Membrane filtration system, membrane filtration method, chemical addition backwash device, and control device for chemical addition backwash device

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

[Technical field]

[0001] The present invention relates to a membrane filtration system that performs membrane filtration of water to be treated using a filtration membrane such as a turbidity removing membrane, a membrane filtration method, a chemical addition backwash device used in the membrane filtration system, and a control device for the chemical addition backwash device. [Background technology]

[0002] In recent years, the demand for water has been increasing, and there is an increasing demand for the recovery and reuse of wastewater. In wastewater recovery, which recovers and reuses wastewater, there is a method in which, after biological treatment, coagulation, and solid-liquid separation, a membrane filtration process is performed on biologically treated water or solid-liquid separated water containing suspended matter, etc., using a filtration membrane such as a turbidity removing membrane. In this method, the biological treatment, coagulation, and solid-liquid separation process may become unstable due to fluctuations in the properties of the water to be treated, and membrane fouling (blockage) may occur in the membrane filtration process. In this case, for example, backwashing is performed by passing backwash water from the secondary side to the primary side of the membrane, and physical cleaning is performed to physically peel off the deposits on the membrane surface or inside the membrane. In order to eliminate membrane fouling that cannot be eliminated by backwashing, chemically enhanced backwashing (CEB: Chemical Enhanced Backwash) may be performed, in which a chemical-added backwash solution in which an oxidizing agent such as sodium hypochlorite, or a chemical such as an alkali or an acid is added to the backwash water is used.

[0003] When the properties of the water to be treated change, it is difficult to stably perform the biological treatment and the coagulation and solid-liquid separation treatments that precede the membrane filtration treatment. When the biological treatment becomes unstable, if the chemical recovery effect by the backwashing with the addition of chemicals in the membrane filtration treatment is insufficient, membrane fouling occurs mainly due to organic matter. When the coagulation and solid-liquid separation treatments become unstable, if the chemical recovery effect by the backwashing with the addition of chemicals in the membrane filtration treatment is insufficient, membrane fouling occurs 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 backwashing with the addition of chemicals will be different.

[0004] When membrane fouling occurs, it becomes difficult to obtain treated water, and the wastewater recovery system must be shut down, or large-scale chemical cleaning of the membranes or the purchase of new membranes must be required. Therefore, there is a demand for a method that can determine optimal cleaning conditions early on and perform chemical backwashing to suppress membrane fouling and enable stable operation even if the properties of the water to be treated fluctuate.

[0005] Patent Document 1 describes a membrane treatment device having a membrane module that performs membrane filtration of water to be treated that contains organic matter, in which at least one series of mini membrane modules having the same membrane material and membrane shape as the membrane module and a membrane area of ​​1 / 2 to 1 / 100 of the membrane module are installed side by side, and the mini membrane module is configured to be able to supply water to be treated that is the same as that of the membrane module.

[0006] However, the membrane treatment device described in Patent Document 1 aims to determine the conditions for chemical cleaning of the membrane, not for backwashing with the addition of chemicals.

[0007] Patent Document 2 describes a wastewater recovery system that includes a membrane filtration means for membrane filtration of wastewater containing organic matter, and a cleaning means for periodically performing chemical cleaning (backwashing with the addition of chemicals) on the membrane of the membrane filtration means using at least two types of chemicals, including one type of acid and one type of alkali, and that selects whether or not to use the same chemical in the next chemical cleaning as the previous one by referring to a preset reference transmembrane pressure ΔPx, calculated from the transmembrane pressure difference (ΔP0) before the chemical cleaning and the transmembrane pressure difference (ΔP1) after the chemical cleaning.

[0008] 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 the device, so it may not be possible to determine optimal conditions for chemical addition backwash early. Determining the chemical conditions for chemical addition backwash based on the transmembrane pressure difference before and after chemical cleaning in the device as in Patent Document 2 not only makes it impossible to select chemicals early, but also requires the device to be stopped for cleaning. Furthermore, there is a disadvantage in that the volume of the membrane module built into the device is large, which increases the amount of chemicals used and the amount of wastewater. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 3656908 [Patent Document 2] Patent No. 6693804 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method and system for membrane filtration that can determine optimal cleaning conditions early and perform chemical addition backwashing to suppress membrane fouling even if the properties of the water to be treated fluctuate in a membrane filtration process using a filtration membrane, thereby enabling 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. [Means for solving the problem]

[0011] The present invention includes a main membrane filtration device that filters water to be treated using a main filtration membrane, a sub-membrane filtration device that filters water to be treated branched off from the water to be treated of the main membrane filtration device using 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, a sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane, and a method for detecting a filtration resistance value before and after the chemical addition backwashing performed by the sub-chemical addition backwashing means, the method comprising: At least one of the following: an alarm, execution of chemical addition backwashing of the main filtration membrane, execution of chemical cleaning of the main filtration membrane, change of cleaning conditions of the main filtration membrane, and proposal for improvement of operating conditions of the main filtration membrane. An output means for outputting the 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 filtration resistance values ​​before and after the chemical addition backwashing detected by the sub filtration resistance detection means; Equipped with In the sub-membrane filtration device, water is passed through at a higher flux than in the main membrane filtration device. It is a membrane filtration system.

