JP2022178133A - Membrane filtration system, membrane filtration method, chemical agent addition backwash device, and control device for chemical agent addition backwash device - Google Patents

Abstract

To provide a membrane filtration system which, in membrane filtration treatment with a filtration membrane, can carry out chemical agent addition backwash with an optimum washing condition early determined irrespective of variation in properties and states of water to be treated to suppress membrane fouling and thereby carry out stable operation.SOLUTION: A membrane filtration system 1 includes: a main membrane filtration device 10 which filters water to be treated using a main filtration membrane; a sub-membrane filtration device 12 which filters water to be treated which branches from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane; main chemical agent addition backwash means to carry out chemical agent addition backwash of the main filtration membrane; sub-chemical agent addition backwash means to carry out chemical agent addition backwash of the sub-filtration membrane; a pressure gage 26 as sub-filtration resistance detection means to detect a filtration resistance value of the sub-filtration membrane; and an output part 14 as output means to carry out a predetermined output on the basis of the filtration resistance value detected by the pressure gage 26 before and after the chemical agent addition backwash carried out by the sub-chemical agent addition backwash means.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 cause of membrane fouling is different, the type of chemical used for the chemical addition backwash is different.

When membrane fouling occurs, it becomes difficult to obtain treated water, and it becomes necessary to stop the wastewater recovery system, to clean large-scale membranes with chemicals, or to purchase new membranes. Therefore, even if the properties of the water to be treated fluctuate, there is a demand for a method that enables stable operation by determining the optimum cleaning conditions at an early stage and performing backwashing with chemical addition to suppress membrane fouling. ing.

In Patent Document 1, 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 1, the objective is to determine the conditions for chemical cleaning of the membrane, not the chemical addition backwash.

In Patent Document 2, 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 wastewater recovery system described in Patent Document 2, the conditions for the next chemical addition backwash are selected based on the transmembrane pressure difference in this device, so the optimal chemical addition backwash conditions are determined early. may not be possible. Determining the chemical conditions for chemical addition backwashing by the transmembrane pressure before and after chemical cleaning in this device as in Patent Document 2 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.

Japanese Patent No. 3656908 Japanese Patent No. 6693804

The object of the present invention is to suppress fouling of the membrane by determining the optimum washing conditions at an early stage and performing chemical addition backwashing even if the properties of the water to be treated fluctuate in the membrane filtration process using a filtration membrane. To provide a method membrane filtration system capable of stable operation, 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.

The present invention provides a main membrane filtration device for filtering water to be treated using a main filtration membrane, and a sub-membrane for filtering water to be treated branched from the water to be treated of the main membrane filtration device using 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. Based on the filtration resistance values before and after the chemical addition backwashing performed by the sub chemical addition backwashing means detected by the sub filtration resistance detection means for detecting the filtration resistance value of and output means for outputting a predetermined output through the membrane filtration system.

In the sub-membrane filtration device in the membrane filtration system, it is preferable to pass water with a higher flux than the main membrane filtration device.

In the membrane filtration system, chemical addition backwashing of the main filtration membrane is performed by the main chemical addition backwashing means based on the filtration resistance values before and after the chemical addition backwashing detected by the sub-filtration resistance detection means. It is preferable to further include control means for controlling the conditions of.

The present invention provides a main membrane filtration step of filtering water to be treated using a main filtration membrane, and a sub-membrane filtering water to be treated branched from the water to be treated in the main membrane filtration step using a sub-filtration membrane. In a filtration step, 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, and the sub-chemical addition backwashing step and an output step of performing a predetermined output based on the filtration resistance values before and after chemical addition backwash.

In the sub-membrane filtration step in the membrane filtration method, it is preferable to pass water with a higher flux than in the main membrane filtration step.

In the membrane filtration method, it is preferable to control conditions for chemical addition backwashing of the main filtration membrane performed in the main chemical addition backwashing step based on filtration resistance values before and 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 that filters water to be treated using a main filtration membrane, wherein the main membrane filtration device is treated using a sub-filtration membrane. A sub-membrane filtration device for filtering water to be treated branched from water, a main chemical-added backwashing means for performing chemical-added backwashing of the main filtration membrane, and a chemical-added backwashing of the sub-filtration membrane. sub-chemical addition backwashing means, sub-filtration resistance detection means for detecting the filtration resistance value of the sub-filtration membrane, and filtration resistance before and after the chemical addition backwash detected by the sub-filtration resistance detection means 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 value.

