JP7181809B2 - Membrane filtration device - Google Patents

Description

The present invention relates to membrane filtration devices having reverse osmosis membranes or nanofiltration membranes.

Membrane filtration devices having reverse osmosis membranes (RO membranes) or nanofiltration membranes (NF membranes) are known as water treatment devices for removing impurities contained in water to be treated. In this apparatus, the water to be treated (raw water) supplied to the RO membrane or NF membrane at a predetermined supply pressure is separated into permeated water and concentrated water by the RO membrane or NF membrane. As a result, treated water (permeated water) from which impurities have been removed is obtained.

In many cases, in a membrane filtration device having an RO membrane or an NF membrane, from the viewpoint of effective use of water (water saving), part of the concentrated water containing impurities is discharged to the outside as concentrated waste water, and the rest is discharged as concentrated reflux water. A configuration is adopted in which the gas is returned to the upstream side of the RO membrane or the NF membrane. As a result, the recovery rate (the ratio of the permeate flow rate to the sum of the permeate flow rate and the concentrated wastewater flow rate) can be improved compared to the case where all the concentrated water is discharged as concentrated waste water, resulting in water savings. can be realized. At the same time, in the membrane filtration device, in order to respond to changes in the flow rate of permeate due to changes in water temperature (i.e., changes in water viscosity), the rotation speed of the pressure pump is controlled to allow the RO or NF membrane to Flow rate control is performed to maintain a constant flow rate of permeate by adjusting the supply pressure of raw water.

By the way, a change in the flow rate of permeated water also occurs due to deterioration in the performance of the RO membrane or the NF membrane. For example, when raw water containing residual free chlorine is supplied to an RO membrane or NF membrane, the membrane may be oxidized and deteriorated. The permeate flow rate increases. In addition, if the recovery rate is increased from the viewpoint of effective use of water (water saving), scaling where impurities (especially silica or calcium) precipitate on the membrane surface is likely to occur, thereby clogging the RO membrane or NF membrane. may occur. In this case, the flow rate of the permeated water is reduced by blocking the permeation pores of the membrane. Such a change in permeate flow rate is offset by the above-described permeate flow rate control, but on the other hand, membrane deterioration and clogging reduce the salt removal performance of the membrane and cause deterioration in permeate water quality. end up In addition, as the clogging of the membrane progresses, the required raw water supply pressure rises, making it impossible to operate the membrane filtration apparatus. Therefore, in a membrane filtration device having an RO membrane or an NF membrane, it is required to accurately determine whether or not the membrane is degraded or clogged, and to take prompt action.

In Patent Document 1, the permeation flux of the RO membrane is calculated based on the detection results of the flow sensor, temperature sensor, and pressure sensor connected to the primary side and the secondary side of the RO membrane, and the calculated permeation flux A method is described to determine if an RO membrane is deteriorating or clogging by comparing the flux to the initial permeate flux.

JP 2005-288220 A

However, with the determination method described in Patent Document 1, even if membrane deterioration or clogging occurs, it can only be determined when it has progressed to some extent. Therefore, it may be difficult to take some countermeasures before a serious problem such as the membrane filtration apparatus becoming inoperable occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a membrane filtration device capable of judging signs of deterioration or clogging in filtering means.

In order to achieve the above object, the membrane filtration device of the present invention comprises filtration means having a reverse osmosis membrane or nanofiltration membrane for separating water to be treated into permeated water and concentrated water; a supply line for supplying the permeate, a permeate line for circulating the permeated water from the filtering means, a concentrated water line for circulating the concentrated water from the filtering means, and a concentrated water line branched from the concentrated water line and the concentrated water line and a drain line for discharging part of the flowing concentrated water to the outside, and the water temperature of any one of the water to be treated supplied to the filtering means, the permeated water from the filtering means, and the concentrated water from the filtering means. a first flow rate detection means for detecting the flow rate of the permeated water flowing through the permeate line; a first conductivity detection means for detecting the conductivity of the water to be treated flowing through the supply line; second conductivity detection means for detecting the conductivity of the permeate flowing through the permeate line; first pressure detection means for detecting the pressure of the water to be treated flowing through the supply line; and permeate flowing through the permeate line. Second pressure detection means for detecting pressure, third pressure detection means for detecting pressure of concentrated water flowing through the concentrated water line, and determination means for determining whether there is a sign of deterioration or clogging of the filtering means. and have The determination means corrects the value detected by the first pressure detection means based on the value detected by the water temperature detection means and the value detected by the first flow rate detection means , thereby determining the pressure that eliminates the influence of water temperature fluctuations. A correction value is calculated, and a second conductivity detection is performed based on a detection value by the water temperature detection means, a detection value by the first conductivity detection means, and a detection value by the first to third pressure detection means. By correcting the values detected by the means, fluctuations in water temperature, fluctuations in the conductivity of the water to be treated flowing through the supply line, and the sum of the flow rate of the permeate flowing through the permeate line and the flow rate of the concentrated water flowing through the drain line Calculate the conductivity correction value that eliminates the influence of fluctuations in the recovery rate, which is the ratio of the flow rate of the permeate flowing through the permeate line to the Based on the slope of the second regression line obtained from the temporal change of the rate correction value , it is determined whether or not there is a sign of deterioration or clogging of the filtering means.

According to such a membrane filtration device, by monitoring the slope of the regression line obtained from the change over time of the calculation result reflecting the deterioration or clogging of the filtration means, deterioration or clogging in the filtration means can be detected at the earliest possible stage. can be detected. As a result, before a serious problem such as the membrane filtration device becoming inoperable occurs, for example, it becomes possible to automatically shift to a life-prolonging operation that delays the progress of deterioration or clogging of the filtration means.

As described above, according to the present invention, it is possible to provide a membrane filtration device capable of determining signs of deterioration or clogging in the filtering means.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the structure of the membrane filtration apparatus which concerns on one Embodiment of this invention. 4 is a graph showing changes over time in pressure correction values under conditions in which clogging occurs in filtering means. 4 is a graph showing changes over time in the slope of the pressure regression line in the first period; FIG. 10 is a graph showing changes over time in the slope of the pressure regression line during the second period; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of a membrane filtration device according to one embodiment of the present invention.

The membrane filtration device 10 of the present embodiment is a device that removes impurities contained in raw water (water to be treated) to generate treated water. It has filtering means 11 for separating from water. The filtering means 11 has a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane).

In addition, the membrane filtration device 10 includes a plurality of lines respectively connected to the filtration means 11, that is, a supply line 1 that supplies raw water to the filtration means 11, and a permeated water line 2 that distributes the permeated water from the filtration means 11. , and a concentrated water line 3 for circulating the concentrated water from the filtering means 11 . In addition, the membrane filtration device 10 has two lines branched from the concentrated water line 3, that is, a drain line 4 for discharging a part of the concentrated water flowing through the concentrated water line 3 to the outside, and a supply line for the rest of the concentrated water. It has a reflux water line 5 for refluxing to 1. After being branched from the concentrated water line 3, the reflux water line 5 is connected to the supply line 1 on the upstream side of the pressure pump 21, which will be described later. Note that the return water line 5 may be connected to a raw water tank (not shown) provided on the supply line 1 instead of being directly connected to the supply line 1 .

