Coagulant injection control method and coagulant injection control device

Abstract

To provide a flocculant injection control method and a flocculant injection control device which perform injection control of flocculant properly.SOLUTION: A flocculant injection control device according to an embodiment comprises: a flocculation / settlement processing prediction part 61 that calculates predicted values of turbidity of treated water and of the number of particles in suspended matters in a flocculation / settlement processing facility; a filtration processing prediction part 62 that calculates predicted values of turbidity of treated water and of rise velocity of lost water head in a filtration processing facility; an evaluation part 63 that makes the flocculation / settlement processing prediction part 61 and the filtration processing prediction part 62 calculate the predicted values repeatedly while changing search parameters, until the predicted values output from the filtration processing prediction part 62 reach a preset management target value, and outputs the predicted values of turbidity of treated water and of the rise velocity of loss water head in the filtration processing facility in which the predicted values attain the management target value; and a flocculation injection control part 64 that performs injection control of flocculant, using a minimum flocculant injection rate calculated using the predicted values of the turbidity of treated water and of the rise velocity of the lost water head in the filtration processing facility in which the predicted values attain the management target value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a method and an apparatus for controlling coagulant injection. [Background technology]

[0002] Solid-liquid separation, which removes solids from water, plays an important role in the treatment of drinking water, sewage, industrial wastewater, and other water resources. The most commonly used solid-liquid separation process involves adding a coagulant to aggregate fine solids in the water, followed by filtration, either directly or after a sedimentation process. For example, in water purification plants, coagulants are added to raw water to aggregate fine suspended particles, forming aggregates called flocs. Flocs that grow to sizes ranging from a few millimeters to a few centimeters have a high settling rate and can be separated and removed by sedimentation. The clear supernatant water is then passed through a sand filter, which removes any remaining fine suspended particles and flocs, resulting in water with extremely low turbidity that meets drinking water quality standards.

[0003] 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 are not fully precipitated during the coagulation-sedimentation process and are instead fed to the subsequent filtration process, accelerating head loss in the filter and resulting in increased backwash frequency. Furthermore, fine suspended components are not fully removed in the filter, resulting in insufficiently filtered water being sent to the subsequent filtration process. Therefore, the general method is to appropriately adjust the amount of coagulant injected during the coagulation-sedimentation process, manage the coagulation process to achieve optimal treatment, and then send the water to the subsequent filtration process. Therefore, various methods have been proposed for controlling coagulant injection.

[0004] 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 flocculation state of the flocs is evaluated based on the results, and the injection of a flocculant is controlled accordingly. This makes it possible to achieve operation under appropriate flocculation conditions based on the water quality characteristics of the raw water.

[0005] Furthermore, for example, Patent Document 2 proposes a method for adjusting the filtration speed per filter unit to fall within a certain range when the amount of raw water changes in a gravity filter. By returning treated water to the raw water, the treatment amount can be kept constant, enabling stable filtration operation to be maintained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-054603 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-045448 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, many methods have been proposed for optimizing the operation of the coagulation-sedimentation process and the filtration process separately, but no method has been proposed for operating both processes together. In actual operation, because operational management is performed to optimize the coagulation-sedimentation process, there is a margin of capacity in the filtration process, and little suspended solids are removed by the filter bed, resulting in little increase in head loss in the filter bed. In such cases, backwashing is required every certain period of time to suppress the growth of microorganisms in the filter bed, even if the head loss is sufficiently low. For example, if both the coagulation-sedimentation process and the filtration process could be treated as a single process and operational management could be performed to share some of the processing load with the filtration process, the burden on the coagulation-sedimentation process could be reduced, enabling operation that minimizes the amount of coagulant used.

