JP2023107656A - Membrane filtration system, membrane filtration method, chemical-added backwash device, and control device for chemical-added backwash device - Google Patents

Abstract

To provide a membrane filtration system capable of suppressing fouling on the secondary side of the membrane by determining optimal cleaning conditions at an early stage and performing chemical additive backwashing, even if the properties of the treated water fluctuate, to ensure stable operation in membrane filtration treatment using a filtration membrane.SOLUTION: A membrane filtration system 1 includes a main membrane filtration unit 10 for filtering treated water using a main filtration membrane, a sub-membrane filtration unit 12 with a sub-filtration membrane, main chemical adding backwashing means for performing chemical adding backwashing of the main filtration membrane, sub-chemical adding backwashing means for performing chemical adding backwashing of the sub-filtration membrane, and an output part 16 that provides predetermined output based on the blockage behavior detected by the blockage detection means after chemical addition backwashing performed by the sub-chemical addition backwashing means detected by a flow meter 28, a pressure gauge 30, and blockage detection means for detecting blockages on the secondary side of the sub-filtration membrane.SELECTED DRAWING: Figure 1

Description

The present invention provides a membrane filtration system for performing membrane filtration of water to be treated using a filtration membrane such as a turbidity removal membrane, a membrane filtration method, a chemical addition backwashing device used in the membrane filtration system, and a chemical addition backwashing device. control device.

Due to the recent increase in demand for water, there is an increasing demand for recovering and reusing wastewater. Membrane filtration treatment of biologically treated water containing suspended solids and solid-liquid separated water using filtration membranes such as turbidity removal membranes after biological treatment, coagulation and solid-liquid separation treatment in wastewater recovery that recovers and reuses wastewater. There is a way to do In this method, the biological treatment, coagulation, and solid-liquid separation treatment become unstable due to changes in the properties of the water to be treated, and fouling (clogging) of the membrane may occur in the membrane filtration treatment. In this case, for example, backwash water is passed from the secondary side of the membrane to the primary side to perform backwashing, and physical cleaning is performed in which deposits on the membrane surface or inside the membrane are physically removed. In order to eliminate membrane fouling that cannot be eliminated by backwashing, chemical backwashing is performed using a chemical-added backwashing liquid in which oxidizing agents such as sodium hypochlorite and chemicals such as alkalis and acids are added to the backwashing water. A chemically enhanced backwash (CEB) may also be performed.

When the property of the water to be treated changes, it is difficult to stably perform biological treatment, coagulation, and solid-liquid separation before membrane filtration. When the biological treatment becomes unstable, fouling of the membrane occurs mainly due to organic substances if the chemical recovery effect by chemical addition backwash in the membrane filtration process is insufficient. When the coagulation and solid-liquid separation process becomes unstable, if the chemical recovery effect by chemical addition backwash in the membrane filtration process is insufficient, membrane fouling will occur mainly due to metal-based coagulants that have become small particles. . If the fouling factor of the membrane is different, for example, the type of chemical used for chemical addition backwash is changed.

In the wastewater recovery system, a large amount of metal-based coagulant is required for the preceding coagulation and solid-liquid separation treatment, and changes in the properties of the water to be treated tend to cause inorganic fouling due to excess metal-based coagulant. In particular, when the water to be treated contains dissolved metals, the dissolved metals may permeate to the secondary side of the membrane. In this case, if chemical addition backwashing is performed using a solution obtained by adding an oxidizing agent to the permeated water, which is the membrane-treated water, as the chemical-added backwashing solution, part of the dissolved metals present in the membrane-treated water is oxidized. It precipitates on the film surface on the secondary side and causes fouling to occur on the secondary side of the film. Further, fouling on the secondary side of the film due to this deposited metal is difficult to detect.

If fouling occurs on the secondary side of the membrane, it becomes difficult to obtain treated water, and it becomes necessary to stop the wastewater recovery system, to clean the membrane with chemicals on a large scale, or to purchase a new membrane. Therefore, even if the properties of the water to be treated fluctuate, it is possible to determine the optimum cleaning conditions at an early stage and perform chemical addition backwashing to suppress fouling on the secondary side of the membrane, enabling stable operation. A method is needed.

In Patent Document 1, at the time of backwashing, an oxidizing disinfectant such as sodium hypochlorite is added to the treated water of the membrane, and after filtering with a nanofiltration membrane, backwashing is performed to reduce the secondary side. Suppresses fouling. However, the method of Patent Document 1 does not determine the conditions for chemical addition backwashing. In addition, when the nanofiltration membrane becomes clogged, maintenance such as membrane replacement is required.

Patent Literature 2 describes a method of diagnosing membrane fouling risk using a fluorescence sensor. However, the method of Patent Document 2 is a method that requires a huge amount of equipment and does not determine the conditions for chemical addition backwashing. In addition, when the membrane becomes clogged, it is necessary to stop the apparatus for maintenance such as membrane replacement, which lowers the operating rate of the apparatus.

In Patent Document 3, a membrane treatment apparatus having a membrane module for membrane filtration of water to be treated containing organic matter has the same membrane material and membrane shape as the membrane module, and the membrane area is 1/2 to 1/100. A membrane treatment apparatus is disclosed in which at least one or more mini-membrane modules are installed side by side, and the mini-membrane modules are configured to be able to supply the same water to be treated as the membrane modules.

However, in the membrane treatment apparatus described in Patent Document 3, the objective is to determine the conditions for chemical cleaning of the membrane, not the chemical addition backwash. After the transmembrane pressure difference in the mini-membrane module exceeds 150 kPa (that is, after the membrane is clogged), the membrane is chemically washed. In addition, there is no description of suppression of fouling on the secondary side of the membrane.

In Patent Document 4, a membrane filtration means for membrane filtration treatment of waste water containing organic matter, and a membrane of the membrane filtration means are chemically washed (chemical added ΔPa ( =ΔP0−ΔP1), a preset reference transmembrane pressure difference ΔPx is referenced to select whether or not to use the same chemical as the previous chemical in the next chemical cleaning.

