to a coagulant injection control method and a coagulant injection control device.

The solid-liquid separation process, which removes solids from water, plays an important role in the treatment of drinking water, sewage, industrial wastewater, and other water sources. The most commonly used method of solid-liquid separation involves adding a coagulant to aggregate fine solids in the water, then filtering the water either directly or after a sedimentation process. For example, at water purification plants, coagulants are added to raw water to cause the fine suspended solids in the water to aggregate, forming aggregates of suspended solids called flocs. Flocs that grow to sizes of several millimeters to several centimeters have a high settling rate and can be separated and removed by sedimentation. The clear supernatant water is passed through a sand filter, which uses sand as the filtering material, to remove any remaining fine suspended solids and flocs, resulting in water with extremely low turbidity that meets drinking water quality standards.

Generally, the process of adding a coagulant to form flocs and then settling and separating them is called the coagulation-sedimentation process, while the process of filtering and separating suspended components using a filter bed made of sand or other filter media is called the filtration process. In the coagulation-sedimentation process, it is necessary to maintain an appropriate coagulant injection rate to form flocs with good settling properties and maintain low turbidity in the coagulation-sedimentation treated water. If the coagulant injection rate is too high or too low, the flocs will not be completely precipitated during the coagulation-sedimentation process and will instead be supplied to the subsequent filtration process, accelerating the head loss in the filter and resulting in increased backwash frequency. Furthermore, fine suspended components may not be completely removed in the filter, resulting in insufficiently filtered water being sent to the subsequent filtration process. Therefore, the general method is to carefully adjust the amount of coagulant injected in the coagulation-sedimentation process, manage the coagulation treatment process to achieve optimal treatment, and then send the water to the subsequent filtration process. For this reason, various methods have been proposed for controlling coagulant injection.

For example, Patent Document 1 proposes a method in which water is collected from the mixing basin 20, a voltage is applied to measure the movement speed of multiple flocs, and the results are used to evaluate the quality of the flocculation state and control the injection of flocculant. This makes it possible to achieve operation with appropriate flocculation conditions set based on the water quality characteristics of the raw water.

For example, Patent Document 2 proposes a method for adjusting the filtration process in a gravity filtration device so that the change in filtration speed per filtration device falls within a certain range when the amount of raw water changes. By returning treated water to the raw water, the treatment volume can be kept constant, allowing for stable filtration operation to be maintained.

JP 2014-054603 A JP 2012-045448 A

As mentioned above, many methods have been proposed for optimizing the operation of the coagulation and sedimentation processes separately, but no method has been proposed for operating both processes together appropriately. In actual operation, because operation is managed to optimize the coagulation and sedimentation process, there may be excess processing capacity in the filtration process, with very little suspended matter being removed by the filter layer and the head loss in the filter layer barely increasing. In such cases, in order to suppress the growth of microorganisms in the filter layer, backwashing must be performed every certain amount of time, even if the head loss is sufficiently low. For example, if both the coagulation and sedimentation processes could be treated as a single process and operation could be managed in such a way that the filtration process also shares some of the processing load, the burden on the coagulation and sedimentation process could be reduced, making it possible to operate in a way that reduces the amount of coagulant used.

Embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a flocculant injection control method and flocculant injection control device that appropriately control the injection of flocculant.

