JP7592405B2 - Membrane Differential Pressure Control Device - Google Patents

Description

An embodiment of the present invention relates to a membrane differential pressure control device.

In water treatment processes, solid-liquid separation techniques such as sedimentation and filtration to separate solids and liquids are frequently used. In particular, in the field of water purification, membrane separation processes using membranes are becoming increasingly popular due to their reliable removal of protozoa such as Cryptosporidium and bacteria. Membrane separation processes have advantages over other solid-liquid separation processes in terms of space saving and stability of treated water quality.

On the other hand, when using solid-liquid separation technology, not only the initial cost but also the running cost should be considered, and there is a growing technical need to reduce the running cost of membrane separation processing. A characteristic phenomenon in membrane separation processing is clogging of the membrane (membrane fouling). As the membrane fouling phenomenon progresses, the energy required for filtration by pressurization or suction changes. In addition, in order to suppress the membrane fouling phenomenon, backwashing in which water or air is passed in the opposite direction to the filtration direction, physical cleaning such as aeration cleaning of the membrane surface, and chemical cleaning with chemicals are performed. Therefore, the running cost includes the electricity cost and chemical cost required for these. In other words, the electricity cost and chemical cost change depending on the operation and control. However, with conventional control, there were cases where the running cost was not reduced to the maximum due to membrane fouling.

In membrane separation processes, membrane separation processes are generally operated based on physical measurements such as transmembrane pressure (transmembrane pressure). In the period immediately following membrane replacement or chemical cleaning, the transmembrane pressure rises slowly, but as fouling progresses, the rate at which the transmembrane pressure rises increases. The rate at which the transmembrane pressure rises (fouling) varies depending on the quality of the raw water, the pretreatment conditions of the membrane separation process, and the membrane surface cleaning method. Therefore, if the transmembrane pressure suddenly rises and the pretreatment conditions or membrane surface cleaning method are changed, it is difficult to suppress the rise in pressure difference, and there is a risk of membrane filtration operation becoming unstable.

To solve the problems mentioned above, a control technology has been proposed that predicts the fouling phenomenon using a transmembrane pressure difference model to appropriately control the cleaning air volume and minimize running costs such as electricity and chemical costs. With the proposed technology, the increase in transmembrane pressure can be suppressed by actively changing the cleaning air volume as a control operation variable, and energy can be saved when the increase in transmembrane pressure is small. Because the cleaning air is generated by a blower installed in the membrane filtration device, it was possible to predict future transmembrane pressure differences from the transmembrane pressure differences inside the membrane filtration device and change the cleaning method for the membrane surface.

JP 2019-25437 A

Generally, membrane separation treatment processes are often installed divided into multiple lines. This is because each membrane separation treatment process has a spare line so that the overall processing volume does not need to be changed if it is forced to stop operating due to cleaning, malfunction, or membrane replacement. By designing in this way, even if one of the multiple lines is taken out of operation, the processing volume of the other lines can be temporarily increased, making it possible to carry out maintenance such as cleaning and membrane replacement while maintaining the overall processing volume.

On the other hand, the pretreatment process may also be divided into multiple lines, but depending on the design conditions, the number of lines in the pretreatment process may differ from the number of lines in the membrane separation process. In particular, the chemical injection point in the pretreatment process is often only one, rather than multiple, in order to keep installation costs down. As described above, since the number of lines in the membrane separation process and the number of pretreatment processes do not necessarily correspond one-to-one, it has been difficult to change the pretreatment conditions depending on the rate at which the transmembrane pressure rises in the membrane filtration device.

The embodiment of the present invention was made in consideration of the above circumstances, and aims to provide a membrane differential pressure control device that minimizes the running costs of a water treatment process.

A transmembrane pressure control device according to an embodiment is a device for controlling a transmembrane pressure of a separation membrane in a water treatment process including a plurality of membrane filtration devices each having a separation membrane for separating a solid contained in the liquid from the liquid, and a pretreatment device for injecting a chemical into a liquid flowing into at least some of the membrane filtration devices, the device including a target resistance value calculation unit that calculates a target resistance value of the separation membrane during a chemical cleaning period from the start to the end of use of the separation membrane, using a transmembrane pressure upper limit value of the separation membrane and a chemical cleaning period from the start to the end of use of the separation membrane, so that the membrane resistance value of the separation membrane at the end of the chemical cleaning period becomes the membrane resistance value at the transmembrane pressure upper limit value; The system includes a pretreatment condition control unit that calculates a required chemical injection rate of the chemical for each of several series of membrane filtration devices so that an actual resistance value, which is the resistance value when a liquid passes through the separation membrane, follows the target resistance value, and a pretreatment condition integration unit that determines the chemical injection rate of the chemical to be injected from the pretreatment device to the liquid using the multiple required chemical injection rates supplied from the pretreatment condition control unit, wherein the pretreatment condition integration unit determines the chemical injection rate to be the maximum, average or median of the multiple required chemical injection rates, or the average of values obtained by weighting the multiple required chemical injection rates according to the priorities of the multiple membrane filtration devices .

FIG. 1 is a schematic diagram showing an example of a water treatment process including a membrane separation treatment process in which solid-liquid separation is performed using a separation membrane. FIG. 2 is a diagram showing an example of a target value of membrane resistance, and actual and predicted values of membrane resistance during a chemical cleaning period. FIG. 3 is a diagram illustrating a schematic configuration example of a water treatment process including the transmembrane pressure difference control device of the first embodiment. FIG. 4 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the second embodiment. FIG. 5 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the third embodiment. FIG. 6 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the fourth embodiment. FIG. 7 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the fifth embodiment. FIG. 8 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the sixth embodiment. FIG. 9 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the seventh embodiment. FIG. 10 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the eighth embodiment.

Hereinafter, a transmembrane pressure difference control device according to a number of embodiments will be described with reference to the drawings.
First, a water treatment process including one membrane separation treatment process will be taken as an example to explain matters common to a number of embodiments. Here, the operation of membrane pressure difference control to suppress clogging (fouling) during solid-liquid separation using a separation membrane will be explained, without taking into account the operating state of the pretreatment process.

FIG. 1 is a schematic diagram showing an example of a water treatment process including a membrane separation treatment process in which solid-liquid separation is performed using a separation membrane.
The water treatment process shown in Fig. 1 includes a pretreatment process and a membrane separation process. In the water treatment process, raw water passes through a pretreatment device 20 that performs the pretreatment process, and then flows through a membrane filtration device in the membrane separation process, and is discharged as membrane filtered water.

The membrane filtration apparatus includes a membrane filtration tank 10 including a separation membrane that separates solids contained in a liquid from the liquid, a pump (not shown), a cleaning blower B, and a control unit 100. The separation membrane is housed in the membrane filtration tank 10 and is disposed in a flow path within the membrane filtration apparatus.
The pump generates a flow of water to be filtered by the separation membrane. The water that has passed through the pretreatment device 20 is passed through the membrane filtration device by the pump and discharged as membrane-filtered water through the separation membrane. Note that, depending on the structure of the separation membrane, suction filtration or pressure filtration may be performed, so the structure of the pump differs depending on the structure of the separation membrane.