However, in the waste water recovery system described in Patent Document 4, there is no description about suppression of fouling on the secondary side of the membrane. Moreover, since the conditions for the next chemical addition backwash are selected based on the transmembrane pressure difference in this apparatus, it may not be possible to determine the optimal chemical addition backwash conditions at an early stage. Determining the chemical conditions for chemical addition backwashing by the transmembrane pressure before and after chemical cleaning in this device as in Patent Document 4 makes it impossible to select chemicals at an early stage and stops this device for cleaning. There is a need. Furthermore, since the volume of the membrane module incorporated in this device is large, there is also a demerit that the amount of chemicals used increases and the amount of wastewater increases.

JP-A-11-009972 Japanese Patent No. 5677476 Japanese Patent No. 3656908 Japanese Patent No. 6693804

An object of the present invention is to determine the optimum washing conditions at an early stage and perform chemical addition backwashing even if the properties of the water to be treated fluctuate in membrane filtration using a filtration membrane, thereby preventing fouling on the secondary side of the membrane. It is an object of the present invention to provide a membrane filtration system, a membrane filtration method, a chemical addition backwashing device used in the membrane filtration system, and a control device for the chemical addition backwashing device, which are capable of suppressing ring formation and stably operating.

The present invention provides a main membrane filtration device for filtering water to be treated using a main filtration membrane, a sub-membrane filtration device having a sub-filtration membrane, and a main chemical addition backwash for performing chemical addition backwashing of the main filtration membrane. washing means, sub-chemical addition backwashing means for performing chemical addition backwashing of the sub-filtration membrane, clogging detection means for detecting clogging on the secondary side of the sub-filtration membrane, and the clogging detection means and output means for outputting a predetermined output based on the detected clogging behavior after the chemical addition backwash performed by the sub-chemical addition backwash means.

In the sub-membrane filtration device in the membrane filtration system, backwashing is preferably performed with a flux higher than that of the main membrane filtration device.

In the membrane filtration system, conditions for chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means based on the clogging behavior after the chemical addition backwashing detected by the clogging detection means It is preferable to further include control means for controlling the

The present invention comprises a main membrane filtration step of filtering water to be treated using the main filtration membrane, a main chemical addition backwashing step of performing chemical addition backwashing of the main filtration membrane, and a chemical addition backwashing of the sub-filtration membrane. and an output step of performing a predetermined output based on the clogging behavior of the sub-filtration membrane after the chemical addition backwashing performed in the sub-chemical addition backwashing step. Filtration method.

In the membrane filtration method, it is preferable to control the conditions for the chemical addition backwashing of the main filtration membrane performed in the main chemical addition backwashing step based on the clogging behavior after the chemical addition backwashing.

The present invention is a chemical addition backwashing device for performing chemical addition backwashing of a main membrane filtration device for filtering water to be treated using a main filtration membrane, comprising a sub-membrane filtration device having a sub-filtration membrane, and the main filtration. main chemical addition backwashing means for performing chemical addition backwashing of the membrane, sub-chemical addition backwashing means for performing chemical addition backwashing of the sub-filtration membrane, and clogging of the secondary side of the sub-filtration membrane. and a blockage detection means for detecting, based on the blockage behavior detected by the blockage detection means after the chemical addition backwashing performed by the sub-chemical addition backwashing means, the main chemical addition backwashing means and a control means for controlling the conditions of the chemical addition backwashing of the main filtration membrane to be performed.

The present invention is a control device for a chemical addition backwashing device that performs chemical addition backwashing of a main membrane filtration device that filters water to be treated using a main filtration membrane, wherein the chemical addition backwashing device includes a sub-filtration membrane. a main chemical addition backwashing means for performing chemical addition backwashing of the main filtration membrane, a sub chemical addition backwashing means for performing chemical addition backwashing of the sub filtration membrane, clogging detection means for detecting clogging on the secondary side of the sub-filtration membrane, and after chemical addition backwashing performed by the sub-chemical addition backwashing means detected by the clogging detection means A control device for a chemical addition backwashing device, comprising control means for controlling the conditions of the chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means based on the clogging behavior.

In the present invention, in the membranous filtration process using a filtration membrane, even if the properties of the water to be treated fluctuate, the optimum washing conditions are determined at an early stage and chemical addition backwashing is performed to prevent fouling on the secondary side of the membrane. It is possible to provide a membrane filtration system, a membrane filtration method, a chemical addition backwashing device used in the membrane filtration system, and a control device for the chemical addition backwashing device, which can be suppressed and stably operated.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the membrane filtration system which concerns on embodiment of this invention. It is a flow chart which shows an example of a membrane filtration method concerning an embodiment of the present invention. 5 is a graph showing the backwash flux decrease rate (%) with respect to the number of days of filtration after chemical addition backwash was performed in the sub-membrane filtration device of Example 1. FIG. 4 is a graph showing the transmembrane pressure difference (kPa) with respect to the number of days of filtration after chemical addition backwashing was performed in the main membrane filtration device of Example 1. FIG.

An embodiment of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

An outline of an example of a membrane filtration system according to an embodiment of the present invention is shown in FIG. 1, and its configuration will be described.