A flocculant injection control device according to an embodiment is an apparatus applicable to a water treatment facility that performs solid-liquid separation, the water treatment facility having a flocculant injection facility that injects a flocculant into water to be treated, a flocculation and sedimentation treatment facility that is located downstream of the flocculant injection position and that performs a sedimentation treatment of flocs formed in the water to be treated, and a filtration treatment facility that is located downstream of the flocculation and sedimentation treatment facility and that performs a filtration treatment, the apparatus comprising: a flocculation and sedimentation treatment prediction unit that calculates predicted values of the treated water turbidity and the number of suspended solid particles in the flocculation and sedimentation treatment facility; a filtration treatment prediction unit that calculates predicted values of the treated water turbidity and the rate of rise of head loss in the filtration treatment facility; and a control unit that controls the flocculant injection control device according to an embodiment, the flocculant injection control device, the flocculant injection control device, the filtration treatment facility, and the mixing basin, the mixing basin, the filtration basin, the filtration treatment facility, and the filtration treatment facility, the control unit ... the flocculation treatment prediction value evaluation unit causes the coagulation-sedimentation treatment prediction unit and the filtration treatment prediction unit to repeatedly calculate predicted values by changing parameters using at least one of information on the civil structure of the flocculation basin, the civil structure of the sedimentation basin, the rotation speed of the agitator in the mixing basin, information on the shape of the agitator in the mixing basin, the rotation speed of the agitator in the flocculation basin, information on the shape of the agitator in the flocculation basin, the coagulant injection rate, the particle size of the sand in the filter bed, information on the shape of the sand in the filter bed, and the thickness of the sand layer, and outputs predicted values of the treated water turbidity and the rate of rise of head loss in the filtration treatment equipment that will achieve the management target values; and a coagulant injection control unit that controls the injection of the coagulant at the minimum coagulant injection rate calculated using the predicted values of the treated water turbidity and the rate of rise of head loss in the filtration treatment equipment that will achieve the management target values.

FIG. 1 is a diagram schematically illustrating an example of the configuration of a flocculant injection control device according to the first embodiment. FIG. 2 is a flowchart illustrating an example of a coagulant injection control method according to an embodiment. FIG. 3 is a diagram schematically illustrating a configuration example of a flocculant injection control device according to the second embodiment.

Hereinafter, a coagulant injection control method and a coagulant injection control device according to an embodiment will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically illustrating an example of the configuration of a flocculant injection control device according to the first embodiment.
The water treatment system to which the coagulant injection control method and the coagulant injection control device of the present embodiment are applied may be either a drinking water treatment system or a sewage treatment system. In the following description, an example in which the method and the device are applied to a drinking water purification treatment system in a water purification plant will be described as an example.

Generally, a water treatment system in a water purification plant includes a receiving well 10, a mixing basin 20, a flocculation basin 30, and a settling basin 40.
Raw water to be treated is taken in by a receiving well 10, and the treated water is sent from the receiving well 10 to the mixing basin 20. A flow meter S1 and a water quality meter S2 are attached to the path along which the treated water is sent from the receiving well 10 to the mixing basin 20. The flow meter S1 measures the flow rate of the treated water flowing into the mixing basin 20. The water quality meter S2 measures the water quality, such as turbidity, number of suspended solid particles, pH, and water temperature, of the treated water flowing into the mixing basin 20. The water quality meter S2 may include individual measuring instruments for measuring the water quality, such as turbidity, number of suspended solid particles, pH, and water temperature, of the treated water. The measurement results of the flow meter S1 and the water quality meter S2 are supplied to the coagulant injection control device 60.

The water to be treated is delivered to the mixing basin 20 from the receiving well 10, and a flocculant is injected from the flocculant injection equipment 50. The flocculant used here can be an aluminum-based inorganic flocculant such as polyaluminum chloride (PAC) or aluminum sulfate. Of these, PAC is primarily used in water purification plants. The flocculant injection equipment 50 adjusts the amount of flocculant injected into the mixing basin 20 according to information specifying the injection amount (e.g., flocculant injection rate) input from the flocculant injection control device 60.

The mixing basin 20 includes an agitator 22, and the rotation of the agitator 22 agitates the water to be treated, promoting mixing with the coagulant. The water to be treated discharged from the mixing basin 20 is sent to a flocculation basin 30.
The mixing basin 20 may be equipped with a water quality meter S3 that measures the zeta potential or streaming potential (or streaming current) of the water to be treated (mixing basin outlet water) sent to the flocculation basin 30. In this case, the measurement results of the water quality meter S3 can be supplied to the coagulant injection control device 60.