The cleaning blower B blows out air to clean and diffuse the surface of the separation membrane. The control unit 100 may, for example, control the cleaning air volume of the cleaning blower B at a constant volume, or may actively change the cleaning air volume of the cleaning blower B as a control operation variable to control the membrane pressure difference of the separation membrane. In addition, a flowmeter F for measuring the processing volume of the membrane filtered water and a pressure gauge P for monitoring the state of the membrane may be installed as measuring instruments. In addition, a water thermometer T may be installed because the water permeability of the separation membrane changes depending on the water temperature.

The increase in transmembrane pressure obtained from the pressure gauge P is affected not only by membrane fouling but also by the viscosity of the fluid and the filtration flow rate. In general, the transmembrane pressure ΔP can be expressed by the following basic equation (1) of membrane filtration, and can be expressed as the product of the fluid viscosity μ, the membrane resistance R, and the transmembrane filtration flux J (the transmembrane filtration flow rate divided by the membrane cross-sectional area).
The fluid viscosity μ is largely dependent on the water temperature, and the fluid viscosity μ may be referred to as a temperature correction factor (TCF).

Considering the behavior of the transmembrane pressure difference using the above basic equation (1) of membrane filtration, the membrane resistance R, which indicates a value that changes substantially due to the membrane fouling phenomenon, can be expressed by the following equation (2).

Because the membrane resistance R may take an extremely small value depending on the unit system of physical quantities used, in such cases it can be calculated by multiplying it by a certain coefficient so that it is approximately the same magnitude as other physical quantities. In a membrane separation treatment process, the fouling phenomenon progresses over time, so the membrane resistance R increases monotonically during the operation period accordingly. When the membrane resistance increases, the transmembrane pressure difference ΔP also increases accordingly, unless there is a change in the membrane filtration flux J or fluid viscosity μ. When the membrane resistance reaches a certain upper limit, it is necessary to restore function by chemical cleaning and reduce the membrane resistance again.

The control unit 100 can, for example, determine the cleaning air volume for the separation membrane and control the cleaning blower B so that the current value of the membrane resistance R or the future predicted value of the membrane resistance R follows a predetermined target value of the membrane resistance (target resistance value).

The control unit 100 has at least one processor and a memory in which a program executed by the processor is recorded, and can control the cleaning blower B by software or a combination of software and hardware.

FIG. 2 is a diagram showing an example of a target value of membrane resistance, and actual and predicted values of membrane resistance during a chemical cleaning period.
The curve that becomes the target resistance value can be derived from the desired chemical cleaning period and the upper limit of the transmembrane pressure at the start of membrane filtration operation (e.g., the first operation after membrane replacement). That is, the target resistance value for the period from the start of operation to the end of the chemical cleaning period is set so that the membrane resistance value at the end of the chemical cleaning period is the membrane resistance value at the upper limit of the transmembrane pressure.

The actual resistance, which is the actual value of the membrane resistance, can be calculated using equation (2) by converting the values measured by the pressure gauge P, flow meter F, and water temperature gauge T. The actual cleaning air volume can be determined based on the magnitude of deviation between the target resistance value and the predicted resistance value. If the difference between the target resistance value and the predicted resistance value is large, the predicted resistance value, which is the predicted value of the membrane resistance, is smaller than the target, so the cleaning air volume can be made smaller than when the target resistance value is used. Conversely, if the difference between the target resistance value and the predicted resistance value is a negative value (target resistance value - predicted resistance value < 0), the predicted resistance exceeds the target resistance, so it is possible to control the cleaning air volume to be larger than when the target resistance value is used in order to suppress the increase in membrane pressure difference.

The predicted resistance value, which is the future value of the transmembrane pressure difference, can be calculated by a prediction formula that uses the measured values of sensors installed in the membrane separation treatment process or pretreatment process as inputs. For example, in the configuration of Figure 1, in addition to the cleaning air volume, water quality information such as hydrogen ion concentration (pH) measured in the pretreatment process and the chemical injection rates of activated carbon, coagulants, etc. correspond to the inputs of the prediction formula.

As described above, if the operating conditions of the pretreatment process affect the prediction of the membrane resistance, it can be said that it is possible to suppress the increase in membrane resistance by manipulating the operating conditions of the pretreatment process. On the other hand, for example, in the case of a membrane separation treatment process having a plurality of membrane filtration units, the pretreatment unit 20 and the membrane filtration unit do not necessarily correspond one-to-one, so that the same control method as in the case of a single unit may not be applicable.
Hereinafter, a transmembrane pressure difference control device that controls the transmembrane pressure difference using an actual value and a target value of the membrane resistance in a membrane separation treatment process having a plurality of lines will be described.

FIG. 3 is a diagram illustrating a schematic configuration example of a water treatment process including the transmembrane pressure difference control device of the first embodiment.
For the sake of explanation, Fig. 3 shows an example of a water treatment process including two membrane filtration systems (first and second systems) and a pretreatment system 20 having one chemical injection point. Note that the number of membrane filtration systems is not limited to the number shown in the figure, and the number of membrane filtration system systems may be two or more, and the chemical injection point may be multiple or different from the number of membrane filtration system systems.

In the water treatment process shown in FIG. 3, the raw water passes through a pretreatment device 20, branches off and flows through a first line of membrane filtration devices and a second line of membrane filtration devices in the membrane separation treatment process, and is discharged from each line as membrane filtered water.

The pretreatment device 20 is equipped with a detector for detecting organic indicators (TOC (total organic carbon), Tu (turbidity), UV (ultraviolet), EEM (excitation-emission matrix)), a detector for detecting hydrogen ion exponent (pH), a chemical (chlorine, activated carbon, coagulant) injection section 24, and a pretreatment condition integration section 21.

The first series of membrane filtration devices includes a membrane filtration tank 11 in which a separation membrane is housed, a pump (not shown), a cleaning blower B1, a water temperature gauge T1, a pressure gauge P1, a flow meter F1, and a control unit 101. The separation membrane is housed in the membrane filtration tank 11 and is disposed in the water flow path of the membrane filtration device.

The second series of membrane filtration equipment includes a membrane filtration tank 12 in which a separation membrane is housed, a pump (not shown), a cleaning blower B2, a water temperature gauge T2, a pressure gauge P2, a flow meter F2, and a control unit 102. The separation membrane is housed in the membrane filtration tank 12 and is disposed in the water flow path of the membrane filtration equipment.

The membrane differential pressure control device of this embodiment includes at least a control unit 101, a control unit 102, and a pretreatment condition integration unit 21. The membrane differential pressure control device includes at least one processor and a memory in which a program executed by the processor is recorded, and can realize various operations by software or a combination of software and hardware.

Because the first and second series membrane filtration devices have the same configuration, the configuration of the first series membrane filtration device will be described below, and a description of the second series membrane filtration device will be omitted.