[0014] The present invention includes a main membrane filtration process for filtering water to be treated using a main filtration membrane, a sub-membrane filtration process for filtering water to be treated branched from the water to be treated in the main membrane filtration process using a sub-filtration membrane, a main chemical addition backwashing process for adding chemicals to the main filtration membrane and backwashing the main filtration membrane, a sub-chemical addition backwashing process for adding chemicals to the sub-filtration membrane and a method for calculating a chemical backwashing amount based on a filtration resistance value before and after the chemical addition backwashing process performed in the sub-chemical addition backwashing process. At least one of the following: an alarm, execution of chemical addition backwashing of the main filtration membrane, execution of chemical cleaning of the main filtration membrane, change of cleaning conditions of the main filtration membrane, and proposal for improvement of operating conditions of the main filtration membrane. An output process for outputting the In the sub-membrane filtration process, water is passed through at a higher flux than in the main membrane filtration process, and conditions for chemical addition backwashing of the main filtration membrane performed in the main chemical addition backwashing process are controlled based on filtration resistance values ​​before and after the chemical addition backwashing. , a membrane filtration method.

[0017] The present invention provides 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, the device comprising: a sub-membrane filtration device that uses a sub-filtration membrane to filter water to be treated branched off from the water to be treated of the main membrane 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; a sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane; and a control means for controlling conditions for chemical addition backwashing of the main filtration membrane 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. In the sub-membrane filtration device, water is passed through at a higher flux than in the main membrane filtration device. This is a chemical addition backwash device.

[0019] The present invention relates to 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, and the chemical addition backwashing device includes a sub-membrane filtration device that uses a sub-filtration membrane to filter water to be treated branched off 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 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 backwashing detected by the sub-filtration resistance detection means, ,before The main filtration membrane is provided with a control means for controlling the conditions of chemical addition and backwashing. In the sub-membrane filtration device, water is passed through at a higher flux than in the main membrane filtration device. This is a control device for a chemical addition backwash device. Effect of the Invention

[0021] The present invention provides a membrane filtration system that can operate stably in a membrane filtration process using a filtration membrane, by determining optimal cleaning conditions early on and performing chemical addition backwashing to suppress membrane fouling even if the properties of the water to be treated fluctuate, and 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. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic configuration diagram illustrating an example of a membrane filtration system according to an embodiment of the present invention. [Diagram 2] 1 is a flowchart illustrating an example of a membrane filtration method according to an embodiment of the present invention. [Diagram 3] 1 is a graph showing an example of the filtration resistance ( / m) versus the filtration volume (m3 / m2) when backwashing is performed in a membrane filtration device. [Figure 4] 1 is a graph showing an example of the filtration resistance ( / m) versus the filtration volume (m3 / m2) when backwashing and chemical-addition backwashing were performed in a membrane filtration device. [Diagram 5] 1 is a graph showing the transmembrane pressure difference (MPa) versus the number of filtration days when cleaning condition 1 was performed with chemical addition backwashing in the main membrane filtration apparatus of Example 1. [Figure 6] 1 is a graph showing the filtration resistance ( / m) versus the filtration volume (m3 / m2) when cleaning condition 1 was performed with chemical addition backwashing in the sub-membrane filtration device of Example 1. [Figure 7] 1 is a graph showing the transmembrane pressure difference (MPa) versus the number of filtration days when cleaning condition 1+cleaning condition 2 were performed with chemical addition backwashing in the main membrane filtration apparatus of Example 2. [Figure 8] 1 is a graph showing the filtration resistance ( / m) versus the filtration volume (m3 / m2) when cleaning condition 1+cleaning condition 2 were performed with chemical addition backwashing in the sub-membrane filtration apparatus of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0024] An example of a membrane filtration system according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0025] The membrane filtration system 1 includes a main membrane filtration device 10 that filters the water to be treated using a main filtration membrane, a sub-membrane filtration device 12 that filters the water to be treated branched off from the water to be treated of the main membrane filtration device 10 using a sub-filtration membrane, a main backwash piping 32 as main chemical addition backwash means for performing chemical addition backwashing of the main filtration membrane of the main membrane filtration device 10, a sub-backwash piping 42 as sub chemical addition backwash means for performing chemical addition backwashing of the sub filtration membrane of the sub-membrane filtration device 12, a flowmeter 25 and a pressure gauge 26 as sub filtration resistance detection means for detecting the filtration resistance value of the sub filtration membrane of the sub-membrane filtration device 12, and an output unit 14 as output means that performs 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. The main backwash piping 32 may function as a main backwash means for backwashing the main filtration membrane of the main membrane filtration device 10, and the sub-backwash piping 42 may function as a sub-backwash means for backwashing the sub filtration membrane of the sub-membrane filtration device 12.

[0026] 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, a main treated water pipe 30 is connected to the main treated water outlet, and a main backwash liquid inlet is connected to the main backwash liquid pipe 32. 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, a sub treated water pipe 40 is connected to the sub treated water outlet, and a sub backwash liquid inlet is connected to the sub backwash liquid pipe 42. A chemical outlet of an acid tank 18, which is an example of a first chemical tank, and the main backwash pipe 32 are connected via a pump 22 through an acid pipe 34, which is a first chemical pipe. A chemical outlet of an oxidizer tank 20, which is an example of a second chemical tank, and the main backwash pipe 32 are connected via a pump 24 through an oxidizer pipe 36, which is a second chemical pipe. An acid pipe 44 branched off from the acid pipe 34 is connected to the sub-backwash pipe 42, and an oxidant pipe 46 branched off from the oxidant pipe 36 is connected to the sub-backwash pipe 42. A flowmeter 25 and a pressure gauge 26 are installed in the sub-treated water pipe 38. An output unit 14 is installed in the pressure gauge 26.

