JP7656512B2 - Membrane filtration system, membrane filtration method, flocculant addition device, and control device for flocculant addition device - Google Patents

Description

The present invention relates to a membrane filtration system that performs membrane filtration of water to be treated using a filtration membrane such as a turbidity removing membrane, a membrane filtration method, a flocculant addition device used in the membrane filtration system, and a control device for the flocculant addition device.

In recent years, the demand for water has increased, leading to an increased demand for the recovery and reuse of wastewater. In wastewater recovery, which involves the recovery and reuse of wastewater, one method is to carry out membrane filtration of the biologically treated water or solid-liquid separated water containing suspended matter using a filtration membrane such as a turbidity removal membrane after biological treatment, coagulation, and solid-liquid separation. In this method, the biological treatment, coagulation, and solid-liquid separation processes can become unstable due to changes in the properties of the water to be treated, which can lead to membrane fouling (blockage) during the membrane filtration process.

In order to perform control linked to fluctuations in the properties of the water being treated, a method is known in which the coagulation conditions are changed according to the turbidity, color, ultraviolet absorbance, etc., of the water being treated (see, for example, Patent Document 1).

When control linked to fluctuations in the properties of the treated water is performed using turbidity, color, ultraviolet absorbance, etc., if membrane fouling is caused by other water qualities that cannot be detected by these methods (for example, alkalinity), membrane fouling may occur even if control linked to fluctuations in the properties of the treated water is performed. Also, increasing the number of water quality measurement devices to respond to various water quality fluctuations is less economical.

JP 2013-223846 A

The object of the present invention is to provide a membrane filtration system, a membrane filtration method, a flocculant addition device used in the membrane filtration system, and a control device for the flocculant addition device that can suppress membrane fouling and operate stably even if the properties of the water to be treated fluctuate in a membrane filtration process using a filtration membrane.

The present invention is a membrane filtration system comprising a main membrane filtration device that filters water to be treated using a main filtration membrane, a sub-membrane filtration device that filters branched water to be treated branched from the water to be treated of the main membrane filtration device using a sub-filtration membrane, a main coagulant adding means that adds a main coagulant to the water to be treated of the main membrane filtration device, a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, an output means that performs a predetermined output based on the filtration resistance value detected by the sub-filtration resistance detection means, a control means that controls the conditions of the main coagulant adding means based on the filtration resistance value detected by the sub-filtration resistance detection means, and a recording unit that stores data on the filtration resistance value detected by the sub-filtration resistance detection means, and the data stored in the recording unit is used as teacher data .

In the membrane filtration system, it is preferable that the sub-membrane filtration device is a device that filters branched treated water that is branched off from the treated water to which the main coagulant has been added by the main coagulant adding means.

The membrane filtration system preferably further includes a sub-flocculant addition means for adding a sub-flocculant to the branched treated water of the sub-membrane filtration device, and the sub-membrane filtration device is preferably a device for filtering the branched treated water that is branched from the treated water before the main flocculant is added and to which the sub-flocculant has been added by the sub-flocculant addition means.

In the membrane filtration system, it is preferable that the sub-membrane filtration device passes water at a higher flux than the main membrane filtration device.

The present invention is a membrane filtration method including a main membrane filtration process for filtering water to be treated using a main filtration membrane, a sub-membrane filtration process for filtering branched water to be treated branched from the water to be treated in the main membrane filtration process using a sub-filtration membrane, a main flocculant addition process for adding a main flocculant to the water to be treated in the main membrane filtration process, a sub-filtration resistance detection process for detecting a filtration resistance value of the sub-filtration membrane, and an output process for performing a predetermined output based on the filtration resistance value detected by the sub-filtration resistance detection process, in which the conditions of the main flocculant addition process are controlled based on the filtration resistance value detected by the sub-filtration resistance detection process, and data on the filtration resistance value detected by the sub-filtration resistance detection process is used as teacher data .

In the sub-membrane filtration process of the membrane filtration method, it is preferable to filter branched treated water that is branched from the treated water to which the main flocculant has been added in the main flocculant addition process.

The membrane filtration method preferably further includes a sub-flocculant addition step of adding a sub-flocculant to the branched treated water in the sub-membrane filtration step, and in the sub-membrane filtration step, the branched treated water that is branched from the treated water before the main flocculant is added and to which the sub-flocculant has been added in the sub-flocculant addition step is filtered.

In the membrane filtration method, it is preferable that water is passed through the sub-membrane filtration process at a higher flux than that in the main membrane filtration process.

The present invention is a flocculant addition device that adds a main flocculant to the water to be treated in a main membrane filtration device that filters the water to be treated using a main filtration membrane, and includes a sub-membrane filtration device that filters branched water to be treated branched from the water to be treated in the main membrane filtration device using a sub-filtration membrane, a main flocculant addition means that adds a main flocculant to the water to be treated in the main membrane filtration device, a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, a control means for controlling the conditions of the main flocculant addition means based on the filtration resistance value detected by the sub-filtration resistance detection means, and a recording unit in which data on the filtration resistance value detected by the sub-filtration resistance detection means is stored , and the flocculant addition device uses the data stored in the recording unit as teacher data .