Furthermore, the membrane filtration device 10 includes a permeate flow meter (first flow rate detection means) 12 that detects the flow rate of the permeate flowing through the permeate line 2, and a permeate flow rate control mechanism ( It has a first flow control means) 20 .

The permeate flow rate control mechanism 20 is provided in the supply line 1 and includes a pressure pump (pressure adjustment means) 21 for adjusting the pressure of the raw water flowing through the supply line 1 (supply pressure of the raw water to the filtration means 11), and the permeate It also has a permeate water flow rate control unit 22 that controls the pressure pump 21 based on the permeate water flow rate (detection value) detected by the flow meter 12 .

The permeate flow rate control unit 22 includes an inverter (not shown) that controls the rotation speed of the pressure pump 21, and the permeate flow rate of the pressure pump 21 is controlled so that the permeate flow rate detected by the permeate flow meter 12 is constant. It controls the number of revolutions. For example, when the water temperature changes, the flow rate of the permeate separated by the RO or NF membrane also changes due to the change in the viscosity of the water. The permeate water flow control unit 22 controls the rotation speed of the pressure pump 21 according to this change. That is, the lower the water temperature, the higher the viscosity of the water, resulting in a decrease in the flow rate of the permeate separated by the RO or NF membrane. Therefore, the permeate water flow rate control unit 22 increases the supply pressure of the raw water by increasing the rotational speed of the pressure pump 21 so as to compensate for this decrease. Also, as the water temperature increases, the viscosity of the water decreases, resulting in an increase in the flow rate of the permeate separated by the RO or NF membrane. Therefore, the permeate water flow rate control unit 22 reduces the supply pressure of the raw water by reducing the rotational speed of the pressure pump 21 so as to cancel out this increase. The rotation speed of the pressurizing pump 21 is controlled by the permeate flow control unit 22 so as not to exceed a preset upper limit value or fall below a preset lower limit value. Therefore, even if the rotation speed of the pressurizing pump 21 is controlled to the lower limit, the flow rate of the permeated water may exceed the set flow rate. A manual valve or a proportional control valve may be provided between the pump 21 and the filtering means 11 to adjust the supply pressure of the raw water.

Thus, in the present embodiment, the flow rate of the permeated water is maintained constant (preset target flow rate) by adjusting the rotation speed of the pressurizing pump 21, that is, the supply pressure of the raw water. The flow rate of the concentrated water separated by the RO membrane or NF membrane also changes according to the change in the supply pressure. In order to suppress such a change in the flow rate of the concentrated water itself, the concentrated water line 3 is provided with a constant flow valve 13 that keeps the flow rate of the concentrated water flowing through the concentrated water line 3 constant. As a result, even when the rotation speed of the pressure pump 21 is changed by the permeated water flow rate control unit 22 and the supply pressure of the raw water to the filtering means 11 is changed, the flow rate of the concentrated water can be kept constant. .

Here, the specified flow rate of the constant flow valve 13 should be such that clogging of the membrane due to fouling or scaling does not occur on the one hand, and that the membrane is not damaged due to an increase in pressure loss. However, if the specified flow rate of the constant flow valve 13 is increased more than necessary, the flow rate required of the pressure pump 21 will be increased more than necessary, and as a result the size of the pressure pump 21 will increase, resulting in energy consumption. It is not preferable in terms of Therefore, the specified flow rate of the constant flow valve 13 is set in consideration of the permeation flux of the filtration means 11 and the minimum flow rate of concentrated water required for the filtration means 11. For example, the diameter of the filtration means 11 is about 20.32 cm. (8 inch) RO membrane, it ranges from 1 to 15 m ³ /h. The minimum flow rate of the concentrated water required for the filtering means 11 means the minimum flow rate of the concentrated water to be flowed through the concentrated water line 3 so as not to cause clogging of the membrane due to fouling or scaling.

By the way, the constant flow valve 13 is defined with an operating differential pressure range (permissible range of pressure difference between the primary side and the secondary side of the constant flow valve) for normal operation of the constant flow valve 13 . Therefore, depending on the conditions, for example, when a medium- and high-pressure RO membrane is used as the filtration means 11, or when the water temperature drops extremely, the supply pressure of the raw water rises significantly and the pressure of the concentrated water rises. The pressure difference between the primary side and the secondary side of the constant flow valve 13 may exceed the operating differential pressure range. In that case, the flow rate of the concentrated water flowing through the concentrated water line 3 may not be kept constant.

Therefore, the pressure of the concentrated water flowing through the concentrated water line 3 on the upstream side of the constant flow valve 13 is reduced (that is, the pressure on the secondary side can be made lower than the pressure on the primary side). A pressure reducing valve may be provided. As a result, even when the supply pressure of raw water to the filtering means 11 rises significantly, the pressure difference between the primary side and the secondary side of the constant flow valve 13 is kept within the operating differential pressure range. It can be operated normally, and the flow rate of the concentrated water flowing through the concentrated water line 3 can be kept constant. In addition, by providing the pressure reducing valve, peripheral members (such as pipes) downstream of the pressure reducing valve are not required to have such a high pressure resistance performance. Therefore, installation of a pressure reducing valve is not only advantageous in terms of safety, but is also advantageous in terms of cost, since inexpensive general-purpose products with not so high pressure resistance can be used. The type of pressure reducing valve is not particularly limited as long as it can reduce the pressure of the concentrated water to within the operating differential pressure range of the constant flow valve 13. or the pressure on the secondary side is greater than the water flow differential pressure of the drainage line 4 and the recirculated water line 5 .

As described above, the installation of the constant flow valve 13 prevents the flow rate control of the permeated water from affecting the flow rate of the concentrated water. easily feasible. Therefore, the membrane filtration device 10 of the present embodiment includes a waste water flow meter (second flow rate detection means) 14 that detects the flow rate of concentrated water (hereinafter referred to as "concentrated waste water") flowing through the waste water line 4, and the flow rate and a drainage flow rate control mechanism (second flow rate control means) 30 for adjusting the set flow rate. The flow rate control of the concentrated waste water by the waste water flow rate control mechanism 30 is performed independently of the flow rate control of the permeated water by the permeated water flow rate control mechanism 20 .

The drainage flow rate control mechanism 30 adjusts the opening degree of the flow rate adjustment valve 31 based on the flow rate adjustment valve 31 provided in the drainage line 4 and the detected flow rate (detection value) of the concentrated drainage by the drainage flow meter 14. and a control unit 32 .