In the flocculation basin 30, the flocs formed in the mixing basin 20 aggregate to form larger flocs. The flocculation basin 30 has, for example, a slow mixing device that slowly mixes the water to be treated. The slow mixing device is designed to gradually decrease the mixing intensity downstream. This causes repeated collisions between flocs in the water to be treated, causing the flocs to grow larger and more likely to settle. After the flocs have grown in size in the flocculation basin 30, the water to be treated is sent to the sedimentation basin 40.

In the settling basin 40, the water supplied from the flocculation basin 30 is retained for a predetermined time (for example, about 3 hours) or more, allowing the flocs contained in the water to settle. After the water to be treated is retained in the settling basin 40 for a predetermined time or more and the flocs in the water to be treated are settled and removed, the water to be treated is transferred to the filtration treatment facility, which is the next process. The flocs that grow large and settle in the settling basin 40 are discharged as sludge to a waste sludge basin. For example, an inclined plate may be placed in the settling basin 40. The inclined plate may promote the growth of flocs and may improve the settling ability of the flocs.
The sludge basin may be provided with a measuring device S10 for measuring the water level of the sludge basin. In this case, the measurement results of the measuring device S10 may be supplied to the coagulant injection control device 60.

A water quality meter S4 is installed in the sedimentation tank 40 downstream of the position where flocs are settled and removed. The water quality meter S4 measures water quality information such as pH, turbidity, color, organic matter concentration, and suspended particle count of the water discharged from the sedimentation tank 40 (the water to be treated), and outputs the measurement results (water quality information of the water to be treated) to the coagulant injection control device 60. Note that the water quality information of the water to be treated in the sedimentation tank 40 may also be measured by a water quality meter S5 installed at a position where water sent from the sedimentation tank 40 to the filtration treatment equipment is stored. It is sufficient that at least one of the water quality meter S4 and water quality meter S5 is installed, and it is sufficient that either the water quality meter S4 or S5 is installed downstream of the coagulant injection position.

In the filter basin 70 of the filtration treatment equipment, flocs and suspended solids that were not settled and removed in the sedimentation basin 40 are removed in the filtration layer, for example, by sand filtration. The purified water from which the flocs and suspended solids have been removed by the filter basin 70 is subjected to sterilization with chlorine or the like in a purified water distribution reservoir (not shown) and then distributed to distribution pipes. The wastewater generated when washing away the flocs and suspended solids removed in the filter basin 70 is discharged into a wastewater reservoir, and the supernatant, relatively clear water, is supplied from the wastewater reservoir to the receiving well 10.
The drainage pond may be provided with a measuring device S11 for measuring the water level of the drainage pond. In this case, the measurement results of the measuring device S11 may be supplied to the coagulant injection control device 60.

The filtration treatment equipment is equipped with a head loss measuring device S7 that measures the head loss of the filtration treatment equipment, and a measuring device S8 that measures the turbidity of the filtered water. It is also equipped with at least one of a flow meter S6 and a flow meter S9 that measure the flow rate of the filtration treatment equipment. Flow meter S6 measures the flow rate of the water to be treated flowing into the filtration basin 70. Flow meter S9 measures the flow rate of the water to be treated discharged from the filtration basin 70. The measurement results of the head loss measuring device S7, measuring device S8, flow meter S6, and flow meter S9 can be supplied to the coagulant injection control device 60.

After being treated in the filtration facility, chlorine is added to the water to be treated, and the water is distributed to the distribution pipes via a distribution reservoir (not shown). In addition, the water to be treated may also be subjected to ozonation or biological activated carbon treatment as appropriate before being passed through the sand filter.

The flocculant injection control device 60 is, for example, a computing device that includes at least one processor and memory that stores programs executed by the processor. The flocculant injection control device 60 can achieve various functions through software or a combination of software and hardware.

The flocculant injection control device 60 includes a predicted value calculation unit 60A, a filtration treatment predicted value evaluation unit 63, and a flocculant injection control unit 64. The predicted value calculation unit 60A includes a flocculation/sedimentation treatment prediction unit 61 and a filtration treatment prediction unit 62.