In the coagulant addition device, it is preferable that the sub-membrane filtration device is a device that filters branched treated water that is branched from the treated water to which the main coagulant has been added by the main coagulant addition means.

It is preferable that the flocculant addition device further includes a sub-flocculant addition means for adding a sub-flocculant to the branched treated water of the sub-membrane filtration device, and that the sub-membrane filtration device is a device for filtering the branched treated water that is branched from the treated water before the main flocculant is added and to which the sub-flocculant has been added by the sub-flocculant addition means.

In the coagulant addition device, it is preferable that the sub-membrane filtration device passes water at a higher flux than the main membrane filtration device.

The present invention is a control device for a coagulant addition device that controls the addition of a main coagulant to the treated water of a main membrane filtration device that filters the treated water using a main filtration membrane, and the coagulant addition device comprises a sub-membrane filtration device that filters branched treated water branched from the treated water of the main membrane filtration device using a sub-filtration membrane, a main coagulant addition means that adds a main coagulant to the treated water of the main membrane filtration device, and a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and is a control device for a coagulant addition device that comprises a control means that controls the conditions of the main coagulant addition means based on the filtration resistance value detected by the sub-filtration resistance detection means, and a recording unit that stores data on the filtration resistance value detected by the sub-filtration resistance detection means, and uses the data stored in the recording unit as teacher data .

In the control device for the coagulant addition device, it is preferable that the sub-membrane filtration device is a device that filters branched treated water branched from the treated water to which the main coagulant has been added by the main coagulant addition means.

In the control device of the coagulant addition device, the coagulant addition device preferably further includes a sub-coagulant addition means for adding a sub-coagulant to the branched treated water of the sub-membrane filtration device, and the sub-membrane filtration device is preferably a device for filtering the branched treated water that is branched from the treated water before the main coagulant is added and to which the sub-coagulant has been added by the sub-coagulant addition means.

In the control device of the coagulant addition device, it is preferable that water is passed through the sub-membrane filtration device at a higher flux than the main membrane filtration device.

The present invention provides a membrane filtration system, a membrane filtration method, a flocculant addition device used in the membrane filtration system, and a control device for the flocculant addition device that can suppress membrane fouling and operate stably even if the properties of the water being treated fluctuate in a membrane filtration process that uses a filtration membrane.

FIG. 1 is a schematic configuration diagram illustrating an example of a membrane filtration system according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a membrane filtration system according to an embodiment of the present invention.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

<Membrane filtration method and membrane filtration system>
FIG. 1 shows an outline of an example of a membrane filtration system according to an embodiment of the present invention, and the configuration thereof will be described.

The membrane filtration system 1 includes a main membrane filtration device 10 that filters the water to be treated using a main filtration membrane, a sub-membrane filtration device 12 that filters branched water to be treated branched from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane, a main coagulant addition device 20 as a main coagulant addition means that adds a main coagulant to the water to be treated of the main membrane filtration device 10, a sub-filtration resistance detection device 14 as a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and an output unit 16 as an output means that performs a predetermined output based on the filtration resistance value detected by the sub-filtration resistance detection device 14. The membrane filtration system 1 may include a control device 18 as a control means. The membrane filtration system 1 may include a treated water tank 22 for storing treated water obtained in the main membrane filtration device 10, a main backwash pipe 30 as a main backwash means for backwashing the main filtration membrane of the main membrane filtration device 10 and backwashing with the addition of chemicals, and a sub-backwash pipe 36 as a sub-backwash means for backwashing the sub filtration membrane of the sub membrane filtration device 12 and backwashing with the addition of chemicals.

In the membrane filtration system 1 of FIG. 1, a main treated water pipe 24 is connected to the treated water inlet of the main membrane filtration device 10. The main treated water outlet and the inlet of the treated water tank 22 are connected by a main treated water pipe 26, and the main treated water outlet of the treated water tank 22 is connected to a main treated water pipe 28. The main backwash liquid outlet of the treated water tank 22 and the main backwash liquid inlet on the secondary side of the main membrane filtration device 10 are connected by a main backwash pipe 30. The main backwash drainage outlet on the primary side of the main membrane filtration device 10 is connected to a main backwash drainage pipe 32. The outlet of the main flocculant addition device 20 and the main treated water pipe 24 are connected by a main flocculant addition pipe 42.

The branched treated water inlet of the sub-membrane filtration device 12 is connected to a sub-branched treated water pipe 34 that branches off from the downstream side of the connection point of the main flocculant addition pipe 42 in the main treated water pipe 24, and the sub-treated water outlet is connected to a sub-treated water pipe 40. The sub-backwash liquid outlet of the treated water tank 22 and the sub-backwash liquid inlet on the secondary side of the sub-membrane filtration device 12 are connected by a sub-backwash pipe 36. The sub-backwash discharge liquid outlet on the primary side of the sub-membrane filtration device 12 is connected to a sub-backwash discharge liquid pipe 38. A sub-filtration resistance detection device 14 is installed on the secondary side of the sub-membrane filtration device 12.