The wastewater flow rate control unit 32 determines the set flow rate of the concentrated wastewater in consideration of the recovery rate, which is the ratio of the flow rate of the permeated water to the sum of the flow rate of the permeated water and the flow rate of the concentrated wastewater, and the value detected by the wastewater flow meter 14 is the set flow rate, the opening degree of the flow control valve 31 is adjusted. The recovery rate at this time is preferably as high as possible from the viewpoint of effective use of water (water saving). That is, it is preferable that the flow rate of the concentrated waste water is as small as possible. However, since the flow rate of the concentrated water is kept constant by the constant flow valve 13, when the flow rate of the concentrated waste water decreases, naturally, the flow rate of the concentrated water flowing back from the reflux water line 5 to the supply line 1 increases. do. As a result, when the concentration of impurities in the raw water increases, scaling, in which impurities (especially silica or calcium) are deposited on the membrane surface of the RO membrane or NF membrane of the filtering means 11, tends to occur. Therefore, the flow rate of the concentrated wastewater is set so that the recovery rate is maximized in a range in which the concentration of impurities in the concentrated water does not exceed the solubility, that is, the recovery rate is maximized in a range in which the impurities silica or calcium do not precipitate. is set to

However, the solubility of impurities varies depending on the water temperature. For example, for silica, its solubility increases proportionally with temperature, and for calcium (calcium carbonate), its solubility decreases with increasing temperature. Therefore, when the water temperature is low, the solubility of silica is relatively low, and silica tends to precipitate (silica scale is likely to occur). is likely to precipitate (calcium scale is likely to occur). Therefore, in this embodiment, a temperature sensor (water temperature detection means) 16 for detecting the water temperature of the raw water supplied to the filtration means 11 is provided in the supply line 1, and based on the water temperature detected by this temperature sensor 16, , the optimum set flow rate of the concentrated wastewater is calculated. The temperature sensor 16 may be adapted to detect the water temperature of either the permeated water or the concentrated water from the filtering means 11. That is, the temperature sensor 16 may be provided in the permeated water line 2 or the concentrated water line 3 good.

Specifically, first, the theoretical recovery rate at which silica precipitates at the detected water temperature (hereinafter referred to as "silica precipitation recovery rate") and the theoretical recovery rate at which calcium (calcium carbonate) precipitates at the detected water temperature The recovery rate of (hereinafter referred to as "calcium deposition recovery rate") is calculated. Methods for calculating the silica precipitation recovery rate and the calcium precipitation recovery rate will be described later. Next, the silica deposition recovery rate and the calcium deposition recovery rate are compared, and the smaller deposition recovery rate is set as the target recovery rate. Then, based on this target recovery rate and the flow rate of permeated water detected by the permeated water flow meter 12, the target flow rate of the concentrated waste water is calculated and set by the following equation (1).
(Target flow rate of concentrated wastewater) =
(Detected flow rate of permeated water/Target recovery rate) - (Detected flow rate of permeated water) (1)

From the viewpoint of reliably suppressing the occurrence of scaling, it is possible to set a flow rate that exceeds the target flow rate calculated by the above formula (1) as the set flow rate of the concentrated wastewater, considering the safety factor. , it is preferable to set the calculated target flow rate as the set flow rate of the concentrated waste water. As the recovery rate (target recovery rate), a value expressed in percent is usually used, but in the above formula (1), it goes without saying that a value expressed in decimals is used.

Here, the methods for calculating the silica deposition recovery rate and the calcium deposition recovery rate will be described respectively.

(Method for calculating precipitation recovery rate of silica)
The silica precipitation recovery rate Y _S is expressed as follows, where _CS is the solubility of silica (mg/L) at the detected water temperature and _FS is the silica concentration (mg/L) of the raw water measured in advance. It is calculated from the formula (2).
Y _S =(C _S −F _S )/C _S (2)

As a method for calculating the solubility of silica, a method specified in ASTM (American Society for Testing and Materials) D4993-89 or the like can be used.

(Method for calculating precipitation recovery rate of calcium)
The precipitation recovery rate of calcium is calculated using a method for calculating the Langerier index of concentrated water. Here, the Langerier index (saturation index) is an index indicating the possibility of precipitation of calcium (calcium carbonate), and the actual pH of water and the theoretical pH (pHs: calcium carbonate in water neither dissolves nor precipitates It means the difference (pH - pHs) from the pH at equilibrium. That is, the larger the absolute value of the positive value of the Langerier index, the easier it is for calcium carbonate to precipitate, while the negative value does not precipitate calcium carbonate. Therefore, the precipitation recovery rate of calcium is calculated as the recovery rate when the Langelier index of the concentrated water becomes zero. In order to set a safer value, the recovery rate of calcium precipitation may be the recovery rate when the Langelier index of the concentrated water becomes a negative value.

The Langerier index of the concentrate is calculated from the pH of the concentrate, the concentration of impurities in the concentrate (calcium concentration, total alkalinity, and evaporation residue concentration), and the detected water temperature. As a method for calculating the Langelier index, for example, the method described in Japanese Patent Application Laid-Open No. 11-267687 (paragraphs [0025] to [0027]) can be used. In addition, the concentration of impurities in the concentrated water (calcium concentration, total alkalinity, and concentration of evaporation residue) is calculated from the previously measured impurity concentration of raw water (calcium concentration, total alkalinity, and concentration of evaporation residue) and the recovery rate. calculated from Therefore, the calcium deposition recovery rate Y _C is _the impurity concentration (mg / L) of the concentrated water when the Langerier index of the concentrated water becomes zero, and the impurity concentration (mg / L) of the raw water measured in advance. is represented by the relationship of the following _formula (3).
Y _C =(C _C −F _C )/C _C (3)

The recovery rate, which is the ratio of the permeate flow rate to the sum of the permeate flow rate and the concentrated wastewater flow rate, is the ratio of the concentrated water flow rate to the sum of the permeate flow rate and the concentrated wastewater flow rate. It can be expressed as a magnification. That is, the recovery rate Y can be expressed by the following formula (4), where N is the allowable concentration factor.
Y=(N−1)/N (4)

Therefore, the above formulas (1) to (3) can be expressed as follows using the above formula (4).
(Target flow rate of concentrated wastewater) = (Detected flow rate of permeated water) / (Allowable concentration ratio - 1) (1')
N _S =C _S /F _S (2′)
N _C =C _C /F _C (3′)
Here, N _S is the permissible concentration ratio corresponding to the precipitation recovery rate of calcium, and N _C is the permissible concentration ratio corresponding to the precipitation recovery rate of silica.

The method for calculating the precipitation recovery rate of silica and calcium and the method for calculating the set flow rate of concentrated wastewater may be used when there are restrictions on the recovery rate and flow rate in advance due to restrictions on device design such as the capacity of the pressurizing pump and the flow rate of raw water. is not limited to the above. In addition, a preset target flow rate of permeate can be used to calculate the set flow rate of concentrated wastewater. This is not preferable because the recovery rate of the product may deviate from the target recovery rate. That is, if the actual permeate flow rate is greater than the target flow rate, scaling occurs due to the actual recovery exceeding the target recovery rate, or if the actual permeate flow rate is less than the target flow rate. If the actual recovery rate falls below the target recovery rate, it becomes impossible to save water.

Therefore, as described above, it is preferable to use the detected flow rate of the permeated water by the permeated water flow meter 12 for calculating the set flow rate of the concentrated waste water. As a result, even if the flow rate control of the permeated water is not appropriately performed, it is possible to prevent the actual recovery rate from deviating from the target recovery rate. In actual calculation, it is preferable to use an average flow rate for a predetermined detection time or a predetermined number of times of detection in order to minimize the influence of variations in the detected flow rate of permeated water.