The membrane filtration system 1 includes a main membrane filtration device 10 that filters water to be treated using a main filtration membrane, a sub-membrane filtration device 12 that has a sub-filtration membrane, and a chemical addition reverse filter of the main filtration membrane of the main membrane filtration device 10 . A main backwashing pipe 36 as a main chemical addition backwashing means for washing, and a sub backwashing pipe 42 as a subchemical addition backwashing means for performing chemical addition backwashing of the sub-filtration membrane of the sub-membrane filtration device 12 , as blockage detection means for detecting blockage on the secondary side of the sub-filtration membrane, flowmeter 28 and pressure gauge 30, and sub-chemical addition backwashing means detected by flowmeter 28 and pressure gauge 30. and an output unit 16 as output means for performing a predetermined output based on the blockage behavior after chemical addition backwash. The membrane filtration system 1 may include a main treated water tank 14 for storing treated water (permeated water) of the main membrane filtration device 10 . The main backwashing pipe 36 serves as main backwashing means for backwashing the main filtration membrane of the main membrane filtration device 10, and the sub backwashing pipe 42 backwashes the subfiltration membrane of the sub membrane filtration device 12. It may function as a sub-backwash means for

In the membrane filtration system 1 of FIG. 1 , a main water-to-be-treated pipe 32 is connected to the main water-to-be-treated inlet of the main membrane filtration device 10 . A main treated water outlet of the main membrane filtration device 10 and the main treated water tank 14 are connected by a main treated water pipe 34 . A main backwashing liquid outlet of the main treated water tank 14 and a main backwashing liquid inlet on the secondary side of the main membrane filtration device 10 are connected by a main backwashing pipe 36 . A main backwashing wastewater outlet on the primary side of the main membrane filtration device 10 is connected to a main backwashing wastewater pipe 38 .

A sub-backwashing liquid inlet on the secondary side of the sub-membrane filtration device 12 and a sub-backwashing liquid outlet of the main treatment water tank 14 are connected by a sub-backwashing pipe 42 . A sub-backwashing drainage pipe 44 is connected to a sub-backwashing drainage outlet on the primary side of the sub-membrane filtration device 12 . In this way, the backwashing pipe of the main membrane filtration device 10 and the backwashing pipe of the sub-membrane filtration device 12 are branched from the main treated water tank 14, and the main membrane filtration membrane of the main membrane filtration device 10 and the sub-membrane filtration device 12 The filtration membrane is configured to be backwashed using the main treated water.

The chemical outlet of the acid tank 20 and the main backwash line 36 are connected by the main acid line 40 via the pump 24 . The chemical outlet of the acid tank 20 and the sub-backwash pipe 42 are connected by the sub-acid pipe 41 via the pump 25 . The chemical outlet of the oxidant tank 22 and the main backwash pipe 36 are connected by the main oxidant pipe 45 via the pump 27 . The chemical outlet of the oxidant tank 22 and the sub-backwashing pipe 42 are connected by a sub-oxidant pipe 46 via the pump 26 . A flow meter 28 and a pressure gauge 30 are installed on the downstream side of the connection point of the sub acid pipe 41 and the sub oxidant pipe 46 in the sub backwash pipe 42 . The output unit 16 is communicably connected to each of the flowmeter 28 and the pressure gauge 30 by wired or wireless electrical connection or the like.

The membrane filtration system 1 may include a control device 18 as control means. The control device 18 may be communicably connected to the output unit 16, the pumps 24, 25, 26, 27, flow meter 28, pressure gauge 30, etc. by wired or wireless electrical connections. The membrane filtration system 1 may further include a communication device as communication means. The communication device is connected to the control device 18, for example via the Internet, to a server. The server is provided with at least a recording unit or a computing unit. The recording unit stores, for example, data measured by the blockage detection means. The calculation unit performs calculations using the data measured by the blockage detection means, and may output an alarm, execution of chemical addition backwash, execution of chemical cleaning, etc., or may be stored in the recording unit. The data may be used together to calculate, store, or output the history of chemical addition backwashing and chemical cleaning, the amount of chemicals used, the cost of chemicals, and the like. The output is sent again to the control device 18 via the Internet, and an alarm may be issued to the output unit 16, chemical addition backwashing or chemical cleaning may be performed, or cleaning conditions may be changed.

The operation of the membrane filtration method and 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 water to be treated pipe 32, and in the main membrane filtration device 10, the water to be treated is subjected to membrane filtration using the main filtration membrane (main membrane filtration process). The obtained main treated water is sent to the main treated water tank 14 through the main treated water pipe 34 and stored therein.

In the membrane filtration system 1, when the main membrane filtration device 10 is continuously operated, for example, the main membrane filtration device 10 is cleaned periodically. The cleaning of the main filtration membrane is carried out, for example, by sending at least a part of the main treated water as main backwash water from the main treated water tank 14 through the main backwash pipe 36 to the secondary side of the main membrane filtration device 10, and then to the oxidant tank. The oxidant is supplied from 22 to the main backwash water in the main backwash pipe 36 through the main oxidant pipe 45 by the pump 27 and is flowed back from the secondary side to the primary side of the main membrane filtration device 10 (main backwash water). washing process). The main backwash drainage is discharged from the primary side of the main membrane filtration device 10 through the main backwash drainage pipe 38 .

If the fouling of the main filtration membrane is not eliminated even after performing this main backwashing, chemical addition backwashing is performed with a main chemical-added backwashing liquid in which a chemical such as an acid is added to the main backwashing water (main chemical addition backwash process). In the main chemical addition backwash step, for example, acid is supplied from the acid tank 20 to the main backwash water in the main backwash pipe 36 through the main acid pipe 40 by the pump 24 to perform chemical washing. The main chemical-added backwash waste liquid is discharged from the primary side of the main membrane filtration device 10 through the main backwash waste liquid pipe 38 . In the main chemical addition backwashing step, an immersion step of immersing the main filtration membrane in the main chemical addition backwash liquid for a predetermined time may be performed. Further, in the main chemical addition backwash step, the main chemical addition backwash waste liquid 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, in the membrane filtration process for wastewater recovery, for example, when the water to be treated contains dissolved metals, the dissolved metals permeate the secondary side of the membrane, and the permeated water, which is the membrane-treated water, is used as the backwash liquid. If backwashing is performed using a liquid to which an oxidizing agent has been added, some of the dissolved metals present in the membrane-treated water are precipitated, and fouling may occur on the secondary side of the membrane.