The output unit 16 and the sub-filtration resistance detection device 14, the output unit 16 and the control device 18, the sub-filtration resistance detection device 14 and the control device 18, and the control device 18 and the main flocculant addition device 20 may be connected to each other so as to be able to communicate with each other by wired or wireless electrical connection or the like. The membrane filtration system 1 may further include a communication device as a communication means. The communication device is connected to the control device 18, and is connected to a server, for example, via the Internet. The server is provided with at least a recording unit or a calculation unit. The recording unit stores, for example, data such as the filtration resistance value measured by the sub-filtration resistance detection device 14. The calculation unit performs calculations using data such as the filtration resistance value measured by the sub-filtration resistance detection device 14, and may output an alarm or the execution of main flocculant addition by the main flocculant addition device 20, or the data stored in the recording unit may be used together to calculate the execution history of flocculant addition, the amount of flocculant used, the flocculant cost, etc., and may be stored or output. The output may be sent to the control device 18 again via the Internet, and an alarm may be issued to the output unit 16, flocculant addition may be performed, or the flocculant addition conditions may be changed.

The membrane filtration method and the operation of the membrane filtration system 1 according to this embodiment will be described.

The water to be treated is sent to the main membrane filtration device 10 through the main treated water pipe 24. Here, in the main treated water pipe 24, the main flocculant is added to the water to be treated from the main flocculant addition device 20 through the main flocculant addition pipe 42 (main flocculant addition process). In the main membrane filtration device 10, membrane filtration processing of the water to be treated is performed using the main filtration membrane (main membrane filtration process). The obtained main treated water is sent to the treated water tank 22 through the main treated water pipe 26 as necessary and stored there. The main treated water stored in the treated water tank 22 is discharged through the main treated water pipe 28.

Meanwhile, the branched treated water branched off from the treated water to which the main flocculant has been added by the main flocculant addition device 20 is sent to the sub-membrane filtration device 12 through the sub-branched treated water piping 34. In the sub-membrane filtration device 12, the branched treated water is subjected to membrane filtration processing using a sub-filtration membrane (sub-membrane filtration process). The obtained sub-treated water is discharged through the sub-treated water piping 40.

The main membrane filtration device 10 and the sub-membrane filtration device 12 repeatedly perform a membrane filtration process and a cleaning process. There are two types of cleaning processes: a backwash process in which treated water is used to pass from the secondary side of the filtration membrane to the primary side, and a chemical addition backwash process in which chemicals such as acids, alkalis, and oxidizing agents are added during the backwash process. At least one of the cleaning processes needs to be performed.

In the sub-membrane filtration device 12, the sub-filtration resistance value is measured during the filtration process by the sub-filtration resistance detection device 14.

In the membrane filtration system 1, the main membrane filtration device 10 is cleaned, for example, periodically, when the main membrane filtration device 10 is operated continuously. The main filtration membrane is cleaned, for example, by backflowing at least a portion of the main treated water from the treated water tank 22 through the main backwash piping 30 as main backwash water from the secondary side to the primary side of the main membrane filtration device 10 (main backwash process). The main backwash effluent is discharged from the primary side of the main membrane filtration device 10 through the main backwash effluent piping 32.

If the fouling of the main filtration membrane is not eliminated even after the main backwash is performed, chemical-added backwashing is performed with a main chemical-added backwashing solution in which a chemical has been added to the main backwash water (main chemical-added backwashing process). In the main chemical-added backwashing process, for example, the main chemical-added backwashing solution in which a chemical has been added to at least a part of the main treated water is backflowed from the secondary side to the primary side of the main membrane filtration device 10 through the main backwashing piping 30 (main chemical-added backwashing process). The main chemical-added backwashing drainage is discharged from the primary side of the main membrane filtration device 10 through the main backwashing drainage piping 32. In the main chemical-added backwashing process, an immersion process may be performed in which the main filtration membrane is immersed in the main chemical-added backwashing solution for a predetermined time. In the main chemical-added backwashing process, the main chemical-added backwashing drainage discharged from the primary side of the main membrane filtration device 10 may be circulated to the secondary side of the main membrane filtration device 10.

As described above, due to fluctuations in the properties of the water to be treated, the biological treatment, coagulation, and solid-liquid separation processes in the upstream stages can become unstable, and membrane fouling (blockage) can occur in the membrane filtration process. In addition to the main membrane filtration process by the main membrane filtration device 10, the membrane filtration system 1 provides a sub-membrane filtration process by a sub-membrane filtration device 12 equipped with a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and based on the filtration resistance value in the sub-membrane filtration process detected by the sub-filtration resistance detection device 14, which is the sub-filtration resistance detection means, an output according to the state of membrane filtration in the sub-membrane filtration device 12 is issued, for example, an alarm or other output when the filtration resistance value exceeds a predetermined threshold value.