However, if the flow rate of the permeate is not stable and the variation in the detected flow rate is very large, such as when starting up the device or restarting operation, the permeate Using the target flow rate of, the set flow rate of the concentrated waste water may be calculated. Further, the flow rate of the permeated water used for calculating the set flow rate of the concentrated waste water may be switched according to the difference between the target flow rate and the actual flow rate of the permeated water. That is, if the difference is within a predetermined range, the target flow rate may be used for calculation, and if the difference is outside the predetermined range, the actual flow rate may be used for calculation.

When performing recovery rate control as described above, it is preferable to use an electric proportional control valve as the flow control valve 31 . As a result, the degree of opening can be finely adjusted according to the resolution of the electric proportional control valve, and the recovery rate can be adjusted more smoothly than when adjusting the degree of opening in a stepwise manner using a combination of solenoid valves. For example, in a staged formula that can only control the recovery rate in the range of 50 to 70% in 5 stages (50%, 55%, 60%, 65%, 70%), when the target recovery rate is set to 64%, The recovery rate can only be adjusted to 60%, resulting in useless concentrated waste water. Therefore, the use of the electric proportional control valve as the flow control valve 31 is advantageous from the viewpoint of saving water because it is possible to reduce waste of such concentrated waste water.

However, when an electric proportional control valve is used as the flow control valve 31, it is necessary to pay attention to the relationship between the opening/closing speed and the calculation speed (computation speed) of the set flow rate of the concentrated waste water by the waste water flow control unit 32. For example, if the two speeds are significantly different, hunting may occur if the set flow rate of the concentrated waste water is changed before the electric proportional control valve is completely opened and closed and the flow rate of the concentrated waste water is stabilized. . In addition, since the set flow rate of the concentrated waste water is determined based on the flow rate of the permeated water detected by the permeated water flow meter 12, the flow rate control of the concentrated waste water also depends on the response speed of the inverter that controls the rotation speed of the pressure pump 21. may be affected. Therefore, when determining the calculation speed of the set flow rate of the concentrated waste water by the waste water flow control unit 32, it is preferable to consider the opening/closing speed of the electric proportional control valve and the response speed of the inverter. That is, it is preferable to slow the response speed of the inverter when the opening/closing speed of the electric proportional control valve is slow, and to increase the response speed of the inverter when the opening/closing speed of the electric proportional control valve is fast. In this embodiment, as described above, the flow control of the permeated water and the flow control of the concentrated water are performed independently by installing the constant flow valve 13, so that the mutual flow control is prevented from interfering. be able to. As a result, the occurrence of hunting as described above can be suppressed as much as possible, and deviation of the actual recovery rate from the target recovery rate can be suppressed. Also from this point, it is preferable that the concentrated water line 3 is provided with the constant flow valve 13 .

In this embodiment, the target value of the recovery rate is set higher, and in order to further save water, a scale inhibitor is added to the raw water for the purpose of increasing the precipitation recovery rate described above. can be In this case, the specified flow rate of the constant flow valve 13 can be reduced, and as a result, energy can be saved by using a pressure pump 21 with a smaller capacity. The addition of scale inhibitor can be done by a dosing pump.

The scale inhibitor is not particularly limited as long as it is a substance capable of suppressing precipitation of scale components such as silica and calcium. Examples thereof include phosphonic acids such as 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, ethylenediaminetetramethylenephosphonic acid, nitrilotrimethylphosphonic acid, and salts thereof. Phosphonic acid-based compounds; phosphoric acid-based compounds such as orthophosphates and polymerized phosphates; maleic acid-based compounds such as polymaleic acid and maleic acid copolymers; are copolymers such as poly(meth)acrylic acid, maleic acid/(meth)acrylic acid, (meth)acrylic acid/sulfonic acid, (meth)acrylic acid/nonionic group-containing monomers, and (meth)acrylic acid/sulfonic acid /nonionic group-containing monomer, (meth)acrylic acid/acrylamide-alkylsulfonic acid/substituted (meth)acrylamide, and (meth)acrylic acid/acrylamide-arylsulfonic acid/substituted (meth)acrylamide terpolymer. Examples of the (meth)acrylic acid constituting the terpolymer include methacrylic acid, acrylic acid, and (meth)acrylic acid salts such as sodium salts thereof. Examples of acrylamide-alkylsulfonic acids constituting the terpolymer include 2-acrylamido-2-methylpropanesulfonic acid and salts thereof. Examples of substituted (meth)acrylamides constituting the terpolymer include t-butylacrylamide, t-octylacrylamide and dimethylacrylamide.

Among these, it is preferable to use one containing at least one of a phosphonic acid-based compound and an acrylic acid-based polymer. In order to simultaneously suppress scale derived from calcium and silica, 2-phosphonobutane-1,2,4-tricarboxylic acid, acrylic acid and (meth)acrylic acid/2-acrylamido-2-methylpropanesulfonic acid It is particularly preferred to use a scale inhibitor consisting of a mixture of /substituted (meth)acrylamide with a terpolymer.

Commercially available scale inhibitors for RO membranes include the "Orpersion" series manufactured by Organo Corporation, the "Flocon (registered trademark)" series manufactured by BWA Water Additives, and the "PermaTreat (registered trademark)" manufactured by Nalco. series, General Electric Company's "Hypersperse (registered trademark)" series, and Kurita Water Industries Ltd.'s "Kuriverter (registered trademark)" series.

By the way, in many cases, the supply line 1 on the upstream side of the confluence with the reflux water line 5 is provided with an activated carbon filter for removing residual free chlorine contained in the raw water. However, since the chlorine removal capacity of the activated carbon filter depends on the temperature and flow rate of raw water and the concentration of residual free chlorine, in some cases, residual free chlorine may leak downstream of the activated carbon filter. Residual free chlorine may oxidize and deteriorate the RO membrane or NF membrane of the filtering means 11 . When such membrane deterioration occurs, the film thickness becomes thinner and the pore size of the membrane increases, which not only increases the flow rate of the permeate, but also reduces the salt removal performance of the membrane, resulting in a decrease in the quality of the permeate. Connect.

On the other hand, it is preferable that the recovery rate is as high as possible from the viewpoint of effective use of water (water saving). calculated based on Therefore, when the concentration of impurities in the raw water fluctuates and exceeds the preset value measured in advance, even if the flow rate control of the concentrated wastewater is performed so as to achieve the target recovery rate, the risk of scale generation increases, and the filtration means 11 clogging can occur in the RO or NF membranes. When such membrane clogging occurs, the permeation pores of the membrane are clogged, which not only reduces the flow rate of the permeate, but also lowers the salt removal performance of the membrane, leading to deterioration in the water quality of the permeate.