The coagulation and sedimentation treatment prediction unit 61 uses, for example, information on the quality of the inflow water to the mixing basin and operational information as search parameters to calculate the floc growth pattern (e.g., floc size (volume, maximum diameter, minimum diameter) and growth size per unit time under the conditions of the input information), and based on the calculated floc growth pattern, calculates predicted values for the amount of suspended solids (weight, mass, etc.) to be settled and separated in the coagulation and sedimentation treatment equipment, the turbidity of the sedimentation treatment water, and the number of suspended solid particles to be settled and separated.

Information on the quality of the influent water to the mixing basin can include at least one of the following: raw water turbidity, number of suspended solid particles, pH, and water temperature. If the information on the quality of the influent water to the mixing basin includes alternative indicators of the charge state of suspended solids, such as the zeta potential of the raw water, the zeta potential of the mixing basin water after coagulant injection, or streaming potential (or streaming current), the coagulation and sedimentation treatment prediction unit 61 can more accurately calculate the growth of flocs. Furthermore, operation information can include at least one of the following: flow rate, the civil structure of the mixing basin, the civil structure of the flocculation basin, the civil structure of the sedimentation basin, the rotation speed and shape of the agitator in the mixing basin, the rotation speed and shape of the agitator in the flocculation basin, and the coagulant injection rate.

The filtration treatment prediction unit 62 includes a suspended solids removal amount calculation unit 621 and a head loss calculation unit 622, which are described below, and uses information on the inflow water quality to the filter basin and operational information to calculate predicted values for the turbidity of the filtered water and the rate of increase in head loss in the filter basin in the filtration treatment equipment. Information on the inflow water quality to the filter basin can use, for example, at least one piece of information such as the turbidity (predicted value) of the sedimentation treatment water in the coagulation sedimentation treatment equipment, the number of suspended solid particles (predicted value), pH, or water temperature. Information on operation can use, for example, at least one piece of information such as the flow rate, particle size of the sand in the filter bed, shape information of the sand in the filter bed, thickness of the sand layer, or coagulant injection rate.

The filtration treatment predicted value evaluation unit 63 compares the predicted value output from the filtration treatment prediction unit 62 with a predetermined control target value, and repeatedly calculates the predicted value of the turbidity of the filtered water and the predicted value of the rate of rise of head loss in the filter basin by changing the search parameters input to the coagulation and sedimentation treatment prediction unit 61 and the filtration treatment prediction unit 62 until the predicted value becomes smaller than the control target value (until the control target value is achieved). When multiple predicted values are output from the filtration treatment prediction unit 62, the filtration treatment predicted value evaluation unit 63 sets a control target value for each predicted value. The filtration treatment predicted value evaluation unit 63 can repeatedly cause the coagulation and sedimentation treatment prediction unit 61 and the filtration treatment prediction unit 62 to calculate predicted values until all of the multiple predicted values become smaller than the control target value.

When the output value of the filtration treatment prediction unit 62 is smaller than the control target value (when the target value is achieved), the filtration treatment prediction value evaluation unit 63 outputs the predicted value of the turbidity of the filtered water and the predicted value of the rate of rise of the head loss of the filtration basin to the coagulant injection control unit 64. If there are multiple sets of predicted values that are smaller than the control target value, the filtration treatment prediction value evaluation unit 63 may, for example, output the set of predicted values whose predetermined predicted value is the smallest. Methods for searching for the smallest value of the predicted value of the turbidity of the filtered water and the predicted value of the rate of rise of the head loss of the filtration basin include GA (genetic algorithm) and linear programming. Note that it is desirable to set the calculation speed of the optimization so that it is within a specified time (for example, within 30 seconds).

The flocculant injection control unit 64 calculates the minimum flocculant injection rate that achieves the predicted value of turbidity of the filtered water and the predicted value of the rate of increase of head loss in the filtration basin output from the filtration treatment predicted value evaluation unit 63, and outputs the calculated flocculant injection rate value (information specifying the injection amount) to the flocculant injection equipment 50.