The pump generates a flow of water that is filtered by the separation membrane. The water that has passed through the pretreatment device 20 is passed by the pump to the membrane filtration device, where it passes through the separation membrane and is discharged as membrane-filtered water. Depending on the structure of the separation membrane, suction filtration or pressure filtration may be used, so a pump with an appropriate structure is used depending on the structure of the separation membrane.

The cleaning blower B1 blows out air for cleaning and dispersing the surface of the separation membrane. In this embodiment, the cleaning blower B1 is controlled by the control unit 101 so as to blow out air at a predetermined volume.
The flow meter F1 measures the amount of the membrane-filtered water being processed. The value measured by the flow meter F1 is supplied to the control unit 101.

The pressure gauge P1 measures the transmembrane pressure difference (transmembrane pressure difference) from the pressure on the primary side and the pressure on the secondary side of the separation membrane to monitor the state of the separation membrane. The value measured by the pressure gauge P1 is supplied to the control unit 101.

The water thermometer T1 measures the temperature of the membrane filtered water because the water permeability of the separation membrane changes depending on the water temperature. The value measured by the water thermometer T1 is supplied to the control unit 101. Note that the water thermometer T1 is included in each of the first and second series, but a water thermometer that measures the water temperature after passing through the pretreatment device 20 and before branching into each series may be provided in one location. In that case, the water temperature in the first and second series will be a common value.

The control unit 101 includes an actual resistance calculation unit 111 , a target resistance calculation unit 112 , and a pre-processing condition control unit 113 .
The actual resistance calculation unit 111 can obtain the measured values from the water temperature gauge T1, the pressure gauge P1, and the flow meter F1, and calculate the membrane resistance (actual resistance value) R by the above-mentioned formula (1) and formula (2). The actual resistance value is the resistance value when the liquid permeates the separation membrane. The transmembrane pressure difference ΔP can be expressed by the above-mentioned basic formula (1) of membrane filtration, and the transmembrane pressure difference ΔP can be expressed as the product of the fluid viscosity μ, the membrane resistance R, and the membrane filtration flux J (the membrane filtration flow rate divided by the membrane cross-sectional area). In addition, the membrane resistance R can be expressed by the above-mentioned formula (2).

The target resistance calculation unit 112 calculates the target resistance value from the upper transmembrane pressure difference upper limit, the chemical cleaning period, and the water temperature after the cleaning period. The curve that gives the target resistance value can be derived from the desired chemical cleaning period and the upper limit of the transmembrane pressure difference at the start of operation of the membrane filtration device (e.g., the first time the device is operated after membrane replacement). In other words, the target resistance value for the period from the start of operation to the end of the chemical cleaning period is set so that the membrane resistance value at the end of the chemical cleaning period is the membrane resistance value at the upper limit of the transmembrane pressure difference.

The pretreatment condition control unit 113 changes the operating conditions of the pretreatment device 20 based on the deviation between the target resistance value and the actual resistance value. The pretreatment condition control unit 113 can, for example, increase or decrease the chemical injection rate, increase or decrease the stirring speed of the stirrer in the chemical mixing tank, or increase or decrease the flow rate of the pretreatment device 20 to control the residence time, as operating conditions of the pretreatment device 20.

For example, when the pretreatment condition control unit 113 decides to increase or decrease the chemical injection rate, since injecting chemicals generally has the effect of removing turbidity and the like that can cause membrane fouling, if the actual membrane resistance value is greater than the target membrane resistance value, the chemical injection rate can be increased, and if the actual membrane resistance value is less than the target membrane resistance value, there is still room to increase the membrane resistance, so the chemical injection rate can be decreased in order to reduce chemical costs.

Even if the pretreatment condition control unit 113 controls the stirring speed of the stirrer (not shown) or the flow rate of the pretreatment device 20, these are factors that contribute to electricity costs and chemical costs, so costs can be optimized by changing the operating conditions of the pretreatment device 20 in response to changes in membrane resistance.

In this embodiment, the pretreatment condition control unit 113 will be described using PID control (Proportional-Integral-Derivative Control) as an example of a feedback control method that utilizes the deviation between the actual membrane resistance value and the target resistance value, but is not limited to this example. The pretreatment condition control unit 113 may also determine whether to increase or decrease the chemical injection rate by comparing the magnitude of the actual membrane resistance value with the target resistance value.

In this embodiment, the pretreatment condition control unit 113 calculates the chemical injection rate from the actual membrane resistance value and the target membrane resistance value of the membrane filtration device of the first series so that the actual membrane resistance value tracks the target membrane resistance value, and calculates the required chemical injection rate as the required value for the target series.

Similarly, the pretreatment condition control unit 123 calculates the chemical injection rate from the actual membrane resistance value and the target membrane resistance value of the second series membrane filtration device so that the actual membrane resistance value tracks the target resistance value, and calculates the required chemical injection rate as the required value.

The pre-processing condition integration unit 21 obtains required values from the pre-processing condition control unit 113 of the first series and the pre-processing condition control unit 123 of the second series.
The pretreatment condition integration unit 21 may, for example, set the maximum value of the chemical injection rate requested by the membrane filtration devices of each series as the chemical injection rate to be actually injected, based on a conservative viewpoint of minimizing the increase in transmembrane pressure difference.

In addition, if it is desired to equalize the increase in membrane pressure difference of multiple series of membrane filtration devices, the pretreatment condition integration unit 21 may set the actual chemical injection rate to a representative value such as the average, median, or trim mean value of multiple chemical injection rates obtained as required values.

In addition, for example, if there is a membrane filtration device in a series that is to be prioritized, the pretreatment condition integration unit 21 may calculate a weighted average of multiple chemical injection rates, with the priority expressed as a weight, and use this as the chemical injection rate to be actually injected. For example, if the membrane filtration flow rate differs for each series, the flow measurement value (or a preset flow rate value) may be used as the weight.

As described above, the pretreatment conditions (chemical injection rate) required by the pretreatment condition control units 113, 123 are calculated from information on the actual membrane resistance values and target resistance values of the membrane filtration devices in multiple series, and these are integrated by the pretreatment condition integration unit 21, making it possible to optimize costs for a membrane separation treatment process having multiple series that do not correspond one-to-one to the pretreatment device 20. In addition, by appropriately selecting the processing of the pretreatment condition integration unit 21, it is possible to provide a function for adjusting the increase in membrane resistance of the membrane filtration device between each series.

Therefore, according to this embodiment, it is possible to provide a membrane differential pressure control device that appropriately controls the pretreatment conditions and minimizes the running costs, such as the electricity costs and chemical costs, required for the water treatment process.

Next, a transmembrane pressure difference control device according to a second embodiment will be described in detail with reference to the drawings.
In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, the pretreatment condition integration unit 21 differs from the first embodiment described above in that it has a function of switching the integration method of the required values obtained from multiple membrane filtration processes depending on the conditions. In this embodiment, by switching the integration method in the pretreatment condition integration unit 21, it is possible to further reduce the running costs of the membrane filtration process.