For this reason, the performance of the RO membrane or NF membrane of the filtering means 11, especially the presence or absence of deterioration or clogging, is accurately determined, and when deterioration or clogging occurs, it is detected at the earliest possible stage. is desirable. Therefore, in the present embodiment, a sign determination unit (determining means) 40 is provided to determine whether or not there is a sign of deterioration or clogging in the filtering means 11 . Furthermore, in this embodiment, a plurality of detection means are provided in order to acquire data used by the portent determination unit 40 to perform portent determination. That is, a raw water conductivity meter (first conductivity detecting means) 17a for detecting the conductivity of the raw water flowing through the supply line 1, and a permeated water conductivity meter (a first conductivity detecting means) for detecting the conductivity of the permeated water flowing through the permeated water line 2 A second conductivity detection means) 17b, a raw water pressure gauge (first pressure detection means) 18a that detects the pressure of raw water flowing through the supply line 1, and a permeate that detects the pressure of the permeated water flowing through the permeate line 2 A water pressure gauge (second pressure detection means) 18b and a concentrated water pressure gauge (third pressure detection means) 18c for detecting the pressure of the concentrated water flowing through the concentrated water line 3 are provided. It should be noted that the installation positions of these detection means are not limited to the positions shown in the figure.

A method for determining a sign of deterioration or clogging of the filtering means 11 by the sign determination unit 40 will be described below.

As described above, the deterioration or clogging of the filtering means 11 appears as a decrease in the quality of the permeated water (that is, an increase in the conductivity of the permeated water) and a change in the flow rate of the permeated water. However, when the flow rate of permeated water flowing through the permeated water line 2 is maintained constant by the permeated water flow rate control mechanism 20, it appears as a change in the raw water supply pressure instead of as a change in the flow rate of the permeated water. Therefore, deterioration or clogging of the filtering means 11 can be determined by detailed analysis of changes over time in the conductivity of the permeate water and changes over time in the supply pressure of the raw water. However, the conductivity of the permeated water varies depending not only on whether or not the filtration means 11 is deteriorated or clogged, but also on the water temperature and the water quality (conductivity) of the raw water, and also on the recovery rate. Moreover, the supply pressure of the raw water also changes depending on the water temperature. Therefore, in order to accurately determine the presence or absence of deterioration or clogging of the filtering means 11, the detection result of the conductivity of the permeated water or the detection result of the supply pressure of the raw water is not directly analyzed. Analysis must be performed using the excluded correction values.

ここで、Ｑ_ｐｏは透過水流量計１２により検出された透過水の流量［Ｌ／ｈ］、Ｑ_ｐｓはその参照値である。また、Ｋ_Ｔは水温補正係数であり、以下の式（６）によって与えられる。

ここで、Ａは水温によって決まる定数、Ｔ_ｏは温度センサ１６により検出された原水の水温［℃］、Ｔ_ｓはその参照値である。 Therefore, when the supply pressure of raw water is detected by the raw water pressure gauge 18a, the detected value of the supply pressure is corrected, and a correction value (hereinafter referred to as "pressure correction value") that eliminates the influence of water temperature fluctuation is calculated. be done. Specifically, based on the value detected by the temperature sensor 16 and the value detected by the permeated water flowmeter 12, the value detected by the raw water pressure gauge 18a is corrected to calculate the pressure correction value. Assuming that the raw water supply pressure detected by the raw water pressure gauge 18a is P _fo [bar], the pressure correction value P _fs [bar] is given by the following equation (5).

Here, Q _po is the permeate flow rate [L/h] detected by the permeate flow meter 12, and Q _ps is its reference value. Also, _KT is a water temperature correction coefficient and is given by the following equation (6).

Here, A is a constant determined by the water temperature, _To is the water temperature [°C] of the raw water detected by the temperature sensor 16, and _Ts is its reference value.

Ｐ_ｆｏ：原水圧力計１８ａにより検出された原水の供給圧力［ｂａｒ］
Ｐ_ｆｓ：式（５）により算出された圧力補正値［ｂａｒ］
ΔＰ_ｏ：原水がろ過手段１１の一次側を通過する際の圧力損失［ｂａｒ］
ΔＰ_ｓ：同参照値［ｂａｒ］
Ｐ_ｐｏ：透過水圧力計１８ｂにより検出された透過水の圧力［ｂａｒ］
Ｐ_ｐｓ：同参照値［ｂａｒ］
Ｃ_ｆｏ：原水導電率計１７ａにより検出された原水の導電率［μＳ／ｃｍ］
Ｃ_ｆｓ：同参照値［μＳ／ｃｍ］
Ｃ_ｐｏ：透過水導電率計１７ｂにより検出された透過水の導電率［μＳ／ｃｍ］
Ｃ_ｐｓ：同参照値［μＳ／ｃｍ］
Ｔ_ｏ：温度センサ１６により検出された原水の水温［℃］
Ｔ_ｓ：同参照値［℃］ In addition, when the conductivity of the permeated water is detected by the permeated water conductivity 17b, the detected value of the conductivity is corrected, and the influence of water temperature fluctuation, raw water quality (conductivity) fluctuation, and recovery rate fluctuation is calculated (hereinafter referred to as "conductivity correction value"). Specifically, the permeate water A conductivity correction value is calculated by correcting the value detected by the conductivity meter 17b. Assuming that the conductivity of the permeated water detected by the permeated water conductivity meter 17b is C _po [μS/cm], the conductivity correction value C _ps [μS/cm] is given by the following equation (7).

P _fo : Raw water supply pressure [bar] detected by the raw water pressure gauge 18a
P _fs : Pressure correction value [bar] calculated by Equation (5)
ΔP _o : Pressure loss [bar] when raw water passes through the primary side of the filtration means 11
ΔP _s : same reference value [bar]
P _po : Permeate pressure [bar] detected by the permeate pressure gauge 18b
P _ps : same reference value [bar]
C _fo : Conductivity of raw water detected by raw water conductivity meter 17a [μS/cm]
C _fs : same reference value [μS/cm]
C _po : Conductivity of permeated water detected by permeated water conductivity meter 17b [μS/cm]
C _ps : same reference value [μS/cm]
_To : Water temperature of raw water detected by temperature sensor 16 [°C]
T _s : same reference value [°C]

Here, the pressure losses ΔP _o and ΔP _s are indirectly detected (calculated) by the raw water pressure gauge 18a and the concentrated water pressure gauge 18c, and the pressure of the raw water flowing through the supply line 1 and the concentrated water flowing through the concentrated water line 3 Expressed as a difference. The reference values in the formulas (5) to (7) include the detected value (calculated value) immediately after the start of use of the filtration means 11 (immediately after the start of operation of the membrane filtration device 10), and After that, the detected value (calculated value) after the performance stabilizes can be used. However, immediately after the filtration means 11 is started to be used, the conductivity of the permeated water changes with time due to the ions diffused especially before the start of operation. Therefore, as the reference value, it is preferable to use a value obtained after a certain period of time has elapsed from immediately after the start of use of the filtering means 11 and the performance has stabilized. The period until the performance of the filtration means 11 (RO membrane or NF membrane) stabilizes varies depending on how the membrane was stored until then. for both wet-type (stored in wet conditions) and wet-type (stored in damp conditions) membranes, typically hours to days. That is, the salt removal performance of the membrane is generally improved for several hours to several days after the start of use, and then stabilizes thereafter. Therefore, as the reference value, it is possible to use a value acquired after a preset time or days have elapsed from immediately after the start of use of the filtering means 11 .