Next, an example of the operation of the flocculant injection control device 60 of this embodiment will be described.
FIG. 2 is a flowchart illustrating an example of a coagulant injection control method according to an embodiment.
First, the coagulation-sedimentation treatment prediction unit 61 uses the input search parameters to calculate predicted values of the turbidity of treated water and the number of particles of suspended matter in the coagulation-sedimentation treatment facility (step S1).

The filtration treatment prediction unit 62 calculates a predicted value for the turbidity of the filtered water and a predicted value for the rate of increase in head loss of the filtration basin based on information on the quality of the water inflowing into the filtration basin and operational information (step S2).

The suspended solids removal amount calculation unit 621 calculates the amount of suspended solids removed from the water and calculates the turbidity of the filtered water based on the following Iwasaki formula, which assumes that suspended solids are removed at a constant rate as the treated water passes through the filter layer of the filtration basin 70.

(C (particles/mL): concentration of suspended matter, z (cm): depth of filter layer)
The filtration coefficient λ is a coefficient that is affected by information such as the flow rate, the diameter and shape of the sand that makes up the filter layer, the porosity ε of the filter layer, the particle size of the suspended solids in the influent, the amount of coagulant remaining in the influent water, etc. As filtration progresses, the porosity ε of the filter layer changes in the process of suspended solids in the influent being captured and filtered by the filter layer (ε is a function of time), so λ also becomes a function of time that changes as filtration progresses.

The turbidity removal amount calculation unit 621 calculates λ as a time-varying coefficient using information on the inflow water quality to the filter basin, such as the turbidity of the sedimentation treatment water, the number of suspended solid particles, pH, and water temperature, and information on operation, such as the flow rate, sand particle size and shape information for the filter layer, the thickness of the sand layer, and the coagulant injection rate. When calculating, the turbidity removal amount calculation unit 621 calculates λ using ε at that point in time (the calculation point in time), calculates the turbidity of the filtered water, and, assuming that the inflow water quality information and operation information at that point in time will continue, calculates the turbidity of the filtered water for the next few hours as the calculation result, taking into account changes in ε and λ over time.

The head loss calculation unit 622 calculates the head loss of the filter layer based on the following Kozeny-Carman equation, which is an equation for pressure loss in a granular layer flow in a laminar flow state.
Δp: g/cm/s ² pressure loss (1g/cm/s ² =0.1Pa)
L: cm Total height of the filter media packed bed V ₀ : cm/s Superficial velocity (velocity assuming no packed bed) (= filtration rate)
μ: g/cm/s Fluid viscosity coefficient ε: Porosity (= void ratio of the filter layer)
Φ _s : - Sphericity of the filter material in the packed bed D _P : cm Equivalent spherical diameter of suspended matter

The head loss calculation unit 622 calculates the above formula using the time-varying porosity ε of the filter bed, calculates the time change in pressure loss Δp, and outputs the calculated rate of head loss increase over the next few hours.

As described above, the filtration treatment prediction unit 62 can calculate the predicted value of the turbidity of the filtered water and the predicted value of the rate of increase in the head loss of the filtration basin from information on the current inflow water quality to the filtration basin and operational information.

The filtration treatment predicted value evaluation unit 63 first sets the turbidity of the filtered water and the rate of rise in head loss of the filtration basin as management target values for operational management of the filtration basin. The evaluation value is determined by comparing the predicted value output from the filtration treatment prediction unit 62 with the set management target value, and repeatedly calculating the predicted value by changing the search parameters in the coagulation sedimentation treatment prediction unit 61 and the filtration treatment prediction unit 62 until a predicted value smaller than the management target value is obtained. When a predicted value smaller than the management target value is obtained, the filtration treatment predicted value evaluation unit 63 outputs the predicted value to the coagulant injection control unit 64. Methods such as GA (genetic algorithm) and linear programming can be used to optimize the turbidity of the sedimentation treatment water.