For example, it is preferable to record the filtration resistance value of the sub-membrane filtration device 12, and when certain conditions are met, control the amount of coagulant added to the main membrane filtration device 10, etc.

In the membrane filtration system 1 of FIG. 1, for example, at least one of the following controls (1) to (3) may be performed using the sub-filtration resistance value.

(1) For example, when the rate of increase in the sub-filtration resistance value during the filtration process of the sub-membrane filtration device 12 reaches or exceeds a predetermined value, the amount of main coagulant added by the main coagulant addition device 20 in the main membrane filtration device 10 is increased.

(2) For example, when the "sub-filtration resistance value after cleaning" vs. the "slope of the filtration amount of the sub-membrane filtration device" in the sub-membrane filtration device 12 becomes equal to or greater than a predetermined value, the amount of main coagulant added by the main coagulant addition device 20 in the main membrane filtration device 10 is increased.

(3) For example, while changing the amount of main coagulant added in the main membrane filtration device 10, the "sub-filtration resistance value after cleaning" versus the "slope of the filtration amount of the sub-membrane filtration device" is calculated, and the amount of main coagulant added by the main coagulant adding device 20 in the main membrane filtration device 10 is controlled to find the condition that reduces the slope or to approach that condition.

This allows early detection of fouling of the sub-filtration membrane in the sub-membrane filtration device 12. If the conditions for adding the coagulant are changed in the main membrane filtration device 10 when the occurrence of fouling of the sub-filtration membrane is detected, membrane fouling can be suppressed even if the properties of the water to be treated fluctuate, enabling stable operation of the main membrane filtration device 10. By providing the sub-membrane filtration device 12 separately from the main membrane filtration device 10, the conditions for adding the coagulant can be changed without stopping the main membrane filtration device 10, and the main membrane filtration process may be continued. This allows the operating time of the main membrane filtration device 10 to be maximized.

Another example of a membrane filtration system according to an embodiment of the present invention is shown in FIG. 2. The membrane filtration system 3 shown in FIG. 2 includes a main membrane filtration device 10 that filters the water to be treated using a main filtration membrane, a sub-membrane filtration device 12 that filters the branched water to be treated branched from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane, a main flocculant addition device 20 as a main flocculant addition means for adding a main flocculant to the water to be treated of the main membrane filtration device 10, a sub-flocculant addition device 46 as a sub-flocculant addition means for adding a sub-flocculant to the branched water to be treated of the sub-membrane filtration device 12, a sub-filtration resistance detection device 14 as a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and an output unit 16 as an output means for performing a predetermined output based on the filtration resistance value detected by the sub-filtration resistance detection device 14. The membrane filtration system 1 may include a control device 18 as a control means. The membrane filtration system 1 may include a treated water tank 22 for storing treated water obtained in the main membrane filtration device 10, a main backwash pipe 30 as a main backwash means for backwashing the main filtration membrane of the main membrane filtration device 10 and backwashing with the addition of chemicals, and a sub-backwash pipe 36 as a sub-backwash means for backwashing the sub filtration membrane of the sub membrane filtration device 12 and backwashing with the addition of chemicals.

In the membrane filtration system 3 of FIG. 2, the main treated water pipe 24 is connected to the treated water inlet of the main membrane filtration device 10. The main treated water outlet and the inlet of the treated water tank 22 are connected by the main treated water pipe 26, and the treated water outlet of the treated water tank 22 is connected to the main treated water pipe 28. The main backwash liquid outlet of the treated water tank 22 and the main backwash liquid inlet on the secondary side of the main membrane filtration device 10 are connected by the main backwash pipe 30. The main backwash drainage outlet on the primary side of the main membrane filtration device 10 is connected to the main backwash drainage pipe 32. The outlet of the main flocculant addition device 20 and the main treated water pipe 24 are connected by the main flocculant addition pipe 42.

The branched treated water inlet of the sub-membrane filtration device 12 is connected to a sub-branched treated water pipe 34 that branches off from the upstream side of the connection point of the main flocculant addition pipe 42 in the main treated water pipe 24, and the sub-treated water outlet is connected to a sub-treated water pipe 40. The sub-backwash liquid outlet of the treated water tank 22 and the sub-backwash liquid inlet on the secondary side of the sub-membrane filtration device 12 are connected by a sub-backwash pipe 36. The sub-backwash drainage outlet on the primary side of the sub-membrane filtration device 12 is connected to a sub-backwash drainage pipe 38. The sub-filtration resistance detection device 14 is installed on the secondary side of the sub-membrane filtration device 12. The outlet of the sub-flocculant addition device 46 and the sub-branched treated water pipe 34 are connected by a sub-flocculant addition pipe 44.