The pressure correction value and the conductivity correction value are calculated continuously or periodically, and the values thus calculated are collected as data (time-series data) indicating changes over time. In addition, deterioration or clogging of the filtering means 11 does not occur suddenly, and the effect does not appear suddenly on the pressure correction value and the conductivity correction value. The values may be collected and the period over which the moving average is calculated may be hours to days.

Then, in parallel with the collection of time-series data, regression analysis (linear regression) is performed on the time-series data, and based on the slope of the calculated regression line, there is a sign of deterioration or clogging of the filtering means 11. It is determined whether or not When the filtering means 11 is not deteriorated or clogged, the pressure correction value and the conductivity correction value do not change, and the slope of the regression line becomes zero. Therefore, in this sign determination, it is determined whether or not the slope of the regression line with respect to the time-series data of the pressure correction value (hereinafter simply referred to as "pressure regression line") is within a predetermined range including zero. It is determined whether or not the slope of the regression line with respect to the time-series data of the correction values (hereinafter also simply referred to as the "conductivity regression line") is within a predetermined range including zero. As a result, when the slope of the pressure regression line is out of the predetermined range or the slope of the conductivity regression line is out of the predetermined range, it is determined that there is a sign of deterioration or clogging of the filtering means 11 .

When the filtering means 11 deteriorates, the pressure correction value decreases because the raw water easily passes through the filtering means 11. When the filtering means 11 is clogged, the raw water becomes difficult to pass through the filtering means 11. To increase. Therefore, when the slope of the pressure regression line is equal to or less than the predetermined lower limit, it is determined that there is a sign of deterioration of the filtering means 11, and when the slope of the pressure regression line is equal to or greater than the predetermined upper limit, filtration is performed. It is determined that the means 11 has a sign of clogging. On the other hand, the conductivity correction value increases due to deterioration of the salt removal performance of the filtering means 11 even if the filtering means 11 is deteriorated or clogged. When this occurs, the conductivity correction value does not change until it has progressed considerably. Therefore, no upper limit value corresponding to the clogging of the filtering means 11 is set, and it is determined that the filtering means 11 has a sign of deterioration when the slope of the conductivity regression line exceeds a predetermined upper limit value.

Deterioration or clogging of the filtering means 11 may occur in a relatively short period of time or slowly over a long period of time. That is, each of the pressure correction value and the conductivity correction value has a change that appears in a relatively short period of time and a change that appears gradually over a long period of time. In order to detect these two types of changes, regression analysis is performed on two types of time-series data: a first period that is short and a second period that is longer. is preferred. Here, the time-series data of the first period is, for example, time-series data for the most recent 5 to 90 days including the current time. In addition, the time-series data of the second period is the time-series data of the most recent period including the current time, which is longer than the first period, or the period from the time when the above-mentioned reference value is obtained to the current time. If it exceeds the period of , it is the time-series data for the entire period. Even when regression analysis is performed on such two types of time-series data, the presence or absence of deterioration or clogging of the filtering means 11 is determined based on the same criteria as described above based on the slope of each regression line. can do.

That is, when the slope of the pressure regression line in the first period is out of the predetermined range or the slope of the pressure regression line in the second period is out of the predetermined range, it is determined that there is a sign of deterioration or clogging of the filtering means 11. be judged. Specifically, when the slope of the pressure regression line in the first period or the second period falls below the lower limit of the predetermined range, it is determined that there is a sign of deterioration of the filtering means 11 . Further, when the slope of the pressure regression line in the first period or the second period is equal to or greater than the upper limit value of the predetermined range, it is determined that there is a sign of clogging in the filtering means 11 . These upper and lower limits can be set by experimentally verifying the limits within which deterioration or clogging does not occur. Note that the predetermined ranges (upper limit and lower limit) may be changed and set for the first period and the second period depending on the difference in the device configuration and the membrane used in the filtering means 11 . As an example, the upper limit is set between +0.0001 and +0.01, and the lower limit is set between -0.0001 and -0.01. On the other hand, when the slope of the conductivity regression line in the first period becomes a predetermined value or more, or the slope of the conductivity regression line in the second period becomes a predetermined value or more, it is a sign of deterioration of the filtering means 11. It is determined that there is As an example, the predetermined value is set between +0.01 and +1.0.

Here, experimental results for confirming the effect of the sign determination unit 40 of the present embodiment will be described.

The present inventors performed continuous operation for 24 hours using the membrane filtration device shown in FIG. The time to judgment was measured. Tap water was used as raw water, and an RO membrane (manufactured by Dow Chemical Co., Ltd., product number: XLE-4040) was used as a filtration means. In addition, as an element of the time-series data, the daily average value (average value per day) of the pressure correction value calculated from the formula (5) is used, and as the time-series data of the first period, the most recent The time-series data for 30 days of the second period was used, and the time-series data for the entire period including the current time was used as the time-series data for the second period. Therefore, in practice, the calculation of the slope of the pressure regression line in the first period is performed 30 days after the start date of use of the filtration means, and the calculation of the slope of the pressure regression line in the second period is performed by the filtration means. 31 days after the start of use. For example, in the case of the 35th day from the first day of use of the filtration means, the slope of the pressure regression line in the first period is calculated for 30 points of time series data for 6 to 35 days. , Calculation of the slope of the pressure regression line in the second period was performed on 35-point time-series data for days 1 to 35. As each reference value in the formulas (5) to (7), the detected value (calculated value) on the first day of use of the filtering means was used.

The operation of the membrane filtration device is performed under conditions where clogging occurs in the filtration means, specifically, under conditions such that the time-dependent change in the pressure correction value (daily average value) calculated from Equation (5) is shown in FIG. I went with Under these conditions, clogging of the filtration means occurred when the pressure correction value exceeded 1.0 MPa (on the 109th day).

3 and 4 are graphs showing temporal changes in the slope of the pressure regression line in the first period and the second period, respectively. In both cases of the first period and the second period, if the threshold value (upper limit value) for determining the sign of clogging is set to +0.001, the slope of the pressure regression line in the first period is shown in FIG. As shown in FIG. 4, it was possible to determine that there was a sign of clogging of the filtering means on the 78th day, and on the 94th day, as shown in FIG. That is, by focusing on the slope of the pressure regression line, the pressure (0.7 to 0.8 MPa) lower than the pressure (1.0 MPa) when the clogging actually occurs in the filtration means. It was determined that there was a sign of clogging. In addition, it is considered that the fact that the sign of clogging was determined at an earlier time in the slope of the pressure regression line in the first period made it possible to observe the pressure increase in a shorter period of time. Therefore, it was also confirmed that even if the symptom of clogging of the filtering means is the same but progresses at different speeds, it is possible to distinguish between them and make a determination.

As described above, according to the present embodiment, by monitoring the slope of the regression line obtained from the time-dependent changes in the pressure correction value and the conductivity correction value, the presence or absence of deterioration or clogging is determined by a simple comparison with the initial value. It is possible to detect deterioration or clogging of the filtering means 11 at the earliest possible stage, compared to the conventional method.