The flocculant injection control unit 64 calculates the flocculant injection rate that achieves the predicted value output from the filtration treatment predicted value evaluation unit 63, and controls the flocculant injection using the calculated value (step S3). The method of flocculant injection control may be manual setting of the flocculant injection rate by an operator, feedforward control, or feedback control. In the case of manual operation by an operator, for example, the injection rate may be determined according to a correspondence table that defines the flocculant injection rate according to the turbidity of the filtered water. The injection rate can be determined by creating similar correspondence tables for multiple cases, such as when the predicted value of the turbidity of the filtered water output from the filtration treatment predicted value evaluation unit 63 is high and when it is low.

In feedforward control, a similar approach can be used, for example, to accommodate multiple cases, such as when the predicted value output from the filtration treatment predicted value evaluation unit 63 is high and when it is low, by setting coefficients in the coagulant injection rate calculation formula for feedforward control.

When performing feedback control, the flocculant injection control unit 64 can continuously measure the charge neutralization status of the surface charge of suspended solids in the raw water due to the addition of flocculant while measuring, for example, the zeta potential and streaming potential (or streaming current) of the water exiting the mixing area after the addition of flocculant, and control the flocculant injection. In this case, the values of the zeta potential and streaming potential (or streaming current) set as control target values can be adjusted according to the turbidity of the sedimentation water output from the filtration treatment prediction value evaluation unit 63. If the turbidity of the sedimentation water output from the filtration treatment prediction value evaluation unit 63 is high, operation can be performed with a slightly reduced processing load in the coagulation and sedimentation process, so charge neutralization by the flocculant in the mixing area can be slightly weaker, and the values of the zeta potential and streaming potential (or streaming current) set as control target values can be set to slightly negative values. A control period of approximately 1 to 10 minutes is desirable.

As explained above, the flocculant injection control method and flocculant injection control device of this embodiment can predict the treatment results in the coagulation and sedimentation process and the filtration process, and based on the predicted results, can calculate target values for the treated water quality in the coagulation and sedimentation process that allocate an appropriate treatment load to the filtration process. By operating flocculant injection control based on the calculated target values, it is possible to reduce the total flocculant injection rate compared to the coagulation and sedimentation process that always achieves optimal treatment, while maintaining the same level of turbidity, which is the treated water quality in the filtration process.

Furthermore, according to the coagulant injection control method and coagulant injection control device of this embodiment, since it has a coagulation sedimentation treatment prediction unit, it is possible to predict the treatment status of the coagulation sedimentation process in detail, making it possible to control in accordance with the situation.
Furthermore, according to the coagulant injection control method and coagulant injection control device of this embodiment, the total coagulant injection rate can be reduced, thereby reducing the load on wastewater treatment and reducing the amount of sludge generated.
That is, according to this embodiment, it is possible to provide a flocculant injection control method and a flocculant injection control device that perform appropriate control of flocculant injection.

Next, a second embodiment of the flocculant injection control method and flocculant injection control device will be described in detail with reference to the drawings. Note that in the following description, components similar to those in the first embodiment described above will be assigned the same reference numerals and will not be described again.

FIG. 3 is a diagram schematically illustrating a configuration example of a flocculant injection control device according to the second embodiment.
The flocculant injection control device 60 of this embodiment differs from the flocculant injection control device of the first embodiment in the configuration of the flocculant injection control unit 64.

The flocculant injection control device 60 of this embodiment includes a predicted value calculation unit 60A, a filtration treatment predicted value evaluation unit 63, and a flocculant injection control unit 64. The predicted value calculation unit 60A includes a flocculation/sedimentation treatment prediction unit 61 and a filtration treatment prediction unit 62. The flocculant injection control unit 64 includes an injection rate determination unit 65 and a feedback control unit 66.
The configurations and operations of the coagulation-sedimentation process prediction unit 61, the filtration process prediction unit 62, and the filtration process predicted value evaluation unit 63 are similar to those of the coagulant injection control device of the first embodiment described above.

The feedback control unit 66 has the function of feedback-controlling the coagulant injection so that the measurement value of the water quality meter S3, which measures the charge state of suspended solids in the water after coagulant injection, is reached as a set target value. The charge state of suspended solids in the water after coagulant injection measured by the water quality meter S3 may be an alternative indicator of the charge state of suspended solids, such as the zeta potential or streaming potential (or streaming current) of the mixing basin water.