In the sub-membrane filtration device in the chemical addition backwashing device, it is preferable that water is passed with a flux higher than that of the main membrane filtration device.

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 sub-membrane filtration device for filtering the water to be treated branched from the water to be treated of the main membrane filtration device using the a sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane, and based on the filtration resistance values before and after the chemical addition backwash detected by the sub-filtration resistance detection means, the main 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 chemical addition backwashing means.

In the sub-membrane filtration device in the control device for the chemical addition backwashing device, it is preferable that water is passed with a flux higher than that of the main membrane filtration device.

In the present invention, in membrane filtration using a filtration membrane, 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 backwash to suppress membrane fouling. 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 that can be operated stably.

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. It is a graph which shows an example of the filtration resistance (/m) with respect to the amount of filtration ( ^m3 / ^m2 ) at the time of backwashing in a membrane filtration apparatus. 2 is a graph showing an example of filtration resistance (/m) versus filtration amount (m ³ /m ² ) when backwashing and chemical addition backwashing are performed in a membrane filtration device. 4 is a graph showing the transmembrane pressure difference (MPa) with respect to the number of days of filtration when washing condition 1 is carried out with chemical addition backwashing in the main membrane filtration device of Example 1. FIG. 4 is a graph showing the filtration resistance (/m) against the filtration amount (m ³ /m ² ) when the sub-membrane filtration device of Example 1 is subjected to washing condition 1 with chemical addition backwash. 4 is a graph showing the transmembrane pressure difference (MPa) with respect to the number of days of filtration when washing conditions 1+washing conditions 2 are carried out with chemical addition backwashing in the main membrane filtration device of Example 2. FIG. 10 is a graph showing the filtration resistance (/m) versus the filtration amount (m ³ /m ² ) when the sub-membrane filtration device of Example 2 is subjected to washing condition 1+washing condition 2 with chemical addition backwash.

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, and filters water to be treated that is branched from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane. The sub membrane filtration device 12, the main backwashing pipe 32 as a main chemical addition backwashing means for performing chemical addition backwashing of the main filtration membrane of the main membrane filtration device 10, and the chemical of the sub filtration membrane of the sub membrane filtration device 12 A sub-backwash pipe 42 as a sub-chemical addition backwash means for performing addition backwash, and a flow meter 25 and a pressure and an output unit 14 as output means for performing a predetermined output based on the filtration resistance values before and after the chemical addition backwashing performed by the sub-chemical addition backwashing means detected by the flowmeter 25 and the pressure gauge 26. , provided. The main backwashing pipe 32 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 treated water pipe 28 is connected to the treated water inlet of the main membrane filtration device 10, and a main treated water pipe 30 is connected to the main treated water outlet. A main backwash pipe 32 is connected to the washing liquid inlet. A sub-treated water pipe 38 branched from the main treated-water pipe 28 is connected to the treated water inlet of the sub-membrane filtration device 12, and a sub-treated water pipe 40 is connected to the sub-treated water outlet. A sub backwash pipe 42 is connected to the washing liquid inlet. The chemical outlet of the acid tank 18, which is an example of the first chemical tank, and the main backwash pipe 32 are connected via the pump 22 by the acid pipe 34, which is the first chemical pipe. The chemical outlet of the oxidant tank 20, which is an example of the second chemical tank, and the main backwash pipe 32 are connected via the pump 24 by the oxidant pipe 36, which is the second chemical pipe. An acid pipe 44 branched from the acid pipe 34 is connected to the sub backwash pipe 42 , and an oxidant pipe 46 branched from the oxidant pipe 36 is connected to the sub backwash pipe 42 . A flow meter 25 and a pressure gauge 26 are installed in the sub-to-be-treated water pipe 38 . The pressure gauge 26 is provided with the output section 14 .