In the membrane filtration system 1, in addition to the main membrane filtration step by the main membrane filtration device 10, a sub-chemical addition backwashing step is provided by the sub-membrane filtration device 12 having the sub-backwashing means and the sub-chemical addition backwashing means, and the clogging is performed. Chemical addition backwashing in the sub-membrane filtration device 12 is detected based on the blockage behavior of the sub-filtration membrane after chemical addition backwashing in the sub-chemical addition backwashing step, which is detected by the flow meter 28 and the pressure gauge 30 as detection means. Output according to the situation, for example, when the difference in flux after chemical addition backwashing exceeds a predetermined reference value, outputs an alarm or the like. As a result, even if the properties of the water to be treated fluctuate, the sub-membrane filtration device 12 quickly determines the optimum washing conditions, and the main membrane filtration device 10 performs chemical addition backwash under the washing conditions to remove the membrane. Secondary side fouling can be suppressed, and stable operation becomes possible.

By providing the sub-membrane filtration device 12 separately from the main membrane filtration device 10, it is possible to determine the optimum cleaning conditions for the chemical addition backwash without stopping the main membrane filtration device 10. can maximize uptime. The water to be treated may be passed through the sub-membrane filtration device 12 in the same manner as the main membrane filtration device 10, but by not passing the water to be treated through the sub-membrane filtration device 12, it is difficult to detect the presence of the membrane. It is possible to detect fouling caused by metal deposited on the secondary side.

In addition, for example, by utilizing the fact that the flux during backwashing of the sub-membrane filtration decreases, the behavior of membrane clogging on the secondary side of the sub-membrane filtration device 12, for example, the flux during backwashing in the sub-membrane filtration device 12 From the decrease rate of , the behavior of membrane clogging of the main membrane filtration device 10 can be predicted, and the timing of chemical addition backwashing in the main membrane filtration device 10 can be determined.

An example of a method for determining optimum cleaning conditions for chemical addition backwash using the sub-membrane filtration device 12 will be described below.

In the membrane filtration system 1, when the main membrane filtration device 10 is continuously operated, the sub membrane filtration device 12 is also periodically cleaned, for example. As with the main filtration membrane, for example, at least part of the main treated water is sent as sub backwash water from the main treated water tank 14 to the secondary side of the sub membrane filtration device 12 through the sub backwash pipe 42. Then, the oxidant is supplied from the oxidant tank 22 to the sub-backwash water in the sub-backwash pipe 42 through the sub-oxidant pipe 46 by the pump 26, and flows back from the secondary side to the primary side of the sub-membrane filtration device 12. (sub-backwashing step). The sub-backwashing wastewater is discharged from the primary side of the sub-membrane filtration device 12 through the sub-backwashing wastewater pipe 44 .

If fouling of the sub-filtration membrane is not eliminated even after performing this sub-backwashing, chemicals such as acid are added to the sub-backwashing water with a sub-chemical-added backwashing liquid under the washing conditions (CEB ₀ ). Backwashing is performed (sub chemical addition backwashing step). In the sub-chemical addition backwashing step, for example, acid is supplied from the acid tank 20 to the sub-backwash water in the sub-backwashing pipe 42 through the sub-acid pipe 41 by the pump 25 to perform chemical addition backwashing. The sub-chemical-added backwashing wastewater is discharged from the primary side of the sub-membrane filtration device 12 through the sub-backwashing wastewater pipe 44 . In the sub-chemical addition backwashing step, an immersion step of immersing the sub-filtration membrane in the sub-chemical addition backwash liquid for a predetermined time may be performed. Further, in the sub-chemical addition backwashing step, the sub-chemical addition backwash waste liquid discharged from the primary side of the sub-membrane filtration device 12 may be circulated to the secondary side of the sub-membrane filtration device 12 .

In the main backwashing process, the main treated water tank 14, the main backwashing pipe 36, the oxidizing agent tank 22, the pump 27, the main oxidizing agent pipe 45, etc. function as the main backwashing means, and in the sub-backwashing step, the main treatment The water tank 14, the sub-backwashing pipe 42, the oxidant tank 22, the pump 26, the sub-oxidant pipe 46, etc. function as the sub-backwashing means. In the main chemical addition backwash process, the main treated water tank 14, the acid tank 20, the pump 24, the main acid pipe 40, the main backwash pipe 36, etc. function as the main chemical addition backwash means. In the sub-chemical addition backwash process, the main treatment water tank 14, the acid tank 20, the pump 25, the sub-acid pipe 41, the sub-backwash pipe 42, etc. function as the sub-chemical addition backwash means.

Here, the flux is measured from the flow rate and pressure after the sub-chemical addition backwash step is completed by the flow meter 28 and the pressure gauge 30, which are clogging detection means. The flux (backwash flux _CEB0 ) at the time of backwashing after the sub-chemical addition backwash under the cleaning conditions ( _CEB0 ) calculated from the flow rate and pressure detected by the flow meter 28 and the pressure gauge 30 is predetermined, for example. When the CEB reference value (backwashing flux _CEB ), which is a reference value, is exceeded (backwashing flux _CEB0 < backwashing flux _CEB ), a predetermined output such as an alarm is issued (output step). If the water temperature of the sub-chemical added backwashing liquid fluctuates and it is desired to eliminate the temperature dependence of the flux, a thermometer is further installed in the sub-backwashing pipe 42 to measure the viscosity based on the water temperature of the sub-chemicals added backwashing liquid. It is desirable to calculate the flux at the time of backwashing the sub-filtration membrane in consideration of the above.

As a result, occurrence of fouling on the secondary side of the sub-filtration membrane in the sub-membrane filtration device 12 can be detected early. When the occurrence of fouling on the secondary side of the sub-filtration membrane is detected, the sub-membrane filtration device 12 determines the optimum chemical addition backwash conditions, and the main membrane filtration device 10 determines the optimum conditions determined by the sub-membrane filtration device 12. If chemical addition backwashing is performed under suitable washing conditions, fouling on the secondary side of the membrane can be suppressed even if the property of the water to be treated fluctuates, and stable operation of the main membrane filtration device 10 is possible. By determining the optimal chemical addition backwash conditions in the sub-membrane filtration device 12 in advance, the operation of the main membrane filtration device 10 may not be stopped, and the main membrane filtration step may be continued. This allows the operating time of the main membrane filtration device 10 to be maximized.