[0027] The membrane filtration system 1 may include a control device 16 as a control means. The control device 16 may be communicatively connected to the output unit 14, the pump 22, the pump 24, the flowmeter 25, the pressure gauge 26, etc., by wired or wireless electrical connection or the like. The membrane filtration system 1 may further include a communication device as a communication means. The communication device is connected to the control device 16, and is connected to a server, for example, via the Internet. The server is provided with at least a recording unit or a calculation unit. For example, data measured by the sub-filtration resistance detection means is stored in the recording unit. The calculation unit performs calculations using data on the sub-filtration resistance, and may output an alarm, chemical addition backwashing, chemical cleaning, etc., or the data stored in the recording unit may be used together to calculate the implementation history of chemical addition backwashing and chemical cleaning, the amount of chemical used, and the cost of chemicals, and may be stored or output. The output may be sent to the control device 16 again via the Internet, and an alarm may be issued to the output unit 14, chemical addition backwashing and chemical cleaning may be performed, or cleaning conditions may be changed.

[0028] The membrane filtration method and the operation of the membrane filtration system 1 according to this embodiment will be described.

[0029] The water to be treated is sent to the main membrane filtration device 10 through the main treated water piping 28, and the main membrane filtration device 10 performs membrane filtration of the water to be treated using a main filtration membrane (main membrane filtration step). The obtained main treated water is discharged through the main treated water piping 30.

[0030] In the membrane filtration system 1, the main membrane filtration device 10 is cleaned, for example, periodically, when the main membrane filtration device 10 is continuously operated. The cleaning of the main filtration membrane is performed, for example, by backflowing at least a part of the main treated water as main backwash water from the secondary side to the primary side of the main membrane filtration device 10 through the main backwash piping 32 (main backwash process). The main backwash wastewater is discharged from the primary side of the main membrane filtration device 10.

[0031] If the fouling of the main filtration membrane is not eliminated even after the main backwashing is performed, chemical-added backwashing is performed with a main chemical-added backwashing solution obtained by adding a chemical to the main backwashing water (main chemical-added backwashing process). In the main chemical-added backwashing process, for example, acid is supplied from the acid tank 18 to the main backwashing water in the main backwashing pipe 32 through the acid pipe 34 by the pump 22, and acid washing is performed, or an oxidant is supplied from the oxidant tank 20 to the main backwashing water in the main backwashing pipe 32 through the oxidant pipe 36 by the pump 24, and oxidant washing is performed. An alkali may be used in addition to the oxidant. The main chemical-added backwashing effluent is discharged from the primary side of the main membrane filtration device 10. In the main chemical-added backwashing process, an immersion process may be performed in which the main filtration membrane is immersed in the main chemical-added backwashing solution for a predetermined time. In the main chemical-added backwashing process, the main chemical-added backwashing effluent 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.

[0032] As described above, membrane fouling (blockage) may occur in membrane filtration treatment for wastewater recovery, etc. The main causes of membrane fouling in membrane filtration treatment are organic matter resulting from the preceding biological treatment process, and metal particles derived from inorganic coagulants resulting from the preceding coagulation and solid-liquid separation treatment processes. When the properties of the water to be treated change, the main cause is that the biological treatment, coagulation, and solid-liquid separation treatment in the preceding stages of membrane filtration treatment become unstable, and the amount of organic matter, metal particles, etc. flowing into the main membrane filtration device 10 changes, so the main cause of fouling also changes. If the main cause of membrane fouling is different, the type of chemical used for chemical addition backwashing will be different.

[0033] In the membrane filtration system 1, a sub-membrane filtration process by a sub-membrane filtration device 12 equipped with a sub-backwashing means and a sub-chemical-addition backwashing means is provided in addition to the main membrane filtration process by the main membrane filtration device 10, and an output according to the status of the chemical-addition backwashing in the sub-membrane filtration device 12 is output based on the filtration resistance value in the sub-membrane filtration process detected by a flowmeter 25 and a pressure gauge 26, which are sub-filtration resistance detection means, for example, an output such as an alarm is output when the difference in the filtration resistance value before and after the chemical-addition backwashing exceeds a predetermined threshold. As a result, even if the properties of the water to be treated fluctuate, optimal cleaning conditions can be determined early in the sub-membrane filtration device 12, and chemical-addition backwashing can be performed under those cleaning conditions in the main membrane filtration device 10 to suppress membrane fouling, enabling stable operation.

[0034] By providing the sub-membrane filtration device 12 separately from the main membrane filtration device 10, it is possible to determine optimal cleaning conditions for chemical addition backwashing without having to stop the main membrane filtration device 10, thereby maximizing the operating time of the main membrane filtration device 10.

[0035] An example of a method for determining optimal cleaning conditions for chemical addition backwashing using the sub-membrane filtration device 12 will be described below.

[0036] The water to be treated branched off from the main water to be treated piping 28 is sent to the sub-membrane filtration device 12 through the sub-water to be treated piping 38, where the water to be treated is subjected to membrane filtration using a sub-filtration membrane (sub-membrane filtration step). The resulting sub-treated water is discharged through the sub-treated water piping 40.