The membrane filtration system 1 may include a control device 16 as control means. The control device 16 may be communicably connected to the output unit 14, the pump 22, the pump 24, the flow meter 25, the pressure gauge 26, and the like by wired or wireless electrical connection or the like. The membrane filtration system 1 may further include a communication device as communication means. The communication device is connected to the control device 16, 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 sub-filtration resistance detection means. In the calculation unit, calculation using the data of the sub-filtration resistance is performed, and outputs such as alarm, execution of chemical addition backwash, execution of chemical cleaning, etc. may be performed, and data stored in the recording unit may be combined. , the execution history of chemical addition backwashing and chemical cleaning, the amount of chemicals used, the cost of chemicals, etc. may be calculated and stored or output. The output is sent again to the control device 16 via the Internet, and an alarm may be issued to the output unit 14, 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 28, 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 discharged through the main treated water pipe 30 .

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 main filtration membrane is washed by, for example, at least part of the main treated water flowing back as main backwash water from the secondary side to the primary side of the main membrane filtration device 10 through the main backwash pipe 32 (main backwash process). Main backwash waste water is discharged from the primary side of the main membrane filtration device 10 .

If the fouling of the main filtration membrane is not resolved even after the main backwashing, chemical addition backwashing is performed with the main chemical addition backwashing liquid in which chemicals are added to the main backwashing water (main chemical addition backwashing washing process). In the main chemical addition backwash process, for example, acid is supplied from the acid tank 18 through the acid pipe 34 to the main backwash water in the main backwash pipe 32 by the pump 22 to perform acid washing, or the oxidant tank 20 The pump 24 supplies the oxidant to the main backwash water in the main backwash pipe 32 through the oxidant pipe 36 to perform oxidant washing. Alkali may be used in addition to the oxidizing agent. The main chemical-added backwash waste liquid is discharged from the primary side of the main membrane filtration device 10 . 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 backwashing 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, fouling (clogging) of the membrane may occur in the membrane filtration process in wastewater recovery or the like. Membrane fouling factors in membrane filtration are mainly two: organic substances resulting from the preceding biological treatment process, and metal particles derived from inorganic flocculants resulting from the preceding coagulation and solid-liquid separation process. . When the properties of the water to be treated fluctuate, the main factor is that the biological treatment, coagulation, and solid-liquid separation in the preceding stages of the membrane filtration process become unstable. Since the amount of fouling etc. changes, the main factor of fouling also changes. Different main factors of membrane fouling require different types of chemicals to be used for chemical backwashing.

In the membrane filtration system 1, in addition to the main membrane filtration step by the main membrane filtration device 10, a sub-membrane filtration step by a sub-membrane filtration device 12 having a sub-backwashing means and a sub-chemical addition backwashing means is provided, and the sub-filtration resistance is Based on the filtration resistance value in the sub-membrane filtration process detected by the flow meter 25 and the pressure gauge 26, which are detection means, an output corresponding to the situation of chemical addition backwash in the sub-membrane filtration device 12, for example, the chemical addition backwash When the difference between the front and rear filtration resistance values exceeds a predetermined threshold value, an alarm or the like is output. As a result, even if the properties of the water to be treated fluctuate, the sub-membrane filtration device 12 quickly determines the optimum cleaning conditions, and the main membrane filtration device 10 performs chemical addition backwash under the cleaning conditions to remove the membrane. 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.

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.

The water to be treated branched from the main water to be treated pipe 28 is sent to the sub-membrane filtration device 12 through the sub-to-be-treated water pipe 38, and in the sub-membrane filtration device 12, the membrane of the water to be treated is Filtration is performed (sub-membrane filtration step). The obtained sub-treated water is discharged through the sub-treated water pipe 40 .

Thus, in the membrane filtration system 1 , the water to be treated branched from the main water-to-be-treated pipe 28 is also passed through the sub-membrane filtration device 12 when the main membrane filtration device 10 is continuously operated. Also in the sub-membrane filtration device 12, for example, the sub-filtration membrane is cleaned periodically. As with the main filtration membrane, for example, at least part of the sub-treated water is reversed from the secondary side of the sub-membrane filtration device 12 to the primary side through the sub-backwashing pipe 42 as sub-backwashing water. (sub-backwashing step). The sub-backwash waste water is discharged from the primary side of the sub-membrane filtration device 12 . The sub-backwashing step may be performed periodically, and based on the filtration resistance values detected by the flowmeter 25 and the pressure gauge 26, for example, when the filtration resistance values detected by the flowmeter 25 and the pressure gauge 26 are It may also be done when a predetermined backwash threshold is exceeded.