FIG. 4 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the second embodiment.
The transmembrane pressure control device of this embodiment differs from the above-described first embodiment in that a switching condition that serves as a trigger for switching the integration method is input to the pretreatment condition integration unit 21. The switching condition that serves as a trigger for switching the integration method may be due to an event obtained by a comparison of signals or the like, or may be a signal based on time such as a specified time.

It is known that the rate of increase in membrane resistance due to fouling is greater in the latter and final stages than in the initial stage, as shown in Figure 2. For this reason, for example, from the initial point of the chemical cleaning period until a specified period has elapsed, the average value of multiple required values (chemical injection rates) may be set as the actual chemical injection rate to equalize the increase in transmembrane pressure of multiple membrane filtration devices, and after the specified period has elapsed, the maximum value of multiple required values (chemical injection rates) may be set as the actual chemical injection rate to suppress the increase in transmembrane pressure.

In this case, the trigger signal (switching condition) may be, for example, a signal notifying that six months have passed since the start of chemical cleaning, or a signal notifying that the maximum membrane resistance value of the separation membranes of multiple series of membrane filtration devices has exceeded 30 kPa (threshold value), or other time signals or membrane resistance values that serve as a basis for judgment may be used.

The switching condition is not limited to the above, and may be, for example, a signal notifying an abnormal state in which the rate of increase in the membrane resistance value of a separation membrane in a certain series becomes greater than a predetermined threshold value, or a signal notifying an abnormal state in which the quality of the membrane-filtered water has deteriorated. When an abnormal state is notified, the pretreatment condition integration unit 21 prioritizes responding to the abnormality over reducing running costs, and may, for example, set the maximum of the multiple requested chemical injection rates as the chemical injection rate to be actually injected.

The actual resistance calculation units 111 and 121 may monitor the actual resistance value to determine whether the rate of increase in the membrane resistance value is normal, and may notify an abnormal state when it is determined to be abnormal. Regarding the membrane filtrate water quality, a monitoring means for monitoring the membrane filtrate water quality may be provided externally, and an abnormal state may be notified when it is determined to be abnormal by the monitoring means.

As described above, by switching the integration method of the pretreatment condition integration unit 21, it is possible to adjust the increase in membrane resistance of the separation membrane of the membrane filtration device between multiple series in a water treatment process that includes a pretreatment device 20 and a membrane separation treatment process having multiple series, thereby enabling more flexible optimization of costs and water quality.

Furthermore, according to the transmembrane pressure difference control device of this embodiment, when the membrane filtration device is in an abnormal state, it is possible for the pretreatment device 20 to take measures against the abnormality.
Therefore, according to this embodiment, it is possible to provide a transmembrane pressure difference control device that appropriately controls the pretreatment conditions and minimizes the running costs, such as the electricity costs and chemical costs, required for the water treatment process.

Next, a transmembrane pressure difference control device according to a third embodiment will be described in detail with reference to the drawings.
FIG. 5 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the third embodiment.
The transmembrane pressure control device of this embodiment differs from the first embodiment described above in that a second required value (chemical injection rate) determined by control in an external control device is input to the pretreatment condition integration unit 21.

It is desirable to determine the pretreatment conditions taking into consideration not only the state of the separation membrane but also the quality of the raw water and the quality of the membrane filtered water. Therefore, in the membrane differential pressure control device of this embodiment, pretreatment conditions such as the required chemical injection rate from control functions other than the pretreatment condition control units 113 and 123 are integrated in the pretreatment condition integration unit 21.

Pretreatment conditions can be determined based on information about the raw water quality and the membrane-filtered water quality. For example, other control functions include determining the amount of chlorine to be injected based on the chlorine demand amount according to the concentration of ammonia and manganese contained in the raw water, determining the amount of coagulant to be injected based on information about turbidity and organic matter indicators such as the turbidity, color, and ultraviolet absorbance of the membrane-filtered water, and various other control methods are possible.

In the membrane differential pressure control device of this embodiment, the pretreatment condition integration unit 21 integrates the chemical injection rate (second required value) requested by other control functions as described above with the required value from the pretreatment condition control units 113 and 123 to set the actual chemical injection rate.

For example, the pretreatment condition integration unit 21 may set the coagulant injection rate obtained based on the water quality information of the membrane filtered water as one of the required chemical injection rates, and combine it with the coagulant injection rate, which is the required chemical injection rate from the pretreatment condition control units 113, 123 of the multiple membrane filtration device series, to set the maximum value of the multiple required chemical injection rates as the actual chemical injection rate. In this case, if the coagulant injection rate obtained from the water quality information of the membrane filtered water is greater than the coagulant injection rate obtained from the other membrane filtration device series, the membrane filtered water quality is prioritized, and conversely, if the maximum value of the coagulant injection rate obtained from the other membrane filtration device series is greater than the coagulant injection rate obtained from the water quality information, suppression of the transmembrane pressure is prioritized.

In addition to the information on raw water quality and membrane filtration water quality, for example, if there is a membrane filtration series or sand filtration series of other types installed in parallel with the membrane filtration equipment series, the pretreatment conditions recommended for those series may be integrated by the pretreatment condition integration unit 21 as the required pretreatment conditions.

For example, when applying the membrane pressure difference control device of this embodiment to a water treatment process such as a water purification plant, not only is the entire system designed from scratch, but some parts may also be updated, and the treatment methods of the parallel series may differ. In such cases, the membrane pressure difference control device of this embodiment can be used in combination with the control performed in the existing water treatment process.

Even if it is not an upgrade, for example, when it is desired to optimize the entire water treatment process by installing filtration systems in parallel using different filtration methods, the idea of integrating the pretreatment conditions required by the pretreatment condition integration unit 21 in the membrane differential pressure control device of this embodiment is effective.

As described above, according to the membrane differential pressure control device of this embodiment, the actual chemical injection rate can be set by combining conditions calculated based on information on raw water quality and membrane filtered water quality other than membrane resistance, or conditions output by controlling pretreatment conditions of other series, with the required values from the pretreatment condition control units 113 and 123, making it possible to optimize costs and water quality more flexibly.

In other words, this embodiment can provide a membrane differential pressure control device that appropriately controls pretreatment conditions and minimizes running costs, such as electricity costs and chemical costs, required for the water treatment process.

Next, a transmembrane pressure difference control device according to a fourth embodiment will be described in detail with reference to the drawings.
FIG. 6 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the fourth embodiment.

The membrane differential pressure control device of this embodiment differs from the first embodiment described above in that it controls the operating conditions of the membrane filtration device and the operating conditions of the pretreatment process based on membrane resistance information.