[0037] In this manner, in the membrane filtration system 1, when the main membrane filtration device 10 is continuously operated, the water to be treated branched from the main water to be treated piping 28 is also passed through the sub-membrane filtration device 12. The sub-filtration membrane of the sub-membrane filtration device 12 is also washed, for example, periodically. The washing of the sub-filtration membrane is performed, for example, by backflowing at least a part of the sub-treated water as sub-backwash water from the secondary side to the primary side of the sub-membrane filtration device 12 through the sub-backwash piping 42 as sub-backwash water, as in the case of the main filtration membrane (sub-backwash process). The sub-backwash drainage is discharged from the primary side of the sub-membrane filtration device 12. The sub-backwash process may be performed periodically, or may be performed based on the filtration resistance value detected by the flowmeter 25 and the pressure gauge 26, for example, when the filtration resistance value detected by the flowmeter 25 and the pressure gauge 26 exceeds a predetermined backwash reference value.

[0038] If the fouling of the sub-filtration membrane is not eliminated even after the sub-backwashing is performed, a chemical-added backwashing process is performed using a sub-chemical-added backwashing solution obtained by adding a chemical to the sub-backwashing water (sub-chemical-added backwashing process). In the sub-chemical-added backwashing process, for example, an acid is supplied from the acid tank 18 to the sub-backwashing water in the sub-backwashing pipe 42 through the acid pipe 34 and the acid pipe 44 by the pump 22, and acid washing is performed, or an oxidant is supplied from the oxidant tank 20 to the sub-backwashing water in the sub-backwashing pipe 42 through the oxidant pipe 36 and the oxidant pipe 46 by the pump 24, and oxidant washing is performed. An alkali may be used in addition to the oxidant. The sub-chemical-added backwashing wastewater is discharged from the primary side of the sub-membrane filtration device 12. In the sub-chemical-added backwashing process, an immersion process may be performed in which the sub-filtration membrane is immersed in the sub-chemical-added backwashing solution for a predetermined time. In addition, in the sub-chemical addition backwashing step, the sub-chemical addition backwashing effluent 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.

[0039] 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 backwashing process, the acid tank 18, the pump 22, the acid pipe 34, etc. function as the first chemical supplying means, for example, the acid supplying means, the oxidizer tank 20, the pump 24, the oxidizer pipe 36, etc. function as the second chemical supplying means, for example, the oxidizer supplying means, and in addition to the acid supplying means and the oxidizer supplying means, the main backwashing pipe 32 functions as the main chemical addition backwashing means. In the sub-chemical addition backwashing process, the acid tank 18, the pump 22, the acid pipe 34, the acid pipe 44, etc. function as the first chemical supplying means, for example, the acid supplying means, the oxidizer tank 20, the pump 24, the oxidizer pipe 36, the oxidizer pipe 46, etc. function as the second chemical supplying means, for example, the oxidizer supplying means, and in addition to the acid supplying means and the oxidizer supplying means, the sub-backwashing pipe 42 functions as the sub-chemical addition backwashing means.

[0040] Here, the water to be treated is passed through the sub-membrane filtration device 12 before and after the start and end of the sub-chemical addition backwashing process, and the filtration resistance value is measured from the flow rate and pressure before and after the start and end of the sub-chemical addition backwashing process by the flowmeter 25 and pressure gauge 26, which are sub-filtration resistance detection means. Based on the filtration resistance value calculated from the decrease in flow rate and the increase in pressure detected by the flowmeter 25 and pressure gauge 26, for example, when ΔR1 (R0-R1) calculated from the filtration resistance value before chemical addition backwashing (R0) and the filtration resistance value after chemical addition backwashing when the sub-chemical addition backwashing is performed exceeds a CEB reference value, which is a predetermined threshold value, for example, a predetermined output such as an alarm is performed (output process). If the temperature of the water to be treated fluctuates and it is desired to eliminate the temperature dependency of the filtration resistance value, it is desirable to further install a thermometer in the sub-treated water piping 38 and calculate the filtration resistance value of the sub-filtration membrane taking into account the viscosity based on the measured water temperature of the water to be treated.

[0041] This allows early detection of the occurrence of fouling of the sub-filtration membrane in the sub-membrane filtration device 12. When the occurrence of fouling of the sub-filtration membrane is detected, the optimal conditions for chemical addition backwashing are determined in the sub-membrane filtration device 12, and chemical addition backwashing is performed in the main membrane filtration device 10 under the optimal cleaning conditions determined in the sub-membrane filtration device 12. This makes it possible to suppress membrane fouling even if the properties of the water to be treated fluctuate, and enables stable operation of the main membrane filtration device 10. By determining the optimal conditions for chemical addition backwashing in the sub-membrane filtration device 12 in advance, it is not necessary to stop the operation of the main membrane filtration device 10, and the main membrane filtration process may be continued. This allows the operating time of the main membrane filtration device 10 to be maximized.

[0042] The sub-filtration membrane in the sub-membrane filtration apparatus 12 has, for example, the same membrane material, membrane shape, and membrane pore size as the main filtration membrane in the main membrane filtration apparatus 10, but has a smaller membrane area than the main filtration membrane. If optimal cleaning conditions for chemical addition backwashing are determined in the sub-membrane filtration apparatus 12, which is smaller than the main membrane filtration apparatus 10, the amount of chemical solution consumption required to determine the optimal conditions for chemical addition backwashing can be minimized.