The output unit 16 and the sub-filtration resistance detection device 14, the output unit 16 and the control device 18, the sub-filtration resistance detection device 14 and the control device 18, the control device 18 and the main flocculant addition device 20, and the control device 18 and the sub-flocculant addition device 46 may be connected to each other so as to be able to communicate with each other by wired or wireless electrical connection or the like. The membrane filtration system 1 may further include a communication device as a communication means. The communication device is connected to the control device 18, and is connected to a server, for example, via the Internet. The server is provided with at least a recording unit or a calculation unit. The recording unit stores, for example, data such as the filtration resistance value measured by the sub-filtration resistance detection device 14. The calculation unit performs calculations using data such as the filtration resistance value measured by the sub-filtration resistance detection device 14, and may output an alarm or the execution of flocculant addition by the main flocculant addition device 20 or the sub-flocculant addition device 46, or the data stored in the recording unit may be used together to calculate the execution history of flocculant addition by the main flocculant addition device 20 or the sub-flocculant addition device 46, the amount of flocculant used, and the flocculant cost, etc., and may be stored or output. The output is again sent to the control device 18 via the Internet, and an alarm may be issued to the output unit 16, the main flocculant addition device 20 or the sub flocculant addition device 46 may add flocculant, or the flocculant addition conditions may be changed. The data recorded in the recording unit may be used as training data for AI (machine learning, deep learning, etc.). For example, a model may be created using the filtration resistance value measured by the sub filtration resistance detection device 14 for the flocculation conditions and water quality recorded in the recording unit as training data, and flocculation conditions may be presented or controlled so that the filtration resistance value is lower for future water quality. In addition, for example, the output such as the execution of an alarm or flocculant addition performed after the calculation is correct may be checked by a jar test or maintenance of the device, and the correctness of the calculation may be given as a label and used as training data to adjust the model and improve the accuracy of the alarm or flocculant addition.

The water to be treated is sent to the main membrane filtration device 10 through the main treated water pipe 24. Here, in the main treated water pipe 24, the main flocculant is added to the water to be treated from the main flocculant addition device 20 through the main flocculant addition pipe 42 (main flocculant addition process). In the main membrane filtration device 10, membrane filtration processing of the water to be treated is performed using the main filtration membrane (main membrane filtration process). The obtained main treated water is sent to the treated water tank 22 as necessary through the main treated water pipe 26 and stored there. The main treated water stored in the treated water tank 22 is discharged through the main treated water pipe 28.

Meanwhile, the branched treated water branched off from the treated water before the main flocculant is added by the main flocculant addition device 20 is sent to the sub-membrane filtration device 12 through the sub-branched treated water piping 34. Here, in the sub-branched treated water piping 34, the sub-flocculant is added from the sub-flocculant addition device 46 to the branched treated water through the sub-flocculant addition piping 44 (sub-flocculant addition process). In the sub-membrane filtration device 12, membrane filtration of the branched treated water is performed using a sub-filtration membrane (sub-membrane filtration process). The obtained sub-treated water is discharged through the sub-treated water piping 40.

The main membrane filtration device 10 and the sub-membrane filtration device 12 repeatedly perform the membrane filtration process and the cleaning process. The cleaning process is performed in the same manner as in the membrane filtration system 1 of FIG. 1.

In the sub-membrane filtration device 12, the sub-filtration resistance value may be measured during the filtration process by the sub-filtration resistance detection device 14.

In the membrane filtration system 3, in addition to the main membrane filtration process by the main membrane filtration device 10, a sub-membrane filtration process by a sub-membrane filtration device 12 equipped with a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane is provided, and based on the filtration resistance value in the sub-membrane filtration process detected by the sub-filtration resistance detection device 14, which is the sub-filtration resistance detection means, an output according to the membrane filtration status in the sub-membrane filtration device 12 is issued, for example, an alarm or the like is output when the filtration resistance value exceeds a predetermined threshold value.

For example, it is preferable to record the filtration resistance value of the sub-membrane filtration device 12, and when certain conditions are met, to control the amount of coagulant added to at least the main membrane filtration device 10 out of the main membrane filtration device 10 and the sub-membrane filtration device 12.

In the membrane filtration system 3 of FIG. 2, for example, at least one of the following controls (1) to (3) may be performed using the sub-filtration resistance value.

(1) For example, when the rate of increase in the sub-filtration resistance value during the membrane filtration process of the sub-membrane filtration device 12 reaches or exceeds a predetermined value, the amount of main coagulant added by the main coagulant addition device 20 in the main membrane filtration device 10 and the amount of sub-coagulant added by the sub-coagulant addition device 46 in the sub-membrane filtration device 12 are increased.

(2) For example, when the "sub-filtration resistance value after cleaning" vs. the "slope of the filtration amount of the sub-membrane filtration device" in the sub-membrane filtration device 12 becomes equal to or greater than a predetermined value, the amount of main coagulant added by the main coagulant addition device 20 in the main membrane filtration device 10 and the amount of sub-coagulant added by the sub-coagulant addition device 46 in the sub-membrane filtration device 12 are increased.

(3) For example, while changing the amount of sub-flocculant added in the sub-membrane filtration device 12, the "sub-filtration resistance value after cleaning" versus the "slope of the filtration amount of the sub-membrane filtration device" is calculated, and the amount of main flocculant added by the main flocculant addition device 20 is controlled to find the condition that reduces the slope or to approach that condition.