The control unit 101 of the membrane filtration device of the first line includes an actual resistance calculation unit 111 , a target resistance calculation unit 112 , a pretreatment condition/air volume control unit 114 , and a subtractor 115 .
The control unit 102 of the membrane filtration device of the second line includes an actual resistance calculation unit 121 , a target resistance calculation unit 122 , a pretreatment condition/air volume control unit 124 , and a subtractor 125 .
Since the first-line membrane filtration device and the second-line membrane filtration device have the same configuration, the following description will be given of the first-line membrane filtration device, and a description of the second-line membrane filtration device will be omitted.

The subtractor 115 calculates the difference obtained by subtracting the actual resistance value calculated by the actual resistance calculation unit 111 from the target resistance value calculated by the target resistance calculation unit 112, and outputs the difference to the pre-processing condition/air volume control unit 114.

The pretreatment condition/air volume control unit 114 calculates and outputs the required value of the pretreatment condition (required value of the chemical injection rate) and the required value of the cleaning air volume, for example by PID control, so that the input values become zero. The required value of the pretreatment condition calculated by the pretreatment condition/air volume control unit 114 is input to the pretreatment condition integration unit 21, and the required value of the cleaning air volume is supplied to the cleaning blower B1.

As described above, by controlling the chemical injection rate and the amount of air washing the separation membrane, the membrane resistance of the separation membrane can be controlled with higher accuracy. For example, when suppressing the membrane resistance of the separation membrane of the entire plurality of membrane filtration devices, it is effective to change the operating conditions of the pretreatment process, but it is difficult to affect only the membrane resistance of the separation membrane of a specific membrane filtration device. In addition, if a difference in the increase in membrane resistance occurs between the plurality of membrane filtration devices for some reason, it is difficult to operate the water treatment process so as to eliminate the difference between the series only by the operating conditions of the pretreatment process. In contrast, the membrane differential pressure control device of this embodiment can control not only the operating conditions of the pretreatment process but also the amount of air washing the separation membrane of each of the plurality of membrane filtration devices, so that the membrane resistance of the separation membrane of the plurality of membrane filtration devices can be individually controlled.

In the above, an example was given of controlling the airflow rate for cleaning the separation membrane as an operating condition of the membrane filtration device. However, if the operating condition of the membrane filtration device is one, the airflow rate for cleaning the separation membrane does not have to be the control target. For example, other operational variables such as the backwash time interval or the timing of sludge discharge may be the control target as an operating condition of the membrane filtration device, and multiple of these may be the control targets.

As described above, this embodiment provides a membrane differential pressure control device that appropriately controls pretreatment conditions and minimizes running costs, such as electricity costs and chemical costs, required for the water treatment process.

Next, a membrane pressure difference control device according to a fifth embodiment will be described in detail with reference to the drawings.
FIG. 7 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the fifth embodiment.

In this embodiment, an example of controlling the membrane filtration flow rate will be described as an example of an operating device for a membrane filtration device. The membrane filtration flow rate is the filtration flow rate of the separation membrane divided (normalized) by the membrane area of the separation membrane. In other words, since the membrane filtration flow rate is the membrane filtration flow rate per unit area of the separation membrane, it can be considered as a load related to the membrane resistance when considering an increase in membrane resistance. In addition, when the membrane areas of the separation membranes of multiple membrane filtration devices are different, the filtration flow rate and the filtration flow rate of each membrane filtration device will not be in the same ratio, but when the membrane areas of each membrane filtration device are equal, it can be considered as the membrane filtration flow rate. The membrane filtration flow rate can be converted to the membrane filtration flow rate by multiplying it by the membrane area.

The transmembrane pressure control device of this embodiment further includes a transmembrane filtration flow rate determining unit 22 .
The control unit 101 of the first-line membrane filtration apparatus includes an actual resistance calculation unit 111, a target resistance calculation unit 112, and a subtractor 115. In the first-line membrane filtration apparatus, the pump PO1 is disposed in the rear stage of the membrane filtration tank 11, and can control the membrane filtration flow rate of the first-line membrane filtration apparatus by sucking in the membrane filtration water. The pump PO1 may be disposed in the front stage of the membrane filtration tank 11.

The control unit 102 of the second-line membrane filtration apparatus includes an actual resistance calculation unit 112, a target resistance calculation unit 122, and a subtractor 125. In the second-line membrane filtration apparatus, the pump PO2 is disposed in the rear stage of the membrane filtration tank 12, and can control the membrane filtration flow rate of the second-line membrane filtration apparatus by sucking in the membrane filtrate. The pump PO2 may be disposed in the front stage of the membrane filtration tank 12.
In this embodiment, the subtractors 115 and 125 output the difference obtained by subtracting the actual resistance value from the target resistance value as the membrane resistance deviation to the membranous filtration flow rate determination unit 22 and the pretreatment condition integration unit 21 .

The membrane filtration flow rate determination unit 22 receives the required filtration volume from the outside and the membrane resistance deviation from the control units 101 and 102. The membrane filtration flow rate determination unit 22 determines the membrane filtration flow rate of each membrane filtration device according to the membrane resistance deviation value while ensuring that the filtration flow rate obtained by the multiple membrane filtration devices satisfies the required filtration volume.

The method of determining the membrane filtration flow rate in the membrane filtration flow rate determination unit 22 may involve allocating the flow rate at a predetermined ratio according to the order of the magnitude of the multiple membrane resistance deviations, or the flow rate may be determined so that the difference between the flow rates allocated to the multiple membrane filtration devices is proportional to the magnitude of the membrane resistance deviation. The membrane filtration flow rates of each of the multiple series of membrane filtration devices determined by the membrane filtration flow rate determination unit 22 are input to the corresponding pumps PO1 and PO2, and the operation of the pumps PO1 and PO2 is controlled to achieve the membrane filtration flow rate of each series.

In this way, by using the membrane resistance deviation to allocate the membrane filtration flow rate, it is possible to lower the membrane filtration flow rate of the membrane filtration series where the transmembrane pressure difference is elevated compared to the target value, thereby equalizing the load, and achieving equalization of the load across the entire water treatment process. In addition, at this time, the necessary flow rate can be guaranteed by determining the membrane filtration flow rate so that the sum of the membrane filtration flow rates, obtained by multiplying each membrane filtration flow rate by the membrane area of the separation membrane, is equal to the required filtration flow rate.

The pretreatment condition integration unit 21 receives the membrane filtration flow rates for the multiple membrane filtration devices from the membrane filtration flow rate determination unit 22 and the membrane resistance deviation calculated by the subtractors 115 and 125. The pretreatment condition integration unit 21 can calculate information about the load of each of the multiple membrane filtration devices according to the membrane filtration flow rate and membrane resistance. In this embodiment, the pretreatment condition integration unit 21 has in advance information about the cleaning period and the target resistance curve for each of the multiple membrane filtration devices, and may be configured to be able to calculate the actual resistance value from the membrane resistance deviation and the target resistance value.