[0008] The embodiments of the present invention have been made in consideration of the above circumstances, and an object of the present invention is to provide a coagulant injection control method and a coagulant injection control device that perform appropriate control of coagulant injection. [Means for solving the problem]

[0009] 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 flocculant injection control device that controls the flocculation and sedimentation treatment facility until the predicted values ​​output from the filtration treatment prediction unit reach a predetermined management target value. At least one of the following information was used: 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, coagulant injection rate, particle size of the sand in the filter layer, information on the shape of the sand in the filter layer, and thickness of the sand layer. The system is equipped with a filtration treatment prediction value evaluation unit that changes parameters to repeatedly cause the coagulation sedimentation treatment prediction unit and the filtration treatment prediction unit to calculate predicted values, 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 value, 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 value. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration example of a flocculant injection control device according to a first embodiment. [Figure 2] FIG. 2 is a flowchart illustrating an example of a method for controlling coagulant injection according to an embodiment. [Figure 3] FIG. 3 is a diagram schematically illustrating a configuration example of a flocculant injection control device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 a configuration example of a flocculant injection control device according to a 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.

[0012] 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. The 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 a 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 be equipped with 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 a coagulant injection control device 60.

[0013] The water to be treated is sent 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 may be an aluminum-based inorganic flocculant such as polyaluminum chloride (PAC) or aluminum sulfate. Of these, PAC is mainly used in water purification plants. The flocculant injection equipment 50 adjusts the amount of flocculant to be 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.

[0014] 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 the 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.

[0015] 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 so that the mixing intensity gradually decreases 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 settling basin 40.

[0016] In the settling tank 40, the water supplied from the flocculation tank 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 tank 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 tank 40 are discharged as sludge to a wastewater tank. For example, an inclined plate may be placed in the settling tank 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 sludge basin water level. In this case, the measurement results of the measuring device S10 may be supplied to the coagulant injection control device 60.

[0017] A water quality meter S4 is attached to 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 solid particle count of the water (water to be treated) discharged from the sedimentation tank 40, 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 be measured by a water quality meter S5 attached to 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 the water quality meter S5 is attached, and it is sufficient that either the water quality meter S4 or the water quality meter S5 is attached downstream of the coagulant injection position.

[0018] 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 in a purified water distribution reservoir (not shown) and then distributed to distribution pipes. The wastewater generated when washing 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. A measuring device S11 for measuring the water level of the drainage pond may be attached to the drainage pond. In this case, the measurement results of the measuring device S11 can be supplied to the coagulant injection control device 60.

[0019] 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. The flow meter S6 measures the flow rate of the water to be treated flowing into the filter basin 70. The flow meter S9 measures the flow rate of the water to be treated discharged from the filter 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.

[0020] 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). Note that 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.

[0021] The coagulant injection control device 60 is, for example, a computing device including at least one processor and a memory storing a program executed by the processor. The coagulant injection control device 60 can realize various functions by software or a combination of software and hardware.

[0022] 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.

[0023] The coagulation and sedimentation treatment prediction unit 61 uses, for example, information on the quality of the water inflowing into the mixing basin and information on operation as search parameters to calculate the growth state of flocs (for example, the size of the flocs (volume, maximum diameter, minimum diameter) under the conditions of the input information, the size of growth per unit time, etc.), and based on the calculated growth state of the flocs, calculates predicted values ​​for the amount of suspended matter (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 particles of suspended matter to be settled and separated.

[0024] As information on the quality of the influent water to the mixing basin, at least one piece of information such as the turbidity of the raw water, the number of particles of suspended solids, pH, water temperature, etc. can be used. Note that if the information on the quality of the influent water to the mixing basin includes, for example, the zeta potential of the raw water, the zeta potential of the mixing basin water after coagulant injection, or an alternative indicator of the charge state of suspended solids such as streaming potential (or streaming current), the coagulation-sedimentation treatment prediction unit 61 can more accurately calculate the growth state of flocs. Furthermore, as information on operation, at least one piece of information such as the 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 injection rate of the coagulant can be used.