This allows early detection of fouling of the sub-filtration membrane in the sub-membrane filtration device 12. If the conditions for adding the coagulant are changed in the main membrane filtration device 10 when the occurrence of fouling of the sub-filtration membrane is detected, membrane fouling can be suppressed even if the properties of the water to be treated fluctuate, enabling stable operation of the main membrane filtration device 10. By providing the sub-membrane filtration device 12 separately from the main membrane filtration device 10, the conditions for adding the coagulant can be changed without stopping the main membrane filtration device 10, and the main membrane filtration process may be continued. This allows the operating time of the main membrane filtration device 10 to be maximized.

The sub-filtration membrane in the sub-membrane filtration device 12 has, for example, the same membrane material, membrane shape, and membrane pore size as the main filtration membrane in the main membrane filtration device 10, and has a smaller membrane area than the main filtration membrane. If fouling is detected by the sub-membrane filtration device 12, which is smaller than the main membrane filtration device 10, fouling in the main membrane filtration device 10 can be predicted at an early stage.

In the sub-membrane filtration device 12 (sub-membrane filtration process), it is preferable to pass water at a higher flux than in the main membrane filtration device 10 (main membrane filtration process). This allows the occurrence of fouling of the sub-filtration membrane in the sub-membrane filtration device 12 to be detected earlier. If the conditions for adding the coagulant in the main membrane filtration device 10 are changed when the occurrence of fouling of the sub-filtration membrane is detected, membrane fouling can be suppressed even if the properties of the water to be treated fluctuate, and stable operation of the main membrane filtration device 10 becomes possible.

The flux in the sub-membrane filtration device 12 (sub-membrane filtration process) is, for example, 2 to 10 times, and preferably 4 to 6 times, the flux in the main membrane filtration device 10 (main membrane filtration process). If the flux in the sub-membrane filtration device 12 is less than twice the flux in the main membrane filtration device 10, it may not be possible to detect the occurrence of fouling in the sub-filtration membrane at an earlier stage, whereas if it exceeds 10 times, the occurrence of fouling may be over-evaluated, resulting in a reduced prediction accuracy.

In addition, for example, the conditions for adding the main coagulant in the main membrane filtration device 10 and the conditions for adding the sub-coagulant in the sub-membrane filtration device 12 may be controlled based on the filtration resistance value in the sub-membrane filtration device 12 detected by the sub-filtration resistance detection device 14. For example, the conditions for adding the coagulant in the main membrane filtration process, such as the type of coagulant and the amount added, may be controlled based on the tendency of resistance increase in the sub-membrane filtration device 12. These controls may be performed manually or automatically.

The sub-filtration resistance detection device 14 is not particularly limited as long as it can detect the filtration resistance value in the sub-membrane filtration device 12, but examples include a pressure measurement means such as a pressure gauge, and a flow rate measurement means such as a flow meter. It is preferable that the sub-filtration resistance detection device 14 is equipped with both a pressure measurement means such as a pressure gauge, and a flow rate measurement means such as a flow meter. When considering the temperature dependency of the water to be treated, it is preferable to further include a thermometer as a temperature measurement means.

The control device 18 may store data measured on the pressure and flow rate, etc., when the branched treated water is passed through the sub-membrane filtration device 12, calculate data on the increase in filtration resistance, and based on this, automatically control the conditions for adding the main coagulant by the main coagulant addition device 20 in the main membrane filtration device 10 (e.g., type of main coagulant, amount added, etc.) and the conditions for adding the sub coagulant by the sub coagulant addition device 46 in the sub-membrane filtration device 12 (e.g., type of sub coagulant, amount added, etc.).

The output from the output unit 16 may include visually and audiovisually perceptible alarms such as a display or sound indicating the state of membrane filtration in the sub-membrane filtration device 12, as well as methods of dealing with the state of membrane filtration and improvement suggestions. The output unit 16 may be, for example, anything that can display and output information, and is not particularly limited. Examples of the output unit 16 include a display device that is a display means such as a liquid crystal display or an organic EL display, and an audio output device that is an audio output means such as a speaker. For example, the method of issuing an alarm may include displaying on a touch panel of a control panel, notifying an operator via Internet communication, or notifying a monitoring room, etc.

The output unit 16 may output an alarm or the like when the filtration resistance value in the sub-membrane filtration device 12 exceeds, for example, a predetermined threshold value. The alarm threshold value may be preset to one value, or may be changed in stages or proportionately.

The control device 18 is composed of a microcomputer and electronic circuits, which include, for example, a calculation means such as a CPU that calculates a program, and storage means such as a ROM and RAM that store the program and the calculation results. The control device 18 has a function to control the conditions of main coagulant addition by the main coagulant addition device 20 in the main membrane filtration device 10 and the conditions of sub-coagulant addition by the sub-coagulant addition device 46 in the sub-membrane filtration device 12, based on the filtration resistance value detected by the sub-filtration resistance detection means. The control device 18 has a function to control the amount of coagulant added to the water to be treated, for example, by adjusting the on/off and flow rate of the pump used to add coagulant in the main coagulant addition device 20 or the sub-coagulant addition device 46, the opening and closing of the valve, etc.