The pretreatment condition integration unit 21 of this embodiment calculates the required value of the pretreatment condition (required value of the chemical injection rate) so that the membrane resistance deviation follows zero, and can set the actual chemical injection rate using, for example, a plurality of membrane filtration flow rates (or loads) as weights or parameters. That is, the transmembrane pressure control device of this embodiment includes the functions of the pretreatment condition control units 113, 124 in the above-mentioned first to fourth embodiments.
In addition, if the control periods of the membranous filtration flow rate determination unit 22 and the pretreatment condition integration unit 21 are about the same length, there may be cases where the operations of the two do not mesh well, so it is preferable to make the control period of the higher-ranking membranous filtration flow rate determination unit 22 longer than the control period of the pretreatment condition integration unit 21. In addition, in cases where there is little variation in the membranous filtration flow rates of the membrane filtration devices, the pretreatment condition integration unit 21 may be configured not to use the value of the membranous filtration flow rate as a weight.

As described above, by using information on membrane resistance to control the operating conditions of the pretreatment process and the membrane filtration flow rate, it is possible to respond to the difference in transmembrane pressure that occurs between multiple series of membrane filtration devices while satisfying the constraints of the required filtration flow rate, making it possible to more flexibly optimize costs and water quality throughout the entire water treatment process.
That is, according to this embodiment, it is possible to provide a transmembrane pressure difference control device that appropriately controls pretreatment conditions and minimizes running costs such as electricity costs and chemical costs required for the water treatment process.

Next, a transmembrane pressure difference control device according to a sixth embodiment will be described in detail with reference to the drawings.
FIG. 8 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the sixth embodiment.
In the transmembrane pressure control device of this embodiment, the configuration of the transmembrane filtration flow rate determining unit 22 is different from that of the fifth embodiment described above.

In this embodiment, the membrane filtration flow rate determination unit 22 receives the purified water reservoir water level and the membrane resistance deviation. For example, the filtration flow rate can be passively determined according to the purified water reservoir water level in which the filtered water that has undergone the water treatment process is stored. When the purified water reservoir water level is lower than the reference water level, the membrane filtration flow rate determination unit 22 can set the required filtration flow rate to be greater than the reference value, and when the purified water reservoir water level is higher than the reference water level, the membrane filtration flow rate determination unit 22 can set the required filtration flow rate to be smaller than the reference value. In this case, it is possible to handle cases where the operable membrane filtration flow rate is not continuous but is a discrete value determined only by starting or stopping the pumps PO1 and PO2. The membrane filtration flow rate when the pump is started corresponds to the rated flow rate divided by the membrane area, and the membrane filtration flow rate when the pump is stopped corresponds to 0.

More specifically, when the purified water reservoir water level is 1 to 2 m, for example, the membrane filtration flow rate determination unit 22 sets the total filtration flow rate to Qm ³ /h. When the purified water reservoir water level is 1 to 2 m, for example, the membrane filtration flow rate determination unit 22 may set the total filtration flow rate to Qm ³ /h, and then calculate the membrane filtration flow rate of each membrane filtration device for that total filtration flow rate, and adjust the purified water reservoir water level to a predetermined value.

Furthermore, when controlling the membrane filtration flow rate by starting and stopping the pump, the membrane filtration flow rate determination unit 22 may change the number of membrane filtration device series that operate the pumps PO1 and PO2 according to the purified water reservoir water level. In this case, compared to the case where the required filtration flow rate is a constraint, the constraint is relaxed when the filtration flow rate of the entire water treatment process is considered based on the purified water reservoir water level, and the water treatment process can be operated more flexibly.
The transmembrane pressure control device of this embodiment is similar to that of the above-described fifth embodiment, except for the configuration of the transmembrane filtration flow rate determining unit 22.

As described above, by controlling the operating conditions and membrane filtration flow rate of the pretreatment device 20 using information on the membrane resistance of the separation membrane and the water level of the purified water reservoir, it is possible to respond to differences in the membrane resistance values between multiple membrane filtration devices, making it possible to more flexibly optimize costs and water quality throughout the entire water treatment process.
That is, according to this embodiment, it is possible to provide a transmembrane pressure difference control device that appropriately controls pretreatment conditions and minimizes running costs such as electricity costs and chemical costs required for the water treatment process.

Next, a transmembrane pressure difference control device according to a seventh embodiment will be described in detail with reference to the drawings.
FIG. 9 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the seventh embodiment.
In the above-mentioned fifth and sixth embodiments, the operating conditions of the pretreatment device 20 (required value of chemical injection rate) were determined after determining the membrane filtration flow rate, but in the membrane differential pressure control device of this embodiment, the operating conditions of the pretreatment process and the membrane filtration flow rates (operating conditions) of multiple series of membrane filtration devices are formulated as an optimization problem and optimized simultaneously.

The transmembrane pressure control device of this embodiment differs from the transmembrane pressure control devices of the fifth and sixth embodiments described above in that it has an operating condition integration unit 23 instead of the membrane filtration flow rate determination unit 22 and the pretreatment condition integration unit 21.

For example, in a water treatment process having two lines of membrane filtration devices, the membrane resistance value at the next step of the control cycle can be formulated as a multiple regression between the PAC (polyaluminum chloride) injection rate and the membrane filtration flow rate (pump power consumption) as shown below.

In the above formula, PAC is the PAC injection rate of the pretreatment process, P _i is the power consumption of the membrane filtration pump of the i series, α is the unit price of PAC, β is the unit price of electricity per unit membrane filtration flow rate, k _ij , a _i , and b _i are regression coefficients that are preset. In addition, R _i is the current membrane resistance of the i series, R _iSV is the membrane resistance target value of the next step of the i series, and m _i is the membrane area of the i series. In this embodiment, the operating condition integration unit 23 may be configured to have information on the cleaning period and the curve of the target resistance value of each of the membrane filtration devices of the multiple series in advance, and to be able to calculate the actual resistance value from the membrane resistance deviation and the target resistance value.

The above optimization problem is written as a linear optimization problem, so it can be solved using methods such as the simplex method or the interior point method. Even if the problem is expanded to a nonlinear one, it can be solved using metaheuristic methods such as simulated annealing or particle swarm optimization. Other chemical injection rates can also be calculated in the same way as the above calculation method for the PAC injection rate.

The increase in the membrane resistance of a separation membrane generally progresses at a speed on the order of hours, so the time required to solve the optimization problem can be at a similar speed (period), and as long as the structure of the transmembrane pressure prediction equation, etc., is not made too complicated, it is considered to be sufficient in terms of calculation processing time.

As described above, by simultaneously optimizing the operating conditions of the pretreatment process and the membrane filtration flow rate using information on the membrane resistance of the separation membrane, it is possible to deal with cases in which differences in the membrane resistance of multiple membrane filtration devices occur, thereby enabling further optimization of the running costs and water quality of the water treatment process.
That is, according to this embodiment, it is possible to provide a transmembrane pressure difference control device that appropriately controls pretreatment conditions and minimizes running costs such as electricity costs and chemical costs required for the water treatment process.