In the sub-membrane filtration device 12, chemical addition backwashing can be performed, for example, automatically to eliminate membrane clogging, so no particular maintenance is required. In the membrane filtration method and the membrane filtration system according to the present embodiment, the membrane clogging time can be predicted in the sub membrane filtration device 12, and the chemical addition backwash of the main membrane filtration device 10 can be performed. Long-term operation is possible without stopping the operation and backwashing with chemical addition, and it is possible to suppress the decrease in the operating rate of the equipment and the decrease in the water recovery rate.

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. be done. If the optimum cleaning conditions for chemical addition backwashing are determined by the sub-membrane filtration device 12 which is smaller than the main membrane filtration device 10, the amount of chemical consumption required for determining the optimum chemical addition backwashing conditions is minimized. be able to.

In the sub-backwashing step of the sub-membrane filtration device 12 , it is preferable to backwash with a higher flux than in the main backwashing step of the main membrane filtration device 10 . As a result, the occurrence of fouling on the secondary side of the sub-filtration membrane in the sub-membrane filtration device 12 can be detected earlier. When the occurrence of fouling on the secondary side of the sub-filtration membrane is detected, the sub-membrane filtration device 12 quickly determines the optimal chemical addition backwash conditions, and the main membrane filtration device 10 determines the sub-membrane filtration device 12. If chemical addition backwashing is performed under optimal washing conditions, fouling on the secondary side of the membrane can be suppressed even if the properties of the water to be treated fluctuate, and stable operation of the main membrane filtration device 10 is possible. Become.

The flux in the sub-backwashing step of the sub-membrane filtration device 12 is, for example, 1.3 to 10 times the flux in the main backwashing step of the main membrane filtration device 10, preferably 1.3 to 5 times. , more preferably 1.5 to 2 times. If the flux in the sub-backwashing step of the sub-membrane filtration device 12 is less than 1.3 times the flux in the main backwashing step of the main membrane filtration device 10, the occurrence of fouling on the secondary side of the sub-filtration membrane will occur earlier. If it exceeds 10 times, the secondary side fouling occurrence may be overestimated and the prediction accuracy may decrease.

Further, for example, based on the backwash flux during the sub backwash in the sub membrane filtration device 12 and the backwash flux after the sub chemical addition backwash in the sub membrane filtration device 12 detected by the flow meter 28 and the pressure gauge 30, the main membrane filtration device The conditions for the main backwashing of the main filtration membrane and the conditions for the main chemical addition backwashing performed in 10 may be controlled. For example, from the tendency of the flux decrease immediately after backwashing and the flux decrease immediately after chemical addition backwashing in the sub membrane filtration device 12, the backwashing conditions of the main membrane filtration process, for example, the frequency of the main backwashing, the chemical addition backwashing For example, the frequency of main chemical addition backwashing, the chemical concentration of the main chemical addition backwash liquid used in the main chemical addition backwashing, the type of chemicals used in the main chemical addition backwashing, and the like may be controlled. These controls may be performed manually or automatically.

An example of a more specific method for determining the chemical addition backwash conditions will be described with reference to the flowchart shown in FIG.

In the sub-membrane filtration device 12, for example, sub-backwashing is performed periodically. After the sub-membrane filtration of the sub-membrane filtration device 12 is backwashed using the main treated water that has undergone membrane filtration in the main membrane filtration device 10, the pressure P ₀ detected by the pressure gauge 30 and the flow meter 28 A backwash flux (backwash Flux ₀ ) is calculated from the detected flow rate F ₀ (S10). Backwashing of the sub-membrane filtration of the sub-membrane filtration device 12 is performed using the main treated water to which a predetermined amount of oxidizing agent such as sodium hypochlorite is added, and after the backwashing, the pressure gauge 30 The backwash flux (backwash Flux 1 ) is calculated from the pressure P ₁ detected by the flow meter 28 and the flow rate F ₁ detected by the flow meter ₂₈ (S12). For the calculated backwash flux ₁ , refer to the standard backwash flux (backwash flux: preset standard filtration rate per unit membrane area after backwash, for example, about 80 to 90% of backwash flux ₀ ). When backwashing Flux ₁ ≥ backwashing Flux, it is determined that the flux is sufficiently maintained. It doesn't have to be. Sub-backwashing may be performed again in the sub-membrane filtration device 12 after a predetermined period of time.

When backwash flux ₁ <backwash flux, it _is determined that chemical addition backwash is necessary, and sub-chemical Addition backwashing is performed, and the backwashing flux (backwashing flux _CEB0 ) after the sub-chemical addition backwashing is calculated from the pressure P _CEB0 detected by the pressure gauge 30 and the flow rate F _CEB0 detected by the flow meter 28. (S14). For the calculated backwash flux _CEB0 , referring to the standard backwash flux after chemical addition backwash (backwash flux _CEB : preset standard filtration rate per unit membrane area after chemical addition backwash), backwash When the washing flux _CEB0 ≧ the backwashing flux _CEB , it is judged that the flux has sufficiently recovered under the CEB conditions (CEB ₀ ) (that is, the CEB conditions (CEB ₀ ) are sufficiently effective). Also in the main membrane filtration device 10 of , main chemical addition backwashing is performed under the CEB conditions (CEB ₀ ) (S16). In this case, the sub-membrane filtration device 12 may be terminated without chemical addition backwashing under the following cleaning conditions.