Before coagulant injection, suspended solids in the water have a negative charge and repel each other. Because coagulants contain aluminum, which has a positive charge, injecting the coagulant neutralizes the charges, weakening the repulsive forces between particles and making it easier for flocs to form. As mentioned above, the charge state of suspended solids in the water after coagulant injection can be used as an indicator for calculating the coagulant injection rate.

The feedback control unit 66 utilizes the above properties to calculate the coagulant injection rate through feedback control, using the charge state of suspended solids in the water as an indicator. For example, the feedback control unit 66 measures the zeta potential and streaming potential (or streaming current) of the mixing area outlet water, while continuously measuring the charge neutralization status of the surface charge of suspended solids in the raw water through coagulant injection, and calculates the coagulant injection rate through feedback control.

The injection rate determination unit 65 calculates the optimal value of the flocculant injection rate from the minimum flocculant injection rate that satisfies the management target value for the turbidity of the filtered water and the management target value for the rate of rise of head loss in the filter basin, and the flocculant injection rate obtained by feedback control in the feedback control unit 66. The injection rate determination unit 65 controls the flocculant injection rate based on the optimal value of the flocculant injection rate. Specifically, to prevent under-injection of flocculant, the injection rate determination unit 65 normally uses the output value of the flocculant injection control in the feedback control as the optimal injection rate, and only adopts the minimum flocculant injection rate as the optimal injection rate when the minimum flocculant injection rate that satisfies the management target value for the rate of rise of head loss in the filter basin is greater than the output value of the feedback control.

As explained above, the flocculant injection control method and device of this embodiment make it possible to predict the treatment results in the coagulation and sedimentation process and the filtration process. By operating flocculant injection control that allocates an appropriate treatment load to the filtration process based on the predicted results, it is possible to reduce the total flocculant injection rate compared to the coagulation and sedimentation process at an optimal rate, while maintaining the same level of turbidity, which is the treated water quality in the filtration process.

Furthermore, according to the coagulant injection control method and device of this embodiment, since it has a coagulation sedimentation treatment prediction unit, it is possible to predict the treatment status of the coagulation sedimentation process in detail, making it possible to control according to the situation.
That is, according to this embodiment, it is possible to provide a flocculant injection control method and a flocculant injection control device that perform appropriate control of flocculant injection.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

10...receiving well, 20...mixing basin, 22...agitator, 30...flocculation basin, 40...sedimentation basin, 50...coagulant injection equipment, 60...coagulant injection control device, 60A...prediction value calculation unit, 61...coagulation and sedimentation treatment prediction unit, 62...excess treatment prediction unit, 621...suspended matter removal amount calculation unit, 622...head loss calculation unit, 63...filtration treatment predicted value evaluation unit, 64...coagulant injection control unit, 65...injection rate determination unit, 66...feedback control unit, S1, S6, S9...flow meter, S8, S10-S11...measuring device, S7...head loss measuring device, S2-S5...water quality meter

Claims (7)