[0025] The filtration treatment prediction unit 62 includes a turbidity removal amount calculation unit 621 and a head loss calculation unit 622, which will be described later, and calculates predicted values ​​for the turbidity of the filtered water and the rate of increase in head loss in the filtration treatment equipment using information on the quality of the water inflowing into the filtration basin and operational information. Information on the quality of the water inflowing into the filtration basin can be, for example, at least one of the following: the turbidity (predicted value) of the sedimentation treatment water in the coagulation sedimentation treatment equipment, the number of suspended solid particles (predicted value), pH, water temperature, etc. Information on the operation can be, for example, at least one of the following: 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, and injection rate of coagulant.

[0026] The filtration treatment predicted value evaluation unit 63 compares a predetermined control target value with the predicted value output from the filtration treatment prediction unit 62, 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 / 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 / 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.

[0027] 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 filter basin to the coagulant injection control unit 64. If there are multiple sets of predicted values ​​smaller than the control target value, the filtration treatment prediction value evaluation unit 63 may output, for example, the predicted value whose predetermined value is the smallest among the multiple sets of predicted values. 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 filter basin include GA (genetic algorithm) and linear programming. Note that the optimization calculation speed is preferably set so that it is completed within a predetermined time (for example, within 30 seconds).

[0028] The coagulant injection control unit 64 calculates the minimum coagulant injection rate that achieves the predicted value of the turbidity of the filtered water output from the filtration treatment predicted value evaluation unit 63 and the predicted value of the rate of increase of the head loss of the filtration tank, and outputs the calculated value of the coagulant injection rate (information specifying the injection amount) to the coagulant injection equipment 50.

[0029] 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 method for controlling coagulant injection 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).

[0030] The filtration treatment prediction unit 62 calculates a predicted value of the turbidity of the filtered water and a predicted value of the rate of rise in head loss of the filtration basin from information on the quality of the water inflowing into the filtration basin and information on operation (step S2).

[0031] The turbidity removal amount calculation unit 621 calculates the amount of suspended matter removed from the water and calculates the turbidity of the filtered water based on the following formula by Iwasaki, which assumes that turbidity is removed at a constant rate as the treated water passes through the filter layer of the filtration tank 70.

[0032]

number

[0033] 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 of the filter bed, sand layer thickness, and coagulant injection rate.When calculating, the turbidity removal amount calculation unit 621 calculates λ using ε at that time (the time of calculation), calculates the turbidity of the filtered water, and, assuming that the inflow water quality information and operation information at that time will continue, calculates the turbidity of the filtered water for the next few hours as the calculation result, taking into account the changes in ε and λ over time.

[0034] 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.

number

[0035] The head loss calculation unit 622 calculates the above formula using the void fraction ε of the filter bed, which changes with time, calculates the change in pressure loss Δp over time, and outputs the rate of increase in head loss over the next few hours as the calculation result.

[0036] 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 head loss of the filtration basin from information on the current quality of the water inflowing into the filtration basin and information on operation.

[0037] 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 control 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 control target value, and changing the search parameters until a predicted value smaller than the control target value is obtained, causing the coagulation sedimentation treatment prediction unit 61 and the filtration treatment prediction unit 62 to repeatedly calculate the predicted value. When a predicted value smaller than the control target value is obtained, the filtration treatment predicted value evaluation unit 63 outputs the predicted value to the coagulant injection control unit 64. Methods that can be used to optimize the turbidity of the sedimentation treatment water include GA (genetic algorithm) and linear programming.

[0038] The flocculant injection control unit 64 calculates the flocculant injection rate that realizes the predicted value output from the filtration treatment predicted value evaluation unit 63, and performs flocculant injection control 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.

[0039] In feedforward control, a similar idea can be applied, for example, to multiple cases, such as when the predicted value output from the filtration treatment predicted value evaluation unit 63 is high or low, by setting coefficients in the coagulant injection rate calculation formula for feedforward control.

[0040] When performing feedback control, the coagulant injection control unit 64 can continuously measure the charge neutralization status of the surface charge of suspended solids in the raw water by adding a coagulant while measuring, for example, the zeta potential and streaming potential (or streaming current) of the water exiting the mixing area after the addition of a coagulant. 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. Therefore, charge neutralization by the coagulant 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 ​​are set to slightly negative values. A control period of approximately 1 to 10 minutes is desirable.