[0043] In the sub-membrane filtration apparatus 12 (sub-membrane filtration process), it is preferable to pass water at a higher flux than in the main membrane filtration apparatus 10 (main membrane filtration process). This allows the occurrence of fouling of the sub-filtration membrane in the sub-membrane filtration apparatus 12 to be detected earlier. If optimal conditions for chemical addition backwashing are determined early in the sub-membrane filtration apparatus 12 when the occurrence of fouling of the sub-filtration membrane is detected, and chemical addition backwashing is performed in the main membrane filtration apparatus 10 under the optimal cleaning conditions determined in the sub-membrane filtration apparatus 12, membrane fouling can be suppressed even if the properties of the water to be treated fluctuate, and stable operation of the main membrane filtration apparatus 10 becomes possible.

[0044] In the embodiment of the membrane treatment device described in Patent Document 1, water is passed through the device and the mini membrane module at the same flux, and the membrane is chemically cleaned only after the transmembrane pressure difference in the mini membrane module exceeds 150 kPa. This makes it difficult to detect the occurrence of fouling at an early stage and to respond quickly to changes in the properties of the water to be treated.

[0045] The flux in the sub-membrane filtration apparatus 12 (sub-membrane filtration step) is, for example, 2 to 10 times, and preferably 4 to 6 times, the flux in the main membrane filtration apparatus 10 (main membrane filtration step). If the flux in the sub-membrane filtration apparatus 12 is less than twice the flux in the main membrane filtration apparatus 10, the occurrence of fouling in the sub-filtration membrane may not be detected at an early stage, whereas if it exceeds 10 times, the occurrence of fouling may be over-evaluated, resulting in a risk of reduced prediction accuracy.

[0046] In addition, for example, the conditions of the main backwash of the main filtration membrane and the conditions of the main chemical-addition backwash performed in the main membrane filtration device 10 may be controlled based on the filtration resistance values ​​before and after the sub-backwash in the sub-membrane filtration device 12 detected by the pressure gauge 26 and the filtration resistance values ​​before and after the sub-chemical-addition backwash. For example, the conditions of the backwash in the main membrane filtration process, for example, the frequency of the main backwash and the conditions of the chemical-addition backwash, for example, the frequency of the main chemical-addition backwash, the chemical concentration of the main chemical-addition backwash solution used in the main chemical-addition backwash, the type of chemical used in the main chemical-addition backwash, etc. may be controlled based on the tendency of the resistance increase immediately after the backwash in the sub-membrane filtration device 12 and the resistance increase immediately after the chemical-addition backwash. These controls may be performed manually or automatically.

[0047] An example of a method for determining more specific conditions for chemical addition backwashing will be described with reference to the flow chart shown in FIG.

[0048] In the sub-membrane filtration device 12, after the membrane filtration process is performed for a predetermined time on the water to be treated branched from the main water to be treated pipe 28 of the main membrane filtration device 10, for example, sub-backwashing is performed periodically, and if the fouling of the sub-filtration membrane is not eliminated even after the sub-backwashing, chemical backwashing is performed. The filtration resistance value (R0) before the chemical backwashing when the chemical backwashing is performed is measured (S10), and after the chemical backwashing is performed under cleaning condition 1 (for example, an oxidizing agent is used as the chemical) (S12), the filtration resistance value (R1) after the chemical backwashing is measured, and ΔR1 (R0-R1), which is the difference between the filtration resistance value before the chemical backwashing and the filtration resistance value after the chemical backwashing, is calculated by, for example, the control device 16 (S14). The control device 16 calculates the CEB chemical condition change standard ΔR, which is a preset standard filtration resistance increase degree, for the calculated ΔR1. ref For more information, please refer to.

[0049] ΔR1≦CEB drug condition change standard ΔR ref If this occurs, it is determined that the filtration resistance has been sufficiently reduced by the first evaluated cleaning condition 1 (i.e., chemical-addition backwashing is sufficient), so the control device 16 issues an instruction to perform chemical-addition backwashing of the main membrane filtration device 10 under cleaning condition 1, and chemical-addition backwashing is performed in the main membrane filtration device 10 under cleaning condition 1 (S20). In this case, the process may end without performing chemical-addition backwashing under the second cleaning condition 2 in the sub-membrane filtration device 12.

[0050] ΔR1>CEB drug condition change standard ΔR ref If this occurs, cleaning condition 2, which is a different chemical condition from the previous one, will be used in the next chemical addition backwash. For example, after chemical addition backwashing is performed under cleaning condition 2 (e.g., acid is used as the chemical) (S16), the filtration resistance value (R2) after chemical addition backwashing is measured, and ΔR2 (R0-R2), which is the difference between the filtration resistance value (R0) before chemical addition backwashing and the filtration resistance value (R2) after chemical addition backwashing, is calculated by, for example, the control device 16 (S18). For example, the control device 16 sets the CEB chemical condition change standard ΔR ref For more information, please refer to.

[0051] ΔR2≦CEB drug condition change standard ΔR ref If this occurs, it is determined that the filtration resistance has been sufficiently reduced by the secondly evaluated cleaning condition 2 (i.e., chemical addition backwashing is sufficient), so the control device 16 issues an instruction to perform chemical addition backwashing of the main membrane filtration device 10 under cleaning condition 2, and chemical addition backwashing is performed in the main membrane filtration device 10 under cleaning condition 2 (S22). In this case, the process may end without performing chemical addition backwashing under the next cleaning condition in the sub-membrane filtration device 12.