The water to be treated is water that contains, for example, suspended solids, organic matter, inorganic matter such as metal particles, and the like. There are no particular limitations on the water to be treated. Examples include biologically treated water (biological treatment process) in which wastewater containing organic matter discharged from semiconductor manufacturing plants, food factories, etc. is biologically treated, solid-liquid separation treated water that has been subjected to coagulation and solid-liquid separation treatment (coagulation/solid-liquid separation treatment process), and solid-liquid separation treated water that has been biologically treated and then coagulated and solid-liquid separation treatment. Water that has been treated through other processes before or after the biological treatment process or coagulation/solid-liquid separation treatment process may also be used.

There are no particular limitations on the biological treatment, so long as it uses microorganisms to treat the water to be treated. There are no particular limitations on the coagulation and solid-liquid separation treatment, so long as it uses a coagulant, such as an inorganic coagulant, such as polyaluminum chloride, or a polymer coagulant, to perform coagulation treatment and solid-liquid separation treatment of the water to be treated.

The membrane filtration system and membrane filtration method according to this embodiment are suitable for use when the properties of the water to be treated are such that the content of organic matter as indicated by TOC varies in the range of 1 to 50 mg/L, or the content of metal particles such as iron, aluminum, manganese, and other inorganic matter such as dissolved metals as indicated by ICP analysis varies in the range of 0.01 to 20 mg/L.

The main filtration membrane and the sub-filtration membrane are, for example, turbidity removing membranes such as ultrafiltration membranes (UF membranes) or microfiltration membranes (MF membranes). The shape of the membrane is, for example, a hollow fiber membrane.

Chemicals used in chemical backwashing include acids, oxidizing agents, and alkalis. There are no particular limitations on the acids, but examples include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and citric acid. From the standpoint of recovery during chemical backwashing, it is preferable to use organic acids such as oxalic acid and citric acid.

There are no particular limitations on the oxidizing agent used in chemical backwashing, but examples include chlorine-based oxidizing agents such as sodium hypochlorite.

There are no particular restrictions on the alkali used for chemical backwashing, but it is preferable to use relatively inexpensive alkalis such as sodium hydroxide and sodium hypochlorite.

When backwashing with chemicals, chemicals other than acids, alkalis, and oxidizing agents, such as membrane cleaning agents such as surfactants, may be used as necessary.

<Flocculant Addition Device>
The flocculant addition device according to the embodiment of the present invention is a flocculant addition device that adds a main flocculant to the water to be treated in a main membrane filtration device 10 that filters the water to be treated using a main filtration membrane, as shown in Figures 1 and 2. The flocculant addition device includes a sub-membrane filtration device 12 that filters branched water to be treated branched from the water to be treated in the main membrane filtration device 10 using a sub-filtration membrane, a main flocculant addition device 20 as a main flocculant addition means that adds a main flocculant to the water to be treated in the main membrane filtration device 10, a sub-filtration resistance detection device 14 as a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and a control device 18 as a control means for controlling the conditions of the main flocculant addition device 20 based on the filtration resistance value detected by the sub-filtration resistance detection device 14.

In the flocculant addition device shown in FIG. 1, the sub-membrane filtration device 12 is a device that filters the branched treated water that is branched off from the treated water to which the main flocculant has been added by the main flocculant addition device 20.

The flocculant addition device shown in FIG. 2 further includes a sub-flocculant addition device 46 as a sub-flocculant addition means for adding a sub-flocculant to the branched treated water of the sub-membrane filtration device 12. The sub-membrane filtration device 12 is a device that filters the branched treated water that is branched from the treated water before the main flocculant is added and to which the sub-flocculant has been added by the sub-flocculant addition device 46.

It is preferable to pass water through the sub-membrane filtration device 12 in the coagulant addition device at a higher flux than through the main membrane filtration device 10.

<Control device for flocculant addition device>
The control device of the flocculant addition device according to the embodiment of the present invention is a control device of the flocculant addition device that controls the addition of a main flocculant to the water to be treated of a main membrane filtration device 10 that filters the water to be treated using a main filtration membrane. The flocculant addition device includes a sub-membrane filtration device 12 that filters branched water to be treated branched from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane, a main flocculant addition device 20 as a main flocculant addition means that adds a main flocculant to the water to be treated of the main membrane filtration device 10, and a sub-filtration resistance detection device 14 as a sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane. The control device of the flocculant addition device includes a control device 18 as a control means that controls the conditions of the main flocculant addition device 20 based on the filtration resistance value detected by the sub-filtration resistance detection device 14.

In the flocculant addition device in the control device for the flocculant addition device shown in FIG. 1, the sub-membrane filtration device 12 is a device that filters the branched treated water that is branched off from the treated water to which the main flocculant has been added by the main flocculant addition device 20.