If fouling of the sub-filtration membrane is not eliminated even after performing this sub-backwashing, chemical-added backwashing is performed with a sub-chemical-added backwash liquid in which chemicals are added to the sub-backwash water (sub-chemical-added backwashing). washing process). In the sub-chemical addition backwash step, for example, acid is supplied from the acid tank 18 to the sub-backwash water in the sub-backwash pipe 42 through the acid pipe 34 and the acid pipe 44 by the pump 22 to perform acid washing, or An oxidant is supplied from the oxidant tank 20 to the sub-backwash water in the sub-backwash pipe 42 through the oxidant pipe 36 and the oxidant pipe 46 by the pump 24, and oxidant washing is performed. Alkali may be used in addition to the oxidizing agent. The sub-chemical added backwash waste liquid is discharged from the primary side of the sub-membrane filtration device 12 . 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 backwashing pipe 32 functions as the main backwashing means, and in the sub-backwashing process, the sub-backwashing pipe 42 functions as the sub-backwashing means. In the main chemical addition backwash process, the acid tank 18, the pump 22, the acid pipe 34, etc. serve as the first chemical supply means, for example, the acid supply means, and the oxidant tank 20, the pump 24, the oxidant pipe 36, etc. serve as the second chemical supply means. means, for example, the oxidant supply means, and in addition to the acid supply means and the oxidant supply means, the main backwash pipe 32 functions as the main chemical addition backwash means. In the sub-chemical addition backwash step, the acid tank 18, the pump 22, the acid pipe 34, the acid pipe 44, etc. serve as the first chemical supply means, for example, the acid supply means, the oxidant tank 20, the pump 24, the oxidant pipe 36, the oxidant The agent pipe 46 and the like function as a second chemical supply means, for example, an oxidant supply means, and in addition to the acid supply means and oxidant supply means, the sub backwash pipe 42 functions as a sub chemical addition backwash means.

Here, the water to be treated is passed through the sub-membrane filtration device 12 before and after the sub-chemical addition backwashing step, and the sub-chemical addition backwashing step is detected by the flow meter 25 and the pressure gauge 26, which are sub-filtration resistance detection means. Filtration resistance is measured from the flow rate and pressure before and after the start and end of . Based on the filtration resistance value calculated from the decrease in flow rate and the increase in pressure detected by the flow meter 25 and the pressure gauge 26, for example, the filtration resistance value before the chemical addition backwash when performing the sub-chemical addition backwash. When ΔR ₁ (R ₀ −R ₁ ) calculated from (R ₀ ) and the filtration resistance value after chemical addition backwash (R ₁ ) exceeds, for example, the CEB standard value which is a predetermined threshold, a predetermined alarm such as is output (output step). If the temperature of the water to be treated fluctuates and it is desired to eliminate the temperature dependence of the filtration resistance value, a thermometer is further installed in the sub-to-be-treated water pipe 38, and the viscosity, etc. based on the measured water temperature of the water to be treated is considered. It is desirable to calculate the filtration resistance value of the sub-filtration membrane.

As a result, occurrence of fouling of the sub-filtration membrane in the sub-membrane filtration device 12 can be detected early. When the occurrence of fouling in 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 uses the optimum washing conditions determined by the sub-membrane filtration device 12. By performing chemical addition backwashing, fouling 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 becomes 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.

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-membrane filtration device 12 (sub-membrane filtration step), it is preferable to pass water with a higher flux than in the main membrane filtration device 10 (main membrane filtration step). Thereby, occurrence of fouling of the sub-filtration membrane in the sub-membrane filtration device 12 can be detected earlier. When the occurrence of fouling in 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 performs the optimal cleaning determined by the sub-membrane filtration device 12. If chemical addition backwashing is performed under certain conditions, fouling 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 becomes possible.

In the example of the membrane treatment apparatus described in Patent Document 1, the same flux is passed through this apparatus and the mini-membrane module, and the membrane is chemically cleaned after the transmembrane pressure difference in the mini-membrane module exceeds 150 kPa. Therefore, it is difficult to detect the occurrence of fouling at an early stage, and it is difficult to respond to changes in the properties of the water to be treated at an early stage.