[0052] ΔR2>CEB drug condition change standard ΔR ref If this occurs, the next chemical addition backwash will use different chemical conditions from the previous one, and thereafter, ΔR N ≦CEB drug condition change standard ΔR ref (N is an integer equal to or greater than 1), the same flow as S10 to S14 is continued.

[0053] From cleaning condition 2 onwards, it is sufficient to use cleaning conditions different from the previous time. For example, a different chemical may be used than in cleaning condition 1, or the same chemical as in cleaning condition 1 may be used at a different chemical concentration, or a different cleaning concentration or cleaning time may be used.

[0054] ΔR N ≦CEB drug condition change standard ΔR ref In this case, the control device 16 may control the cleaning conditions for the chemical addition backwashing of the main membrane filtration device 10. For example, the control device 16 may control the pump 22 and the pump 24.

[0055] In cases where it is believed that fouling caused by organic matter is more prevalent than fouling caused by inorganic matter based on the properties of the water to be treated, for example, a condition in which an oxidizing agent and alkali effective in removing organic matter are used as the chemicals for the backwashing with added chemicals in cleaning condition 1 is evaluated first, and then a condition in which an acid effective in removing inorganic matter is used as the chemical for the backwashing with added chemicals in cleaning condition 2 is evaluated. In cases where it is believed that fouling caused by inorganic matter is more prevalent than fouling caused by organic matter based on the properties of the water to be treated, for example, a condition in which an acid effective in removing inorganic matter is used as the chemical for the backwashing with added chemicals in cleaning condition 1 is evaluated first, and then a condition in which an oxidizing agent and alkali effective in removing organic matter are used as the chemical for the backwashing with added chemicals in cleaning condition 2 is evaluated.

[0056] In addition, the filtration resistance increase degree (ΔR cake ,ΔR backwash ,ΔR CEB ) and may output a warning or operational improvement proposal based on the membrane clogging behavior to the output unit 14. 3 / m 2 Figure 4 shows an example of the filtration resistance ( / m) for a membrane filtration device when backwashing and chemical addition backwashing are performed. 3 / m 2 1 is a graph showing an example of filtration resistance ( / m) versus filter size.

[0057] Filtration resistance increase ΔR cake is the filtration resistance that increases with one membrane filtration process, and is the slope of the resistance caused by cake, etc., adhering to the membrane surface. Cake resistance is a reversible membrane blockage that can be recovered by backwashing. Filtration resistance increase ΔR backwash is the slope of the filtration resistance that is difficult to recover by backwashing. CEB is a filtration resistance that is difficult to recover even with backwashing with the addition of chemicals, and is an irreversible membrane blockage.

[0058] For example, ΔR cakebecomes higher than normal, an alarm is issued to the output unit 14, and suggestions for improving the operating conditions are presented. Examples of the alarm include "abnormal cake resistance." Since cake resistance abnormality is considered to be due to an increase in the concentration of suspended solids in the raw water for membrane filtration, suggestions for improving the operating conditions include, for example, "check the turbidity of the pre-treated water and adjust the operation," "reduce the filtration time by half," and so on.

[0059] For example, ΔR backwash becomes higher than normal, an alarm is issued to the output unit 14, and suggestions for improving the operating conditions are presented. Examples of the alarm include "backwash recovery abnormality." Backwash recovery abnormality is considered to be due to poor organic matter treatment in the upstream stage (e.g. biological treatment or coagulation sedimentation, etc.), so suggestions for improving the operating conditions include, for example, "optimization of the upstream coagulation treatment (reconsidering the amount of coagulant added, changing the pH, etc.)."

[0060] For example, ΔR CEB When the value of the CEB chemical solution becomes higher than normal, an alarm is issued to the output unit 14, and suggestions for improving the operating conditions are presented. Examples of the alarm include "abnormality in backwash recovery after chemical addition." Examples of suggestions for improving the operating conditions include "change the type of CEB chemical solution," "increase in CEB concentration," and so on.

[0061] The control device 16 may store data measured on the pressure, flow rate, etc. when the treated water is passed through the sub-membrane filtration device 12, calculate data on the increase in filtration resistance immediately after backwashing and the increase in filtration resistance immediately after chemical addition backwashing, and automatically control the conditions for chemical addition backwashing of the main membrane filtration device 10 and the sub-membrane filtration device 12 based on this data (e.g., the frequency of chemical addition backwashing, the type of chemical, the concentration of chemical, the time for chemical addition backwashing, etc.).

[0062] A pressure gauge may be installed in the main treated water piping 28 of the main membrane filtration device 10 to measure the filtration resistance before and after backwashing and before and after backwashing with the addition of chemicals, and the increase in transmembrane pressure difference may be confirmed as a cross-check.

[0063] The output from the output unit 14 may be an audiovisual alarm such as a display or sound indicating the status of the chemical addition backwash in the sub-membrane filtration apparatus 12, as well as a response method for responding to the status of the chemical addition backwash, improvement suggestions, etc. The output unit 14 may be, for example, anything that can display and output information, and is not particularly limited, but examples of the output unit 14 include a display device that is a display means such as a liquid crystal display or an organic EL display, and an audio output device that is an audio output means such as a speaker. For example, examples of the method of issuing an alarm include displaying on a touch panel of a control panel, notifying an operator via Internet communication, notifying a monitoring room, etc.