The flocculant addition device in the control device for the flocculant addition device shown in FIG. 2 further includes a sub-flocculant addition device 46 as a sub-flocculant addition means for adding a sub-flocculant to the branched treated water of the sub-membrane filtration device 12. The sub-membrane filtration device 12 is a device that filters the branched treated water that is branched from the treated water before the main flocculant is added and to which the sub-flocculant has been added by the sub-flocculant addition device 46.

In the coagulant addition device in the control device of the coagulant addition device, it is preferable to pass water through the sub-membrane filtration device 12 at a higher flux than the main membrane filtration device 10.

1, 3 Membrane filtration system, 10 Main membrane filtration device, 12 Sub-membrane filtration device, 14 Sub-filtration resistance detection device, 16 Output section, 18 Control device, 20 Main coagulant addition device, 22 Treated water tank, 24 Main treated water pipe, 26, 28 Main treated water pipe, 30 Main backwash pipe, 32 Main backwash drain pipe, 34 Sub-branched treated water pipe, 36 Sub-backwash pipe, 38 Sub-backwash drain pipe, 40 Sub treated water pipe, 42 Main coagulant addition pipe, 44 Sub-coagulant addition pipe, 46 Sub-coagulant addition device.

Claims (8)

A main membrane filtration device that filters the water to be treated using a main filtration membrane;
A sub-membrane filtration device that filters a branched treated water branched from the treated water of the main membrane filtration device using a sub-filtration membrane;
A main flocculant adding means for adding a main flocculant to the water to be treated in the main membrane filtration device;
A sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane;
an output means for outputting a predetermined output based on the filtering resistance value detected by the sub filtering resistance detection means;
A control means for controlling the conditions of the main flocculant adding means based on the filtration resistance value detected by the sub filtration resistance detecting means;
A recording unit in which data of the filtering resistance value detected by the sub filtering resistance detection means is stored;
Equipped with
A membrane filtration system characterized in that the data stored in the recording unit is used as teaching data . 2. The membrane filtration system of claim 1,
A membrane filtration system characterized in that the sub-membrane filtration device is a device for filtering branched treated water branched off from the treated water to which the main flocculant has been added by the main flocculant adding means. 2. The membrane filtration system of claim 1,
The sub-membrane filtration apparatus further includes a sub-flocculant adding means for adding a sub-flocculant to the branched treated water of the sub-membrane filtration apparatus,
The sub-membrane filtration device is a membrane filtration system characterized in that it is a device that filters branched treated water that is branched off from the treated water before the main coagulant is added and to which the sub-coagulant has been added by the sub-coagulant adding means. The membrane filtration system according to any one of claims 1 to 3,
A membrane filtration system, characterized in that the sub-membrane filtration device passes water at a higher flux than the main membrane filtration device. a main membrane filtration process for filtering the water to be treated using a main filtration membrane;
a sub-membrane filtration process for filtering a branched water to be treated that is branched from the water to be treated in the main membrane filtration process using a sub-filtration membrane;
a main flocculant addition step of adding a main flocculant to the water to be treated in the main membrane filtration step;
A sub-filtration resistance detection step for detecting a filtration resistance value of the sub-filtration membrane;
an output step of performing a predetermined output based on the filtering resistance value detected by the sub filtering resistance detection step;
Including,
Controlling conditions of the main flocculant addition step based on the filtration resistance value detected by the sub-filtration resistance detection step;
A membrane filtration method , characterized in that data on the filtration resistance value detected in the sub-filtration resistance detection process is used as teaching data . A flocculant addition device that adds a main flocculant to the water to be treated in a main membrane filtration device that filters the water to be treated using a main filtration membrane,
A sub-membrane filtration device that filters a branched treated water branched from the treated water of the main membrane filtration device using a sub-filtration membrane;
A main flocculant adding means for adding a main flocculant to the water to be treated in the main membrane filtration device;
A sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane;
A control means for controlling the conditions of the main flocculant adding means based on the filtration resistance value detected by the sub filtration resistance detecting means;
A recording unit in which data of the filtering resistance value detected by the sub filtering resistance detection means is stored;
Equipped with
A flocculant addition device, characterized in that the data stored in the recording unit is used as teaching data . The flocculant addition device according to claim 6 ,
A coagulant addition device, characterized in that in the sub-membrane filtration device, water is passed through at a higher flux than in the main membrane filtration device. A control device for a flocculant addition device that controls addition of a main flocculant to water to be treated in a main membrane filtration device that filters the water to be treated using a main filtration membrane,
The coagulant addition device includes a sub-membrane filtration device that uses a sub-filtration membrane to filter branched treated water branched from the treated water of the main membrane filtration device, a main coagulant addition means that adds a main coagulant to the treated water of the main membrane filtration device, and a sub-filtration resistance detection means that detects the filtration resistance value of the sub-filtration membrane,
A control means for controlling the conditions of the main flocculant adding means based on the filtration resistance value detected by the sub filtration resistance detecting means ;
A recording unit in which data of the filtering resistance value detected by the sub filtering resistance detection means is stored;
Equipped with
A control device for a flocculant addition device, characterized in that the data stored in the recording unit is used as teaching data .

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