When the backwash flux _{CEB0 <} the backwash flux _CEB , it is determined that the CEB conditions (CEB ₀ ) performed in the sub-membrane filtration device 12 are insufficient. _{The backwashing} flux ₍ Backwash Flux _CEB1 ) is calculated (S18). When backwashing flux _CEB0 <backwashing flux _CEB , an output such as an alarm may be output to the output unit 16 . With respect to the calculated backwash flux _CEB1 , when backwash flux _CEB1 ≧backwash flux _CEB , the flux was sufficiently recovered under the CEB conditions (CEB ₁ ) (that is, the CEB conditions (CEB ₁ ) were sufficiently effective), the main chemical addition backwashing is performed under the CEB conditions (CEB ₁ ) also in the actual main membrane filtration device 10 (S20). In this case, the sub-membrane filtration device 12 may be terminated without chemical addition backwashing under the following cleaning conditions.

When backwashing flux _CEB1 <backwashing flux _CEB , it _is determined that the CEB conditions (CEB ₁ ) performed in the sub-membrane filtration device 12 are insufficient. Chemical addition backwash is performed, and the backwash flux (backwash Flux _CEBn ) after the sub-chemical addition backwash is calculated from the pressure P _CEBn detected by the pressure gauge 30 and the flow rate F _CEBn detected by the flow meter 28. (S22), until the backwash flux _CEBn ≧the backwash flux _CEB , that is, it is determined that the flux has been sufficiently recovered by the CEB conditions (CEB _n ) (that is, the CEB conditions (CEB _n ) are sufficiently effective). Sub chemical addition backwash may be performed by changing the CEB conditions until the chemical is added (n is an integer of 1 or more). When backwashing flux _CEB(n−1) <backwashing flux _CEB , an output such as an alarm may be output to the output unit 16 . An alert is preferably issued from CEB ₂ onwards, when the condition of the CEB is evaluated more than once. When the backwashing flux _CEBn ≧the backwashing flux _CEB , it is determined that the flux is sufficiently recovered under the CEB conditions (CEB _n ) (that is, the CEB conditions (CEB _n ) are sufficiently effective). Also in the actual main membrane filtration device 10, main chemical addition backwashing is performed under the CEB conditions (CEB _n ) (S24). In this case, the sub-membrane filtration device 12 may be terminated without chemical addition backwashing under the following cleaning conditions.

The timing at which the sub-chemical addition backwash is performed in the main membrane filtration device 10 may be calculated from the measured backwash flux decrease rate (backwash Flux ₀ /backwash flux) in the sub-membrane filtration device 12 .

The washing conditions ( _CEB conditions) following CEB ₀ , CEB ₁ , CEB ₂ , . After the washing conditions (CEB ₁ ) of 1, washing conditions different from those of the previous time may be used. For example, using the same chemical as (CEB ₀ , CEB ₁ , . . . )=(chemical concentration 0.1% by weight, chemical 0.2% by weight, . or (CEB ₀ , CEB ₁ , . . . )=(Chemical ₁ , Chemical ₂ , . )=(time 1, time 2, . . . ). For example, the inorganic acid may be changed to the organic acid. For example, an organic acid is suitable for eliminating fouling of metal particles such as manganese and iron, and if the water to be treated has a property change to water containing metal particles, evaluation is performed under the cleaning conditions using an organic acid. Thus, stable operation of the membrane can be performed.

The cleaning conditions (CEB conditions) to be evaluated may be two conditions or three conditions or more, but considering the time required for evaluation, two to three conditions are preferable.

If the rate of decrease in the backwash flux calculated in the preliminary evaluation is exceeded and membrane clogging progresses faster than expected, an output such as an alarm may be output to the output unit 16 . The content of the warning is, for example, "increase of inorganic substances in the water to be treated", and the proposal for improvement of operating conditions is, for example, "optimization of organic matter treatment (biological treatment and flocculation) in the previous stage, such as pH adjustment and addition of flocculant Confirmation of quantity” and the like. After confirming the alarm, it may be suggested to implement a backwash with added chemicals.

The control device 18 stores the data obtained by measuring the pressure, flow rate, etc. when backwashing using the main treated water in the sub-membrane filtration device 12, and the backwash flux decrease immediately after backwashing and the backwashing flux immediately after chemical addition backwashing. Data on the decrease in washing flux is calculated, and based on this, the conditions for chemical addition backwashing of the main membrane filtration device 10 and the sub membrane filtration device 12 (for example, the frequency of chemical addition backwashing, the type of chemical, the concentration of the chemical, the chemical addition backwashing time, etc.) may be automatically controlled.

For example, when Backwash Flux _CEBn ≧Backwash Flux _CEB , the controller 18 may control the cleaning conditions for the chemical addition backwash of the main membrane filtration device 10 . For example, controller 18 may control pump 24 . When Backwash Flux _CEBn <Backwash Flux _CEB , the control device 18 may control the cleaning conditions for the chemical addition backwash of the sub-membrane filtration device 12 . For example, controller 18 may control pump 25 .

A pressure gauge is installed in the main water-to-be-treated pipe 32 of the main membrane filtration device 10, and the filtration resistance values before and after backwashing and backwashing with chemical addition are measured, and the increase in the transmembrane pressure difference is confirmed as a cross-check. good too.

The output from the output unit 16 includes an audiovisually recognizable alarm such as a display and sound indicating the status of chemical addition backwashing in the sub-membrane filtration device 12, as well as a response to respond to the chemical addition backwashing status. Methods, improvement suggestions, etc. may be displayed. The output unit 16 is not particularly limited as long as it can display and output information, for example. An audio output device or the like, which is output means, may be mentioned. For example, warning methods include displaying on a touch panel of a control panel, notifying an operator via Internet communication, and notifying a monitor room or the like.

The output unit 16 may issue an output such as an alarm when the decrease in backwash flux after chemical addition backwash exceeds, for example, a predetermined reference value. One reference value for alarm may be determined in advance, or may be changed stepwise and proportionally.