Next, a transmembrane pressure difference control device according to an eighth embodiment will be described in detail with reference to the drawings.
FIG. 10 is a diagram illustrating a schematic configuration example of a water treatment process including a transmembrane pressure difference control device according to the eighth embodiment.
In the transmembrane pressure control device of the first to seventh embodiments described above, the target resistance value and the actual resistance value of the separation membrane are compared to determine the operating conditions of the pretreatment device 20. On the other hand, if the residence time of the treated water in the pretreatment device 20 is long, a time lag occurs between the change in the manipulated variable and the effect on the transmembrane pressure of the separation membrane, so that the change in the manipulated variable due to the control may not be reflected in the result in time. In addition, if the control period is long or the membrane resistance increases quickly, the control may be delayed with respect to the change in the transmembrane pressure. Therefore, in the transmembrane pressure control device of this embodiment, a predicted value of the membrane resistance is used instead of the actual resistance value, and the pretreatment conditions are determined so that the predicted value follows the target resistance value.

In the transmembrane pressure control device of this embodiment, the control units 101 and 102 include resistance change prediction units 116 and 126 and adders 117 and 127 .
The resistance change prediction units 116, 126 determine a predicted resistance change value ΔR that represents the change in membrane resistance after a predetermined period from the actual resistance value. The predetermined period Δt represents the period from the timing when the actual resistance value is calculated to the timing when the resistance value is predicted. The predicted resistance change value ΔR is calculated based on the sensor measurement value or the operating conditions of the membrane separation treatment process or the pretreatment process. For example, the resistance change prediction units 116, 126 determine the predicted resistance change value using the following formula.

In the above formula, the membrane filtration flux J and the cleaning air volume Q are used as input values, but other sensor measurement values may be used. The membrane filtration flux indicates the action of delivering substances that cause membrane fouling (e.g., impurities such as turbidity and dissolved organic matter) to the membrane surface of the filtration membrane. In addition to the membrane filtration flux, for example, the concentration measurement value or alternative index of the fouling factor substance in the water flowing into the membrane filtration device may be used. For example, the fouling factor substance or alternative index may be, for example, measurement values such as turbidity, chromaticity, SS (Suspended Substance), SDI (Silt Density Index), FI (Fouling Index), ultraviolet absorbance (E260), fluorescence intensity, or total organic carbon.

In the above formula, the cleaning air volume indicates the effect of suppressing the membrane fouling phenomenon on the membrane surface of the filtration membrane. In addition to the cleaning air volume, sensor measurement values and operating conditions that suppress the membrane fouling phenomenon, such as the operating conditions of the pretreatment process, may also be used. For example, the pH of the water flowing into the membrane filtration device, residual chlorine, pH adjuster injection rate, chlorine injection rate, ozone injection rate, coagulant injection rate, activated carbon injection rate, etc. may be included.

In addition, data showing the changes in these inputs and membrane resistance may be collected before operating the membrane separation treatment process. The user may determine the unknown variables a _i and k _i in the above formula offline using the collected data. When determining the unknown variables a _i and k _i , the least squares method, PLS (Partial Least Square) regression, ridge regression, lasso regression, or the like may be used. The unknown variables may be updated online, such as by the online least squares method. Any method may be used to determine the unknown variables.

The predicted resistance change value ΔR output from the resistance change prediction units 116 and 126 is added to the actual resistance value by the adders 117 and 127, and input to the pre-processing condition control units 113 and 123 as a predicted resistance value.
The pretreatment condition control units 113 and 123 calculate and output a required chemical injection rate so that the predicted resistance value follows the target resistance value.

The transmembrane pressure difference control device of this embodiment is similar to the transmembrane pressure difference control device of the first embodiment except for the above-mentioned configuration.
By using the above method and using the predicted membrane resistance to compare with the target membrane resistance, it is possible to avoid the possibility that the control will not be able to change the manipulated variable in time, and to optimize the running costs for a membrane separation treatment process having multiple series that do not correspond one-to-one with the pretreatment process.

In other words, this embodiment can provide a membrane differential pressure control device that appropriately controls pretreatment conditions and minimizes running costs, such as electricity costs and chemical costs, required for the water treatment process.

Although some 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 implemented 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 in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
The following is a summary of the claims as originally filed in this application.
[Appendix 1]
A water treatment process including a plurality of membrane filtration apparatuses each having a separation membrane for separating a solid contained in the liquid from the liquid, and a pretreatment apparatus for treating a liquid flowing into at least a part of the plurality of membrane filtration apparatuses, comprising:
A pretreatment condition control unit that calculates a required value of an operating condition of the pretreatment device for each of the membrane filtration devices of the multiple series so that an actual resistance value, which is a resistance value when a liquid permeates the separation membrane, follows a target value of the actual resistance value;
a pretreatment condition integrating unit that integrates the plurality of required values supplied from the pretreatment condition control units to determine operating conditions of the pretreatment device.
[Appendix 2]
The membrane differential pressure control device according to [Appendix 1], wherein the pretreatment condition integration unit sets an average value or a median value of the multiple required values as the operating condition of the pretreatment device.
[Appendix 3]
The membrane differential pressure control device according to [Appendix 1], wherein the pretreatment condition integration unit sets an average value of a plurality of the required values multiplied by weights as an operating condition of the pretreatment device.
[Appendix 4]
The membrane differential pressure control device according to any one of [Appendix 1] to [Appendix 3], wherein the pretreatment condition integration unit acquires a switching condition and switches the integration method of the required value in the pretreatment device using the switching condition as a trigger.
[Appendix 5]
The pretreatment condition integration unit acquires a second requirement value from an external control device, integrates the second requirement value with a plurality of the requirement values, and determines the operating conditions of the pretreatment device. A membrane differential pressure control device as described in any one of [Appendix 1] to [Appendix 4].
[Appendix 6]
The pretreatment condition control unit includes a control unit that controls an operation amount of the membrane filtration device so that the actual resistance value follows the target value. The membrane differential pressure control device described in any one of [Appendix 1] to [Appendix 5].
[Appendix 7]
A water treatment process including a plurality of membrane filtration apparatuses each having a separation membrane for separating a solid contained in the liquid from the liquid, a pretreatment apparatus for treating a liquid flowing into at least a part of the membrane filtration apparatuses, and a plurality of pumps for adjusting a flow rate of the liquid permeating each of the membrane filtration apparatuses, the apparatus controlling the transmembrane pressure difference of the separation membrane,
A membrane filtration flow rate determination unit that calculates the membrane filtration flow rates of the multiple membrane filtration devices based on an actual resistance value, which is a resistance value when a liquid passes through the separation membrane, and a target value of the actual resistance value, and controls the pump so that the sum of the membrane filtrate water that has passed through the multiple membrane filtration devices satisfies the filtration flow rate required for the water treatment process, or so that the water level of a purified water reservoir in which the filtrate water that has passed through the water treatment process is a predetermined value;
a pretreatment condition integration unit that calculates required values of the operating conditions of the pretreatment device for each of the multiple series of membrane filtration devices so that the actual resistance value tracks the target value, and integrates the multiple required values using a weight or parameter based on the membrane filtration flow rate to determine the operating conditions of the pretreatment device.
[Appendix 8]
A water treatment process including a plurality of membrane filtration apparatuses each having a separation membrane for separating a solid contained in the liquid from the liquid, a pretreatment apparatus for treating a liquid flowing into at least a part of the membrane filtration apparatuses, and a plurality of pumps for adjusting a flow rate of the liquid permeating each of the membrane filtration apparatuses, the apparatus controlling the transmembrane pressure difference of the separation membrane,
A membrane differential pressure control device equipped with an operating condition integration unit that determines the operating conditions of the pretreatment device and the operating conditions of the membrane filtration device by performing a preset calculation that solves an optimization problem between the operating conditions of the pretreatment device and the operating conditions of multiple series of membrane filtration devices based on the filtration flow rate required for the water treatment process, an actual resistance value that is the resistance value when liquid permeates the separation membrane, and a target value for the actual resistance value.
[Appendix 9]
Further provided is a resistance change prediction unit that calculates a change in the actual resistance value of the separation membrane from the present to the future using the operating conditions of the pretreatment device or the operating conditions of each membrane filtration device, and an adder that calculates a predicted resistance value by adding the actual resistance value and the change value,
The pretreatment condition control unit calculates the required value of the operating conditions of the pretreatment device so that the predicted resistance value follows the target value in the future. A membrane differential pressure control device as described in any one of [Appendix 1] to [Appendix 6].
[Appendix 10]
The membrane differential pressure control device described in [Appendix 9], wherein the resistance change prediction unit calculates the change value based on at least one value of the chlorine injection rate, the coagulant injection rate, the activated carbon injection rate in the pretreatment device, or the pH of the treated water discharged from the pretreatment device.
[Appendix 11]
The membrane differential pressure control device according to [Appendix 9], wherein the resistance change prediction unit calculates the change value based on at least one value of turbidity, chromaticity, E260, fluorescence intensity, or total organic carbon.