The flux in the sub-membrane filtration device 12 (sub-membrane filtration step) is, for example, 2 to 10 times, preferably 4 to 6 times, the flux in the main membrane filtration device 10 (main membrane filtration step). If the flux in the sub-membrane filtration device 12 is less than twice the flux in the main membrane filtration device 10, the occurrence of fouling in the sub-filtration membrane may not be detected earlier. There is a risk that the evaluation of ring occurrence will be excessive and the prediction accuracy will decrease.

Further, for example, based on the filtration resistance values before and after the sub backwash in the sub membrane filtration device 12 and the filtration resistance values before and after the sub chemical addition backwash in the sub membrane filtration device 12 detected by the pressure gauge 26, The conditions for the main backwashing of the main filtration membrane and the conditions for the main chemical addition backwashing may be controlled. For example, from the tendency of resistance increase immediately after backwashing in the sub-membrane filtration device 12 and resistance increase immediately after chemical addition backwashing, backwashing conditions in the main membrane filtration process, for example, frequency of main backwashing, 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, the water to be treated branched from the main water-to-be-treated pipe 28 of the main membrane filtration device 10 is subjected to membrane filtration for a predetermined time, and then sub-backwashing is performed periodically, for example. If the fouling of the sub-filtration membrane is not eliminated even after performing the sub-backwashing, chemical addition backwashing is performed. The filtration resistance value (R ₀ ) before chemical addition backwashing when chemical addition backwashing was performed was measured (S10), for example, chemical addition backwashing was performed under cleaning condition 1 (for example, an oxidizing agent was used as the chemical). (S12), the filtration resistance value (R ₁ ) after chemical addition backwashing is measured, for example, the control device 16 compares the filtration resistance value (R ₀ ) before chemical addition backwashing and after chemical addition backwashing _{is calculated} (S14 _{) .} The controller 16 refers to the CEB chemical condition change reference ΔR _ref , which is the preset reference filtration resistance increase degree, for the calculated ΔR ₁ .

When ΔR ₁ ≤ CEB chemical condition change reference ΔR _ref , it is determined that the filtration resistance has sufficiently decreased under the first evaluated cleaning condition 1 (that is, chemical addition backwash is sufficient). Therefore, the control device 16 issues an instruction to perform chemical addition backwashing of the main membrane filtration device 10 under the cleaning condition 1, and chemical addition backwashing is performed in the main membrane filtration device 10 under the cleaning condition 1 (S20). In this case, the chemical addition backwashing according to the second cleaning condition 2 in the sub-membrane filtration device 12 may be terminated without being performed.

If ΔR ₁ >CEB chemical condition change reference ΔR _ref , cleaning condition 2, which is a different chemical condition from the previous time, is used in the next chemical addition backwash. For example, after chemical addition backwashing is performed (S16) under cleaning condition 2 (for example, an acid is used as the chemical), the filtration resistance value (R ₂ ) after chemical addition backwashing is measured, for example, by the control device 16 ΔR ₂ (R ₀ −R ₂ ), which is the difference between the filtration resistance value (R ₀ ) before chemical addition backwashing and the filtration resistance value (R ₂ ) after chemical addition backwashing, is calculated (S18). For example, controller 16 references CEB drug reconditioning reference ΔR _ref for calculated ΔR ₂ .

When ΔR ₂ ≤ CEB chemical condition change reference ΔR _ref , it is determined that the filtration resistance has sufficiently decreased under the second evaluated cleaning condition 2 (that is, chemical addition backwash is sufficient). Therefore, the control device 16 issues an instruction to perform chemical addition backwashing of the main membrane filtration device 10 under the cleaning condition 2, and chemical addition backwashing is performed in the main membrane filtration device 10 under the cleaning condition 2 (S22). In this case, the sub-membrane filtration device 12 may be terminated without chemical addition backwashing under the following cleaning conditions.

If ΔR ₂ >CEB chemical condition change reference ΔR _ref , the next chemical addition backwash uses cleaning conditions that are different chemical conditions from the previous time, and thereafter ΔRN _≤ CEB chemical condition change reference ΔR _ref . (N is an integer equal to or greater than 1), the same flow as S10 to S14 is continued.