[0041] As described above, according to the coagulant injection control method and coagulant injection control device of this embodiment, it is possible to predict the processing results in the coagulation and sedimentation process and the filtration process, and based on the predicted results, calculate a target value for the treated water quality in the coagulation and sedimentation process that allocates an appropriate processing load to the filtration process.By operating the coagulant injection control based on the calculated target value, it is possible to achieve an operation in which the total coagulant injection rate is reduced compared to the coagulant injection rate that always ensures optimal processing in the coagulation and sedimentation process, while maintaining the same level of turbidity, which is the treated water quality in the filtration process.

[0042] 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.

[0043] 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. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and will not be described again.

[0044] 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.

[0045] 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.

[0046] The feedback control unit 66 has a function of feedback-controlling the coagulant injection so that the target value is reached, using as an index the measurement value of the water quality meter S3 that measures the charge state of suspended solids in the water after coagulant injection. Note that the charge state of suspended solids in the water after coagulant injection measured by the water quality meter S3 may be an alternative index of the charge state of suspended solids, such as the zeta potential or streaming potential (or streaming current) of the mixing basin water.

[0047] Before coagulant injection, suspended solids in the water are negatively charged and repel each other. Because coagulants contain aluminum, which has a positive charge, the injection of the coagulant neutralizes the charges, weakening the repulsive forces between the 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.

[0048] The feedback control unit 66 utilizes the above-mentioned properties to calculate the coagulant injection rate through feedback control, using the charge state of suspended solids in the water as an index. For example, the feedback control unit 66 measures the zeta potential and streaming potential (or streaming current) of the mixing area outlet water, and continuously measures the charge neutralization state of the surface charges of suspended solids in the raw water through coagulant injection, and calculates the coagulant injection rate through feedback control.

[0049] The injection rate determination unit 65 calculates an optimal value for the coagulant injection rate from the minimum coagulant 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 coagulant injection rate obtained by feedback control in the feedback control unit 66. The injection rate determination unit 65 controls the coagulant injection rate based on the optimal value. Specifically, to prevent under-injection of coagulant, the injection rate determination unit 65 normally uses the output value of the coagulant injection control in the feedback control as the optimal injection rate, and only when the minimum coagulant 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, does it adopt the minimum coagulant injection rate as the optimal injection rate.

[0050] As described above, according to the flocculant injection control method and device of this embodiment, it is possible to predict the processing results in the coagulation sedimentation process and the filtration process, and by operating flocculant injection control that allocates an appropriate processing load to the filtration process based on the predicted results, it is possible to reduce the total flocculant injection rate compared to the coagulation sedimentation process at which optimal processing is always achieved, while maintaining the same level of turbidity, which is the treated water quality in the filtration process.

[0051] 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.

[0052] Although 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 can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0053] 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...turbidity removal amount calculation unit, 622...head loss calculation unit, 63...filtration treatment prediction 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 measurement device, S2-S5...water quality meter

Claims

1. 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 equipment; 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.

2. 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.

3. The coagulant injection control device according to claim 1 , wherein the filtration treatment equipment includes a filter layer filled with a filter medium.

4. 4. The coagulant injection control device according to claim 3, wherein the filtration treatment prediction unit calculates predicted values ​​of the turbidity of the treated water and the rate of rise of 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 number of particles 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, the particle diameter of the filter material contained in the filtration layer, shape information of the filter material, the layer thickness of the filtration layer, and the injection rate of the coagulant.

5. 2. The coagulant injection control device according to claim 1, wherein the filtration treatment prediction unit calculates the turbidity of the treated water in the filtration treatment equipment and the rate of increase of the head loss using at least one of the turbidity of the inflow water to the filtration treatment equipment, the number of particles 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.

6. The flocculant injection control device according to claim 1 , wherein the flocculant injection control unit calculates the injection rate of the flocculant using an electric charge state of suspended solids contained in the treated water after the flocculant injection as an index.

7. 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 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.

Images