The apparatus is applicable to a water treatment facility that performs solid-liquid separation and includes a flocculant injection facility that injects a flocculant into water to be treated, a coagulation sedimentation treatment facility that is located downstream of the injection position of the flocculant and performs a precipitation treatment of flocs formed in the water to be treated, and a filtration treatment facility that is located downstream of the coagulation sedimentation treatment facility and performs a filtration treatment,
a coagulation-sedimentation treatment prediction unit that calculates predicted values of treated water turbidity and suspended particle count in the coagulation-sedimentation treatment facility;
a filtration treatment prediction unit that calculates predicted values of treated water turbidity and rising speed of head loss in the filtration treatment equipment;
a filtration treatment prediction value evaluation unit which repeatedly causes the coagulation-sedimentation treatment prediction unit and the filtration treatment prediction unit to calculate predicted values by changing a parameter using at least one of information on the influent water quality into the mixing basin, information on the influent water quality into the filtration basin, flow rate, the civil structure of the mixing basin, the civil structure of the flocculation basin, the civil structure of the sedimentation basin, the rotation speed of the agitator in the mixing basin, information on the shape of the agitator in the flocculation basin, the rotation speed of the agitator in the flocculation basin, information on the shape of the agitator in the flocculation basin, the injection rate of a coagulant, the particle size of the sand in the filter bed, information on the shape of the sand in the filter bed, and the thickness of the sand layer , until the predicted values output from the filtration treatment prediction unit reach a predetermined control target value, and outputs predicted values of the treated water turbidity and the rate of increase in head loss in the filtration treatment equipment.
a flocculant injection control unit that controls the injection of the flocculant using a flocculant injection rate calculated using predicted values of the treated water turbidity and the rate of increase in head loss in the filtration treatment equipment that will achieve the management target value. The coagulant injection control unit
a feedback control unit that calculates a coagulant injection rate by feedback control so that the coagulant injection rate reaches a predetermined target value using a measured value of the charge state of suspended solids in the water after the coagulant injection as an index;
2. The flocculant injection control device according to claim 1, further comprising an injection rate determination unit that controls the injection of the flocculant using either a flocculant injection rate calculated using predicted values of the treated water turbidity and the rate of increase of head loss in the filtration treatment equipment that achieves the management target value, or a flocculant injection rate calculated by the feedback control. The coagulant injection control device of claim 1, wherein the filtration treatment equipment includes a filtration layer filled with filter media. The flocculant injection control device of claim 3, wherein the filtration treatment prediction unit calculates predicted values of the treated water turbidity and the rate of increase in the head loss in the filtration treatment equipment using at least one of the following: the turbidity of the influent water to the filtration treatment equipment, the particle count of suspended solids in the influent water, the pH of the influent water, the water temperature of the influent water, the flow rate of the influent water, the particle diameter of the filter media contained in the filtration layer, shape information of the filter media, the layer thickness of the filtration layer, and the flocculant injection rate. The coagulant injection control device described in claim 1, wherein the filtration treatment prediction unit calculates the turbidity of the treated water and the rate of increase in the head loss in the filtration treatment equipment using at least one of the turbidity of the inflow water to the filtration treatment equipment, the particle count of suspended matter in the inflow water, the pH of the inflow water, the water temperature of the inflow water, the flow rate of the inflow water, and the coagulant injection rate. The flocculant injection control device described in claim 1, wherein the flocculant injection control unit calculates the flocculant injection rate using the charge state of suspended solids contained in the treated water after the flocculant injection as an index. A control method applicable to a water treatment facility that performs solid-liquid separation, the water treatment facility having a flocculant injection facility that injects a flocculant into water to be treated, a coagulation sedimentation treatment facility that is disposed downstream of the injection position of the flocculant and performs a precipitation treatment of flocs formed in the water to be treated, and a filtration treatment facility that is disposed downstream of the coagulation sedimentation treatment facility and performs a filtration treatment,
calculating predicted values of treated water turbidity and suspended matter particle count in the coagulation sedimentation treatment facility;
Calculating predicted values of treated water turbidity and head loss increase rate in the filtration treatment equipment;
repeatedly calculating predicted values of treated water turbidity and rate of rise in head loss in the filtration treatment facility by changing parameters using at least one of information on the quality of influent water into the mixing basin, information on the quality of influent water into the filtration basin, flow rate, civil structure of the mixing basin, civil structure of the flocculation basin, civil structure of the sedimentation basin, rotation speed of the agitator in the mixing basin, information on the shape of the agitator in the flocculation basin, rotation speed of the agitator in the flocculation basin, information on the shape of the agitator in the flocculation basin, injection rate of coagulant, particle size of sand in the filter bed, information on the shape of the sand in the filter bed, and thickness of the sand layer, until a predetermined control target value is achieved;
A coagulant injection control method for controlling the injection of the coagulant using the minimum coagulant injection rate calculated using predicted values of the treated water turbidity and the rate of increase in head loss in the filtration treatment equipment that achieves the management target value.