When the sign determination unit 40 determines that the filtering means 11 has a sign of deterioration or clogging, it is preferable to replace or clean the filtering means 11 . However, it is necessary to stop the operation of the membrane filtration device 1 in order to replace or clean the filtration means 11. If this is not possible, the deterioration or clogging of the filtration means 11 progresses, and the membrane filtration device 10 becomes inoperable. It may develop into a serious problem such as falling. Therefore, if it is determined that there is a sign of deterioration or clogging in the filtration means 11, but the operation of the membrane filtration device 1 cannot be stopped, a life extension method that delays the progress of deterioration or clogging of the filtration means 11 is used. Driving is preferred. Furthermore, even when sufficient time is required to examine specific countermeasures such as replacement or cleaning of the filtering means 11, the life-prolonging operation of the filtering means 11 can be performed. A specific life-prolonging operation method is selected appropriately according to the cause of deterioration or clogging of the filtering means 11, as described below. Note that such life-prolonging operation may be automatically performed after the sign determination by the sign determination unit 40 .

As a main cause of deterioration of the filtering means 11, for example, as described above, the chlorine removing ability of the activated carbon filter installed upstream of the filtering means 11 is lowered, and raw water containing residual free chlorine is filtered. It is conceivable that the means 11 were fed. In this case, by setting the recovery rate to a value higher than the initial target value, the flow rate of the concentrated waste water is reduced, and accordingly the concentrated water flowing through the reflux water line 5 (hereinafter referred to as "concentrated reflux water") ) can be increased. Alternatively, if the permeate usage at the point of use is less than the preset target permeate flow rate, change the target flow rate to a lower minimum value to reduce the permeate flow rate. can also As a result, the flow rate of the raw water flowing through the supply line 1 on the upstream side of the confluence with the reflux water line 5 and flowing into the activated carbon filter can be reduced, and the chlorine load on the activated carbon filter can be reduced. In this way, leakage of residual free chlorine from the activated carbon filter can be minimized, and progress of deterioration of the filtering means 11 can be delayed to prolong its life. As the initial target value of the recovery rate, if the recovery rate at which the maximum silica concentration or calcium concentration at which silica or calcium does not precipitate is set, further increasing the recovery rate will reduce the risk of scale generation. lead to an increase. Therefore, when there is a concern about leakage of residual free chlorine from the activated carbon filter, the initial target value for the recovery rate is the maximum silica concentration or calcium concentration at which silica or calcium does not precipitate, and the safety factor is added to the recovery rate. It is preferable to set a value.

Other causes of the deterioration of the filtering means 11 are conceivable, for example, contamination of the raw water with an oxidizing agent. Furthermore, due to breakage of the filtering means 11 or erroneous installation of O-rings at pipe connection portions, changes similar to those due to deterioration may appear in the pressure correction value and the conductivity correction value. Therefore, when it is determined that there is a sign of deterioration in the filtering means 11, first, whether the cause is residual free chlorine, that is, whether the raw water supplied to the filtering means 11 contains residual free chlorine. Whether or not is specified (detected), and then an appropriate life-prolonging operation of the filtering means 11 is selected. Methods for detecting residual free chlorine include, for example, a colorimetric method using a diethyl-P-phenylenediamine (DPD) reagent, or direct detection of residual free chlorine in raw water using a residual chlorine meter. can also If residual free chlorine is not detected, priority may be given to suppressing deterioration of permeate water quality by setting the recovery rate to a value lower than the initial target value.

On the other hand, as described above, the main cause of clogging of the filtering means 11 is scaling due to fluctuations in the concentration of impurities in the raw water, and fouling due to adhesion of organic substances and fine particles in the raw water. . When clogging occurs in the filtering means 11 due to scaling, the primary cause is a high recovery rate. ) can be lowered, the progress of clogging of the filtering means 11 can be delayed, and the life can be extended. It should be noted that the recovery rate set here is preferably a value higher than the minimum allowable recovery rate that is determined by restrictions on device design such as the capacity of the pressurizing pump and the flow rate of the raw water. On the other hand, when clogging occurs in the filtering means 11 due to fouling, flushing can slow down the progress of the clogging of the filtering means 11 and, in some cases, recover the clogging. Flushing is performed by discharging concentrated water through a drainage line (not shown) for flushing, thereby obtaining the required membrane flow velocity for flushing. The cause of clogging of the filtering means 11 can be identified by sampling the raw water and analyzing its water quality, but it may take time to identify the cause. In this case, first, perform flushing multiple times or flushing for several days. If the clogging does not recover even after that, scaling is likely to be the cause of the clogging. It is preferable to move to driving.

In addition, when it is determined that there is a sign of deterioration or clogging in the filtering means 11, it is preferable that an alarm notifying of this is output. This prompts the operator of the membrane filtration device 1 to determine whether to replace or clean the filtration means 11, or specifies the cause of deterioration or clogging when performing the life extension operation of the filtration means 11. You can also let them know when it's time to work.

In addition, when it is determined that there is a sign of deterioration or clogging in the filtering means 11, for example, when the filtering means 11 is replaced, each reference value in formulas (5) to (7) is The pressure correction value and the conductivity correction value are calculated using the newly obtained reference value. Therefore, the sign determination unit 40 preferably includes storage means for storing each reference value in the equations (5) to (7). is reset and updated each time

As described above, in the present embodiment, since the flow rate of the concentrated water is maintained constant by the constant flow valve 13, the flow rate of the concentrated water flowing through one of the drain line 4 and the recirculated water line 5 can be determined only by specifying the flow rate of the concentrated water flowing through the other. A flow rate of the concentrate flowing through the can also be defined. Therefore, in the illustrated embodiment, the drainage line 4 is provided with a drainage flow meter 14 and a flow rate control means (flow control valve 31), and the reflux line 5 is provided with concentrated water flowing through the drainage line 4 and the reflux water line 5. A manual valve (pressure regulating valve) 15 is provided for regulating the pressure balance, but the reverse is also possible. That is, the recirculated water line 5 may be provided with a flow meter and a flow control valve (proportional control valve) as flow control means, and the drain line 4 may be provided with a manual valve for pressure balance adjustment. Alternatively, both the drain line 4 and the return water line 5 may be provided with flow meters and flow control valves (proportional control valves) as flow control means. Further, in the above-described embodiment, the permeate flow rate control unit and the waste water flow rate control unit are provided separately, but one flow control unit adjusts the flow rate of the permeated water and the concentrated waste water. It can be like this.

Also, the number of filtering means is not limited to one, and two or more filtering means may be connected in series. Even in that case, the constant flow valve is provided in the concentrated water line connected to the most upstream filtering means among the two or more filtering means, and the permeated water separated by the most downstream filtering means is the set flow rate. (Preset target flow rate). However, it is needless to say that the flow rate distribution between the permeated water and the concentrated water needs to be appropriately set and adjusted by any flow rate adjusting means in all the filtering means except for the most upstream filtering means. Furthermore, in calculating the set flow rate of concentrated wastewater from the most upstream filtration means, the flow rate of the permeated water separated by the most upstream filtration means, not the permeated water separated by the most downstream filtration means ( Note that the detected flow rate) is used. Here, "connected in series" means that the water to be treated is sequentially treated by a plurality of filtration means, and in two adjacent filtration means, separated by the upstream filtration means It means that the permeated water is supplied to the filtering means on the downstream side as the water to be treated. Moreover, each filtering means may be composed of a plurality of RO membranes or NF membranes. In this case, a plurality of RO membranes or NF membranes are connected in series on the primary side (distribution side of raw water and concentrated water) and finally connected to the concentrated water line, and the secondary side (distribution side of permeated water) is It will be connected in parallel and finally connected to the permeate line.