The control device 18 is composed of, for example, a microcomputer and an electronic circuit including arithmetic means such as a CPU for calculating programs, storage means such as ROM and RAM for storing programs and arithmetic results, and the like. The control device 18 detects the blockage behavior after the chemical addition backwash performed by the sub-membrane filtration device 12, detected by the blockage detection means, and controls the chemical addition backwash of the main filtration membrane performed by the main membrane filtration device 10. It has the function of controlling the washing conditions. The control device 18 has a function of controlling the amount of chemicals added to the main treated water by, for example, adjusting the on/off and flow rate of the pumps 24 and 25 .

The water to be treated to be treated is, for example, water containing suspended solids, organic substances, inorganic substances such as metal particles, etc., and is not particularly limited, but includes, for example, organic substances discharged from semiconductor manufacturing factories, food factories, etc. Biologically treated water in which wastewater has been biologically treated (biological treatment process), solid-liquid separation treated water in which coagulation and solid-liquid separation treatment (coagulation/solid-liquid separation treatment process) has been performed, and coagulation of the biologically treated water after being biologically treated and solid-liquid separation treated water. It may be water that has undergone other processes before and after the biological treatment process and the coagulation/solid-liquid separation process.

Biological treatment is not particularly limited as long as it treats water to be treated using microorganisms. The flocculation and solid-liquid separation treatment may be performed using an inorganic flocculant such as polyaluminum chloride or a flocculant such as a polymer flocculant to perform flocculation treatment and solid-liquid separation treatment of the water to be treated, and there are particular restrictions no.

When the properties of the water to be treated are water in which the content of metal particles such as iron, aluminum, manganese, etc. and inorganic substances such as dissolved metals shown by the ICP analysis fluctuates in the range of 0.01 to 20 mg / L, respectively. , the membrane filtration system and the membrane filtration method according to the present embodiment are suitably applied. The water to be treated may be water in which, in addition to the content of inorganic substances, the content of organic substances represented by TOC varies in the range of 1 to 50 mg/L.

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

Examples of chemicals used for chemical addition backwashing include acids, oxidizing agents, alkalis, and the like. In particular, when the water to be treated contains dissolved metals, the dissolved metals are effective for inorganic fouling in order to suppress fouling on the secondary side of the membrane caused by the dissolved metals permeating to the secondary side of the membrane. It is preferable to examine the cleaning conditions (CEB conditions) in sub-chemical backwashing using acid.

The acid is not particularly limited, but includes inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and citric acid. It is preferable to use an organic acid such as

In the acid cleaning, the acid is preferably added so that the pH of the acid-added chemical-added backwash liquid is in the range of 1 to 3. From the viewpoint of cost effectiveness, etc., the pH is in the range of 2 to 3 More preferably, an acid is added to the

The oxidizing agent used for backwashing is not particularly limited, but examples thereof include chlorine-based oxidizing agents such as sodium hypochlorite. The oxidizing agent used in S12 is not particularly limited as long as it causes precipitation of dissolved metals in the main treated water, and examples thereof include chlorine-based oxidizing agents such as sodium hypochlorite. The concentration of sodium hypochlorite added during backwashing of the sub-filtration membrane is preferably in the range of 50 to 100 ppm. If the concentration of sodium hypochlorite is less than 50 ppm, there is a risk that the accuracy will decrease due to the decrease in the effective chlorine concentration due to organic substances in the water, and if the concentration is higher than 100 ppm, the consumption of chemicals will increase and the cost will be high. There is a concern that the film will be easily deteriorated by sodium hypochlorite.

The alkali used for backwashing is not particularly limited, but it is preferable to use relatively inexpensive sodium hydroxide, sodium hypochlorite, or the like.

In the cleaning using an oxidizing agent and an alkali, it is preferable to add the alkali so that the pH of the backwash liquid to which the alkali is added is in the range of 10 to 13, and from the viewpoint of cost effectiveness etc., the pH is in the range of 11 to 12. It is more preferable to add an alkali so that

In backwashing and backwashing with added chemicals, chemicals other than acids, alkalis, and oxidizing agents, such as membrane cleaning agents such as surfactants, may be used as necessary. Membrane detergents include, for example, the ULTRASIL series manufactured by ECOLABO.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

<Example 1>
Using the membrane filtration system 1 shown in FIG. 1, simulated water containing 0.5 mg / L of dissolved Mn as the water to be treated is passed through the main membrane filtration device under the conditions shown in Table 1 and filtered to remove sodium hypochlorite. Backwashing with added backwashing water was performed, and backwashing with backwashing water to which sodium hypochlorite was added and chemical addition backwashing (CEB) were performed in a sub-membrane filtration device. In the main membrane filtration device, backwashing was performed with a backwashing flux of 1.5 (m/d), and in the sub membrane filtration device, backwashing and CEB were performed with a backwashing flux of 2 (m/d) (main 1.3 times the backwash flux of the membrane filtration equipment).

In the sub-membrane filtration device, backwashing and CEB were performed once a day. Considering the quality of the water to be treated, a 0.2% by mass aqueous solution of oxalic acid can be considered as a basic CEB condition. In the sub-membrane filtration device, backwashing is performed five times for 30 minutes. The load applied to the sub-membrane filtration device is calculated as the load when replacing the actual equipment with "filtration time of 29 minutes + backwashing of 1 minute". Since the actual equipment performs backwashing for 48 minutes per day (24 hours/30 minutes), the load on the sub-membrane filtration device is 150/48≈3 days when the load is replaced by the actual equipment.

In the embodiment, the standard for the timing of performing CEB of the main membrane filtration device is set to "when the backwash flux is reduced by 50% from the new product", that is, "when the backwash flux reduction rate reaches 50%". do. Based on this standard, the timing for performing CEB is calculated from the backwash flux decrease behavior of the sub-membrane filtration device. FIG. 3 shows the backwash flux reduction rate (%) with respect to the number of days of filtration when chemical addition backwash is performed in the sub-membrane filtration apparatus of Example 1. FIG.

As a result of performing backwashing in the sub-membrane filtration device, the backwashing flux reduction rate was 19% with a load period of 3 days. From this, the number of days until the backwash flux reduction rate reaches 50% is 50÷19×3≈8 days. The results are summarized in Table 2.