[0064] The output unit 14 may output an alarm or the like when the difference in the filtration resistance value before and after the chemical addition backwashing exceeds, for example, a predetermined threshold. The alarm threshold may be previously set to one, or may be changed in stages or proportionately.

[0065] The control device 16 is composed of, for example, a microcomputer and electronic circuits, which are configured to include a calculation means such as a CPU that calculates a program, and storage means such as a ROM and RAM that store the program and the calculation results. The control device 16 has a function of controlling the conditions of the chemical addition backwash of 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, detected by the sub-filtration resistance detection means. The control device 16 has a function of controlling the amount of chemicals added to the main chemical addition backwash solution, for example, by adjusting the on / off and flow rate of the pumps 22 and 24.

[0066] The water to be treated is water containing, for example, suspended solids, organic matter, inorganic matter such as metal particles, and the like, and is not particularly limited, and examples thereof include biologically treated water obtained by biologically treating wastewater containing organic matter discharged from semiconductor manufacturing plants, food factories, etc. (biological treatment process), solid-liquid separation treated water obtained by coagulation and solid-liquid separation treatment (coagulation / solid-liquid separation treatment process), and solid-liquid separation treated water obtained by coagulation and solid-liquid separation treatment of the biologically treated water after it has been biologically treated. Water that has been treated through other processes before or after the biological treatment process or the coagulation / solid-liquid separation treatment process may also be water that has been treated.

[0067] The biological treatment is not particularly limited as long as it uses microorganisms to treat the water to be treated. The coagulation and solid-liquid separation treatment is not particularly limited as long as it uses an inorganic coagulant such as polyaluminum chloride or a polymer coagulant to perform coagulation treatment and solid-liquid separation treatment of the water to be treated.

[0068] The membrane filtration system and membrane filtration method according to the present embodiment are preferably applied when the properties of the water to be treated are such that the organic matter content as indicated by TOC varies within a range of 1 to 50 mg / L, or the inorganic matter content as indicated by ICP analysis, such as metal particles such as iron, aluminum, manganese, and the like, and dissolved metals, each varies within a range of 0.01 to 20 mg / L.

[0069] The main filtration membrane and the sub-filtration membrane are, for example, turbidity removing membranes such as ultrafiltration membranes (UF membranes) or microfiltration membranes (MF membranes), etc. The shape of the membranes is, for example, a hollow fiber membrane.

[0070] The acid used for the chemical addition backwash is not particularly limited, but examples thereof include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and citric acid. From the viewpoint of recovery during chemical addition backwash, it is preferable to use organic acids such as oxalic acid and citric acid.

[0071] In acid washing, it is preferable to add acid so that the pH of the backwash solution containing the chemical to which the acid has been added is in the range of 1 to 3, and from the standpoint of cost-effectiveness, it is more preferable to add acid so that the pH is in the range of 2 to 3.

[0072] The oxidizing agent used in the chemical backwashing is not particularly limited, but examples thereof include chlorine-based oxidizing agents such as sodium hypochlorite.

[0073] The alkali used for chemical backwashing is not particularly limited, but it is preferable to use relatively inexpensive sodium hydroxide, sodium hypochlorite, etc.

[0074] In cleaning using an oxidizing agent and alkali, it is preferable to add alkali so that the pH of the backwash solution to which alkali has been added is in the range of 10 to 13, and from the standpoint of cost-effectiveness, etc., it is more preferable to add alkali so that the pH is in the range of 11 to 12.

[0075] In the chemical backwash, chemicals other than acids, alkalis, and oxidizing agents, such as membrane cleaners such as surfactants, may be used as necessary. Examples of membrane cleaners include the ULTRASIL series manufactured by ECOLABO. EXAMPLES

[0076] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0077] <Example 1> Using the membrane filtration system 1 shown in Figure 1, the coagulation and solid-liquid separation treated water was passed through under the conditions shown in Table 1, and backwashing and chemical addition backwashing were performed. Water was passed through the main membrane filtration device at a flux of 1.2 (m / d), and through the sub-membrane filtration device at a flux of 7 (m / d) (5.83 times the flux of the main membrane filtration device).

[0078] [Table 1]

[0079] Possible cleaning conditions for chemical backwashing are cleaning condition 1: sodium hypochlorite, an oxidizing agent, plus sodium hydroxide, an alkali (effective against fouling caused by organic matter); cleaning condition 2: oxalic acid, an acid (effective against fouling caused by inorganic matter).

[0080] [Cleaning condition 1: Sodium hypochlorite + sodium hydroxide] In cleaning condition 1, an aqueous solution of sodium hypochlorite and sodium hydroxide (sodium hypochlorite concentration: 900 mg / L, sodium hydroxide concentration: 280 mg / L) was used as the chemical-added backwashing solution. Figure 5 shows the transmembrane pressure difference (MPa) versus the number of filtration days when cleaning condition 1 was performed with chemical-added backwashing in the main membrane filtration apparatus. Figure 6 shows the filtration volume (m 3 / m 2 ) indicates the filtration resistance ( / m).