1 supply line 2 permeated water line 3 concentrated water line 4 drain line 5 reflux water line 10 membrane filtration device 11 filtering means 12 permeated water flow meter 13 constant flow valve 14 drain flow meter 15 manual valve 16 temperature sensor 17a raw water conductivity meter 17b Permeated water conductivity meter 18a Raw water pressure gauge 18b Permeated water pressure gauge 18c Concentrated water pressure gauge 20 Permeated water flow rate control mechanism 21 Pressure pump 22 Permeated water flow rate control section 30 Drainage flow rate control mechanism 31 Flow rate adjustment valve 32 Drainage flow rate control section 40 Prediction determination part

Claims (13)

Filtration means having a reverse osmosis membrane or nanofiltration membrane for separating the water to be treated into permeated water and concentrated water, a supply line for supplying the water to be treated to the filtration means, and circulating the permeated water from the filtration means a permeated water line, a concentrated water line for circulating the concentrated water from the filtering means, and a drain line branching from the concentrated water line and discharging a part of the concentrated water flowing through the concentrated water line to the outside. A membrane filtration device,
water temperature detection means for detecting the water temperature of any one of the water to be treated supplied to the filtering means, the permeated water from the filtering means, and the concentrated water from the filtering means;
a first flow rate detection means for detecting the flow rate of the permeate flowing through the permeate line;
a first conductivity detection means for detecting the conductivity of the water to be treated flowing through the supply line;
a second conductivity detection means for detecting the conductivity of the permeate flowing through the permeate line;
a first pressure detection means for detecting the pressure of the water to be treated flowing through the supply line;
a second pressure detection means for detecting the pressure of the permeate flowing through the permeate line;
a third pressure detection means for detecting the pressure of the concentrated water flowing through the concentrated water line;
and determination means for determining whether or not there is a sign of deterioration or clogging in the filtering means,
The determination means corrects the value detected by the first pressure detection means based on the value detected by the water temperature detection means and the value detected by the first flow rate detection means, so that Calculating a pressure correction value that eliminates the influence, based on the value detected by the water temperature detection means, the value detected by the first conductivity detection means, and the values detected by the first to third pressure detection means By correcting the value detected by the second conductivity detection means, the fluctuation of the water temperature, the fluctuation of the conductivity of the water to be treated flowing through the supply line, and the flow rate of the permeate flowing through the permeate water line and the flow rate of the concentrated water flowing through the drainage line, which is the ratio of the flow rate of the permeate flowing through the permeate line to the sum of Based on the slope of the first regression line obtained from the change over time and the slope of the second regression line obtained from the change over time of the conductivity correction value , whether there is a sign of deterioration or clogging of the filtering means. A membrane filtration device that determines whether The determining means determines whether the slope of the first regression line is within a predetermined range including zero and whether the slope of the second regression line is within a predetermined range including zero. 2. The membrane filtration device according to claim 1 , wherein it is determined whether or not there is a sign of deterioration or clogging of said filtering means. 3. The membrane filtration device according to claim 2 , wherein said determining means determines that there is a sign of deterioration or clogging of said filtering means when the slope of said first regression line deviates from a predetermined range including zero. The determination means calculates the slope of the first regression line in a first period and a second period longer than the first period, and calculates the slope in the first period and the slope in the second period 4. The membrane filtration device according to claim 3 , wherein when one of the slopes is out of a predetermined range including zero, it is determined that there is a sign of deterioration or clogging of the filtering means. 3. The membrane filtration device according to claim 2 , wherein said determination means determines that there is a sign of deterioration of said filtering means when the slope of said second regression line is equal to or greater than a predetermined value. The determination means calculates the slope of the second regression line in a first period and a second period longer than the first period, and calculates the slope in the first period and the slope in the second period 6. The membrane filtration device according to claim 5 , wherein when one of said slopes is equal to or greater than a predetermined value, it is determined that there is a sign of deterioration of said filtration means. The determination means detects a value detected by the water temperature detection means, a value detected by the first flow rate detection means, and the first 7. The device according to any one of claims 1 to 6 , further comprising means for storing a value detected by said conductivity detecting means and a value detected by said first to third pressure detecting means as respective reference values. Membrane filtration device. a second flow rate detection means for detecting a flow rate of concentrated water flowing through the drainage line;
a first flow rate control means for adjusting the flow rate of the permeated water flowing through the permeate line to a set flow rate, the pressure adjusting means being provided in the supply line and adjusting the pressure of the water to be treated flowing through the supply line; , a control unit that controls the pressure adjusting means based on the value detected by the first flow rate detecting means;
A second flow rate control means for adjusting the flow rate of the concentrated water flowing through the drainage line to a set flow rate, based on a flow rate adjustment valve provided in the drainage line and a value detected by the second flow rate detection means 8. The membrane filtration device according to any one of claims 1 to 7 , further comprising: a second flow rate control means comprising: a controller for adjusting the degree of opening of the flow rate adjustment valve. The control unit of the second flow rate control means changes the target value of the recovery rate when the determination means determines that there is a sign of deterioration or clogging of the filtering means, and changes the target value to the changed target value. 9. The membrane filtration device according to claim 8 , wherein the set flow rate of the concentrated water flowing through the drainage line is determined based on the values detected by the first flow rate detection means. The control unit of the second flow rate control means changes the target value of the recovery rate to a higher value when the determination means determines that there is a sign of deterioration in the filtering means, and the determination means When it is determined that there is a sign of clogging in the filtering means, the target value of the recovery rate is changed to a lower value, and the flow rate of permeated water flowing through the permeated water line and the flow rate of concentrated water flowing through the drainage line 10. The membrane filtration device according to claim 9 , wherein the permissible concentration ratio, which is a ratio of the flow rate of the concentrated water flowing through the concentrated water line to the sum of , is reduced. The control unit of the second flow rate control means subtracts the value detected by the first flow rate detection means from the value obtained by dividing the value detected by the first flow rate detection means by the target value of the recovery rate. is determined as the set flow rate of the concentrated water flowing through the drainage line. The control unit of the second flow rate control means controls the reverse osmosis membrane or nanofiltration membrane of the filtration means based on the value detected by the water temperature detection means and the impurity concentration of the water to be treated that has been measured in advance. 10. From claim 9 , wherein a recovery rate that provides the maximum silica concentration or calcium concentration at which silica or calcium does not precipitate on the surface is calculated, and a value obtained by adding a safety factor to the calculated value is set as the initial target value of the recovery rate. 1. The membrane filtration device according to any one of 1.1 . The control unit of the first flow rate control means changes the set flow rate of the permeate flowing through the permeate line to a lower value when the determination means determines that there is a sign of deterioration in the filtration means. The membrane filtration device according to claim 8 , wherein

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