From the above, it was estimated that the timing of performing CEB of the main membrane filtration device (reduction rate of backwash flux 50%) was 8 days after the start of water supply.

Next, FIG. 4 shows the result of water flow of the backwash flux.

Since the initial differential pressure of the main membrane filtration device was 33 kPa, the differential pressure when the backwash flux decrease rate was 50% was 66 kPa. As can be seen from FIG. 4, the increase in differential pressure gradually increased sharply from 4 days after the start of water flow, reaching 66 kPa 9 days after the start of water flow. Table 3 summarizes the results of the sub-membrane filtration device in Table 2 and the results of the main membrane filtration device in FIG.

From Table 3, comparing the number of days until the backwash flux reduction rate reaches 50%, it can be seen that the calculated values of the sub-membrane filtration device and the actual values of the main membrane filtration device match with an accuracy of 20% or less. It could be confirmed.

From the above, it was confirmed that the backwash flux reduction rate of the main membrane filtration system can be estimated using the sub-membrane filtration system, so it is possible to determine the timing of performing CEB according to the backwash flux reduction of the sub-membrane filtration system. it is conceivable that.

In this way, in the membrane filtration process using a filtration membrane, even if the properties of the water to be treated fluctuate, the optimum cleaning conditions are determined at an early stage and chemical addition backwashing is performed to prevent fouling on the secondary side of the membrane. It was found that the noise can be suppressed and stable operation becomes possible.

1 Membrane Filtration System, 10 Main Membrane Filtration Device, 12 Sub Membrane Filtration Device, 14 Main Treatment Water Tank, 16 Output Part, 18 Control Device, 20 Acid Tank, 22 Oxidant Tank, 24, 25, 26, 27 Pump, 28 Flow Rate meter, 30 pressure gauge, 32 main treated water pipe, 34 main treated water pipe, 36 main backwash pipe, 38 main backwash drain pipe, 40 main acid pipe, 41 sub-acid pipe, 42 sub-backwash pipe, 44 sub backwash drain line, 45 main oxidant line, 46 sub oxidant line.

Claims (10)

a main membrane filtration device that filters water to be treated using a main filtration membrane;
a sub-membrane filtration device having a sub-filtration membrane;
main chemical addition backwashing means for performing chemical addition backwashing of the main filtration membrane;
a sub-chemical addition backwash means for performing chemical addition backwashing of the sub-filtration membrane;
clogging detection means for detecting clogging on the secondary side of the sub-filtration membrane;
output means for outputting a predetermined output based on the blockage behavior detected by the blockage detection means after the chemical addition backwashing performed by the sub-chemical addition backwashing means;
A membrane filtration system comprising: The membrane filtration system according to claim 1,
A membrane filtration system characterized in that, in the sub-membrane filtration device, chemical addition backwashing is performed with a flux higher than that of the main membrane filtration device. The membrane filtration system according to claim 1 or 2,
a control means for controlling the conditions of the chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means based on the clogging behavior after the chemical addition backwashing detected by the clogging detection means; A membrane filtration system, further comprising: A main membrane filtration step of filtering the water to be treated using the main filtration membrane;
a main chemical addition backwashing step of performing chemical addition backwashing of the main filtration membrane;
A sub-chemical addition backwashing step of performing chemical addition backwashing of the sub-filtration membrane;
an output step of performing a predetermined output based on the clogging behavior of the sub-filtration membrane after the chemical addition backwashing performed in the sub-chemical addition backwashing step;
A membrane filtration method comprising: The membrane filtration method according to claim 4,
A membrane filtration method, wherein in the sub-membrane filtration step, chemical addition backwashing is performed with a flux higher than that in the main membrane filtration step. The membrane filtration method according to claim 4 or 5,
A membrane filtration method, wherein conditions for chemical addition backwashing of the main filtration membrane performed in the main chemical addition backwashing step are controlled based on blockage behavior after the chemical addition backwash. A chemical addition backwashing device that performs chemical addition backwashing of a main membrane filtration device that filters water to be treated using a main filtration membrane,
a sub-membrane filtration device having a sub-filtration membrane;
main chemical addition backwashing means for performing chemical addition backwashing of the main filtration membrane;
a sub-chemical addition backwash means for performing chemical addition backwashing of the sub-filtration membrane;
clogging detection means for detecting clogging on the secondary side of the sub-filtration membrane;
Chemical addition to the main filtration membrane performed by the main chemical addition backwashing means based on the clogging behavior detected by the clogging detection means after the chemical addition backwashing performed by the sub-chemical addition backwashing means. a control means for controlling the conditions of backwashing;
A chemical addition backwashing device comprising: The chemical addition backwashing device according to claim 7,
A chemical addition backwashing device characterized in that, in the sub-membrane filtration device, chemical addition backwashing is performed with a flux higher than that of the main membrane filtration device. A control device for a chemical addition backwashing device that performs chemical addition backwashing of a main membrane filtration device that filters water to be treated using a main filtration membrane, wherein the chemical addition backwashing device includes a sub-membrane having a sub-filtration membrane A filtration device, a main chemical addition backwashing means for performing chemical addition backwashing of the main filtration membrane, a sub-chemical addition backwashing means for performing chemical addition backwashing of the sub-filtration membrane, and the sub-filtration membrane. a blockage detection means for detecting blockage on the secondary side of the
Chemical addition to the main filtration membrane performed by the main chemical addition backwashing means based on the clogging behavior detected by the clogging detection means after the chemical addition backwashing performed by the sub-chemical addition backwashing means. A control device for a chemical addition backwashing device, comprising control means for controlling backwashing conditions. A control device for a chemical addition backwashing device according to claim 9,
A control device for a chemical addition backwashing device, characterized in that, in the sub-membrane filtration device, the chemical addition backwashing is performed with a flux higher than that of the main membrane filtration device.