10, 11, 12...Membrane filtration tank, 20...Pretreatment device, 21...Pretreatment condition integration section, 22...Membrane filtration flow rate determination section, 23...Operation condition integration section, 24...Chemical injection section, 100, 101, 102...Control section, 111, 121...Actual resistance calculation section, 112, 122...Target resistance calculation section, 113, 123...Pretreatment condition control section, 114, 124...Pretreatment condition/air volume control section, 115, 125...Subtractor, 116, 126...Resistance change prediction section, 117, 127...Adder, B1, B2...Blower, F1, F2...Flow meter, PO1, PO2...Pump, P1, P2...Pressure gauge, T1, T2...Water temperature system

Claims (8)

A water treatment process including a plurality of membrane filtration apparatuses each having a separation membrane for separating a solid contained in the liquid from the liquid, and a pretreatment apparatus for injecting a chemical into a liquid flowing into at least a part of the plurality of membrane filtration apparatuses, the apparatus controlling the transmembrane pressure difference of the separation membrane,
a target resistance value calculation unit that calculates a target resistance value of the separation membrane during the chemical cleaning period using a transmembrane pressure upper limit value of the separation membrane and a chemical cleaning period from the start to the end of use of the separation membrane so that a membrane resistance value of the separation membrane at the end of the chemical cleaning period is equal to a membrane resistance value at the transmembrane pressure upper limit value;
A pretreatment condition control unit that calculates a required chemical injection rate of the chemical for each of the membrane filtration devices of the multiple series so that an actual resistance value, which is a resistance value when a liquid permeates the separation membrane, follows the target resistance value;
a pretreatment condition integration unit that determines a chemical injection rate of the chemical to be injected from the pretreatment device into the liquid using the multiple required chemical injection rates supplied from the pretreatment condition control unit ,
The pretreatment condition integration unit sets the chemical injection rate to the maximum value, average value, or median value of the multiple required chemical injection rates, or the average value of values obtained by weighting the multiple required chemical injection rates according to the priority of the multiple membrane filtration devices . The membrane differential pressure control device as described in claim 1, wherein the pretreatment condition integration unit acquires a trigger signal notifying that a predetermined time has elapsed since the start of the chemical cleaning period or that an abnormal state has occurred, and the acquisition of the trigger signal is used as a trigger to set the maximum value of the multiple required chemical injection rates as the chemical injection rate. The membrane differential pressure control device according to claim 1 or 2, wherein the pretreatment condition integration unit acquires a second required chemical injection rate based on the water quality of the liquid flowing into the pretreatment device or after membrane filtration, which is supplied from a control function other than the pretreatment condition control unit, or the chemical injection rate for the liquid flowing into another series of filtration devices connected in parallel to the multiple series of membrane filtration devices, and determines the chemical injection rate using the second required chemical injection rate and the multiple required chemical injection rates. The transmembrane pressure control device according to claim 1 , wherein the pretreatment condition control unit includes a control unit that controls an operation amount of the membrane filtration device so that the actual resistance value follows the target resistance value. An apparatus for controlling a transmembrane pressure difference of the separation membrane in a water treatment process further including a plurality of pumps for adjusting a flow rate of a liquid permeating each of the plurality of membrane filtration apparatuses,
A membrane filtration flow rate determination unit is provided that calculates the membrane filtration flow rates of the plurality of membrane filtration devices based on an actual resistance value, which is a resistance value when a liquid passes through the separation membrane, and the target resistance value, and controls the pump so that the sum of the membrane filtrate water that has passed through the plurality of membrane filtration devices satisfies the filtration flow rate required for the water treatment process, or so that the water level of a purified water reservoir in which the filtrate water that has passed through the water treatment process is stored reaches a predetermined value.
The membrane differential pressure control device according to claim 1, wherein the pretreatment condition integration unit calculates, for each of the membrane filtration devices in a plurality of series, the required chemical injection rate of the chemical to be injected into the liquid by the pretreatment device so that the actual resistance value tracks the target resistance value, and determines the chemical injection rate of the chemical to be injected into the liquid by the pretreatment device using the multiple required chemical injection rates weighted by the multiple membrane filtration flow rates. Further provided is a resistance change prediction unit that calculates a change in the actual resistance value of the separation membrane from the present to the future using the chemical injection rate or the flow rate in the plurality of membrane filtration devices, and an adder that calculates a predicted resistance value by adding the actual resistance value and the change value,
The membrane differential pressure control device according to any one of claims 1 to 4, wherein the pretreatment condition control unit calculates the required chemical injection rate of the chemical to be injected into the liquid by the pretreatment device so that the predicted resistance value tracks the future target resistance value. The membrane differential pressure control device according to claim 6, wherein the resistance change prediction unit calculates the change value based on at least one value of the chlorine injection rate, the coagulant injection rate, the activated carbon injection rate in the pretreatment device, or the pH of the treated water discharged from the pretreatment device . The transmembrane pressure control device according to claim 6 , wherein the resistance change prediction unit calculates the change value based on at least one value of turbidity, chromaticity, ultraviolet absorbance (E260), fluorescence intensity, or total organic carbon.