[0081] As shown in Figure 6, the measurement results of the filtration resistance value of the sub-membrane filtration device showed that the filtration resistance increase ΔR CEB It was determined that the level of cleaning by backwashing with added chemicals was insufficient.

[0082] As shown in Figure 5, the measurement results of the filtration resistance value of the main membrane filtration device where chemical backwashing was performed under cleaning condition 1 also confirmed an increase in transmembrane pressure, confirming that the cleaning effect of chemical backwashing was insufficient.

[0083] [Cleaning condition 1: Sodium hypochlorite + Sodium hydroxide + Cleaning condition 2: Oxalic acid] Therefore, in addition to cleaning condition 1, which uses sodium hypochlorite, which is effective against fouling caused by organic matter, we also carried out chemical-added backwashing under cleaning condition 2, which uses oxalic acid, which is effective against fouling caused by inorganic matter.

[0084] In cleaning condition 2, an aqueous solution of oxalic acid (oxalic acid concentration: 0.2 wt %) was used as the chemical-added backwashing solution. FIG. 7 shows the transmembrane pressure difference (MPa) versus the number of filtration days when cleaning condition 1+cleaning condition 2 were performed with chemical-added backwashing in the main membrane filtration apparatus of Example 2. FIG. 8 shows the filtration volume (m 3 / m 2 ) indicates the filtration resistance ( / m).

[0085] As shown in Figure 8, the filtration resistance increase rate ΔR CEB It was confirmed that the increase in pH had been suppressed, and therefore it was determined that the cleaning was sufficient.

[0086] As shown in Figure 7, there was almost no increase in the filtration resistance of the main membrane filtration device, which underwent chemical addition backwashing under cleaning condition 1 + cleaning condition 2, and stable operation was possible.

[0087] By using cleaning conditions 1 and 2 in combination 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 achieved for six months.

[0088] In this way, in membrane filtration processes using filtration membranes, even if the properties of the water to be treated fluctuate, it is possible to determine optimal cleaning conditions early on and perform backwashing by adding chemicals to suppress membrane fouling, making stable operation possible. [Explanation of symbols]

[0089] 1 Membrane filtration system, 10 main membrane filtration device, 12 sub-membrane filtration device, 14 output section, 16 control device, 18 acid tank, 20 oxidizer tank, 22, 24 pump, 25 flow meter, 26 pressure gauge, 28 main treated water piping, 30 main treated water piping, 32 main backwash piping, 34, 44 acid piping, 36, 46 oxidizer piping, 38 sub treated water piping, 40 sub treated water piping, 42 sub backwash piping.

Claims

1. A main membrane filtration device that filters the water to be treated using a main filtration membrane; A sub-membrane filtration device that filters the water to be treated branched from the water to be treated of the main membrane filtration device using 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; A sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane; an output means for outputting at least one of a warning, execution of chemical addition backwashing of the main filtration membrane, execution of chemical cleaning of the main filtration membrane, change of cleaning conditions of the main filtration membrane, and a proposal for improving operating conditions of the main 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; 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 filtration resistance values ​​before and after the chemical addition backwashing detected by the sub filtration resistance detection means; Equipped with A membrane filtration system, characterized in that the sub-membrane filtration device passes water at a higher flux than the main membrane filtration device.

2. a main membrane filtration process for filtering the water to be treated using a main filtration membrane; A sub-membrane filtration process of filtering the water to be treated branched from the water to be treated in the main membrane filtration process using a sub-filtration membrane; A main chemical addition backwashing process for adding chemicals to the main filtration membrane and backwashing the main filtration membrane; A sub-chemical addition backwashing process for adding chemicals to the sub-filtration membrane and backwashing the sub-filtration membrane; an output process for outputting at least one of an alarm, execution of chemical addition backwashing of the main filtration membrane, execution of chemical cleaning of the main filtration membrane, change of cleaning conditions of the main filtration membrane, and a proposal for improving operating conditions of the main filtration membrane, based on the filtration resistance values ​​before and after the chemical addition backwashing performed in the sub-chemical addition backwashing process; Including, In the sub-membrane filtration process, water is passed through at a higher flux than in the main membrane filtration process, A membrane filtration method, characterized in that conditions for chemical addition backwashing of the main filtration membrane performed in the main chemical addition backwashing process are controlled based on filtration resistance values ​​before and after the chemical addition backwashing.

3. A chemical addition backwashing device that adds chemicals to a main membrane filtration device that filters water to be treated using a main filtration membrane, A sub-membrane filtration device that filters the water to be treated branched from the water to be treated of the main membrane filtration device using 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; A sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane; A control means for controlling the conditions of the chemical addition backwashing of the main filtration membrane 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; Equipped with A chemical addition backwash device, characterized in that water is passed through the sub-membrane filtration device at a higher flux than that of the main membrane filtration device.

4. 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, the chemical addition backwashing device comprising: a sub-membrane filtration device that uses a sub-filtration membrane to filter water to be treated that is branched off 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 a sub-filtration resistance detection means for detecting a filtration resistance value of the sub-filtration membrane; A control device for a chemical addition backwash device, comprising: a control means for controlling the conditions of the chemical addition backwash of the main filtration membrane based on the filtration resistance values ​​before and after the chemical addition backwash detected by the sub-filtration resistance detection means, and characterized in that water is passed through the sub-membrane filtration device at a higher flux than that of the main membrane filtration device.

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