For cleaning condition 2 and subsequent cleaning conditions, cleaning conditions different from the previous cleaning conditions may be used. Cleaning concentration and cleaning time may be used.

When ΔRN _≦ CEB chemical condition change reference ΔR _ref , the control device 16 may control the cleaning conditions for the chemical addition backwash of the main membrane filtration device 10 . For example, the controller 16 may control the pumps 22 and 24 .

When it is considered that the fouling caused by organic matter acts more predominantly than the fouling caused by inorganic matter from the properties of the water to be treated, for example, under the cleaning condition 1, the chemical added for backwashing is effective in removing organic matter. The conditions using a certain oxidizing agent and alkali are evaluated first, and then the conditions using an acid that is effective in removing inorganic matter as a chemical for backwashing with added chemicals in cleaning condition 2 are evaluated. When it is considered that fouling caused by inorganic substances acts more predominantly than fouling caused by organic substances from the properties of the water to be treated, for example, under the cleaning condition 1, chemical addition backwashing chemicals are effective in removing inorganic substances. The condition using a certain acid is evaluated first, and then the condition using an oxidizing agent and an alkali, which are effective in removing organic substances, as a chemical for chemical addition backwashing under the cleaning condition 2 is evaluated.

In addition, the degree of increase in filtration resistance (ΔR _cake , ΔR _backwash , _ΔRCEB ) is calculated from the filtration resistance value of the chemical addition backwash of the sub-membrane filtration device 12, and alarms and operation improvement suggestions that can be considered from the membrane clogging behavior are generated. You may output to the output part 14. FIG. FIG. 3 shows an example of filtration resistance (/m) with respect to filtration amount (m ³ /m ² ) when backwashing is performed in the membrane filtration device. FIG. 4 is a graph showing an example of filtration resistance (/m) versus filtration amount (m ³ /m ² ) when backwashing and chemical addition backwashing are performed in the membrane filtration device.

The degree of increase in filtration resistance ΔR _cake is the filtration resistance that increases in one membrane filtration step, and is the slope of the resistance generated by the cake or the like adhering to the membrane surface. Cake resistance is a reversible membrane blockage that reverses with backwash. The degree of increase in filtration resistance ΔR _backwash is the slope of filtration resistance that is difficult to recover by backwashing. The filtration resistance increase degree ΔR _CEB is a filtration resistance that is difficult to recover even by chemical addition backwash, and is irreversible membrane clogging.

For example, when ΔR _cake becomes higher than normal, an alarm is issued to the output unit 14, and a proposal for improvement of the operating conditions is presented. Contents of the alarm include, for example, "abnormal cake resistance". In cases where the cake resistance is abnormal, the concentration of suspended solids in the membrane filtration raw water is considered to be increasing. Therefore, the content of the improvement proposal for the operating conditions is, for example, "check the turbidity of the pre-processed water and adjust the operation." , "halve the filtration time", and the like.

For example, when the ΔR _backwash becomes higher than normal, an alarm is issued to the output unit 14, for example, and a proposal for improving operating conditions is presented. Contents of the alarm include, for example, "backwash recovery abnormality". In the case of abnormal backwash recovery, it is possible that the previous organic matter treatment (for example, biological treatment, coagulation sedimentation, etc.) is defective. optimization (reexamination of the amount of coagulant added, change of pH, etc.)”.

For example, when ΔR _CEB becomes higher than normal, an alarm is issued to the output unit 14, and a proposal for improvement of operating conditions is presented. Contents of the alarm include, for example, "chemical addition backwash recovery abnormality". The contents of the proposal for improvement of the operating conditions include, for example, "change of CEB chemical type" and "increase of CEB concentration".

The control device 16 stores data obtained by measuring the pressure, flow rate, and the like when the water to be treated is passed through the sub-membrane filtration device 12. Data is calculated, and based on this, conditions for chemical addition backwashing of the main membrane filtration device 10 and sub membrane filtration device 12 (for example, frequency of chemical addition backwash, type of chemical, concentration of chemical, chemical addition backwash time, etc.) may be automatically controlled.

A pressure gauge is installed in the main water-to-be-treated pipe 28 of the main membrane filtration device 10, and the filtration resistance values before and after backwashing and backwashing with chemical addition are measured, and an increase in the transmembrane pressure is confirmed as a cross-check. good too.

The output from the output unit 14 includes an audiovisually recognizable alarm such as a display and sound indicating the state of chemical addition backwashing in the sub-membrane filtration device 12, as well as a response for responding to the chemical addition backwashing state. Methods, improvement suggestions, etc. may be displayed. The output unit 14 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 14 may output an alarm or the like when the difference in the filtration resistance values before and after chemical addition backwashing exceeds, for example, a predetermined threshold value. A single alarm threshold may be determined in advance, or may be changed stepwise and proportionally.

The control device 16 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 16 controls the main filtration membrane performed in the main membrane filtration device 10 based on the filtration resistance values before and after the chemical addition backwash performed in the sub membrane filtration device 12, which are detected by the sub filtration resistance detection means. It has a function to control the conditions of chemical addition backwash. The control device 16 has a function of controlling the amount of chemicals added to the main chemical-added backwash liquid by, for example, adjusting the on/off and flow rates of the pumps 22 and 24 .

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, and the flocculation treatment and solid-liquid separation treatment of the water to be treated may be performed. no.

The properties of the water to be treated vary from 1 to 50 mg/L of organic matter content indicated by TOC, or metal particles such as iron, aluminum, manganese, etc., and inorganic matter, such as dissolved metals, indicated by ICP analysis. The membrane filtration system and the membrane filtration method according to the present embodiment are preferably applied to water whose content varies in the range of 0.01 to 20 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.

The acid used for backwashing with chemicals is not particularly limited, but inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and citric acid can be mentioned. , oxalic acid, citric acid and the like are preferably used.

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 chemical addition backwashing is not particularly limited, but examples thereof include chlorine-based oxidizing agents such as sodium hypochlorite.

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

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

In chemical addition backwashing, 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, coagulation and solid-liquid separation treated water was passed under the conditions shown in Table 1 to perform backwashing and chemical addition backwashing. In the main membrane filtration device, water was passed at a flux of 1.2 (m/d), and in the sub-membrane filtration device, water was passed at a flux of 7 (m/d) (the flux of the main membrane filtration device was 5.83 times).

The cleaning conditions for chemical addition backwash are cleaning condition 1: sodium hypochlorite as an oxidizing agent + sodium hydroxide as an alkali (effective for fouling caused by organic matter), cleaning condition 2: oxalic acid as an acid. (Effective for fouling caused by inorganic substances) is conceivable.

[Washing condition 1: sodium hypochlorite + sodium hydroxide]
In washing condition 1, an aqueous solution of sodium hypochlorite + sodium hydroxide (sodium hypochlorite concentration: 900 mg/L, sodium hydroxide concentration: 280 mg/L) was used as the chemical-added backwash liquid. FIG. 5 shows the transmembrane pressure difference (MPa) with respect to the number of days of filtration when cleaning condition 1 is carried out with chemical addition backwashing in the main membrane filtration device. FIG. 6 shows the filtration resistance (/m) against the filtration amount (m ³ /m ² ) when the sub-membrane filtration device of Example 1 is subjected to washing condition 1 with chemical addition backwash.

As shown in FIG. 6, from the measurement results of the filtration resistance value of the sub-membrane filtration device, the degree of increase in filtration resistance ΔR _CEB increases in the chemical addition backwash of sodium hypochlorite + sodium hydroxide. It was judged that washing by washing was insufficient.

As shown in FIG. 5, even in the measurement results of the filtration resistance value of the main membrane filtration device in which chemical addition backwashing was performed under cleaning condition 1, an increase in transmembrane pressure difference was confirmed, and the cleaning effect of chemical addition backwashing was insufficient. was confirmed.

[Washing condition 1: sodium hypochlorite + sodium hydroxide + washing condition 2: oxalic acid]
Therefore, in addition to cleaning condition 1 using sodium hypochlorite, which is effective against fouling caused by organic substances, chemical addition backwashing under cleaning condition 2 using oxalic acid, which is effective against fouling caused by inorganic substances, was also performed.

In the cleaning condition 2, an aqueous solution of oxalic acid (concentration of oxalic acid: 0.2% by weight) was used as the chemical-added backwash liquid. FIG. 7 shows the transmembrane pressure difference (MPa) with respect to the number of days of filtration when washing conditions 1+washing conditions 2 are carried out in chemical addition backwashing in the main membrane filtration apparatus of Example 2. FIG. FIG. 8 shows the filtration resistance (/m) with respect to the filtration amount (m ³ /m ² ) when the sub-membrane filtration apparatus of Example 2 is subjected to washing condition 1+washing condition 2 with chemical addition backwash.

As shown in FIG. 8, it was confirmed from the measurement results of the filtration resistance value of the sub-membrane filtration device that the increase in the degree of increase in filtration resistance ΔR _CEB was suppressed, so it was judged that the washing was sufficient.

As shown in FIG. 7, almost no increase in the filtration resistance value of the main membrane filtration device subjected to chemical addition backwashing under cleaning condition 1+cleaning condition 2 was observed, and stable operation was possible.

By using cleaning conditions 1 and 2 together in the main membrane filtration device based on the measurement results of the filtration resistance value of the sub-membrane filtration device, membrane fouling was suppressed and stable operation was possible for 6 months. .

In this way, in the membranous filtration process using a filtration membrane, even if the properties of the water to be treated fluctuate, it is possible to determine the optimum washing conditions at an early stage and perform chemical addition backwashing to suppress membrane fouling. This enabled stable operation.

1 membrane filtration system, 10 main membrane filtration device, 12 sub-membrane filtration device, 14 output unit, 16 control device, 18 acid tank, 20 oxidant tank, 22, 24 pump, 25 flow meter, 26 pressure gauge, 28 main subject Treated water piping, 30 main treated water piping, 32 main backwashing piping, 34, 44 acid piping, 36, 46 oxidizing agent piping, 38 sub-treated water piping, 40 sub-treated water piping, 42 sub-backwashing piping.

Claims (10)

a main membrane filtration device that filters water to be treated using a main filtration membrane;
a sub-membrane filtration device that uses a sub-membrane filtration device to filter the water to be treated that is branched from the water to be treated of the main membrane filtration device;
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;
Sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane;
output means for performing a predetermined output based on the filtration resistance values before and after the chemical addition backwashing performed by the sub chemical addition backwashing means, which are detected by the sub filtration resistance detection 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, water is passed with a flux higher than that of the main membrane filtration device. The membrane filtration system according to claim 1 or 2,
Based on the filtration resistance values before and after the chemical addition backwashing detected by the sub-filtration resistance detection means, the conditions for the chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means are controlled. A membrane filtration system, further comprising control means. A main membrane filtration step of filtering the water to be treated using the main filtration membrane;
a sub-membrane filtration step of filtering the water to be treated branched from the water to be treated in the main membrane filtration step using a sub-membrane filtration;
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 filtration resistance values before and after the chemical addition backwash performed in the sub-chemical addition backwash 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, water is passed with a higher flux than 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 filtration resistance values before and after the chemical addition backwashing. 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 that uses a sub-membrane filtration device to filter the water to be treated that is branched from the water to be treated of the main membrane filtration device;
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;
Sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane;
Based on the filtration resistance values before and after the chemical addition backwashing detected by the sub-filtration resistance detection means, the conditions for the chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means are controlled. a control means;
A chemical addition backwashing device comprising: The chemical addition backwashing device according to claim 7,
In the sub-membrane filtration device, the chemical addition backwash device is characterized in that water is passed 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 uses a sub-filtration membrane to perform the above-mentioned A sub-membrane filtration device for filtering the water to be treated branched from the water to be treated of the main membrane filtration device, a sub-chemical addition backwashing means for performing chemical addition backwashing of the sub-filtration membrane, and the sub-filtration membrane A sub-filtration resistance detection means for detecting a filtration resistance value,
Based on the filtration resistance values before and after the chemical addition backwashing detected by the sub-filtration resistance detection means, the conditions for the chemical addition backwashing of the main filtration membrane performed by the main chemical addition backwashing means are controlled. A control device for a chemical addition backwashing device, comprising control means. 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, water is passed with a flux higher than that in the main membrane filtration device.

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